Solution-processable, hypercrosslinked polymer via post-crosslinking for electrochromic supercapacitor with outstanding electrochemical stability

Electrochromic supercapacitor (SC) have great research significance on the exploration of smart energy storage device. Conjugated polymer (CP) as a promising electrode material for electrochromic SC, has advantages of low price, structural controllability, ease of processing, and excellent flexibility. However, low mechanical stability and limit cycle life constraint the performance of conducting polymer in SC. Herein, we have designed and synthesized a carbazole based polymer PCBDTP with the side chain terminal linked with vinyl groups, which can simply be solution processed to form a thin film and subsequently undergo thermal cross-linking to provide a stable and cross-linked polymer (PCBDTP-X) network. An asymmetric supercapacitor (ASC) fabricated with PCBDTP-X as the positive electrode material, exhibited outstanding electrochemical stability and electrochromic behavior, resulting in a smart energy storage device in which its energy storage level can be visualized through the color change. The PCBDTP-X//PEDOT electrochromic ASC with PMMA-based solid electrolyte yielded maximum energy density of 18.4 W h kg(-1), across a wide potential window of 2.4 V. More importantly, the capacitance could still retain above 99.1% of the initial value after 5000 charging/discharging cycles, which indicated its outstanding cyclic stability. Meanwhile, the device exhibited high optical contrast at the wavelength of 480 nm with a noticeable and reversible color change from yellow-brown (discharged state) to gray-blue (charged state). In summary, we present here a new strategy to design the conjugated polymer with outstanding electrochemical stability and superior performance for electrochromic supercapacitor as next-generation smart energy storage device.