Piezoresistive Free‐standing Microfiber Strain Sensor for High‐resolution Battery Thickness Monitoring

Highly sensitive microfiber strain sensors are promising for the detection of mechanical deformations in applications where limited space is available. In particular for in situ battery thickness monitoring where high resolution and low detection limit are key requirements. Herein, the realization of a highly sensitive strain sensor for in situ lithium‐ion (Li‐ion) battery thickness monitoring is presented. The compliant fiber‐shaped sensor is fabricated by an upscalable wet‐spinning method employing a composite of microspherical core‐shell conductive particles embedded in an elastomer. The electrical resistance of the sensor changes under applied strain, exhibiting a high strain sensitivity and extremely low strain detection limit of 0.00005 with high durability of 10 000 cycles. To demonstrate the accuracy and ease of applicability of this sensor, the real‐time thickness change of a Li‐ion battery pouch cell is monitored during the charge and discharge cycles. This work introduces a promising approach with the least material complexity for soft microfiber strain gauges. In a straightforward approach, a freestanding and conformable piezoresistive microfiber based on conductive microspheres is developed for lithium‐ion battery deformation detection. Employing microspheres provides high‐resolution strain sensitivity and fast response. The microfiber developed in this work is capable to detect 1 µm deformation in addition to high durability against overload strain.