Synthesis and electrochemical characterization of LiCoxMn1−xPO4/C nanocomposites

LiCoxMn1−xPO4/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% H2 + N2 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 LiCoxMn1−xPO4/C samples were agglomerates with approximately 100 nm primary particles. The LiCoxMn1−xPO4/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 LiPF6 in EC:DMC = 1:1ǀLiCoxMn1−xPO4/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 LiCoPO4 in comparison with LiMnPO4, the cycleability of cell became worse with increasing the amount of cobalt. The existence of Mn2+ seemed to enhance the cycleability of LiCoxMn1−xPO4/C nanocomposite cathode.

► LiCoxMn1−xPO4/C nanocomposites (0 ≤ x ≤ 1.0) were prepared by a novel preparation method.
► The formation of LiCoxMn1−xPO4 solid solution could be confirmed by XRD analysis.
► LiCoxMn1−xPO4/C samples were agglomerates with approximately 100 nm primary particles.
► The existence of Mn2+ enhanced the cycleability of LiCoxMn1−xPO4/C nanocomposite cathode.