Cathode porosity is a missing key parameter to optimize lithium-sulfur battery energy density

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• High sulfur loading is crucial for high-energy lithium-sulfur batteries.
• Cathode porosity in sulfur/carbon composites is often high, unlike dense lithium-ion battery electrodes.
• Lowering cathode porosity can minimize electrolyte intake, weight, and cost in lithium-sulfur batteries.

Purpose of the Study:

• To investigate the impact of cathode porosity on lithium-sulfur battery performance.
• To understand the relationship between porosity, sulfur utilization, and polysulfide conversion.
• To determine an optimal cathode porosity for maximizing volumetric energy density.

Main Methods:

• Fabrication of lithium-sulfur battery cathodes with varying porosities (70% to 40%).
• Electrochemical testing to evaluate discharge polarization, reversible capacity, and cycling life.
• Development of a mechanism-based analytical model to explain observed phenomena.

Main Results:

• Decreasing cathode porosity from 70% to 40% profoundly impacted discharge polarization, reversible capacity, and cell cycling life.
• Sulfur utilization is limited by lithium-polysulfide solubility.
• Conversion of lithium-polysulfides to Li2S is constrained by the accessible surface area of the carbon matrix.

Conclusions:

• Cathode porosity is a critical parameter for high-energy lithium-sulfur batteries.
• Optimizing porosity enhances sulfur utilization and battery longevity.
• A balance between low porosity and accessible surface area is key for maximizing volumetric energy density.