Battery Handout

Rechargeable Batteries

Electrochemical Discharge Reactions

1) NiCd ("Nicad" batteries)

cathode: NiOOH + H₂O + e^- ==> Ni(OH)₂ + OH^-
anode: Cd + 2OH^- ==> Cd(OH)₂ + 2e^-

net: Cd + 2NiOOH + 2H₂O ==> Cd(OH)₂ + 2Ni(OH)₂

2) NiMH ("Nimh" batteries)

cathode: NiOOH + H₂O + e^- ==> Ni(OH)₂ + OH^-
anode: Alloy[H] + OH^- ==> Alloy + H₂O + e^-

net: Alloy[H] + NiOOH ==> Alloy + 2Ni(OH)₂

(Alloy = a complex rare earth/nickel alloy based on LaNi₅.)

3) Pb/Acid ("Lead acid" batteries)

cathode: PbO₂ + 4H⁺ + SO₄^2- + 2e^- ==> PbSO₄ + 2H₂O
anode: Pb + SO₄^2- ==> PbSO₄ + 2e^-

net: Pb + PbO₂ + 2H₂SO₄ ==> 2PbSO₄ + 2H₂O

4) Zn/MnO₂ ("Alkaline" batteries)

cathode: MnO₂ + H₂O + e^- ==> MnOOH + OH^-
anode: Zn + 4OH^- ==> Zn(OH)₄^2- + 2e^-
Zn + 2OH^- ==> Zn(OH)₂ + 2e^-

net: 2MnO₂ + Zn + 2H₂O ==> 2MnOOH + Zn(OH)₂

(First anode reaction occurs until the solution is saturated with zincate ions.)

5) Li ("Lithium" batteries)

cathode: TiS₂ + Li⁺ + e^- ==> Li(TiS₂)
anode: Li ==> Li⁺ + e^-

net: TiS₂ + Li ==> Li(TiS₂)

(Aprotic organic solvent or conducting polymer electrolyte used.)
(Li(TiS₂) = Li intercalation positive electrode.)

6) Li ion ("Lithium ion" batteries)

cathode: MO₂ + Li⁺ + e^- ==> LiMO₂
anode: LiC₆ ==> Li⁺ + C₆ + e^-

net: LiC₆ + MO₂ ==> Li(MO₂) + C₆
(C₆ = graphite; LiMO₂ = Li intercalation positive electrode with M=Ni,Co.)

Compiled by R. M. Corn
Fall 2005

Rechargeable Batteries

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