Interpreting the entropy of silicon-graphite blended electrodes

The state of charge (SoC) dependent voltage and entropy of two lithium-ion battery cells with silicon-graphite blended anodes consisting of different material composition, were analysed and compared to a graphite only cell. Voltage and entropy showed a significant hysteresis regarding the charge/discharge history and both are increasing with the proportion of silicon. However, the share of silicon has a marginal impact on the general behaviour of the cell's entropy. This behaviour seems only to be influenced by the graphite. Furthermore, the entropy hysteresis of the anode vanishes, when plotting it against its half cell potential. An interpretation of this effect can be done, when regarding statistical thermodynamics. Thereby, a suggestion can be made that the measured entropy by dU/dT on a cell level is not equal to the effective entropy of the electrode, when the cell is operated. Through that effect, the amount of heat produced by the entropy is not in line with the formerly presumed measurements.

Automated summary

This study analyzed and compared the voltage and entropy of two lithium-ion battery cells with silicon-graphite blended anodes and a graphite only cell. The results showed that both voltage and entropy had significant hysteresis based on the charge/discharge history and increased with the proportion of silicon. However, the impact of silicon on the cell's entropy behavior was marginal, indicating that the behavior was influenced mainly by the graphite. Furthermore, the entropy hysteresis of the anode disappeared when plotted against its half cell potential, suggesting a difference between the measured entropy at a cell level and the effective entropy of the electrode during operation.