Gayoung Youn, Seunghyeop Baek, Munseok S. Chae, Kang Taek Lee
ABSTRACT The Jahn–Teller distortion, often regarded as a structural drawback in Mn‐based cathodes, is re‐evaluated in this study through a comprehensive investigation of LiMn 0.6 Fe 0.4 PO 4 (LMFP). Compared to conventional LiFePO 4 (LFP), LMFP exhibits improved rate capability and enhanced Li transport, underpinned by a continuous single‐phase reaction pathway during delithiation. Operando XRD and Rietveld refinement reveal that LMFP undergoes a minimal volume change (0.8%) upon charging, in stark contrast to the 7.1% shrinkage and two‐phase transition in LFP. Soft bond‐valence calculations further confirm a reduced lithium migration barrier (0.44 eV vs. 0.48 eV), highlighting the role of Mn 3+ ‐induced local lattice distortions in enhancing ionic conductivity. These results reveal a previously underexplored beneficial role of Jahn–Teller distortion, showing that Mn‐induced local lattice flexibility contributes to Li + mobility and rate capability. This work suggests Jahn–Teller engineering as a viable strategy for designing structurally adaptive phosphate cathodes with improved ionic transport and electrochemical performance.