Synthesis And Electrochemical Performance Of LiFePO₄Particles For Lithium-ion Batteries

LiFePO4has attracted lots of attention ever since it was discovered to be the cathode of rechargeable Li-ion batteries because of the high theoretical capacity, low cost, environmental benignity and high safety. However, the disadvantage in the structure has led to low conductivity for both electron and lithium-ion, so the electrochemical property of LiFePO4was not so good including low rate capability and bad cycle performance. A lot of researches have been done to make LiFePO4the most widely used cathode for Li-ion batteries. In this paper solvothermal method and solid-state method were used to synthesize LiFePO4, of which the structure and electrochemical performance were studied.LiFePO4was prepared through solvothermal process. The results showed that smaller particles arranged regularly with better electrochemical properties were synthesized using FeSO4as Fe source and ethylene glycol as solvent. Platelet type and hollow spherical particles were obtained respectively when3wt.%PEG and5wt.%Tween were added in reactants, which is not reported before. Compared to the sample without surfactants, the samples with special shapes had a slight increase in electrochemical performance. The sample which was prepared with5wt.%Tween mixed with60wt.%glucose was calcined to get LiFePO4particles coated with carbon. Although the special hollow spherical shape was disappeared, flat voltage plateaus were observed and at0.1C discharge rate the sample delivered a discharge capacity of140mAh/g at the first cycle.The nano-LiFePO4/C composite was directly synthesized via a simple one-step salicylic acid-assisted solid-sate method to study the influences of quantity of salicylic acid and calcination temperature on the structure and electrochemical properties. The results showed that a uniform in situ carbon layer was coated on the LiFePO4particles. With the increasing addition of salicylic acid, the size of the particles was reduced, but the calcination temperature did not affect the particle size obviously. The75wt.%salicylic acid-treated LiFePO4/C composite calcined at700℃exhibited a superior electrochemical performance of154.6mAh/g at0.2C,154.1mAh/g after20cycles, and105mAh/g at5C.