The electrons take the long way around

In a lithium-ion battery the ions cross the cell. The electrons cannot. They leave the terminal, do the work in your device, and come back the other terminal.

A charged cell holds lithium ions crowded into the negative electrode, parked between layers of carbon. Connect a phone and the ions drift through the electrolyte toward the positive electrode, where they settle into a metal oxide. The electrolyte will not conduct electrons. If it did, the cell would short itself and the ions would make the trip without ever doing work outside. So the electrons are sent the long way: out the wire, through the processor, the screen, the radio, and back. The chemistry’s only job is to make that outside trip downhill.

Charging is the same path in reverse, forced by a voltage. The Nobel prize in 2019 went to Whittingham, Goodenough, and Yoshino for building electrodes that survive the trip thousands of times. The fussiness — the heat, the dendrites, the batteries that are not allowed to be crushed — is the price of an electrolyte that must carry ions and refuse electrons, in a package that gets angry when the two paths touch.