Stretchable Carbon Nanotube Dilatometer for In Situ Swelling Detection of Lithium-Ion Batteries

Advances in lithium-ion batteries (LIBs) have enabled the realization of lightweight power sources with high energy density, specific capacity, and cyclic stability. As LIBs are inherently subjected to thermomechanical stress during operation, their volume change can be indicative of their electrochemical reactions and safety status. In this study, a carbon nanotube (CNT)-based dilatometer that is stretchable and can be conformally mounted on the surface of LIBs has been developed for sensitive and in situ measurements of the LIB swelling. The CNTs form a percolation network on top of a thin elastomer and exhibit a positive gauge factor of ∼50 and a negative temperature coefficient of resistance of −0.075% K–1, enabling a quantitative extraction of the extent of swelling. As a result, both regular (∼50 μm swelling by lithiation/delithiation cycles) and irregular (a few millimeter swelling by abnormal gas evolution because of increased temperature) reactions of LIBs are successfully detected in real time. Unlike the conventional dilatometers that are complex, expensive, and bulky, the CNT sensor, because of its simplicity, portability, and sensitivity, is useful for understanding electrochemical reactions and preventing serious failures of portable LIBs, without disassembling them from the other components of the device.