Electrochemical Performance Optimization Of V₂O₅and Exploration Of Novel Vanadate Cathode Materials

Based on micro/nano structures, in order to explore and push the limitation ofvanadium oxides and vanadate electrode materials to a higher level, interconnectedV2O5nanorods, ultrathin V2O5nanosheets, three-dimensional (3D) porous V2O5particles,3D hollow-porous V2O5quasi-microspheres, Na0.76V6O15nanorodsandFe5V15O39(OH)9·9H2O nanosheets were designed and synthesized followed bycharacterization and electrochemical performance. The following interesting resultswere achieved:(1) A facile and energy-saving approach has been developed to prepareinterconnected V2O5nanorods via a water bath method followed by annealing at350oC in air. The as-synthesized V2O5nanorods with a diameter of about20nm formed ahighly interconnected structure. When evaluated as a cathode material for lithiumbatteries, the interconnected V2O5nanorods display relatively high-capacity retention(capacity retention reach up to97.3%after100cycles) and long-cycle life.Particularly, they also show excellent high-rate cycling capability, with more than96.36%capacity retention after1000cycles at2.0Ag-1. To the best of our knowledge,it may be the longest cycle for pure V2O5materials without any decoration. Theexcellent electrochemical performance suggests that the unique interconnected V2O5nanorodsis a promising cathode material for long-life lithium batteries.(2) Ultrathin V2O5nanosheets (about6nm) were successfully prepared throughsupercritical solvothermal reaction followed by annealing treatment. The formation ofultrathin nanosheets is owing to Oswald ripening and supercritical fluids effect. Ascathode material for lithium batteries, the ultrathin V2O5nanosheets cathode exhibitsa capacity of108mAh g-1at high rate up to10C in2.4-4V and excellent cycleabilitywith little capacity loss after200cycles. The enhanced rate performance is attributedto the shortened diffusion distance and increased electrode-electrolyte contact area ofthe ultrathin nanostheet structure.(3) A facile top-down fabrication approach has been developed to preparethree-dimensional (3D) porous V2O5quasi-hexagonal microplates, via one stepthermal decomposition of NH4VO3microplates and ammonium vanadium oxideoctahedrons. When evaluated as a cathode material for lithium batteries, the V2O5 microplates show excellent rate capability, with a capacity of110mA h g-1at2000mA g-1. While the resultant V2O5octahedrons display relatively stable cycleperformance, the capacity is retained to96.9%of the initial capacity after500cycles.The excellent electrochemical performance suggests that the unique3D porousstructured V2O5are promising cathode material for lithium batteries. Meanwhile, it isconvinced that this effective top-down stratagy can be extended to fabricate othermicro/nanomaterials with unique structures.(4) Nanoflakes-assembled3D hollow-porous V2O5(HP-V2O5) have beensuccessfully synthesized by the facile solvothermal method followed by annealing at450oC in air. The morphology of the V2O5can be tailored by adjusting thesolvothermal reaction conditions and calcination temperature. The resultant HP-V2O5delivers promising Li storage properties with high specific capacities, stablecyclabilities, and good rate performances. It depicts a specific capacity of173mAhg-1at2A g-1, which is attractive for the development of Li batteries with high powerdensities and high energy densities. The excellent electrochemical performances areattributed to the nanosized building blocks of the3D V2O5hollow-porous structure,which provides a short Li+ions difusion distance, effective strain relaxation and largeactive contact area.(5) Na0.76V6O15nanorods were successfully prepared through a facile annealingtreatment, it exhibits a first-cycle discharge capacity of210mAh g-1at current densityof0.1A g-1in1.5-4V. And the capacity retention successfully increased from26%to80%by optimizing the voltage test range (2.0to4.0V), which suggests that shallowdischarge/charge is a promissing method to improve the reversibility of electrodematerials during the electrochemical reaction.(6) Fe5V15O39(OH)9·9H2O nanosheets were prepared through water bath reaction,it exhibits a high capacity of423mAh g-1and excellent rate performance (a capacityof140mAh g-1was obtained at high rate up to10A g-1). Such electrode material withhigh capacity and high rate performance shows a potential application value.