Stress accumulation in Ni-rich layered oxide cathodes: Origin, impact, and resolution

LiNixCoyMnzO2 (NCM, x + y + z = 1) is one of the most promising cathode candidates for high energy density lithium-ion batteries (LIBs). Due to the potential in enhancing energy density and cyclic life of LIBs, Ni-rich layered NCM (NCM, x ≥ 0.6) have garnered significant research attention. However, improved specific capacity lead to severer expansion and shrinkage of layered lattice, accelerating the stress generation and accumulation even microcracks formation in NCM materials. The microcracks can promote the electrolyte permeation and decomposition, which can consequently reduce cyclic stabilities. Therefore, it is significant to provide an in-depth insight into the origin and impacts of stress accumulation, and the available modification strategies for the future development of NCM materials. In this review, we will first summarize the origin of stress accumulation in NCM materials. Next, we discuss the impact of stress accumulation. The electrolyte permeation along microcracks can enhance the extent of side reaction at the interface, trigger phase transformation and consequential capacity fading. To cushion the impact of stress accumulation, we will review five main strategies. Finally, concise perspectives to reduce stress accumulation and enhance particle strength in further works will be presented.