Insight into the capacity degradation mechanism of LiNi0.5Co0.2Mn0.3O2 caused by rate-dependent kinetic limitations

The energy and power density of LiNi0.5Co0.2Mn0.3O2 (NCM523) can be improved by enhancing the upper -limit voltage and the charging/discharging rate respectively, but it would cause severe capacity decay during cycling. The high-voltage capacity fading mechanism of NCM523 has been widely studied, but the one affected by the charging/discharging rate still remains unclear. Therefore, from the aspect of Li+ kinetics, this work systematically reveals the long-cycle capacity degradation mechanism of NCM523 caused by rate -dependent kinetic limitations. Through Raman spectroscopy and electrochemical measurements, the ki-netic limitation on Li+ de/intercalation is regarded as an important factor for the long-cycle capacity loss. Moreover, as indicated by structural characterizations, the origin of Li+ kinetic degradation is rate -depen-dent. Under the low-rate (0.2 C) condition, it can be mainly ascribed to the surface structural passivation of NCM523. While at the high rate (5 C), the microcracks of NCM523 particles and the uneven lithium de-position/stripping at the anode side would be dominant. With the change of charging/discharging rates, there is a "trade-off" between the above-mentioned factors, which would regulate the Li+ kinetics jointly. Thus, this work can promote the rational design and improvement of high-energy/power-density lithium -ion batteries.(c) 2023 Elsevier B.V. All rights reserved.