Degradation Pathways of Cobalt‐Free LiNiO ₂ Cathode in Lithium Batteries

Abstract Electrode‐electrolyte reactivity (EER) and particle cracking (PC) are considered two main causes of capacity fade in high‐nickel layered oxide cathodes in lithium‐based batteries. However, whether EER or PC is more critical remains debatable. Herein, the fundamental correlation between EER and PC is systematically investigated with LiNiO ₂ (LNO), the ultimate cobalt‐free lithium layered oxide cathode. Specifically, EER is found more critical than secondary particle cracking (SPC) in determining the cycling stability of LNO; EER leads to primary particle cracking, but mitigates SPC due to the inhibition of H2‐H3 phase transformation. Two surface degradation pathways are identified for cycled LNO under low and high EERs. A common blocking surface reconstruction layer (SRL) containing electrochemically‐inactive Ni ₃ O ₄ spinel and NiO rock‐salt phases is formed on LNO in an electrolyte with a high EER; in contrast, an electrochemically‐active SRL featuring regions of electron‐ and lithium‐ion‐conductive LiNi ₂ O ₄ spinel phase is formed on LNO in an electrolyte with a low EER. These findings unveil the intrinsic degradation pathways of LNO cathode and are foreseen to provide new insights into the development of lithium‐based batteries with a minimized EER and a maximized service life.