| With the rapid development of portable electronic devices and electric vehicles,the demand for high performance of secondary batteries such as lithium ion batteries increased.Long life-span,fast charging and short time with high power outputting were the technical problems need to urgently solve.Reducing the cost and improving the stability of cycle were effective way to solve the above problems.The choice of the cathode material directly determined the performance and cost of the secondary batteries.In this paper,V2O5 was used as the research object,and V2O5 nanomaterials with different morphologies were prepared by hydrothermal method and freeze drying method.As cathode materials of lithium/sodium ion batteries,the methods of improving the electrochemical performance and the corresponding mechanism were studied by adjusting morphology of V2O5 and its composites.The main results of this paper are as follows:Based on controlling morphology different morphologies of V2O5 with micro-/nano-structures,which were nanowire,microsphere and microflower,were successfully prepared by hydrothermal method.The results revealed that V2O5 nanowire was favorable cathode materials for lithium/sodium ion batteries.Compared with microsphere and microflower,nanowire was very easy to form a three-dimensional network structure.Therefore,it could greatly increase the contact area between electrode material and electrolyte,the diffusion capacity of lithium/sodium ion and the electrochemical active sites.As cathode material of lithium ion batteries,after the 200 cycles the discharge specific capacity of V2O5 nanowire was 109.4 mA h g-1 which was 2.1 higher than microsphere and 2.4 times higher than microflower,respectively.As cathode material for sodium ion batteries,after the 100 cycles the discharge capacity of the V2O5 nanowires was 86.7 mA h g-1 which was 1.7 times higher than microsphere and 2 times higher than microflower,respectively.In order to further improve electrochemical performance of V2O5 nanowire,V2O5-NWs/Graphene composites were prepared via freeze drying method.The results showed that the introduction of graphene reduced the polarization of electrode materials and impedance of charge transferring,shortened the diffusion transport distance of ion and electron,and increased the storage performance and cycle stability of lithium/sodium ion batteries.As cathode materials of lithium ion batteries,after 150 cycles the discharge capacity of V2O5 nanowire and V2O5-NWs/Graphene was 104.4 mA h g-1 and 190.9 mA h g-1,respectively.Accordingly,the capacity retention of V2O5 nanowire and V2O5-NWs/Graphene rate was 76.5%and 96.6%,respectively.As cathode material of sodium ion batteries,after the 100 cycles the discharge capacity of V2O5 nanowire and V2O5-NWs/Graphene was 57.2 mA h g-1 and 82 mA h g-1,respectively.Layered V2O5 and V2O5-NLs/Graphene were successfully prepared by freeze drying method.The results proved that layered V2O5 had a significant effect on alleviating the stress in the process of charging and discharging.The layered V2O5 could effectively alleviate the stress in the intercalation/deintercalation process of lithium/sodium ion,and reduce the structure damage of electrode materials the in the cycle process.As the cathode material of lithium ion batteries,after 200 cycles the capacity retention of the layered V2O5and V2O5-NLs/Graphene was 58.9%and 48.5%,respectively.As cathode material of sodium ion batteries,graphene could effectively increase the active site of the layered V2O5and the contact area between electrode material and electrolyte,and improve the embedding capacity of sodium ions.After 200 cycles the specific discharge capacity of layered V2O5and V2O5-NLs/Graphene was 63.2 mA h g-1 and 134.3 mA h g-1,respectively.Accordingly,the capacity retention of the layered V2O5 and V2O5-NLs/Graphene was 86.1%and 69.2%,respectively.Porous layered V2O5 was prepared by freeze drying method followed by annealing treatment.The results found that porous layered V2O5 had obvious advantages of improving electrochemical performance.Porous layered V2O5 increased the the active sites of electrochemical reaction,the capacity of charge diffusion at the interface between electrode materials and electrolyte and the diffusion of ion.As cathode material of lithium ion batteries,the initial discharge specific capacity of bulk V2O5 and porous layered V2O5 was142.0 mA h g-1 and 199.8 mA h g-1,respectively.As cathode materials of sodium ion batteries,after 200 cycles the discharge of porous layered V2O5 was 123.9 mA h g-1 which was 2.3 times higher than commercial V2O5.The capacity retention of bulk V2O5 and porous layer V2O5 was 37.3%and 59.4%,respectively. |
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