First principles calculation of Li2+2xZn1-xSiO4 (x = 0.125–0.5) as solid electrolyte for lithium-ion battery

Li2ZnSiO4 has the structural characteristics of superionic conductor for Li, but the actual measured Li conductivity is not high. Based on first-principles calculations, the Li diffusion properties of varied configurations are studied, in which Li replaces Zn with different concentrations. Particularly, topological analysis is used to obtain the possible Li interstitial sites of Li2ZnSiO4. These interstitial sites can accommodate more lithium ions and increase the concentration of lithium ions. The Li ion conductivity of the Li-doped Li2+2xZn1-xSiO4 with increased lattice Li and interstitial Li is improved dramatically. When x = 0.375, the Li ion conductivity reaches 2.006 mS/cm and the Ehull is 23 meV/atom. The mean square deviation (MSD) and probability density indicate that Li2+2xZn1-xSiO4 (x = 0.125–0.5) is a three-dimensional Li conductor. In addition, the calculation of energy band structures shows the bandgap width of 5.7 eV and 5.8 eV for Li2ZnSiO4 and Li2.5Zn0.75Si4, respectively, indicating that these materials are poor conductors of electron. These characteristics (fast Li diffusion, good phase stability, and poor electronic conductivity) make Li-doped Li2ZnSiO4 one promising solid electrolyte for solid-state Li-ion batteries.