Impact of Binder Thin-Films on Surface Chemistry of Silicon Anodes in Lithium-Ion Batteries

The effect of polymer binder on the nature and location of solid-electrolyte interphase (SEI) formation on Si active material was investigated. Thin layers of polymeric binder (polyvinylidene fluoride and sodium carboxymethyl cellulose) were spin-coated onto polished single crystal Si wafers. The samples were cycled against a Li counter/reference electrode under various electrochemical conditions in a coin cell configuration. The electrolyte was 1 M of LiPF6 in 1:1:1 wt% EC:DEC:DMC. After cycling, the samples were extracted from the coin cell under inert conditions and X-ray photoelectron spectroscopy (XPS) was performed. Electron microscopy and atomic force microscopy indicate that the binder films are smooth and continuous across the wafer surface, and no impact on the electrochemical behavior was observed. However, notable differences were detected using XPS, which revealed both difference in SEI composition and location relative to the binder-electrolyte and binder-substrate interfaces. These observations and insights will be useful in cell designs, binder selection, and reliability estimates because the location of SEI formation may influence cyclic performance of electrodes.