Synthesis and electrochemical characterization of LiCo xMn 1− xPO 4/C nanocomposites

Abstract

LiCo x Mn 1− x PO 4/C nanocomposites (0 ≤ x ≤ 1.0) were prepared by a combination of spray pyrolysis at 300 °C and wet ball-milling followed by heat treatment at 500 °C for 4 h in 3% H 2 + N 2 atmosphere. X-ray diffraction analysis indicated that all samples had the single phase olivine structures indexed by orthorhombic Pmna. The lattice parameters linearly decreased with increasing cobalt content, which confirmed the existence of solid solutions. It was clearly seen from the scanning electron microscopy observation that the LiCo x Mn 1− x PO 4/C samples were agglomerates with approximately 100 nm primary particles. The LiCo x Mn 1− x PO 4/C nanocomposites were used as cathode materials for lithium batteries, and electrochemical performance was comparatively investigated with cyclic voltammetry and galvanostatic charge–discharge test using the Liǀ1 M LiPF 6 in EC:DMC = 1:1ǀLiCo x Mn 1− x PO 4/C cells at room temperature. The cells at 0.05 C charge–discharge rate delivered first discharge capacities of 165 mAh g −1 (96% of theoretical capacity) at x = 0, 136 mAh g −1 at x = 0.2, 132 mAh g −1 at x = 0.5, 125 mAh g −1 at x = 0.8 and 132 mAh g −1 (79% of theoretical capacity) at x = 1.0, respectively. While the first discharge capacity increased with the cobalt content at high charge–discharge rates more than 0.5 C due to higher electronic conductivity of LiCoPO 4 in comparison with LiMnPO 4, the cycleability of cell became worse with increasing the amount of cobalt. The existence of Mn 2+ seemed to enhance the cycleability of LiCo x Mn 1− x PO 4/C nanocomposite cathode.