Electrochemical Cells (Batteries) SNC1D

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 can’t be recharged. When these materials have been used up, the cell is said to be discharged and cannot be recharged.*

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.

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.

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.

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.

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

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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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. Modern Battery Chemicals http://electronics.howstuffworks.com/battery7.htm

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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? Milliamp-Hour & 9 Volt Cutaway It contains six, very small batteries producing 1.5 volts each in a serial arrangement!

Battery Cutaway

Figure 7 One of the Cells in a 12-V Lead Storage Battery (LSM 14.1C)

Figure 6 A Common Dry Cell Battery (LSM 14.1C)