What Is the Electrochemical Principle of Ni-MH Battery?

Ni-MH batteries use Ni oxide as the positive electrode, hydrogen storage metal as the negative electrode, and lye (mainly KOH) as the electrolyte.

• When the nickel-hydrogen battery is charged:

Positive electrode reaction: Ni(OH)2 + OH- → NiOOH + H2O–e-

Negative reaction: M+H2O +e-→ MH+ OH-

• When the Ni-MH battery is discharged:

Positive electrode reaction: NiOOH + H2O+e- → Ni(OH)2 + OH-

Negative electrode reaction: MH+OH- →M+H2O+e-