Enhancing Performance Stability of Electrochemically Active Polymers by Vapor‐Deposited Organic Networks

Abstract

Performance stability of electrochemically active polymers (EAPs) remains one of the greatest and long-standing challenges with regard to EAP-based technologies for a myriad of energy, biomedical, and environmental applications. The performance instability of EAPs originates from their structural alteration under repeated charge-discharge cycling and/or flexing. In this work, a conceptually new "soft confinement" strategy to enhance EAP performance stability, including cyclic and mechanical, by using rationally designed, vapor-deposited organic networks is presented. These chemically cross-linked networks, when in contact with an electrolyte solution, turn into ultrathin, elastic hydrogel coatings that encapsulate conformally the EAP micro-/nanostructures. Such hydrogel coatings allow easy passage of ions that intercalate with EAPs, while simultaneously mitigating the structural pulverization of the EAPs and/or their detachment from substrates. Fundamentally distinct from extensively studied "scaffolding" or "synthetic" approaches to stabilizing EAPs, this soft confinement strategy relies on a postmodification step completely decoupled from the EAP synthesis/fabrication, and enjoys the unique advantage of substrate-independency. Hence, this strategy is broadly applicable to various types of EAPs. The proposed stability enhancement strategy is demonstrated to be effective for a range of EAP systems with differing chemical and morphological characteristics under various testing conditions (repeated charging/discharging, bending, and twisting). electronic devices. [14][15][16] Possible mecha nisms causing the cycling instability of EAPs include structural pulverization due to repeated swelling and shrinkage of polymer backbones, and collapse of initially present ion channels resulting in difficulty of subsequent redoping. [14,[17][18][19][20] A widely adopted approach to enhancing EAP stability is integration of the EAPs with conductive scaffolds, such as porous graphite foams, [21] carbon nanotube sponges, [22] nickel foams, [23] and partially exfoliated graphite. [18] These scaffolds are usually porous and dimensionally stable, and thus act as robust supports for EAP films to reduce their structural alteration. Such a "scaffolding" approach relies on effective hybridization of the EAP with the underlying conductive substrate, a non trivial task. The integration process often requires judicious surface modification of the scaffold materials to create specific interactions (e.g., covalent bonding, π-π stacking) with the EAP, and a lengthy screening process to determine the reac tion conditions for the growth of a certain EAP on the scaffold. A few less common methods based on deliberate synthetic strategies for improving EAP stability have also been dem onstrated, such as creation of supramolecular structures, [24] synthesis of hyperbranched EAPs, [25] and dopant/EAP engi neering. [26,27] These scaffolding and synthetic approaches have shown great promise when applied to certain types of EAP sys tems, but are highly...

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