Homogeneous lithium electrodeposition with pyrrolidinium-based ionic liquid electrolytes

Area of Science:

• Electrochemistry
• Materials Science
• Ionic Liquids

Background:

• Lithium-ion batteries require efficient lithium electroplating and stripping.
• Ionic liquids offer potential as electrolytes due to their unique properties.
• Understanding the solid electrolyte interphase (SEI) is crucial for battery performance.

Purpose of the Study:

• To investigate lithium electroplating and stripping in N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (Pyr14FSI) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) based ionic liquids.
• To evaluate the Li cycling efficiency and analyze the morphology of lithium deposits.
• To demonstrate the SEI-forming ability and dendrite suppression capabilities of these electrolytes.

Main Methods:

• Electroplating and stripping of lithium on nickel and lithium electrodes.
• Utilizing an improved method for evaluating Li cycling efficiency.
• Scanning electron microscope (SEM) imaging to observe surface features and SEI formation.
• Analysis of lithium deposition morphology and SEI characteristics.

Main Results:

• Homogeneous electroplating and stripping of lithium were confirmed with TFSI-based ionic liquids.
• Native surface features on lithium electrodes demonstrated enhanced SEI-forming ability and suppressed dendrite growth.
• Observed SEI cracking revealed bundled Li fibers and non-rod-shaped protuberances from Li extrusion.

Conclusions:

• TFSI-based ionic liquids are promising electrolytes for stable lithium electroplating and stripping.
• The electrolytes exhibit fast cathodic reactivity and effective dendrite suppression.
• Inhomogeneous deposition provides new insights into SEI behavior and lithium extrusion mechanisms.