High-Performance Lithium Metal Batteries Enabled by a Fluorinated Cyclic Ether with a Low Reduction Potential

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• High-performance lithium metal batteries (LMBs) are critical for next-generation energy storage.
• Electrolyte engineering is a key factor in improving LMB stability and efficiency.
• Developing stable solid-electrolyte interphases (SEI) is essential for preventing dendrite formation and ensuring battery longevity.

Purpose of the Study:

• To investigate the impact of novel cosolvents on lithium metal battery performance.
• To compare the efficacy of methyl bis(fluorosulfonyl)imide (MFSI) and 3,3,4,4-tetrafluorotetrahydrofuran (TFF) as electrolyte additives.
• To understand the degradation mechanisms of electrolyte components and their effect on battery cycling.

Main Methods:

• Synthesis of two novel cosolvents: MFSI and TFF.
• Addition of cosolvents to LiFSI-DME electrolytes for lithium metal battery testing.
• Evaluation of Coulombic efficiency (CE) in Li||Cu half-cells over 200 cycles.
• Performance assessment in anode-free Cu||LiNi0.8Mn0.1Co0.1O2 full cells.

Main Results:

• The LiFSI/TFF-DME electrolyte achieved an average Li Coulombic efficiency of 99.41% over 200 cycles.
• The MFSI-based electrolyte demonstrated a lower average Li CE of 98.62%.
• TFF-based electrolytes exhibited superior reversible performance compared to state-of-the-art fluorinated electrolytes.

Conclusions:

• 3,3,4,4-tetrafluorotetrahydrofuran (TFF) is a promising cosolvent for high-performance lithium metal batteries.
• The decomposition products of bis(fluorosulfonyl)imide (MFSI) can degrade the SEI, negatively impacting cell performance.
• Rational design of electrolyte solvents and cosolvents is crucial for advancing LMB technology.