Cells and Batteries

1. Cells and Batteries

2. Electric Circuit: a closed path along which electrons flow - To function, a circuit needs an energy source which is often a battery

3. Electric and Hybrid Vehicles • Electric cars were first built a century ago • Electric vehicles use only electricity; hybrid vehicles use batteries and a gasoline motor

4. Voltaic Slide • Alessandro Volta designed the first battery in 1800 • he stacked alternating silver and zinc discs separated by cloth soaked in salt water known as a voltaic "pile"

5. From Cells to Batteries • The batteries we know are actually voltaic cells • Voltaic cells: generate an electric current by chemical reactions that involve two different metals and a conducting solution • Battery: A connection of two or more cells: you make a battery when you place two or more cells in a flashlight • Electrodes: The metal terminals on a cell made of different metals with different abilities to hold onto electrons • The electrodes are submersed in a conducting solution known as an electrolyte • Chemical reactions take place at the surface of each electrode and involves the movement of electrons

6. Example: Aluminum gives up 3 electrons forming Al3+ which is attracted to the copper electrode. The electrons flow through the wire to the copper electrode.

7. http://www.youtube.com/watch?annotation_id=annotation_482751&feature=iv&src_vid=KkRwuM4S8BQ&v=gWKOjncBMCQhttp://www.youtube.com/watch?annotation_id=annotation_482751&feature=iv&src_vid=KkRwuM4S8BQ&v=gWKOjncBMCQ

8. Types of Cells Dry Cells: • Most cells are dry cells • Contain electrolyte that is a paste • Invented in 1887 by Carl Gassner • Gassner's cell used carbon and zinc as electrodes and plaster soaked with NH4Cl as electrolyte • Little has changed with the modern dry cell

9. Wet Cells: Contain a liquid electrolyte (usually a mixture of sulphuric acid)

10. Primary Cell: • A cell that only be used once and then is discarded • Secondary Cell: • A cell that can be recharged by passing an electric current in the opposite direction through the cell • The charging reverses the chemical reactions restoring the cell to full capacity • Secondary cells: lead-acid batteries, nickel-cadmium cells, nickel metal hydride cells and lithium-ion cells

11. Fuel Cells • Originally designed for the US space program to keep astronauts warm • Generate electricity through the chemical reactions of fuel stored outside the cell • A hydrogen fuel cell combines hydrogen stored in a tank with O2 from the air • The only by-products are heat and H2O

12. Fuel Cell Vehicles • Ballard Power Systems (BC Canada), develops and makes hydrogen fuel cells • Ballard is collaborating with other companies to make fuel cells for cars and city buses

13. Solar Cells • Earth receives more energy from the Sun in one hour than all energy used by humans in one year!! Solar Cell: converts sunlight into electrical energy • When sunlight strikes a silicon semiconductor, electrons are released from atoms providing electricity that can be used