Reactive polymer-supported porous film for battery separator, method for producing the porous film, method for producing battery using the porous film, and electrode/porous film assembly

Abstract

A reactive polymer-supported porous film for separator, that has sufficient adhesiveness between electrodes and separator and can suitably be used to produce a battery having low internal resistance and high rate performance, a method for producing the porous film, a method for producing a battery using the porous film, and an electrode/porous film assembly are disclosed. The reactive polymer-supported porous film for battery separator includes a porous film substrate having supported thereon a reactive polymer obtained by reacting a crosslinkable polymer having at least one reactive group selected from the group consisting of 3-oxetanyl group and epoxy group in the molecule, with an acid anhydride, thereby partially crosslinking the polymer.

1 . A reactive polymer-supported porous film for battery separator, comprising a porous film substrate having supported thereon a reactive polymer obtained by reacting a crosslinkable polymer having at least one reactive group selected from the group consisting of 3-oxetanyl group and epoxy group in the molecule, with an acid anhydride, thereby partially crosslinking the polymer.  
     
     
         2 . The reactive polymer-supported porous film as claimed in  claim 1 , wherein the crosslinkable polymer is radical copolymers of at least one radically polymerizable monomer selected from the group consisting of a radically polymerizable monomer having 3-oxetanyl group and a radically polymerizable monomer having epoxy group, and other radically polymerizable monomer.  
     
     
         3 . The reactive polymer-supported porous film as claimed in  claim 1 , wherein the crosslinkable polymer is radical copolymers of 5-50% by weight of at least one radically polymerizable monomer selected from the group consisting of a radically polymerizable monomer having 3-oxetanyl group and a radically polymerizable monomer having epoxy group, and 95-50% by weight of other radically polymerizable monomer.  
     
     
         4 . The reactive polymer-supported porous film as claimed in  claim 1 , wherein the reactive polymer has an insoluble content of 1-90%.  
     
     
         5 . The reactive polymer-supported porous film as claimed in  claim 1 , wherein the 3-oxetanyl group-containing radically polymerizable monomer is 3-oxetanyl group-containing (meth)acrylate represented by the following formula (I):  
       
         
           
           
               
               
           
         
       
       wherein R 1  represents hydrogen atom or methyl group; and R 2  represents hydrogen atom or an alkyl group having 1-6 carbon atoms.  
     
     
         6 . The reactive polymer-supported porous film as claimed in  claim 1 , wherein the epoxy group-containing radically polymerizable monomer is an epoxy group-containing (meth)acrylate represented by the following formula (II):  
       
         
           
           
               
               
           
         
       
       wherein R 3  represents hydrogen atom or methyl group; and R 4  represents an epoxy group-containing group represented by the following formula (1) or (2):  
       
         
           
           
               
               
           
         
       
     
     
         7 . The reactive polymer-supported porous film as claimed in  claim 1 , wherein the other radical-polymerizable monomer is preferably at least one selected from (meth)acrylates represented by the following formula (III):  
       
         
           
           
               
               
           
         
       
       wherein R 5  represents hydrogen atom or methyl group; A represents an oxyalkylene group having 2 or 3 carbon atoms (preferably, oxyethylene group or oxypropylene group): R 6  represents an alkyl group having 1-6 carbon atoms or a fluorinated alkyl group having 1-6 carbon atoms; and n is an integer of 0-3, and vinyl ester represented by the following formula (IV):  
       
         
           
           
               
               
           
         
       
       wherein R 7  represents methyl group or ethyl group; and R 8  represents hydrogen atom or methyl group.  
     
     
         8 . The reactive polymer-supported porous film as claimed in  claim 1 , wherein the crosslinkable polymer has a glass transition temperature of 70° C. or lower.  
     
     
         9 . The reactive polymer-supported porous film as claimed in  claim 1 , wherein the porous film substrate has a thickness of 3-50 μm and a porosity of 20-95%.  
     
     
         10 . A method for producing the reactive polymer-supported porous film for battery separator as claimed in  claim 1 , comprising: 
 supporting a crosslinkable polymer having at least one reactive group selected from the group consisting of 3-oxetanyl group and epoxy group in the molecule, and an acid anhydride on a porous film substrate;    reacting a part of the reactive groups with the acid anhydride to partially crosslink the reactive polymer; and    forming the reactive polymer on the porous film substrate.    
     
     
         11 . The method as claimed in  claim 10 , comprising: 
 applying a solution containing the crosslinkable polymer and acid anhydride to a release sheet;    drying the solution to form a crosslinkable polymer/acid anhydride layer on the release sheet; and    transferring the layer on the porous film substrate, thereby supporting the crosslinkable polymer and acid anhydride on the porous film substrate.    
     
     
         12 . The method as claimed in  claim 11 , comprising heating the crosslinkable polymer/acid anhydride layer having a glass transition temperature of 70° C. or lower to a temperature of 100° C. or lower, and transferring the layer to the porous film substrate.  
     
     
         13 . A method for producing a battery, comprising: 
 laminating electrodes on the reactive polymer-supported porous film as claimed in  claim 1  to prepare a laminate of reactive polymer-supported porous film/electrodes,    placing the laminate in a battery container, and    pouring an electrolyte solution containing a cationic polymerization catalyst in the battery container to swell at least a part of the reactive polymer in the electrolyte solution or dissolve at least a part of the reactive polymer into the electrolyte solution in at least the vicinity of an interface of the porous film and the electrodes, thereby inducing cationic polymerization of residual reactive groups in the reactive polymer to further crosslink the reactive group, and gelling at least a part of the electrolyte solution to adhere the porous film and the electrodes.    
     
     
         14 . The method as claimed in  claim 13 , wherein the cationic polymerization catalyst is an onium salt.  
     
     
         15 . The method as claimed in  claim 13 , wherein the electrolyte solution contains at least one selected from the group consisting of lithium hexafluorophosphate and lithium tetrafluoroborate, as an electrolyte which also functions as a cationic polymerization catalyst.  
     
     
         16 . An electrode/porous film assembly obtained by laminating electrodes on the reactive polymer-supported porous film as claimed in  claim 1  to prepare a laminate of reactive polymer-supported porous film/electrodes, and adhering electrodes to the laminate.  
     
     
         17 . The electrode/porous film assembly as claimed in  claim 16 , wherein the porous film of the assembly has a coefficient of area heat shrinkage after heating at 150° C. for 1 hour of 20% or less.