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Battery Chargers

There are two types of Batteries:

1. Primary or Disposable Batteries

2. Secondary or Rechargeable Batteries

PRIMARY BATTERIES

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a) Alkaline Cells
Anode: Zn
Cathode: Manganese dioxide (MnO2) powder
Electrolyte: Potassium hydroxide (KOH)

Alkaline batteries have all but superseded the old zinc-carbon cells and even zinc chloride in terms of performance. The alkaline cell delivers up to ten times the ampere-hour capacity at high and continuous drain conditions, the performance at low temperature also being superior. With most major brands now guaranteed leak proof it is the consumers most popular primary cell.
Zinc in a powdered form increases the surface area of the anode, allowing more particle interaction. This lowers the internal resistance and increases the power density. The cathode, MnO2, is synthetically produced because of its superiority to naturally occurring MnO2. This increases the energy density. Just as in the zinc carbon cell, graphite is added to the cathode to increase conductivity. The electrolyte, KOH, allows high ionic conductivity. Zinc oxide is often added to slow down corrosion of the zinc anode. A cellulose derivative is thrown in as well as a gelling agent. These materials make the alkaline cell more expensive than the zinc-carbon, but its improved performance makes it more cost effective, especially in high drain situations where the alkaline cell's energy density is much higher.

Half-reactions:

Zn + 2 OH- -> ZnO + H2O + 2 e-
2 MnO2 + H2O + 2 e- ->Mn2O3 + 2 OH-

Overall reaction:

Zn + 2MnO2 -> ZnO + Mn2O3 E=1.5 V

The Alkaline battery comes in many shapes and sizes the most popular begin the AA or LR6, other types / sizes include; AAA, AAAA, C, D, PP3, button cell, high voltage camera battery.

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b) Aluminium/Air Cells
Anode: Al
Cathode: O2
Electrolyte: KOH or neutral salt solution
Aluminum is attractive for such cells because it is highly reactive, the aluminum oxide protective layer is dissolved by hydroxide electrolytes, and it has a nice, high voltage.

Half-reactions:
Al + 4 OH--> Al(OH)4- + 3e
3/4 O2 + 3/2 H2O + 3e-> 3OH-
Overall reaction:

Al + 3/2 H2O + 3/4 O2 -> Al(OH)3 E=2.75 V
As mentioned above, alkali (chiefly potassium hydroxide) electrolytes are used, but so also are neutral salt solutions. The alkali cell has some problem with the air electrode, because the hydroxide ion makes a gel in the porous electrode, polarizing it. The typical aluminum hydroxide gel is a problem on either electrode because it sucks up a lot of water. Using a concentrated caustic solution prevents this, but is very reactive with the aluminum electrode, producing hydrogen gas. Another way to prevent the gel formation is to seed the electrolyte with aluminum trihydroxide crystals. These act to convert the aluminum hydroxide to aluminum trihydroxide as the crystals grow. To prevent hydrogen gas evolution tin and zinc have been used as corrosion inhibitors. A number of additives are used to control the reactions. A disadvantage of the alkaline electrolyte is that it reacts with atmospheric carbon dioxide.

Air electrodes of Teflon-bonded carbon are used without a catalyst.

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c) Leclanché Cell (Zinc Carbon or Dry Cell) Anode: Zinc
Cathode: Manganese Dioxide (MnO2)
Electrolyte: Ammonium chloride or zinc chloride dissolved in water
In an ordinary Leclanché cell the electrolyte consists (in percent of atomic weight) of 26% NH4Cl (ammonium chloride), 8.8% ZnCl2 (zinc chloride), and 65.2% water.

The overall cell reaction can be expressed:
Zn + 2MnO2 +2NH4Cl -> 2MnOOH + Zn(NH3)2Cl2 E=1.26
The electrolyte in a typical zinc chloride cell consists of 15-40% ZnCl2 and 60-85% water, sometimes with a small amount of NH4Cl for optimal performance.
The overall cell reaction of the zinc chloride as the electrolyte can be expressed:

Zn + 2MnO2 + 2H2O + ZnCl2 -> 2MnOOH + 2Zn(OH)Cl
MnO2, is only slightly conductive, so graphite is added to improve conductivity. The cell voltage increases by using synthetically produced manganese dioxide instead of that found naturally (called pyrolusite). This does drive the cost up a bit, but it is still inexpensive and environmentally friendly, making it a popular cathode.

These cells are the cheapest ones in wide use, but they also have the lowest energy density and perform poorly under high-current applications. Still, the zinc carbon design is reliable and more than adequate for many everyday applications.