Reactive polymer-supporting porous film for battery seperator and use thereof

Abstract

The invention provides a reactive polymer-supporting porous film for use as a battery separator which comprises a porous substrate film and a partially crosslinked reactive polymer supported on the porous substrate film, the partially crosslinked reactive polymer being obtained by the reaction of 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 a polycarboxylic acid. The reactive polymer-supporting porous film for use as a battery separator has a separator and electrodes sufficiently bonded to each other and low inner resistance so that it is suitably used for production of battery excellent in high rate performance. Further, the invention provides a method of producing a battery which comprises placing the electrode/reactive polymer-supporting porous film layered body in a battery container; introducing an electrolytic solution containing a cationic polymerization catalyst into the battery container thereby bonding the porous film and the electrodes together.

1 . A reactive polymer-supporting porous film for use as a battery separator which comprises a porous substrate film and a partially crosslinked reactive polymer supported on the porous substrate film, the partially crosslinked reactive polymer being obtained by the reaction of 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 a polycarboxylic acid.  
     
     
         2 . The reactive polymer-supporting porous film according to  claim 1 , wherein the crosslinkable polymer is a radical copolymer of at least one radical polymerizable monomer selected from the group consisting of 3-oxetanyl group-containing radical polymerizable monomers and epoxy group-containing radical polymerizable monomers with another radical polymerizable monomer.  
     
     
         3 . The reactive polymer-supporting porous film according to  claim 1 , wherein the crosslinkable polymer is a radical copolymer of 5 to 50% by weight of a 3-oxetanyl group-containing radical polymerizable monomer and/or an epoxy group-containing radical polymerizable monomer with 95 to 50% by weight of another radical polymerizable monomer.  
     
     
         4 . The reactive polymer-supporting porous film according to  claim 1 , wherein the reactive polymer has insoluble matter in an amount of 1 to 90%.  
     
     
         5 . The reactive polymer-supporting porous film according to  claim 2 , wherein the 3-oxetanyl group-containing radical polymerizable monomer is 3-oxetanyl group-containing (meth)acrylate represented by the general formula (I)  
       
         
           
           
               
               
           
         
       
       wherein R 1  is a hydrogen atom or a methyl and R 2  is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.  
     
     
         6 . The reactive polymer-supporting porous film according to  claim 2 , wherein the epoxy group-containing radical polymerizable monomer is an epoxy group-containing (meth)acrylate represented by the general formula (II)  
       
         
           
           
               
               
           
         
       
       wherein R 3  is a hydrogen atom or a methyl group and R 4  is an epoxy group-containing group represented by the formula (1)  
       
         
           
           
               
               
           
         
       
     
     
         7 . The reactive polymer-supporting porous film according to  claim 2 , wherein said another radical polymerizable monomer is at least one selected from the group consisting of (meth)acrylates represented by the following general formula (III)  
       
         
           
           
               
               
           
         
       
       wherein R 5  is a hydrogen atom or a methyl group; A is an oxyalkylene group having 2 or 3 carbon atoms; R 6  is an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms; and n is an integer of 0 to 3; and vinyl esters represented by the general formula (IV)  
       
         
           
           
               
               
           
         
       
       wherein R 7  is a methyl or an ethyl group and R 8  is a hydrogen atom or a methyl group.  
     
     
         8 . The reactive polymer-supporting porous film according to  claim 1 , wherein the crosslinkable polymer has a glass transition temperature of 70° C. or lower.  
     
     
         9 . The reactive polymer-supporting porous film according to  claim 1 , wherein the porous substrate film has a thickness in a range of 3 to 50 μm and a porosity in a range of 20 to 95%.  
     
     
         10 . A method of producing a battery which comprises obtaining an electrode/reactive polymer-supporting porous film layered body by layering electrodes on the reactive polymer-supporting porous film according to  claim 1;  placing the electrode/reactive polymer-supporting porous film layered body in a battery container; introducing an electrolytic solution containing a cationic polymerization catalyst into the battery container so that at least a portion of the reactive polymer is swelled or dissolved in the electrolytic solution at least in the vicinity of the interface of the porous film and the electrodes and cationic-polymerized thereby gelling at least a portion of the electrolytic solution so that the the electrodes are bonded to the porous film.  
     
     
         11 . The method of producing a battery according to  claim 10 , wherein the cationic polymerization catalyst is an onium salt.  
     
     
         12 . The method of producing a battery according to  claim 10 , wherein the electrolytic solution contains at least one selected from the group consisting of lithium hexafluorophosphate and lithium tetrafluoroborate as an electrolytic salt working also as a cationic polymerization catalyst.  
     
     
         13 . A method of producing the reactive polymer-supporting porous film for use as a battery separator according to  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 a polycarboxylic acid on a porous substrate film; reacting a part of the reactive groups with the polycarboxylic acid thereby partially crosslinking the crosslinkable polymer and forming the reactive polymer on the porous substrate film.  
     
     
         14 . The method of producing the reactive polymer-supporting porous film according to  claim 13 , wherein the crosslinkable polymer and the polycarboxylic acid are supported on a porous substrate film by applying a solution containing the crosslinkable polymer and the polycarboxylic acid to a release sheet; 
 drying the solution to form a crosslinkable polymer/polycarboxylic acid layer on the release sheet; and transferring the layer to the porous substrate film from the release sheet.    
     
     
         15 . The method of producing the reactive polymer-supporting porous film according to  claim 14 , wherein the crosslinkable polymer having a glass transition temperature of 70° C. or lower/polycarboxylic acid layer is transferred to the porous substrate film by heating at a temperature of 100° C. or lower.  
     
     
         16 . An electrode/porous film layered adherent obtained by layering electrodes on the reactive polymer-supporting porous film according to  claim 1  thereby obtaining an electrode/reactive polymer-supporting porous film layered body and bonding the electrodes to the reactive polymer-supporting porous film.  
     
     
         17 . The electrode/porous film layered adherent according to  claim 16 , wherein the porous film has an area thermal shrinkage ratio of 20% or less after it has been heated at 150° C. for 1 hour.