Building a Thermal Shutdown Cathode for Li-Ion Batteries Using Temperature-Responsive Poly(3-Dodecylthiophene)

Thermal shutdown electrodes can provide a safety control for lithium-ion batteries (LIBs) under a wide range of applications. However, developing such an electrode is difficult due to the lack of electrochemically compatible materials with suitable temperature-responsive functions. Herein, a new thermal-responsive conductive polymer-poly(3-dodecylthiophene) (P3DDT)-is reported, and this polymer is used as a coating layer of electrode substrate to fabricate a thermal shutdown cathode of Al/P3DDT/LiCoO2 (LCO-P3DDT). Benefited by the high room-temperature conductivity, strong positive-temperature-coefficient (PTC) effect, and appropriate transition temperature of the P3DDT layer, the LCO-P3DDT cathode not only exhibits similar electrochemical performance as a conventional LCO cathode at normal operating temperatures, but also plays a desired shutdown function to switch off the electrode reaction at elevated temperatures of >= 90 degrees C, thus protecting the cell from thermal runaway. This PTC effect of p-doped P3DDT is found to be given rise by the thermal de-doping of anions from the doped P3DDT skeleton at elevated temperature. This temperature-responsive mechanism may provide a new insight for designing better thermal shutdown electrodes for a wide variety of battery applications.