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Discussion Starter · #1 ·
Last year, PAnasonic announced the production of the 18650 3.1Ah Li cells that will be used for the Tesla model S battery pack. Despite lesser cycle life compared to LiFePO4, this new bat is nearly 3x more energy dense (LiFEPo4 18650 is about 1100mAh and a bit lower in voltage). Panasonic also announced availability of 3.4Ah(4Ah on other articles) 18650 Li battery by 2012 and 4Ah by 2014. Panasonic is projecting 11% annual density increase. (http://techon.nikkeibp.co.jp/article/HONSHI/20100223/180545/)

GM-Argonne lab-Nexia also announced commercial testing of their new battery which has a reported density of "twice the energy density" of the present bat pack that the Volt uses.

Interestingly, both Panasonic and Nexia are working on Silicon anodes instead of graphite, which is found on most Lithium bat. Nexia uses Manganese on the cathode. (http://www.greencarcongress.com/201...r-advanced-li-ion-cathode-materials.html#more)
 

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Discussion Starter · #3 ·
Hi!

I'm not sure but I read from another forum a guy ordering some Panasonic 18650 2.9Ah cells from a vendor. I think the one from Envia will not be available outside OEMs.

JohnM
 

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Interestingly, both Panasonic and Nexia are working on Silicon anodes instead of graphite, which is found on most Lithium bat.
I was just reading about that yesterday. Sillicon anodes swell up 400% when they accept lithium which causes rapid anode degredation. There are two technologies to make it work now, one being sillicon bound to carbon tree-branching structure and the other is sillicon wires. Theoretically they can increase battery capacity 10 fold over carbon anodes.
 

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Yes. they're doing a lot to improve on the silicon. I posted this topic because: 1. These two batteries are either in production or in "commercial testing"( whatever), which means that it is a real deal. Also, the Panasonic battery is nearing or exceeded the 200Wh/kg density level. There are many "breakthrough" announcements on high density battery: nano-something here and nano-something there. Visit them later and you cant find even a drawing of their supposed super battery. There are also other lithium tech that are high density but are too expensive.

2. Tesla actually uses the Panasonic 18650 3.1Ah and that mean they prefer energy density more than battery life(e.g. LiFePO4- which I speculate that the Volt use because of the 8 year warranty).
In some ways, at that energy density, you can full charge it to under 70%, help extend cycle life(which is only 300), and the battery still have twice the energy density of a LiFePo4 cell. Add water cooling and you may still extend cell life even more. About the price, Elon Musk is now saying that the Panasonic bat is "dirt cheap", because he can order it in maybe hundreds of thousands. If Tesla gets it below $2.9 each, it is cheaper than comparable LifePo4 battery.
 

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There is a Youtube video that someone recorded and posted where Elon Musk said that they the Model S will be a highly modified cell produced with energy density in mind that will contain Nickel in its chemistry. This is the first time I've read about Si. No reason not to combine different features to produce the best battery for the application though. The Tesla battery is so large that cycle life becomes less of an issue because with range over 200 miles, each cycle is small and in its default mode for intermediate range, the cycles are placed in the middle of the SOC constantly and unless you set it to its range mode it never fully charges the pack and most drivers are generally not going to run it that close to empty too often.
 

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I get that if you double the energy density then the effective number of cycles the battery experiences given the same driving conditions is reduced, but how large is that effect?

What if you discharge 25% every day for 400 days. Is that exactly the same as 100 full cycles? Half as much? Maybe doesn't count at all unless you discharge over 50% or some other number?

:confused:
 

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From all that I've read, it's a fairly straightforward. If a battery has 300 cycles at 100% DOD, it'll have 600 cycles at 50% DOD, or 1200 cycles at 25% DOD.
 

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From all that I've read, it's a fairly straightforward. If a battery has 300 cycles at 100% DOD, it'll have 600 cycles at 50% DOD, or 1200 cycles at 25% DOD.
Well in theory, theory and practice are identical. In Practice, they never are.

If I read that right, then a battery has a theoretical number of watt-hours you can run through it, and it doesn't matter how heavily you load it or how dead you run it. That sounds fishy.

I find it hard to believe that running most batteries DOD doesn't hurt the max number of theoretical charge cycles (cycles * watt hours). Then again, I'm not a battery engineer. It's true for Edison cells, why not for other batteries?
 

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Well in theory, theory and practice are identical. In Practice, they never are.

If I read that right, then a battery has a theoretical number of watt-hours you can run through it, and it doesn't matter how heavily you load it or how dead you run it. That sounds fishy.

I find it hard to believe that running most batteries DOD doesn't hurt the max number of theoretical charge cycles (cycles * watt hours). Then again, I'm not a battery engineer. It's true for Edison cells, why not for other batteries?
You're right, being in the top 10% or the bottom 10% of the capacity of a lifepo4 battery will shorten its lifetime. But it won't be that dramatical to diviate far from the theoretical number of watt-hours for the cell. Things like high C discharges, possible overcharge or overdischarge, and temperature changes will be the main cause of capacity loss.
 

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From all that I've read, it's a fairly straightforward. If a battery has 300 cycles at 100% DOD, it'll have 600 cycles at 50% DOD, or 1200 cycles at 25% DOD.
Thundersky shows 3000 cycles at 80% DOD and 5000 cycles at 70% DOD at .5C. Higher C rates give fewer cycles, probably due to localized internal heating.
 

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Thundersky shows 3000 cycles at 80% DOD and 5000 cycles at 70% DOD at .5C. Higher C rates give fewer cycles, probably due to localized internal heating.
So, if you get more batteries (and/or batteries with higher watt/hr ratings) and keep the C rates modest, then you get more battery life as well as additional range for those one or two times per year when you need it.

That sounds like a no-brainer.
 

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Yup, one of the reasons I've argued against spending money on an expensive BMS and instead using that money on up sizing your cell size and pack as much as possible. A123 has shown 10,000+ cycles on shallow cycled cells. Frankly if you get 2000 cycles from only a 50 mile pack that's 100K miles, so 3000-5000 cycles isn't really necessary in most cases.
 

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I wouldn't mind taking the pack from one car, should I get bored of it, and move it, along with most of the components to another car. ...especially if the equipment I buy is high quality such as an HPEVS AC31 or AC50 system, or I go high performance like a Soliton 1 and a Warp 9. I would just find my next car to be fitting to the motor, controller, and batteries, which most vehicles can fit that equipment just as long as the batteries have space, and I'd be set.
 

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Even if that is the case, I'd probably unload those cells into a different electric car so they are still in use with a different conversion. If they lose their discharge current capability through internal impedance, I'd find other uses such as solar storage, use the better cells in a lower range conversion, or if they are really bad, in an electric land mower and snow blower conversion. I'm considering buying a used lot of older 100Ah cells with a 1C continuous and 3C 15 second right now since there are enough for a higher voltage series DC conversion if they can still do the full 3C and have most of their capacity but the info being provided is 'tested to 300 amps', no further details, no age info, and I'm convinced I can't get any further testing unless I was to travel there and do it myself, which I wouldn't have the ability to charge/discharge it as a pack to really find out the performance. They were used for testing by a racer so I have a feeling they might just be toast so I'm not sure I'm willing to drive across the country and fork out a few thousand to drag them home and find out. If they could still provide 300 amps I'd have a use for the set, otherwise I'd be stuck with making an electric battery powered snowblower and riding lawn mower with a massive multiple acre range. :rolleyes:

Send me a PM if you ever want to upgrade, even if it is 10 years down the line.

..what I'm trying to say is, there will always be the person who wants a lead-acid price and the older stuff probably won't quite be a lead-acid price but the stuff we have today is energy dense enough for me so if I were to pay less now rather than get the next generation for the same price, I probably would, pulling a short term 10 second 1000 amps from 130Ah+ CALB cells is as good as I really need. Their 100Ah is 8C at 10 seconds, and the new 70Ah and lower is at 10C. If I was offered older spec 200Ah Thunder Sky cells in the 160Ah package size that only really did 3C at a killer price, I'd take them. Right now I'd go with CALB since the rest of the options IMHO are too close priced to not go with CALB but if the price difference was bigger, I'd probably jump on price. Jack does have a pretty convincing argument in his recent video with this discussion, most people probably will go with the better tech, but I think that the better tech will probably be the only option in the future, it will likely also come at a better price than we have today at the same time too. If it turns out a slightly better price over time WITH better cells, it would be hard to say no unless cells came along at a pretty big discount, such as 25% or more off of the better option and the needs of the conversion don't require the better cells. ...my opinion though, I'm just trying to get off gas for everything but out of state trips until I can afford it I'll be traveling 70mpg in the summer and dreaming of 200wh/mile. :)
 

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It's not as if they just stop working after 2K cycles you know. 2K cycles to 80% capacity still allows all the secondary use options you are talking about.
I know, that is why I'd be willing to have a 10 year old pack. Abuse will kill them however. 80% capacity would still be okay for my uses, whether secondary or not.

My experience with lithium cobalt is this. Not that I'm saying that the experience with LiFePO4 would be the same but I might as well share this.

Lithium Cobalt when it gets down to about 80% capacity starts a rapid decline with every cycle even if each cycle is a full cycle. I used them in an application where I charged them to 4.2v, down to 3.5v and back up again, sometimes twice a day. After about 500 cycles I was at 80% capacity, once they were at that point, another 200 cycles or so I was at 60% capacity, another 100 cycles 50%, a few hundred more and a charge that lasted me 5 hours now lasts me 45 minutes and I replaced the cells.

This Lithium Cobalt was rated for 300 cycles, so more than it was advertised before it hit 80% but after it hit that 80%, it all goes downhill quickly with them, with an advanced number of cycles they dropped like rocks.

Abuse them by discharging one too low too many times and I didn't lose capacity, I lost my discharge power, I had devices smacking a 2 volt LVC but could still draw .5C at close to the same capacity as before, voltage sag went nuts and made them useless.

Not sure what correlates to these LiFePO4 but I still consider 80% close to end of life and I don't believe they continue a flat curve on the graph down past that.

Also take a look at the Thunder Sky/Winston cycles chart, they demonstrate internal resistance rise with cycles, which I've also experienced with aged Lithium Cobalt cells.

Experience from someone using early Lithium Cobalt from Thunder Sky babying them at 50% DOD, said they lasted about 7 years before shelf life got to them in the form of internal resistance, LiFePO4 is supposed to be different in terms of shelf life and cycle life but when things do end up going down, I think I've got a good idea of the two signs to look for. Internal resistance and capacity. I'm banking on internal resistance more than capacity issues. If they are anything like Lithium Cobalt or the NiMh I've used, even though all the cells came from the same batch, you wouldn't think so towards the end of their life.

I'm optimistic about LiFePO4 living a long life though but in the end, I've made my predictions.
 

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My assumption is that in the 10 years or so it takes to get that many cycles on a pack newer tech will be so much better and cheaper most people will want to upgrade anyway.
Which leads you to have a smaller less expensive pack, because it will be outdated and cheaper for a bigger better one later.

The other issue is if you have a huge expensive pack you expect to last 10 years, what if you damage it? These are DIY cars, not OEM tested.
Or it doesn't really perform as expected or there is "shelf life" problem that shows up in 3 years. It is just not proven technology yet. It has become so much cheaper now that it is reasonable to use Lithium, but I'd still be cautious and make a more minimized investment.
 
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