Controllable Preparation And Electrochemical Performance Of Various Dimensions V₂O₅ Electrode Materials

For now,lithium ion batteries?LIBs?have been massively applied in small and medium-sized energy storage devices,and however,it still cannot satisfy the demand of large power energy storage due to the low energy density,poor power density,and unsatisfied service-life.Vanadium pentoxide?V₂O₅?,one of the most promising cathode materials,has been extensively studied resulting from its high theoretical capacity as well as better safety.Unfortunately,this kind of oxide electrode materials normally possess relatively low electronic conductivity,ionic diffusion coefficient,and electrochemical activity,especially the bulk materials,which significantly confine the effective use of their high specific capacities,and often lead to poor cycling stabilities.In view of the potential drawbacks of preparation and modification existing in the previous works,the main concentration of this paper is the controllable preparation of V₂O₅ micro/nanomaterials for making the best of high energy/power density of V₂O₅.Our results can also provide valuable guidance for developing and designing the high performance electrode materials for LIBs.Firstly,the 1D hierarchical V₂O₅ nanofibers with high quality are successfully synthesized via a low-cost and facile electrospinning method.The electrochemical tests demonstrate that the as-prepared 1D V₂O₅ nanofibers exhibit superior rate capability and cyclic stability.After 100 cycles at a current density of 0.8 A/g,the specific capacity of the V₂O₅ nanofibers retains 133.9 mAh/g,corresponding to the high capacity retention of 96.05%.The superior performance of the obtained V₂O₅ nanofibers can be mainly attributed to the porous 1D hierarchical nanofiber structure that provides efficient 1D electron transport along the longitudinal direction,short distances of Li+-ion diffusion,as well as improving electrode-electrolyte contact area for high Li+-ion flux across the interface.Meanwhile,the hierarchical nanoplate structure can effectively alleviate the structural strain resulted from the repeated lithium intercalation/deintercalation processes.Finally,the kinetic study reveals some insight strategies thatcan further improve the electrochemical performance of V₂O₅ cathode material.Secondly,the 2D V₂O₅ nanosheets are successfully fabricated by a novel solvothermal system using commercial vanadium pentoxide and citric acid as starting materials and NH4 F as structure-directing additive.The electrochemical tests demonstrate that the as-prepared 2D V₂O₅ nanosheets display excellent rate capability and cyclic stability.At the current density of 0.1 A/g,the first discharge specific capacity of the obtained electrode can reach up to 291.7 mAh/g.Meanwhile,after 200 cycles at a current density of 1.5 A/g,the specific capacity of the V₂O₅ nanosheets retain 139 mAh/g,corresponding to high capacity retention of 94%.Such superior performancecan be mainly ascribed to the short distances of Li+-ion diffusion due to the lamellar structure as well as the improvement of electrode-electrolyte contact area because of the porous texture.Finally,the kinetic studies prove that the 2D V₂O₅ nanosheets possess high Li+diffusion coefficient and improved electrode reaction kinetics.Thirdly,the crumpled reduced graphene oxide encapsulated 3D V₂O₅ nano/microspheres are successfully fabricated for the first time on the basis of one-step solvothermal treatment followed by subsequent annealing.The electrochemical tests demonstrate that the conformally wrapped crumpled reduced graphene oxide has a profound influence on the lithium storage performance of V₂O₅,especially the energy/power density,deriving from the simultaneous improvements in electronic conductivity,structural stability,and charge transfer resistance.The study of formation mechanism reveals that the proposed solvothermal reaction system with high versatility can be extended to encapsulate other solid powders,which provides an effective shortcut to construct crumpled graphene based functional materials.Finally,to clarify the lithiation mechanism of V₂O₅ anode,we design nanoflake-assembled 3D hollow porous V₂O₅ microspheres via a one-step template-free solvothermal-based method to enhance its electrochemical activity as well as structural stability.The study of the lithiation behavior of V₂O₅ anode demonstrates that the Li+ intercalation/deintercalation mechanism dominates the lithiation behavior of V₂O₅ anode,and the stable charge/discharge processes,with the theoretical specific capacity of 588 mAh/g,only involve the deinsertion/insertion of Li+ into LixVO2 after the LiVO2 isformed in the first irreversible conversion reaction.Furthermore,the kinetic studies suggest that the typical sign of activation is the regular diminution of bulk resistance.Note that such a more insightful and tenable lithiation mechanism provides a valuable inspiration for clarifying the reaction mechanism of other vanadium oxide anode materials in lithium/sodium ions storage.