Microfiber sensor integrated inside solid-state lithium-metal batteries for reducing invasiveness

Embedded fiber optic sensors are considered a promising technology that can unlock the black box within a battery and understand the fundamental internal chemical and physical states during operation. However, the interfacial compatibility between the implanted fiber sensor and electrode materials has not yet been investigated. In this study, a fiber Bragg grating (FBG) sensor is incorporated into a solid-state lithium-metal coin cell at different interfaces to explore the resulting variations in electrochemical property. The presence of the fiber sensor accelerates the capacity fade compared with that of a pristine cell. To address this issue, a new method is employed to reduce the sensor diameter from 250 μm to 30 μm while preserving its sensing function. The reduction in the sensor diameter enhances its compatibility with the size of the electrode materials. Integrating a micro-FBG (MFBG) sensor into the solid-state cell also alleviates the defects related to interface stratification and void growth, leading to the improved capacity retention. Moreover, the feasibility of utilizing MFBG for in-situ monitoring of internal stress within a lithium-metal cell is demonstrated. This technique offers a scalable solution for the noninvasive monitoring of battery state, thereby improving the reliability and safety of cells.