Negative Electrode Material for Lithium Battery, and Lithium Battery

Abstract

The present invention relates to a negative electrode material for a lithium battery characterized by comprising a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more, a binder formed of styrene-butadiene rubber and a carbon fiber having a fiber diameter of 1 to 1,000 nm; and to a lithium battery using the negative electrode material, which has excellent characteristics, i.e., low electrode resistance, high electrode strength, excellent electrolytic solution permeability, high energy density, and good high-speed charging/discharging performance. The negative electrode material contains carbon fiber in the amount of 0.05 to 20 mass % and the binder formed of styrene-butadiene rubber in 0.1 to 6.0 mass %, and may further contain a thickner such as carboxymethyl cellulose in the amount of 0.3 to 3 mass %.

1 . A negative electrode material for a lithium battery characterized by comprising a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more, a binder formed of styrene-butadiene rubber and a carbon fiber having a fiber diameter of 1 to 1,000 nm.  
   
   
       2 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the binder formed of styrene-butadiene rubber is in the form of fine particles having an average particle size of 10 to 500 nm.  
   
   
       3 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the amount of the carbon fiber is 0.05 to 20 mass % and the amount of the binder formed of styrene-butadiene rubber is 0.1 to 6.0 mass %, on the basis of the total amount of the carbonaceous negative electrode active substance, the binder, and the carbon fiber.  
   
   
       4 . The negative electrode material for a lithium battery as claimed in  claim 1 , which further comprises a thickener.  
   
   
       5 . The negative electrode material for a lithium battery as claimed in  claim 4 , wherein the amount of the thickener is 0.1 to 4 mass % on the basis of the total amount of the carbonaceous negative electrode active substance, the binder, the carbon fiber and the thickener.  
   
   
       6 . The negative electrode material for a lithium battery as claimed in  claim 4 , wherein the thickener is carboxymethyl cellulose.  
   
   
       7 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein a negative electrode formed of the electrode material exhibits a specific resistance of 0.5 Ωcm or less at 25° C.  
   
   
       8 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the carbon fiber is a graphite carbon fiber which has undergone thermal treatment at 2,000° C. or higher.  
   
   
       9 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the carbon fiber is a graphite carbon fiber having a surface to which an oxygen-containing functional group has been introduced through oxidation treatment.  
   
   
       10 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the carbon fiber is a graphite carbon fiber containing boron in an amount of 0.1 to 100,000 ppm.  
   
   
       11 . The negative electrode material for a lithium battery as claimed in  claim 8 , wherein the graphite carbon fiber has an average interlayer distance (d 002 ) of a (002) plane of 0.344 nm or less as measured by X-ray diffractometry.  
   
   
       12 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the carbon fiber has a structure with a hollow space.  
   
   
       13 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the carbon fiber contains a branched carbon fiber.  
   
   
       14 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the carbonaceous negative electrode active substance contains Si.  
   
   
       15 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the carbonaceous negative electrode active substance is a non-graphite carbon material, and the layer of the compound comprising a negative electrode active substance, binder and electrically conductive additive exhibits a bulk density of 1.5 g/cm 3  or more.  
   
   
       16 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein, before the electrode material is formed into an electrode, the carbonaceous negative electrode active substance is in the form of carbonaceous particles satisfying the following requirements: 
 (1) average roundness as measured by use of a flow particle image analyzer is 0.70 to 0.99; and    (2) average particle size as measured by laser diffractometry is 1 to 50 μm.    
   
   
       17 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein the carbonaceous negative electrode active substance contains a graphite carbonaceous material in an amount of 50 mass % or more.  
   
   
       18 . The negative electrode material for a lithium battery as claimed in  claim 17 , wherein the graphite material contains boron.  
   
   
       19 . The negative electrode material for a lithium battery as claimed in  claim 1 , wherein, before the electrode material is formed into an electrode, the carbonaceous negative electrode active substance is in the form of carbonaceous particles containing, in an amount of 50 mass % or more, graphite particles satisfying the following requirements: 
 (1) average roundness as measured by use of a flow particle image analyzer is 0.70 to 0.99; and    (2) average particle size as measured by laser diffractometry is 1 to 50 μm.    
   
   
       20 . The negative electrode material for a lithium battery as claimed in  claim 17 , wherein the graphite carbonaceous material is in the form of carbonaceous particles containing, in an amount of 50 mass % or more, graphite particles satisfying the following requirements: 
 (1) C 0  of a (002) plane as measured by X-ray diffractometry is 0.6900 nm or less, La (the size of a crystallite as measured along the a-axis) is greater than 100 nm, and Lc (the size of a crystallite as measured along the c-axis) is greater than 100 nm;    (2) specific surface area is 1.0 to 10 m 2 /g;    (3) true density is 2.20 g/cm 3  or more; and    (4) laser Raman R value (the ratio of the intensity of a peak at 1,360 cm −1  in a laser Raman spectrum to that of a peak at 1,580 cm −1  in the spectrum) is 0.01 to 0.9.    
   
   
       21 . The negative electrode material for a lithium battery as claimed in  claim 15 , wherein the layer of the compound comprising a negative electrode active substance, binder and electrically conductive additive exhibits a bulk density of 1.7 g/cm 3  or more.  
   
   
       22 . A method for producing a composition for forming a negative electrode material for a lithium battery, comprising adding an aqueous styrene-butadiene rubber dispersion to a carbon fiber/active substance dispersion prepared by dispersing, in an aqueous thickener solution, a carbon fiber having a fiber diameter of 1 to 1,000 nm, a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more; and stirring the resultant mixture.  
   
   
       23 . The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in  claim 22 , wherein the carbon fiber/active substance dispersion is prepared by dispersing a carbon fiber having a fiber diameter of 1 to 1,000 nm in an aqueous thickener solution under stirring; and by adding thereto a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more followed by mixing with stirring.  
   
   
       24 . The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in  claim 22 , wherein the carbon fiber/active substance dispersion is prepared by dispersing a carbon fiber having a fiber diameter of 1 to 1,000 nm in an aqueous thickener solution under stirring; by adding thereto a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more followed by mixing with stirring; and by being regulated using an aqueous thickener solution.  
   
   
       25 . The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in  claim 22 , wherein the carbon fiber/active substance dispersion is prepared by adding, to an aqueous thickener solution, a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more followed by mixing with stirring; and by dispersing a carbon fiber having a fiber diameter of 1 to 1,000 nm in the resultant mixture under stirring.  
   
   
       26 . The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in  claim 22 , wherein the carbon fiber/active substance dispersion is prepared by dry-mixing a carbon fiber having a fiber diameter of 1 to 1,000 nm with a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more to thereby disperse the carbon fiber in the resultant mixture; and by adding an aqueous thickener solution to the resultant mixture, followed by mixing with stirring.  
   
   
       27 . The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in  claim 22 , wherein the content of the thickener in the aqueous thickener solution is 0.3 to 5 mass %, and the content of the styrene-butadiene rubber in the aqueous styrene-butadiene rubber dispersion is 10 to 60 mass %.  
   
   
       28 . The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in  claim 22 , wherein the thickener is carboxymethyl cellulose.  
   
   
       29 . A composition for forming a negative electrode material for a lithium battery, which composition is produced by means of a method as claimed in  claim 22 .  
   
   
       30 . A composition for forming a negative electrode material for a lithium battery, which composition comprises an aqueous thickener solution, wherein carbon fiber having a fiber diameter of 1 to 1,000 nm is dispersed.  
   
   
       31 . The composition for forming a negative electrode material for a lithium battery as claimed in  claim 30 , wherein the content of the thickener in the aqueous thickener solution is 0.3 to 5 mass %, and the amount of the carbon fiber is 0.1 to 10 mass % on the basis of the entirety of the composition.  
   
   
       32 . The composition for forming a negative electrode material for a lithium battery as claimed in  claim 30 , wherein the thickener is carboxymethyl cellulose.  
   
   
       33 . The negative electrode material for a lithium battery as claimed in  claim 1 , which is produced by applying the composition for forming the negative electrode material for a lithium battery as claimed in  claim 29  onto a metallic collector foil, and drying the thus-applied composition, followed by pressure molding.  
   
   
       34 . The negative electrode material for a lithium battery as claimed in  claim 33 , wherein the metallic collector foil is a copper foil or copper alloy foil having a thickness of 1 to 50 μm.  
   
   
       35 . A lithium battery comprising the negative electrode material for a lithium battery as recited in  claim 1 .  
   
   
       36 . A lithium secondary battery comprising the negative electrode material for a lithium battery as claimed in  claim 1 .  
   
   
       37 . The lithium secondary battery as claimed in  claim 36 , which comprises a non-aqueous electrolyte and a non-aqueous solvent for the non-aqueous electrolyte, which is at least one species selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene carbonate and vinylene carbonate.