▎ 摘　　要

NOVELTY - The diaphragm has functional coating that is compounded on the surface of the polymer diaphragm, the functional coating being prepared from vanadium sulfide, tannic acid and reduced graphene oxide. The polymer membrane is selected from the group consisting of polypropylene PP membrane, polyethylene PE membrane or a composite membrane formed by PP membrane and PE membrane. The functional coating slurry is coated on the surface of the polymer diaphragm to prepare a composite diaphragm that is used for metal lithium batteries and metal sodium batteries. USE - Composite diaphragm for metal lithium battery and metal sodium battery. ADVANTAGE - The circulation stability and safety of the metal lithium/sodium battery are effectively improved and the method is simple and the cost is low are ensured. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for the method for preparing a composite diaphragm. DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the composite diaphragm for metal lithium battery and metal sodium battery.