Toward Commercial Lithium Manganese Iron Phosphate for High-Energy and Advanced Lithium-Ion Batteries and Beyond

Lithium manganese iron phosphate LiMnxFe1−xPO4 (x ≤ 0.5)-based cathode materials were synthesized via a hydrothermal method to investigate their composition effect on structure and electrochemical performance. The X-ray diffraction results confirmed a single-phase olivine structure (Pnma) for all the compositions, with minor lithium phosphate (Li3PO4) impurities detected at high manganese (Mn) contents (x ≥ 0.4). The morphological evolution from small particles with low Mn content to compact rod-like particles at x = 0.3 indicates optimized crystal growth and improved interparticle connectivity. Electrochemical testing revealed that the discharge capacity initially increased with the substituted Mn content to a maximum of 140 mAh g−1 at 0.5 C for LiMn0.3Fe0.7PO4/C with remarkable cycling stability. This high capacity is attributed to the activation of Fe2+/Fe3+ and Mn2+/Mn3+ redox couples and the minimal formation of electrochemically inactive phases. Further Mn incorporation (x > 0.3) caused structural distortion, Li3PO4 formation, and overall capacity loss. Codoping with Mg (LiMg0.05MnxFe1−xPO4) improved stability but lowered discharge capacity owing to the electrochemical inactivity of Mg2+ and impurity formation. Notably, an optimal x value of ~0.3 exhibited an effective balance between high energy density, rate capability, and structural integrity in Mn-doped LiFePO4 cathodes for next-generation lithium-ion batteries.