High-Performance Complementary Electrochromic Batteries using NbWO by the Synergistic Effects of Aqueous Al/K Dual-Ion.

Multivalent ions, especially Al in aqueous electrolyte contributes to higher capacity and color contrast for more sustainable post-lithium electrochromism and energy storages. However, the lack of suitable cathodic and anodic electrochromic materials is a major challenge for Al-ion electrochromic batteries, which limits their optical contrast and lifespan. Herein, we report that Wadsley-Roth phase NbWO with open structure achieves Al intercalation/extraction reversibly. The complementary electrochromic energy storage devices based on NbWO coupled with Prussian blue using hybrid Al/K aqueous electrolytes show a fast response, a high capacity and a large coloring efficiency. The superior performances are due to the cations of Al and K selectively insert/extract in the electrode of NbWO and Prussian blue, respectively. This work provides an effective strategy for high-performance and low-cost electrochromic batteries with higher sustainability.