Lattice Engineering of Niobium Tungsten Titanium Oxide Metamaterial Paired With Multi‐Ionic Electrolyte for High Performance Electrochromic Devices

ABSTRACT Multivalent‐ion‐based electrochromic devices have attracted considerable attention for their excellent coloration efficiency and optical modulation. However, they remain limited by slow switching speeds and insufficient cycling stability due to the strong interactions between multivalent ions and host materials. To address this, we report a niobium tungsten titanium oxide metamaterial (Nb 18 W 8 Ti 8 O 85 , NbWTO) as a high‐performance Ca 2+ ‐based electrochromic material. The introduction of Ti expands the lattice channels and enhances the electrical conductivity, facilitating rapid Ca 2+ diffusion and improving structural robustness. By integrating NbWTO with a Ca 2+ /K + hybrid electrolyte and a Prussian Blue (PB) ion storage layer, we construct a device where Ca 2+ primarily drives the NbWTO coloration while K + enables fast and reversible PB redox. This ion division of labor, along with enhanced conductivity of NbWTO and well‐matched charge capacity between NbWTO and PB, yields exceptional performance: high optical modulation of 76.4% at 633 nm, sub‐second coloration time of 0.5 s, high coloration efficiency of 191.1 cm 2 C −1 , and excellent cycling stability. Furthermore, a large‐area device (20 × 20 cm 2 ) demonstrates scalability. This work provides a holistic design strategy integrating lattice engineering and dual ion synergy for advanced multivalent ion electrochromic devices.