A post-processing method of carbon nanofiber conductive agent material and application thereof

Abstract

The application discloses a post-treatment method of carbon nanofiber conductive agent material and application thereof. The post-treatment method specifically comprises the following steps: mixing carbon nanofibers with deionized water according to a mass ratio of 0.1-0.6 to prepare a carbon nanofiber cleaning solution; filtering and compressing the prepared carbon nanofiber cleaning solution, controlling the moisture content to be within 20%, and then baking to control the moisture content to be within 1%; high-temperature graphitizing the prepared carbon nanofibers to prepare high-purity graphitized carbon nanofibers; mixing a dispersant with the prepared high-purity graphitized carbon nanofibers according to a mass ratio of 0.02-0.5, and then adding deionized water to uniformly mix to prepare a conductive slurry; and performing spray drying on the prepared conductive slurry in a spray drying tower, controlling the moisture content to be within 0.1%, and preparing dispersed carbon nanofiber conductive agents. The post-treatment method provided by the application does not damage the structure of the carbon nanofibers, and can simply and effectively untwist the carbon nanofibers.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery material processing, in particular to a post-processing method of carbon nanofiber conductive agent material and application thereof. BACKGROUND

[0002] Carbon nanofiber is a fibrous nanometer carbon material curled from multiple layers of graphite sheets, which has high strength, light weight, good thermal conductivity and high conductivity, and is often used as a conductive agent in battery materials. Due to the easy winding and agglomeration of carbon nanofiber during production, it is not easy to disperse uniformly during the preparation of conductive glue, which affects the subsequent coating and rolling process, and finally affects the performance of the battery.

[0003] The existing post-processing technology of carbon nanofiber conductive agent is ball milling, taking carbon nanofiber and zirconia ball grinding medium in proportion to mechanically stir and mix first, then add to a vertical stirring grinder, select alcohol as refrigerant to cool and insulate the tank body of the grinder, the rod-shaped staggered distribution of grinding members inside the grinder shears, grinds and disperses the carbon nanofiber powder, and finally performs jet classification to obtain carbon nanofiber dry powder conductive agent. However, the ball milling method will damage the structure of the carbon nanofiber itself, and the length after grinding is only one third of that before grinding, which affects the conductivity effect. SUMMARY

[0004] The present application proposes a post-processing method that does not damage the structure of carbon nanofiber itself and can simply and effectively open the winding of carbon nanofiber.

[0005] The technical scheme adopted by the present application is as follows: the present application provides a post-processing method of carbon nanofiber conductive agent material, which specifically includes the following steps:

[0006] Step one, carbon nanofiber conductive agent cleaning: uniformly mix carbon nanofiber and deionized water in a mass ratio of 0.1-0.6 to prepare a carbon nanofiber cleaning solution. Mixing carbon nanofiber with deionized water for cleaning can remove metal impurities remaining in carbon nanofiber during preparation, and can also compress the volume of carbon nanofiber powder. If the mass ratio of carbon nanofiber to deionized water is too low, the cleaning efficiency will be low, and if the mass ratio of carbon nanofiber to deionized water is too high, the carbon nanofiber will not be cleaned sufficiently. Specifically, the mass ratio of carbon nanofiber to deionized water in step one is 1:3, and under the premise of sufficient cleaning, the cleaning efficiency is relatively high.

[0007] Step two, carbon nanofiber conductive agent compression drying: the prepared carbon nanofiber cleaning solution is transported to a filter press for filtration and compression, the moisture is controlled to be within 20%, and then baking is performed in an oven, the baking temperature is 150-300℃, and the moisture is baked to be within 1%.

[0008] Step three, carbon nanofiber conductive agent graphitization: the carbon nanofiber prepared in step two is subjected to high-temperature graphitization in a graphitization furnace, the graphitization temperature is 1600-2500℃, and high-purity graphitized carbon nanofiber is prepared. The disordered structure of carbon fiber can be formed into a relatively regular structure through graphitization, which meets the requirements and improves the conductivity.

[0009] Optionally, the post-processing method of the present application, after step one, step two and step three, further comprises step four, carbon nanofiber conductive agent pre-dispersion treatment: the dispersant and the high-purity graphitized carbon nanofiber prepared in step three are mixed in a mass ratio of 0.02-0.5 to form a solid mixture, and then deionized water is added to uniformly mix to prepare a conductive slurry. The high-purity graphitized carbon nanofiber is dispersed in deionized water, which opens the structure of the carbon nanofiber agglomerated and wound in the previous two steps.

[0010] Step five, carbon nanofiber conductive agent spray drying: the conductive slurry prepared in step four is subjected to spray drying in a spray drying tower, the moisture is controlled to be within 0.1%, and a dispersed carbon nanofiber conductive agent is prepared.

[0011] Optionally, the viscosity of the organic impurities is relatively high, so that the carbon nanofiber is more prone to agglomeration, and the high-temperature graphitization in step three can effectively remove the organic impurities in the carbon nanofiber. The graphitization degree of the high-purity graphitized carbon nanofiber is greater than 70%, which can not only remove the organic impurities and reduce agglomeration, but also form a relatively regular structure through graphitization to improve the conductivity.

[0012] Optionally, step four is the pre-dispersion treatment of carbon nanofiber, the dispersant and the carbon nanofiber after graphitization are mixed in a mass ratio of 0.02-0.5 to form a solid mixture, 95-99% deionized water is added in a solid content ratio of 1-5%, pre-mixed in a planetary disperser at a low speed of 10-20Hz for 10-20min, and then dispersed in a centrifugal disperser at a high speed of 25-35Hz for 100-240min to prepare a conductive material. The dispersant can be a modified alcohol, an ester or other small molecule dispersant, and specifically can be PVP, PVB or other dispersants. The conductive slurry has a viscosity of 500-1000mpa·s and a fineness of 5-10μm, which can effectively disperse and open the agglomeration of carbon nanofiber.

[0013] Preferably, the viscosity of the conductive paste is 800 mpa·s, the solid content is 3%, the fineness is 8 μm, the carbon nanofiber paste has the best dispersion effect, and it is beneficial to open the agglomeration and subsequent drying.

[0014] Optionally, step two is carbon nanofiber compression drying. The prepared carbon nanofiber cleaning solution in step one is first pumped to a filter press for filtration and compression, and then dried through an oven. The baking temperature is 150-300℃. The volume of the carbon nanofiber after baking and drying is 75% of the volume after compression by the filter press. Through compression, part of the water in the pores between the carbon nanofibers can be squeezed out, and then further drying is performed through baking to ensure the drying efficiency of the carbon nanofibers.

[0015] Optionally, step one is carbon nanofiber cleaning. Deionized water is added to a disperser container, and then carbon nanofibers are added. The pre-mixing is performed at a low speed in a planetary disperser at a frequency of 10-20 Hz for 10-20 min, and then high-speed dispersion is performed in a centrifugal disperser at a frequency of 25-35 Hz for 180-240 min. The temperature in the dispersion container is maintained at 33-45℃. The carbon nanofiber cleaning solution is prepared. Low-speed pre-mixing can fully soak and is not prone to form agglomeration structure. Direct high-speed mixing may have problems of insufficient soaking and uneven dispersion. High-speed dispersion stirring generates heat, and the temperature needs to be controlled to 33-45℃ through external cooling water.

[0016] The beneficial effects of the present application are: (1) The produced carbon nanofibers are subjected to cleaning and dispersion, high-speed centrifugation, high-temperature graphitization, and post-processing processing of spray drying to open the winding and agglomeration parts and form branched carbon nanofibers. The branched carbon nanofibers greatly improve the dispersibility in the homogenate and effectively improve the subsequent coating and rolling processing of the battery.

[0017] (2) Since the dispersion of the carbon nanofiber conductive agent is good, the conductive effect is obvious, and the cycle performance of the battery is effectively improved.

[0018] (3) The treated carbon nanofiber conductive agent of the present application can be applied to various types and formulations of lithium batteries. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a flow chart of the post-processing of the carbon nanofibers of the present application;

[0020] Figure 2 is an SEM image of the post-processing of the carbon nanofibers of the present application;

[0021] Figure 3 is an SEM image of the existing carbon nanofibers before post-processing;

[0022] Figure 4is a cycle number curve comparison chart of the carbon nanofiber conductive agent of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0023] The application will be described in detail below with reference to the accompanying drawings and specific examples.

[0024] Example 1

[0025] Step one: take carbon nanofiber and deionized water according to the mass ratio of 1:3 in the planetary disperser, pre-mix at a frequency of 15 Hz at medium-low speed for 15 min, then disperse at a high speed in the centrifugal disperser at a frequency of 20 Hz for 210 min, keep the container of the centrifugal disperser at 39℃, and prepare carbon nanofiber cleaning solution.

[0026] Step two: deliver the carbon nanofiber cleaning solution prepared in step one to the filter press for filtration and compression, control the moisture to 15%, and then bake in the oven, the baking temperature is 250℃, bake the moisture to 0.5%.

[0027] Step three: carry out high-temperature graphitization of the carbon nanofiber prepared in step two in a graphitization furnace, the graphitization temperature is 2000℃, and prepare high-purity graphitized carbon nanofiber with a graphitization degree of 78%.

[0028] Step four: take PVP dispersant and high-purity graphitized carbon nanofiber prepared in step three according to the mass ratio of 1:30, add them into the planetary disperser, then add 97% deionized water according to the solid content of 3%, pre-mix at a low speed of 15 Hz for 15 min, and then uniformly mix in the centrifugal disperser at a high speed of 30 Hz for 170 min to prepare conductive slurry with a viscosity of 800 mpa·s and a fineness of 8 μm.

[0029] Step five: spray dry the conductive slurry prepared in step four in a spray drying tower, control the moisture to 0.05%, and prepare dispersed carbon nanofiber conductive agent.

[0030] Please refer to Figure 1 and 2 As shown, the carbon nanofiber conductive agent prepared by the post-processing method of the application does not agglomerate in the homogenization process, and there is no agglomeration in the SEM observation of the pole piece after coating.

[0031] Example 2

[0032] Step one: take carbon nanofiber and deionized water according to the mass ratio of 1:3 in the planetary disperser, pre-mix at a frequency of 15 Hz at medium-low speed for 15 min, then disperse at a high speed in the centrifugal disperser at a frequency of 20 Hz for 210 min, keep the container of the centrifugal disperser at 39℃, and prepare carbon nanofiber cleaning solution.

[0033] Step two: the carbon nanofiber washing solution prepared in step one is transported to a filter press for filtration and compression, the moisture is controlled to 15%, and then baking is performed in an oven, the baking temperature is 250°C, and the moisture is baked to 0.5%.

[0034] Step three: the carbon nanofiber prepared in step two is subjected to high-temperature graphitization in a graphitization furnace, the graphitization temperature is 2000°C, and high-purity graphitized carbon nanofiber with a graphitization degree of 78% is prepared.

[0035] The pre-dispersion treatment of step four and the spray drying of step five are not performed. Please refer to Figure 3 As shown in FIG. 1, the carbon nanofiber is severely agglomerated in the homogenization process, and the agglomeration is obvious after coating.

[0036] Example 3

[0037] Step one: carbon nanofiber and deionized water are taken in a planetary disperser at a mass ratio of 1:3, pre-mixed at a frequency of 15 Hz at low speed for 15 min, and then dispersed at a high speed in a centrifugal disperser at a frequency of 20 Hz for 210 min, the container of the centrifugal disperser is kept at 39°C, and a carbon nanofiber washing solution is prepared.

[0038] Step two: the carbon nanofiber washing solution prepared in step one is transported to a filter press for filtration and compression, the moisture is controlled to 15%, and then baking is performed in an oven, the baking temperature is 250°C, and the moisture is baked to 0.5%.

[0039] Step three: the carbon nanofiber prepared in step two is subjected to high-temperature graphitization in a graphitization furnace, the graphitization temperature is 1600°C, and high-purity graphitized carbon nanofiber with a graphitization degree of 48% is prepared.

[0040] Step four: PVP dispersant and high-purity graphitized carbon nanofiber prepared in step three are taken into a planetary disperser at a mass ratio of 1:30, then 97% deionized water is added at a solid content of 3%, pre-mixed at a low speed of 15 Hz for 15 min, and then uniformly mixed by high-speed dispersion at 30 Hz in a centrifugal disperser for 170 min to prepare a conductive slurry with a viscosity of 800 mpa·s and a fineness of 8 μm.

[0041] Step five: the conductive slurry prepared in step four is subjected to spray drying in a spray drying tower, the moisture is controlled to 0.05%, and a dispersed carbon nanofiber conductive agent is prepared.

[0042] Example 4

[0043] Step one: take carbon nanofiber and deionized water according to the mass ratio of 1:3 in the planetary disperser, with a frequency of 15 Hz in the low speed pre-mixing 15 min, and then with a frequency of 20 Hz in the centrifugal disperser high speed dispersion 210 min, the container of centrifugal disperser keeps 39℃, the carbon nanofiber cleaning fluid is prepared.

[0044] Step two: the carbon nanofiber cleaning fluid prepared in step one is transported to the filter press for filtration and compression, the moisture is controlled to 15%, and then baking is carried out in the oven, the baking temperature is 250℃, and the moisture is baked to 0.5%.

[0045] Step three: the carbon nanofiber prepared in step two is high temperature graphitized in the graphitization furnace, the graphitization temperature is 2500℃, and the high purity graphitized carbon nanofiber with a graphitization degree of 76% is prepared.

[0046] Step four: take PVP dispersant and high purity graphitized carbon nanofiber prepared in step three according to the mass ratio of 1:30 into the planetary disperser, then add 97% deionized water according to the solid content of 3%, pre-mix at a low speed of 15 Hz for 15 min, and then uniformly mix in the centrifugal disperser at a high speed of 30 Hz for 170 min to prepare the conductive slurry with a viscosity of 800 mpa·s and a fineness of 8 μm.

[0047] Step five: the conductive slurry prepared in step four is dried by spray drying tower, the moisture is controlled to 0.05%, and the dispersed carbon nanofiber conductive agent is prepared.

[0048] Example 5

[0049] Step one: take carbon nanofiber and deionized water according to the mass ratio of 1:3 in the planetary disperser, with a frequency of 15 Hz in the low speed pre-mixing 15 min, and then with a frequency of 20 Hz in the centrifugal disperser high speed dispersion 210 min, the container of centrifugal disperser keeps 39℃, the carbon nanofiber cleaning fluid is prepared.

[0050] Step two: the carbon nanofiber cleaning fluid prepared in step one is transported to the filter press for filtration and compression, the moisture is controlled to 15%, and then baking is carried out in the oven, the baking temperature is 250℃, and the moisture is baked to 0.5%.

[0051] Step three: the carbon nanofiber prepared in step two is high temperature graphitized in the graphitization furnace, the graphitization temperature is 1400℃, and the high purity graphitized carbon nanofiber with a graphitization degree of 41% is prepared.

[0052] Step four: take PVP dispersant and high purity graphitized carbon nanofiber prepared in step three according to 1:30 mass ratio into planetary disperser, then add 97% deionized water according to 3% solid content, pre-mix at 15 Hz for 15 min, and uniformly mix in centrifugal disperser at 30 Hz for 170 min to prepare conductive slurry with viscosity of 800 mpa-s and fineness of 8 μm.

[0053] Step five: spray dry the conductive slurry prepared in step four in spray drying tower, control moisture to 0.05%, and prepare dispersed carbon nanofiber conductive agent.

[0054] Example 6

[0055] Step one: take carbon nanofiber and deionized water according to 1:3 mass ratio in planetary disperser, pre-mix at 15 Hz for 15 min, and high-speed disperse in centrifugal disperser at 20 Hz for 210 min, keep the container of centrifugal disperser at 39℃, and prepare carbon nanofiber cleaning solution.

[0056] Step two: deliver the carbon nanofiber cleaning solution prepared in step one to filter press for filtration and compression, control moisture to 15%, and bake in oven, bake at 250℃, and bake moisture to 0.5%.

[0057] Step three: high-temperature graphitize the carbon nanofiber prepared in step two in graphitization furnace, graphitize at 2700℃, and prepare high purity graphitized carbon nanofiber with graphitization degree of 86%.

[0058] Step four: take PVP dispersant and high purity graphitized carbon nanofiber prepared in step three according to 1:30 mass ratio into planetary disperser, then add 97% deionized water according to 3% solid content, pre-mix at 15 Hz for 15 min, and uniformly mix in centrifugal disperser at 30 Hz for 170 min to prepare conductive slurry with viscosity of 800 mpa-s and fineness of 8 μm.

[0059] Step five: spray dry the conductive slurry prepared in step four in spray drying tower, control moisture to 0.05%, and prepare dispersed carbon nanofiber conductive agent.

[0060] Table 1 is the conductive performance and cycle performance test of each embodiment of the application

[0061]

[0062] Through table 1 and the description of the drawings Figure 4Comparative Example 1 and Example 2 can be obtained, after high temperature graphitization of carbon nanofiber, pre-dispersing treatment and spray drying treatment, the electrode sheet resistance can be reduced by 47%, and the conductive effect is significantly improved; the battery capacity retention rate after 600 charge-discharge cycles is also increased by 6.6%.

[0063] Table 1 and the description of the accompanying drawings Figure 4 Comparative Example 1, Example 3, Example 4, Example 5 and Example 6 can be obtained, when the graphitization temperature is 2000℃, 1600℃ and 2500℃, the electrode sheet resistance is relatively low, and the capacity retention rate after 600 cycles can reach about 85%. When the graphitization temperature is 1400℃ and 2700℃, the electrode sheet resistance increases significantly, and the cycle performance is poor. This is because the appropriate graphitization temperature can effectively change the disordered structure of carbon fiber into a regular structure, when the graphitization temperature is lower than 1600℃, the organic impurities cannot be removed sufficiently, and there is still a part of the aggregation phenomenon; when the graphitization temperature is higher than 2500℃, it may be because the graphitization degree is too high, which can cause the carbon fiber to sinter and adhere during the graphitization process, resulting in that the carbon fiber cannot form a uniform conductive network in the electrode, the battery internal resistance increases, and the cycle performance becomes poor.

[0064] The above only describes the preferred embodiments of the present application, and does not limit the patent protection scope of the present application, any equivalent structural transformation, direct or indirect application in other related technical fields, are also included in the protection scope of the present application.

Claims

1. A post-processing method for carbon nanofiber conductive agent materials, characterized in that, Specifically, the steps include the following: Step 1, cleaning of carbon nanofiber conductive agent: carbon nanofibers and deionized water are mixed uniformly at a mass ratio of 1:3, and a carbon nanofiber cleaning solution is prepared by low-speed premixing and high-speed dispersion. Step 2, carbon nanofiber conductive agent compression drying: The prepared carbon nanofiber cleaning solution is sent to a filter press for filtration and compression, and the moisture content is controlled to be below 20%. Then it is baked in an oven at a temperature of 150-300℃ to reduce the moisture content to below 1%. Step 3, graphitization of carbon nanofiber conductive agent: The carbon nanofibers obtained in step 2 are graphitized at high temperature in a graphitization furnace at a temperature of 1600-2500℃ to obtain high-purity graphitized carbon nanofibers; wherein the graphitization degree of the obtained high-purity graphitized carbon nanofibers is greater than 70%. Step 4, pre-dispersion treatment of carbon nanofiber conductive agent: The dispersant and the high-purity graphitized carbon nanofibers obtained in step 3 are added at a mass ratio of 0.02-0.5 to form a solid mixture, and then deionized water is added and mixed evenly. The conductive slurry is obtained by low-speed premixing and high-speed dispersion. Step 5, spray drying of carbon nanofiber conductive agent: The conductive slurry obtained in step 4 is spray dried in a spray drying tower, and the moisture content is controlled to be less than 0.1% to obtain dispersed carbon nanofiber conductive agent.

2. The post-processing method for the carbon nanofiber conductive agent material according to claim 1, characterized in that, The conductive paste described in step four has a solid content of 1-5%, a viscosity of 500-1000 mPa·s, and a fineness of 5-10 μm.

3. The post-processing method for the carbon nanofiber conductive agent material according to claim 2, characterized in that, The conductive paste mentioned in step four has a solid content of 3%, a viscosity of 800 mPa·s, and a fineness of 8 μm.

4. The post-processing method for the carbon nanofiber conductive agent material according to claim 1, characterized in that, In step two, the volume of the carbon nanofibers after baking and drying is 75% of that after compression by the filter press.

5. The post-processing method for the carbon nanofiber conductive agent material according to claim 1, characterized in that, The mixing in step one specifically includes premixing at a low speed of 10-20Hz for 10-20 minutes, followed by dispersing at a high speed of 25-35Hz for 180-240 minutes.

6. The post-processing method for the carbon nanofiber conductive agent material according to claim 1, characterized in that, The mixing in step four specifically includes premixing at a low speed of 10-20 Hz for 10-20 min, followed by dispersing at a high speed of 25-35 Hz for 100-240 min.

7. The application of a post-processing method for carbon nanofiber conductive agent materials according to any one of claims 1-6 in the field of battery manufacturing.

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