Advanced Understanding of Micro Structures in Fuel Cells and Batteries through X-ray Imaging (ADMIST)
3D rendering of a tomographic scan: vertical cut along the fl ow fi eld channel of an in-operando HT-PEFC (orange: phosphoric acid and catalyst layer; olive: fl ow fi eld; gray: carbon fi - bers). Source: Eberhardt, S. et al., J. Electrochem. Soc. 2015 volume 162, issue 3, F310-F316, Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/)
Scope of project
The project ADMIST aims at improving the durability and performance of high (HT) and low (LT) temperature polymer electrolyte fuel cells (PEFC) and Li-ion batteries (LIBs). The lifetime and the performance of these three technologies is largely determined by the microstructure of the constituents, the temporal changes to the microstructure, and the related mass transport properties in the micro-porous domains. In HT-PEFC the loss of phosphoric acid (PA), evaporating in the high surface area gas diffusion layers is the major life limiting process. However today little is known about the ratelimiting step of the PA loss and thus directed material development is difficult. Precise characterization of the PA fraction and concentration and its temporal changes in the microporous gas diffusion layer is required, so the evaporation process is better understood. This will lead to higher lifetimes of HT-PEFC. In LT-PEFC condensed water in the gas diffusion layer leads to performance loss and/or catalyst degradation at high current densities and/or condensing operating conditions. Despite considerable efforts, the processes of liquid water (transport, condensation, evaporation) in the porous structure are not well understood. Better understanding leads to higher power density and durability. In LIBs, performance and lifetimes are linked to both materials selection and porous electrode microstructure. Mechanical degradation of the porous electrode driven by volume changes of the active materials during reduction and oxidation is particularly dramatic for many high capacity materials undergoing conversion and/or alloying reactions that are being considered for next generation LIBs. At the same time, unoptimized microstructures can lead to poor rate capabilities, inhomogeneous lithiation, and metallic lithium plating. Despite this general understanding that material selection and microstructure can play an important role in battery performance, the exact mechanisms that lead to shortened battery life are far from understood. In order to successfully engineer materials and battery architectures to improve performance and mitigate degradation, it is critical to understand the reasons for high performance or degradation and their relationship to controllable parameters during LIB manufacturing. All of the above technologies require the understanding of the structure of the different phases in the porous material. X-ray imaging methods are powerful tools to characterize the opaque structures, in- and ex-situ. The aim of ADMIST is to further develop by X-ray imaging for all three applications, leading to a profound understanding and thus the basis of significant improvements for the complex materials.
Dr. Felix Büchi
Paul Scherrer Institute,
Electrochemical Energy Conversion, Fuel Cell Systems and Diagnostics
Phone: +41 56 310 2411