KR-20260066527-A - CATHODE SLURRY COMPOSITION FOR LITHIUM SECONDARY BATTERY USING BASIC CARBON NANOTUBE SLUDGE, CATHODE AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME

Abstract

The present invention relates to a positive electrode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, a positive electrode containing the same, and a lithium secondary battery. The present invention is technically characterized in that, in a positive electrode slurry composition comprising a positive electrode active material, a conductive material, and a polymer binder, the conductive material comprises carbon nanotubes, and the carbon nanotubes are basic carbon nanotubes in the form of sludge that are debundled by introducing oxygen-based functional groups containing oxygen and hydrogen, and then deprotonated under basic conditions so that the oxygen-based functional groups are charged with a negative charge, and the carbon nanotubes are uniformly dispersed within the polymer binder by suppressing re-bundling through the repulsion between negative charges.

Inventors

• 서선희
• 이나라
• 정희진
• 최해영
• 엄승욱

Assignees

• 한국전기연구원

Dates

Publication Date

20260512

Application Date

20241104

Claims (9)

1. In an anode slurry composition comprising an anode active material, a conductive material, and a polymer binder, The above conductive material includes carbon nanotubes, and The above carbon nanotubes are, It is a sludge-type basic carbon nanotube that is debundled by introducing oxygen-based functional groups containing oxygen and hydrogen, and then deprotonated under basic conditions so that the oxygen-based functional groups are negatively charged. A positive electrode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, characterized in that re-bundling is suppressed by the repulsion between the negative charges, thereby uniformly dispersing the carbon nanotubes within the polymer binder.
2. In Article 1, A positive electrode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, characterized in that the oxygen-based functional group is one or more selected from the group consisting of hydroxyl groups and carboxyl groups.
3. In Article 1, A positive electrode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, wherein the basic carbon nanotube in the form of the sludge is characterized by having a pH of at least 9.
4. In Article 1, A positive electrode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, characterized in that the basic carbon nanotubes have crystallinity satisfying the following relationship 1: [Relationship 1] 5 ≤ I G /I D ≤ 50 (Note: I G / I D is a value calculated as the ratio of the maximum peak intensity (I G ) measured at 1,580 ± 50 cm⁻¹ in the wavenumber region of the Raman spectrum to the maximum peak intensity (I D ) measured at 1,360 ± 50 cm⁻¹ .)
5. In Article 1, A positive electrode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, characterized in that the oxygen atoms present in the basic carbon nanotubes are at least 20 at%.
6. In Article 1, A positive electrode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, characterized in that the length of the basic carbon nanotubes is 2 to 40 μm.
7. In Article 1, A cathode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, characterized in that the carbon nanotubes are one or more selected from the group consisting of single-walled carbon nanotubes and double-walled carbon nanotubes.
8. An anode comprising an anode active material layer formed by applying an anode slurry composition of any one of claims 1 to 7 to at least one surface of a current collector.
9. A lithium secondary battery comprising the positive electrode of claim 8.

Description

Cathode slurry composition for lithium secondary battery using basic carbon nanotube sludge, cathode and lithium secondary battery comprising the same The present invention relates to a positive electrode slurry composition for a lithium secondary battery using a basic carbon nanotube sludge, a positive electrode containing the same, and a lithium secondary battery. Carbon nanotubes, discovered by Sumio Iijima in 1991, consist of three neighboring carbon atoms bonded to a single carbon atom to form a honeycomb-shaped hexagon. As the hexagonal structure repeats, they form a tube shape that is rolled into a cylinder, and depending on the number of tubes, they are classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT). Due to their excellent electrical and mechanical properties, thermal stability, and adsorption and transport characteristics, carbon nanotubes are the subject of much research for application in various fields, such as conductive materials for secondary batteries. While multi-walled carbon nanotubes, which offer relatively superior cost competitiveness, can be localized, single-walled and double-walled carbon nanotubes, which possess particularly excellent electrical conductivity, have not yet been localized and remain dependent on imports. Unlike multi-walled carbon nanotubes with a diameter of 4 nm or more, carbon nanotubes with a diameter of 3 nm or less have a flake appearance of several mm in size in the form of highly concentrated bundles after synthesis due to strong van der Waals forces caused by the small diameter and the large aspect ratio according to length/diameter, so the dispersion stability is inevitably low. Therefore, it is important to de-bundle the bundles to weaken the strong van der Waals forces and achieve dispersion of carbon nanotubes in the dispersion medium. Conventional debundling typically utilized physical grinding methods using machines such as probe-type ultrasonic dispersion or high-pressure homogenizers, or chemical oxidation methods that apply strong shear stress while using oxidizing agents. However, while these methods can improve the dispersion stability of carbon nanotubes in a dispersion solution by shortening their length to 0.1 to 3 μm, the inherent sp² hexagonal carbon ring structure of the carbon nanotubes is destroyed during the process, causing the electrical conductivity to drop to less than 100 S/cm. Consequently, a separate post-treatment reduction process is required to restore the structure to the sp² form, and the electrical conductivity does not exceed 1,000 S/cm even after reduction, making it chemically unstable. Even when electrical conductivity is maintained at the level of 1,000 S/cm, the use of a separate dispersant or a low-molecular-weight binder with a molecular weight of 90,000 g/mol or less is required for the uniform dispersion of carbon nanotubes. Additionally, additional dilution and redispersion processes are necessary to maximize dispersibility. Furthermore, if the materials of the dispersant and the conventionally used polymer binder are different, mutual compatibility between the two materials must be ensured; failure to meet this requirement may result in limitations on applications or usage amounts. In this regard, 'low-defect carbon nanotube sludge and method for manufacturing the same (KR 10-2023-0055818 A)' discloses a technology that enables the manufacturing of carbon nanotube sludge without the need for a separate dispersant or a complex dispersion process, while stably maintaining the inherent sp2 hexagonal carbon ring structure of carbon nanotubes. This allows for effective dispersion by facilitating penetration between carbon nanotube bundles due to the small molecular size of the dispersant or low-molecular-weight binder. Recently, in applications requiring high energy density such as lithium secondary batteries, electrode plate binder materials with a high molecular weight of 200,000 g/mol or more are being applied to ensure high viscosity and electrode adhesion for securing the coating properties of the electrode slurry while minimizing the use of binders that do not contribute to lithium storage, and thus the demand for carbon nanotube materials applicable to this is increasing. In conventional low-defect carbon nanotube sludge, when carbon nanotubes are dispersed in a high-viscosity electrode binder for lithium secondary batteries with a molecular weight of 200,000 g/mol or more, there is a problem in that the polymer binder is difficult to penetrate between the carbon nanotube bundles, causing a re-bundling phenomenon. Therefore, there is a need for technology development regarding anode slurry compositions and anodes and lithium secondary batteries to which high-concentration, highly crystalline carbon nanotubes can be applied, which do not require a separate dispersant or low-molecular-weight binder when dispersed in a polyme