Redox-Flow Batteries: From Metals to Organic Redox-Active Materials.

Research on redox-flow batteries (RFBs) is currently experiencing a significant upturn, stimulated by the growing need to store increasing quantities of sustainably generated electrical energy. RFBs are promising candidates for the creation of smart grids, particularly when combined with photovoltaics and wind farms. To achieve the goal of "green", safe, and cost-efficient energy storage, research has shifted from metal-based materials to organic active materials in recent years. This Review presents an overview of various flow-battery systems. Relevant studies concerning their history are discussed as well as their development over the last few years from the classical inorganic, to organic/inorganic, to RFBs with organic redox-active cathode and anode materials. Available technologies are analyzed in terms of their technical, economic, and environmental aspects; the advantages and limitations of these systems are also discussed. Further technological challenges and prospective research possibilities are highlighted.

Poly(TEMPO)/Zinc Hybrid-Flow Battery: A Novel, "Green," High Voltage, and Safe Energy Storage System.

The combination of a polymer-based 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) catholyte and a zinc anode, together with a cost-efficient size-exclusion membrane, builds a new type of semi-organic, "green," hybrid-flow battery, which features a high potential range of up to 2 V, high efficiencies, and a long life time.

Dithiophenedione-containing polymers for battery application.

Redox-active polymers have received recently significant interest as active materials in secondary organic batteries. We designed a redox-active monomer, namely 2-vinyl-4,8-dihydrobenzo[1,2-b:4,5-b']dithiophene-4,8-dione that exhibits two one-electron redox reactions and has a low molar mass, resulting in a high theoretical capacity of 217 mAh/g. The free radical polymerization of the monomer was optimized by variation of solvent and initiator. The electrochemical behavior of the obtained polymer was investigated using cyclic voltammetry. The utilization of lithium salts in the supporting electrolyte leads to a merging of the redox waves accompanied by a shift to higher redox potentials. Prototype batteries manufactured with 10 wt % polymer as active material exhibit full material activity at the first charge/discharge cycle. During the first 100 cycles, the capacity drops to 50%. Higher contents of polymer (up to 40 wt %) leads to a lower material activity. Furthermore, the battery system reveals a fast charge/discharge ability, allowing a maximum speed up to 10C (6 min) with only a negligible loss of capacity.