Specifications

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Figure 11 – Charging States of Lithium Ion Battery
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Lithium ion batteries also experience a second stage of charging after the battery is
charged to 70%. This topping charge stage, however, does not always charge the
battery to max capacity. This is to prevent overcharging in the battery, as lithium ion
batteries become very stressed when they go over the threshold voltage. This,
combined with the fact the lithium ion batteries can operate at voltages below their
maximum, makes it unnecessary and undesirable to fully charge a lithium ion battery to
its threshold voltage. Though this will result in a lower runtime of the battery, it will
increase the overall life of the battery.
Though it is not desirable to overcharge any battery, lithium ion batteries are particularly
dangerous when the voltage passes the threshold. From prolonged charging, the
cathode material of the battery will begin oxidizing, become unstable, and start
producing carbon dioxide. Cell pressure also begins to rise, and may result in the
eruption of a safety membrane, possibly leading to the battery catching on fire. Under
these conditions, there is a threat that the battery will explode. Though most batteries
could experience these conditions, lithium ion batteries are more susceptible to them,
and would thus require the utmost attention while charging if used in our final design.
The charging process of each of the lead acid, nickel-metal hydride, and lithium ion
batteries, though discussed in detail above, will need to be further looked at once a
battery is picked for the final design. Our group will need to look at and fully understand
the charging procedure specified for the battery by the manufacturer and will need to act