Effects of Constituent Materials on Heat Generation in Individual EDLC Electrodes

This study aims to investigate the effect of electrode composition on heat generation in electric double layer capacitor (EDLC) electrodes under galvanostatic cycling. EDLCs consist of two identical electrodes usually made of a mixture of (i) carbon-based material, (ii) binder, and (iii) other conductive additives. These constituents were found to influence the capacitance and internal resistance of the device and the heat generation rate in the positive and negative electrodes. Indeed, the heat generation rate was measured using an isothermal calorimeter in both electrodes of five EDLC devices with different electrode compositions but the same electrolyte consisting of 1 M LiPF 6 in EC:DMC. The reversible heat generation rates at the positive and negative electrodes were nearly identical in absence of CMC. However, in devices containing CMC, the reversible heat generation rate in the positive electrode was significantly larger than that in the negative electrode. Such asymmetric heating was attributed to asymmetry in the charging mechanism due to the overscreening effect caused by interactions between the anionic functional groups of CMC and the cations at the negative electrode.