Flexible multifunctional sensor based on laser direct writing for battery safety monitoring.

Electric vertical take-off and landing (eVTOL) vehicles and IoT devices rely on reliable battery technologies. However, lithium-ion batteries face risks of thermal runaway triggered by overheating and mechanical strain. Existing battery monitoring sensors are either rigid (poorly adaptable to battery expansion), single-mode (only monitoring temperature or strain), or multimode but prone to inter-signal interference. In this article, we propose a flexible multifunctional sensor fabricated by the laser direct writing (LDW) process for real-time strain-temperature monitoring of batteries. This method enables the simultaneous reduction of the precursor material and sintering with the substrate material in a single step, streamlining the fabrication of both strain and temperature sensing components. By doping reduced graphene oxide (rGO) in silver nanoparticles, the gauge factor of the strain sensor raises from 47.4 to 515.5, and a temperature sensor with a temperature coefficient of resistance (TCR) of -0.872 % /K. The sensors exhibit ultra-low detection limits (0.05 % strain, 0.1 • C resolution), exceptional stability (2, 000 cycles). In battery safety tests, they accurately track rapid temperature spikes (response time of 2.58 s ) and micro-deformation during chargedischarge, matching commercial reference devices. This capability enables early detection of internal mechanical failures without compromising structural integrity.