Understanding Slurry Degradation for Silicon–Graphite Anodes: Role of Silicon–Water Reaction and Hydrogen Evolution

In contrast to conventional graphite electrodes, silicon-graphite electrodes allow a considerable increase in specific energy and energy density of lithium-ion batteries. Nevertheless, the degradation of silicon-rich slurries during rest times in production before electrode coating remains a central challenge for direct implementation of such electrodes on an industrial scale. In this study, the degradation of five slurry variations with different Si contents is investigated with a focus on rheological changes, the quantification of temperature dependent gas formation and its impact on cycle life in battery full cells. Our results show that H 2 is formed as a reaction product between the electrochemically active silicon component and water that is used as a solvent in the coating process. Gas volume measurements and mass spectrometry are used to determine the extent of H 2 gas formation from different slurry formulations and under different storage conditions. In addition, electrochemical tests with 40 coin full cells show that changes during slurry storage and with the associated silicon oxidation impairs cell cyclability. Our study provides insights into the mechanisms of slurry degradation for silicon-graphite electrodes and identifies strategies to mitigate H 2 formation, which improves the cycle life of high-energy lithium-ion battery cells.