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+).