Method for producing positive electrode active material for nonaqueous electrolyte secondary battery

Abstract

A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery includes crystallizing a nickel-cobalt-manganese composite hydroxide by neutralizing a salt containing at least nickel, a salt containing at least cobalt, and a salt containing at least manganese; and firing a lithium mixture obtained by mixing the nickel-cobalt-manganese composite hydroxide with a lithium compound in an oxygen atmosphere to obtain a lithium-metal composite oxide, wherein in the crystallization process, an oxygen concentration in an atmosphere above a solution surface of the aqueous reaction solution is controlled in a range of 0.2% to 2% by volume, a temperature of the aqueous reaction solution is controlled between 38° C. to 45° C., a pH value of the aqueous reaction solution is controlled between 11.0 to 12.5, and a dissolved nickel concentration in the aqueous reaction solution is controlled in a range of 300 mg/L to 900 mg/L.

1 . A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, the positive electrode active material represented by a general formula: Li a Ni x Co y Mn z M t O 2+α  (0.95≤a≤1.50, 0.30≤x≤0.70, 0.10≤y≤0.35, 0.20≤z≤0.40, 0≤t≤0.1, x+y+z+t=1, and 0≤α≤0.5; and M represents at least one element selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W) and containing a secondary particle formed of a plurality of flocculated primary particles, the method comprising:
 a crystallization process of crystallizing a nickel-cobalt-manganese composite hydroxide by neutralizing a salt containing at least nickel, a salt containing at least cobalt, and a salt containing at least manganese in an aqueous reaction solution; and 
 a firing process of firing a lithium mixture obtained by mixing the nickel-cobalt-manganese composite hydroxide with a lithium compound in an oxygen atmosphere to obtain a lithium-metal composite oxide, wherein 
 in the crystallization process, an oxygen concentration in an atmosphere above a solution surface of the aqueous reaction solution is controlled in a range of at least 0.2% by volume and up to 2% by volume, a temperature of the aqueous reaction solution is controlled in a range of at least 38° C. and up to 45° C., a pH value of the aqueous reaction solution is controlled in a range of at least 11.0 and up to 12.5 based on solution temperature of 25° C., and a dissolved nickel concentration in the aqueous reaction solution is controlled in a range of at least 300 mg/L and up to 900 mg/L. 
 
     
     
         2 . The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to  claim 1 , wherein the crystallization process includes continuously adding a mixed aqueous solution including nickel, cobalt, and manganese into a reaction vessel, and overflowing slurry including nickel-cobalt-manganese composite hydroxide particles formed by neutralization to recover the particles. 
     
     
         3 . The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to  claim 2 , wherein in the crystallization process, concentration of the mixed aqueous solution ranges from at least 1.5 mol/L and up to 2.5 mol/L. 
     
     
         4 . The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to  claim 1 , wherein in the firing process, firing is carried out at a temperature of at least 800° C. and up to 1000° C. 
     
     
         5 . The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to  claim 1 , wherein in the firing process, lithium hydroxide, lithium carbonate, or a mixture of these is used as the lithium compound.