Nanostructures boost performance of lithium-sulfur batteries.
Source: “A highly ordered nanostructured carbon-sulfur cathode for lithium-sulfur batteries”
Linda F. Nazar et al.
Nature Materials 8: 500-506
Results: Researchers at the University of Waterloo in Ontario have demonstrated that a new nanostructured cathode material for rechargeable lithium-sulfur batteries can store three times as much energy as the cathodes in lithium-ion batteries on the market. The new batteries retained this ability to store energy when repeatedly charged and discharged completely over the course of 10 hours.
Why it matters: Lithium-sulfur batteries could store a lot of energy, making them attractive for portable electronics and electric cars. But the low electrical conductivity of sulfur has limited how easily they can be charged and discharged without losing much of their energy-storage capacity, and rapid electrochemical degradation has limited their useful lifetime. The new electrode structure largely overcomes these problems, allowing the batteries to be charged and discharged repeatedly at useful rates while retaining about 80 percent of their theoretical storage capacity.
Methods: The researchers created a material made of regularly spaced nanoscale carbon rods. Then they applied molten sulfur, which was sucked in between the closely packed rods by capillary action (picture sucking up liquid with a bundle of straws). Since carbon is more conductive than sulfur, it allows charge to flow more freely to and from the sulfur. The structure also helps prevent the electrochemical degradation that results when lithium and sulfur fail to react completely, forming intermediate reaction products called polysulfides. The incomplete reaction limits the energy storage of the battery, and the polysulfides can accumulate, further degrading the battery’s performance. The tightly packed rods trap polysulfides until the reaction between lithium and sulfur is complete. A polymer coating on the rods helps keep the polysulfides in place.
Next steps: The researchers are developing ways to further improve the stability of the electrode to increase the number of times a battery using it can be recharged. They’re also devising ways to manufacture the necessary nanostructures at large scales.