Additive comprised in cathode material for secondary battery, cathode material comprising the same, and secondary battery comprising cathode material
Provided is an irreversible additive contained in a cathode material for a secondary battery, wherein the irreversible additive is an oxide represented by the following Chemical Formula 1, and wherein the oxide has a trigonal crystal structure, a cathode material including the same, and a secondary battery including the cathode material, Li 2+a Ni 1−b M b O 2+c (1) in Chemical Formula 1, −0.2≤a≤0.2, 0≤b<0.5, 0≤c≤0.2, and M is one or more elements selected from the group consisting of Cu, Mg, Pt, Al, Co, P, and B.
1. A secondary battery comprising a cathode in which a cathode material is coated onto a cathode current collector,
wherein the cathode material includes an additive including an oxide represented by the following Chemical Formula 1, and a cathode active material,
wherein a content of the additive is 0.1% by weight to 10% by weight based on a total weight of the cathode material;
wherein the additive initially has a trigonal crystal system and is converted into a monoclinic crystal system in a reversible structural conversion manner within a range in which the operating range of the secondary battery is 4.0V or more,
wherein the additive is reversibly maintained between the trigonal crystal structures and the monoclinic crystal structures, and
Li 2+a Ni 1-b M b O 2+c (1)
in Chemical Formula 1, −0.2≤a≤0.2, 0≤b<0.5, 0≤c≤0.2, and
M is one or more elements selected from the group consisting of Cu, Mg, Pt, Al, Co, P, and B.
2. The secondary battery according to claim 1 , wherein the additive belongs to a space group of C2/m when the crystal structure is a monoclinic crystal system.
3. The secondary battery according to claim 1 , wherein the cathode active material comprises an oxide represented by the following Chemical Formula 2,
Li(Ni a Co b Mn c )O 2 (2)
in Chemical Formula 2, 0<a<1, 0<b<1, 0<c<1, a+b+c=1.
4. The secondary battery according to claim 1 , wherein the secondary battery has a structure in which an electrode assembly is built in a battery case together with an electrolyte, with the electrode assembly including:
the cathode;
an anode in which an anode material including an anode active material is coated onto an anode current collector; and
a separator that is interposed between the cathode and the anode.
5. The secondary battery according to claim 1 , wherein the secondary battery is a lithium secondary battery.
6. The secondary battery according to claim 1 , wherein the oxide belongs to a space group of P3-m1.
7. The secondary battery according to claim 1 , wherein the oxide has a crystal lattice of a=3.0954 Å, c=5.0700 Å, γ=120.00°.
8. The secondary battery according to claim 1 , wherein the oxide is Li 2 NiO 2 .
9. The secondary battery according to claim 3 , wherein the cathode active material comprises nickel, cobalt, and manganese.
10. The secondary battery according to claim 3 , wherein the cathode active material comprises the oxide represented by Chemical Formula 2 in an amount of 80% by weight or more based on a total weight of the cathode active material.
11. The secondary battery according to claim 1 , wherein the cathode material further comprises:
a conductive material in an amount of 1% to 30% by weight based on the total weight of the cathode material; and
a binder in an amount of 1% to 30% by weight based on the total weight of the cathode material.