Synthesis And Characterization Of XLiVPO₄F·yLi₃V₂?PO₄?₃/C Composite Cathode Materials For Lithium-ion Batteries

With the popularization of hybrid electrical vehicle,lithium-ion battery has entered the golden period of development.On the basis of lithium-ion battery and the cathode materials research status,the aims of the present study were focus on the synthetic methods,physical structure,surface morphology and the electrochemical performances of LiVPO₄F,Li₃V₂?PO₄?₃ and composite materials xLi VPO₄F·yLi₃V₂?PO₄?₃.The cathode material of xLi VPO₄F·yLi₃V₂?PO₄?₃/C?x:y=1:0,1:1,2:1,3:1,7:1,0:1?were prepared by two step carbon coating auxiliary ball-milling.The structure,morphology and electrochemical performance of cathode material were researched.The research results are as follows:The LiVPO₄F/C is pure phase at 750°C for 1h and the particle has uniform particle size distribution.The LiVPO₄F/C shows initial discharge capacity of 147.2,129.4,113.5,97.1,75.7 mAh·g^-1 at 0.1,0.2,0.5,1,2 C,respectively.The cell only retains 71.78%of initial discharge capacity after 50 cycles at 0.1 C;The Li₃V₂?PO₄?₃/C at 750°C for 12h has uniform size distribution and optimal electrochemical properties.The Li₃V₂?PO₄?₃/C shows initial discharge capacity of 141.5,131.6,127.4,119.8,109.4 mAh·g^-1 at 0.1,0.2,0.5,1,2 C,respectively.The sample retains 97.7%of initial discharge capacity after 50 cycles at 0.1 C;The structure,morphology and electrochemical performance of xLiVPO₄F·yLi₃V₂?PO₄?₃/C?x:y=1:1,2:1,3:1,7:1?cathode material were researched.XRD results show that the xLiVPO₄F·yLi₃V₂?PO₄?₃/C?x:y=1:1,2:1,3:1,7:1?composites consist of LiVPO₄F and Li₃V₂?PO₄?₃.SEM results show that2LiVPO₄F·Li₃V₂?PO₄?₃/C composite has minimum particle size and uniform size distribution.Electrochemical tests show that 2LiVPO₄F·Li₃V₂?PO₄?₃/C has the best electrochemical performance and combines with the advantages of LiVPO₄F and Li₃V₂?PO₄?₃.The sample has four discharge platforms about 4.2,4.1,3.7 and 3.6 V and deliveres initial discharge capacities of 143.9,142.6,130.4,119.1,112.6 mAh·g^-1 at 0.1,0.2,0.5,1,2C,respectively.The cell retains 98.1%of initial discharge capacity after 40cycles?0.1-2 C?at 0.1 C.The cathode material of xLiVPO₄F·yLi₃V₂?PO₄?₃/C?x:y=1:0,2:1,0:1?was synthesized by sol-gel.The structure,morphology and electrochemical performance of cathode material were researched.The research results are as follows:The LiVPO₄F/C is pure phase at 750°C for 1h and the particle has porous structure.The LiVPO₄F/C shows initial discharge capacity of 141.1,125.2,106.3,87.9,71.5 mAh·g^-1 at 0.1,0.2,0.5,1,2 C,respectively.The cell only retains 89.22%of initial discharge capacity after 50 cycles at0.1 C;The Li₃V₂?PO₄?₃/C at 750°C for 16h has uniform pore size distribution and the optimal electrochemical properties.The Li₃V₂?PO₄?₃/C shows initial discharge capacity of136.1,138.8,130.2,124.4,115.7 mAh·g^-1 at 0.1,0.2,0.5,1,2 C,respectively.The sample retains 96.9%of initial discharge capacity after 50 cycles at 0.1 C;The structure,morphology and electrochemical performance of 2LiVPO₄F·Li₃V₂?PO₄?₃/C cathode material were researched.XRD results show that the composite consists of LiVPO₄F and Li₃V₂?PO₄?₃.SEM results show that composite has porous structure and flakes adhered on the surface.Electrochemical tests show that 2LiVPO₄F·Li₃V₂?PO₄?₃/C composite combines with the advantages of Li VPO₄F and Li₃V₂?PO₄?₃.The sample has four discharge platforms about 4.2,4.1,3.7 and 3.6 V and delivers initial discharge capacities of143.4,141.6,133.2,124.1,117.6 mAh·g^-1 at 0.1,0.2,0.5,1,2C,respectively.After 40cycles?0.1-2 C?and return to 0.1 C,the discharge specific capacity is close to the initial discharge capacity.The cathode material of xLiVPO₄F·yLi₃V₂?PO₄?₃/C?x:y=1:0,2:1,0:1?was synthesized by Spray drying.The structure,morphology and electrochemical performance of cathode material were researched.The research results are as follows:The LiVPO₄F/C is pure phase at 750°C for 1h and the particle has spherical structure.The LiVPO₄F/C shows initial discharge capacity of 137.9,131,115.2,95.7,77.2 mAh·g^-1 at 0.1,0.2,0.5,1,2 C,respectively.The cell only retains 91.59%of initial discharge capacity after 50 cycles at0.1 C;The Li₃V₂?PO₄?₃/C has good crystallinity and uniform ball diameter distribution at750°C for 8h.The sample shows initial discharge capacity of 143.6,140.4,132.6,126.4,111.9 mAh·g^-1 at 0.1,0.2,0.5,1,2 C,respectively.The capacity attenuation of Li₃V₂?PO₄?₃/C is 2.79%after 50 cycles at 0.1C;The structure,morphology and electrochemical performance of 2LiVPO₄F·Li₃V₂?PO₄?₃/C cathode material were researched.XRD results show that the composite consists of LiVPO₄F and Li₃V₂?PO₄?₃.SEM results show that composite has spherical structure and diameter in 2-5?m.Electrochemical tests show that 2LiVPO₄F·Li₃V₂?PO₄?₃/C composite presents excellent electrochemical performance.The sample has four discharge platforms about 4.2,4.1,3.7and 3.6 V and delivers initial discharge capacities of 139.4,134.7,129.8,123.8,114.8mAh·g^-1 at 0.1,0.2,0.5,1,2C,respectively.After 40 cycles?0.1-2 C?and return to 0.1 C,the cell retains 94.8%of initial discharge capacity.