Lithium-Sulfur Battery Project Aims to Double the Range of Electric Airplanes

https://spectrum.ieee.org/energywise/aerospace/aviation/lithiumsulfur-battery-project-aims-to-double-the-range-of-electric-airplanes

by pross356 • 7 years ago

95 114 7 years ago

spectrum.ieee.org

adammunich2• 7 years ago

Have they solved the problems of

1. sulfur plating the anode? 2. The cathode swelling during charge and mechanically damaging the cell?

If so, I'm excited! But last I checked thier solution to #2 was to clamp the cell between metal plates, which nullified the gains in energy density when considering the mass of the clamps.

chrisdwyer• 7 years ago

1 & 2. Not really and not really.

Curious, have you ever heard of Boron-Nitride Nanotubes (BNNT)? Basically a new nanomaterial that is similar to carbon nanotubes except it has the rare property of being a high energy band-width semiconductor whilst having excellent thermal conductivity (basically solves problems 1. and 2.). Only problem is that its really hard to produce in mass quantity... well maybe... have a look at the company PPK

philipkglass3• 7 years ago

No lithium-sulfur battery (so far) survives enough charge-discharge cycles to be attractive for portable electronics or electric cars. But higher energy density makes it potentially attractive over lithium ion batteries for aircraft. Even if you have to replace the batteries after e.g. only 100 cycles, that could enable multi-month missions for solar powered high altitude UAVs.

The Airbus Zephyr was using lithium-sulfur batteries back in 2015:

https://cosmosmagazine.com/technology/lighter-cheaper-satell...

RcouF1uZ4gsC• 7 years ago

They said the Oxis battery would provide “in excess” of 500 Wh/kg, a number which appears to apply to the individual cells, rather than the battery pack, with all its packaging, power electronics, and other paraphernalia.

For comparison the energy density of gasoline is 12,200 Wh/kg

https://xtronics.com/wiki/Energy_density.html

scotchmi_st• 7 years ago

Although it's more complicated than that, because IC engines are only have about 15% efficiency, whereas electric motors are up at about 80%.

nradov2• 7 years ago

Real world efficiency for modern gasoline engines is closer to 20%. In hybrid applications they can get up to 35%.

userbinator• 7 years ago

https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio...

Over 30% efficiency for gasoline, and over 50% for diesels.

bretpiatt• 7 years ago

You cannot look at the energy density of the fuel by itself.

Electric motors are lighter than ICE engines per HP and torque unit.

Emrax 268 (electric engine designed for aircraft) - 6.12 HP/lb

GE 90-115B (jet engine used in 777) - 6.10 HP/lb

Junkers Jumo 205A (diesel engine used in Ju 86C-1) - 0.66 HP/lb

Electric also scale down better so for light weight UAV a higher energy density battery will open up a bunch of use cases.

korethr3• 7 years ago

Absent notes to the contrary, I'm going to assume that's just the raw energy density. However, by my understanding the typical gasoline engine in a passenger car has an efficiency of something in the low-to-mid-30s percent. So, assuming 33%, that's 4026 Wh/kg of actually-useful energy density, the rest of the energy wasted as exhaust heat.

Looking things up, I see different numbers for electric motor efficiency, ranging from the low 70s to the low 90s percent. As an overly simplified example, let's assume an electric motor in a car has an efficiency of 80% (in reality, they may be better). At that efficiency, a battery pack only has to get to 5032.5 Wh/kg to achieve the same practical energy density as gasoline, less than half the actual raw energy density. That is probably an easier number to reach than trying to achieve the same raw energy density of gasoline.

Nobody has made this argument in this thread (yet, as I type this), but I've seen it made before and made it myself. Yes, at those energy densities, batteries are highly dangerous if something goes wrong (like a crash) and they release all their energy at once, but so is gasoline. At practical ranges, you're potentially sitting on a pile of high-explosives either way. But, I'd hope a 5032.5 Wh/kg battery is easier to make safer in a crash than 12,200 Wh/kg gasoline is.

ProfessorLayton• 7 years ago

It's worth noting that the latest generation of the Prius has reached 40% thermal efficiency [1]

[1] https://newsroom.toyota.eu/new-2019-toyota-prius-with-intell...

the84725• 7 years ago

On the other hand a plane loses weight as it burns fuel, this isn't true for batteries.

DesiLurker3• 7 years ago

I agree with most of what you said, however, internal combustion engine is nowhere near as efficient or complete combustion as a jet engine which can get to high 60s with heat recovery. I with somebody had thought of making a series hybrid with a small but optimal turbine based battery charger.

the other benefit is the weight of gas goes down as the flight progresses which is about 1/3 of the total weight so make the design a bit worse but I believe it would still be compensated by cheapness of solar electricity based charging.

on a related note, IMO this is the reason the whole fuel cell shtick from toyota is BS. Because if it were anywhere near economical & scalable then we would be seeing fuel cell powered drones all over.

hcknwscommenter• 7 years ago

5032.5 Wh/kg

As far as I know, there are simply no rechargeable battery chemistries that have any (even theoretical) hope of achieving this level of specific energy.

ogre_codes3• 7 years ago

That's looking at the energy density of the fuel itself, not counting the weight of the engine, several gallons of oil, air filters, fuel pumps, etc etc. The weight of equipment required to extract that energy from gasoline is a lot higher than the weight of an electric motor.

Already__Taken• 7 years ago

90something% efficient electric motors vs 40-60% efficient gas engines however.

If you can make up in other areas like drag in the design because of the different power plant it's not such a mental gap to close.

aazaa• 7 years ago

See also lithium-air (aka lithium oxygen) battery:

https://en.wikipedia.org/wiki/Lithium–air_battery

svara2• 7 years ago

Electric aviation always strikes me as an odd idea, given the low power densities that batteries achieve.

By contrast, biofuels are available today and can be made from agricultural waste products (2nd gen), in bioreactors using salt water algae (3rd gen) or electrochemically (4th gen).

They're potentially a drop in replacement for regular fuel - for planes, but also for cars.

Due to the lower energy requirements for building ICE cars versus batteries, a biofuel powered car will be much better for CO2 emissions than an electric one, which you need to drive for many years before it beats a similar sized gasoline fueled car on sum CO2 emissions.

So why are we not heavily investing in biofuel infrastructure? Why are electric motors and batteries hyped up as being the tech of the future? That's an honest question, since I've yet to hear a well-founded physical or engineering argument against it.

jeffreyrogers• 7 years ago

Don't biofuels take up way too much land to be economical? A large portion of US crop area is for corn and soybeans for ethanol and biodiesel. I can see the reasoning behind biofuels for aircraft, but I don't think biofuels are sustainable if people continue driving as much as they do now.

JumpCrisscross3• 7 years ago

Don't biofuels take up way too much land to be economical?

Can we turn solar energy into hydrocarbons? (Water and CO2 are total feedstocks.)

throwawayhhakdl• 7 years ago

Biofuels always sounded wasteful to me. But this post makes a lot of good points on its merits that I hadn’t considered.

How efficient is producing biofuels using renewable energy as a way of storing power long term?

nradov2• 7 years ago

Alternatively, we can use electricity and heat from renewable power sources to synthesize kerosene from CO2 and water.

organsnyder• 7 years ago

For me, the experience of operating an electric vehicle is so much better than biofuels: refueling at home, simplicity of the drivetrain, and quietness/smoothness all are huge improvements over ICE vehicles.

For your comparison between ICE and electric vehicles, are you counting the fuel processing and delivery infrastructure? Electric delivery infrastructure has very low emissions once it's in place, and production continues to get better (especially with distributed models like rooftop solar). Also, do you have a citation for "...lower energy requirements for building ICE cars versus batteries"? Yes, battery production is fairly intensive (economically and resource use), but (like I said above) the drivetrain is vastly simpler.

I can't see how electric general aviation will become widespread without a monumental breakthrough. But it's hard to beat electric for ground-based transportation, IMHO.

svara2• 7 years ago

This article addresses your questions:

https://www.carbonbrief.org/factcheck-how-electric-vehicles-...

Check out the "lifecycle greenhouse gas emissions" figures. It's really interesting in how it shows how different the total emissions are depending on which country you charge your electric car in. Also, depending on which electric car model you have, the lifecycle emission improvement over a conventional one might be relatively slim, depending on where and how much you drive it.

By and large, electrics are at a substantial disadvantage due to both battery production and fuel cycle emissions, which then gets compensated over time as you drive the car.

Edit: There's also this super interesting article on Wikipedia: https://en.wikipedia.org/wiki/Environmental_aspects_of_the_e... which is largely consistent with the Carbonbrief article.

maelito• 7 years ago

Due to the lower energy requirements for building ICE cars versus batteries, a biofuel powered car will be much better for CO2 emissions than an electric one

What's the GHG emissions for the different types of biofuels ? What's the land use needed ? How abundant ? Etc.

biggieshellz• 7 years ago

For general aviation (small prop planes), it's because so much of the cost of running one comes from the engine. The most common piston engines are supposed to make it 1500-2000 hours between overhauls, and an overhaul runs around $16K, so you have to save $10-15 per flight hour in engine reserve to pay for the overhaul when it comes due and to cover any unexpected maintenance between overhauls. Plus, there are consumables that aren't cheap -- oil changes, spark plugs, and so forth. A brushless electric motor has a lot fewer moving parts, and a lot less vibration, so overhauls could be cheaper and with a larger interval between them, and regular maintenance would be cheaper as well. Plus, no leaded avgas to mess with, no worries about reduced power at higher altitudes where the air is thinner, no worries about carburetor icing or adjusting the air/fuel mixture. Sounds like a win to me.

TrueDuality• 7 years ago

Unfortunately the reduced power is still a problem at higher altitudes but for different reasons. Instead of oxygen starvation, the props will have less to push against.

This is still less of an issue as the electric motor can spin faster due to the reduced resistance. Higher speeds will create higher resistances from within the motor itself (which will in turn be increase the heat generated in the motor).

That heat will also be harder to dissipate in lower pressures, but I suppose alternative cooling could be added as well.

blendo• 7 years ago

And the motor _should_ be a lot more reliable.

But discouragingly, just last August, in Norway, a Pipistrel Alpha Electro lost power shortly after takeoff and crashed. https://aviation-safety.net/wikibase/228207

Hopefully, these folks in Fresno, CA will get their electric aircraft flight school up and running sometime soon. But summertime in California's central valley is challenging: https://sustainableaviationproject.com/2018/10/28/we-hit-the...

squarefoot• 7 years ago

"A brushless electric motor has a lot fewer moving parts"

Not to mention it makes a lot less weight to lift; the difference is huge.

the84725• 7 years ago

Combustion engines are quite inefficient and so are fuel synthesis processes. batteries have a high energy round-trip efficiency. The energy density does not matter as much in cars, which after mobile compute have been the primary drivers for technology. The density may make more sense for planes.

Additionally 1st gen biofuels have poisoned the well to some extent due to competing with food crops.

throwawaycanada• 7 years ago

The only reason we have electric cars being pushed as much as they are is because of Tesla, specifically Elon Musk. It is not some government program. If it weren't for them we would have the Nissan Leaf and that is about it. And it wouldn't have half the performance that even it has today.

Short answer: Monied interests don't really care, or don't think it is possible or feasible.

elihu2• 7 years ago

Electric motors and batteries are very efficient, and therefore extremely cheap to operate.

Biofuels make sense I think for aviation because you need that energy density to get a usable range, but the fuel is likely to be expensive for a long time. If you can figure out how to make liquid fuel for about fifty cents a gallon or so, it might be competitive with electricity for car use.

I don't know what the energy requirements are for modern batteries, but I expect it varies a lot depending on battery chemistry. Battery sizes vary a lot, too.

nbanks• 7 years ago

For very short distance flights, electric aircraft are already viable. For example, Harbour Air Seaplanes operates a 20 minutes flight between Vancouver, BC and Victoria, BC. They use float planes because both cities are on the coast. Their first electric aircraft should take off in a couple months.

One nice thing about electricity is that it's much cheaper than biofuels. This is because motors are much more efficient than engines, and because large generating stations are more efficient than small aircraft engines. BC is 95% hydroelectric which makes electricity even cheaper.

tim3332• 7 years ago

So why are we not heavily investing in biofuel infrastructure?

I think the problems are more economics than physics. There was a huge investment in algal biofuels but it never proved economic. (eg https://www.greentechmedia.com/articles/read/lessons-from-th...)

I was a fan of Algenol for a while who were supposed to have algae that gave off ethanol cheaper than normal fossil fuel but it never worked out. Maybe something like that in the future will work.

ctocoder• 7 years ago

Whoever creates a better battery, which moves us away from Li, will be a trillionaire.

I do not think lithium or a chemical battery is the right solution. Too expensive and polluting. I am hoping for a silicon battery that will take over the world.

rvz• 7 years ago

Whoever creates a better battery, which moves us away from Li, will be a trillionaire.

So now it should be a golden age to be a chemical engineer or a physicist specialising in battery technology research I suppose.

I am hoping for a silicon battery that will take over the world.

Chemical Engineers and Battery Technologists will be the new 'Software Engineers'.

Xcelerate• 7 years ago

As a chemical engineer who did my Ph.D in Li-ion battery anodes, I switched to data science immediately afterward. So I wish you were right, but I wouldn’t count on it any time soon.

adammunich2• 7 years ago

Lithium is here to stay for a while because it has the best ion mobility of any reactive metal. Sodium is much fatter and slower, but might be good for grid storage.

PowerfulWizard• 7 years ago

This reminded me of a graph I thought was really interesting from a thesis on a solar powered UAV that shows energy density and power per weight for different sources of energy, I've highlighted the 500wh/kg line which is being claimed in the article:

https://i.imgur.com/nZSWpW1.png

Should be very interesting if they can deliver that level of performance.

The source document for that graph is here: https://ethz.ch/content/dam/ethz/special-interest/mavt/robot...

And described here: https://spie.org/news/1649-designing-solar-airplanes-for-con...

m4633• 7 years ago

24,965,421,631,578 wh/kg (antimatter)

23,222,915,000 wh/kg (plutonium 239)

https://en.wikipedia.org/wiki/Energy_density#Table_of_energy...

the84725• 7 years ago

If your goal is to use exciting power sources then those two have a flaw, they can be scaled down to fit the power needs of the plane, which would limit the spectacle you could achieve. The penrose process may be a better choice since there's a miniaturization limit.

joshfraser• 7 years ago

Flying at higher altitudes reduces drag and increases efficiency due to the thinner air. Ideally, we'd be flying planes a lot higher than we do today. The problem is combustion engines need oxygen and the higher you go, the less oxygen you have available. Electric planes don't have that problem which could be the secret to faster global travel.

Scramblejams4• 7 years ago

The SR-71 and U-2 flew plenty high and had enough oxygen. When you’re high enough that there’s no oxygen, you have no atmosphere, and then your wings and turbines don’t do anything useful. That means it’s rocket time.

Also, depressurization happens, and the risks and complexity of workarounds increase with altitude.

namirez2• 7 years ago

The SR-71 and U-2 flew plenty high and had enough oxygen

Actually none those two planes had fully pressurized cockpits. I guess they were pressurized at 26k feet altitude pressure. That's why the pilots were literally wearing spacesuits.

https://images.app.goo.gl/KjqGARoyiddhDxAE6

ohazi2• 7 years ago

Unless you're thinking supersonic travel, the "coffin corner" (difference between stall speed and Mach 1 (or Vne)) also narrows as you get higher. In an extreme case, the U-2 cruises at 70,000 ft, and at that altitude the stall speed is about 10 knots below the maximum speed.

ogre_codes3• 7 years ago

Turbos go a long ways to overcoming the thinner air problem with ICE engines. There is another, arguably bigger reason flying above 10k feet is uncommon—oxygen requirements. Few small planes are pressurized and O2 systems are expensive extras which require additional maintenance and filling. Systems which service passengers as well even more-so.

I flew a Cessna 206U for a few years and it was fine up to 15k feet or more, but I'd almost always skim just below 10,500 so I didn't have to bring along supplemental oxygen. I suspect that's where most of these guys will live, in the 7,000-10,000 foot range. It's much faster then flying near sea level but without the problems with O2.

mrfusion2• 7 years ago

Why can’t planes just pressurize the outside air for breathing? No need to bring your own o2?

mrfusion2• 7 years ago

Is the speed of sound barrier higher too?

Scramblejams4• 7 years ago

The speed of sound decreases as altitude goes up, unfortunately.

t0mas88• 7 years ago

No, it's lower, speed of sound is 38.94 * sqrt(temperature) with the speed in knots and the temperature in Kelvin.

Every airliner notices this when climbing, you get closer to the Mmo speed (maximum Mach number for operating) while at the same time the IAS decreases and you get closer to a stall due to decreasing airdensity. At some point you cannot go faster due to maximum Mach while you also cannot go slower due to minimum IAS to avoid a stall. At that point you cannot climb higher even if your engines have the power.

monomyth• 7 years ago

Flying at higher altitudes also increases chance of developing cancer due to cosmic radiation.

https://www.ncbi.nlm.nih.gov/pubmed/12862322 https://www.cdc.gov/niosh/topics/aircrew/cosmicionizingradia... https://www.cdc.gov/nceh/radiation/air_travel.html

Dibes• 7 years ago

Couldn't this be curbed by better radiation shielding on the plane itself?

stareatgoats2• 7 years ago

The first study:

METHODS: A cohort of 10,051 male and 160 female airline pilots [...] was followed for cancer incidence [...].
RESULTS: Among male pilots, there were 466 cases of cancer diagnosed vs. 456 expected.

So, a heightened risk of (466-456)/10051 = 0,001% if I read this correctly.

Or am I misunderstanding something here? I guess so, because this seems close to negligible.

henrikschroder2• 7 years ago

Electric planes don't have that problem which could be the secret to faster global travel.

However, to make it feasible for commercial air travel, you need much faster charging times, because airlines want to have as short of a turnaround as possible for their planes.

But I can totally see how electric planes would work for hobby piloting in the first place.

yxhuvud• 7 years ago

They could also make the battery swappable. That is more of a logistic problem, but perhaps easier.

tropo2• 7 years ago

On short routes, passenger loading time dominates. Electric could work for going between islands for Hawaii, Isle of Mann, New Zealand, and Japan. It could connect Martha's Vineyard or Long Island with various nearby places.

It's a ferry replacement.

LegitShady• 7 years ago

The majority of air passed through modern jets is bypass air. I don't think the availability of oxygen is the clincher.

Things like refueling speed, the weight of the batteries themselves (which don't burn up as you consume them like combustibles, and the overall better energy density of combustibles probably make the whole thing more attractive at today's tech.

gusgordon• 7 years ago

Flying at higher altitudes in lower density air also reduces lift, though [1]. A plane does get extra benefit from flying higher as drag on the fuselage is reduced, but there is a limit — the plane has to go faster to make up for the reduction in lift due to the reduction in air density. An electric plane ends up being able to fly a little higher, but not by much. See these notebooks for details:

https://github.com/gusgordon/atmosat/blob/master/atmosat.ipy...

https://github.com/gusgordon/electric_jet/blob/master/plane....

[1] https://en.wikipedia.org/wiki/Lift_(force)#Lift_coefficient

namirez2• 7 years ago

This is not correct. Here are the formulae:

Lift = weight = 0.5 * \rho * v^2 * S * C_L

Power = drag * speed = 0.5 * \rho * v^3 * S * C_D

where \rho is the air density. A good assumption for cruise is (C_L/C_D)_max. If you do the math, you realize that for a constant weight, the power output must be proportional to:

Power \propto \rho^{-0.5}

For example, to fly a plane at 10km above sea level you need twice as much power than sea level. This is totally independent of your propulsion system.

tropo2• 7 years ago

It's not just that they need oxygen. Cold air is good for thermal efficiency. Even if the heat source were nuclear (as in https://en.wikipedia.org/wiki/Project_Pluto engines) there would be a problem with the thermal efficiency. (see https://en.wikipedia.org/wiki/Thermodynamic_cycle and https://en.wikipedia.org/wiki/Carnot_cycle for why) Air temperature rises from about 217 Kelvin to about 270 Kelvin as you climb up the stratosphere. The temperature goes back down again as you get up to around 50 km (80 miles) but that is really high altitude.

There is an upside though. Subsonic aircraft can go faster as the temperature rises because the speed of sound increases. It goes from about 295 m/s to 329 m/s. The extra 11% is nice.

Graph of the air by altitude: https://upload.wikimedia.org/wikipedia/commons/9/9d/Comparis...

taf2• 7 years ago

I can imagine two really amazing effects from electric airplanes

1. Noise pollution could be significantly reduced . So many flight paths over homes.

2. Cost efficiencies could be amazing with fuel anywhere from 25% - 35% fluctuations, https://www.statista.com/statistics/591285/aviation-industry...

I imagine the operating cost of electric would be even less due to the simpler design of engines for electric vs gas

In my dreams airplanes could be designed to be more comfortable due to fixed operating costs... that would be nice

Tade02• 7 years ago

I've been following this company since their announcement of "300Wh/kg soon" a few years ago.

The pace of their progress is not jaw-dropping, but if anyone has a shot at bringing this chemistry to the market, it's them.

Lithium-Sulfur Battery Project Aims to Double the Range of Electric Airplanes

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