Lithium-sulfur (Li-S) batteries, despite their high theoretical specific energy, face practical challenges including polysulfide shuttling and low cell-level energy density.
Researchers at the University of Waterloo have now shown that the lightweight superconductor MgB2 (magnesium diboride)—the average mass/atom of which is comparable with carbon—as a metallic sulfur host fulfills both electron conduction and polysulfide immobilization properties.
In a paper in the journal Joule the teams reports that, by using first-principles calculations, they found that borides are unique in that both B- and Mg-terminated surfaces bond exclusively with the Sx2− anions (not Li+), and hence enhance electron transfer to the active Sx2− ions.
The surface-mediated polysulfide redox behavior results in a much higher exchange current in comparison with MgO and carbon. By sandwiching MgB2 nanoparticles between graphene nanosheets to form a high-surface-area composite structure, they demonstrated sulfur cathodes that achieve stable cycling at a high sulfur loading of 9.3 mg cm−2.
They conclude that this new avenue toward Li-S cathodes, when coupled with a protected lithium metal anode, may lead to practical implementation of batteries that are lighter, yet robust.
Quan Pang, Chun Yuen Kwok, Dipan Kundu, Xiao Liang, Linda F. Nazar (2018) “Lightweight Metallic MgB2 Mediates Polysulfide Redox and Promises High-Energy-Density Lithium-Sulfur Batteries,” Joule doi: 10.1016/j.joule.2018.09.024