Positive electrode, lithium secondary battery containing the same, and method for manufacturing the positive electrode

Abstract

The present invention provides a positive electrode with improved lifespan and / or performance for a lithium secondary battery by adjusting the reaction resistance of the positive electrode, which is one of the components of the lithium secondary battery, thereby indirectly adjusting the reaction amount of the negative electrode. The present invention relates to a positive electrode comprising a positive electrode active material having a resistance component ratio of 2 or more as defined by the following formula 1: [Formula 1]R ct / R s In the above formula, R ct This refers to the charge transfer resistance of the positive electrode measured in the first frequency domain for a secondary battery including the positive electrode, and the R s This refers to the surface or interface resistance of the positive electrode measured in a second frequency region for a secondary battery including the positive electrode, wherein the first frequency region is a frequency region of 1 Hz to 1 kHz, and the second frequency region is a frequency region of over 1 kHz and up to 1,000 kHz.

Claims

1. A positive electrode containing a positive electrode active material, wherein the resistance component ratio defined by the following formula 1 is 2 or more, [Formula 1] R ｃｔ / R ｓ In the above formula 1, the R ｃｔ This refers to the charge transfer resistance of the positive electrode measured in the first frequency range for a secondary battery including the positive electrode, The aforementioned R ｓ This refers to the surface or interface resistance of the positive electrode measured in the second frequency range for a secondary battery including the positive electrode. The first frequency range is a frequency range of 1 Hz to 1 kHz. The second frequency range is the positive electrode, which has a frequency range of over 1 kHz and up to 1,000 kHz.

2. The aforementioned R ｃｔ This is determined based on the impedance information obtained by performing electrochemical impedance analysis (EIS) on the secondary battery, followed by a distribution of relaxation time (DRT) analysis to generate an impedance graph related to frequency, and then integrating the first region corresponding to the first frequency region of the impedance graph. The aforementioned R ｓ The positive electrode according to claim 1, wherein the positive electrode is determined based on a value obtained by integrating the second region corresponding to the second frequency region of the impedance graph, which is generated by performing a relaxation time distribution analysis on the secondary battery based on impedance information obtained by performing an electrochemical impedance analysis on the secondary battery.

3. The positive electrode active material has an average particle size D ５０ The positive electrode according to claim 1, wherein the first positive electrode active material and the second positive electrode active material are different from each other.

4. The positive electrode active material comprises a first positive electrode active material represented by the following chemical formula 1, It contains a second positive electrode active material represented by the following chemical formula 2, [Chemical formula 1] Li １＋ａ１ Ni ｘ１ Co ｙ１ Mn ｚ１ Al ｗ１ M １ ｖ１ O ２ In the aforementioned chemical formula 1, 0≦a1≦0.3, 0.6≦x1≦1.0, 0≦y1≦0.2, 0≦z1≦0.2, 0≦w1≦0.2, 0≦v1≦0.1, M １ This is a doping element comprising at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, Ba, and Mo. [Chemical formula 2] Li １＋ａ２ Ni ｘ２ Co ｙ２ Mn ｚ２ Al ｗ２ M ２ ｖ２ O ２ In the aforementioned chemical formula 2, 0≦a²≦0.3, 0.6≦x²≦1.0, 0≦y²≦0.2, 0≦z²≦0.2, 0≦w²≦0.2, 0≦v²≦0.1, M ２ The positive electrode according to claim 1, wherein is a doping element comprising at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, Ba, and Mo.

5. The average particle size D of the first positive electrode active material ５０ The positive electrode according to claim 1, wherein the thickness is 6 μm to 12 μm.

6. The average particle size D of the second positive electrode active material ５０ The positive electrode according to claim 1, wherein the particle is 1.5 μm to 5 μm in size.

7. The positive electrode according to claim 1, wherein the first positive electrode active material and the second positive electrode active material are contained in a weight ratio of 80:20 to 40:

60.

8. The positive electrode according to claim 1, wherein the positive electrode active material is obtained by mixing the positive electrode active material in distilled water, washing it with water, and then drying it.

9. A positive electrode containing a positive electrode active material, wherein the resistance component ratio defined in the following formula 1 is 2 or more, The negative electrode and, Electrolytes, A lithium secondary battery including, [Formula 1] R ｃｔ / R ｓ In the above formula, R ｃｔ This refers to the charge transfer resistance of the positive electrode measured in the first frequency range for the lithium secondary battery, The aforementioned R ｓ This refers to the surface or interface resistance of the positive electrode measured in the second frequency range for the lithium secondary battery, The first frequency range is a frequency range of 1 Hz to 1 kHz. The second frequency range is a lithium secondary battery with a frequency range of over 1 kHz and up to 1,000 kHz.

10. The aforementioned R ｃｔ This is determined based on the impedance information obtained by performing electrochemical impedance analysis (EIS) on the lithium secondary battery, followed by a distribution of relaxation time (DRT) analysis to generate an impedance graph related to frequency, and then integrating the first region corresponding to the first frequency region of the impedance graph. The aforementioned R ｓ The lithium secondary battery according to claim 9, wherein the impedance is determined based on the impedance information obtained by performing an electrochemical impedance analysis on the lithium secondary battery, a relaxation time distribution analysis is performed based on the impedance graph relating to frequency is generated, and the second region corresponding to the second frequency region of the impedance graph is integrated to obtain the value obtained.

11. The aforementioned negative electrode comprises a negative electrode current collector and A negative electrode active material layer containing a negative electrode active material, The lithium secondary battery according to claim 9, wherein the negative electrode active material comprises at least one of a silicon-based negative electrode active material and a carbon-based negative electrode active material.

12. The lithium secondary battery according to claim 11, wherein the silicon-based negative electrode active material is included in an amount of 1 wt% to 30 wt% based on the total weight of the negative electrode active material layer.

13. The anode active material includes the silicon-based anode active material and the carbon-based anode active material. The lithium secondary battery according to claim 11, wherein the silicon-based anode active material and the carbon-based anode active material are contained in a weight ratio of 1:99 to 30:

70.

14. (A) A step of mixing the positive electrode active material in distilled water and washing it with water, (B) A step of drying the washed positive electrode active material, (C) A step of applying the positive electrode slurry containing the dried positive electrode active material onto the positive electrode current collector, A method for manufacturing a positive electrode, including the method described above.

15. The aforementioned (A) stage is, (a1) A step of mixing the first positive electrode active material with the distilled water and performing a first water wash, (a2) A step of mixing the second positive electrode active material into the distilled water and performing a second water wash, Includes, The first positive electrode active material and the second positive electrode active material have an average particle size D ５０ A method for manufacturing a positive electrode according to claim 14, wherein the elements are different from each other.

16. The method for manufacturing a positive electrode according to claim 15, wherein the first washing step is performed at a higher temperature than the second washing step.

17. The method for manufacturing a positive electrode according to claim 15, wherein the first washing step is performed at 20°C to 40°C.

18. The method for manufacturing a positive electrode according to claim 15, wherein the second washing step is performed at 3°C ​​to 18°C.

19. The method for producing a positive electrode according to claim 15, wherein the first washing step is carried out by mixing the first positive electrode active material with the total weight of the distilled water in an amount of 50% to 70% by weight.

20. The method for manufacturing a positive electrode according to claim 15, wherein the second washing step is carried out by mixing the second positive electrode active material with the total weight of the distilled water in an amount of 65% to 85% by weight.

Images