Preparation method of single-walled carbon nanotube aqueous slurry
Through the methods of dry grinding premixing and ultrasonic dispersion, the dispersion problem of single-walled carbon nanotubes in aqueous systems was solved, their uniform dispersion and stability in the sulfur positive electrode of lithium-sulfur batteries were achieved, and the electrochemical performance and stability of the battery were improved.
Patent Information
- Application Number
- CN202510680278.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-26
- Publication Date
- 2025-09-16
AI Technical Summary
Existing technologies make it difficult to effectively disperse single-walled carbon nanotubes in aqueous systems, resulting in problems such as uneven dispersion, unstable rheological properties, and dispersant residues that increase interfacial impedance in the sulfur positive electrode of lithium-sulfur batteries, limiting their large-scale application.
The method of dry grinding premixing and ultrasonic dispersion is adopted. Single-walled carbon nanotubes and sodium hydroxymethyl cellulose are mixed in a certain proportion and then added into water. Magnetic stirring and ultrasonic treatment are performed to reduce the particle size and maintain stable dispersion.
The uniform dispersion of single-walled carbon nanotubes was achieved, meeting the requirements of the wet coating process, reducing production costs while maintaining their excellent performance, and improving the electrochemical performance and stability of lithium-sulfur batteries.
Smart Images
Figure CN120657119A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a preparation method of an electromagnetic material, and in particular to a method for preparing an aqueous slurry. The aqueous slurry can be applied to a sulfur positive electrode in a lithium-sulfur battery. Background Art
[0002] Single-walled carbon nanotubes (SWCNTs) have a unique tubular structure and a high specific surface area (about 1300 m 2 / g) and excellent mechanical properties (elastic modulus>1TPa) and electrical properties (carrier mobility>10 5 cm 2 / V·s), has become a representative of new nano-functional materials. When used as a conductive network building unit, it can form a three-dimensional permeation structure through nano-level entanglement, significantly improving the conductivity and mechanical strength of the composite material, showing great application potential in energy storage, flexible electronics, composite materials and other fields. However, the high surface energy of SWCNT (about 50mJ / m 2 ) and strong van der Waals interactions (binding energy of about 500 eV / μm), which leads to the easy formation of tubular aggregates with diameters of hundreds of nanometers in the liquid phase system. This characteristic seriously restricts the performance of its nanoscale effect.
[0003] Current SWCNT dispersion technologies are primarily categorized into physical and chemical methods. While physical methods such as high-energy ball milling and ultrasonication can temporarily disaggregate, they can also lead to high energy consumption and irreversible damage such as tube wall rupture. Chemical methods such as covalent modification and non-covalent dispersion significantly alter the intrinsic properties of SWCNTs. In aqueous systems, traditional dispersion processes struggle to break through the "dispersion-reaggregation" dynamic equilibrium, manifesting as significant sedimentation within 24 hours when the absolute value of the zeta potential is <40 mV. This technical bottleneck directly leads to three major drawbacks in existing SWCNT slurries: low bundle dissociation, increased viscosity after 72 hours of dispersion stability, and compromised functional integrity.
[0004] In the typical application scenario of preparing sulfur cathodes for lithium-sulfur batteries using a wet coating process, the above-mentioned single-walled carbon nanotube dispersion defects are particularly evident. The wet coating process requires that the active slurry simultaneously meet submicron dispersion (D50 < 20 μm) and thixotropic fluid properties (viscosity 3000-5000 mPa·s). However, the slurry prepared by traditional SWCNT dispersion technology has the following application obstacles: 1) Micron-scale agglomerates hinder the uniform coating of sulfur / carbon composites, resulting in low utilization of active substances; 2) The instability of the rheological properties of the dispersion system causes cracks in the coating film layer, resulting in the breakage of the conductive network of the electrode; 3) Excessive dispersant residue increases the interfacial impedance. These technical pain points severely limit the large-scale application of SWCNT in sulfur cathodes, and also reflect the urgent need to develop new and efficient dispersion technologies. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to provide a method for preparing a uniformly dispersed aqueous slurry of single-walled carbon nanotubes in response to the above technical status quo.
[0006] The technical solution adopted by the present invention to solve the above technical problems is: a method for preparing an aqueous slurry of single-walled carbon nanotubes, characterized by comprising the following steps:
[0007] ① Dry grinding premixing: Grind the single-walled carbon nanotubes and sodium hydroxymethyl cellulose in a mass ratio of 1:3 to 1:1 to fully mix the single-walled carbon nanotubes and sodium hydroxymethyl cellulose to obtain a mixed powder;
[0008] ② Stirring and dissolving: Add the above mixed powder to water in an amount such that the solid content of the mixed powder in the water is 1% to 5%, and use magnetic stirring to obtain a mixed aqueous solution;
[0009] ③Ultrasonic dispersion: ultrasonically treat the mixed aqueous solution.
[0010] Preferably, the grinding in step ① is performed by mechanical grinding for 20 to 60 minutes. Mechanical grinding can be performed by mortar grinding, ball milling, etc., or manual grinding can also be performed.
[0011] Preferably, the magnetic stirring time in step ② is 1 to 3 hours.
[0012] Preferably, the ultrasonic dispersion in step ③ adopts the following conditions:
[0013] 100 ml of the mixed aqueous solution is subjected to ultrasonic treatment at 300-400 W for 5-60 minutes.
[0014] Compared with the existing technology, the advantages of the present invention are: good dispersion effect: through dry grinding pre-mixing, CMC is allowed to enter the gaps between SWCNT tube bundles. After adding water, CMC absorbs water and swells to expand the SWCNT agglomeration structure. Combined with ultrasonic dispersion, the SWCNT particle size can be reduced to about 10 μm, meeting the slurry particle size requirements of the wet coating process. The resulting aqueous solution can still maintain stable dispersion after being left for 10 days.
[0015] Simple process: The entire processing process only requires conventional operating steps such as grinding, stirring, and ultrasound, without the need for complex equipment and processes, and is easy to industrialize.
[0016] Low cost: The raw material CMC used is cheap, and the entire preparation process has low energy consumption, which reduces production costs.
[0017] Less damage to SWCNTs: Dry grinding premixing reduces the minimum time and intensity of ultrasound, reduces the damage to the SWCNT structure during the ultrasound process, and is conducive to maintaining its excellent performance.
[0018] Dry grinding can reduce the proportion of dispersants used. The sulfur cathode prepared using the aqueous slurry of the present invention exhibits excellent electrochemical performance in lithium-sulfur batteries, with higher capacity and battery stability at 0.1C, 0.2C, and 0.5C rates. The initial specific capacity at a 0.1C rate reached 1043 mAh / g, and the capacity retention rate after 200 cycles at a 0.5C rate was 65.5%, a significant improvement compared to the sample without SWCNTs. Furthermore, the addition of SWCNTs effectively suppressed the volume expansion of the sulfur cathode during cycling. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 TEM image 1 of single-walled carbon nanotubes.
[0020] Figure 2 TEM image 2 of single-walled carbon nanotubes.
[0021] Figure 3 TEM image 1 of the mixture of single-walled carbon nanotubes and CMC in Example 1.
[0022] Figure 4 This is the second TEM image of the mixture of single-walled carbon nanotubes and CMC in Example 1.
[0023] Figure 5 These are comparative photographs of single-walled carbon nanotubes and the aqueous solution of single-walled carbon nanotubes and CMC in Example 1 after being placed for 10 days.
[0024] Figure 6 This is a photograph of single-walled carbon nanotube and CMC slurry coated into a thin film after ultrasonication for 60 minutes.
[0025] Figure 7 These are photographs of the slurries prepared by dry-grinding and pre-mixing single-walled carbon nanotubes and CMC slurry and then ultrasonicating for 10 minutes in Example 1, which were then coated into thin films.
[0026] Figure 8 Comparison of the cycle life curves of the sulfur cathode prepared using CMC and CMC and SWCNT in Example 1 at 0.1C.
[0027] Figure 9 Comparison of the cycle life curves of the sulfur cathode prepared using CMC and CMC and SWCNT in Example 1 at 0.2C.
[0028] Figure 10 Comparison of the cycle life curves of the sulfur cathode prepared using CMC and CMC and SWCNT in Example 1 at 0.5C.
[0029] Figure 11The figure shows the capacity retention rate comparison of the battery prepared with CMC and CMC+SWCNT in Example 1 after 200 cycles at different rates.
[0030] Figure 12 This is an SEM cross-sectional view of the sulfur positive electrode sheet prepared with CMC+SWCNT in Example 1 before cycling.
[0031] Figure 13 This is an SEM cross-sectional view of the sulfur positive electrode sheet prepared with CMC+SWCNT in Example 1 after 200 cycles at 0.1C.
[0032] Figure 14 This is an SEM cross-sectional view of the sulfur positive electrode sheet prepared with CMC in Example 1 before cycling.
[0033] Figure 15 This is an SEM cross-sectional view of the sulfur positive electrode sheet prepared with CMC in Example 1 after 200 cycles at 0.1C. DETAILED DESCRIPTION
[0034] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.
[0035] Example 1:
[0036] Preparation of the SWCNT / CMC aqueous solution: 0.1 g of SWCNTs and 0.3 g of CMC were added to a mortar and ground for 30 minutes. The mixed powder was then added to 10 ml of water and stirred using a magnetic stirrer for 2 hours. The mixed solution was then sonicated for 10 minutes using a 350 W cell disruptor.
[0037] Preparation of SWCNT / CMC film: The prepared CMC / SWCNT aqueous slurry was coated on aluminum foil with a coating thickness of 50 μm.
[0038] Preparation of sulfur cathode slurry containing CMC / SWCNT: 1.8g of sulfur / carbon composite powder was added to 0.3g of Super P powder and 0.1g of Ketjen Black powder as a conductive agent in a glass bottle and dry-mixed on a magnetic stirrer at 500 rpm for 3 hours. The dry-mixed powder was then slowly added to 8g of the prepared CMC / SWCNT aqueous slurry in several portions and stirred thoroughly on a magnetic stirrer at 500 rpm for 12 hours to prepare the cathode slurry.
[0039] Assembly of button cells: Assemble button cells according to conventional methods.
[0040] Example 2:
[0041] Preparation of the SWCNT / CMC aqueous solution: 0.15 g of SWCNTs and 0.15 g of CMC were added to a mortar and ground for 20 minutes. The mixed powder was then added to 15 ml of water and stirred using a magnetic stirrer for 1 hour. The mixed solution was then sonicated for 5 minutes using a cell disruptor at 300 W.
[0042] Preparation of sulfur cathode slurry containing CMC / SWCNT: 1.8g of sulfur / carbon composite powder was added to 0.4g of Super P powder and 0.1g of Ketjen Black powder as a conductive agent in a glass bottle and dry-mixed on a magnetic stirrer at 500 rpm for 3 hours. The dry-mixed powder was then slowly added to 9g of the prepared CMC / SWCNT aqueous slurry in several portions and stirred thoroughly on a magnetic stirrer at 500 rpm for 12 hours to prepare the cathode slurry.
[0043] Assembly of button cells: Assemble button cells according to conventional methods.
[0044] Example 3:
[0045] Preparation of the SWCNT / CMC aqueous solution: 0.1 g of SWCNTs and 0.2 g of CMC were added to a mortar and ground for 60 minutes. The mixed powder was then added to 12 ml of water and stirred using a magnetic stirrer for 3 hours. The mixed solution was then sonicated for 15 minutes using a 400 W cell disruptor.
[0046] Preparation of sulfur cathode slurry containing CMC / SWCNT: 1.8g of sulfur / carbon composite powder was added to 0.3g of Super P powder and 0.2g of Ketjen Black powder as a conductive agent in a glass bottle and dry-mixed on a magnetic stirrer at 500 rpm for 3 hours. The dry-mixed powder was then slowly added to 10g of the prepared CMC / SWCNT aqueous slurry in several portions and stirred thoroughly on a magnetic stirrer at 500 rpm for 12 hours to prepare the cathode slurry.
[0047] Assembly of button cells: Assemble button cells according to conventional methods.
[0048] Comparative Example 1:
[0049] CMC was dissolved in 10 ml of water. 0.1 g of SWCNTs was then added to the CMC solution. The mixture was stirred for 2 hours using a magnetic stirrer, followed by ultrasonic treatment at 350 W for 10 minutes. Sulfur cathode slurry was then prepared and button cells were assembled using the same method as in Example 1.
[0050] Comparative Example 2: CMC was dissolved in 10 ml of water. 0.1 g of SWCNT was then added to the CMC solution. The mixture was stirred for 2 hours using a magnetic stirrer, followed by ultrasonic treatment at 350 W for 60 minutes. The resulting SWCNT / CMC slurry was then coated onto aluminum foil to a thickness of 50 μm.
[0051] Performance Testing
[0052] Particle size and zeta potential testing: The SWCNT / CMC aqueous solutions prepared in each example and comparative example were tested for particle size and zeta potential. The results showed that the sample obtained by dry-milling premixing ultrasonic dispersion in Example 1 had an average volume diameter of 10.58 μm and a zeta potential of -60.09 mV. The sample obtained by ultrasonication for 10 minutes in Comparative Example 1 had a particle size of 122.88 μm. The sample obtained by ultrasonication for 60 minutes in Comparative Example 2 had a particle size of 87.21 μm and a zeta potential of -65.36 mV. This demonstrates that the dry-milling premixing ultrasonic dispersion method can effectively reduce SWCNT particle size.
[0053] Coating Performance Test: Coating experiments were conducted on the slurries prepared in Example 1 and Comparative Example 2. The sample in Comparative Example 2, which was ultrasonically treated for 60 minutes, could not be coated into a uniform film, resulting in an uneven film surface. However, the slurry prepared in Example 1 using dry milling premixing and ultrasonic dispersion could be well coated into a uniform film.
[0054] Figure 1 and Figure 2 It shows that SWCNTs tend to aggregate when not dispersed, forming a network structure and entangled into a "hemp rope" morphology; Figure 3 and Figure 4 It shows that CMC enters the gaps between SWCNT bundles during dry milling premixing, which helps dispersion; Figure 5 The left side is the aqueous solution of SWCNT with CMC added, which has agglomeration and poor dispersion. The right side is the SWCNT / CMC aqueous solution obtained by dry grinding premixing ultrasonic dispersion method, which has no agglomeration and has good dispersion and stability.
[0055] Figure 6 It shows that the slurry subjected to ultrasonication for 60 minutes cannot be coated uniformly. Figure 7 The advantages of the slurry prepared by dry grinding premixing ultrasonic dispersion method in coating performance are intuitively demonstrated, and it can be coated into a uniform film.
[0056] from Figures 8 to 11 As shown in the figure, the comparison of the charts clearly shows the improvement of the capacity and battery stability of the sulfur cathode at different rates after adding SWCNTs.
[0057] from Figures 12-15 As shown, the inhibitory effect of adding SWCNTs on the volume expansion of the sulfur cathode is demonstrated from a microscopic perspective.
[0058] Battery Electrochemical Performance Testing: Electrochemical performance tests were conducted on button-type cells assembled from each example and comparative example. The sulfur cathode prepared in Example 1 exhibited higher capacity and battery stability at 0.1C, 0.2C, and 0.5C rates. After 200 cycles at 0.5C, the capacity retention rate of Example 1 was 65.5%, while that of Comparative Example 1 was only 54.1%. Furthermore, SEM cross-sectional images revealed that the volume expansion of the sulfur cathode prepared in Example 1 was effectively suppressed during cycling.
Claims
1. A method for preparing an aqueous slurry of single-walled carbon nanotubes, characterized in that The steps include: ① Dry grinding premixing: Grind the single-walled carbon nanotubes and sodium hydroxymethyl cellulose in a mass ratio of 1:3 to 1:1 to fully mix the single-walled carbon nanotubes and sodium hydroxymethyl cellulose to obtain a mixed powder; ② Stirring and dissolving: Add the above mixed powder to water in an amount such that the solid content of the mixed powder in the water is 1% to 5%, and use magnetic stirring to obtain a mixed aqueous solution; ③Ultrasonic dispersion: ultrasonically treat the mixed aqueous solution.
2. The method for preparing an aqueous slurry of single-walled carbon nanotubes according to claim 1, characterized in that The grinding in step ① is performed by mechanical grinding, and the grinding time is 20 to 60 minutes.
3. The method for preparing an aqueous slurry of single-walled carbon nanotubes according to claim 1, characterized in that The magnetic stirring time in step ② is 1 to 3 hours.
4. The method for preparing an aqueous slurry of single-walled carbon nanotubes according to claim 1, characterized in that The ultrasonic dispersion in step ③ adopts the following conditions: 100 ml of the mixed aqueous solution is subjected to ultrasonic treatment at 300-400 W for 5-60 minutes.