Electrochemical Deposition of Si-C-O Composite Layers: Lithiation and Sodiation Behavior

Abstract

Silicon has become an essential part of today´s world. Its physical properties make it an important component for solar energy conversion and electronic industry. The possibility to form reversibly Si-Li alloys and to enhance the energy density of the next generation rechargeable batteries provides a new important perspective for the development of advanced energy storage. However, the industrial production of pure silicon is extremely energy consuming since the chemical reduction of SiO2, involved in this process, is performed at 2000 °C. Furthermore, depending on its application, a refining of the metallurgical silicon is afterwards necessary. The additional available technologies for example, need high vacuum, which can be applied with a very complex and expensive equipment [1].Electrochemical deposition enables less complicated and low-cost fabrication processes than high vacuum technologies. However, due to the very negative reduction potential and high reactivity of silicon precursors towards water, room temperature deposition of this element is impossible in aqueous media. Therefore, much effort has been focused on performing Si deposition from different organic electrolytes with larger electrochemical windows of stability, i.e. based on propylene carbonate, acetonitrile, dichloromethane, ionic liquids and sulfolane [1-3].However, it was found that beside elemental silicon the electrochemically obtained deposits contain substantial quantities of carbon and oxygen, resulting from electrolyte decomposition and high reactivity of the new silicon phase. Although the silicon layers are highly contaminated, the electrochemical stability of these Si-O-C composites has been markedly enhanced, compared to pure elemental silicon. This can be attributed to the buffering effect of the C-O matrix, which accumulates the mechanical stress during lithiation and sodiation [4,5].The present talk will deliver recent results from the authors’ lab on the electrodeposition of Si-C-O composite layers. Attention will be paid to the influence of different factors (i.e. electrolyte composition, deposition potential and substrate type) on the chemical composition and physical properties of the layers. The reversible lithiation and sodiation of the Si-C-O materials will be demonstrated and discussed.