A unique reversible conversion-type mechanism is reported in the amorphous molybdenum polysulfide (a-MoS5.7) cathode material. The lithiation products of metallic Mo and Li2S2 rather than Mo and Li2S species have been detected. This process could yield a high discharge capacity of 746 mAh g–1. Characterizations of the recovered molybdenum polysulfide after the delithiaiton process manifests the high reversibility of the unique conversion reaction, in contrast with the general irreversibility of the conventional conversion-type mechanism. As a result, the a-MoS5.7 electrodes deliver high cycling stability with an energy-density retention of 1166 Wh kg–1 after 100 cycles. These results provide a novel model for the design of high-capacity and long-life electrode materials.Keywords: a-MoS5.7; high capacity; high energy density; Li2S2; reversible conversion reaction;

•LiFePO4 precursors were successfully prepared in pure water phase under atmosphere.•LiFePO4 nanostructures were also regenerated by recycling filtrate.•LiFePO4/C delivers high discharge capacity of 160 mAh g−1 at 0.2 C and high rate capacity of 107 mAh g−1 at 20C.•LiFePO4/C delivers a capacity retention rate closed to 97% after 240 cycles at 20C.An economical and scalable synthesis route of LiFePO4 nanoplate precursors is successfully prepared in pure water phase under atmosphere without employing environmentally toxic surfactants or high temperature and high pressure compared with traditional hydrothermal or solvothermal methods, which also involves recycling the filtrate to regenerate LiFePO4 nanoplate precursors and collecting by-product Na2SO4. The LiFePO4 precursors present a plate-like morphology with mean thickness and length of 50–100 and 100–300 nm, respectively. After carbon coating, the LiFePO4/C nanoparticles with particle size around 200 nm can be observed which exhibit a high discharge capacity of 160 mAh g−1 at 0.2 C and 107 mAh g−1 at 20 C. A high capacity retention closed to 91% can be reached after 500 cycles even at a high current rate of 20C with coulombic efficiency of 99.5%. This work suggests a simple, economic and environmentally benign method in preparation of LiFePO4/C cathode material for power batteries that would be feasible for large scale industrial production.Download high-res image (119KB)Download full-size image

•Layered SnSe2 single crystal with integrated Se–Se buffer layers is prepared.•Se–Se buffer layers could accommodate the intercalation process.•Autogenous Na2Se layers could confine the structural damage of tin sequences.•SnSe2 single crystal realizes efficient, fast and long-term sodium-ion storage.•Sodiation/desodiation processes of the SnSe2 single crystal are investigated.Se−Se buffer layers are introduced into tin sequences as SnSe2 single crystal to enhance the cycling stability for long-term sodium-ion storage by blazing a trail of self-defence strategy to structural pulverization especially at high current density. Specifically, under half-cell test, the SnSe2 electrodes could yield a high discharge capacity of 345 mAh g−1 after 300 cycles at 1 A g−1 and a high discharge capacity of 300 mAh g−1 after 2100 cycles at 5 A g−1 with stable coulombic efficiency and no capacity fading. Even with the ultrafast sodium-ion storage at 10 A g−1, the cycling stability still makes a positive response and a high discharge capacity of 221 mAh g−1 is demonstrated after 2700 cycles without capacity fading. The full-cell test for the SnSe2 electrodes also demonstrates the superior cycling stability. The flexible and tough Se–Se buffer layers are favourable to accommodate the sodium-ion intercalation process, and the autogenous Na2Se layers could confine the structural pulverization of further sodiated tin sequences by the slip along the Na2Se–NaxSn interfaces.

Lithium sulfide (Li2S) is a promising cathode material for Li–S batteries with high capacity (theoretically 1166 mAh g–1) and can be paired with nonlithium–metal anodes to avoid potential safety issues. However, the cycle life of coarse Li2S particles suffers from poor electronic conductivity and polysulfide shuttling. Here, we develop a flexible slurryless nano-Li2S/reduced graphene oxide cathode paper (nano-Li2S/rGO paper) by simple drop-coating. The Li2S/rGO paper can be directly used as a free-standing and binder-free cathode without metal substrate, which leads to significant weight savings. It shows excellent rate capability (up to 7 C) and cycle life in coin cell tests due to the high electron conductivity, flexibility, and strong solvent absorbency of rGO paper. The Li2S particles that precipitate out of the solvent on rGO have diameters 25–50 nm, which is in contrast to the 3–5 μm coarse Li2S particles without rGO.

A combination of electrospinning and a frozen section has been used to gradually lower the scale of the active materials, thus effectively avoiding nano-reunion, to a certain extent, during electrode fabrication. The as-fabricated electrode-based supercapacitor possesses high electrochemical capacitance and good stability. Our results demonstrate a universal top-down route for the controllable fabrication of homodisperse nanoparticle electrodes for use in high performance electrochemical devices.

A low-cost, mass-produced, dry-gel-based method for fabricating graphene based electroactive materials relevant to energy storage has been reported. This technique combines thermal decomposition of carbon-based materials for the formation of ultramicropores/micropores and freeze drying of graphene gels for the formation of mesopores/macropores. The as-fabricated pore-rich carbon materials show electrochemical performances with superior characteristics of stabilization, specific capacitance and rate capability, demonstrating their great potential applications in clean energy.

•A free-standing and binder-free S-rGO paper served directly as electrode for Li-S battery.•The macro-porous graphene paper was obtained without template.•Sulfur thin film was covered on rGO surface with strong combination.•Good conductivity and stability leads to excellent electrochemical performance.A macroporous free-standing nano-sulfur/graphene (S-rGO) paper is introduced directly as an electrode for lithium-sulfur battery. The S-rGO paper is synthesized through a facile freeze drying route followed by low-temperature heat treatment. The flexible S-rGO paper not only provides a conductive framework for electron transport but also alleviates volume effect during cycling. The as-designed S-rGO paper exhibits excellent rate capability and cyclability. The specific discharge capacity is 800 mAh g−1 after 200 cycles at a current density of 300 mA g−1 and the capacity fading rate is only 0.035% per cycle. Even at a high current density of 1500 mA g−1, it still shows a good performance. We ascribe the high performance of the S-rGO paper to stable macroporous structure and strong interaction between sulfur nanoparticles and graphene.Macroporous S-rGO paper is used as a binder-free and free-standing cathode electrode for Li-S battery and shows excellent electrochemical performance.

Owing to the layered structure and high theoretical capacity, MoS2 has attracted more and more interest as a potential anode material for lithium-ion batteries. However, it suffers from rapid capacity decay and low rate capability. In this work, we introduce a novel hierarchical material consisting of ultrathin MoS2 nanosheets grown on the surface of an active carbon fiber (ACF) cloth fabricated by a facile morphogenetic process. The ACF cloth acts as both a template and a stabilizer. The obtained MoS2/ACF cloth composite possesses hierarchical porosity and an interconnected framework. Serving as a free-standing and binder-free anode, it shows high specific capacity and excellent reversibility. A discharge capacity as high as 971 mA h g−1 is attained at a current density of 0.1 A g−1, and the capacity fade is only 0.15% per cycle within 90 cycles. Even after 200 cycles at a high current density of 0.5 A g−1, the composite still shows a capacity of 418 mA h g−1. The superior electrochemical performance of MoS2/ACF can be attributed to its robust structure and to the synergistic effects of ultrathin MoS2 nanosheets and ACF. This single-component anode that we propose benefits from a simplified electrode preparation process. The morphogenetic strategy used for the material production is facile but effective, and can be extended to prepare other metal sulfides with elaborate textural characteristics.

A porous three-dimensional nitrogen-doped graphene (3D-NG) was introduced as an interconnected framework for sulfur in lithium–sulfur batteries. The 3D-NG-sulfur composite (3D-NGS) with a high sulfur content of 87.6 wt% was synthesized via a facile one-pot solution method and sulfur was well dispersed within it. The as-designed 3D-NGS composite exhibits excellent rate capability and cyclability. The discharge specific capacity is 792 mA h g−1 after 145 cycles at a current density of 600 mA g−1 and the capacity fading rate is 0.05% per cycle. Even at a high rate of 1500 mA g−1, the composite still shows a good cycle performance with a capacity of 671 mA h g−1 after 200 cycles. The outstanding electrochemical performance can be attributed to the flexible porous 3D structure and N-doping in graphene. The flexible 3D-NG can provide a conductive framework for electron transport and alleviate the volume effect during cycling. N-doping can facilitate the penetration of Li ions across the graphene and restrain sulfur due to the strong chemical bonding between S and the nearby N atoms.

3D porous MnO/C anode materials with controllable pore size are rationally designed and synthesized by a facile template-free strategy. The MnxZn1–xCO3 (x = 1, 2/3, 1/2 and 1/3) precursors were prepared by an ultrasonic-assisted co-precipitation method, and then heated with glucose in a reducing atmosphere to obtain a series of MnO/C microspheres through topochemical conversion. These MnO/C microspheres consist of nanosized primary particles and have interconnected pore architectures with high specific surface areas of up to 111.4 m2 g−1. Adjusting the Zn/Mn molar ratio of MnxZn1–xCO3 can easily tune the pore size of the MnO/C materials from 14.9 nm to 31.8 nm. Electrochemical performances of the MnO/C materials were found to be strongly correlated with their porous structures. The MnO/C material with optimized pore size exhibits a high reversible capacity (846 mA h g−1 at 100 mA g−1), superior rate capability (406 mA h g−1 at 3200 mA g−1) and excellent cycling stability. This strategy can be extended to prepare other candidate electrode materials.

Nano-dumbbells via electrospinning: controllable nano-dumbbells are fabricated via electrospinning. The weight block parts and the length of nanowires between them can be adjusted through changing the experimental conditions. This nanostructure enables ultralow-limit gas sensing properties of the resulting polypyrrole-based microsensor.

Spherical LiFe0.6Mn0.4PO4/C particles with high tap density were successfully synthesized by sintering spherical precursor powders prepared by a modified spray drying method with a double carbon coating process. The obtained secondary spheres were made of carbon-coated nanocrystallines (∼100 nm), exhibiting a high tap density of 1.4 g cm−3. The LiFe0.6Mn0.4PO4/C microspheres had a reversible capacity of 160.2 mAh g−1 at 0.1C, and a volume energy density of 801.5 Wh L−1 which is nearly 1.4 times that of their nano-sized counterparts. This spherical material showed remarkable rate capability by maintaining 106.3 mAh g−1 at 20C, as well as excellent cycleablity with 98.9% capacity retention after 100 cycles at 2C and 200 cycles at 5C. The excellent electrochemical performance and processability of the LiFe0.6Mn0.4PO4/C microspheres make them very attractive as cathode materials for use in high rate battery application.

Lithium–sulfur batteries are promising electrochemical devices for future energy conversion and storage. Its theoretical capacity is 1675 mA h g−1, much higher than that of conventional lithium-ion batteries. However, it suffers from rapid capacity decay and low energy efficiency. In this work, we introduce a novel dual core–shell structured sulfur composite with multi-walled carbon nanotubes (MWCNTs) and polypyrrole (PPy), MWCNTs@S@PPy, as a cathode material for Li–S batteries. The composite is synthesized via a facile one-pot method. In the structure, MWCNTs and PPy work as a combined conductive framework to provide access to Li+ ingress and egress for reaction with sulfur, and to inhibit the diffusion of polysulfide out of the cathode, and hence reduce the capacity decay. Meanwhile, LiNO3 additive is added into the electrolyte to improve the coulombic efficiency. The as-designed MWCNTs@S@PPy composite shows excellent rate capability and cyclability. The initial discharge specific capacity is as high as 1517 mA h g−1, and remains at 917 mA h g−1 after 60 cycles at a current density of 200 mA g−1. Even at a high current density of 1500 mA g−1, the composite still shows a good cycle performance with a capacity of 560 mA h g−1 after 200 cycles.

A novel acetate-assisted antisolvent precipitation method combined with ball milling and heat treatment is developed to synthesize nanosized carbon-coated LiMnPO4 material. The precursor prepared by the precipitation process is composed of Mn3(PO4)2 and Li3PO4 nanoparticles. After heat treatment of the ball-milled mixture of precursor and glucose, the carbon-coated LiMnPO4 with the particle size of around 60 nm is obtained. The LiMnPO4 nanocomposite synthesized at the optimized conditions delivers specific discharge capacities of 154, 134, 120, 90, and 61 mAh g−1 at the rates of 0.05, 0.2, 1, 5, and 10C, respectively, which are comparable to some of the best reported C-LiMnPO4 materials prepared by other synthesis methods. This material further exhibits good cycling stability, especially at high discharge rates of 5C and 10C.Highlights► A novel antisolvent precipitation method is developed to synthesize LiMnPO4 material. ► The precursor is composed of Mn3(PO4)2 and Li3PO4 nanoparticles. ► The carbon-coated LiMnPO4 with the particle size of 60 nm is obtained. ► The C-LiMnPO4 material exhibits excellent rate capability and stable cyclability.

•A LiCoPO4/Li4Ti5O12 (LCP/LTO) full battery is designed.•This battery takes profit of high energy of LCP and high reliability of LTO.•This battery affords a work voltage of 3.2 V and a capacity of 122 mAh g− 1.A LiCoPO4/Li4Ti5O12 battery prototype is designed to fully take profit of high energy density of LiCoPO4 and superior reliability of Li4Ti5O12. Electrochemical test results show that the battery affords an operational voltage of 3.2 V and delivers a reversible capacity of 122 mAh g− 1. Based on the mass of LiCoPO4, the energy density of such a battery can reach 378 mWh g− 1. Provided the long-term cyclability of the LiCoPO4 cathode could be well addressed, this LiCoPO4/Li4Ti5O12 system offers an alternative for large-scale energy storage application.

There is great interest in utilization of silicon-containing nanostructures as anode materials for lithium-ion batteries but usually limited by manufacturing cost, their intrinsic low electric conductivity, and large volume changes during cycling. Here we present a facile process to fabricate graphene-wrapped silicon nanowires (GNS@Si NWs) directed by electrostatic self-assembly. The highly conductive and mechanical flexible graphene could partially accommodate the large volume change associated with the conversion reaction and also contributed to the enhanced electronic conductivity. The as-prepared GNS@Si NWs delivered a reversible capacity of 1648 mAh·g–1 with an initial Coulombic efficiency as high as 80%. Moreover, capacity remained 1335 mAh·g–1 after 80 cycles at a current of 200 mA·g–1, showing significantly improved electrochemical performance in terms of rate capability and cycling performance.

The high-temperature cycling stability at a high cutoff voltage of LiNi0.5Co0.2Mn0.3O2 was improved by TiO2 coating. The mechanism of enhancement was elucidated by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses. TiO2 coating formed a uniform layer on the surface of LiNi0.5Co0.2Mn0.3O2 particles without changing the crystal structure. Electrochemical tests indicated that TiO2 coating can improve the lithium ion intercalation stability at 328 K and at a high cutoff voltage of 4.4 V. The 1.0% TiO2-coated LiNi0.5Co0.2Mn0.3O2 discharged 149.2 mAh g−1 after 100 cycles at 0.5C, and maintained 92.1% of the initial discharge capacity. By contrast, the bare sample discharged only 87.7 mAh g−1 with 48.2% capacity retention. ICP-AES results proved that the TiO2 coating layer can reduce the dissolution of transition metal ions from LiNi0.5Co0.2Mn0.3O2. EIS and XPS confirmed that the improved cycling stability can be attributed to the suppression of the reaction between cathode and electrolyte in lithium-ion batteries.Highlights► TiO2 coating improves cycling stability of LiNi0.5Co0.2Mn0.3O2 at 328 K and 4.4 V. ► TiO2 coating can prevent the increase of charge-transfer resistance (Rct). ► LiF/MFx species deposited on the electrode lead to capacity deterioration. ► The deposition of LiF/MFx species can be suppressed by TiO2 coating. ► TiO2 coating reduces metal dissolution at a highly delithiated state.

Al2O3-modified Li(Ni1/3Co1/3Mn1/3)O2 is synthesized by a modified Al2O3 coating process. The Al2O3 coating is carried out on an intermediate, (Ni1/3Co1/3Mn1/3)(OH)2, rather than on Li(Ni1/3Co1/3Mn1/3)O2. As a comparison, Al2O3-coated Li(Ni1/3Co1/3Mn1/3)O2 also is prepared by traditional Al2O3 coating process. The effects of Al2O3 coating and Al2O3 modification on structure and electrochemical performance are investigated and compared. Electrochemical tests indicate that cycle performance and rate capability of Li(Ni1/3Co1/3Mn1/3)O2 are enhanced by Al2O3 modification without capacity loss. Al2O3 coating can also enhance the cycle performance but cause evident capacity loss and decline of rate capability. The effect of Al2O3 coating and Al2O3 modification on kinetics of lithium-ion transfer reaction at the interface of electrode/electrolyte is investigated via electrochemical impedance spectra (EIS). The result support that the Al2O3 modification increase Li+ diffused coefficient and decrease the activation energy of Li+ transfer reaction but the traditional Al2O3 coating lead to depression of Li+ diffused coefficient and increase of activation energy.

Spinel Li4Ti5O12 (LTO) is a promising candidate anode material for Li-ion batteries due to its well-known zero-strain merits. To improve the electronic properties of spinel LTO, which are intrinsically poor, we processed the material into a nanosized architecture to shorten the distance for Li-ion and electron transport using the versatile electrospinning method. Graphene was chosen as an effective carbon coating to improve the surface conductivity of the nanocomposites. The as-prepared graphene-embedded LTO anode material showed improved discharging/charging and cycling properties, particularly at high rates, such as 22 C, which makes the nanocomposite an attractive anode material for applications in electric vehicles.

A porous three-dimensional nitrogen-doped graphene (3D-NG) was introduced as an interconnected framework for sulfur in lithium–sulfur batteries. The 3D-NG-sulfur composite (3D-NGS) with a high sulfur content of 87.6 wt% was synthesized via a facile one-pot solution method and sulfur was well dispersed within it. The as-designed 3D-NGS composite exhibits excellent rate capability and cyclability. The discharge specific capacity is 792 mA h g−1 after 145 cycles at a current density of 600 mA g−1 and the capacity fading rate is 0.05% per cycle. Even at a high rate of 1500 mA g−1, the composite still shows a good cycle performance with a capacity of 671 mA h g−1 after 200 cycles. The outstanding electrochemical performance can be attributed to the flexible porous 3D structure and N-doping in graphene. The flexible 3D-NG can provide a conductive framework for electron transport and alleviate the volume effect during cycling. N-doping can facilitate the penetration of Li ions across the graphene and restrain sulfur due to the strong chemical bonding between S and the nearby N atoms.

Spherical LiFe0.6Mn0.4PO4/C particles with high tap density were successfully synthesized by sintering spherical precursor powders prepared by a modified spray drying method with a double carbon coating process. The obtained secondary spheres were made of carbon-coated nanocrystallines (∼100 nm), exhibiting a high tap density of 1.4 g cm−3. The LiFe0.6Mn0.4PO4/C microspheres had a reversible capacity of 160.2 mAh g−1 at 0.1C, and a volume energy density of 801.5 Wh L−1 which is nearly 1.4 times that of their nano-sized counterparts. This spherical material showed remarkable rate capability by maintaining 106.3 mAh g−1 at 20C, as well as excellent cycleablity with 98.9% capacity retention after 100 cycles at 2C and 200 cycles at 5C. The excellent electrochemical performance and processability of the LiFe0.6Mn0.4PO4/C microspheres make them very attractive as cathode materials for use in high rate battery application.

Lithium–sulfur batteries are promising electrochemical devices for future energy conversion and storage. Its theoretical capacity is 1675 mA h g−1, much higher than that of conventional lithium-ion batteries. However, it suffers from rapid capacity decay and low energy efficiency. In this work, we introduce a novel dual core–shell structured sulfur composite with multi-walled carbon nanotubes (MWCNTs) and polypyrrole (PPy), MWCNTs@S@PPy, as a cathode material for Li–S batteries. The composite is synthesized via a facile one-pot method. In the structure, MWCNTs and PPy work as a combined conductive framework to provide access to Li+ ingress and egress for reaction with sulfur, and to inhibit the diffusion of polysulfide out of the cathode, and hence reduce the capacity decay. Meanwhile, LiNO3 additive is added into the electrolyte to improve the coulombic efficiency. The as-designed MWCNTs@S@PPy composite shows excellent rate capability and cyclability. The initial discharge specific capacity is as high as 1517 mA h g−1, and remains at 917 mA h g−1 after 60 cycles at a current density of 200 mA g−1. Even at a high current density of 1500 mA g−1, the composite still shows a good cycle performance with a capacity of 560 mA h g−1 after 200 cycles.

3D porous MnO/C anode materials with controllable pore size are rationally designed and synthesized by a facile template-free strategy. The MnxZn1–xCO3 (x = 1, 2/3, 1/2 and 1/3) precursors were prepared by an ultrasonic-assisted co-precipitation method, and then heated with glucose in a reducing atmosphere to obtain a series of MnO/C microspheres through topochemical conversion. These MnO/C microspheres consist of nanosized primary particles and have interconnected pore architectures with high specific surface areas of up to 111.4 m2 g−1. Adjusting the Zn/Mn molar ratio of MnxZn1–xCO3 can easily tune the pore size of the MnO/C materials from 14.9 nm to 31.8 nm. Electrochemical performances of the MnO/C materials were found to be strongly correlated with their porous structures. The MnO/C material with optimized pore size exhibits a high reversible capacity (846 mA h g−1 at 100 mA g−1), superior rate capability (406 mA h g−1 at 3200 mA g−1) and excellent cycling stability. This strategy can be extended to prepare other candidate electrode materials.

A low-cost, mass-produced, dry-gel-based method for fabricating graphene based electroactive materials relevant to energy storage has been reported. This technique combines thermal decomposition of carbon-based materials for the formation of ultramicropores/micropores and freeze drying of graphene gels for the formation of mesopores/macropores. The as-fabricated pore-rich carbon materials show electrochemical performances with superior characteristics of stabilization, specific capacitance and rate capability, demonstrating their great potential applications in clean energy.