Li-Ion Diffusion Correlations in LiAlGeO₄: Quasielastic Neutron Scattering and Ab Initio Simulation

Abstract

We investigated the impact of Li stoichiometry and host flexibility on Li+ diffusion processes in LiAlGeO4 at the microscopic level using quasielastic neutron scattering (QENS) and ab initio molecular dynamics (AIMD) simulations. Using sufficiently long AIMD trajectories, we could simulate the observed QENS signal and identify the localized dynamics of Li in crystalline LiAlGeO4. Such information is vital to identify the bottleneck of diffusion processes and design materials for battery application. Our AIMD simulations in LiAlGeO4 reveal that the Li+ conductivity can be significantly improved by manipulating the Li stoichiometry and/or host flexibility via amorphization. We determined that excess Li stoichiometry enhances the Coulomb repulsion of neighboring Li sites and softens the host structure to enable faster Li+ diffusion along the hexagonal c-axis. In the amorphous structure, random orientations of AlO4 and GeO4 polyhedral units create a wide distribution of intersite distances and significantly soften the host structure, greatly enhancing the Li+ diffusion. The simulations are used to understand the nature of diffusion, especially the role of the host structure, the possible hopping pathways, and the diffusion behavior in various structures of LiAlGeO4.

Multiscale modeling for enhanced battery health analysis: Pathways to longevity

“…DFT calculations indicated that organic Reproduced with permission: Copyright 2022, American Chemical Society. [80] | 355 ligand with multiple active sites had a higher theoretical capacity. Given that Co(II) possesses more electrons near the Fermi level compared to Ni(II), Co-OPCA demonstrates a higher electron density, allowing each structural unit to bind with more lithium ions, thereby enhancing lithium storage performance.…”

“…Utilizing AIMD to calculate the theoretical diffusion coefficients of materials plays a crucial role in assessing the material's influence on lifespan and constructing multiscale models. Kumar et al [ 80 ] employed AIMD simulations to investigate the diffusion of Li + in LiAlGeO 4 (LAGO) compounds under various engineering strategies, including crystalline, with vacancies, with excess Li (exc‐LAGO), and in amorphous structures. AIMD simulations provide a detailed microscopic understanding of the lithium diffusion process and the key structural and dynamic features associated with lithium diffusion.…”

“…(a) Trajectory of randomly selected Li atoms in exc‐LAGO at 1100 K; (b,c) Projection of Li trajectories in the ac and ab planes; (d) Anisotropic mean square displacements of Li atoms in exc‐LAGO calculated using AIMD at 1100 K. Reproduced with permission: Copyright 2022, American Chemical Society. [ 80 ]…”