Beyond LiF: Tailoring Li₂O-Dominated Solid Electrolyte Interphase for Stable Lithium Metal Batteries.

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Solid-electrolyte interphase (SEI) components critically impact lithium metal battery (LMB) stability.
• Lithium fluoride (LiF) is a common SEI component, but lithium oxide (Li2O) offers a lower Li+ diffusion barrier.
• The electrochemical performance of Li2O-dominated SEI remains largely unexplored.

Purpose of the Study:

• To design a novel diluent, 2,3-difluoroethoxybenzene (DFEB), for modulating solvation structure.
• To tailor a Li2O-dominated SEI for enhanced stability and performance in LMBs.
• To investigate the electrochemical advantages of Li2O-rich SEI compared to LiF-rich SEI.

Main Methods:

• Designed 2,3-difluoroethoxybenzene (DFEB) as a cosolvation diluent.
• Utilized DFEB in a lithium-ion hybrid capacitor electrolyte (LHCE) to form a Li2O-dominated SEI.
• Evaluated SEI characteristics and electrochemical performance in Li||Cu half cells, symmetrical cells, and full cells (Li||LFP, Li||NCM811, Li||S).

Main Results:

• DFEB-based LHCE formed an inorganic-rich, Li2O-dominated SEI, distinct from conventional LiF-dominated SEIs.
• Achieved high Coulombic efficiency (99.58%) in Li||Cu cells with stable voltage profiles and uniform lithium deposition.
• Demonstrated effective inhibition of lithium dendrite formation and superior cycling stability (85% capacity retention after 650 cycles in Li||LFP).
• A 1.5 Ah practical lithium metal pouch cell showed 89% capacity retention after 250 cycles with 99.93% average CE.

Conclusions:

• Unraveled the electrochemical superiority of Li2O-dominated SEI for stable LMBs.
• Demonstrated the feasibility of tailoring SEI components through solvation structure modulation.
• Highlighted DFEB as a promising component for developing high-performance and stable lithium metal batteries.