A lithium-ion capacitor (LIC) is a hybrid energy storage device combining the energy storage mechanisms of lithium-ion batteries (LIBs) and electric double-layer capacitors (EDLCs), and it incorporates the advantages of both technologies and eliminates their drawbacks. This technology has shown a long cycle life in a wide temperature range. This article presents a lifetime model for LIC technology considering different operating conditions and stress factors that affect the lifetime of LICs. The capacity degradation trend and internal resistance growth are discussed thoroughly. Later, the capacity degradation and internal resistance growth models are explained. Finally, the lifetime model is combined with the developed electrothermal model and is validated using a validation profile that involves dynamic cycling in a variable temperature profile with an acceptable error of less than 5%.