Mitigating the Rock‐Salt Phase Transformation in Disordered LNMO Through Synergetic Solid‐State AlF ₃ /LiF Modifications

High-voltage disordered spinel LiNi_0.5Mn_1.5O₄ is a promising cathode material for high power density in lithium-ion batteries. However, it suffers from poor cycle life associated with the rock-salt phase transformation. This study presents a straightforward synthesis approach to enhance the electrochemical performance of LiNi_0.5Mn_1.5O₄ through a synergistic solid-state modification with LiF and AlF₃. This dual modification promotes rapid Li⁺ diffusion, enables near-complete delithiation/lithiation, approaching the theoretical capacity of disordered LiNi_0.5Mn_1.5O₄, and, more importantly, effectively mitigates the formation of the rock-salt phase, thereby enhancing structural stability, as confirmed by operando X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (SXRD). As a result, the optimized LiNi_0.5Mn_1.5O₄ (10 mg AlF₃ + 30 mg LiF) delivers high reversible capacities of 142.1, 139.1, 129.2, 121.6, 110.3, 93.5, and 76.1 mAh∙g^-1 at 0.2C, 0.5C, 1.0C, 2.0C, 3.0C, 4.0C, and 5.0C, respectively. Full cells using graphite as the anode and a high-loading cathode exhibit excellent cycling performance. They retain 80% of their capacity after 200 cycles at 0.5C within a voltage window of 3.5-4.9 V with cathode loading of 11 mg∙cm^-2. The findings of this study will significantly advance high-power LiNi_0.5Mn_1.5O₄ materials, offering improved battery life and thereby enhancing their potential for practical applications.