Dear everyone,

It is explained from the phase change of the positive electrode that the plateau of the charge / discharge curve occurs, using the Gibbs phase rule (F = 2-P). However, the battery should also have a negative electrode reaction. I wondered there. Considering the negative electrode, what is the form of the Gibbs phase rule and how should it be used? By the way, I thought as follows. If you make a mistake, feel free to point it out.

Consider the case of a lithium metal battery. The general formula of Gibbs' phase rule is F = C-P + m, and since the extensive instruction variable of the battery is voltage only, m = 1

Positive electrode reaction: A → B

Negative electrode reaction: Li → Li +

Assuming that the independent component C = 2 (A and C), the applied Gibbs phase rule is F = 3-P. Therefore, the charge / discharge curve can be interpreted as follows.

1. When no phase change occurs at the positive electrode

Since P = 2 (A, Li), F = 1, that is, the voltage changes.

2. When a phase change occurs at the positive electrode

Since P = 3 (A, B, Li), F = 0, that is, the voltage is constant.