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Discussion Starter #41
Very interesting.. LEAF wont have any warranty issues due to coolant leaks inside the battery case :)

How much energy would it take to route cold air from the LEAF's AC into the battery case?.. perhaps a diverter air valve that would not air condition the inside of the car while its parked but keeps the battery cool instead?

BTW, do you know if Nissan is using electrical heaters in the LEAF's battery case?
> How much energy would it take to route cold air from the LEAF's AC into
> the battery case? ... perhaps a diverter air valve that would not air condition
> the inside of the car while its parked but keeps the battery cool instead?

That is how the TMS works in the Chevy S10-E, and Coda is going to take a similar approach. I don’t know the exact energy consumption figures for that type of active TMS.

> BTW, do you know if Nissan is using electrical heaters in the LEAF's battery case?

Good question. I don’t know.
 

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"Unless George has got a car that is an EV with a battery pack underneath the passenger cabin, sticking a thermometer under his car probably won’t tell you as much as someone who does have an EV with a battery pack underneath the passenger cabin, as I do, with our Toyota RAV4-EVs, similar in that respect to the Leaf. I see the battery temps get up into the 105-115F range when the car has been parked baking in the hot South Florida sun. "

The nimh cells in your RAV4 are about 90% efficient when used, if you have been doing your errands and then park the car under the sun, battery temperatures will continue to increase for quite some time.. thermal inertia. What I would like to know if you let the car sit out overnight, completely off, how hot would the batteries get by the afternoon of the next day?
 

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Discussion Starter #43
Good information, but why would GM keep the battery at 71 deg F, the optimum battery temp? I would think the TMS would keep it just below the upper threshold temp to minimize power draw when the Volt is not plugged in, which I assume is higher than 71 deg F. That said, does anyone know what the upper threshold temp of this chemistry battery?
You might want to go back and take a look at the lithium-manganese battery calendar life graph, as a function of temperature, that I attached/uploaded with an earlier post in this thread, which will help to answer your question and put things in perspective.

Also, just to reiterate some of what I wrote in my original post that started this thread, here in my hot climate, the Tesla Roadster’s TMS keeps the batteries at an average temperature of 95F, within a band with a lower limit of 75F and an upper limit of 118F, which explains why the Roadster’s $36k battery pack only has a 4 to 5 year life (and a 3-year warranty).

The question I asked in my original post to start this thread is whether anyone knows the temperature band, and the average or optimal temperature within that band, that the Volt’s TMS keeps the batteries at.

Thanks to some digging and research that ChrisC kindly did, we got a partial answer to that question from GM, which is that the average/optimal temperature that the Volt’s TMS seeks to keep the batteries at is 71F, but GM has not revealed what the upper and lower limits are to the TMS’ temperature band.

Furthermore, as I mentioned in yet another post in this thread, EV drag racers put a heater and thermal blanket on their lithium battery packs to warm them up to 120F, in order to lower their *instantaneous* internal resistance so as to provide the highest possible (safe) power/discharge rate capability/performance, but at the expense of a shorter battery life.

If what you’re asking is ... what is the absolute maximum temperature threshold for these lithium batteries before they start to go into thermal runaway (technically, the LiMn2O4 molecule releases its oxygen bond), the answer to that is ... 320F (160C).
 

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Discussion Starter #45
I thought Coda would be using a liquid cooling system.
No, Coda ducts the same A/C used for the passenger cabin into the battery compartment:

“Coda senior vice president of sales and distribution Mike Jackson ... points to Coda’s active thermal management of batteries. The LEAF’s system is passive—air flows over the batteries via a single fan to either warm or cool the batteries—while Coda’s cabin and batteries share the same heating and cooling system.”

www.plugincars.com/coda-grasps-straws-differentiate-its-electric-sedan-59046.html
 

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You might want to go back and take a look at the lithium-manganese battery calendar life graph, as a function of temperature, that I attached/uploaded with an earlier post in this thread, which will help to answer your question and put things in perspective.

If what you’re asking is ... what is the absolute maximum temperature threshold for these lithium batteries before they start to go into thermal runaway (technically, the LiMn2O4 molecule releases its oxygen bond), the answer to that is ... 320F (160C).
Sorry,

I missed your lithium-manganese battery calendar life graph the first time around, thanks for pointing it out to me. I was not referring to the thermal runawy temp

So if I interpret this graph correctly, 8 years of lifes equates to a max battery temp no greater than approx 71 deg F? Thus, for every temp cycle above 71 deg F, the life will be decreased below 8 years by a discrete amount? If yes, then that is what I would define as the upper temperature theshold limit, and it is much lower than I expected. I was guessing that temp would have been in the 80-90 deg F range.
 

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Discussion Starter #47
If you're plugged into the grid, but in the hot sun in AZ, it makes sense to have the TMS keep the battery at optimal temp because it can. However, if you not plugged, doesn't it still makes sense to have the TMS manage the battery temp as long as the battery has sufficient power available? However, rather than maintain the battery at it's optimal temp (which will use a lot of Watts); why not maintain it at the upper threshold temp (for example 85 degrees), which is warm but not enough to degrade the life of the battery (that's how I would define the upper temperature threshold). As soon as you power on the car, the ICE could be programed on to provide power to quickly lower the battery temp back down to the optimal temp?
Per previous discussion in this thread, from what GM has said about the Volt’s TMS, it doesn’t operate when the car is turned off and not plugged in. This is a serious design flaw for an EV in a hot climate. But, as has been pointed out, that is also 20-month old information from GM. So it’s quite possible that in their ongoing development of the TMS over the last year and a half, GM has moved to correct this design deficiency such that hopefully the final version of the car that goes into production in just a few weeks will have a TMS that can operate for at least some initial time period (like 8 hours, would be ideal) after the car is turned off, as needed and as available battery reserve capacity above 30% SOC allows.

To reiterate another point I recently explained again, GM has revealed that the Volt’s TMS has an optimal temperature of 71F at which the TMS seeks to keep the batteries, but GM has not revealed what the upper and lower limits of the TMS’ temperature band are.

> “rather than maintain the battery at its optimal temp (which will use a lot of Watts)”

“Using a lot of Watts” ... is a rather vague and imprecise statement. It’s also somewhat relative and has to be put in context of the total battery pack capacity (which is 16kWh in the Volt, 8kWh of which is usable), and looked at in percentage terms of that total or usable capacity over a certain time period, typically a day (24 hours). Would you care to define or characterize what you would consider to be “a lot of Watts”?

The Tesla Roadster’s TMS consumed upwards of 10-12 kWh/day when it first came out, which was definitely “a lot” (to use your characterization) and excessive really, even for a 53kWh battery pack. Tesla later was able to damp that down to 3-4 kWh/day, which is much more reasonable and, arguably, not “a lot” for a 53kWh battery pack.

A well-designed, highly energy efficient (with good insulation and sealing of the battery compartment), active-cooled TMS for a 16kWh battery pack like that in the Volt, in a single battery compartment, can be designed to operate on 60 Watts, or a maximum of around 1.44kWh/day, keeping the batteries at 71F. That’s not “a lot”, or excessive amount of energy to expend for a 16kWh battery pack. The only thing we don’t know --(because GM hasn’t revealed it) -- is the width of the TMS’ temperature band.
 

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Discussion Starter #48
"Unless George has got a car that is an EV with a battery pack underneath the passenger cabin, sticking a thermometer under his car probably won’t tell you as much as someone who does have an EV with a battery pack underneath the passenger cabin, as I do, with our Toyota RAV4-EVs, similar in that respect to the Leaf. I see the battery temps get up into the 105-115F range when the car has been parked baking in the hot South Florida sun. "

The nimh cells in your RAV4 are about 90% efficient when used, if you have been doing your errands and then park the car under the sun, battery temperatures will continue to increase for quite some time.. thermal inertia. What I would like to know if you let the car sit out overnight, completely off, how hot would the batteries get by the afternoon of the next day?
105-115F is what I typically see under those circumstances.
 

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Discussion Starter #49 (Edited)
Sorry,

I missed your lithium-manganese battery calendar life graph the first time around, thanks for pointing it out to me. I was not referring to the thermal runawy temp

So if I interpret this graph correctly, 8 years of lifes equates to a max battery temp no greater than approx 71 deg F? Thus, for every temp cycle above 71 deg F, the life will be decreased below 8 years by a discrete amount? If yes, then that is what I would define as the upper temperature theshold limit, and it is much lower than I expected. I was guessing that temp would have been in the 80-90 deg F range.
Technically, lithium battery calendar life is a function of 4 variables ...
f[µ(T), σ(T), µ(SOC), σ(ΔSOC)],
that varies negatively (inversely) with all 4 of those variables.

The results given in the calendar life graph are for a steady-state, constant temperature T (thus where σ(T) = 0) and a steady-state, constant SOC equal to 60% SOC (thus where σ(ΔSOC) = 0). [Well, technically, in such tests the batteries *are* cycled once a month, so I guess it's not strictly speaking a zero σ(ΔSOC). But the point is that SOC is held constant for 29 days out of the month in the type of testing that the graph given corresponds to.] If the average SOC over time is greater than 60% SOC, calendar life will be less than that given in the graph. As the variability of both temperature [σ(T)] and the SOC cycling band [σ(ΔSOC)] increase, calendar life will decrease.

There have been dozens of (highly mathematical) technical papers published on this subject over the last decade by leading battery engineers and scientists at Argonne National Labs (Ira Bloom et al), NREL (Kandler Smith, Ahmad Pesaran, et al), Idaho National Labs (Jon Christophersen et al), Lawrence Berkeley National Labs (Vince Battaglia et al), and Sandia National Labs (Dan Doughty et al), many of them in the Journal of Power Sources.
 

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Charles,
I spent a little time googling the µ and σ variables but did not find a simple explanation. Would you mind explaining??

Also, could you comment on the reasoning for selecting Mn chemistry vs Fe. I gather from some discussions that A123's Fe battery withstands high temps better than the Mn chemistry.

Any idea why A123's battery (or Fe in general) was not selected for the Volt or the Leaf??--Thx- GSB
 

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Charles,
I spent a little time googling the µ and σ variables but did not find a simple explanation. Would you mind explaining??

Also, could you comment on the reasoning for selecting Mn chemistry vs Fe. I gather from some discussions that A123's Fe battery withstands high temps better than the Mn chemistry.

Any idea why A123's battery (or Fe in general) was not selected for the Volt or the Leaf??--Thx- GSB
 

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I've mentioned the charging travails of the Phoenix to Fargo issue in another thread, but it's sounding like weathering the summer in the 'zone isn't a good idea for EVs. 'zonie Volters can migrate to San Diego for the season (which isn't unlikely, since they tend to do that anyway, and we really like the tourist money here). But 'zonie Leafers have a problem.

From Phoenix, if there are fast charging stations in Gila Bend (68 miles), Dateland (50 miles), Yuma (60 miles), El Centro (64 miles), and Pine Valley (71 miles - though there's a 4500' climb there), then they can finally make it to PB (50 miles). But at half an hour a charge that makes a 6 hours trip closer to 9 hours...

And if they wait too late in the season, they have to do it in the middle of the night so that the battery isn't too hot to charge.

There are big stretches out here with no towns or infrastructure...
 

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Discussion Starter #53 (Edited)
Charles,
I spent a little time googling the µ and σ variables but did not find a simple explanation. Would you mind explaining??

Also, could you comment on the reasoning for selecting Mn chemistry vs Fe. I gather from some discussions that A123's Fe battery withstands high temps better than the Mn chemistry.

Any idea why A123's battery (or Fe in general) was not selected for the Volt or the Leaf??--Thx- GSB
µ is mean, and σ is standard deviation.

Cost is one factor in the decision to use LiMn2O4 over LiFePO4. Iron-phosphate is relatively cheap, but manganese is even cheaper.

Furthermore, LiMn2O4 is a safer chemistry than LiFePO4. When they go into thermal runaway, LiMn2O4 reaches a peak combustion rate of 2.5C/min, while LiFePO4 reaches a peak combustion rate of 3.4C/min. Contrast those to the combustion rates of the batteries that Tesla uses -- in the Roadster, LiCoO2 reaches a peak combustion rate of 360C/min, and in the Model S, LiNi.8Co.15Al.05O2 reaches a peak combustion rate of 280C/min.

After extensive evaluation of A123’s LiFePO4 batteries, there were a number of reasons why GM decided not to use them, and to use LG Chem’s LiMn2O4 instead.

First, A123 is violating the Goodenough/UT/Phostech/SudChemie patents on LiFePO4 batteries. All reputable battery manufacturers (including Johnson Controls-Saft and many others) comply with the Goodenough/UT/Phostech/SudChemie patent licensing. No large, established OEM would use A123’s batteries as long as they are violating the LiFePO4 patents. A123 has lost all its big OEM contracts and now has only one small contract with a small start-up, Fisker, and was only able to poach and wrest that supply contract away from EnerDel by investing heavily in Fisker to capitalize Fisker, to fund its cash burn and keep it afloat.

Second, A123 was having a lot of problems trying to scale their batteries up to large-format. Few, if any, large automakers would be willing to use Tesla’s method of assembling many thousands of small-format cells (like A123’s) into an automotive traction pack. That approach works OK for small-scale production of a few hundred cars a year like Tesla is doing, but it’s not practical for large-scale production of tens of thousands of EVs a year. GM is using large-format cells from LG Chem.

Third, spiral-wound cylindrical cells, like those A123 uses, have the worst thermal properties of all the different cell form factors. Furthermore, GM found in testing A123’s cells that the end-caps fail in vibration and short out the cell. A123’s cells have serious safety problems; they have catastrophic failure modes where they go into thermal runaway and explode when they short. There have been a number of A123 battery pack fires, including at least one that has completely destroyed an EV on the road.

A123 has more recently developed flat pouch cells, but there have just been too many cumulative problems with A123’s cells over the last few years.

GM chose LG Chem’s cells because they are safer and more reliable, with better manufacturing and quality control than A123 and its cells, and because LG Chem’s size, capitalization, history, experience, reputation, and production volume as an established, dominant, leading manufacturer in the lithium battery industry just make it a better, safer, more stable, reliable partner with whom to establish a long-term supply relationship.

Nevertheless, GM is still very much interested in LiFePO4 chemistry; its battery scientists and engineers continue to actively work in this chemistry (and have presented at recent battery conferences some very interesting development work they’ve done in this chemistry); and GM is actively considering LiFePO4 chemistry batteries for its EVs in the future. While LiMn2O4 has both better specific power and better specific energy than LiFePO4, on the other hand LiFePO4 has a number of advantages over LiMn2O4, including better cycle life and calendar life and better heat tolerance properties. The LiMn2O4 chemistry that GM and Nissan are using in the first generation of the Volt and Leaf is very sensitive to heat and has a high rate of degradation once you get above 95F. LiFePO4 is less sensitive to heat and holds up better and lasts longer in hot climates. LiFePO4 would be my preference; for my hot climate, I definitely think it’s a much better chemistry than LiMn2O4.

I should also mention that Ford is also very interested in LiFePO4 and is working on that with Johnson Controls-Saft. When Ford first hooked up with Saft and took a look at Saft’s state-of-the-art LiNi.8Co.15Al.05O2 chemistry (which Tesla is going to use in its Model S, though from a different manufacturer, Panasonic), Ford was concerned about the safety problems with that particular chemistry and decided that it couldn’t take that kind of risk. So they steered Saft into working on development of LiFePO4 batteries for them. (When Saft gives presentations on automotive traction batteries at battery conferences, they now talk about their work on LiFePO4 chemistry, not their state-of-the-art, current generation, high-energy-density LiNi.8Co.15Al.05O2 batteries, which they produce for the military/defense/aerospace market, like for satellite applications.

LiCoO2 and LiNi.8Co.15Al.05O2 are so unsafe -- the most volatile of all the lithium chemistries, by an order of magnitude of more than 100X (I gave the combustion rates above) over the two safest lithium chemistries, LiMn2O4 and LiFePO4 -- that no large, established automaker could afford to take that kind of risk, to use either of those two chemistries (LiCoO2 or LiNi.8Co.15Al.05O2) in a mass-market commercial EV. A large OEM like GM or Ford has just too much at stake and too much to lose to take a risk like that. Only a struggling small start-up like Tesla, which is an extremely risky venture to begin with, on the perilous edge of survival, can afford to take an enormous risk like that.

I will attempt to attach/upload a JPEG of a safety graph of the various lithium cathodic chemistries. I’m not sure if this will succeed, however, as it’s a large file, 953KB, which I think might exceed the allowable limits for the GM-Volt forums. We’ll see in a minute whether it works or not.
 

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Charles,
Do you think it would be possible to design a simplified TMS (ie convective cooling, not liquid cooling) using LiFePO4 batteries. It seems to me that the biggest detractor to using the liquid cooling is cost, so being able to eliminate the liquid cooling would hasten the acceptance of EV's which of course is a good thing.

PS thanks for the sigma mue explanation I should have guessed sigma but mue is mean (it rhymes).
 

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Discussion Starter #55 (Edited)
Charles,
Do you think it would be possible to design a simplified TMS (ie convective cooling, not liquid cooling) using LiFePO4 batteries. It seems to me that the biggest detractor to using the liquid cooling is cost, so being able to eliminate the liquid cooling would hasten the acceptance of EV's which of course is a good thing.

PS thanks for the sigma mue explanation I should have guessed sigma but mue is mean (it rhymes).
I would think an ambient forced-air cooling system would be the way to go for a relatively simple, inexpensive TMS (... though of course it’s much less efficient at cooling than a liquid-based system, but it’s a trade-off of giving up efficiency in exchange for substantially reducing complexity and cost).

Nevertheless, even with LiFePO4’s greater heat tolerance, if I have a choice between two different LiFePO4-powered EVs -- one with a simple, inexpensive, ambient forced-air cooling system, and the other with an advanced active-cooling TMS like that in the Volt, at a premium price like that ($8,220) of the Volt over the Leaf -- for me here in my hot climate, knowing what I know, I personally would choose (like how I am doing now, in my choice of the Volt over the Leaf) to pay a premium for the EV with the advanced active-cooling TMS.

It will be great to have a variety of different EVs on the market (as indeed we will increasingly see over the next several years) that give the consumer a range of different TMS (passive cooling vs. forced-air cooling vs. A/C ducting vs. liquid-cooled) and other technological choices and trade-offs (e.g. specific lithium battery chemistry, LiMn2O4 vs. LiFePO4, etc., PHEV vs. BEV, series vs. parallel vs. 2-mode, and all-electric range: PHEV13, PHEV25, PHEV40, BEV70, BEV100, BEV120, BEV150, BEV200, etc.) to choose from, so that the consumer can do his own research and analysis and make the choice that is right for him based on all the various considerations of climatic factors and needs and applications of typical driving mission range and variability thereof, etc., vis-a-vis the consumer’s budget, what he can afford to pay in upfront cost versus recurring periodic and delayed costs, such as expected timing and cost of battery replacements.

Of course all of that will require an educated consumer, ... that consumers get educated on lithium battery technology, including the kinds of technical details we’ve discussed in this thread. This will in turn require that automotive journalists, who at present don’t yet understand any of this, get up to speed on all of this, as they eventually will. Heck, even the journalists who specialize in covering the EV space don’t yet really have a good understanding of lithium battery technology, at least not to the level of technical detail discussed in this thread. But all of that is starting to change and will start to happen over the next few years, as the EV market, just now in its infancy, starts to gradually develop into a market that will someday (hopefully) be as varied, deep, mature, and sophisticated as the conventional ICEV market is today.
 

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for me here in my hot climate, knowing what I know, I personally would choose (like how I am doing now, in my choice of the Volt over the Leaf) to pay a premium for the EV with the advanced active-cooling TMS.
I would tend to worry about coolant leaks inside the battery case.. make a bulkier pack with some finned heat sinks and circulate AC cooled air over them as needed..use cabin air, the batteries like the same temps as humans do. The heatsinks can be on both sides of the 4 cell modules as used in the LEAF
 

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Air vs Liquid cooled packs

It will be extremely interesting to see how this plays out. Whether liquid cooled packs become the mainstay of electric vehicles or a simpler air cooled pack with cells that have a high heat tolerance wins out. Isn't Toyota going w/ an air cooled pack in the plug-in Prius?? Also, the NiMH packs in the existing Prius are air cooled and I have not heard of any issues here in Phoenix. It definitely is not a slam dunk in favor of the liquid cooled pack.

Here is a dumb analogy: In the 60's, if you asked almost anyone if a water cooled motorcycle would be a good alternative to air cooled you would have been met with an overwhelming---NO WAY!! Air cooling is lighter and less expensive--right???

Well look what happened. Most bikes are water cooled now. and they are extremely reliable systems. Remember when we all changed water hoses and fan belts once every 2 years??--not anymore. It's a good example of a counter intuitive approach to something that ends up being adopted as mainstream. ---a lot like Boeing convincing us that 2 engines are more reliable than 4.

Having said that, I still can't help but think that a pack with a simple air cooling system and cells designed for heat tolerance is a strong contender.

Time will tell.
 

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Discussion Starter #59
It will be extremely interesting to see how this plays out. Whether liquid cooled packs become the mainstay of electric vehicles or a simpler air cooled pack with cells that have a high heat tolerance wins out. Isn't Toyota going w/ an air cooled pack in the plug-in Prius?? Also, the NiMH packs in the existing Prius are air cooled and I have not heard of any issues here in Phoenix. It definitely is not a slam dunk in favor of the liquid cooled pack.

Here is a dumb analogy: In the 60's, if you asked almost anyone if a water cooled motorcycle would be a good alternative to air cooled you would have been met with an overwhelming---NO WAY!! Air cooling is lighter and less expensive--right???

Well look what happened. Most bikes are water cooled now. and they are extremely reliable systems. Remember when we all changed water hoses and fan belts once every 2 years??--not anymore. It's a good example of a counter intuitive approach to something that ends up being adopted as mainstream. ---a lot like Boeing convincing us that 2 engines are more reliable than 4.

Having said that, I still can't help but think that a pack with a simple air cooling system and cells designed for heat tolerance is a strong contender.

Time will tell.
George,

I agree and think you’re definitely on the right track in seeing where things are headed and projecting out to the end game, several years down the road, to what I expect the ultimate solution will be. I’ve written about this before and will just repeat it here.

Looking out 5-10 years, towards 4th and 5th generation EVs [with the current generation of Roadster, Volt, and Leaf being 2nd generation EVs, (at least from the perspective of those of us who have been driving 1st generation EVs for a number of years now), and vehicle generation development cycles getting shorter, being compressed toward 3 years, instead of the traditional 4-5 years], I don’t think sophisticated thermal management systems will ultimately be the solution to this problem. They are really just a short-term, somewhat kludgey (and very expensive) fix for the current (2nd) and next (3rd) generation vehicles, to get us through the next 5-6 years. We’re going to have real problems, in terms of the economic viability of EVs and their adoption and penetration rates, as intended mass-market vehicles, if we’re still using these expensive, complex, sophisticated, liquid-cooled thermal management systems (like that in the first generation of the Volt) to solve this hot climate battery life problem, as we get into the second half of this decade and approaching 2020. But I don’t expect that to be the case.

No, the ultimate answer to this problem is to be found in the electrochemistry, with an electrochemical solution, where the cathode, anode, and electrolyte are specifically designed, developed, and optimized for life and operation in a hot climate. Then the OEM doesn’t really have to worry so much about the thermal management system and can just go with a simple ambient forced-air type system that only runs during discharge and charge. For example, on the cathode side, carbon-coated nano-LiMnPO4 and carbon-coated nano-LiMn.8Fe.2PO4 both show excellent morphological and structural stability in solution at high temperature (60 degrees C) over time. (The specific mechanism of internal resistance increase at elevated temperatures, for current generation lithium battery chemistries, is primarily due to film growth on the particle surfaces, both at the cathode and at the anode, with the amount of such film growth being a function primarily of the level of heat exposure over time.) Such promising electrochemical solutions to the hot climate battery life problem have been well known and understood for several years now. It’s just a matter of scaling them up, working out licensing issues, and commercializing them. I expect to see such electrochemistry-based approaches and solutions employed in vehicles as we get into the second half of this decade, certainly as we approach 2020. We will definitely need them in order commercialize EVs for the mass market, if they are ever to become economically viable beyond the initial 5% early-adopter segment. I’m very hopeful and optimistic that that will indeed be the case.
 

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Discussion Starter #60
Very interesting revelation in the article on the main page today, which suggests that the TMS likely has an energy consumption very close to what I had estimated it might be (in some of my previous posts in this thread), right around 1.44 kWh/day.

http://gm-volt.com/2010/10/08/chevrolet-volt-uses-more-than-8-kwh-of-stored-battery-energy-to-achieve-ev-range/

If the Volt’s usable battery capacity is, say, 8.3 kWh, and the battery charger is 97% efficient in that SOC operating band from 29% SOC to 81% SOC, then:

10 kWh – 8.3 kWh/.97 = 1.44 kWh per day to run the TMS.
 
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