Mn-Rich Induced Alteration\non Band Gap and Cycling\nStability Properties of LiMn<sub><i>x</i></sub>Fe<sub>1–<i>x</i></sub>PO<sub>4</sub> Cathode Materials

Olivine-type LiMn<sub><i>x</i></sub>Fe<sub>1–<i>x</i></sub>PO<sub>4</sub> (LMFP) has inherited\nthe excellent\nheat-stable structure of LiFePO<sub>4</sub> (LFP) and the high-voltage\nproperty of LiMnPO<sub>4</sub> (LMP), which shows great promise as\na high-safety, high-energy-density cathode material. In order to combine\nthe high energy density and excellent electrochemical performance,\nit is essential to consider the Mn/Fe ratio. This paper presents a\ntheoretical investigation of the lattice structure parameters, embedded\nlithium voltage, local electron density, migration barrier, and lithium\nion delithiation and lithiation mechanism of different LiMn<sub><i>x</i></sub>Fe<sub>1–<i>x</i></sub>PO4 (0.5\n≤ <i>x</i> ≤ 0.8) compounds. In situ-coated\nLiMn<sub><i>x</i></sub>Fe<sub>1–<i>x</i></sub>PO<sub>4</sub> (0.5 ≤ <i>x</i> ≤ 0.8)\ncomposite cathode materials with a size of 100–200 nm were\nprepared by a hydrothermal method to verify the theoretical study.\nLiMn<sub>0.6</sub>Fe<sub>0.4</sub>PO<sub>4</sub>/C exhibited a specific\ncapacity of 140.2 and 97.58 mA h·g<sup>–1</sup> at 1 and\n5C, respectively, and a remarkable capacity retention rate of 88.5%\nafter 200 cycles at 1C. When LiMn<sub>0.6</sub>Fe<sub>0.4</sub>PO<sub>4</sub>/C was assembled into a flexible pouch battery and subjected\nto long cycle tests at different rates and squeeze and extrusion tests,\nit demonstrated a capacity retention rate of 99.35% for 100 cycles\nat 0.2C and 93.2% for 200 cycles at 0.5C. Moreover, the structural\nevolution of LiMn<sub>0.6</sub>Fe<sub>0.4</sub>PO<sub>4</sub>/C \nwere analyzed in situ XRD, indicating a high stability and the resulted\nas obtine electrochemical performance, paving the way for optimization\nof high-energy-density LMFP cathode materials.