Impact of surface Li-containing rock-salt phase on electrochemical performance of Li- and Mn-rich cathodes

• Published in: Journal of power sources Vol. 649; p. 237445
• Main Authors: Zhao, Tian, Cai, Guanqun, Zhai, Xinyue, Wang, Suning, Yang, Xiaoxia, Peng, Kang-Shun, Chen, Meng-Cheng, Hung, Sung-Fu, Kong, Xiangyang, Li, Mingtao, Tang, Wei, Zhou, Leidang, Hua, Weibo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2025
• Subjects: Formation kinetics; Li- and Mn-rich oxides; Li-containing rock-salt-type phase; Lithium-ion batteries; Structural stability; Lithium-ion batteries; Li-containing rock-salt-type phase; Structural stability; Li- and Mn-rich oxides; Formation kinetics
• ISSN: 0378-7753
• DOI: 10.1016/j.jpowsour.2025.237445

The synthesis of Li- and Mn-rich layered oxides is often hindered by the formation of a disordered rock-salt-type phase, which is believed to have a negative impact on their electrochemical performance due to the inherently low electrochemical activity of this phase. Herein, we employ a two-step approach involving spray pyrolysis followed by calcination to prepare Co-free Li[Li0.2Ni0.2Mn0.6]O2 (LLNMO) oxides. The disordered Li-containing rock-salt-type phase emerges on the surface of LLNMO crystallites at elevated heating temperatures (≥930 °C). The formation kinetics of the Li-containing rock-salt-type phase is determined to follow a reaction-diffusion process. For LLNMO-950 (950 °C) with a coherent structure comprising both layered and thicker Li-containing rock-salt-type phases, the discharge capacity exhibits a progressive increase within the initial 52 cycles. The lattice parameters of the rock-salt structure undergo variations during electrochemical cycling, indicating that the rock-salt-type phase is not completely electrochemically inactive. By adjusting the heating temperature (930 °C, denoted as LLNMO-930), we introduce a thin disordered Li-containing rock-salt-type phase (approximately 2 nm thick) on the primary particle surface of LLNMO. The LLNMO-930 exhibits good electrochemical performance, with a high energy density retention of 95 % and a voltage decay of 0.3 V after 100 cycles at 0.1 C. [Display omitted] •The formation kinetics of the surface rock-salt-type phase were investigated.•Surface rock-salt-type phase thickness affects the electrochemical performance.•The surface rock-salt-type phase is not completely electrochemically inactive.•LLNMO-930 with a thin rock-salt-type phase shows good electrochemical performance.