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

High‐voltage disordered spinel LiNi 0.5 Mn 1.5 O 4 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 0.5 Mn 1.5 O 4 through a synergistic solid‐state modification with LiF and AlF 3 . This dual modification promotes rapid Li⁺ diffusion, enables near‐complete delithiation/lithiation, approaching the theoretical capacity of disordered LiNi 0.5 Mn 1.5 O 4 , 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 0.5 Mn 1.5 O 4 (10 mg AlF 3 + 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 0.5 Mn 1.5 O 4 materials, offering improved battery life and thereby enhancing their potential for practical applications.