Porous membrane slurry for secondary batteries, negative electrode for secondary batteries and method for producing negative electrode for secondary batteries

Abstract

A porous membrane slurry for secondary batteries including non-conductive particles, a porous membrane polymer, and an organic solvent, wherein the non-conductive particles are particles of a polymer that contains 50% by weight or more of a structural unit formed by polymerization of a (meth)acrylate, the polymer having a softening starting point or decomposition point of 175° C. or higher, and wherein the porous membrane polymer is in a non-particulate form and has a cross-linkable group. A secondary battery negative electrode, and a method for producing a secondary battery negative electrode, are also provided.

1 . A porous membrane slurry for secondary batteries, comprising non-conductive particles, a porous membrane polymer and an organic solvent, wherein
 the non-conductive particles are particles of a polymer that contains 50% by weight or more of a structural unit formed by polymerization of a (meth)acrylate, the polymer having a softening starting point or decomposition point of 175° C. or higher, and   the porous membrane polymer is in a non-particulate form and has a cross-linkable group.   
     
     
         2 . The porous membrane slurry according to  claim 1 , wherein the cross-linkable group includes one or more types of groups selected from the group consisting of an epoxy group, a carboxyl group and a sulfo group. 
     
     
         3 . The porous membrane slurry according to  claim 1 , wherein the (meth)acrylate to form the structural unit includes a dimethacrylate. 
     
     
         4 . The porous membrane slurry according to  claim 1 , wherein
 a number average particle diameter of the non-conductive particles is 100 nm to 2,000 nm, and   a variation coefficient in diameter of the non-conductive particles is 26% or less.   
     
     
         5 . The porous membrane slurry according to  claim 1  containing two or more types of the organic solvents, wherein the difference in boiling point between the two or more types of the organic solvents is 40° C. or more. 
     
     
         6 . A secondary battery negative electrode comprising a current collector, a negative electrode active material layer, and a porous membrane, wherein
 the negative electrode active material layer contains a negative electrode active material and a particulate negative electrode polymer,   the porous membrane contains non-conductive particles and a porous membrane polymer that is in a non-particulate form and has a cross-linkable group, and   the non-conductive particles are particles of a polymer that contains 50% by weight or more of a structural unit formed by polymerization of a (meth)acrylate, the polymer having a softening starting point or decomposition point of 175° C. or higher.   
     
     
         7 . The secondary battery negative electrode according to  claim 6 , wherein the negative electrode active material is a composite particle containing a material including silicon. 
     
     
         8 . The secondary battery negative electrode according to  claim 6 , wherein the negative electrode active material contains a combination of carbon and one or both of metallic silicon and a silicon-based active material. 
     
     
         9 . The secondary battery negative electrode according to  claim 6 , wherein the porous membrane polymer contains a structural unit formed by polymerization of a (meth)acrylic acid ester. 
     
     
         10 . The secondary battery negative electrode according to  claim 6 , wherein an amount of the porous membrane polymer in the porous membrane based on 100 parts by weight of the non-conductive particles is 2 parts by weight or more and 37 parts by weight or less. 
     
     
         11 . A secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the negative electrode is the secondary battery negative electrode according to  claim 6 . 
     
     
         12 . A method for producing a secondary battery negative electrode including a current collector, a negative electrode active material layer, and a porous membrane, the method comprising:
 applying a negative electrode slurry containing a negative electrode active material, a particulate negative electrode polymer, and water onto the current collector and then drying the negative electrode slurry to thereby obtain the negative electrode active material layer;   applying a porous membrane slurry onto the negative electrode active material layer and drying the applied porous membrane slurry, the porous membrane slurry containing: non-conductive particles that are particles of a polymer that includes 50% by weight or more of a structural unit formed by polymerization of a (meth)acrylate and has a softening starting point or decomposition point of 175° C. or higher; a porous membrane polymer that is in a non-particulate form and has a cross-linkable group; and an organic solvent; and   cross-linking the porous membrane polymer by heating.