Synthesis of Complex, Multi-Phase Solid Electrolytes by a Vapor Phase Process

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NON-TECHNICAL: This work focuses on the synthesis of materials that will be used in batteries to store electrical energy generated by various renewable sources (such as solar, wind) as well as using natural gas and biogas. The batteries made using such materials are also ideally suited for load leveling, which means storage of electrical energy produced during off peak times and used during peak usage times. Load leveling batteries have the potential to reduce the size of the carbon dioxide-producing power plants which has a direct influence on our environment. The current method of making such materials used as electrolytes involves high temperatures and the materials produced easily degrade under typical atmospheric conditions. This approach builds on the very basics of thermodynamic stability of materials and multi-species transport, central to the fabrication of new types of oxide materials in various applications in chemical industry and other processes, and has the potential to make durable materials in environmentally clean ways. Two undergraduate students are recruited to work on the project each year. At least one of the students is from an underrepresented group. As well, one graduate student is being trained throughout the duration of the project. The students are gaining expertise in science and engineering related to ceramic processing. TECHNICAL DETAILS: Transport in ionically bonded systems most always involves coupling of fluxes. This coupling is typically electrical. For years, all transport processes (e.g., amibipolar transport) have been described using diffusion equations applied to single phase systems. For example, many studies have described transport through single phase materials, e.g., alumina, magnesia, and zirconia. In such systems, the slowest moving species dictates the kinetics, and thus governs the processes such as sintering. This work shows that electrical coupling (which can in principle be described by Onsager equations and linear non-equilibrium thermodynamics) is not limited to single phase systems. Thus, it is possible to envision parallel transport to multi-phase systems, which is still governed by electrical coupling. The principal scientific advance is in using this concept to increase the kinetics of transport by orders of magnitude. As a specific example, transport in single phase alumina (or Na-beta"-alumina) is very sluggish due to slow oxygen diffusion. However, by providing a rapid path for the transport of oxygen (using an oxygen ion conductor as a constituent in a two phase system), the process kinetics is enhanced. Additionally, this approach allows a precise control over thermodynamics such that unwanted side reactions are suppressed. This approach is not limited to oxides, but can be extended to many other types of technologically important materials (halides, sulfides, etc.) and can also be extended to more than two phases. The approach has the potential to lead to processes for the synthesis of materials with novel properties and new directions of research.