Enhanced Electrolyte‐Wettability and Thermal Stability of Hydrogen‐Bonded PVDF‐HFP‐Coated Paper‐Based Separators Fabricated by a Simple Dip Coating for Lithium‐Ion Battery

Abstract Traditional polyolefin‐based separators, characterized by their simple side‐chain structures and lacking polar functional groups, exhibit inherent limitations in terms of thermal stability and electrolyte wettability. To overcome this, we used a straightforward dip‐coating method to fabricate a hydrogen‐bonded polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP)‐coated paper‐based (PH‐CP) separator. The resultant composite separator showed exceptional electrolyte wettability, as evidenced by a contact angle of 0° and an electrolyte uptake ratio of 263%. This excellent improvement can be attributed to the incorporation of numerous polar groups derived from the highly polar PVDF‐HFP coating. Thermogravimetric analysis (TGA) revealed that the PH‐CP separator exhibited outstanding thermal stability, maintaining dimensional integrity without any shrinkage at temperatures exceeding 200 °C and achieving a 5% weight loss temperature of 375 °C. This enhanced thermal performance is attributed to the integration of PVDF‐HFP, a material known for its high‐temperature resistance. The presence of PVDF‐HFP suppresses likelihood of pyrolysis reactions during thermal exposure, thereby mitigating thermogravimetric loss by up to 60% compared to conventional polyolefin separators. Furthermore, when integrated into a LiFePO 4 /Li battery configuration, the PH‐CP separator facilitated low interfacial impedance and showed excellent cycle stability. These highlights the potential of the PH‐CP separator as a promising candidate for advanced lithium‐ion battery applications, offering improved safety, performance, and longevity.