Heterocations Synergistic Doping for Kinetically Enhanced and Structurally Stable LiMn _0.6 Fe _0.4 PO ₄

LiMn_<i>x</i>Fe_1-<i>x</i>PO₄ (LMFP) is a promising olivine cathode material successor to LiFePO₄, offering a higher operating voltage platform for enhanced energy density. However, its commercial application is hindered by inherent poor kinetics. Herein, a dual-site doping strategy involving Na⁺ and Co²⁺ is proposed to synergistically enhance the ionic and electronic conductivity of LMFP. The codoped LMFP-Na-Co cathode delivers a specific capacity of 135.8 mAh/g at 1 C and exhibits outstanding cycling stability with 92.5% capacity retention after 200 cycles. Remarkably, it also maintains 90.2% capacity retention after 300 cycles even at 0 °C. Theoretical calculations reveal that Na⁺ doping expands the one-dimensional lithium-ion diffusion channels, while Co²⁺ doping elevates the intrinsic electronic conductivity and suppresses the Jahn-Teller distortion associated with Mn³⁺, collectively lowering the Li⁺ diffusion barrier and improving structural stability. This work demonstrates that Na⁺-Co²⁺ dual-site doping is a highly promising strategy for developing high-performance LiMn_<i>x</i>Fe_1-<i>x</i>PO₄ cathodes.