In-Operando AFM Characterization of Mechanical Property Evolution of Si Anode Binders in Liquid Electrolyte

Understanding mechanochemical behaviors of binders facilitates the development of advanced binder materials to accelerate the adoption of Si-based anode materials. We demonstrated an approach to characterizing in-operando mechanical behaviors of binders while wetting in electrolyte solvents at nanoscale using atomic force microscopy (AFM). To reproduce Si–binder interfaces in anodes, we designed a model system and measured force spectroscopy between Si microcantilevers and binder films made with two representative materials: sodium (Na) alginate and poly(vinylidene fluoride) (PVdF). Na-alginate has orders-of-magnitude higher adhesive forces with Si than PVdF after being immersed in dimethyl carbonate (DMC), which can be explained by (i) strong hydrogen bonds between Si surface’s oxidation layer and hydroxyl/carboxyl groups in Na-alginate and/or (ii) ion-dipole interactions between these two components. Na-alginate demonstrates a Young’s modulus ∼56 times greater than that of PVdF after several hours of immersion in DMC and reaching their steady-state conditions. The results correlate well with cycle life of Si anodes in battery cells considering that Na-alginate’s retention of mechanical strength and higher adhesive forces can help withstand the large volume expansions of Si.