From the abstract: A lithium-air battery based on lithium oxide (Li2O) formation can theoretically deliver an energy density that is comparable to that of gasoline.
This particular Li2O battery is a little under 700 Wh/kg, with the theoretical maximum being 11k Wh/kg, compared to gasoline's 13k Wh/kg. It's an incredible accomplishment that they have managed to get such a reaction reasonably stable. Minor improvements to the battery cited in the paper would be beyond the theoretical limits of existing commercial lithium chemistries.
> The results shown in fig. S9 indicate that this solid-state Li-air battery cell can work up to a capacity of ~10.4 mAh/cm2, resulting in a specific energy of ~685 Wh/kgcell. In addition, the cell has a volumetric energy density of ~614 Wh/Lcell because it operates well in air with no deleterious effects (supplementary materials, section S6.3)
Especially when considering that most of that 13 Wh/kg for petrol is typically delivered as waste heat. You can get a decent estimate of how bad it is comparing miles per kwh for an EV to miles per gallon for a typical petrol car. It's about 3-4 miles per kwh vs. about 20 miles per gallon. EVs just use their kwh a lot more efficiently than petrol cars. Because batteries and electrical motors are just really efficient.
An 11 wh/kg battery would result in a battery that delivers about 5-6 times more miles per kg of battery than petrol. You get weight parity around 3-4 kg. If you factor in the weight of the engine (they can be quite heavy) it gets a little better. Of course the weight matters far less than people think. The amount of energy needed to move a vehicle does not necesseily scale linearly with weight of the vehicle. Which is why a heavy cyber truck and much lighter / smaller EVs can have miles per kwh metrics that aren't that far apart. Same with petrol cars. Halving the weight doesn't given them twice as much range. Heavy batteries are not that big of a deal. Unless you put them in a plane. Weight matters a lot in planes.
So, a battery like this would be amazing news for battery electric planes that currently fly with 200-300 wh/kg batteries (at best). 11kwh/kg would be a 70x improvement in energy density. That's a lot of range. Even a small fraction of that would be a massive improvement. 700wh/kg more than doubles the range already.
I think we'll see batteries break 1kwh/kg next decade or so. 500 wh/kg is already on its way to production. So, a doubling is only a modest step up. At 1kwh/kg, most GA flight will become electric. 3-6 hours of range with dirt cheap electricity turns a 100$ hamburger into a Starbucks coffee run. That's game over for ICE engines in small planes.
I think your point still stands but modern engines cluster toward the higher end of that range and some do exceed the 30% efficiency mark, hybrid drivetrains can approach 40%.
Indeed. Tesla Model 3 consumes about 50MJ of battery energy per 100 km. Toyota Prius consumes about 4.5 liters of gasoline. That gives roughly 150 MJ. So a electrical car consumes 3 times less or about 33% of energy of one of the best hybrid drivetrain.
Is that fresh out of the factory or after a few years of service? I think a lot of the metrics around hybrids are a bit optimistic. In the same way that official metrics for EV ranges are usually a bit more than is realistic.
Hybrids running on battery are about as efficient as an EV. When you enter the highway, they turn into ordinary ICE engines. If you use your prius exclusively for traffic in your neighborhood, you only use petrol to charge the battery, which is efficient and about as good as it gets with a hybrid. Unless you can plug it in of course. It won't use any petrol at all in that case.
Not that any of the tech is practical for every day cars or how they're used, but F1 engines with the multiple energy recovery systems are up to 52% efficient if they are to be believed (we'll ignore the rules subterfuge around tricking the fuel sensors, injecting oil, and who knows what else).
Is there a similar volumetric equivalent measurement or is it all about energy density by weight? Like, if the batteries are lightweight but massive, that would also be a bit of a problem since the structure to safely transport a large volume could be expensive and heavy.
Looks like the created cell is 614 Wh/L from the above comment. Gasoline is ~2.2kWh/L [0]. So my take is that even with the created cell the density is not going to be an issue with car or grid batteries -- only <4 times the size even at this non-theoretical cell. Who knows how the packs will be configured though as I am sure airflow will be a design consideration when making larger packs.
[0] This uses the 3kWh/kg that was provided above and a density of gasoline of .75g/mL
units
You have: 0.7429 g/mL * 3 kWh/kg
You want: kWh/L
* 2.2287
That 3 kWh/kg estimated by the poster above corresponds to an abysmal efficiency of an internal-combustion engine, of less than 25%.
Modern cars with good high-compression engines have efficiencies over 40%.
A fuel cell with hydrocarbons could reach efficiencies of 60% or more.
So no lithium battery can reach volumic energies or specific energies comparable to what can be achieved with hydrocarbons.
The reason to use lithium rechargeable batteries is to obtain a better total efficiency of using energy, not the hope that it is possible to match the densities achievable with energy stored in hydrocarbons.
Among lithium rechargeable batteries, the lithium-air batteries should achieve the best energy per mass, perhaps also per volume.
Usually the weak point of metal-air batteries is the power per mass or the power per volume, because the reaction with air is slow, therefore the electrical current density in the electrodes is low, so to obtain a given amount of power requires great areas for the electrodes.
A lithium-air battery (in general all metal-air batteries) is likely to have lower efficiencies for a complete cycle than other lithium-based batteries, perhaps not much above 80%, if not even less. The lower efficiency is caused by one of the reactants being a gas, which causes certain thermodynamic constraints.
A fuel cell with hydrocarbons would have a slightly better efficiency than the best mobile thermal engines, e.g. of 60%, while the ideal energy per mass ratio is more than double for hydrocarbons in comparison with lithium-air batteries, so even with a better efficiency lithium can never match hydrocarbons in usable energy per mass, not even in lithium-air batteries.
The claim from the parent article is wrong and it is based on an incorrect method for computing the ideal energy per mass ratio for lithium-air batteries.
> A lithium-air battery (in general all metal-air batteries) is likely to have lower efficiencies for a complete cycle than other lithium-based batteries, perhaps not much above 80%, if not even less.
This paper directly contradicts this claim with actual measurements of efficiency.
> The energy efficiency of the first cycle was 92.7%, and it gradually dropped to 87.7% after 1000 cycles.
Which is centered just above the 90% mark the person you are replying to gave.
> The claim from the parent article is wrong and it is based on an incorrect method for computing the ideal energy per mass ratio for lithium-air batteries.
Basically, Li-Air elements are wasting the energy from the phase change of oxygen. When a Li-Ion battery is discharged, you get the gaseous oxygen and bind it into a solid state molecule.
To do that, you need to expend roughly the same amount of energy that is needed to first liquify and then solidify the oxygen.
In fancy chemistry-speak it's called "entropic loss". You do gain some of that energy back when the battery is charged, as oxygen goes from a well-ordered solid state into the gaseous state. But it's not 100%.
The parent article has claimed that lithium-air batteries can have an energy per mass close to gasoline.
That claim is based on dividing the stored energy by the mass of lithium, which is incorrect.
The product of the reaction, i.e. lithium oxide, is stored in the battery, so a lithium-air battery can never be lighter than the lithium oxide.
Because the mass of lithium oxide is what counts, the energy per mass of pure lithium, which is indeed not much less than for gasoline, must be divided by a factor that varies between 2.14 and 5.57, depending on the construction of the lithium-air battery.
The best value of 2.14 is when the discharged battery contains only Li2O. The worst value of 5.57 is when the discharged battery contains only lithium superoxide, LiO2.
In the parent article, they claim that their discharged battery contains mostly Li2O, with only small quantities of peroxide Li2O2 and superoxide LiO2, but the exact amounts of peroxide and superoxide have not been measured.
So when computing correctly the energy per mass ratio, for lithium-air batteries it is limited to a value less than half of that for hydrocarbons. In practice batteries need a lot of materials besides the active reactants, so the achievable energy per mass ratio will be several times lower.
The advantage of hydrocarbons, regardless whether they are used in living cells, thermal engines or fuel cells, is that their reaction products are eliminated into the atmosphere, so their mass does not matter. The energy per mass for carbon atoms in hydrocarbons and for lithium atoms in lithium metal is approximately the same, but with lithium it is impossible to neglect the mass of the oxidant, like with carbon, because the reaction products cannot be dumped outside.
So for any battery except for fuel cells, what counts is the sum of the masses of the reactants, e.g. lithium + oxygen in the best case, or e.g. zinc + manganese in the cheap non-rechargeable batteries. It is wrong to compute the minimum mass of a battery by using only the mass of one of the reactants, like in the parent article, instead of both masses.
That theoretical maximum for a lithium-air battery seems much too high, so it is likely to be computed in the wrong way, in order to provide an optimistic but false value.
The mass that must be used for computing the theoretical maximum is that of Li2O, not the mass of lithium. Per atom of lithium, the mass of Li2O is 2.14 times greater, so it is likely that the number quoted by you must be divided by 2.14.
Indeed, computing very approximately 1 electron x the value of the elementary charge x 3 volt x the number of Avogadro (per kmol) / 15 kilogram / 3600 seconds, gives about 5500 Wh/kg, so the value quoted by you is indeed wrong.
This statement about energy density is false, the result of an incorrect computation. The correct ideal energy density of lithium-air batteries is less than half of that of gasoline.
If it can be made small enough for use in mobile devices, I wonder whether the need for air/oxygen might require compromising on water-tightness. Would an oxygen permeable waterproof membrane allow enough through for operation? It would be interesting if instead of just for cooling, future high powered devices might also need a fan to feed the battery!
Not really. In a fuel cell the reaction products are discarded (the reactants cannot be discarded, as they are needed for the reaction to take place).
In a metal-air battery, air from the atmosphere is taken into the battery and the oxygen from it becomes bound to the metal, in a metal oxide.
So unlike for a fuel cell, where the vehicle becomes lighter after the fuel is consumed and the reaction products are discarded, a metal-air battery becomes heavier when the metal fuel is spent, because the reaction product is stored inside the battery.
The metal-air battery becomes lighter again when it is charged and the oxygen stored inside it is released into the atmosphere.
A lithium-air battery can have a much better energy per mass than any other kind of lithium battery, but it cannot reach the energy per mass of hydrocarbons.
The reason is that for hydrocarbons the mass that counts is just the mass of the hydrocarbons, while for lithium-air batteries the mass that counts is not the mass of lithium, but the mass of the lithium oxide, i.e. the mass of the battery when it is mostly discharged.
A carbon atom from hydrocarbons can provide 6 electrons per atom, while a lithium atom provides only 1 electron per atom, albeit at a voltage more than 3 times greater than carbon atoms. The mass of a lithium atom is half of that of a CH2 group from hydrocarbons, so if the mass of lithium would have been the one that mattered, the ideal energy per mass would have been about the same for hydrocarbons and for lithium. However the additional mass in lithium oxide reduces the ideal energy per mass more than 2 times (when Li2O is the reaction product) or even 3 to 5 times (when peroxide or superoxide of lithium are the reaction products).
Just use drop pod technology; some jet fighters have AFAIK disposable under-wing fuel tanks.
Only dropping one that self-tests to high enough confidence/quality, and using e.g. GPS or laser guided bomb technology with a parachute and catch net at the landing site:
With a good net you can drop a human in a wind proof ski-suit (cold air!) and with an oxygen bottle from the Armstrong limit where their blood starts to boil, something like 18km, notably without a parachute.
So it will be easy to catch a pod that falls sideways on a drouge chute to trade off parachute size (weight!) and net height/give.
Per each electron provided in the circuit, the mass of aluminum is 9/7 of lithium and the maximum voltage is around 93% of that of lithium, which results in an energy per mass for aluminum of around 73% of that of lithium, when only the mass of the metal is considered.
In an aluminum-air battery vs. a lithium-air battery, the mass per electron is, in the most favorable case for lithium, of 17 for aluminum vs. 15 for lithium, which results in an energy per mass for aluminum of around 82% of that of lithium. However lithium forms by oxidation not only Li2O, but also peroxide Li2O2 and superoxide LiO2, which may worsen a lot the energy per mass.
In the parent article, they have succeeded to produce mostly Li2O, but even so their batteries have still produced some amounts of peroxide and superoxide during deep discharges.
So the energy per mass for aluminum-air batteries could be up to 80% to 85% of that of lithium-air batteries.
Most other oxidants besides the oxygen from air are heavier, which would reduce the advantage of lithium vs. aluminum (because the oxidant mass would be a greater fraction of the battery mass), so aluminum-ion batteries, if possible, could have an energy per mass very close to that of lithium-ion batteries.
On the other hand, aluminum metal and aluminum oxides are much denser than lithium metal and lithium oxides, so aluminum batteries could have much better energy per volume than lithium batteries. Unfortunately, until now the problems caused by aluminum as a cathode material have not been solved.
Alcoa and Phinergy demonstrated an aluminium-air battery over a decade ago that enabled 1600km range. The downside is that it had to be swapped out and recycled after it was spent (which explains why Alcoa's interest since it would gain business from the ongoing re-processing of aluminium).
So suppose a car had methane and oxygen onboard like a rocket and held on to its exhaust products, and you were able to reverse the reaction back to methane and oxygen, it would be a battery not a fuel cell.
I thought the problem with all of these metal air batteries is the sluggish oxygen reduction reaction at the air cathode. It just seems too slow for a high power density - need high surface area. The air cathode in this experiment is a gas diffusion layer embedded with trimolybdenum phosphide nanoparticle (seems common with these, others use platinum and iridium), with a current density of 0.1 mA/cm2. Need 1m2 of air cathode for 10 amps. I wonder how that ORR can be sped up or use smaller surface area. Could some kind of forced induction supercharger type thing work for these? I'm not a chemist.
Is there a way to determine how miles per kWh would change with different batteries in currently sold EVs? Would it be fair to say like half the weight but same energy content means double the distance per kWh
I'm a bit excited but also a bit tired of hearing about all these batteries. I just want someone to wake me up when we have a commercially available 1kwh+/kg with decent durability, decent price, and good safety.
Maybe this is a good idea for an ammoseek website but for batteries that can send alerts. I'm honestly surprised a quick search didn't turn one up.
That feels like a very high bar. A really good 500Wh/kg battery would already be completely revolutionary. That’s when you start to unlock practical short range electric flights for instance. It’d probably be enough for all forms of land transportation as well (except very small niches, like if you need to cross a huge desert off-road)
If you get to 1kwh/kg I don’t think you even need good durability and low price to have a revolutionary battery. At that energy density it could make economic sense to do medium range battery electric planes, even if you need to replace the battery every year. The operational costs related to using jet fuel (both fuel costs and engine maintenance) are huge. So the airplane industry can work with batteries that are more expensive and that requires more maintenance than what the EV market would accept.
I’m sure there’s a bunch of other niches for such a battery.
It's definitely a high bar. I set it that way because there have been a handful of battery announcements claiming they can get to that number over the past 5 years. I want it and I want it now. Haha
/Up to 1000 charge cycles/ is a big damper on the excitement, for me. Does anyone know if a limitation like that is inherent to the chemistry here or is this something that they could potentially (hopefully, vastly) surpass?
That's a comparable rating to the NMC Lithium cells used in an electric car, yet an EV can typically get > 200,000 miles from their cells. A charge cycle is defined as 0% -> 100% -> 0%. If you never do that, you get a lot more effective charge cycles.
Edit:
That's not the full explanation. 300 miles of range for a typical EV * 1000 cycle rating gives 300,000 mile rating.
You likely charge a lot more than 1000 times over those 300,000 miles, but a partial charge counts as a partial cycle.
It should be said that at that point you don’t have very many charge cycles left after the capacity drops below 80%, and the capacity will drop a lot faster for every charge cycle after that point.
I don’t have exact numbers.. based on graphs I’ve seen I would guess that if the original cycle life was 1000 cycles you may have another 500 cycles until the battery is actually unusable. But it probably depends a lot on the specific chemistry and how the car is used.
A study[1] was recently posted[2] which found that for lithium-ion batteries, dynamic use lead to much better battery life compared to fixed-current discharges which is typically used in labs to determine battery life.
From the paper: Specifically, for the same average current and voltage window, varying the dynamic discharge profile led to an increase of up to 38% in equivalent full cycles at end of life.
This tracks well with actual real-world data on BEV battery performance in cars with decent battery management.