Binder for a lithium-sulfur battery, positive active material composition comprising same and lithium-sulfur battery using same

Abstract

Disclosed is a binder for a lithium-sulfur battery including a butadiene-based copolymer. The binder exhibits chemical resistance to polysulfides, is stable a battery working temperatures, forms an emulsion in organic solvents and exhibits high adherence to positive active materials and electrodes used in the lithium-sulfur battery. The disclosed binder compositions, due to their high adherence to positive active materials allow for higher relative amounts of positive active materials to be used in the battery resulting in a high capacity lithium-sulfur battery.

1 . A lithium-sulfur battery, comprising: 
 a positive electrode comprising a positive active material, a conductive agent, and a binder comprising a butadiene-based copolymer;    a negative electrode; and    an electrolyte.    
   
   
       2 . The lithium-sulfur battery of  claim 1 , wherein the butadiene-based copolymer is selected from the group consisting of an acrylonitrile-butadiene-styrene copolymer, an acrylonitrile-butadiene copolymer, and a modified styrene-butadiene copolymer.  
   
   
       3 . The lithium-sulfur battery of  claim 2 , wherein the butadiene-based copolymer is selected from the group consisting of an acrylonitrile-butadiene-styrene rubber, an acrylonitrile-butadiene rubber, and a modified styrene-butadiene rubber.  
   
   
       4 . The lithium-sulfur battery of  claim 1 , wherein the butadiene-based copolymer is represented by Formula 1:  
     
       
         
         
             
             
         
       
       and wherein:  
       when x is 0, y ranges from about 5 to about 40, and z ranges from about 60 to about 95;  
       when z is 0, x ranges from about 60 to about 95 and y ranges from about 5 to about  40; and    
       when x, y, and z do not equal 0, x ranges from about 20 to about 75, y ranges from about 5 to about 20, and z ranges from about 20 to about 75.  
     
   
   
       5 . The lithium-sulfur battery of  claim 1 , wherein the butadiene-based copolymer is non-aqueous.  
   
   
       6 . The lithium-sulfur battery of  claim 1 , further comprising a fluorine-based polymer.  
   
   
       7 . The lithium-sulfur battery of  claim 6 , wherein the fluorine-based polymer is represented by Formula 2:  
     
       
         
         
             
             
         
       
       and wherein a ranges from about 0.5 to about 1.0, and b ranges from about 0 to about 0.5.  
     
   
   
       8 . The lithium-sulfur battery of  claim 6 , wherein the fluorine-based polymer is selected from the group consisting of a homopolymer prepared from monomers selected from the group consisting of C 2 F 3 Cl, C 2 H 3 F and CH 3 (CF 3 C 2 H 4 )SiO, and a copolymer including a first monomer and a second monomer, wherein the first monomer is selected from the group consisting of C 2 F 4 , C 2 F 3 Cl, CH 2 CF 2 , C 2 H 3 F and CH 3 (CF 3 C 2 H 4 )SiO, and the second monomer is selected from the group consisting of C 2 H 4 , C 3 H 6 , CH 2 ═CHOR where R is a C 1  to C 20  alkyl group, C 3 F 6  and CF 2 ═CFOR f  where R f  is a C 1  to C 20  alkyl group with at least one fluorine atom.  
   
   
       9 . The lithium-sulfur battery of  claim 1 , wherein the agent for controlling viscosity is selected from the group consisting of a cellulose-based polymer, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyacrylamide, polyethyleneoxide, and polyethyleneimine.  
   
   
       10 . The lithium-sulfur battery of  claim 9 , wherein the cellulose-based polymer is selected from the group consisting of methyl cellulose, hydroxypropyl methylcellulose, hydroxyethyl-cellulose, or carboxymethyl cellulose.