Coordination Li diffusion chemistry in NASICON Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte

The NASICON Al-doped LiGe2(PO4)3 (Li1.5Al0.5Ge1.5(PO4)3: LAGP) is one of the promising solid electrolytes that is intensively optimized in solid-state Li-ion batteries. However, its underlying fast Li-ion diffusion kinetic has not been fully understood yet. In this context, density functional theory (DFT) calculations were performed to comprehend the Li-ion migration behaviors in LAGP, especially under the emergence of metastable interstitial sites by the doped Al-ions to transform the Li-ion migration to an interlaced interstitial and multi-ionic concerted hopping mechanisms. The sluggish lattice 6b Li-ion are driven to accelerate and itinerate by the strong Coulombic repulsion of 36f Li-ions in the LAGP lattice. Moreover, the Li-ion migration energy barrier further decreases for the LAGP with Li/Al antisite, which, however, could also deteriorate the conducting performance with the amount increasing to a critical value. These important findings uncover the regulation of metastable sites in the inter-connected channels that is crucial for outstanding Li-ion conductors and may shed light on future design of high-performance solid electrolyte for solid state batteries