Modified lithium-ion cell design enabling operando gas sensing using optical fiber photothermal spectroscopy

A modified lithium-ion cell integrated with a hollow-core fiber photothermal spectroscopy (HCF-PTS) sensor was developed for operando monitoring of gas evolution during electrochemical cycling. The platform enabled simultaneous measurements of cell voltage, internal pressure, and gas-phase concentrations of C 2 H 4 and CO 2 in a sealed LiFePO 4 /graphite cell. The HCF-PTS system with limits of detection of 1.2 ppm for C 2 H 4 and 1.7 ppm for CO 2 were obtained. Measurements from two independently assembled modified cells showed similar voltage, pressure, and gas-evolution profiles, demonstrating good reproducibility under the present experimental conditions. Comparison with a conventional coin cell further showed similar initial charge–discharge voltage characteristics. In addition, CH 4 detection was separately demonstrated with a limit of detection of 1.1 ppm, illustrating the scalability of the sensing architecture toward additional gas species. The proposed platform provides a minimally invasive approach for correlating electrochemical behavior with gas-phase reaction dynamics in working lithium-ion cells.