关键词: LiNi_0.83Co_0.12Mn_0.05O₂, 45 °C循环失效, 电化学阻抗谱, 固体电解质界面膜, 电荷转移阻抗

Abstract:

Nickel-rich layered material has been considered as the most promising one for lithium ion batteries due to its high specific capacity. To further improve the lifetime performance, it is significant to investigate the degradation mechanisms deeply. In this study, the degradation mechanism of NCM811 (LiNi_0.83Co_0.12Mn_0.05O₂) being cycled at 45^oC was systematically researched. Electrochemical impedance spectrum (EIS) results showed that the SEI resistance (R_SEI) and charge transfer resistance (R_ct) went up to 83.41% and 211.34% before and after the NCM811 material being cycled at 45^oC, respectively. The main factors that influenced the R_SEI and R_ct were analyzed by means of XPS, TEM, XRD and XANES. The increase of R_SEI was mainly ascribed to the conversion of some organic components to inorganic components such as lithium carbonate. Besides, the thickness of SEI film increased due to the side product of lithium fluoride (LiF) accumulated around the active materials. The increase of R_ct was ascribed to the destruction of crystal structure, the phase transformations from R-3m to Fd-3m and to Fm-3m, and the micro-cracks appeared inside of the active particles. In addition, the solid mass transfer resistance (R_w) was found to become larger, which was mainly affected by the enhanced Li/Ni mixing and dissolutions of transition metal elements.

Key words: LiNi_0.83Co_0.12Mn_0.05O₂, 45 °C cycle degradation, electrochemical impedance spectrum, solid electrolyte interphase, charge transfer resistance