Multimodal Operando Analysis of High-Capacity Electrodes with Photons and Neutrons

Abstract

High-capacity electrodes such as sulfur cathodes and silicon anodes are promising candidates for sustainable electrochemical energy storage in a post-lithium-ion era. While lithium-sulfur (Li/S) batteries have five times higher theoretical gravimetric energy density (about 2500 Wh/kg) than modern lithium-ion batteries [1], silicon is an interesting anode material for lithium-ion batteries because its specific capacity is ten times higher than that of commercially used graphite anodes. However, despite decades of research, the sharp drop in capacity with the increasing number of cycles is still a major obstacle to widespread technical use of both electrodes. Operando techniques [2,3] are well suited to gaining a mechanistic understanding of the degradation processes. In particular, the simultaneous combination of several independent measurements (multimodal) during the operation of the electrodes allows deep insights into the degradation mechanisms. It enables a more advanced mechanistic understanding of the two complex chemical processes.This conference contribution presents the results of novel experimental setups in which multiple independent measurements were performed simultaneously. Electrochemical impedance spectroscopy (EIS), temperature measurement and X-ray imaging or neutron techniques such as neutron small angle scattering and neutron reflectometry were performed over several cycles. Simultaneously, cells were charged and discharged galvanostatically or potentiostatically. Structural changes at the macroscopic and microscopic levels and chemical compositions can be correlated with characteristic signals in the EIS and charge-discharge curves.In particular, imaging and spectroscopic techniques on button cells with X-rays, especially at a synchrotron source, allowed essential insights into the processes in lithium/sulfur batteries [4–8]. But also, applying this characterization method on industrially relevant pouch cells could provide important information about processes in this cell format [9].Neutron reflectometry is particularly well suited for analyzing electrochemical interfaces on silicon electrodes [10], which was also performed in operando mode [11–13]. Furthermore, for this electrode material, important insights into electrode processes could be obtained using operando X-ray spectroscopy and X-ray imaging at the synchrotron [14,15].