Improved ion conductivity and interface characteristics of the Te-doped solid NASICON electrolyte Li1.5Al0.5Ge1.5(PO4)3 with graphite coating

Solid Te-doped Li1.5Al0.5TexGe1.5-x(PO4)3 (LATGP) electrolyte materials are successfully prepared by the sol-gel method. The structure, morphology, and ionic and electronic conductivities of samples with different doping concentrations are analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and DC polarization. The results reveal that Te doping can effectively promote the ionic conductivity of LAGP material, reaching a value of 6.33 × 10−4 S cm−1 at room temperature for Li1.5Al0.5Te0.06Ge1.44(PO4)3. Then, LATGP sheets are coated with graphite (G) by the magnetron sputtering method to improve the interfacial characteristics between the Li metal and LAGP electrolyte at high current densities. The polarization voltage curves of the symmetric graphite-modified Li/G@LATGP@G/Li cells remain stable after 800 h at high current densities of 0.5 mA cm−2 and 1 mA cm−2. The solid-state Li/G@LATGP/LiFePO4 full cell presents an initial specific discharge capacity of 154.4 mAh·g−1 at a current density of 0.1 mA cm−2 as well as a capacity retention of 87.8% after 100 cycles. These results indicate that Te doping combined with graphite surface coating can effectively improve the ion transport and interfacial characteristics of solid LAGP electrolyte.