Tuning core-shell structural architecture for high-performance Li-Mn-O layered oxides

Being free of cobalt and nickel, Li-Mn-O layered oxides are considered as one of the most promising candidate cathodes due to the low cost and high specific capacity. The relatively poor thermal stability of Li-Mn-O layered oxides can lead to battery safety issues, and thus needs to be improved for practical applications. Herein, we systemically investigated the heat-induced structural/chemical evolution of a Li-Mn-O material, revealing a two-step phase transition process through concurrent Li and O loss, heterogeneously occurring in the bulk and at the surface of the primary particles. Based on the understanding of structural change, two new Li-Mn-O materials with different core-shell microstructures, one with a spinel shell and another with an orthorhombic shell, were synthesized. Experimentally, the one with the spinel shell achieved an ultrahigh decomposition temperature of ~300 °C, which is vital for battery safety. This material also exhibited greatly enhanced cycling stability and rate capability due to the protection role of the spinel shell. This work paves new routes to produce high-performance cathode materials with various heterostructure architectures through the tunning temperature-sensitive structure evolution process.