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Battery Chargers

Type of Primary Batteries can be summarized as follows:

Battery Type	Advantages	Disadvantages	Applications
Alkaline Cell	High energy density, long shelf life, good leak resistance, performs well under heavy or light use.	Costlier than zinc-carbon cell but more efficient	General purpose, digital, high drain appliances - CD Players, Toys, Tape Recorders
Aluminum/Air Cell	Can operate exposed to sea water (neutral salt solution), easily replaceable electrolytes/electrodes	Anode quickly degrades, short-shelf life,short operational life	Marine applications
Leclanché Cell (Zinc Carbon or Dry Cell)	Cheap and common (oldest available battery type)	Poor performance under heavy or continuous use.	Flashlights, toys, moderate drain use
Lithium Cell	Very high energy density, long shelf life, long operational life	Poor performance under heavy use, vulnerable to leaks or explosions	Pacemakers, defibrillators, watches, meters, cameras, calculators, portable, low-power use
Mercury Oxide Cell	Higher energy density than (Zn/MnO2) alkaline cell	High cost and being phased out due to toxicity concerns	Small electronic equipment, hearing aids, photography, alarm systems, emergency beacons, detonators, radio microphones
Zinc/Air Cell	Environmentally benign, cheap, very high energy density, and virtually unlimited shelf life	Short operational life, low power density	Hearing aids, medical monitoring instruments, pagers

SECONDARY BATTERIES

a) Iron Nickel Cells
Anode:Iron
Cathode:Nickel oxyhydroxide
Electrolyte:Potassium hydroxide
This battery was introduced by Thomas Edison in 1905. It is a very robust battery: it can withstand overcharge, overdischarge, and remaining discharged for long periods of time without damage. It is good for high depths of discharge and can have very long life even if so treated. It has low energy density, a high self-discharge rate, and evolves hydrogen during both charge and discharge. It is often used in backup situations where it can be continuously charged and can last for 20 years.
The chemistry involves the movement of oxygen from one electrode to the other:

3Fe + 8NiOOH + 4H₂O=8 Ni(OH)₂ +Fe₃O₄.

Half-reactions:

Fe + 2OH- -> Fe(OH)₂ +2e-
3Fe(OH)₂ + 2OH- -> Fe₃O₄ + 4H₂O + 2e-

The open circuit voltage of this system is 1.4 V, and the discharge voltage is about 1.2 V. The electrolyte is 30% KOH solution, with some additives

b)Lead-acid Cells

Anode: Sponge metallic lead

Cathode: Lead dioxide (PbO₂)

Electrolyte: Dilute mixture of aqueous sulfuric acid

Invented in 1859 by French physicist Gaston Planté, are a type of galvanic cell and are the most commonly used rechargeable batteries today. They also represent the oldest design with one of the worst energy-to-weight ratios, although the power-to-weight ratio can be quite good. Also, the energy-to-volume ratio is good compared to other types of batteries. They are cheap and can supply high surge currents needed in starter motors. Every reasonably modern car uses a lead-acid battery for this purpose. They are also used in vehicles such as forklifts, in which the low energy-to-weight ratio may in fact be considered a benefit since the battery can be used as a counterweight.

Lead-acid car batteries consist of six cells of 2 V nominal voltage. Each cell contains (in the charged state) electrodes of lead metal (Pb) and lead (IV) oxide (PbO₂) in an electrolyte of about 37 % w/w sulfuric acid (H₂SO₄). Modern designs have gelified electrolytes. In the discharged state both electrodes turn into lead(II) sulfate and the electrolyte turns into water. (This is why discharged lead-acid batteries can freeze.)

The chemical reactions are (charged to discharged):

Anode (oxidation): Pb + SO₄2- -> PbSO₄ + 2e- E = 0 .356 V
Cathode (reduction): PbO₂ + SO₄2- + 4H+ + 2e- -> PbSO₄ + 2H₂O E = 1.685V

Because of the open cells with liquid electrolyte in most cheap car batteries, overcharging with excessive charging voltages will generate oxygen and hydrogen gas, forming an extremely explosive mix. This should be avoided. Caution must also be observed because of the extremely corrosive nature of sulphuric acid.