CARBON NANOTUBE DISPERSION AND METHOD FOR PRODUCING SAME

Abstract

The present disclosure relates to a carbon nanotube dispersion liquid comprising bundle-type carbon nanotubes; a dispersion medium; and a polyvinyl butyral resin having a weight average molecular weight of greater than 50,000, a method for preparing the same, methods for preparing electrode slurry and an electrode using the same, and an electrode and a secondary battery prepared using the carbon nanotube dispersion liquid.

Claims

1. A carbon nanotube dispersion liquid comprising: bundle-type carbon nanotubes; a dispersion medium; and a polyvinyl butyral resin having a weight average molecular weight of greater than 50,000, wherein dispersed particle diameters of the bundle-type carbon nanotubes have particle size distribution D.sub.50 of 3 m to 10 m.

2. The carbon nanotube dispersion liquid of claim 1, wherein the polyvinyl butyral resin has a weight average molecular weight of 150,000 or greater.

3. The carbon nanotube dispersion liquid of claim 1, wherein the polyvinyl butyral resin has a weight average molecular weight of 200,000 or greater.

4. The carbon nanotube dispersion liquid of claim 1, wherein a content of a hydroxyl group-containing repeating unit of the polyvinyl butyral resin is 15% by weight or greater.

5. The carbon nanotube dispersion liquid of claim 1, wherein a content of a hydroxyl group-containing repeating unit of the polyvinyl butyral resin is 20% by weight or greater.

6. The carbon nanotube dispersion liquid of claim 1, wherein the polyvinyl butyral resin comprises a first polyvinyl butyral resin having a weight average molecular weight of greater than 50,000; and a second polyvinyl butyral resin having a lower weight average molecular weight than the first polyvinyl butyral resin.

7. The carbon nanotube dispersion liquid of claim 1, wherein dispersed particle diameters of the bundle-type carbon nanotubes have D.sub.50 is from 3 m to 10 m, D.sub.10 is 1 m or greater, and D.sub.90 is 30 m or less.

8. A method for preparing the carbon nanotube dispersion liquid of claim 1 comprising mixing bundle-type carbon nanotubes, and a polyvinyl butyral resin having a weight average molecular weight of greater than 50,000.

9. A method for preparing electrode slurry comprising mixing the carbon nanotube dispersion liquid of claim 1, an electrode active material and a binder resin.

10. A method for preparing an electrode comprising: preparing electrode slurry by mixing the carbon nanotube dispersion liquid of claim 1, an electrode active material and a binder resin; and forming an electrode using the electrode slurry.

11. Electrode slurry comprising: the carbon nanotube dispersion liquid of claim 1; an electrode active material; and a binder resin.

12. An electrode prepared using electrode slurry comprising the carbon nanotube dispersion liquid of claim 1, an electrode active material and a binder resin.

13. A secondary battery comprising the electrode of claim 12.

Description

EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 to 7

[0086] To an N-methyl pyrrolidone (NMP) solvent, bundle-type carbon nanotubes having a monomer diameter of 10 nm to 15 nm and BET of 240 m.sup.2/g to 250 m.sup.2/g, and a polyvinyl butyral resin of the following Table 1 were mixed in a content as shown in the following Table 2 to prepare a carbon nanotube dispersion liquid. % by weight in Table 1 is based on 100% by weight of the polyvinyl butyral resin, and % by weight in Table 2 is based on 100% by weight of the carbon nanotube dispersion liquid. Herein, a beads mill was used. Dispersed particle diameters and viscosity of the prepared dispersion liquid were measured and are shown in the following Table 3.

[0087] In order to prepare electrode slurry (100 parts by weight of solid), the carbon nanotube dispersion liquid prepared above was mixed with 97.8 parts by weight of a ternary positive electrode active material and 1 parts by weight of a PVdF-based binder. Herein, the carbon nanotubes and the polyvinyl butyral resin were present in 1 parts by weight and 0.2 parts by weight, respectively. Subsequently, the electrode slurry was coated on an aluminum current collector, and the result was rolled using a roll press to prepare a positive electrode polar plate (mix density 3.3 g/cc) .

[0088] Meanwhile, negative electrode slurry comprising 97.3 parts by weight of a negative electrode active material, 0.7 parts by weight of a conductor, 1 parts by weight of a viscosity agent (CMC) and 1 parts by weight of a binder (SBR) was coated on a copper current collector, and the result was rolled to prepare a negative electrode polar plate having mix density of 1.6 g/cc.

[0089] A monocell was manufactured using the positive electrode applying the dispersion liquid prepared above and the negative electrode. Specifically, a polyethylene separator was placed between the negative electrode polar plate and the positive electrode polar plate, the result was introduced to a battery case, and then a liquid, electrolyte was injected thereto to manufacture a battery. Herein, as the liquid electrolyte, a 1.0 M LiPF.sub.6-dissolved mixed solution of ethylene carbonate, ethylmethyl carbonate and diethyl carbonate (1/2/1 volume ratio) was used.

Adhesive Strength Measurement

[0090] In order to measure adhesive strength, the positive electrode polar plate (prior to manufacturing a battery) prepared as above was cut to pieces having a same size of 15 mm150 mm, the pieces were fixed on slide glass, and peeled off from a current collector to measure 180 degree peel strength. As for the evaluation, peel strength of 5 or more was measured, and the average value was determined. Results of measuring adhesive strength are shown in the following Table 3.

Monocell Evaluation

[0091] The battery manufactured above went through 1.0 C/1.0 C charge and discharge 3 times at room temperature, and SOC was established based on the last discharge capacity. 10 second resistance was measured by applying discharge pulse with 6.5 C at SOC 50.

TABLE-US-00001 TABLE 1 Polyvinyl Butyral Resin (wt %) PVB PVAc PVA Molecular Weight (Chemical (Chemical (Chemical (DMF) Formula Formula Formula MW 1) 2) 3) (1,000 g/mol) PDI Example 1 68.3 0.9 30.8 270 3.8 Example 2 75.0 1.2 23.8 350 3.2 Example 3 74.1 2.3 23.6 160 3.6 Example 4* 73.5 1.8 24.7 190 6.3 Example 75.0 1.2 23.8 350 3.2 4(1)* Example 72 2.5 25.5 57 2.7 4(2)* Example 5** 74.6 1.8 23.7 250 4.4 Example 75.0 1.2 23.8 350 3.2 5(1)** Example 74.1 2.3 23.6 160 3.6 5(2)** Example 6 82.6 2.4 14.9 180 3.4 Comparative Not Used Example 1 Comparative Commercial Dispersant AFCONA Example 2 4570 Comparative Commercial Dispersant PVP Example 3 Comparative 78.0 2.5 19.5 37 2.7 Example 4 Comparative 68.3 0.9 30.8 270 3.8 Example 5 Comparative 68.3 0.9 30.8 270 3.8 Example 6 Comparative 68.3 0.9 30.8 270 3.8 Example 7 *The constitution unit content and molecular weight of Example 4 are values based on the whole carbon nanotube dispersion liquid when using both the polyvinyl butyral resin of Example 4(1) and the polyvinyl butyral resin of Example 4(2). **The constitution unit content and molecular weight of Example 5 are values based on the whole carbon nanotube dispersion liquid when using both the polyvinyl butyral resin of Example 5(1) and the polyvinyl butyral resin of Example 5(2).

TABLE-US-00002 TABLE 2 Dispersion Composition (wt %) Dispersion Polyvinyl Butyral Medium CNT Type CNT Resin (NMP) Example 1 Bundle- 2 0.4 97.6 type Example 2 Bundle- 2 0.4 97.6 type Example 3 Bundle- 2 0.4 97.6 type Example 4 Bundle- 2 0.4 97.6 type Example 5 Bundle- 2 0.4 97.6 type Example 6 Bundle- 2 0.4 97.6 type Comparative Bundle- 2 0 98 Example 1 type Comparative Bundle- 2 0.4 97.6 Example 2 type Comparative Bundle- 2 0.4 97.6 Example 3 type Comparative Bundle- 2 0.4 97.6 Example 4 type Comparative Entangled- 2 0.4 97.6 Example 5 type Comparative Bundle- 2 0.4 97.6 Example 6 type Comparative Bundle- 2 0.4 97.6 Example 7 type

TABLE-US-00003 TABLE 3 Battery Performance (DC-IR Dispersion Property (ohm)) Dispersed Electrode 6.5 C, Particle Diameter Viscosity Adhesive 25 C. (m) (@1.2/s) Strength Discharge D.sub.10 D.sub.50 D.sub.90 Pa .Math. s gf/cm SOC 50 Example 1 1.88 5.60 14.20 65.0 32 1.269 Example 2 2.10 5.89 15.80 61.0 36 1.283 Example 3 2.47 6.75 19.60 57.0 28 1.277 Example 4 2.37 6.66 18.00 54.0 25 1.271 Example 5 2.02 5.82 19.30 60.0 29 1.264 Example 6 2.58 6.47 19.60 72.0 15 1.632 Comparative Unable to Secure CNT Wetting (Dispersion liquid was Example 1 not prepared) Comparative Unable to Secure CNT Wetting (Dispersion liquid was Example 2 not prepared) Comparative 8.11 22.20 51.90 120.0 Unable to Prepare Example 3 Electrode Comparative 1.42 11.10 27.30 55.0 8 Unable to Example 4 Manufacture Cell Due to Adhesive Strength Problem Comparative 2.30 7.06 14.60 4.0 11 Unable to Example 5 Manufacture Cell Due to Adhesive Strength Problem Comparative 4.89 14.20 37.80 110.0 Electrode Coating Example 6 Defects Occurred Comparative 1.13 2.45 5.21 75.0 10 Unable to Example 7 Manufacture Cell Due to Adhesive Strength Problem

[0092] Hereinbefore, preferred examples of the present disclosure have been described, however, the scope of a right of the present disclosure is not limited thereto, and various modified and improved forms made by those skilled in the art using the basic concept of the present disclosure defined in the attached claims also belong to the scope of a right of the present disclosure.