Wearable Thermoelectric Cooler Based on a Two-Layer Hydrogel/Nickel Foam Heatsink with Two-Axis Flexibility

A wearable thermoelectric cooler (w-TEC) shows promising prospects in personal thermal management due to its zero emission, high efficiency, lightweight, and long-term stability. The flexible heatsinks are able to promote the cooling effect of coolers, but the cooling capacity of current coolers still has much room for improvement because of the relatively large thermal resistance between the cooler and heatsink. In this work, the two-layer heatsink units composed of hydrogel and nickel foam are fabricated and attached to a thermoelectric cooler via the thermal silica gel. Thanks to the high thermal conductivity of nickel foam and a tight bond between the hydrogel and nickel foam, effective heat conduction from the cooler to the body of the heatsink was achieved. In addition, the discrete heatsink units endow the w-TEC with excellent flexibility. The bending radius of this w-TEC is as small as 7.5 mm, and a long-term temperature reduction of ∼10 °C can be realized at an input current of 0.3 A for a flat or bent w-TEC. In the on-body testing, a stable temperature reduction of 7 °C can be obtained using an AA battery with an input voltage of 1.5 V.