Researchers at Stanford University have recently discovered how they can increase the lifespan of lithium-sulfur batteries, by up to ten times.
Lithium-ion batteries may be the accepted norm for most automotive traction applications, and with good reason. Lithium-ion can withstand thousands of cycles without losing too much of their capacity, and they are the most energy-dense batteries that are commercially viable.
Cost, though, remains a major concern, as some lithium-ion battery packs in electric vehicles today can easily comprise up to 50% of the cost of a new electric vehicle. The Tesla Motors Model S 85kWh battery, for example, is worth $12,000.
Drivers of electric vehicles can always adjust their driving habits to get around the range and recharging characteristics, but cost is another major factor blocking the purchase of such vehicles. There are cheaper battery technologies, such as nickel-metal hydride [NiMH], which Toyota still uses in all their hybrid electric vehicles, but the energy-density is no match for lithium-ion, especially in a pure electric vehicle application. Lithium-sulfur batteries look promising, with similar energy-density to lithium-ion, but are cheaper to manufacture.
The only problem with lithium-sulfur batteries is they have a very short lifespan, just a few cycles, which would make absolutely no sense in an electric vehicle designed to cycle hundreds of times, over three hundred cycles in the hundred-thousand-mile lifespan of the Tesla Model S, over 1,300 cycles in a Nissan Leaf.
The lithium-sulfur cathode breaks down over just a few cycles, because it shrinks from the carbon outer wall. Researchers at Stanford University have recently discovered how they can increase the lifespan of lithium-sulfur batteries, by up to ten times, tweaking the surface of the cathode inner wall on the nanoscale and adding a polymer.
The resulting combination of nanostructured carbon and polymers keeps the lithium-sulfur from breaking away, maintaining electrical contact for more cycles. The first few attempts at the new process resulted in just 20% capacity loss over 300 cycles.
“Using the amphiphilic polymer idea… together with nanoscale materials design and synthesis, it is possible to improve the cycle life up to 10,000 cycles,” said Stanford professor of materials science and engineering, Yi Cui. “My group is working on this. Our recent results on nanomaterials design already improved to 1000 cycles.”