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

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.