Unveiling Electrochemical Properties of Silicon for Stable Cycling Performance of Silicon Anode Materials

Research on silicon (Si) as an anode material for Li-ion batteries has spanned two decades; however, certain electrochemical properties of Si remain unclear. Specifically, the cyclic voltammogram (CV) pattern of Li/Si cells varies from case to case, influenced not only by the material but also by the experimental conditions. In this work, slow cyclic voltammetry is employed to investigate Li/Si cells, resulting in three distinct CV patterns. It is further observed that the CV pattern, particularly during the delithiation, is contingent on the state-of-lithiation (SOL) during lithiation and correlates with the capacity fade of Li/Si cells in subsequent cycles. Additionally, it is revealed that the primary mechanism for capacity fade differs between nano-sized silicon (Si-NP) and micro-sized silicon (Si-MP). In brief, capacity fade in Li/Si-NP cells predominantly arises from parasitic reactions between the highly lithiated Li-Si alloy and electrolyte solvents, exacerbated by the large specific surface area of Si-NP materials, whereas capacity fade in Li/Si-MP cells is primarily attributed to the Li electrode rather than the Si-MP electrode due to the restricted lithiation of Si-MP materials. Finally, this work concludes that limiting the SOL of Li/Si cells offers a straightforward and effective pathway to achieving stable cycling performance.