Activating Anionic Redox of Li-Rich Mn-Based Layered Oxide in All-Solid-State Batteries by Tailoring the Cathode Microstructure

Lithium-rich manganese-based layered oxides (LRMOs) are promising cathodes for high-energy-density Li-ion batteries. However, their cycle life is highly limited by gas release and Mn dissolution in liquid electrolytes. All-solid-state batteries (ASSBs) could overcome these issues by using solid electrolytes, provided that a stable cathode-catholyte interface is maintained. A key challenge is that the capacity of conventional polycrystalline LRMOs is difficult to activate in ASSBs due to the sluggish kinetics of anionic redox-limiting Li diffusivity. We demonstrate here that, by using monolithic LRMO particles without any surface modification, oxygen redox can be largely activated, enabling a capacity of 268.4 mAh g^-1, in stark contrast with ∼70 mAh g^-1 of conventional polycrystalline particles. We attribute this enhancement to improved cathode-electrolyte contact and a shortened Li⁺ diffusion pathway in the monolithic cathode microstructure. Our work provides a crucial step toward practical LRMO-based ASSBs by tailoring cathode microstructure in addition to interface engineering.