Multi-walled carbon nanotube dispersion and its preparation method and application

Abstract

The present invention relates to a multi-walled carbon nanotube dispersion, a preparation method, and applications thereof. The preparation method comprises the following steps: subjecting multi-walled carbon nanotube powder to a swelling treatment to separate a first intermediate product; mixing the first intermediate product with manganese dioxide and a non-thickening surfactant, then adding hydrogen peroxide for swelling, and separating a second intermediate product; mixing the second intermediate product with a thickening surfactant and a solvent to form a pre-dispersion liquid, and then dispersing the pre-dispersion liquid at least twice to obtain a multi-walled carbon nanotube dispersion liquid, wherein the mass fraction of the second intermediate product in the pre-dispersion liquid is less than 1.5%. The preparation method of the present invention can overcome the problem of multi-walled carbon nanotubes being easily broken during the dispersion process, and the resulting dispersion liquid has uniformly dispersed and highly stable multi-walled carbon nanotubes. Application of the dispersion in ion batteries can effectively improve the battery's electrical conductivity and capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon nanotubes, and in particular to a multi-walled carbon nanotube dispersion liquid, a preparation method and an application thereof. Background Art

[0002] Multi-walled carbon nanotubes and single-walled carbon nanotubes have the same graphitized structure on the surface. However, compared with flexible single-walled carbon nanotubes, multi-walled carbon nanotubes have more walls and a larger diameter, which makes them more rigid and therefore more brittle. They are easy to break during the dispersion process and have large defects. As a result, when used as a conductive agent in ion batteries, they cannot well wrap the entire active material particles, which is not conducive to building a good conductive network. At the same time, the "needle effect" in the silicon-based negative electrode causes GPa-level compressive stress on the carbon nanotubes during the cycle, which will puncture the SEI and coating layer. Therefore, single-walled carbon nanotubes are currently mainly used as conductive agents in ion batteries.

[0003] However, compared with single-walled carbon nanotubes, multi-walled carbon nanotube powder has a higher yield. If the brittleness of multi-walled carbon nanotubes can be overcome during the dispersion process and their breakage can be avoided to the greatest extent, the cost of ion batteries can be greatly reduced. Summary of the Invention

[0004] Based on this, it is necessary to provide a multi-walled carbon nanotube dispersion and its preparation method and application to address the above problems. The preparation method can overcome the problem that multi-walled carbon nanotubes are easily broken during the dispersion process, and the multi-walled carbon nanotubes in the obtained dispersion are evenly dispersed and highly stable. Applying it to ion batteries can effectively improve the battery's conductivity and battery capacity.

[0005] A method for preparing a multi-walled carbon nanotube dispersion comprises the following steps:

[0006] Swelling the multi-walled carbon nanotube powder to obtain a first intermediate product;

[0007] The first intermediate product is mixed with manganese dioxide and a non-thickening surfactant, and then hydrogen peroxide is added to perform expansion treatment, and a second intermediate product is obtained by separation;

[0008] The second intermediate product is mixed with a thickening surfactant and a solvent to form a pre-dispersion liquid, and then the pre-dispersion liquid is subjected to at least a secondary dispersion treatment to obtain a multi-walled carbon nanotube dispersion liquid, wherein the mass fraction of the second intermediate product in the pre-dispersion liquid is less than 1.5%.

[0009] In one embodiment, in the step of subjecting the multi-walled carbon nanotube powder to swelling treatment, the multi-walled carbon nanotube powder is mixed with acid to perform the swelling treatment.

[0010] In one embodiment, the step of mixing the multi-walled carbon nanotube powder with an acid for swelling treatment satisfies at least one of the following conditions:

[0011] (1) The acid is selected from at least one of chlorosulfonic acid, concentrated nitric acid, concentrated sulfuric acid, and concentrated hydrochloric acid;

[0012] (2) The mass ratio of the acid to the multi-walled carbon nanotube powder is 10:1-100:1;

[0013] (3) The swelling treatment temperature is 10°C-60°C, and the time is 15 minutes-8 hours.

[0014] In one embodiment, in the step of adding hydrogen peroxide for expansion treatment, the hydrogen peroxide is added in batches.

[0015] In one embodiment, the expansion step further satisfies at least one of the following conditions:

[0016] (1) The mass ratio of the hydrogen peroxide to the manganese dioxide is 10:1-50:1;

[0017] (2) The mass ratio of the hydrogen peroxide to the multi-walled carbon nanotube powder is 5:1-50:1;

[0018] (3) The expansion treatment temperature is 10°C-85°C and the time is 15 minutes-8 hours;

[0019] (4) The mass ratio of the non-thickening surfactant to the multi-walled carbon nanotube powder is 1:10-10:10;

[0020] (5) The non-thickening surfactant is selected from at least one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium polystyrene sulfonate, lithium polystyrene sulfonate, sodium lignin sulfonate, alkali lignin, polyvinyl pyrrolidone or sodium lauryl sulfate.

[0021] In one embodiment, the pre-dispersion liquid further satisfies at least one of the following conditions:

[0022] (1) The mass ratio of the thickening surfactant to the multi-walled carbon nanotube powder is 2.5:10-15:10;

[0023] (2) The thickening surfactant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium hexametaphosphate or sodium alginate;

[0024] (3) The solvent is selected from water.

[0025] In one embodiment, the dispersion treatment method is selected from air flow grinding, emulsification shearing, colloid milling, ball milling, ultrasonic crushing, high-pressure homogenization or sand milling.

[0026] In one embodiment, the pre-dispersion liquid is subjected to a primary dispersion treatment and a secondary dispersion treatment in sequence, wherein the primary dispersion treatment is selected from at least one of air flow crushing, emulsification shearing, colloid milling or ball milling, and the secondary dispersion treatment is selected from at least one of ultrasonic crushing, high-pressure homogenization or sand milling.

[0027] The present invention also provides a multi-walled carbon nanotube dispersion prepared by the method for preparing the multi-walled carbon nanotube dispersion.

[0028] The present invention also provides an application of a multi-walled carbon nanotube dispersion in preparing a battery.

[0029] In the preparation method of the present invention, the multi-walled carbon nanotube powder is first subjected to a swelling treatment to obtain a relatively loose multi-walled carbon nanotube powder structure, and then bubbles are generated by the hydrogen peroxide reaction. The cavitation effect generated by the bubbles is used to expand and disperse the relatively loose multi-walled carbon nanotube powder structure. At the same time, the addition of a non-thickening surfactant can significantly improve the expansion and dispersion treatment effect, thereby making the multi-walled carbon nanotube powder easier to disperse by external force. Moreover, before the dispersion treatment, the present invention also reduces the degree of free movement between molecules by controlling the concentration of the pre-dispersion liquid and increasing the viscosity of the pre-dispersion liquid by using a thickening surfactant, thereby reducing the source of force and the interaction force generated by the dispersion medium distributed to the sites on the carbon nanotubes. Therefore, the preparation method of the present invention can overcome the problem that multi-walled carbon nanotubes are easily broken during the dispersion process, and the multi-walled carbon nanotubes in the obtained dispersion are uniformly dispersed and highly stable. Applying it to ion batteries can effectively improve the conductivity and battery capacity of the battery and reduce the cost of ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a SEM image of the multi-walled carbon nanotube dispersant obtained in Example 1;

[0031] Figure 2 This is a SEM image of the multi-walled carbon nanotube dispersant obtained in Example 7;

[0032] Figure 3 This is a SEM image of the multi-walled carbon nanotube dispersant obtained in Comparative Example 1;

[0033] Figure 4 This is an SEM image of the multi-walled carbon nanotube dispersant obtained in Comparative Example 2;

[0034] Figure 5 This is an SEM image of the multi-walled carbon nanotube dispersant obtained in Comparative Example 5;

[0035] Figure 6 This is the SEM image of the multi-walled carbon nanotube dispersant obtained in Comparative Example 6. DETAILED DESCRIPTION

[0036] To facilitate understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments or embodiments and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, including any two related listed items, any more related listed items, or the combination of all related listed items.

[0038] The method for preparing a multi-walled carbon nanotube dispersion provided by the present invention comprises the following steps:

[0039] S1, performing swelling treatment on multi-walled carbon nanotube powder to separate and obtain a first intermediate product;

[0040] S2, mixing the first intermediate product with manganese dioxide and a non-thickening surfactant, then adding hydrogen peroxide for expansion treatment, and separating to obtain a second intermediate product;

[0041] S3, mixing the second intermediate product with a thickening surfactant and a solvent to form a pre-dispersion liquid, and then dispersing the pre-dispersion liquid at least twice to obtain a multi-walled carbon nanotube dispersion liquid, wherein the mass fraction of the second intermediate product in the pre-dispersion liquid is less than 1.5%.

[0042] In step S1, the multi-walled carbon nanotube powder is subjected to a swelling treatment to obtain a relatively loose multi-walled carbon nanotube powder structure. The multi-walled carbon nanotube powder is obtained by a fluidized bed method or other methods. The present invention does not limit the source of the multi-walled carbon nanotubes.

[0043] The method for swelling multi-walled carbon nanotube powder in the present invention is not particularly limited. As some specific examples, the swelling treatment method includes but is not limited to treating multi-walled carbon nanotube powder with acid, treating multi-walled carbon nanotube powder with lipid solvent, etc.

[0044] Preferably, in the present invention, multi-walled carbon nanotube powder is added to acid to perform intercalation swelling on the multi-walled carbon nanotube powder. After a period of reaction, the multi-walled carbon nanotube powder is washed with water to neutrality and filtered to obtain a first intermediate product.

[0045] The acid is selected from at least one of chlorosulfonic acid, concentrated nitric acid, concentrated sulfuric acid, and concentrated hydrochloric acid, more preferably chlorosulfonic acid. The mass ratio of the acid to the multi-walled carbon nanotube powder is 10:1-100:1. The swelling treatment temperature is 10°C-60°C, and the time is 15 min-8 h.

[0046] In step S2, the first intermediate product is mixed with manganese dioxide and a non-thickening surfactant, and then hydrogen peroxide is added. The hydrogen peroxide reacts under the catalysis of manganese dioxide to produce bubbles. The cavitation effect generated by the bubbles causes the swollen carbon nanotubes to expand and disperse, and can prevent the multi-walled carbon nanotubes from breaking. At the same time, the non-thickening surfactant can be fully adsorbed and wrapped on the surface of the multi-walled carbon nanotubes or intercalated into the gaps entangled by the multi-walled carbon nanotubes during the expansion process, and the shrinkage and agglomeration of the multi-walled carbon nanotubes are prevented by steric hindrance and electrostatic repulsion, thereby greatly improving the dispersion of the multi-walled carbon nanotube powder in the solution, so that the multi-walled carbon nanotube powder is evenly suspended in the solution, and significantly improving the expansion treatment effect.

[0047] Optionally, in the step of adding hydrogen peroxide for expansion treatment, the hydrogen peroxide is added in batches, such as dropwise addition. The batch addition can be continuous or intermittent, thereby controlling the rate of manganese dioxide-catalyzed hydrogen peroxide reaction, thereby controlling the rate of bubble generation, improving the expansion and dispersion effects, and avoiding the breakage of the multi-walled carbon nanotubes.

[0048] Optionally, the mass ratio of the hydrogen peroxide to the manganese dioxide is 10:1-50:1, and the mass ratio of the hydrogen peroxide to the multi-walled carbon nanotube powder is 5:1-50:1.

[0049] Optionally, the expansion treatment is performed at a temperature of 10°C to 85°C and for a time of 15 minutes to 8 hours;

[0050] Optionally, the mass ratio of the non-thickening surfactant to the multi-walled carbon nanotube powder is 1:10-10:10, and the non-thickening surfactant is selected from at least one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium polystyrene sulfonate, lithium polystyrene sulfonate, sodium lignin sulfonate, alkali lignin, polyvinyl pyrrolidone or sodium lauryl sulfate.

[0051] After the swelling and expansion treatment of the present invention, the multi-walled carbon nanotube powder is more easily dispersed by external force. In step S3, at least two dispersion treatments are performed, such as two dispersion treatments, three dispersion treatments, etc., to reduce the mechanical force of each dispersion treatment and avoid the breakage of the multi-walled carbon nanotubes.

[0052] In addition, before the dispersion process, the present invention first mixes the second intermediate product with a thickening surfactant and a solvent to form a pre-dispersion liquid, wherein the thickening surfactant can increase the viscosity of the pre-dispersion liquid and reduce the degree of free movement between molecules. At the same time, by controlling the concentration of the pre-dispersion liquid, the source of force and the interaction force generated by the dispersion medium can be reduced and distributed to the sites on the dispersed carbon nanotubes, thereby avoiding the breakage of the multi-walled carbon nanotubes.

[0053] Optionally, the solvent is selected from water, the mass ratio of the thickening surfactant to the multi-walled carbon nanotube powder is 2.5:10-15:10, and the thickening surfactant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium hexametaphosphate or sodium alginate.

[0054] Optionally, the dispersion treatment method is selected from air flow grinding, emulsification shearing, colloid milling, ball milling, ultrasonic crushing, high-pressure homogenization or sand milling.

[0055] Optionally, the pre-dispersion liquid is subjected to a primary dispersion treatment and a secondary dispersion treatment in sequence, wherein the primary dispersion treatment is selected from at least one of air flow crushing, emulsification shearing, colloid milling or ball milling, and the secondary dispersion treatment is selected from at least one of ultrasonic crushing, high-pressure homogenization or sand milling.

[0056] Among them, the primary dispersion treatment method is preferably emulsification shearing, the emulsification shearing processing rate is 4000rpm-16000rpm, and the processing time is 15min-360min; the secondary dispersion treatment method is preferably high-pressure homogenization and ultrasonic crushing, the high-pressure homogenization pressure is 3000psi-16000psi, the ultrasonic crushing power is 80W-150W, and the time is 15min-1.5h.

[0057] The present invention also provides a multi-walled carbon nanotube dispersion prepared by the method for preparing the multi-walled carbon nanotube dispersion.

[0058] The multi-walled carbon nanotubes in the multi-walled carbon nanotube dispersion prepared by the preparation method of the present invention have good dispersibility and high stability. When applied to ion batteries, they can better wrap around the active material particles in the ion batteries, significantly improving the battery's conductivity and battery capacity.

[0059] The present invention also provides application of the multi-walled carbon nanotube dispersion in batteries.

[0060] After the swelling and expansion treatment of the present invention, the multi-walled carbon nanotube powder is more easily dispersed by external force. Furthermore, before the dispersion treatment, the present invention also reduces the degree of free movement between molecules by controlling the concentration of the pre-dispersion liquid and increasing the viscosity of the pre-dispersion liquid using a thickening surfactant, thereby reducing the distribution of the interaction force generated by the source of force and the dispersion medium to the sites on the dispersed carbon nanotubes. Therefore, the preparation method of the present invention can overcome the problem of multi-walled carbon nanotubes being easily broken during the dispersion process, and the multi-walled carbon nanotubes in the resulting dispersion are evenly dispersed and highly stable. Application of the method in ion batteries can effectively improve the battery's electrical conductivity and capacity, thereby reducing the cost of ion batteries.

[0061] Hereinafter, the multi-walled carbon nanotube dispersion, its preparation method and application will be further described through the following specific examples.

[0062] Example 1

[0063] At 50° C., 6 g of multi-walled carbon nanotube powder was added to 60 g of chlorosulfonic acid for swelling. After swelling for 8 hours, the mixture was washed with water until neutral and filtered to obtain a first intermediate product.

[0064] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the mixture was washed with water until neutral and filtered to obtain a second intermediate product.

[0065] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 2988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000rpm for 1 hour, followed by high-pressure homogenization at 4000psi, 6000psi, and 3000psi. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0066] Example 2

[0067] At 50° C., 6 g of multi-walled carbon nanotube powder was added to 60 g of chlorosulfonic acid for swelling. After swelling for 8 hours, the mixture was washed with water until neutral and filtered to obtain a first intermediate product.

[0068] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0069] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.6%. The pre-dispersion was then emulsified and sheared at 7000 rpm for 1 hour, followed by high-pressure homogenization at 4000 psi, 6000 psi, and 3000 psi. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0070] Example 3

[0071] 6 g of multi-walled carbon nanotube powder was swollen in 60 g of chlorosulfonic acid at 50° C. for 8 hours, then washed with water until neutral and filtered to obtain a first intermediate product.

[0072] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone, and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0073] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 2988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000 rpm for 30 minutes, followed by high-pressure homogenization at pressures of 4000 psi, 6000 psi, and 3000 psi. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0074] Example 4

[0075] 6 g of multi-walled carbon nanotube powder was swollen in 60 g of chlorosulfonic acid at 50° C. for 8 hours, then washed with water until neutral and filtered to obtain a first intermediate product.

[0076] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0077] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 2988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000rpm for 1 hour, followed by high-pressure homogenization at 10,000psi, 13,000psi, and 16,000psi. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0078] Example 5

[0079] 6 g of multi-walled carbon nanotube powder was swollen in 60 g of chlorosulfonic acid at 50° C. for 8 hours, then washed with water until neutral and filtered to obtain a first intermediate product.

[0080] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0081] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 2988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000rpm for 1 hour, followed by high-pressure homogenization at 4000psi, 6000psi, and 3000psi. Finally, ultrasonication was performed at 80W for 2 hours to obtain a multi-walled carbon nanotube dispersion.

[0082] Example 6

[0083] 6 g of multi-walled carbon nanotube powder was swollen in 60 g of chlorosulfonic acid at 50° C. for 8 hours, then washed with water until neutral and filtered to obtain a first intermediate product.

[0084] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0085] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 2988ml of deionized water were added to obtain a 0.2% pre-dispersion. The pre-dispersion was then sheared in a colloid mill for 1 hour, followed by high-pressure homogenization at 4000psi, 6000psi, and 3000psi. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0086] Example 7

[0087] 6 g of multi-walled carbon nanotube powder was swollen in 60 g of chlorosulfonic acid at 50° C. for 8 hours, then washed with water until neutral and filtered to obtain a first intermediate product.

[0088] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0089] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 2988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000 rpm for 1 hour, followed by sand milling. 50μm zirconium oxide was added and sand milled at 1100 rpm for 2 hours. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0090] Example 8

[0091] 6 g of multi-walled carbon nanotube powder was swollen in 60 g of chlorosulfonic acid at 50° C. for 8 hours, then washed with water until neutral and filtered to obtain a first intermediate product.

[0092] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0093] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 2988ml of deionized water were added to obtain a 0.2% pre-dispersion solution. The pre-dispersion solution was then emulsified and sheared at 7000 rpm for 1 hour. Ultrasonication at 80W for 60 minutes was then performed to obtain a multi-walled carbon nanotube dispersion.

[0094] Comparative Example 1

[0095] 6g of multi-walled carbon nanotube powder, 2g of sodium lignin sulfonate, 1g of polyvinyl pyrrolidone, 3g of sodium carboxymethyl cellulose, and 2988ml of deionized water were mixed to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000 rpm for 1 hour. High-pressure homogenization was then performed at pressures of 4000 psi, 6000 psi, and 3000 psi. Finally, ultrasonication was performed at 100 W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0096] Comparative Example 2

[0097] At 50° C., 6 g of multi-walled carbon nanotube powder was added to 60 g of chlorosulfonic acid for swelling. After swelling for 8 hours, the mixture was washed with water until neutral and filtered to obtain a first intermediate product.

[0098] The first intermediate product, 2g of sodium lignin sulfonate, 1g of polyvinyl pyrrolidone, 3g of sodium carboxymethyl cellulose, and 2988ml of deionized water were mixed to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000 rpm for 1 hour, followed by high-pressure homogenization at 4000 psi, 6000 psi, and 3000 psi. Finally, ultrasonication was performed at 100 W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0099] Comparative Example 3

[0100] At 50° C., 6 g of multi-walled carbon nanotube powder was added to 60 g of chlorosulfonic acid for swelling. After swelling for 8 hours, the mixture was washed with water until neutral and filtered to obtain a first intermediate product.

[0101] 4 g of manganese dioxide was added to the first intermediate product, and 40 g of hydrogen peroxide was slowly added dropwise. The mixture was reacted at 50° C. for 8 hours, washed with water until neutral, and filtered to obtain a second intermediate product.

[0102] To the second intermediate product, 2g of sodium lignin sulfonate, 1g of polyvinyl pyrrolidone, 3g of sodium carboxymethyl cellulose, and 2988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000 rpm for 1 hour, followed by high-pressure homogenization at 4000 psi, 6000 psi, and 3000 psi. Finally, ultrasonication was performed at 100 W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0103] Comparative Example 4

[0104] At 50° C., 6 g of multi-walled carbon nanotube powder was added to 60 g of chlorosulfonic acid for swelling. After swelling for 8 hours, the mixture was washed with water until neutral and filtered to obtain a first intermediate product.

[0105] 3 g of sodium carboxymethyl cellulose and 4 g of manganese dioxide were added to the first intermediate product, and 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0106] To the second intermediate product, 3 g of sodium lignin sulfonate and 2988 ml of deionized water were added, and emulsification and shearing were performed at 7000 rpm for 1 hour. Then, high-pressure homogenization was performed at homogenization pressures of 4000 psi, 6000 psi, and 3000 psi respectively. Finally, ultrasonic crushing was performed at a power of 80 W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0107] Comparative Example 5

[0108] At 50° C., 6 g of multi-walled carbon nanotube powder was added to 60 g of chlorosulfonic acid for swelling. After swelling for 8 hours, the mixture was washed with water until neutral and filtered to obtain a first intermediate product.

[0109] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0110] To the second intermediate product, 3g of sodium lignin sulfonate and 2988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000 rpm for 1 hour, followed by high-pressure homogenization at 4000 psi, 6000 psi, and 3000 psi. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0111] Comparative Example 6

[0112] At 50°C, 6g of multi-walled carbon nanotube powder, 60g of chlorosulfonic acid, 4g of manganese dioxide and 40g of hydrogen peroxide were swollen and expanded, 2g of sodium lignin sulfonate and 1g of polyvinyl pyrrolidone were added, and the mixture was washed with water until neutral and filtered to obtain a first intermediate product.

[0113] To the first intermediate product, 3g of sodium carboxymethyl cellulose and 2988ml of deionized water were added to obtain a pre-dispersion with a concentration of 0.2%. The pre-dispersion was then emulsified and sheared at 7000rpm for 1 hour, followed by high-pressure homogenization at 4000psi, 6000psi, and 3000psi. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0114] Comparative Example 7

[0115] At 50° C., 6 g of multi-walled carbon nanotube powder was added to 60 g of chlorosulfonic acid for swelling. After swelling for 8 hours, the mixture was washed with water until neutral and filtered to obtain a first intermediate product.

[0116] 2 g of sodium lignin sulfonate, 1 g of polyvinyl pyrrolidone and 4 g of manganese dioxide were added to the first intermediate product, and then 40 g of hydrogen peroxide was slowly added dropwise. After reacting at 50° C. for 8 hours, the product was washed with water until neutral and filtered to obtain a second intermediate product.

[0117] To the second intermediate product, 3g of sodium carboxymethyl cellulose and 288ml of deionized water were added to obtain a 2% pre-dispersion. The pre-dispersion was then emulsified and sheared at 7000rpm for 1 hour, followed by high-pressure homogenization at 4000psi, 6000psi, and 3000psi. Finally, ultrasonication was performed at 80W for 30 minutes to obtain a multi-walled carbon nanotube dispersion.

[0118] The multi-walled carbon nanotube dispersions obtained in Examples 1 to 8 and Comparative Examples 1 to 7 were subjected to particle size analysis and viscosity characterization. The results are shown in Table 1.

[0119] Particle size analysis steps: add the multi-walled carbon nanotube dispersion dropwise into a laser particle size analyzer beaker filled with deionized water until the transmittance is between 5% and 10%;

[0120] Viscosity measurement steps: Weigh 2 ml of multi-walled carbon nanotube dispersion and place it on the sample stage of the high and low temperature viscometer, set the temperature to 25 ° C, adjust the gap, and measure the viscosity at 18.6s. -1 The viscosity is measured at a shear rate of 1.

[0121] Table 1

[0122]

[0123] As can be seen from Table 1, the multi-walled carbon nanotubes in the dispersion obtained by the preparation method of the present invention are evenly dispersed and highly stable. At the same time, the dispersion prepared by the present invention has a low viscosity and excellent processability.

[0124] In addition, the multi-walled carbon nanotube dispersions obtained in some examples and comparative examples were tested by scanning electron microscopy (SEM test). The test steps were as follows: take a drop of multi-walled carbon nanotube dispersion and dilute it 100 times, then ultrasonicate it for 10 minutes, drop the ultrasonicated sample on the surface of the silicon wafer and observe it. The results are as follows: Figures 1 to 6 shown.

[0125] from Figure 1 and Figure 2 The gaps between the multi-walled carbon nanotubes are clear, with little agglomeration, and the nanotubes are mainly relatively independent, indicating that they are evenly dispersed in the dispersion. In addition, the multi-walled carbon nanotubes in the dispersion are relatively long and have little breakage.

[0126] Comparative Example 1 uses conventional dispersion methods to disperse multi-walled carbon nanotube powder without swelling and expansion treatment. The D50 particle size of the dispersion is larger than the D50 particle size of all the examples. Figure 3It can be seen that since the dispersion has not undergone the swelling and expansion process, there are still many large-sized multi-walled carbon nanotube powders in the dispersion, and most of the multi-walled carbon nanotubes are still tightly entangled after dispersion, with poor dispersibility. Therefore, the absorbance of the dispersion is poor, the optical density is lower than that of the embodiment, and the optical density after centrifugation is also significantly different from that before centrifugation, and the stability is poor.

[0127] Comparative Example 2 does not undergo the expansion process compared to all the examples. Compared with Comparative Example 1, the particle size D50 of the dispersion is smaller than that of Comparative Example 1, indicating that the dispersibility of the multi-walled carbon nanotube powder is relatively improved after swelling. Figure 4 It can be seen that the multi-walled carbon nanotube powder in the dispersion begins to have a tendency to disentangle and loosen, but compared with the examples, the particle size D50 of the dispersion is larger than that of all the examples.

[0128] In Comparative Example 3, no non-thickening surfactant was added during the expansion process, and the particle size D50 in the dispersion was larger than that in all the examples, indicating that the introduction of the non-thickening surfactant during the expansion process can effectively prevent the agglomeration of multi-walled carbon nanotubes during the filtration process.

[0129] Comparative Example 4 introduced a thickening dispersant during the expansion process, resulting in a higher viscosity than the dispersion in the examples. Particle size analysis revealed that the larger particles in Comparative Example 4 resulted in a high number of large aggregates in the dispersion, which in turn affected its dispersibility. This demonstrates that a high-viscosity environment significantly affects dispersion efficiency and increases dispersion resistance.

[0130] Comparative Example 5 uses a non-thickening surfactant in both the expansion and subsequent dispersion processes, resulting in a lower viscosity. As shown in Table 1, the particle size D50 of the dispersion is smaller than that of Example 1 and the comparative example, with fewer agglomerated structures and smaller particle sizes. Figure 5 It can be seen that there are almost no agglomerates and undispersed multi-walled carbon nanotube powders in the slurry, and the dispersibility is excellent. However, since the viscosity of the system is relatively low, almost similar to that of the solvent, the degree of free movement of the particles in the solvent environment reaches the maximum, and the interaction between the force and the dispersion medium is more easily distributed to the sites on the dispersed medium. Therefore, the shear force, cavitation effect and impact effect are stronger in the high viscosity environment, making the originally rigid multi-walled carbon nanotube powder easier to break during the dispersion process. Therefore, the length of the multi-walled carbon nanotubes in the dispersion is shorter than that in the embodiment.

[0131] Comparative Example 6 was subjected to both swelling and expansion processes. As shown in Table 1, the particle size D50 of the dispersion was larger than that of all the other examples. Figure 6It can be seen that the carbon nanotube powders in the dispersion are completely dispersed, and no array structure exists in the dispersion. However, the dispersed multi-walled carbon nanotubes are severely entangled and broken. Most of the multi-walled carbon nanotubes are tightly intertwined with each other and distributed in blocks at various positions. This is because the strong acidity during the swelling and expansion process inhibits the ionization ability of the non-thickening surfactant in the solution, thereby weakening the ability of the non-thickening surfactant molecules to adsorb and wrap around the surface of the multi-walled carbon nanotubes, thereby generating steric hindrance and electrostatic repulsion to prevent their agglomeration. At the same time, polymer surfactants such as PVP are easily denatured and inactivated under strong acid conditions, so their ability to provide adsorption and steric hindrance is greatly reduced, causing the multi-walled carbon nanotubes to still shrink after expansion, thereby causing entangled agglomeration.

[0132] The concentration of the second intermediate product in Comparative Example 7 is greatly increased compared with that in Example. As shown in Table 1, the particle size of the dispersion is similar to that in Comparative Example 4, and both are much larger than the particle size D50 in Example. It can be seen that there are still many large-sized agglomerate structures in the dispersion, and the dispersibility is poor. This is because the increase in the number of particles in the system also affects the interaction between the source of force and the dispersion medium.

[0133] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0134] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a multi-walled carbon nanotube dispersion for preparing a battery, characterized in that: The steps include: Swelling the multi-walled carbon nanotube powder to obtain a first intermediate product; The first intermediate product is mixed with manganese dioxide and a non-thickening surfactant, and then hydrogen peroxide is added for expansion treatment, and a second intermediate product is obtained by separation, wherein the mass ratio of the non-thickening surfactant to the multi-walled carbon nanotube powder is 1:10-10:10; The second intermediate product is mixed with a thickening surfactant and a solvent to form a pre-dispersion liquid, and the pre-dispersion liquid is then dispersed at least twice to obtain a multi-walled carbon nanotube dispersion liquid for preparing a battery, wherein the mass ratio of the thickening surfactant to the multi-walled carbon nanotube powder is 2.5:10-15:10, and the mass fraction of the second intermediate product in the pre-dispersion liquid is less than 1.5%.

2. The method for preparing a multi-walled carbon nanotube dispersion for preparing a battery according to claim 1, characterized in that: In the step of subjecting the multi-walled carbon nanotube powder to swelling treatment, the multi-walled carbon nanotube powder is mixed with acid to perform swelling treatment.

3. The method for preparing a multi-walled carbon nanotube dispersion for preparing a battery according to claim 2, characterized in that: The step of mixing the multi-walled carbon nanotube powder with an acid for swelling treatment satisfies at least one of the following conditions: (1) The acid is selected from at least one of chlorosulfonic acid, concentrated nitric acid, concentrated sulfuric acid, and concentrated hydrochloric acid; (2) the mass ratio of the acid to the multi-walled carbon nanotube powder is 10:1-100:1; (3) The temperature of the swelling treatment is 10°C-60°C, and the time is 15 minutes-8 hours.

4. The method for preparing a multi-walled carbon nanotube dispersion for preparing a battery according to claim 1, characterized in that: In the step of adding hydrogen peroxide for expansion treatment, the hydrogen peroxide is added in batches.

5. The method for preparing a multi-walled carbon nanotube dispersion for preparing a battery according to claim 1 or claim 4, characterized in that: The expansion step further satisfies at least one of the following conditions: (1) The mass ratio of the hydrogen peroxide to the manganese dioxide is 10:1-50:1; (2) The mass ratio of the hydrogen peroxide to the multi-walled carbon nanotube powder is 5:1-50:1; (3) The expansion treatment temperature is 10°C-85°C and the time is 15 minutes-8 hours; (4) The non-thickening surfactant is selected from at least one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium polystyrene sulfonate, lithium polystyrene sulfonate, sodium lignin sulfonate, alkali lignin, polyvinyl pyrrolidone or sodium lauryl sulfate.

6. The method for preparing a multi-walled carbon nanotube dispersion for preparing a battery according to claim 1, characterized in that: The pre-dispersion liquid also satisfies at least one of the following conditions: (1) The thickening surfactant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium hexametaphosphate or sodium alginate; (2) The solvent is selected from water.

7. The method for preparing a multi-walled carbon nanotube dispersion for preparing a battery according to claim 1, characterized in that: The dispersion treatment method is selected from air flow crushing, emulsification shearing, colloid milling, ball milling, ultrasonic crushing, high-pressure homogenization or sand milling.

8. The method for preparing a multi-walled carbon nanotube dispersion for preparing a battery according to claim 1 or claim 7, characterized in that: The pre-dispersion liquid is sequentially subjected to a primary dispersion treatment and a secondary dispersion treatment, wherein the primary dispersion treatment is selected from at least one of air flow crushing, emulsification shearing, colloid milling or ball milling, and the secondary dispersion treatment is selected from at least one of ultrasonic crushing, high-pressure homogenization or sand milling. 9 . A multi-walled carbon nanotube dispersion for preparing a battery, prepared by the method for preparing a multi-walled carbon nanotube dispersion for preparing a battery according to any one of claims 1 to 8 .

10. Use of the multi-walled carbon nanotube dispersion for preparing batteries according to claim 9 in preparing batteries.

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