Graphite power for negative electrode active material of lithium-ion secondary battery

Abstract

A graphite powder, preferably including scale-like particles, which satisfies the following formulae (1) and (2), wherein e(0.5) represents the initial charge-discharge efficiency of a coin cell fabricated from an electrode (work electrode) produced by compressing an electrode material employing graphite powder as an active material under a pressure of 0.5 t/cm 2 , a lithium metal counter electrode, a separator and an electrolytic solution; and e(3) represents the initial charge-discharge efficiency of a coin cell fabricated from an electrode (work electrode) produced by compressing an electrode material employing graphite powder as an active material under a pressure of 3 t/cm 2 , a lithium metal counter electrode, a separator and an electrolytic solution: e (3)(%)− e (0.5)(%)≥1,  formula (1): e (3)(%)>85.  formula (2): Also disclosed is a method of producing the graphite powder; a graphite material for a battery electrode; an electrode for a lithium ion; and a lithium-ion secondary battery.

1 . A method for producing a graphite powder, comprising a process of graphitizing a scale-like coke at 2,400 to 3,600° C., and a process of bringing the coke into contact with oxygen during a cooling process after the graphitization. 
     
     
         2 . The method for producing a graphite powder as claimed in  claim 1 , comprising dry mixing of one or more member of carbon materials selected from petroleum pitch, coal pitch and phenol resin with coke before the graphitization. 
     
     
         3 . The method for producing a graphite powder as claimed in  claim 2 , wherein the petroleum pitch or the coal pitch contains a quinoline insoluble component in an amount of 10 mass % or less and a beta-resin component in an amount of 20 mass % or more. 
     
     
         4 . A method for producing a graphite powder, comprising a process of graphitizing a scale-like coke at 2,400 to 3,600° C. and a process of bringing the coke into contact with oxygen under heating,
 wherein the total pore volume by the nitrogen gas adsorption method of the graphite powder is 8.0 μl/g to 20.0 μ1/g, the particles of the graphite powder are scale-like particles, and a peak ratio (x) of a rhombohedral structure in the graphite powder obtained by the expression x=P2/(P1+P2) is 0.05 or less, 
 wherein P1 is an actually measured peak strength of a hexagonal structure (100) plane measured by powder X-ray diffraction, and P2 is an actually measured peak strength of a rhombohedral structure (101) plane by powder X-ray diffraction. 
 
     
     
         5 . The method for producing the graphite powder as claimed in  claim 4 , wherein the process of bringing the coke into contact with oxygen under heating is to bring the coke into contact with oxygen at the time of a heating for the graphitization. 
     
     
         6 . The method for producing the graphite powder as claimed in  claim 4 , wherein the process of bringing the coke into contact with oxygen under heating is to bring the coke into contact with oxygen during the cooling process after the graphitization. 
     
     
         7 . The method for producing the graphite powder as claimed in  claim 4 , wherein the process of bringing the coke into contact with oxygen under heating is to bring the coke into contact with oxygen during an independent heating treatment after the completion of the graphitization process. 
     
     
         8 . The method for producing a graphite powder as claimed in  claim 4 , comprising dry mixing of one or more member of carbon materials selected from petroleum pitch, coal pitch and phenol resin with coke before the graphitization. 
     
     
         9 . The method for producing a graphite powder as claimed in  claim 8 , wherein the petroleum pitch or the coal pitch contains a quinoline insoluble component in an amount of 10 mass % or less and a beta-resin component in an amount of 20 mass % or more. 
     
     
         10 . The method for producing a graphite powder as claimed in  claim 4 , wherein a thickness of a crystal in the direction of C-axis (Lc) of the graphite powder is 50 nm or more and 1,000 nm or less. 
     
     
         11 . The method for producing a graphite powder as claimed in  claim 5 , wherein a thickness of a crystal in the direction of C-axis (Lc) of the graphite powder is 90 nm or more and 1,000 nm or less.