Voltaic cell

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aka battery, rechargeable battery, storage battery, dry cell, wet cell

We use the term "voltaic cell" to encompass any source of steady voltage potential which sources the energy from a chemical, rather than mechanical, source. Mechanical sources of voltage potential are referred to here as generators.

General notes

Terminology: Anode, Cathode, Electrode, Plate

Terminology problems (no pun intended): The terms anode and cathode are confusing in this context. Consider a voltaic cell driving a chemical reaction in an electrolysis bath. The anode from the perspective of the electrolyte in the battery is the cathode from the perspective of the electrolyte in the bath being powered. Solution: (also no pun intended) We use "positive plate" and "negative plate" to differentiate, the positive plate of the battery is connected to the positive terminal. It receives electrons from the circuit. Likewise the negative plate of the battery supplies electrons to the cicuit. Electrode is used as a neutral (third pun also not intended) term.

Internal charge carriers

  • Positive charge carriers (usually H+) travel from the negative plate to the positive plate. (In the same direction as the current.)
  • Negative charge carriers (usually OH-) travel from the positive plate to the negative plate. (In the opposite direction as the current.)

Plate potential and cell voltage

While you should be able to add the absolute value of the potentials of the plates to get the cell voltage, the two values are, in practice, unrelated. Too many microphysical changes take place to simply add them up and get the result.

Wet cells

Wet cells are defined herein to be "battery" type devices where the electrolyte is neither solid nor fixed within a solid.

Lead-acid cell

Lead-acid cell
Cell
Electrolyte sulfuric acid
Net reaction Pb + PbO2 + 2 H2SO4 2 PbSO4 + 2 H2O
Voltage 2v 
Internal charge carrier H+ 
Energy density, volume(J/L) 7
Positive plate
Material lead (II) oxide
Reaction PbO2(s) + H2SO4(aq) + 2 H +  + 2 e- PbSO4(s) + 2 H2O(l)
Negative plate
Material lead
Reaction PbO(s) + H2SO4(aq) PbSO4 + 2 H +  + 2 e

The standard by which all other voltaic cells are measured.

Advantages

  • Easy to recharge at 2.17-2.34v reverse potential.
  • Simple to recycle since both plates become the same substance.

Disadvantages

  • The container (cell) must be able to withstand concentrated sulfuric acid

Hazards

  • Can evolve hydrogen gas

Construction details

  • A glass or ceramic container filled with sulfuric acid, with two plates (lead and lead (II) oxide) suspended in the solution but separated from each other.
  • The lead (II) oxide plate is frequently made of a lead frame press-filled with lead (II) oxide.


LeClanch Cell

LeClanche cell
Cell
Electrolyte Ammonium chloride
Net reaction Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) ZnCl2 + Mn2O3(s) + H2O + 2 NH3
Voltage 1.4v 
Internal charge carrier H+
Positive plate
Material Manganese dioxide
Reaction 2 MnO2 + 2 H +  + 2 e- Mn2O3 + H2O
Negative plate
Material Zinc
Reaction Zn + 2 NH4Cl 2 H +  + 2 e- + ZnCl2 + 2 NH3

Advantages

  • long shelf life

Disadvantages

  • Brief duty period (internal resistance)
  • Produces ammonia (low vapor pressure, irritant, noxious) during normal operation

Hazards

Construction Details


Trough Cell

Volta cell
Cell
Electrolyte cloth or paper soaked in water containing salt
Net reaction Zn(s) + Cu(s) + H2O ZnSO4 + Cu(s) + H2
Voltage 1.4v 
Internal charge carrier H+
Positive plate
Material Copper
Reaction Cu + 2 H +  + 2 e- Cu + H2
Negative plate
Material Zinc
Reaction Zn + H2SO4 ZnSO4 + 2 H +  + 2 e-

Advantages

  • Requiring only copper, zinc, salt water, and a nonconductive container, a Trough cell is probably the simplest to implement.

Disadvantages

  • Low available energy (internal resistance shuts down cell)
  • Rapid rise in internal resistance
  • This cell is not easily recycled since the zinc sulfate must be reduced to elemental zinc again

Hazards

  • Produces hydrogen gas during normal operation

Construction Details

Trough containing saltwater filled with zinc-silver-cloth triplets

Dry Cells

Zinc-Carbon

Gassner dry cell
Cell
Electrolyte cloth or paper soaked in ammonium chloride
Net reaction Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) Mn2O3(s) + Zn(NH3)2Cl2(aq) + H2O(l)
Voltage 1.5v 
Internal charge carrier Cl-
Positive plate
Material manganese dioxide
Reaction 2 MnO2(s) + 2 e− + 2 NH4Cl(aq) Mn2O3(s) + 2 NH3(aq) + H2O(l) + 2 Cl− 
Potential(v) +0.74
Negative plate
Material Zinc
Reaction Zn(s) + 2 Cl- ZnCl2(aq) + 2 e- 
Potential(v) -0.7626

Advantages

  • Simple construction dry cell

Disadvantages

  • Ammonium chloride electrolye is not easy to produce
  • Hard to recycle, since zinc is removed completely

Hazards

Construction Details

  • Metal-capped carbon rod is conductor to manganese dioxide core
  • Electrolye typically completely absorbed in paper, but could be sawdust, etc
  • Zinc forms outer container, so no additional material required


Alkaline

Alkaline cell
Cell
Electrolyte potassium hydroxide (not consumed)
Net reaction Zn(s) + 2 MnO2(s) ZnO(s) + Mn2O3(s)
Voltage 1.5v 
Internal charge carrier OH-
Positive plate
Material mixture of carbon and manganese dioxide
Reaction 2 MnO2(s) + H2O(l) + 2 e- Mn2O3(s) + 2 OH− 
Potential(v) +0.15
Negative plate
Material Zinc powder
Reaction Zn(s) + 2 OH− ZnO(s) + H2O(l) + 2 e− 
Potential(v) -1.28

Advantages

  • High energy density
  • Long shelf life
  • High discharge rate
  • Electrolyte is not consumed
  • Mn and Zn do not intermix, but remain separated by permeable separator (easier purification)

Disadvantages

  • Construction is more complicated
    • may require steel
    • Separate conductive electrode materials for anode and cathode
    • Requires conductive neutral barrier between manganese dioxide and carbon/zinc/KOH mixture

Hazards

  • Can leak potassium hydroxide

Construction Details

  • Concentric cylinders (outer to inner)
    • steel case
    • manganese dioxide / carbon mixture
    • conductive separator permeable to KOH
    • Zinc powder
    • steel spike electrode


Silver oxide

Silver oxide cell
Cell
Electrolyte potassium hydroxide
Net reaction 4 Zn + Ag4O4 4 ZnO + 4 Ag
Voltage 1.59v 
Internal charge carrier OH-
Positive plate
Material Mixture of silver peroxide and potassium hydroxide.
Reaction Ag4O4(s) + 4 H2O(l) + 8 e- 8 Ag(s) + 8 OH- 
Potential(v) +0.34
Negative plate
Material zinc
Reaction Zn + 2 OH- ZnO + H2O + 2 e- 
Potential(v) -1.25

Advantages

  • Very high energy density
  • Long shelf life
  • High discharge rate
  • Electrolyte is not consumed

Disadvantages

Hazards

  • Can leak KOH

Construction Details


See Also

  • Lithium Cells[1]

References

  1. Types of Lithium Ion
    courtesy Battery University.