High-performance electrochromic aqueous batteries enabled by Li₄Ti₅O₁₂ anodes: Bridging Electrochromism and efficient...

Electrochromic aqueous batteries (EABs) have shown immense potential in different fields like energy-saving architectures and wearable systems with visible energy levels. However, due to the mismatch in electrode redox potentials and incompatibility of electrochromic materials with aqueous electrolytes, current EABs often display unsatisfied electrochromic behavior and poor energy storage function. Here, we report the use of Li₄Ti₅O₁₂ (LTO), which exhibits low redox potential and stable cycling in a sucrose-rich ammonium-ion-based electrolyte, as an efficient EAB anode for the first time. Using Prussian blue (PB) as the cathode, the complementary EAB not only show excellent electrochromic metrics like long cycling stability (10,000 cycles), high optical contrast(73.3 %), uniform coloring at large size (10 cm × 10 cm) and fast switching speed (5.99 s/1.87 s for coloring/bleaching), but also exhibits good battery characteristics like high energy density/power density (63.21 mWh m^-2/1042 mW m^-2) high energy efficiency (74.86 %) and high average voltage (1.04 V). Mechanistic studies reveal that the complementary structure and the reversible interactions of NH₄⁺ ions with the robust electrodes give rise to the remarkable electrochromic performances. The outstanding energy storage behavior can be attributed to the large redox potential difference between LTO and PB and the stable sucrose-rich electrolyte under high voltage. This work establishes a design paradigm for developing high-performance complementary EABs, offering dual functionalities for applications ranging from smart windows to self-display energy devices.