The invention discloses a method for preparing a composite
polypropylene microporous film by a
phase conversion method and product and application of the composite
polypropylene microporous film. According to the preparation method, a
coating layer is introduced to surface(s) of one side or two sides of the film by a first mode (immersion precipitant
phase conversion method) or a second mode (dryphase
conversion method) during the fabrication process of bidirectionally stretching a
polypropylene microporous substrate layer, the
coating layer is only stretched in a longitudinal direction and atransverse direction or is only stretched in the transverse direction, and the preparation of the composite polypropylene microporous film is achieved. With the adoption of the method, the productionprocess of the composite polypropylene microporous film is simplified, the fabricated
coating layer is high in
porosity, the microporous structure is uniform, and the performance of the polypropylenemicroporous substrate layer can be improved very well. The composite polypropylene microporous film is applied into a
lithium battery, the coating layer is a
polymer or a composition capable for forming gel with an
electrolyte, and thus, the cycle property and the safety of the
lithium battery can be improved. The invention also provides a
lithium battery diaphragm, and the
lithium battery diaphragm comprises the composite polypropylene microporous film.