Inside of lithium battery charging and discharging

Why does the voltage drop when lithium iron phosphate is full and rise after discharge?

We could see very often that after the battery stops charging and discharging,what's the principle inside?

The movement of electrons forms a current. When charging, the positive lithium ion moves from the positive to the negative. Lithium ions include protons and neutrons, and electrons move from the negative to the positive. Because lithium ions have weight and electrons do not, electrons move faster than lithium ions. For example, there are 100 lithium ions and electrons, and 100 electrons will reach the positive before lithium ions, but some lithium ions have not migrated in the past, which will lead to the decline of the whole voltage and reach the equilibrium state.