Dual-Interphase Modulation with a Locally Concentrated Ionic Liquid Electrolyte toward High-Performance Lithium Metal...

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Stable electrode/electrolyte interphases (EEIs) are critical for practical lithium metal batteries (LMBs).
• Existing electrolytes often struggle to form robust protective layers on battery components, limiting cycle life and performance.
• Developing advanced electrolytes is key to unlocking the potential of high-energy-density LMBs.

Purpose of the Study:

• To design and investigate a novel ionic liquid electrolyte system for stabilizing EEIs in LMBs.
• To utilize a functional diluent, 1,3,5-trifluorobenzene (3FB), to promote the formation of stable solid electrolyte interphases (SEIs) and cathode electrolyte interphases (CEIs).
• To evaluate the electrochemical performance of the developed electrolyte in a Li/LiFePO4 full battery under demanding conditions.

Main Methods:

• Designed locally concentrated ionic liquid electrolytes (FPB2) incorporating 1,3,5-trifluorobenzene (3FB) as a diluent.
• Investigated the solvation structure and ion transport mechanisms within the electrolyte.
• Analyzed the composition and stability of the interphases formed on the lithium metal anode (LMA) and LiFePO4 (LFP) cathode using electrochemical techniques.
• Performed long-term cycling tests on a Li/LFP full battery to assess performance metrics like capacity retention and Coulombic efficiency.

Main Results:

• The addition of 3FB promoted Li+ association with anions, forming an anion-dominated solvation structure that facilitated anion decomposition and rapid Li+ transport.
• 3FB underwent reductive decomposition on the LMA surface, synergizing with anion decomposition to form a uniform and stable SEI.
• A stable, LiF-rich CEI was formed on the LFP cathode, effectively suppressing electrolyte oxidation.
• The Li/LFP full battery demonstrated excellent cycling stability, achieving 81.5% capacity retention and 99.4% average Coulombic efficiency over 200 cycles under demanding conditions.

Conclusions:

• The functional diluent 3FB effectively stabilizes both the anode SEI and cathode CEI, leading to dual-interphase stabilization.
• This electrolyte design strategy offers a new approach for developing high-performance lithium metal batteries.
• The findings present a promising pathway for advancing the practical application of LMBs through tailored electrolyte engineering.