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

Abstract

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.