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Electrochemical Potential Effects on Structural Degradations of the Ni-rich NCM Cathode Surface: How thick is the surface?

Journal of Power Sources
To commercialize the Ni-rich NCM cathode based rechargeable battery, a promising candidate cathode for next-generation Li-ion batteries, the cycling performance is a critical issue to improve. In this research, we studied the structural degradation of the Ni-rich NCM/Graphite 18650 cylindrical type cells as a function of the cut-off voltage from 4.2V to 4.4V using the STEM-EELS, STEM-HAADF, and DFT calculation. Our electrochemical analysis showed that the cell performance deterioration mainly comes from the diffusion resistance growth in the positive electrode. We observed 10~25nm cation mixing layer on the cathode surface after 300 cycles which surface layer getting thicker when charging voltage increase. Our simulation also showed that cathode surface losses oxygen spontaneously at higher electrochemical potential. Therefore, our experimental and computational investigation presented the performance deterioration mechanisms of Ni-rich NCM cathode which is begin with the transition metal migrates along with the oxygen evolution.
Journal of Power Sources 490 (2021) 229542