A Laser-Scribed Wearable Strain Sensing System Powered by an Integrated Rechargeable Thin-Film Zinc-Air Battery for a Long-Time Continuous Healthcare Monitoring

Abstract

Wearable sensors with long cruising times without the need for an external wire-connected power supply are urgently required for a continuous physiological signal monitoring. Herein, we report the design and fabrication of a wearable all-in-one sensing system that integrates a sensitive strain sensor and a rechargeable zinc-air battery on the same laser-induced graphene (LIG) platform. The sensing electrode of the strain sensor, the catalytic air electrode of the zinc-air battery and the interconnection lines between the two are simultaneously fabricated through the same laser-scribing process on polyimide (PI) followed by pattern transfer to a flexible and stretchable polydimethylsiloxane (PDMS) substrate. In the sensor, the conductive porous LIG exhibits a high gauge factor (~27028.1), a wide detection range (~40%) and a well cyclic loading-unloading stability (>20000 cycles). In the zinc-air battery, Co 3 O 4 nanoparticles are in-situ laser-sintered on LIG to form an excellent electrode/electrolyte/air three-phased interfacing structure for a high catalytic performance, and a moisturized tetraethyl ammonium hydroxide (TEAOH)-KOH/polyvinyl alcohol (PVA) gel electrolyte tightly binds the Co 3 O 4 /LIG air electrode and zinc foil electrode together into an integrate thin-film energy device, which provides a high open-circuit voltage (~1.39 V) and a high specific capacity (712 mAh g -1 at 0.2 mA cm -2 ). For a proof-of-concept, an intelligent wristband based on the sensing system was fabricated and worn on the wearer’s wrist for a long-time continuous pulse monitoring of up to 10 h. The health state of the wearer can be depicted upon the acquired pulse waveforms. The developed LIG-based sensing system with a high internal powering capability will be promising in wearable sensing applications.

Keywords: laser-induced graphene (LIG), all-in-one integrated system, flexible strain sensor, rechargeable zinc-air battery, gel polymer electrolyte