To meet the requirements of electronic vehicles (EVs) and hybrid electric vehicles (HEVs), the high energy density LiNi0.8Co0.15Al0.05O2 (NCA) cathode and Si–C anode have attracted more attention. Here we report the thermal behaviors of NCA/Si–C pouch cell during the charge/discharge processes at different current densities. The total heat generations are derived from the surface temperature change during electrochemical Li+ insertion/extraction in adiabatic surrounding. The reversible heat is determined by the entropic coefficients, which are related with open-circuit voltage at different temperatures; while the irreversible heat is determined by the internal resistance, which can be obtained via V–I characteristic, electrochemical impedance spectroscopy and hybrid pulse power characterization (HPPC). During the electrochemical process, the reversible heat contributes less than 10% to total heat generation; and the heat generated in charge process is less than that in discharge process. The results of thermal behaviors analyses are conducive to understanding the safety management and paving the way for building a reliable thermal model of high energy density lithium ion battery.