Electrochemical Lithiation and Delithiation Properties of FeSi2/Si Composite Electrodes in Ionic-Liquid Electrolytes

We investigated the applicability of ionic-liquid electrolytes to FeSi2/Si composite electrode for lithium-ion batteries. In conventional organic-liquid electrolytes, a discharge capacity of the electrode rapidly faded. In contrast, the electrode exhibited a superior cycle life with a reversible capacity of 1000 mA h g(Si)−1 over 850 cycles in a certain ionic-liquid electrolyte. The difference in the cycle life was explained by surface film properties. In addition, the rate performance of the FeSi2/Si electrode improved in another ionic-liquid electrolyte. Remarkably, lithiation of only Si in FeSi2/Si composite electrode occurred whereas each FeSi2- and Si-alone electrode alloyed with Li in the ionic-liquid electrolyte. FeSi2 certainly covered the shortcomings of Si and the FeSi2/Si composite electrode exhibited improved cycle life and rate capability compared to Si-alone electrode.