Silicon (Si) is a promising candidate to enhance the specific charge of graphite electrode, but there is no consensus in the literature on its cycling mechanism. Our aim in this study was to understand Si electrochemical behavior in commercially viable graphite/Si electrodes. From the comparison of three types of commercial Si particles with a producer-declared particle sizes of 30–50 nm, 70–130, and 100 nm, respectively, we identified the presence of micrometric Si agglomerates and the Si micro- and mesoporosity as the main physical properties affecting the cycling performance. Moreover, ex situ SEM, XRD, and Raman investigations allowed us to understand the lithiation/delithiation mechanism for each type of Si particles. For nanoscale Si particles, the entire Si particle is utilized, resulting in high specific charge, and the stress induced by the formation of Li₁₅Si₄ alloy upon deep lithiation is well managed within the Si mesoporosity. This leads to reversible cycling behavior and, thus, to good cycling stability. On the other hand, micrometric Si aggregates undergo a two-phase lithiation mechanism with early Li₁₅Si₄ formation in the particle shell. This leads to stress-induced core disconnection during the first lithiation, and shell pulverization during the following delithiation, resulting in overall low specific charge and rapid performance fading.

中文翻译：

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含硅石墨电极的循环行为，B部分：硅源的影响

硅（Si）是增强石墨电极的比电荷的一种有前途的候选物，但是在其循环机理方面，文献上尚无共识。我们在这项研究中的目的是了解在商业上可行的石墨/ Si电极中的Si电化学行为。通过对三种类型的商业化Si颗粒的比较，生产者宣布的粒径分别为30–50 nm，70–130和100 nm，我们发现存在微米级的Si团聚体，而Si的微孔和中孔性为影响循环性能的主要物理性能。此外，异位SEM，XRD和拉曼研究使我们能够了解每种类型的Si颗粒的锂化/去锂化机理。对于纳米级的Si颗粒，整个Si颗粒都会被利用，从而导致较高的比电荷，在Si介孔率范围内，深层锂化处理的₁₅ Si ₄合金得到了很好的管理。这导致可逆的循环行为，并因此导致良好的循环稳定性。另一方面，微米级的Si团聚体经历了两相锂化机制，并在颗粒壳中早期形成了Li ₁₅ Si ₄。这会导致在第一次锂化过程中应力引起的岩心断开，并在随后的锂化过程中导致壳粉化，从而导致总体上较低的比电荷和快速的性能衰减。