Unveiling a Stable Polysulfide Transport Framework in a Fluorine-Free Li-S Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium-sulfur (Li-S) batteries face challenges like polysulfide shuttling, unstable lithium interfaces, and parasitic reactions, limiting their cycle life and efficiency.
• These issues are primarily caused by the solubility of polysulfide intermediates and inadequate interfacial control in traditional electrolytes.

Purpose of the Study:

• To develop a fluorine-free electrolyte that modifies the redox chemistry in Li-S batteries.
• To investigate a new reversible Li3PS4-Li2S mechanism that enhances battery performance and stability.

Main Methods:

• Development of a novel fluorine-free phosphate-based electrolyte.
• In situ transformation to create Li-rich thiophosphate phases.
• Spectroscopic and microscopic analyses to study phase transitions and interfacial behavior.

Main Results:

• The new electrolyte shifted the redox chemistry from S8-Li2S to a reversible Li3PS4-Li2S pathway.
• In situ formed Li-rich thiophosphate phases suppressed polysulfide diffusion and cathode expansion.
• Cells demonstrated sustained performance with a stable capacity of 765 mAh g-1 over 200 cycles.

Conclusions:

• The fluorine-free phosphate electrolyte establishes a new class of solid-state-like Li-S redox chemistry.
• This approach offers a promising strategy for developing durable, high-performance lithium-sulfur batteries.
• The findings pave the way for overcoming key limitations in current Li-S battery technology.