Advanced High-Voltage Electrolyte Design Using Poly(ethylene Oxide) and High-Concentration Ionic Liquids for...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) offer safety for lithium metal batteries (LMBs).
• Current PEO-based SPEs face challenges with low ionic conductivity (<10⁻⁶ S cm⁻¹) and limited oxidation stability (<4 V).
• These limitations hinder their application in high-energy-density solid-state LMBs.

Purpose of the Study:

• To design and investigate a novel polymer-in-high-concentrated ionic liquid (PiHCIL) electrolyte.
• To enhance the ionic conductivity and electrochemical stability of SPEs for solid-state LMBs.
• To explore the structure-property relationships within the new electrolyte system.

Main Methods:

• Synthesis of a novel PiHCIL electrolyte using PEO, a specific ionic liquid (C3mpyrFSI), and LiFSI.
• Systematic variation of the EO/[Li/IL] ratio to optimize electrolyte properties.
• Characterization using Fourier-transform infrared spectroscopy and solid-state magic-angle spinning nuclear magnetic resonance to study Li-coordination and solvation.
• Electrochemical testing including ionic conductivity measurements, oxidative stability tests, and Li|Li symmetric cell cycling.
• Assembly and testing of all-solid-state cells with a lithium iron phosphate cathode.

Main Results:

• The developed PiHCIL electrolyte exhibits a high oxidative stability of 5.1 V.
• Achieved ambient temperature ionic conductivity of 5.6 × 10⁻⁴ S cm⁻¹ at 30 °C.
• Demonstrated stable and reversible lithium metal cycling over 100 cycles in Li|Li symmetric cells with dendrite-free morphology.
• All-solid-state cells showed 99.2% capacity retention after 100 cycles at C/5 rate.

Conclusions:

• The novel PiHCIL electrolyte design overcomes key limitations of traditional PEO-based SPEs.
• This approach provides a promising pathway for developing high-performance SPEs for energy-dense solid-state LMBs.
• The enhanced ionic conductivity and stability are crucial for safe and efficient battery operation.