4 ms·

If it's per unit space, it's effectively a bomb. Doesn't mean it has to be unsafe. We drive around with big tanks of gasoline. But stored energy is stored energ

by api 8y ago

If it's per unit space, it's effectively a bomb. Doesn't mean it has to be unsafe. We drive around with big tanks of gasoline. But stored energy is stored energy.

hwillis 8y ago
> If it's per unit space, it's effectively a bomb. No, not particularly- the energy stored in an li ion cell is only a small amount of its potential energy. The cathode (eg cobalt oxide) and the organic electrolyte act as an oxidizer and fuel, >10x more energetic than the energy stored in the lithium. Solid state batteries carry far less energy than a normal battery.
- api 8y ago
  How could that be the case if they hold more energy or are more dense? It's just physics. I wasn't saying they couldn't work, just that if they did fail they'd have the potential to fail spectacularly. Same is true for a gasoline tank.
  - hwillis 8y ago
    If solid state cells had 3x more energy per volume, they'd have slightly less energy to release than a normal li ion cell, and those aren't bombs. Flamethrowers at worst. A bomb requires way more than just energy, it needs to have a mechanism to release quickly. Li ion has a mechanism like that, but solid state batteries don't.
InclinedPlane 8y ago
Not necessarily. Ordinary matter contains about 90,000 terajoules of energy per kg. But that hardly makes everything a bomb. There needs to be a way to explosively release the energy for it to be a bomb, and for some types of energy storage there isn't such a mechanism.
- rmu09 8y ago
  Whatever non-ordinary matter would be, E=mc² should apply as well. That number is an upper bound, I don't believe any process is known to convert matter into a useable form of energy with reasonable efficiency and yield. Neither fusion nor fission count as they only "convert"/release a tiny fraction.
  - InclinedPlane 8y ago
    Some processes are highly efficient in that conversion, accretion disks around black holes can convert 10-40% of rest-energy (mass) into "pure" energy. Annihilation is 100% efficient. My point is that energy density doesn't make a bomb, it's also necessary to have a mechanism for the spontaneous and rapid release of that energy. Ordinary matter has a very high energy density (the highest), but as you point out it takes special processes to release that energy. Similarly, I can have a soda can filled with Lithium-Deuteride (a fusion fuel) and that can have a very high energy content (terajoules per kilogram) but it's not a bomb unless it's connected to a system that can actually release the fusion energy in that fuel all at once. It's not something that could even remotely happen spontaneously without those other components that make it a bomb. Another example would be Potassium. Naturally occurring Potassium contains about 400 megajoules of radioactive energy per kilogram, which is about 100x as much as TNT. Even in the form of, say, a Potassium salt that would avoid the issue of the chemical energy of Potassium metal, that material would still have enormous energy density. And there's nothing you need to do for the energy release to happen, it'll happen automatically. But it's still not a bomb because it will take over a billion years for just half of that energy to be released, and there's no known way to substantially speed up that release of energy (without inputting even more energy) to make a bomb.

by api 8y ago

If it's per unit space, it's effectively a bomb. Doesn't mean it has to be unsafe. We drive around with big tanks of gasoline. But stored energy is stored energy.

hwillis 8y ago

> If it's per unit space, it's effectively a bomb. No, not particularly- the energy stored in an li ion cell is only a small amount of its potential energy. The cathode (eg cobalt oxide) and the organic electrolyte act as an oxidizer and fuel, >10x more energetic than the energy stored in the lithium. Solid state batteries carry far less energy than a normal battery.

api 8y ago
How could that be the case if they hold more energy or are more dense? It's just physics. I wasn't saying they couldn't work, just that if they did fail they'd have the potential to fail spectacularly. Same is true for a gasoline tank.
- hwillis 8y ago
  If solid state cells had 3x more energy per volume, they'd have slightly less energy to release than a normal li ion cell, and those aren't bombs. Flamethrowers at worst. A bomb requires way more than just energy, it needs to have a mechanism to release quickly. Li ion has a mechanism like that, but solid state batteries don't.

InclinedPlane 8y ago

Not necessarily. Ordinary matter contains about 90,000 terajoules of energy per kg. But that hardly makes everything a bomb. There needs to be a way to explosively release the energy for it to be a bomb, and for some types of energy storage there isn't such a mechanism.

rmu09 8y ago
Whatever non-ordinary matter would be, E=mc² should apply as well. That number is an upper bound, I don't believe any process is known to convert matter into a useable form of energy with reasonable efficiency and yield. Neither fusion nor fission count as they only "convert"/release a tiny fraction.
- InclinedPlane 8y ago
  Some processes are highly efficient in that conversion, accretion disks around black holes can convert 10-40% of rest-energy (mass) into "pure" energy. Annihilation is 100% efficient. My point is that energy density doesn't make a bomb, it's also necessary to have a mechanism for the spontaneous and rapid release of that energy. Ordinary matter has a very high energy density (the highest), but as you point out it takes special processes to release that energy. Similarly, I can have a soda can filled with Lithium-Deuteride (a fusion fuel) and that can have a very high energy content (terajoules per kilogram) but it's not a bomb unless it's connected to a system that can actually release the fusion energy in that fuel all at once. It's not something that could even remotely happen spontaneously without those other components that make it a bomb. Another example would be Potassium. Naturally occurring Potassium contains about 400 megajoules of radioactive energy per kilogram, which is about 100x as much as TNT. Even in the form of, say, a Potassium salt that would avoid the issue of the chemical energy of Potassium metal, that material would still have enormous energy density. And there's nothing you need to do for the energy release to happen, it'll happen automatically. But it's still not a bomb because it will take over a billion years for just half of that energy to be released, and there's no known way to substantially speed up that release of energy (without inputting even more energy) to make a bomb.