Preparation and ion conduction of Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte films using radio frequency sputtering

Abstract

Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte films are successfully prepared on silicon substrates by radio frequency magnetron sputtering for the first time. X-ray diffraction, energy dispersive spectroscopy, and scanning electron microscopy are used to analyze the composition, structure, and morphology of the LAGP films, respectively. The effects of deposition conditions on the ion transport properties of the LAGP thin films are also evaluated via electrochemical impedance spectroscopy measurements. An evolution from a uniform and smooth amorphous structure to a coarse-grained structure of the surface morphology is observed for the films prepared at different temperatures. The results show that low growth temperature is beneficial to the formation of amorphous LAGP films with smooth surface and uniform thickness, and crystalline films with preferred orientation of (104) crystal plane are successfully deposited when the substrate temperature reaches 500 °C. The LAGP amorphous film with a thickness of 1.2 μm deposited at 200 °C exhibits a high ionic conductivity of 1.29 × 10−6 Scm−1. The ionic activation energy of the sample is determined to be 0.25 eV based on Arrhenius equation, indicating good ionic conductivity of the LAGP film. The good ionic conductivity of amorphous LAGP is attributed to its open and disordered structure with large excessive volumes.