One‐Step Synthesized Al/Mg Codoped LiNi _0.9 Mn _0.1 O ₂ Cathodes with Enhanced Structural and Electrochemical Stability for Lithium‐Ion Batteries

LiNi 0.9 Mn 0.1 O 2 (LNM91) cathode has attracted significant attention in lithium‐ion batteries (LIBs) due to its high capacity and low cost. However, its poor electrochemical performance and thermal stability hinder its application in electric vehicles. To overcome these limitations, this study proposes a novel one‐step solid‐state method for doping Al 3+ and Mg 2+ into the Ni and Li sites of LNM91, respectively, by directly mixing hydroxide precursors followed by calcination. Unlike the pristine cathode, which exhibits obvious cracking, the resultant Al/Mg codoped LNM91 maintains its structural integrity well after 100 cycles. The capacity retention significantly increases from 78.5 to 93.0% after 100 cycles at 0.5 C. Mechanistic studies reveal that Al 3+ stabilizes the oxygen framework through strong AlO bonds, while Mg 2+ suppresses Li + /Ni 2+ disorder via electrostatic repulsion. Their synergistic effect mitigates the detrimental H2‐H3 phase transition and microcrack propagation, thereby bolstering rate capability and cycling performance. These results highlight the significance of Al/Mg codoping as a promising approach for developing high‐performance cobalt‐free and nickel‐rich cathodes for LIBs.