Surface morphology and reactivity of the solid electrolyte lithium thiophosphate for all solid state batteries at the atomistic scale

• Applicant: Dr. Hanna Türk
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation ; Theoretical Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 534232519

Lithium thiophosphate (LPS) is a promising electrolyte for solid-state lithium ion batteries, which offer superior energy storage and less flammable components in comparison to conventional electrolytes. However, the high reactivity of the solid electrolyte with air, water and common electrode materials hinders commercialization of such cells. Although passivation strategies by e.g. material doping or coating with lithium ion conducting materials such as aluminum oxide exist, the unknown structure, morphology, and chemical behavior of LPS’s surface is a bottleneck in the rational improvement of this material class. In this project, we aim at the identification of passivating surface reactions of LPS with small contaminant molecules by molecular modeling. As an adequate description of this complex energy material requires large simulation cells, obtaining a detailed picture of the relevant properties and processes is unfeasible with conventional methods such as first-principle calculations e.g. density functional theory. We thus take a twofold, machine learning (ML) based approach to fully capture all physicochemical, electrochemical, and mechanical properties of the surface of the solid electrolyte LPS. On the one hand, we extend a ML potential for bulk LPS developed by the host group to be able to describe surfaces and additional elements that can react with this surface i.e. hydrogen and oxygen. Therewith, the reaction mechanisms of the surface with water become accessible. On the other hand, as the ML potential neglects the electronic properties of the battery material, we develop a ML model to predict the electronic Hamiltonian, yielding an accurate electronic structure information of given atomic environments. As this approach has only been used for molecules so far, we adapt it in a first step to bulk materials. This allows us to investigate the electronic structure of crystal and amorphous regions, as well as their grain boundaries. We then extend this model to LPS surfaces towards vacuum and the additional element hydrogen and oxygen, which we use to identify all possible reaction sites on the surface and to gain electronic structure insights of the passivation reaction. In combination, the two parts of the project will provide a fundamental understanding of the reaction mechanism of the surface of LPS with water. The gained knowledge will serve as guiding principle to design surface coatings and dopings, which improve the stability of the solid electrolyte by suppressing undesired surface reactions. Hence, this opens the gate to rationally enhance surface properties via interfacial engineering and enable the design of solution-processable solid electrolytes with enhanced stability.

• DFG Programme: WBP Fellowship
• International Connection: Switzerland
• Host: Professor Dr. Michele Ceriotti