•A thin and lightweight PI-SiO2 fibrous membrane was successfully synthesized.•The PI-SiO2 membrane possesses high porosity and excellent electrolyte wettability.•The PI-SiO2 membrane shows superior flexibility and thermal stability up to 250 °C.•LiMn2O4/Li cell using the PI-SiO2 separator exhibits excellent rate capability.•LiMn2O4/Li cell using the PI-SiO2 separator displays long cycle life at 55 °C.The commercial polyolefin separators still possess two well-known drawbacks: poor wettability and thermal stability. Herein, a thin and lightweight silica filled in polyimide (PI) nanofibers membrane is prepared by electrospinning. Without any binders, the nano-silica particles are firmly embedded in the PI nanofibers with high structure stability. The PI-SiO2 membrane with high porosity (90%) presents enhanced conductivity due to the excellent electrolyte wettability and large electrolyte uptake (about 2400%). In addition, the PI-SiO2 membrane displays good mechanical flexibility and enhanced thermal stability up to 250 °C, which significantly improve the safety of lithium-ion batteries when used as a separator. The LiMn2O4/Li cell with the PI-SiO2 separator exhibits highly improved rate capability and cycling stability at different temperatures (25 °C and 55 °C), which make PI-SiO2 membrane as a promising secure separator candidate for high-performance and safety lithium-ion batteries.Download high-res image (168KB)Download full-size image

•A flexible porous carbon nanofiber film was fabricated by electrospinning.•Ultrafine titanium dioxide and graphene were adopted to modify the nanofibers.•The sulfur cathode film exhibits good flexibility and foldability.•The flexible film cathode shows excellent electrochemical performance.Lithium-sulfur (Li-S) batteries are regarded as a promising next-generation electrical-energy-storage technology due to their low cost and high theoretical energy density. Furthermore, flexible and wearable electronics urgently requires their power sources to be mechanically robust and flexible. However, the effective progress of high-performance, flexible Li-S batteries is still hindered by the poor conductivity of sulfur cathodes and the dissolution of lithium polysulfides as well as the weak mechanical properties of sulfur cathodes. Herein, a new type of flexible porous carbon nanofiber film modified with graphene and ultrafine polar TiO2 nanoparticles is designed as a sulfur host, in which the artful structure enabled the highly efficient dispersion of sulfur for a high capacity and a strong confinement capability of lithium polysulfides, resulting in prolonged cycle life. Thus, the cathode shows an extremely high initial specific discharge capacity of 1501 mA h g−1 at 0.1 C and an excellent rate capability of 668 mA h g−1 at 5 C as well as prolonged cycling stability. The artful design provides a facile method to fabricate high-performance, flexible sulfur cathodes for Li-S batteries.Download high-res image (310KB)Download full-size image

Porous Na3V2(PO4)3@C nanocomposites enwrapped in a 3D graphene network were prepared using a simple freeze-drying-assisted thermal treatment method. The carbon layer and 3D graphene network provide not only a 3D conductive network but also a double restriction on the aggregation of Na3V2(PO4)3 particles that have a high crystallinity under high temperature treatment. Due to the high electrochemical activity of the highly crystalline Na3V2(PO4)3 nanoparticles and 3D conductive network, the novel NVP@C/G material displays a superior rate capability (76 mA h g−1 at 60C) and ultra-long cyclability (82% capacity retention for 1500 cycles at 40C) when used in sodium-ion batteries.

•Co3O4@PPynanowirearraysaresynthesizedbyatwo-stepmethod(*).•Co3O4@PPy NWAs exhibit improved rate capability and long cycle life.•The enhanced performance is attributed to the conductive PPy coating layer.Coaxial Co3O4@polypyrrole (Co3O4@PPy) nanowire arrays have been successfully synthesized via a simple hydrothermal method and further a polymerization process. According to the composition and morphology characterization, it is found that a thin layer of amorphous PPy is uniformly coated on the surface of the Co3O4 nanowire. When directly used as an anode material for lithium-ion batteries, the Co3O4@PPy nanowire arrays electrode exhibits high reversible capacity, good rate capability, and improved cycling stability. A reversible capacity of 700 mAh g−1 is sustained at the current of 3 A g−1 after 500 cycles, showing better cycling stability than the bare Co3O4 nanowire arrays (only 150 mAh g−1 at the current of 3 A g−1after 100 cycles). Even at a high current of 20 A g−1, the Co3O4@PPy nanowire arrays can still maintain a capacity of 470 mAh g−1, which is much higher than that of the bare Co3O4 nanowire arrays (158 mAh g−1). The synergetic effect of the arrays structure and the PPy buffer layer contributes to the enhanced electrochemical performance of the Co3O4@PPy nanoarrys. As a result, the introduction of conductive polymer coating layer is an effective strategy to enhance the electrochemical performance of nanoarrays structure for advanced energy storage.

•TiN-coated micron-sized Ta-doped Li4Ti5O12 was synthesized via a facile method.•Both TiN coating and Ta doping of Li4Ti5O12 improved the electronic conductivities.•LTOTaN30 anode showed better anodic performance than the bare and mono doped LTO.Micron-sized Li4Ti5O12 with both surface modification (TiN) and inner Ta5+ doping has been synthesized via a combination of solid-state reaction and surface thermal nitridation. The physical and chemical properties of all samples are tested systematically. The results demonstrate that tantalum is successfully doped in the lattice of Li4Ti5O12 and a thin amorphous TiN coated on the surface of the Li4Ti5O12 particles. The TiN coating layer enhances surface electronic conductivity and electrical contact between particles, while Ta5+ bulk doping in the lattice improves the intrinsic ionic conductivity and electronic conductivity inside particles. Being used as anode materials for lithium-ion batteries, the co-doped Li4Ti5O12 electrode shows much better electrochemical performance (144.5 mAh g−1 at 5 C after 500 cycles with a capacity retention of 91.63%) than that of pristine Li4Ti5O12 and mono tantalum doped or TiN coated Li4Ti5O12, only Ta-doped Li4Ti5O12 delivers 112.1 mAh g−1 at 5 C after 500 cycles and the TiN-coated Li4Ti5O12 electrode only retains 122.6 mAh g−1 at 5 C after 500 cycles. This design by exploring both surface modification and bulk doping is highly attractive for high performance Li4Ti5O12 manufacturing and may be applicative to other micron-sized electrode materials with inferior conductivity.

Structure stability and fast charge–discharge capacity are highly desirable for electrode materials applied in lithium ion batteries (LIBs). In this report, binder-free Co–CoOx nanowire arrays (NWAs) were obtained by a simple H2 reduction of Co3O4 NWAs. The resulting Co–CoOx NWAs were grown directly on the current collector with enough open space between each nanowire, which provides fast charge transfer channels and large accessible surface area to the electrolyte. More importantly, the introduction of electrochemically inactive Co without volume change during cycling for LIBs could improve the structural stability of the Co–CoOx NWA electrode and the high electronic conductivity of metallic Co in the array structure greatly enhances the electron transfer ability of Co–CoOx nanowires. Benefitting from those designed structural features, the binder-free Co–CoOx NWAs achieved remarkable electrochemical performances with excellent cycle stability at high rates and high rate capacity. The Co–CoOx NWA electrode maintains highly stable capacities of 990 and 740 mA h g−1 after 1000 cycles at 10 and 20 A g−1, respectively. At an ultrahigh rate of 50 A g−1, a high reversible capacity of 413 mA h g−1 is achieved. The result demonstrates that such a novel Co–CoOx nanowire array structure is a new strategy to design high performance anode materials for LIBs.

Nitrogen-doped Li4Ti5O12 (LTO) is first synthesized by thermal decomposition of LTO and melamine. As indicated by TG, XPS and TEM analysis, nitrogen is successfully doped in LTO and the generated TiN layer is deposited on the surface of the LTO particle. The LTO with certain nitrogen modification (LTON12) on the surface exhibits enhanced electronic conductivity and Li ion diffusivity. The LTON12 electrode exhibits much better rate capability and cycling performance than the pristine LTO. The LTON12 electrode delivers a capacity of 124.2 mA h g−1 after 500 cycles at 5 C with a high capacity retention of 89.1% while the capacity retention of the pristine LTO is only 43.7%. In addition, the LTON12 exhibits a capacity of 74.3 mA h g−1 at even 100 C with a fixed discharge rate of 1 C. The excellent electrochemical performance of N-doped LTO is attributed to the improved electronic and ion conductivities provided by the thin TiN coating layer on the particle surface.

Perovskites show excellent specific catalytic activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline solutions; however, small surface areas of the perovskites synthesized by traditional sol–gel methods lead to low utilization of catalytic sites, which gives rise to poor Li–O2 batteries performance and restricts their application. Herein, a hierarchical mesporous/macroporous perovskite La0.5Sr0.5CoO3-x (HPN-LSC) nanotube is developed to promote its application in Li–O2 batteries. The HPN-LSC nanotubes were synthesized via electrospinning technique followed by postannealing. The as-prepared HPN-LSC catalyst exhibits outstanding intrinsic ORR and OER catalytic activity. The HPN-LSC/KB electrode displays excellent performance toward both discharge and charge processes for Li–O2 batteries, which enhances the reversibility, the round-trip efficiency, and the capacity of resultant batteries. The synergy of high catalytic activity and hierarchical mesoporous/macroporous nanotubular structure results in the Li–O2 batteries with good rate capability and excellent cycle stability of sustaining 50 cycles at a current density of 0.1 mA cm–2 with an upper-limit capacity of 500 mAh g–1. The results will benefit for the future development of high-performance Li–O2 batteries using hierarchical mesoporous/macroporous nanostructured perovskite-type catalysts.Keywords: bifunctional catalysts; electrospinning; hierarchical mesoporous/macroporous nanotubes; lithium−oxygen batteries; perovskites

•Ta doping in Li4Ti5O12 would enlarge the lattice parameter of Li4Ti5O12.•The ionic conductivity and electronic conductivity of Li4Ti5O12 are improved by Ta doping.•The Li4Ti5O12 with only 0.1 at% Ta doping exhibits superior electrochemical performance.A series of Tantalum-doped lithium titanate (Ta-doped Li4Ti5O12) samples have been successfully synthesized by one step solid-state method using TiO2, Li2CO3, and Ta2O5 as raw materials. The Li4Ti5O12 with only 0.1 at% Ta doping (Li4Ti4.995Ta0.005O12) exhibits higher rate capability and better cyclic stability than the pristine Li4Ti5O12. Li4Ti4.995Ta0.005O12 could deliver 95.1 mAh g−1 at 10C with much lower overpotential (216.1 mV) while the pristine Li4Ti5O12 delivers only 50.4 mAh g−1 at 10C with higher overpotential of 392.2 mV. As indicated by XRD, HRTEM and electrochemical characterizations, Ta doping in Li4Ti5O12 would enlarge the lattice parameter of the Li4Ti5O12, and facilitate the Li+ diffusion during the charge/discharge process. In addition, the higher charge compensation of the stoichiometric reduction of Ti4+ to Ti3+ by introducing Ta increases the electronic conductivity of Li4Ti5O12. The improved ionic conductivity and electronic conductivity are beneficial to the electrochemical performance of Li4Ti5O12. As a result, Ta doping is a new strategy for enhancing the electrochemical performance of Li4Ti5O12.

•The V2O5 nanotubes are prepared by eletrospinning with using low-cost inorganic vanadium source.•The as-prepared V2O5 has porous, hollow and interconnected nanostructures.•By controlling the annealing time, a small amount of carbon can be retained in V2O5 nanotubes.•The V2O5 nanotubes with carbon exhibit excellent high rate performance and cycling stability.In this work, porous vanadium pentoxide (V2O5) nanotubes have been synthesized by a simple electrospinning technique followed by an annealing process with using low-cost inorganic vanadium precursor. By controlling the annealing time at 400 °C, a small amount of polymer pyrolysis carbon can be retained which improves the conductivity of the porous V2O5 nanotubes. When evaluated as a cathode material for lithium ion batteries, the porous V2O5 nanotubes delivered capacities of 114.9, 99.7 and 79.6 mAh g−1 at 10, 20 and 50C in the voltage range of 2.5-4.0 V, respectively. Moreover, the porous V2O5 nanotubes display good cycling performance, the capacity retention is 97.4% after 200 cycles at 50C. The results indicate that fabricating nanostructured V2O5 with a porous interconnected morphology is an effective way to improve the electrochemical performance of V2O5.

•A novel facile synthesis of graphene nanosheets involving freeze-drying technology.•The as-prepared materials exhibit superior cycle stability and rate performance.•The freeze-drying helps to enlarge the interlayer distance and specific surface area.Graphene nanosheets are synthesized by a novel facile method involving freeze-drying technology and thermal reduction. The microstructure and morphologies are characterized by X-ray diffraction, Brunauer–Emmett–Teller measurements, Fourier transform infrared spectroscopy, and high resolution transmission electron microscope. The results indicate that graphene nanosheets with high specific surface area (358.3 m2 g−1) and increased interlayer distance (0.385 nm) are successfully obtained through the freeze-drying process. The electrochemical performances are evaluated by using coin-type cells versus lithium. A high initial reversible capacity of 1132.9 mAh g−1 is obtained at a current density of 100 mA g−1. More importantly, even after 300 cycles at a high current density of 1000 mA g−1, a stable specific capacity of 556.9 mAh g−1 can be achieved, suggesting the graphene nanosheets exhibit superior cycle stability. The fascinating electrochemical performance could be ascribed to the high specific surface area and the increased layer distance between the graphene nanosheets.

Porous Na3V2(PO4)3@C nanocomposites enwrapped in a 3D graphene network were prepared using a simple freeze-drying-assisted thermal treatment method. The carbon layer and 3D graphene network provide not only a 3D conductive network but also a double restriction on the aggregation of Na3V2(PO4)3 particles that have a high crystallinity under high temperature treatment. Due to the high electrochemical activity of the highly crystalline Na3V2(PO4)3 nanoparticles and 3D conductive network, the novel NVP@C/G material displays a superior rate capability (76 mA h g−1 at 60C) and ultra-long cyclability (82% capacity retention for 1500 cycles at 40C) when used in sodium-ion batteries.

Nitrogen-doped Li4Ti5O12 (LTO) is first synthesized by thermal decomposition of LTO and melamine. As indicated by TG, XPS and TEM analysis, nitrogen is successfully doped in LTO and the generated TiN layer is deposited on the surface of the LTO particle. The LTO with certain nitrogen modification (LTON12) on the surface exhibits enhanced electronic conductivity and Li ion diffusivity. The LTON12 electrode exhibits much better rate capability and cycling performance than the pristine LTO. The LTON12 electrode delivers a capacity of 124.2 mA h g−1 after 500 cycles at 5 C with a high capacity retention of 89.1% while the capacity retention of the pristine LTO is only 43.7%. In addition, the LTON12 exhibits a capacity of 74.3 mA h g−1 at even 100 C with a fixed discharge rate of 1 C. The excellent electrochemical performance of N-doped LTO is attributed to the improved electronic and ion conductivities provided by the thin TiN coating layer on the particle surface.

Structure stability and fast charge–discharge capacity are highly desirable for electrode materials applied in lithium ion batteries (LIBs). In this report, binder-free Co–CoOx nanowire arrays (NWAs) were obtained by a simple H2 reduction of Co3O4 NWAs. The resulting Co–CoOx NWAs were grown directly on the current collector with enough open space between each nanowire, which provides fast charge transfer channels and large accessible surface area to the electrolyte. More importantly, the introduction of electrochemically inactive Co without volume change during cycling for LIBs could improve the structural stability of the Co–CoOx NWA electrode and the high electronic conductivity of metallic Co in the array structure greatly enhances the electron transfer ability of Co–CoOx nanowires. Benefitting from those designed structural features, the binder-free Co–CoOx NWAs achieved remarkable electrochemical performances with excellent cycle stability at high rates and high rate capacity. The Co–CoOx NWA electrode maintains highly stable capacities of 990 and 740 mA h g−1 after 1000 cycles at 10 and 20 A g−1, respectively. At an ultrahigh rate of 50 A g−1, a high reversible capacity of 413 mA h g−1 is achieved. The result demonstrates that such a novel Co–CoOx nanowire array structure is a new strategy to design high performance anode materials for LIBs.