Nuclear magnetic resonance method for characterizing dispersion of carbon nanotube paste

Abstract

The application discloses a nuclear magnetic resonance method for in-situ characterization of dispersion of carbon nanotube slurry, and belongs to the technical field of dispersion test of carbon nanotube slurry, and comprises the following steps: testing T2 relaxation spectrum of a solvent in the carbon nanotube slurry to obtain a spectrum peak of the solvent; testing T2 relaxation spectrum of the carbon nanotube slurry to obtain a spectrum peak of the slurry; comparing the number and width of the spectrum peak of the solvent and the spectrum peak of solid particles; if the spectrum peak of the slurry T2 relaxation spectrum is a single peak, and the width variation of the spectrum peak is less than the width variation of the spectrum peak of the solvent, then the dispersion of the slurry is qualified. The method has the advantages of fast detection speed, high measurement accuracy, good repeatability and consistency, and no need for any treatment of the slurry, can realize real-time and in-situ detection of the dispersion of the slurry, and makes up for the shortcomings and deficiencies of traditional slurry dispersion test methods.

Description

Technical Field

[0001] This invention belongs to the field of carbon nanotube slurry dispersibility testing technology, and particularly relates to a nuclear magnetic resonance method for characterizing the dispersibility of carbon nanotube slurry. Background Technology

[0002] Carbon nanotubes (CNTs) are one-dimensional carbon nanomaterials with excellent chemical, mechanical, thermal, and electrical properties, leading to their widespread application across various industries. However, due to their large aspect ratio (L / D > 100), high specific surface area, and extremely high surface energy, carbon nanotubes are prone to particle aggregation or entanglement, resulting in a significant deterioration in material performance. Therefore, preparing highly dispersed carbon nanotube slurries is crucial, but only reliable quantitative characterization of the slurry's dispersibility can accurately determine whether its quality meets application requirements.

[0003] Traditional methods for testing the dispersibility of slurries, including laser particle size distribution, Zeta potential method, and multiple light scattering method, have the following drawbacks:

[0004] (1) The laser particle size method indirectly judges the dispersibility of the slurry by measuring the particle size in the slurry. Before the test, the slurry needs to be diluted hundreds or thousands of times to prevent the light-blocking effect. However, the state of the diluted slurry has obviously changed from that of the thick slurry. Many particle agglomerates in the thick state may be dispersed again after dilution. Therefore, the laser particle size method cannot obtain accurate slurry dispersibility.

[0005] (2) The Zeta potential method characterizes the dispersibility of colloidal systems by measuring the solid-liquid interface electrical properties of particulate matter in a dispersion system. For example, Chinese Patent CN110323416B discloses an aqueous negative electrode stable slurry and its preparation method, as well as negative electrode sheets and lithium batteries. The dispersibility of the slurry is determined using the Zeta potential method. However, many factors affect the Zeta potential, such as the pH value, conductivity, solid content, electroosmotic motion, cross-contamination of the sample, signal-to-noise ratio of the instrument, and test temperature. These factors can significantly affect the measured Zeta potential value, causing the result to deviate greatly from the true value. In addition, the Zeta potential is based on the electrostatic dispersion theory, which is not very applicable to slurries using sterically hindered dispersants, which are currently widely used in slurries.

[0006] (3) The multiple light scattering method determines the stability of a slurry by irradiating it with a pulsed laser and then detecting changes in the intensity of the laser transmitted through the sample cell. The drawback of this method is its low sensitivity and limited sample differentiation, especially for samples with good slurry stability, where it is difficult to obtain ideal test results. These seemingly stable slurries may actually have poor dispersibility. Therefore, when performing multiple light scattering tests, it is generally necessary to simultaneously age the sample, such as through high-temperature treatment. This is because significant changes occur in the slurry during aging, and only under these conditions can the multiple light scattering method detect these changes.

[0007] Therefore, there is an urgent need for an in-situ testing method for characterizing the dispersibility of carbon nanotube slurries that is fast in detection and highly accurate in measurement. Summary of the Invention

[0008] The technical problem to be solved by this invention is: how to solve the problem of low accuracy and slow detection efficiency in the existing determination of carbon nanotube slurry dispersibility.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0010] A nuclear magnetic resonance method for characterizing the dispersion of carbon nanotube slurries includes the following steps:

[0011] The T2 relaxation spectrum of the solvent in the carbon nanotube slurry was tested to obtain the solvent's spectral peaks;

[0012] The T2 relaxation spectrum of the carbon nanotube slurry was tested to obtain the spectral peaks of the slurry;

[0013] The number and width of the peaks in the solvent and the slurry were compared.

[0014] The beneficial effects of this invention are as follows: It provides a nuclear magnetic resonance method for characterizing the dispersibility of carbon nanotube slurries. By separately testing the T2 relaxation spectra of the carbon nanotube slurry and the solvent, the greater the particle aggregates in the slurry and the wider the size distribution of the encapsulated solvent, the larger the relaxation spectrum width of the slurry. By comparing the number and width of the solvent peaks and the slurry peaks, real-time and in-situ detection of slurry dispersibility can be achieved. This method has advantages such as fast detection speed, high measurement accuracy, good repeatability and consistency, and no need for any slurry treatment, thus overcoming the shortcomings and deficiencies of traditional slurry dispersibility testing methods. This method is not only applicable to carbon nanotube slurries, but also to slurries made from other small molecule solvents, such as water, ethanol, NMP (N-methylpyrrolidone), toluene, methanol, and other solvents with small molecular weights, showing great scalability and a wide range of applications. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the technical process of the present invention.

[0016] Figure 2 The T2 relaxation spectrum of the slurry with good dispersibility according to the present invention;

[0017] Figure 3 The T2 relaxation spectrum of the poorly dispersible slurry of the present invention;

[0018] Figure 4 The solvent echo train signal acquired by the CPMG (Positron Resonance Pulse Sequence) of this invention;

[0019] Figure 5 The T2 relaxation spectrum of the solvent of this invention;

[0020] Figure 6 The slurry echo train signal acquired by the CPMG of this invention;

[0021] Figure 7 The T2 relaxation spectrum of the slurry of the present invention;

[0022] Figure 8 This is a comparison diagram of the T2 relaxation spectra of slurries with different degrees of dispersion according to the present invention. Detailed Implementation

[0023] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0024] Please refer to Figures 1 to 8 A nuclear magnetic resonance method for characterizing the dispersion of carbon nanotube slurries includes the following steps:

[0025] The T2 relaxation spectrum of the solvent in the carbon nanotube slurry was tested to obtain the solvent's spectral peaks;

[0026] The T2 relaxation spectrum of the carbon nanotube slurry was tested to obtain the spectral peaks of the slurry;

[0027] Compare the number and width of the peaks in the solvent and slurry. If the peak in the T2 relaxation spectrum of the slurry is a single peak and the change in the width of the peak is less than the change in the width of the solvent peak, then the dispersibility of the slurry is qualified.

[0028] As can be seen from the above description, the beneficial effects of this invention are as follows: T2 relaxation spectroscopy is a mature data processing method in nuclear magnetic resonance analysis, and it has been widely used in the pore structure analysis of porous materials such as rocks and cement. However, slurries are a completely different system from rock materials, and there are no specific applications of T2 relaxation spectroscopy in the field of slurries, especially not for the quantitative analysis of slurry dispersibility.

[0029] The basic principle of this invention is as follows: In a slurry system, particles are surrounded by solvent. Due to interfacial interactions, the T2 relaxation time of the bound solvent adsorbed by the particles becomes very short, while the T2 relaxation time of the free solvent not adsorbed by the particles is very long. Sufficient and rapid energy exchange can occur between the bound and free solvents, thus shortening the equivalent T2 relaxation time of the slurry, equivalent to a leftward shift in the T2 relaxation spectrum. If the slurry has excellent dispersion, meaning all particles are monodisperse and completely coated with solvent, with a layer of bound solvent adsorbed on the particle surface, the measured T2 relaxation spectrum of the slurry will show a very narrow single-peak structure. If the slurry has poor dispersion, with some particles agglomerating or entangled, these agglomerated or entangled particles will surround a portion of the solvent, forming a structure similar to a porous material. This surrounded solvent is isolated from the solvent outside the particles. Due to the inability to undergo rapid energy exchange, the relaxation time of this portion of the solvent will be significantly different from that of the external solvent, thus generating a new peak in the relaxation spectrum. The more particles agglomerate or entangle in the slurry, the wider the size distribution of the encapsulated solvent, and the greater the relaxation spectrum width of the slurry.

[0030] Further, the T2 relaxation spectrum of the solvent is tested, including the following steps:

[0031] S1.1 Measure the CPMG echo train signal of the solvent using a CPMG pulse sequence;

[0032] S1.2. Using the inverse Laplace inversion algorithm, the CPMG echo train signal is converted into T2 relaxation spectrum data to obtain the T2 relaxation spectrum of the solvent.

[0033] As described above, the T2 relaxation spectrum of a solvent is generally a single-peak structure. The position and width of the peak are related to the composition of the solvent. Generally, the higher the content of pure solvent, the more to the right the peak is located, and the narrower the peak width is.

[0034] Further, the T2 relaxation spectrum of the slurry is tested, including the following steps:

[0035] S2.1 Measure the CPMG echo train signal of the slurry using a CPMG pulse sequence;

[0036] S2.2. Using the inverse Laplace inversion algorithm, the CPMG echo train signal is converted into T2 relaxation spectrum data to obtain the T2 relaxation spectrum of the slurry.

[0037] As described above, carbon nanotube slurries are divided into aqueous slurries and NMP slurries. Generally, aqueous slurries are used in battery anode materials, while NMP slurries are used in battery cathode slurries.

[0038] Furthermore, the comparison of the number and width of the spectral peaks is as follows: if the peak of the T2 relaxation spectrum of the slurry is a single peak, and the change in the width of the peak is within 20% of the change in the width of the solvent peak, then the dispersibility of the slurry is Grade I; if the peak of the T2 relaxation spectrum of the slurry is a single peak, and the change in the width of the peak is within 20% to 40% of the change in the width of the solvent peak, then the dispersibility of the slurry is Grade II, where Grade I indicates excellent dispersibility and Grade II indicates good dispersibility.

[0039] As described above, if the slurry has excellent dispersibility, meaning all solid particles are monodisperse and completely coated by the solvent, then the T2 relaxation spectrum of the solid particles in the slurry will exhibit a single-peak structure. The CPMG echo train signal will satisfy the following single exponential decay formula:

[0040]

[0041] as follows Figure 2 As shown, the relaxation time of the solvent is always greater than that of the slurry. Therefore, the peak position of the slurry is to the left, while the peak position of the solvent is to the right. The peak width of the slurry is slightly wider, but it is still a single peak structure. At this time, the slurry has good dispersibility.

[0042] Furthermore, the number and width of the spectral peaks are compared as follows: if the spectral peaks of the T2 relaxation spectrum of the slurry have more than one peak and the signal proportion of the main peak is less than 95%, then the dispersibility of the slurry is unqualified.

[0043] Furthermore, a comparison of the number and width of the spectral peaks is conducted: if the peak width of the T2 relaxation spectrum of the slurry increases by more than 40%, the dispersibility of the slurry is unqualified.

[0044] As described above, if the slurry is poorly dispersed, some of the solid particles may agglomerate. These agglomerated particles will surround a portion of the solvent, forming a structure similar to a porous material. This surrounded solvent is isolated from the solvent outside the solid particles. Due to the inability to exchange energy rapidly, the relaxation time of this solvent will differ significantly from that of the external solvent, resulting in a new peak in the relaxation spectrum. The more particle agglomerates in the slurry and the wider the size distribution of the encapsulated solvent, the greater the width of the slurry's relaxation spectrum. The total NMR signal generated by the solvent under different particle environments satisfies the following formula:

[0045]

[0046] as follows Figure 3 The image shows the T2 relaxation spectrum of a poorly dispersible slurry, with multiple peaks indicating that the solvent has multiple states and the slurry has poor dispersibility.

[0047] Furthermore, the solvent is any one or more combinations of water, NMP, dispersant, and binder.

[0048] As described above, the position and width of the spectral peaks are related to the solvent composition. The smaller the molecular weight of the solvent, the better its fluidity, resulting in a longer relaxation time and a narrower peak; conversely, the larger the molecular weight of the solvent, the worse its fluidity, resulting in a shorter relaxation time and a larger peak. The solvents used in this invention are mainly water or NMP, both low molecular weight solvents with excellent fluidity and a relaxation time of approximately 3000 ms.

[0049] Please refer to Figures 4-8 Embodiment 1 of the present invention is as follows:

[0050] A nuclear magnetic resonance method for characterizing the dispersibility of carbon nanotube slurries involves selecting carbon nanotube slurry samples, slurry 1, slurry 2, and slurry 3, and determining their dispersibility. The method includes the following steps:

[0051] The T2 relaxation spectrum of the solvent in the carbon nanotube slurry was tested:

[0052] S1.1 The CPMG echo train signal of the solvent was measured using a CPMG pulse sequence, and the results are as follows: Figure 4 ;

[0053] S1.2. Using the inverse Laplace inversion algorithm, the CPMG echo train signal is converted into T2 relaxation spectrum data to obtain the T2 relaxation spectrum of the solvent. The results are as follows: Figure 5 .

[0054] The T2 relaxation spectrum of the carbon nanotube slurry was tested:

[0055] S2.1. The CPMG echo train signal of the slurry was measured using a CPMG pulse sequence, and the results are as follows: Figure 6 ;

[0056] S2.2. Using the inverse Laplace inversion algorithm, the CPMG echo train signal is converted into T2 relaxation spectrum data to obtain the T2 relaxation spectrum of the slurry. The results are as follows: Figure 7 .

[0057] The number and width of the peaks in the solvent and slurry spectra were compared. If the peak in the slurry's T2 relaxation spectrum was a single peak, and the change in peak width was less than that of the solvent peak, then the slurry's dispersibility was acceptable. If the peak in the slurry's T2 relaxation spectrum was multi-peaked, or the peak width increased, then the slurry's dispersibility was unacceptable. The results are as follows: Figure 8 .

[0058] Depend on Figure 8It can be seen that CNT slurries 1 and 2 both have a three-peak structure, indicating poor dispersibility and failing to meet quality requirements. The main peak signal proportion of slurry 1 is greater than that of slurry 2, therefore, slurry 1 has slightly better dispersibility than slurry 2. Slurry 3 has only two peaks, with the main peak being the smallest and having the largest signal proportion; therefore, slurry 3 has the best dispersibility among the three carbon nanotube slurries.

[0059] In summary, the NMR method for characterizing the dispersion of carbon nanotube slurries provided by this invention has advantages such as fast detection speed, high measurement accuracy, good repeatability and consistency, and no need for any slurry treatment. It can realize real-time and in-situ detection of slurry dispersion, overcoming the shortcomings and deficiencies of traditional slurry testing methods. This method is not only applicable to carbon nanotube slurries, but also to slurries made of other small molecule solvents, such as water, ethanol, NMP, toluene, methanol, and other solvents with low molecular weight, showing great scalability and a wide range of applications.

[0060] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A nuclear magnetic resonance method for characterizing the dispersibility of carbon nanotube slurries, characterized in that, Includes the following steps: The T2 relaxation spectrum of the solvent in the carbon nanotube slurry was tested to obtain the solvent's spectral peaks; the solvent is any one or more combinations of water, NMP, dispersant, and binder; The T2 relaxation spectrum of the carbon nanotube slurry was tested to obtain the spectral peaks of the slurry; The number and width of the peaks in the solvent and slurry spectra were compared: If the peak in the T2 relaxation spectrum of the slurry is a single peak, and the change in the width of the peak is less than that of the solvent peak, and the change in the width of the peak is within 20% of that of the solvent peak, then the dispersibility of the slurry is classified as Grade I; if the peak in the T2 relaxation spectrum of the slurry is a single peak, and the change in the width of the peak is less than that of the solvent peak, and the change in the width of the peak is within 20% to 40% of that of the solvent peak, then the dispersibility of the slurry is classified as Grade II, where Grade I indicates excellent dispersibility and Grade II indicates good dispersibility.

2. The nuclear magnetic resonance method for characterizing the dispersibility of carbon nanotube slurry according to claim 1, characterized in that, The T2 relaxation spectrum of the solvent is tested, including the following steps: S1.1 Measure the CPMG echo train signal of the solvent using a CPMG pulse sequence; S1.

2. Using the inverse Laplace inversion algorithm, the CPMG echo train signal is converted into T2 relaxation spectrum data to obtain the T2 relaxation spectrum of the solvent.

3. The nuclear magnetic resonance method for characterizing the dispersibility of carbon nanotube slurry according to claim 1, characterized in that, The T2 relaxation spectrum of the slurry is tested, including the following steps: S2.1 Measure the CPMG echo train signal of the slurry using a CPMG pulse sequence; S2.

2. Using the inverse Laplace inversion algorithm, the CPMG echo train signal is converted into T2 relaxation spectrum data to obtain the T2 relaxation spectrum of the slurry.

4. The nuclear magnetic resonance method for characterizing the dispersibility of carbon nanotube slurry according to claim 1, characterized in that, The comparison of the number and width of spectral peaks is as follows: if the spectral peaks of the T2 relaxation spectrum of the slurry have more than one spectral peak and the signal proportion of the main peak is less than 95%, then the dispersibility of the slurry is unqualified.

5. The nuclear magnetic resonance method for characterizing the dispersibility of carbon nanotube slurry according to claim 1, characterized in that, The comparison of the number and width of the spectral peaks is as follows: if the peak width of the T2 relaxation spectrum of the slurry increases by more than 40%, the dispersibility of the slurry is unqualified.

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