How does a lithium-ion battery work?

ll batteries work by having two electrodes—an anode and a cathode—with a bunch of a material called electrolyte between. When you plug a battery into a completed circuit, a chemical reaction starts taking place at the anode and electrons start building up over there. Those electrons want to travel to the cathode, where it's less crowded, but the electrolyte between these two parts keeps the electrons from taking the short way there. The only way through is the circuit that the battery is crammed into, and those electrons power your device in the process. Meanwhile, the positively charged lithium ions the electrons leave behind travel through the electrolyte to meet the electrons on the cathode side.Once all the electrons have made the trip, your battery is dead. Except! If you're using a rechargeable battery like a lithium-ion, you can reverse the process. If you dump energy into a circuit using a charger, you can force the reaction to go in the other direction and get that electron party at the anode all crowded again. Once your battery is recharged, it'll mostly stay that way until there's something for it to power again, though all batteries leak some charge over time.What determines the capacity of the battery—how long it can power your stuff—is the number of lithium ions that can nestle themselves into the tiny, porous craters of the anode or the cathode. Over time, with repeated charge the anode and the cathode degrade, and can't fit as many ions as they used to. As that happens, the battery stops holding a charge as well as it once did.