Study On LiFePO₄ Synthesized By Microwave Heating As Lithium Ion Battery Cathode Materials

Olivine-structured LiFePO₄ is gaining particular interest as a potential candidate cathode material for rechargeable lithium ion batteries due to its advantages of economic, no toxicity and good cycling performance. In this paper, LiFePO₄/C and LiFePO₄/ (C+La³⁺) composite cathode materials were synthesized using microwave heating. The microstructure and morphologies of these composites were investigated by XRD, TEM and SEM. The electrochemical performances were evaluated by galvanostatic charge-discharge.The single-phase LiFePO₄ without C and Fe³⁺ impurities was synthesized using microwave heating for 35 min at 10% microwave heating power, the carbon exists in amorphous phase and plays a role as reducing agent to prevent the oxidation of Fe²⁺. There were also no other phases detectable in the synthesized materials.Carbon-coated LiFePO₄ composite was synthesized using sucrose as carbon source. The material with 3%carbon exhibited the best electrochemical performance. Its initial charge specific capacity is 144.1 mAh/g at 0.1C, the capacity maintained to be 133.3 mAh/g after 20 cycles, the capacity loss ratio is 6.6%. The initial charge specific capacity is 122.5 mAh/g at 0.3C and the cycling behavior was very good. It is verified that the carbon would be effective in enhancing the electronic conductivity of LiFePO₄ and hindering the grain size growth during microwave heating, consequently improving its electrochemical performance.LiFePO₄/C compsite synthesized using PVA as carbon source delivered a high initial specific discharge capacity of 168.8 mAh/g with 2wt% PVA, which is very close to the theoretical value of 170 mAh/g. The capacity maintained to be 144.3 mAh/g after 10 cycles. The material with 1wt% PVA showed the best cycling performance.It is confirmed that the initial specific discharge capacity of LiFePO₄/(C+La³⁺) composites (116.3 mAh/g) was better than those of LiFePO₄/C (105.4 mAh/g). The addition of La³⁺ improved the electrochemical properties. So the complex doping is an effective way to improve the electrochemical performance.