New Cathode Material Boosts Lithium-Sulfur Battery Performance

Lithium-sulfur batteries can store as much as five times the energy of lithium-ion chemistries. They also perform well at low temperatures and use cheaper, nontoxic materials.

Such batteries exchange lithium ions between lithium and sulfur-carbon electrodes. Under ideal circumstances, each sulfur atom can absorb two lithium ions, making sulfur an excellent storage material.

But storage isn't everything. Sulfur is a poor conductor of electrons, which makes lithium-sulfur batteries difficult to charge and discharge.

Researchers at LMU Munich (German) and the University of Waterloo (Canada) say they have largely overcome that problem by applying a thin layer of sulfur atoms to a super-porous cathode material made carbon nanoparticles. The seven-member team reports its results in the weekly online technical journal Angewandte Chemie.

The researchers describe their material as spherical ordered mesoporous carbon nanoparticles. The conductive material contains pores measuring only 3-6 nanometers across and has a pore volume of 2.3 cubic centimeters per gram.

The high porosity creates an extraordinarily large surface area of 2,445 square meters per gram, according to the researchers. They say a chunk of their material the size of a sugar cube has the surface area of 10 tennis courts.

When coated with sulfur, the substrate makes almost all the sulfur atoms available to accept lithium ions. It also places the sulfur atoms close to the conductive carbon substrate.

The researchers say they achieved excellent cycling efficiency and an initial energy storage capacity as great at 1,200 milliamp hours per gram. The team adds that it was able to reduce the undesirable formation of polysulfides, which inhibit battery charging and discharging, by coating the carbon material with a thin layer of silicon oxide.