Role of the rest period in capacity fade of Graphite/LiCoO₂ batteries

Degradation of lithium-ion batteries is known to be affected by various operational and environmental conditions, including temperature, discharge and charge C-rates, and depth of discharge. Another factor is the open rest period, which occurs in all laptops, smartphones, and electric vehicles that are kept connected to a charger, even after the battery is fully charged. This paper investigates the effects of the rest period after full charge on the capacity degradation behavior of graphite/LiCoO2 pouch batteries under four different ambient temperatures. The interplay between rest time, battery state of charge, and number of cycles is investigated to explain the capacity fade trends. A capacity fade trend model is then developed and applied to the experimental data, and the applicability of rest time as an accelerating stress factor for lithium-ion battery testing is presented.