Mitigating Mn‐Driven Interfacial Instability in LiMn 0.5 Fe 0.5 PO ₄ Cathodes for Lithium‐Ion Batteries via Surface‐Intensive Ta Doping

LiMnxFe1-xPO₄ (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 Mn³⁺ species are involved, LMFP exhibits increased polarization and progressive performance degradation under high-rate and low-temperature conditions. Consequently, the Mn²⁺/Mn³⁺ 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 Ta⁵⁺ to selectively enrich the near-surface region of LiMn0.5Fe0.5PO₄ particles in Ta. Ta doping strengthens the M─O framework and widens the Li─O diffusion pathways while increasing the near-surface Mn²⁺ fraction from 53.9% to 59.7%, thereby suppressing Mn³⁺ 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.