Diagnosis of Mechanisms of Kinetics in Lithium-Rich Manganese-Based Cathode Materials
Dongye Liu, Jiantuo Gan, Xu Xue, Zhijun Wu, Shengnan He, Chao Zheng, Chenchen Li, Yaxiong Yang, Yanxia Liu, Wubin Du, Fulai Qi, Mingxia Gao, Hongge PanAbstract
The rate-determining step (RDS), which determines rate capability in lithium-rich manganese-based oxide (LRMO) cathode materials, remains unclear. In this work, we establish a quantitative diagnostic method for the RDS in LRMOs using in-situ electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) at different states of charge (SOC) and C-rates. From our results, the SOC determines the intrinsic bottleneck of the RDS, while the C-rate drives the transition from single-step to mixed control. Upon discharging to 4.4 V, the RDS is dominated by electron transfer at the interface accompanied by layered-to-spinel phase transition, whereas it is strongly influenced by solid-state diffusion in the bulk with depletion of Li vacancies arising from Jahn–Teller distortion when discharging to 3.0 V. Furthermore, Li+ diffusion, instead of charge transfer, plays a major part in the RDS of LRMOs when the C-rates are increased. These findings establish quantitative criteria for designing future cathode materials.