High‐Entropy Surface Complex Stabilized LiCoO2 Cathode

Abstract Elevating the charge voltage of LiCoO 2 increases the energy density of batteries, which is highly enticing in energy storage implementation ranging from portable electronics to e‐vehicles. However, hybrid redox reactions at high voltages facilitate oxygen evolution, electrolyte decomposition and irreversible phase change, and accordingly lead to rapid battery capacity decay. Here significantly improved high‐voltage cycling stability of Mg‐Al‐Eu co‐doped LiCoO 2 is demonstrated. It is found that element co‐doping induces a near‐surface high‐entropy zone, including an innately thin disordered rock‐salt shell and a dopant segregation surface. The high‐entropy complex can effectively suppress oxygen evolution and near‐surface structure deconstruction. The phase change reversibility between O3 and H1‐3 and thermal stability of the cathode are greatly enhanced as well. As a result, the co‐doped LiCoO 2 exhibits a remarkable cycling performance, retaining 86.3% and 72.0% of initial capacity over 800 and 2000 cycles, respectively, with a high cut‐off voltage of 4.6 V. The feasible co‐doping approach broadens the perspective for the development of stable lithium‐ion batteries with high operating voltages.