The Research Of Preparation And Characterization Of LiFePO₄ Cathode Materials Doped With Vanadium

Lithium iron phosphate as cathode material of lithium ion battery has been widely studied due to its advantages of low cost,non-toxic,non-polluting etc.However,the low ion conductivity and electrical conductivity of lithium iron phosphate affect its electrochemical performance in lithium ion battery.To address this issue,we synthesize lithium iron phosphate doped with vanadium by using biological template-carbon thermal reduction method.Na₂ ATP is biological self-assembly templates,phosphorus and carbon source,FeCl₃?6H₂O is source of iron,Li₂CO₃ is the source of lithium,NH₄VO₃ is the source of vanadium,glucose is the reducing agent.The mole ratio of iron element and vanadium element,sintering temperature,methods of doped vanadium and hydrothermal treatment as single variable to explore the synthesis of lithium iron phosphate with vanadium doped,respectively.The optimized lithium iron phosphate with doped vanadium sample was determined by XRD test analysis,it contains lithium iron phosphate,sodium vanadate iron and porous glass.The microstructure of the optimized lithium iron phosphate doped with vanadium sample was researched,the results suggest that this composite materials not only possess spherical or flower-like morphology,which was constructed by particles or flake structure,but also exist the unique composite structure of lithium iron phosphate and sodium vanadate iron,besides,the sample possess multilevel pore structure and graphitized carbon structure.The XRD analysis results was verified by test of the charge and discharge,CV and EIS,which further determines the lithium iron phosphate with doped vanadium sample,and the optimum synthesis conditions of sample: iron and vanadium mole ratio is 1 : 1,no hydrothermal treatment,solid phase doped vanadium,700 ? sintering.The first discharge capacity of the optimized lithium iron phosphate doped with vanadium is 202.8 mAh g^-1 at 0.1 C ratio,in 2.5⁴.2 voltage range,which is beyond the theoretical specific capacity of lithium iron phosphate(170 mAh g^-1),besides,the discharge capacity of sample can maintain 100.4 mAh g^-1 at 10.0 C ratio.We study the synthetic mechanism of the sample based on the process,composition,structure and performance,and it was confirmed as the following: the self-assembly of biological templates and metallic ions.The ion transport mechanism is rapid phase transition through the mobile interface for structural rearrangement without crystal nucleus formation and crystal growth,which promote ion transport of sample during the charge and discharge.