Study on Polymer Binders for High-Capacity SiO Negative Electrode of Li-Ion Batteries

High-capacity SiO powder composite electrodes for rechargeable lithium-ion batteries are prepared with different polymer binders of poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), sodium carboxymethyl cellulose (CMCNa), and conventional poly(vinylidene fluoride) (PVdF). Electrode performance of the SiO composites highly depends on selection of binders, and their electrochemical reversibility is drastically improved by using PAA as the binder in comparison to the PVdF, CMCNa, and PVA binders. Coulombic efficiency at the initial cycle is improved for the SiO–PAA composite electrode, and the reversible capacity reaches 700–750 mAh g–1 for continuous fifty cycling test at a rate of 100 mA g–1. The improvement mechanism of SiO–PAA composite electrode is characterized by X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, self-discharge test, and adhesive strength test. Amorphous PAA polymer not only tightly binds but also covers the individual SiO particles. Moreover, the PAA binder suppresses swelling of the composite electrode with the electrolyte solution compared to the PVdF binder. Through-thickness electric resistance of the PAA composite electrode is much lower than that of the PVdF when it is wet with the electrolyte. It is proposed that these characters of the PAA binder effectively suppress isolation of the SiO powders in the composite electrode associated with the large volume expansion/shrinkage during the lithiation/delithiation processes.