Study On Preparation And Coating Modificaton Of Li₃V₂（PO₄）₃/C Cathode Materials

The monoclinic Li3V2（PO4）3（LVP）has attracted much attention as a cathode material for lithium-ion batteries due to its good ion mobility,high theoretical specific capacity（197 mAh g-1）and high operating voltage.Unfortunately,the LVP has low conductivity,which greatly restricts its practical application in lithium-ion batteries for electric vehicles（EV）and hybrid electric vehicles（HEV）.In this work,Li3V2（PO4）3/C（LVP/C）was modified with different methods of modification,it focuses on the effect of three different coating materials on the electrochemical properties of LVP/C.The conclusion are drawn as follows:1.The Cu3（PO4）2-modified LVP/C cathode materials with different coating contents were synthesized via chemical deposition method.It shows that LVP/C cathode coated with 2 wt.%Cu3（PO4）2 has the best electrochemical performance.The initial discharge capacities of bare LVP/C material and 2 wt.%Cu3（PO4）2-coated LVP/C material at 1 C rate are 123.9 and 128.8 mAh g-1,respectively.The capacity retention after 200 cycles is 81.1%and 96.7%.The capacity retention rate of LVP/C at 1 C₃ C and 10 C after 200 cycles is 81.1%,81%,75.7%,respectively and it is 96.7%,93.1%_and 87.8%for 2 wt.%Cu3（PO4）2-modified LVP/C.The capacity fading of Cu3（PO4）2-coated LVP/C and its cycle performance are improved obviously.It demonstrates that Cu3（PO4）2 modification is an effective way to improve the electrochemical performance of LVP/C.2.The nanolayer MnO-GO co-coated Li3V2（PO4）3/C cathode materials was prepared via wet grinding method.It indicates that the 0.7 wt.%MnO-GO coated LVP/C has the best electrochemical performance.The MnO-GO nanocoating can improve the cyclic performance and rate performance of LVP/C.In the range of 3.0-4.3 V,the discharge specific capacity of 0.7 wt.%MnO-GO coated LVP/C is lower than that of the LVP/C in the first cycle due to the electrochemical inactivity of MnO particles.However,the capacity retention of 0.7 wt.%MnO-GO coated LVP/C increases.The capacity retention rates of LVP/C at 1 C,3 C and 10C after 100 cycles is 92.6%,88.1%and 86.2%,respectively and it is 92.8%,94%and 89.6%for 0.7 wt.%MnO-GO coated LVP/C.3.The MnO2-coated Li3V2（PO4）3/C cathode materials with different coating contents were synthesized via co-precipitation method.It shows that LVP/C cathode coated with 0.5 wt.%MnO2 has the best electrochemical performance.The MnO2 coating can improve the rate performance and cyclic performance of LVP/C.In the range of 3.0-4.3 V_the discharge capacity of LVP/C pure phase sample at 1 C rate decay quickly,with 15.7%capacity loss after 100 cycles,but for 0.5 wt.%MnO2 coated LVP/C samples the capacity losts only 6.1%after 100 cycles.The capacity retention rate of LVP/C at 1 C,3 C and 10 C after 100 cycles is 92.6%,88.1%and 86.2%,respectively and it is 93.9%,91.9%and 95%for 0.5 wt.%MnO2-modified LVP/C.