Brammo Owners Forum
General => Off Topic => Topic started by: protomech on February 27, 2012, 01:53:02 AM
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Envia claims 400 wh/kg and $125/kwh, production batteries in 3 years.
Supposing their claims are accurate, that's about twice as good as the best current production capacity and quite a bit less expensive. Raw cell cost for a 20 kwh battery would be $2500, might be around the same size.
http://gigaom.com/cleantech/a-battery-breakthrough-that-could-bring-electric-cars-to-the-masses/ (http://gigaom.com/cleantech/a-battery-breakthrough-that-could-bring-electric-cars-to-the-masses/)
I haven't really dug into their site yet, they're presenting later today at an ARPA-E conference. They claim they had independent tests done by a naval warfare office, looks like the tests were quite low discharge and the capacity drops off very quickly in the first dozen cycles. They compare against panasonic's 18650 cells, which supposedly also have a sharp dropoff in the first few cycles.
Edit August 2012: Either I missed this initially or their chart has been updated. The "sharp dropoff" on the Envia chart is due to running the first few charge/discharge cycles to 100% DOD at varying charge rates, 80% DOD and C/3 charge/discharge is used for all subsequent tests.
http://enviasystems.com/announcement/ (http://enviasystems.com/announcement/)
Anyhow, worth looking at.
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I just heard that announcement on the local radio news station a few minutes ago. Here's hoping that this isn't another one of those trolling for investors' dollars press releases again.
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Expect Envia to be touted throughout the ARPA-E event, as proof that its program is working to develop green innovation in the U.S.
I hope that this doesn't turn into another political punching bag (http://www.bloomberg.com/news/2012-01-25/volt-delay-shows-obama-s-unnatural-gm-ties-republicans-say.html), where Republicans (or Fox News) try to associate failure here with failure of Obama, and then do what they can to make the technology look like a failure.
On the other hand, all this scrutiny is probably good as it will (hopefully) weed out investor trolls from the real deal.
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I'm going to try and get a copy of the NSWC's report.
While Envia is billing the battery as a 46 Ah cell, the cell shows a sharp decline in capacity after the first dozen cycles, after which point it has the more standard linear dropoff as if it was originally a 35 Ah cell. In many ways it makes more sense to treat the cell as a 35 Ah cell with extra capacity while brand new.
Note also that calling it a 35 Ah cell also decreases the specific capacity of the battery, down to about 310 Wh/kg. This is still very good, probably 50-60% better than a very good lithium battery today.
At 500 cycles the cell should be around 25 Ah, or 70% original "35 Ah" capacity. This is pretty poor durability, though it may not matter in a big battery bike application. If it enables a reasonably-priced 16-20 kWh bike battery then you're just not going to put as many cycles on it as a smaller battery.
For example, a fresh 16 kwh battery should give you approximately 90 miles on the freeway @ 70 mph or 160 miles on surface streets @ 45 mph. 500 cycles on the battery would reduce your range to approximately 60 miles on the freeway or 110 miles on surface streets; but you won't hit this point until you have about 37k freeway miles or 67k surface street miles on the bike.
And here's the other key point: if they can hit their price point (which is closer to $165/kWh for the "35 Ah" cell), then the raw cell cost for a 16 kWh battery should be around $2700. Total battery replacement costs may be around $3500-4000 at the time the battery ships, and of course likely less by the time you actually need to replace the battery. If the costs are low enough then it's no big deal to replace the battery that "early" - since the batteries will likely die as often to aging effects as simply to high cycle counts. Raise your hand if you expect the ZF9 zeros to get 300k miles on their original batteries at 5-10k miles per year..
Assuming the more favorable 67k surface street miles to replacement, in 500 cycles you'll probably use around 7.7 MWh in total to charge the battery. At $0.11/kWh you'll pay around $850 in your utility bill, making your total "fuel train" (battery depreciation + electricity) cost after 67k miles around $4800 or 7.2 cents per mile.
Meanwhile, my gas GS500 gets about 50 mpg, at $3.50/gal that's about 7.0 cents per mile. Neglecting additional maintenance on the gas bike and oil changes, and assuming electricity + gas prices don't increase further and battery prices don't drop further, these batteries are price-competitive with gas.
Some more technical discussion here, including a visit by Envia's CEO in the comments thread:
http://www.greencarcongress.com/2012/02/envia-20120227.html (http://www.greencarcongress.com/2012/02/envia-20120227.html)
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I told my insurance company that I expected to ride about 2000 miles a year on my Zero S. I don't think I will live long enough to ride that claimed 300K miles before the battery needs replacing. In fact, my guess is that I would want to replace the bike after about 3 years, anyway and give it to my granddaughters as a great bike for them to use to learn how to ride a motorcycle. Assuming that is what they want to do and that their mother goes along with the plan. ;)
In any case, I think that a battery life expectancy of about 50K miles should be about right for a motorcycle. After all, how many people keep an IC motorcycle for more than that number of miles. Not to many, is my guess (before it is crashed or retired to the barn). And putting big miles on a gas-burner is a lot easier than putting big miles on an EV that has to be recharged every night.
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This story hit the business section of my newspaper today. In an article written by Dana Hull of Mercurynews.com, it is stated that “Envia (Systems) was awarded a $4 million grant from ARPA-E in December 2009 to develop advanced lithium-ion batteries for electric cars. It went on to raise $17 million in venture capital from General Motors Ventures, Bay Partners, Redpoint and Pangaea Ventures. In a separate agreement, GM secured the right to use Envia's technology for GM's future electrically driven vehicles.”
An interesting comment in the article was provided by Mike Omososo, a senior auto analyst with LMC Automotive, who said: “It does sound very impressive, but it remains to be seen if it will work outside the lab”. “Since most EV and plug-in makers have already got battery suppliers in place, it may be a few years before we see the Envia batteries in vehicles on the road”.
The article continues with a statement by Envia that “When commercialized its 400 wh/kg battery, which will provide a range of 300 miles and cost about $25,000, will slash the price of electric vehicles, making them more affordable for mainstream customers”.
The article concludes with the following statements: “While there's been talk in the industry of moving beyond lithium and using new materials, many expect lithium-ion batteries to remain dominant in the coming decades.” “The rumors of the demise of lithium-ion batteries were greatly exaggerated.” (A quote by Evia's CEO Atul Kapadia.)
The article also mentions that there are "at least two dozen battery start-ups" in the Silicon Valley area. To me, that sounds like a risky business to be in, unless you are very well funded, have a lot of industry connections and are working on a "world beater" battery design.
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The missing bit of the bolded reference is that Envia predicts $25k 300 mile electric vehicles, not that the 300 mile battery cost is $25k.
That's a little optimistic - Tesla's Model S has a 300 mile range with an 85 kwh battery pack, the raw cell cost at $125/kwh is $10.7k. And as I mentioned earlier, if the battery decays 30% of its capacity in the first dozen cycles, then it makes more sense to treat it as a 310 wh/kg battery and $160/kwh.
I may have misinterpreted the conditions the cell was tested under. Elsewhere they claim >1000 cycles @ 80% DOD, which is more typical. 1000 cycles on a 300 mile battery (even if only discharged to 80% = 240 miles) is basically the useful life for 95% of automobiles.
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I took another look at the article and I quoted it correctly. I think someone didn't proof read it before putting it into print, or maybe the paragraph just wasn't constructed carefully. I read it to be $25K for the battery (which is why I highlighted the cost), but $25K for an entire car with a 300-mile range makes more sense. Don't you just love the English language? ???
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I'm going to try and get a copy of the NSWC's report.
Good luck. If Envia paid for Crane to do the research, it should be completely proprietary and unreleasable. If DOD paid for the study, it would be releasable under FOIA unless an exception applies.
On a side topic - I used to work at Crane as a buyer for their battery division. There's a good chance I purchased the equipment used to test the batteries ;D
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Well, they have a "contact us to get the full version of the report". Not trying to go through back channels or anything : P
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Mercury News interviewed the CEO of Envia on Jan 4.
http://www.mercurynews.com/business/ci_22312503/mercury-news-interview-atul-kapadia-battery-maker-envia-systems (http://www.mercurynews.com/business/ci_22312503/mercury-news-interview-atul-kapadia-battery-maker-envia-systems)
Here's the bit worth reading:
Q: In February, Envia made a big splash when it announced it achieved a critical milestone: a rechargeable lithium-ion battery with an energy density of 400 watt-hours per kilogram, the highest energy density known. What's happened since then? Are you in commercialization?
A: We now have to prove our business model, and that means getting Envia's battery into a car. We're working with several automakers. We currently have more customer traction and partnerships in Japan than in the United States. 2013 is all about customers and proving the technology.
We're still two years out from the original 2015 date. If Envia makes it through manufacturer validation and selection tests, I would expect one of the big automakers to move very fast and either snap the company up or to obtain an exclusivity agreement.
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I don't think battery weight is a huge problem. There's room to improve, certainly - but the 2013 Zero bikes are significantly lighter than comparable gas bikes. They could handle a small amount of weight gain .. volume and price are the more important things to my mind.
Look at the 2012 Zero S battery:
EIG C020 cell: 3.65V 20Ah, 73 Wh, 0.43 kg = 170 Wh/kg. Cell dimensions 130 x 216 x 7.2mm.
ZF3 18s2p module: 2.7 kWh, 18.6 kg = 145 Wh/kg. 36 cells weigh 15.3 kg, packaging weighs 3.3 kg.
ZF3 battery box: 2.7 kWh, 24.5 kg = 110 Wh/kg. Module weighs 18.6 kg, enclosure weighs 5.9 kg.
ZF6 battery box: 5.3 kWh, 50.8 kg = 104 Wh/kg. Modules weigh 37.2 kg, enclosure weighs 13.6 kg.
ZF9 battery box: 7.9 kWh, 69.4 kg = 114 Wh/kg. Modules weigh 55.8 kg, enclosure weighs 13.6 kg.
Suppose this battery was now rebuilt with Envia 400 Wh/kg cells.
Envia 46Ah cell: 3.2V 46Ah, 147 Wh, 0.365 kg = 403 Wh/kg. Cell dimensions 97 x 190 x 10mm.
Because the chemistry is lower voltage, you would need 20 cells in series to make the same voltage as the EIG cells. A 20s2p pack wouldn't quite fit into the existing ZF3 battery box, but a redesigned battery box would be very close to the same volume so let's assume the same material weight.
ZF6.5 20s2p module: 5.9 kWh, 17.9 kg = 330 Wh/kg. 40 cells weigh 14.6 kg, packaging weighs 3.3 kg.
ZF6.5 battery box: 5.9 kWh, 23.8 kg = 248 Wh/kg. Module weighs 17.9 kg, packaging weighs 5.9 kg.
ZF13 battery box: 11.8 kWh, 49.4 kg = 239 Wh/kg. Modules weigh 37.8 kg, enclosure weighs 13.6 kg.
ZF19 battery box: 17.7 kWh, 67.3 kg = 263 Wh/kg. Modules weigh 53.7 kg, enclosure weighs 13.6 kg.
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Note that Neil Saiki's proposed 18650 16.1 kWh pack (http://www.ntsworks.com/Battery.html) using Panasonic NCR18650A 3.1Ah batteries, same batteries shipping in the 85 kWh Tesla Model S, would weigh around 200 pounds / 90 kg .. even with a pack this heavy, his proposed bike would weigh less @ 400 pounds than most gas bikes today.
Panasonic is supposed to produce 3.4V 4.1 Ah 18650 cells this year, which would bring Saiki's pack up to 17.9 kWh nominal.
Panasonic's 2013 18650 cells have more mass per unit energy vs the Envia cells.. but energy density is still very good, offering twice the energy of the Empulse battery in - potentially - a lighter bike.
It will be interesting to see if Envia announces a partnership this year. Certainly I would expect to see some news if they secure a design win.. but by 2015 they may be merely competitive with the best instead of being hugely superior.
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protomech sez:
"Envia 46Ah cell: 3.2V 46Ah, 147 Wh, 0.365 kg = 403 Wh/kg. Cell dimensions 97 x 190 x 10mm."
Where did you get 3.2v? I assume this is meant to be the average discharge voltage. From Envia's website it looks like the average discharge voltage is more like the 3.65v of the EIG cells with the peak voltage being about 4.6v.
protomech sez:
"Note that Neil Saiki's proposed 18650 16.1 kWh pack using Panasonic NCR18650A 3.1Ah batteries, same batteries shipping in the 85 kWh Tesla Model S".
I think you are referring to Panasonic's NCA-based high capacity cells but Tesla has said they are using custom Tesla-designed Panasonic cells and other sources say those cells are using NMC cathodes (like the EIG cells). I'm not aware of anyone opening an 85 kWh Model S pack to determine which cells are actually being used.
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Suppose this baterry was now rebuilt with Envia 400 Wh/kg cells.
Envia 46Ah cell: 3.2V 46Ah, 147 Wh, 0.365 kg = 403 Wh/kg. Cell dimensions 97 x 190 x 10mm.
Because the chemistry is lower voltage, you would need 20 cells in series to make the same voltage as the EIG cells.
Where did you get 3.2v? I assume this is meant to be the average discharge voltage. From Envia's website it looks like the average discharge is quite a bit higher than 3.2v with the peak voltage being about 4.6v.
Note that Neil Saiki's proposed 18650 16.1 kWh pack (http://www.ntsworks.com/Battery.html) using Panasonic NCR18650A 3.1Ah batteries, same batteries shipping in the 85 kWh Tesla Model S, would weigh around 200 pounds / 90 kg...
I think you are referring to Panasonic's NCA-based high capacity cells but Tesla has said they are using custom Tesla-designed Panasonic cells and other sources say those cells are using NMC cathodes (like the EIG cells). I'm not aware of anyone opening an 85 kWh Model S pack to determine which cells are actually being used.
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protomech sez:
"Envia 46Ah cell: 3.2V 46Ah, 147 Wh, 0.365 kg = 403 Wh/kg. Cell dimensions 97 x 190 x 10mm."
Where did you get 3.2v? I assume this is meant to be the average discharge voltage. From Envia's website it looks like the average discharge voltage is more like the 3.65v of the EIG cells with the peak voltage being about 4.6v.
From here:
http://enviasystems.com/announcement/ (http://enviasystems.com/announcement/)
The Envia Systems cells are prototype lithium pouch rechargeable cells. The cells have a capacity of 46 Ah and an energy density of 400Wh/Kg. The cell's dimensions are approximately 97 mm wide, 190 mm long and 10 mm thick. The cell's approximate weight is 365 grams. Cell serial numbers are 400WhK-07-005-111205 (designated as 005) and 400WhK-07-006-111205 (designated as 006).
400 Wh/kg * 365 g / 46 Ah = 3.17 V averaged out. Close enough to 3.2 V nominal.
protomech sez:
"Note that Neil Saiki's proposed 18650 16.1 kWh pack using Panasonic NCR18650A 3.1Ah batteries, same batteries shipping in the 85 kWh Tesla Model S".
I think you are referring to Panasonic's NCA-based high capacity cells but Tesla has said they are using custom Tesla-designed Panasonic cells and other sources say those cells are using NMC cathodes (like the EIG cells). I'm not aware of anyone opening an 85 kWh Model S pack to determine which cells are actually being used.
It's the general consensus of the folks at teslamotorsclub. It may be a slightly tweaked NCR18650A (nickel cobalt aluminum NCA), but it's definitely not NMC.
http://www.teslamotorsclub.com/showthread.php/12709-18650-Batteries (http://www.teslamotorsclub.com/showthread.php/12709-18650-Batteries)
I'd like to see definitive proof too. But that's the best I've got.
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http://enviasystems.com/pdf/Press_Release_400WHK.pdf (http://enviasystems.com/pdf/Press_Release_400WHK.pdf)
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protomech sez:
"Envia 46Ah cell: 3.2V 46Ah, 147 Wh, 0.365 kg = 403 Wh/kg. Cell dimensions 97 x 190 x 10mm."
Where did you get 3.2v? I assume this is meant to be the average discharge voltage. From Envia's website it looks like the average discharge voltage is more like the 3.65v of the EIG cells with the peak voltage being about 4.6v.
From here:
http://enviasystems.com/announcement/ (http://enviasystems.com/announcement/)
When I look at the specific capacity graph at the above Envia URL in your reply I see a fairly linear voltage drop during discharge from 4.6v to 3.0v and it drops like a rock with very little remaining energy output down to 2.0v. So, roughly 4.6 / 3.0 is closer to 3.75v average than 3.2v.
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The top left chart plots voltage vs specific cathode capacity for Li/Li+ and Envia chemstries, not cell voltage vs % DOD which is more typically seen. At least that's how I'm reading it.
Cell capacity is more than just cathode capacity anyhow, though I'm fuzzy on details.
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The top left chart plots voltage vs specific cathode capacity for Li/Li+ and Envia chemstries, not cell voltage vs % DOD which is more typically seen. At least that's how I'm reading it.
Cell capacity is more than just cathode capacity anyhow, though I'm fuzzy on details.
I'm not sure how the specific cathode capacity differs from DoD, but I'm assuming that the two graphs are a charge and a discharge - at least the insert talks about a charge to 290 mAh/g which matches the endpoint of the light green line and a discharge for 275 mAh/g which matches where the knee in the dark green line happens. So the light green line is charging and the dark green line is discharging.
The vertical axis lists (V vs. Li/Li+) and I'm not sure what that "vs." is referring to - would that be "voltage potential vs. the positive ion state"?
Also, the insert mentions a C/20 rate which implies a plot of charging and discharging.
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From here:
http://enviasystems.com/announcement/ (http://enviasystems.com/announcement/)
The Envia Systems cells are prototype lithium pouch rechargeable cells. The cells have a capacity of 46 Ah and an energy density of 400Wh/Kg. The cell's dimensions are approximately 97 mm wide, 190 mm long and 10 mm thick. The cell's approximate weight is 365 grams. Cell serial numbers are 400WhK-07-005-111205 (designated as 005) and 400WhK-07-006-111205 (designated as 006).
400 Wh/kg * 365 g / 46 Ah = 3.17 V averaged out. Close enough to 3.2 V nominal.
What's odd to me is that the cell very clearly drops in capacity over the first 3 charge cycles. They throw a loop in to the equation by switching from 100% DOD to 80% DOD after the first 3 cycles, but if you divide it out then really the cell drops under 40 in terms of Ah after just a few cycles. Do manufacturers really quote an unrealistically high Ah rating that is only achievable on the first couple of cycles off of the manufacturing table? I know when I read measurements of my cell phone batteries with a battery app the mAh measured is very close to the rated mAh listed on the battery, even after several cycles.
Also, what is the "approximate" in the findings at the NSWC? Didn't they actually weigh it? Combine that with the fact that Envia is claiming 45Ah cells, but the NSWC claims they are 46Ah cells and something is odd about the data...the cells weren't sent in to be estimated...
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You're right about the discharge / charge plot in the chart. At the very gentle discharge rate C/20 it looks like 3.5 - 3.6V nominal. So perhaps 3.2V is off - though it still looks a little lower than a conventional lithium voltage curve.
The first three discharge cycles for the anode (top right plot) are done at C/20, C/10, C/5. All discharge cycles after are done at C/3.
The real plot that I can grasp is the lower left plot. It shows 3 discharged @ 100% DOD, C/20 (~48 Ah), C/10 (~46 Ah), C/3 (~45 Ah). The next cycles appear to be 80% DOD, and appear to linearly degrade from 33 Ah down to 26 Ah at 460 cycles.
Humor me for a moment and let's say the nominal voltage at C/3 is 3.5 volts. 100% DOD then would represent a gradual capacity loss from 144 Wh down to 114 Wh over 460 cycles. Given an approximate cell weight of 365 g - perhaps the approximate is included because of non-production fittings or test apparatus? - that drops from 394 Wh/kg down to 312 Wh/kg over 460 cycles (79% capacity retention).
That's not great - especially in a lab environment - but perhaps it will improve before it reaches market. 400 Wh/kg and $125/kWh should allow a future Leaf to fit a 60 kWh battery pack (~150 mile range) and a future Brammo or Zero bike to fit 15-20 kWh battery packs (150-200 mile range). 460 cycles with those ranges are 70-90k miles. That's still not great for 80% in-lab capacity retention .. but replacement costs at $2k (bike) and $7k (car) averaged out are still cheap-ish (2-3c/mile bike, 10c/mile car.
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What's odd to me is that the cell very clearly drops in capacity over the first 3 charge cycles. They throw a loop in to the equation by switching from 100% DOD to 80% DOD after the first 3 cycles, but if you divide it out then really the cell drops under 40 in terms of Ah after just a few cycles. Do manufacturers really quote an unrealistically high Ah rating that is only achievable on the first couple of cycles off of the manufacturing table?
No, not in promotional materials, but it's normal for Lithium-ion batteries to lose substantial capacity after the first few cycles because some if the Lithium gets sucked into parts of the cell structure permanently. Normally, these cycles are performed at the factory and the quoted specifications are based on the "real" capacity after the first few cycles and their losses.
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Envia. What a mess.
This quartz article is worth a read for anyone interested in the sordid tale. Short version: Envia is likely toast.
http://qz.com/158373/envia-the-mysterious-story-of-the-battery-startup-that-promised-gm-a-200-mile-electric-car/ (http://qz.com/158373/envia-the-mysterious-story-of-the-battery-startup-that-promised-gm-a-200-mile-electric-car/)
Bullet list:
- company CEO (Kapadia) and CTO (Kumar) are at odds, with lawsuits in flight claiming that Kumar stole technical work from a previous employer
- Envia can't replicate 400 Wh/kg performance from the 2012 Crane tests, possibly due to an improperly licensed anode
- cell durability is still very suspect .. 50% loss of capacity in 400 cycles
It sounds like there are still some technical merits to the Envia technology, but it's still far from delivering on a production-quality cell with the claimed cost and weight benchmarks. Hopefully those technical merits can be salvaged in future production cell technology.
Unfortunate as we go into 2014 .. nearly as much for the display of deception and greed as for the failure to deliver on the benchmark targets.
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Interesting and sad article. This passage caught my attention and led to my naive question:
"An additional plus for electric car batteries is the ability to draw out the lithium fast—that is the power that allows a driver to speed up immediately on depressing the accelerator. But these traits tend to work against each other—you can pack in a lot of lithium, but only draw it out of the two electrodes slowly, which means that you can drive non-stop between New York and Washington, but may be in trouble if you need to quickly maneuver out of someone’s way. Or you can choose the alternative—you can generally accelerate fast, but go only a relatively short distance on a single charge."
Why isn't it possible to have two sorts of batteries in one vehicle with a chip deciding which bank to use. Sensing the demand for quick acceleration, the chip would switch the draw to the "fast lithium" type of battery, whereas cruising at a constant speed would employ the "slow lithium" bank, giving the driver the best of both worlds?
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Shinyside - I always wondered about have a capacitor for the power demand, and the batteries for longevity. Most hydrogen fuel cells have to have a battery for that very reason, but why not go a step further with caps?
If you read deep enough into the story, you'll see that Envia did in fact get 400 wh/kg, just like Crane tested. But for only one cycle. That one cycle capacity is what they marketed, not the useful capacity. It's a matter of semantics, but I am very surprised that GM did not look deeper into the Crane results before investing. Reality eventually catches up.
Envia licensed the cathode from Argonne, alongside GM and others. The only thing GM lost is the performance that was promised...they still own essentially all of the valuable technology/IP Envia was using.
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Interesting and sad article. This passage caught my attention and led to my naive question:
"An additional plus for electric car batteries is the ability to draw out the lithium fast—that is the power that allows a driver to speed up immediately on depressing the accelerator. But these traits tend to work against each other—you can pack in a lot of lithium, but only draw it out of the two electrodes slowly, which means that you can drive non-stop between New York and Washington, but may be in trouble if you need to quickly maneuver out of someone’s way. Or you can choose the alternative—you can generally accelerate fast, but go only a relatively short distance on a single charge."
Why isn't it possible to have two sorts of batteries in one vehicle with a chip deciding which bank to use. Sensing the demand for quick acceleration, the chip would switch the draw to the "fast lithium" type of battery, whereas cruising at a constant speed would employ the "slow lithium" bank, giving the driver the best of both worlds?
I don't think you need 2 different kinds of batteries. The speed at which you can draw current is only limited for a single cell, but the batteries in EVs are made up of multiple, sometimes thousands of cells (more in a car than in our bikes). If one cell is sluggish, you combine the output of a hundred of them and you can draw as much power as you want at a time. EV batteries already do this to customize the voltage and current they can achieve. You just have to factor this maximum power draw into the electrical strategies in how you wire them up and how the motor controller accesses and combines the output from the battery banks. (assuming protomech will correct me if I've missed something?)
This is why the 0-60 times of the Tesla get faster as the battery pack increases in capacity. More batteries means higher current draw...
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Yes, it is possible to have heterogenous inputs into a motor/controller.
- energy cells and power cells in a hybrid battery
- fuel cell and battery
- engine/generator (Volt) and battery
- super-caps and battery
liveforphysics (engineer @ Zero) wrote a pretty good post detailing why super-capacitors aren't a good match with a battery pack. Short version: super-caps weigh too much and a well-designed battery pack delivers plenty of power for vehicle applications. Noone ever accused an Empulse RR (small power pack) or a Tesla Model S (large energy pack) of being short on power..
https://www.elmoto.net/showthread.php?2732-How-about-adding-a-capacitor-in-parallel-to-my-current-battery-pack-to-boost-power&p=34574&viewfull=1#post34574 (https://www.elmoto.net/showthread.php?2732-How-about-adding-a-capacitor-in-parallel-to-my-current-battery-pack-to-boost-power&p=34574&viewfull=1#post34574)
As for hybrid cell pack, this is possible as well.
Consider the following two cells:
EIG C020 energy cell
- 3.7 V 20 Ah 0.43 kg
- 174 Wh/kg 1463 W/kg (@ 15% voltage sag, 10C)
EIG F007 power cell
- 3.2 V 7 Ah 0.25 kg
- 95 Wh/kg 2300 W/kg (@ 15% voltage sag, 30C)
When you build a hybrid pack, you have to worry about matching the battery voltage, etc. Ignore that for a minute.
Suppose you want to build a pack to supply 100 kW peak.
- 100% of power from F007. 100 kW, 4.1 kWh, 43.5 kg (95 Wh/kg)
- 50% of power from C020, 50% from F007. 100 kW, 8.0 kWh, 56.0 kg (143 Wh/kg)
- 100% of power from C020. 100 kW, 11.9 kWh, 68.4 kg (174 Wh/kg)
Now, the power pack is definitely lighter. And sometimes, light weight is of paramount importance.
But consider this:
- going from the pure power to the hybrid pack adds 3.9 kWh, 12.5 kg (300+ Wh per kg added)
- going from the hybrid to the pure energy pack adds 3.9 kWh, 12.5 kg (300+ Wh per kg added)
Ignoring the complexity of the hybrid pack, in most vehicle applications where you care about both energy and power, you're generally better served by a homogenous pack.