This is good news, Chuck. Many of us keep cars well beyond eight years. Stats show that the way to get the most out of a car economically is to run it till it falls apart. That can mean 15 to 20 years. If EVs and hybrids can't make it that long, it's a mark against them. So a long-life battery is good news.
It's especially good news, Rob, when you consider the price of replacement batteries. A year ago, when a Tesla customer fried his Roadster battery, Tesla gave him a "friends and family" price of $40,000 for a new one. Most batteries are smaller than the Roadster's, but a few are even larger, so cost is a big consideration.
@Charles – yes replacing a battery costs a lot, you feel better when you hear that a battery could be used for 15 – 20 years. I wonder if this is the same for all the brands in the market. I am sure the cheaper ones are low in quality and would not last this long.
Good point Shehan. It will be interesting to see whether EV owners will replace worn-out batteries or whether they will turn to a new vehicle. With the high cost of batteries, I'm not sure we'll see a lot of new batteries dropped into 10-year-old cars.
I agree, Rob. A 10-year-old car is an old car, so I wonder how many people would change the battery if it costs $10,000 or more. I also wonder what effect the battery cost would have on resale value. Would I buy a used car that might need a $10,000 battery? I don't think so.
One point that hasn't been mentioned by our commenters, as far as I can see: Cugnet says that fast-charging would have an effect on battery life. He suggests that users refrain from it, aside from a few isolated cases. Would that affect the desirability of electric cars?
Charles, I think this could be a real detriment. The whole "hot shot" chargiing technique is an attempt to mitigate both range anxiety (but this presumes a major infrastucture upgrade to place "hot shot" chargers in some percentage of fuel stations or equivalent convenient locations) and the inconvenience factor of full charging cycles (with "normal" rate chargers) lasting much of a day or night. If it became common knowledge that this would take a severe toll in battery life, that would certainly affect those of us who consider total life cycle costs in our vehicle purchase decisions. Admittedly, we are definitely a minority, but a goodly chunk of the market none the less.
Good point, Chuck. The resale value of hybrids could make a huge difference for middle class buyers. The EVs seem to be in the territory of a toy for the well to do -- hardly a large enough market to make the vehicles viable in the long run.
Chuck, With possible replacement costs potentially that high, it makes sense that buyers would be concerned to get some kind of long term service agreement to protects against catastrophe. Do you have any idea if this is common? I have heard with some hybrids that these agreements are available.
Most of the warranties that I hear about are like the Volt's, which is eight years/100,000 miles on its 16-kWh battery. That's less important for a conventional hybrid, which will typically have a 1-kWh or 2-kWh battery that may use a less costly nickel-metal hydride chemistry.
@apresher – I don't think the battery manufacturers would provide a service agreement to protect against catastrophe. It's not that they can't do that but simply they don't want to take the burden. I am using a Toyota Prius Hybrid but didn't get such service agreement.
I note that getting 15 to 20 years is contingent on power and cooling management systems, which adds to the cost of the battery subsystem. New chemistries may reduce or eliminate the need for these systems; the cost reduction this will make possible is needed to penetrate the burgeoning stop-start market.
Full disclosure: I'm affiliated with Leyden Energy, which is developing such a chemistry.
If it can be done, it certainly makes sense, davtrowbridge. Right now, the cells make up only about half of the pack costs, according to most of the estimates that I hear. If you can cut the cost of the cooling system, that pack cost could drop significantly.
@Charles – It could be a miracle if it could be done, it would definitely reduce the price of a hybrid vehicle making it more affordable. Most of the users are afraid to by a hybrid due to the battery replacement cost.
"Sensing systems may, in fact, be able to detect bad batteries that have already passed factory tests. These parts suffer from an internal short circuit, a defect that is difficult to identify. As a private consultant to lithium-ion battery manufacturers and device makers that use those batteries, Brian Barnett, vice president of the Lexington, Mass.–based technology-development company TIAX, has examined many case studies of lithium-ion problems. "Frequently, the level of destruction was too great to determine what transpired," he says. "However, when you could find a cause, overwhelmingly we discovered proof that there had been a foreign metal particle that had got into the cell." What was particularly worrisome was that in "a couple hundred incidents, it showed that none of them occurred in the first three months," he says. Many internal short circuits, in other words, cannot be detected at the factory."
"The contaminants were often tiny shards of crimped, scraped, or flaked metal of various sizes that could be as small as tens of micrometers, Barnett says. Battery manufacturers already have many tricks—including using strong magnets and shrouded cutting areas—to keep contaminants out of battery assemblies. But, he says, the persistence of rare but catastrophic battery fires from cells made at even the best lithium-ion factories in the world suggests that some baseline level of contamination exists—and has to be rooted out in other ways.
Further experiments and computer models of these metal particles in lithium-ion batteries also revealed a likely mechanism for time-delayed thermal runaways. If the metal shard is near the cathode, Barnett says, the battery's voltage oxidizes the contaminant particle, which is often iron, copper, nickel, or zinc. And the resulting nanoscale charged particles can then migrate across the battery's microporous separator. The contaminant particles then reach the anode.
"At the voltages of the anode," Barnett says, "you have a process that's not so different than electroplating....It plates out. And when that process happens progressively over time, you get a metal deposit. It's shaped largely like a dendrite. It starts to fill the holes in the separator, eventually making contact with the cathode. And it's only at that moment when you get a short." "
@davetrowbridge – It sounds interesting, we a re all looking for ways to reduce the cost on these systems. As technology develops I'm sure there should be an affordable way to do the same thing in a different way.
I'd be suprised if Lithium ion batteries made today will last that long. They have made giant leaps forward - particularly in terms of weight to power ratio when compared to lead-acid or nickel-cadmium. Eight years sounds more realistic if they are maintained and kept cool...
Shehan, Yes I presume it is much easier to market a car with '20 year batteries than '8 year batteries. The 98 Jaguar, XJ8 has a Maintainence Free automatic 4 speed transmission. I can see the blog "Maintainence Free Automatic Tranmission". The tranmission has no dipstick to monitor fluid level and fluid integrity - one way to prevent a failure. Are we to believe that this trans is going to run forever? As a mechanical engineer, I dont think so. GM says service their transmssions every 50,000 miles. Turns out the Jag Tranny often fails between 50K and 100K and of course they cost 3 times as much as a GM transmission. And now a car which sold for 55k is now worth $1100. Why is it so expensive? Because it is a Jaguar...
As a person with an iPhone, I do not have the ability to easily change the lithium ion battery every year. I am impressed with it heading toward 3 years now and no real change in operation time on a charge. I was not expecting that.
Any device that uses only ONE cell for power like most phones, can not be compared to EV, as any system that uses more than 12 batteries;be they in parallel, series, or combination - ABSOLUTLEY needs Battery management system (BMS), definitely for charging, and in case of Li batteries also for discharging.
Without properly designed and tested and verified BMS, even the best battery will have very short life span.
Yeah, I'm with you too. Well made cells, carefully packaged, handled with the utmost of care MAY last a good long time. Our experiences with secondary cells in the 700 A-hr range are that the manufacturers turn out really good cells at the beginning when you are qualifying the cells. Later as you get into a high-rate production, the quality of the cells "normalizes" and you start seeing more issues with the cells.
If the care of the battery requires any prudent use and thought by the consumer, forget it. The battery designers need to think in terms of dumb and dumber.
Cells produced by the hundreds of thousands should be consistent in their performance (good but not stellar), but I think the researcher presenting his findings may have been into the New Riders of the Purple Sage stuff.
There was speculation that accelerated life testing increases temperature which artificially shortens battery lifespan. Would it be possible to incorporate cooling during accelerated testing to determine life span data at more reasonable temperatures? I'm thinking that life testing has already been performed at cooler temperatures (which would prove/disprove this hypothesis).
There seems to be a major misunderstanding here of the whys and hows of accelerated testing. This is pretty basic stuff going back many years of fairly accurate life predictions. Several steps: first determine the failure mechanisms and the underlying physics/chemistry. Every physical degradation process can be characterized by an activation energy. Virtually all such processes are gaussian in nature, and what you need to do to calculate lifetime is understand that in a gaussian process, there are curves (the gaussian distribution) that are temperature-dependent. What you actually do with accelerated testing is measure the activation energy for the dominant failure mechanisms. For most physical processes, the acceleration factor is for every X degrees K increase in ambient temperature, the failure rate doubles. X is often in the area of 10 degrees K. Thus, if you conduct your life testing at, say, 40 degrees over the expected "real" upper exposure range, you have an acceleration factor of 16: each hour of test time is equivalent to 16 hours of predicted life in the "real world." Only limitation is you can't exceed the absolute maximum operating temperature of the UUT (often determined by a phase change or other destructive effect). Then you have to test for along enough period to accumulate a statistically significant number of failures. At that point you can predict the lifetime of the design being evaluated. The accuracy of the prediction will depend primarily on the statistical significance of the number of failures (which will depend on the number of units tested). The only other way to obtain this level of accuracy is to test under "real-world" conditions for (in this example) maybe 40 years for a predicted lifetime of 20 years!
Even that could be misleading. Testing for (relatively) short times (much less than the resulting predicted lifetime) ignores the relationship between the gaussian process, the activation energy, and the failure rate "bathtub" curve I have written about before. Projecting the"in-service life "failure rate" to predict lifetime ignores the fact that life is determined primarily by the "wear-out" part of the bath-tub curve. I sincerely hope that this fellow's work does not include projecting failures for nuclear reactors!
I understand that 104F is "above the mean temp", but 104F is nothing compared to summer heat soak temperatures of (112°C- according to SAE.) Am I missing something or are they underestimating how harsh the EV battery environment really is?
No, you're not. However, there is another factor to consider: that SAE number is really "under-hood" for a vehicle with IC engine. The actual temperature extreme experienced by EV batteries will depend strongly on battery location within the vehicle structure and other factors of vehicle design. Even so, "in-cabin" temperatures can easily hit the high 80s C range. This is especially true for designs with large "greenhouses" and dark interiors. Try touching the black dashboard of a car parked in Phoenix on a summer afternoon! Third degree burns are likely.
I don't think you're missing anything, Curious_Device. It's a harsh environment and it's very, very tough to predict the outcome using accelerated testing. People will debate this --and if they are qualified, we'll give them their due here -- but I think we won't really know the effects of every day wear and tear until we have about ten years of user experience to draw from.
I suspect the lifetime will depend a lot on how the batteries are used. If one may draw any parallels from lead-acid and other established types, batteries don't like to be discharged, and especially charged, at too fast a rate. They hate being drained flat, or overcharged. Thus to get maximum life from a propulsion battery, one must treat it gently. This implies gradual acceleration and (regenerative) braking. Also, one should recharge at a modest rate well before the battery is totally discharged, and make sure the charge controller (or manual charging process) is working properly. Just as with any machinery or equipment, you treat it right and it will serve you much longer. (Pardon my anthromorphizing the battery but I thought it would make for better reading.)
The most surprising part to me is that accelerated testing is being done and not corrected back to nominal conditions. If you do life testing of anything that is temperature dependent, usually you would have a relationship of life-temperature and use that to correct ALT data back to typical use. There may also be statistical methods involved. It is hard to believe that labs are testing at elevated temperature then stating results as actual life estimates. I wonder if the real argument here is about the temperature-life equations being used?
Of course the batteries being tested are warmer than a cool ambient, but they will certainly be warm in a vehicle being driven. That is beyond any doubt that most of the active part of a batterie's life will be warm, because charging and discharging does heat them, that is the physics of the beast. And of course fast charging does take out a lot of life, which quite probably is what a lot of thhem in the real world will see, since charging them at home will be inconvenient for many lazy folks. What the accellerated testing does not take into account is all of the temperature cyccling as the assemblies heat and cool. So while one is certainly allowed to wish that the battery life will be a lot longer, that does not make it so. (Sorry about that, Jim Moore) Wishing something were so only makes it happen in cartoons and kid's movies.
Of course it is also true that some small portion of folks who have a non-standard useage profile will indeed experience greater battery life. Things like that do happen. BUT probably a similar number will also experience much shorter battery life. And it is undoubtedly true that a small portion of the battery packs will, after 20 years, be able to deliver enough power to back a car out of the garage, but not much more than that.
When evaluating the life expectancy of a system, you normally use a range of conditions, for example three temperatures, three charge-discharge speeds, etc, from which one can calculate the acceleration factor for various fail conditions, and then estimate the reliability of the said system in real life, using assumptions for real life conditions. When you use accelerated stress conditions, it is obvious that these are not real-life conditions: it would take 20 years to evaluate the life span of a battery!!!
Also, if it is true that cold weather is somehow good for battery life expectancy, it also adds a lot of stress to it, since you have to use more power for heating and defrosting. Driving in snow will also drive a lot of power, as wipers, headlights, less efficient tires, wheel spinning on ice, higher resistance on snowy roads... The regenerating braking systems may also work in a less efficient way if the ABS systems gets on (???).
It really is not of any significance how long anything can or will last, what ultimately really matters is how much it cost per measurable unit of use, be it mile, kilometer, hour, or work done.
As Engineers we all know that we can design unbreakable widget that will last centuries that will cost fortune to produce.
But consumer will almost always vote with their available resources for whatever costs least NOW, and even long term value if there is one, seldom wins.
With specific cost per fuel that has to be replenished every few days, we are much more aware of the approximate cost per mile for example, but if you have to change something like battery - even conventional starting battery - in 2, 3 or even 5 years and it cost more than even a tank full on SUV people complain about the price!
Same goes for set of tires, etc.
No matter what is the government forced warranty in order to get ZEV credits, if the battery needs to be replaced someone pays for it, in case of big OEM the people who drive the conventional cars subsidize now the EV's.
Company that only bets their future on EV only offerings, however will have lot of trouble when the replacements will come due.
Perhaps the solution offered by few companies in Europe, may be the way to go, that is to "lease" the use of the battery, that equates the monthly or even weekly cost of driving to that of ICE.
Excellent post Charles. I'm one of those engineers that never trades cars with mileage too much under 100,000 if that often. Life-time of any component or part is important to me as well as availability. In the southeast, it is not uncommon for an individual hoping to save money to "shop" at the local automotive junk yard; therefore, one of the questions I have asked, but never gotten an answer for is: Is a Li-Ion battery assembled in an automobile transferrable from car to car? Can this be accomplished without spending a fortune for labor in doing so? This is assuming there is no damage to the original system. This probably sounds somewhat weird but if it can be done without hazard, it will be tried.
Transferrable between different models of EVs? Probably not; they're not designed for that (yet). Most EV batteries take up a non-negligible fraction of the volume of the car. There isn't really any standard battery shape or location, so there'd be significant labor just in getting the thing shoehorned into a different car. And then there's matching electrical specifications, charging, integration with electronics, etc.
AySz88 is correct, bobjengr. As it stands now, EV batteries are not transferrable. Today, it seems like every manufacturer has a different way of cooling their batterioes -- some air cooled, some liquid cooled, all having different configurations. Also, some manufacturers use flat battery packs under the floor (Tesla), while others (GM) use a T-shaped, liquid-cooled pack in the tunnel. Some day, maybe manufacturers will get together on this, but I don't see it happening any time soon.
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