Charging Rate
Battery life is also influenced by the charging rate.The capacity reduction at high discharge rates occurs because the transformation of the active chemicals cannot keep pace with the current drawn. The result is incomplete or unwanted chemical reactions and an associated reduction in capacity as noted in the paragraph on Chemical Changes above. This may be accompanied by changes in the morphology of the electrode crystals such as cracking or crystal growth which adversely affect the internal impedance of the cell. Similar problems occur during charging. There is a limitation as to how quickly the Lithium ions can enter into the intercalation layers of the anode. Trying to force too much current through the battery during the charging process results in surplus ions being deposited on the anode in the form of Lithium metal. Known as Lithium plating, this results in an irreversible capacity loss. At the same time, maintaining the higher voltages needed for fast charging can lead to breakdown of the electrolyte which also results in capacity loss. From the above we can expect that with each charge/discharge cycle the accumulated irreversible capacity loss will increase. Although this may be imperceptible, ultimately the capacity reduction will result in the cell being unable to store the energy required by the specification. In other words it reaches the end of its useful life and since the capacity loss is brought on by high current operation, we can expect that battery cycle life will be shorter, the higher the current it carries. The graph below demonstrates that this is the case in practice.