Xinxin Cao

Nanorod-Nanoflake Interconnected LiMnPO4·Li3V2(PO4)3/C Composite for High-Rate and Long-Life Lithium-Ion Batteries

Olivine-type structured LiMnPO4 has been extensively studied as a high-energy density cathode material for lithium-ion batteries. However, preparation of high-performance LiMnPO4 is still a large obstacle due to its intrinsically sluggish electrochemical kinetics. Recently, making the composites from both active components has been proven to be a good proposal to improve the electrochemical properties of cathode materials. The composite materials can combine the advantages of each phase and improve the comprehensive properties. Herein, a LiMnPO4·Li3V2(PO4)3/C composite with interconnected nanorods and nanoflakes has been synthesized via a one-pot, solid-state reaction in molten hydrocarbon, where the oleic acid functions as a surfactant. With a highly uniform hybrid architecture, conductive carbon coating, and mutual cross-doping, the LiMnPO4·Li3V2(PO4)3/C composite manifests high capacity, good rate capability, and excellent cyclic stability in lithium-ion batteries. The composite electrodes deliver a high reversible capacity of 101.3 mAh g-1 at the rate up to 16 C. After 4000 long-term cycles, the electrodes can still retain 79.39% and 72.74% of its maximum specific discharge capacities at the rates of 4C and 8C, respectively. The results demonstrate that the nanorod-nanoflake interconnected LiMnPO4·Li3V2(PO4)3/C composite is a promising cathode material for high-performance lithium ion batteries.

Uniform MnCo2O4 Porous Dumbbells for Lithium-Ion Batteries and Oxygen Evolution Reactions

Three-dimensional (3D) binary oxides with hierarchical porous nanostructures are attracting increasing attentions as electrode materials in energy storage and conversion systems because of their structural superiority which not only create desired electronic and ion transport channels but also possess better structural mechanical stability. Herein, unusual 3D hierarchical MnCo2O4 porous dumbbells have been synthesized by a facile solvothermal method combined with a following heat treatment in air. The as-obtained MnCo2O4 dumbbells are composed of tightly stacked nanorods and show a large specific surface area of 41.30 m2 g-1 with a pore size distribution of 2-10 nm. As an anode material for lithium-ion batteries (LIBs), the MnCo2O4 dumbbell electrode exhibits high reversible capacity and good rate capability, where a stable reversible capacity of 955 mA h g-1 can be maintained after 180 cycles at 200 mA g-1. Even at a high current density of 2000 mA g-1, the electrode can still deliver a specific capacity of 423.3 mA h g-1, demonstrating superior electrochemical properties for LIBs. In addition, the obtained 3D hierarchical MnCo2O4 porous dumbbells also display good oxygen evolution reaction activity with an overpotential of 426 mV at a current density of 10 mA cm-2 and a Tafel slope of 93 mV dec-1.

Encapsulation of CoS x Nanocrystals into N/S Co-Doped Honeycomb-Like 3D Porous Carbon for High-Performance Lithium Storage

Abstract A honeycomb‐like 3D N/S co‐doped porous carbon‐coated cobalt sulfide (CoS, Co9S8, and Co1– xS) composite (CS@PC) is successfully prepared using polyacrylonitrile (PAN) as the nitrogen‐containing carbon source through a facile solvothermal method and subsequent in situ conversion. As an anode for lithium‐ion batteries (LIBs), the CS@PC composite exhibits excellent electrochemical performance, including high reversible capacity, good rate capability, and cyclic stability. The composite electrode delivers specific capacities of 781.2 and 466.0 mAh g−1 at 0.1 and 5 A g−1, respectively. When cycled at a current density of 1 A g−1, it displays a high reversible capacity of 717.0 mAh g−1 after 500 cycles. The ability to provide this level of performance is attributed to the unique 3D multi‐level porous architecture with large electrode–electrolyte contact area, bicontinuous electron/ion transport pathways, and attractive structure stability. Such micro‐/nanoscale design and engineering strategies may also be used to explore other nanocomposites to boost their energy storage performance.

In situ formation of porous graphitic carbon wrapped MnO/Ni microsphere networks as binder-free anodes for high-performance lithium-ion batteries

Flexible hybrid electrodes with high electronic conductivity and porosity have attracted great attention for energy storage and conversion systems. Herein, we report the fabrication of a porous graphitic carbon wrapped MnO/Ni microsphere network (MnO/Ni/CNF) by a combined solvothermal and electrospinning method followed by stabilization and carbonization processes. Carbon nanofibers which link porous MnO/Ni/C microspheres function as both a 3D conductive network and a current collector for the flexible composite electrode. Meanwhile, the porous MnO/Ni microspheres are coated with porous graphene-like carbon layers, further improving the electronic conductivity and facilitating the electrolyte penetration. When directly utilized as an anode material for LIBs, the MnO/Ni/CNF electrode exhibits excellent electrochemical performances, including high reversible capacity, good cycle stability and rate capability. The as-prepared flexible electrode delivers a capacity of 534.5 mA h g−1 at 200 mA g−1 after 100 cycles (based on the whole electrode mass) and possesses a capacity retention of 95.7% even after long-term 600 cycles at 1 A g−1, suggesting its promising applicability in lithium ion batteries as a flexible binder-free anode.

Electrospun Single Crystalline Fork-Like K2V8O21 as High-Performance Cathode Materials for Lithium-Ion Batteries

Single crystalline fork-like potassium vanadate (K2V8O21) has been successfully prepared by electrospinning method with a subsequent annealing process. The as-obtained K2V8O21 forks show a unique layer-by-layer stacked structure. When used as cathode materials for lithium-ion batteries, the as-prepared fork-like materials exhibit high specific discharge capacity and excellent cyclic stability. High specific discharge capacities of 200.2 and 131.5 mA h g−1 can be delivered at the current densities of 50 and 500 mA g−1, respectively. Furthermore, the K2V8O21 electrode exhibits excellent long-term cycling stability which maintains a capacity of 108.3 mA h g−1 after 300 cycles at 500 mA g−1 with a fading rate of only 0.043% per cycle. The results demonstrate their potential applications in next-generation high-performance lithium-ion batteries.

Caging Na3V2(PO4)2F3 Microcubes in Cross-Linked Graphene Enabling Ultrafast Sodium Storage and Long-Term Cycling

Abstract Sodium‐ion batteries are widely regarded as a promising supplement for lithium‐ion battery technology. However, it still suffers from some challenges, including low energy/power density and unsatisfactory cycling stability. Here, a cross‐linked graphene‐caged Na3V2(PO4)2F3 microcubes (NVPF@rGO) composite via a one‐pot hydrothermal strategy followed by freeze drying and heat treatment is reported. As a cathode for a sodium‐ion half‐cell, the NVPF@rGO delivers excellent cycling stability and rate capability, as well as good low temperature adaptability. The structural evolution during the repeated Na+ extraction/insertion and Na ions diffusion kinetics in the NVPF@rGO electrode are investigated. Importantly, a practicable sodium‐ion full‐cell is constructed using a NVPF@rGO cathode and a N‐doped carbon anode, which delivers outstanding cycling stability (95.1% capacity retention over 400 cycles at 10 C), as well as an exceptionally high energy density (291 Wh kg−1 at power density of 192 W kg−1). Such micro‐/nanoscale design and engineering strategies, as well as deeper understanding of the ion diffusion kinetics, may also be used to explore other micro‐/nanostructure materials to boost the performance of energy storage devices.