Simple Evaluation of Mechanical Properties of Polymer Binder in Negative Electrode for Lithium-Ion Battery (Application to PVDF-based Binder and SBR-based Binder)

Binders affect both the mechanical properties and electrochemical performance of electrode materials for lithium-ion batteries. This study has developed and applied a mechanical model of electrode materials on negative electrodes made of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR) based binders. A series of tensile tests was performed on carbon-based negative electrodes with several concentration ratios of the binders, and the stress, strain and dissipated strain energy of the binders inside the electrodes were estimated using the mechanical model. The results were summarized as follows. (1) Both the PVDF-based and SBR-based specimens fractured microscopically due to the rupture of the binder inside the specimen. This indicates that the structure of the negative electrode is supported by the binder. (2) The mechanical model was valid for the PVDF-based specimen in that the constituent of the PVDF-based binder formed inside the specimen did not change with respect to the binder concentration. (3) The tensile strength and permanent strain of the SBR-based specimen showed the same tendency as those of the PVDF-based specimen, and the mechanical model was valid for the SBR-based specimen as well. The dissipated strain energy showed a bipolarized tendency between the low and middle binder concentrations. This tendency would be caused by the adhesion mechanism between carbon particles, SBR and CMC, and the dispersibility of carbon particles.