Enhanced electrochemical properties of LiMnPO4/C via Li-site substitution with Mg

Li_0.94Mg_0.03MnPO₄/C composite cathode materials for lithium ion battery with different carbon contents are synthesized by sol–gel method followed by heat treatment in the air. Environmental scanning electron microscopy measurements show that both firing temperature and carbon content affect the morphology of the end products. X-ray powder diffraction analysis indicates that the samples are olivine-structured. The galvanostatic charge–discharge results show that the optimal firing temperature registers 400 °C and that the electrochemical performances of Li_0.94Mg_0.03MnPO₄/C are improved by elevating its carbon amount. The sample with an initial conductive carbon content of 20 wt.% gives the best performances; when tested at the rate of 0.02C, 0.1C, and 1.0C between 2.8 and 4.4 V, its initial discharge capacity reaches 145.8, 103.0, and 72.8 mAhg⁻¹, respectively, and maintains at 100.1, 77.6, and 65.4 mAhg⁻¹, respectively, after 100 cycles.