Direct Visualization of Lithium Polysulfides and Their Suppression in Liquid Electrolyte

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Lithium/sulfur (Li/S) batteries offer high theoretical specific energy but are hindered by the polysulfide shuttle.
• Direct observation of soluble lithium polysulfide (Li-PS) behavior in electrolytes is crucial for Li/S cell development.

Purpose of the Study:

• To visualize the formation and diffusion of Li-PS during lithiation in Li/S cells.
• To investigate the effect of ionic liquid (IL) addition on Li-PS behavior and Li/S cell performance.

Main Methods:

• In situ graphene liquid cell electron microscopy to observe Li-PS formation and sulfur nanoparticle evolution.
• Chronoamperometric shuttle current measurements to quantify Li-PS diffusion.

Main Results:

• Direct visualization of Li-PS formation and diffusion alongside sulfur nanoparticle morphological and phase changes.
• Ionic liquid addition was found to retard Li-PS diffusion and morphological changes.
• IL addition reduced the experimental diffusion coefficient of Li-PS by two orders of magnitude, suppressing the shuttle current.

Conclusions:

• Ionic liquid addition effectively inhibits the polysulfide shuttle phenomenon in Li/S cells.
• This electrolyte modification leads to improved battery cyclability and Coulombic efficiency.
• The findings offer critical insights for designing advanced electrolytes to enhance Li/S battery performance.