Investigation and Suppression of Oxygen Release by LiNi0.8Co0.1Mn0.1O2 Cathode under Overcharge Conditions

The safety issue of lithium-ion batteries is a crucial factor limiting their large-scale application. Therefore, it is of practical significance to evaluate the impact of their overcharge behavior because of the severe levels of oxygen release of cathode materials during this process. Herein, by combining a variety of in situ techniques of spectroscopy and electron microscopy, this work studies the structural degradation of LiNi0.8Co0.1Mn0.1O2 (NCM811) accompanying the oxygen release in the overcharge process. It is observed that a small amount of O-2 evolves from the initial surface at approximate to 4.7 V. When charging to a higher voltage (approximate to 5.5 V), a large amount of O-2 evolves on the newly formed surface due to the occurrence of microcracks. Based on experimental results and theoretical calculations, it is determined that the oxygen release mainly occurs in the near-surface regions, where the remaining oxygen vacancies accumulate to create voids. To suppress the oxygen release, single-crystalline NCM811 with integrated structure is introduced and serves as a cathode, which can effectively inhibit morphology destruction and reduce the activation of lattice oxygen in the surface region. These findings provide a theoretical basis and effective strategy for improving the safety performance of Ni-rich cathode materials in practical applications.