 Thermal runaway is posing big threat towards common electrochemical devices, such as lithium ion batteries and supercapacitors. It is caused by heat accumulated within electrochemical device and can cause devices to lose functionality, shorten service-life, or even cause hazardous fires and explosions. One effective approach to tackle thermal runaway is to break the electrochemical reaction Arrhenius thermal loop by introducing reaction inhibiting components into the system. Herein, through facile wet casting method, a temperature responsive polymer, poly(N-isopropylacrylamide) (PNIPAM) was cast into thin film and sandwiched in between polypropylene (PP) to make into a temperature responsive separator. It was found that once the temperature rose to 70 °C, instead of increasing in capacitance like in the control, PNIPAM-included batches decreased in capacitance. This capacitance reduction was mainly contributed by increased charge transfer resistance, which was caused by the sol–gel transition and precipitating PNIPAM chains residing upon PP membrane. A similar capacitance reduction was also observed for the ferricyanide redox system. Further investigation also revealed thicker PNIPAM films exhibited enhanced capacitance reduction and scan rate dependency. Temperature responsive polymer separators may prove to be an effective method to suppress high temperature electrochemical reactions and thus offer promise to reversible, thermally stabilized electrochemical devices.