Electrochemical-Mechanical Coupling at Li Metal / Solid Electrolyte Interfaces and the Safety of Li Metal Solid-State Batteries

Abstract

Using Li and Na metal with a solid electrolyte in high-energy and safe batteries for consumer applications is of great interest, but our understanding of the behavior of this interface, as well as the expected safety of high-energy cells built with Li or Na metal and a solid electrolyte, requires improvement. In this talk I will describe (1) our work in both modeling and measuring electrochemical-mechanical coupling at a Li or Na metal / solid electrolyte interface, as well as (2) modeling and experimental work on Li metal solid state battery safety.The electrochemical-mechanical coupling topic (1) will focus on the influence on the current distribution of expected mechanical loadings at a metal/solid electrolyte influence, taking into account the expected plastic deformation of the metal electrode. We find that the mechanical boundary conditions, and inclusion of plastic deformation of a metal electrode such as Na or Li, strongly influences the resulting impact on the interfacial current distribution. Our approach and recent experimental work for parameterizing and validating electrochemical-mechanical coupling will also be presented. Here, we focus on interfacial characterization and methods to study thin films of solid state battery materials under well-defined mechanical loads.The solid-state battery topic (2) will focus on a quantitative understanding of temperature rise in Li metal solid state batteries, based on the thermochemistry of the reactions that occur upon heating due to an external source (e.g., an oven test) or an internal short. Previously reported differential scanning calorimetry experiments as well as those we collect provide heat flows vs. temperature for the reactions among cell components (e.g., Li metal, cathode powder, solid electrolyte, cathode binder and conductive additive, current collectors). This data serves as a basis for modeling temperature rise in large-format cells. We find that oxygen release from metal oxide cathodes that reacts with molten Li in the cell can drive significant temperature rise, and discuss methods to improve the safety of Li metal solid state batteries.