Improved High Voltage Electrochemical Stability of Single‐Crystal LiNi _0.5 Co _0.2 Mn _0.3 O ₂ by Mg‐Fe Co‐Doped Li ₃ AlF ₆ Coating

The single‐crystal LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) offers a substantial theoretical specific capacity along with outstanding cycle stability. Despite the superior stability of the single‐crystal structure compared to its polycrystalline counterpart, the NCM523 single‐crystal material may experience structural changes, such as oxygen release and transition metal dissolution, under high‐voltage conditions (greater than 4.3 V). These changes can lead to capacity decay or battery failure. Enhancing the electrochemical performance of single‐crystal NCM523 under high‐voltage conditions is crucial for advancing lithium‐ion battery performance. In this work, a Mg‐Fe co‐doped Li 3 AlF 6 ‐coated single‐crystal NCM523 material via a liquid‐phase method is prepared. The Mg‐Fe co‐doped Li 3 AlF 6 ‐coated NCM523 exhibits excellent electrochemical properties at a voltage of 4.5 V, reaching a specific discharge capacity of 215.5 mAh g −1 . Following 200 cycles at 1 C, the retention rate is 91.33%, significantly outperforming the original NCM523, which shows a capacity of 178.84 mAh g −1 and a retention ratio of 44.16%. The co‐doping of Mg and Fe enhances the conductivity of Li 3 AlF 6 . The stability of the material under high voltage is enhanced by this modified coating, which also lowers its charge transfer resistance. This research provides important perspectives for developing high‐performance cathode materials for lithium‐ion batteries.