Beyond Volume Variation: Anisotropic and Protrusive Lithiation in Bismuth Nanowire

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Alloying materials offer higher energy density for lithium-ion batteries (LIBs) compared to graphite anodes.
• Previous studies attributed cycling-induced structural failure solely to volumetric expansion during lithiation.

Purpose of the Study:

• To investigate alternative structural failure mechanisms in alloying-based anodes.
• To analyze the lithiation process and resulting structural changes in single-crystalline bismuth nanowires.

Main Methods:

• Experimental characterization of single-crystalline bismuth nanowires during lithiation.
• Density functional theory (DFT) calculations to study alloying kinetics and energetics.
• Atomic-scale analysis of nanostructure evolution and failure mechanisms.

Main Results:

• The Li-Bi alloying process involves a two-step transition (Bi-Li 1 Bi and Li 1 Bi-Li 3 Bi).
• Anisotropic lithiation facilitated by Bi-(012) occurs in the bulk.
• Nanoscale protrusions of Li 1 Bi dominate surface morphology, driven by dislocation-assisted strain relaxation and Bi migration.
• These protrusions detach, contributing to capacity decay.

Conclusions:

• Structural failure in alloying anodes is more complex than volumetric expansion.
• Nanoscale protrusions formed during cycling are a significant factor in capacity fade for bismuth-based LIB anodes.
• Understanding these mechanisms is crucial for designing stable, high-energy-density LIBs.