A lignin/polyvinyl alcohol (lignin/PVA) composite membrane has been prepared as a separator for lithium-ion batteries (LIBs) using a simple, low-cost, environment-friendly, water-based method. Lignin is a low-cost, naturally occurring, widely abundant, sustainable, biodegradable, and biocompatible material. Polyvinyl alcohol (PVA) has good hydrophilicity, biocompatibility, chemical and thermal stability, mechanical strength, and abrasion resistance. PVA can serve as a host skeleton to draw fibers out of the lignin/PVA composite using a spinning method. In this work, Lignin and polyvinyl alcohol (PVA) were dissolved in water separately, and the water-based solution was mixed together to make the dope – from where the electrospun fibers were drawn to form a non-woven lignin/PVA membrane. A highly porous interpenetrating network structure resulted, which was revealed by scanning electron microscopy. Electrolyte compatibility, uptake tests, and contact angle measurements were examined with three different electrolytes focusing different anodes and supercapacitors, and they all showed favorable results. Thermal shrinkage test and thermogravimetric analysis showed high thermal stability and good flame retardant properties of the membrane. Electrochemical cycling performances were investigated comparing to commercial Celgard separator, using Li/Li(Ni_1/3Mn_1/3Co_1/3)O₂ electrodes, and they showed good results for lignin/PVA membrane. Rate performance and electrochemical impedance spectroscopy revealed high rate performance using the lignin/PVA membrane that is caused by its high ionic transport property. The lignin/PVA composite separator showed enhanced physical, thermal and electrochemical properties, and can be considered as a suitable separator for LIBs with graphite or silicon anodes, as well as for supercapacitors.