In this third and final article in our Kibbles and Bytes series on batteries, I’m going to discuss the one that makes all our modern portable gadgets possible: The lithium-ion battery. Without this technology, many (if not most) of our gadgets would be clunky, not last very long, and generally not be very useful. So what is it about lithium batteries that makes them so unique and successful?
First, we should define what we’re talking about. There are two broad types of lithium batteries. The first type are the primary cells. These are not rechargeable. Examples include some camera and flashlight batteries as well as most coin-cell type watch batteries. The second type are secondary cells. These are rechargeable, and they’re the ones we’re going to focus on. They have a lot of different names, but they all operate under the same principle of lithium ions being shifted back and forth between the positive and negative electrodes. So a secondary lithium battery will almost always be referred to as a lithium-ion battery.
You may hear lots of different names for lithium-ion batteries, like Li-NMC, LiFePO4, LMO, Li-Poly*, but these are all the same thing. The variations are simply describing a different cathode material. Different materials change the characteristics of the battery to make it longer lasting, safer, or shaped differently, but they work the same way.
By far the number one reason lithium-ion batteries are so useful is their high specific energy. This is a measurement of how much power a battery has vs how much it weighs. Lead acid batteries have a specific energy of around 40 watt hours per kilogram. Lithium-ion on the other hand has a specific energy of around 200 watt hours per kilogram. So they’re around five times as energy dense as lead acid. A larger amount of power can be crammed into a smaller package. This is what allows your iPad Air to be so incredibly thin and light, yet still last all day.
Another benefit of lithium-ion is their lifespan. Most types can be recharged several hundred times without any performance loss, but many variations can be recharged thousands of times. Not only does this mean your device will last longer, but it’s also better for the environment to not have to keep making new batteries.
The only real drawback to lithium-ion batteries is their cost. They cost 4-6 times more than a lead acid battery with equivalent power. But because lithium-ion can do tasks no lead acid battery could ever do (heaviest iPhone ever?), we happily accept the additional cost. As they become more and more common though, the price has dropped considerably, and it will likely continue to do so.
The future of lithium-ion batteries is looking brighter all the time too. Because of their high specific energy, better lithium-ion batteries are being developed for things like electric cars, battery backup systems, grid-level electricity storage and more. If you want to know more about batteries, the internet has some great resources. I like this wikipedia chart that shows an overview of a wide array of battery types.
Thanks for following along on our sometimes technical, but hopefully informative series on batteries. Power on!
Extra: What’s the deal with lithium polymer? (I was confused, too.) You’ll hear this term a lot, but really a lithium polymer battery is just a regular lithium-ion battery, most likely using lithium manganese dioxide as the cathode material, but it could be anything. The “polymer” part is really referring to how these batteries are assembled. Instead of being housed in rigid casings, the cells are laminated together. This allows greater variety in shape, but also makes them even lighter. Most electronics, including the MacBook Pro and iPhone use Li-Poly batteries.