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Olivine LiMnPO4 cathode materials are favored for their low cost and higher operating voltage compared to those of LiFePO4. However, significant volume changes due to the Jahn–Teller effect of Mn3+, slow lithium-ion diffusion, and poor electronic conductivity limit their structural stability and electrochemical performance. Through a straightforward solid-state reaction, LiMnxFe1–xPO4/C (x = 0.7, 0.8, 0.9) cathode materials were synthesized using FePO4·2H2O and MnPO4·H2O precursors at varying calcination temperatures. Optimal results were obtained at 650 °C, leading to further investigation to identify the most suitable Mn/Fe ratio. LiMn0.7Fe0.3PO4/C exhibited a higher initial discharge capacity of 149.1 mAh g–1 at 0.1 C compared to LiMn0.8Fe0.2PO4/C (146.9 mAh g–1) and LiMn0.9Fe0.1PO4/C (125.6 mAh g–1), and a superior capacity retention of 96.1% after 160 cycles. Additionally, it showed improved rate capability with average discharge capacities of 138.7, 131.1, and 110.6 mAh g–1 at 0.2, 0.5, and 1 C rates, respectively. Furthermore, the phase transitions of LiMn0.7Fe0.3PO4/C cathodes during (de)lithiation were monitored via operando XRD. During charging, the orthorhombic LiMn0.7Fe0.3PO4 transitioned to orthorhombic Mn0.7Fe0.3PO4, maintaining the same space group Pmnb. Simultaneously, a solid-solution reaction within LixMn0.7Fe0.3PO4 and a two-phase reaction between LixMn0.7Fe0.3PO4 and Mn0.7Fe0.3PO4 were observed to occur successively.
Wang et al. (Thu,) studied this question.