why do lipo batteries puff up?
Anybody who uses lipos will eventually encounter a puffy or swollen battery.
And the first question that inevitably comes up is “What should I do?”
This post is all about what causes that swelling and what to do when it happens to one of your lipos.
Are Swollen Lipo Batteries Dangerous?
Yes. Next question.
Seriously, there are so many examples of puffed batteries that start on fire that this shouldn't even be a question.
That doesn't mean that every battery that is puffed is going to explode as soon as you use it but it does mean that a high enough percentage of them are going to be dangerous that it isn't worth the risk.
What Causes Lipo Batteries to Puff Up?
Puffed lipo battery Gas generation in lithium ion batteries is a normal thing. Even if you don't abuse your battery, the normal everyday use of your battery will generate gas through a process called electrolyte decomposition.
The electrolyte decomposition occurs even faster if you over discharge a battery or overheat a battery.
What is electrolyte decompostion?
Simply put, a battery is made of three things: the anode, the cathode and the electrolyte. The cathode and the anode are the positive and negative terminals on your battery.
The electrolyte is a chemical inside the battery that allows charged ions to flow from the anode to the cathode during discharge (and the other way during charging).
Electrolyte decomposition is what happens when that electrolyte chemically breaks down. So in a lipo battery, as the electrolyte breaks down you end up with lithium and oxygen. This forms lithium oxide on the anode and cathode (depending whether you are charging or discharging).
But what you also end up with is excess oxygen that doesn't adhere to the anode or cathode. This excess oxygen is part of what causes a battery swell. And oxygen likes to burn. See here for more details. He also goes over some other reasons a battery might swell.
Other gases that can be found in the battery during the normal chemical reactions of a battery are carbon dioxide (CO2) and carbon monoxide (CO). For a technical overview of this, see this paper.
How to Fix a Swollen Battery
Dispose of it properly (see below) and buy a new one.
It's not worth injuring yourself or burning your house down to save a few bucks.
How to Dispose of Puffed Lipo Batteries?
The proper way to dispose of a swollen lipo battery is the same as what you would do when you throw out any old battery. You need to discharge it completely first.
The two main methods that people use to discharge a battery completely is to hook it up to a light bulb or to put it in a bucket of salt water. There are debates about which method is better but I will avoid that debate here for now.
After you've completely discharged the battery, I recommend finding your nearest battery recycling drop-off point and bringing it there. Make sure you call ahead and ask if they accept damaged batteries.
Tips to Avoid a Swollen Battery
Proper charging – Make sure you charge your battery properly using a quality battery charger. For safety, make sure you put your batteries in a lipo bag while charging. If you don't have a lipo bag, I highly recommend you buy one. For around $10, you can insure that if something does go wrong at will at least be contained.
Don't over-discharge – Make sure you stop using your battery before the voltage gets to the minimum cut-off voltage.
Heat kills batteries – Don't use batteries or charge batteries when they are warm. After you're done using them, give them a little time to cool off before you charge them. And after you are done charging them, give them a little time before you use them.
Proper storage – Do not store your batteries in a hot location. (For example, don't keep them in the trunk of your car during in the summer.) Store lipo's at the proper storage voltage. The article I linked to above showed that swelling increased significantly after only 4 hours of storage when batteries were at a state of charge above 80%.
To sum up: As lipo's age and if they are misused, gases start to form in the battery and cause it to swell. Once you have a puffy lipo, the safe thing to do is to discharge it completely and then recycle it.