Guidelines for Correlative Imaging and Analysis of Reactive Lithium Metal Battery Materials

TL;DR

This paper develops a protocol for correlative imaging of reactive lithium metal and its SEI, enabling high-resolution, minimally damaging characterization crucial for advancing lithium battery technology.

Contribution

It systematically evaluates sample handling, imaging techniques, and electron dose limits, establishing a robust method for atomic-level analysis of lithium metal and SEI.

Findings

High-resolution imaging of lithium metal at room temperature is feasible with inert gas transfer.

SEI components like Li2CO3 and LiF are highly sensitive to electron beams, requiring cryogenic conditions.

A protocol minimizing damage and contamination during sample preparation and imaging is proposed.

Abstract

To unlock the full potential of lithium metal batteries, a deep understanding of lithium metal reactivity and its solid electrolyte interphase is essential. Correlative imaging, combining focused ion beam and electron microscopy offers a powerful approach for multi-scale characterization. However, the extreme reactivity of lithium metal and its SEI presents challenges in investigating deposition and stripping mechanisms. In this work, we systematically evaluated the storage stability of lithium metal in glovebox before and after electrochemical deposition. We then assessed different FIB ion sources for their impact on lithium metal lamella preparation for transmission electron microscopy. Furthermore, we examined cryogenic-TEM transfer methods, optimizing for minimal contamination during sample handling. Contrary to prior assumptions, we demonstrate that high resolution imaging of pure lithium metal at room temperature is achievable using inert gas transfer with an electron dose rate exceeding 1000 e/A2/s, without significant detectable damage. In contrast, SEI components, such as Li2CO3 and LiF display much greater sensitivity to electron beams, requiring cryogenic conditions and precise dose control for nano/atomic scale imaging. We quantified electron dose limits for these SEI components to track their structural evolution under irradiation. Based on these findings, we propose a robust protocol for lithium metal sample handling - from storage to atomic-level characterization - minimizing damage and contamination. This work paves the way for more accurate and reproducible studies, accelerating the development of next-generation lithium metal batteries by ensuing the preservation of native material properties during analysis.