system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:why do lithium-ion batteries wear out over time (and so quickly)?

I did a quick search and couldn't find a sufficiently similar, "explained" ELI5.
gpt
In a lithium ion battery, the cathode and the anode (where electrons are collected/deposited) are made of layered materials that can accept lithium between the layers. Traditionally, these have been Cobalt oxide (CoO2) and graphite). On charge or discharge, you move lithium in and out of the interlayer space. The layers have to move closer together when lithium is taken out or further apart when lithium goes in. This causes wear and tear leading to chemical changes in the electrodes so they can't store as much energy.