Abstract: In order to improve the energy density of LiFePO₄ power lithium ion batteries, a small amount of S was introduced to the LiFePO₄ cathode materials to obtain the LiFePO₄/S composite materials by a ball-milling method. The crystalline structure, morphology and electrochemical performance were characterized by X-ray diffraction, scanning electron microscopy and electrochemical tests by coin cells/pouch cells. The results showed that the sulfur particles were covered with nanosized LiFePO₄ nanoparticles on the surface, which is analogous to the core-shell structure. The results of electrochemical tests of coin cells showed that the LiFePO₄/S composite with 15% S content had the best electrochemical performance, which exhibited a reversible capacity up to 251.5 mA·h·g^-1 at 0.1 C and an excellent long-term cycling stability with 94.9% capacity retention after 100 cycles. Moreover, 0.5A·h pouch cell with LiFePO₄/S-85/15 composite as cathode LiFePO₄ showed a capacity retention of 80.1% after 100 cycles. As a polar carrier, LiFePO₄ has a certain adsorption for polysulfides. The addition of a small amount of sulfur can greatly improve the discharge capacity of LiFePO₄ materials, while maintaining excellent cycling stability. The LiFePO₄/S composites can provide a new strategy for the development of LiFePO₄ power lithium ion batteries.

Key words: lithium iron phosphate, sulfur, composite materials, power lithium ion batteries