# News Researchers unveil rapid-charge aluminium battery tech

Discussion in 'Article Discussion' started by Gareth Halfacree, 7 Apr 2015.

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2. ### mute1What's a Dremel?

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aluminum... *shudder*

3. ### andrew8200mModder

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Its an interesting read but why not just use the battery's in series to bump voltage rather than falling at the first hurdle and saying "only 2v"??

4. ### Gareth HalfacreeWIIGII!Lover of bit-techAdministratorSuper ModeratorModerator

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They're aiming to replace lithium-ion batteries in mobile devices. Using two of the batteries in series, you'd double the voltage but halve the capacity because you're having to make the batteries half the size to fit in your device. Let's assume for a moment that the prototype has a 2,400mAh capacity like a smartphone battery (which it almost certainly won't, seeing as it's a prototype an' all). So, to boost the 2V to 4V (we need 3.7V, but let's not overcomplicate things) you have to halve the size of the two batteries - which drops the capacity of the overall system to 1,200mAh at 4V. Sure, you can recharge 'em quickly - but you have to, 'cos your phone now only lasts 'til lunchtime.

5. ### RazyreWhat's a Dremel?

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Not true. A 1200mah @ 4V is equivalent in energy density to the 2400mah @ 2V battery.

Do the mah to wh calculation:

1200 * 4 / 1000 = 4.8wh
2400 * 2 / 1000 = 4.8wh

Both can sustain a 4.8W power drain for an hour.

The difference is that the 4V battery has a higher potential and is much easier to scale up to 5V as is done with current Lion cells. A single 2V cell is going to yield worse discharge potential with a boost converter than a 3.7 or 4V battery. You can also discharge at twice the maximum discharge rate of a single cell as the draw is spread evenly across the two cells.

If you want to do that with these batteries you need 2 in series really and this is likely to increase the size of the device. Cell balancing may also be required if the chemistry is anything like Lithium, though perhaps not since this is a much safer chemistry if what they say is true.

6. ### SuicideNeilWhat's a Dremel?

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Without knowing the capacity and dimensions possible from a pre-production final prototype, it's hard to argue about needing to make the cells smaller in order to fit 2 in series inside a phone; for all we know they are half the size for the same capacity, so having two in series is a non-issue.

7. ### BlacksharkWhat's a Dremel?

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Razyre - I think Gareth was stating that if the new battery had roughly the same space requirement as 3.7V lithium, but required 2 cells in series to reach the same voltage. So the maths was more along the lines of:

1200 * 4 / 1000 = 4.8wh
2400 * 3.7 /1000 = 8.9wh

However, if I could drop my aluminium battery on a wireless charge pad at home, in the car, at the office - and it charged fully in an hour, I dont mind if my phone only has 5-6hrs of life. Be a bit of a pita for those that go hiking out in the sticks, but then you could take a power booster pack (ie. a big battery) with you.

8. ### Gareth HalfacreeWIIGII!Lover of bit-techAdministratorSuper ModeratorModerator

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Re-read my post: you're actually in complete agreement with me.
Exactly.

9. ### AlectoMinimodder

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Murricans ...

10. ### schmidtbagWhat's a Dremel?

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I'm interested to know why exactly some batteries charge quicker than others. Think of it in this perspective - suppose that you have this aluminum-based battery and a Li-ion battery with the same power capacity. If the aluminum battery charges in 1 minute, what happens to all the power (not) being pumped into the Li-ion? Is it just simply not used? I know some of the power goes to waste, since there is heat generated, but there's got to be something else that makes it so slow.

The reason I bring this up is because these batteries could be amazing for electric cars. Most electric cars use lilthium-based batteries, and use regenerative braking to help recharge the batteries a little bit. But braking is such a brief action, and with the slow recharge rate of lithium-based batteries, I'm sure they get very little out of regenerative braking. Depending on why the aluminum batteries recharge quicker, it wouldn't surprise me if you could drive a much greater distance on them compared to the lithium batteries. Especially if they end up weighing less. Aluminum is a heavier metal, but if they need less to get the job done then it still might weigh less.

11. ### r4tch3thmmmm....

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When you charge a Li-ion battery the lithium ions have to move from the cathode to the anode and there is a limit to how quickly they can move, different chemistries can have different ion mobilities. The other thing is the efficiency of charging, if you have 95% efficiency and you charge a 1000mAh 4V cell you have 1800 joules of wasted heat to dissipate so efficiency will have an impact.
In regenerative braking systems they usually have a few big super capacitors to capture the energy and feed it back to the battery. Some systems don't actually recharge the battery with the braking and instead just store the energy in a capacitor and use it to supply more power when you accelerate.
The increased charging rate doesn't necessarily have much to do with capacity although with new chemistry there is always potential.

Last edited: 9 Apr 2015
12. ### schmidtbagWhat's a Dremel?

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Ah cool, thanks for the explanation. But yeah, I didn't think charge rate was correlated to capacity. What I was getting at is the increased charge rate means (in a case like rengerative braking) you could potentially capture most (or maybe all) power created by the brakes, whereas with lithium batteries there just isn't enough space in capacitors or enough time to put all that energy back into the battery.

13. ### r4tch3thmmmm....

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You will find that in cars at least they will have a capacitor that is big enough for 95% of use cases in everyday driving, in racing they have larger capacitors as they brake/accelerate harder and more often.
With this technology you could have the benefit of having a smaller capacitor as the battery would be able to take some of the charge faster. I would think that no matter the battery technology you would still use capacitors for capturing the initial energy and then passing it on to the battery. Even if the battery could handle the charge rate the capacitor would smooth things out.
The other advantage to a capacitor based system is efficiency, you lose a lot less power charging a capacitor than a battery.

EDIT: If the battery has a large capacity it would likely have multiple cells in parallel in which case each cell would be able to be charged separately so a 2 cell battery could charge twice as fast as a single cell battery for the same capacity.

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