Smart current collector for high-energy-density and high-contrast electrochromic supercapacitors toward intelligent and wearable power application

Integrating electrochromism and energy storage into supercapacitor is highly desirable for the development of intelligent and wearable sustainable power system and electronics. However, simultaneous realization of high energy storage and high electrochromic performances remains a major challenge in electrochromic energy storage due to their inherent contradiction in transmissive-type device designs. Herein we demonstrate a smart current collector (SCC) strategy for simultaneously realizing a high energy density and a high electrochromic contrast in supercapacitors. SCC is designed by sandwiching an electrochromic polypyrrole layer between transparent substrate and porous Ag reflective layer, which possesses high reflective-type electrochromic performances, excellent conductivity and enables a high-mass loading of active energy storage material without sacrificing good ion access to electrochromic layer. While achieving high electrochromic-contrast performances at a high mass loading of active material, the electrochromic supercapacitor based on SCC can deliver a high energy density of 112.2 μWh cm−2, significantly outperforming the reported electrochromic supercapacitors to date. Moreover, SCC design perfectly suits for wearable power supply application as it is hardly affected by the wearable-background lightness. The delicate design of current collector in this work provides a new technology for developing high-performance intelligent wearable electrochemical energy storage devices toward real applications.