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

Nanocomposite electrodes comprising LaSi 2 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 LaSi 2 matrix phase, was formed before cycling. The elastic LaSi 2 relieved Si-generated stress and suppressed electrode disintegration. Contrarily, the LaSi 2 phase in the metallographic structure was surrounded by the Si matrix phase after cycling. The positional relationship between the two phases was reversed, and LaSi 2 could not relieve the stress. For a nanocomposite electrode containing CrSi 2 , 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 LaSi 2 /Si composite could improve the cycle life. Thus, this study prepared nanocomposite electrodes containing elastic LaSi 2 , stiff M Si 2 (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 LaSi 2 /NbSi 2 /Si electrode exhibited the best cycle life without changes in its metallographic structure owing to the synergistic effect of stiff and elastic silicides.