
Ultralight lithium-sulfur batteries for electric airplanes - pross356
https://spectrum.ieee.org/aerospace/aviation/with-ultralight-lithiumsulfur-batteries-electric-airplanes-could-finally-take-off
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dougmwne
Here's a fun bit: in the article they say that lithium-sulfur is hard to
measure charge level for due to the voltage properties of charging and
discharging.

"The upshot is that voltage is not a good proxy for the state of charge and,
to make things even more complicated, the voltage curve is asymmetrical for
charge and for discharge."

Since it would be bad if your battery suddenly died and you dropped out of the
sky, they had to develop complex statistical and neural network algorithms to
accurately determine state of charge to within a few percent. One black box
for staying in the sky and another in case you end up on the ground!

~~~
cameldrv
Or you could do what they did on Apollo (forget if it was the CM or LM). They
had the problem of measuring how much was in a tank, but the tank was in 0G,
so a float is no good. The proposed solution was some sophisticated radiation
based thing where they measured the attenuation of some radioactive source
through the tank. This wound up being highly complex, and the solution was
simply to have a reserve tank. When the main tank ran out, you knew you had
exactly the amount in the reserve tank.

~~~
brianpan
This is the solution used on motorcycles (which don't usually have fuel
gauges). There's only one tank, but in the normal position you get fuel only
to a certain depth.

As you're riding along, if you notice the engine running out of fuel, you
reach down and flip the fuel switch and you have access to a little more fuel
(and you know to head to a gas station soonish).

~~~
boardwaalk
Just for correctness: A vast majority of new motorcycles for quite a while
have had fuel gauges. There are only a few brands who are obtuse about it
(e.g. Aprilia).

~~~
barrkel
More like sports bikes don't have fuel gauges (saves weight, amirite?) and
make do with low fuel warnings instead, which serves the same purpose as a
reserve tank without the need for a switch.

Neither my MV Agusta nor my BMW S1000R have fuel gauges. The BMW does the
odometer trick itself though to estimate remaining mileage. It's often way out
of course, depending on throttle usage.

(It's possible the BMW has a meter but it doesn't present a level, only miles
remaining. I still think it's a style thing - something you don't put on sport
bikes.)

~~~
hwillis
Pretty sure all the S1000R years have fuel, but yeah it's as miles remaining.
S1000RR didn't have anything until 2019.

It never really made any sense, but now that race bikes have tire pressure
sensors and full color LCD instruments it is really spectacularly dumb to not
have gauges.

Any of the popular crotch rockets have had fuel gauges forever. I think it's
mostly just crazy race/rep bikes like BMW and Aprilla (so i guess the guys
that only make sport bikes in 300 or 1000+) that don't have gauges

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rolleiflex
> Oxis recently developed a prototype lithium-sulfur pouch cell that proved
> capable of 470 Wh/kg, and we expect to reach 500 Wh/kg within a year.

Meanwhile, gasoline / petrol / benzin (wherever you are in the world) has an
energy density of 12200 Wh/kg.

In other words, even in a world where all petroleum is perfectly depleted, we
would still be producing synthetic gasoline for high-demand applications and
capturing 100% of the emissions for recycling — essentially using gasoline as
a battery. It’s just too good an energy storage to ignore.

I’ve been looking at cars and geeking out on internal combustion engines for
the past few weeks since I had to buy a car, and for the usual Silicon Valley
guy such as yours truly whose standpoint on cars hadn’t been much more than ‘I
want a Tesla’, it was an outright revelation.

ICEs are real technology — and for a software guy it is easy to understand
because the complexity is bounded by physical dimensions of parts (i.e they
don’t work past a certain small size) so you literally see human-size
machinery with human size movements. It’s been a refreshing change from
potentially unbounded complexity of software.

~~~
phonon
Electric motors are simpler, more reliable, smaller, lighter, almost perfectly
efficient, and have better torque characteristics than ICE.

You can't compare the energy storage density in isolation. Engines are
heavy...Model S's motor generates 362 horsepower (according to the official
specs), and only weighs 70 pounds...the equivalent ICE would be 500+ :-)

(Yes, the inverter weighs something, but the transmission is much simpler as
well for electric...overall you save a few hundred pounds easily...A Model 3
battery pack is between 600 and 1000 pounds--so pretty close to the crossover
point.)

~~~
throwaway189262
We're still not at the point where weight savings from motor offsets battery.
Tesla cars are all extremely heavy for their size

~~~
froh
The mass is a problem of you don't t recuperate braking energy. Tesla's do
recuperate braking energy. A heavy ICE driven vehicle in contrast just loses
braking energy as heat.

Edit: typo

~~~
throwaway189262
Energy recovery from regen is minimal unless you're stuck in stop and go
traffic. Usually less than 5%.

~~~
usrusr
The argument made wasn't so much about getting more range from regen as about
regen lessening the impact of added mass: with perfect regenerative braking, a
ten ton vehicle wouldn't use much more energy than a one ton vehicle if they
shared the same outer hull.

Real life doesn't have perfect regen, but on the other side of the equation
real life ICE cars actually lose more efficiency to added weight than just
what is converted to heat while breaking because they tend to compensate worth
a bigger engine to get comparable (or better even) acceleration than a lighter
counterpart and that means that during cruise where the mass is irrelevant the
engine is running at all an even worse load point in terms of efficiency. ICE
are terribly inefficient at partial load and when your engine is sized to get
decent acceleration despite high total mass you simply can't gear long enough
to get the engine to a reasonable load point in a moderate speed cruise.
Electric motors don't have this problem (or a much, much smaller version of
it), so they wouldn't suffer quite as hard from added mass as ICE even worth
no regen at all.

~~~
throwaway189262
> ICE are terribly inefficient at partial load

Yes, but this doesn't happen much anymore. Torque converter, electronic
throttle control, variable valves, and 6+ speed gearboxes means the engine is
usually near full throttle even if your foot is barely on the gas.

Turbochargers also help, along with cylinder deactivation for some V8s.

Modern engines are nearly always at a relatively efficient load point. This
wasn't true until about a decade ago though.

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elihu
Higher energy density makes electric planes a little bit more reasonable, but
they'd still be quite range-limited compared to gas. For some use cases, that
might be okay.

I'm more interested in how this affects cars. Getting four or five hundred
miles out of a battery pack that's lighter than what's in a typical Tesla
would be a great thing, especially if it's cheap.

I'm currently working on an electric conversion of a Mazda RX-8. I just bought
about 450 pounds of lithium iron phosphate batteries. They're the most
expensive component, and provide about 27kwh; maybe enough for 100 miles if
I'm lucky. I sort of assumed that in about ten years or so I'll probably
replace the whole pack with whatever great new technology can provide more
range with less weight, and probably cost less too. It would be wonderful if
we had awesome batteries now.

(I considered used tesla modules; they have much better energy density, but
they're more dangerous and they wouldn't have fit well in the odd-shaped
places I wanted to put them.)

~~~
highfrequency
Sweet project! How much did the batteries cost? I see this works out to ~130
Wh/kg--did you avoid batteries with higher energy density for cost reasons, or
are they just difficult to get?

~~~
elihu
The batteries cost me about six thousand dollars. Lithium iron phosphate is
generally recommended for conversions because they're about as safe as you can
reasonably expect a battery to be and tolerant of abuse.

Used tesla packs have much higher energy density and are actually reasonably
inexpensive, but I couldn't really figure out how to make them work in my
setup. They're awkwardly long and don't really fit where I wanted to put them,
and need liquid cooling. They're also quite a bit more dangerous if they're
damaged or catch on fire, which is unlikely in a vehicle carefully designed to
protect them but considerably more likely in conversion. So I went with the
simpler, safer option.

LG Chem has some pretty good batteries as well, but I would have needed
multiple series groups connected in parallel, which would have required a
pretty complicated battery management system to keep everything balanced.

~~~
phaedrus
I have a largish 20AH 48V LiFePO4 I bought from PingBattery.com ten years ago
for powering a dual motor e-bike project. I ended up also using it to power a
mobile robot (rover) project, and sometimes used it for emergency power during
blackouts.

I went with lithium iron phosphate because it was perceived safer and more
durable. Over the past ten years when it wasn't bouncing around inside a rover
or e-bike it spent months or years on a shelf when I forgot about it. Most
recently I've dusted it back off and use it to power a large shop fan. Because
of it's long storage and infrequent charging/balancing the subset of cells
that actually power the microcontroller in the BMS were alarmingly low
compared to the others, but after a few cycles it seems to have recovered and
all but one of the low cells has balanced to the others. The battery still
seems to perform well overall.

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inamberclad
Everyone is talking energy density but nobody is talking about Urban Air
Mobility.

Electric is the name of the game for a VTOL plane that will take you from SFO
to downtown or Santa Cruz. They don't have to have all the performance in the
world, they just need to have enough performance to do their job.

Also, pilots will appreciate the operating costs and simplicity of these
aircraft. Student pilots will love a plane that costs $10/hr instead of
$100/hr in the Bay Area. 90 minutes of flight time (1 hour lesson + 30 minute
VFR 'fuel' reserve) is all it needs.

Neighbors will appreciate higher torque motors that turn modern props at 1500
RPM instead of 2200 for the noise reduction.

~~~
Antipode
How much of a prop plane's noise is from its propeller vs its engine?

~~~
jillesvangurp
Depends on the size of the propeller. The main issue is the tip of the
propeller breaking the sound barrier. This limits the RPM. Bigger propellers
mean more noise at lower RPM. Smaller propellers enable higher RPM.

So the noise profile of a plane with smaller, faster propellers and engines is
going to be very different from a big noisy helicopter where you can clearly
hear the engine over the already substantial noise of the very loud propeller.
Faster also means the noise is of a higher frequency and carries less far.

Comparatively the engine noise for electrical engines is not going to be a
factor. Think of the noise level of your vacuum cleaner; most of which is in
fact the spinning blade inside hitting a few thousand rpm; 3-5K is pretty
common for vacuum cleaners. Dysons apparently go way beyond that. A typical
Cessna would max out at around 2700 RPM and be cruising at around 2200.

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adammunich
With every lithium-sulfur battery I've come across you need to have a lot of
steel clamping plates together because they expand so much when charging, and
will otherwise delaminate. So ultimately they become the same mass.

This includes the oxis energy battery mentioned here.

~~~
cmrdporcupine
This might sound crazy but is it possible to do that in some way such that the
clamping plates etc. are only there during the charging process? Prevent the
delamination during charging and then remove the prevention mechanism?

Or just charge really really slowly? Airports etc. could just have terminals
full of trickle-charged batteries to swap in and out.

~~~
ngold
That was my first thought as well. But I don't have a clue if it's practical.

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ncmncm
Can I just say this was an extremely well-written article? Each time a
question came to mind, it was answered within the next two sentences.

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zzedd
For speculative (near future) fiction, that uses a lightweight electrically-
powered aircraft as a linking device, "News From Gardenia" by Robert
Llewellyn, is a good read.

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tuatoru
Just yesterday I threw out a print of a DoE paper from 1997 that talked about
lithium-sulfur as imminent new storage tech.

Impressed with the persistence here.

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akrymski
Surely hydrogen makes more sense for electric airplanes?

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foxylad
Wow. So much geekery comparing ICE to electric, without a single mention of
global warming.

Big oil has done an amazing job making the subject unmentionable.

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ddoice
Still orders of magnitude less energy-dense than jet fuel.

~~~
umvi
Yes but presumably electricity is order(s) of magnitude cheaper than jet fuel.
And also order(s) of magnitude more available than jet fuel. And also order(s)
of magnitude cleaner than jet fuel (depending on the source).

~~~
bronco21016
I'd debate the 'more available' statement. It is more widely available overall
but not in the places you'd want it. Of course that can be fixed but someone
will have to build out that infrastructure to make electric planes viable.

It's a bit like Tesla. Prior to them building out their charging network,
electric cars had a bit of a chicken and the egg problem. You might buy a car
but have no where to charge it, but nobody wanted to build places to charge
them because nobody has an electric car.

~~~
harg
That’s not the case at all. Everyone has electricity at their home. You can
charge basically any electric car from a domestic wal socket and higher power
chargers are easily available. Commercial charge points only really need to be
used for long distance travel. Most EV owners can do the majority of charging
at home.

~~~
lacksconfidence
One confounding factor is parking arrangements. If you have a garage then a
wall socket is reasonable, but for many years the only place i could park a
car was somewhere on the street, hopefully within 100m of my address. In that
situation commercial charge points (hopefully near my employer, if lucky)
would be the only reasonable charge point.

