Quantifying Degradation Parameters of Single-Crystalline Ni-Rich Cathodes in Lithium-Ion Batteries |
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| Authors: | Dr Wengao Zhao Dr Kuan Wang Prof Xinming Fan Fucheng Ren Xieyu Xu Dr Yangyang Liu Dr Shizhao Xiong Dr Xiangsi Liu Zhengfeng Zhang Mayan Si Ruizhuo Zhang Dr Wessel van den Bergh Prof Pengfei Yan Dr Corsin Battaglia Dr Torsten Brezesinski Prof Yong Yang |
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| Institution: | 1. Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany;2. Beijing Key Laboratory of Microstructure and Properties of Solids, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124 China;3. School of Metallurgy and Environment, Central South University, Changsha, 410083 China;4. College of Chemistry and Chemical Engineering & State Key Lab for Physical Chemistry of Solid Surfaces & College of Energy, Xiamen University, Xiamen, 361005 China;5. State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049 China;6. Department of Physics, Chalmers University of Technology, 41296 Göteborg, Sweden;7. Materials for Energy Conversion, Empa—Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland |
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| Abstract: | Single-crystal LiNixCoyMnzO2 (SC-NCM, x+y+z=1) cathodes are renowned for their high structural stability and reduced accumulation of adverse side products during long-term cycling. While advances have been made using SC-NCM cathode materials, careful studies of cathode degradation mechanisms are scarce. Herein, we employed quasi single-crystalline LiNi0.65Co0.15Mn0.20O2 (SC-NCM65) to test the relationship between cycling performance and material degradation for different charge cutoff potentials. The Li/SC-NCM65 cells showed >77 % capacity retention below 4.6 V vs. Li+/Li after 400 cycles and revealed a significant decay to 56 % for 4.7 V cutoff. We demonstrate that the SC-NCM65 degradation is due to accumulation of rock-salt (NiO) species at the particle surface rather than intragranular cracking or side reactions with the electrolyte. The NiO-type layer formation is also responsible for the strongly increased impedance and transition-metal dissolution. Notably, the capacity loss is found to have a linear relationship with the thickness of the rock-salt surface layer. Density functional theory and COMSOL Multiphysics modeling analysis further indicate that the charge-transfer kinetics is decisive, as the lower lithium diffusivity of the NiO phase hinders charge transport from the surface to the bulk. |
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| Keywords: | Single-Crystal Cathodes Structural Stability Rock-Salt Formation Multiphysics Analysis Transfer Kinetics |
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