电极水分对磷酸铁锂电池性能的影响

Impact of Water Content on the Performance of LiFePO_4 Based Lithium-Ion Battery

通过库仑法水分测试仪标定不同水分含量（0.3‰~0.7‰）的磷酸铁锂正极片,将其制备成软包型锂离子电池,对其电化学循环性能、倍率性能、交流阻抗进行了测试.结果表明,不同水分含量极片制备的电池循环性能及倍率性能与电极水分含量有密切关系,水分含量在0.4‰~0.5‰之间时循环性能最优,水分含量超过0.6‰时电化学性能衰减严重,电池的内阻和电化学反应阻抗明显增加.将循环200周后的软包电池进行拆解,分别使用激光粒度仪、XRD、SEM对循环后磷酸铁锂正极片进行微观形貌分析,发现水分含量超过0.6‰时极片表面发生颗粒破裂现象.XRD晶相分析表明,随着水分含量的升高,衍射峰晶面的位置有所偏移,但主要衍射峰的位置基本相同,晶型并未发生改变.

Through different dry conditions and measuring by moisture test instrument, cathode pole pieces with different water contents of 0.3‰ ~ 0.7‰ were obtained to prepare lithium-ion batteries. Cycling performance and high rate performance at 1C ~5C discharge rates were tested. Moreover, ASR performances of Li Fe PO4 base lithium-ion batteries after 200 cycles with different water contents were investigated by EIS. The results showed that the cycle performance and rate performance were closely related to the water content of the electrode. When the water content went up to 0.6‰ the cycle stability and rate performance fell. Meanwhile, the internal resistance and the electrochemical reaction impedance increased after 200 cycles. The cells after running 200 cycles were dismantled to obtain the powder material which was studied by laser particle size analyzer, XRD and SEM to research the microstructure. The results revealed that when the water content exceeded 0.6‰ the obvious particle fracture phenomenon appeared. The XRD data indicated that the position of the main diffraction peak kept nearly the same and the crystal phase of the cathode material remained unchanged.