Homogeneous Spinel FeMn₂O₄ Precursor Enables LiMn_0.67Fe_0.33PO₄ as Durable High-Rate Lithium-ion Cathode

Lithium manganese iron phosphate (LiMn_xFe_1-xPO₄, LMFP) offers higher energy density than LiFePO₄ but suffers from sluggish kinetics and unfavorable cycling stability caused by Fe/Mn segregation and severe Jahn-Teller distortion of Mn³⁺. Herein, a precursor-engineered strategy is proposed using a homogeneous spinel FeMn₂O₄ precursor synthesized via solution combustion. Molecular-level chelation and rapid combustion pre-lock Fe and Mn cations into a uniform solid-solution framework, enabling the formation of LiMn_0.67Fe_0.33PO₄ with highly homogeneous cation distribution and reduced lattice distortion. As a result, the LMFP cathode exhibits markedly reduced polarization (38 mV and 101 mV for Fe and Mn plateaus), enhanced Li⁺ diffusion coefficients (up to 6.75 × 10⁻¹² cm² s⁻¹), and excellent rate capability, delivering ∼76 mAh g⁻¹ at 10 C. Superior cycling stability is achieved with 89.2% capacity retention after 1000 cycles at 5 C. This work demonstrates precursor-level cation organization as an effective route to overcoming the kinetic and stability bottlenecks of manganese-based olivine cathodes.