Atomic-Scale Observation of Electrochemically Reversible Phase Transformations in SnSe₂ Single Crystals

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Two-dimensional (2D) materials offer potential for next-generation lithium-ion batteries.
• Tin-based chalcogenides undergo complex phase transformations during lithium insertion (intercalation, conversion, alloying), but their reversibility and structural changes are not fully understood.

Purpose of the Study:

• To provide the first real-time, atomic-scale observation of reversible phase transformations in SnSe2 during lithiation and delithiation.
• To elucidate the atomistic mechanisms governing these transformations and their impact on structural integrity and electrochemical cyclability.

Main Methods:

• In situ high-resolution transmission electron microscopy (HRTEM) for real-time atomic-scale observation.
• First-principles calculations to complement experimental findings and understand reaction pathways.

Main Results:

• Observed sequential lithiation via intercalation, conversion, and alloying (SnSe2 → LiₓSnSe2 → Li₂Se + Sn → Li₂Se + Li₁₇Sn₄) while maintaining structural integrity.
• Delithiation forms well-aligned SnSe2 nanodomains through deconversion, but orientation coherence is lost over cycling.
• Alloying/dealloying induce significant structural reorganization, reducing stability and cyclability, suggesting avoidance of deep discharge for Sn chalcogenide electrodes.

Conclusions:

• The study elucidates the atomistic mechanisms of lithiation and delithiation in SnSe2.
• Findings have implications for designing and optimizing 2D metal chalcogenides for advanced battery applications.
• Deep discharge should be avoided in Sn chalcogenide electrodes to maintain structural stability and electrochemical performance.