For renewable energy sources such as solar, wind, and hydroelectric to be effectively used in the grid of the future, flexible and scalable energy-storage solutions are necessary to mitigate output fluctuations. Redox-flow batteries (RFBs) were first built in the 1940s and are considered a promising large-scale energy-storage technology. A limited number of redox-active materials--mainly metal salts, corrosive halogens, and low-molar-mass organic compounds--have been investigated as active materials, and only a few membrane materials, such as Nafion, have been considered for RFBs. However, for systems that are intended for both domestic and large-scale use, safety and cost must be taken into account as well as energy density and capacity, particularly regarding long-term access to metal resources, which places limits on the lithium-ion-based and vanadium-based RFB development. Here we describe an affordable, safe, and scalable battery system, which uses organic polymers as the charge-storage material in combination with inexpensive dialysis membranes, which separate the anode and the cathode by the retention of the non-metallic, active (macro-molecular) species, and an aqueous sodium chloride solution as the electrolyte. This water- and polymer-based RFB has an energy density of 10 watt hours per litre, current densities of up to 100 milliamperes per square centimetre, and stable long-term cycling capability. The polymer-based RFB we present uses an environmentally benign sodium chloride solution and cheap, commercially available filter membranes instead of highly corrosive acid electrolytes and expensive membrane materials.

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.

Electricity users expect energy on demand. This poses a problem for renewables, such as solar, wind or hydroelectric, as the supply is naturally intermittent. Building scalable and inexpensive energy storage is the answer, and here we describe a new rechargeable battery system that uses salt solutions of organic polymers and a cheap filter membrane.

Water-soluble polymers for application in polymer-based redox-flow batteries (pRFB) were synthesized and their properties were studied in detail.

The utilization of boron-dipyrromethene (BODIPY) as active group for the charge storage process in a battery application is reported. Two BODIPY-containing copolymers were synthesized and electrochemically characterized. The polymers feature redox processes at 0.7 V and −1.5 V vs AgNO3/Ag, which enable the application in a redox-flow battery setup.