In Situ Neutron Reflectometry Study of a Tungsten Oxide/Li-Ion Battery Electrolyte Interface.

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• The solid electrolyte interphase (SEI) is critical for lithium-ion battery performance.
• Understanding SEI formation on conversion electrodes like tungsten oxide is essential for battery development.

Purpose of the Study:

• To characterize SEI formation on a model tungsten oxide (WO3) conversion electrode.
• To study the lithiation process of WO3 using in situ neutron reflectometry.
• To interpret SEI behavior on tungsten-based electrodes.

Main Methods:

• In situ neutron reflectometry (NR) was employed to analyze the interface between a WO3 electrode and a LiPF6 electrolyte.
• Electrochemical potentials were varied to induce and observe SEI formation and electrode lithiation.
• NR data were analyzed to determine neutron scattering length density (SLD) depth profiles, inferring composition.

Main Results:

• As the WO3 electrode was polarized to reducing potentials, the oxide layer expanded and incorporated lithium.
• A multi-layered SEI formed, potentially comprising LiOH/LiH (inner SEI) and solvent-derived species (outer SEI).
• Reversing potentials showed qualitative reversal of layer evolution, indicating hysteresis.

Conclusions:

• The study provides detailed insights into the dynamic SEI formation and lithiation of WO3 conversion electrodes.
• The observed layered structure and lithium incorporation mechanism offer valuable data for battery design.
• Reaction kinetics were not diffusion-limited within the evolving electrode film.