Single-Ion\nLi⁺, Na⁺, and Mg²⁺ Solid Electrolytes\nSupported by a Mesoporous Anionic Cu–Azolate\nMetal–Organic Framework

Abstract

A novel Cu­(II)–azolate\nmetal–organic framework (MOF)\nwith tubular pores undergoes a reversible single crystal to single\ncrystal transition between neutral and anionic phases upon reaction\nwith stoichiometric amounts of halide or pseudohalide salts. The stoichiometric\ntransformation between the two phases allows loading of record amounts\nof charge-balancing Li⁺, Na⁺, and Mg²⁺ ions for MOFs. Whereas the halide/pseudohalide anions are bound\nto the metal centers and thus stationary, the cations move freely\nwithin the one-dimensional pores, giving rise to single-ion solid\nelectrolytes. The respective Li⁺-, Na⁺-, and\nMg²⁺-loaded materials exhibit high ionic conductivity values\nof 4.4 × 10^–5, 1.8 × 10^–5, and 8.8 × 10^–7 S/cm. With addition of LiBF₄, the Li⁺ conductivity improves to 4.8 × 10^–4 S/cm. These are the highest values yet observed for\nMOF solid electrolytes.