Hysteresis Behavior in the Sorption Equilibrium of Water in Anodes for Li-Ion Batteries

Hysteresis in the sorption equilibrium influences the production process of many multicomponent material systems. Electrodes for Li-ion batteries consist of several materials, some of which exhibit hysteresis in their sorption equilibrium with water. The moisture content adsorbed and absorbed in the electrodes of the Li-ion battery turned out to be an issue for its electrochemical performance and is reduced in the post-drying process. During this process, hysteresis in the sorption equilibrium needs to be overcome in order to achieve a low residual moisture content of the electrode. Modeling the post-drying process requires a description of the sorption equilibria of water in the components of the battery. This paper builds on previous research about the sorption equilibria and examines the hysteresis behavior of typical graphite anodes, with the active material graphite, carbon black as the conductive additive, and sodium carboxymethyl cellulose as well as styrene butadiene rubber as polymeric binders. Moreover, the mechanisms for the occurrence of hysteresis are presented, and how sorption equilibria during drying can be described is shown by applying models from the literature on the materials of battery electrodes. Theoretical deliberations on hysteresis mechanisms are validated, investigating graphite anodes of different material compositions and their materials.