Nanosheet-constructing porous CeO2 microspheres with silver nanoparticles anchored on the surface were developed as a highly efficient oxygen reduction reaction (ORR) catalyst. The aluminum–air batteries applying Ag–CeO2 as the ORR catalyst exhibit a high output power density and low degradation rate of 345 mW cm−2 and 2.6% per 100 h, respectively.

For the development of high-performance Li–S batteries, the issues of the insulating nature of sulfur and shuttle effect of polysulfides need to be well addressed simultaneously, which require elaborate structure design of a suitable host for sulfur. In this work, a novel bifunctional and free-standing sulfur cathode consisted of a hierarchical porous carbon network as the conductive host for sulfur and an in situ formed graphene shell as the top layer for physical blocking of the shuttle effect is carefully fabricated. Owing to filtration assembly, an ultrathin graphene shell (∼100 nm in thickness) is in situ formed firstly, on which a macroporous graphene architecture is gradually deposited afterwards. Subsequent chemical vapor deposition of interwoven CNTs on both sides of graphene sheets generates numerous nano-sized cavities for loading of sulfur nanoparticles. The rationally designed electrode possesses a relatively high areal sulfur loading of ∼3.6 mg cm−2, and shows excellent rate capability at ∼6.0 mA cm−2 and cyclic stability over 200 cycles. And as the graphene nano-shell blocks the diffusion of polysulfides, the anti-self-discharge capability of the cell is remarkably improved.

Perovskites have been proposed as one of the best oxygen reduction reaction catalysts (ORRCs) to substitute noble metals though their catalytic activity still need to be improved. It is well accepted that improving the oxygen adsorption capacity is beneficial to the catalytic activity of La1−xSrxMnO3 (LSM) perovskites. Herein, we synthesized the LSM-based composite by compositing La0.7Sr0.3MnO3 with Ce0.75Zr0.25O2 (CZ) which is used as an excellent oxygen storage material by a two-step solution method. The LSM–CZ composite is revealed as a novel electrocatalyst for the oxygen reduction reaction with the direct four-electron transfer mechanism and a positive onset potential in comparison with the commercial Pt/C catalyst. And its onset potential is almost the most positive one among those of the perovskites stemmed from LaMnO3. In addition, the stability of LSM–CZ is even superior to that of Pt/C, and LSM–CZ almost accumulates no intermediate product of HO2− (∼0.8%) after aging for 100 000 seconds. By using LSM–CZ as the ORRC, the maximum power density of the aluminum–air battery can reach 233.4 mW cm−2. Our work paves the way for the development of perovskite catalysts for energy conversion and storage.

Lithium-rich layered oxides (LrLOs) deliver extremely high specific capacities and are considered to be promising candidates for electric vehicle and smart grid applications. However, the application of LrLOs needs further understanding of the structural complexity and dynamic evolution of monoclinic and rhombohedral phases, in order to overcome the issues including voltage decay, poor rate capability, initial irreversible capacity loss and etc. The development of aberration correction for the transmission electron microscope and concurrent progress in electron spectroscopy, have fueled rapid progress in the understanding of the mechanism of such issues. New techniques based on the transmission electron microscope are first surveyed, and the applications of these techniques for the study of the structure, migration of transition metal, and the activation of oxygen of LrLOs are then explored in detail, with a particular focus on the mechanism of voltage decay.Download high-res image (276KB)Download full-size image

To develop high-power and high-energy batteries with a long life remains a great challenge, even combining the benefits of metal (fast kinetics and high capacity) and carbon materials (robust structure). Among them, Al-ion batteries based on aluminum anode and graphite carbon cathode have gained lots of interests as one of the most promising technologies. Here, it is demonstrated that the size of graphitic material in ab plane and c direction plays an important role in anion intercalation chemistry. Sharply decreasing the size of vertical dimension (c direction) strongly facilitates the kinetics and charge transfer of anions (de)intercalation. On the other hand, increasing the size of horizontal dimension (ab plane) contributes to improving the flexibility of graphitic materials, which results in raising the cycling stability. Meanwhile, chloroaluminate anions are reversibly intercalated into the interlayer of graphite materials, leading to the staging behaviors. In the end, an ultrafast Al-ion battery with exceptional long life is achieved based on large-sized few-layer graphene as a cathode and aluminum metal as an anode.

•Sheet-like SiOx are first prepared by delaminated siloxene which derives topotactic transformation of layered CaSi2.•Silicon suboxides exhibit Si nanodomains confined in amorphous SiO2.•The delicate designed carbon coated SiOx anodes deliver superior cycling performance and rate capability.SiOx owing to high reversible capacity and moderate volume expansion has been attracting a lot of attention as state-of-the-art anodes for the next generation of Li-ion batteries. However, poor cycling performance and poor rate capability, respectively associated with detrimental volume expansion and insulative amorphous SiO2, are still challenging issues which need to be addressed for the actual employment as anodes for Li-ion batteries. In this regard, here we design, synthesize, characterize and test carbon coated sheet-like SiO1.1 nanocomposites formed by Si-nanodomains confined inside amorphous SiO2 (nano-Si/a-SiO2). As a proof-of-concept, we achieve sheet-like SiOx nanocomposites via in-situ transformation of delaminated siloxene. In particular, self-prepared siloxene with oxygen-inserted Si6 rings terminated with H and OH ligands is prepared by delamination of CaSi2 in dilute HCl. Importantly, the resulting carbon coated nano-Si/a-SiO2 material shows enhanced reaction kinetics and structural stability leading to 946 mAh g−1 capacity at 0.15 A g−1. Intriguingly, 38.0% (~360 mAh g−1) of the maximum capacity is maintained even at 7.5 A g−1, corresponding to a remarkable less than 3 min charge/discharge time. Finally, the electrode shows merely 24% of volume expansion and minor cracks with capacity retention of 92% after 300 cycles at 7.5 A g−1.We introduce a strategy to prepare sheet-like Si/SiO2 nanocomposites from siloxene. Siloxene was delaminated from layered CaSi2. After CVD process, sheet-like Si/SiO2@C showing Si nanodomains well confined within amorphous SiO2 matrix exhibits superior electrochemical performance as anode for Li-ion batteries.Download high-res image (441KB)Download full-size image

•A novel LSM-CeO2 hybrid catalyst has been synthesized by a facile one-pot method.•The LSM particles about 150 nm are well distributed on the flower-like CeO2.•The flower-like CeO2 particles are formed from nanosheets, approx. 40 nm thick.•Hybrid material shows the remarkable catalytic activity and stability during ORR.•Pmax of the Al-air battery with LSM-CeO2 hybrid material reaches 238 mW cm−2.A novel La0.7Sr0.3MnO3-CeO2 (LSM-CeO2) hybrid catalyst for oxygen reduction reaction (ORR) has been synthesized by a facile one-pot method. The flower-like CeO2 with the diameter of about 3 μm is formed by the agglomeration of nanosheets with the thickness of about 40 nm. The LSM particles with the diameter of about 150 nm are well distributed on the flower-like CeO2, thus the interaction between LSM and CeO2 is built. Therefore, the LSM-CeO2 composite catalyst exhibits the much higher catalytic activity toward ORR with the direct four-electron transfer mechanism in alkaline solution than LSM or CeO2. Furthermore, the stability of LSM-CeO2 is superior to that of Pt/C, and the current retention is 93% after 100000 s. The maximum power density of the aluminum-air battery using LSM-CeO2 as the ORRC can reach 238 mW cm-2, which is about 29% higher than that with LSM (184 mW cm-2). It indicates that LSM-CeO2 composite material is a promising cathodic electrocatalyst for metal-air batteries.

•Sr is substituted with Pd in LSM by a facile sol-gel method.•Oxygen desorption ability can be enhanced with the appropriate Pd substitution.•LSPM-15 shows the remarkable catalytic activity and stability during ORR.•Pmax of the Al-air battery with LSPM-15 reaches 265.6 mW cm−2.The La1-xSrxMnO3 (LSM) perovskites have been proposed as the promising oxygen reduction reaction catalysts (ORRCs) to substitute the noble metal. However, their ORR catalytic activities still need to be further improved. Here, the La0.7(Sr0.3-xPdx)MnO3 (LSPM) perovskites with the substitution of Sr with Pd are synthesized by a facile sol-gel method. The structure, morphology, valence state of Mn, oxygen adsorption behaviors of the different LSPM catalysts are investigated, and their ORR catalytic activities are studied by the rotating ring-disk electrode (RRDE) and aluminum air battery technologies. The results demonstrate that the appropriate substitution of Sr with Pd can effectively improve the ORR catalytic activity of La0.7Sr0.3MnO3 due to the regulation of the Mn valence and enhancement of the oxygen adsorption capacity. Among the LSPM perovskites, the LSPM-15 catalyst exhibits the best catalytic activity toward ORR. In addition, the current retention of LSPM-15 is as high as 98.9% after 10000 s with the generation of a few HO2− (0.96% ∼ 1.56%) during the whole aging test. Moreover, the maximum power density of the aluminum air battery using LSPM-15 can reach 265.6 mW cm−2, which indicates that LSPM-15 can be used as a promising ORRC for the aluminum air batteries.

In this work, the La0.8Sr0.2Co1-xMnxO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) perovskites (LSCM) were synthesized by a facile improved sol–gel method. The crystalline structures, morphologies, Co/Mn valence states and oxygen adsorption/desorption behavior of the LSCM materials are systematically studied, and their catalytic activities toward ORR and OER are investigated by the rotating-disk electrode (RDE) and zinc-air battery techniques. It is found that the proper substitution of Co with Mn can efficiently improve the ORR and OER activities of La0.8Sr0.2CoO3 perovskite at the same time. The LSCM-60 catalyst exhibits the optimum bi-functional activity. It is mainly attributed to the regulation of the Bi-site Co/Mn valence states and the improvement of the oxygen adsorption/desorption capability. Besides of the good bi-functional property, LSCM-60 shows superior durability compared with Pt/C and IrO2 catalysts. When using LSCM-60 as the cathode catalyst of zinc-air batteries, the low charge-discharge overpotential (1.05 V at 50 mA cm−2) and the excellent long-term cycle stability were obtained. This study exhibits the possibility to improve the bi-functional activity of La0.8Sr0.2CoO3 through a simple doping process.Download high-res image (122KB)Download full-size image

The LaMnO3 (LMO) perovskite catalyst has been proposed as one of the best oxygen reduction reaction catalysts (ORRCs) to substitute noble metals. However, its ORR catalytic activity needs to be further improved. Here, La1−xAgxMnO3 (LAM) perovskites doped with Ag are synthesized by a facile improved sol–gel method. The structures, morphologies and valence states of Mn and oxygen adsorption behaviors of these LAM samples are characterized, and their catalytic activities toward ORR are studied by the rotating ring-disk electrode (RRDE) and aluminum air battery technologies. The results demonstrate that the doping of 30% Ag in the A-site of LMO (LAM-30) can effectively improve its ORR catalytic activity due to the regulation of the manganese valence and improvement of the oxygen adsorption capacity. Besides the remarkable ORR catalytic activity, the LAM-30 catalyst exhibits good durability. The current retention is as high as 98% after the aging test for 10 000 seconds. In addition, the maximum power density of the aluminum air battery using LAM-30 as the ORRC can reach 230.2 mW cm−2, which indicates that LAM-30 can be used as a promising ORRC in aluminum air batteries.

Well-designed structures constructed from graphene are excellent sulfur host matrices which can improve the electrochemical performance of lithium–sulfur (Li–S) batteries by alleviating the dissolution of polysulfide and improving the electrical conductivity of the electrode. Herein, high quality graphene powder with a nanoshell inside was successfully designed and fabricated through a simple spray-drying and Fe-catalyzed chemical vapor deposition (CVD) process. In this structure, the intrinsic interconnected graphene nanoshells afford sufficient space for accommodating the active sulfur material, provide effective entrapment for the dissolution of polysulfide and facilitate fast electron and mass transport. Benefiting from this unique architecture, a high specific discharge capacity of 400 mA h g−1 with well-maintained two-step galvanostatic discharge profiles can be obtained at an ultra-high current density of 13.4 A g−1.

MnO is a promising anode material for lithium-ion batteries due to its high theoretical capacity and low conversion potential, but it exhibits poor electrical conductivity and volume expansion and hence its practical application is hindered. In this work, we describe a high-conductive and low-expansion MnO/porous-graphene aerogel (MnO/PGA) hybrid with hierarchical pore structure, which was synthesized by a novel site-localized nanoparticle-induced etching strategy. While graphene network intrinsically guarantees fast electron transfer, it is the characteristic presence of nanosized pores on the graphene sheets that lead to high reversible capacity, favorable rate capability and cycling stability by (i) facilitating the electrolyte infiltration and shortening the diffusion distances of Li-ions, (ii) providing more defects on the graphene sheets to increase the lithium-storage active sites. As a result, the MnO/PGA hybrid exhibits a reversible electrochemical lithium storage capacity as high as 979.6 mA h g−1 at 0.5 A g−1 after 300 cycles and excellent rate capability of delivering 493.6 mA h g−1 at a high current density of 2 A g−1.

Much attention has been focused on the fabrication of large-scale single-crystalline graphene due to its high quality and impressive physical properties, which are essential and significant in electronics and optoelectronics applications. Here, well-aligned submillimeter-sized single-crystalline graphene arrays were successfully fabricated by a commercial printing-assisted chemical vapor deposition process. In this method, carbon precursor dots can be printed on Cu foil with a designed pattern, which can serve as the nucleation centers to induce the growth of graphene domains at the designed locations. This work provides a facile route to synthesize single-crystalline graphene arrays on a large scale, which is of great significance in building graphene devices for practical applications.

Graphene, a new carbon material with the highest thermal conductivity (TC) in known materials, is a good candidate for polymer-based thermally conductive material applications. However, the homogeneous dispersion of graphene and effective construction of graphene-based thermally conductive network in the polymer matrix still remains a big challenge. In this paper, we report an effective way to avoid aggregation of graphene in polymers through the fabrication of 3D porous graphene foam (GF) in advance by a simple solvent evaporation induced self-assembly method. The as-prepared GF is proved to be an effective thermally conductive network after the epoxy perfusion, giving rise to a high TC of 11.58 W (m−1 K−1) for the GF/epoxy composite. In addition, anisotropic TC in the GF/epoxy composites is observed because of the oriented arrangement of graphene sheets in the GF due to solvent evaporation. Besides, further improvement of TC to 16.69 W (m−1 K−1) can be achieved by addition of polyvinyl pyrrolidone (PVP) during the preparation of GF, which can be ascribed to the reduction of interfacial thermal resistance by amorphous carbon generated from pyrolysis of PVP.

Graphene, a new carbon material with the highest thermal conductivity (TC) in known materials, is a good candidate for polymer-based thermally conductive material applications. However, the homogeneous dispersion of graphene and effective construction of graphene-based thermally conductive network in the polymer matrix still remains a big challenge. In this paper, we report an effective way to avoid aggregation of graphene in polymers through the fabrication of 3D porous graphene foam (GF) in advance by a simple solvent evaporation induced self-assembly method. The as-prepared GF is proved to be an effective thermally conductive network after the epoxy perfusion, giving rise to a high TC of 11.58 W (m−1 K−1) for the GF/epoxy composite. In addition, anisotropic TC in the GF/epoxy composites is observed because of the oriented arrangement of graphene sheets in the GF due to solvent evaporation. Besides, further improvement of TC to 16.69 W (m−1 K−1) can be achieved by addition of polyvinyl pyrrolidone (PVP) during the preparation of GF, which can be ascribed to the reduction of interfacial thermal resistance by amorphous carbon generated from pyrolysis of PVP.

Three dimensional (3D) porous silicon/reduced graphene oxide (Si/rGO) composites with typical networks have suffered damage during electrode preparation, which evidently affects the cycle and rate capabilities of Si/rGO anodes. Here, a controllable evaporation dry method is proposed to fabricate structure-preserved 3D porous Si/rGO anode materials by tuning the pore size distribution of the networks. As a result, after evaporation drying for 3.5 h, the optimal sample of 3D porous Si/rGO anode (denoted as Si–G-3.5) with a pore size of ∼500 nm could preserve its 3D network during the electrode preparation process. While the structures of Si/rGO composites with different drying times (denoted as Si–G-0, Si–G-2.5 and Si–G-4) failed to be preserved. Consequently, The Si–G-3.5 anode exhibits a high reversible specific capacity of 1563 mA h g−1 at 50 mA g−1, 90% capacity retention after 100 cycles and superior rate capability (955 mA h g−1 at 2 A g−1).

The cyclability of lithium-ion batteries (LIBs) is often affected by the components of the solid electrolyte interphase (SEI) layer which is generated from electrochemical decomposition of electrolyte. Here, lithium difluorophosphate (LiPO2F2) is studied in this work. When 1.6 wt% LiPO2F2 additive is incorporated into the reference electrolyte, the capacity retention of graphite/Li half-cell is increased from 82.53% to 98.04% and the capacity retention of LiCoO2/Li half-cell is increased from 89.60% to 97.53% after 160 cycles. Electrochemical impedance spectroscopy (EIS) indicates that the SEI layer containing LiPO2F2 can decrease the surface impedance of cells in the last stage cycle. In situ atomic force microscopy (AFM), DFT calculations and X-ray photoelectron spectroscopy (XPS) results show that LiPO2F2 is deposited on the surface of both LiCoO2 and graphite electrodes, which effectively protects the graphite anode and suppresses the degradation of the cathode during the long-term cycling of LIBs.

Aluminum is a very good candidate anode for metal–air batteries due to its negative electrode potential, high theoretical electrochemical equivalent value, abundant reserves and environmental friendliness. The corrosion behavior and electrochemical properties of the Al–1.5Bi–1.5Pb–0.035Ga alloy were investigated by self-corrosion tests and electrochemical techniques, and compared with that of pure Al and Al–Bi–Pb alloys. The performances of Al–air batteries based on these alloy anodes were studied by constant current discharge and I–V discharge tests. The corrosion morphology and discharge surface were also investigated by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The results show that the Al–Bi–Pb–Ga alloy provides a more negative potential and exhibits an enhanced activity in NaCl solution compared with pure Al and Al–Bi–Pb alloys, and gives high power density (253.4 ± 2.5 mW cm−2) and desirable anode efficiency (85.4 ± 0.5%) when used as an anode for Al–air batteries in KOH solution. Moreover, the dissolution mechanism of the Al–Bi–Pb–Ga alloy is also characterized based on the electrochemical measurements and microstructure observations.

Non-flammable and low-cost aqueous batteries operating on “M+/N+-dual shuttles” (AMIB) offer great opportunities in large-scale utility grid applications. Here, for the first time, we demonstrate a series of high-voltage AMIB (>1.23 V) based on open-framework copper hexacyanoferrates (CuHCFs) as cathode materials, and TiP2O7 & NaTi2(PO4)3 as anode materials. Among them, CuHCF/NaTi2(PO4)3 possesses high power density as an ultra-capacitor (3006 W kg−1), but with a higher energy density (56 W h kg−1). Through multiple characterization techniques combined with ab initio calculations, the intercalation chemistry of alkali cations in CuHCF is revealed. With increasing ionic size, the most stable interstitial site changes from the face-centered site (24d) to the body-centered site (8c). The intercalation voltage for the alkali cations follows the order: K+ > Na+ > Li+. Meanwhile, the ion-selectivity among them follows the same order as the intercalation voltage, which accounts for the higher voltage outputs of AMIB in contrast to aqueous batteries operating on one shuttle.

As rechargeable Li-ion batteries have expanded their applications into on-board energy storage for electric vehicles, the energy and power must be increased to meet the new demands. Li-rich layered oxides are one of the most promising candidate materials; however, it is very difficult to make them compatible with high volumetric energy density and power density. Here, we develop an innovative approach to synthesize three-dimensional (3D) nanoporous Li-rich layered oxides Li[Li0.144Ni0.136Co0.136Mn0.544]O2, directly occurring at deep chemical delithiation with carbon dioxide. It is found that the as-prepared material presents a micrometer-sized spherical structure that is typically composed of interconnected nanosized subunits with narrow distributed pores at 3.6 nm. As a result, this unique 3D micro-/nanostructure not only has a high tap density over 2.20 g cm–3 but also exhibits excellent rate capability (197.6 mA h g–1 at 1250 mA g–1) as an electrode. The excellent electrochemical performance is ascribed to the unique nanoporous micro-nanostructures, which facilitates the Li+ diffusion and enhances the structural stability of the Li-rich layered cathode materials. Our work offers a comprehensive designing strategy to construct 3D nanoporous Li-rich layered oxides for both high volumetric energy density and power density in Li-ion batteries.Keywords: 3D nanoporous; cathode materials; lithium-ion batteries; lithium-rich oxides; power energy density; volumetric energy density;

Graphene nanosheets have shown a significant strengthening effect for metal matrixes. In this paper, we develop a novel eletroless plating method to prepare Ni decorated graphene as an enhancing component in a copper matrix. A good dispersion of Ni nanoparticles on graphene sheets is achieved, which effectively enhances the interfacial compatibility between graphene and copper. The electroless plated graphene-copper composite bulk has a better performance in the mechanical tensile strength compared to pure copper, and also maintains superior ductility, elongation and electrical conductivity.

•Hydroxyl-containing agents cross-linked graphene monolith is prepared.•Such graphene monolith shows high stability and high removal capacity of Pb2+.•The mechanism of enhanced removal capacity is revealed by quantitative analysis.Three-dimensional (3D) graphene-based architectures are one new type of adsorption materials for environmental purification. Here, we report a facile approach to fabricate 3D graphene oxide (GO) monoliths based on the auxiliary cross-linkage of simple organic molecules with double hydroxyls/carboxyls. Hydroxyl-containing molecules are more conducive than carboxyl-containing agents to induce GO macrostructures with well structural stability and plasticity. The GO-based monoliths cross-linked by hydroxyl-containing agents, especially glycol with double hydroxyls, show a high removal capacity for Pb2+, which also exhibit excellent recyclability via easy regeneration. Quantitative analysis reveals that the organic molecules with hydroxyl groups generate more dissociable groups in the 3D monolith, which provide more active sites for Pb2+ binding. Thus GO-based monoliths derived from the cross-linkage of hydroxyl-containing agents have a great potential for heavy metal removal.Download high-res image (132KB)Download full-size image

A novel layered graphene-based architecture is achieved via an ordered self-assembly process. Amphipathic graphene nanosheets are joined horizontally into large sheets via edge splicing, and a cross-linking agent of poly(vinyl alcohol) bridges them into integrated three-dimensional monoliths with tunable interlayer spacing. This layered architecture possesses highly ordered and favorable microchannels for molecular transfer.

Graphene-based electrodes with high gravimetric and high volumetric capacity simultaneously are crucial to the realization of high energy storage density, but still proved to be challenging to prepare. Herein, we report a three-dimensional porous graphene/Co aerogel with hierarchical porous structure and compressible features as a high-performance binder-free lithium-ion battery anode. In this composite aerogel, graphene nanosheets interconnect to form continuous macropores, and cobalt nanoparticles stemming from decomposition of cobalt salt not only react with carbon atoms of graphene to form nanopores on the graphene nanosheets, but also increase the conductivity of the aerogel. With efficient ion and electron transport pathways as well as high packing density, the compressed porous graphene/Co electrode exhibits significantly improved electrochemical performance including high gravimetric and volumetric capacity, excellent rate capability, and superior cycling stability. After compression, such a porous graphene/Co nanocomposite can deliver a gravimetric capacity of 900 mA h g−1 and a volumetric capacity of 358 mA h cm−3 at a current density of 0.05 A g−1. Furthermore, after 300 discharge/charge cycles at 1 A g−1, the specific capacity still remains at 163 mA h cm−3, corresponding to 90.5% retention of its initial capacity.

•Concentration-gradient LiMn0.8Fe0.2PO4 is constructed through solvothermal method.•The Mn dissolution of concentration cathode material is suppressed.•The rate capability of this concentration material is improved.•The cycle stability is improved, especially at elevated temperature.It is a great challenge to combine good cycling performance with high rate capability for LiMn1–xMxPO4 cathode materials owing to the Mn dissolution upon cycling and its low electronic/ionic conductivity. Here, we report a novel concentration-gradient structure of LiMn0.8Fe0.2PO4 material constructed by solvothermal treatment. This material shows a linear increase of Mn concentration from the edge to the particle centre, but the inverse trend for Fe concentration, which leads to the formation of Mn-rich phase in bulk and Fe-rich phase at surface. The Fe-rich phase effectively suppresses the corrosion from the electrolyte that minimizes the Mn dissolution and also improves the electronic/ionic conductivity of the surface that decreases the cathode/electrolyte interface resistance. Consequently, this concentration-gradient material achieves superior capacity retention with 98% after 50 cycles at 1 °C even at elevated temperature, and also exhibits an excellent rate capability with the reversible capacity of 130 mA h g−1 at 5 °C rate. These results suggest that the concentration-gradient LiMn0.8Fe0.2PO4 is an ideal type of cathode material for high performance Lithium ion batteries.

•Copper sulfide (CuS) nanorods were successfully synthesized.•A facile sol–gel method without using template and complicated treatment was used.•The as-prepared CuS nanorods as anode achieve great electrochemical performance.Copper sulfide (CuS) nanorods with the size of sub-10 nm are synthesized via a facile sol–gel method without post–thermal treatment. The as-prepared CuS nanorods are characterized by X-ray diffraction, transmission electron microscope, and energy dispersive X-ray spectroscopy as hexagonal covellite CuS. The as-prepared CuS nanorods utilized as anode material exhibit a high reversible capacity and excellent cycling stability up to 250 cycles, as well as high Coulombic efficiency. The unique structure of the CuS nanorods should be responsible for their excellent electrochemical performance.

•Small B3+ is doped into tetrahedral sites in Li-rich layered oxides.•Rietveld refinement indicates enlarged cell parameters of B doped samples.•Doped B blocks the migrated path of the transition metal ions.•B doped materials manifest greatly enhanced capacity and voltage stability.Migration of transition metal (TM) ions to tetrahedral sites plays a crucial role on structural transformation and electrochemical behaviors for Li-rich layered oxides. Here, incorporating small B3+ in the tetrahedral interstice is employed to block the migration channel of TM ions and stabilize the crystal structure. Benefiting from their good structural stability, Li-rich layered materials with B-doped Li1.198Ni0.129Co0.129Mn0.535B0.01O2 and Li1.196Ni0.127Co0.127Mn0.529B0.02O2, exhibit excellent cycling performance and voltage stability. After 51 cycles at 0.2 C, 1 mol.% boron incorporated sample can deliver 211 mAh g−1 with capacity retention of 89.9%, which is much higher than that of the undoped sample of 177 mAh g−1 with the retention of 79.2%. Moreover, the declined voltage per cycle decreases from 3.6885 mV to 2.7530 mV after 2 mol.% boron doping. XRD patterns after extended cycling verified the suppression of the structural transformation by the incorporation of boron.

•Micron Li-rich oxides have been synthesized by a new two-step method.•Micron particles result in high pellet density and good cycling performance.•High capacity of the micron Li-rich oxide was achieved after Na2S2O8 treatment.Li-rich layered oxides with micro-sized primary particles usually exhibit higher pellet density and better cycling performance. However, it is often at the expense of high reversible capacity. Here, we reported a simple strategy through a new chemical lithiation with micro-sized spinel-precursors and Na2S2O8 surface treatment to obtain micro-sized particles in the Li-rich Li1.172Ni0.135Co0.135Mn0.539O2 oxide without compromising its discharge capacity (260 mAh/g at 0.1C). Benefited from its larger particles and lower specific surface area, the obtained micron Li-rich layered material manifests its higher pellet density (3.18 g/cm3) and better cycling performance in comparison with the nano-sized Li-rich layered material. After 100 cycles at 0.1 C, it can still deliver a capacity of 192 mAh/g with retention of 74%, much higher than 167 mAh/g with retention of 67% of the nano-sized sample. Moreover, the micron Li-rich layered material also exhibits good rate performance with a capacity of 174 mAh/g at 2C benefited from the 3D Li+ insertion/extraction channel of its surface spinel content. These results may provide a new insight on improving pellet density of high-performance Li-rich layered cathode materials.

•The durable carbon layer is constructed by CVD coating method, successfully.•Mn dissolution of treated cathode material is effectively suppressed.•Long-term cycling performance of the treated cathode material is improved.•The rate capability of the treated material is enhanced.LiMn0.8Fe0.2PO4 is becoming one of the most promising cathode materials for lithium ion batteries. However, the capacity suffers from a loss during long-term cycling, which is directly associated with Mn dissolution due to the disproportionation reaction of Mn3+. Here, we report a chemical vapor deposition (CVD) approach to modify LiMn0.8Fe0.2PO4 particles with carbon so as to minimize Mn dissolution from cathode. The deposited carbon layer not only protects LiMn0.8Fe0.2PO4 cathode from electrolyte corrosion, but also enhances the electronic/ionic conductivity owing to its higher graphitize degree. As a consequence, the electrochemical performances have a significant improvement. The capacity retention achieves 96% after 450 cycles at 1 C at room temperature (25 °C). Even at elevated temperature (55 °C), the capacity retention also reaches at 97 % after 50 cycles at 1 C rate, which is much higher than that of untreated sample (89%). Hence, the cathode material based on LiMn0.8Fe0.2PO4 encapsulated with durable carbon by CVD method represents a promising strategy for developing its long-term cycling performance through suppressing Manganese dissolution.

In this paper, the hybrid catalysts of manganese oxide decorated by silver nanoparticles (Ag-MnOx) are fully investigated and show the excellent oxygen reduction reaction (ORR) activity. The Ag-MnO2 is synthesized by a facile strategy of the electroless plating of silver on the manganese oxide. The catalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Then, the ORR activities of the catalysts are systematically investigated by the rotating disk electrode (RDE) and aluminum-air battery technologies. The Ag nanoparticles with the diameters at about 10 nm are anchored on the surface of α-MnO2 and a strong interaction between Ag and MnO2 components in the hybrid catalyst are confirmed. The electrochemical tests show that the activity and stability of the 50%Ag-MnO2 composite catalyst (the mass ratio of Ag/MnO2 is 1:1) toward ORR are greatly enhanced comparing with single Ag or MnO2 catalyst. Moreover, the peak power density of the aluminum-air battery with 50%Ag-MnO2 can reach 204 mW cm−2.

Silicon (Si)/carbon nanotubes (CNTs) composites are ideal anode materials for lithium ion batteries. However, due to the large volume expansion mismatch between Si and CNTs, the cycle life of conventional Si/CNTs composites fabricated by different approaches is still very limited. Here, a novel Si/nickel-Si alloy (NiSix)/CNTs composite has been successfully designed and fabricated through a chemical vapor deposition method with the assistance of uniformly embedded Ni nanoparticles. The CNTs grow up from the composite and serve as strong rivets, which greatly improves the electrical connection stability at the interface between Si and CNTs. Consequently, the corresponding discharge capacity can remain at around 550 mA h g−1 with a capacity retention of 84% for 300 cycles, while a high rate capability can be achieved with a discharge capacity of 420 mA h g−1 at 4 A g−1.

Three-dimensional (3D) graphene networks are attracting ever-increasing attention in the field of energy storage because their unique architecture at macroscopic scales is beneficial for effective electron and ion transport. Herein, a novel interconnected 3D graphene mesh network (3D GMN) was successfully designed and fabricated by folded Ni meshes assisted chemical vapor deposition method. The structure parameters of 3D GMN can be controlled well by tuning the period of Ni mesh and the electroplating time. With the increase of the density of 3D GMN, the electrical conductivity of 3D GMN and the thermal conductivity of 3D GMN/epoxy composite are greatly improved compared to that of the 3D graphene foam. This 3D GMN enables the high capacity of 57 mA h g−1 in an aluminum ion battery at the ultra-high rate of 40C with capacity retention of 96.5% after 200 cycles.

Pore size is a critical parameter that affects the basic physicochemical properties and applications of porous graphene foam, but the preparation of graphene foam with controllable pore size is still a big challenge, especially by a self-assembly method. In this work, graphene oxide (GO) sheets with different lateral sizes by controlling the delamination conditions of graphite oxide were used as building blocks to form graphene foams with adjustable pore size, by a convenient one-step hydrothermal self-assembly method. The pore sizes of graphene foams can be effectively controlled by simply altering the sheet sizes of GO, and the smallest average pore size is ∼500 nm, which is much smaller than the micrometer-scale pores in the reported graphene foam materials. Static contact angles, nitrogen adsorption–desorption isotherms and adsorption of methylene blue are measured to demonstrate the strong dependence of some important physicochemical properties of graphene foams on their pore sizes. This simple method offers a novel way to rationally synthesize graphene foam with appropriate pore size for various practical applications.

Silicon, as a next generation anode material, suffers from low electronic conductivity and large volume changes during the lithiation/delithiation process, resulting in very large capacity fading upon cycling. Herein, we design a novel sandwich-structured Si/C electrode formed between two conductive carbon layers. In this configuration, the bottom carbon layer functions as a buffer layer to increase the adhesion to the Cu foil and to avoid peeling-off of the active materials, whereas the top carbon layer on the electrolyte side serves as a barrier layer to prevent the electrode surface from cracking and delaminating. As expected, the sandwich-structured Si/C electrode delivers a high reversible capacity of 1230 mA h g−1 at current density of 150 mA g−1 and exhibits excellent cycling stability without obvious capacity decay after 70 cycles. This simple and effective design would be a promising approach to obtain high performance and cost-effective Si anodes on a large-scale, especially for industrial manufacturing of high energy density Li-ion batteries.

Graphene nanosheets have shown great potential in enhancing the strength of metal composites. In previous researches, reduced graphene oxide (rGO) are usually used as the additive. Here, we demonstrate that pristine graphene (PG) prepared by intercalation and exfoliation of graphite, with negligible oxygen-containing functional groups, much less defects and higher electrical conductivity than rGO, exhibits better performance than rGO as additives for the enhancement of the strength of metal composites. Surface modification of PG and Cu was conducted to enhance the interaction between two components, resulting in homogeneous distribution of PG in Cu matrix. The PG/Cu composite exhibits yield strength σ0.2 and 5% compression strength up to 172 and 228 MPa, respectively, which is a 90% and 81% promotion comparing to pure Cu, while its electrical conductivity still stays at 84.2% IACS. As to rGO/Cu composite, yield strength σ0.2 and 5% compression strength is 156 and 208 MPa, respectively, and its electrical conductivity is 73.4% IASC. Such significant improvement on strength can be explained by the two-dimensional geometry and high crystallinity of PG whose high strength and modulus effectively constrain the movement of dislocations.

Flexible, lightweight and reliable lithium-ion batteries have attracted tremendous attention and research interest to meet the requirements of portable and bendable devices. Here, flexible, free-standing and porous graphene/Ni film with vertical nano-channels inside is prepared by metal etching of graphene film. Compared with dense graphene film, the porous graphene/Ni film employed as a binder-free anode in lithium-ion batteries exhibits higher capacity and much better rate capability, due to its unique interior channel architecture which is favorable for fast ion transport. At a high current density of 2 A g−1, it can reach a specific capacity of 117 mAh g−1. The porous film also shows low charge transfer resistance and good cycling stability. After 300 cycles at 1 A g−1, its specific capacity still remains at 147 mAh g−1, with high Coulombic efficiency of nearly 100%. Furthermore, the strategy developed here is very simple and of great importance to rational design of porous graphene film or graphene-based hybrids with various applications.

The Li-rich layered oxides are attractive electrode materials due to their high reversible specific capacity (>250 mA h g−1); however, the origin of their abnormal capacity is still ambiguous. In order to elucidate this curious anomaly, we compare the lattice oxygen oxidation states among the Li-rich layered oxide Li1.14Ni0.136Co0.136Mn0.544O2, Li2MnO3 and LiNi0.5Co0.2Mn0.3O2, the two components in Li-rich layered oxides, and the most common layered oxide LiCoO2 before and after initial charge–discharge. For simplicity, we employ chemical treatments of NO2BF4 and LiI acetonitrile solutions to simulate the electrochemical delithiation and lithiation processes. X-ray photoelectron spectroscopy (XPS) studies reveal that part of lattice oxygen in Li1.14Ni0.136Co0.136Mn0.544O2 and Li2MnO3 undergoes a reversible redox process (possibly O2− ↔ O22−), while this does not occur in LiNi0.5Co0.2Mn0.3O2 and LiCoO2. This indicates that the extra capacity of Li-rich layered oxides can be attributed to the reversible redox processes of oxygen in the Li2MnO3 component. Thermogravimetric analysis (TGA) further suggests that the formed O22− species in the delithiated Li1.14Ni0.136Co0.136Mn0.544O2 can decompose into O2 at about 210 °C. This phenomenon demonstrates a competitive relationship between extra capacity and thermal stability, which presents a big challenge for the practical applications of these materials.

Activated graphene has been considered as an ideal electrode material for supercapacitors. In order to reveal the relationship between activated graphene and its precursor and controllably synthesize activated graphene, the structural parameters of the precursor (reduced graphene oxide, RGO) such as crystallinity and attached oxygen-functional groups were controllably adjusted during the synthesis of activated graphene and the effects of the precursor structure on the microstructure of activated graphene were investigated. The activation results reveal that the structure of RGO obviously affects the porous structure of activated graphene. Specifically, the crystallinity and oxygen-functional groups play an important role in the porosity development of activated graphene. By combining the simplified Brodie method and the subsequent post-oxidation process, porous activated graphene with a specific surface area of as high as 2406 m2 g−1 and high pore volume has been successfully prepared. The as-prepared activated graphene exhibits good capacitive characteristics and delivers high energy density (55.7 W h kg−1) when measured in a two-electrode cell with the EMIMBF4 ionic liquid as the electrolyte. The results demonstrate that the obtained activated graphene can be considered as a candidate for advanced electrode materials for supercapacitors.

A composite membrane with an ultra-thin ion exchangeable layer is specially designed as a separator in lithium ion batteries with manganese-based cathode materials. The composite membrane features a Mn2+ capture function which originates from the ion exchanging process, especially at high temperature, and is proven to help to alleviate the capacity decay of lithium ion batteries effectively. The enhanced thermal stability, improved wettability and higher lithium ion transference number of the composite membrane further suggest its promising application in lithium ion batteries.

Novel two-dimensional (2D) porous metal oxides with micro-/nanoarchitecture have been successfully fabricated using graphene oxide (GO) as a typical sacrificial template. GO as a 2D template ensures that the growth and fusion of metal oxides nanoparticles is restricted in the 2D plane. A series of metal oxides (NiO, Fe2O3, Co3O4, Mn2O3, and NiFe2O4) with similar nanostructure were investigated using this simple method. Some of these special nanostructured materials, such as NiO, when being used as anode for lithium-ion batteries, can exhibit high specific capacity, good rate performance, and cycling stability. Importantly, this strategy of creating a 2D porous micro/nano architecture can be easily extended to controllably synthesize other binary/polynary metal oxides nanostructures for lithium-ion batteries or other applications.Keywords: graphene; lithium-ion battery; metal oxides; nanostructure; two dimensional;

•Porous Si–C composites were fabricated by a facile sacrificing method.•Cycle life can be greatly improved by building 0D, 1D and 2D electrical bridges.•The capacity reaches 800 mAh/g for 220 cycles in rGO bridged electrode.•The content of porous active materials can be kept at as high as 80%.Porous silicon–carbon (Si–C) composites have been considered to be one of the most effective architectures to improve the cycle life of Si based anode because of its native ability to accommodate the large volume change during discharge/charge process. It is found that lots of reported porous Si–C electrodes employed large amount of binder materials to enhance the structural stability which significantly decreased gravimetric capacity of the whole electrode with limited active materials. In this work, without loss of active materials, various conducting agents were used to build electrical bridges between porous Si–C composites, which significantly improved the structural stability and hence the cycle life. Due to the increase of connection possibilities, cycle life of zero-dimensional MCMB bridged electrode reaches 80 cycles with a capacity retention of 80%, and it can be further promoted to 200 cycles for the VGCF bridged electrode and 220 cycles for the rGO bridged electrode. This work paves an effective route to construct stable Si electrode with porous structures as building blocks without the decrease of active materials.

•Transition metal ion migration occurs at the potential above the activation energy.•The charge/discharge lower-limit voltages have no impact on voltage decay.•Voltage decay becomes severer with increased upper-limit voltages.•Holding at high voltages for a prolonged time also accelerates voltage decay.Voltage decay of Li-rich cathode material is caused by migration of transition metal (TM) ions and layered phase transformation to spinel phase. Here electrochemical studies demonstrate that charge/discharge voltage ranges have a strong impact on the voltage decay. For cells cycling in the charge/discharge condition of voltage range at 2.0–4.6 V, 3.2–4.6 V and 4.2–4.6 V, voltage decay phenomena occur to the same extent. While for the serial conditions of 2.0–4.2 V, 2.0–4.4 V, 2.0–4.6 V, 2.0–4.8 V and 2.0–4.6V + hold at 4.6 V for 5 h, voltage decay starts to occur at a typical voltage when the potential is high enough, and then phase transformation becomes severer with increased potentials, or prolonged time holding at high voltages. TM ions at high voltages have high enough energy, which can be denoted as “activation energy”, to stride across the transition state and migrate to Li vacancy, which results in spinel formation and voltage decay.

•Preparation of the interconnected regular pores in the GDL.•Gas permeability of the GDL with the regular pores was improved.•Pmax of the Mg air batteries with the regular porous GDL was elevated.•The porous GDL exhibited the improved the long term stability.The uniform micropore distribution in the gas diffusion layers (GDLs) of the air-breathing cathode is very important for the metal air batteries. In this work, the super-hydrophobic GDL with the interconnected regular pores is prepared by a facile silica template method, and then the electrochemical properties of the Mg air batteries containing these GDLs are investigated. The results indicate that the interconnected and uniform pore structure, the available water-breakout pressure and the high gas permeability coefficient of the GDL can be obtained by the application of 30% silica template. The maximum power density of the Mg air battery containing the GDL with 30% regular pores reaches 88.9 mW cm−2 which is about 1.2 times that containing the pristine GDL. Furthermore, the GDL with 30% regular pores exhibits the improved the long term hydrophobic stability.

•Thiophene derivatives (THs) can serve as novel electrolyte additives for LIBs.•THs tend to be electro-polymerized on LiCoO2 cathode prior to the solvents.•A conducting polymer film can be formed using THs additives in the electrolyte.•The cycling stability of high voltage LiCoO2 is obviously improved using additives.Thiophene derivatives (THs) are examined as novel functional additives for improving the cycling performance of high-voltage LiCoO2. Our investigation reveals that 2,2′-Bithiophene (2TH) and 2,2′:5′,2′′-Terthiophene (3TH) can be electrochemically polymerize prior to the electrolyte solvent decomposition to form a protective layer of conducting polymer film on the cathode surface, which blocks off severe electrolyte decomposition at high voltages and, therefore, improves the cycling stability of high voltage LiCoO2 cathode. After 100 cycles at a high cutoff voltage of 4.4 V, the discharge capacity retention is 50% in the base electrolyte, in contrast, the LiCoO2 cathode cycled in the electrolyte containing 0.1 wt% 3TH displays a high capacity retention of 84.8% at 0.25 C rate. This work demonstrates that these thiophene derivatives have considerable potential as functional additives for the applications in high-voltage lithium-ion batteries.

A TiO2(B)–CNT–graphene ternary composite material was prepared by in situ growth of TiO2(B) on a conductive network composed of both graphene and CNTs. TiO2(B) has nanorod morphology and is dispersed uniformly in the carbon matrices. Graphene in this composite acts as sheet-like mini-current collectors that loads TiO2(B), whereas CNTs further enhance the electrical conductivity of TiO2(B) by intimate contact between the two components in local regions, and also prevent the restacking between graphene layers. The composite anode material exhibits a capacity of 190 mA h g−1 even after 200 cycles at 1 C, presenting excellent rate performance.

A simple method has been developed to prepare nitrogen-doped porous graphene–activated carbon (AC) composites as high-performance electrode materials for supercapacitors. The graphene-based “bucky gels”, prepared by simple mixing and grinding of graphene in ionic liquids (ILs), are carbonized to form an “untractable char” intermediate product, and finally converted to the nitrogen-doped porous graphene–AC composite by chemical activation using KOH. Results demonstrate that the introduction of graphene sheets into the composite not only effectively enhance the specific surface area and conductivity of graphene–AC composite, but also enlarge the pore size in the electrode material compared with pure AC. In addition, the nitrogen-doping can further improve the kinetics for both charge transfer and ion transport throughout the electrode. It's found that the composite has a large specific surface area of 2375.2 m2 g−1, and also contains plenty of mesopores and appreciable nitrogen-doping amount. It exhibits a specific capacitance up to 145 F g−1 at 20 mV s−1 in 6 M KOH electrolyte, and the specific capacitance decreases by only 1.6% after 5000 cycles. This kind of nitrogen-doped composite represents an alternative promising candidate as electrode material for supercapacitors.

To develop a kind of gel polymer electrolyte with high ion conductivity and good mechanical strength and thermal stability, a polyimide (PI) matrix-enhanced cross-linked gel separator is designed and fabricated by a simple dip-coating and heat treatment method. The PI nonwoven substrate provides high-temperature thermal stability for the gel separator and the crosslinked gel part yields enhanced affinity with the liquid electrolyte. Besides, the cross-linked polymer network could solve the issue of long-term durability of the composite separator in batteries. The gel separator shows better cyclability and rate capability than the traditional PP separator, implying a promising potential application in high-power, high-safety lithium ion batteries. The preparation process is compatible with the traditional manufacturing process of nonwoven membranes, and can be easily converted into continuous production on the industrial scale.

A simple solution-based oxidative process and subsequent chemical activation combination method has been developed to prepare edge-enriched porous graphene nanoribbons (GNRs) as a high-performance electrode material for supercapacitors. The precursor aligned carbon nanotubes are cut longitudinally and unzipped by a modified Brodie method to form tube-like GNRs with abundant edges. The intermediate GNRs were subsequently chemically activated using KOH to generate a suitable porosity and create more edge sites. These edge sites contribute a larger capacitance than the basal plane of graphene and the nanopores facilitate the fast immigration of ions. As a result, the edge-enriched GNRs exhibit a capacitance uptake per specific surface area almost two times higher than that of conventional activated graphene sheets, which gives rise to the high energy density of the porous GNR electrode. The highly efficient utilization of the edge planes and easy, low-cost scale-up production will make porous GNRs potentially applicable to high-performance supercapacitors.

Electrode films fabricated with lithium-rich layered 0.3Li2MnO3–0.7LiNi5/21Co5/21Mn11/21O2 cathode materials have been successfully modified with ZnO coatings via a reactive magnetron sputtering (RMS) process for the first time. The morphology and chemical composition of coating films on the electrodes have been in deep investigated by transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) characterizations. The results clearly demonstrate that ZnO film coatings are ultrathin, dense, uniform, and fully covered on the electrodes. The RMS-2 min (deposition time) coated electrode exhibits much higher initial discharge capacity and coulombic efficiency with 316.0 mAh g–1 and 89.1% than that of the pristine electrode with 283.4 mAh g–1 and 81.7%. In addition, the discharge capacity also reaches 256.7 and 187.5 mAh g–1 at 0.1 and 1.0 C-rate, as compared to that of 238.4 and 157.8 mAh g–1 after 50 cycles. The improved electrochemical performances of RMS-coated electrodes are ascribed to the high-quality ZnO film coatings that reduce charge transfer resistance and effectively protect active material from electrolyte oxidation.Keywords: initial coulombic efficiency; lithium-ion batteries; lithium-rich layered oxide cathode; reactive magnetron sputtering; zinc oxide coating;

•The Fe-doping LiMnPO4 nanomaterials were synthesized by a solvothermal method.•The particle morphology could be controlled simply by adjusting the pH values of precursor suspensions.•The nanoplates along with [010] crystallographic axis with 20–30 nm could deliver the largest discharge capacity.•Fe doping could significantly increase the initial reversible capacity.The Fe-doping LiMnPO4 (LiMn1−xFexPO4, x ≤ 0.5) nanomaterials are solvothermally synthesized in a mixed solvent of water and polyethylene glycol (PEG). The particle morphology can be controlled simply by adjusting the pH values of precursor suspensions. Electrochemical test shows that LiMn0.9Fe0.1PO4 nanoplates with a thickness of 20–30 nm could deliver the largest discharge capacity, which is attributed to the fast Li+ diffusion in the diffusion path of [010] crystallographic axis along the short radial direction of the nanoplates. It is demonstrated that Fe doping could significantly increase the initial reversible capacity, cycle performance and rate capability. The first discharge capacities of Fe-doped LiMnPO4 are all above 150 mAh g−1 at the discharge rate of 0.05 C. Especially, LiMn0.5Fe0.5PO4 delivers 100% capacity retention with the reversible capacity of 147 mAh g−1 at the discharge rate of 1 C, and losses only about 23.4% capacity with the discharge rate varying from 0.1 C to 5 C. The variation of energy density predicts that LiMn0.5Fe0.5PO4 shows the potential application for high-power devices.

•The surface structure transforms from layered to spinel during heat treatment.•The surface spinel undergoes an internal structural evolution at high temperature.•The electrochemical performances are obviously improved after heat treatment.•The mechanism of structural transformation is discussed.A surface modification strategy through soaking in Na2S2O8 aqueous solution and then annealing has been developed for Li-rich layered cathode materials for Li-ion batteries. The modified materials have a significant improvement on electrochemical performances. The initial discharge capacity increases from 257 to 285 mAh g−1, and the initial coulombic efficiency increases from 85.4% to 93.2% in the voltage rang of 2.0–4.6 V. The electrochemical enhancement mechanism has been revealed by detailed investigations on the surface structural conversion of the material. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectrometry (ICP) confirm that Na2S2O8 oxidizes lattice oxygen to formal O22− species and the corresponding Li+ is extracted from the material surface. On the subsequent annealing, the formal O22− species turn to O2 and release from the particle surface. The increased oxygen vacancies induce structural rearrangement and lead to the phase transition from layered (R-3m or C2/m) to spinel (Fd3m) at the particle surface, which is supported by X-Ray Diffraction (XRD) and high resolution transmission electron microscope (HRTEM). It is also found that the spinel phase increases with the increasing annealing temperature, and an internal structural evolution from LiM2O4-type spinel to M3O4-type spinel takes place at the same time.

•The ICE for Li-rich layered oxides is significantly dependent on the testing temperature.•The lithium intercalation into MnO2-like component greatly dominates the ICE.•The ICE reproducibly approaches 92% when discharged at 50 °C regardless of charging temperature.In this study we report on the temperature dependence of the initial coulombic efficiency (ICE) in Li-rich layered Li[Li0.144Ni0.136Co0.136Mn0.544]O2 oxide, consisting of rhombohedral LiNi1/3Co1/3Mn1/3O2 and monoclinic Li2MnO3 component confirmed by SXRD and SAED. The electrochemical result shows that the ICE increases from 74.6 to 91.5% with the applied charging/discharging temperature from 0 to 50 °C, and it reproducibly approaches 92% when discharged at 50 °C, regardless of the applied charging temperature. From the dQ/dV plots, it is observed that the discharging temperature significantly influences the lithium intercalation into the MnO2-like component derived from Li2MnO3 component, i.e. the discharge process determines the ICE. This phenomenon indicates that the lithium re-intercalation into the MnO2-like component appears to be the most important factor.

•As-prepared carbonate precursor possesses concentration gradient.•Spherical LiNi0.5Mn1.5O4 material is core–shell structure.•The batteries have superior rate capability and high-temperature cycle performance.•Excellent electrochemical properties come from its unique core–shell structure.Spherical LiNi0.5Mn1.5O4 material with a core–shell structure is synthesized by a urea-assisted hydrothermal method followed by heat treatment with LiOH at high temperature. After the process of hydrothermal treatment, the carbonate precursor with a concentration gradient is produced, in a single spherical particle, the content of Ni in the surface is higher than that in the center while Mn has a reversal trend. LiNi0.5Mn1.5O4 synthesized through the hydrothermal route has a great improvement in cycling stability at elevated temperature and rate capability. The capacity retention can maintain at 95% after 30 cycles at 55 °C. Furthermore, it can deliver a discharge capacity of 118 mAh g−1 at a high rate of 10 C at room temperature. Such excellent electrochemical properties of LiNi0.5Mn1.5O4 can be ascribed to its unique core–shell structure and nano-size particle.

•Porous graphene/activated carbon was prepared via hydrothermal carbonization and subsequent two-step chemical activation.•The composites owe a high packing density and has a specific capacitance of 210 F g−1.•A high capacity retention rate of 94.7% after 5000 cycles can be achieved.A simple method has been developed to prepare graphene/activated carbon (AC) nanosheet composite as high-performance electrode material for supercapacitor. Glucose solution containing dispersed graphite oxide (GO) sheets is hydrothermally carbonized to form a brown char-like intermediate product, and finally converts to porous nanosheet composite by two-step chemical activation using KOH. In this composite, a layer of porous AC coats on graphene to from wrinkled nanosheet structure, with length of several micrometers and thickness of tens of nanometer. The composite has a relatively high packing density of ∼0.3 g cm−3 and large specific surface area of 2106 m2 g−1, as well as containing plenty of mesopores. It exhibits specific capacitance up to 210 F g−1 in aqueous electrolyte and 103 F g−1 in organic electrolyte, respectively, and the specific capacitance decreases by only 5.3% after 5000 cycles. These results indicate that the porous graphene/AC nanosheet composite prepared by hydrothermal carbonization and chemical activation can be applied for high performance supercapacitors.

•The (1-x)LiMnPO4·LixTix(PO4)δ samples were synthesized through a solid-state method.•The content of Ti additive greatly affects the electrochemical performance of LiMnPO4.•The sample synthesized with 10% Ti exhibits the best electrochemical performance.The (1-x)LiMnPO4·LixTix(PO4)δ (x = 0, 0.01, 0.05, 0.10, 0.15, 0.20) cathode materials are successfully synthesized through a solid-state method. The structures and electrochemical properties of the prepared samples have been characterized comprehensively. It is found minority phases containing LiTi2(PO4)3 and TiP2O7 were formed. The addition of Ti has obviously reduced the size of grains. Electrochemical tests indicate that the discharge capacities of LiMnPO4 samples can be significantly improved with the addition of Ti. Especially, the (1-x)LiMnPO4·LixTix(PO4)δ sample with x = 0.1 has the largest discharge specific capacity, which is more than 131 mAh g−1 at 0.05 C. And EIS tests1demonstrate that the 0.9LiMnPO4·Li0.1Ti0.1(PO4)δ sample has lower charge transfer resistance and higher diffusion coefficient than the pristine LiMnPO4 sample.

The electrochemical performance of the 18650 lithium-ion batteries for layered Li-excess oxide Li1.144Ni0.136Co0.136Mn0.544O2(LNCMO) cathode material and mesocarbon microbead (MCMB) anode material is investigated. The battery shows an excellent rate capability with the capacity of 227 mAh g−1 at 8 C-rate (the cut-off voltage is 4.5 V). Furthermore, it exhibits excellent cycle performance that the capacity retention over 300 cycles in the voltage ranges of 2.5-4.5 V (vs. MCMB) and at 0.2 C-rate is about 85%. Although the medium voltage of the battery greatly reduces during the first 30 cycles, it keeps stable in the following cycles. The mechanisms of the capacity fade and voltage decay are also studied based on energy dispersive spectrometry, X-ray photoelectron spectroscopy, charge-discharge curves, and dQ/dV plots.

•A series of (1−x)LiMnPO4·xLi3V2(PO4)3/C were synthesized by solid-state method.•The ratios of LiMnPO4 to Li3V2(PO4)3 are correlated with the properties of samples.•The 0.6LiMnPO4·0.4Li3V2(PO4)3 exhibits the best electrochemical performance.A series of (1−x)LiMnPO4·xLi3V2(PO4)3/C (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 1) composites cathode materials are successfully synthesized by solid-state method. The structures and properties of the composites have been studied with X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental mapping, high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS) and electrochemical measurements. XRD results reveal that the composites comprise Li3V2(PO4)3 phase and LiMnPO4 phase with a small amount of LiVP2O7 impurity. The electrochemical measurement results show that the ratios of LiMnPO4 to Li3V2(PO4)3 are correlated with the electrochemical performances of the composite materials. Among these composites, the 0.6LiMnPO4·0.4Li3V2(PO4)3 exhibits the best electrochemical performance, it can deliver specific capacity of 154 mA h g−1 at 0.05 C charge–discharge rate.

A simple method to prepare nitrogen-doped graphene (NG) by a pressure-promoted process at relatively low temperatures is demonstrated. The NG with an atomic N content higher than 10% can be obtained by heating graphene oxide and NH4HCO3 in a sealed autoclave at a temperature as low as 150 °C. The product exhibits a specific capacitance of 170 F g−1 at 0.5 A g−1 in 5 M KOH, and a high retention rate of 96.4% of its initial capacitance after 10,000 charge/discharge cycles at a current density of 10 A g−1. Such an easy, cost-effective and low-temperature doping process will be promising for preparing devices based on NG.

A flexible composite film composed of carbon nanotubes (CNTs) and sulfur as the cathode for lithium–sulfur (Li–S) batteries is prepared by coating an ultrathin sulfur nanolayer on a preprepared CNT film through a simple two-step heating process. The sulfur–CNT composite film with an areal density of ∼5 mg cm–2 has a high sulfur content of 65 wt % and is tough enough to be directly employed as the cathode in Li–S cells without binders, conductive additives, and current collectors. The porous and film-like CNT matrices enormously improve the electrical conductivity of sulfur and offer 3D pathways for fast Li ion diffusion, while the strong covalent bonds formed between sulfur and CNTs ensure the stability of sulfur during charge/discharge. Consequently, the film electrode delivers an initial capacity of 1100 mA h g–1 and can retain a reversible capacity of 740 mA h g–1 after 100 charge/discharge cycles at 0.1 C. It also shows good rate capability that a reversible capacity of 520 mA h g–1 can be reached at the rate of 2 C. Moreover, the high sulfur content gives rise to a high energy density of ∼1200 W h kg–1 based on the total mass of the electrode.

Morphology-controlled monodispersed LiMnPO4 nanocrystals as high-performance cathode materials for Li-ion batteries have been successfully synthesized by a solvothermal method in a mixed solvent of water and polyethylene glycol (PEG). Morphology evolution of LiMnPO4 nanoparticles from a nanorod to a thick nanoplate (∼50 nm in thickness) and to a smaller thin nanoplate (20–30 nm in thickness) is observed by increasing the pH value of the reaction suspension. Electrochemical measurements confirm that the LiMnPO4 thin nanoplates display the best charge–discharge performance, thick nanoplates the intermediate, nanorods the worst, which can be mainly ascribed to the difference in their morphologies and particle sizes in three dimensions. Further modification of LiMnPO4 thin nanoplates with graphene gives rise to an improved electrochemical performance compared with conventional pyrolytic carbon coated ones. The LiMnPO4 thin nanoplate/graphene composites deliver a high capacity of 149 mA h g−1 at 0.1 C, 90 mA h g−1 at 1 C, and even 64 mA h g−1 at 5 C charge–discharge rate, with an excellent cycling stability.

A 3D porous architecture of Si/graphene nanocomposite has been rationally designed and constructed through a series of controlled chemical processes. In contrast to random mixture of Si nanoparticles and graphene nanosheets, the porous nanoarchitectured composite has superior electrochemical stability because the Si nanoparticles are firmly riveted on the graphene nanosheets through a thin SiOx layer. The 3D graphene network enhances electrical conductivity, and improves rate performance, demonstrating a superior rate capability over the 2D nanostructure. This 3D porous architecture can deliver a reversible capacity of ∼900 mA h g−1 with very little fading when the charge rates change from 100 mA g−1 to 1 A g−1. Furthermore, the 3D nanoarchitechture of Si/graphene can be cycled at extremely high Li+ extraction rates, such as 5 A g−1 and 10 A g−1, for over than 100 times. Both the highly conductive graphene network and porous architecture are considered to contribute to the remarkable rate capability and cycling stability, thereby pointing to a new synthesis route to improving the electrochemical performances of the Si-based anode materials for advanced Li-ion batteries.

Solid solutions between Li[Li1/3Mn2/3]O2 and LiMO2 (M = Ni1/3Mn1/3Co1/3, Ni0.4Mn0.4Co0.2, Ni0.45Mn0.45Co0.1, Ni0.5Mn0.2Co0.3, and Ni0.5Mn0.3Co0.2) have been synthesized by a solid-state reaction method. The as-prepared Li1.2Ni0.13Mn0.54Co0.13O2, Li1.2Ni0.16Mn0.56Co0.08O2, Li1.2Ni0.18Mn0.58Co0.04O2, Li1.2Ni0.2Mn0.48Co0.12O2, and Li1.2Ni0.2Mn0.52Co0.08O2 solid solutions cathode materials can deliver discharge capacities of 267, 262, 253, 235, and 238 mAh g−1, respectively, at a charge/discharge current density of 25 mA g−1 in the voltage range of 2.5–4.7 V. These cathodes all have initial coulombic efficiencies larger than 80%, and show capacity loss less than 0.13% per cycle while cycling at 125 mA g−1 for 50 cycles. From Rietveld refinement results and electrochemical impedance spectra (EIS) analysis, it is found that the highest charge/discharge capacity values of Li1.2Ni0.13Mn0.54Co0.13O2 cathode with the lowest Ni content among them are attributed to the lowest cation mixing. While both the Li1.2Ni0.2Mn0.48Co0.12O2 and Li1.2Ni0.2Mn0.52Co0.08O2 cathode materials with higher Ni content exhibit better rate capabilities due to their lower charge transfer resistances and higher electrical conductivities than those of other samples.Highlights► Li-rich solid solutions have been synthesized by a solid-state reaction method. ► Li1.2Ni0.18Mn0.58Co0.04O2 and Li1.2Ni0.2Mn0.52Co0.08O2 are firstly reported. ► The higher Ni content is, the higher cation mixing is, and the lower resistance is. ► Cation mixing influences capacity, while resistance affects rate capability.

A simple and scalable method is developed to synthesize TiO2/graphene nanostructured composites as high-performance anode materials for Li-ion batteries using hydroxyl titanium oxalate (HTO) as the intermediate for TiO2. With assistance of a surfactant, amorphous HTO can condense as a flower-like nanostructure on graphene oxide (GO) sheets. By calcination, the HTO/GO nanocomposite can be converted to TiO2/graphene nanocomposite with well preserved flower-like nanostructure. In the composite, TiO2 nanoparticles with an ultrasmall size of several nanometers construct the porous flower-like nanostructure which strongly attached onto conductive graphene nanosheets. The TiO2/graphene nanocomposite is able to deliver a capacity of 230 mA h g–1 at 0.1 C (corresponding to a current density of 17 mA g–1), and demonstrates superior high-rate charge–discharge capability and cycling stability at charge/discharge rates up to 50 C in a half cell configuration. Full cell measurement using the TiO2/graphene as the anode material and spinel LiMnO2 as the cathode material exhibit good high-rate performance and cycling stability, indicating that the TiO2/graphene nanocomposite has a practical application potential in advanced Li-ion batteries.Keywords: anode; graphene; Li-ion battery; nanocomposite; titania

This paper describes the synthesis of α-phase Co–Ni hydroxides hexagonal platelets through homogeneous precipitation, using hexamethylenetetramine (HMT) or urea as a hydrolytic agent. In the CoCl2–NiCl2–HMT system, pure α-phase can be synthesized at the concentrations of both metal ions higher than 20 mM, while in the CoCl2–NiCl2–urea system, the formation of pure α-phase is independent of the concentrations of the metal ions. When using HMT, monodisperse hexagonal platelets of α-phase Co–Ni hydroxides can be produced in the presence of polyvinylpyrrolidone (PVP). Cyclic voltammogram curve of the hexagonal platelets prepared with HMT demonstrates electrochemical performance superior to that of urea.Monodisperse hexagonal platelets of α-phase Co–Ni hydroxides, synthesized with hexamethylenetetramine as hydrolytic agent and in the presence of polyvinylpyrrolidone, exhibit better electrochemical performance as compared to that with urea as hydrolytic agent.

Graphene-modified LiFePO4 composite has been developed as a Li-ion battery cathode material with excellent high-rate capability and cycling stability. The composite was prepared with LiFePO4 nanoparticles and graphene oxide nanosheets by spray-drying and annealing processes. The LiFePO4 primary nanoparticles embedded in micro-sized spherical secondary particles were wrapped homogeneously and loosely with a graphene 3D network. Such a special nanostructure facilitated electron migration throughout the secondary particles, while the presence of abundant voids between the LiFePO4 nanoparticles and graphene sheets was beneficial for Li+ diffusion. The composite cathode material could deliver a capacity of 70 mAh g−1 at 60C discharge rate and showed a capacity decay rate of <15% when cycled under 10C charging and 20C discharging for 1000 times.

Layered lithium transition metal oxide cathode materials (Li1.2Ni0.2Mn0.6O2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2), of spherical morphology with primary nanoparticles assembled in secondary microparticles, were generally synthesized through a simple carbonate co-precipitation method. In this method, various carbonates such as Na2CO3, NaHCO3 and (NH4)2CO3 could be employed as the precipitants without careful control of the pH value. Aging treatment on the carbonate slurries at 80 °C could yield spherical microparticles assembled with very fine primary nanoparticles. The carbonate microparticle precursors were calcined at 500 °C and further lithiated at 900 °C to prepare the layered cathode materials. The as-prepared Li1.2Ni0.2Mn0.6O2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2 cathode materials could deliver a capacity of 230, 190 and 153 mAh g−1, respectively, at a charge–discharge current density of 25 mA g−1 in the voltage range of 2.5–4.6 V. When the charge–discharge current density was increased to 250 mA g−1, the Li1.2Ni0.2Mn0.6O2 and LiNi1/3Co1/3Mn1/3O2 showed an initial discharge capacity of 150 and 166 mAh g−1; as for the LiNi0.5Mn0.5O2, the discharge capacity decreased to 67 mAh g−1. After 150 cycles at a current density of 250 mA g−1, both LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2 showed a capacity decay rate of >25%, while the Li1.2Ni0.2Mn0.6O2 exhibited an excellent cycling performance with almost no capacity decay.

A simple solution-based synthesis route, based on an oxidation–reduction reaction between graphene oxide and SnCl2•2H2O, has been developed to produce a SnO2/graphene composite. In the prepared composite, crystalline SnO2 nanoparticles with sizes of 3–5 nm uniformly clung to the graphene matrix. When used as an electrode material for lithium ion batteries, the composite presented excellent rate performance and high cyclic stability. The effect of SnO2/graphene ratio on electrochemical performance has been investigated. It was found that the optimum molar ratio of SnO2/graphene was about 3.2:1, corresponding to 2.4 wt.% of graphene. The composite could deliver a charge capacity of 840 mAh/g (with capacity retention of 86%) after 30 charge/discharge cycles at a current density of 67 mA/g, and it could retain a charge capacity of about 590 and 270 mAh/g after 50 cycles at the current density of 400 and 1000 mA/g, respectively.

The porous hematite (α-Fe2O3) nanorods, having diameters of 30–60 nm, were prepared through thermal decomposition of FeC2O4·2H2O nanorods that were readily synthesized through poly(vinyl alcohol)-assisted precipitation process. Compared to the commercial α-Fe2O3 powders in submicrometer sizes, the porous α-Fe2O3 nanorods, as an electrode material in lithium-ion batteries, exhibited significantly enhanced rate capability due to their nanorod shape and porous structure. When discharging at 0.1C (1C = 1005 mA/g) and charging at different rates (0.1C, 0.5C, and 1C), the porous α-Fe2O3 nanorods could deliver a capacity of over than 1130 mAh/g; while cycling at 1C rate, the nanorods could maintain a discharge capacity as high as 916 mAh/g after 100 cycles.Highlights► The porous hematite nanorods are prepared by decomposition of FeC2O4•2H2O nanorods. ► The synthesis method shows us a facile, low-cost and highly productive strategy. ► The porous hematite nanorods are suitable for a promising anode material in LIBs. ► Significantly enhanced rate capability is achieved. ► The porous hematite nanorods also show high capacity and good cycling stability.

In this paper, nano-sized LiFePO4 particles with a uniform carbon coating were produced using FePO4 as the iron source and PVA gel as the carbon source. Due to the special ability of PVA gel to form films readily, after it was mixed with the FePO4 during the ball-milling process, PVA films were formed readily around FePO4. As shown by the TEM results, the PVA films were successfully transformed into a perfect carbon coating around the LiFePO4 during calcination. The Raman spectrum showed the high quality of the obtained carbon layer, and the LiFePO4/C composites exhibited a high capacity and rate capacity retention at the rates of 0.1 C and 20 C. These results are indicative of the advantages of using PVA gel as a carbon source and its contribution to the excellent electrochemical performance of LiFePO4/C composite nanoparticles.

LiFePO4 (LFP) nanoparticles (∼50 nm in size), nanoplates (100 nm thick and 800 nm wide) and microplates (300 nm thick and 3 μm wide) have been selectively synthesized by a solvothermal method in a water–polyethylene glycol (PEG) binary solvent using H3PO4, LiOH•H2O and FeSO4•7H2O as precursors. The morphology and size of the LFP particles were strongly dependent on synthetic parameters such as volume ratio of PEG to water, temperature, concentration, and feeding sequence. The carbon coated nanoparticles and nanoplates could deliver a discharge capacity of >155 mAh g−1 at 0.1C rate (i.e. 17 mA g−1 of current density); in comparison, the carbon coated microplates had a discharge capacity as low as 110 mAh g−1 at 0.1C rate. The Li-ion diffusion coefficients of the carbon coated nanoparticles, nanoplates, and microplates were calculated to be 6.4 × 10−9, 4.2 × 10−9, and 2.2 × 10−9 cm2 s−1, respectively. When the content of conductive Super P carbon (SP) was increased to 30 wt.%, the prepared electrodes could charge–discharge at a rate as high as 20C. Over 1000 cycles at 20C, the nanoparticle electrode could maintain 89% of its initial capacity (126 mAh g−1), the nanoplate electrode showed 79% capacity retention compared to an initial capacity (129 mAh g−1), and the microplate electrode retained 80% of its initial capacity (63.5 mAh g−1).

High yield production of graphene oxide and graphene sheets with an ultralarge size (up to ∼200 μm) was realized using a modified solution-phase method.

•The strontium doped (La1−xSrx)0.98MnO3 with A-site deficiencies were synthesized.•Mn valence and Oads species of the LSM can be manipulated by Sr doping.•The LSM30 catalyst showed the highest ORR catalytic activity.•The Pmax of the Al-air battery with 50%LSM30/C reach 191.3 mW cm−2.The strontium doped Mn-based perovskites have been proposed as one of the best oxygen reduction reaction catalysts (ORRCs) to substitute the noble metal. However, few studies have investigated the catalytic activities of LSM with the A-site deficiencies. Here, the (La1-xSrx)0.98MnO3 (LSM) perovskites with A-site deficiencies are prepared by a modified solid-liquid method. The structure, morphology, valence state and oxygen adsorption behaviors of these LSM samples are characterized, and their catalytic activities toward ORR are studied by the rotating ring-disk electrode (RRDE) and aluminum-air battery technologies. The results show that the appropriate doping with Sr and introducing A-site stoichiometry can effectively tailor the Mn valence and increase the oxygen adsorption capacity of LSM. Among all the LSM samples in this work, the (La0.7Sr0.3)0.98MnO3 perovskite composited with 50% carbon (50%LSM30) exhibits the best ORR catalytic activity due to the excellent oxygen adsorption capacity. Also, this catalyst has much higher durability than that of commercial 20%Pt/C. Moreover, the maximum power density of the aluminum-air battery using 50%LSM30 as the ORRC can reach 191.3 mW cm−2. Our work indicates that the LSM/C composite catalysts with A-site deficiencies can be used as a promising ORRC in the metal-air batteries.

Nanosheet-constructing porous CeO2 microspheres with silver nanoparticles anchored on the surface were developed as a highly efficient oxygen reduction reaction (ORR) catalyst. The aluminum–air batteries applying Ag–CeO2 as the ORR catalyst exhibit a high output power density and low degradation rate of 345 mW cm−2 and 2.6% per 100 h, respectively.

High yield production of graphene oxide and graphene sheets with an ultralarge size (up to ∼200 μm) was realized using a modified solution-phase method.

Graphene-based electrodes with high gravimetric and high volumetric capacity simultaneously are crucial to the realization of high energy storage density, but still proved to be challenging to prepare. Herein, we report a three-dimensional porous graphene/Co aerogel with hierarchical porous structure and compressible features as a high-performance binder-free lithium-ion battery anode. In this composite aerogel, graphene nanosheets interconnect to form continuous macropores, and cobalt nanoparticles stemming from decomposition of cobalt salt not only react with carbon atoms of graphene to form nanopores on the graphene nanosheets, but also increase the conductivity of the aerogel. With efficient ion and electron transport pathways as well as high packing density, the compressed porous graphene/Co electrode exhibits significantly improved electrochemical performance including high gravimetric and volumetric capacity, excellent rate capability, and superior cycling stability. After compression, such a porous graphene/Co nanocomposite can deliver a gravimetric capacity of 900 mA h g−1 and a volumetric capacity of 358 mA h cm−3 at a current density of 0.05 A g−1. Furthermore, after 300 discharge/charge cycles at 1 A g−1, the specific capacity still remains at 163 mA h cm−3, corresponding to 90.5% retention of its initial capacity.

A simple solution-based oxidative process and subsequent chemical activation combination method has been developed to prepare edge-enriched porous graphene nanoribbons (GNRs) as a high-performance electrode material for supercapacitors. The precursor aligned carbon nanotubes are cut longitudinally and unzipped by a modified Brodie method to form tube-like GNRs with abundant edges. The intermediate GNRs were subsequently chemically activated using KOH to generate a suitable porosity and create more edge sites. These edge sites contribute a larger capacitance than the basal plane of graphene and the nanopores facilitate the fast immigration of ions. As a result, the edge-enriched GNRs exhibit a capacitance uptake per specific surface area almost two times higher than that of conventional activated graphene sheets, which gives rise to the high energy density of the porous GNR electrode. The highly efficient utilization of the edge planes and easy, low-cost scale-up production will make porous GNRs potentially applicable to high-performance supercapacitors.

To develop a kind of gel polymer electrolyte with high ion conductivity and good mechanical strength and thermal stability, a polyimide (PI) matrix-enhanced cross-linked gel separator is designed and fabricated by a simple dip-coating and heat treatment method. The PI nonwoven substrate provides high-temperature thermal stability for the gel separator and the crosslinked gel part yields enhanced affinity with the liquid electrolyte. Besides, the cross-linked polymer network could solve the issue of long-term durability of the composite separator in batteries. The gel separator shows better cyclability and rate capability than the traditional PP separator, implying a promising potential application in high-power, high-safety lithium ion batteries. The preparation process is compatible with the traditional manufacturing process of nonwoven membranes, and can be easily converted into continuous production on the industrial scale.

Morphology-controlled monodispersed LiMnPO4 nanocrystals as high-performance cathode materials for Li-ion batteries have been successfully synthesized by a solvothermal method in a mixed solvent of water and polyethylene glycol (PEG). Morphology evolution of LiMnPO4 nanoparticles from a nanorod to a thick nanoplate (∼50 nm in thickness) and to a smaller thin nanoplate (20–30 nm in thickness) is observed by increasing the pH value of the reaction suspension. Electrochemical measurements confirm that the LiMnPO4 thin nanoplates display the best charge–discharge performance, thick nanoplates the intermediate, nanorods the worst, which can be mainly ascribed to the difference in their morphologies and particle sizes in three dimensions. Further modification of LiMnPO4 thin nanoplates with graphene gives rise to an improved electrochemical performance compared with conventional pyrolytic carbon coated ones. The LiMnPO4 thin nanoplate/graphene composites deliver a high capacity of 149 mA h g−1 at 0.1 C, 90 mA h g−1 at 1 C, and even 64 mA h g−1 at 5 C charge–discharge rate, with an excellent cycling stability.

LiFePO4 (LFP) nanoparticles (∼50 nm in size), nanoplates (100 nm thick and 800 nm wide) and microplates (300 nm thick and 3 μm wide) have been selectively synthesized by a solvothermal method in a water–polyethylene glycol (PEG) binary solvent using H3PO4, LiOH•H2O and FeSO4•7H2O as precursors. The morphology and size of the LFP particles were strongly dependent on synthetic parameters such as volume ratio of PEG to water, temperature, concentration, and feeding sequence. The carbon coated nanoparticles and nanoplates could deliver a discharge capacity of >155 mAh g−1 at 0.1C rate (i.e. 17 mA g−1 of current density); in comparison, the carbon coated microplates had a discharge capacity as low as 110 mAh g−1 at 0.1C rate. The Li-ion diffusion coefficients of the carbon coated nanoparticles, nanoplates, and microplates were calculated to be 6.4 × 10−9, 4.2 × 10−9, and 2.2 × 10−9 cm2 s−1, respectively. When the content of conductive Super P carbon (SP) was increased to 30 wt.%, the prepared electrodes could charge–discharge at a rate as high as 20C. Over 1000 cycles at 20C, the nanoparticle electrode could maintain 89% of its initial capacity (126 mAh g−1), the nanoplate electrode showed 79% capacity retention compared to an initial capacity (129 mAh g−1), and the microplate electrode retained 80% of its initial capacity (63.5 mAh g−1).

Layered lithium transition metal oxide cathode materials (Li1.2Ni0.2Mn0.6O2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2), of spherical morphology with primary nanoparticles assembled in secondary microparticles, were generally synthesized through a simple carbonate co-precipitation method. In this method, various carbonates such as Na2CO3, NaHCO3 and (NH4)2CO3 could be employed as the precipitants without careful control of the pH value. Aging treatment on the carbonate slurries at 80 °C could yield spherical microparticles assembled with very fine primary nanoparticles. The carbonate microparticle precursors were calcined at 500 °C and further lithiated at 900 °C to prepare the layered cathode materials. The as-prepared Li1.2Ni0.2Mn0.6O2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2 cathode materials could deliver a capacity of 230, 190 and 153 mAh g−1, respectively, at a charge–discharge current density of 25 mA g−1 in the voltage range of 2.5–4.6 V. When the charge–discharge current density was increased to 250 mA g−1, the Li1.2Ni0.2Mn0.6O2 and LiNi1/3Co1/3Mn1/3O2 showed an initial discharge capacity of 150 and 166 mAh g−1; as for the LiNi0.5Mn0.5O2, the discharge capacity decreased to 67 mAh g−1. After 150 cycles at a current density of 250 mA g−1, both LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2 showed a capacity decay rate of >25%, while the Li1.2Ni0.2Mn0.6O2 exhibited an excellent cycling performance with almost no capacity decay.

Graphene-modified LiFePO4 composite has been developed as a Li-ion battery cathode material with excellent high-rate capability and cycling stability. The composite was prepared with LiFePO4 nanoparticles and graphene oxide nanosheets by spray-drying and annealing processes. The LiFePO4 primary nanoparticles embedded in micro-sized spherical secondary particles were wrapped homogeneously and loosely with a graphene 3D network. Such a special nanostructure facilitated electron migration throughout the secondary particles, while the presence of abundant voids between the LiFePO4 nanoparticles and graphene sheets was beneficial for Li+ diffusion. The composite cathode material could deliver a capacity of 70 mAh g−1 at 60C discharge rate and showed a capacity decay rate of <15% when cycled under 10C charging and 20C discharging for 1000 times.

A 3D porous architecture of Si/graphene nanocomposite has been rationally designed and constructed through a series of controlled chemical processes. In contrast to random mixture of Si nanoparticles and graphene nanosheets, the porous nanoarchitectured composite has superior electrochemical stability because the Si nanoparticles are firmly riveted on the graphene nanosheets through a thin SiOx layer. The 3D graphene network enhances electrical conductivity, and improves rate performance, demonstrating a superior rate capability over the 2D nanostructure. This 3D porous architecture can deliver a reversible capacity of ∼900 mA h g−1 with very little fading when the charge rates change from 100 mA g−1 to 1 A g−1. Furthermore, the 3D nanoarchitechture of Si/graphene can be cycled at extremely high Li+ extraction rates, such as 5 A g−1 and 10 A g−1, for over than 100 times. Both the highly conductive graphene network and porous architecture are considered to contribute to the remarkable rate capability and cycling stability, thereby pointing to a new synthesis route to improving the electrochemical performances of the Si-based anode materials for advanced Li-ion batteries.

Activated graphene has been considered as an ideal electrode material for supercapacitors. In order to reveal the relationship between activated graphene and its precursor and controllably synthesize activated graphene, the structural parameters of the precursor (reduced graphene oxide, RGO) such as crystallinity and attached oxygen-functional groups were controllably adjusted during the synthesis of activated graphene and the effects of the precursor structure on the microstructure of activated graphene were investigated. The activation results reveal that the structure of RGO obviously affects the porous structure of activated graphene. Specifically, the crystallinity and oxygen-functional groups play an important role in the porosity development of activated graphene. By combining the simplified Brodie method and the subsequent post-oxidation process, porous activated graphene with a specific surface area of as high as 2406 m2 g−1 and high pore volume has been successfully prepared. The as-prepared activated graphene exhibits good capacitive characteristics and delivers high energy density (55.7 W h kg−1) when measured in a two-electrode cell with the EMIMBF4 ionic liquid as the electrolyte. The results demonstrate that the obtained activated graphene can be considered as a candidate for advanced electrode materials for supercapacitors.

A composite membrane with an ultra-thin ion exchangeable layer is specially designed as a separator in lithium ion batteries with manganese-based cathode materials. The composite membrane features a Mn2+ capture function which originates from the ion exchanging process, especially at high temperature, and is proven to help to alleviate the capacity decay of lithium ion batteries effectively. The enhanced thermal stability, improved wettability and higher lithium ion transference number of the composite membrane further suggest its promising application in lithium ion batteries.

The Li-rich layered oxides are attractive electrode materials due to their high reversible specific capacity (>250 mA h g−1); however, the origin of their abnormal capacity is still ambiguous. In order to elucidate this curious anomaly, we compare the lattice oxygen oxidation states among the Li-rich layered oxide Li1.14Ni0.136Co0.136Mn0.544O2, Li2MnO3 and LiNi0.5Co0.2Mn0.3O2, the two components in Li-rich layered oxides, and the most common layered oxide LiCoO2 before and after initial charge–discharge. For simplicity, we employ chemical treatments of NO2BF4 and LiI acetonitrile solutions to simulate the electrochemical delithiation and lithiation processes. X-ray photoelectron spectroscopy (XPS) studies reveal that part of lattice oxygen in Li1.14Ni0.136Co0.136Mn0.544O2 and Li2MnO3 undergoes a reversible redox process (possibly O2− ↔ O22−), while this does not occur in LiNi0.5Co0.2Mn0.3O2 and LiCoO2. This indicates that the extra capacity of Li-rich layered oxides can be attributed to the reversible redox processes of oxygen in the Li2MnO3 component. Thermogravimetric analysis (TGA) further suggests that the formed O22− species in the delithiated Li1.14Ni0.136Co0.136Mn0.544O2 can decompose into O2 at about 210 °C. This phenomenon demonstrates a competitive relationship between extra capacity and thermal stability, which presents a big challenge for the practical applications of these materials.

For the development of high-performance Li–S batteries, the issues of the insulating nature of sulfur and shuttle effect of polysulfides need to be well addressed simultaneously, which require elaborate structure design of a suitable host for sulfur. In this work, a novel bifunctional and free-standing sulfur cathode consisted of a hierarchical porous carbon network as the conductive host for sulfur and an in situ formed graphene shell as the top layer for physical blocking of the shuttle effect is carefully fabricated. Owing to filtration assembly, an ultrathin graphene shell (∼100 nm in thickness) is in situ formed firstly, on which a macroporous graphene architecture is gradually deposited afterwards. Subsequent chemical vapor deposition of interwoven CNTs on both sides of graphene sheets generates numerous nano-sized cavities for loading of sulfur nanoparticles. The rationally designed electrode possesses a relatively high areal sulfur loading of ∼3.6 mg cm−2, and shows excellent rate capability at ∼6.0 mA cm−2 and cyclic stability over 200 cycles. And as the graphene nano-shell blocks the diffusion of polysulfides, the anti-self-discharge capability of the cell is remarkably improved.

Perovskites have been proposed as one of the best oxygen reduction reaction catalysts (ORRCs) to substitute noble metals though their catalytic activity still need to be improved. It is well accepted that improving the oxygen adsorption capacity is beneficial to the catalytic activity of La1−xSrxMnO3 (LSM) perovskites. Herein, we synthesized the LSM-based composite by compositing La0.7Sr0.3MnO3 with Ce0.75Zr0.25O2 (CZ) which is used as an excellent oxygen storage material by a two-step solution method. The LSM–CZ composite is revealed as a novel electrocatalyst for the oxygen reduction reaction with the direct four-electron transfer mechanism and a positive onset potential in comparison with the commercial Pt/C catalyst. And its onset potential is almost the most positive one among those of the perovskites stemmed from LaMnO3. In addition, the stability of LSM–CZ is even superior to that of Pt/C, and LSM–CZ almost accumulates no intermediate product of HO2− (∼0.8%) after aging for 100000 seconds. By using LSM–CZ as the ORRC, the maximum power density of the aluminum–air battery can reach 233.4 mW cm−2. Our work paves the way for the development of perovskite catalysts for energy conversion and storage.