Researchers at U.S. Department of Energy’s (DOE) Argonne National Laboratory have found a polar, nonconductive cathode can increase the performance of lithium-sulfur batteries.
Using physical and electrochemical probes, the researchers discovered that under varying cycling rates and loadings, even at high current densities, a silica-based cathode showed better cycle-life in lithium-sulfur batteries.
The team came to the conclusion after developing two cathode structures: one using polar but nonconductive mesoporous silica while the other used conductive, but nonpolar mesoporous carbon.
The two cathodes were designed to be exact replicas of one another apart from the use of either silica or carbon.
The findings, by DOE in cooperation with the National Research Foundation of Korea, were publishing in Advanced Energy Materials.
Assistant Chemist at Argonne and a co-author of the paper, Guiliang Xu, told BEST: “The electrochemical performance was tested in a conventional coin-cell configuration, with an areal S loading ranging from 2mg cm-2 to 6.5 mg cm-2.
“The cathode developed showed very good cycle stability, confirming that polarity is a more critical parameter for the design of durable Li-S batteries compared to electronic conductivity.”
In theory, lithium-sulfur batteries (LSBs) have a much higher charge density and are cheaper than lithium-ion batteries but in practice the technology has suffered from poor life-cycling and low energy efficiency.
The shortened life-cycle can be attributed to a ”polysulfide shuttle”, which leaches material from the cathode of the battery.
Senior materials group leader/Argonne distinguished fellow Khalil Amine, said the removal of material degrades the cathode and results in a decreased lifespan for the battery.
He said: “Our work shows that the key to enhancing the long-term stability of LSBs is enhancing the polarity and enhancing the interactions with the polysulfides at the cathode. If you can stabilise the sulfur, then you can stabilise the battery.
“The stronger interaction between the polysulfides and the silica immobilises these intermediaries thus decreasing the effect of the polysulfide shuttle and extending the life of the battery.”
Not only is the polysulfide shuttle an issue with the technology, but the sulfur itself is incredibly insulative, making it significantly less conductive.
Assistant Chemist Gui-Liang Xu, said: “It’s the combined issues of dissolution and lack of conductivity that present significant obstacles to the development of long-life LSBs.”
While earlier work in the field had shown that the introduction of carbon into the cathode structure can address the conductivity issues, there exists debate over what would improve the performance of LSBs the most: addressing the conductivity or addressing the polarity of the cathode.