Aramid nanofiber-poly(vinyl alcohol) composite gel polymer electrolytes for lithium chloride-based supercapacitors

Gel polymer electrolytes (GPEs) are key components in electrochemical energy-storage devices, as they simultaneously serve as ion-conducting media and separators. However, their performance is often limited by the trade-off between mechanical robustness and ionic conductivity, which becomes particularly problematic in highly concentrated aqueous electrolytes due to electrolyte-induced dimensional instability. Here, we report a composite GPE based on a rigid aramid nanofiber (ANF) network coated with a hydrophilic poly(vinyl alcohol) (PVA) layer, designed for compatibility with water-in-salt electrolyte systems. The ANF scaffold provides a high-modulus framework for dimensional stability, while hydrogen-bonding interactions at the ANF-PVA interface enable effective stress redistribution without significantly impeding ion transport. The ANF-PVA composite hydrogel was impregnated with a lithium chloride-based water-in-salt electrolyte to form a GPE and subsequently coated onto activated-carbon-decorated carbon-fiber electrodes to fabricate supercapacitors. The resulting devices exhibit stable electric double-layer capacitive behavior, reliable rate capability, and excellent cycling stability over a wide temperature range from -20 to 50 °C, together with scalable electrochemical performance upon increasing device length. These results highlight the effectiveness of composite polymer-network engineering for mechanically robust and ionically efficient aqueous GPEs suitable for low-temperature energy-storage applications.