Building a Safer Lithium-ion Battery
By Josh Landess
EVWorld: I'm speaking with Marc Kohler of Valence Technology. Tom Gage of AC Propulsion got the attention of a lot of us with the Lithium-Ion version of the T-Zero. Although the batteries that he used may not have been purpose built for EVs, what can you tell us about where all this is going?
MK: I know that we're excited that somebody has put a Lithium Ion battery pack in a vehicle to demonstrate the exceptional density energy of those batteries, but in the case of AC Propulsion they chose some that they could get readily available. That has always been a big challenge: Can you go out and buy Lithium Ion batteries, and if you can, are they cost-prohibitive? In large format applications like automotive cases, if you can find them available and you deal with the up-front cost, you have to be concerned with safety. In the case of AC Propulsion they chose a commercially available Lithium Cobalt Oxide cell, and that's probably the most common.
EVWorld: Another Valence person was mentioning safety, so what is it that makes yours safer?
MK: Basically, it's the cathode material. The most common one is Lithium Nickel, Lithium Cobalt, Lithium Manganese... All these are oxides and they all are thermally unstable in abuse conditions (hot box, over-voltage type situations) so that when they decompose, ...in the case of the Cobalt Oxide, it provides the oxygen for the burn or the flame to continue, so it's almost un-extinguishable.
In ours, we have a cathode based on phosphate material, which, in abuse conditions, when it decomposes, it just dies. It doesn't have a thermal runaway condition.
EVWorld: I assume you've run simulations or tests where you try to come up with a worst case scenario. What can you do to abuse your batteries or somebody else's batteries and what will happen?
MK: Right. I don't want to do a scare campaign or anything. We want Lithium Ion technology to prosper, but we don't want a Cobalt cell, for instance in a cell phone, catching on fire and giving Lithium Ion a bad name because people don't know that there are different flavors of Lithium Ion batteries.
In our case there's a set of UL tests that are available. Nail puncture, crush, hot box, over-voltage, those kinds of things that almost all battery manufacturers try and pass. You can go a step further and say... Can we do a round bar crush test, a drop test? What if you extend the time period? UL says test it for 30 minutes. What if you do it for 64 hours?
You can extend outside this envelope that UL felt was a good test for a Lithium Cobalt cell. Some other chemistries address the safety fact, either by doping the material, which is what SAFT does. They dope it to make it safer. They add expensive electronics, battery management systems, very tight controlled charging, discharging, so you don't go outside this envelope, and they add safety separators and so forth and in that environment everything can work fine.
What we're saying is: You shouldn't [just] test to inside that environment. What happens if everything fails? You still need your battery inherently to be safe so that if you can't control the conditions what happens? “Test to fail”, not just “test to pass a test”.
EVWorld: Makes sense to me.
Performance and The Competition
When you put your batteries on board a vehicle what specs come up? How far will it go, what does it weigh?
MK: The one good thing about the Cobalt technology is that it has excellent energy density. SAFT, LG Chem, even we make some Lithium Cobalt cells, and people like using Lithium Cobalt application cell phones because they have very good energy on board. Our batteries do not have as good energy density as that chemistry, but we're safer.
So, for instance, depending on your requirements.... If you're a car manufacturer or you have designs for a certain performance, either power, range or a little combination of both, you also have to meet safety for the application and you have to meet a cost target. So: we feel the safety is most important. Our energy is 90% to 95% of other technologies.
EVWorld: What about power delivery, is it a strength as it is in some of these other Lithium batteries?
MK: Absolutely. We have a Saphion technology that can, depending on the design of the cell, be made for a high rate application such as a hybrid electric vehicle. Designing cells for a hybrid electric vehicle is different than designing for high-energy battery electric vehicles. Our chemistry can be accommodated for both. Not only fast discharge – fast recharge too.
Lithium Batteries in HEVs
EVWorld: I spoke with a person who had worked with Chrysler in their attempts to integrate some Lithium Ion batteries into a hybrid, and they had apparently decided not to go forward with the project because of issues of cost, and perhaps for some other reasons. Even though that one project didn't work out, what would you say to somebody who questions the viability of using such a battery with an HEV? Can it be cost effective with one of your batteries?
MK: Sure, I believe so. As far as just staying within the Lithium Ion realm our cathode material, using the phosphate, is much cheaper than Cobalt or Nickel or Manganese in the processing. So, we're able to make our batteries cheaper than our competition from that standpoint.
Now let's go over to an application. In the Chrysler example, they may say: “In this application, we high-rate-discharge using this chemistry. We may not get the life cycle that we expected from Lithium Ion that we have gotten in low rates of charge or discharge.”
So, they may have said no for several reasons. One – up-front costs. Two – in the application it may not have performed as well as they thought.
[In the case of] our chemistry: Not only do we use cheap components and precursors, (our method of making our cathode is called a carbothermal [sp?] process in which case we increase the ability rate – discharge and charge rate - by adding carbon), but it's added at the same time the material is made. So instead of having one or two or three step process, it's at the same time.
So: our process is cheaper, our materials are cheaper and as far as cycle-life during high discharge and charge rates, we don't see the degradation that some other chemistries are prone to.
EVWorld: Replacement cost of a Nickel Metal Hydride battery pack in a Prius...?
MK: I called a dealership and they said around around 4 to $4,500.
EVWorld: OK. What if there was such a thing as a new car with Lithium Ion batteries in it? Is there any way to guestimate what it would cost?
MK: We know that Nickel Metal Hydride is in the hybrids of the present but we also know several programs that are looking at Lithium Ion for the next wave of hybrid electric vehicles, and due to our very high cycle life [versus NiMH] we may be able to put less energy on board, or a smaller pack, which will cost less or equivalent to what they have available. So, depending on different characteristics you can have some flexibility of how much battery you need.
EVWorld: So you think you could be competitive with that price you're hearing on the Prius?
MK: Yes, absolutely. We're going to have to be competitive or beat NiMH in the future. ...You're going to be probably even in cost, but you're going to have better performance in all these other areas, or, if you want to focus on equal performance, yes, you're going to have the cheaper cost to displace it.
EVWorld: Is Lithium rare? Is it expensive to buy?
MK: No.[...] Lithium is not the problem. Cobalt is rare and Nickel is expensive.
EVWorld: Although you do make Cobalt batteries, …
MK: We do.
EVWorld: …they're not really the focus of this Saphion product?.
MK: Not at all. Saphion is the trademark for the Phosphate-based cathode material for these batteries. The Cobalt ones we make say for some military applications that specifically require it.
EVWorld: So there's no material in yours [Saphion] that's inherently outrageously rare?
MK: In fact, it's not outrageously expensive. It is, in fact, cheap. In one case: Iron Phosphate ...Phosphates are readily available. Nothing is rare, nothing is expensive and there's nothing harmful to the environment as far as disposal.
In Cobalt's case, you don't want to dispose of it in the environment, and it's so expensive a commodity that they're willing to get it back and try and recover it.
EVWorld: What about performance in the cold? Say it goes below freezing and I had a Valence-powered pure EV. That doesn't cause a problem? Mr. Gage mentioned that in his presentation on the LG-powered tzero. I figure we're not gonna see them in Detroit in the winter.
MK: No, I don't think [that's correct for our batteries]. Right now our batteries don't perform any different in cold applications than other Lithium Ion. My understanding is it has to be severely cold temperatures like negative 20 degrees C.
EVWorld: For the battery to start not performing as well as you want?
MK: Exactly. That's for the battery just sitting by itself. Once it's integrated into a car there are all kinds of things. One, there is self-heating of the battery when it's being used. There is all kinds of thermal management – just blowing cabin air through the battery. There is preheating of the battery. There's lots of things that a designer can do to overcome those issues.
EVWorld: Does your battery operate at a high temperature generally?
MK: No. Ambient.
EVWorld: In the Avestor [another competitor] presentation, their battery turned out to be a “warm battery”.
MK: Yes a warm battery ... about 60 or 70 degrees C.
EVWorld: But your battery is not that?
MK: No. Ours work between negative 20 and positive 60 so it likes temperatures the way we like temperatures. I know there are Zebra [not Lithium-based] batteries that are very high temperature – two, three hundred degrees C.
EVWorld: There was a really good question asked in that Avestor lecture about what if you turn the car off and leave it and go somewhere for two weeks and come back? [Interviewer's Note: my recollection, doubtless imperfect, is that the question had to do with the Avestor battery being a warm battery and needing to expend energy for that reason.]
MK: Well we don't have any of those issues. Our self-discharge rate is very low. I'd say probably the lowest of any of the chemistries.
More On Safety
EVWorld: My recollection of when laptop computers first started coming out, some of them used Lithium Ion. They did have some problems with safety. Then Nickel Metal Hydride, and perhaps others, seemed to make inroads, and then something seems to have cleared up for the Li-Ions. So: what went on there?
MK: In the early days, Apple computers, I think were the first ones with the Lithium Ion packs. And one, I think, caught on fire or something and you're right. I heard the same thing.
I think what designers did... they still used the same chemistry, Lithium Cobalt, but the cell manufacturers did a much better job. They integrated safety separators in between the electrodes. They integrated a device called a PTC, Positive Temperature Coefficient -- when the pressure builds or the temperature gets too high it shuts down. They have a current interrupt device. That's internal to the battery. And then external, the electronics got more sophisticated. You were able to monitor things ...the learning curve of how to protect batteries. So, I would say the chemistry didn't change. The knowledge of how to handle this battery changed.
EVWorld: I've just not heard of a problem with them.
MK: Recently, within the last six weeks, there's a few cell phones.
EVWorld: A cell phone problem?
MK: Of burning somebody's ear. Maybe isolated cases. It may be a non-OEM battery that was replaced. I have no idea about the specifics.
EVWorld: That's kind of strange. I mean they've been out there for so long, why now?
MK: Well, like I said, I don't know. If somebody used a battery that did not work with the charging algorithm that was supposed to. Did they use a battery that didn't have the safety apparatus on the inside?
EVWorld: I'll tell you where I've heard about fires. When the model airplane people who fed in to Tom Gage's project were all excited about their ideas for using Lithium batteries, on the discussion boards one of the persons posted that in recharging he had either a fire or some sort of thermal incident. Obviously in the hands of a hobbyist, who's just gung-ho on experimenting, they may or may not be following every single instruction. But at the same time you have to idiot-proof the product if you want to put in billions of hands [who aren't bargaining for such problems].
MK: We agree. [...] I guess we want to get the message out that there are some differences in Lithium Ion. I mean Lithium Ion is an area of batteries but there are many flavors, and that a Lithium Ion battery can be made safe and has been made safe through our Saphion technology. So in that case the RC guy – no matter what he would have done to the cell -- it would not have caught on fire or burned anybody. Now he may have gotten to the situation where he killed the cell and it no longer functioned, but it would not have that problem [of catching fire]. And that's where we try and go where safety meets power.
The Inevitable Price Question
EVWorld: Let's say a guy was building an EV and he wanted to call you and put one of your packs into his car, could you do that?
MK: Sure. Yes.
EVWorld: Does it have to be some giant manufacturer or can it be a little guy?
MK: No, it can be a little guy.
EVWorld: Can you give me a cost or is that confidential?
MK: It's not confidential but it's really primarily based on quantity. We're saying in production we feel that we can get down to $450.00 per kilowatt hour.
EVWorld: But right now if a guy called you and said I want one battery pack for my university research project, for example?
MK: Right. That's probably gonna be two to three times that cost.
EVWorld: About $1,000.00 per kilowatt hour?
MK: Something like that.
EVWorld: That'd be about 30 grand for a 30 kilowatt hour pack in very, very general terms.
EVWorld: Any special pricing considered for a University or just any small guy calling?
MK: Well, we'll work on a case-by-case basis. We want to have fixed price – general pricing, but depending on the application, and getting started and getting our batteries out there, we are willing to work with companies that are either high profile or can lead to getting Lithium Ion batteries in production because production is what’s going to bring the cost down.
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