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The INQUIRER Guide to Exploding Batteries

Bang, crash, wallop!
Sun Feb 29 2004, 10:53
ONE OF the hottest topics in tech news today is exploding batteries, in phones, laptops, and other devices. You see an article every week or two with a headline screaming about someone in a far off land who got his or her buttocks toasted by an errant cell phone. It makes great copy, better pictures, and you will keep seeing them in the coming days and weeks. With all the press the subject is getting, the most disturbing thing is most people can't tell you why these things blow up.

OK, there is one thing that is even more disturbing and that's how easy it is to get them to blow up. First, a word of caution before the hardcore chemistry, don't try this. Those little batteries pack a lot of energy, and will violently explode if you screw around with them. You can't do it in a safe way, and from what I am told, it happens so fast you can't get away. If you make a battery explode, you will get hurt. I am not saying this from a disclaimer/PR/lawyer driven sense of self-righteousness, I like things that blow up. I like fireworks, and things that go bang. This is not one of those things that you can do safely, stick with the traditional ways of killing and maiming yourself, please.

Let's start off with the basic chemistry. Rechargeable batteries started out with good old lead-acid cells like those in your car. They worked well enough, but were rather temperamental, heavy and full of acid. During recharging, they could emit pure Hydrogen gas, which would blow up if there was a spark nearby and some Oxygen. Before you say "what comes around", trust me when I say this is a rather different way of blowing up. Technology has mostly conquered these problems, and modern lead-acid batteries are safe and don't blow up often. They are still heavy and filled with acid though.

The next major trend was Nickel-Cadmium batteries. These were much better in that they only got warm when you charged them. No boom bang a bang. They had this nasty tendency to quickly lose charging ability if used improperly - this was called a "memory effect". Add in the fact that Cadmium is rather toxic, and you have an unpleasant mix that was better than everything else, so it stuck around.

The things that replaced NiCd cells are all Lithium based. Li, in its various battery forms, is still toxic, but holds a lot more charge and doesn't have memory effects. While these admirable traits are in the "good thing" category, the fact that they can blow up has a tendency to counterbalance the good parts quite nicely.

Let's go to some basic chemistry. Lithium is a very useful light metal, and is found in a bunch of alloys, nuclear reactors, drugs and batteries. As a raw metal, it is very reactive, if you try to melt it, it will catch fire, and is very hard to put out. If you put it in water, it "reacts violently". That is the polite way of saying it catches fire and can blow up. I have never done this in my previous career as a ChemE student, so I can't vouch for it's properties personally, but it sounds a lot like some experiments with Lithium I have conducted.

Moving along, we have the Lithium Ion batteries that are all the rage nowadays, they are made mainly out of LiCoO2. Take note of two elements in there Lithium and Oxygen, they will be featured later on. There are other variants of this that make up various flavours of Lithium Ion batteries, almost all of them substitute the Cobalt in the middle for another metal, the Li and the O stay the same.

LiCoO2 has a rather happy property -- it can be made to decompose under not all that far fetched circumstances, the big one being heat. When it decomposes, it releases Oxygen, and Oxygen as you know, makes things burn. No Oxygen, no fire.

When you charge rechargeable batteries, they all tend to do something that makes a bit of sense if you think about it, they heat up. When you discharge them, they also heat up. Have you ever talked for a long time on a cell phone and then realised how warm it is? How about pulling a laptop battery out, and noticing it is rather toasty, or pulling an AA out of the charger. Warm? You bet. When batteries charge or discharge, they heat up.

The more rapidly you charge or discharge them, the more rapidly they heat up. The hotter they are, the more they decompose, and free Oxygen. Under most circumstances, this decomposition is rather negligible, and there is no problem. Once you get above about 150C, it happens a lot more rapidly. The free Oxygen can then react with some other chemicals in the battery and if you have Lithium plated out internally, you can have a really interesting time. Add in the fact that there is a lot of energy in an enclosed space, and the fireworks begin, figuratively at this point.

With Oxygen oxidising things willy-nilly, that is burning for you non-chemists, you get heat as a by-product. This heat decomposes more LiCoO2, and in turn feeds the reaction. This can lead to a condition lovingly known as "thermal runaway". Once this happens, the fireworks become much more literal. Yes, it goes boom in a big way.

That is the chemistry part. Now for a bit of physical battery technology. Most modern batteries are cylindrical, and if you view them in cross-section, they look like a rolled up mat. The term most often used to describe this format is a jelly roll. Each of these rolls is called a "cell", and multiple cells are chained together to form a battery pack. If you read the specs on a modern laptop, they list the battery design as an 8-cell, 12-cell, or multiple cell. The more cells you have, the more battery life you can get, but the heavier and more expensive it is.

The basic cell talked about in battery circles is the 18650, the AA of the rechargeable world. If you have a laptop, you probably have a battery pack made up of 18650s. They come in almost infinite sizes and shapes, and if they don't, someone will probably design one.

When Lithium Ion batteries first came out, a single 18650 was good for about 1350mAh. Since their debut, they have grown to 2200mAh or so in common use, with 2400 soon, and 2600 "in the labs". Most of the gains modern cells give are from physical changes, thinner walls that allow more materials inside and the like. The chemistry is rather well known, and not going to change in a significant way.

So, what you have is a tightly packed, high energy brew of unstable things that you would whine about if you didn't have. Take away someone's cell phone and they tend to get pissy in a hurry. Think about that next time you slide your phone into your pocket.

So, how safe are they? Actually, pretty safe. How many people out there have a Lithium based battery, and how many have blown up? How many people even know someone who has had one blow? Not many, and when they do blow, manufacturers are quite keen to put a lid on it, hush money does wonders. So, it is possible, but uncommon and usually well covered up. There is very little to fear, but tell that to a person with a char-broiled thigh.

How do you get them to blow? Easy, you just short them out internally, and they are fairly likely to generate enough heat to explode. How do you short them? Well, buy a defective battery for one. Another way is to dent them enough to compress the jelly roll so that internal parts that should not touch come in contact with one another. Then, boom! You can also heat them up to above 150C for more than 10 minutes or so, and they and you may also meet a violent demise. Basically, don't hit your battery with a hammer, or drop it off a high ledge onto concrete or into an oven.

If you are thinking of trying this at home, as I said earlier, don't. When asked about how rapid the reaction was, a person familiar with such things responded with "How fast can you blink". You simply can't do this safely without a lab setup to protect you. As the old joke goes, what were the last words of the redneck? Watch this.

There are a lot of technologies that will protect you if your battery is about to blow up, and more are probably coming down the pike. Technologies that will limit the amount of current drawn to prevent rapid discharge, or batteries with separators that melt and kill the battery long before they "overheat" are two of the more promising avenues.

Both of these technologies are band-aids, they stop the end result from happening, but do not address the critical issue at hand, the basic substances that form the battery are prone to blowing up. Batteries can be made safer, but not safe. Think about this. If a cell phone can hurt a person badly when it blows, how much damage would a power drill with a battery 50 times as big do? Think about that next time you are walking by a construction site.

The safer, but still not safe problem has limited the uptake of Lithium based batteries in the marketplace. While the energy density of the batteries would do wonders for the anemic range of an electric car, you will never see one on the road. Cars are known to meet violent ends even when used correctly. Having one with a large, explosion-prone mass in the centre that is more touchy than gasoline isn't appealing to car companies, or more importantly, their lawyers. Ever wonder why electric cars stick with relatively stone-age lead-acid batteries?

So, what do you do to solve this impasse? Change the fundamental chemistry behind the battery. That is just what Valence ( here) set out to do. The basic chemistry of batteries is fairly well understood, but making it work in the real world is not as easy. Think about putting someone on the moon. It's easy to describe but much harder to do and the devil is in the details.

Valence has a technology, called Saphion, that fixes the problem. Simply put, the basic chemistry is not prone to blowing up. Saphion is made up of LiFePO4 rather than LiCoO2, a rather fundamental difference. The LiFePO4 molecules will line up in zigzag chains, and without going into the details of the chemistry, will basically stabilise each other. This leads to a battery that is less likely to decompose under adverse conditions.

You will notice I said "less likely", not "will not". The self-stabilisation can only go so far, and if you throw one in an autoclave, it will decompose, rest assured, but it will take more doing than a standard battery. The important part to you and I is that when it does decompose, it liberates a phosphate group (PO4), not an Oxygen molecule. Phosphates don't react violently with Lithium, and will not blow up in the same way.

If you put a nail through a Cobalt based cell, you stand a very good chance of injury. If you put one through a Phosphate cell, you will waste a good cell, and walk away underwhelmed. That is a good thing. We like our readers, and even if they die in a way that makes a good story, we don't like it. We can find other material on our own thank you.

So, the main thing it brings to the table is lack of violent explosions, but how does it perform? After, all, a concrete block will not blow up, but does not power your laptop very well. Valence says that at launch, its Saphion based 18650 cell is good for about 1750 mAh and expects it to be 2000 mAh by early 2005. The theoretical potential of a Saphion cell is better than a Cobalt one, so with a similar development programme, it could be a better battery from a user perspective as well as from an explosion perspective.

Valence also says that the chemistry and materials of a Saphion battery are similar enough to the current batteries that you can make the new cells on the same lines as the old with much of the same infrastructure. Changeover would not be a horrific and costly endeavour. Add in that Iron costs much less than Cobalt, and you have a potentially lower material cost. In a world where manufacturers try to squeeze every last cent out of everything, this could be significant.

Today, the energy density is slightly lower, and the cost is a bit higher due mainly to production volumes, but that can, and most likely will change. The one catch that will take a bit more doing is a psychological issue. If you happen to be a large computer maker, or a cell phone company, and you are hot to replace your exploding batteries, how do you sell the new safer ones? The fact that they cost a little more is one thing, a few dollars more on a high end laptop for safety isn't hard to swallow. A little shorter run time isn't an insurmountable sell either. What is a little trickier is how to tell someone you just sold them a bomb, but the new ones "won't kill them as much we hope".

This is a problem. You either stand up and say "our old ones were dangerous", and promptly sink sales and invite lawsuits, or you stealth launch it. If you take the quiet and lawyer-free route, it becomes a much harder sell. "Our new laptops are more expensive, but the batteries have less run time" is hardly an ad man's dream headline.

This, more than anything, is slowing the uptake of Saphion batteries. It will happen, safer technology that is potentially better in most, if not all respects is here. Uptake is almost assured, but as usual, it will take time. Valence has put out several products for home and industrial use that features the technology, and is looking for companies to license the tech. Give it some time, and all those exploding battery stories will go away, and we will have to look harder for sensationalist headlines. Companies like this make my life harder. µ

 

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