Method for preparing positive electrode active material for secondary battery
A method for preparing a positive electrode active material for a secondary battery includes the steps of: providing a positive electrode active material precursor including a core portion and a shell portion, wherein the core portion contains nickel (Ni), cobalt (Co), and manganese (Mn), and the shell portion contains cobalt (Co) and surrounds the core portion; and forming a lithium composite transition metal oxide in a single particle form by mixing the positive electrode active material precursor with a lithium raw material to obtain a mixture, and firing the mixture at a temperature of 970° C. or more.
1 . A method for preparing a positive electrode active material for a secondary battery, the method comprising:
providing a positive electrode active material precursor including
a core portion of nickel-cobalt-manganese hydroxide and
a shell portion of cobalt hydroxide that surrounds the core portion;
forming a lithium composite transition metal oxide in a single particle form by mixing the positive electrode active material precursor with a lithium raw material to obtain a mixture, and firing the mixture at a temperature ranging from 980 to 1050° C.,
wherein the positive electrode active material precursor has a nickel (Ni) content of 60 mol % or less in the total transition metal, and a cobalt (Co) content greater than a manganese (Mn) content, and
wherein the positive electrode active material precursor includes a core portion consisting of nickel-cobalt-manganese hydroxide and a shell portion consisting of cobalt hydroxide.
2 . The method for preparing the positive electrode active material for a secondary battery of claim 1 , wherein the core portion is formed by coprecipitating a first transition metal solution including nickel (Ni), cobalt (Co), and manganese (Mn).
3 . The method for preparing the positive electrode active material for a secondary battery of claim 1 , wherein the shell portion is formed by coprecipitating a second transition metal solution including cobalt (Co).
4 . The method for preparing the positive electrode active material for a secondary battery of claim 1 , wherein the shell portion has 5 to 30 parts by volume based on 100 parts by volume of the positive electrode active material precursor.
5 . The method for preparing the positive electrode active material for a secondary battery of claim 1 , wherein the positive electrode active material precursor is in a form of secondary particles in which primary particles are aggregated.
6 . The method of claim 5 , wherein an average particle diameter (D 50 ) of the secondary particles is from 3 μm to 8 μm.
7 . The method for preparing the positive electrode active material for a secondary battery of claim 1 , wherein the firing is performed so that the positive electrode active material comprises primary particles having an average particle diameter (D50) of 2-10 μm.
8 . The method for preparing the positive electrode active material for a secondary battery of claim 1 , wherein the firing is performed so that the positive electrode active material includes a crystallite size of 210 nm or more.
9 . The method for preparing the positive electrode active material for a secondary battery of claim 1 , wherein the lithium raw material is mixed so that a molar ratio (Li/M) of lithium (Li) in the lithium raw material to all metal elements (M) contained in the lithium composite transition metal oxide is 1.06 or less.
10 . The method of claim 9 , wherein the molar ratio (Li/M) is 1 to 1.06.
11 . The method for preparing the positive electrode active material for a secondary battery of claim 1 , the method further comprising forming a coating portion by mixing and heat-treating the lithium composite transition metal oxide with a coating raw material including at least one selected from the group consisting of Al, B, Zr, Ti, Mg, Ta, Nb, Mo, W and Cr.
12 . The method of claim 1 , wherein the cobalt (Co) content is at least 5 mol % greater than the manganese (Mn) content.
13 . The method of claim 1 , wherein the firing of the mixture consists of a single temperature treatment at a temperature ranging from 980-1050° C.