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.
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).
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
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> 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)
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.
So to reach similar kWh/g we're looking at ~3k Wh/kg
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.
See other comments for the correct computation.
Or with a tank of pure oxygen, have the EV act like it was gasoline engine on nitrous oxide.
Somebody should calculate a ballpark figure for the number of grams or kilos of oxygen that would be needed per mile for an average vehicle.
No it won't. At most, the battery might need a small fan. Turbochargers are needed for regular cars because internal combustion engines just suck.
Would this technically make it a fuel cell and not a battery, since some of the reactants are discarded :)
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).
I know that is decades out, of course.
Well. No. Not yet.
https://ouros.energy/