SU-102 Is a Versatile Anionic Quasi-Solid Electrolyte for Fast Li⁺, Na⁺, and Al³⁺Transport

Rapid and selective ion transport defines the effectiveness of quasi-solid-state electrolytes (QSSEs) in next-generation solid-state batteries. Although metal–organic frameworks (MOFs) hold promise in this sense due to their compositional variety, tunable porosity, and ability to host electrolytes in the pores while maintaining solid-state processability, MOF-based QSSEs exhibit lower ionic conductivity, transference numbers, and electrochemical stability than often expected. We envision enhancing these parameters by using anionic MOFs with mobile pore cations and diffuse anionic charges. In this study, we present a postsynthetic modification approach for the anionic MOF SU-102 ([(CH₃)₂NH₂]₂[Zr(HL)₂]; H₄L = ellagic acid), involving substitution of charge-balancing dimethylammonium with various single metal cations (SU-102-M; M = Li⁺, Na⁺, K⁺, Mg²⁺, Al³⁺). This modification yields solid electrolytes with Li⁺, Na⁺, and Al³⁺ conductivities that rival current top-performing materials (5.16 × 10^–4, 1.49 × 10^–3, and 7.14 × 10^–5 S/cm, respectively). These MOFs demonstrate high cation transference numbers for Li⁺ (0.899), Na⁺ (0.833), and Al³⁺ (0.706) as well as broad and stable operational potential windows spanning up to 4 V.