High water-retaining, antifreeze micro-supercapacitor without encapsulation for all-weather

The development of portable electronics puts forward new challenges for miniaturization of energy storage devices to match them. Micro-supercapacitors (MSCs) with significant advantages have attracted increasing attention recently. MSCs are usually encapsulated in practical use to ensure a stable performance due to uncertainty of electrolyte in open system, even quasi-solid electrolyte such as hydrogels electrolyte which gradually dries once exposed to air for a few hours or freezes in cold environment. Herein, we demonstrate a high water-retaining and antifreeze micro-supercapacitor (AW-MSC) without encapsulation adaptable to all-weather for the first time. Ion conductive hydrogel through copolymerizing sulfobetaine methacrylate and sodium acrylate acts as electrolyte after soaking by lithium chloride aqueous solution. The resultant polyelectrolyte exhibits an outstanding water holding capacity even in simulated dry desert climate (lower than 20% relative humidity) and high freeze resistance in cold environment (under −20 °C). Consequently, the assembled AW-MSC without encapsulation exhibits the capacitance retention above 85.0% after 32 days in either severe cold, drought, or high heat environments, superior to those MSCs-based on hydrogels reported previously. In various harsh simulation scenarios, the AW-MSC connected in series can steadily power an electronic watch for a long time.