Carbon fiber positive electrode material slurry as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion battery positive electrode materials, and discloses carbon fiber positive electrode material slurry as well as a preparation method and application thereof. According to the invention, a two-step dispersion method is adopted, the conductive agent is pre-dispersed at first, then the positive electrode active material and the binder are added for secondary dispersion, and the dispersing aid is added at a proper time before or after secondary dispersion, so that the compatibility among particles and the uniformity of the slurry are improved. High-speed shearing dispersion and ultrasonic dispersion are combined, so that a multi-scale dispersion process is formed, and the uniformity is ensured; through the method, the slurry has excellent dispersity, and the positive electrode active material, the conductive agent and the binder can be uniformly dispersed in the slurry to form a stable suspension system; long-term stability is achieved, obvious sedimentation and layering do not exist after the product is placed at the room temperature for several days, and continuity and reproducibility of the production process are guaranteed; and the coating has good wetting and adhesion characteristics with the surface of the carbon fiber, so that the uniformity and firmness of a coating layer are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for lithium - ion batteries, and particularly relates to a carbon fiber cathode material slurry, a preparation method thereof, and an application thereof. Background Art

[0002] When combining cathode active materials (such as NCM, NCA, LiFePO 4 , lithium - rich layered materials), conductive agents (such as CNT, graphene, carbon black), and binders (such as PVDF) to prepare a cathode slurry suitable for coating on the surface of carbon fibers, problems such as poor slurry dispersibility, serious agglomeration, difficult viscosity control, sedimentation or stratification are often faced. These problems will directly affect the uniformity and adhesion of the coating, thereby reducing the electrochemical performance and cycle life of the carbon fiber cathode material.

[0003] In the prior art, simple stirring or ball - milling dispersion means are mostly used, and it is difficult to simultaneously consider the rheological properties, stability, wettability, and adhesion to the surface of carbon fibers of the slurry. To meet the stringent requirements of the structure - energy storage integrated composite material for the electrode quality, it is necessary to provide a new slurry preparation method to ensure that the carbon fiber cathode material slurry has excellent dispersion, appropriate viscosity, and stability. Summary of the Invention

[0004] The purpose of the present invention is to provide a carbon fiber cathode material slurry, a preparation method thereof, and an application thereof, so as to solve the problem that it is difficult to consider multiple properties of the existing cathode slurry preparation method.

[0005] In order to achieve the above - mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a carbon fiber cathode material slurry, comprising the following steps:

[0007] Pre - disperse the conductive agent in a solvent, then add a dispersion aid for dispersion, and then add the cathode active material and the binder for secondary dispersion to obtain the carbon fiber cathode material slurry;

[0008] Or pre - disperse the conductive agent in a solvent, then add the cathode active material and the binder for secondary dispersion, and then add a dispersion aid for dispersion to obtain the carbon fiber cathode material slurry.

[0009] Preferably, in the above - mentioned preparation method of a carbon fiber cathode material slurry, the solid content of the carbon fiber cathode material slurry is 30 - 60 wt%.

[0010] Preferably, in the above - mentioned preparation method of a carbon fiber cathode material slurry, the method of pre - dispersion is ultrasonic treatment and / or high - speed shear dispersion; the rotation speed of the high - speed shear dispersion is 5000 - 10000 rpm.

[0011] Preferably, in the above preparation method of a carbon fiber positive electrode material slurry, the mass fraction of the dispersion aid in the carbon fiber positive electrode material slurry is 0.1-1%.

[0012] Preferably, in the above preparation method of a carbon fiber positive electrode material slurry, the dispersion aid is a fluorosurfactant, an amphiphilic surfactant, polyvinylpyrrolidone or carboxymethyl cellulose.

[0013] Preferably, in the above preparation method of a carbon fiber positive electrode material slurry, the dispersion method is ultrasonic treatment and / or high-speed shear dispersion; the rotation speed of the high-speed shear dispersion is 5000-10000 rpm.

[0014] Preferably, in the above preparation method of a carbon fiber positive electrode material slurry, the secondary dispersion method is high-speed shear dispersion and / or low-speed stirring dispersion; the rotation speed of the high-speed shear dispersion is 5000-10000 rpm; the rotation speed of the low-speed stirring dispersion is 200-600 rpm.

[0015] Preferably, in the above preparation method of a carbon fiber positive electrode material slurry, the viscosity of the carbon fiber positive electrode material slurry is 1000-2000 mPa·s.

[0016] The present invention also provides a carbon fiber positive electrode material slurry prepared by the preparation method of a carbon fiber positive electrode material slurry.

[0017] The present invention also provides an application of a carbon fiber positive electrode material slurry prepared by the preparation method of a carbon fiber positive electrode material slurry or the above carbon fiber positive electrode material slurry in a structure-energy storage integrated composite material.

[0018] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention adopts a two-step dispersion method. First, the conductive agent is pre-dispersed, and then the positive electrode active material and the binder are added for secondary dispersion, ensuring the uniform construction of the conductive network. Adding a specific dispersion aid at an appropriate time before or after the secondary dispersion can improve the compatibility between particles and the homogeneity of the slurry. Combining high-speed shear dispersion and ultrasonic dispersion forms a multi-scale dispersion process to ensure uniformity from the micron scale to the nanoscale. By precisely controlling the solid content and solvent ratio, the viscosity range of the slurry is ensured without damaging the intrinsic properties of the positive electrode material. Through the above methods, the slurry prepared by the present invention has excellent dispersibility, and the positive electrode active material, conductive agent, and binder can be uniformly dispersed in the slurry to form a stable suspension system. It also has good rheological properties and an appropriate viscosity range, being suitable for coating processes such as impregnation, spraying, spin coating, or layer-by-layer self-assembly. It also has long-term stability. When placed at room temperature for several hours to several days, the slurry shows no obvious sedimentation and stratification, ensuring the continuity and reproducibility of the production process. Moreover, it has good wetting and adhesion characteristics with the surface of carbon fiber, ensuring the uniformity and firmness of the coating layer. Detailed Embodiment

[0020] The present invention provides a method for preparing a carbon fiber positive electrode material slurry, comprising the following steps:

[0021] Pre-disperse the conductive agent in a solvent, then add a dispersion aid for dispersion, and then add the positive electrode active material and the binder for secondary dispersion to obtain the carbon fiber positive electrode material slurry;

[0022] Or pre-disperse the conductive agent in a solvent, then add the positive electrode active material and the binder for secondary dispersion, and then add a dispersion aid for dispersion to obtain the carbon fiber positive electrode material slurry.

[0023] In the present invention, the conductive agent is preferably one or more of carbon nanotubes (CNT), graphene, and carbon black, more preferably a mixture of CNT, graphene, and carbon black, and even more preferably a mixture of CNT, graphene, and SuperP with a mass ratio of 3:2:2.

[0024] In the present invention, the solvent is preferably N-methylpyrrolidone (NMP).

[0025] In the present invention, the method for pre-dispersion is preferably ultrasonic treatment and / or high-speed shear dispersion; the time for ultrasonic treatment is preferably 5 - 30 min, more preferably 10 - 25 min, and even more preferably 20 min; the rotation speed for high-speed shear dispersion is preferably 5000 - 10000 rpm, more preferably 6000 - 9000 rpm, and even more preferably 8000 rpm; the time for high-speed shear dispersion is preferably 10 - 60 min, more preferably 15 - 30 min, and even more preferably 20 min.

[0026] In the present invention, the mass fraction of the dispersion aid in the carbon fiber cathode material slurry is preferably 0.1 to 1%, more preferably 0.1 to 0.5%, and even more preferably 0.2%.

[0027] In the present invention, the dispersion aid is preferably a fluorosurfactant, an amphiphilic surfactant, polyvinylpyrrolidone (PVP), or carboxymethyl cellulose (CMC), more preferably a fluorosurfactant or PVP, and even more preferably a fluorosurfactant. The fluorosurfactant in the present invention is Capstone TM FS-10 of Chemours; the amphiphilic surfactant is orafuor.

[0028] In the present invention, the dispersion method is preferably ultrasonic treatment and / or high-speed shear dispersion; the time of ultrasonic treatment is preferably 5 to 30 min, more preferably 10 to 25 min, and even more preferably 20 min; the rotation speed of high-speed shear dispersion is preferably 5000 to 10000 rpm, more preferably 6000 to 9000 rpm, and even more preferably 8000 rpm; the time of high-speed shear dispersion is preferably 10 to 60 min, more preferably 15 to 30 min, and even more preferably 20 min.

[0029] In the present invention, the cathode active material is preferably one or more of NCM811 cathode material, NCA cathode material, high-nickel lithium-rich NCM cathode material, and LiFePO 4 and further preferably NCM811 cathode material or NCA cathode material, and even more preferably NCM811 cathode material.

[0030] In the present invention, the binder is preferably polyvinylidene fluoride (PVDF).

[0031] In the present invention, the secondary dispersion method is preferably high-speed shear dispersion and / or low-speed stirring dispersion; the rotation speed of high-speed shear dispersion is preferably 5000 to 10000 rpm, more preferably 8000 to 10000 rpm, and even more preferably 10000 rpm; the time of high-speed shear dispersion is preferably 10 to 60 min, more preferably 20 to 40 min, and even more preferably 30 min; the rotation speed of low-speed stirring dispersion is preferably 200 to 600 rpm, more preferably 300 to 500 rpm, and even more preferably 500 rpm; the time of low-speed stirring dispersion is preferably 10 to 60 min, more preferably 10 to 30 min, and even more preferably 20 min.

[0032] In the present invention, the mass ratio of the conductive agent, the cathode active material, and the binder is preferably 0.1-1:7-9:0.1-1, more preferably 0.3-0.8:8-9:0.1-0.5, and even more preferably 0.7:9:0.3.

[0033] In the present invention, the viscosity of the carbon fiber cathode material slurry is preferably 1000-2000 mPa·s, more preferably 1200-1800 mPa·s, and even more preferably 1500 mPa·s.

[0034] In the present invention, the solid content of the carbon fiber cathode material slurry is preferably 30-60 wt%, more preferably 40-50 wt%, and even more preferably 48 wt%.

[0035] The present invention also provides a carbon fiber cathode material slurry prepared by a preparation method of a carbon fiber cathode material slurry.

[0036] The present invention also provides an application of a carbon fiber cathode material slurry prepared by a preparation method of a carbon fiber cathode material slurry or the above-mentioned carbon fiber cathode material slurry in a structure-energy storage integrated composite material.

[0037] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] Example 1

[0039] This example provides a preparation method of a carbon fiber cathode material slurry, including the following steps:

[0040] Taking a mixture of CNT:graphene:SuperP with a mass ratio of 3:2:2 as the conductive agent, adding the conductive agent to NMP and ultrasonically treating for 20 min, adding 0.2 wt% of a fluorine-containing surfactant, ultrasonically treating for 20 min first, and then performing high-speed shear dispersion at 8000 rpm for 20 min; subsequently adding the NCM811 cathode material and PVDF, controlling the mass ratio of the conductive agent, the NCM811 cathode material, and PVDF to be 0.7:9:0.3, and performing high-speed shear dispersion at 10000 rpm for 30 min to obtain a carbon fiber cathode material slurry with a solid content of 48 wt% and a viscosity of 1500 mPa·s.

[0041] Placing the carbon fiber cathode material slurry at room temperature for 24 h, there is no obvious sedimentation.

[0042] The surface of T700 carbon fiber was coated with the carbon fiber cathode material slurry to form a uniform and dense cathode layer. Using this as the cathode and metallic lithium as the anode, a button cell was assembled for electrochemical performance testing. As a comparison, the slurry obtained by the conventional stirring method (conductive agent, cathode active material, and PVDF were mixed and stirred at 8000 rpm for 30 min) was coated. It can be seen that the battery composed of the slurry obtained by the preparation method of the present invention has an 8% increase in the capacity retention rate at a 1C rate.

[0043] Example 2

[0044] This example provides a preparation method for a carbon fiber cathode material slurry, which includes the following steps:

[0045] Using a mixture of CNT: graphene: SuperP with a mass ratio of 1:4:2 as the conductive agent, the conductive agent was added to NMP and ultrasonically treated for 30 min, then LiFePO 4 and PVDF were added, and the mass ratio of the conductive agent, LiFePO 4 and PVDF was controlled to be 0.5:9:0.5, and stirred and dispersed at 600 rpm for 40 min; then 0.5 wt% CMC was added, ultrasonically treated for 10 min first, and then high-speed shear dispersed at 5000 rpm for 20 min; a carbon fiber cathode material slurry with a solid content of 42 wt% and a viscosity of 1200 mPa·s was obtained.

[0046] The carbon fiber cathode material slurry was placed at room temperature for 48 h, and there was no obvious sedimentation.

[0047] The surface of M55J carbon fiber was coated with the carbon fiber cathode material slurry to form a uniform and dense cathode layer. Using this as the cathode and metallic lithium as the anode, a button cell was assembled for electrochemical performance testing. As a comparison, the slurry obtained by the conventional stirring method (conductive agent, cathode active material, and PVDF were mixed and stirred at 8000 rpm for 30 min) was coated. It can be seen that the battery composed of the slurry obtained by the preparation method of the present invention has a 6% increase in the capacity retention rate at a 1C rate.

[0048] Example 3

[0049] This example provides a preparation method for a carbon fiber cathode material slurry, which includes the following steps:

[0050] Using a mixture of CNT: graphene: SuperP with a mass ratio of 3:2:2 as the conductive agent, the conductive agent was added to NMP and ultrasonically treated for 5 min, 0.3 wt% PVP was added, ultrasonically treated for 20 min first, and then sheared and dispersed at a high speed of 8000 rpm for 20 min; subsequently, NCA cathode material and PVDF were added, and the mass ratio of the conductive agent, NCA cathode material, and PVDF was controlled to be 1:8:1, sheared and dispersed at a high speed of 8000 rpm for 20 min, and then stirred and dispersed at 500 rpm for 10 min to obtain a carbon fiber cathode material slurry with a solid content of 45 wt% and a viscosity of 1300 mPa·s.

[0051] The carbon fiber cathode material slurry was placed at room temperature for 24 h without obvious sedimentation.

[0052] The surface of T700 carbon fiber was coated with the carbon fiber cathode material slurry to form a uniform and dense cathode layer. Using this as the cathode and metallic lithium as the anode, a button cell was assembled for electrochemical performance testing. The slurry obtained by the conventional stirring method (after mixing the conductive agent, cathode active material, and PVDF and stirring at 8000 rpm for 30 min) was used as a comparison after coating. It can be obtained that the battery composed of the slurry prepared by the preparation method of the present invention has a 7% increase in the capacity retention rate at a 1C rate.

[0053] Example 4

[0054] This example provides a preparation method of a carbon fiber cathode material slurry, including the following steps:

[0055] Using a mixture of CNT: graphene: SuperP with a mass ratio of 3:2:2 as the conductive agent, the conductive agent was added to NMP and ultrasonically treated for 10 min, 0.1 wt% amphiphilic surfactant was added, ultrasonically treated for 10 min first, and then sheared and dispersed at a high speed of 10000 rpm for 15 min; subsequently, high-nickel and lithium-rich NCM cathode material and PVDF were added, and the mass ratio of the conductive agent, high-nickel and lithium-rich NCM cathode material, and PVDF was controlled to be 0.8:9:0.2, sheared and dispersed at a high speed of 8000 rpm for 30 min to obtain a carbon fiber cathode material slurry with a solid content of 50 wt% and a viscosity of 1700 mPa·s.

[0056] The carbon fiber cathode material slurry was placed at room temperature for 48 h without obvious sedimentation.

[0057] The surface of T800 carbon fiber was coated with the carbon fiber cathode material slurry to form a uniform and dense cathode layer. Using this as the cathode and metallic lithium as the anode, a coin cell was assembled for electrochemical performance testing. The slurry obtained by the conventional stirring method (the conductive agent, cathode active material, and PVDF were mixed and stirred at 8000 rpm for 30 min) was used as a comparison after coating. It can be seen that the capacity retention rate of the cell composed of the slurry obtained by the preparation method of the present invention increased by 8% at a 1C rate.

[0058] Example 5

[0059] This example provides a preparation method for a carbon fiber cathode material slurry, which includes the following steps:

[0060] Using a mixture of CNT and graphene with a mass ratio of 3:5 as the conductive agent, the conductive agent was added to NMP and ultrasonically treated for 10 min. Then 1 wt% CMC was added, and it was ultrasonically treated for 20 min first and then sheared and dispersed at a high speed of 10000 rpm for 10 min. Subsequently, the NCM811 cathode material and PVDF were added, and the mass ratio of the conductive agent, NCM811 cathode material, and PVDF was controlled to be 1:8:1. It was stirred and dispersed at 500 rpm for 60 min to obtain a carbon fiber cathode material slurry with a solid content of 50 wt% and a viscosity of 1800 mPa·s.

[0061] The carbon fiber cathode material slurry was placed at room temperature for 48 h without obvious sedimentation.

[0062] The surface of T700 carbon fiber was coated with the carbon fiber cathode material slurry to form a uniform and dense cathode layer. Using this as the cathode and metallic lithium as the anode, a coin cell was assembled for electrochemical performance testing. The slurry obtained by the conventional stirring method (the conductive agent, cathode active material, and PVDF were mixed and stirred at 8000 rpm for 30 min) was used as a comparison after coating. It can be seen that the capacity retention rate of the cell composed of the slurry obtained by the preparation method of the present invention increased by 7% at a 1C rate.

[0063] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a carbon fiber positive electrode material slurry, characterized in that: The following steps are involved: The conductive agent is pre-dispersed in a solvent, and then a dispersing aid is added for dispersion, and then a positive electrode active material and a binder are added for secondary dispersion to obtain a carbon fiber positive electrode material slurry; Or the conductive agent is pre-dispersed in a solvent, and then the positive electrode active material and the binder are added for secondary dispersion, and then a dispersing aid is added for dispersion to obtain a carbon fiber positive electrode material slurry.

2. The method for preparing a carbon fiber positive electrode material slurry according to claim 1, characterized in that: The solid content of the carbon fiber positive electrode material slurry is 30-60wt%.

3. The method for preparing a carbon fiber positive electrode material slurry according to claim 2, characterized in that: The pre-dispersion method is ultrasonic treatment and / or high-speed shear dispersion; the rotation speed of the high-speed shear dispersion is 5000-10000 rpm.

4. The method for preparing a carbon fiber positive electrode material slurry according to claim 1 or 2, characterized in that: The mass fraction of the dispersing aid in the carbon fiber positive electrode material slurry is 0.1-1%.

5. The method for preparing a carbon fiber positive electrode material slurry according to claim 4, characterized in that: The dispersing aid is a fluorine-containing surfactant, an amphiphilic surfactant, polyvinyl pyrrolidone or carboxymethyl cellulose.

6. The method for preparing a carbon fiber positive electrode material slurry according to claim 5, characterized in that: The dispersion method is ultrasonic treatment and / or high-speed shear dispersion; the rotation speed of the high-speed shear dispersion is 5000-10000 rpm.

7. The method for preparing a carbon fiber positive electrode material slurry according to claim 6, characterized in that: The secondary dispersion method is high-speed shear dispersion and / or low-speed stirring dispersion; the rotation speed of the high-speed shear dispersion is 5000-10000 rpm; the rotation speed of the low-speed stirring dispersion is 200-600 rpm.

8. The method for preparing a carbon fiber positive electrode material slurry according to claim 1 or 7, characterized in that: The viscosity of the carbon fiber positive electrode material slurry is 1000-2000 mPa·s.

9. A carbon fiber positive electrode material slurry prepared by the method for preparing a carbon fiber positive electrode material slurry according to any one of claims 1 to 8.

10. Use of a carbon fiber positive electrode material slurry obtained by the method for preparing a carbon fiber positive electrode material slurry according to any one of claims 1 to 8 or a carbon fiber positive electrode material slurry according to claim 9 in a structure-energy storage integrated composite material.