Identifying the components of the solid-electrolyte interphase in Li-ion batteries

Area of Science:

• Electrochemistry
• Materials Science
• Solid-state Chemistry

Background:

• The solid-electrolyte interphase (SEI) is critical for Li-ion battery function, but its exact composition is debated.
• Current understanding suggests lithium ethylene di-carbonate (LEDC) is the primary organic SEI component, believed to offer good Li+ conductivity and electronic insulation.

Purpose of the Study:

• To synthesize and characterize authentic lithium ethylene di-carbonate (LEDC) and lithium ethylene mono-carbonate (LEMC).
• To compare these compounds with the SEI formed on graphite anodes.
• To elucidate the structural and conductive properties of LEMC and LEDC.

Main Methods:

• Synthesis of LEDC and LEMC.
• Structural characterization using single-crystal X-ray diffraction.
• Spectroscopic analysis.
• Measurement of Li+ conductivity.
• Investigation of LMC, LEMC, and LEDC interconversions in solution.

Main Results:

• Direct comparison indicates LEMC is likely the major SEI component on graphite anodes, challenging the LEDC consensus.
• Single-crystal X-ray diffraction revealed unique layered structures and Li+ coordination in LEMC and lithium methyl carbonate (LMC).
• LEMC demonstrates significant Li+ conductivity (>1 × 10^-6 S cm^-1), whereas LEDC exhibits insulating properties.

Conclusions:

• The findings suggest LEMC, not LEDC, is the predominant organic component of the SEI in Li-ion batteries.
• The distinct structural and conductive properties of LEMC highlight its importance for SEI function and battery performance.
• Understanding these SEI components is vital for developing next-generation Li-ion batteries.