Increasing the cycle life of lithium ion cells by partial state of charge cycling

• The cycle life of Li-ion cells can be increased inversely proportional to the depth of discharge.
• Cycle life can also be increased by discharging from a lower state of charge.
• Combining these two effects, the cycle life can be extended even further.
• The main contribution to the degradation is growth of the resistance of the solid-electrolyte interface.

In this study, the possibilities to enhance the cycle life of Li-ion cells were explored. Cells were charge-cycled in different ways. Discharging from the fully charged state down to several levels showed that the cycle life is determined by the total amount of transferred charge. Cycling a fixed amount of charge from a partially charged state leads to longer cycle life as the initial state of charge is lower. Impedance spectroscopy showed that the solid electrolyte interface forms the main contribution to the degradation of the cells.