Silicon-Based Nanocomposite Anodes with Excellent Cycle Life for Lithium-Ion Batteries Achieved by the Synergistic Effect of Two Silicides

Abstract

Nanocomposite electrodes comprising LaSi2 and Si exhibit satisfactory charge–discharge cycling performances but their capacity is degraded after repeated cycles. A metallographic structure, in which the Si phase was finely dispersed in the LaSi2 matrix phase, was formed before cycling. The elastic LaSi2 relieved Si-generated stress and suppressed electrode disintegration. Contrarily, the LaSi2 phase in the metallographic structure was surrounded by the Si matrix phase after cycling. The positional relationship between the two phases was reversed, and LaSi2 could not relieve the stress. For a nanocomposite electrode containing CrSi2, which exhibits stiffness to withstand the Si-generated stress, the structural changes were suppressed after cycling, resulting in good cycling stability. Here, we considered that the addition of stiff silicides as a third phase to the LaSi2/Si composite could improve the cycle life. Thus, this study prepared nanocomposite electrodes containing elastic LaSi2, stiff MSi2 (where M = Cr, Mo, Nb, Ta, Ti, or W), and elemental Si and investigated their electrochemical performances. Reaction behaviors, such as the metallographic structure, electrode thickness, and phase transition, were also clarified. The LaSi2/NbSi2/Si electrode exhibited the best cycle life without changes in its metallographic structure owing to the synergistic effect of stiff and elastic silicides.