Motifs in an Amorphous Aluminum Oxychloride Solid-State Electrolyte (LAOC) from NMR Crystallography

Abstract

Noncrystalline solid-state electrolytes are attractive for solid-state batteries because they can combine compositional flexibility, processability, and intimate solid–solid contact, yet their atomic structures remain difficult to determine. The absence of long-range order limits diffraction-based methods, whereas solid-state nuclear magnetic resonance (NMR) is sensitive to local environments but often relies on empirical spectral assignments. Here, we show that a prototype aluminum oxychloride amorphous electrolyte contains recurring local motifs, revealed by a multinuclear NMR crystallography approach assisted by ab initio molecular dynamics and first-principles NMR calculation. The material demonstrates an ensemble of heterogeneous aluminum oxychloride networks, higher-coordinate aluminum regimes, proton-containing domains, framework-bound and weakly associated chloride species, and distributed lithium environments. These motifs encode the local chemistry experienced by mobile Li ions. This work provides a route to determine short-range order in noncrystalline ion conductors, linking amorphous structure determination to the rational design of solid-state battery materials.