Batteries made with a lithium-sulfur chemistry rather than the typical lithium-ion hold a great deal of potential, and have for quite some time. Though they offer up to five times more energy per weight, one major roadblock has been a far shorter lifespan. An international team of scientists believes it has now overcome this hurdle through a new type of bonding architecture, resulting in an unprecedented battery charge/discharge efficiency in a lithium-sulfur battery that could keep a smartphone running for days.
“Ironically, a main challenge to mass adoption of lithium-sulfur batteries until now, has been that the storage capacity of sulfur electrode is so large that it cannot manage the resultant stress,” Monash University’s Dr Mahdokht Shaibani, study lead author, explains to New Atlas. “Instead it breaks apart, in the same way we might when placed under stress.”
Shaibani tells us this is because the stress leads to the distortion of key components, namely the carbon matrix responsible for passing electrons to the insulating sulfur, and the polymer binder that holds those two materials together. The resulting breakdown of this connection causes a rapid deterioration in the battery’s performance.
So Shaibani and a team of international collaborators started looking at new ways of holding it all together. Rather than using the binding material to form a dense network with little room to spare, she decided to “give the sulfur particles some space to breath!”
The new battery relies on a traditional binding agent, but processed in a different way to form ultra-strong bridging bonds between the carbon matrix and sulfur particles that allow for extra space as the battery expands during charging. These bonds can be seen in figure b below.
“In other words, I created a web-like network where only a minimum amount of binder is in place between the neighboring particles, leaving increased space for accommodating the changes in the structure and the resultant stress,” Shaibani says.
The team’s experiments with its new lithium-sulfur battery have produced some promising signs. In testing over more than 200 cycles, the battery exhibited a charge/discharge efficiency of more than 99 percent, “which to the best of our knowledge is unprecedented for such high capacity electrodes,” says Shaibani.
The researchers say the battery could power a smartphone for five continuous days or enable an electric vehicle to drive more than 1,000 km without recharging. They are poised to trial the battery further over the coming year, both in electric cars and as a storage option for solar power. They have also filed a patent for the technology, which in addition to improved performance promises lower cost and less environmental impact than traditional lithium-ion batteries.
“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,” says study co-author Matthew Hill.
The team has published its research in the journal Science Advances.