Deconvoluting Cell Entropy Coefficients via a Versatile Reference Electrode

The entropy coefficient is considered a key parameter in lithium-ion battery modeling and system analysis that contributes to the overall heat generated during operation. In this work, we demonstrate the use of a versatile reference electrode placed in the separator layer in an automotive relevant pouch cell to provide for in situ deconvolution of the entropy coefficient of the battery cell into the individual anode and cathode active material entropy coefficients. Cell entropy coefficients obtained in this manner were found to compare well with those measured on a large format commercial cell of the identical chemistry tested using the hybrid time frequency domain analysis method and were utilized in simulations to predict battery pack-level heat generation for various electric vehicle charging scenarios. Measured values and trends for the NCM811 cathode and graphite anode were found to be in good agreement with published half-cell data. The sensitivity of cell entropy to the designed N/P ratio and shifts in electrode utilization over life were apparent in observing the electrode data in the context of the full cell.