Composite battery diaphragm and preparation method thereof

The invention discloses a composite battery diaphragm and a preparation method thereof, the surface of the composite battery diaphragm is flat and smooth, the whole composite battery diaphragm is of a three-layer structure including a melt-blown layer, a spunbond layer and a nano cellulose fiber layer, the melt-blown layer is located in the middle as a middle layer, the spunbond layer is located below the melt-blown layer, and the nano cellulose fiber layer is located below the spunbond layer. The nano cellulose fiber layer is positioned above the melt-blown layer; the melt-blown layer is prepared from PP with a melt index of 1200-1500 g/10 min as a raw material, the spunbond layer is prepared from PP with a melt index of 30-45 g/10 min as a raw material, and the nano-crystalline cellulose fiber layer is prepared from nano-crystalline cellulose fiber slurry added with pure water. The composite diaphragm obtained by the invention has excellent high temperature resistance, thermal dimensional stability, good ly