Towards Operando Secondary Ion Mass Spectrometry Imaging of Lithium Redistribution in Solid-State Lithium-Ion Batteries—Correlation of Structural, Chemical and Electrochemical Characteristics

Innovations in lithium-ion batteries rely crucially on the availability of advanced characterization techniques. High-resolution chemical imaging of low-Z elements e.g., lithium (Li) is often difficult in many conventional chemical analysis techniques such as Energy-Dispersive X-ray Spectroscopy. High-resolution Secondary Ion Mass Spectrometry (SIMS) imaging is a well-known technique for the analysis of all elements including isotopes. For this reason, SIMS imaging is used in numerous studies related to Li-ion battery research. While direct imaging of Li in post-mortem battery components is helpful to understand parts of the degradation mechanisms, a complete dynamic view of the evolution of the Li distribution at high resolution during operation (‘<i>operando</i>’) of batteries is required to fully understand the local interfacial processes, charge transport characteristics and the degradation mechanisms. A few reports presenting <i>operando</i> Time-of-Flight SIMS imaging of batteries have recently been published [1], but the lateral resolution demonstrated in these reports is not adequate to study local processes that occur at nanoscale.<br/><br/>In order to demonstrate <i>operando</i> SIMS chemical imaging with sub-20 nm lateral resolution, we developed a novel <i>operando</i> methodology suitable for Focused Ion Beam (FIB)-SIMS imaging and analysis. An in-house designed magnetic-sector mass spectrometer [2] attached to a ThermoFisher SCIOS Ga⁺ FIB is used for SIMS chemical imaging. A special <i>operando</i> sample holder was designed to enable electrochemical cycling of batteries within the FIB-SIMS instrument. The micromanipulator inside the FIB (typically used for preparing thin lamellae for Transmission Electron Microscopy) is used to contact one of the battery electrodes through the <i>operando</i> sample holder and complete the electrical circuit. An external potentiostat is then connected to the instrument to drive the charging/discharging of batteries. The proof-of-concept experiments were performed using Li|Li₇La₃Zr₂O₁₂|Li symmetric half-cells. Galvanostatic cycling was performed <i>in-situ</i> inside the FIB-SIMS instrument until the sample failed. SIMS chemical mapping revealed a redistribution of Li during cycling. Lithium rich phases appeared during cycling which likely percolated through grain-boundaries and pores of the solid electrolyte causing a short-circuit failure. These results validate our methodology for <i>operando</i> analysis of Li-ion batteries with the possibility to obtain SIMS chemical images with sub-20 nm lateral resolution [3, 4].<br/><br/>This work was funded by Horizon Europe project OPINCHARGE and by the Luxembourg National Research Fund (FNR) through the grant INTER/MERA/20/13992061 (INTERBATT).<br/><br/>[1] Y. Yamagishi et al., <i>J. Phys. </i><i>Chem. Lett.</i> 2021, 12, 19, 4623–4627<br/>[2] O. De Castro et al., <i>Analytical Chemistry,</i> 2022, 94, 30, 10754–10763.<br/>[3] L. Cressa et al., <i>Analytical Chemistry, 2023, </i>95, 9932–9939<br/>[4] L. Cressa et al., Electrochimica Acta 494 (2024) 144397