Today’s electric vehicles are typically powered by lithium-ion batteries. But the chemistry of lithium-ion batteries limits how much energy they can store. As a result, electric vehicle drivers are often anxious about how far they can go before needing to charge. One promising solution is the lithium-sulfur battery, which can hold as much as four times more energy per mass than lithium-ion batteries. This would enable electric vehicles to drive farther on a single charge, as well as help store more renewable energy. The down side of lithium-sulfur batteries, however, is they have a much shorter lifespan because they can’t currently be charged as many times as lithium-ion batteries. Pacific Northwest National Laboratory researchers have developed a nickel-based metal organic framework to hold onto polysulfide molecules in the cathodes of lithium-sulfur batteries and extend the batteries’ life spans.
(H/T New Energy and Fuel)
Metal organic frameworks — also called MOFs — are crystal-like compounds made of metal clusters connected to organic molecules, or linkers. Together, the clusters and linkers assemble into porous 3-D structures. MOFs can contain a number of different elements. PNNL researchers chose the transition metal nickel as the central element for this particular MOF because of its strong ability to interact with sulfur.
During lab tests, a lithium-sulfur battery with PNNL’s MOF cathode maintained 89 percent of its initial power capacity after 100 charge-and discharge cycles. Having shown the effectiveness of their MOF cathode, PNNL researchers now plan to further improve the cathode’s mixture of materials so it can hold more energy. The team also needs to develop a larger prototype and test it for longer periods of time to evaluate the cathode’s performance for real-world, large-scale applications.
PNNL is also using MOFs in energy-efficient adsorption chillers and to develop new catalysts to speed up chemical reactions.
“MOFs are probably best known for capturing gases such as carbon dioxide,” Xiao said. “This study opens up lithium-sulfur batteries as a new and promising field for the nanomaterial.”
A new, PNNL-developed nanomaterial called a metal organic framework could extend the lifespan of lithium-sulfur batteries, which could be used to increase the driving range of electric vehicles. Publicly available for use with the credit line, “Courtesy of Pacific Northwest National Laboratory.”
PNNL developed a nickel-based metal organic framework, shown here in an illustration, to hold onto polysulfide molecules in the cathodes of lithium-sulfur batteries and extend the batteries’ lifespans. The colored spheres in this image represent the 3D material’s tiny pores into with the polysulfides become trapped. Publicly available for use with the credit line, “Courtesy of Pacific Northwest National Laboratory.”
ABSTRACT
Lithium–sulfur (Li–S) battery is one of the most promising energy storage systems because of its high specific capacity of 1675 mAh g–1 based on sulfur. However, the rapid capacity degradation, mainly caused by polysulfide dissolution, remains a significant challenge prior to practical applications. This work demonstrates that a novel Ni-based metal organic framework (Ni-MOF), Ni6(BTB)4(BP)3 (BTB = benzene-1,3,5-tribenzoate and BP = 4,4′-bipyridyl), can remarkably immobilize polysulfides within the cathode structure through physical and chemical interactions at molecular level. The capacity retention achieves up to 89% after 100 cycles at 0.1 C. The excellent performance is attributed to the synergistic effects of the interwoven mesopores (2.8 nm) and micropores (1.4 nm) of Ni-MOF, which first provide an ideal matrix to confine polysulfides, and the strong interactions between Lewis acidic Ni(II) center and the polysulfide base, which significantly slow down the migration of soluble polysulfides out of the pores, leading to the excellent cycling performance of Ni-MOF/S composite.
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