One-Step Bimetallic Doping Strategy: Achieving Structural Stabilization and Performance Enhancement of Ultrahigh Nickel Cobalt-Free Cathode Materials

Ultrahigh-nickel cobalt-free layered oxide LiNi0.9Mn0.1O2 is one of the most promising cathode materials for next-generation lithium-ion batteries due to its low cost and high energy density. However, its surface/interfacial side reactions and anisotropic stress during long cycling cause microcrack formation and structural degradation, leading to capacity fading and poor cycling stability, which severely limit its commercial application. To this end, a three-in-one modification strategy was proposed for LiNi0.9Mn0.1O2, which includes microstructure modification, suitable cation mixing degree, and enhancement of TM–O covalent bonds. Specifically, the double doping of Nb5+ and Ti4+ was utilized to introduce the “pinning effect”, which effectively refines the primary grains and enhances the mechanical toughness to inhibit the accumulation of internal stresses and the formation of microcracks. Due to the charge compensation effect, the high-valent cation doping promotes the Li+/Ni2+ mixing, and the Ni2+ ions located in the Li layer act as pillars in the deeply delithiated state, effectively inhibiting both the continuous migration of Ni2+ into the Li layer and the structural collapse. In addition, the stronger Nb/Ti–O bond allowed the transition metal layer to shrink and the Li layer spacing to increase, which not only promoted the diffusion kinetics of lithium ions but also helped to stabilize the oxygen framework and crystal structure and inhibited the lattice oxygen release and interlayer slip phenomena. As a result, the Nb5+ and Ti4+ double-doped LiNi0.9Mn0.1O2 cathode has a significantly improved cycling performance, with its capacity retention greatly improved from 72.55% to 91.32% after 200 cycles at 1 C, and the capacity loss is only 2% after 500 cycles of the full cell, which shows a certain potential for commercial application. This study provides an extremely simple and effective method for solving the problems of the high nickel cathode material LiNi0.9Mn0.1O2 in terms of structure and cycling stability, facilitating its commercial application.