Mitigating Silicon Amorphization in Si-Gr Anodes: A Pathway to Stable, High-Energy Density Anodes for Li-Ion Batteries.

Silicon-Graphite (SiGr) blended anodes represent a promising approach for enhancing the energy density of commercial Li-ion batteries (LIBs). However, the ≈300% volume change of the silicon component during lithiation and delithiation induces significant mechanical stress, leading to particle cracking and pulverization that compromise electrode stability. This study presents the first evidence of controlled Si lithiation in Si-rich blended anodes, where a crystalline silicon (c-Si) core remains unreacted while the outer shell undergoes complete amorphization. Operando synchrotron X-ray diffraction analysis of SiGr anodes over five consecutive cycles reveals a reversible lithiation of c-Si, which was not previously reported. Complementary transmission electron microscopy (TEM) analysis of focused ion beam (FIB)-prepared lamellae from cycled electrodes confirms the formation of an amorphous shell and preservation of the c-Si core. These findings validate the feasibility of a partial lithiation strategy for SiGr anodes and provide unprecedented insights for the design of mechanically stable electrodes. Additionally, the interpretation of lithiation/delithiation differential capacity plots is discussed in light of the observed structural evolution, offering both fundamental and practical advancements for the development of robust SiGr anodes for high-energy-density LIBs.