Study On The Preparation And Modification Of Lithium Vanadium Phosphate As Cathode Material For Lithium-ion Batteries

Nowadays,rechargeable lithium-ion batteries are widely used in human life and play a very important role in people's lives.At present,many electrode materials are used in the market,such as LiCoO₂,LiFePO₄,layered ternary materials,and phosphate cathode materials.The application of phosphate cathode materials as a large-capacity battery has a very broad prospect and has attracted much attention.Lithium vanadium phosphate has excellent electrochemical properties and is a promising candidate material due to abundant vanadium reserves and a large theoretical capacity.However,Li₃V₂?PO₄?₃ has a problem of low electron conductivity,which is a major disadvantage in practical applications.In this paper,the coating and ion doping modification of LVP were studied to improve the electrochemical properties such as conductivity,cycle performance and structural stability of the material.First,the LVP/C material was synthesized by carbon thermal reduction method using polyvinyl butyral and acetylene black as two carbon sources.The sample particles are small and the particle size distribution is uniform.The initial discharge capacity of the sample is123.20mAhg^-1 at a 0.2C rate between 3.0-4.3 V while the retention rate of capacity is 97.54%and the capacity retention rate was higher after 20 cycles at a 0.5C rate,which indicates it has excellent cycle performance,and the rate performance was also improved.Then,the Li₃V_2-xNi_x?PO₄?₃/C and Li₃V_2-xMnx?PO₄?₃/C were synthesized by sol-gel method doping using Ni²⁺?Mn²⁺.When x=0.1 and x=0.08,the samples have the best electrochemical performance after some electrochemical testing.The initial discharge capacity of the samples are128.89mAh/g and 125.92mAh/g at a 0.2C rate between 3.0-4.3 V respectively,while the retention rate of capacity are higher and the capacity retention rate are higher after 20 cycles at a 0.5C rate than the un-doped sample,which indicates they have excellent cycle performances,and the rate performances are also improved.Finally,the LVP cathode material coated with MnO and C were synthesized by sol-gel method.The sample coated amount 4%MnO has the best electrochemical performance.The initial discharge capacity of the samples is 128.89mAh/g at a 0.2C rate between 3.0-4.3 V respectively,while the retention rate of capacity is higher and the capacity retention rate are higher after 50cycles at a 0.5C rate than the un-doped sample,which indicates they have excellent cycle performances,and the rate performances are also improved.