Investigation of the LiCo1−xMgxPO4 (0 ⩽ x ⩽ 0.1) system

LiCo1−xMgxPO4 (0 ⩽ x ⩽ 0.1) compounds are prepared by Pechini assisted sol–gel method coupled with the 2-steps annealing process (T = 300 °C for 5 min in flowing air, then at T = 730 °C for t = 12 h in flowing nitrogen). The XRD patterns show LiCoPO4 as major crystalline phase, Co2P and Co2P2O7 as secondary phases independently of the Mg-content. The morphology of the powders consists of a spongy-like structure with plate grains and coarse particles separated on the surface. The CV curves show a very good electrochemical reversibility with very close values of the mean peak maxima in the cathodic region, 4.4 V for x ⩽ 0.05 and 4.6 V for x = 0.1 respectively. The electrochemical measurements, at a discharge rate of C/10 at room temperature, show the increase of the discharge specific capacity from 61 mA h g−1 for x = 0.0–88 mA h g−1 for x = 0.025, then the decrease to 36 mA h g−1 for x = 0.1. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity at low Mg-ions content into the LiCoPO4 system (x = 0.025).