Assessing Long‐Term Cycling Stability of Single‐Crystal Versus Polycrystalline Nickel‐Rich NCM in Pouch Cells with 6 mAh cm<sup>−2</sup> Electrodes
Wengao Zhao, Lianfeng Zou, Leiting Zhang, Xinming Fan, Hehe Zhang, Francesco Pagani, Enzo Brack, Lukas Seidl, Xing Ou, Konstantin Egorov, Xueyi Guo, Guorong Hu, Sigita Trabesinger, Chongmin Wang, Corsin Battaglia
Abstract
Abstract Lithium‐ion batteries based on single‐crystal LiNi 1− x − y Co x Mn y O 2 (NCM, 1− x − y ≥ 0.6) cathode materials are gaining increasing attention due to their improved structural stability resulting in superior cycle life compared to batteries based on polycrystalline NCM. However, an in‐depth understanding of the less pronounced degradation mechanism of single‐crystal NCM is still lacking. Here, a detailed postmortem study is presented, comparing pouch cells with single‐crystal versus polycrystalline LiNi 0.60 Co 0.20 Mn 0.20 O 2 (NCM622) cathodes after 1375 dis‐/charge cycles against graphite anodes. The thickness of the cation‐disordered layer forming in the near‐surface region of the cathode particles does not differ significantly between single‐crystal and polycrystalline particles, while cracking is pronounced for polycrystalline particles, but practically absent for single‐crystal particles. Transition metal dissolution as quantified by time‐of‐flight mass spectrometry on the surface of the cycled graphite anode is much reduced for single‐crystal NCM622. Similarly, CO 2 gas evolution during the first two cycles as quantified by electrochemical mass spectrometry is much reduced for single‐crystal NCM622. Benefitting from these advantages, graphite/single‐crystal NMC622 pouch cells are demonstrated with a cathode areal capacity of 6 mAh cm −2 with an excellent capacity retention of 83% after 3000 cycles to 4.2 V, emphasizing the potential of single‐crystalline NCM622 as cathode material for next‐generation lithium‐ion batteries.