Thermally activated ionic conduction and local structure in solid LiPON thin films

Abstract

Compact lithium phosphorous oxynitride (LiPON) thin films, as a solid-state electrolyte for all solid-state Li batteries and electrochromic (EC) devices, with the high ratio of the triply coordinated –N< (Nt) over the doubly coordinated –N= (Nd) structural units was deposited by a conventional reactive RF magnetron sputtering of a Li3PO4 target at a low pure N2 pressure. The effect of heat treatment from 200 to 500 °C on the ionic conductivity and local structure of LiPON thin films were investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) core level analysis. A dramatical improvement of ionic conductivity from 1.1 to 3.28 μS/cm and microstructure changes were happened on the LiPON thin films while annealed for 1 h at 300 °C, which was linked to structural differences with a highest ratio of –N< over –N= structural units. The work proves that a proper heat treatment on LiPON thin film can effectively improve its ionic conductivity and change its microstructure.