High-performance all-inorganic portable electrochromic Li-ion hybrid supercapacitors toward safe and smart energy storage

Li-ion hybrid supercapacitors (LHSs) bridged the gap between batteries and supercapacitors, and simultaneously attracted tremendous attention because of their potential applications in intelligent portable electronic devices. Nevertheless, obtaining all-inorganic LHSs with excellent environmental compatibility and smart display features remains a remarkable challenge. Herein, we designed and constructed a novel ultrathin all-inorganic electrochromic Li-ion hybrid supercapacitor (ELHS) by incorporating battery-type (LiMn₂O₄) and supercapacitor-type (WO₃) electrochromic materials into one cell. The resultant ELHS achieved stable and reversible chromatic transitions during the electrochemical process, providing sufficient real-time information on the working status. Benefiting from the matching potential windows of the individual active electrodes and the all-inorganic construction of the whole device, the optimized ELHS exhibited an extended working voltage of 2.5 V. Impressively, the ELHS demonstrated an ultrahigh volumetric energy/power density (16.2 W cm⁻³/0.21 Wh cm⁻³) and remarkable cycling stability with ~95.4% capacitance retention after 5000 cycles. The observed performance characteristics outperformed most previously reported electrochromic energy storage devices and were comparable to some commercial devices. Significantly, inorganic electrolytes were introduced into the ELHS, which endowed it with outstanding environmental adaptability and ability to work at progressively varying temperatures (0–75 °C). We envision that this work may open new avenues for the development of next-generation safe and portable hybrid energy storage devices.