Separator for rechargeable battery, method of preparing the same and rechargeable lithium battery including the same

Abstract

A separator for a rechargeable battery includes a porous substrate; and a coating layer on the porous substrate, the coating layer includes a fluorine-containing binder, a filler, and an additive, the additive is included in an amount of 0.35 wt % to 1.25 wt %, an infrared spectral intensity of a C-F group of the fluorine-containing binder is greater than 0.0030 to less than 0.0050, the infrared spectral intensity of the C-F group of the fluorine-containing binder is measured as a functional group of the fluorine-containing binder to evaluate a distribution of the fluorine-containing binder when separator specimens are mounted on an ATR crystal of a FT-IR spectroscopy and infrared rays are entered at a 45 degree angle, the additive includes a hydrocarbon polymer compound that includes a carboxyl group, and the hydrocarbon polymer compound has a weight average molecular weight of about 5,000 g/mol to about 15,000 g/mol.

What is claimed is: 
     
         1 . A separator for a rechargeable battery, the separator comprising:
 a porous substrate; and   at least one coating layer on one surface of the porous substrate,   wherein:   the at least one coating layer includes a fluorine-containing binder, a filler, and an additive,   the additive is included in an amount of greater than 0.35 wt % to less than 1.25 wt %, the wt % being based on a total weight of the at least one coating layer,   an infrared spectral intensity of a C-F group of the fluorine-containing binder is greater than 0.0030 to less than 0.0050,   the infrared spectral intensity of the C-F group of the fluorine-containing binder is measured as a functional group of the fluorine-containing binder to evaluate a distribution of the fluorine-containing binder when separator specimens are mounted on an ATR crystal of a FT-IR spectroscopy and infrared rays are entered at a 45 degree angle,   the additive includes a hydrocarbon polymer compound that includes a carboxyl group, and   the hydrocarbon polymer compound has a weight average molecular weight of about 5,000 g/mol to about 15,000 g/mol.   
     
     
         2 . The separator as claimed in  claim 1 , wherein the fluorine-containing binder has a concentration gradient in which a concentration thereof in the at least one coating layer increases toward an outer surface of the separator in a thickness direction of the separator. 
     
     
         3 . The separator as claimed in  claim 1 , wherein the fluorine-containing binder has a crystallinity degree of 48% to about 58%. 
     
     
         4 . The separator as claimed in  claim 1 , wherein the fluorine-containing binder is included in an amount of about 20 wt % to about 30 wt %, based on a total weight of the coating layer. 
     
     
         5 . The separator as claimed in  claim 1 , wherein the infrared spectral intensity of the C-F group of the fluorine-containing binder is greater than 0.0035 to less than 0.0050. 
     
     
         6 . The separator as claimed in  claim 1 , wherein the fluorine-containing binder has a crystal size of about 1 nm to about 5 nm. 
     
     
         7 . The separator as claimed in  claim 1 , wherein the fluorine-containing binder is a vinylidene fluoride polymer. 
     
     
         8 . The separator as claimed in  claim 1 , wherein the fluorine-containing binder is a vinylidene fluoride homopolymer or a copolymer including a structural unit of a vinylidene fluoride monomer and a structural unit of another monomer. 
     
     
         9 . The separator as claimed in  claim 1 , wherein the fluorine-containing binder includes a functional group including a carboxyl group. 
     
     
         10 . The separator as claimed in  claim 1 , wherein the fluorine-containing binder has a weight average molecular weight of about 800,000 g/mol to about 1,300,000 g/mol. 
     
     
         11 . The separator as claimed in  claim 1 , wherein the filler includes a metal oxide, a semi-metal oxide, a metal fluoride, a metal hydroxide, or a combination thereof. 
     
     
         12 . The separator as claimed in  claim 1 , wherein the filler has a concentration gradient in which a concentration thereof in the at least one coating layer decreases toward an outer surface of the separator in a thickness direction of the separator. 
     
     
         13 . The separator as claimed in  claim 1 , wherein the at least one coating layer has a surface roughness (Rq) of about 150 nm to about 300 nm. 
     
     
         14 . The separator as claimed in  claim 1 , wherein the at least one coating layer has a surface pore size of about 50 nm to about 1,000 nm. 
     
     
         15 . A method of preparing a separator, the method comprising:
 preparing a composition for forming a coating layer by dispersing a fluorine-containing binder, a filler, and an additive in a solvent;   coating the composition for forming the coating layer on one or both surfaces of a porous substrate to form at least one coating layer; and   drying the at least one coating layer under a humidified atmosphere of about ° C. to about 80° C. and an absolute aqueous vapor amount of about 10 g/m 3  to about g/m 3 ,   wherein:   the additive includes a hydrocarbon polymer compound that includes a head group including a carboxyl group and a tail group including a substituted or unsubstituted aliphatic hydrocarbon polymer structure,   the additive is included in an amount of greater than 0.35 wt % to less than 1.25 wt %, the wt % being based on a total weight of the at least one coating layer, and the hydrocarbon polymer compound has a weight average molecular weight of about 5,000 g/mol to about 15,000 g/mol.   
     
     
         16 . The method as claimed in  claim 15 , the fluorine-containing binder has a concentration gradient in which a concentration thereof in the at least one coating layer increases toward an outer surface of the separator in a thickness direction of the separator. 
     
     
         17 . The method as claimed in  claim 15 , the fluorine-containing binder has a crystallinity degree of 48% to about 58%. 
     
     
         18 . The method as claimed in  claim 15 , the fluorine-containing binder is included in an amount of about 20 wt % to about 30 wt %, based on a total weight of the coating layer. 
     
     
         19 . The method as claimed in  claim 15 , wherein the drying is performed in a humidified atmosphere of a temperature of about 50° C. to about 70° C. and an absolute aqueous vapor amount of about 10 g/m 3  to about 20 g/m 3.    
     
     
         20 . A rechargeable battery, comprising:
 a positive electrode;   a negative electrode;   the separator for a rechargeable battery as claimed in  claim 1  between the positive electrode and the negative electrode; and   an electrolyte solution.   
     
     
         21 . The rechargeable battery as claimed in  claim 20 , wherein:
 at least one of the positive electrode and the negative electrode includes an electrode active material and an electrode binder, and   a ratio (C2/C1) of a crystallinity degree (C2) of the electrode binder to a crystallinity degree (C1) of the fluorine-containing binder is about 1.40 to about 1.60.   
     
     
         22 . The rechargeable battery as claimed in  claim 21 , wherein the electrode binder has a crystallinity degree of about 70% to about 80%. 
     
     
         23 . The rechargeable battery as claimed in  claim 21 , wherein the electrode binder is a vinylidene fluoride homopolymer or a copolymer including a structural unit of a vinylidene fluoride monomer and a structural unit of another monomer.