High‐Voltage Spinel and Li₂MnO₃ Composite Structure Construction in LiMn_0.8Ni_0.2O₂ for Manganese‐Based Lithium‐Ion Battery Cathode Materials

Abstract Layered Mn‐based oxides are promising candidates for next‐generation high‐energy‐density cathodes of rechargeable batteries owing to their prominent energy density and cost‐effectiveness. However, the obvious structural degradation such as the layered‐to‐spinel transformation, associating with deteriorated electrochemical cycle stability, hinder their extensive applications in batteries. Herein, a composite structure is designed based on a Mn‐based oxide of LiMn_0.8Ni_0.2O₂ with a high‐voltage spinel crystal domain pre‐introduced into the parent layered structure, showing good structural stability during electrochemical process. Results show that Li₂MnO₃ crystal domain suffers from sluggish Li⁺ ions kinetics and structural transformation from layered to metastable spinel, while the pre‐introduced high‐voltage spinel crystal domain exhibits almost maintained structure, and the optimal performance near to theoretical capacity of LiMn_0.8Ni_0.2O₂ cathode can be harvested after electrochemical activation. This design is useful for stabilizing the entire structure prior to the degradation of the parent structures, and the electrochemical contributions of layered Li₂MnO₃ and pre‐introduced high‐voltage spinel crystal domains are also discerned. This study provides new guidelines for designing high‐performance composite‐structure Mn‐based cathode materials by pre‐introduction of stable crystal domains.