Li-ion battery: Li+ Co (s) + e. ? LiCo (s) E 0.855 V + CoO2(s) LieLiCoO2 (s) E2.

Question

Li-ion battery: Li+ Co (s) + e. ? LiCo (s) E 0.855 V + CoO2(s) LieLiCoO2 (s) E2.745 V NiCad battery: Cd(OH2 (s) 2eCd (s) 2 OH (aq) E -0.40 V Eo 1.32 V 2NiOOH (s) + 2H2O(l) + 2e' ? 2 Ni(OH)2 (s) +2OH-(aq) Answer the following questions for each of the two batteries above. Does oxidation or reduction take place at the anode in an electrochemical cell? Why? For each battery, which reaction will take place at the anode? a. b. Calculate the cell potential, Eel ( cathode E'anode) c. Write the overall reaction that takes place in the electrochemical cell.

Explanation / Answer

a. The anode is the electrode at which the oxidation half-reaction occurs, and the cathode is the electrode at which the reduction half-reaction occurs. Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion. Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion. Oxidation happens at the anode because electrons are lost. Reduction happens at the cathode because electrons are gained.

For Li-ion battery

LiC6?C6+Li++e?

For NiCad battery

b. EoCell=EoCathode?EoAnode

For Li-ion battery

EoCell=EoCathode?EoAnode

        =0.855- (-2.745)

        =3.6V

For NiCad battery

EoCell=EoCathode?EoAnode

        =1.32-(-0.40)

         =1.72 V

c. Overall reaction that takes place in the electrochemical cell:

Li-ion battery

At the cathode    CoO2+Li++e??LiCoO2

At the anode       LiC6?C6+Li++e?

Overall reaction   LiC6+CoO2 ?C6+LiCoO2

NiCad battery

At the cathode    2NiO(OH)(s)+2H2O(l)+2e??2Ni(OH)2(s)+2OH?(aq)

At the anode         Cd(s)+2OH?(aq)?Cd(OH)2(s)+2e?

Overall reaction Cd(s)+2NiO(OH)(s)+2H2O(l)?Cd(OH)2(s)+2Ni(OH)2(s)

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