Mechanical properties of solid state batteries

Solid state batteries are an emerging technology in energy storage applications. They have significant advantages over traditional lithium ion batteries including higher energy density and increase safety. They have been identified as a key tool in the electrification of transport. However little is understood about the mechanical properties of the material components of the system and especially the interfaces between, solid state ionic conductors, anodes and cathodes with most work focusing on the chemistry of the systems even though them mechanical data is key to deployment in industrial applications.

The project will initially focus on the mechanical properties of solid electrolytes. This will include the sodium-beta alumina system for solid state sodium batteries and LLZO for use in the lithium ion batteries. Due to the highly reactive nature of these materials and their air sensitive nature all work must be carried out in inert atmosphere. The project will leverage recent investments in Oxford in novel glove box based, in SEM micromechanical testing equipment. Taking methods usually used in nuclear and aerospace materials and applying them to energy storage materials for the first time. This will use specimens produced through focused ion beam machining then tested using in-situ nanoindentation. In this way basic information on the failure mechanism will be obtained. Following this the project will move onto look at the mechanical properties between the electrolyte and the anode and cathode materials. The degradation of these interfaces during operation is known to limit battery life, and understanding how they fail is key. This would include looking at the electrolyte cathode and electrolyte anode interface. As these are likely to be metal-ceramic and metal-polymer interfaces they will exhibit very different mechanical responses and understanding the failure mechanisms in these is important to the development of battery life models. To understand the physical basis of the mechanical data finite element modelling of simple systems will be used with the model seeded with data from the experimental work.

This project will use a range of novel nano and mico-mechanical indentation methods to study, the hardness, elastic modulus, yield stress and fracture toughness of solid state battery materials processed in both bulk and thin film forms. These properties will be related to local microstructural features through the use of scanning electron microscopy (SEM), Electron back scattered diffraction (EBSD) and Raman Spectroscopy. Finally these micromechanical properties will be compared to bulk fracture properties obtained through four point bend flexure tests. The data produced in this way will not only be useful for seeding models but allow optimisation of processing routes for producing electrolytes with improved lifetime . This work fits into the EPSRC energy theme.