Cathode active material, lithium secondary battery having same, and method for preparing same
The present invention relates to a cathode active material, a lithium secondary battery having the same, and a method for preparing the same, and the purpose of the present invention is to provide battery properties and thermal stability under a high temperature environment even if the Ni content of M in LiMO 2 (M=Ni, Co, Ti, Zr, etc.) of layered oxide is increased to 65% or more. The present invention provides a cathode active material for a lithium secondary battery which is represented by chemical formula 1 below and is obtained by substituting a part of Ni, Co and Mn for a dissimilar metal (M) through heat treatment with a lithium source after coating the dissimilar metal (M) on the surface of a transition metal precursor comprising Ni, Co and Mn. LiNi a Co b Mn c M d O 2 [Chemical Formula 1] (0.6<a≤0.9, 0<d≤0.1, a+b+c+d=1, M represents at least one metal element selected from the group consisting of Ti, Al, Mg, Fe, Cu, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si and Zr.).
1. A cathode active material for lithium secondary batteries which is represented by Chemical Formula 1 below and is obtained by coating a dissimilar metal (M) on a surface of a transition metal precursor comprising Ni, Co and Mn and then heat-treating the transition metal precursor together with a lithium source so that a portion of Ni, Co and Mn is substituted with the dissimilar metal (M):
LiNi a Co b Mn c M d O 2 [Chemical Formula 1 ]
wherein 0.65≤a ≤0.7, 0<d ≤0.1, a+b+c+d=1, and M is Ti.
2. The cathode active material of claim 1 , wherein the transition metal precursor comprises a nickel-based transition metal hydroxide or a nickel-based transition metal carbonate prepared by a coprecipitation method.
3. The cathode active material of claim 1 , wherein the content (a) of Ni in Chemical Formula 1 is equal to 0.7.
4. A lithium secondary battery comprising a cathode active material which is represented by Chemical Formula 1 below and is obtained by coating a dissimilar metal (M) on a surface of a transition metal precursor comprising Ni, Co and Mn and then heat-treating the transition metal precursor together with a lithium source so that a portion of Ni, Co and Mn is substituted with the dissimilar metal (M):
LiNi a Co b Mn c M d O 2 [Chemical Formula 1]
wherein 0.65≤a≤0.7, 0<d≤0.1, a+b+c+d=1, and M is Ti.
5. The lithium secondary battery of claim 4 , wherein the cathode active material has an exothermic temperature peak observed at 275° C. or more, as evaluated by differential scanning calorimetry (DSC) when the lithium secondary battery is charged to 4.3 V.
6. The lithium secondary battery of claim 4 , wherein the content (a) of Ni in Chemical Formula 1 is equal to 0.7.
7. A method for preparing a cathode active material for lithium secondary batteries, comprising:
coating a dissimilar metal compound on a surface of a transition metal precursor including Ni, Co and Mn by adding the transition metal precursor to a dissimilar metal (M) compound coating solution and stirring and drying the resulting mixture; wherein the coating comprises
preparing a Ti compound,coating solution comprising one or more Ti compounds selected from the group consisting of a nanosized Ti oxide and a precursor thereof; and
coating the Ti compound on a surface of the transition metal precursor by adding the transition metal precursor to the Ti compound coating solution and stirring and drying the resulting mixture, and
preparing a cathode active material represented by Chemical Formula 1 below by heat-treating the transition metal precursor coated with the dissimilar metal compound together with a lithium source so that a portion of Ni, Co and Mn is substituted with the dissimilar metal (M):
LiNi a Co b Mn c M d O 2 [Chemical Formula 1 ]
wherein 0.65≤a≤0.7, 0<d≤0.1, a+b+c+d=1, and M is Ti.
8. The method of claim 7 , wherein the transition metal precursor comprises a nickel-based transition metal hydroxide or a nickel-based transition metal carbonate prepared by a coprecipitation method.
9. The method of claim 7 , wherein the Ti compound is included at a content of 0.1 to 5% by weight, based on the weight of the transition metal precursor.
10. The method of claim 7 , wherein the transition metal precursor is represented by Chemical Formula 2 below:
Ni a Co b Mn c O 2 [Chemical Formula 2 ]
wherein 0.65≤a≤0.7, and a+b+c=1.