Design guidelines to use optical fibers as state of charge sensors: an operando micro wide and small angle X-ray scattering study of an IR-fiber equipped smart Na-ion battery

This work aims to evaluate the accuracy of state-of-sodiation determination using an optical fiber. Along that line, an optical fiber is introduced inside a Na-ion battery and used to measure operando infra-red (IR) spectra of the Prussian blue analogs (PBA) positive electrode material during the first three cycles. The fourth cycle is performed while the battery is scanned with a micro X-ray beam (ESRF), allowing the measurement of wide and small-angle scattering (WAXS/SAXS) maps.