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

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.