Effect of Ca,Mg-ions on the properties of LiCo0.9M0.1PO4/graphitic carbon composites
By Dimesso, Lucangelo; Becker, Dirk; Spanheimer, Christina & Jaegermann, Wolfram
Published in Progress in Solid State Chemistry
2014
Abstract
LiCo0.9M0.1PO4 (M = Co2+, Mg2+, Ca2+)/graphitic carbon composites are synthesized by Pechini-assisted sol–gel process and annealed by the 2-steps annealing process (300 °C for 5 min in air, then at 730 °C for 12 h in nitrogen). The structural investigation, performed on powders, reveals the presence of LiCoPO4 as the major crystalline phase and of CoP2O7 (M = Co), of Co2P (M = Mg), of Co2P, Li3PO4, (Ca,Co)3(PO4)2 (M = Ca) as impurities. The morphological investigation of the composites shows the formation of crystalline “islands-likeâ€? structures with acicular crystallites with different dimensions (typically 5–50 μm) on the top of them. The voltammetric analysis shows a very good reversibility of the (de)intercalation processes and the presence of two mean peak maxima in the cathodic region at ∼5.01 V and ∼5.05 V respectively. The discharge specific capacities, at a discharge rate of C/10 and room temperature, were 100 mAh g-1 for M = Co, 68 mAh g-1 for M = Mg and 104 mAh g-1 for M = Ca respectively. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity in the Ca and Mg ions containing composites.