Smart Energy Storage: W₁₈O₄₉ NW/Ti₃C₂T_x Composite-Enabled All Solid State Flexible Electrochromic Supercapacitors

Developing a highly efficient electrochromic energy storage device with sufficient color fluctuation and significant electrochemical performance is highly desirable for practical energy-saving applications. Here, to achieve a highly stable material with a large electrochemical storage capacity, a W₁₈O₄₉ NW/Ti₃C₂T_x composite has been fabricated and deposited on a pre-assembled Ag and W₁₈O₄₉ NW conductive network by Langmuir-Blodgett technique. The resulting hybrid electrode composed of 15 layers of W₁₈O₄₉ NW/Ti₃C₂T_x composite exhibits an areal capacitance of 125 mF cm^-2, with a fast and reversible switching response. An optical modulation of 98.2% can be maintained at a current density of 5 mA cm^-2. Using this electrode, a bifunctional symmetric electrochromic supercapacitor device having an energy density of 10.26 µWh cm^-2 and a power density of 0.605 mW cm^-2 is fabricated, with high capacity retention and full columbic efficiency over 4000 charge-discharge cycles. Meanwhile, the device displays remarkable electrochromic characteristics, including fast switching time (5 s for coloring and 7 s for bleaching), and a significant coloration efficiency of 116 cm² C^-1 with good optical modulation stability. In addition, the device exhibits significant mechanical flexibility and fast switching while being stable over 100 bending cycles, which is promising for real-world applications.