Commercial Cells and Batteries

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Commercial Cells and Batteries

• Edward A. Mottel
• Department of Chemistry
• Rose-Hulman Institute of Technology

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Commercial Cells Batteries

• Reading assignment
• Chang Chapter 19.6-19.7
• Commercial cells involve both electrochemical
  principles and important design considerations.

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Commercial Cells Batteries

• Non-rechargeable
• Zinc-Carbon
• Alkaline
• Mercury
• Air-Zinc

• Rechargeable
• Lead-Acid
• NiCad
• Metal-hydride
• Lithium
• Fuel Cells
• Research Areas

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Zinc-Carbon Cell(LeClanche Dry Cell)
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Zinc-Carbon Cell(LeClanche Dry Cell)
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Zinc-Carbon Cell(LeClanche Dry Cell)
Problems Decline in potential under high current
loads.
High current load leads to gaseous product side
reactions.
Side reactions give poor "shelf life".
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Zinc-Carbon Cell ReactionsVarious equations are
given for this reaction
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Zinc-Carbon Cell
cathode
2 NH3(aq) Mn2O3 (s) H2O(l)
E ½
anode
E ½ 0.76 V
overall
E cell
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Why is an Expansion Chamber Needed?
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Zinc-Carbon Cell Performs Poorly
Nernst Equation
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Alkaline Cell
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Alkaline Cell
1.54 V
Under alkaline conditions, gaseous side reactions
are eliminated.
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Alkaline Cell
cathode
E ½
anode
E ½
overall
E cell
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Alkaline Cell
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Alkaline Cell
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Mercury Cell
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Mercury Cell
Which end is the negative electrode?
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Mercury Cell (Ruben-Mallory)

• 1.35 V
• Positives
• Very stable potential, high capacity, long life
• Negatives
• Mercury compounds are poisonous
• Applications
• Pacemakers, hearing aids, watches

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Mercury Cell
cathode
E ½
anode
E ½
overall
E cell
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Other Common Cells

• Silver Oxide
• Zinc-Air

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Storage (Rechargeable) Cells and Batteries

• Lead Acid Battery
• Nickel-Cadmium
• Metal-hydride
• Lithium
• Fuel Cells

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Lead-Acid Battery
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What is the Difference Betweena Cell and a
Battery?

• Cell a receptacle (cup or jar) containing
  electrodes and an electrolyte, either for
  generating electricity by chemical action, or for
  use in electrolysis.
• Battery a number of similar machines, devices or
  articles arranged in a group or set.

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Lead-Acid Battery
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Lead Acid Cell
cathode
E ½ 0.356 V
anode
E ½ 1.685 V
overall
E cell 2.041 V
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• 6 M sulfuric acid
• determined by specific gravity, 1.2 gmL-1

As the battery discharges, does the specific
gravity of the electrolyte increase or decrease?
What would be the expected potential of a six
cell fully charged lead acid battery at room
temperature?
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Six Cell Lead Acid Battery
Six cells 6 x 2.215 V 13.3 V
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Recharging a Lead Acid Battery

• What device in an automobile is used to recharge
  the battery?
• What potential must be provided to recharge the
  battery?

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Recharging a Lead Acid Battery
If 14 volts is good, is 18 volts better?
Competing reactions Recharging a lead acid cell
E cell -2.22 V Electrolysis of water
(hydrolysis)2 H2O(l) 2 H2(g) O2(g) E cell
-1.23 V
Overvoltage
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Lead Acid Battery

• Problems
• Side reactions
• Weight
• Advantage
• Where is the salt bridge for this cell?

Pb(s) H2SO4 (6 M) H2SO4 (6 M) PbO2(s)
Pb(s) H2SO4 (6 M)
PbO2(s)
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NiCad Cell

• 1.4 V
• Constant potential
• Rechargeable

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NiCad Cell
cathode
E ½
anode
E ½
overall
E cell
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NiCad Cell
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Lithium Cell

• 3 V
• Solid, polymeric "salt bridge"
• High "energy density"

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Lithium Cell
Anode
Cathode
Li
TiS2
Solid polymer electrolyte
Li Li e
TiS2 e TiS2
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Fuel Cells

• An electrochemical method to burn reactants.
• Continuously consume a stream of reactants
  electrochemically.

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Fuel Cell Reactants

• Reducers
• hydrogen, methane, hydrocarbons, hydrazine,
  formic acid
• Oxidizers
• oxygen, air

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Hydrogen-Oxygen Fuel Cell
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Hydrogen-Oxygen Fuel Cell
Observed potential of 0.9 V
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Fuel Cell Operating Conditions

• Typical conditions
• 70 ºC - 250 ºC
• Efficiency comparison
• Fuel Cells - 75-95 efficient
• Combustion - typical power plant - 40
• Theoretical limit (Carnot cycle) is 62

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Research Areas

• Finding electrodes with catalytic surfaces which
  allow the reaction to occur rapidly.
• Reduce cell resistance.
• Remove products of the reaction.

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