Abstract
Li-rich Mn-based layered oxides are promising cathodes for high-specific-energy lithium-ion batteries because they combine high reversible capacity with relatively abundant manganese. Their capacity advantage originates from coupled cationic–anionic redox but is accompanied by first-cycle irreversibility, voltage decay, oxygen loss, gas evolution, and charged-state thermal instability. This review connects the intrinsic chemistry of Li-rich Mn-based cathodes with battery safety across material, electrode, and cell scales. Oxygen-redox-driven structural evolution provides a shared origin for electrochemical degradation and charged-cathode instability, but material-level oxygen activity alone does not determine full-cell thermal-runaway behavior. The integrated cell response depends on the timing and coupling of heat- and gas-generating reactions involving both electrodes, the electrolyte, separator, cell architecture, and thermal boundary. We therefore distinguish intrinsic cathode decomposition, cathode–electrolyte reactions, and cell-level thermal runaway, while separating direct LMR observations from evidence obtained for other layered oxides and from general lithium-ion battery safety principles. Instantaneous state of charge, high-voltage activation history, and cycling/aging history are treated as coupled state variables that influence two complementary response dimensions: trigger sensitivity and runaway severity. Quantitative material-to-cell comparisons and the measurement coverage of representative mitigation strategies are summarized to identify experimentally supported links and the remaining requirements for predictive safety assessment.