Synthesis Of LiFePO₄ Cathode Material By Solid-Liquid Phase Reaction And Study Of The Electrochemical Performance

Olivine-structured LiFePO₄, due to its advantages such as low cost, nontoxicity, environmental friendliness and high safety, is considered as a promising cathode material for lithium-ion batteries in place of expensive and toxic LiCoO₂. However, the commercialization of LiFePO₄ as cathode material for lithium-ion batteries is limited by its low electronic conductivity and slow lithium-ion diffusion. In addition, another problem is large-scale synthesis technique suitable for industrialization. In this paper, a novel method was developed and LiFePO₄ was synthesized by solid-liquid phase reaction with (NH₄)₂SO₃ or glycol as reducing agents.For the novel method using (NH₄)₂SO₃ as reducing agent, the synthesis conditions were optimized through a series of experiments. The LiFePO₄ prepared by this method exhibits ordered olivine-type structure, good powder morphology and micro-structure which were examined by XRD, SEM and TEM. The Particle size distribution is 100-300nm and the diffusion coefficient of lithium-ion in LiFePO₄ is～10^-9cm² s^-1 which was calculated through EIS. All of these good properties lead to excellent electrochemical performance. As results, LiFePO₄/C delivers specific capacities of 153mAh g^-1(1C), 138mAh g^-1(5C) and 122mAh g^-1(10C), respectively. The high-rate charge performance is also good and the capacity at 5C rate for both charge and discharge can reach 134mAh g^-1 if constant current charge and constant voltage charge at 4.2V were employed. In addition to the excellent high-rate capability, LiFePO₄/C can also maintain high electrochemical reversibility and cycle...