Question

Consider the phenomena of Li intercalation of graphite at the anode of a Lithium Ion battery, something you should have run across in your review. Intercalation of lithium metal in between the layers of graphite forms a thermodynamically stable compound whose formula is LiC₆. At the cathode of a lithium ion battery is another bizarre chemical, typically lithium cobalt oxide (LiCoO₂). The two half cell reactions can be expressed as follows:

Li⁺¹ + e- + C₆ à LiC₆                            E_o = -2.84 V

Li⁺¹ + e- + CoO₂ à LiCoO₂         E_o = +0.25 V

A. Which of the two reactions will undergo reduction and which one will undergo oxidation when the battery discharges (spontaneous reaction)?

B. What is the theoretical voltage that can be produced by this cell at standard conditions? Show your work.

C. Use the above information to write the complete spontaneous redox reaction that combines the half cell reactions.

D. Calculate the standard Gibb’s free energy, DG_o for this reaction. Calculate the equilibrium constant for this reaction at 25^oC.

E. Explain how your typical LiCO₂/LiC₆ cell could possibly have a higher voltage (3.6 V) than the voltage you calculated above for a cell at standard conditions?

Answer 1

A) anode : the elctrode having lower reduction potentail act as anode.

      = LiC6 -electrode

   at anode oxidation takes place .

the elctrode having Higher reduction potentail act as cathode .

    = LiCoO2-electrode

at cathode reduction takes place.

b) E0cell = E0cathode - E0anode

           = 0.25-(-2.84)

           = 3.09 v

c) cell reaction : LiC6 + CoO2 ----> C6 + LiCoO2

d) DG0 = - nFE0cell

       = - 1*96500*3.09

       = -298.185 kj/mol

   DG0 = -RTlnK

   -298185 = -8.314*298lnK

K = 1.86*10^52

by increasing the concentration of ions,voltage of cell increases.