Isothermal microcalorimetry as a tool to study solid-electrolyte interphase formation in lithium-ion cells

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• The solid-electrolyte interphase (SEI) is crucial for Li-ion battery performance and longevity.
• Understanding SEI formation mechanisms is key to developing advanced battery technologies.

Purpose of the Study:

• To investigate the SEI formation reactions in Li-ion cells using isothermal microcalorimetry (IMC) and electrochemical measurements.
• To analyze the impact of electrolyte additives (VC, FEC, PBF, PES) on SEI formation.

Main Methods:

• Utilized isothermal microcalorimetry (IMC) to measure heat flow during SEI formation.
• Performed electrochemical measurements, including differential capacity (dQ/dV vs. Q) analysis.
• Studied Li-ion cells with and without specific electrolyte additives.

Main Results:

• Observed complex SEI formation for vinylene carbonate (VC) and fluoroethylene carbonate (FEC) additives, not aligning with simple reduction-polymerization models.
• Found that pyridine boron trifluoride (PBF) reduction minimally impacts ethylene carbonate (EC) reduction at higher voltages.
• Heat flow in PBF- and prop-1-ene-1,3-sultone (PES)-containing cells correlated with published reaction pathway energies.

Conclusions:

• Isothermal microcalorimetry (IMC) is a valuable tool for studying SEI formation chemistry in Li-ion batteries.
• IMC, especially when integrated with computational studies, provides deeper insights into SEI reaction mechanisms.
• The study highlights the complex electrochemical and thermal behavior during SEI formation with various additives.