Charge-clustering induced fast ion conduction in 2LiX-GaF 3 : A strategy for electrolyte design.

2LiX-GaF 3 (X = Cl, Br, I) electrolytes offer favorable features for solid-state batteries: mechanical pliability and high conductivities. However, understanding the origin of fast ion transport in 2LiX-GaF 3 has been challenging. The ionic conductivity order of 2LiCl-GaF 3 (3.20 mS/cm) > 2LiBr-GaF 3 (0.84 mS/cm) > 2LiI-GaF 3 (0.03 mS/cm) contradicts binary LiCl (10 -12 S/cm) < LiBr (10 -10 S/cm) < LiI (10 -7 S/cm). Using multinuclear 7 Li, 71 Ga, 19 F solid-state nuclear magnetic resonance and density functional theory simulations, we found that Ga(F,X) n polyanions boost Li + -ion transport by weakening Li + -X - interactions via charge clustering. In 2LiBr-GaF 3 and 2LiI-GaF 3 , Ga-X coordination is reduced with decreased F participation, compared to 2LiCl-GaF 3 . These insights will inform electrolyte design based on charge clustering, applicable to various ion conductors. This strategy could prove effective for producing highly conductive multivalent cation conductors such as Ca 2+ and Mg 2+ , as charge clustering of carboxylates in proteins is found to decrease their binding to Ca 2+ and Mg 2+ .