Revisiting Coulombic Efficiency Paradigm: Electrolyte Additive Design for Lithium Metal Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• Electrolyte additives are crucial for enhancing lithium metal battery performance.
• Selecting effective additives for lithium metal anode stabilization remains a significant challenge.
• Coulombic efficiency (CE) in Li°||Cu° cells is a key metric, but often shows unexpected results based solely on additive structure.

Purpose of the Study:

• To investigate the role of fluorinated electrolyte additives in stabilizing lithium metal electrodes.
• To understand the structure-property relationships of additives through statistical analysis and simulations.
• To develop a robust framework for screening electrolyte additives for lithium metal batteries.

Main Methods:

• Statistical analysis of Coulombic efficiency (CE) data from Li°||Cu° cell cycling.
• Compositional characterization of electrode interfaces.
• Atomistic and chemical simulations of electrolyte-additive-anion interactions.
• Investigated nonafluorobutanesulfonyl fluoride as a fluorinated additive.

Main Results:

• Nonafluorobutanesulfonyl fluoride showed minimal impact on Aurbach CE in short-term Li°||Cu° cell cycling.
• Statistical analysis revealed divergent effects of the additive in TFSI⁻ and FSI⁻ based electrolytes during extended cycling.
• The interplay between the additive's film-forming chemistry and anion involvement dictates the solid-electrolyte interphase (SEI) properties.

Conclusions:

• Additive functionality is directly linked to interphase chemistry and SEI formation.
• Anion choice (TFSI⁻ vs. FSI⁻) significantly influences the effectiveness of fluorinated additives.
• A statistically robust framework is established for screening electrolyte additives for practical lithium metal batteries.