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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.

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