Single-walled carbon nanotube material, single-walled carbon nanotube purification method, conductive paste, and lithium ion battery

Abstract

The application discloses a single-walled carbon nanotube material, a single-walled carbon nanotube purification method, a conductive paste and a lithium ion battery, and relates to the technical field of single-walled carbon nanotubes. The purification method realizes efficient removal of large-particle metal catalysts and impurities such as alumina and silicon oxide which are peeled off at high temperature through liquid-phase dispersion of single-walled carbon nanotube crude products, centrifugal separation, destabilization treatment, oxidation treatment and acid pickling treatment. The purification method is simple and easy to operate, has high process safety and strong popularization. The single-walled carbon nanotube material provided has low impurity content, can effectively avoid physical damage of large-particle impurities to electrode active materials, reduce side reactions caused by impurities, and thus significantly improve the cycle stability and capacity retention rate of the battery. When applied to a lithium battery electrode conductive agent, the capacity retention rate of a button cell is greater than 90% after 100 cycles of cyclic charging and discharging at a current density of 0.5 C.

Description

Technical Field

[0001] This invention relates to the field of single-walled carbon nanotube technology, and more specifically, to single-walled carbon nanotube materials, single-walled carbon nanotube purification methods, conductive slurries, and lithium-ion batteries. Background Technology

[0002] Single-walled carbon nanotubes are seamless tubular structures formed by rolling a single layer of graphite sheets at a specific helical angle. In this structure, all carbon atoms are in sp[…]. 2 Hybridized with C-C bonds and π bonds, it has a stable structure and exhibits excellent properties such as good conductivity, high charge conduction rate, high toughness, and recovery after stretching. It is suitable as a conductive agent for next-generation lithium battery materials such as silicon-based anodes.

[0003] Currently, the mainstream methods for preparing single-walled carbon nanotubes (SWCNs) are plasma methods and floating catalytic methods. Both methods generate two typical, difficult-to-remove impurities during the synthesis of crude SWCNs: large-particle metal catalysts and insulation materials that detach during high-temperature sintering. The large-particle metal catalysts are secondary particles formed by the agglomeration of nano-metals within the reactor chamber. The insulation materials in the synthesis equipment of both methods are typically corundum refractory bricks, which serve to maintain the high temperature (>1600K) required for SWCN growth within the reactor. These bricks are mainly composed of alumina and silicon dioxide. Corundum refractory bricks have poor thermal shock resistance, and temperature fluctuations are unavoidable during daily SWCN production. The significant thermal stress differences between high and low temperatures cause the corundum refractory bricks to slag and detach. These detached corundum refractory brick particles are decomposed into micron-sized particles under the erosion of hot airflow and are collected within the SWCN fibers. These two types of impurities adhere to the SWCNs, posing difficulties for the purification and application of SWCNs.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide single-walled carbon nanotube materials, methods for purifying single-walled carbon nanotubes, conductive slurries, and lithium-ion batteries to solve or improve the aforementioned technical problems.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a method for purifying single-walled carbon nanotubes, used to prepare single-walled carbon nanotube materials according to any of the foregoing embodiments, comprising the following steps: The crude single-walled carbon nanotubes, dispersant, and solvent were mixed to form a slurry, which is referred to as the first system. After centrifuging the first system, the upper and middle liquid is taken and recorded as the second system. A destabilizing agent is added to the second system, and after filtration, washing and drying, the resulting powder is referred to as the third system. The third system was subjected to oxidation and acid washing treatment, and the resulting precipitate was a single-walled carbon nanotube material.

[0007] Secondly, the present invention provides a single-walled carbon nanotube material.

[0008] Thirdly, the present invention provides a conductive paste comprising the single-walled carbon nanotube material.

[0009] Fourthly, the present invention provides a lithium-ion battery comprising the single-walled carbon nanotube material.

[0010] The present invention has the following beneficial effects: The single-walled carbon nanotube (SUV) purification method provided by this invention efficiently removes large-particle metal catalysts and high-temperature detached impurities through liquid-phase dispersion of crude SUVs, followed by centrifugation, destabilization, oxidation, and acid washing. Specifically, the addition of a destabilizing agent causes the SUVs to re-aggregate; oxidation removes the carbon shell of the embedded metal-containing carbon nanotubes; and the acid solvent used in the acid washing process is both hydrophilic and attracted to SUVs, facilitating thorough contact between the SUVs and the acid solvent, resulting in a more complete reaction and efficient removal of metal catalyst impurities. This method achieves efficient removal of large-particle metal catalysts and high-temperature detached impurities such as alumina and silica. Furthermore, the purification method is simple to operate, highly safe, and widely applicable.

[0011] The single-walled carbon nanotube material provided by this invention has low impurity content in large particles (0.2μm~2μm in diameter), which can effectively avoid physical damage to the electrode active material caused by large particles of impurities (such as crushing due to compression), reduce side reactions caused by impurities, and thus significantly improve the cycle stability and capacity retention of the battery.

[0012] The single-walled carbon nanotube material of the present invention can be used as a conductive agent for lithium battery electrodes, and the resulting coin cell has a capacity retention rate of >90% after 100 cycles of charge and discharge at a current density of 0.5C. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 SEM images of crude single-walled carbon nanotubes before and after purification: (a) crude unpurified single-walled carbon nanotubes, (b) high-purity single-walled carbon nanotubes after purification. Figure 2 SEM microstructure of crude unpurified single-walled carbon nanotubes: (a) large-particle metal catalyst, (b) impurities detached at high temperature; Figure 3 EDS surface scan analysis of crude single-walled carbon nanotubes and single-walled carbon nanotubes in the second system prepared in Example 1: (a) crude unpurified single-walled carbon nanotubes, (b) high-purity single-walled carbon nanotubes in the second system prepared in Example 1. Figure 4 EDS surface scan analysis of the purified single-walled carbon nanotube material obtained in Example 1; Figure 5 XRD analysis of crude single-walled carbon nanotubes and single-walled carbon nanotubes in the second system prepared in Example 1: (a) crude unpurified single-walled carbon nanotubes, (b) high-purity single-walled carbon nanotubes in the second system prepared in Example 1. Figure 6 XRD analysis of the purified single-walled carbon nanotube material obtained in Example 1. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] In a first aspect, the present invention provides a method for purifying single-walled carbon nanotubes, used to prepare single-walled carbon nanotube materials according to any of the foregoing embodiments, comprising the following steps: The crude single-walled carbon nanotubes, dispersant, and solvent were mixed to form a slurry, which is referred to as the first system. After centrifuging the first system, the upper and middle liquid is taken and recorded as the second system. A destabilizing agent is added to the second system, and after filtration, washing and drying, the resulting powder is referred to as the third system. The third system was subjected to oxidation and acid washing treatment, and the resulting precipitate was a single-walled carbon nanotube material.

[0017] Specifically, the purification method for single-walled carbon nanotubes includes the following steps: The crude single-walled carbon nanotubes, dispersant, and solvent are mixed in proportion to form a slurry, which is referred to as the first system. The slurry is then processed in a colloid mill and then in a homogenizer to ensure thorough dispersion of the materials, thus obtaining the first system.

[0018] It should be noted that the homogenization treatment of the slurry obtained from crude single-walled carbon nanotubes in this invention employs a dual dispersion method using a colloid mill and a homogenizer. The colloid mill also has the effect of shortening the single-walled carbon nanotubes. In other embodiments of this invention, the homogenization treatment can be replaced by ultrasonic treatment as needed, but this may result in incomplete dispersion.

[0019] In this invention, the production method of crude single-walled carbon nanotubes is rationally selected from either plasma method or CVD floating catalytic method according to actual needs; specifically, in the embodiments of this invention, the preparation method of crude single-walled carbon nanotubes adopts plasma method, and the catalyst is iron. It can be understood that the production method of crude single-walled carbon nanotubes can also use CVD floating catalytic method.

[0020] After centrifuging the first system, the liquid in the upper middle part is taken and referred to as the second system. The centrifugation process in this invention is a physical method of impurity removal, which is conducive to the rapid and efficient sedimentation of impurities such as high-density large-particle-size metal catalysts and high-temperature detached alumina at the bottom of the centrifuge. The dispersion liquid in the upper middle part of the centrifuge is taken, which is the second system, and is a dispersion system for removing impurities such as large-particle-size metal catalysts and high-temperature detached alumina.

[0021] It should be noted that the particle size of large-particle metal catalysts is typically between 50 nm and 150 nm, such as... Figure 2 As shown in (a), the particle size of the alumina and silica impurities that detach at high temperatures is typically between 0.2 μm and 2 μm, such as... Figure 2 As shown in (b), the larger the particle size, the lower the chemical activity, and the more difficult it is to remove the catalyst by chemical methods after the catalyst and alumina and silica impurities agglomerate irregularly. Therefore, a physical method is used for removal: first, the crude single-walled carbon nanotubes are dispersed in an aqueous solution of surfactant. At this time, the crude single-walled carbon nanotubes and impurities are suspended in water under the action of surfactant. Then, the large-particle metal catalyst and the alumina and silica impurities that fall off at high temperature are separated by centrifugation using the density difference between the large-particle impurities and the single-walled carbon nanotubes.

[0022] A destabilizing agent is added to the second system. After filtration, washing, and drying, the resulting powder is referred to as the third system. The destabilizing agent used is a soluble acid, alkali, or salt, which can disrupt the double-layer structure of the colloid, causing the single-walled carbon nanotubes to detach from the dispersant and re-aggregate. After filtration, washing, and drying, single-walled carbon nanotubes with large-particle metal catalyst and high-temperature detached alumina impurities removed are obtained. In some embodiments of the present invention, the alumina content in the third system is reduced from 3% before treatment to below 0.2%, and the metal catalyst content is reduced from 10% before treatment to 6%.

[0023] Without theoretical constraints, if a destabilizing agent is not used for destabilization treatment, the dispersant will always coat the single-walled carbon nanotubes. In the subsequent oxidation and acid washing stages, the oxidant cannot freely pass through the carbon nanotubes and carbon nanotubes to react with the internal metal catalyst. This results in a high iron content in the obtained high-purity single-walled carbon nanotube material, and impurities cannot be effectively removed, affecting its performance.

[0024] The methods of filtration, washing, and drying are not particularly limited. For example, filtration can be performed by centrifugation, vacuum filtration, etc., as needed. The reagents used in washing can be selected from pure water, ultrapure water, deionized water, and distilled water, etc., and the number of washing times is 3 to 5. Drying can be performed by vacuum drying, forced air drying, freeze drying, or supercritical drying, etc.

[0025] The third system was subjected to oxidation and acid washing treatments, and the resulting precipitate was a single-walled carbon nanotube material. In this process, amorphous carbon impurities were removed by oxidation, and the small-particle-size metal catalyst in the embedded metal carbon nanotubes was oxidized into metal oxides. The volume expansion of the embedded metal caused the outer carbon shell to be stressed and broken, which facilitated the exposure of the embedded metal. Then, acid washing was performed to efficiently remove the remaining small-particle-size metal catalyst.

[0026] Adding an organic solvent that is both hydrophilic and attracted to single-walled carbon nanotubes during the pickling stage allows for more thorough contact between the acid and the single-walled carbon nanotubes, resulting in a better pickling effect. Ultimately, the obtained single-walled carbon nanotube material has high purity, with catalyst element content ≤0.1%, aluminum content ≤0.1%, and silicon content ≤0.05%.

[0027] In some embodiments, the ratio of crude single-walled carbon nanotubes, dispersant, and solvent is (3~6):(3~6):(88~94); further, the ratio of crude single-walled carbon nanotubes, dispersant, and solvent is 5:5:90. In other embodiments of the present invention, the ratio of crude single-walled carbon nanotubes, dispersant, and solvent can be reasonably adjusted according to actual needs.

[0028] In some embodiments, the slurry is processed in a colloid mill to shorten the single-walled carbon nanotubes, and then dispersed in a homogenizer to obtain the first system.

[0029] In an optional embodiment, the colloid mill is operated at a speed of 1500 rpm to 2500 rpm for 20 min to 30 min; the homogenizer is operated at 300 bar to 500 bar for 1 to 5 passes.

[0030] In some embodiments, the dispersant includes sodium dodecyl sulfate (SDS), and / or sodium dodecylbenzene sulfonate (SDBS), and / or Triton X-100; the addition of the dispersant is beneficial for encapsulating single-walled carbon nanotubes, so that they are suspended and fully dispersed in the aqueous solution system along with large-particle metal catalysts and high-temperature detached alumina and silica impurities. During centrifugation, the density difference between large-particle impurities and single-walled carbon nanotubes is used to efficiently separate and remove large-particle metal catalysts and high-temperature detached alumina and silica impurities.

[0031] In some implementations, the solvent is selected from any one of pure water, ultrapure water, deionized water, and distilled water; the specific selection is made according to actual needs.

[0032] In some embodiments, the destabilizing agent is at least one of a soluble acid, base, and salt that can disrupt the colloidal double-layer structure.

[0033] In some embodiments, the mass ratio of the destabilizer to the dispersant is 1:2 to 3:1. Exemplarily, the mass ratio can be any one of 1:2, 1:1, 2:1, and 3:1, or any value between 1:2 and 3:1.

[0034] It should be noted that the addition of the destabilizing agent can promote the detachment of single-walled carbon nanotubes from the dispersant and their re-aggregation. This invention does not impose any particular limitation on the substances used as destabilizing agents, which can be reasonably selected according to actual needs. For example, soluble acids can be hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or organic acids (such as formic acid, acetic acid, etc.); soluble bases can be sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, and ammonia, etc.; soluble salts can be sodium salts (such as sodium chloride, sodium sulfate, sodium nitrate), potassium salts (such as potassium chloride, potassium sulfate, potassium nitrate), magnesium salts (such as magnesium chloride, magnesium nitrate), barium salts (such as barium chloride, barium nitrate), and calcium salts (such as calcium chloride, calcium nitrate), etc.

[0035] In some implementations, the centrifugation speed is 2000 rpm / min to 10000 rpm / min, and the time is 0.5 h to 5 h. It should be noted that the centrifugation speed and time are negatively correlated. If the centrifugation speed is high, the centrifugation time is short and efficient. If the centrifugation speed is low, the centrifugation time will be longer, which may result in poor centrifugation effect and ineffective separation of impurities.

[0036] For example, the centrifugation speed can be selected from any one of 2000 rpm / min, 4000 rpm / min, 6000 rpm / min, 8000 rpm / min and 10000 rpm / min, or other values ​​within the range of 2000 rpm / min to 10000 rpm / min; the centrifugation time can be selected from any one of 0.5h, 1.5h, 2h, 3.5h, 4.5h and 5h, or other values ​​within the range of 0.5h to 5h.

[0037] In some embodiments, the oxidation process is carried out in an oxidizing gas atmosphere, wherein the oxidizing gas is selected from at least one of air, oxygen and carbon dioxide; The oxidation treatment temperature is 400℃~800℃, and the time is 2h~5h.

[0038] It should be noted that if the oxidation temperature is too low, iron impurities may not be completely removed. If the oxidant used is weak, the structural integrity of the single-walled carbon nanotubes is preserved, resulting in a high content of single-walled carbon nanotubes in the high-purity single-walled carbon nanotube material. However, the etching effect on the carbon nanotubes is poor, and the removal of catalysts (such as iron) is also poor. Although the conductive structure of the single-walled carbon nanotube material is intact during the charge-discharge cycle, which is conducive to the performance of the three-dimensional conductive network, the high impurity content causes the metal impurities to squeeze the silicon-carbon anode active material as the electrode expands during the charge-discharge cycle, leading to the fragmentation of the active material. The fragmented active material continues to react with the electrolyte to form an SEI film (solid electrolyte interface film), consuming lithium and causing a decrease in cycle capacity retention.

[0039] In some embodiments, the acid solution used for pickling is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, and dilute hydrofluoric acid; the purpose of pickling is to remove metallic impurities from the single-walled carbon nanotubes.

[0040] More preferably, the solvent (diluent) of the acid solution is an organic solvent that is both hydrophilic and hydrophilic to single-walled carbon nanotubes, including acetone, ethylene glycol, and / or ethanol, and / or N,N-dimethylformamide (DMF), and / or N-methylpyrrolidone (NMP).

[0041] It should be noted that the acid solutions used in the embodiments of the present invention are prepared by diluting high-concentration acids and diluents at a volume ratio of 1:1. The concentrations of the high-concentration acids are those labeled on the market, and the specific concentration depends on the actual product purchased; for example, the mass concentration of concentrated hydrochloric acid is 36%~38%, the mass concentration of hydrofluoric acid is 48%~51%, and the mass concentration of concentrated sulfuric acid is 95%~98%.

[0042] If acid washing is not performed, the resulting single-walled carbon nanotube material will have high iron and aluminum content and high impurity content. Iron and aluminum impurities have poor conductivity, and during the charge and discharge cycle of the battery, as the electrode expands, the unremoved metal impurities will squeeze the silicon-carbon anode active material, causing the active material to break. The broken active material continues to react with the electrolyte to form an SEI film, consuming lithium and causing a significant decrease in cycle capacity retention.

[0043] In some embodiments, the pickling process is followed by a drying process at a temperature of 90°C to 110°C, and the moisture content of the single-walled carbon nanotube material after drying is ≤5%.

[0044] This invention does not impose special limitations on the temperature and time of the drying process. They can be reasonably selected according to actual needs. If a large amount of material is to be dried at one time, the drying time needs to be reasonably extended if the drying temperature is constant. Ultimately, the moisture content in the single-walled carbon nanotube material should be ≤5%.

[0045] Secondly, the present invention provides a single-walled carbon nanotube material. The single-walled carbon nanotube material of the present invention can be prepared using the method provided in the first aspect; the embodiments are illustrated using the above method as an example.

[0046] In some embodiments, field emission scanning electron microscopy is used to take SEM images of single-walled carbon nanotube materials. Twenty SEM images are randomly selected, and SEM images containing impurity particles with a particle size of 0.2 μm to 2 μm are recorded as images containing impurities. The ratio of the number of images containing impurities to the total number of SEM images is recorded as the impurity content, and the impurity content is ≤10%.

[0047] Specifically, in this embodiment of the invention, a Regulus 8100 field emission scanning electron microscope is used. When capturing SEM images, factors such as the height of the sample stage, the model of the equipment, and the magnification all affect the observation of the number of impurity particles in the captured SEM images. In this embodiment, the selected SEM images are those taken at the same magnification, specifically at 5000x magnification. In other embodiments of the invention, other magnifications can be selected as needed.

[0048] For example, in some embodiments, the impurity content can be 10%, 5%, or 0%.

[0049] Particle size definition: When a single-walled carbon nanotube material is photographed at 10,000x magnification using SEM, non-fibrous particles are considered impurities. The diameter of the circle with the same projected area as the particle is recorded as the particle size of the impurity.

[0050] Unconstrained by theory, the single-walled carbon nanotube material provided by this invention has low content of large-particle impurities (0.2μm~2μm in diameter), which can effectively avoid physical damage to the electrode active material caused by large-particle impurities (such as crushing due to compression), reduce side reactions caused by impurities, and thus significantly improve the cycle stability and capacity retention of the battery. Furthermore, the single-walled carbon nanotube material of this invention is particularly suitable for silicon-based anode active materials (such as silicon-carbon anode active materials).

[0051] For example, as can be seen from the SEM images, the impurity particles (such as...) in the purified single-walled carbon nanotube material of this invention... Figure 1 (b) shows impurities (such as those shown in the image) that are coarser than single-walled carbon nanotubes. Figure 1 (a) shows a significant reduction.

[0052] In some embodiments, a Regulus 8100 field emission scanning electron microscope is used to take SEM images of the single-walled carbon nanotube material at a magnification of 5000x.

[0053] In some implementations, the impurity content of the single-walled carbon nanotube material is ≤5%. Single-walled carbon nanotube materials have a lower content of large-particle impurities and superior performance.

[0054] In some implementations, ImageJ software is used to calculate the area of ​​impurity particles with a diameter of 0.2 μm to 2 μm in any SEM image based on pixel counting, where the area of ​​the impurity particles is <0.3 μm. 2 .

[0055] Specifically, select any one of the 20 SEM images and use ImageJ software to calculate the area of ​​large-particle impurities (0.2μm~2μm in diameter) using pixel counting. At this 5000x (5Kx) magnification, the area of ​​the large-particle impurities is <0.3μm. 2 Understandably, the overall area of ​​the SEM image (length × width of the captured area) at this magnification is approximately 120 μm. 2 If the ratio of the area of ​​impurity particles to the area of ​​any SEM image is recorded as the impurity particle area ratio, then the impurity particle area ratio in the obtained high-purity single-walled carbon nanotube material is <0.25%.

[0056] In this invention, the content of large particle impurities is low, and even if individual large particle impurities exist, their overall particle size is small enough to minimize or avoid damaging the material system when applied to electrodes.

[0057] In some embodiments, in the XRD patterns of single-walled carbon nanotube materials, A SWCNT A MWCNT≥9, and / or A SWCNT A 催化剂元素 ≥300, and / or A SWCNT A Al ≥400, where A SWCNT A is the integral peak area of ​​the characteristic peak of single-walled carbon nanotubes. MWCNT A represents the integrated peak area of ​​the characteristic peaks of multi-walled carbon nanotubes. 催化剂元素 A is the integrated peak area of ​​the characteristic peak of the oxide of the catalyst element. Al This represents the integrated peak area of ​​the characteristic peak of alumina.

[0058] For example, in some implementations, A SWCNT A MWCNT It can be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20, etc.; when the catalyst element is Fe, A SWCNT A Fe It can be 300, 450, 475, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, and 1800, etc.; A SWCNT A Al It can be 400, 450, 475, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000 and 1800, etc.

[0059] It is understood that the peak near 2θ=25.6° in the XRD pattern is designated as a characteristic peak of single-walled carbon nanotubes. The peak near 2θ=45° is designated as a characteristic peak of multi-walled carbon nanotubes. The peak near 2θ=43.5° is a characteristic peak of the alumina standard card. The catalyst element includes at least one of iron, cobalt, and nickel. For example, in some embodiments, the catalyst element is iron. In this case, the peak near 2θ=35.6° is a characteristic peak of the ferric oxide standard card, and the peak near 2θ=65° is a characteristic peak of the iron standard card. It is understood that in other embodiments, if the catalyst element is another element, the corresponding characteristic peak positions can be determined from the standard cards of the corresponding element and its oxides.

[0060] It is understood that the single-walled carbon nanotube material of this invention is mainly composed of single-walled carbon nanotubes, with extremely low content of non-target carbon structures such as multi-walled carbon nanotubes, ensuring excellent conductivity and structural uniformity. The content of metal oxide impurities (such as Fe2O3 and Al2O3) has been reduced to extremely low levels.

[0061] In some embodiments, the catalyst element content in the single-walled carbon nanotube material is ≤0.3wt%, the aluminum content is ≤0.2wt%, and the silicon content is ≤0.1wt%.

[0062] Single-walled carbon nanotubes (SWNTs) exhibit low levels of iron, silicon, and aluminum impurities, resulting in high purity. When used as conductive agents in lithium-ion batteries, SWNTs help avoid harmful side reactions such as the catalytic decomposition of electrolytes and damage to the solid electrolyte interphase (SEI) film caused by metallic impurities in the electrochemical environment.

[0063] In some alternative embodiments, the catalyst element content in the single-walled carbon nanotube material is ≤0.1wt%, the aluminum content is ≤0.1wt%, and the silicon content is ≤0.05wt%.

[0064] In some embodiments, the single-walled carbon nanotube material is used as a conductive agent in lithium battery electrodes, resulting in coin cells that retain >90% of their capacity after 100 charge-discharge cycles at a 0.5C current density. Batteries made with single-walled carbon nanotube material exhibit fewer side reactions caused by impurities and higher capacity retention during charge-discharge cycles.

[0065] Thirdly, the present invention provides a conductive paste comprising the single-walled carbon nanotube material.

[0066] Fourthly, the present invention provides a lithium-ion battery comprising the single-walled carbon nanotube material.

[0067] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0068] Example 1 This embodiment provides a single-walled carbon nanotube material, which is obtained by the following method, including the following steps: (1) Mix the crude single-walled carbon nanotubes, dispersant (SDBS) and solvent (deionized water) into a slurry according to the proportion. Place it in a colloid mill for shearing treatment. The shearing speed is 2000 r / min and the shearing time is 30 min. Then place it in a homogenizer for dispersion treatment. The homogenizing pressure is 400 bar and the homogenization is performed 4 times. The resulting system is called the first system. The mass ratio of crude single-walled carbon nanotubes, dispersant (SDBS), and solvent (water) is 5:5:90, with a total mass of 1000g.

[0069] (2) After centrifuging the first system obtained in step (1), take the upper part of the liquid and record it as the second system; The centrifugation process was carried out at a speed of 4000 rpm / min for 5 hours. The resulting second system was a single-walled carbon nanotube slurry after removing large-particle-size metal catalysts and high-temperature detachment impurities.

[0070] (3) Add a destabilizing agent (5g calcium chloride) to the second system obtained in step (2) to make the single-walled carbon nanotubes detach from the dispersant and re-aggregate. After filtration, washing and drying, the resulting powder is recorded as the third system.

[0071] The filtration process involves Buchner funnel filtration; the washing process uses deionized water and involves three washing cycles; and the drying process uses a blower drying oven.

[0072] (4) The third system obtained in step (3) is subjected to oxidation and acid washing treatment, and the resulting precipitate is a single-walled carbon nanotube material; The oxidation treatment was carried out at a temperature of 400℃ for 2 hours in an air atmosphere; the acid solution for the pickling treatment was hydrochloric acid and ethanol (anhydrous ethanol) in a volume ratio of 1:1; and the resulting single-walled carbon nanotube material was a high-purity single-walled carbon nanotube material.

[0073] Example 2 This embodiment provides a single-walled carbon nanotube material. The purification method is basically the same as that in Example 1, except for the following steps: (1) The dispersant is SDS.

[0074] (2) The centrifugation speed was 6000 rpm / min and the time was 3h.

[0075] (3) The destabilizing agent is 5g of magnesium chloride.

[0076] (4) The oxidation treatment temperature is 450℃, the time is 3h, and the oxidation atmosphere is air; the acid solvent for pickling treatment is a mixture of acid and ethanol (anhydrous ethanol) with a volume ratio of 1:1, wherein the mixture of acid is concentrated hydrochloric acid and hydrofluoric acid with a mass ratio of 1:1.

[0077] Example 3 This embodiment provides a single-walled carbon nanotube material. The purification method is basically the same as that in Example 1, except for the following steps: (1) The dispersant is Triton X-100.

[0078] (2) The centrifugation speed was 8000 rpm / min and the time was 1 h.

[0079] (3) The destabilizing agent is 5g of sodium chloride.

[0080] (4) The oxidation treatment temperature is 600℃, the time is 4h, and the oxidation atmosphere is water vapor; the acid solvent for pickling treatment is a mixture of acid and DMF with a volume ratio of 1:1, wherein the mixture of acid is concentrated hydrochloric acid and hydrofluoric acid with a mass ratio of 5:1.

[0081] Example 4 This embodiment provides a single-walled carbon nanotube material. The purification method is basically the same as that in Example 1, except for the following steps: (2) The centrifugation speed was 10000 rpm / min and the time was 0.5 h.

[0082] (3) The destabilizing agent is 5g of hydrochloric acid.

[0083] (4) The oxidation treatment temperature is 800℃, the time is 5h, and the oxidation atmosphere is carbon dioxide; the acid solvent for pickling treatment is hydrochloric acid and NMP in a volume ratio of 1:1.

[0084] Example 5 This embodiment provides a single-walled carbon nanotube material. The purification method is basically the same as that in Example 1, except for the following steps: (1) The dispersant is SDS.

[0085] (2) The centrifugation speed was 2000 rpm / min and the time was 5 h.

[0086] (3) The destabilizing agent is 5g of sodium hydroxide.

[0087] (4) The oxidation treatment temperature is 800℃, the time is 4h, and the oxidation atmosphere is water vapor; the acid solvent for pickling treatment is hydrochloric acid and anhydrous ethanol in a volume ratio of 1:1.

[0088] Comparative Example 1 This comparative example provides a single-walled carbon nanotube material. The purification method differs from that in Example 1 in the following steps: If steps (1) to (3) are missing, proceed directly to step (4).

[0089] The crude single-walled carbon nanotubes are directly subjected to oxidation and acid washing treatment, and the resulting precipitate is single-walled carbon nanotube material. The oxidation treatment was carried out at a temperature of 400℃ for 2 hours in an air atmosphere; the acid solution for the pickling treatment was hydrochloric acid and ethanol (anhydrous ethanol) in a volume ratio of 1:1.

[0090] Comparative Example 2 This comparative example provides a single-walled carbon nanotube material. The purification method differs from that in Example 1 in the following steps: (3) After the second system obtained in step (2) is directly subjected to filtration, washing and drying, the resulting powder is recorded as the third system. That is, no destabilizing agent is used in step (3).

[0091] The settings for filtration, washing, and drying are the same as in Example 1.

[0092] Comparative Example 3 This comparative example provides a single-walled carbon nanotube material. The purification method differs from that in Example 1 in the following steps: (4) The acid solvent for pickling is hydrochloric acid and water in a volume ratio of 1:1.

[0093] Test Example 1 The following performance tests were conducted in this test case: SEM microstructure analysis was performed on the unpurified crude single-walled carbon nanotubes and the purified single-walled carbon nanotubes from Example 1. The test results are shown below. Figures 1-2 ,in, Figure 1 The tests were conducted using a Regulus 8100 field emission scanning electron microscope. The samples were placed under 5Kx (5000x magnification) for SEM microscopic morphology analysis. Figure 1 (a) is crude, unpurified single-walled carbon nanotubes. Figure 1 (b) is the purified high-purity single-walled carbon nanotube material; Figure 2 (a) is a large-particle-size metal catalyst in crude, unpurified single-walled carbon nanotubes. Figure 2 (b) refers to impurities that detached at high temperatures in the unpurified crude single-walled carbon nanotubes.

[0094] from Figure 1 It can be seen that the number of impurity particles in the purified single-walled carbon nanotube material is significantly reduced.

[0095] from Figure 2 It can be seen that the particle size of large-particle metal catalysts is usually between 50nm and 150nm, while the particle size of impurities (alumina and silicon oxide) that fall off at high temperatures is usually between 0.2μm and 2μm.

[0096] Test Example 2 Based on Test Example 1, the following performance test analysis was conducted in this test example: 20 SEM images at a magnification of 5K were randomly selected. SEM images containing particles with a diameter of 0.2μm to 2μm were recorded as images containing impurities. The ratio of the number of images containing impurities to the total number of SEM images was recorded as the impurity content. The impurity content of the single-walled carbon nanotube material obtained in Example 1 was 5%.

[0097] Test Example 3 For any one of the 20 SEM images of the high-purity single-walled carbon nanotube material described above, impurity particles with a diameter between 0.2 μm and 2 μm were analyzed using ImageJ software based on pixel counting. For the high-purity single-walled carbon nanotube material obtained in Example 1, the area of ​​large impurity particles at 5Kx magnification is <0.12 μm. 2Because of this magnification, the overall area of ​​the image (length of the shooting area) The width is approximately 120 μm. 2 The ratio of impurity particle area to image area is recorded as the impurity particle area percentage. Therefore, the impurity particle area percentage in the high-purity single-walled carbon nanotube material obtained in Example 1 is 0.1%.

[0098] Test Example 4 The following performance tests and analyses were conducted in this test example: EDS surface scan analysis was performed on the crude single-walled carbon nanotubes, the single-walled carbon nanotubes in the second system prepared in Example 1, and the purified carbon nanotube materials. The test results are shown in the figure. Figures 3-4 and Table 1, where, Figure 3 (a) is crude, unpurified single-walled carbon nanotubes. Figure 3 (b) High-purity single-walled carbon nanotubes in the second system prepared in Example 1, that is, single-walled carbon nanotubes after the separation of large particle impurities; Figure 4 The carbon nanotube material is purified; Table 1 shows the percentage of EDS content in single-walled carbon nanotubes before and after separation of large particle impurities.

[0099] Table 1 shows the percentage of EDS element content in single-walled carbon nanotubes before and after separating large particulate impurities.

[0100] Combination Figures 3-4 It can be seen that after separating large particulate impurities, the peak intensities of aluminum, iron and oxygen in the EDS surface scan spectrum are significantly reduced. In Table 1, after separating large particulate impurities, the proportion of carbon increases and the proportion of oxygen, iron, aluminum and silicon decreases significantly. All of the above indicate that the content of aluminum oxide, iron and iron oxide in the sample is reduced.

[0101] Test Example 5 The following performance tests and analyses were conducted in this test example: XRD analysis was performed on the crude single-walled carbon nanotubes, the single-walled carbon nanotubes in the second system prepared in Example 1, and the purified carbon nanotube materials. The test results are shown in [Figure 1]. Figures 5-6 ,in, Figure 5 (a) is crude, unpurified single-walled carbon nanotubes. Figure 5 (b) High-purity single-walled carbon nanotubes in the second system prepared in Example 1, that is, single-walled carbon nanotubes after the separation of large particle impurities; Figure 6 The carbon nanotube material after purification.

[0102] Combination Figures 5-6As can be seen, in the XRD pattern of the sample after separating large particulate impurities, the peak intensities of the characteristic peaks of iron oxide and aluminum oxide decreased significantly, while the peak intensities of the characteristic peaks of single-walled carbon nanotubes increased significantly, which also indicates that the content of aluminum oxide and iron oxide in the sample decreased. Combined with the changes in the EDS element content ratio of single-walled carbon nanotubes after separating large particulate impurities in Table 1, this demonstrates that the pre-dispersion-centrifugation-destabilization-filtration and drying route in this invention has a significant effect on impurity removal.

[0103] The peak near 2θ=25.6° in the XRD pattern is designated as the characteristic peak of single-walled carbon nanotubes, the peak near 2θ=35.6° as the characteristic peak of the ferric oxide standard card, the peak near 2θ=43.5° as the characteristic peak of the alumina standard card, and the peak near 2θ=65° as the characteristic peak of the iron standard card. Since the peak intensity of each substance is positively correlated with its content, the ratio of the integrated peak area of ​​the single-walled carbon nanotube characteristic peak to the integrated peak area of ​​the iron oxide characteristic peak is denoted as A. SWCNT A Fe Then, compared with the single-walled carbon nanotubes after the separation of large particulate impurities, the A of the single-walled carbon nanotubes before the separation of large particulate impurities is... SWCNT A Fe The value increased from 9.6 to 16.4. The ratio of the integrated peak area of ​​the characteristic peak of single-walled carbon nanotubes to the integrated peak area of ​​the characteristic peak of alumina is denoted as A. SWCNT A Al Then, compared with the single-walled carbon nanotubes after the separation of large particulate impurities, the A of the single-walled carbon nanotubes before the separation of large particulate impurities is... SWCNT A Al It has been improved from 5.8 to 19.1.

[0104] The peak near 2θ = 25.6° in the XRD pattern is denoted as the characteristic peak of single-walled carbon nanotubes, and the peak near 2θ = 45° is denoted as the characteristic peak of multi-walled carbon nanotubes. The ratio of the integrated peak area of ​​the characteristic peak of single-walled carbon nanotubes to that of multi-walled carbon nanotubes is denoted as A. SWCNT A MWCNT The A of the obtained high-purity single-walled carbon nanotube sample SWCNT A MWCNT It is 9, A SWCNT A Fe For 450, A SWCNT A Al It is 900.

[0105] Test Example 5 In this test example, the single-walled carbon nanotube materials obtained in Examples 1-5 and Comparative Examples 1-3 were dispersed at a single-walled carbon nanotube content of 0.4 wt% to obtain single-walled carbon nanotube conductive slurry. The slurry was prepared by mixing high-purity single-walled carbon nanotubes, silicon-carbon anode active material (silicon-carbon deposited by CVD method, silicon content 49%), conductive agent (SP), and binder (PAA) in a mass ratio of 1:80:9:10. The slurry was then coated to form an electrode sheet, with a lithium sheet as the counter electrode. A Zhuogao C490 type separator and Tianci TC-ESC-9 type electrolyte were used to make a coin cell. Under a charge-discharge cutoff voltage of 0.05V~2V and a current density of 0.5C, the coin cell corresponding to the example was cycled 100 times. The capacity retention rate was >90%.

[0106] The performance test data involved in test cases 1-5 are summarized in Table 2.

[0107] Table 2 Performance Test Data

[0108] As shown in Table 2, Example 2 exhibits the largest product of centrifugal force and time, indicating the best relative centrifugal effect. This results in the best removal of large-particle-size iron, silicon, and aluminum impurities, leading to the lowest iron, aluminum, and silicon impurity content in the resulting single-walled carbon nanotube material. Consequently, the battery produced exhibits fewer impurity-induced side reactions and the highest capacity retention during charge-discharge cycles. Example 1 shows the second best centrifugal effect. The aluminum and silicon content in the resulting high-purity single-walled carbon nanotube material is similar to that of Example 2, while the iron content is slightly higher due to insufficient iron removal caused by the low oxidation temperature during the acid washing stage. Similarly, Example 3 yields a high-purity single-walled carbon nanotube material with lower iron content but higher silicon and aluminum content, resulting in a lower cycle capacity retention rate for the battery.

[0109] Examples 4-5 show the worst centrifugation effect, resulting in high-purity single-walled carbon nanotube materials with high silicon and aluminum impurity content. During the oxidation stage, the use of a weak oxidant resulted in poor etching of the carbon nanotubes, leading to poor iron removal. While the weak oxidant's low etching effect on single-walled carbon nanotubes helps preserve their structural integrity, the resulting high-purity materials still exhibit the highest single-walled carbon nanotube content, with a single-walled to multi-walled carbon nanotube ratio reaching 19. Consequently, the resulting batteries experience a decrease in cycle capacity retention during charge-discharge cycles. Without theoretical constraints, the analysis is as follows: Although the single-walled carbon nanotube material has a complete conductive structure, facilitating the development of a three-dimensional conductive network, its high impurity content causes metallic impurities to compress the silicon-carbon anode active material during charge-discharge cycles, leading to fragmentation. This fragmented active material continues to react with the electrolyte to form an SEI film, consuming lithium and ultimately resulting in a decrease in the battery's cycle capacity retention.

[0110] Comparative Example 1 did not undergo pre-dispersion-centrifugation-destabilization-washing and drying operations, resulting in the large-particle metal catalyst and large-particle alumina impurities not being removed by centrifugation. These large-particle impurities have poor chemical activity and cannot be completely removed in the subsequent oxidation and acid washing stages. Therefore, the product obtained has a high iron and aluminum content.

[0111] In Comparative Example 2, the dispersant was not destabilized and separated after dispersing the single-walled carbon nanotubes, resulting in the dispersant always encapsulating the single-walled carbon nanotubes. Therefore, in the subsequent oxidation and acid washing stage, the oxidant could not freely pass through the carbon nanotubes and carbon nanotubes to react with the internal metal catalyst, resulting in a high iron content in the obtained high-purity single-walled carbon nanotube material.

[0112] Comparative Example 3 did not use a diluent that is compatible with single-walled carbon nanotubes during the pickling stage. Due to the hydrophobicity of single-walled carbon nanotubes, the contact between the pickling solution and the single-walled carbon nanotubes was insufficient, resulting in higher iron and aluminum content in the final high-purity single-walled carbon nanotube material compared to Examples 1-5. The iron and aluminum impurities in Comparative Examples 1-3 were significantly higher than those in Examples 1-5. On the one hand, the conductivity of metallic impurities is poor; on the other hand, during the cyclic charge-discharge process, as the electrode expands, metallic impurities will squeeze the silicon-carbon anode active material, causing the active material to break down. The broken active material continues to react with the electrolyte to form an SEI film, consuming lithium and causing a significant decrease in cycle capacity retention.

[0113] In summary, the purification method for single-walled carbon nanotubes (SUVs) provided in this invention efficiently removes large-particle metal catalysts and high-temperature detached impurities through liquid-phase dispersion of crude SUVs, followed by centrifugation, destabilization, oxidation, and acid washing. Specifically, the addition of a destabilizing agent causes the SUVs to re-aggregate; oxidation removes the carbon shell of the embedded metal-containing carbon nanotubes; and the acid solvent used in the acid washing process is both hydrophilic and attracted to SUVs, facilitating thorough contact between the SUVs and the acid solvent, resulting in a more complete reaction and efficient removal of metal catalyst impurities. This method achieves efficient removal of large-particle metal catalysts and high-temperature detached impurities such as alumina and silica. Furthermore, the purification method is simple to operate, highly safe, and widely applicable. The coin cell capacity retention rate is >90%.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for purifying single-walled carbon nanotubes, characterized in that, Includes the following steps: A crude single-walled carbon nanotube, a dispersant, and a solvent are mixed to form a slurry, which is referred to as the first system; the mass ratio of the crude single-walled carbon nanotube, the dispersant, and the solvent is (3~6):(3~6):(88~94). After centrifuging the first system, the upper and middle liquid is taken and recorded as the second system; the centrifugation speed is 2000 rpm / min to 10000 rpm / min, and the time is 0.5 h to 5 h; A destabilizing agent is added to the second system, and after filtration, washing, and drying, the resulting powder is referred to as the third system. The destabilizing agent is at least one of a soluble acid, alkali, and salt that can disrupt the colloidal double-layer structure. The mass ratio of the destabilizing agent to the dispersant is 1:2 to 3:

1. The third system was subjected to oxidation and acid washing treatments, and the resulting precipitate was a single-walled carbon nanotube material; the oxidation treatment was carried out at a temperature of 400℃~800℃ for 2h~5h. The acid solution used for pickling is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, and dilute hydrofluoric acid; the solvent of the acid solution is an organic solvent that is both hydrophilic and attracted to single-walled carbon nanotubes, including acetone, and / or ethylene glycol, and / or ethanol, and / or N,N-dimethylformamide (DMF), and / or N-methylpyrrolidone.

2. The method according to claim 1, characterized in that, The production methods for crude single-walled carbon nanotubes include plasma method and floating catalysis method; And / or, after the slurry is processed in a colloid mill to shorten the single-walled carbon nanotubes, it is then dispersed in a homogenizer to obtain the first system; And / or, the dispersant comprises sodium dodecyl sulfate, and / or sodium dodecylbenzene sulfonate, and / or Triton X-100; And / or, the solvent is selected from any one of pure water, ultrapure water, deionized water and distilled water.

3. The method according to claim 1, characterized in that, The oxidation process is performed in an oxidizing gas atmosphere, wherein the oxidizing gas is selected from at least one of air, oxygen, and carbon dioxide.

4. The method according to claim 1, characterized in that, The mass concentration of the acid solution used in the pickling treatment is 5% to 20%.

5. The method according to claim 1, characterized in that, The pickling process is followed by a drying process, which is carried out at a temperature of 90℃~110℃. The moisture content of the single-walled carbon nanotube material after drying is ≤5%.

6. A single-walled carbon nanotube material, characterized in that, Obtained by means of any one of claims 1 to 5.

7. A conductive paste, characterized in that, Including the single-walled carbon nanotube material as described in claim 6.

8. A lithium-ion battery, characterized in that, Including the single-walled carbon nanotube material as described in claim 6.

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