Why the graphite potential near the separator is the lowest during charging process?

[HerrnWang]

My main question is : during charging process, why the anode particle potential near the separator is higher than the potential near the current collector. During charging, we know that the lithium concentration of the graphite particle near the separator is the highest, so the graphite potential should be the lowest, since higher lithium concentration inside graphite particle lead to lower solid potential. I don' t understand the simulation results of the negative electrode potential below.

The code I run is simple, it just runs a basic model. And i also wonder, why in the simulation results all negative electrode potential has unit [1e-5 V], that is too tiny. Maybe it is because the parameter inside the model?