Electric double layer capacitors consist of two identical electrodes usually made of a mixture of (i) carbon-based material, (ii) binder, and (iii) other additives (e.g. carbon black). These constituents can influence the thermal behavior in the positive and negative electrodes. This study aims to investigate the effect of electrode composition on the thermal behavior of the EDLC electrodes using an isothermal calorimeter. The heat generation measurements were performed on five devices with different electrode compositions in 1M of LiPF₆ in EC:DMC. First, the irreversible heat generation rate was in excellent agreement with Joule heating predicted from the internal resistance. The reversible heat generation rates in electrodes containing CMC were significantly different in the positive and negative electrodes. It was exothermic during charging and endothermic during discharging at the positive electrodes. By contrast, at the negative electrodes, it featured both exothermic and endothermic heat generation during both charging and discharging. However, in absence of CMC in the electrode, the reversible heat generation rates at the positive and negative electrodes were nearly identical. This can be attributed to that the charging mechanism in the absence of CMC was the same in both electrodes. However, in presence of CMC, the anionic functional groups formed in the electrodes interact with cations in the negative electrodes resulting in asymmetric heat generation associated with asymmetric charging mechanism.