Temperature Dependence of the Intercalation/Deintercalation Dynamics in Ionic Liquid-based Multilayer Graphene Devices

In this work, we report the dependency of electrochemically-driven intercalation of multilayered graphene devices on the temperature range from -80℃ to 100℃. The device consists of a Chemical vapor deposition grown multilayer graphene (MLG) anode and a copper cathode separated by an alumina membrane impregnated with ionic liquid [DEME⁺][TFSI^-]. Application of a positive voltage of 3.5V-4V drives the intercalation of [TFSI^-] anions into the interstitial spaces in the MLG, resulting in dramatic changes in the free carrier density and thermal emissivity of the material. The intercalation of [TFSI^-] anions shows an increasing trend with the increase in temperature, as observed from the Raman spectrum over the temperature range. The apparent temperature change due to intercalation is also a function of device temperature, with a maximum apparent temperature change of 22.4℃, as measured by a thermal imaging camera sensitive over the range from 7 µm to 14 µm. This change in the thermal emissivity arises from a two-order-of-magnitude shift in the free carrier concentration upon intercalation, which ultimately modulates the complex dielectric function of the material (i.e., ε(ω) = ε₁ + iε₂). While our previous efforts were limited to static temperature measurements, the work reported here explores the temperature dependence of this phenomenon.