High‐Performance Complementary Electrochromic Batteries using Nb₁₈W₁₆O₉₃ by the Synergistic Effects of Aqueous Al³⁺/K⁺ Dual‐Ion

Multivalent ions, especially Al³⁺ 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 Nb₁₈W₁₆O₉₃ with open structure achieves Al³⁺ intercalation/extraction reversibly. The complementary electrochromic energy storage devices based on Nb₁₈W₁₆O₉₃ coupled with Prussian blue using hybrid Al³⁺/K⁺ aqueous electrolytes show a fast response, a high capacity and a large coloring efficiency. The superior performances are due to the cations of Al³⁺ and K⁺ selectively insert/extract in the electrode of Nb₁₈W₁₆O₉₃ and Prussian blue, respectively. This work provides an effective strategy for high-performance and low-cost electrochromic batteries with higher sustainability.