Lithiation/Delithiation Properties of Lithium Silicide Electrodes in Ionic-Liquid Electrolytes.

We investigated the impact of electrolyte difference on lithiation and delithiation properties of a LiSi electrode to improve the Coulombic efficiency (CE) of Si-based electrodes. The results of X-ray diffraction, Raman spectroscopy, and soft X-ray emission spectroscopy demonstrated that a portion of the Li in LiSi desorbed by simply immersing the electrode in an ionic-liquid electrolyte, that is, the phase transition of LiSi to Si occurred. In contrast, this phenomenon was not confirmed in an organic-liquid electrolyte. Instead, the desorbed Li was consumed for the formation of a surface film; thus, the Li in LiSi did not elute into the electrolyte. The addition of vinylene carbonate (VC) to the ionic-liquid electrolyte suppressed the phase transition of LiSi to Si. Although the LiSi electrode showed a low initial CE and poor cycling performance in a VC-free electrolyte, the electrode exhibited a high CE and a remarkable cycle life in the VC-added electrolyte. It was considered that no desorption of the mechanically added Li in LiSi contributed to the superior cycle life; thus, the characteristic ductility, malleability, and high electrical conductivity of lithium silicide should improve the electrochemical performance.