A Leap toward Quasi-Solid-State Chloride-Ion Batteries with Metal–Organic Frameworks

The development of solid-state electrolytes is a major focus in energy storage, offering improvements in both safety and performance. In chloride-ion batteries (CIBs), where electrode dissolution in liquid electrolytes remains a critical challenge, solid-state alternatives are especially attractive. Herein, we demonstrate for the first time the suitability of a metal–organic framework (MOF) as a quasi-solid-state single-ion electrolyte for CIBs. The cationic Al-based MOF MIP-213 ([Al₁₈(μ₂-OH)₂₄(OH₂)₁₂(mdip)₆]6Cl·6H₂O) exhibits a chloride ion conductivity of 1.1 × 10^–6 S cm^–1 at 25 °C, is nonflammable, electrochemically stable up to 4.2 V vs Li⁺/Li, and enables single-ion transport in a Li|MIP-213|FeOCl full cell over 100 cycles with Coulombic efficiency > 90%, while maintaining structural integrity. Although further optimization of the CIB components will be needed to enable cycling at higher current regimes and approach practical application, these findings establish MOFs as promising platforms for designing stable and efficient quasi-solid-state batteries.