Primary Researcher: Yang-Duan Su, Dr. Chenhu Sun

Monitoring the internal states of batteries ranging from cell to pack and stack level to extend lifetime and prevent thermal runaway due to cell degradation has been an essential task for Battery Management Systems (BMS). Our study aims to embed both existing and newly developed low-cost fiber optic sensors internal to Li-ion pouch cells for extraction of critical operational information about the cell state-of-health (SOH) and performance. This is done either by attaching them onto the cell surface with epoxy or by embedding them in between two separators central to cell internal structure, the latter expected to be the most informative area to measure from. Potential parameters of interest include internal temperature, strain, acoustic emission and CO2/ O2 concentration.

Given that the state-of-charge (SOC) of a battery is a function of cell temperature, the locally-measured temperature serves as input to the SOC estimation algorithm for general cell operation, while the temperature gradient measured by Raman-based distributed FO sensors indicates the temperature hot spots for incipient thermal runaway detection. And the strain variation is correlated with electrode intercalation stages and charge/discharge capacity fade, which can then be used to estimate both SOC and SOH of the battery. Rather than relying on estimation methods, the cell SOC can also be directly measured by sensing the acoustic emissions resulting from the electrode density change during the Li-ion intercalation when discharging. The density of active material on the electrode is proportional to the acoustic impedance being measured. On the other hand, CO2/ O2 concentration, an indication to electrolyte decomposition and capacity fade, and is another parameter that can be measured via fiber optic evanescent field sensors or fiber Bragg grating sensors.