University of Waterloo chemistry professor Linda Nazar has found herself mining some 19th century science in order to understand the basis for the next generation of 21st century batteries. Since 2009, Nazar’s research group has been exploring the feasibility of lithium-sulphur as a cost-effective means of improving the storage capacity of batteries that could find their way into everything from cell phones to automobiles.
“Sulphur battery technology has been around since the 1960s but it is mainly used in high-temperature settings,” Nazar says, pointing to the Japanese company Nippon Gaishi Kaisha (NGK), which manufactures high capacity sodium-sulphur cells that operate at more than 300 C. Nazar adds that there has been little incentive to consider such alternative materials because the current crop of lithium batteries has proved more than adequate to sustain the global proliferation of portable electronic devices. However, the development of power-hungry equipment such as electric vehicles would definitely grow if power storage could be boosted by as much as 300 percent.
Lithium-sulphur batteries can potentially deliver that kind of improvement but first they have to overcome a major limitation. In most formulations, incoming electrons reduce sulphur to form polysulphides; because of this, the cathode will no longer hold a charge after just a few recharging cycles. Nazar identified the process as similar to the production of polythionic acids — a class of sulphur-based polymers with the general formula H2SnO6 — in water solution, which was discovered and described by German chemists in the 1840s.
After revisiting this fundamental work, Nazar and her colleagues looked at whether the production of polysulfides could be stopped by a layer of carbon atoms. They subsequently found that nanosheets of metallic oxides did an even better job. In a paper published in Nature Communications at the beginning of the year, they reported that MnO2 effectively recycles the sulphides necessary to maintain the integrity of the battery’s cathode so that it could be recharged more than 2,000 times.
Nazar notes that sulphur is an abundant by-product of oil sands production, making it a low-cost input for battery manufacturing. In February she presented these findings on the potential of this technology at the annual meeting in San Jose, Calif. of the American Association for the Advancement of Science, a non-profit organization supporting scientific education and science outreach for the betterment of humanity. “This is an example of how looking back in the literature enabled us to gain the fundamental understanding we needed to make this progress,” she says.