Method of preparing composite cathode active material, composite cathode active material, and cathode and lithium battery containing the composite cathode active material
Provided are a method of preparing a cathode active material, a composite cathode active material, and a cathode and a lithium battery containing the composite cathode active material. The method includes mixing a transition metal source and a reducing agent to prepare a cathode active material precursor; and mixing and calcining the cathode active material precursor to prepare a lithium transition metal oxide, wherein a supplied amount of the reducing agent is about 0.003 mole/hr or less with respect to 1 mole/hr of a supplied amount of the transition metal source.
1. A method of preparing a composite cathode active material, the method comprising:
mixing a transition metal source and a reducing agent to prepare a composite cathode active material precursor; and
mixing and calcining the composite cathode active material precursor and a lithium source to prepare a lithium transition metal oxide,
wherein the reducing agent is supplied at about 0.015 mole/hr or less with respect to 1 mole/hr of the transition metal source.
2. The method of claim 1 , wherein the mixing of the transition metal source and the reducing agent is performed by continuously or intermittently supplying each of a first solution including a transition metal source and a second solution including the reducing agent to a reactor.
3. The method of claim 2 , wherein a concentration of the reducing agent in the second solution is about 350 mM or less.
4. The method of claim 2 , wherein the second solution is supplied at about 40 ml/hr or less.
5. The method of claim 2 , wherein a concentration of the transition metal source in the first solution is about 2 M or more.
6. The method of claim 2 , wherein the first solution is supplied at about 300 ml/hr or more.
7. The method of claim 1 , wherein a molar ratio of the composite cathode active material precursor and the lithium source being mixed is from about 1:1.05 to about 1:1.50.
8. The method of claim 1 , wherein, in an X-ray diffraction (XRD) spectrum of the cathode active material precursor, a first peak is observed at a diffraction angle (2θ) of about 19.1°±0.50°, a second peak is observed at a diffraction angle (2θ) of about 37.2°±0.50°, and an intensity ratio (I 2 /I 1 ) of the second peak to the first peak is about 0.30 or more.
9. The method of claim 1 , wherein the reducing agent is a reducing sugar.
10. The method of claim 1 , wherein the reducing agent is at least one selected from the group consisting of glucose, glyceraldehydes, galactose, lactose, maltose, and fructose.
11. The method of claim 1 , wherein the lithium metal compound comprises a compound represented by Formula 1:
Li[Li x Ni a Co b Mn c ]O 2+d <Formula 1>
wherein, in Formula 1, x+a+b+c=1; 0<x≦0.5, 0<a<1, 0<b<1, 0<c<1, and 0≦d≦0.1.
12. The method of claim 1 , wherein the lithium transition metal oxide comprises a compound represented by Formula 2:
p Li 2 MnO 3- (1- p )LiNi a Co b Mn c O 2 <Formula 2>
wherein, in Formula 2, 0<p<1, 0<a<1, 0<b<1, 0<c<1, and a+b+c=1.
13. The method of claim 1 , wherein the calcining is performed in an air atmosphere at a temperature of about 700° C. to about 1000° C. for about 5 hours to about 300 hours.
14. A composite cathode active material comprising a lithium transition metal oxide represented by Formula 1 , wherein secondary particles of the composite cathode active material are formed by binding primary particles of the composite cathode active material, an average particle diameter (D50) of the secondary particles is 5 μm or less, a specific surface area of the composite cathode active material is about 3.0 m 2 /g or more, an initial discharge capacity of the composite cathode active material is about 260 mAh/g or more, and the primary particles have a plate shape,
wherein the composite cathode active material is a calcined product of a cathode active material precursor and a lithium source,
wherein, in an X-ray diffraction (XRD) spectrum of the cathode active material precursor, a first peak is observed at a diffraction angle (2θ) of about 19.1°±0.50°, a second peak is observed at a diffraction angle (2θ) of about 37.2°±0.50°, and an intensity ratio (I2/I1) of the second peak to the first peak is about 0.30 or more:
Li[Li x Ni a Co b Mn c ]O 2+d <Formula 1>
wherein, in Formula 1, x+a+b+c=1; 0<x≦0.5, 0<a<1, 0<b<1, 0<c<1, and 0≦d≦0.1.
15. The composite cathode active material of claim 14 , wherein a thickness of the primary particles is about 200 nm or less.
16. The composite cathode active material of claim 14 , wherein an aspect ratio of a thickness and a length of the primary particles is about 1:5 or greater.
17. A cathode comprising the composite cathode active material of claim 14 .
18. A lithium battery containing the cathode of claim 17 .