Batteries are magic, part 2

I've spotted a Li-ion battery powered motorcycle.

Welcome back for part 2 (of 2) of how Li-ion batteries work, and thus their magic. (Rest assured that this educational material is a quick departure for Dots.) We left off discussing the importance of the two electrodes, named the anode and the cathode. Li-ions are stored in the anode when the batteries are charged, but much prefer life in the cathode.

Continuing...


The cathodes are also thin layers of materials, but instead of graphite particles they are made up of transition metal oxides. You know what else is a transition metal oxide? Rust, and the "minerals" in mineral sunscreen. Oxides, of course, contain oxygen, and Li+ ions like being around oxygen. Why? Charge balance. Since lithium wants to stay positive and oxygen wants to be negative (carry extra electrons), together they are two peas in a pod.

The transition metals (like cobalt) of the cathode do the dirty work of gaining electrons, dropping down in their own positive charge (which they don’t mind) when the Li+ comes in so that charge is balanced in the material. Then they give up that electron when the Li+ is pulled back to the anode (when you charge your battery). They switch it up on command, and for that they are awesome.

So Li+ ions go back and forth between where they hate (the anode) and where they love (the cathode) every time you charge or use your battery, respectively. The electrolyte is the highway that lets them swim back and forth. This next part is totally key -- every time Li+ goes one way inside the battery, negatively charged electrons move the other way (charge conservation is a rather important law of physics), and those electrons make up the current that flows through external circuits and gives us our juice. Everything we've talked about here - the magic of batteries - is the shrouded chemistry that gives access to electronic current that fuels modern lives.

There’s a lot more to Li-ion batteries like the material that holds the anode and cathode pieces together (the graphite anodes and metal oxide cathodes are made into small powders that are cast and stuck onto metal foil current collectors), separating plastics that make sure the anodes and cathodes don’t touch each other, and the electronics. But that’s perhaps for another day.

Here are a few tips before you go – a reward for reading this far.

• Don’t let your battery charge and charge and charge once it’s charged. Your batteries have built-in overcharge protection (in the electronics), but nevertheless, adverse side reactions happen mostly when the batteries are held in the fully charged state. This is why I don’t sleep with my battery plugged-in if I can help it.
• High temperatures will degrade your batteries. Don’t leave your laptop in your car on a hot day (it will get stolen too, of course). Cool temperatures can make the battery sluggish, but this causes no permanent damage.
• Li-ion batteries don’t suffer the “memory effect”, so you don’t have to worry that your battery will “think” it has less charge if you only drain it halfway before recharging. Drain and recharge at any state and it’s none-the-wiser.
• Li-ion batteries are still getting better – about 5% better each year. In addition to engineering advances at the battery pack level (we’ve only talked about one “cell”, but a “battery” can contain many cells hooked up to each other), research is going on to make each electrode and the electrolyte better (higher capacity to store Li+, better voltage, more stable, less flammable, cheaper, etc.). 

This concludes your lesson on the magic of Li-ion batteries. I’m happy to take any questions, large or small, in the comments.