General Motors Researchers Develop Improved Li-S Cathode Material

3 years ago by Mark Kane 16

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General Motors Researchers Develop Improved Li-S Cathode Material

General Motors Researchers Develop Improved Li-S Cathode Material

A research team from General Motors Global Research & Development Center recently published an article on their progress in improving lithium-sulfur batteries.

Li-S batteries have a few times greater energy density then today’s lithium-ion batteries.  However, Li-S batteries typically don’t last long.

The GM team achieved for now 900 mA h g–1 at 0.2 C after 150 cycles and 630 mA h g–1 at 0.6 C after 600 cycles. The capacity is high, however 0.6 C current is still too low for EVs (charging and discharging in 100 minutes).

This result translates to 30 kW of available continuous power in a car with 50 kWh battery pack (without any higher pulse discharge currents for acceleration, which would need some kind of buffer in the form of ultracapacitors).

The good thing is that the double-layered core–shell structure of polymer-coated carbon–sulfur offers near 100% Culombic efficiency and capacity is not fading rapidly, so maybe even 1,000 cycles would be possible to 70-80% of nominal value.

We look forward to more improvements and hope that someday we see Li-S batteries in production EVs.

“To better confine the sulfur/polysulfides in the electrode of lithium–sulfur (Li/S) batteries and improve the cycling stability, we developed a double-layered core–shell structure of polymer-coated carbon–sulfur. Carbon–sulfur was first prepared through the impregnation of sulfur into hollow carbon spheres under heat treatment, followed by a coating polymerization to give a double-layered core–shell structure. From the study of scanning transmission electron microscopy (STEM) images, we demonstrated that the sulfur not only successfully penetrated through the porous carbon shell but also aggregated along the inner wall of the carbon shell, which, for the first time, provided visible and convincing evidence that sulfur preferred diffusing into the hollow carbon rather than aggregating in/on the porous wall of the carbon. Taking advantage of this structure, a stable capacity of 900 mA h g–1 at 0.2 C after 150 cycles and 630 mA h g–1 at 0.6 C after 600 cycles could be obtained in Li/S batteries. We also demonstrated the feasibility of full cells using the sulfur electrodes to couple with the silicon film electrodes, which exhibited significantly improved cycling stability and efficiency. The remarkable electrochemical performance could be attributed to the desirable confinement of sulfur through the unique double-layered core–shell architectures.”

Nano Letters via Green Car Congress

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16 responses to "General Motors Researchers Develop Improved Li-S Cathode Material"

  1. DaveMart says:

    Another hassle with lithium sulphur is that although the specific energy is high, ie there is a lot of energy per kilogram, the energy density ain’t much better than current batteries, ie the energy per litre.

    That means that the batteries if they held a lot more energy would be very bulky.

    So plenty of things to work on before they are ready for use in cars.

    1. Anthony says:

      If Tesla can manage to engineer a pure EV with today’s batteries and get 200+ miles, so can other car manufacturers. The Li-S batteries just offer lighter cells to reduce vehicle weight. And lower materials costs.

      What the traditional car makers needs to do is stop trying to jam battery cells into chassis built for gasoline cars.

      1. Yes says:

        Of course other manufacturers can do it. All Tesla did was buy the highest density cells from Panasonic and throw as much in as they could fit.

        The problem is that if every manufacturer did that, then all purpose built EVs would be just as big, heavy, and expensive as the Tesla. Not everyone can or wants to spend $75k+ on a car.

        1. Mint says:

          No, other manufacturers can’t do what
          Tesla did. If they could, they wouldn’t have put out such compromised EVs/PHEVs.

          Look at how Ford’s Energi models lose 5 cubic ft of space for just 6 kWh of extra battery.

          Look at how Marchionne says the $32k Fiat 500e loses $14k on each sale. They couldn’t possibly build a profitable 200-mile full-size EV sedan for the ~$60k it costs Tesla to build the base Model S.

          1. unbiased says:

            “Yes” is correct- Tesla’s pack is well-engineered, but GM or Ford could buy the exact same cells. They are not willing to build the car to sell for the price that would be required. Also, a $75k Tesla would be $100k if GM built it, in part bc of the UAW.

            1. liberty says:

              Tesla builds in california, I doubt gm costs are higher. The problem is gm would put in some cheaper parts or do something wrong. Just fear would have you go buy tesla on the internet versus go to the gm steelership if they were around the same price/performance.

              Tesla has first mover advantages, but not pricing advantages. They don’t have the bad management or bad dealership overhead that prevents them from innovation.

    2. Dr. Kenneth Noisewater says:

      So, basically suitable for lighter hybrids for a direct NiMH swap?

      That, coupled with 96-120V drive and accessory system would be a pretty nice upgrade.

      1. GeorgeS says:

        No the cycle life is too low.
        600 cycles is only good on a 200 mile or more EV.

  2. ptrubey says:

    The 0.6C number in the result just means thats the charge/discharge rate they tested at. It DOESN’T mean thats the maximum discharge rate of the battery. So this battery might be able to discharge at a higher rate. Where batteries typically fall down is real world energy storage degradation since charge and discharge rates are a lot different from lab tests done at 0.6C or whatever.

    Frankly, these research papers aren’t very interesting – you can find a new one touting some result almost every day. What matters is what the battery manufacturers are selling…

    1. Dr. Kenneth Noisewater says:

      Indeed. Deliver 1000 finished cells that can be tested to destruction before getting too excited.

      1. Brian says:

        You guys realize that one of the technologies being worked out in the lab today is what will be sold in cars tomorrow, right? This is how advances work.

        The same things could have been said about Li-Ion batteries 10 years ago. In fact, many were. When NiMH was the state-of-the art commercially available batteries, scientists were working feverishly on Li-Ion technology. At the time, though, they either couldn’t provide the cycle life of NiMH, or would simply overheat and self-destruct. The protection mechanisms for the latter, at first, made the end result less appealing than NiMH. The naysayers all said that Lithium in general was a dead end, and look at us now.

        Give it time. The next gen may be Li-S, Li-Air, or something else even more far fetched. In the meantime, enjoy the insight into the research that is striving to bring us what we all want – 200+ mile EVs that can recharge in less than 30 minutes.

    2. Ambulator says:

      Yeah, but look at the drop in battery performance going from 0.2C to 0.6C. I see no reason not to expect that to worsen going to faster rates.

      What 900 mAh/g or 630 mAh/g really really mean for battery performance isn’t clear, though. It’s probably going to be at a lower voltage than we’re used to, anyway.

  3. Priusmaniac says:

    The more research the better. Go for it.

  4. Jim Bo says:

    Might make a cost effective and relatively light weight range extender that kicks in at 100 miles, 600 cycles might equal 2000 on the main batteries in that application

    1. Brian says:

      A dual-technology hybrid battery system? What a great idea! Now where have I heard that before…

      http://insideevs.com/could-this-patent-be-what-tesla-will-use-for-the-model-e/

      1. Jim Bo says:

        Thanks for sharing that article. The Li-S battery seems a very good candidate for that application.