Synthesis And Modification Of Electrochemical Performance Of LiFe PO₄ Cathode Materials

LiFePO₄ is one of the most promising cathode materials for its excellent Li storing features,lithium iron phosphate LiFePO₄ with an olivine structure has been thought as a promising cathode material for LIBs owing to its significant advantages,such as acceptable operating voltage,high theoretical capacity,environmental friendliness,and excellent safety performance.However,the main problems associated with LFP still lie in the fact of its poor electrical conductivity and low Li⁺diffusivity and thus limiting its high-rate capability and practical application.Correspondingly,the rate performance of the LiFePO₄ electrode has been improved by doping with alien ions to enhance Li⁺diffusion velocity,surface modification with electronic or ionic conductive layers to increase electronic conductivity,and optimizing particle size and morphology to shorten the Li⁺diffusion path.?1?Ag@LiFePO₄ cathode materials have been prepared successfully by performing solid-state reactions between AgNO₃ and the ascorbic acid in the presence of LiFePO₄powders at ambient temperature.Metallic Ag nanoparticles of 10 nm in diameter can be produced with the environmental benign approach and efficiently attached onto the surfaces of commercial LiFePO₄ cathode materials.The as-prepared composites show highly enhanced electrochemical performances in storing Li with 22%increase in their discharge specific capacity from 128 mAh/g to 156 mAh/g at C/10 rate,after loading Ag additive of 2wt%.The coulombic efficiency of the composites can retain 97%,after cycling for 80 times.They can also remain up to 94 mAh/g of their discharge specific capacity at high rate of 5 C,which is almost twice higher than that of LiFePO₄ cathode materials.After that,we coated a layer carbon on the surface of Ag@LiFePO₄ composite material,improving the cycle and rate performance of LiFePO₄.?2?LiFePO₄ was prepared by solvothermal method.The size of LiFePO₄ was controlled by changing the reaction temperature,time,and addition quantity of surfactant.The optimizing particle size and morphology to shorten the Li⁺diffusion path.We successfully prepared LiFePO₄ nanoplates,nanorods and nanoparticles.Nanoparticles have better electrochemical properties than nanorods and nanoplatelets.From nanoplatelets to nanoparticles,the electrochemical performance gradually increases with decreasing size.The capacity gradually increased from 65 mAh/g to 105 mAh/g.?3?LiFePO₄ nanoparticles synthesized by solvothermal process are modified by reduced graphene oxide/Ag nanoparticles?rGO/Ag?composites via a facile heat treatment route.rGO/Ag@LiFePO₄ cathodes exhibit excellent performances,with the discharge capacity reaching 161 mAh/g at 0.1C and 133 mAh/g at 5C,due to the introducing of rGO and Ag nanoparticles with high electronic conductivity.Which is attributed to the improved electronic conductivity and the enhanced electrochemical reaction kinetics through introducing graphene and Ag.