Two Carboxyl-Decorated Anionic Metal–Organic Frameworks as Solid-State Electrolytes Exhibiting High Li+ and Zn2+ Conductivity

A highly electronegative carboxyl-decorated anionic metal-organic framework (MOF), (Me2NH2)2[In2(THBA)2](CH3CN)9(H2O)21 (InOF; H4THBA = [1,1':4',1″-terphenyl]-2',3,3″,5,5',5″-hexacarboxylic acid), with high-density electronegative functional sites was designed and constructed. One unit cell of InOF possesses 12 negative sites that originate from the negatively charged secondary building unit [In(COO)4]- and exposed carboxyl groups on the ligand. The abundant electronegative sites can facilitate the hopping of ions in channels and thus result in highly efficient ion conductivities for various metal ions. Our results show that Li+-loaded materials have a remarkably high ion conductivity of 1.49 × 10-3 S/cm, an ion transference number of 0.78, and a relatively low activation energy of 0.19 eV. The Na+, K+, and Zn2+ ion conductivities of InOF are 7.97 × 10-4, 7.69 × 10-4, and 1.22 × 10-3 S/cm at 25 °C, respectively.