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This might seem a very naïve question. Maybe the comparison of electric vehicle to aircraft is hugely inappropriate. But I couldn't find a clear answer in web search.

Lithium-ion batteries have a high power-to-weight ratio, high energy efficiency and good high-temperature performance. Even then they are not preferred to be used in aircraft.

If safety is the concern, aren't there enough protection mechanisms which have enabled their widespread proliferation in electric vehicle industry.

Why is the weight to power-to-weight advantage not being exploited by aerospace industry? What are the other aspects to be considered- extreme environmental conditions or so?

Edit: I am asking about the battery usage as in typical aircraft, not for electric propulsion. Sorry for not being clear earlier

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    $\begingroup$ If you're asking about using batteries as a replacement for conventional jet fuel, this question may be helpful (or even a dupe). $\endgroup$
    – Pondlife
    Jan 12 at 16:25
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    $\begingroup$ If you are asking about batteries for propulsion this question could also be a dupe: aviation.stackexchange.com/questions/45040/… $\endgroup$
    – GdD
    Jan 12 at 20:50
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    $\begingroup$ Li-Ion has a high Power/Weight compared to other battery chemistries. But when compared to jet fuel, Li-Ion batteries have about 50x less energy per weight. Jet Fuel is still among the most energy dense material we have. $\endgroup$
    – abelenky
    Jan 12 at 22:04
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    $\begingroup$ @abelenky: * (non-nuclear) $\endgroup$ Jan 13 at 1:51
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    $\begingroup$ Note that this question was previously asked on EE.SE: electronics.stackexchange.com/questions/604059/… $\endgroup$ Jan 13 at 4:31
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Boeing put them in 787. They caused the type to be grounded for a bit over two months in 2013 due to battery fires.

Li-ion battery fires of consumer electronic devices are also semi-regular occurrence on passenger flights, and the reason they are not allowed in checked luggage so the cabin crew can deal with the fire when it happens.

Boeing did manage to improve the battery and get it certified for the very strict requirement of failure rate of less than 1 per 10⁹ hours, and they are used on that plane. But it's much stricter than what is required on ground vehicles, because land vehicles can be easily abandoned when they start to burn, which is not possible in airplane. In many cases the work to ensure the battery is safe enough for a plane is simply not worth it.

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    $\begingroup$ Airline regulations are also the reason that Laptops have a maximum battery size. Back in the early 2000s there were laptops with very large batteries. Then airlines limited how much lithium you can carry on board which forced manufacturers to limit laptop battery sizes. $\endgroup$
    – slebetman
    Jan 13 at 8:02
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    $\begingroup$ And Li-Ion fires are very hard to extinguish. Those shooting jets of flames can occur in a vacuum because the packs themselves provide enough fuel and oxygen to feed the fire. The stuff also reacts with water and air. $\endgroup$
    – Nelson
    Jan 13 at 9:15
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    $\begingroup$ @Nelson. Though at least for the batteries in consumer electronics, throwing them in a bucket of water is good enough, and is the standard procedure for cabin crews. I believe the lithium itself almost never gets exposed to air or water and it's mainly the package and electrolyte burning that can be extinguished and a bucket of water is enough to absorb the heat a short circuit in a phone or notebook battery can release. But big batteries are indeed a problem. $\endgroup$
    – Jan Hudec
    Jan 13 at 12:06
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    $\begingroup$ Obligatory XKCD. $\endgroup$ Jan 13 at 13:20
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    $\begingroup$ Li-ion batteries are actually allowed in checked luggage, but with certain restrictions (only in equipment, no spares, devices entirely off). See iata.org/contentassets/6fea26dd84d24b26a7a1fd5788561d6e/… $\endgroup$
    – jcaron
    Jan 13 at 23:41
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If we're talking about using the batteries for propulsion (and we're talking about aircraft that can carry at least one person) then it boils down to, in a word, weight, or in two words energy density. Li-ion batteries have a pretty good energy density for a battery, but they aren't even in the same league as aviation fuel. Heck, they aren't even playing the same sport.

Something like Avgas has a Specific Energy of ~44.65 MJ/kg, Jet fuel ~43.15 MJ/kg and at the moment Li-ion batteries as used in electric road vehicles are around 0.72 MJ/kg so for the same take-off weight you're going to get a frankly pitiful amount of range.

That's not to say it isn't being looked in to - e.g. Vertical Aerospace's proposed VA-1X

This paper does some modelling around the concept of an e-VTOL aircraft like the VA-1X, and for a Gross Take Off Mass of 2500kg (about the same as a fully laden Cessna 172) you get less than a hundred miles of range. And that's when the batteries are new - once you start putting charge cycles on them the figure is only going to drop (no pun intended).

The weight of the batteries needed to replicate the range/performance of even a modest passenger jet is mind-bogglingly huge.

Of course that doesn't mean we'll never see battery-powered aircraft - Tesla have been teasing a substantial step in pack energy density for a couple of years now, and an alternative battery chemistry of Lithium-Sulfur (Li-S) offers a potential solution as they're already hitting nearly double the energy density of Li-ion (and improving rapidly) and if they can solve or mitigate the current issues Li-S has with rapid degradation and power-to-volume ratio then they could be very promising.

Texas aircraft are working on a Li-S-powered electric version of the Colt that could have a range of around 200 nautical miles

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    $\begingroup$ Even if the Li-S battery can double the energy density of a Li-ion battery, it's still a paltry 1.42 MJ/kg which is still only 1/30th the energy density of Jet fuel. That's a long way from commercial use on large passenger or cargo flights. The Colt would end up being much like the Tesla Roadster - an expensive toy for the hyper rich to brag about, more than a practical vehicle for transport. $\endgroup$
    – FreeMan
    Jan 12 at 17:12
  • $\begingroup$ @FreeMan I agree it's got a long (long) way to go before it becomes viable for real-world practical use. Li-S is supposed to have a theoretical energy density of 2,700Wh/kg which is around 10x what we're currently achieving with Li-ion. Still not up to jet fuel, would at least get something vaguely practical. $\endgroup$ Jan 12 at 17:44
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    $\begingroup$ It's not a completely fair comparison to say that it's 1/30th @FreeMan, electric motors are lighter than jet engines so the weight savings improves that a bit, but it's still a huge disparity. Plus, I don't want to be waiting for 8 hours while they recharge my plane. $\endgroup$
    – GdD
    Jan 12 at 20:48
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    $\begingroup$ The "but the engines weigh less" argument is rather irrelevant. Takeoff weight for a modern jet is about 30% fuel and 3% engine. If your alternative energy source is only 10% less efficient, no amount of engine weight saving can compensate. Batteries are not 10% but 98% less efficient. $\endgroup$
    – MSalters
    Jan 13 at 10:47
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    $\begingroup$ Don't forget, once you burn avgas, it becomes reaction mass. You have to drag the reusable, discharged battery with you to the destination as deadweight. $\endgroup$
    – obscurans
    Jan 13 at 13:12
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Actually, Li-ion batteries are used in aeroplanes - the grounding of the Boeing 787 in 2013 was caused by problems with them. From Wikipedia:

In 2013, the second year of service for the Boeing 787 Dreamliner, a widebody jet airliner, several aircraft suffered from electrical system problems stemming from its lithium-ion batteries. Incidents included an electrical fire aboard an All Nippon Airways 787 and a similar fire found by maintenance workers on a parked Japan Airlines 787 at Boston's Logan International Airport.

They are also used in the Airbus A350, as FlightGlobal mentions in this archived article:

Despite having similar functions, the Boeing design contrasts significantly with the lithium ion batteries installed in the Airbus A350-900. The Airbus supplier, Saft, designed a system with four batteries, each composed of 14 cells delivering 25V nominally combined. Thus, the A350-900 uses more batteries, with less power demanded from each cell than the 787 system.

The B787 problems were sufficiently fixed by providing more insulation between the cells, and installing an overboard ventilation system as a backup. No more incidents since.

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Why are Li-ion batteries not being used in aircraft

Actually they are. They are widely used in model airplanes, "drones", etc, which the (U.S.) Federal Aviation Administration refers to as "Unmanned Aircraft Systems". See for example this link.

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  • $\begingroup$ Which is, incidentally, why flight times on these are very short compared to petroleum-fueled aircraft. It makes a lot more sense for light UAVs, though, as electric motors can be easily scaled down to the very small sizes needed for these UAVs that weigh not more than a few pounds, whereas internal combustion engines can't scaled down that low quite as easily (though larger model airplanes do indeed commonly use ICE engines.) The flight times on most Li-ion powered UAVs literally wouldn't be enough to even meet the legally required reserves on manned flights. It would be illegal to take off. $\endgroup$
    – reirab
    Jan 14 at 15:53
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Lithium Ion main ship batteries (non-propulsion) have been making their way into general aviation, helicopters, and business jets over the last 5 - 10 years.

Certification of new technology in aircraft almost always takes a significant amount of effort and time. After the issues Boeing experienced on the 787, the industry went through a period of scrutiny and enhanced requirement development.

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Lithium Polymer (LiPo) batteries, are successfully used in smaller aircraft. Larger aircraft require a non-linear increase in power.
I would expect batteries to be especially suitable for lighter than air applications such as airships.

Apart from energy density, batteries do not shed mass as they discharge in the same way a fuel tank might.

This does not mean we cannot use them in a hybrid fashion, with a low capacity installation ultimately powered from turbofans with generators for takeoff or emergency power.

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  • $\begingroup$ "Larger aircraft require a non-linear increase in power." Do they? AFAIK, L/D ratio is actually significantly better on very large aircraft like airliners vs. most light singles, for example. $\endgroup$
    – reirab
    Jan 14 at 16:02
  • $\begingroup$ You need more than double the surface area to double the payload. Air is proportionally less dense as we scale up. Smaller aircraft can afford to be less aggressively designed. The airliner advantage is the 8m sweet spot (or thereabouts) for turbofans. $\endgroup$
    – mckenzm
    Jan 15 at 2:27

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