Structural and transport properties of lithium alumino-phosphate glass solid electrolytes: A molecular dynamics study

Abstract

Lithium aluminophosphate glasses with the composition $50{\mathrm{Li}}_{2}O-x{\mathrm{Al}}_2{O}_3-(50-x)P_2{O}_5$, where x varies from 0 to 5 mol% studied using molecular dynamics simulations. We analyzed the structural and dynamical properties associated with the introduction of alumina and correlate them with the variation of conductivity. We uncovered how the environment of phosphorus and lithium is impacted by the introduction of aluminum. The bond length and coordination number of lithium-oxygen remain constant, and the distance lithium also does not change with compositions. For the phosphorus environment, changes are observed. At x=5%, the radial distribution function (RDF) of Phosphorus-Aluminum reveals the presence of one aluminum situated between two phosphorus atoms. The computed fraction of $P_m^{n^{\prime }}$ ($n^{\prime }$ and $m$ denoting the number of phosphorus and aluminum linked to phosphorus, respectively) shows an increase in $P_{1\mathrm{Al}}^2$ and $P_{1\mathrm{Al}}^1$. Aluminum is founded in a four-coordinated state, and the number of $P-O-\mathrm{Al}$ noticeably increases with aluminum, forming $\mathrm{Al}{\left(\mathrm{PO}\right)}_4$. The diffusion coefficient and conductivity at room temperature increase with the addition of alumina, indicating a change in the dynamics of atoms. This change could be explained by the environment change of lithium with the addition of aluminum.