Improved Operando Raman Cell Configuration for Commercially-Sourced Electrodes in Alkali-Ion Batteries

Operando Raman spectroscopy is a well-established technique for monitoring chemical changes in active materials during electrochemical cycling of alkali-ion cells. To date, however, its application to the study of commercial electrodes under realistic operating conditions has been severely limited by cell design constraints. We present here an improved configuration for performing operando Raman spectroscopy on coated metal foil electrodes used in standard laboratory cell testing. Electrochemical modeling predicts much improved lithiation homogeneity compared to a previously used configuration; this observation is validated experimentally for a commercially-sourced graphite electrode. The new configuration delivers improved electrochemical performance at higher specific currents than was previously possible, ensuring that Raman measurements at a single location are representative of the entire electrode. Finally, the broad applicability of the configuration is demonstrated through a study of hard carbon sodium-ion negative electrodes over 50 cycles. These results provide a new configuration for performing reliable, validated operando Raman spectroscopy on commercial battery electrodes, as well as establishing a general methodological framework for the validation of operando spectroscopic techniques to ensure that their performance is relevant to the practical systems to which they are applied.