Why does battery life get worse over time?

[Windows Central]

The chemistry that can provide power from metals makes those metals degrade over time and there's not much we can do about it.
I'm sure you've noticed that you see a noticeable difference in how well a phone battery holds a charge after a year or so. If you keep a phone long enough, its battery may not even have enough charge to survive a whole day. Have you ever wondered why?
[h=2]Batteries: How do they work?[/h]

Full story from the WindowsCentral blog...