摘要：为探讨LiFePO₄锂离子电池容量衰减、电池循环性能失效的原因,对LiFePO₄锂离子电池进行循环性能测试,通过拆解电池,采用X射线衍射、扫描电子显微镜结构测试手段,对多次充、放电循环前后锂离子电池LiFePO₄正极材料和石墨负极材料的物理性能进行表征。结果表明,石墨负极在200次循环后,衍射峰的位置略微右移,晶体粒径结构几乎没变化,但是LiFePO₄正极材料的晶体结构却发生不可逆变化,晶粒从3.73 nm减小到2.75 nm;在0.25 C倍率下循环200次,容量衰减11.6%;随着循环次数的增加,LiFePO₄正极材料微观结构和晶粒度细化造成Li+传输阻力增大,是造成LiFePO₄锂离子电池容量衰减的主要原因。

关键词：锂离子电池；磷酸铁锂；衰减机制；电化学性能

Abstract：To investigate the failure reasons of lithium ion batteries with LiFePO₄ as anode materials and the main reason for the reducing of capacity,the cycle performances of lithium ion batteries with LiFePO₄ as anode materials were tested.Through dismantling those batteries,physical performances of lithium ion batteries with LiFePO₄ as anode materials and graphite as cathode materials before and after cycle were characterized by XRD and SEM.The results indicate that the position of diffraction peak moves to right slightly after graphite cathode cycling 200 times.The crystal structure almost has no change.But the crystal structure of LiFePO₄ anode materials has irreversible change of amorphous transformer.The grain size decreases from 3.73 nm to 2.75 nm.The capacity of LiFePO₄ batteries reduces by 11.6% after cycling 200 times at 0.25 C discharge current.The microstructure and grain size of LiFePO₄ anode materials become smaller with the increase of cycle number.So the transfer resistance of Li+ increases.That is the main failure reason of lithium ion batteries with LiFePO₄ as anode materials.

Keywords：lithium ion battery;lithium ferric phosphate;failure mechanism;electrochemical performance