Ab initio calculations for crystalline PEO6:LiPF6 polymer electrolytes

Dry polymer electrolytes have been studied extensively because of their enhanced mechanical properties. Experimental studies have demonstrated that crystalline PEO6 LiPF6 has higher ionic conductivity than that of the amorphous phase, which seemingly contradicts the prevailing theory that amorphous polymer electrolytes have higher conduction performance. Also, the underlying mechanism at the atomic scale has remained elusive. In this work, the atomic and electronic structures of crystalline PEO6 LiPF6 are studied using ab initio density-functional theory. The results agree with experimental measurements. Additionally, the atomic-scale mechanisms of lithium ion transport in the polymer electrolytes are investigated with the climbing nudged elastic band method. The diffusion pathway and activation energy (similar to 0.87 eV) of lithium ions in crystalline PEO6 LiPF6 are determined.