Developing high-performance and low-cost electrocatalysts for oxygen reduction reaction (ORR) is still a great challenge for Al–air batteries. Herein, CeO2, a unique ORR promoter, was incorporated into ketjenblack (KB) supported Co3O4 catalyst. We developed a facile two-step hydrothermal approach to fabricate Co3O4–CeO2/KB as a high-performance ORR catalyst for Al–air batteries. The ORR activity of Co3O4/KB was significantly increased by mixing with CeO2 nanoparticles. In addition, the Co3O4–CeO2/KB showed a better electrocatalytic performance and stability than 20 wt % Pt/C in alkaline electrolytes, making it a good candidate for highly active ORR catalysts. Co3O4–CeO2/KB favored a four-electron pathway in ORR due to the synergistic interactions between CeO2 and Co3O4. In full cell tests, the Co3O4–CeO2/KB exhibited a higher discharge voltage plateau than CeO2/KB and Co3O4/KB when used in cathode in Al–air batteries.Keywords: adsorption of oxygen; Al−air batteries; Co3O4−CeO2/C; hydrothermal; oxygen reduction reaction; synergistic effects;

Rutile TiO2 is seldom studied as anode material for Na-ion battery for its much poorer Na storage performance than anatase phase. Herein, strategies of carbon coating and nitrogen doping are proposed and achieved together by a facile ball milling method followed by a high temperature sintering process to improve its electrochemical properties. The feature of this work lies in the dual N doping, not only to the carbon layers but also to the TiO2 lattice, resulting in sufficient oxygen vaccancies and defects in TiO2/C. Although the pristine TiO2 prepared by the similar method shows only 10 mAh g−1 capacity, the Na storage performance of N-doped TiO2/C is significantly enhanced. It demonstrates a high reversible discharge capacity of 211.2 mAh g−1 at 16.8 mA g−1 (0.1C). Moreover, a capacity retention of 92.3% is achieved after 500 cycles at 168 mA g−1 (1C), verifying ultrahigh reversible capacity and excellent cycling performance for rutile TiO2. The excellent Na storage performance of N-doped TiO2/C should be ascribed to the improved electronic and ionic conductivity resulting from dual N-doping strategy and shortened Na ion diffusion length due to the particle downsizing.Download high-res image (183KB)Download full-size image

•3D MoO2 nanotextile has been synthesized by a novel modified hydrothermal method.•The MoO2 nanotextiles are assembled from large quantities of elongated nanowires.•The nanotextiles exhibit a high discharge capacity and superior cycling stability.The fabrication of an ideal electrode architecture consisting of robust three dimensional (3D) nanowire networks have gained special interest for energy storage applications owing to the integrated advantages of nanostructures and microstructures. In this work, 3D MoO2 nanotextiles assembled from highly interconnected elongated nanowires are successfully prepared by a facile stirring assisted hydrothermal method and followed by an annealing process. In addition, a methylbenzene/water biphasic reaction system is involved in the hydrothermal process. When used as an anode material in Li ion batteries (LIBs), this robust MoO2 nanotextiles exhibit a high reversible capacity (860.4 mAh g−1 at 300 mA g−1), excellent cycling performance (89% capacity retention after 160 cycles) and rate capability (577 mAh g−1 at 2000 mA g−1). Various synthetic factors to the fabrication of 3D nanotextiles structure are discussed here and this design of 3D network structures may be extended to the preparation of other functional nanomaterials.Download high-res image (223KB)Download full-size image

Inferior rate capability is a big challenge for LiTi2(PO4)3 anode for aqueous lithium-ion batteries. Herein, to address such issue, we synthesized a high-performance LiTi2(PO4)3/carbon/carbon nanotube (LTP/C/CNT) composite by virtue of high-quality carbon coating and incorporation of good conductive network. The as-prepared LTP/C/CNT composite exhibits excellent rate performance with discharge capacity of 80.1 and 59.1 mAh g−1 at 10 C and 20 C (based on the mass of anode, 1 C = 150 mA g−1), much larger than that of the LTP/C composite (53.4 mAh g−1 at 10 C, and 31.7 mAh g−1 at 20 C). LTP/C/CNT also demonstrates outstanding cycling stability with capacity retention of 83.3 % after 1000 cycles at 5 C, superior to LTP/C without incorporation of CNTs (60.1 %). As verified, the excellent electrochemical performance of the LTP/C/CNT composite is attributed to the enhanced electrical conductivity, rapid charge transfer, and Li-ion diffusion because of the incorporation of CNTs.

Morphology controllable fabrication of electrode materials is of great significance but is still a major challenge for constructing advanced Li ion batteries. Herein, we propose a novel space constraint assembly approach to tune the morphology of Mn(terephthalic acid) (PTA)-MOF, in which benzonic acid was employed as a modulator to adjust the available MOF assembly directions. As a result, Mn(PTA)-MOFs with microquadrangulars, microflakes, and spindle-like microrods morphologies have been achieved. MnO/C hybrids with preserved morphologies were further obtained by self-sacrificial and thermal transformation of Mn(PTA)-MOFs. As anodes for Li ion batteries, these morphologies showed great influence on the electrochemical properties. Owing to the abundant porous structure and unique architecture, the MnO/C spindle-like microrods demonstrated superior electrochemical properties with a high reversible capacity of 1165 mAh g–1 at 0.3 A g–1, excellent rate capability of 580 mAh g–1 at 3 A g–1, and no considerable capacity loss after 200 cycles at 1 A g–1. This strategy could be extended to engineering the morphology of other MOF-derived functional materials in various structure-dependent applications.Keywords: Li ion battery; metal−organic frameworks; MnO/C anode; morphology tuning; space constraint assembly;

Stabilizing the layer structures of Mo-based anode materials is still a challenge for Li ion batteries. Herein, we proposed an electrochemical presodiation strategy for MoS2 and MoO3 to improve their cycling stability. It is interesting to note that the cycling stability of as-treated MoS2 and MoO3 was significantly improved. Although the reversible discharge capacity was slightly decreased, the capacity of the pretreated MoS2 at 300 mA g−1 was retained at 345 mA h g−1 after 100 cycles while that of the pristine one decreased to 151 mA h g−1. The capacity of the pretreated MoO3 after 60 cycles was also improved from 275 mA h g−1 (the pristine one) to 460 mA h g−1. The stabilizing effect was further verified by scanning electron microscope (SEM) analysis. Electrochemical presodiation here could be a promising modification strategy for Mo-based anode materials.

Although LiFePO4 has been widely studied and also used as a promising cathode material for Li ion batteries, its inferior tap density is still a big challenge for practical application. Well-defined three-dimensional porous LiFePO4 microspheres composed of nanosheets were successfully synthesized by a simple one-step solvothermal method. The porous spherical morphology could not only retain the excellent electrochemical performance characteristics of the LiFePO4 nanosheet but also meet the requirements of high tap density of the powder particles, leading to highly improved volumetric energy density. These micro-nano structured LiFePO4 microspheres have a high tap density of about 1.4 g cm−3. A growth mechanism is also proposed based on time-dependent experiments. This work provides an efficient route for designing a desirable micro–nano structure, which could also be extended to synthesize other hierarchical structures used in different fields.

Mesoporous LiTi2(PO4)3@nitrogen-rich doped carbon composites have been synthesized by a novel bi-nitrogen sources doping strategy. Tripolycyanamide (C3H6N6) and urea are proposed for the first time as both nitrogen and carbon sources to achieve a homogeneous nitrogen-doped carbon coating layer via an in situ method. The electrode delivers ultrahigh rate performance and outstanding cycling stability in lithium ion batteries (LIBs). In an organic electrolyte system, the electrode demonstrates high discharge capacities of 120 mAh g–1 and 87 mAh g–1 at 20C and 50C, respectively. Moreover, 89.5% of initial discharge capacity is retained after 1000 cycles at 10C. When used as an anode for aqueous LIBs, the electrode also demonstrates superior rate capability with the discharge capacity of 103 mAh g–1 at 10C, corresponding to 84% of that at 1C. Outstanding cycling stability with capacity retention of 91.2% after 100 cycles at 30 mA g–1 and 90.4% over 400 cycles at 150 mA g–1 are also demonstrated. The uniform nitrogen-rich carbon coating and unique mesoporous structure play important roles in effectively suppressing the charge-transfer resistance and facilitating Li ion/electron diffusion, thus leading to the superior electrochemical properties.Keywords: aqueous lithium ion battery; cycling performance; mesoporous LiTi2(PO4)3/C; nitrogen doping; rate performance

Here we report a hybrid of MnOx–CeO2/Ketjenblack as a novel catalyst for oxygen reduction reaction (ORR) by a facile strategy. This hybrid exhibits comparable activity and better stability towards ORR than the commercial 20 wt% Pt/C due to the synergistic effect.

•A three layered Al2O3/LixV2O5/LiV3O8 nanostructure is well formed.•The hybrid demonstrates excellent cycling stability.•The reasons for the outstanding electrochemical properties are well discussed by XRD and CV.Al2O3 coating is utilized in this work to further improve the cycling stability of LiV3O8 nanoflakes. Surprisingly, three layered Al2O3/LixV2O5/LiV3O8 nanostructure is well formed as confirmed by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) results. When used as a cathode for Li-ion battery, the hybrid demonstrates significantly improved cycling stability with a discharge capacity of 203 mAh g−1 remaining after 200 cycles at 150 mA g−1 and 87.5% of the initial capacity maintaining after 500 cycles at 300 mA g−1. Such superior cycling performance should be attributed to the mutual protection of Al2O3 and LixV2O5 layer between Al2O3 and LiV3O8, which can well suppress the damage of LiV3O8 during the long-term cycling process. More importantly, the LixV2O5 middle layer could contribute to the improvement of interfacial electrochemical properties of the hybrid electrode.

Poor cycling performance is still the big challenge for aqueous rechargeable lithium batteries (ARLBs), in which the instability of the anode is considered to be the main issue. In this work, NaV6O15 nanoflakes were synthesized by a two-step approach and a NaV6O15//LiMn2O4 ARLB system with superior cycling performance was constructed. The galvanostatic charge–discharge result demonstrates an initial discharge capacity of 110.7 mA h g−1 (based on anode mass) at 150 mA g−1 and the capacity retention of ca. 90% and 80% at 300 mA g−1 after 100 and 400 cycles, respectively. Such superior cycling performance of ARLBs is mainly due to the intrinsic 3-D tunneled structure of NaV6O15, nanoflake morphology and relatively stable electrode surface, as verified by the X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) results of the tested electrodes. Moreover, a simple single-phase reaction mechanism during the lithium ion insertion/extraction process is observed for NaV6O15 by XRD analysis.

High-performance, low cost catalyst for oxygen reduction reaction (ORR) remains a big challenge. Herein, nanostructured NiCo2O4/CNTs hybrid was proposed as a high-performance catalyst for metal/air battery for the first time. The well-formed NiCo2O4/CNTs hybrid was studied by steady-state linear polarization curves and galvanostatic discharge curves in comparison with CNTs-free NiCo2O4 and commercial carbon-supported Pt. Because of the synergistic effect, NiCo2O4/CNTs hybrid exhibited significant improvement of catalytic performance in comparison with NiCo2O4 or CNTs alone, even outperforming Pt/C hybrid in ORR process. In addition, the benefits of Ni incorporation were demonstrated by the improved catalytic performance of NiCo2O4/CNTs compared to Co3O4/CNTs, which should be attributed to improved electrical conductivity and new, highly efficient, active sites created by Ni cation incorporation into the spinel structure. NiCo2O4/CNTs hybrid could be used as a promising catalyst for high power metal/air battery.

Poor cycling stability and rate capability are the main challenges for LiV3O8 as the cathode material for Li-ion batteries. Here a novel strategy involving the self-transformation of superficial LiV3O8 in a reducing atmosphere (H2–Ar) was reported to fabricate LixV2O5/LiV3O8 nanoflakes. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) results demonstrate that LixV2O5/LiV3O8 nanoflakes could be in situ formed and that the thickness of the LixV2O5 layer is controllable. When used as a cathode for a Li-ion battery, the LixV2O5/LiV3O8 nanoflakes exhibit significantly improved cycling stability with a capacity retention of ca. 82% over 420 cycles at a 1 C-rate (1 C = 300 mA g−1), and much better rate performance compared with bare LiV3O8. The improvement of the electrochemical performance could be attributed to the unique core–shell structure, in which the ultrathin LixV2O5 layer could not only protect the internal LiV3O8 from dissolution, but also increase the Li ion diffusion coefficient and suppress the charge-transfer resistance, as verified by electrochemical impedance spectroscopy (EIS) and XRD results.

In this work, NaV3O8 nanowires are proposed as a novel cathode for a Na-ion battery for the first time. The as-prepared nanowires are characterized well by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Sodium insertion/extraction properties of as-prepared nanowires with or without thermal treatment are compared. It is found that thermal treatment could remove some crystal water in the host, resulting in a contracted crystal volume. In comparison with the untreated sample, although the reversible discharge capacity of annealed NaV3O8·xH2O nanowires is decreased from 169.6 mA h g−1 to 145.8 mA h g−1 when cycled at 10 mA g−1, it shows good capacity retention of ca. 91.1% after 50 cycles, much higher than that (51.9%) of the untreated sample. Annealed NaV3O8 nanowires exhibit much better cycling stability and charge–discharge plateaus during the Na-ion insertion/extraction processes, which should be attributed to the contracted crystal volume and the increased crystallinity.

•Lithium deficient mesoporous Li2−xMnSiO4 compounds are first proposed.•Li2−xMnSiO4 compounds exhibit improved electrochemical performance.•Li1.8MnSiO4 delivers a discharge capacity of 110.9 mAh g−1, with 90.8 mAh g−1 remaining after 25 cycles.•The superior properties are due to the improvement of electronic conductivity and structure stability.Li2−xMnSiO4 compounds with mesoporous structure are first proposed in the present work. It is interesting to note that the lithium deficient compounds exhibit much higher electrochemical performance in comparison with the stoichiometric one. Among these compounds, Li1.8MnSiO4 shows the best electrochemical performance. It is found that mesoporous Li1.8MnSiO4 without carbon coating delivers a maximum discharge capacity of 110.9 mAh g−1 at 15 mA g−1, maintaining 90.8 mAh g−1 after 25 cycles, while that of the stoichiometric one is only 48.0 mAh g−1, with 12.5 mAh g−1 remaining. The superior properties are mainly due to the great improvement of electronic conductivity and structure stability, as well as suppressed charge-transfer resistance.

In the current work, NaV3O8 nanoflakes were fabricated by a novel two-step approach using VO2(B) nanoflakes as a sacrificial template. The as-prepared NaV3O8 was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that NaV3O8 sintered at 400 °C had a suitable degree of crystallinity and demonstrated uniform nanoflake morphology, 100–200 nm in width, 500–800 nm in length and 30–50 nm in thickness. When used as a cathode material for Li-ion batteries, it showed good cyclic performance (a discharge capacity of 210 mA h g−1 remained after 30 cycles at 30 mA g−1 and no capacity fading occurred over 100 cycles at 150 mA g−1). The rate capability was 113.4 mA h g−1 and 91.5 mA h g−1 in 6 C and 10 C, respectively. XRD patterns of NaV3O8 electrodes at different voltages revealed a single-phase reaction mechanism and small crystal volume change (∼3%) during the lithium intercalation/deintercalation processes.

In this work, a novel electrocatalyst, Mn0.3Ce0.7O2, with relatively high power performance has been, for the first time, proposed for metal/air batteries. The as-prepared samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma (ICP) and nitrogen sorption experiments. Meanwhile, electrocatalytic activity towards the reduction of oxygen of Mn0.3Ce0.7O2 is compared with those of the pure MnO2 and CeO2. It is observed that the Mn0.3Ce0.7O2 solid solution is well formed after the calcination. Electrochemical results show that Mn0.3Ce0.7O2 exhibits much higher electrocatalytic activity in the oxygen reduction reaction (ORR) than pure MnO2 under high discharge current density, which is probably attributed to the effective activation of molecular oxygen over the Mn0.3Ce0.7O2 solid solution and higher surface area.

•Mg2Ni alloy was rapidly quenched in a static magnetic field.•The as-prepared alloy has directional columnar structures and high internal strain.•High quenching rate goes against the formation of directional columnar crystals.•The as-prepared alloy exhibits improved electrochemical performance.Mg2Ni alloy prepared by vacuum induction melting is rapidly quenched in the presence of an external magnetic field. The effects of magnetic field on the microstructure and electrochemical hydrogen storage behavior of Mg2Ni alloy are well investigated for the first time. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) studies show that the applied magnetic field results in a preferred orientation growth during the rapid solidification of alloy melt, which induces the generation of columnar crystals. Meanwhile, decreased grain size and increased internal strain are noted for this alloy, as well as the eliminated composition segregation. It is found on the charge–discharge experiments that the as-prepared alloy displays an increased capacity and improved cycle stability compared to the alloys without magnetic field treatment. The potentiodynamic polarization results indicate that the Mg2Ni alloy exhibits relatively high corrosion resistance against the alkaline solution. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results demonstrate enhanced electrochemical kinetics for the treated Mg2Ni alloy, consistent with the enhanced electrochemical properties.

The development of aqueous rechargeable lithium battery (ARLB) is greatly restricted by the anode material. Herein, Na2V6O16·0.14H2O nanowires with high cycling stability in the aqueous solution are firstly proposed as a novel anode material for ARLB. The effect of pH value of the electrolyte on electrochemical behavior of Na2V6O16·0.14H2O is optimized. The CV results demonstrate that the studied electrode possesses high reversible lithium insertion/extraction ability and it is more stable in neutral solution. The ARLB consisting of LiMn2O4 as cathode, Na2V6O16·0.14H2O as anode and saturated Li2SO4 as electrolyte indicates good cycling stability. An initial specific discharge capacity of 122.7 mAh g−1 (based on the mass of anode material) can be reached at 60 mA g−1. The capacity retention is up to 80.1% and 77% of the initial discharge capacity at 300 mA g−1 after 100 and 200 cycles, respectively. The good cycling performance of the ARLB is partially due to suppression of the charge-transfer resistance.Highlights► A novel anode material, Na2V6O16·0.14H2O nanowire was first proposed for aqueous lithium-ion battery. ► The effect of pH value of the electrolyte on electrochemical behavior of Na2V6O16·0.14H2O was optimized. ► ARLB of Na2V6O16·0.14H2O//LiMn2O4 was constructed and showed good electrochemical performance.

The effect of static magnetic field treatment for synthesis of Mg2Ni0.8Mn0.2 alloys during rapid quenching was investigated in this paper. X-ray diffraction (XRD) and scanning electron microscope (SEM) results show that the transversal static magnetic field can effectively refine the grain size, producing nanocrystalline inside. This distinct phenomenon is probably attributed to the Lorentz force suppressing the crystallization of the hydrogen storage alloys and the thermoelectric effect. Mainly due to the grain refinement, the discharge capacity of Mg2Ni0.8Mn0.2 alloy is raised from 79 to about 200 mA h g−1. It is confirmed that Mg2Ni0.8Mn0.2 alloy by magnetic field assisted approach possesses enhanced electrochemical kinetics and relatively high corrosion resistance against the alkaline solution, thus resulting in higher electrochemical properties.

In this study, AlF3 was successfully coated on the surface of LiV3O8 nanosheets, as verified by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). AlF3 coated LiV3O8 exhibited the significantly improved cycling stability with the capacity retention of ca. 91% over 50 cycles at 150 mA g− 1, while that of the bare one was only 61%. When cycling at 55 °C, the bare electrode delivered a much larger capacity loss (44.8%) in comparison with that (19.1%) of the coated one. On the basis of the XRD, CV and EIS results, it was suggested that the AlF3 coating layer could protect the bulk material well and facilitate the kinetics of Li-ion diffusion, leading to smaller electrochemical impedance, thus resulted in improvement of cycling stability for LiV3O8.Highlights► AlF3 was successfully coated on the surface of LiV3O8 nanosheets. ► AlF3 coated LiV3O8 exhibited the significantly improved cycling stability. ► Electrochemical property of the coated one at elevated temperature was improved. ► AlF3 layer could protect the bulk material well.

A novel two-step approach was developed to fabricate well-dispersed Na1.08V3O8nanosheets, which consist of ultra-thin monolayer sheets with a thickness of ca. 10 nm. The formation mechanism of nanosheets involves the fusion and conversion of nanorods. When used as a cathode material for Li-ion batteries, the nanosheets show superior rate capability, with discharge capacities of ca. 200.0, 131.3, 109.9, 94.2 and 72.5 mA h g−1 at 0.4, 10, 20, 30 and 50 C, respectively. Excellent cycling stability without considerable capacity loss over 200 cycles is observed at 600 and 1000 mA g−1. It is believed that the unique nanosheet morphology as well as its intrinsic structural features greatly facilitate the kinetics of Li-ion diffusion and excellent structure stability, thus resulting in superior electrochemical performance.

Single crystalline Na2V6O16·2.36H2O nanowires are synthesized by a facile hydrothermal method as a new cathode material for Li-ion battery. The nanowires show a diameter of 60–100 nm and a length of up to 5 μm. Appropriate thermal treatment could effectively improve the cycling performance, although the discharge capacity is sacrificed to some extent. Na2V6O16·0.86H2O after heat treatment under 300 °C delivers an initial specific discharge capacity of 235.2 mAh g−1 at 30 mA g−1, with a capacity retention of 91.1% after 30 cycles. Long cycling test is demonstrated by the retention of 90.4% and 94.4% at 150 and 300 mA g−1, respectively, after 80 cycles. Good rate capability is also achieved for this material. It is proposed that the improved cycling stability of the electrode after thermal treatment is mainly attributed to the removal of a part of crystal water, accompanied with certain structural arrangement.Highlights► Single crystalline Na2V6O16·2.36H2O nanowires are synthesized by hydrothermal method. ► Na2V6O16·0.86H2O exhibits high discharge capacity and excellent cycling stability. ► Improved cycling stability after heating is mainly due to the part removal of crystal water. ► Annealed Na2V6O16·xH2O could be proposed as a potential cathode for Li-ion battery.

A novel cathode material, NH4V3O8 nanorods with high discharge capacity and good rate capability are hydrothermally prepared in the presence of sodium dodecyl benzene sulfonate (SDBS). The diameter of nanorods is about 30 nm and the length is less than 1 μm. In comparison with the ammonium trivanadate flakes prepared without surfactant, the nanorods are better suited as lithium inserting electrode material, with superior lithium ion insertion/deinsertion plateaus, higher discharge capacity and better cycling stability. The nanorods deliver a maximum specific discharge capacity of 327.1 mAh g−1 at 30 mA g−1. It also demonstrates good rate capability with the capacity of 207.6 mAh g−1 at 300 mA g−1, 201.2 mAh g−1 at 450 mA g−1, and 181.8 mAh g−1 at 600 mA g−1. Good cycling stability is also shown at 150 mA g−1 for the nanorods, with no capacity loss over 60 cycles.Highlights► NH4V3O8·0.37H2O nanorod was hydrothermally prepared using SDBS as soft template. ► It shows high discharge capacity, rate capability and good cycling stability. ► The nanorod is better suited as lithium inserting electrode than that without SDBS.

LiV3O8 nanosheets with a thickness of 15–30 nm and width of 200–500 nm were synthesized by a facile hydrothermal approach combined with a solid state process, using uniform (NH4)0.5V2O5 nanosheets as the precursor. The nanosheets show a discharge capacity of 260.0, 232.4, 173.9 and 148.7 mA h g−1 at 0.4, 1.0, 3.0 and 5.0 C, respectively. Good cycling stability is also demonstrated by the capacity retention of 85.3% at 1000 mA g−1 after 100 cycles. The unique nanosheet structure greatly contributes to the short Li+ diffusion pathways and a good contact between the active material and electrolyte, as well as a good tolerance of the morphology change, which mainly result in high rate performance and good cycling stability for LiV3O8 nanosheets.

NH4V3O8/carbon nanotubes (CNTs) composites are synthesized by one-step hydrothermal method. All the samples show the flake-like morphology with the width of up to 5 μm and thickness of 500 nm and the CNTs are clearly observed on the surface of modified NH4V3O8. It is found that incorporation of 0.5 wt% CNTs into NH4V3O8 could greatly improve its discharge capacity and cycling stability. It delivers a maximum discharge capacity of 358.7 mAh g−1 at 30 mA g−1, 55 mAh g−1 larger than that of the pristine one. At 150 mA g−1, the composite shows 226.2 mAh g−1 discharge capacity with excellent capacity retention of 97% after 100 cycles. The much improved electrochemical performance of NH4V3O8 is attributed to incorporation of CNTs, which facilitates the interface charge transfer and Li+ diffusion.Highlights► NH4V3O8/CNTs composites were synthesized by one-step hydrothermal method. ► NH4V3O8/0.5 wt% CNTs showed high discharge capacity and excellent rate capability. ► Incorporation of CNTs is highly beneficial to interface charge transfer and Li+ diffusion.

Here we report a hybrid of MnOx–CeO2/Ketjenblack as a novel catalyst for oxygen reduction reaction (ORR) by a facile strategy. This hybrid exhibits comparable activity and better stability towards ORR than the commercial 20 wt% Pt/C due to the synergistic effect.

Poor cycling performance is still the big challenge for aqueous rechargeable lithium batteries (ARLBs), in which the instability of the anode is considered to be the main issue. In this work, NaV6O15 nanoflakes were synthesized by a two-step approach and a NaV6O15//LiMn2O4 ARLB system with superior cycling performance was constructed. The galvanostatic charge–discharge result demonstrates an initial discharge capacity of 110.7 mA h g−1 (based on anode mass) at 150 mA g−1 and the capacity retention of ca. 90% and 80% at 300 mA g−1 after 100 and 400 cycles, respectively. Such superior cycling performance of ARLBs is mainly due to the intrinsic 3-D tunneled structure of NaV6O15, nanoflake morphology and relatively stable electrode surface, as verified by the X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) results of the tested electrodes. Moreover, a simple single-phase reaction mechanism during the lithium ion insertion/extraction process is observed for NaV6O15 by XRD analysis.

In this work, a novel electrocatalyst, Mn0.3Ce0.7O2, with relatively high power performance has been, for the first time, proposed for metal/air batteries. The as-prepared samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma (ICP) and nitrogen sorption experiments. Meanwhile, electrocatalytic activity towards the reduction of oxygen of Mn0.3Ce0.7O2 is compared with those of the pure MnO2 and CeO2. It is observed that the Mn0.3Ce0.7O2 solid solution is well formed after the calcination. Electrochemical results show that Mn0.3Ce0.7O2 exhibits much higher electrocatalytic activity in the oxygen reduction reaction (ORR) than pure MnO2 under high discharge current density, which is probably attributed to the effective activation of molecular oxygen over the Mn0.3Ce0.7O2 solid solution and higher surface area.

In this work, NaV3O8 nanowires are proposed as a novel cathode for a Na-ion battery for the first time. The as-prepared nanowires are characterized well by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Sodium insertion/extraction properties of as-prepared nanowires with or without thermal treatment are compared. It is found that thermal treatment could remove some crystal water in the host, resulting in a contracted crystal volume. In comparison with the untreated sample, although the reversible discharge capacity of annealed NaV3O8·xH2O nanowires is decreased from 169.6 mA h g−1 to 145.8 mA h g−1 when cycled at 10 mA g−1, it shows good capacity retention of ca. 91.1% after 50 cycles, much higher than that (51.9%) of the untreated sample. Annealed NaV3O8 nanowires exhibit much better cycling stability and charge–discharge plateaus during the Na-ion insertion/extraction processes, which should be attributed to the contracted crystal volume and the increased crystallinity.

Poor cycling stability and rate capability are the main challenges for LiV3O8 as the cathode material for Li-ion batteries. Here a novel strategy involving the self-transformation of superficial LiV3O8 in a reducing atmosphere (H2–Ar) was reported to fabricate LixV2O5/LiV3O8 nanoflakes. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) results demonstrate that LixV2O5/LiV3O8 nanoflakes could be in situ formed and that the thickness of the LixV2O5 layer is controllable. When used as a cathode for a Li-ion battery, the LixV2O5/LiV3O8 nanoflakes exhibit significantly improved cycling stability with a capacity retention of ca. 82% over 420 cycles at a 1 C-rate (1 C = 300 mA g−1), and much better rate performance compared with bare LiV3O8. The improvement of the electrochemical performance could be attributed to the unique core–shell structure, in which the ultrathin LixV2O5 layer could not only protect the internal LiV3O8 from dissolution, but also increase the Li ion diffusion coefficient and suppress the charge-transfer resistance, as verified by electrochemical impedance spectroscopy (EIS) and XRD results.