Electrochemical Cycling of Redox-Active Boron Cluster-Based Materials in the Solid State

This work demonstrates the first successful electrochemicalcyclingof a redox-active boron cluster-based material in the solid state.Specifically, we designed and synthesized an ether-functionalizeddodecaborate cluster, B-12(OCH3)(12), which is the smallest redox-active building block in the B-12(OR)(12) family. This species can reversibly accessfour oxidation states in solution, ranging from a dianion to a radicalcation. We show that a chemically isolated and characterized neutral[B-12(OCH3)(12)](0) clustercan be utilized as a cathode active material in a PEO-based rechargeableall-solid-state cell with a lithium metal anode. The cell exhibitsan impressive active material utilization close to 95% at C/20 rate,a high Coulombic efficiency of 96%, and reversibility, with only 4%capacity fade after 16 days of cycling. This work represents a conceptualdeparture in the development of redox-active components for electrochemicalstorage and serves as an entry point to a broader class of borane-basedmaterials.