Operando visualization of Li distribution in solid-state batteries using focused ion beam-secondary ion mass spectrometry imaging

• Development of a new FIB-SIMS methodology for operando chemical imaging of solid-state batteries. This method addresses the limitations of previously reported techniques by allowing simultaneous SIMS analysis and battery operation. • Real-time visualization of Li ion migration from electrode into electrolyte in presence of external electrical current via isotope tracing. • Investigation of measurement artifacts in operando experiments caused by probing ion beams and chemical crosstalk between the electrode and electrolyte. A thorough understanding of lithium transport pathways through electrode/electrolyte during battery operation is crucial for developing high-performance all-solid-state batteries (SSBs). However, limitations in existing characterization techniques make real-time tracking of lithium transport challenging. In this article, we report on the development of a setup for operando secondary electron (SE) and secondary ion mass spectrometry (SIMS) imaging of SSBs. We designed a specialized electrochemical cycling setup and a sample holder, enabling simultaneous battery operation and SE-SIMS imaging inside a prototype platform that combines a dual-beam focused ion beam-scanning electron microscope (FIB-SEM) with a double-focusing magnetic sector SIMS system (referred hereafter as FIB-SEM-SIMS). The developed setup allows battery cycling using a commercial potentiostat while maintaining the necessary sample bias for simultaneous SIMS imaging. To demonstrate the capabilities of this setup, we imaged lithium-ion transport in a solid-state Li-half cell with a ⁶Li rich foil working electrode. A chronopotentiometry (CP) sequence was applied to the half-cell within the FIB-SEM-SIMS instrument. SIMS analysis at various stages of the CP sequence captured changes in ⁶Li content in the electrolyte, resulting from ⁶Li ion migration from the working electrode due to the applied current. The methodology described here enables real-time visualization of transient changes in the spatial distribution of Li during battery operation, making it highly valuable for detailed investigations of ion transport pathways in SSBs. We also discuss strategies to minimize probable measurement artifacts arising from use of charged ion and electron beams for operando analysis.