MOST Grant Awarded - Synthesis, Structural and Electrochemical Analysis of Lithium Silicates

Silicon monoxide is an inorganic ceramic material by co-heating silicon and silica (molar ratio 1:1) under high temperature followed by rapid quenching, which is usually in amorphous phase. Currently, silicon monoxide is employed in anode materials of Li-ion batteries and optical coatings as mainstream applications. When silicon monoxide is used for the anode, during electrochemical lithiation processes, silicon-oxygen bonds will react with lithium ions to form various lithium silicate crystals. However, in previous literature, there were no systematically qualitative and quantitative analyses, not to mention advanced in-situ analysis results. There were no detailed discussions on the electrochemical activity and mechanical properties of any specific lithium silicates, either. Therefore, it would be difficult to design an appropriate silicon monoxide anode material by adjusting the composition ratio of lithium silicates formed during lithiation without knowing their properties. This research project aims to study various lithium silicates under different processing conditions. The physical, chemical, mechanical, and electrochemical properties of lithium silicates synthesized or formed under different electrochemical lithiation depths will be investigated. We plan to utilize solid-state chemical and hydrothermal methods to synthesize lithium silicates (LixSiyOz) with various lithium/silicon ratios, and analyze their characteristics in details to understand how to optimize the anode structure. Since a disproportional reaction can be carried out in the silicon monoxide by heating with inert gases, amorphous silicon will transform into nanocrystals or even large crystals. This will impact the composition, size, and quantity of lithium silicates formed after electrochemical lithiation processes. In the meantime, we will also utilize advanced ex-situ and in situ analysis methods to understand how a specific lithium silicate crystalline structure can form and be controlled by a certain electrochemical lithiation depth. After investigating the forming mechanisms and electrochemical/mechanical properties of lithium silicates, we can further design the best structure of pre-lithiated silicon monoxide for lithium-ion battery applications. This pre-lithiated silicon monoxide will avoid excess lithium loss during initial cycles due to the oxide structure in the anode will transform into lithium silicates in advance. As a result, a high-Coulombic-efficiency and high-energy-density pre-lithiated silicon monoxide anode material will be developed. Additionally, we will also utilize lithium silicates as a protective layer for lithium metal anode to suppress lithium dendrite and dead lithium formation, thereby enhancing the cycle life performance of next-generation high-energy-density lithium metal batteries. We are highly confident that lithium silicates will become an emerging anode structural stabilizer after scrutinized investigation in this project.