Mitigating Mn‐Driven Interfacial Instability in LiMn _0.5 Fe _0.5 PO ₄ Cathodes for Lithium‐Ion Batteries via Surface‐Intensive Ta Doping

ABSTRACT LiMn _x Fe _1−x PO ₄ (LMFP) holds promise for next‐generation olivine‐type cathodes for Li‐ion batteries but suffers from sluggish Li ⁺ diffusion along 1D [010] channels. Moreover, because Jahn‐Teller‐active Mn ³⁺ species are involved, LMFP exhibits increased polarization and progressive performance degradation under high‐rate and low‐temperature conditions. Consequently, the Mn ²⁺ /Mn ³⁺ redox becomes surface‐intensive at the near‐surface region, thereby triggering Mn dissolution and electrolyte side reactions. To address this problem, we use surface‐intensive Ta doping, exploiting the slow diffusion kinetics of Ta ⁵⁺ to selectively enrich the near‐surface region of LiMn _0.5 Fe _0.5 PO ₄ particles in Ta. Ta doping strengthens the M─O framework and widens the Li─O diffusion pathways while increasing the near‐surface Mn ²⁺ fraction from 53.9% to 59.7%, thereby suppressing Mn ³⁺ accumulation. Electrochemically, Ta1@LMFP delivers 105.58 mAh g ⁻¹ at 20 C (71.1% of the 0.1 C capacity), outperforming Ta0@LMFP (82.27 mAh g ⁻¹ , 54.8%). In addition, under high‐SOC storage conditions (60°C, 10d), Ta1@LMFP maintains 99.5% of its initial capacity, whereas Ta0@LMFP retains 83.1%, confirming that self‐discharge and interfacial degradation are suppressed at high temperature and high SOC. This work demonstrates that surface‐intensive Ta doping enables the wide‐temperature‐range and high‐power operation of LMFP‐based cathodes and provides compositional and structural design guidelines for developing robust cathode materials for Li‐ion batteries.