Positive active material, positive electrode including the same, and lithium secondary battery including the positive electrode
Provided are a positive active material, a positive electrode including the same, and a lithium secondary battery including the positive electrode. The positive active material includes lithium cobalt oxide containing a metal element, and the lithium cobalt oxide containing a metal element has a ratio of a peak intensity of the O3 phase to a peak intensity of the H1-3 phase, I O3 /I H1-3 , that is greater than 1 in a X-ray diffraction (XRD) analysis spectrum using Cu-Kα radiation. Accordingly, a lithium secondary battery including the positive active material may have improved lifespan characteristics even at a high voltage.
1. A positive active material for a lithium secondary battery, the positive active material comprising:
a lithium cobalt oxide containing a metal element,
wherein the lithium cobalt oxide containing a metal element is represented by Formula 1:
Li a (Co 1.0-x-y Mg x Mn y )O 2 Formula 1
wherein, in Formula 1,
0.8≦a≦1.2, 0.0025≦x≦0.005, and 0.0025≦y≦0.0075,
wherein the lithium cobalt oxide containing a metal element has a ratio of a peak intensity of an O3 phase to a peak intensity of an H1-3 phase, I O3 /I H1-3 , that is greater than 1 in an X-ray diffraction (XRD) analysis spectrum using Cu-Kα radiation, and
wherein an average particle diameter D50 of the lithium cobalt oxide containing a metal element is in a range of about 8 μm to about 20 μm, and
the metal element is placed in a site of the cobalt in a crystal lattice of the lithium cobalt oxide.
2. The positive active material of claim 1 , wherein the I O3 /I H1-3 is greater than 1.0 and equal to or less than 5.0.
3. The positive active material of claim 1 , wherein the lithium cobalt oxide containing a metal element does not comprise a spinel compound.
4. The positive active material of claim 1 , wherein the metal element has an oxidation number of 2 or 3.
5. The positive active material of claim 1 , wherein
the lithium cobalt oxide containing a metal element is Li(Co 0.995 Mg 0.0025 Mn 0.0025 )O 2 , Li(Co 0.9925 Mg 0.0025 Mn 0.005 )O 2 , Li(Co 0.99 Mg 0.0025 Mn 0.0075 )O 2 , or a combination thereof.
6. The positive active material of claim 1 , wherein
an average oxidation number N of a metal element contained in the lithium cobalt oxide is in a range of about 2.1 to about 2.75.
7. The positive active material of claim 1 , wherein
a c-axis lattice parameter of a unit lattice of the lithium cobalt oxide containing a metal element is 14.050 Å or more.
8. A positive electrode for a lithium secondary battery, the positive electrode comprising:
the positive active material of any one of claim 1 .
9. A lithium secondary battery comprising the positive electrode of claim 8 .
10. The lithium secondary battery of claim 9 , wherein
a charging cutoff voltage of the lithium secondary battery is 4.5 V or more.
11. The lithium secondary battery of claim 10 , wherein,
after charging, the lithium cobalt oxide containing a metal element in the positive electrode has a ratio of a peak intensity of the O3 phase to a peak intensity of the H1-3 phase, I O3 /I H1-3 , that is greater than 1 in an XRD analysis spectrum using Cu-Kα radiation.
12. The lithium secondary battery of claim 10 , wherein,
the I O3 /I H1-3 is greater than 1.0 and equal to or less than 5.0.