Preparation And Properties Of Porous Micro-nano Structure V₂O₅/C Cathode Materials For Lithium Ion Batteries

New energy materials with high performance,ranging from the specific energy,specific power to cycle stability of lithium-ion batteries,has great value.As a typical layered material,V₂O₅ has a unique lithium-intercalation feature,and its theoretical specific capacity is much higher than that of commercial cathode materials,such as Li Co O2,Li Mn2O4 and Li Fe PO4.However,V₂O₅ has some shortcomings including poor cycle and rate performance,which limit their pratical application in lithium ion batteries.In this work,a new method for the synthesis of porous V₂O₅/C material by electrostatic spraying is proposed.The porous structures can not only accomodate the volume change which occurred in the process of cycling,but also shorten the diffusion path of lithium ions.In addition,the carbon layer can improve the conductivity of the positive electrode material.The V₂O₅/C material with porous micro-nano sphere structure was prepared and the optimum conditions were studied.With the increase of the molecular weight of PVP,the diameter of the micro-nanosphere increased gradually and a mixture of spherical structure and linear structure appeared.Besides,when the calcination temperature reached at 450 ?,the spherical structure begun to collapse.So the optimum conditions were gotten as following: the amount of PVP?10000?were 2 g;The best calcination temperature and time were 400 ? and 30 min,respectively.The particle size of V₂O₅/C material was from 0.7 to 3 ?m,and the surface of V₂O₅/C material has obvious pores and was formed by small particles.After 50 cycles and 100 cycles,the capacity was 188 m Ah·g-1?0.5 C?and 147 m Ah·g-1?1 C?,respectively.The discharge capacities were 257,223,194,149 and 100 m Ah·g-1,respectively,at different current densities of 0.5 C,1 C,2 C,5C and 10 C after 10 cycles,which showing a good rate performance.The V₂O₅/C material with porous micro-nano tube structure was synthesized and the optimum conditions were studied.With the increase of the electrostatic spraying rate,the diameter of the tube increased.And with the distance and voltage of electrostatic spraying increasing,the diameter of the tube decreased.So the optimum preparation conditions were gotten as following: the amount of PVP?1300000?was 2 g;The rate,distance and voltage of electrostatic spraying were 0.5 m L·h-1,20 cm and 20 k V,respectively;And the optimal calcination temperature was 400 ?.The diameter of the V₂O₅/C material was between 400 nm and 50 0nm,and the length was micron-sized.After 50 cycles and 100 cycles,the capacity was 182 m Ah·g-1?0.5 C?and 157 m Ah·g-1?1 C?,respectively.The discharge capacities were 237,205,191,172 and 105 m Ah·g-1,respectively,at different current densities of 0.5 C,1 C,2 C,5 C and 10 C after 10 cycles.The results showed that the V₂O₅/C material exhibited good rate performance.Compared with the V₂O₅/C material containg porous micro-nano sphere structures,the micro-nano tube V₂O₅/C structures delivered better cyling performance and rate perforamce at high current densities.