Wettability of Lithium-Ion Battery Graphite Anodes: A Quantitative Tensiometer Study Considering Electrode Microstructure and Material Properties

Wetting of lithium-ion battery electrodes with electrolyte represents a challenge that is a mostly neglected aspect of electrode optimization. In the production of large-format cells, the rate of electrolyte wetting after filling is of particular importance, as wetting time often represents a significant bottleneck. This study employs a systematic, quantitative investigation of the wetting behavior of lithium-ion battery electrodes using a tensiometer and considering the Washburn equation. This approach facilitates a fundamental understanding of the wetting behavior of porous electrodes. To consider the influence of microstructural differences and intrinsic electrode properties, two water-based graphite anodes were employed, which exhibit the same microscopic properties but differ in their pore size distribution and binder system. The developed tensiometer method demonstrates that by employing the average pore radius obtained from pore size distribution measurements, it is feasible to consider separately microstructural and material-specific influencing factors of wetting. Further investigation revealed that one of the two electrodes exhibited superior wetting, whereby the improved wetting could be clearly attributed to the used binder system. The findings were verified by contact angle measurements of the individual binder system films, by a drop shape analyzer and by electrochemical impedance spectroscopy measurements in symmetrical pouch cells.