Revealing cooperative Li-ion migration in Li1+xAlxTi2-x(PO4)3 solid state electrolyte with high Al doping
Li1+xAlxTi2-x(PO4)3 (LATP) is attracting attention as a promising inorganic solid electrolyte (ISE) with potential use in all-solid-state lithium-ion batteries. The objective of this paper is to examine and understand the effect of the Al-dopant concentration on the Li-ion diffusion of LATP using density functional theory and molecular dynamics method. By comparing Li1.16Al0.16Ti1.84(PO4)3 (LATP-0.16) and Li1.33Al0.33Ti1.67(PO4)3 (LATP-0.33) with Li1.5Al0.5Ti1.5(PO4)3 (LATP-0.50), LATP-0.50 is expected to have higher ionic conductivity. The trapping effect of Al-dopants on Li-ions is greatly reduced in LATP-0.50 due to the delocalization of polarization interactions and the depopulation of oxygen atoms, which results in a smooth energy landscape and destabilization of Li-ions. The energy difference of adjacent Li-ions and binding interaction of Li-Li due to specific local two Li-ions’ configuration alternately enable Li-ions’ cooperative migration. This understanding of high Li-ion diffusion is important in interpreting experimental results aiming to assess the effects of Al-dopant in Li-ion conductivity and can be used by researchers to engineer this material for batteries.