Assessing Long‐Term Cycling Stability of Single‐Crystal Versus Polycrystalline Nickel‐Rich NCM in Pouch Cells with 6 mAh cm−2 Electrodes. Issue 14 (18th February 2022)

• Record Type: Journal Article
• Authors: Zhao, Wengao; Zou, Lianfeng; Zhang, Leiting; Fan, Xinming; Zhang, Hehe; Pagani, Francesco; Brack, Enzo; Seidl, Lukas; Ou, Xing; Egorov, Konstantin; Guo, Xueyi; Hu, Guorong; Trabesinger, Sigita; Wang, Chongmin; Battaglia, Corsin
• Is Part Of: Small. Volume 18:Issue 14(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-18
• Subjects: cracking -- excellent capacity retention -- gas evolution -- single‐crystal NCM -- transition metal dissolution; Nanotechnology -- Periodicals; Nanoparticles -- Periodicals; Microtechnology -- Periodicals; 620.5
• DOI: 10.1002/smll.202107357
• Languages: English
• ISSNs: 1613-6810

Abstract

Abstract: Lithium‐ion batteries based on single‐crystal LiNi1− x − y Co x Mn y O2 (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 LiNi0.60 Co0.20 Mn0.20 O2 (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, CO2 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. Abstract : The graphite/SC‐NCM622 cell reaches an excellent capacity retention of 82.6% after 3000 cycles, while the graphite/PC‐NCM622 exhibits 80% retention after 1375 cycles. The improvement would be ascribed to the superior stable bulk structure of SC‐NCM622 after prolonged cycling, while PC‐NCM622 particles suffer from severe cracking, although the unexpected disordered rock‐salt layers are comparable on the exposed surface of both cathodes.