Preparation And Electrochemical Performance Of Li₃V₂?PO₄?₃ Cathode Materials For Lithium Ion Batteries

Lithium-ion batteries are essential energy storage devices that power the electronics that let us share information and connect with people anywhere at any time.As the demand for uninterrupted energy performance rises,corresponding challenges need to be overcome in both industry and academia.The application of lithium-ion battery has greatly promoted the development of energy.Nowsdays,lithium ion battery has shown its great potential,and has become a kind of new performance,energy saving,clean type of a new generation of battery.As the core of lithium-ion battery,Lithium ion cathode material has become an important factor restricting the electrochemical performance of lithium-ion battery.In particular,Li₃V₂?PO₄?₃ has attracted much attention because of its low cost,high voltage,stable structure and high theoretical specific capacity.It is expected to replace LiCoO₂ as a promising cathode material.In this paper,we mainly discussed the properties of Li₃V₂?PO₄?₃,using the hydrothermal method and sol-gel method to prepare monoclinic Li₃V₂?PO₄?₃ material with multiple charge and discharge platforms.The characterization and electrochemical properties of the composites are studied by XRD,SEM and LAND.The optimum process parameters of the material are found by experiments with different synthesis methods and sintering temperature.And then the doping and coating experiments are carried out to explore the high performance Li₃V₂?PO₄?₃ cathode material.The main research work is as follows:?1?Hydrothermal method is used to synthesize Li₃V₂?PO₄?₃/C.First,the microstructure and morphology of Li₃V₂?PO₄?₃/C materials at the same calcination temperature and different hydrothermal temperature are studied.With the increase of hydrothermal reaction temperature,the grain size becomes uniform,the particle dispersion is better and crystallization tends to be more full.Second,the microstructure and morphology of Li₃V₂?PO₄?₃/C materials at the same hydrothermal temperature and different calcination temperature are studied.With the increase of calcination temperature,the sample presents a spherical shape,and the size is moderate,and the grain size distribution is more uniform at 750?.The experimental results show that when the calcination temperature is 750? and the hydrothermal temperature is 160?,the integrated electrochemical performance is the best.The first discharge capacity is 113.7mAh / g.After 40 cycles of charge and discharge,the capacity is 103.4 mAh / g,the capacity retention rate is 90.9%.?2?By comparing the different content of glucose coated Li₃V₂?PO₄?₃,it can be concluded that when the glucose content is 10%wt,the first discharge capacity of the sample is the highest,reaching 127.3 mAh/g.After 40 charge and discharge cycles,the capacity is maintained at 117.5 mAh/g,the capacity retention rate is 92.3%.?3?We have studied confirmed that the content of Cr existed an optimum value?x=0.1?,namely Li₃V_1.9Cr_0.1?PO₄?₃/C material,prepared by sol–gel method.Li₃V_2-xBa_x?PO₄?₃/C?x=0,0.10,0.15,0.20?materials,the initial discharge specific capacity of Li₃V_1.9Cr_0.1?PO₄?₃/C material is higher than other materials.The capacity retention rate of Li₃V_1.9Cr_0.1?PO₄?₃/C is lower than Li₃V_1.8Cr_0.2?PO₄?₃/C after 40 charge and discharge cycles.But the capacity retention rate of Li₃V_1.8Cr_0.2?PO₄?₃/C is the best.In a word,Li₃V_1.9Cr_0.1?PO₄?₃/C have a better comprehensive electrochemical performance.?4?We have studied confirmed that the content of Ba existed an optimum value?x=0.1?,namely Li₃V_1.9Ba_0.1?PO₄?₃/C material,prepared by sol–gel method.Li₃V_2-xBa_x?PO₄?₃/C?x=0,0.10,0.15,0.20?materials,the initial discharge specific capacity of Li₃V_1.9Ba_0.1?PO₄?₃/C is higher than that other materials.the capacity retention rate of Li₃V_1.9Ba_0.1?PO₄?₃/C is the best after 40 charge and discharge cycles.In a word,Li₃V_1.9Ba_0.1?PO₄?₃/C have a better comprehensive electrochemical performance.?5?The samples with different carbon coated vanadium phosphate are prepared by sol-gel method.The first-order discharge capacity of the samples prepared with sucrose was the highest,and the capacity retention rate after the 40 charge-discharge cycles was higher than that of the other two carbon source,the optimum carbon source for the preparation of carbon-coated Li₃V₂?PO₄?₃ is sucrose.?6?Li₃V₂?PO₄?₃ composite is prepared by sol-gel method before acetylene black and carbon nanotubes are uniformly dispersed into it,then the monoclinic Li₃V₂?PO₄?₃ composite is o btained by high temperature treatment.The results show that the acetylene black and the active substance in the sample LVP-AB can react with the point contact mode,which can not effectively limit the grain growth and improve the conductivity,and the material performance is very small.However,the physical and electrochemical properties of Li₃V₂?PO₄?₃ composite with three-dimensional network structure carbon nanotubes have been improved obviously.And particle size,morphology,crystallinity and electrochemical properties are the best.