Laminated porous film, method for producing same, non-aqueous electrolyte secondary battery separator, laminated electrode sheet, and non-aqueous electrolyte secondary battery

Abstract

Provided is a laminated porous film suitable as a non-aqueous electrolyte secondary battery separator, which includes a heat resistant layer excellent in morphological stability at a high temperature and ion permeability and more resistant to fall-off of a filler. A laminated porous film in which a heat resistant layer including a binder resin and a filler and a base porous film including a polyolefin as a principal component are laminated, wherein the filler included in the heat resistant layer substantially consists of an inorganic filler (a) having a primary particle diameter of 0.2 to 1 μm and an inorganic filler (b) having a primary particle diameter of 0.01 to 0.1 μm, and the particle diameter of secondary aggregates of the inorganic filler (b) is not more than 2 times the primary particle diameter of the inorganic filler (a) in the heat resistant layer.

1 . A method for producing a laminated porous film in which a heat resistant layer including a binder resin and a filler and a base porous film including a polyolefin as a principal component are laminated,
 the filler included in the heat resistant layer substantially consisting of an inorganic filler (a) having a primary particle diameter of 0.2 to 1 μm and an inorganic filler (b) having a primary particle diameter of 0.01 to 0.1 μm,   the particle diameter of secondary aggregates of the inorganic filler (b) being not more than 2 times the primary particle diameter of the inorganic filler (a) in the heat resistant layer, and   the primary particle diameters of the inorganic fillers (a) and (b) being average particle diameters determined by observing the cross section of the heat resistant layer with a scanning electron microscope, and the particle diameter of the secondary aggregates of the inorganic filler (b) being a maximum particle diameter of the secondary aggregates determined by observing the cross section of the heat resistant layer with a scanning electron microscope,   the method comprising the steps of;   applying a coating fluid containing the inorganic filler (a), the inorganic filler (b), the binder resin, and a solvent to the surface of the base porous film; and then   removing the solvent to form a heat resistant layer on the surface of the base porous film.   
     
     
         2 . The method for producing a laminated porous film according to  claim 1 , wherein the volume ratio of the inorganic filler (a) to the inorganic filler (b) is 80/20 to 99/1. 
     
     
         3 . The method for producing a laminated porous film according to  claim 1 , wherein the inorganic filler (a) includes, as a principal component, nonspherical coupled particles in which a plurality of primary particles are firmly stuck together. 
     
     
         4 . The method for producing a laminated porous film according to  claim 3 , wherein the nonspherical coupled particles are partially melted and firmly stuck together by heating. 
     
     
         5 . The method for producing a laminated porous film according to  claim 1 , wherein both the inorganic filler (a) and the inorganic filler (b) are alumina. 
     
     
         6 . The method for producing a laminated porous film according to  claim 1 , wherein the binder resin is a water-soluble polymer. 
     
     
         7 . The method for producing a laminated porous film according to  claim 6 , wherein the water-soluble polymer is at least one selected from the group consisting of cellulose ether, starch, polyvinyl alcohol and sodium alginate. 
     
     
         8 . The method for producing a laminated porous film according to  claim 1 , wherein the inorganic filler (b) is produced by a gas phase method. 
     
     
         9 . The method for producing a laminated porous film according to  claim 1 , wherein the solvent is a mixed solvent of water and an organic polar solvent. 
     
     
         10 . The method for producing a laminated porous film according to  claim 9 , wherein a water content in the mixed solvent is 50% by weight or more. 
     
     
         11 . The method for producing a laminated porous film according to  claim 9 , wherein the organic polar solvent is an alcohol. 
     
     
         12 . The method for producing a laminated porous film according to  claim 1 , wherein the base porous film is previously subjected to a hydrophilic treatment before applying the coating fluid. 
     
     
         13 . The method for producing a laminated porous film according to  claim 12 , wherein the hydrophilic treatment is any one of a chemical treatment, a corona treatment and a plasma treatment. 
     
     
         14 . The method for producing a laminated porous film according to  claim 1 , wherein the solvent is removed by drying. 
     
     
         15 . The method for producing a laminated porous film according to  claim 1 , wherein a filler content is 95.2% by weight or more based on the total amount of the binder resin and the filler in the heat resistant layer.