We thought it would be interesting to explore the reasons why lithium-ion cells are mostly round by design. Certainly, we are confident nobody suggested let’s make a penny-shape battery. Yet for some reason we want to know, there are hardly any square or rectangular ones. With the obvious exception of the lithium-ion batteries in our laptops and phones, that is.
Why Most Batteries Are Round in Shape
Batteries comprise two materials with thin, permeable sheets between acting as electrolytes. We can think of two ways to increase their density.
In the first instance, we could scale them up until they were a huge flat sheet. Or in the second instance, we could roll the sheet up and pop it in a tube
But there’s a more compelling reason. It is easier to collapse a cube than a sphere – assuming the cube does not have reinforcement inside. This may be the reason why beverages come in round, damage-resistant cans. Although these do have flat tops and bottoms to make stacking easier.
More Reasons Why Lithium-Ion Cells are Mainly Round
Did you ever wonder why drain lids in streets are round? It’s because this makes it impossible to drop them down the hole, and they fit easily every which way. The same principle makes it simpler to drop round batteries into devices.
A rectangular 9-volt battery is just a little harder to fit. So now you know why lithium-ion cells are mostly round with flat tops and bottoms, and alkaline and zinc-cadmium batteries too. Being more damage-resistant, they are also better able to resist pressure from inside.
This may be the reason why flat lithium ones in smartphones and laptops are more likely to swell. You see, they have soft edges and sharp corners making them relatively weak, unlike two-dimensional round ones with more consistent strength.
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Preview Image: 12-Volt Batteries