Rational Design of Asymmetric Lithium Salts with Multi-Functional Capabilities for Stable Lithium Metal Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium metal batteries (LMBs) suffer from interfacial instability in carbonate electrolytes, leading to fragile solid-electrolyte interphases (SEIs).
• Current strategies focus on solvent engineering, leaving lithium salt design underexplored for SEI improvement.

Purpose of the Study:

• To design and investigate an asymmetric lithium salt, LiDMTFSI, for enhanced interfacial stability in LMBs.
• To shift the solvation structure towards anion-rich environments for improved SEI formation.
• To explore anion molecular design as a strategy for interphasial engineering in high-energy LMBs.

Main Methods:

• Synthesized an asymmetric lithium salt, lithium (N, N-dimethylsulfamoyl) (trifluoromethanesulfonyl)imide (LiDMTFSI).
• Analyzed solvation structures and interfacial chemistry using electrochemical techniques.
• Fabricated and tested full LMB cells with Li anodes and NMC811 cathodes.

Main Results:

• LiDMTFSI induced an anion-rich solvation structure, promoting the formation of a compact, inorganic-rich SEI (LiF, Li2O, Li3N, Li2S).
• Achieved high Li plating/stripping Coulombic efficiency (99.1%) in dilute carbonate electrolytes.
• Demonstrated stable cycling in full cells (120+ cycles, 83% capacity retention at 4.3 V).

Conclusions:

• Anion molecular design, exemplified by LiDMTFSI, is a potent strategy for engineering stable interphases in LMBs.
• The developed LiDMTFSI facilitates uniform Li deposition and mitigates side reactions, enhancing battery performance.
• This approach offers a promising pathway towards realizing high-energy, long-lifespan lithium metal batteries.