Mg 2+ Doped LiFe 0.4 Mn 0.6-x Mg x PO 4 /C (x = 0, 0.01 and 0.03) with a 3D Carbon Network: Structural, Morphological, and Electrochemical Characterization for Lithium-Ion Batteries

Abstract In this study, LiFe 0.4 Mn 0.6 PO 4 (LFMP) and two Mg 2+ -doped materials, LiFe 0.4 Mn 0.6-x Mg x PO 4 (LFMP-0.01Mg and LFMP-0.03Mg), were synthesized via a solvothermal method and characterized structurally, morphologically, and electrochemically. XRD analysis confirmed their orthorhombic olivine structure (Pmnb), with a slight unit cell contraction, attributed to the partial Mg 2+ substitution at the M2 (Fe/Mn) octahedral site. SEM and HRTEM analyses revealed agglomerated nanoparticles with rectangular morphologies and a uniform amorphous carbon coating, as confirmed by Raman spectroscopy (ID/IG = 0.6). BET analysis showed a mesoporous structure with pore sizes of 1.8–1.9 nm. Electrochemical evaluations at 0.1C revealed discharge capacities of 113 mAh/g for undoped LFMP, 143.4 mAh/g for LFMP-0.01Mg and 125.7 mAh/g for LFMP-0.03Mg. Furthermore, an additional discharge plateau at ~3.6-3.7 V, attributed to the sluggish Mn 3+ reduction kinetics during the MnPO 4 /LiMnPO4 phase transition, was observed. Its capacity contribution was characterized as a function of Mg 2+ doping level, and this variation is consistent with previous reports in which dopant substitution facilitates the kinetics of this redox process, suggesting an analogous effect for Mg 2+ .