Lithium Sulfur Batteries Slated For Takeoff

Spectrum recently published a post on a new lithium sulfur battery technology specifically targeting electric aviation applications. Although lots of electric vehicles could benefit from the new technology, airplanes are especially sensitive to heavy batteries and lithium-sulfur batteries can weigh much less than modern batteries of equivalent capacity. The Spectrum post is from Oxis Energy who is about to fly tests with the new batteries which they claim have twice the energy density of conventional lithium-ion batteries. The company also claims the batteries are safer, which is another important consideration when flying through the sky.

The batteries have a cathode comprised of aluminum foil coated with carbon and sulfur — which avoids the use of cobalt, a cost driver in traditional lithium cell chemistries. The anode is pure lithium foil. Between the two electrodes is a separator soaked in an electrolyte. The company says the batteries go through multiple stages as they discharge, forming different chemical compounds that continue to produce electricity through chemical action.

The safety factor is due to the fact that, unlike lithium-ion cells, the new batteries don’t form dendrites that short out the cell. The cells do degrade over time, but not in a way that is likely to cause a short circuit. However, ceramic coatings may provide protection against this degradation in the future which would be another benefit compared to traditional lithium batteries.

We see a lot of exciting battery announcements, but we rarely see real products with them. Time will tell if the Oxis and similar batteries based on this technology will take root.

60 thoughts on “Lithium Sulfur Batteries Slated For Takeoff

  1. So if these new batteries, a ‘bank’ of them would weight less than the aviation fuel , also the reduced weight of brushless DC motors from the prop(s), would that concept ‘fly’?

    1. Bear in mind there’s a lot more variables than just weight. Are they as dense? Almost certainly not. They will still take up far more space than an equivalent amount of energy stored as aviation fuel, which will also incur lots of structural weight.

      Also doesn’t scale as well. Cell charge/discharge management and bus requirements go up and up, whereas a larger tank of liquid might need some baffles but that’s about it.

      There will be a few interesting and novel electric planes, but I doubt we’ll see electric airliners anytime soon barring a very unexpected and dramatic breakthrough.

      1. A battery powered aircraft will always weigh the same. Same weight flying 10,000 km as flying 100 km.

        And I would like to see the situation where the pilot has to “dump fuel” to make an emergeny landing! Some jet fuel falling from the sky like rain is not *so* bad, but a several tonne battery?

        1. Lol why would they need to dump a battery? It’s not as though it gets lighter as it gets discharged. If it cant take off, turn around then land, it couldn’t take off, fly 5000km, and then land either.

          The first electric planes will be like the first electric cars, they will do short trips more efficiently while the technology matures. Take-off alone is a huge consumer of energy compared to cruising, so if we replace that with something more environmentally friendly we are already off to a good start,

          1. The purpose of dumping fuel before an unscheduled landing is not only to reduce flammables, but also mass. A battery that is a roman candle in waiting certainly counts as flammable enough to be something you’d want to be able to dump before a crash. The mass part is obvious.

          2. It is nearly only a question of mass. Many modern planes do not even have feul dump valves, because they are specified in a way, that an emergency landing with the full take off mass is possible.

          3. @Martin On larger airliners omitting a fuel dump option is on the stuhpid side. If an unscheduled off-airport landing is about to take place, every bit of fuel that’s dumped won’t be a fire liability on the ground. And fire should be something to worry about, given that most deaths in airliner crashes is from smoke inhalation. On the upside, most (all?) larger aircraft have a MTOW well above MLW so they come with the dump capability.

        2. Plenty of planes cannot dump fuel, those that can have it because the max takeoff weight is substantially higher than the max landing weight. They can land overweight but it might damage the plane

          1. Absolutely brilliant. Better still, have multiple parachutes that can gently lower the whole plane with its load, batteries and all. It is the best option, a series of parachutes that can both deploy in the aft and overhead regions of the aircraft. Like that little 5 seater jet with 1 engine (i forget its name, Cirrus or something) or the Sling tsi.

    2. The NASA X57 Maxwell was designed to experiment with what happens when you have the entire leading edge of the wing covered in small electric driven propellers, meaning the whole wing sees a far higher airspeed than the aircraft airspeed. A result of this is a much smaller wing, resulting in lower weight and lower drag (both skin friction and induced drag). At cruise speed, all the small motors shut down and feather (or possibly retract) and the aircraft relies on two medium-sized tip-located electric motors. They’re only used for takeoff/climb and landing, when the aircraft needs high lift. The small motors may also be capable of handling a lot of the aircraft maneuvering through differential lift, so there might not be any need for ailerons or flaps, meaning the whole wing volume can be used for batteries.
      Jet turbines start at about $250,000 each, and rebuilds of them are also very expensive, even though they have pretty long lifetimes. So that’s also a big driver towards electric-based propulsion.

      1. Just wait until we all see how much a “FAA certified” electric motor really costs. And even if it’s reasonable at first, the regulations (and hence the costs) will go up with every smoking hole in the ground. I’m not against the regulations, but just pointing out that apparent cost savings might not be there by the time those things get settled in.

        1. An electric motor has far less moving parts than a combustion engine. The control electronic is a little more complex (inverter vs. ignition box), but that can easily be made FAA certifiable.

          1. At this point, I really think that the main issues around certification holding back electric aircraft, especially EVTOLs, revolve around safety especially what to do in case of an emergency within the death zone where the parachutes will be considered of significant use. One school of thought proposes the inclusion of “airbag systems” that deploy well before impact or balloons that inflate once things go haywire in the death zone, similar to how the mars landing of one probe was achieved several years back. Shock absorbing airbags will save lives on those things and hasten certification.

    3. “So if these new batteries, a ‘bank’ of them would weight less than the aviation fuel , also the reduced weight of brushless DC motors from the prop(s), would that concept ‘fly’?”

      No. The batteries are lighter than regular lithium ion batteries but nowhere near as light as jet fuel.

      Very doubtfully half the weight of the next lightest lithium models though. This metric relies on there being a spectrum of weights of lithium batteries and very likely the inclusion of older, less optimised and thus heavier types in the comparison. They’re of the flat sandwich type and can come in largish models which are favourable to 18650 type as there’s a better ratio of active material to packaging and connectors. So combine that win with a pretty light chemistry solution and you’ll get about the twice the regular Jo metric.

      Nearly purchased some of their batteries for a UPS but at prototype production they were too expensive. Very cool though and great to walk around their lab.

  2. “see a lot of exciting battery announcements, but we rarely see real products with them. ” Did you say that about lithium cells? From zinc carbon and lead-acid through NiCad, alkaline NiMH and Lithium the energy and power of batteries has been amazing in my lifetime. The next step whether it is lithium sulphur or aluminium air or something else, looks likely to break the fossil fuel energy density barrier, which will make hydrocarbons obsolete as a fuel source. Can’t wait!

    1. That would be neat. But until the airline can “turn over” an electric aircraft in an hour after it just made a 4 hour flight across the country, It won’t be replacing fossil fuels for long range – fast turn around applications. If they have extra planes sitting there on chargers, then it might work, but that is not cost effective. If they had swap-able battery packs that may work, but greatly reduces your cargo space.

    2. Lithium is the one that typically has the exciting announcements. Some of the variants are on the market, yes. But its amount of exciting battery announcements that are still forthcoming that is worth calling out.

      1. while lithium chem cells have a lot of bullshit hype claims every now and then, they are steadily getting better and better. You can now buy a 18650 cell that is past 3Ah capacity AND capable of 10C discharge (but it’ll co$t you). You can buy cells that will survive being discharged to literal 0V.
        This was sci-fy 20 years ago. Now you can buy them online and have them delivered to your door.

    3. Every few months there’s news of a groundbreaking battery with greater energy density, faster charge rate, reduced cost per W-h and/or improved safety. Far fewer about new types in the market. It seems a lot happens between the prototype and the factory.

    4. I too have seen the transitions from NiCad to NiMh to Li… but the transition to Lithium took place about 20 years ago and, since then, nothing new has made it to market. I don’t think it’s unreasonable to state that we rarely see real products based on new tech when it’s been 20 years since the last major change. No doubt there are HAD readers for which that covers their entire lifetime.

      As for making fossil fuels obsolete, A- I don’t think it’s necessary to match or exceed it’s energy density. Current batteries are really close to being viable alternatives in all but the most extreme range cases, so if there’s even a modest increase, be it in energy density, charge rate and/or manufacturing cost, it really crosses the tipping point where everyone would choose electric. And B- there’s so much infrastructure in place, fossil fuels won’t be obsoleted overnight or by any one major breakthrough. We still heat our homes with oil, aircraft are much more difficult to convert both because of the need for quick turnaround, the need for maximum energy density and the efficiencies that come from reducing weight in-flight by literally burning up your energy source. We don’t need to obsolete fossil fuels in all forms to effect a massive beneficial change.

      1. Apropos of nothing, really, but I ditched gas for all my outdoor tools (mower, leaf blower, weed whacker etc) and went lithium because it’s getting really cheap and if you have a few batteries to hot swap, you can do plenty of work without waiting to charge. I’ll only use the mower every week or two, so it doesn’t matter how long charging up takes. And sure, in those tiny tool batteries you might only get a few hundred cycles, but they’ll literally last me for years and require no maintenance. I’m not too concerned about the environmental impact overall, just the fact that it doesn’t stink and I’ll never ever have to clean a carb is worth it to me.

        1. Similar for me. For two reasons:
          1.) Electric makes less noise. Being in the garden mostly on weekends, my neighbors would not like the noisy 2-stroke chainsaw or weed-whacker. With battery tools I did not yet get any complaints.
          2.) No need to buy gasoline – the batteries are charge with PV power.

  3. Hmm. Your article says that these Li-S cells don’t form dendrites and don’t short internally, but the Spectrum article makes no such claim. In fact, many studies have shown that Li dendrites can penetrate thick, dense solid ceramic separators (not merely coatings), so I am skeptical. Also, I really wish that “energy density “ was not used synonymously with specific energy. Watt hours per kilogram (specific energy) is not the same as watt hours per liter (energy density). Li-S batteries may have a future in applications where weight is critical, such as aviation, but are unlikely to be relevant in applications where volume is critical (e.g. automotive), where their low density works against them. The Spectrum article is unclear on whether these cells include a liquid electrolyte, but seems like they must. If so, you have to keep in mind that ~85% of the energy in a Li ion cell is the chemical energy of the flammable electrolyte, so any suggestion that these are safer has to be carefully backed up.

    1. You: Hmm. Your article says that these Li-S cells don’t form dendrites and don’t short internally, but the Spectrum article makes no such claim

      Spectrum Article: “However, this occurs via a very different mechanism, one that does not involve the formation of dendrites.“

    2. >where volume is critical (e.g. automotive)

      On the contrary. Battery weight is a pretty critical factor for cars as well. The volumetric energy density is already “good enough”. A reasonable sized battery for a car with all the structure to secure it down weighs approximately as much as a Fiat 127, so you’re hauling around the mass of an entire small car for no good reason – and in cold climates you have to spend considerable energy in heating it up, because lithium batteries don’t work below 0 C.

      1. For example, the Model 3 battery weighs 1,054 pounds (478 kg) which adds up with the necessary chassis reinforcement, mounting points and armoring, to around 600-700 kg which was the curb weight of a series 2 Fiat 127 at 688 kg (1,517 lb).

        A good rule of thumb is that you can add a third more to the mass of your battery to account for all this necessary structure. If the battery was lighter, the car would be lighter and use a lot less energy.

        1. But such a Fiat 127 leaves out many things which male a modern car more comfortable and crash-safer. Yes I like, A/C, automatic transmission, electric windows and sunroof, etc.

          1. “But such a Fiat 127 leaves out many things…” That’s a silly objection; it’s the weight of the car not the car itself. If it had been “the weight of an Edsel” would you say “But I like popular cars!”? Silly.

      2. Or another comparison between cars built on the same platform (latest model):

        Nissan Pulsar / Tiida: 1,265 kg (2,789 lb)
        Nissan Leaf : 1,538 kg (3,391 lb)

        The electric car is by rule one battery mass heavier, so obviously it would be nice if the battery wasn’t so damn heavy.

      3. “A reasonable sized battery for a car with all the structure to secure it down weighs approximately as much as a Fiat 127”

        Yea, batteries and related structures are heavy, but so are internal combustion engines. And a 6lbs per gallon, gasoline itself can add 100lbs. I believe a Tesla motor weighs about 70 lbs. where you average V8 can easily weigh 500+ lbs. You’re probably still carrying around more weight with electric, but it’s not as if a battery is a 100% addition to a vehicle’s overall weight. You have to factor everything in.

        1. >but so are internal combustion engines

          But so are electric motor and their related components. The Tesla motor, just the motor, can weigh 70 lbs, but that’s not all there is to it. The entire drive unit with all the necessary parts is pretty much as heavy as a typical engine, because you also have thick copper bus-bars and heat-sinks for the drive inverter, DC-DC converter, BMS and charger, brake hydraulic assist, AC pump, plus all the casings etc.

          > it’s not as if a battery is a 100% addition to a vehicle’s overall weight

          It pretty much is. As I said, having such a heavy mass on-board requires additional structure to bolt it down safely, keep it from being punctured, keep it cooled and heated… etc. so the weight savings elsewhere are lost, and the EV ends up 300-700 kg heavier.

          And these are already compact/subcompact cars that don’t have a big heavy V8 as an option anyways.

          1. What I mean; take some ultralight kit car, and you can get away with making the floorpan out of plywood because it doesn’t matter that your car has crazy body twist as long as it stays in one piece. Of course it drives like s…

            Then add a floor full of batteries, and suddenly you have to care about torsional rigidity, because you can’t have them battery cells squeezing and chafing against each other as the car goes through bumps and potholes. The 8,000 little tab welds would start to break off. That’s an engineering challenge when you have 400-500 kg of battery cells and you have to make them not move around, and it has to fit under the car so you don’t mess up with the weight distribution.

    3. “Your article says that these Li-S cells don’t form dendrites and don’t short internally, but the Spectrum article makes no such claim”

      FTFA: “With lithium-sulfur cells, degradation of the lithium-metal anode is also a problem. However, this occurs via a very different mechanism, one that does not involve the formation of dendrites.”

    1. I was thinking the same thing about the Pure Lithium reference. Safer?

      But I am looking forward to the technology for my R/C airplanes/jets. Less weight/same power that much better performance. Hopefully volume shrinks accordingly as well. So we can go the other direction… same weight, more energy = longer flights. Since I started flying with NiMh (big jump from NiCd at the time) to LiPo it’s been a great time to get into model electric flying! It is actually quite doable now compared to the NiCd days.

    2. Previous paragraph: “The company also claims the batteries are safer”

      Next paragraph: “The safety factor is due to the fact that, unlike lithium-ion cells, the new batteries don’t form dendrites that short out the cell. The cells do degrade over time, but not in a way that is likely to cause a short circuit.”

      That’s one less thing that can go wrong.

      1. No, its not.

        Not when you need 25,000 pounds of thrust (per engine). You would need a gigantic rotor (helicopter size), or a massive ducted fan, and a brushless motor that weighs far too much to work.

        For example the CFM56-5A engines used on the 737 weighs ~5000 pounds and produces ~28,000 lb/f maximum.

        Most of the volume of a jet engine is air. Electric motors don’t scale up in a way that is useful in this application.

    1. however an ICE power pack (yes, we’re including complex gearboxes and anything else that in ICE needs and an electric solution would not) is almost always bigger and heavier for the same power rating…

      A 100kg 60kW/h battery pack would be good enough for at least 50% of todays cars users and a 200kg 120kW/h would easily squish in another 20-25% of the user base. Heck, at that kind of density, even small electric commercial cargo trucks don’t sound so stupid.

      Planes and heavy fright on the other hand…well…

  4. They probably forgot to mention Li to LiS compound tranformation is associated with large volume expansion. It would be interesting to see how they tackle this problem and potential risk of failure.

  5. Brings to mind the room temperature Na-S batteries that I was thinking would be to market by now. The high temperature Na-S batteries have been around for a while. Definitely plenty of Na in the environment. Then again, for stationary battery banks, I’m one for securing the most toxic materials and using in highly controlled monitored sites for utility… like say grid balancing and energy storage.

  6. a lot of people are pointing out that improvements to lithium battery chemistry have been all talk and no product. i don’t think that’s really true. lifepo etc. none of them are quite the game-changer that the first hype suggests, but quite a few things do turn into products that are 10% or 50% better for certain roles in certain ways. and quite a few of the ones that didn’t turn into products, it’s just because another novel product beat them to it. the gain was real, just insufficient or too late or not economical enough at scale to make a dent in the market.

    1. It’s not so much going forwards, as taking some drunken straggles to the sidelines. You push the envelope one way and it closes in from the other side – so like with LiFePO you got a robust battery that has relatively low specific energy, relatively low charge/discharge rate, high cost, and doesn’t work in the cold so it’s still struggling to find any real application. People try to use them in cars as a lead-acid replacement, but the requirement to stay above 0 C to accept a charge is a deal-breaker.

  7. The key points of BEVs are that they are emissions-free, quiet, economical, reliable and nearly maintenance-free, a huge motivator. A full recharge can be accomplished in an hour, with no other ground maintenance required. This makes them highly attractive for commuter aviation, as a couple of early adopters have demonstrated. As battery and fuel cell tech improves and is adapted, conversion to electric aviation (battery and hybrid fuel cell) is inevitable.

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