Study On The Electrochemical Performance And Preparation Of Lithium Vanadium Phosphate/Carbon Composites

Lithium vanadium phosphate?Li₃V₂?PO₄?₃,LVP?are considered good commercial cathode due to high capacity density,long cycle life and safty,however,the low electrical conductivity and diffusion rate of lithium ion of LVP prevented the development of LVP.In this thesis,carbon materials?the amorphous carbon;reduce oxide graphene;MWCNTs of oxidative functionalization?combined with LVP was used to promote the electrochemical performance of LVP.LVP/C composites was synthesized by sol-gel methods with different content of carbon source in precursors and studied the optimum content.The ratio of vanadium and carbon source was 1?1 which was optimum experiment condition,in 3.0?4.3 V,0.5 C the best sample exhibited 122 mAh/g at 0.5 C,after 80 cycles,the retention of capacity was 98.7%,the discharge capacity was 78 mAh/g at 10 C.LVP/C@rGO composites has been prepared via microwave digestion methods with different content oxide graphene,which investigated the optimum oxide graphene additive content in precursors;The result shown that the best content of oxide graphene was 7.0 wt.%,In 3.0?4.3 V,0.5 C discharge,the best sample of LVP/C@rGO composites exhibited 130mAh/g at first charge-discharge;at 0.5 C and 10 C,after 100 cycles,the retention of capacity was 99.5%and 98.1%,respectively.Even at 20 C,that capacity 95 mAh/g can be reached.LVP/C+FMWCNTs composites were synthesized by sol-gel methods and explored the best additive content of MWCNTs of oxidative functionalization;The result proved that the content of 3.0 wt.%MWCNTs of oxidative functionalization was the best sample of LVP/C+FMWCNTs composites.The initial discharge of the best sample was 126 mAh/g at0.5 C,after 100 cycles,retention of capacity was 99.2%and 93.1%at 0.5 C and 10 C,respectively,at 10 C discharge,the capacity was 87 mAh/g.Comparing the best sample of three types composites,the result shown that the electrochemical performance of composites properly added reduce oxide graphene better than MWCNTs of oxidative functionalization and the amorphous carbon.