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Earlier quoted context omitted.
Usual disclaimer regarding the energy density of gasoline: current gasoline engines have an efficiency of 10-30% while EVs are around 90%. So to reach similar kWh/g we're looking at ~3k Wh/kg
Does the engine and drive train weight make these calculations even better for electric vehicles?
/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?
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.
Does it use external air? 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).
Earlier quoted context omitted.
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 th…
Usual disclaimer regarding the energy density of gasoline: current gasoline engines have an efficiency of 10-30% while EVs are around 90%. So to reach similar kWh/g we're looking at ~3k Wh/kg
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 th…
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.
/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 o…
Earlier quoted context omitted.
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 th…
Usual disclaimer regarding the energy density of gasoline: current gasoline engines have an efficiency of 10-30% while EVs are around 90%. So to reach similar kWh/g we're looking at ~3k Wh/kg
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.
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.
See other comments for the correct computation.
Earlier quoted context omitted.
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 [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
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.