A Comparison of Voltage Hold and Voltage Decay Methods for Side Reactions Characterization

Abstract

This study conducts a qualitative comparison between two methods for detecting side reactions - the voltage hold and voltage decay methods using a high precision coulometry (HPC) tester. The measurements were conducted with Si-G/NMC811 commercial cells for three different temperatures and four different states of charge (SoC) in order to determine the voltage and the temperature dependency of side reactions. Here, we show that the voltage hold and the voltage decay methods deliver comparable results when determining the differential capacity with an incremental capacity analysis (ICA) instead of a single pulse for the voltage decay method. Both methods presented a good agreement for high temperatures and high SoC cases. Only at 90% SoC was there a discrepancy of 15% on the leakage capacities, which was attributed to the peak shape of the ICA curve. Therefore, it was found advantageous to analyse the ICA shape of the respective cells when performing such measurements. In addition, with the end of charge point and end of discharge point slippage evaluation, it was possible to observe that couple side reactions dominate the leakage currents at higher SoCs and lead to reversible losses. The irreversible losses remain almost constant for SoCs higher than 50%.