Probing the Liquid Solid Interfaces of 2D SnSe MXene Battery Anodes at the Nanoscale

TL;DR

The study addresses degradation of SnSe MXene battery anodes caused by volume changes during Li alloying/conversion and current-collector deterioration. It introduces a cryo FIB slice-and-view coupled with depth-resolved cryo APT workflow to visualize both mesoscale morphology and nanoscale chemistry at buried interfaces under cryogenic conditions. Key findings include extensive depth-dependent expansion, delamination, partial SnSe dissolution, Sn clustering, electrolyte infiltration, and the first direct observation of copper corrosion with Cu ion migration from the current collector into the electrode. The integrated approach provides a powerful framework for diagnosing degradation in reactive, beam-sensitive battery materials, with implications for current collector design and the development of more durable next-generation anodes.

Abstract

Understanding degradation processes in lithium ion batteries is essential for improving long term performance and advancing sustainable energy technologies. Tin selenide (SnSe) has emerged as a promising anode material due to the high theoretical capacity of tin. Unlike conventional intercalation based electrodes, SnSe undergoes conversion and alloying reactions with lithium to form Li4.4Sn, Sn, and Li2Se, enabling high lithium storage but inducing large volume changes that cause mechanical instability and capacity fading. Embedding SnSe nanoparticles within a Ti3C2Tx MXene framework offers a strategy to mitigate these effects by enhancing conductivity and structural resilience. Here, cryogenic focused ion beam (cryo FIB) slice and view revealed progressive material redistribution and morphological transformation during cycling, underscoring the need for site specific chemical analysis. Cryogenic atom probe tomography (cryo APT) of selected regions provided high spatial and chemical resolution while preserving beam sensitive phases, uncovering nanoscale degradation mechanisms including phase transformations, partial dissolution of active material, and, importantly, the first direct evidence of copper corrosion and copper ion migration from the current collector into the electrode. The observation of copper redistribution demonstrates that current collector degradation contributes directly to chemical contamination and capacity fading in composite electrodes. Together, cryo FIB and cryo APT provide a powerful workflow for elucidating electrode degradation in reactive, beam sensitive systems, offering critical insights for designing more durable and stable next generation battery materials.

Figures (14)

• Figure 1: Cryogenic FIB and SEM slice and view imaging of the expansion and damage occurring within the SnSe electrode during cycling showing. (a) SEM image and corresponding schematic of the native SnSe MXene electrode pre-cycling soaked with electrolyte. (b) SEM imaging showing the expansion of the electrode material after lithium electrochmical cycling. All SEM images were taken using the TLD detector in SE-mode
• Figure 2: SEM images of cycled SnSe electrodes permeated with electrolyte, showing a) several low magnification slices with a thin capping layer of Pt, significant amounts of electrolyte, and particles of SnSe both at the bottom as well as spread throughout the electrolyte, b) a high magnification image of a mostly intact SnSe particle in the process of delaminating (circled in red), and c) a high magnification image of a mix of SnSe and MXene in electrolyte
• Figure 3: (a) Schematic of a cycled electrode, showing the principle of taking samples at different depths and reconstructing needles from them, (b) a reconstructed needle from near the top of an electrode, (c) a reconstructed needle from the bulk of an electrode, and (d) a reconstructed needle from the electrode interface with the current collector
• Figure 4: APT Measurement from a needle at the interface with the current collector showing a) the reconstructed needle and individual reconstructions of several different ion species, b) clusters of Cu at the bottom of the specimen from the area marked in blue, rotated to a top-down view, shown as an isosurface at 19 at%, and c) concentration profiles of a selection of elements along the z axis of the needle, in log scale.
• Figure 5: APT measurement from a needle taken from the top of an electrode, showing (a) the reconstructed needle and individual reconstructions of several different ion species and (b) concentration profile of a selection of elements along the z axis of the needle in log scale.