In operando measuring circumferential internal strain of 18650 Li-ion batteries by thin film strain gauge sensors

The state-of-the-art Li-ion batteries undergo severe performance degradation caused by the mechanical failure of the internal jelly roll structure. It is a long-standing challenge to in-situ and real-time measure internal deformation of the electrodes inside the jelly roll structure because of the harsh environment in the Li-ion battery and tight jelly roll structure in the confined space. In this paper, an in-situ internal strain measurement method in the 18650 Li-ion battery is developed. A newly designed strain gauge sensor and a novel integrated method are proposed, which is compatible with the 18650 Li-ion battery assembly process, allowing the integrated 18650 Li-ion battery for delivering stable performance compared with the regular 18650 Li-ion battery. We demonstrate for the first time the evolution of the internal strain in the 18650 Li-ion battery during the charging and discharging processes. The strain changes are divided into three stages during the charging/discharging, which are mainly dominated by the interlayer spacings transition of the negative graphite electrode during the lithiation/delithiation. Finally, the proposed method is a promising tool for fundamentally understanding the internal strain evolution and safety designed of the LIBs under more realistic operation conditions.