Properties of Ca-containing LiCoPO4-graphitic carbon foam composites

LiCo1 − x Ca x PO4–graphitic carbon foam composites are prepared using a sol–gel method. The structural analysis reveals LiCoPO4 as major crystalline phase and Co2P2O7 (for x = 0.0) and Co2P, Li3PO4, and (Ca,Co)3(PO4)2 (for x ≥ 0.05) as secondary phases. The morphology consists of microcrystalline “islands” with acicular crystallites (5–50 μm size). Transmission electron microscopy (TEM) of the powders showed that the Ca is incorporated into the crystal structure evoking exaggerated grain growth. The voltammetric profiles show a decrease of the voltammetric surface between anodic and cathodic sweeps and a shift of the reduction potentials toward higher values (∼4.6 V, x = 0.1). The electrochemical measurements, at a discharge rate of C/10 (room temperature), show an increase of the discharge-specific capacity from 100 mAhg−1 for x = 0.0 to 104 mAhg−1 for x = 0.1. The ac impedance spectroscopy data revealed an improvement of the Li-ion conductivity at high content of Ca ions (x = 0.1).