Amorphous columnar silicon anodes for advanced high voltage lithium ion full cells: Dominant factors governing cycling performance

The effect of the electrolyte solution composition and the cycling protocol on the long-term cycling performance and surface chemistry of monolithic amorphous columnar silicon film electrodes was investigated using electrochemical tools, XPS, SEM and EDS. An excellent cycling stability of Si electrodes in fluoroethylene carbonate (FEC)-based electrolyte solutions was demonstrated. It relates to the ability of FEC to form polyenes, as well as to a high rate of HF formation in its water contaminated LiPF₆ solutions, measured by ¹⁹F NMR spectroscopy. We found that excellent passivation in FEC solutions related to a low content of oxygen containing moieties in surface films. Galvanostatic tests and spectroscopic analyzes revealed also a strong dependence of the composition and properties of the surface films on amorphous Si electrodes on the cycling procedure. Repeated deep discharge of Si electrodes down to 10 mV vs. Li/Li⁺ from the very beginning of the electrodes life ensures the formation of thin effective surface films on their surface and good cycling performance. Cycling stability of Si electrodes in LiPF₆ solutions decreases in the following order FEC/DMC > 3,4-trans-difluoroethylene carbonate (DFEC)/DMC > ethylene carbonate (EC)/DMC > propylene carbonate (PC).