Multifunctional ultra-low voltage sweat-activated battery using piezo-ionic hydrogel

Optimising ultra-low voltage with high capacity in batteries presents a challenge for emerging applications, such as wearable technology. In this study, we developed a multifunctional ultra-low voltage, sweat-activated fabric battery (SFB) using a biomaterial-based piezo-ionic hydrogel from water hyacinth carboxymethyl cellulose, mitigating risks of high-power and toxic materials near human skin. The SFB's multi-layer active material enhances conductivity and reduces resistance, enabling a 1 cm² device to discharge for 10 + h below 0.4 V, with an areal capacity of 4.1 mAh cm⁻² at 400 μA cm⁻². Furthermore, SFB with piezo-ionic hydrogel, when affixed to the elbow, generates a peak current of 115 nA cm⁻² as the elbow is fully flexed. Consequently, SFB can be utilised for energy storage, along with force and bending sensing. This study opens new avenues in advancing research on ultra-low voltage batteries for wearable and biomedical devices.