Common types of rechargeable batteries include lead-acid, nickel cadmium, and lithium ion batteries. They work through the oxidation and reduction of their two cells, each of which contains one of the half reactions.
During charging of the battery, the anode material is oxidized, releasing electrons, and the cathode material is reduced, absorbing electrons. The opposite reaction occurs during discharge, which provides the flow of electrons that constitutes the current produced. In the nickel-cadmium battery, the following reaction occurs during discharge:
Cd + 2OH– → Cd(OH)2 + 2e–
2NiO(OH) + 2H2O + 2e– → 2Ni(OH)2 + 2OH–
The electric potentials for these reactions are E = +0.4 V and E = +0.6 V, respectively.
The energy density and ability to hold charge in batteries varies depending on the type of material used. Typically, the greater the difference in reduction potential and oxidation potential of the two components, the greater the charge that can be held in the battery. For example, lithium ion batteries have a potential of about 3.6 V, whereas typical alkaline batteries which are non-rechargeable have a potential of only 1.5 V.
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