Although lithium-ion batteries are the mainstream technology across most energy storage applications at the moment, alternatives have emerged. Among them, lithium-sulfur batteries are seen as the dark horse in the competition.
Lithium-sulfur batteries have a huge market potential because they can store up to five times as much energy as the current generation of lithium-ion batteries. If the lithium-sulfur technology does become widely adopted one day, people might not have to constantly pay attention to the battery icon on the screens of their smartphones, and the operational range of electric cars might extend farther than ever before. However, there is still a long distance to go before lithium-sulfur batteries are finally commercialized. One major hurdle to overcome is the rapid deterioration of the electrolyte and the electrode caused by the normal charging/discharging process. Compared with batteries based on the conventional lithium-ion technology, ones based on the lithium-sulfur technology have a much shorter cycle life due to the high inclination of material degradation.
Both lithium-ion and lithium-sulfur batteries are susceptible to the growth of lithium dendrites, which are needle-like deposits on the electrode that can pierce the insulator film and break down the electrolyte. Besides increasing the risks of short-circuits and catching fire, dendrite formation appears to be the leading factor that shortens the operational lifespan of lithium-sulfur batteries. Other issues that negatively affect the performance of lithium-sulfur batteries include the low conductivity of sulfur and the highly reactive nature of lithium. All in all, the commercialization of the lithium-sulfur technology requires solving numerous major and minor challenges related to design, material selection, and manufacturing process.
Recently, a team of researchers at the University of Texas at Austin (UT Austin) in the US has published a study that offers a potential solution to maintain the structural integrity of lithium-sulfur batteries. According to the study, the dendrite formation can be suppressed with a coating of tellurium on the electrode. Tellurium is a rare metalloid that is now used in thin-film photovoltaic cells. Amruth Bhargav, who co-authored the study and is a graduate student in the university’s material science and engineering program, said that the tellurium layer prolongs the cycle life by preventing unwanted reactions between the electrode and the electrolyte.
Laboratory experiments conducted to back this study also revealed that the tellurium coating extends the cycle life of lithium-sulfur batteries by four folds. Additionally, the coating process is very simple and does not require expensive equipment. In short, this solution complements the already high price/performance ratio of the lithium-sulfur technology. Despite being prone to structurally degrade quickly, lithium-sulfur batteries have several advantages that keep them in the competition across different energy storage applications. They are light in weight and have a much higher energy density compared with other types of rechargeable batteries. Sulfur is also a very cheap and readily available. Furthermore, the lithium-sulfur technology does not need a fluoride compound in the electrolyte.
Arumugam Manthiram, who is a material engineering professor at UT Austin and the lead author of the study, said that sulfur is “environmentally benign” and quite abundant in Earth’s crust. Hence, there are no significant supply chain issues that could hinder the production of lithium-sulfur batteries in the US. This also means that the real obstacles to commercialization of the technology reside in the aspects of engineering and design. The study, which was published in the journal Joule this April, could help successfully resolve the issue of the short cycle life.
Nevertheless, pushing the lithium-sulfur technology from the laboratory to the market will take some time. The team at UT Austin has helped the technology make a huge step forward in the commercialization process. It remains to be seen whether research teams working on other related challenges will meet expectations in terms of their progress and build prototypes that can rival conventional lithium-ion batteries in performance.
(News source: TechNews. Photo credit: UT Austin.)