Increasing the range of electric vehicles and improving the storage of renewable energy systems are two examples of the benefits offered by lithium-sulfur batteries. Though they can hold four times the energy per mass of the lithium-ion batteries used today, their considerably shorter lifespan has proven something of a roadblock. Researchers from the Pacific Northwest National Laboratory (PNNL) have now designed a lithium-sulfur battery with four times the longevity, bringing the technology that little bit closer to maturity.
The team's research looked to solve a problem posed by a chemical reaction between the batteries two electrodes, where the sulfur-containing cathode corrodes the lithium-containing anode, substantially shortening the battery's life.
Over time, the anode disintegrates, with the sulfur dissolving into molecules called polysulfides which pass into the battery's electrolyte solution. As this liquid works as a highway for ions to move from one electrode to the other, the polysulfides follow suit and ultimately cause a thin film to form on the anode's surface. This film grows thicker until the battery is entirely inoperable, in effect shortening its life dramatically.
Rather than looking at ways to minimize the leakage, as previous research has explored, the team devised a way to protect the anode from the damaging molecules of the sulfur-containing cathode. Building a shield around the anode made from graphite, a material that is used in lithium-ion anodes, the team were able to contain the troublesome polysulfides and improve the lifespan of the battery by a factor of four.
"Sulfur is still dissolved in a lithium-sulfur battery that uses our hybrid anode, but that doesn't really matter," says PNNL Laboratory Fellow and one of the study's authors Jun Liu. "Tests showed a battery with a hybrid anode can successfully be charged repeatedly at a high rate for more 400 cycles, and with just an 11-percent decrease in the battery's energy storage capacity."
The team's research was published in the journal Nature Communications.