Alleviating the irreversible cation migration of Li-rich Mn-based cathodes through Be-dopant steric hindrance for liquid and all-solid-state Li batteries

High-capacity and cost-effective Li-rich Mn-based oxides (LRMs) are regarded as one of the ideal cathode materials for high-energy liquid and all-solid-state Li-ion batteries. However, the phase transition from layered to spinel/rock-salt structure results in severe capacity/voltage decay, thereby limiting their practical applications. Herein, the dopant steric hindrance is proposed to alleviate the irreversible cation migration and phase transition within the highly delithiated LMRs, and further improve their structural stability. It is demonstrated that Be²⁺ dopant, as the alkali metal ion with a relatively low ionic radius and high bulk charge density, preferentially occupies the Li site of the transition metal layer within the C2/m phase. This unique substitution not only suppresses the phase transition by increasing the migration energy barriers of in-plane and out-of-plane Mn-ion movement from the transition metal layer into Li vacancy of the Li layer, but also improves the reversibility of oxygen anion redox by forming the stable Li–O–Be configuration. Consequently, in a liquid LIB system coupled with Li metal and graphite anode, it exhibits significantly improved overall electrochemical performance compared with the pristine LMRs. The Be-doped LMRs also present superior interface compatibility and stability when matching with halide solid-state electrolyte in the all-solid-state batteries, delivering an ultrahigh available capacity of 292.9 mAh·g^–1 and good cycling stability. These findings highlight the significance of doping site in stabilizing the LMRs.