Anionic Metal–Organic Framework as an Ultrafast Single-Ion Conductor for Exceptional Performance Rechargeable Zinc Batteries

Anionic metal–organic frameworks (MOFs) are promising single-ion conductive electrolytes in quasi-solid-state batteries. Herein, we propose an anionic MOF as a promising single Zn²⁺ conductor for high-performance quasi-solid-state zinc-ion battery (ZIB). The anionic MOF is synthesized by reacting carboxylic acid functionalized tetraphenylborate with a Zr₆-oxo cluster, which displays outstanding ionic conductivity (0.83 mS cm^–1 at −40 °C, 2.75 mS cm^–1 at 25 °C, and 7.9 mS cm^–1 at 120 °C), an impressive Zn²⁺ transference number (t_Zn²⁺ = 0.90), low activation energy (0.19 eV), good interfacial compatibility, and excellent rate performance. The fabricated quasi-solid-state ZIB using NH₄V₄O₁₀ cathode delivers a remarkable capacity of 497 mAh g^–1 at 0.3 A g^–1 under ambient conditions and can maintain capacities of 420, 350, and 270 mAh g^–1 at elevated current densities of 1, 5, and 10 A g^–1 with both capacities and Coulombic efficiency retention at 100% after 2500 cycles. Even at a low temperature of −40 °C or with a high current density of 100 A g^–1, excellent reversible capacities and rate performance can still be achieved. This work set up a new direction for designing and developing anionic porous materials as advanced solid electrolytes for zinc and/or other secondary batteries.