Lithium-sulfur batteries are more efficient than their lithium-ion counterparts due to their higher energy density. However, the charging and discharging capacities decrease over time as a result of degradation of the cathode material through a variety of issues including sulfur expansion upon lithiation as well as the release of polysulfides into the electrolyte solution.  Halloysite nanotubes can be used to solve these problems. Halloysite nanotubes are natural, clay aluminosilicates formed by rolling kaolin sheets up to 10-15 revolutions. They have an average diameter of 50-60 nm, a length of 500-800 nm, and mesoporous structure (with a specific surface area of ~ 60 m<sup>2</sup>/g). Compared with other mesoporous materials, they are much cheaper and are available in large quantities (thousands of tons). Sulfur was loaded into halloysite via hydrophobization of the nanotubes’ lumens. This is done by selective electrostatic adsorption of anionic surfactants with C<sub>12</sub> hydrophobic tails. Their negatively charged head groups attach to the positively charged alumina sites on the inner surface of nanotubes, leaving their hydrophobic tails exposed to increase the sulfur loading within the lumen. Because of their non-conductive nature, conductive carbon powder is introduced to ensure conductivity in the assembled batteries. This inexpensive nanomaterial composite can be architecturally designed in this way to form a tubule core-shell structure containing surfactants, ceramics, carbon, and sulfur which is expected to physically restrict sulfur expansion upon lithiation and reduce the dissolution and transport of polysulfides. Its success provides a highly efficient, large-scale production route for cathode materials in lithium-sulfur batteries.

Halloysite nanotube composites for enhancing lithium-sulfur battery efficiency

255th National Meeting (2018)

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