Why can rechargeable batteries only be recharged a certain amount of times?
1 Answer
The interface between the electrodes eventually becomes blocked by residues from the state-changes in the materials.
Explanation:
A battery depends on the change of the oxidation states of two different materials. In rechargeable batteries this can be reversed (recharged) by an opposite and somewhat higher-voltage charge.
The recharging process is not 100%, and during both discharge and recharge cycles a portion of the battery electrodes either does not completely change back to the original state, and/or remains in a stable state on the electrode interface. This both decreases the capacity of the battery and reduces the ability of further cycles due to the blocking of previously open ion exchange pathways.
Eventually, the available discharge capability is less than necessary for the desired battery use. Because a "spent" rechargeable battery still contains significant amounts of active electrode materials - many of which are harmful to the environment in general - they should be disposed of carefully and ideally, recycled.
