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

Abstract

This work demonstrates the first successful electrochemical cycling of a redox-active boron cluster-based material in the solid state. Specifically, we designed and synthesized an ether-functionalized dodecaborate cluster, B12(OCH3)12, which is the smallest redox-active building block in the B12(OR)12 family. This species can reversibly access four oxidation states in solution, ranging from a dianion to a radical cation. We show that a chemically isolated and characterized neutral [B12(OCH3)12]0 cluster can be utilized as a cathode active material in a PEO-based rechargeable all-solid-state cell with a lithium metal anode. The cell exhibits an impressive active material utilization close to 95% at C/20 rate, a high Coulombic efficiency of 96%, and excellent reversibility, with only 4% capacity fade after 16 days of cycling. This work represents a conceptual departure in the development of redox-active components for electrochemical storage and serves as an entry point to a broader class of borane-based materials.

Redox-Active Boron Clusters

“…We developed a microwaveassisted synthesis of this cluster using trimethyl sulfonium bromide as a methylating reagent, followed by an aqueous Ce(IV) oxidation (Figure 7A). Surprisingly, when a model solid-state Li-ion cell was constructed with [B 12 (OCH 3 ) 12 ] 0 as the active cathode material in a poly(ethylene oxide) (PEO) matrix (Figure 7B) and cycled at 60 °C, a reversible one-electron event was observed in the solid-state cyclic voltammogram at 3.45 V vs Li + /Li, which we attributed to the [B 12 (OCH 3 ) 12 ] 0 /[B 12 (OCH 3 ) 12 ] 1− redox couple 4 (Figure 7C). This work represents the first example of a boron cluster undergoing reversible redox in the solid state, and the high Coulombic efficiency and cycling stability (Figure 7D) further support this new approach to utilizing these clusters for energy storage applications.…”

“…, 14345−14353. 4 Our report on the unprecedented ability of a B 12 (OMe) 12 cluster to reversibly undergo redox transitions in the solid state.…”