A tetraphenylborate-based anionic metal-organic framework as a versatile solid electrolyte for fast Li, Na, K, Mg, Ca, and Zn transportation.

Tetraphenylborate (BPh ) has been widely employed in the field of electrolytes and displayed better ionic conductivities in polymer solid-state Li conductors. However, the fabrication of tetraphenylborate monomers into metal-organic frameworks (MOFs) and the exploration of their potential in solid-state electrolytes have never been reported. In this work, carboxylic acid functionalized lithium tetraphenylborate was purposefully synthesized and employed to construct an anionic MOF as a solid electrolyte. The counter cation Li was encapsulated into the anionic channel to become the free mobile charge carrier that produced a lithium-ion solid electrolyte with outstanding ion conductivity (2.75 × 10 S cm at 25 °C), an impressively high lithium-ion transference number ( = 0.89), and low activation energy (0.15 eV). Acting as a solid electrolyte, the anionic MOF-based lithium iron phosphate battery delivered an initial specific capacity of 135 mA h g and retained 95% capacity after 220 charge-discharge cycles with a coulombic efficiency close to 100%. Moreover, by exchanging the free Li with Na, K, Mg, Ca, and Zn, our anionic MOF is also available for other types of solid electrolytes with the corresponding conductivities all above that of the functional battery electrolyte. Our work provided a convenient and tunable route to prepare conducting MOFs for alkali metal ions, alkaline earth metal ions, and other possible metal cations of interest, which could be used in solid-state electrolytic devices in the future.