Lithium-Sulfur Battery Performance Improved Via New Cathode Stabilization Strategy
An effective new strategy to stabilizing the cathodes in lithium-sulfur (Li-S) batteries was recently developed by researchers at the University of Waterloo in Canada + BASF.
The new strategy allows for significantly improved cycle life performance, improving the number of times that the battery can be charged/discharged without losing significant capacity — which addresses one of the main issues with Li-S batteries, that the cathode degrades rapidly.
The new strategy depends largely on the use of nanosheets of manganese dioxide (MnO2) to stabilize the cathode — the mechanism identified by the researchers applies to graphene oxide and other materials as well though.
Here are some of the technical specifics, as explained in the abstract of the new research paper:
Here we report a strategy to entrap polysulfides in the cathode that relies on a chemical process, whereby a host—manganese dioxide nanosheets serve as the prototype—reacts with initially formed lithium polysulfides to form surface-bound intermediates. These function as a redox shuttle to catenate and bind ‘higher’ polysulfides, and convert them on reduction to insoluble lithium sulfide via disproportionation. The sulfur/manganese dioxide nanosheet composite with 75 wt% sulfur exhibits a reversible capacity of 1,300 mA h g−1 at moderate rates and a fade rate over 2,000 cycles of 0.036%/cycle, among the best reported to date. We furthermore show that this mechanism extends to graphene oxide and suggest it can be employed more widely.
Unlike previous strategies to trap polysulfides by physical barriers or simple surface interactions, this chemistry is quite efficient. The discovery and understanding of a transfer mediator, which binds polysulfides and promotes stable redox activity, addresses one of the important challenges that face this chemistry. Along with future anticipated improvements in electrolytes and the lithium-negative electrode, this brings the Li–S battery a step closer to practical realization.
That realization would of course lower batteries costs pretty significantly — that is, if the technology is embraced by the industry and can see the benefits of economies of scale + if it can be easily mass manufactured.
While the research is promising, until the findings are actually being put into practice commercially (economically) it’s very much an unknown what will come of it. Perhaps nothing.
The researchers are now working to explore other materials options — in particular, determining those best-suited to this process/strategy.
The new findings are detailed in a paper just published in the journal Nature Communications.
Image Credit: University of Waterloo; BASF
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There seems to be a breakthrough a day. Some of them are bound to stick.
With Li-S offering a significantly higher energy density than Li-ion this might be a big one – emphasis on the word “might”.
And there are mountains of S (sulfur) laying around, so it is cheap.
Until the capital get’s a hunch and snatches it up 😉
This may be a very dumb question, but would it be possible to rebuild a battery with one of these new cathodes that seem to come out monthly?
They would build new cells, but not rebuild old cells. Battery makers are not really sure how the cells would be recycled, let alone rebuilt.
What am I missing? 2000 cycles x .036%/cycle yields 72% fade. That hardly seems wonderful for an EV.
Those 2000 cycles may be deep cycles, EVs may not be charged and discharged to those levels. The LEAF battery is hoped to be 80% capacity after 5 years and 70% after 10 years. Since the LEAF started selling in 2011, we have yet to see.
If I did the math correctly, I get 49% of initial capacity after 2,000 cycles. Would (1-.00036) ^2000 be the correct formula?
sounds about right
I think you are missing two orders of magnitude. .72 % fade (?) (2000 x .00036)
If one follows the link to the paper there are some pics from it. One has got the cycles vs capacity over time, it starts at 800 mAh/g (100%).
After 2000 cycles for 2C discharge it’s ~200 mAh/g (25%) and for 1/20C discharge it’s ~400 mAh/g (50%).
I think BEVs discharge more in the vicinity of 1-2C and not at 1/20th C.. so currently still a lot of work to do, but they seem to be getting better with Li-S. Bravo! 😉
Source: http://www.nature.com/ncomms/2015/150106/ncomms6682/fig_tab/ncomms6682_F6.html