Low self-discharge all-solid-state electrochromic asymmetric supercapacitors at wide temperature toward efficient energy storage

Abstract

Electrochromic asymmetric supercapacitors (EASs) have attracted tremendous attention in recent years because of their potential for next-generation civilian portable and intelligent electronics. However, obtaining all-solid-state EASs with low self-discharge rates and outstanding environmental compatibility remains a crucial challenge. Herein, a high-performance all-solid-state EAS was fabricated based on MnO2 positive electrochromic electrode and WO3 negative electrochromic electrode. The obtained EAS exhibits high power/energy density (991.2 W kg−1/117 Wh kg−1 and 15840 W kg−1/44.3 Wh kg−1), superior electrochemical cycle-life (remains 98.4% of its initial capacity after 2000 continuous cycles even at 60 °C). Significantly, the fabricated EAS can still maintain a stable and reversible color change even in harsh environments where operating temperatures are constantly changing from −20 °C to 60 °C. In addition, the underlying self-discharge process and mechanisms of EASs were comprehensively demonstrated at various temperatures. The diffusion-controlled mechanism dominates in the initial discharging process at high working temperatures (such as 60 °C), while both charge redistribution and diffusion-controlled mechanism contribute equally at lower operating temperatures (such as −20 °C). Impressively, the EAS presents a small voltage loss (all below 18%) within 10 h when operated at extreme temperatures. This work can enlighten and promote the development of low self-discharge electrochromic devices at widely operating temperatures for efficient energy storage.