Investigation of the LiCo1−xMgxPO4 (0 ≤ x ≤ 0.1)–graphitic carbon foam composites

Abstract

LiCo1−xMgxPO4–graphitic carbon foam (LCMP–GCF with 0 ≤ x ≤ 0.1) composites are prepared by Pechini-assisted sol-gel method and annealed 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 analysis, performed on powders reveals LiCoPO4 as major crystalline phase, Co2P and Co2P2O7 as secondary phases. The morphological investigation revealed the formation and growth of microcrystalline “islands” which consist of acicular crystallites with different dimensions (typically 5–50 μm). By addition of Mg-ions, CV-curves of LCMP–GCF composites show a decrease of the surface between anodic and cathodic sweeps by cycling and a stark contribution of faradaic processes due to the graphitic structured foam. The electrochemical measurements, at a discharge rate of C/10 at room temperature, show the decrease of the discharge specific capacity from 100mAhg−1 for x = 0.0 to ∼35mAhg−1 for 0.025 ≤ x ≤ 0.05, then an increase to 69mAhg−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 high Mg-ions content into the LiCoPO4 phase (x ≥ 0.025).