Cathode active material having excellent electrochemical properties and lithium secondary battery comprising the same
The present disclosure provides a cathode active material comprising: lithium transition metal oxide-based particles; and a titanium dioxide coating layer formed on a part or a whole of a surface of the particle, in which the titanium dioxide coating layer is a partially reduced TiO 2−x (0<x<2), a preparation method thereof, and a lithium secondary battery including the cathode active material. The cathode active material of the present disclosure may significantly improve electrochemical properties of an electrochemical device including the cathode active material, preferably a lithium secondary battery by decomposing lithium-containing impurities remaining on the surface of the cathode active material by a partially reduced titanium dioxide coating layer formed on the surface of the cathode active material and enhancing the electrical conductivity of the cathode active material.
1. A cathode active material comprising:
lithium transition metal oxide-based particles; and
a titanium dioxide coating layer formed on a part or a whole of a surface of the particle,
wherein the titanium dioxide coating layer is a partially reduced TiO 2−x (0 <x<2); and
wherein the cathode active material comprises Li-containing impurities remaining on the surface thereof and a weight ratio (Li 2 CO 3 /LiOH) of Li 2 CO 3 and LiOH contained as the Li-containing impurities is in a range of 1.0 to 5.0.
2. The cathode active material of claim 1 , wherein the titanium dioxide coating layer has a peak present in a range of 452 to 457 eV in the Ti2p spectra by an X-ray photoelectron spectrometry (XPS).
3. The cathode active material of claim 2 , wherein the titanium dioxide coating layer has a ratio (P S /P R ) of peak intensity (P S ) of 452 to 457 eV derived from partially reduced Ti to peak intensity (P R ) of 457 to 460 eV derived from Ti 4+ in a range of 0.01 to 0.5 in the Ti2p spectra by an X-ray photoelectron spectrometry (XPS).
4. The cathode active material of claim 1 , wherein
a content of the Li-containing impurities is 2.0 wt % or less based on a total weight of the cathode active material.
5. The cathode active material of claim 1 , wherein an average particle size of the partially reduced titanium dioxide particles in the coating layer is in a range of 0.5 to 100 nm.
6. The cathode active material of claim 1 , wherein a content of the titanium dioxide coating layer is in a range of 0.05 to 2.0 wt % based on a total wt % of the cathode active material.
7. The cathode active material of claim 1 , wherein the lithium transition metal oxide-based particles are selected from the group consisting of LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , Li 4 Mn 5 O 12 , LiNi 1/3 Mn 1/3 Co 1/3 /O 2 , LiFePO 4 , Li(Co x Ni 1−x )O 2 (0.5≤x<1), Li a Ni b Co c X d O 2 (X is one or more selected from the group consisting of Mn, Al, Mg, Ti, Zr, Fe, V, W, Si, and Sn, and 0.9<a<1.10, 0.6≤b≤1.0, 0.0≤c≤0.2, and 0.0≤d≤0.2), and Li 1+x Mn 2−y−z−w Al y Co z Mg w O 4 (0.03<x<0.25, 0.01<y<0.2, 0.01<z<0.2, 0≤w<0.1, and x+y+z+w<0.4).
8. The cathode active material of claim 1 , wherein the lithium transition metal oxide-based particles have a nickel (Ni) content of 50% or more in the total transition metals.
9. The cathode active material of claim 1 , wherein the cathode active material has a ratio (R TiO2−x /R TiO2 ) of powder resistivity (R TiO2−x ) of partially reduced titanium dioxide to powder resistivity (R TiO2 ) of titanium dioxide of 0.5 or less under a compression condition of 13 to 64 MPa.
10. A cathode comprising the cathode active material of claim 1 .
11. The cathode of claim 10 , wherein the titanium dioxide coating layer has a peak present range of 452 to 457 eV in the Ti2p spectra by an X-ray photoelectron spectrometry (XPS).
12. The cathode of claim 10 , wherein the titanium dioxide coating layer has a ratio (P S /P R ) of peak intensity (PS) of 452 to 457 eV derived from partially reduced Ti to peak intensity (P R ) of 457 to 460 eV derived from Ti 4+ in a range of 0.01 to 0.5 in the Ti2p spectra by an X-ray photoelectron spectrometry (XPS).
13. The cathode of claim 10 , wherein the cathode active material has a ratio (R TiO2−x /R TiO2 ) of powder resistivity (R TiO2−x ) of partially reduced titanium dioxide to powder resistivity (R TiO2 ) of titanium dioxide of 0.5 or less under a compression condition of 13 to 64 MPa.
14. The cathode of claim 10 ,
a content of the Li-containing impurities is 2.0 wt % or less based on a total weight of the cathode active material.
15. A lithium secondary battery comprising the cathode of claim 10 , an anode, a separator interposed therebetween, and an electrolyte.
16. A method for preparing the cathode active material of claim 1 , the method comprising:
(i) coating a surface of a lithium transition metal oxide-based particle with titanium dioxide; and
(ii) subsequently subjecting the coated lithium metal composite oxide-based particles to heat treatment under an atmospheric condition of 550° C. or less for 0.5 to 5 hours, so that the titanium dioxide is partially reduced by an oxidation-reduction reaction with the lithium transition metal oxide-based particle.
17. The method of claim 16 , wherein in Step (i), an amount of titanium dioxide used is 0.05 to 2.0 wt % based on a total wt % of the lithium transition metal oxide-based particles.