16 ms·

Ultralight lithium-sulfur batteries for electric airplanes

217 points by pross356 6y ago

ddoice 6y ago
Still orders of magnitude less energy-dense than jet fuel.
- henearkr 6y ago
  To be fair, you need to compare a complete workflow including the renewable production of the jet fuel. If the overhead of heavy batteries does not annihilate the benefit of the carbon-neutral production rendered possible by using electricity (and associated carbon-neutral sources like photovoltaic etc... heck, even nuclear fission), then batteries are still the path to go. If there are carbon-neutral ways to produce the jet-fuel, and to have a completely carbon-neutral(or even negative) cycle production+consumption, then why not. If it could be done without turning the Earth into a giant bio-fuel crop, that would be nice.
- umvi 6y ago
  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 6y ago
    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 6y ago
      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 6y ago
        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.
      - tuatoru 6y ago
        > Everyone has electricity at their home. I do. But I can't get the car up the stairs. :-(
    - bdamm 6y ago
      Yeah basically all airports that have commercial service also have access to power. There are exceptions like seaplane bases and small country strips, but there are more than enough airports with access to commercial or even industrial grade power to make electric airplanes that require charging viable. The final step of linking up the airport power supply to the airplane charger is peanuts in the world of aviation. Almost all airports have a fleet of fuel trucks, therefore, the cost of buying a fuel truck is the low end of the acceptable cost for ground infrastructure investment to open a new route for an airline.
      - bronco21016 6y ago
        I just reread what I wrote and I think maybe I wasn’t very clear. There’s electricity at every single gas station in the US. Why can’t we pull into any gas station in the US and charge an electric car? Even now that electric cars are gaining market share and becoming more common. Someone has to build, supply, and hook up high power charging systems. You can’t just fly your $5 million eJet into any airport in the US and run a 100’ extension cord into the FBO. If that’s the plan, you certainly can’t hope to leave the same day. It will take at least 3 days for your 1 MWh eJet to finish charging. We’re in the pre-Tesla days of electric aircraft. There’s a few players working on the aircraft and they’re getting close. However, until a ‘Tesla’ comes along where they also install charging infrastructure at the airports their customers are planning on using, we’re not going to see a commercially viable electric aircraft.
  - aphextron 6y ago
    >Yes but presumably electricity is order(s) of magnitude cheaper than jet fuel. It's really not even about the cost of fuel. With aviation it's all about maintenance costs. Electric aircraft will be orders of magnitude simpler and cheaper to maintain than jet turbines. This is what will unlock cost effective small scale commuter routes, allowing you to just hop on a small 10 passenger plane at a neighborhood airport and take a 300 mile flight with no need for security.
  - asdfadsfgfdda 6y ago
    Jet fuel is ~36 kWh/gallon raw energy density (13 kWh/gallon mechanical power assuming 35% engine efficiency). The pre-covid jet fuel price was $2/gallon, or $.15/kWh. The average price of commercial electricity is $.06/kWh in America, or $.08/kWh including charging/motor efficiency. This cost will definitely be higher if you only buy clean electricity, and this ignores battery wear out. But where the economics break down is aircraft utilization. If charge time is greater than ~1 hour typical turn time, all of your costs will grow. Capital cost, crew costs, and airport infrastructure cost will increase. To charge in <1 hr is a challenge, you need a huge power source (tens of megawatts per plane) and serious cooling.
    - ramses0 6y ago
      Or swap the component, although that introduces its own design challenges and provenance risks. Aircraft refueling generally runs in-ground (at the largest airports), then 5-10k gallon trucks (~20-40k liters), then ~500-2000 gallon smaller trucks (2k-10k liters) for smaller aircraft or smaller airports. If you reimagined refueling trucks as "forklifts carrying batteries" instead of "tubes of gasoline on wheels" then you'd likely end up with similar delivery practices (central charging, swap/refuel, discard/recharge batteries instead of refilling the fuel tank on a fuel truck). Effectively it would be standardizing on some way to slot-in pre-charged batteries, and treat them similar to a propane tank rental company, where each removed battery is considered suspect and tested/refurbished/recharged after each use. Otherwise, yeah, putting a bunch of 220v outlets in the ground around an airport... you're going to be sitting there a while to recharge the ten planes that landed that day. It'd effectively be untenable for smaller airports to be able to provide "quick-turn" refueling services, and potentially risky to be able to guarantee overnight refueling. This is all nudging towards personal / corporate aircraft, not commercial aircraft operations, which would "never" want the plane in more than one spot for more than one hour, which would require something similar to battery-swaps that they control, OR some very fancy electrical and heat management associated with the airport/jetbridge that the plane pulls up at.
- DesiLurker 6y ago
  IIRC real-engineering on youtube did a detailed analysis of the current operating limitations with electric planes: https://www.youtube.com/watch?v=VNvzZfsC13o https://www.youtube.com/watch?v=VNvzZfsC13o He also identified a couple of sweet spots where electric flight would make sense factoring in engine efficiency & cost of fuel etc. bottom line is that the picture is more complex than just comparing energy density of jet-fuel & batteries. with batteries becoming much lighter IMO it should open up many more use cases for short haul frequent flights without the need of big central hub airports. which is good. an more importantly give the trajectory of battery energy density it should provide enough justification for heavy investment into research into electric planes so i wouldn't dismiss it out of hand.
- blisterpeanuts 6y ago
  >> Still orders of magnitude less energy-dense than jet fuel. Does that matter, if other aspects of the system compensate with lighter weight? For example, lighter weight electric engines versus heavier fuel-burning engines along with exhaust and cooling systems.
  - asdfadsfgfdda 6y ago
    A PW150 turboshaft engine is ~5 kW/kg. Some electric motors are up to ~10 kW/kg. But, as an example, engines on a Q400 regional airliner are only ~5% of the total weight. Fuel is up to 15% of total weight. So the savings are not significant. Also, the batteries will likely require a cooling solution. This can be challenging (heavy) for high altitudes (where air is cold but very low density). Jet fuel requires no cooling. https://en.wikipedia.org/wiki/Power-to-weight_ratio https://en.wikipedia.org/wiki/Power-to-weight_ratio
  - threeseed 6y ago
    If it's anything like ships/yachts then the lighter weight doesn't come anywhere close to making up for the loss of energy. Could still be very useful for flights between nearby cities e.g. LAX to SF.
adammunich 6y ago
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.
- mulmen 6y ago
  Is there some way to embrace this in the design of the plane? Could the wing structure be built in such a way that an expanding battery actually adds strength?
  - nippoo 6y ago
    The idea of making a battery a structural part of an aircraft wing has come up before, e.g. https://newatlas.com/axial-stack-battery-supersonic-electric-airliners/45537/ https://newatlas.com/axial-stack-battery-supersonic-electric.... I'm not sure if any progress has been made on this front recently, or whether they've come up against a materials-science roadblock!
- cmrdporcupine 6y ago
  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 6y ago
    That was my first thought as well. But I don't have a clue if it's practical.
rolleiflex 6y ago
> 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.
- jmercouris 6y ago
  While energy density as an important measure when talking about a fuel source, we can not forget about the other part of the equation. Energy efficiency, of those units of energy in jet fuel, how much of it can we effectively utilize? In other words, what is the distance travelled for a given weight of jet fuel vs the distance travelled for a given weight of batteries.
- tenuousemphasis 6y ago
  >Meanwhile, gasoline / petrol / benzin (wherever your are in the world) has an energy density of 12200 Wh/kg. Electric motors are 90% efficient, ICE are less than 20%. So in reality gasoline is 2-3x as energy dense, when you look at how much of the fuel's energy can be used to do useful work.
  - tengbretson 6y ago
    You also have to factor in the weight reduction as petroleum fuel is consumed vs the fixed weight of a battery.
zzedd 6y ago
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.
deleted 6y ago
[deleted]
dougmwne 6y ago
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!
- mrfusion 6y ago
  Can you just measure the current coming out of the battery and keep track of it?
  - hn_acc_2 6y ago
    You could use this technique to estimate the remaining capacity starting from a full charge / known charge, but not to arbitrarily measure the remaining capacity of the battery
    - dougmwne 6y ago
      It sounds like the voltage curve is all over the place as the battery phases through its chain of different chemical reactions, unlike a normal battery. I take that to mean there's no way to just measure the voltage at a given point of time to estimate capacity, hence why the statistical method was required.
      - rbanffy 6y ago
        It's a good thing to measure the instant capacity, but the voltage and current (and, hopefully, thermal output) are being measured during the whole flight.
  - hwillis 6y ago
    AKA joule counting- for normal li-ion it gets you to ~5% most of the time, up to 20% off at the start and end. That's assuming the voltage stays constant the entire time- in reality the first bit is at 4.2+ volts, and the last bit is down to ~3 volts. That's a 40% energy difference per electron that leaves the battery. It's also one of the reasons you get electronics that die suddenly at 5%- current gas gauges usually account for it, but older stuff wasn't always good at knowing when the voltage would drop off. Nowadays (and always, for the most part) the sudden shutoff is because electronics often pull very brief power spikes that drop the battery voltage below the minimum voltage temporarily. The chemistry takes a moment to recover after that. The problem with Li-S batteries isn't just that they have a goofy curve- that can be charted and saved, even as the battery degrades (Note- I'm mostly up on conventional chemistry. Don't know much about Li-S). It's more have a couple phases they go through during discharge. Impedance and other properties of the battery change, which changes the discharge characteristics of the battery, which changes the voltage. Proportionally, the swing in voltage is also larger (although this kind of thing is always changing, so I may be out of date). There's also a small amount of self-discharge and parasitic reactions that will consume electrons, but that number is necessarily fairly small and predictable. The main thing is that 50% of the energy variance is in the voltage, and you need to know a lot about the current chemistry inside the battery (as well as the future load profile) to be able to predict the voltage that all the remaining electrons will have as they leave the battery.
msaroff 6y ago
Two things: * The next great battery technology always seems 6 months away. * What, if any, are the combustibility issues with this tech. Higher energy density typically means greater potential for a thermal runaway.
inamberclad 6y ago
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 6y ago
  How much of a prop plane's noise is from its propeller vs its engine?
  - nickff 6y ago
    This varies extremely widely depending on engine selection and propeller design. Urban air mobility vehicles are also very likely to be loudest during vertical take-off and landing, which is not comparable to a conventional small aircraft.
  - jillesvangurp 6y ago
    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.
- 6y ago
ncmncm 6y ago
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.
elihu 6y ago
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 6y ago
  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 6y ago
    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.
tuatoru 6y ago
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.
foxylad 6y ago
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.
akrymski 6y ago
Surely hydrogen makes more sense for electric airplanes?

217 points by pross356 6y ago

ddoice 6y ago

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

henearkr 6y ago
To be fair, you need to compare a complete workflow including the renewable production of the jet fuel. If the overhead of heavy batteries does not annihilate the benefit of the carbon-neutral production rendered possible by using electricity (and associated carbon-neutral sources like photovoltaic etc... heck, even nuclear fission), then batteries are still the path to go. If there are carbon-neutral ways to produce the jet-fuel, and to have a completely carbon-neutral(or even negative) cycle production+consumption, then why not. If it could be done without turning the Earth into a giant bio-fuel crop, that would be nice.
umvi 6y ago
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 6y ago
  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 6y ago
    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 6y ago
      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.
    - tuatoru 6y ago
      > Everyone has electricity at their home. I do. But I can't get the car up the stairs. :-(
  - bdamm 6y ago
    Yeah basically all airports that have commercial service also have access to power. There are exceptions like seaplane bases and small country strips, but there are more than enough airports with access to commercial or even industrial grade power to make electric airplanes that require charging viable. The final step of linking up the airport power supply to the airplane charger is peanuts in the world of aviation. Almost all airports have a fleet of fuel trucks, therefore, the cost of buying a fuel truck is the low end of the acceptable cost for ground infrastructure investment to open a new route for an airline.
    - bronco21016 6y ago
      I just reread what I wrote and I think maybe I wasn’t very clear. There’s electricity at every single gas station in the US. Why can’t we pull into any gas station in the US and charge an electric car? Even now that electric cars are gaining market share and becoming more common. Someone has to build, supply, and hook up high power charging systems. You can’t just fly your $5 million eJet into any airport in the US and run a 100’ extension cord into the FBO. If that’s the plan, you certainly can’t hope to leave the same day. It will take at least 3 days for your 1 MWh eJet to finish charging. We’re in the pre-Tesla days of electric aircraft. There’s a few players working on the aircraft and they’re getting close. However, until a ‘Tesla’ comes along where they also install charging infrastructure at the airports their customers are planning on using, we’re not going to see a commercially viable electric aircraft.
- aphextron 6y ago
  >Yes but presumably electricity is order(s) of magnitude cheaper than jet fuel. It's really not even about the cost of fuel. With aviation it's all about maintenance costs. Electric aircraft will be orders of magnitude simpler and cheaper to maintain than jet turbines. This is what will unlock cost effective small scale commuter routes, allowing you to just hop on a small 10 passenger plane at a neighborhood airport and take a 300 mile flight with no need for security.
- asdfadsfgfdda 6y ago
  Jet fuel is ~36 kWh/gallon raw energy density (13 kWh/gallon mechanical power assuming 35% engine efficiency). The pre-covid jet fuel price was $2/gallon, or $.15/kWh. The average price of commercial electricity is $.06/kWh in America, or $.08/kWh including charging/motor efficiency. This cost will definitely be higher if you only buy clean electricity, and this ignores battery wear out. But where the economics break down is aircraft utilization. If charge time is greater than ~1 hour typical turn time, all of your costs will grow. Capital cost, crew costs, and airport infrastructure cost will increase. To charge in <1 hr is a challenge, you need a huge power source (tens of megawatts per plane) and serious cooling.
  - ramses0 6y ago
    Or swap the component, although that introduces its own design challenges and provenance risks. Aircraft refueling generally runs in-ground (at the largest airports), then 5-10k gallon trucks (~20-40k liters), then ~500-2000 gallon smaller trucks (2k-10k liters) for smaller aircraft or smaller airports. If you reimagined refueling trucks as "forklifts carrying batteries" instead of "tubes of gasoline on wheels" then you'd likely end up with similar delivery practices (central charging, swap/refuel, discard/recharge batteries instead of refilling the fuel tank on a fuel truck). Effectively it would be standardizing on some way to slot-in pre-charged batteries, and treat them similar to a propane tank rental company, where each removed battery is considered suspect and tested/refurbished/recharged after each use. Otherwise, yeah, putting a bunch of 220v outlets in the ground around an airport... you're going to be sitting there a while to recharge the ten planes that landed that day. It'd effectively be untenable for smaller airports to be able to provide "quick-turn" refueling services, and potentially risky to be able to guarantee overnight refueling. This is all nudging towards personal / corporate aircraft, not commercial aircraft operations, which would "never" want the plane in more than one spot for more than one hour, which would require something similar to battery-swaps that they control, OR some very fancy electrical and heat management associated with the airport/jetbridge that the plane pulls up at.
DesiLurker 6y ago
IIRC real-engineering on youtube did a detailed analysis of the current operating limitations with electric planes: https://www.youtube.com/watch?v=VNvzZfsC13o https://www.youtube.com/watch?v=VNvzZfsC13o He also identified a couple of sweet spots where electric flight would make sense factoring in engine efficiency & cost of fuel etc. bottom line is that the picture is more complex than just comparing energy density of jet-fuel & batteries. with batteries becoming much lighter IMO it should open up many more use cases for short haul frequent flights without the need of big central hub airports. which is good. an more importantly give the trajectory of battery energy density it should provide enough justification for heavy investment into research into electric planes so i wouldn't dismiss it out of hand.
blisterpeanuts 6y ago
>> Still orders of magnitude less energy-dense than jet fuel. Does that matter, if other aspects of the system compensate with lighter weight? For example, lighter weight electric engines versus heavier fuel-burning engines along with exhaust and cooling systems.
- asdfadsfgfdda 6y ago
  A PW150 turboshaft engine is ~5 kW/kg. Some electric motors are up to ~10 kW/kg. But, as an example, engines on a Q400 regional airliner are only ~5% of the total weight. Fuel is up to 15% of total weight. So the savings are not significant. Also, the batteries will likely require a cooling solution. This can be challenging (heavy) for high altitudes (where air is cold but very low density). Jet fuel requires no cooling. https://en.wikipedia.org/wiki/Power-to-weight_ratio https://en.wikipedia.org/wiki/Power-to-weight_ratio
- threeseed 6y ago
  If it's anything like ships/yachts then the lighter weight doesn't come anywhere close to making up for the loss of energy. Could still be very useful for flights between nearby cities e.g. LAX to SF.

adammunich 6y ago

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.

mulmen 6y ago
Is there some way to embrace this in the design of the plane? Could the wing structure be built in such a way that an expanding battery actually adds strength?
- nippoo 6y ago
  The idea of making a battery a structural part of an aircraft wing has come up before, e.g. https://newatlas.com/axial-stack-battery-supersonic-electric-airliners/45537/ https://newatlas.com/axial-stack-battery-supersonic-electric.... I'm not sure if any progress has been made on this front recently, or whether they've come up against a materials-science roadblock!
cmrdporcupine 6y ago
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 6y ago
  That was my first thought as well. But I don't have a clue if it's practical.

rolleiflex 6y ago

> 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.

jmercouris 6y ago
While energy density as an important measure when talking about a fuel source, we can not forget about the other part of the equation. Energy efficiency, of those units of energy in jet fuel, how much of it can we effectively utilize? In other words, what is the distance travelled for a given weight of jet fuel vs the distance travelled for a given weight of batteries.
tenuousemphasis 6y ago
>Meanwhile, gasoline / petrol / benzin (wherever your are in the world) has an energy density of 12200 Wh/kg. Electric motors are 90% efficient, ICE are less than 20%. So in reality gasoline is 2-3x as energy dense, when you look at how much of the fuel's energy can be used to do useful work.
- tengbretson 6y ago
  You also have to factor in the weight reduction as petroleum fuel is consumed vs the fixed weight of a battery.

zzedd 6y ago

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.

deleted 6y ago

[deleted]

dougmwne 6y ago

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!

mrfusion 6y ago
Can you just measure the current coming out of the battery and keep track of it?
- hn_acc_2 6y ago
  You could use this technique to estimate the remaining capacity starting from a full charge / known charge, but not to arbitrarily measure the remaining capacity of the battery
  - dougmwne 6y ago
    It sounds like the voltage curve is all over the place as the battery phases through its chain of different chemical reactions, unlike a normal battery. I take that to mean there's no way to just measure the voltage at a given point of time to estimate capacity, hence why the statistical method was required.
    - rbanffy 6y ago
      It's a good thing to measure the instant capacity, but the voltage and current (and, hopefully, thermal output) are being measured during the whole flight.
- hwillis 6y ago
  AKA joule counting- for normal li-ion it gets you to ~5% most of the time, up to 20% off at the start and end. That's assuming the voltage stays constant the entire time- in reality the first bit is at 4.2+ volts, and the last bit is down to ~3 volts. That's a 40% energy difference per electron that leaves the battery. It's also one of the reasons you get electronics that die suddenly at 5%- current gas gauges usually account for it, but older stuff wasn't always good at knowing when the voltage would drop off. Nowadays (and always, for the most part) the sudden shutoff is because electronics often pull very brief power spikes that drop the battery voltage below the minimum voltage temporarily. The chemistry takes a moment to recover after that. The problem with Li-S batteries isn't just that they have a goofy curve- that can be charted and saved, even as the battery degrades (Note- I'm mostly up on conventional chemistry. Don't know much about Li-S). It's more have a couple phases they go through during discharge. Impedance and other properties of the battery change, which changes the discharge characteristics of the battery, which changes the voltage. Proportionally, the swing in voltage is also larger (although this kind of thing is always changing, so I may be out of date). There's also a small amount of self-discharge and parasitic reactions that will consume electrons, but that number is necessarily fairly small and predictable. The main thing is that 50% of the energy variance is in the voltage, and you need to know a lot about the current chemistry inside the battery (as well as the future load profile) to be able to predict the voltage that all the remaining electrons will have as they leave the battery.

msaroff 6y ago

Two things: * The next great battery technology always seems 6 months away. * What, if any, are the combustibility issues with this tech. Higher energy density typically means greater potential for a thermal runaway.

inamberclad 6y ago

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 6y ago
How much of a prop plane's noise is from its propeller vs its engine?
- nickff 6y ago
  This varies extremely widely depending on engine selection and propeller design. Urban air mobility vehicles are also very likely to be loudest during vertical take-off and landing, which is not comparable to a conventional small aircraft.
- jillesvangurp 6y ago
  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.
6y ago

ncmncm 6y ago

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.

elihu 6y ago

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 6y ago
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 6y ago
  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.

tuatoru 6y ago

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.

foxylad 6y ago

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.

akrymski 6y ago

Surely hydrogen makes more sense for electric airplanes?