A composite separator is prepared to improve the safety of lithium ion batteries (LIBs) based on a gravure coating aqueous slurry and post-hot-pressing method. An environmentally friendly aqueous slurry with an Al2O3 ceramic holder and polyvinylidene difluoride-hexafluoropropylene (PVdF-HFP) and carboxymethyl cellulose (CMC) dual-binders is coated on a polyolefin (PE) substrate to form a prototype Al-PHC/PE separator. Then, after assembling the separator in the batteries and hot-pressing at 70°C and 0.8MPa for 3h, the granular PVdF-HFP is transformed into a colloidal structure containing an electrolyte, which can binds the Al2O3 nanoparticles together and increases the battery hardness. Compared with a PE separator (9μm), the Al-PHC/PE-2 separator (12μm, with a Al2O3/PVdF-HFP weight ratio of 7/3) displays a comparative ionic conductivity of 9.3×10−4 Scm−2 and exhibits no obvious thermal deformation at 110°C for 60min. All of the batteries assembled with Al-PHC/PE-2 separators passed nail penetration and impact tests. In addition, the capacity retention increases from 83.4% to 87.6% when the battery is assembled with Al-PHC/PE-2 instead of a PE separator and charge-discharged at 0.7C/1.0C for 350 cycles. The enhanced safety and cycle performance indicate the promising prospect of Al-PHC/PE separators in LIBs.