High‐Performance Electrochromic Energy Storage Devices Based on WO₃ Nanoflower Via In Situ Intercalation With Polyaniline

Abstract Structural design and interlayer architecture of electrochromic (EC) materials play significant role in their performance. Herein, tungsten trioxide (WO₃) nanoflowers have been synthesized through in situ intercalation with polyaniline (PANI), developing a 3D hierarchical structure with optimized interlayered spacing. The PANI‐WO₃ composite showed superior EC stability due to improved ion storage capacity by 3D hierarchical structure with extended surface area for ion interaction. The enlarged layer spacing of PANI‐WO₃ composites allows for accommodating more exchangeable Li⁺. The PANI‐WO₃ film maintains remarkable cycling stability, retaining 80% of its initial capacity after 30000 cycles. The EC device based on PANI‐WO₃ demonstrates high optical modulation (57% at 633 nm), rapid switching speeds (coloration to 23% in 15 s and bleaching to 80% in 10 s) and high coloration efficiency (168 cm² C⁻¹). Meanwhile, the PANI‐WO₃ EC supercapacitor achieves a high specific capacitance (121 mF cm⁻² at 0.2 mA cm⁻²) and prolonged cyclic life (specific capacity remains at 58% and coulombic efficiency at 65% after 1500 cycles). The PANI‐WO₃ serves as an effective candidate for the fabrication of high‐performance EC devices (ECDs) with potential applications in energy‐saving smart windows, outdoor static displays, and other energy‐efficient technologies.