Redox-active polymers: The magic key towards energy storage – a polymer design guideline progress in polymer science

Renewable organic batteries represent a valuable option to store sustainably generated energy and can play a major role in phasing out current carbon-based energy production. Several approaches have emerged over the last 80 years that utilize organic redox materials as active components in batteries. In particular, polymers have gained considerable interest among numerous research groups due to their (1) fast redox chemistry, in comparison to conventional active materials, (2) straight-forward syntheses, and (3) tunable solubility, which represent favored properties for diverse electronic devices. Notably, the beginning of redox-active polymers is linked to the discovery of conductive polymers by Heeger, MacDiarmid and Shirakawa in 1977. Nevertheless, redox-active polymers were studied in 1944 making them a familiar class under the broader polymeric framework, which celebrate its 100th birthday in 2020, based on the pioneering publication by Staudinger in 1920. Since their beginning, redox-active polymers have evolved from an interesting phenomenon into a family of promising, tailor-made, battery materials that also made their way to commercialization. In this regard, this review focusses on the design of interesting polymeric, redox-active materials. Polymerization techniques are discussed regarding novel polymer architectures and utilitarian properties. The polymer architectures are subsequently analyzed within the application scenarios of solid-state batteries, pseudo-capacitors, and redox-flow batteries. Redox moieties are compared and an overview of diverse synthetic aspects as well as battery concepts for the optimal assembly of polymeric battery materials are given.