Initial SEI formation in LiBOB-, LiDFOB- and LiBF₄-containing PEO electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Solid polymer electrolytes (SPEs) are crucial for Li-battery safety and performance.
• The electrolyte decomposition layer at the Li metal anode interface significantly impacts battery functionality.
• Improving this layer is essential for advancing Li-battery technology.

Purpose of the Study:

• To investigate the electrolyte decomposition layer in three different SPEs: PEO:LiBF4, PEO:LiBOB, and PEO:LiDFOB.
• To correlate cell performance with the initial SPE decomposition at the anode interface.
• To understand the formation and impact of the solid electrolyte interphase (SEI).

Main Methods:

• Electrochemical impedance spectroscopy (EIS) for interface analysis.
• Galvanostatic cycling to evaluate cell performance and capacity retention.
• In situ Li deposition photoelectron spectroscopy (PES) for surface characterization.
• Ab initio molecular dynamics (AIMD) simulations for mechanistic insights.

Main Results:

• PEO:LiDFOB demonstrated the highest capacity retention among the investigated SPEs.
• Lower SPE decomposition at the interface correlated with better performance and a more effective protective layer.
• PES and AIMD revealed polyethylene formation in the SEI, originating from ethylene free-radical polymerization.

Conclusions:

• The PEO:LiDFOB electrolyte forms a more effective decomposition layer with less initial decomposition.
• Reduced interface decomposition is key to enhanced Li-battery performance and longevity.
• Polyethylene formation via ethylene polymerization is a significant pathway in PEO-based SPE SEI.