Positive electrode for secondary battery and manufacturing method of positive electrode for secondary battery

Abstract

The positive electrode active material layer includes a plurality of particles of a positive electrode active material and a reaction mixture where reduced graphene oxide is bonded to a polymer having a functional group as a side chain. The reduced graphene oxide has a sheet-like shape and high conductivity and thus functions as a conductive additive by being in contact with the plurality of particles of the positive electrode active material. The reaction mixture serves as an excellent binder since the reduced graphene oxide is bonded to the polymer. Therefore, even a small amount of the reaction mixture where the reduced graphene oxide is covalently bonded to the polymer excellently serves as a conductive additive and a binder.

What is claimed is: 
     
         1 . A positive electrode for a secondary battery comprising:
 a positive electrode active material layer over a current collector,   wherein the positive electrode active material layer comprises:
 a plurality of particles of a positive electrode active material; 
 a graphene oxide; and 
 a polymer having a functional group as a side chain, the polymer bonded to the graphene oxide, and 
   wherein at least a part of the graphene oxide is in contact with at least one of the plurality of particles of the positive electrode active material.   
     
     
         2 . The positive electrode for a secondary battery, according to  claim 1 ,
 wherein the positive electrode active material comprises lithium and phosphorus, and   wherein the positive electrode active material further comprises iron or manganese.   
     
     
         3 . The positive electrode for a secondary battery, according to  claim 1 ,
 wherein the functional group is an amino group.   
     
     
         4 . The positive electrode for a secondary battery, according to  claim 1 ,
 wherein the polymer having a functional group as a side chain is any one of polyarylamine, polyimide, and polyamideimide.   
     
     
         5 . The positive electrode for a secondary battery, according to  claim 1 ,
 wherein the polymer is covalently bonded to the graphene oxide.   
     
     
         6 . The positive electrode for a secondary battery, according to  claim 1 ,
 wherein a carbon atom of the graphene oxide and a nitrogen atom of the polymer are bonded to each other.   
     
     
         7 . The positive electrode for a secondary battery, according to  claim 1  further comprising: an anchor coat layer between the current collector and the positive electrode active material layer. 
     
     
         8 . The positive electrode for a secondary battery, according to  claim 7 ,
 wherein the anchor coat layer comprises a mixture, the mixture comprising:
 one or more of polyvinylidene difluoride, polyimide, carboxymethyl cellulose, and sodium polyacrylate; and 
 one or more of acetylene black, carbon black, graphene, reduced graphene oxide, and a carbon nanotube. 
   
     
     
         9 . A secondary battery comprising:
 the positive electrode for a secondary battery, according to  claim 1 ;   a negative electrode; and   a separator between the positive electrode and the negative electrode.   
     
     
         10 . A manufacturing method of a positive electrode for a secondary battery comprising:
 mixing a plurality of particles of a positive electrode active material, graphene oxide, and water;   adding a polymer aqueous solution to the mixture of the plurality of particles of the positive electrode active material, the graphene oxide, and the water to form a slurry;   applying the slurry to a current collector;   drying the slurry to form a positive electrode active material layer; and   reducing the graphene oxide in the positive electrode active material layer.   
     
     
         11 . The manufacturing method of a positive electrode for a secondary battery, according to  claim 10 ,
 wherein the graphene oxide in the positive electrode active material layer is reduced by supplying a potential at which a reduction reaction of the graphene oxide occurs to the current collector in an electrolyte in which the current collector and a counter electrode are immersed.   
     
     
         12 . The manufacturing method of a positive electrode for a secondary battery, according to  claim 10 ,
 wherein the graphene oxide in the positive electrode active material layer is reduced by heating.   
     
     
         13 . The manufacturing method of a positive electrode for a secondary battery, according to  claim 10  further comprising:
 performing a surface treatment on the current collector before the application of the slurry to the current collector. 
 
     
     
         14 . The manufacturing method of a positive electrode for a secondary battery, according to  claim 10 ,
 wherein the positive electrode active material comprises lithium and phosphorus, and   wherein the positive electrode active material further comprises iron or manganese.