CN103426498A - Carbon nanotube conductive slurry and method for preparing carbon nanotube conductive slurry - Google Patents

Abstract

The invention belongs to the technical field of electrochemical materials, and particularly relates to carbon nanotube conductive slurry and a method for preparing the carbon nanotube conductive slurry. The carbon nanotube conductive slurry is mainly composed of carbon nanotubes, other conductive fillers, dispersing auxiliaries and a solvent, and the carbon nanotube conductive slurry comprises the components, by mass, 0.5-15% of the carbon nanotubes, 0.1-2% of the other conductive substances, 0.1-5% of the dispersing auxiliaries and the balance being solvent. The method for preparing the carbon nanotube conductive slurry includes the steps that firstly the dispersing auxiliaries are dissolved in the solvent, then, the carbon nanotubes and the other conductive fillers are added under the stirring condition, after the carbon nanotubes and the other conductive fillers are fully immersed, a sand mill is utilized to grind the slurry, and the stable and dispersing carbon nanotube conductive slurry can be obtained after the slurry is grinded for a few hours. The method is simple and free of damaging the structures and the electrical conductivity of the carbon nanotubes, the prepared carbon nanotube conductive slurry has good electrical conductivity and is stable and uniform in property, and the stability of the slurry is larger than 90% after standing for 3 months.

Description

A kind of carbon nanotube conductive paste and preparation method thereof

technical field

The invention belongs to the technical field of electrochemical materials, and in particular relates to a carbon nanotube conductive slurry and a preparation method thereof. The material can be used as a conductive agent in the positive or negative electrodes of lithium-ion secondary batteries and capacitors.

Background technique

In the preparation process of lithium-ion secondary batteries and capacitors, it is often necessary to add a certain amount of conductive agent to the positive and negative electrode ingredients. The conductive agent can effectively contact with the positive and negative active materials to form a good conductive network, thereby improving the rate performance of the battery. However, adding too much conductive agent will inevitably reduce the content of electrode active materials and reduce the capacity and energy density of the battery. For high-performance electronic devices, it is particularly important to choose a suitable conductive agent.

Carbon nanotubes are emerging conductive agents in recent years. They generally have a diameter of about 5-60 nanometers and a length of 10-20 microns. They can not only act as "wires" in the conductive network, but also have an electric double layer effect. Taking advantage of the high rate characteristics of the supercapacitor, its good thermal conductivity is also beneficial to the heat dissipation during charging and discharging of the battery, reducing the polarization of the battery, improving the high and low temperature performance of the battery, and prolonging the life of the battery.

Liu et al. (Journal of Power Sources 2008, 184, 522-526.) reported the performance of C-LiFePO ₄ /graphite batteries with multi-walled carbon nanotubes (MWNTs) and carbon black as conductive agents. Compared with carbon black, the battery with MWNTs as additive has better electrochemical performance: the capacity retention rate reaches 99.2% after 50 cycles, and the 1C discharge capacity is 94.6% of 0.1C. The polarization voltage was reduced from 0.3V to 0.2V, and the impedance was reduced from 423.2Ω to 36.88Ω. The crystal form of the positive electrode material LiFePO ₄ is also better maintained after cycling. Jin et al. (Journal of Solid State Electrochemistry 2008, 12, 1549-1554.) studied the influence of using acetylene black and MWNTs as positive electrode conductors on the electrochemical performance of LiFePO ₄ -C positive electrode materials. The LiFePO ₄ -C/Li battery with 5wt% MWNTs added has the best performance, and a reversible capacity of 142mAh/g can be achieved at 0.25C at room temperature.

However, due to the strong van der Waals force between carbon nanotubes, they will be entangled and agglomerated together (Figure 1), and it is difficult to uniformly disperse in the positive and negative electrode materials, thus affecting the performance of the carbon nanotubes' electrical conductivity. . Therefore, how to prepare uniformly dispersed carbon nanotube conductive paste is a major obstacle limiting its industrial application. At present, there are mainly two methods to solve the dispersion problem of carbon nanotubes, chemical and physical. Although chemical methods such as strong oxidizing acid treatment methods can obtain carbon nanotubes with good dispersion properties, strong acids will also destroy the structure of carbon nanotubes and shorten carbon nanotubes, thereby affecting the conductivity of carbon nanotubes and their use as electrical conductors. performance of the agent. Physical methods such as the use of more ultrasonic treatment methods have low efficiency, poor dispersion effect, and stability, and the concentration of the obtained carbon nanotube dispersion is lower than 5mg/mL, so it is difficult to prepare a carbon nanotube dispersion slurry on a large scale.

In the present invention, we propose a simple and easy new method for preparing carbon nanotube conductive paste. The preparation process has good repeatability, and the prepared carbon nanotube conductive paste has high solid content and stable and uniform properties. After one month, the slurry stability was >90%.

Contents of the invention

The object of the present invention is to provide a carbon nanotube conductive paste.

Another object of the present invention is to provide a preparation method of carbon nanotube conductive paste.

The carbon nanotube conductive paste proposed by the present invention is characterized in that the conductive paste is composed of carbon nanotubes, other conductive fillers, dispersion aids and solvents, and its mass percentage is composed of: carbon nanotubes: 0.5-15%, Other conductive fillers: 0.1~2%, dispersing aids: 0.1~5%, and the rest are solvents.

The carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes or a mixture of both.

The other conductive fillers are one or more of carbon black, acetylene black, carbon fiber or conductive graphite.

The dispersing aid is one or more of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA) or hydroxymethylcellulose (CMC).

The solvent is N-methylpyrrolidone (NMP) or water.

The preparation method of the carbon nanotube conductive paste proposed by the present invention is characterized in that the steps are as follows: first, the dispersing aid is dissolved in a solvent, and then carbon nanotubes and other conductive fillers are added under stirring conditions, and the carbon nanotubes and After other conductive fillers are fully infiltrated, the slurry is ground with a sand mill, and a stable dispersed carbon nanotube conductive slurry can be obtained after a few hours. Specifically,

(1) Weigh a certain amount of dispersing aid, dissolve it in a solvent, and configure a solution with a weight percentage of 0.1-5%; under mechanical stirring conditions, add carbon nanotubes or carbon nanotubes with a weight percentage of 0.5-15% The mixture of tubes and 0.1-2% by weight of other conductive fillers is fully stirred to completely infiltrate the solid powder to prepare a carbon nanotube pre-dispersion liquid.

(2) Grinding and dispersing the carbon nanotube pre-dispersion liquid with a sand mill for 0.5-8 hours to obtain a stably dispersed carbon nanotube conductive paste.

The diameter of the zirconia ball used in the sand mill is 0.1-3 mm.

The method of the present invention is simple, does not destroy the structure and conductivity of carbon nanotubes, and the prepared carbon nanotube conductive paste has excellent conductivity and stable and uniform properties. After standing for 3 months, the stability of the paste is >90%. .

Compared with the strong acid oxidation or ultrasonic-assisted dispersion methods currently used at home and abroad, the present invention has the following characteristics: (1) It does not destroy the structure of carbon nanotubes, and can effectively open the aggregates of carbon nanotubes (Figure 2); (2) the obtained The performance of carbon nanotube conductive paste is stable (after standing for 3 months, the stability is >90%), and it has a high solid content (0.5~15%).

Description of drawings

Figure 1. SEM photograph of carbon nanotube aggregates. This result indicates that carbon nanotubes are easy to agglomerate together to form aggregates with a diameter of 10-1000 μm.

Figure 2. SEM photo of carbon nanotube conductive paste. The results indicated that the aggregates of carbon nanotubes in the prepared carbon nanotube slurry were fully opened to form a closely connected conductive network of carbon nanotubes.

Figure 3. (A-F) Drying photos of carbon nanotube premix slurry and 1-5 hour grinding slurry coating. The surface of the premixed slurry is rough and has obvious agglomeration phenomenon. As the grinding time increases, the surface of the slurry coating tends to be smooth and uniform. The results indicated that with the increase of grinding time, the dispersion of carbon nanotube conductive paste became more uniform.

Fig. 4. The change diagram of the solid content of the slurry in the upper layer of carbon nanotubes. Let the slurry stand for 40 days or adopt 3000, 6000, 12000rpm centrifugation to treat the slurry respectively, and the solid content of the upper layer of the slurry has little change with the initial solid content. The results indicated that the prepared carbon nanotube slurry had good stability.

Figure 5. SEM photo of the positive electrode sheet of lithium-ion battery. It can be seen from the photo that the carbon nanotubes are uniformly dispersed among the positive electrode active material lithium iron phosphate particles, forming a three-dimensional conductive network.

Detailed ways

Embodiment 1: 9.25kg N-methylpyrrolidone was added as a solvent carrier in a 20-liter container, and 0.15kg polyvinylpyrrolidone was added thereto as an auxiliary agent. Fully dissolve the polyvinylpyrrolidone in the N-methylpyrrolidone under the mechanical stirring condition of 6000rpm. Then, 0.6 kg of multi-walled carbon nanotubes are added in batches to the solution, and the rest of the carbon nanotubes are added after the added solid powder is fully wetted by the solvent. After all the additions were completed, mechanical stirring was continued for 15 minutes to obtain a pre-dispersed slurry. The carbon nanotube pre-dispersed slurry was transferred to a nano sand mill, and zirconia balls with a diameter of 1 mm were used to grind at 2400 rpm for 2 hours to obtain the carbon nanotube slurry.

The photo of the carbon nanotube pre-dispersed slurry and the hourly grinding slurry coated on the glass slide after drying is shown in Figure 3. The stability of the carbon nanotube slurry was characterized by centrifugation and standing still to measure the solid content of the upper layer slurry, as shown in FIG. 4 .

Example 2: 9.4kg of water was added into a 20-liter container as a solvent carrier, and 0.1kg of hydroxymethylcellulose was added thereto as an auxiliary agent. Fully dissolve the hydroxymethylcellulose in water under the condition of 5000rpm mechanical stirring. Then add 0.17kg Super-p nano-acetylene black conductive agent and 0.33kg single-walled carbon nanotubes to the solution in batches, and then add the rest of the composite conductive agent after the added solid powder is fully wetted by the solvent. After all the additions were completed, mechanical stirring was continued for 15 minutes to obtain a pre-dispersed slurry. The carbon nanotube pre-dispersed slurry was transferred to a sand mill, and zirconia balls with a diameter of 0.3 mm were used to grind at 1800 rpm for 5 hours to obtain a carbon nanotube composite conductive slurry.

Example 3: 9.4 kg of deionized water was weighed in a 20-liter container as a solvent carrier, and 0.1 kg of polyvinylpyrrolidone was added therein as an auxiliary agent. Fully dissolve the polyvinylpyrrolidone in water under the condition of 3000rpm mechanical stirring. Then add 0.5 kg of multi-walled carbon nanotubes in batches to the solution, and add the rest of the carbon nanotubes after the added solid powder is fully wetted by the solvent. After all the additions were completed, mechanical stirring was continued for 15 minutes to obtain a pre-dispersed slurry. The carbon nanotube pre-dispersed slurry was transferred to a sand mill, and zirconia balls with a diameter of 0.6 mm were used to grind at 1500 rpm for 0.5 hour to obtain a carbon nanotube composite conductive slurry.

Example 4: 9.4kg of N-methylpyrrolidone was weighed in a 20-liter container as a solvent carrier, and 0.1kg of polyvinyl alcohol was added thereto as an auxiliary agent. Fully dissolve polyvinyl alcohol in N-methylpyrrolidone under the condition of 4000rpm mechanical stirring. Then add 0.17kg Super-p nano-acetylene black conductive agent and 0.33kg multi-walled carbon nanotubes to the solution in batches, and then add the rest of the composite conductive agent after the added solid powder is fully wetted by the solvent. After all the additions were completed, mechanical stirring was continued for 30 minutes to obtain a pre-dispersed slurry. The carbon nanotube pre-dispersed slurry was transferred to a sand mill, and zirconia balls with a diameter of 0.8 mm were used to grind at 1200 rpm for 6 hours to obtain a carbon nanotube composite conductive slurry.

Example 5: 9.4 kg of water was weighed in a 20-liter container as a solvent carrier, and 0.05 kg of polyvinyl alcohol and 0.05 kg of polyvinylpyrrolidone were added therein as auxiliary agents. Fully dissolve polyvinyl alcohol and polyvinylpyrrolidone in water under the condition of 4000rpm mechanical stirring. Then add 0.17kg Super-p nano-acetylene black conductive agent and 0.33kg multi-walled carbon nanotubes to the solution in batches, and then add the rest of the composite conductive agent after the added solid powder is fully wetted by the solvent. After all the additions were completed, mechanical stirring was continued for 5 minutes to obtain a pre-dispersed slurry. The carbon nanotube pre-dispersed slurry was transferred to a sand mill, and zirconia balls with a diameter of 0.2 mm were used to grind at 1900 rpm for 4.5 hours to obtain a carbon nanotube composite conductive slurry.

Claims (2)

1. a carbon nanotube conducting slurry, it is characterized in that, this electrocondution slurry is mainly by carbon nano-tube, other conductive fillers, dispersing aid and solvent composition, its mass percent consists of: carbon nano-tube: 0.5～15%, other conductive materials 0.1～2%, dispersing aid: 0.1～5%, all the other are solvent, described carbon nano-tube can stably be dispersed in solvent, sedimentation rate in 3 months<10%;

Wherein, carbon nano-tube is one or both mixing in Single Walled Carbon Nanotube or multi-walled carbon nano-tubes;

Other conductive fillers are one or more in carbon black, acetylene black, carbon fiber or electrically conductive graphite;

Dispersing aid is one or more in PVP, polyvinyl alcohol or CMC;

Described solvent is 1-METHYLPYRROLIDONE or water.

2. the preparation method of a carbon nanotube conducting slurry as claimed in claim 1, is characterized in that, it comprises step:

(1) take a certain amount of dispersing aid, be dissolved in solvent, be configured to the solution that contains dispersing aid; Under the mechanical agitation condition, add carbon nano-tube or carbon nano-tube and other conductive fillers, fully stir, make the pressed powder complete wetting, make the carbon nano-tube pre-dispersed liquid.

(2) the carbon nano-tube pre-dispersed liquid is used to sand mill grinding distribution 0.5～8 hour, make the carbon nanotube conducting slurry of stable dispersion; Wherein the diameter of sand mill zirconia ball used is 0.1～3mm.

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