ELECTRODE QUALITY EVALUATION METHOD AND ELECTRODE MANUFACTURING METHOD

Abstract

Provided is a method of evaluating electrode quality capable of simply and quickly filtering out defective electrodes by measuring a color coordinate value of electrodes before roll-pressing, which specifically includes: providing an electrode which includes a current collector and an active material layer formed on the current collector and has not been roll-pressed; measuring a color coordinate value of the active material layer using an optical instrument; and evaluating the electrode as a good product when the measured color coordinate value satisfies a predetermined electrode quality evaluation criterion and as defective when the measured color coordinate value does not satisfy the predetermined electrode quality evaluation criterion.

Claims

1. A method of evaluating quality of an electrode comprising a current collector and an active material and not being rolled, comprising: measuring a color coordinate value of the active material layer using an optical instrument; and evaluating the quality of the electrode as a good product when the color coordinate value satisfies a predetermined electrode quality evaluation criterion and as defective when the color coordinate value does not satisfy the predetermined electrode quality evaluation criterion.

2. The method of claim 1, wherein the color coordinate value is an L* value, and the predetermined electrode quality evaluation criterion for the L* value is 35.4 or more.

3. The method of claim 1, wherein the color coordinate value is an a* value, and the predetermined electrode quality evaluation criterion for the a* value is 0.78 or more.

4. The method of claim 1, wherein the color coordinate value is a whiteness value, and the predetermined electrode quality evaluation criterion for the whiteness value is 7 or more.

5. The method of claim 1, wherein the optical instrument is a spectrophotometer or a colorimeter.

6. The method of claim 5, wherein the colorimeter is a contact colorimeter or a non-contact colorimeter.

7. A method of manufacturing an electrode, comprising: forming an active material layer by applying a slurry including an active material, a conductive material, and a binder onto a current collector; drying the active material layer to manufacture an electrode which is not roll-pressed; evaluating a quality of the electrode by the method of claim 1; and roll-pressing the electrode which are evaluated as a good product.

8. The method of claim 7, wherein the slurry is applied in a loading amount of 0.005 g/cm.sup.2 to 0.050 g/cm.sup.2.

9. The method of claim 7, wherein a total heat amount required for the drying satisfies Equation 1:
Total heat amount required for the drying (kW)=(46.30−L* value)/0.0077,  Equation 1 wherein, in Equation 1, L* value is a predetermined electrode quality evaluation criterion and is 35.4 or more.

10. The method of claim 7, wherein a total heat amount required for the drying satisfies Equation 2:
Total heat amount required for the drying (kW)=(1.09−a* value)/2.19×10.sup.−5,  Equation 2 wherein, in Equation 2, the a* value is a predetermined electrode quality evaluation criterion and is 0.78 or more.

11. The method of claim 7, wherein a total heat amount required for the drying satisfies Equation 3:
Total heat amount required for the drying (kW)=(13.06−whiteness value)/0.0041,  Equation 3 wherein, in Equation 3, the whiteness value is a predetermined electrode quality evaluation criterion and is 7 or more.

12. The method of claim 7, wherein the drying is carried out with a total heat amount of 1,000 kW to 1,450 kW.

13. The method of claim 7, wherein the active material layer has a thickness of 50 μm to 500 μm.

Description

MODES OF THE INVENTION

[0076] Hereinafter, exemplary embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

Preparation Example 1

[0077] A slurry was prepared by adding, to 55 parts by weight of water, 41 parts by weight of natural graphite, 0.5 parts by weight of a conductive material, 2.5 parts by weight of SBR, and 1 part by weight of CMC.

[0078] In order to manufacture an electrode, an active material layer having a thickness of 144 μm was formed by applying the slurry at a loading amount of 0.014 g/cm.sup.2 on one side of a copper current collector having a thickness of 8 μm and drying the same with a total heat amount of 1,190 kW. An active material layer was formed on the other side of the current collector under the same recipe and process conditions, and thus an electrode including active material layers formed on both sides of the copper current collector and having a total active material layer thickness of 288 μm was obtained.

Preparation Example 2

[0079] An electrode was manufactured in the same manner as in Preparation Example 1 except that drying was performed with a total heat amount of 1,257 kW for the manufacture of the electrode.

Preparation Example 3

[0080] An electrode was manufactured in the same manner as in Preparation Example 1 except that drying was performed with a total heat amount of 1,396 kW for the manufacture of the electrode.

Preparation Example 4

[0081] An electrode was manufactured in the same manner as in Preparation Example 1 except that drying was performed with a total heat amount of 1,480 kW for the manufacture of the electrode.

Example: Evaluation of Electrode Quality

[0082] Color coordinate values such as an L* value, an a* value, and a whiteness value were measured from an active material layer of each of the electrodes manufactured in Preparation Examples 1 to 4 using a CM2600d colorimeter manufactured by Konica Minolta, Inc, by setting the measurement mode to SCI and selecting a D65 standard light source (color temperature: 6,500 K) and the CIE 1976 10° standard observer, performing white correction, and then bringing the colorimeter into contact with a location to be measured, and the results are shown in the following Table 1.

TABLE-US-00001 TABLE 1 L* a* Whiteness Preparation Example 1 37.35 0.84 8.32 Preparation Example 2 36.37 0.79 7.76 Preparation Example 3 35.86 0.78 7.66 Preparation Example 4 34.85 0.77 6.93

[0083] When a color coordinate value of an active material layer of each of the electrodes manufactured in Preparation Examples 1 to 4 was compared with a predetermined electrode quality evaluation criterion (L* value: 35.4 or more, a* value: 0.78 or more, whiteness: 7 or more), in the case of the electrodes of Preparation Examples 1 to 3, since all of the measured color coordinates (an L* value, an a* value, and whiteness) satisfied predetermined electrode quality evaluation criteria, the electrodes were evaluated as good products.

[0084] On the other hand, in the case of the electrode of Preparation Example 4, since all of the measured color coordinates (an L* value, an a* value, and whiteness) did not satisfy predetermined electrode quality evaluation criteria, the electrode was evaluated as defective.

Experimental Example: Measurement of Adhesion In Electrode Before Roll-Pressing

[0085] Each of the electrodes manufactured in Preparation Examples 1 to 4 was attached to a glass slide using double-sided tape, and subsequently, the electrode was pulled at an angle of 90° at a speed of 100 mm/min using a UTM (manufactured by Lloyd), and a force required to peel off the electrode from the glass slide was measured. The results are shown in the following Table 2.

TABLE-US-00002 TABLE 2 Adhesive strength Adhesive strength Used before roll-pressing after roll-pressing electrode (gf/20 mm) (gf/20 mm) Evaluation Preparation 69.3 68.5 Normal Example 1 Preparation 52.0 51.1 Normal Example 2 Preparation 44.3 44.0 Normal Example 3 Preparation 33.8 32.9 Adhesion defect Example 4

[0086] As shown in Table 2, in the case of the electrodes of Preparation Example 1 to 3, which were classified as good products according to the electrode quality evaluation method of the present invention, it can be seen that an excellent adhesive strength of 40 gf/20 mm or more was exhibited in the electrodes after roll-pressing.

[0087] On the other hand, in the case of the electrode of Preparation Example 4, in which all of the measured color coordinates, an L* value, an a* value, and whiteness, did not satisfy predetermined electrode quality evaluation criteria, it can be seen that the electrode did not have satisfactory properties to be used as an electrode, due to having an adhesive strength of 32.9 gf/20 mm after roll-pressing. That is, it can be seen that adhesion is poor.

[0088] Therefore, according to the present invention, it can be seen that it is possible to predict adhesion, which is a property attained after roll-pressing, by the simple means of measuring a color coordinate value before roll-pressing and filter out defective electrodes before roll-pressing. That is, it can be seen that it is possible to filter out defective electrodes even before roll-pressing, and therefore, it is possible to significantly reduce a defect rate of finished electrode products.