Positive electrode for lithium secondary battery, preparation method thereof, and lithium secondary battery including same
Provided is a positive electrode for a lithium secondary battery, the positive electrode including a positive electrode mixture layer on a positive electrode current collector, wherein the positive electrode mixture layer includes a positive electrode active material and a lithium ion additive, the lithium ion additive is a lithium ion conductive ceramic material represented by Formula 1 below, and the lithium ion conductive ceramic material has a structure in which lithium ions are additionally inserted into vacancy sites of a NASICON-type (Na super ionic conductors-type) structure. Li 1+x1+y1 M 1 2−x1 M 2 x1 (PO 4 ) 3 [Formula 1] In Formula 1, M 1 is at least one of Ti and Ge, M 2 is one or more selected from the group consisting Al, Cr, Ga, Fe, Sn, In, Lu, Y, and La, and 0<x1≤0.3, and 1.7≤y1≤2.0.
1. A lithium secondary battery, comprising,
a positive electrode;
a negative electrode; and
a separator interposed between the positive electrode and the negative electrode;
wherein the positive electrode comprises a positive electrode mixture layer disposed on a positive electrode current collector, wherein
the positive electrode mixture layer includes a positive electrode active material and a lithium ion additive,
the lithium ion additive is a lithium ion conductive ceramic material represented by Formula 2 below, and
the lithium ion conductive ceramic material has a structure in which lithium ions are additionally inserted into vacancy sites of a NASICON-type (Na super ionic conductors-type) structure,
wherein the lithium ion additive acts as an effective irreversible additive at a charge/discharge voltage range of 3.0 V to 4.5 V,
wherein the positive electrode active material and the lithium ion additive are included in a weight ratio of 8.5:1.5 to 9:1,
wherein the positive electrode active material includes lithium cobalt oxide (LiCoO 2 ): and wherein a capacity retention rate after 30 cycles is 92.1-97.5%
Li 1+x2+y2 Ti 2−x2 Al x2 (PO 4 ) 3 [Formula 2]
in Formula 2, 0<x2≤0.3, and 1.7≤y2≤2.0.
2. The lithium secondary battery of claim 1 , wherein the lithium ion additive is Li 3 Ti 1.7 Al 0.3 (PO 4 ) 3 .
3. The lithium secondary battery of claim 1 , wherein the positive electrode active material and the lithium ion additive are included in an amount of 80 wt % to 98 wt % based on the total weight of the positive electrode mixture layer.
4. The lithium secondary battery of claim 1 , wherein the positive electrode mixture layer further comprises a binder.
5. The positive electrode for a lithium secondary battery of claim 1 , wherein the ratio (N/P) of the capacity of the negative electrode (N) to the capacity of the positive electrode (P) is 1.1 to 1.3.
6. A method for preparing a positive electrode for a lithium secondary battery, the method comprising:
forming, on a positive electrode current collector, a positive electrode mixture layer including a positive electrode active material and a lithium ion additive, wherein
the lithium ion additive is a lithium ion conductive ceramic material represented by Formula 2 below, and
the lithium ion conductive ceramic material has a structure in which lithium ions are additionally inserted into vacancy sites of a NASICON-type (Na super ionic conductors-type) structure,
wherein the lithium ion additive acts as an effective irreversible additive at a charge/discharge voltage range of 3.0 V to 4.5 V, and
wherein the positive electrode active material and the lithium ion additive are included in a weight ratio of 8.5:1.5 to 9:1
wherein the positive electrode active material includes lithium cobalt oxide (LiCoO 2 ): and wherein a capacity retention rate after 30 cycles is 92.1-97.5%
Li 1+x2+y2 Ti 2−x2 Al x2 (PO 4 ) 3 [Formula 2]
in Formula 2, 0<x2≤0.3, and 1.7≤y2≤2.0.
7. The method of claim 6 , wherein the lithium ion additive is prepared by adding n-butyl lithium to lithium titanium aluminum phosphate (LTAP) represented by Formula 4 below:
Li 1+x3 Ti 2−x3 Al x3 (PO 4 ) 3 [Formula 4]
in Formula 4, 0<x3<0.3.
8. The method of claim 6 , wherein the lithium ion additive is Li 3 Ti 1.7 Al 0.3 (PO 4 ) 3 .
9. The method of claim 6 , wherein the positive electrode active material and the lithium ion additive are included in an amount of 80 wt % to 98 wt % based on the total weight of the positive electrode mixture layer.
10. The method of claim 6 , wherein the forming step comprises:
disposing the positive electrode mixture on a surface of the positive electrode current collector;
drying the positive electrode mixture; and
rolling the positive electrode mixture and positive electrode current collector.
11. The method of claim 6 , wherein the forming step comprises:
disposing the positive electrode mixture on a surface of a support material to form a film on the support material; and
laminating the formed film onto the positive electrode current collector.