This review covers recent advances in conjugated polymers and their application in energy storage. Conjugated polymers are promising cost-effective, lightweight, and flexible electrode materials. The operating principles of conjugated polymers are presented within the framework of their potential for energy storage. Special focus is given to polyaniline electrodes. Recent advances are reviewed including new methods of synthesis, nanostructuring, and assembly. Also, covered are applications that take full advantage of the mechanical properties of conjugated polymers and future applications of these novel materials.

Conjugated polymers, such as polyaniline, have been widely explored as sensors, electrodes, and conductive fillers. As an electrode material in electrochemical energy storage systems, polyaniline can be subject to irreversible oxidation that reduces cycle life and electrode capacity, thus, limiting its widespread application. Here we present a simple route to produce and prepare polyaniline-based electrodes that are oxidatively stable up to 4.5 V vs. Li/Li(+). The route uses a polyacid to stabilize the fully oxidized pernigraniline salt form of polyaniline, which is normally highly unstable as a homopolymer. The result is an organic electrode of exceptionally high capacity, energy density, power density, and cycle life. We demonstrate that the polyaniline:polyacid electrode stores 230 mA h g(-1) of polyaniline for over 800 cycles, far surpassing homopolymer polyaniline under equivalent conditions. This approach provides a highly stable, electrochemically reversible replacement for conventional polyaniline.

Polymers have a particularly important place in electrochemical energy storage (EES), not just as the electrolyte, as has been a large focus for solidstate batteries, but also as the electrode. This Viewpoint will introduce how electrochemically active polymers (EAPs) are utilized in electrochemical energy storage with an emphasis on battery cathodes. Recent advances in high capacity EAPs and selected challenges (high voltage stability and ion transport) are presented. Should these needs be met, the resulting electrode would bear a high capacity, energy, power, and cycle life. The low cost, potential application in flexible EES, and synthetic versatility of EAPs offer many unique aspects relative to conventional metal oxides. In composites with metal oxides, EAPs can be used as a means to boost ionic and electronic conductivity. Promising examples regarding high capacity polymeric sulfur electrodes, electrochemically stable polyaniline/ polyacid complexes, porous polyaniline/V 2 O 5 electrodes, and hydrogel-based electrodes are highlighted.

Mechanically robust battery electrodes are desired for applications in wearable devices, flexible displays, and structural energy and power. In this regard, the challenge is to balance mechanical and electrochemical properties in materials that are inherently brittle. Here, we demonstrate a unique water-based self-assembly approach that incorporates a diblock copolymer bearing electron- and ion-conducting blocks, poly(3-hexylthiophene)-block-poly(ethyleneoxide) (P3HT-b-PEO), with V2O5 to form a flexible, tough, carbon-free hybrid battery cathode. V2O5 is a promising lithium intercalation material, but it remains limited by its poor conductivity and mechanical properties. Our approach leads to a unique electrode structure consisting of interlocking V2O5 layers glued together with micellar aggregates of P3HT-b-PEO, which results in robust mechanical properties, far exceeding the those obtained from conventional fluoropolymer binders. Only 5 wt % polymer is required to triple the flexibility of V2O5, and electrodes comprised of 10 wt % polymer have unusually high toughness (293 kJ/m3) and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes. Furthermore, addition of P3HT-b-PEO enhances lithium-ion diffusion, eliminates cracking during cycling, and boosts cyclability relative to V2O5 alone. These results highlight the importance of tradeoffs between mechanical and electrochemical performance, where polymer content can be used to tune both aspects.

2,6-Disubstituted benzobisoxazoles have been synthesized by a highly efficient reaction of diaminobenzene diols with various orthoesters. The scope of this new reaction for the synthesis of substituted benzobisoxazoles has been investigated using four different orthoesters. The utility of these compounds as building blocks for the synthesis of conjugated polymers is demonstrated.