Dispersant Effect in Cathode Electrode Slurry System

As technology development and demand for mobile devices increase, demand for secondary batteries as an energy source is rapidly increasing. Although many studies and innovative materials have been adopted in the industry, research on slurry systems is lacking compared to active materials. If polyvinylidene fluoride (PVDF) used as a binder for battery slurry is in the β phase which induces the crystallization of binders, the charging/discharging efficiency of the lithium-ion batteries (LiBs) is lowered, and problems such as capacity loss and charging time increase are caused. Therefore, although the current method of adding hydrogenated nitrile butadiene rubber (HNBR) to improve the rheological properties of the slurry by minimizing the β phase of PVDF has been commercialized, a detailed study on the relationship between PVDF and HNBR relationship at the atomic scale are not well-known. In this study, the effect of the HNBR dispersant on the crystal phase of the binder PVDF in the slurry system of a lithium-ion battery was analyzed using molecular dynamics (MD) simulation. In this system, n-methyl-2-pyrrolidinone (NMP) was used as the solvent. In the PVDF/NMP/HNBR system with various HNBR configurations, the β phase ratio of PVDF gradually decreased from 71.12% to 30.01% as the Acrylonitrile (ACN) contents of HNBR increased. It was found that the CN groups of HNBR interfered with the crystalline state of PVDF to make it amorphous. Through radial distribution function (RDF) Analysis, we found that the strong attraction between the HNBR nitrogen and the PVDF fluorine was the cause. When the ACN contents of HNBR were fixed at 33.9%, as the number of HNBR increased, HNBR suppressed the β phase, which is the linear conformation of PVDF. Through the analysis of the dispersant effect in the cathode material slurry system, we can develop a large-scale coarse-grained simulation platform for coating process in the future.