Suppressing structural degradation of Ni-rich cathode materials towards improved cycling stability enabled by a Li2MnO3 coating

Abstract

Ni-rich layered LiNi_xCo_yMn_zO₂ (NCM, x ≥ 0.8) oxides have been attractive cathode materials for high-energy lithium-ion batteries for large-scale applications. However, pristine NCM cathode materials with a high Ni content encounter drastic side reactions at the particle surface and inherent phase transitions in the layered structure during cyclic lithiations/delithiations, leading to poor cycling stabilities upon prolonged cycling. Herein, in situ X-ray diffraction (XRD) measurements have been carried out to probe structural evaluations of the Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode material during charge/discharge processes. The operando XRD results demonstrate the undesired structural irreversibility of the NCM811 cathode material in the first cycle. In the subsequent electrochemical cycles enhanced structural stability can be implemented for reversible phase transformations via a Li₂MnO₃ (LMO) coating. The optimized NCM811@LMO-3% cathode material shows high capacity retentions of approximately 93% at 0.1C after 100 cycles and 81% at 1C after 500 cycles, respectively, significantly superior to those of the bare NCM811 material (74% and 63%). This work sheds light on understanding structural evaluations of Ni-rich cathode materials during lithiation/delithiation processes, and further offers a reliable coating to effectively suppress the detrimental structural degradation of Ni-rich cathode materials for improved cycling stability.