Binder Effect on Electrochemical and Mechanical Properties of Flexible Electrodes

Binders are essential electrode materials used to bond active and conductive materials together and fix them to the current collector. Therefore, binders are essential in ensuring mechanical stability and maintaining the microstructure to ensure a smooth flow of ions and electrons. In flexible electrodes, binders have the additional role of enhancing flexibility. Ultraflexible electrodes can be fabricated by exploiting the thermoplastic properties of the poly(vinylidene fluoride) (PVDF) binder using thermally induced phase separation (TIPS). Because binders are insulating materials, excess amounts can affect the specific capacity; therefore, their amount should be determined by considering the interplay between flexibility and capacity. In this study, four TIPS-based electrodes having 10, 20, 30, and 40 wt % PVDF were investigated to understand the effect of binder amount on the electrode properties. The electrodes with 10 and 20 wt % PVDF attained a high capacity (180 mAh g −1 ), significantly outperforming those containing 30 and 40 wt %. Notably, the electrodes containing less PVDF (≤20 wt %) had considerably higher porosity than those containing larger amounts, suggesting that the outstanding capacity is attributed to high porosity, which enhances ionic conductivity. The poor capacity of the higher PVDF electrodes (≥30 wt %) is associated with high ionic and electronic resistances resulting from low porosity and polymer adsorption that blocks the electron conductive network. Conversely, the electrodes containing larger amounts of PVDF achieved a higher tensile strain and greater flexibility. Considering the trade-off between electrochemical and mechanical properties, the preparation of electrodes with smaller quantities of PVDF is suggested. This study provides a systematic approach to understanding the effect of binder on flexible electrodes and can be extended to other devices where binder is applied, including energy storage and biomedical devices.