How does a battery convert chemical energy into electrical energy?
The ingenuity people used in harnessing waterpower can be seen in this medieval-style mill. The waterwheel is turned by a stream and is connected to a shaft that leads into the building. At the other end of the shaft is a gear. The connection of a series of gears translates the power from the stream to a shaft that drives a millstone, which grinds flour from grain.
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A battery converts chemical energy into electrical energy through an electrochemical reaction known as an oxidation-reduction (redox) process.12
This process relies on two electrodes—an anode (negative plate) and a cathode (positive plate)—separated by an electrolyte that allows ions to pass between them. The conversion occurs because the redox reaction is spatially separated:32
- Oxidation: At the anode, a reducing agent loses electrons.42
- Reduction: At the cathode, an oxidizing agent gains those electrons.42
Because these reactions occur at separate electrodes, the electrons are forced to travel through an external circuit to move from the anode to the cathode. This flow of electrons through the external circuit constitutes the electric current that powers devices. The chemical potential difference between the materials at the two electrodes creates the electromotive force, or voltage, that drives this current. Once the chemical reactants are consumed, the battery can no longer produce electricity and is considered exhausted.143