Synthesis And Electrochemical Performance Of Li₃V₂?PO₄?₃/C Composite With Biological Carbon Source

With the rapid development of human society,the burning of fossil fuels,energy crisis and environmental problems have become the important problems that plagued human development.To develop new energy collection and storage system is a hot spot in the current social research.li-ion battery Lithium-ion battery occupies an important position in energy storage devices because of its advantages of high energy,long cycle life,green environmental protection.The cathode material occupies an important position in lithium-ion batteries and has been favored by researchers for many years.In recent years,monoclinic structure of Li₃V₂?PO₄?₃ has attracted great attention due to its high theoretical specific capacity?197 mAh/g?,high charge and discharge voltage platform?up to 4.8V?,excellent thermal stability and good cycle stability.However,the low electron conductivity limits its application.Li₃V₂?PO₄?₃/C composites have been synthesized through evaporation self-assembly,repeated immersion method and vacuum method with three kinds of morphologies and structure biological carbon sources.The morphology and structure were studied using X-ray diffraction,SEM techniques.The coin-type cells were assembled with the prepared carbon as cathode material,and the cellsweretestedwithgalvanostaticcharge-discharge,cyclic voltammograms?CV?and electrochemical impendence spectroscopy?EIS?to verify the influence of the structure on the electrochemical performance.Li₃V₂?PO₄?₃/C composite with frog-egg structure were prepared by using plant protein as carbon source.In the voltage of 3.0-4.3 V,the composite has a high specific capacity of 100 mAh/g at 15C,which is better than the material of pure Li₃V₂?PO₄?₃.Li₃V₂?PO₄?₃/C composite with coaxial structure were prepared through repeated immersion with cotton fibers as the carbon source.The material of Li₃V₂?PO₄?₃/C composite of after three repeated immersion has the best electrochemical performance.In the voltage of 3.0-4.3 V,the material has high specific capacity of 115.7 mAh/g at 15C.In addition,Li₃V₂?PO₄?₃/C composite with N-doping were successfully prepared via repeated immersion method with cattail fibers as the carbon source.The material of Li₃V₂?PO₄?₃/C composite of after three repeated immersion?C-15?has the best electrochemical performance.It has a capacity of 124.9 mAh/g at 0.5C rate between 3.0-4.3 V.After 500 cycles,the reversible capacity of C-15 can still 113.2mAh/g and it delivered capacity retention of 94.5%.Compared with the Li₃V₂?PO₄?₃/C composite with the cotton fiber,the performance of Li₃V₂?PO₄?₃/C composite with N-doping cattail fiber has been enhanced,but the difference between the two sample is not obvious.