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A major breakthrough in the development of lithium-sulfur batteries appears to be imminent. Compared with the current rechargeable lithium-ion batteries, lithium-sulfur batteries theoretically have energy density that is around three to five times higher (i.e. capable of reaching 2,600 watt-hours per kilogram). If this next-generation battery technology is successfully commercialized, then battery life of smartphones in operation could be extended from the usual three hours to around nine or even 15 hours.
Besides achieving higher energy density, lithium-sulfur batteries also have other advantages over lithium-ion batteries such as lower cost, lower environmental impact, and more storage capacity. On the other hand, sulfur as a battery material can become unstable after frequent charge-and-discharge cycles due to its poor conductivity. Furthermore, rechargeable batteries based on lithium metal and liquid electrolyte have issues with the formation of dendrites (crystals) during the charge-and-discharge cycles. These and other issues are hurdles that have hindered the progress in the commercialization of the lithium-sulfur battery technology.
However researchers at the University of Texas at Dallas (UT Dallas) have recently announced that they have found the solution that can stabilize and increase the cycle life of lithium-sulfur batteries. In addition, their version of lithium-sulfur batteries is also more environmentally friendly and offers greater capability. The UT Dallas research team is optimistic that the latest findings will help open up the market for lithium-sulfur batteries in the future.
Kyeongjae Cho, a professor who is part of this research team working in Erik Jonsson School of Engineering and Computer Science at UT Dallas, pointed out that the new technology can prolong the battery life of a single charge up to a week or even longer for smartphones. Currently, the maximum battery life of a single charge for smartphones is about a day. Lithium-sulfur batteries therefore have the potential make people’s daily life much more convenient.
The solution that the research team has discovered is the addition of molybdenum, an element commonly used to harden and strengthen steel. Molybdenum will combine with sulfur atoms to create a layer of molybdenum disulfide (MoS2) that is thinner than the silk of a spider’s web and can protect the lithium anode. Based on this finding, the team has designed a battery with its anode featuring lithium coated with MoS2 and its cathode featuring sulfur plus 3D carbon nanotubes. The integration of these material technologies has resulted in the suppression of dendrites, increased battery stability, and improved conductivity. These effects in turn contribute to greater safety for the application of the lithium-sulfur battery technology.
Cho also noted that scientists have always been looking for similar material solutions that can push lithium-sulfur batteries toward commercialization. Cho and his colleagues are now focusing on ways to further improve the stability of their battery materials so that this technology can quickly move from the laboratory to the market.
The prototype battery that the UT Dallas team has successfully built has a maximum specific energy density of 589 watt-hours per kilogram and a maximum Coulombic efficiency of 98% for over 1,200 cycles at the temperature of 0.5 degree Celsius.
Additionally, this research project is financially backed by two agencies in South Korea – Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the National Research Foundation of Creative Materials Discovery Program.The research team’s work has been published in the journal titled Nature Nanotechnology.
(The above article is an English translation of a Chinese article written by Daisy Chuang. The credit of the photo at the top of the article goes to the University of Texas at Dallas.)