Although lithium-ion batteries (LIBs) are used in various fields, such as small devices and electric vehicles, the low cycling stability due to the acceleration of salt degradation at high temperatures remains a significant challenge. The batteries are typically assembled in a dry room that controls moisture because lithium salts in the electrolytes are highly reactive with moisture, which has a significant effect on the battery performance. In this work, impurity scavenging separator membrane (ISM) was fabricated using a powerful H2O and HF scavenging material. This material was synthesized by an urethane reaction between porous silica (p-SiO2) and (3-isocynatopropyl)triethoxysilane (ICPTES). The p-SiO2 reaction with ICPTES suppressed the acidification of the electrolyte with water and resulted in maintaining the shape of the SiO2 particles. The multifunctional separator exhibited high capacity retention of 87%, 79%, and 74% at various electrodes including LiMn2O4 (LMO)//Li4Ti5O12 (LTO), Li[Ni0.8Co0.1Mn0.1]O2 (NCM)//graphite, and LMO//graphite, respectively, at high temperature (55℃). Furthermore, the ISM improves the cycle stability of batteries that use an electrolyte containing 1000 ppm of water. For the first time, a pouch full-cell was manufactured in a dry room-free system to confirm the excellent H2O and HF scavenging ability of the developed ISM, which was confirmed by the large area of battery size (4ⅹ6 cm2). This method presents a new approach for cost reduction in the electric vehicle market .