|MadSci Network: Chemistry|
Thank you for your question, Miriam. Probably others in the MadSci Network, like Australia's own John Christie, are better qualified to answer you, but let me give it a go. Strictly defined, a "cell" produces a voltage difference and produces electric power through chemistry. Strictly defined, a "battery" comprises cells in series to produce voltages higher than a single cell can. For example, a Nickel-Cadmium (NiCad) cell produces 1.2 volts and a 6.0 volt NiCad battery comprises 5 NiCad cells in series. But common use allows calling both of them "batteries." Cells - rechargeable or not - all use Redox (Reduction-Oxidation) reactions to produce their voltage difference. http://www.duracellusa.com/Education/index.html is a site explaining batteries. Click on Chemistry for (guess what) a description of the chemistry. You will see the redox reactions taking place in a Zinc-Carbon cell. The zinc serves as the anode, where oxidation produces electrons that want to get to the cathode, but they need a path. Provide that path, and they will go, doing work (in the physics sense) as they go. At the cathode, reduction reaction with the cathode material, manganese dioxide, takes place. Note that the carbon doesn't enter into the chemistry. It just provides a place for reduction. http://www.chemistry.ucsc.edu/stanley/teaching/batteries/recharge.html is a site from University of California, Santa Cruz, USA, describing the anode oxidation and cathode reduction for a NiCad cell and a Lead-Acid cell. Professor Michael Lerner, and scientist, Frank McLarnon, in answering a question not too different from yours, at: http://www.scientificamerican.com/askexpert/chemistry/chemistry5.html explain what makes some cells rechargeable and others not. It boils down to chemical and physical reversibility. If, after discharging a cell through a load, you can restore the original chemical and physical configuration to the cell by passing current backwards, (requires voltage higher than the cell voltage), then the cell will be reversible. Another name for an irreversible cell is primary cell. Another name for a reversible cell is secondary cell. Hope this helps. Larry Skarin
Try the links in the MadSci Library for more information on Chemistry.