Enhanced Cycling Stability of Medium‐Entropy Spinel Oxide Anodes for Lithium‐Ion Batteries via Cationic Diversity and Entropy Stabilization

ABSTRACT Transition metal oxide electrodes utilizing the conversion reaction mechanism exhibit high theoretical capacities, making them attractive anodes for next‐generation lithium‐ion batteries. However, significant volume changes during cycling lead to capacity fading, hindering their practical application. This study presents a bottom‐up co‐precipitation method inspired by binary system design strategies. By selecting metal salts with similar cationic radii and chemical properties, we synthesized a high‐phase‐purity spinel medium‐entropy oxide, (FeMnNiCu)O. The unique properties imparted by different elements in composite materials can be effectively utilized in medium‐entropy oxides, where the incorporation of multiple elements enhances configurational entropy, thereby improving cycling stability. As an anode, this material exhibited an initial discharge capacity of 1372 mAh g −1 at 100 mA g −1 , retaining 1049.48 mAh g −1 after 150 cycles. Ex situ XRD and in situ EIS analyses provided insights into the reversible conversion reactions and the formation of a stable SEI film in these electrodes. This work demonstrates the effectiveness of a strategy transitioning from binary composites to medium‐entropy materials through bottom‐up coprecipitation, advancing the design of medium and high‐entropy material systems.