
Lithium-Sulfur Battery Project Aims to Double the Range of Electric Airplanes - pross356
https://spectrum.ieee.org/energywise/aerospace/aviation/lithiumsulfur-battery-project-aims-to-double-the-range-of-electric-airplanes
======
svara
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.

~~~
biggieshellz
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
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.

~~~
dogma1138
I’m not entirely sure how you’ll cool the engines at high altitudes,
combustion engines can use their exhaust to cool the engine.

Using large radiators on an electric engine kinda defeats the purpose
especially when they can’t be effectively be built into the body of the
engine.

~~~
xyzzyz
How exactly does one use exhaust to cool the engine? This is something I've
never heard of in the context of cars of motorcycles, where exhaust is
generally removed as soon as possible, and if it's used for anything, it's for
running turbochargers that make the engine even hotter.

~~~
stevehawk
There are two strategies for keeping cylinders cool in cruise: push the red
mixture knob forward for a rich fuel/air mixture setting that uses unburned
fuel to lower cylinder head temperatures, or pull the mixture knob out to such
a lean setting that an abundance of air and reduction in engine power and heat
cools the cylinders. Running aircraft engines “lean of peak” (LOP) typically
reduces airspeed about 5 percent in cruise while lowering fuel consumption
about 20 percent—but not all engines are capable of LOP operations, and doing
it wrong can cause permanent and costly engine damage.

source: [https://www.aopa.org/news-and-media/all-
news/2019/may/flight...](https://www.aopa.org/news-and-media/all-
news/2019/may/flight-training-magazine/technique-lean-of-peak)

------
PowerfulWizard
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](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...](https://ethz.ch/content/dam/ethz/special-
interest/mavt/robotics-n-intelligent-systems/asl-
dam/documents/phd_thesis/Andre_Noth_Design_of_Solar_Powered_Airplanes_for_Continuous_Flight.pdf)

And described here: [https://spie.org/news/1649-designing-solar-airplanes-for-
con...](https://spie.org/news/1649-designing-solar-airplanes-for-continuous-
flight?SSO=1)

~~~
m463
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...](https://en.wikipedia.org/wiki/Energy_density#Table_of_energy_content)

~~~
the8472
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.

~~~
xyzzyz
You can, in fact, put a functional nuclear reactor on a plane:
[https://en.wikipedia.org/wiki/Tupolev_Tu-95LAL](https://en.wikipedia.org/wiki/Tupolev_Tu-95LAL)
. Of course, it's a terrible idea, but it is feasible.

~~~
agumonkey
Russia sure does like mobile nuclear reactors

~~~
m463
Reading one of the Feynman books, probably "Surely You're Joking, Mr. Feynman"
I remember the section about nuclear-powered patent ideas, like nuclear-
powered spaceship, plane, boat, ... and submarine. We only did the boat and
submarine. I guess we did the spaceship too.

------
philipkglass
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...](https://cosmosmagazine.com/technology/lighter-cheaper-satellite)

------
joshfraser
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.

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

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

~~~
stareatgoats
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.

~~~
gamegoblin
You forgot to multiply by 100 when you went to %, so it's actually 0.1%
higher. Still pretty low.

~~~
stareatgoats
ah, thanks, silly mistake! Anyway, still a surprisingly low risk. Seems within
the margin of error to me.

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RcouF1uZ4gsC
> 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](https://xtronics.com/wiki/Energy_density.html)

~~~
korethr
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.

~~~
the8472
On the other hand a plane loses weight as it burns fuel, this isn't true for
batteries.

~~~
mrpurple_
It is losing weight but only very very little.

~~~
DesiLurker
thats not true, fuel weight is about 1/3 of total plane weight.

~~~
the8472
I assume he's talking about the mass defect in discharged batteries

------
adammunich
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
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

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ctocoder
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
> 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
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.

~~~
cagenut
uh... unless that data science is on like cancer research or something please
go back

------
taf2
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...](https://www.statista.com/statistics/591285/aviation-industry-
fuel-cost/)

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

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

[https://en.wikipedia.org/wiki/Lithium–air_battery](https://en.wikipedia.org/wiki/Lithium–air_battery)

------
Tade0
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.

