With the type of energy density that could see smartphones run for five days or electric planes fly twice as far, lithium-sulfur batteries hold tremendous potential, but inherent instabilities are a key roadblock to their widespread adoption. Scientists in Japan have put forward a promising solution to this problem, integrating a novel sponge material that enables a prototype lithium-sulfur battery to safely endure hundreds of cycles.
Compared to the lithium-ion batteries that power so much of modern society, lithium-sulfur batteries are lighter and offer up to five times more energy per weight, making them particularly well suited to use in electric vehicles. Energy density is a key issue for such applications, where the range of electric cars, trucks and particularly planes are limited by the amount of energy that can be packed into their very heavy battery packs.
“Lithium sulfur batteries can store more energy than the lithium ion batteries that are already commercially available,” says Dr. Hui Zhang, first author of the new study. “To put this in numbers, an electric vehicle that runs on lithium ion batteries can drive an average of 300 km (186 mi) before it needs to be charged. With the improved energy storage provided by lithium sulfur batteries, it should be possible to extend this to 500 km (310 mi).”
While their potential is clear, scientists working on next-generation lithium-sulfur batteries have grappled with issues around their stability, which can cause key components to quickly deteriorate and the device to promptly fail. This new research, carried out by material scientists at Okinawa Institute of Science and Technology Graduate University, takes aim at the formation of polysulfides that significantly reduce the battery's lifespan.
Inside the battery, a chemical reaction between the lithium and sulfur first creates lithium polysulfide, which then tends to quickly dissolve into the troublesome polysulfides. In a perfect lithium-sulfur battery, the lithium polysulfide needs to convert into lithium sulfide or lithium persulfide as quickly as possible, and the team believes it has developed just the thing to hurry things along.
The scientists created a nanoscale porous sponge out of carbon nanotubes and coated it in titanium nitride and titanium dioxide, which offered some useful properties. The titanium nitride serves to accelerate the conversion of lithium polysulfide into the finished product, while the titanium dioxide absorbs any unwanted polysulfides that are created in the process.
“Using these two materials, we developed a hybrid that is low cost and easy to apply,” says Dr. Luis Ono, second author of this study. “We found that it had an excellent ability to improve the battery performance.”
The resulting battery exhibited an improved performance compared to versions without the hybrid sponge material, with a shorter charging time, a longer time between charges thanks to high specific capacity and, importantly, a greater overall lifespan with an ability to endure 200 cycles with no losses in efficiency.
“We will continue to further optimize the materials to improve the performance,” says Professor Yabing Qi, senior author of the study. “There are a lot of brilliant minds working on lithium sulfur batteries and it’s a really promising and exciting technology.”
The research was published in the journal Nature Communications.
Source: Okinawa Institute of Science and Technology Graduate University
