MEASURING INTERFACE EFFECTS IN SOLID-STATE BATTERIES

Abstract

Solid-state batteries with solid metal anodes would be a promising solution for improved energy storage. However, the unstable behaviors of solid-solid interfaces impedes implementation. Further study of these interfaces, both at the planar solid metal anode | electrolyte interface and the grain | grain interface in solid electrolytes is necessary to elucidate practical engineering techniques to improve cycling stability. We assemble three-electrode symmetric cells of Sodium | Sodium β″-Alumina | Sodium to assess the voiding and dendritic behaviors of the sodium metal electrode at varying cycling parameters and operating conditions. By modifying the applied current density and fixing areal capacities at 0.5, 1.0, and 3 mAh cm-2 and utilizing a sodium reference electrode we demonstrate polarization on plate at high current densities. Modeling comparisons with exhaustion strips, unidirectional current application to oxidize the sodium metal electrode until a cutoff potential of 1 V, indicate extensive delamination of the sodium electrode from the solid electrolyte. There is less observed delamination at lower current densities as the cutoff voltage is reached at lower areal capacities. Further study of electrode thickness and operating pressure on critical current densities, the highest achieved current density before failure to 1 V or shorting observed, and achievable capacities show limited benefit to increasing operating pressure beyond 2.0 MPa. We continue our investigation into interfacial behaviors through the assessment of hot pressing effects on argyrodite sulfide electrolytes with respect to morphology, ionic conductivity, and mechanical properties. We find that hot pressing at 150 °C improves ionic conduction without any reliance on external operating pressure with copper electrodes. Hot pressing resulted in smooth fused morphology distinct from the cold pressed (20 °C) samples with an higher modulus. Finally, our efforts in the development of an all solid-state battery database for laboratory scale single set of layer devices is discussed. We identified from the literature the core characteristics and performance metrics for a solid-state batteries and defined the ontology to capture the data for analysis. The ontology was tested and refined through the collection of fifty cells with the target of assessing the state of research, current achievements, gaps, and trends in the literature. The database now contains over 250 cells with plans for further uploads and refinements to the ontology.