A Single-Phase Mixed Ion-Electron Conducting Metal–Organic Framework

Mixed ionic-electronic conductors (MIECs) are highly sought after for electrochemical systems because they support concurrent charge and mass transport. Yet, structurally well-defined single-phase MIECs remain scarce, as most systems rely on physical mixtures of ionic and electronic conductors. Here, we introduce a cation-rich design strategy to realize solid-state mixed Li + -electronic conduction in a two-dimensional copper–catecholate metal–organic framework, Cu 3 (HOTAT) 2, built from the 3-fold symmetric new ligand 2,3,7,8,12,13-hexahydroxytriazatruxene (HHTAT). Owing to the combined redox activity of Cu 2+ /Cu + and the HOTAT ligand, controlled fractional reduction generates a family of Li x Cu 3 (HOTAT) 2 (0 ≤ x ≤ 7.50) phases with tunable transport properties, in good agreement with electronic-structure calculations. The Li-rich phase Li 7.50 Cu 3 (HOTAT) 2 exhibits intrinsic mixed conduction at room temperature, with an electronic conductivity of 2.8 × 10 –3 S cm –1, and solid-state Li + conductivity of 1.1 × 10 –3 S cm –1 . As a proof of concept, Li 7.50 Cu 3 (HOTAT) 2 operates as a homogeneous cathode in all-solid-state Li batteries, delivering 100 mAh g –1 after 100 cycles with ∼99.8% Coulombic efficiency, indicative of highly reversible electrochemical behavior. These results establish cation-rich reduction of redox-active 2D MOFs as an efficient route to engineer solid-state mixed Li + -electronic conductors, opening a pathway toward dual-conducting porous materials for solid-state electrochemical technologies.