Enhanced high-energy-density WO₃-based electrochromic batteries via acid-modified graphite foil cathode

In conventional tungsten oxide-based electrochromic batteries (ECBs), tungsten oxide acts as the cathode and Zn foil as the anode, but low redox potential leads to a limited discharge plateau, low areal capacitance, and power density, restricting practical applications. In this study, a novel WO₃||acid-modified graphite foil (WO₃||AGF) ECB was developed using AGF as the cathode, WO₃ as the anode, and a hybrid Zn²⁺/Al³⁺ electrolyte. The AGF offers advantages, such as high ion storage capacity, fast kinetics, and a high electrode potential, ensuring a high discharge voltage and capacity for the WO₃||AGF ECB. The prepared WO₃||AGF ECB not only exhibits excellent electrochromic performance but also demonstrates superior energy storage capabilities. At a charge/discharge current density of 0.5 mA·cm⁻², the WO₃||AGF ECB achieves a stable discharge capacity of 315.6 mAh·m⁻², which is 7.8 times higher than that of the traditional Zn||WO₃ ECB. Moreover, the rapid ion diffusion kinetics of the AGF ensure the cycling stability of the device at high voltages, maintaining 94.4% optical modulation after 8000 coloring/bleaching cycles. This work provides a novel approach by designing more compatible electrode material systems to achieve ECBs with high energy and power densities.