Understanding the construction of nano-structured LiMn0.6Fe0.4PO4 by a co-precipitation strategy and Mg2+ doping towards high-performance lithium-ion batteries

Abstract

LiMn_1−xFe_xPO₄ has attracted wide attention due to its higher voltage platform and energy density without sacrificing several excellent properties of pure LiFePO₄. However, the conventional co-precipitation route for preparing LiFePO₄ is not applicable to LiMn_1−xFe_xPO₄. In this paper, nano-structured LiMn_0.6Fe_0.4PO₄/C microspheres with high dispersibility and high compaction density are synthesized by using NH₄Mn_0.6Fe_0.4PO₄·H₂O obtained via a co-precipitation strategy as a precursor for the first time, which enables Mn, Fe and P to be uniformly deposited. Furthermore, the in situ Mg²⁺ doping strategy is also carried out to optimize the electrochemical performance. Our results show that the introduction of Mg²⁺ can alleviate the lattice expansion and deformation caused by the Jahn–Teller effect, improving the structural stability of LiMn_0.6Fe_0.4−xMg_xPO₄/C. Meanwhile, the diffusion kinetics are investigated by in situ electrochemical impedance spectroscopy and cyclic voltammetry, revealing that Mg²⁺ doping effectively reduces the interfacial resistance and increases the lithium-ion diffusion coefficient. As a result, the LiMn_0.5978Fe_0.3522Mg_0.0506PO₄/C cathode exhibits superior rate performance, delivering capacities of 150.1, 141.4 and 111.6 mAh g⁻¹ at 0.1, 1 and 5C, respectively. This work provides important guidance for the industrial-scale manufacturing and practical application of LiMn_1−xFe_xPO₄/C, which is conducive to its further development.