Sunday, November 7, 2010

This week in sulfation

First off, I have to apologize to all 7 of my regular readers for not making a post in a while. I have been busy and hence the hiatus. Between watching reruns of Curb your Enthusiasm, election ads, and the Giants world series games, I need more time in a day. But all good things have to come to an end. I hope to resume regular postings starting now.

This week, I was rudely reminded that just because you know how batteries work does not mean that you can deal with a battery problem. But first some background.

Subaru's are excellent cars and I would highly recommend buying one. They are well made, they run great, and they hardly give you any problems (touch wood). But Subaru's also have small quirks that can be bewildering and a bit infuriating. Like not having a remote trunk opener or having only 3 wiper speeds. Or having this one light that does not turn off when the ignition is off and is so hidden that you can't tell that its on in the first place.

The light serves no real purpose, except to make sure to keep the battery industry thriving. Long story short, "someone" left that light on on Sunday (and I'm not saying who).

A bit more background: My car is 7 years old. My battery is (or was as of yesterday, but I'm getting ahead of myself) the original battery.

Monday morning at 7 AM I get to my car to start driving to San Francisco Intl. to catch a flight to Washington DC to be at the center of the action during election day (Tuesday). I was using a meeting on energy storage for grid applications (think storing solar and wind electricity) as an excuse to get someone else to pay for the trip. I was going to be gone all week.

Except my grand plan was crumbling because my car appeared to have a dead battery. I quickly realized what had happened.

When professionals are thrown into a crisis, they do not think, they react. Think Jason Bourne coming across an assassin or Neo coming across Agent Smith (in the Matrix).

Just so there is no confusion: I consider myself to be a professional.

In a matter of seconds the pieces started to fall into place in my brain without any real thinking. I knew my battery was probably pretty sulfated (and corroded with lots of shedding, for that matter). I opened the hood, took one look at the battery and I could literally see the sulfation on the plates (through the grime that covered the hard polypropylene battery shell). I knew that if I jumped the car right away I had a chance of saving the battery. I also knew that if I left it in the discharged state all week, I would probably sulfate it more and maybe end up killing the battery altogether.

To remind you, when you discharge a lead-acid battery you form lead sulfate. Lead sulfate is pretty insulating. But it has a bit of solubility in the electrolyte (sulfuric acid). This leads to some Pb2+ ions in solution. When you charge, these Pb2+ ions allow you to get back to the charged compound. As you react the Pb2+, more lead sulfate dissolves.

Sulfation is a process by which the lead sulfate starts to agglomerate together to form large crystals. This leads to a loss of surface area. What this means is that you don't have enough area for the electrolyte to dissolve the lead sulfate to form Pb2+. So charging the battery gets harder. Sulfation takes a while; maybe in the order or days. Not hours.

Sulfation is reversible. But you have to charge the battery very very (very) slowly so that you slowly dissolve the large crystals of lead sulfate to Pb2+ and convert them back to the charged state. But, who has the patience to wait all week to charge a battery!

What this means is that discharged lead-acid batteries are bad news. You need to avoid them like the plague.

So the path was clear: Get a jump start, drive the car for the next hour and half to SFO and hope that the battery gets its life back. Like I said, a professional does not think. He/she reacts.

But a professional also recognizes his/her limitations. In my case, my limitation was that I was really cheap and had not invested in jumper cables or AAA insurance. A professional also typically has no real friends. I knew that none of my "friends" would be willing to stop by to give me a jump at 7 AM.

So I reacted to this problem by taking BART (i.e., public transport) to the airport.

I dont know if you guys encounter this, but sometimes when you have something on your mind it seems like the whole world is starting to think about the same thing. So here I was thinking about sulfation of lead-acid batteries and at this conference on grid storage, there was all this talk about the UltraBattery (this is a trade name) as a means of preventing sulfation. There were actually two talks completely dedicated to it.

I spoke about this advance a little while ago. The concept is to add some carbon into the negative plate when you make the electrodes. Everything else stays exactly the same. But for some magical reason the sulfation decreases significantly.

The talks were showing data where the battery was being cycled a little bit (like a Prius battery does) where the battery without the carbon tanks after a few hundred cycles but the one with the carbon works much better (thousands of cycles). Apparently, the carbon solves the sulfation issue.

There is a variant of this idea which involves connecting the negative plate in parallel to an electrode made of activated carbon. Activated carbon by itself is used to store energy in the double layer (i.e., a double layer capacitor). So essentially you are connecting a battery electrode in parallel to a capacitor electrode in both these configurations.

What was amazing was that they really had no idea why this was happening (although its been a few years since this first came out). DOE is actually funding a project to try to get to the bottom of this advance. Its sad but true- there is a fundamental change in a 150 year old technology but we have no idea why this change occurred.

Some things in life are really hard to reconcile (e.g., is there a God? why does EVERYBODY make more money than Scientists?) but this problem is not in the same class. I believe that this lack of understanding comes down to limited funding for research combined with the "herding" of research topics.

Lead-acid batteries are cheap. The one that I ultimately replaced my car with cost me $165/Kwh. Assuming I got ripped off (is that even an assumption for things car related?) it stresses the point that these batteries are cheap. Adding a few percent of activated carbon to the paste is not going to break the bank. All through the conference I kept wondering why lead-acid's are not being made with a bit of activate carbon to ensure that sulfation is not a problem.

As an aside, the cheapest battery we know of is the lead-acid battery. For grid applications, the thought is that we need batteries that cost less than $100/kWh. Something pretty radical has to happen for us to make these cost numbers. Making batteries the way we have made them in the past will not allow us to get there. But this is for another post.

So would adding a bit of carbon result in the battery lasting the life of the car (say 15 years)? The company that is commercializing this says it could last 7 or maybe 15. Meaning: they have no idea! Problem with not knowing why something works- there is no way to predict how long it will work. Moreover, the data they show is based on Prius-like cycling. My car does not have the same cycling profile. Unless we understand what is going on, we have no way to knowing how changing conditions will change performance.

In time, this data will show up and we will know if we will can make a better lead-acid car battery. But wouldn't it be better if we understood what was going on?

Truth be told, I'm not at all convinced that my battery was sulfated and could have been saved with a timely jump start. It lasted 7 years! That's a long time. Plates corrode and they shed. Maybe I ought not to expect more from my energy storage devices.

But being able control failure modes in batteries is crucial in ensuring that we can move to electric drive. And they will be crucial if we ever want to store the electricity from the sun. Solar panels last 25 years; do you really want to change your batteries every 5 or 7 years?

But to control the failure, you first need to understand them. And in many cases, we don't quite have life of batteries pinned down. They change with chemistry, multiple failure modes occur at the same time, and in some newer chemistries we just haven't had the time to collect the data to see what the failure mode is.

So we have clues and hypothesis for failure, but we can't quite predict failure rates with cycling conditions. There is no cycle/calendar life simulator for batteries.

Actually that is not true. There are many many life simulation tools for batteries. But none of them actually work!

To me this incident highlights the importance of fundamental research to understand real-world problems. There is quite a bit of fundamental research; and there is no dearth of real world-problems. What we don't do enough of is linking the two (The Program at Berkeley is unique in that its the only one that does this in the whole field of batteries).

It also highlights the fact that I really ought to stop being so cheap, spend some money, and get jumper cables.



  1. Ah, yes - the elusive "parking light" switch on the top of the steering column of Subarus. Many people hit it while dusting or cleaning the dashboard, only to find a discharged battery in the morning. Nevertheless, you are quite right that having the battery last 7 years is very good indeed. My commercial guess is that adding activated carbon may not add much to cost, but if it extends the service life significantly, the battery manufacturers may balk at having a consumable consumed at a slower rate. Of course, we could say the same about the switch from incandescent bulbs to CFLs and LEDs.

  2. Welcome back! glad my feed reader keeps track of your posts.

    You might get a kick out of this: what happens when you leave a car battery underwater for a week. It was in my boat, in a box that did a better job of keeping water in than keeping water out.

  3. As 1/7th of your readership, I'm glad to have you back. But rather than jumper cables, I'd suggest a battery charger with a jumpstart mode. Once, when I was in a similar situation to yourself (with a little more time to spare), I hopped on my bike and bought one from Ace hardware for $50 (Amazon sells them for much less a couple of miles away. (I also have a PhD and the concomitant shortage of friends.)

    I've used the charger/jumpstarter many times since, and it has a trickle-charge mode, so should be good for reversing sulfation.

  4. Took me time to read all the comments, but I really enjoyed the article.audemars piguet watches

  5. Interesting information.

    Would a slow charge (something slower than any charger I've seen sold, but never really looked for it) be recommended as part of maintenance on a Lead-Acid battery? Maybe once a year or two years?

    Would be interesting to see some long-term information

  6. The stupid parking light! Who uses that stuff. Ahhh...
    Brian: Yes a slow charge should, in principle, let you reverse sulfation. The car alternator does this every day (it trickles and therefore allows any sulfated stuff to go back). Its only when the parking light snafu occurs that this becomes an issue. Doing a trickle charge from an external charger every two years is not going to help if you are making sure never to let this happen.

    As a matter of fact, I kept that light on 4 years ago. Caught it after 12 hours and got it jumped. DId not seem to have any problems. The 5 days I left it this time was a bit much!

    Cleanenergywonk: Thanks for the tip. You amazon link does not work.

    Anonymous on the underwater battery: Yikes!


  7. \\amazon link does not work.//

  8. Venkat
    Maybe you should save your money for another 7 years or so and *then* splurge on the jumper cables.

  9. If we were all off grid some day in the future, we could pull out one of our new lead carbon home batteries from its series/parallel configuration and jump start our own cars.

    Actually, that's what I do now - either pull a 31 amp UPS battery out or use one of my paralleled 12 volt ham radio backup batteries.

  10. @Bhaskar: Perfect plan of action!

    Reading your comment made me laugh out loud. That's just how I did it...after calling a Tow Truck for a jump start. Yes, another bereft of friends.

  11. Bhaskar: Exactly my thought. I should be golden for a few more years after which I will again have a new battery/car, so the same logic will work again.

    Actually I've been thinking about this and it seems to me that my battery could have lasted even longer. I drive 35 miles and ~1 h each way. For every one discharge pulse (during the cranking), I charge the battery for an hour. This battery probably had no sulfation! I would probably have to worry more about corrosion of the plates. So the few days sitting in the discharged state was bad, but probably not as bad as I thought.

    I think I should have held on and tried to run the car for a while and see if the battery came back to life. I sort of chickened out and decided to get a new battery and not deal with any more of these issues. But I wonder how many years I could have gotten from this if I had tried to get it back.

    Before you all conclude that I'm being really cheap by not wanting to spend $100 every 7 years; it all in the interest of science :-)


  12. Venkat, I think you are underestimating the number of people waiting for your next post each week.

    I would like to recount the annual motorcycle battery bowling event we used to have when I was much younger. The Great Lakes area is no place to ride a motorcycle in Winter. So, we all parked our bikes and scooters until Spring. Total discharge was inevitable for most.

    Hence the need for poor students to find a way to bring motorcycle batteries back to life. Each Spring we would gather with our dead motorcycle batteries. Understand that this was when battery cases were heavy and strong.

    We started by setting up children's bowling pins in someones yard. Then a controlled but spirited game of bowls was played using the batteries as the balls. The rolling and bumping was enough to knock loose the lead sulfate from most plates.

    Then the electrolyte was poured out and the loose stuff flushed out with tap water. Replacement electrolyte was put in and a short trickle got things charged enough to start up the 2 wheeler and recharge the battery.

    OK, there were broken batteries and shorted plates and success was often limited to a few weeks before a battery failed anyway. But think how much more fun that was! Friends, a rite of Spring, a game, some winners to cheer and some losers to console and an excuse for a very long first ride of the season.

    Who says chemistry isn't fun.

  13. Hi Venkat; nice to read you again. I would like to suggest one theme for your blog: the GE durathon battery, and the other movements in the molten salt area (FZ SONIK). It seems to me there is a bit of a resurgence of the technology, and it would be nice to hear an opinion from an expert on the field, even if you are working on a competing chemistry!