By Allison Proffitt
January 6, 2020 | Researchers at Monash University in Melbourne, Australia, have discovered a new way of making lithium-sulfur batteries that they believe could increase battery capacity far beyond lithium-ion batteries, according to a study published in Science Advances over the weekend (DOI: http://dx.doi.org/10.1126/sciadv.aay2757).
Mahdokht Shaibani from Monash University’s Department of Mechanical and Aerospace Engineering led an international research team that developed an ultra-high capacity Li-S battery that has better performance and less environmental impact than current lithium-ion products.
In general, lithium sulfur batteries have a much higher specific energy than lithium ion batteries, but the energy performance fades rapidly as the sulfur electrode is loaded thanks to substantial volume change. The high-capacity sulfur cathode (1670 mA·hour g−1) in the Li-S system suffers around a 78% change in volume during cycling—typically around eight times higher than that of the electrodes in LIBs.
Monash researchers theorized that a solution might lie in fabrication changes, not chemistry changes.
They focused on common polymer binders, which glue the fillers (active material and conductive agent) together in an electrode. “Very little experimental work has been undertaken to understand the effects of the binder-filler interactions on the cycle-life performance (i.e., durability) of thick sulfur cathodes,” the authors write in the paper.
They set out to find an “expansion-tolerant” (ET) architecture for thick battery electrodes. Their goal was to, “maximize the number of electrochemically available reaction sites while also providing a stronger physical support with which to manage the greater net forces within thick electrodes. Both goals must be met without sacrificing the electrical connections within the cathode that must be maintained throughout cycle life.”
By controlling the dispersion of Na-CMC, a commonly used high-modulus binder with rich carboxylic groups, instead of adding it as a solution, the researchers found mechanically strong bridging bonds between the fillers (in this case, colloidal sulfur and conductive carbon). “These cathodes have very large reaction surfaces, can efficiently accommodate cycling stresses, and have high ion accessibility and electrical conductivity,” the authors write.
Attractive performance, along with lower manufacturing costs, abundant supply of material, ease of processing and reduced environmental footprint make this new battery design attractive for future real-world applications, said Associate Professor Matthew Hill in a press release announcing the paper.
“This approach not only favors high performance metrics and long cycle life, but is also simple and extremely low-cost to manufacture, using water-based processes, and can lead to significant reductions in environmentally hazardous waste,” he said.
The authors of the study say the lithium-sulfur battery could outperform current market leaders by more than four times, and power Australia and other global markets well into the future. They have an approved filed patent (PCT/AU 2019/051239) for their manufacturing process, and prototype cells have been successfully fabricated by German R&D partners Fraunhofer Institute for Material and Beam Technology. Some of the world’s largest manufacturers of lithium batteries in China and Europe have expressed interest in upscaling production, with further testing to take place in Australia in early 2020.
Professor Mainak Majumder, senior author on the paper, called the development a breakthrough that could transform the way phones, cars, computers and solar grids are manufactured in the future.
“Successful fabrication and implementation of Li-S batteries in cars and grids will capture a more significant part of the estimated $213 billion value chain of Australian lithium and will revolutionize the Australian vehicle market and provide all Australians with a cleaner and more reliable energy market,” Majumder said in a press release. “Our research team has received more than $2.5 million in funding from government and international industry partners to trial this battery technology in cars and grids from this year, which we’re most excited about.”