Nanoconfined Supercooled Water in Hydrated Two‐Dimensional Polyaniline for Sub‐Zero Solid‐State Zinc‐Ion Hybrid Capacitor

Abstract Solid‐state electrochemical energy systems have attracted numerous attentions for their excellent performance, high safety, and low cost. Recently, ice of aqueous electrolytes is reported as a new kind solid‐state electrolyte for low‐temperature solid‐state devices. However, the lack of kinetically favorable electrodes hampers the performance of this new class of icy electrolyte‐based solid‐state devices at sub‐zero temperatures. In this work, a hydrated layered polyaniline cathode active material (h‐LPANi) with nanoconfined supercooled water by metatungstate clusters is utilized to improve the performance of sub‐zero solid‐state zinc ion hybrid capacitors (ZIHCs). The interlayer confined hydrated network of h‐LPANi improves kinetics, surpassing pristine polyaniline and conventional porous carbon‐based active materials. At −15 °C, the solid‐state iced ZIHCs with h‐LPANi cathode demonstrate an areal energy density of 580.0 µWh cm⁻² at 1.1 mW cm⁻² and 155.7 µWh cm⁻² at 43.3 mW cm⁻², surpassing other low‐temperature solid‐state ZIHCs with conventional cathodes.