Lithium-ion batteries have safety problems such as explosion and fire due to the low thermal stability of the polyolefin-based separator. In this study, a separator was fabricated using a nonsolvent-induced phase separation (NIPS) method of ethylene-vinyl alcohol (EVOH) polymer surface-modified with (3-Glycidyloxypropyl)trimethoxysilane (GPTMS), and the electrochemical performance was evaluated. When producing the EVOH separator film, the surface was modified with GPTMS to have improved physical properties, and a GPTMS-treated EVOH(G-EVOH) separator having a uniform pore size was produced by selecting a solvent and a non-solvent. It was confirmed that this separator has improved electrolyte wettability and thermal stability(at 140℃) compared to polypropylene separators. Full-cell was fabricated with a configuration of LiCoO2|Graphite electrode and G-EVOH, and as a result of evaluating the life characteristics at 2C, the capacity retention rate after 90 cycles was improved by 75% compared to PP.