# Interesting question on Max Voltage



## Voltswagen (Nov 13, 2008)

If as the "University Professor" says Iron Phosphate & Cobalt chemistry must be charged to 4.2v to achieve "chemical balance" then why does Sky Energy cells suggest only 3.6v ?????? 

Are they not also Iron Phosphate & Cobalt?


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## MN Driver (Sep 29, 2009)

Sky Energy, now known as China Aviation Lithium Battery Co., Ltd, or China Aviation (Luoyang) Co., Ltd., with the name depending on where you look on the sites they post their information, is LiFePO4. As far as I've been able to read on Thunder Sky cells, I don't see any information about them being Cobalt at all, the only difference between Thunder Sky and other cell chemistries is the Yttrium component they added to their specsheets recently.

This is the first I've come across any information saying that there is any cobalt in a Thunder Sky cell, not sure how much I believe it, whether it's true or one persons assumption, we'd need confirmation of this.


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## automd (Feb 5, 2010)

MN Driver said:


> Sky Energy, now known as China Aviation Lithium Battery Co., Ltd, or China Aviation (Luoyang) Co., Ltd., with the name depending on where you look on the sites they post their information, is LiFePO4. As far as I've been able to read on Thunder Sky cells, I don't see any information about them being Cobalt at all, the only difference between Thunder Sky and other cell chemistries is the Yttrium component they added to their specsheets recently.
> 
> This is the first I've come across any information saying that there is any cobalt in a Thunder Sky cell, not sure how much I believe it, whether it's true or one persons assumption, we'd need confirmation of this.


Yeah and I think maybe you could see if EVcomponents could have them brought some in their following shipment.


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## roger (Jan 24, 2010)

Regarding Thundersky cells, they recomment in user manual initial charging to 4,2Volt for LiFeYPo4 chemistry. For which reason? To form the chemistry? Is there anybody here with experience to this question?


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## CroDriver (Jan 8, 2009)

The only reasonable option why they could recommend to charge to 4,2V is because they think that cells balanced at 4,2V are best balanced since they would have very different voltages there if not balanced properly. 

I can't think of any other reason.

Chevrolet is charging the batteries of the Volt to only 75% and discharging to 25% to maximize the battery life. TS cells are also LiFePO4, there is no magic dust inside.

I won't charge my cells to 4,2V. I'm limiting the charge to 3,65V/cell


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## JRP3 (Mar 7, 2008)

Lithium Cobalt cells are different than LiFePO4 cells. In general everyone, including vehicle manufacturers using different lithium chemistries, and Tesla, who are using Lithium Cobalt cells, do not ever fully charge the cells to help prolong life. I think the 4.25 charging recommendation is wrong.


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## Elithion (Oct 6, 2009)

MN Driver said:


> This is the first I've come across any information saying that there is any cobalt in a Thunder Sky cell, not sure how much I believe it, whether it's true or one persons assumption, we'd need confirmation of this.


As I said, I was told that third hand, and in any case I may have misunderstood; and I am not a chemist.

Sky Energy are LiFePO4, and you charge them up to 3.6 V
Thundersky are mostly LiFePO4, but they also have some other element in there (whether it is Cobalt or not, I really can't vouch for) that requires them to be topped at 4.2 V. Why, I don't know. I just know that Thundersky is adamant about it, and the university professor I mentioned, who is an expert in this field, has confirmed it.

I agree that there is no extra energy to speak of going from 3.6 to 4.2 V in a Thundersky cell. It is just that it is supposed to "do something good" to the cell chemistry. Sorry for not being able to address that reason completely.

Davide
________
C-max


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## EVComponents (Apr 20, 2009)

JRP3 said:


> Lithium Cobalt cells are different than LiFePO4 cells. In general everyone, including vehicle manufacturers using different lithium chemistries, and Tesla, who are using Lithium Cobalt cells, do not ever fully charge the cells to help prolong life. I think the 4.25 charging recommendation is wrong.


Tesla cells are lithium cobalt with a maximum voltage of 4.20 volts. 
But they never get charged to that level by the user.

Tesla considers a full charge to be 4.15 volts in the maximum range mode.
The standard charge level is to 4.10 volts for daily use.


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## JRP3 (Mar 7, 2008)

Thundersky's have Yttrium in them. They have also updated their max charge voltage to 4 volts, instead of the previous 4.25 volts. Don't know if this is a result of a change in battery chemistry or discovering that charging to 4.25 wasn't necessary.


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## EVComponents (Apr 20, 2009)

JRP3 said:


> Thundersky's have Yttrium in them. They have also updated their max charge voltage to 4 volts, instead of the previous 4.25 volts. Don't know if this is a result of a change in battery chemistry or discovering that charging to 4.25 wasn't necessary.


That is updated to 4 volts for a future cell that is not yet in production.
We have been clarifying with Thundersky the specifics on the recent changes in their online documentation.


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## JRP3 (Mar 7, 2008)

Wow, talk about jumping the gun.


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## EVComponents (Apr 20, 2009)

JRP3 said:


> Wow, talk about jumping the gun.


The funny part is the revision date is still 2007 on the new document for a cell that is not yet in produciton.


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## MN Driver (Sep 29, 2009)

EVComponents said:


> The funny part is the revision date is still 2007 on the new document for a cell that is not yet in produciton.


Other than seeing the data that changed, I noticed the file name reflected the date that they changed it, the time they changed it before the filename stayed the same. Not a reliable indicator but this time we know when they made the modification. If it is for a new cell not yet in production, I'm surprised the voltage is the only thing they changed on the sheet. I suppose they may still be catching up with the specs they set before.


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