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.

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.

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.

A poly(TEMPO methacrylate)-poly(styrene) block copolymer was utilised as catholyte in polymer/zinc hybrid flow batteries.

both large-and small-scale energy storage, ranging from large pumped hydroelectric storage to very small battery cells for handheld devices.Secondary batteries are among the more promising energy storage technologies, with a wide range of applications. [4] Since the development of the lead acid battery in the second half of the 19th century (Gaston Planté, 1860), a broad range of batteries has been invented. [5] Notable examples are the nickel/cadmium cell (1899) [6] and the lithium-ion battery, which was developed in the 1970s. [7] Today, batteries are omnipresent in the everyday lives of a large part of the world's population. They find application in numerous fields, ranging from handheld or portable devices to electric vehicles (including vehicles with combustion engines) to large-scale energy storage for renewable sources. [8] Each field has unique requirements for the applied batteries, therefore different battery types have been developed to meet the demands.The most dominant type of secondary batteries for modern devices is the lithium-ion battery. Lithium-ion batteries possess high energy densities, good rate capabilities, and a long cycle life. Since their commercialization in 1991, they have been applied in many portable devices, electric vehicles and even in large-scale energy storage systems. [7] Since 2000, the share of the worldwide produced lithium for application in batteries (35% of the total production in 2015) has increased by 20% per year. [9] Another, less known battery type is the redox-flow battery (RFB). With their independent scalability of capacity and power, they are in particular interesting for large-scale storage of renewable energy with regard to grid stability. [10] A recent, so far not commercially available type of batteries is the organic battery. Here, an organic compound (small molecule or polymer) is responsible for charge storage. Organic batteries offer high rate capabilities, cheap starting materials, and are less environmentally challenging compared to metalbased batteries. Possible fields of application are small, lightweight, and easily recyclable products. [11] None of the above-mentioned batteries would work without polymers. Polymers can be found in the electrodes, where they act as binders, ensuring a good adhesion and contact among the different materials. Furthermore, many membranes are based on polymers. Here, the macromolecules have to be ionconducting as well as mechanically and chemically robust. In addition, organic batteries rely on polymeric active materials. This review discusses the diverse possibilities polymers haveIn the light of an ever-increasing energy demand, the rising number of portable applications, the growing market of electric vehicles, and the necessity to store energy from renewable sources on large scale, there is an urgent need for suitable energy storage systems. In most batteries, the energy is stored by exploiting metals or metal-ion-based reactions. However, nearly every modern battery would not function without the help of polymer...