Direct, operando observation of the bilayer solid electrolyte interphase structure: Electrolyte reduction on a...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• The solid electrolyte interphase (SEI) is critical for lithium-ion battery longevity but its formation and evolution are poorly understood.
• Understanding SEI chemistry is essential for designing more durable and efficient batteries.

Purpose of the Study:

• To investigate the structure and composition of the SEI on a tungsten anode.
• To provide direct experimental evidence for proposed dual-layer SEI structures.
• To offer insights into SEI formation dynamics and evolution during battery cycling.

Main Methods:

• Operando neutron reflectometry to analyze SEI structure.
• Quartz crystal microbalance (QCM) to measure SEI mass and dynamics.
• Monte Carlo simulations to determine SEI chemical composition.

Main Results:

• A dual-layer SEI was observed, with a 3.7 nm inner layer and a 15.4 nm outer layer.
• SEI mass per area was measured at 1207.2 ng/cm².
• Results indicate a dense, inorganic inner layer and a porous, organic outer layer.

Conclusions:

• The study provides direct experimental confirmation of dual-layer SEI structures.
• Findings enhance understanding of SEI formation and evolution mechanisms.
• This research enables scientifically-guided design of improved SEI layers for advanced lithium-ion batteries.