Polyether-based solid electrolytes with a homogeneous polymer network: effect of the salt concentration on the Li-ion...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Solid polymer electrolytes are crucial for advanced battery technologies.
• Developing mechanically robust and ionically conductive polymer electrolytes remains a challenge.
• Understanding ion coordination in polymer electrolytes is key to optimizing performance.

Purpose of the Study:

• To synthesize and characterize a solid polymer electrolyte based on tetra-functional poly(ethylene glycol) (TetraPEG) and LiTFSA.
• To investigate the relationship between the mechanical properties, ion coordination, and ionic conductivity of the electrolyte.
• To determine the optimal electrolyte composition for reversible lithium deposition/dissolution.

Main Methods:

• Synthesis of a solid polymer electrolyte using TetraPEG and LiTFSA.
• Mechanical testing (elongation) to assess toughness.
• Raman spectroscopy, high-energy X-ray total scattering, and all-atom molecular dynamics simulations to study ion coordination.
• Electrochemical impedance spectroscopy to measure ionic conductivity.
• Galvanostatic cycling to evaluate Li deposition/dissolution.

Main Results:

• The solid TetraPEG electrolyte exhibited high mechanical toughness with minimal defects (<5%) and up to 11-fold elongation.
• Li-ion coordination transitioned from ion-pair-free Li+-PEG complexes at low salt content (Li/O_PEG = 1:10) to ion pairs and aggregates at higher concentrations.
• Ionic conductivity was highest for the ion-pair-free electrolyte (Li/O_PEG = 1:10) and decreased with increasing salt content due to ion pairing.
• The optimal composition for reversible Li deposition/dissolution was Li/O_PEG = 1:4.

Conclusions:

• TetraPEG-based solid polymer electrolytes offer excellent mechanical properties and tunable ionic conductivity.
• Controlling Li-ion coordination through salt concentration is critical for optimizing electrolyte performance.
• The developed electrolyte shows promise for solid-state lithium batteries, with Li/O_PEG = 1:4 being optimal for reversible Li cycling.