Quantifying the Dynamic and Additives-Dependent Interface Evolution by Operando Neutron Reflectometry.

Area of Science:

• Battery Technology
• Materials Science
• Electrochemistry

Background:

• The solid electrolyte interphase (SEI) is crucial for battery performance.
• Engineering the SEI with electrolyte additives is a promising strategy.
• The dynamic evolution of SEI layers under cycling is not well understood.

Purpose of the Study:

• To quantitatively resolve the SEI's structural dynamics during battery cycling.
• To investigate the impact of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) additives on SEI formation.
• To establish a transferable operando neutron reflectometry (NR) framework for analyzing additive effects.

Main Methods:

• Utilized operando neutron reflectometry (NR) to monitor SEI structural changes in real-time during battery cycling.
• Employed model additives (FEC and VC) with known decomposition mechanisms.
• Developed a robust NR framework for mechanistic insights into additive systems.

Main Results:

• Fluoroethylene carbonate (FEC) forms a thin, inorganic-rich SEI (LiF-dominant), enhancing mechanical integrity and cycling stability.
• Vinylene carbonate (VC) forms a flexible, organic-dominated SEI, mitigating stress-induced microcracking.
• Contrasting SEI architectures were observed, demonstrating distinct roles of FEC and VC.

Conclusions:

• Operando NR provides atomically resolved insights into SEI evolution influenced by electrolyte additives.
• Specific additives like FEC and VC lead to distinct SEI structures with tailored properties.
• These findings offer design principles for advanced electrolyte additives to improve high-energy-density batteries.