Exploring Carbonyl Chemistry in Non‐aqueous Mg Flow Batteries

Abstract

Non-aqueous redox flow batteries (RFBs) are emerging electrochemical technologies for grid energy storage. Non-aqueous Mg RFBs that use Mg metal as the anode are especially promising due to various benefits of the Mg metal anode, including its low potential, high volumetric capacity, SEI-free, highly reversible operation and low cost. Despite the potential, there are rarely any studies on developing non-aqueous Mg RFBs. Herein, a non-aqueous Mg redox flow battery using a polymer catholyte is reported. Through rational molecular engineering, a carbonyl-based moiety is combined with a polyethylene glycol moiety to achieve a polymer with high voltage and high solubility in the ether-based electrolyte. A series of polymers with different polyethylene glycol chain lengths are synthesized and their performances are measured first at the molecular level, and then at the device level in a Mg redox flow battery using a Mg foil as the anode, the polymer solution as the catholyte and a porous membrane as the separator. The flow battery delivers a voltage of 1.8 V, a maximum capacity of 475 mAh/ L, an average Coulombic efficiency of 90.5%, an average voltage efficiency of 67.4%, an energy efficiency of 61.0%, and an energy density of 0.855 Wh/L. Systematic mechanistic studies are performed to understand the performance decay mechanism and possible strategies for future improvement are discussed. This work opens a new avenue for the development of energy storage technologies for grid electricity storage.

Organic electrode materials and carbon/small-sulfur composites for affordable, lightweight and sustainable batteries

“…71–75 Since 2019, Luo et al have reported various linear and porous polymers as cathode materials for alkali-ion and multivalent metal batteries. 76–81 The results illustrate that developing organic salts and high-molecular-weight polymers can effectively overcome the high solubility challenge of organic batteries. Extended conjugation structures in OEMs enhance reaction kinetics and enable fast charging capability.…”

“…11a). 80,81 The polyimides were used as catholyte materials to couple with a Mg metal anode. Here, redox-active polymers rather than small organic molecules are used as catholyte materials in flow batteries because the large size of the polymers can mitigate the crossover of active materials through the membrane, which is a major challenge in redox-flow batteries.…”