system
Given the following post, respond as if you're commenting on Reddit:
human
what is physically happening to Li when a Li-ion battery is charged under load (while on)?

I understand that the battery does not charge and discharge simultaneously, but rather there's a net charge due to opposite polarization. But does this mean that Li is diffusing slower towards the cathode?
gpt
Possibly. The Li diffusion rate is directly proportional to the charging current. The charger circuit may or may not be capable of varying the charging current. It depends on how things are connected, but it's possible to use a power supply that can support charging at the maximum rate regardless of other system load. Some devices will design the charging circuit to only use "free" power (such that total power draw never exceeds some number), and some circuits will just have everything always run off the battery, and the charger may or may not charge it (in this configuration the charger might send current to the battery but a portion of that current goes to the power supply and never enters the battery).

But if the battery is charging slower, it's because there is less charging current going to the battery.