UCLA

Even though it has the highest known theoretical specific capacity of any material (~3600 mAh/g), silicon has limited use as an anode in lithium ion batteries due to the mechanical instability caused by the large volume expansion that occurs upon Li insertion. This volume expansion not only contributes to mechanical instability in the active silicon, but it also contributes to mechanical instability in the solid electrolyte interphase (SEI), a film formed at the end of the first lithiation step. The result of this mechanical instability in the SEI is diminished cycling performance. Modifying the SEI formation by growing a SiO2 layer on silicon nanowires (SiNW) or coating them with LixAlySizO (LASO), we report improved cycle life and rate capability. Here we show SiNW with a thin SiO2 layer achieved nearly 400 cycles at a capacity of 2400 mAh/g and LASO-coated SiNW cycled stably at 5.5C.