Silicon anodes have generated significant interest for their exceptional high capacities, relative low cost, and good operating voltage window. For may silicon electrode materials the inhomogeneous nature of the charged electrode yields a highly reduced surface and a less reduced bulk. Using single phase model compounds of the predominant electrodes structures at various states of charge we have examined the role of surface charge on the stability of the electrode to binder, electrolyte, and various salts. In our presentation we have taken these concepts and devised additives that react with the charged surface to coat the material with a more stable interfacial material that extends cycle life and improves performance versus baseline samples.

Notable examples include the synthesis of Li7Si3, a model compound for a 300mV Li-Si electrode. This material contains simple silicon dimers surrounded by lithium cations. Previous modeling has noted these dimers show double bond character, increasing their reactivity with the components of an electrochemical cell. In our studies crystalline samples were synthesized in Ta tubes and exposed to various solvents. Reactivity, as seen by XRD, NMR, and FTIR, confirmed the oxidation of the dimer species to a more oxidized compound (Li12Si7) and ring opening of EC-type solvents.