Sun Shun, Guan Ting, Cheng Xinqun, Zuo Pengjian, Gao Yunzhi, Du Chunyu, Yin Geping
MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology No. 92, West Dazhi Street Harbin 150001 China
RSC Adv. 2018 Jul 18;8(45):25695-25703. doi: 10.1039/c8ra04074e. eCollection 2018 Jul 16.
The effects of discharge rates (0.5C, 1.0C, 2.0C, 3.0C, 4.0C and 5.0C) on the aging of LiFePO/graphite full cells are researched by disassembling the fresh and aged full cells. The capacity degradation mechanism is analyzed electrochemical performance, surface morphologies and compositions, and the structure of the anode and cathode electrodes. The capacity fade is accelerated with increasing discharge rates. The irreversible loss of active lithium due to the generation of an SEI film is the primary aging factor for the full cells cycled at low discharge rates. However, when the discharge rate is greater than or equal to 4.0C, the performance degradation of the LiFePO electrode is distinct due to structure decay, which is caused by quick and repeated intercalation of lithium ions and elevated temperature during discharging. In addition, the SEI film on the anode tends to be unstable after the rapid extraction of lithium ions at high discharge rates, and this enhances the loss of active lithium. Therefore, it is indicated that the degradation mechanism is changed for the full cells aged at 4.0C and 5.0C. Besides, the high discharge rate also increases the internal resistance of the full cell, which is detrimental to high rate discharge performance.
通过拆解新鲜和老化的全电池，研究了放电速率（0.5C、1.0C、2.0C、3.0C、4.0C和5.0C）对磷酸铁锂/石墨全电池老化的影响。从电化学性能、表面形貌和成分以及正负极结构方面分析了容量衰减机制。随着放电速率的增加，容量衰减加速。在低放电速率下循环的全电池中，由于形成固体电解质界面（SEI）膜导致的活性锂不可逆损失是主要的老化因素。然而，当放电速率大于或等于4.0C时，由于结构衰退，磷酸铁锂电极的性能退化明显，这是由放电过程中锂离子的快速反复嵌入和温度升高引起的。此外，在高放电速率下快速提取锂离子后，阳极上的SEI膜趋于不稳定，这加剧了活性锂的损失。因此，表明在4.0C和5.0C下老化的全电池的退化机制发生了变化。此外，高放电速率还会增加全电池的内阻，这不利于高倍率放电性能。
