Design and Stabilization Principles of O2-Type Li-Rich Mn-Based Layered Oxide Cathodes

Li-rich Mn-based layered oxides (LRMOs) represent a leading class of cathode materials for next-generation high-energy-density lithium-ion batteries (LIBs). Relative to traditional O3-type LRMOs, O2-type LRMOs better mitigate irreversible lattice oxygen loss, complex interfacial side reactions, and persistent voltage decay. However, existing reviews of LRMOs are predominantly focused on comparing O3- and O2-type LRMOs, with limited systematic analysis dedicated to O2-type LRMOs. O2-type LRMOs also pose distinct challenges: metastability complicates synthesis and scale-up, and sluggish Li-ion transport limits rate performance. In this review, we first investigate the intrinsic relationship between the crystal structure and electrochemical behavior of LRMOs, with a particular emphasis on the structural advantages and design principles of the O2-type phase. Furthermore, we consolidate scalable synthesis protocols for metastable O2-type LRMOs. Finally, multiscale regulation strategies are explored to link material design to voltage and cycling stability, which ultimately generalizes O2-type principles for broader application across other oxide cathode systems.