A high-performance all-metallocene-based, non-aqueous redox flow battery

Abstract

Here, a class of organometallic compounds, metallocenes, are explored to serve as both catholyte and anolyte redox species for non-aqueous lithium-based redox flow battery (Li-RFB) applications. The prototype of all-metallocene-based Li-RFB exploits ferrocene (FeCp₂) and cobaltocene (CoCp₂) as the redox-active cathode and anode, respectively. The reaction rate constants of metallocenes are determined to be as high as 10⁻³ cm s⁻¹, two orders greater than most redox-active materials applied in conventional redox flow batteries. This designed Li-RFB yields a working potential of 1.7 V, and by introduction of methyl groups on the ligand rings of CoCp₂, the working potential can be further increased to 2.1 V. The fabricated full cell shows capacity retention of over 99% per cycle with a coulombic efficiency (CE) of >95% and an energy efficiency of >85%. These results demonstrate a generic design route towards high performance non-aqueous RFBs via rational screening and functionalization of metallocenes.