LiCoPO₄-based ternary composite thin-film electrode for lithium secondary battery

Lithium-excessive LiCoPO₄-based thin-film electrodes were fabricated by electrostatic spray deposition (ESD) technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) were used to analyze the structures and Co oxidation state of the electrodes. The electrochemical properties of these electrodes were evaluated by galvanostatic cell cycling. With an excess of lithium in the initial nominal compositions Li_1+xCoPO₄ (x = 0-1), a LiCoPO₄-Li₃PO₄-Co₃O₄ ternary composite was obtained after heat treatment. Li₃PO₄ and Co₃O₄ were introduced and homogeneously distributed in the LiCoPO₄ matrix. We have obtained distinct two-step feature of the voltage plateaus at 4.8 and 4.9 V, high specific capacity and excellent cycling performance for this "5 V"-electrode material. The presence of Co₃O₄ in the electrode can enhance its electronic conductivity and increase the capacity, while Li₃PO₄ can act as an electrolyte separation layer and improve the cycling performance of cells with electrolyte LiPF₆ (EC-DEC, 1:1 v/v).