A lithium-ion cell under discharge generates thermal energy (Q) through five different internal parameters or modes: the electrolyte resistance (R s), anode resistance (R a), cathode resistance (R c), and entropy changes in the cathode (ΔS c), and the anode (ΔS a). This work demonstrates a set of tools to measure/quantify the heat generated by each parameter separately during discharge. These five sources are not dependent upon each other; they are dependent on the state of charge and the environmental temperature (T env). The Q generated by each mode varies with degree of discharge and T env. R s generates most of the Q in the −10 °C to 40 °C range; R c becomes significant at T env <20 °C. Constant current discharge does not cause a monotonic increase in anode and cathode temperatures (T a and T c), due to the direction of change in ΔS c and ΔS a. Negative change in ΔS a for the carbon anode cools it, causing the T a to level off and even decrease with increased discharge. ΔS c for lithium manganese oxide cathode is positive at some SoC and negative at others, preventing a monotonic increase in T c. Measuring the five Qs separately opens the opportunity to study thermal-runaway from the perspective of the anode, cathode and electrolyte.