Solid-State Electrolyte Design: Microstructure and Performance

Abstract

Solid-state batteries hold significant promise for next-generation energy storage devices; however, poor material contact at the cathode/electrolyte interface often impedes their performance by increasing interfacial resistance. To address this issue, solid-state batteries are often manufactured with porous electrodes that dramatically increase interfacial surface area and improve cell kinetics. These porous electrodes often contain complex microstructures whose unique morphologies are determined by the specifics of the manufacturing process, with two popular approaches being tape-casting and, more recently, 3D printing. While the exact relationship between microstructure and performance is not completely understood, cell performance can be predicted numerically through the use of 3D electrochemical-transport simulations. These simulations heavily depend on the accuracy of the geometries studied and therefore require high-resolution reconstructions from characterized samples. These characterizations are resource-intensive to obtain, rendering optimization studies of porous microstructures untenable by conventional methods. This work uses computer-generated microstructures (CGMs) to approximate the microstructures of tape-cast and 3D-printed porous electrodes. While 3D-printed architectures can be modeled with geometric primitives, a stochastic algorithm was created for the synthesis of high-fidelity tape-cast microstructures. This algorithm uses a physics-based molecular simulation that emulates the tape-casting process of multiple media. A rigorous validation suite was developed to assess the faithfulness of these CGMs to several experimental samples characterized with FIB-SEM and X-Ray µCT. An analysis of these microstructures across several geometric parameters (including porosity, specific surface area, tortuosity, etc.) reveals the existence of relationships that are seemingly characteristic to the tape-casting process. An electrochemical-transport model was subsequently developed to predict the performance of tape-cast and 3D-printed solid-state electrolytes. By adjusting the geometric parameters and the applied cycling conditions, this work directly compares the galvanostatic discharge of the cells to further study the impact of microstructure on performance and develop strategies for the manufacture of high-energy porous electrodes.