Carbon-coating strengthens the solid electrolyte interphase to inhibit Si pulverization

Abstract

The huge volume change during cycling causes severe electrode pulverization and rapid capacity fading of Si-based anodes. So far, various carbon-coating methods have been explored to enhance the cycling stability of Si anodes. However, the mechanism behind this strategy receives little attention. In this work, the stability of the solid electrolyte interphase (SEI) formed on carbon-coated Si and its role in the fracture inhibition are verified using X-ray photoelectron spectroscopy with Ar ion sputtering and the amplitude modulation-frequency modulation mode of scanning probe microscopy. A comparative experimental study and density functional theory calculations of the adsorption energy of electrolyte components confirm that fluoroethylene carbonate is more apt to be adsorbed on the surface of the carbon-coating layer to form a robust SEI than on that of Si. The LiF-rich SEI with higher Young's modulus can withstand the volume change upon lithiation/delithiation of Si, and keep itself intact. Therefore, the enhanced SEI can inhibit the cracking of Si and suppress continuous decomposition of electrolyte. This study provides critical insights into the function of the SEI from the perspective of carbon coating/electrolyte interphase protection, and also gives valuable suggestions to the design of electrodes with large volume change.