Cathode active material for lithium-ion secondary batteries, method for producing same, and lithium-ion secondary battery comprising same
Provided are a positive active material for a lithium secondary battery, a method of preparing the positive active material, and a lithium ion secondary battery including the positive active material, the positive active material including a lithium-containing compound represented by the formula of Li 2−x M′O 3−y (wherein M′ is at least one element selected from Mg, Al, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, and F; 0≤x≤1; and 0≤y≤3) on a surface or inside of a lithium metal oxide represented by the formula of Li 1−x Ni y M 1−y O 2−z (wherein M is at least one element selected from Co and Mn; 0≤x≤0.05; 0.6≤y≤1; and 0≤z≤0.05).
1. A method of preparing a positive active material for a lithium secondary battery, the method comprising:
coating a lithium metal oxide represented by Formula 1 and having a layered structure with at least one coating material selected from a metal oxide and a fluorine-containing compound by stirring the lithium metal oxide and the at least one coating material at about 8,000 rpm to about 20,000 rpm; and
thermally treating at about 800° C. to 1,000° C. a resulting powder from the coating step to form a lithium-containing compound represented by Formula 2 on the surface or inside of the lithium metal oxide:
Li 1−x Ni y M 1−y O 2−z [Formula 1]
wherein, in Formula 1, M is at least one element selected from Co and Mn; 0≤x≤0.05; 0.6≤y≤1; and 0≤z≤0.05, and
Li 2−x M′O 3−y [Formula 2]
wherein, in Formula 2, M′ is at least one element selected from Mg, Al, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, and F; 0≤x≤1; and 0≤y≤3.
2. The method of claim 1 , wherein, in the coating of the lithium metal oxide, the stirring is performed for about 10 seconds to about 60 seconds.
3. The method of claim 1 , wherein the coating is performed by dry coating.
4. The method of claim 1 , wherein, in the thermal treating, the at least one coating material reacts with a residual lithium on the surface or inside of the lithium metal oxide, thereby to form the lithium-containing compound represented by Formula 2 on the surface or inside of the lithium metal oxide.
5. The method of claim 4 , wherein an amount of the residual lithium after the thermal treating is reduced by about 10% to about 20%, compared to that when the lithium metal oxide represented by Formula 1 is heated alone.
6. The method of claim 1 , wherein the metal oxide is an oxide including at least one metal element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, and Ru.
7. The method of claim 1 , wherein the metal oxide is at least one selected from the group consisting of MgO, Al 2 O 3 , CaO, TiO 2 , V 2 O 5 , Cr 2 O 3 , Fe 2 O 3 , CuO, ZnO, Ga 2 O 3 , SrO, Y 2 O 3 , ZrO 2 , NbO 2 , MoO 3 , and RuO 2 .
8. The method of claim 1 , wherein the fluorine-containing compound is at least one selected from the group consisting of NaF, NH 3 F, and PVDF.