Phosphorus-enabled reversible Jahn–Teller phase evolution in manganese spinel cathodes

Abstract

Low-voltage operation of manganese-based spinel cathodes can access additional capacity but is typically limited by cooperative Jahn–Teller distortion, cubic-to-tetragonal phase evolution and rapid capacity decay. Stabilization strategies have therefore largely aimed to suppress this low-voltage phase transition. Here, using phosphorus-integrated Li1.67Mn1.5P0.17O4 (LMPO) and phosphorus-free Li1.86Mn1.67O4 (LMO) as a matched model pair, we show that the key to low-voltage reversibility is not preventing tetragonal phase formation, but controlling how the tetragonal phase evolves during cycling. LMPO retains 78.0% of its capacity after 100 cycles, whereas LMO retains only 26.0%, despite both materials forming a discharged tetragonal phase. Combined electrochemical analysis, multiscale structural characterization and first-principles calculations reveal that phosphorus narrows the extended 8a-to-16c two-phase regime and suppresses irreversible tetragonal-phase accumulation. More importantly, phosphorus disrupts the cooperative ordering of Jahn–Teller axes, attenuates MnO6 distortion and reduces the lattice/volume mismatch between cubic and tetragonal phases. These results identify the cooperative character of Jahn–Teller distortion as a critical design target for stabilizing low-voltage cycling in Mn-based spinel cathodes.