Charge-clustering induced fast ion conduction in 2LiX-GaF3: A strategy for electrolyte design | Science Advances

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⁺ .