Water-based conductive ink containing graphene nanosheets and ultrafine carbon powder for high-performance flexible wearable heaters

Abstract

Carbon-based composite conductive material, possessing advantages such as facile processing, cost-effectiveness, and ultralightness, represents a burgeoning electrothermal material. However, developing water-based inks using carbon-based materials that satisfy the requisites of human health safety, low-voltage operability, and durability in the realm of flexible wearable heaters remains an arduous challenge. Here, stable water-based conductive inks, with graphene nanosheets (GNs) and ultrafine carbon powder (UC) as conductive fillers, are prepared by a simple ball milling method. The conductive inks exhibited rheological properties suitable for screen printing, with a print resolution of up to 0.4 mm and an adhesion level of grade 1. When graphene nanosheets accounted for 15% of the total conductive filler content, the printed patterns displayed a “sandwich” type conductive network structure formed by both plane contact and point contact between conductive fillers at the microscale, resulting in a sheet resistance as low as 14.16 Ω sq⁻¹, which was 54.99% lower than that of pure ultrafine carbon-printed patterns. The electrothermal film prepared from these printed patterns demonstrated rapid response within 50 s under low-voltage drive ranging from 4 to 16 V and achieved an adjustable temperature range of 30–90 °C. Also, it maintained stable performance under cyclic heating–cooling and bending conditions for up to 1000 cycles. Wearable heating sleeves with excellent heat uniformity were fabricated to validate their tremendous potential in flexible wearable device applications.