As electric cars become more popular, scientists see the great potential of lithium-sulfur batteries, which are a more environmentally friendly way to drive. This is because they do not rely on expensive and difficult-to-obtain raw materials, such as cobalt, but problems such as stability have so far hindered the development of the technology.
Recently, engineers at (Drexel University) at Drexel University in the United States have made a breakthrough, saying that lithium-sulfur batteries are closer to commercial use by using a rare chemical phase of sulfur to prevent destructive chemical reactions. The research was recently published in the journal Communication Chemistry.
Lithium-sulfur batteries have a bright future in energy storage, not only because they are rich in sulfur, but also because the source of sulfur is not a problem compared with the cobalt, manganese and nickel used in today's batteries. At the same time, lithium-sulfur batteries may also bring some significant performance improvements, and their energy storage potential is several times that of current lithium-ion batteries. But there is one problem that has plagued scientists, and that is the formation of polysulfides.
When the battery is working, these substances enter the electrolyte and initiate chemical reactions, damaging the capacity and life of the battery. Scientists have successfully replaced carbonate electrolytes with an ether electrolyte that does not react with polysulfides. But this also creates other problems, because the C "H" OC "H" electrolyte itself is extremely volatile and contains low boiling point components, which means that if heated above room temperature, the battery may quickly fail or melt.
As a result, chemical engineers at Drexel University have been working on another solution, starting with designing a new cathode that can work with carbonate electrolytes already in commercial applications. The cathode is made of carbon nanofibers and has been shown to slow the movement of polysulfides in ether electrolytes. But it takes some experiments to make it work with carbonate electrolytes.
Lead researcher Vibha Kalra said, "for commercial manufacturers, the carbonate electrolyte currently used can be used as a cathode, which is the path with the least resistance." Therefore, our goal is not to promote the adoption of a new electrolyte in the industry, but to create a cathode that can work in existing lithium-ion electrolyte systems. "
Scientists are trying to use a technique called steam treatment to limit sulfur to a network of carbon nanofibers to prevent dangerous chemical reactions. Although this did not achieve the desired effect, it crystallized sulfur in an unexpected way and turned it into something called monoclinic gamma phase sulfur, a slightly changed form of elements.
It is reported that this chemical phase of sulfur can only be produced at high temperatures in the laboratory or observed in natural oil wells. The researchers were surprised to find that it did not react with carbonate electrolytes, thus eliminating the risk of forming polysulfides.
"at first, it was hard to believe that this was what we detected, because in all previous studies, monoclinic sulfur has been unstable at 95 °C (203 °F)," said Rahul Pai, co-author of the study. "in the last century, only a few studies produced monoclinic gamma sulfur and were stable for 20-30 minutes at most. But we created it in the cathode, which went through thousands of charge-discharge cycles without deterioration in performance. A year later, our examination of it showed that the chemical phase remained the same. "
After a year of testing and 4000 charge-discharge cycles, the cathode remains stable, which scientists say is equivalent to 10 years of regular use. The battery prototype made by the team using the negative electrode can provide three times the capacity of standard lithium-ion batteries, paving the way for more environmentally friendly batteries and enabling electric vehicles to travel farther after each charge.
"while we are still trying to understand the exact mechanism behind this monoclinic sulfur production that stays stable at room temperature, this is still an exciting discovery that could open many doors to the development of more sustainable and economical battery technologies," Kalra said.
