3 ms·

> Batteries are just bundles of electrochemical cells (and 1 cell can be a bundle) Correct. The problem with packing cells tighter is heat production: a ridicu

> Batteries are just bundles of electrochemical cells (and 1 cell can be a bundle) Correct. The problem with packing cells tighter is heat production: a ridiculous amount of heat is released and the individual cells can get up to 80 degrees C / 176 F. (80C is not a "doomsday scenario"; most cells are rated to sit there running at 80C just fine.) When they're all next to each other, tightly packed in with no place for heat to go, you're screwed. The other reason is that volumetric density is usually not what people optimize for; gravimetric density is more useful most of the time, and in that case you don't really have any reason to use tighter packing.

ufo 10y ago
Why is gravimetric density more important than volumetric density? That sounds counter intuitive to me.
- owenversteeg 10y ago
  Places where gravimetric density is more important: - Electric vehicles - Aircraft - R/C - Anything that goes into space - Large scale energy storage (good energy density typically = less lithium used) - Generally: anything that moves Places where both are equally important: - Consumer electronics (you don't want an ultra slim 2lb phone, or a ultra thick featherweight phone) Places where volumetric density is more important: - Batteries in smartcards - Some medical devices - Certain flashlights, IoT devices You'll notice that there are a lot more things where people care more about gravimetric density. Also, the best Li-Ion cells for volumetric density that you can buy are rather inconvenient shapes; a favorite is the 18650, an 18mm diameter by 65mm long cylinder. Yes, the best 18650 technically has much better volumetric density than the iPhone batteries. But if you swapped the iPhone battery with an 18650 you'd have a hilarious looking semi-cylinder protruding from the back.
- tekromancr 10y ago
  Because nobody seems to want a 4 pound cellphone battery.

ufo 10y ago

Why is gravimetric density more important than volumetric density? That sounds counter intuitive to me.

owenversteeg 10y ago
Places where gravimetric density is more important: - Electric vehicles - Aircraft - R/C - Anything that goes into space - Large scale energy storage (good energy density typically = less lithium used) - Generally: anything that moves Places where both are equally important: - Consumer electronics (you don't want an ultra slim 2lb phone, or a ultra thick featherweight phone) Places where volumetric density is more important: - Batteries in smartcards - Some medical devices - Certain flashlights, IoT devices You'll notice that there are a lot more things where people care more about gravimetric density. Also, the best Li-Ion cells for volumetric density that you can buy are rather inconvenient shapes; a favorite is the 18650, an 18mm diameter by 65mm long cylinder. Yes, the best 18650 technically has much better volumetric density than the iPhone batteries. But if you swapped the iPhone battery with an 18650 you'd have a hilarious looking semi-cylinder protruding from the back.
tekromancr 10y ago
Because nobody seems to want a 4 pound cellphone battery.