Ionic crosslinked polymer as protective layer in electrochromic supercapacitors for improved electrochemical stability and ion transmission performance

Abstract Electrochromic supercapacitors (ESCs) have received widespread attention as an emerging smart energy device. Apart from the electrochromic and electrochemical performances, the main obstacle faced by many ESCs is the poor cyclic stability due to the unstable interfacial properties and vulnerable film morphology. Some previous strategies, such as constructing composite or forming crosslinking, may have problems in solubility and ion transport. We present here a strategy of employing solution-processable crosslinked polymer as a protective layer between the electrode and electrolyte. Benefiting from its porous structure and ionic crosslinking structure, the protective layer can greatly improve the stability and ion transport performance. Three crosslinked polymers with different counter anions have been synthesized and employed as the protective layer on WO3 electrode. The influences of different counter anions and processing conditions on cyclic stability and electrochemical performance have been investigated in details. Results indicated that introduction of the crosslinked protective layer not only could greatly improve the electrochemical stability, but also show an obvious increase on the electrochemical property, that is, activation could be observed. The protective layer based on the crosslinked polymer with TFSI− as the counter anion showed the outstanding stable capacitance rising trend, with a capacitance of 136% could be obtained after 2000 cycles and 193% more than that of WO3 electrode after 600 cycles under a scan rate of 100 mV/s. And it also had the best ion transmission performance, and the ion diffusion resistance was only 30% of the WO3 electrode.