Composite PEDOT:PSS‐PEO Layers for Improving Lithium Batteries**

Abstract This work investigates the application of poly(3,4‐ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) with polyethylene oxide (PEO) in lithium batteries (LIBs). This composite film comprising PEDOT:PSS and PEO was 3D printed onto a carbon nanofiber (CNF) substrate to serve as a layer between the polypropylene (PP) separator and the lithium anode in LIBs. The resulting CNF‐PEDOT:PSS‐PEO film exhibited superior mechanical and thermal properties compared to conventional PP separators. Mechanical tests revealed a high Young's modulus and puncture strength for the composite film. Thermal stability tests indicated that the CNF‐PEDOT:PSS‐PEO film remained stable at higher temperatures compared to the commercial PP separator, and combustion tests confirmed its superior fire‐resistance properties. In terms of conductivity, the composite film maintained comparable ionic conductivity to the commercial PP separator. Electrochemical tests demonstrated that LIBs incorporating the CNF‐PEDOT:PSS‐PEO film exhibited slight improvement in cycling performance, with a 7.9 % increase in long‐term cycling capacity compared to LIBs using only the commercial PP separator. These findings indicate that the developed CNF‐PEDOT:PSS‐PEO composite film holds promise to improve safety, while maintaining the electrochemical performance of LIBs by reducing dendrite formation and enhancing thermal stability.