Aging mechanism of Ni-rich cathode-based lithium-ion batteries: Focusing on upper cut-off voltages

Ni-rich cathode-based lithium-ion batteries are subject to certain limitations in electric vehicle applications due to their cycle life. Therefore, this study aims to investigate the aging mechanism of Ni-rich cathode-based lithium-ion batteries with different upper cut-off voltages, providing ideas for improving their cycle life. The change in the cathode lattice during the charging and discharging process obtained by in-situ XRD shows that the H2-H3 phase transition exacerbates the battery capacity degradation. In addition, the capacity degradation caused by lattice strain induced by the rapid release of anisotropic stress accumulation (ASA) in the H2 region cannot be ignored as well. After lowering the upper cut-off voltage, the surplus lithium in the cathode plays a pivotal role in avoiding the above rapid battery degradation, driven by the advantages of its ability to stabilize lattice structure and reduce the degree of Li/Ni cation mixing. Meanwhile, the low upper cut-off voltage effectively avoids side reactions such as electrolyte decomposition and transition metal dissolution. The above results would contribute to slowing down battery degradation, which would provide strong support for the design of high energy density and long-life lithium-ion batteries.