A Practical Longevity Model for Lithium-Ion Batteries: De-coupling the Time and Cycle-Dependence of Capacity Fade

Introduction To predict the longevity of a rechargeable battery in a given application, it is necessary to know how the rate of capacity loss (i.e., capacity fade rate) is influenced by usage condition. In lithium-ion cells, capacity fade is accepted as having separate timeand cycledependent components [1, 2]. On the other hand, highly accelerated cycling primarily assesses the cycledependent fade only, due to the short timescale of the test. Therefore, use of accelerated cycling to predict long-term performance is likely to over-predict longevity by underestimating the time-dependent fade.