Polyolefin porous membrane and preparation method thereof, battery diaphragm and electrochemical device

The invention relates to the technical field of diaphragms for electrochemical devices, and discloses a polyolefin porous membrane and a preparation method thereof, a battery diaphragm and an electrochemical device. The polyolefin porous membrane provided by the invention has a network fiber structure, and is observed according to a 20,000-fold SEM image, and the polyolefin porous membrane has the following characteristics: (1) in a circle with the radius of 1000nm, the fiber orientation result RMD of fibers with the fiber diameter greater than 15nm in the MD direction meets the following conditions: RMD < 2 > is less than 0.5; (2) in a circle with the radius being 1000 nm, the fiber orientation result RTD of the fiber with the fiber diameter larger than 15 nm in the TD direction meets the condition that RTD < 2 > is smaller than 0.5; therefore, the polyolefin porous membrane disclosed by the invention can realize the consistency of mechanical properties of the polyolefin porous membrane as a diaphragm in a b