Separators have directly affected the safety and electrochem. performance of lithium-ion batteries.In this study, an alkali etched enhanced polyimide (PI)/polyacrylonitrile (PAN)@ cellulose acetate (CA)/PI three-layer composite separator is prepared using electrospinning, non-solvent phase separation, and alkali etching methods.The effects of alkali etching on the mech. strength, thermal stability, and electrochem. performance of the PI/PAN@CA/PI separator are explored.The obtained separator has two different pore structures, and the surface of the alkali etched separator has abundant polar groups, further enhancing the migration rate of lithium-ions.The mech. strength and thermal performance decrease with the prolongation of alkali etching time.When the alkali etching time is 3 min, the PI/PAN@CA/PI separator has the best comprehensive performance, with a mech. strength of 17.8 MPa, ion conductivity of 1.22 mS cm-1, and interface impedance of 152 Ω.After 100 cycles of charging and discharging at a c.d. of 1 C, the capacity retention rate is 95.3%.At a c.d. of 5 C, the specific capacity of charging and discharging can reach 114 mAh g-1, which is better than the 87.3 mAh g-1 of the initial PI/PAN@CA/PI separator.