PORTABLE POWER A Study of Cells and Batteries

A Portable Power History Lesson 1786 – Luigi Galvani Connected pieces of iron and brass to a frog’s leg and observed that the frog’s leg would twitch (much like my hand twitching after bringing the generator close to my arm) Connected pieces of iron and brass to a frog’s leg and observed that the frog’s leg would twitch (much like my hand twitching after bringing the generator close to my arm) He thought that living tissue could generate “animal electricity”. He thought that living tissue could generate “animal electricity”.

A Portable Power History Lesson 1800 – Alessandro Volta Could generate a voltage without using a frog’s leg Could generate a voltage without using a frog’s leg Created a “Voltaic Pile” – a combination of copper and zinc discs stacked in a pile with a piece of salt-soaked paper in between each of them Created a “Voltaic Pile” – a combination of copper and zinc discs stacked in a pile with a piece of salt-soaked paper in between each of them Found that this generated a voltage Found that this generated a voltage This is the creation of the first practical battery This is the creation of the first practical battery

Voltaic Pile

Electrochemical Cell Volta’s discovery eventually become known as an Electrochemical Cell a package of chemicals that is designed to generate a small amount of electricity A chemical reaction within the package will create the electricity A cell and a battery are not the same thing – connecting several cells together will create a battery

Composition of Modern-Day Cells In all cells, there are two electrodes surrounded by an electrolyte ELECTRODE – the two metals that make up an electrochemical cell (ex. Zinc and copper) ELECTROLYTE – a paste or liquid that conducts an electric current, and in which the electrodes are placed (ex. Salt-soaked paper) The above are only examples of electrodes and electrolytes – there are many alternatives The above are only examples of electrodes and electrolytes – there are many alternatives

Diagram of Electrochemical Cell

Dry Cells Wet Cells The electrolyte is made of a paste Used in all sorts of small electric devices (flashlights, CD players, etc.) These are the types of cells we used in the activity last week Use a liquid electrolyte (often sulfuric acid) Used in most car and truck batteries Cheaper and easier to make Safety is an issue because electrolyte is corrosive

Primary Cells Secondary Cells Cells that are used a single time and then thrown out Once the chemical reaction takes place inside cell, no more electricity can be produced Cheaper in the short term but can only use once “Rechargeable cells” The chemical reaction occurring can be repeated for perhaps thousands of uses To recharge, electricity will cause the reverse chemical reaction to occur to “restore” electrodes Cost more but will become more cost efficient over the long run

Batteries BATTERY – a combination of cells connected together Example – a 9-volt battery is actually V cells connected together Example – a 9-volt battery is actually V cells connected together

Types of Batteries Alkaline Battery Lead Acid Battery Nickel-Cadmium Battery Lithium Battery

Alkaline Battery Most commonly used battery type Two electrodes – manganese dioxide and powdered zinc Electrolyte – potassium hydroxide paste (DRY CELL) Used in flashlights, CD players, portable games Long lasting, can be expensive

Lead Acid Battery Liquid sulfuric acid is the electrolyte (WET CELL) Electrodes – Lead and Lead Dioxide Used in cars, trucks, motorbikes, snowmobiles, etc. Very dependable, heavy, electrolyte is corrosive

Nickel Cadmium Battery Electrolyte is potassium hydroxide Two electrodes – nickel hydroxide and cadmium oxide Used in cell phones, laptop computers, power tools, electric shavers Rechargeable (SECONDARY CELL)

Fuel Cells Auto companies are developing electric cars running on fuel cells rather than traditional batteries Creation of electricity through combining hydrogen fuel and oxygen The only by-products are water, heat and electricity Very environmentally friendly – no harmful pollutants will enter the air Difficult to find a way to produce hydrogen fuel cheaply and efficiently