Insights into the SiO₂ Stress Effect on the Electrochemical Performance of Si anode

Silicon (Si) is regarded as the most potential anode material for next-generation lithium-ion batteries (LIBs). However, huge volume expansion hinders its commercial application. Here, a yolk-shell structural nitrogen-doped carbon coated Si@SiO₂ is prepared by SiO₂ template and HF etching method. The as-prepared composite exhibits superior cycling stability with a high reversible capacity of 577 mA h g^-1 at 1 A g^-1 after 1000 cycles. The stress effect of SiO₂ on stabilizing the electrochemical performance of Si anode is systematically investigated for the first time. In situ thickness measurement reveals that the volume expansion thickness of Si@SiO₂ upon charge-discharge is obviously smaller than Si, demonstrating the electrode expansion can be effectively inhibited to improve the cyclability. The density functional theory (DFT) calculation further demonstrates the moderate young's modulus and enhanced hardness after SiO₂ coating contribute significantly to the mechanical reinforcement of overall Si@SiO₂@void@NC composite. Various post-cycling electrode analyses also address the positive effects of inner stress from the Si core on effectively relieving the damage to electrode structure, facilitating the formation of a more stable inorganic-rich solid electrolyte interphase (SEI) layer. This study provides new insights for mechanical stability and excellent electrochemical performance of Si-based anode materials.