With growing environmental issues and energy constraints worldwide, the automotive sector is rapidly transitioning to new energy solutions. Lithium batteries, being the predominant energy storage technology for electric vehicles, require extensive scientific investigation. To address this, the paper first analyzes the operational and aging processes of lithium batteries to derive their equivalent circuit and degradation models. Next, by studying heat generation mechanisms, a thermal transfer model is formulated to represent the internal and external temperature interactions, heat transfer and heat dissipation of the lithium battery, and then carries out the parameter coupling to establish the coupled model of electricity-heat-aging, and finally, for the 18,650 battery, the basic parameters of the coupling model are identified. To verify the coupling model's precision, the output voltages under FUDS conditions are compared between two scenarios: one incorporating the aging factor and the other excluding it.