High-voltage high-nickel low-cobalt lithium layered oxide cathodes show great application prospects for lithium-ion batteries due to their low cost and high capacity. However, deterioration of the bulk structure and the electrode-electrolyte interface will significantly endanger the cycle life and thermal stability of the battery as the nickel content and voltage increase. We present here a lattice doping strategy to greatly improve the cell performance by doping a small dose of Ti (2 mol %) in LiNi0.6Co0.05Mn0.35O2. Through density functional theory calculations, we know that the diffusion energy barrier of Li+ decreases and the activation energy of surface lattice oxygen atom loss increases after Ti doping, thereby improving the rate performance and inhibiting the undesired phase transition. The battery in situ X-ray diffraction (XRD) pattern demonstrates that Ti doping tunes the H1-H2 phase-transition process from a two-phase reaction to a single-phase reaction and inhibits the undesired H2-H3 phase transition, minimizing the mechanical degradation. The variable temperature in situ XRD reveals delayed phase-transition temperature to improve thermal stability. These improvements can be attributed to Ti doping to passivate the reactivity of the layered oxide cathode, which is fundamentally related to the strong Ti-O bond and no unpaired electrons for Ti4+. This work provides valuable strategic guidelines for the use of high-voltage high-nickel low-cobalt cathodes in lithium-ion batteries.
Keywords: high voltage; high-nickel low-cobalt cathode; lithium-ion battery; structure passivation; titanium doping.