Fiber optic monitoring of lithium-ion batteries: A novel tool to understand the lithiation of batteries

In this paper we present the implementation of a novel lithium ion pouch cell monitoring system that utilizes an optical fiber sensor (OFS). The OFS allows for direct optical interaction of near infrared light with graphite during its electrochemical lithiation process. This sensing system has been tested over multiple partial and full cycles showing repeatable signals that can be directly correlated with the lithiation of graphite. The results suggest that this sensor can function independently in determining the state of lithiation of graphite within a lithium ion battery, which can be used in a state of charge estimation algorithm.