High‐Performance Complementary Electrochromic Batteries using Nb ₁₈ W ₁₆ O ₉₃ by the Synergistic Effects of Aqueous Al ³⁺ /K ⁺ Dual‐Ion

Abstract Multivalent ions, especially Al 3+ 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 Nb 18 W 16 O 93 with open structure achieves Al 3+ intercalation/extraction reversibly. The complementary electrochromic energy storage devices based on Nb 18 W 16 O 93 coupled with Prussian blue using hybrid Al 3+ /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 3+ and K + selectively insert/extract in the electrode of Nb 18 W 16 O 93 and Prussian blue, respectively. This work provides an effective strategy for high‐performance and low‐cost electrochromic batteries with higher sustainability.