Neutron reflectometry at the Spallation Neutron Source has revealed the composition and growth characteristics of the spontaneous chemical reaction layer formed between a silicon battery anode and an organic electrolyte that ultimately limits the capacity of the battery. We determined that a 3.6 nanometer reaction layer composed of material dominated by silicon-fluorine bonds forms on the anode material. This insight allows us to understand the loss of capacity (ability to store charge) reported for Si anodes and will direct the search for new Si surface chemistries to mitigate this reaction. Si anodes have nearly 8 times the capacity of standard graphite anodes, giving them high potential for use in electric vehicles batteries with longer ranges and lifetimes. However, the Si anodes require much smaller particle sizes to facilitate diffusion and, due to the higher surface area of these smaller Si particles, interfacial reactions become a more significant source of electrolyte consumption, reducing both the capacity and cycle life of the batteries. The ability to control these reactions is critical for maintaining battery capacity required for a practical silicon-based battery.
Gabriel M. Veith, Loïc Baggetto, Robert L. Sacci, Raymond R. Unocic, Wyatt E. Tenhaeff, and James F. Browning, “Direct measurement of the chemical reactivity of silicon electrodes with LiPF6-based battery electrolytes,” Chemical Communications, 2014 – DOI:10.1039/C3CC49269A
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