Electrochemical%20Cells%20(Batteries)

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Electrochemical Cells (Batteries)

• SNC1D

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Electrochemical Cells

• Cell is another name for battery.
• Cells are classified as either primary or
  secondary.
• In a primary cell, chemical reactions use up some
  of the materials in the cell as electrons flow
  from it. They cant be recharged.
• When these materials have been used up, the cell
  is said to be discharged and cannot be recharged.

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Primary Cells

• Primary cells can be further classified as either
  wet or dry.
• The primary wet cell was first developed in 1800
  by Italian scientist, Alessandro Volta.
• This cell is therefore called the voltaic cell.

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Primary Wet Cells

• A wet cell is made up of two pieces of metal that
  are placed in a liquid.
• The metal plates, usually zinc and copper, are
  called electrodes.
• The liquid in the cell is called the electrolyte.
• An electrolyte is any liquid that conducts an
  electric current.

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Primary Wet Cells

• Electrons collect at the positive and negative
  terminals of the cell.
• The cell will only discharge when connected to a
  closed circuit.

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Primary Dry Cells

• The dry cell is similar to the wet cell, but the
  electrolyte is a moist paste instead of a liquid.
• When most of the negative electrode has been used
  up by the chemical reaction, the electrons stop
  flowing and the cell is discharged.
• A group of cells make up a battery.

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• Simple Primary Wet Cell

• Consists of two different metal electrodes
  immersed in
• acidic liquid
• electrolyte.
• In solution, the
• acid molecules
• separate into
• positive and
• negative ions.

Figure 4-1 A simple primary cell
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Secondary Cells

• Unlike primary cells, a secondary cell can be
  discharged and recharged many hundreds of times.
• Secondary cells are often referred to
  rechargeable batteries.
• Secondary cells are so named since there are two
  chemical processes involved
• one to discharge the cell
• one to charge the cell
• A car battery consists of a group of secondary
  cells.

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Battery Arrangements
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Modern Battery Chemicals
Modern Battery Chemicals Modern batteries use a
variety of chemicals to power their reactions.
Typical battery chemistries include Zinc-carbon
battery - Also known as a standard carbon
battery, zinc-carbon chemistry is used in all
inexpensive AA, C and D dry-cell batteries. The
electrodes are zinc and carbon, with an acidic
paste between them that serves as the
electrolyte. Alkaline battery - Used in common
Duracell and Energizer batteries, the electrodes
are zinc and manganese-oxide, with an alkaline
electrolyte. Lithium photo battery - Lithium,
lithium-iodide and lead-iodide are used in
cameras because of their ability to supply power
surges. Lead-acid battery - Used in automobiles,
the electrodes are made of lead and lead-oxide
with a strong acidic electrolyte (rechargeable).
Nickel-cadmium battery - The electrodes are
nickel-hydroxide and cadmium, with
potassium-hydroxide as the electrolyte
(rechargeable). Nickel-metal hydride battery -
This battery is rapidly replacing nickel-cadmium
because it does not suffer from the memory effect
that nickel-cadmiums do (rechargeable).
Lithium-ion battery - With a very good
power-to-weight ratio, this is often found in
high-end laptop computers and cell phones
(rechargeable). Zinc-air battery - This battery
is lightweight and rechargeable. Zinc-mercury
oxide battery - This is often used in
hearing-aids. Silver-zinc battery - This is used
in aeronautical applications because the
power-to-weight ratio is good. Metal-chloride
battery - This is used in electric vehicles.
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Battery Basics
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Milliamp-Hour 9 Volt Cutaway
If you arrange four of these 1.25-volt, 500
milliamp-hour batteries in a serial arrangement,
you get 5 volts (1.25 x 4) at 500 milliamp-hours.
If you arrange them in parallel, you get 1.25
volts at 2,000 (500 x 4) milliamp-hours. Have
you ever looked inside a 9-volt battery?
It contains six, very small batteries producing
1.5 volts each in a serial arrangement!
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Battery Cutaway
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Figure 7 One of the Cells in a 12-V Lead Storage
Battery (LSM 14.1C)
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Figure 6 A Common Dry Cell Battery (LSM 14.1C)