Constructing a Thin Disordered Self‐Protective Layer on the LiNiO₂ Primary Particles Against Oxygen Release

Abstract One of the major challenges facing the application of layered LiNiO₂ (LNO) cathode materials is the oxygen release upon electrochemical cycling. Here it is shown that tailoring the provided lithium content during synthesis process can create a disordered layered Li_1‐xNi_1+xO₂ phase at the primary particle surface. The disordered surface, which serves as a self‐protective layer to alleviate the oxygen loss, possesses the same layered rhombohedral structure (Rm) as the inner core of primary particles of the Li_1‐xNi_1+xO₂ (x ≈ 0). With advanced synchrotron‐based x‐ray 3D imaging and spectroscopic techniques, a macroporous architecture within the agglomerates of LNO with ordered surface (LNO‐OS) is revealed after only 40 cycles, concomitant with the reduction of nickel on the primary particle surface throughout the whole secondary particles. Such chemomechanical degradation accelerates the deterioration of LNO‐OS cathodes. Comparably, there are only slight changes in the nickel valence state and interior architecture of LNO with a thin disordered surface layer (LNO‐DS) after cycling, mainly arising from an improved robustness of the oxygen framework on the surface. More importantly, the disordered surface can suppress the detrimental H2 ⇋ H3 phase transition upon cycling compared to the ordered one.