Homogenizing process, positive electrode slurry and lithium ion battery

Abstract

The invention discloses a homogenizing process, composite conductive agent slurry is used, the composite conductive agent slurry comprises conductive carbon black SP, carbon nanotubes CNT and graphene, and the homogenizing process comprises the following steps: S1, adding PVDF powder and an NMP solvent into a stirring tank according to a certain proportion to prepare a positive electrode glue solution; s2, taking out 40-50% of the positive electrode glue solution prepared in S1 as a first glue solution, taking the rest part as a second glue solution, and adding composite conductive agent slurry into the second glue solution to complete preparation of a conductive glue solution; s3, adding lithium iron phosphate into the conductive glue solution to enable the conductive glue solution to form first slurry; s4, mixing the first slurry and the first glue solution, adding a PVP dispersant during mixing, and carrying out homogenization dispersion to form second slurry; and S5, adjusting and adding an NMP solvent into the second slurry until the viscosity of the second slurry is controlled to be 4000-10000 mPa.s and the solid content is controlled to be 55-65%, thereby completing the preparation of the positive electrode slurry. According to the homogenizing process, the conductive efficiency can be improved, the resistivity of the pole piece is reduced, and the compaction density and the cycle performance are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a homogenizing process, a positive electrode slurry and a lithium ion battery. BACKGROUND

[0002] With the continuous development of lithium ion batteries, there are higher requirements for the rate, cycle life and energy density of lithium ion batteries. The conductivity of lithium iron phosphate positive electrode material is relatively poor, and the performance of lithium iron phosphate batteries can be improved by selecting a suitable conductive agent. The commonly used ones are traditional conductive agents (conductive graphite, conductive carbon black, carbon fiber) and new conductive agents (carbon nanotube, graphene), the conductive carbon black is in point-point contact with the active material, and the carbon nanotube is in point-line contact with the active material, which has good conductivity and thermal conductivity, and greatly improves the battery capacity, rate performance, cycle life and reduces the battery polarization. Due to the unique sheet structure, the contact between graphene and the active material is point-plane contact, which can maximize the role of the conductive agent and reduce the amount of conductive agent. The two or three of carbon nanotube, graphene and conductive carbon black are compounded to form a conductive slurry, which can fully play the mutual synergistic effect of the conductive agents, and excellent performance can be achieved with a very low addition amount, thereby increasing the active material ratio and improving the battery energy density. However, graphene and carbon nanotube have a large specific surface area and aspect ratio, and there is a strong van der Waals force between the nanotubes / graphene layers, which causes the carbon tube and graphene to easily entangle and agglomerate, affecting the stability of the slurry and the resistivity after coating.

[0003] Therefore, it is urgent to design a homogenizing process to solve the above problems. SUMMARY

[0004] To solve the technical problem that graphene and carbon nanotube have a large specific surface area and aspect ratio, and there is a strong van der Waals force between the nanotubes / graphene layers, which causes the carbon tube and graphene to easily entangle and agglomerate, affecting the stability of the slurry and the resistivity after coating mentioned in the background, a homogenizing process is provided.

[0005] To achieve the above-mentioned purpose, the specific technical solutions of the homogenizing process, the positive electrode slurry and the lithium ion battery of the present application are as follows: A homogenizing process uses a composite conductive agent slurry, the composite conductive agent slurry includes conductive carbon black SP, carbon nanotube CNT and graphene, and the homogenizing process includes the following steps: S1, adding PVDF powder and NMP solvent into a stirring tank in a certain proportion to prepare a positive electrode glue solution; S2, take out 40-50% of the positive electrode glue solution prepared in S1 as the first glue solution, and the remaining part as the second glue solution, add the composite conductive agent slurry to the second glue solution, and complete the preparation of the conductive glue solution; S3, add lithium iron phosphate to the conductive glue solution to form a first slurry; S4, mix the first slurry and the first glue solution, add PVP dispersant during the mixing, and perform homogenization and dispersion to form a second slurry; S5, adjust the second slurry by adding NMP solvent until the viscosity of the second slurry is controlled at 4000-10000 mPa.s and the solid content is controlled at 55%-65%, and complete the preparation of the positive electrode slurry.

[0006] Further, the content ratio of the conductive carbon black SP, the carbon nanotube CNT and the graphene is sequentially reduced.

[0007] Further, the composite conductive agent slurry further includes a PVP dispersant for homogenizing and dispersing the mixed conductive carbon black SP, the carbon nanotube CNT and the graphene.

[0008] Further, the stirring tank is a double planetary stirring tank.

[0009] Further, in step S1, the stirring tank is set to a revolution speed of 10-25 rpm, a dispersion speed of 1000-3000 rpm, and a time of 150-300 min to prepare a positive electrode glue solution with a solid content of 6%-10%.

[0010] Further, in step S3, after adding lithium iron phosphate to the conductive glue solution, the solid content of the conductive glue solution is adjusted to 70%-80% to make the conductive glue solution into a muddy first slurry.

[0011] Further, the solid content of the conductive glue solution is controlled by adding NMP solvent to the conductive glue solution, so that the solid content of the conductive glue solution is 70%-80%.

[0012] Further, step S4 specifically includes the following steps: S41, mix the first slurry and the first glue solution, add PVP dispersant during the mixing, and perform homogenization and dispersion; S42, stir the mixture of the first slurry and the first glue solution at a first stirring speed to form a first intermediate slurry; S43, stir the first intermediate slurry at a second stirring speed to form a second intermediate slurry; S44, vacuumize the second intermediate slurry, and set the vacuum degree to -88~-92 kpa to complete the preparation of the second slurry; The first stirring speed is less than the second stirring speed.

[0013] A positive electrode slurry is prepared by using the homogenizing process.

[0014] A lithium ion battery is prepared by using the positive electrode slurry.

[0015] The homogenizing process has the following advantages: the conductive agent slurry prepared by compounding graphene, carbon nanotubes and conductive carbon black in a certain ratio is used in the lithium iron phosphate positive electrode system, a three-dimensional conductive network can be formed, point-line-surface combination is achieved, the conductive efficiency is effectively improved, the electrode sheet resistivity is reduced, the compaction density is improved, the energy density of the battery cell is improved, the liquid retention amount is increased, and the cycle performance is improved.

[0016] The positive electrode slurry has the following advantages: the positive electrode slurry combines the advantages of dry and wet slurry preparation methods and the characteristics of graphene composite conductive slurry, so that the conductive agent such as graphene is uniformly dispersed, and the slurry viscosity changes little and has high stability.

[0017] The lithium ion battery has the following advantages: the lithium ion battery using the positive electrode slurry has reduced conductive agent consumption, improved active material proportion, high energy density, stable electrode sheet structure, significantly increased cycle life and improved cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The flowchart of the homogenizing process is shown in the figure; Figure 2 The flowchart of step S4 of the homogenizing process is shown in the figure. DETAILED DESCRIPTION

[0019] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described in detail below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0020] Those skilled in the art can understand that although some embodiments herein include certain features included in other embodiments rather than other features, the combination of features of different embodiments means to be within the scope of the present application and form different embodiments. For example, in the claims, any one of the claimed embodiments can be used in any combination.

[0021] The following refers to the drawings Figure 1 The homogenizing process, the positive electrode slurry and the lithium ion battery of the present application are described.

[0022] The embodiment provides a homogenizing process, which uses a composite conductive agent slurry, the composite conductive agent slurry comprising conductive carbon black SP, carbon nanotubes CNT and graphene, Figure 1 The homogenizing process is shown in the structural diagram of the homogenizing process of the application, combined with Figure 1 The homogenizing process comprises the following steps: S1, adding PVDF powder and NMP solvent into a stirring tank according to a certain proportion to prepare a positive electrode glue solution; S2, taking out 40-50% of the positive electrode glue solution prepared in S1 as a first glue solution, and adding a composite conductive agent slurry into the remaining part as a second glue solution to complete preparation of a conductive glue solution; S3, adding lithium iron phosphate into the conductive glue solution to form a first slurry; S4, mixing the first slurry and the first glue solution, adding a PVP dispersant during the mixing, homogenizing and dispersing to form a second slurry; S5, adjusting the second slurry by adding NMP solvent until the viscosity of the second slurry is controlled at 4000-10000 mPa.s and the solid content is controlled at 55%-65% to complete preparation of a positive electrode slurry.

[0023] The homogenizing process uses a conductive agent slurry composed of graphene, carbon nanotubes and conductive carbon black in a certain proportion for a lithium iron phosphate positive electrode system, can form a three-dimensional conductive network, combines points, lines and surfaces, effectively improves the conductive efficiency, reduces the sheet resistance, improves the compaction density, improves the energy density of the battery, increases the liquid retention amount and improves the cycle performance.

[0024] Further, the content proportion of the conductive carbon black SP, the carbon nanotubes CNT and the graphene decreases in turn. The conductive carbon black SP as a basic conductive framework has the highest proportion, the CNT for supplementing linear conductive paths has the second highest proportion, and the graphene for exerting the advantage of surface contact has the least proportion, so that the proportion of the three is balanced in cost and performance, and the problem of too high slurry viscosity caused by excessive graphene is avoided.

[0025] Further, the composite conductive agent slurry further comprises a PVP dispersant for homogenizing and dispersing the conductive carbon black SP, the carbon nanotubes CNT and the graphene after mixing.

[0026] It can be understood that the PVP dispersant further inhibits the van der Waals force agglomeration of the CNT / graphene, improves the uniform distribution of the conductive agent in the glue solution, and thus improves the stability of the slurry and the rate performance of the battery.

[0027] Specifically, the above stirring tank is a double-planetary stirring tank. The double-planetary stirring tank has both revolution (macroscopic mixing) and dispersion disc high-speed shearing (microscopic dispersion) functions, and is particularly suitable for disaggregation of nanoscale conductive agents in high-viscosity slurry.

[0028] Further, in step S1, the rotation speed of the stirring tank is set to 10-25 rpm, the dispersion speed is 1000-3000 rpm, and the time is 150-300 min, so as to prepare the positive electrode glue solution with a solid content of 6%-10%.

[0029] The rotation speed (10-25 rpm for rotation and 1000-3000 rpm for dispersion) and the time (150-300 min) in step S1 ensure that the PVDF is fully dissolved and the solid content of the glue solution (6%-10%) is moderate, thereby providing an ideal medium for the addition of the conductive agent.

[0030] Further, in step S3, after the lithium iron phosphate is added to the conductive glue solution, the solid content of the conductive glue solution is adjusted to 70%-80%, so that the conductive glue solution becomes the first slurry in a muddy state.

[0031] Adjusting the solid content of the conductive glue solution to 70%-80% to form the slurry in a muddy state forces the conductive agent to be in close contact with the lithium iron phosphate, thereby preliminarily constructing a conductive network, and the conductive structure is more stable when diluted subsequently.

[0032] Further, the solid content of the conductive glue solution is controlled by adding NMP solvent to the conductive glue solution, so that the solid content of the conductive glue solution is 70%-80%.

[0033] The solid content is accurately controlled by the amount of NMP solvent added, avoiding the imbalance of the proportion caused by directly adjusting the solid material, and the process is more controllable.

[0034] Further, Figure 2 The flow chart of the homogenization process step S4 of the present application is shown in Figure 1 and Figure 2 As shown in the figures, step S4 specifically includes the following steps: S41, mixing the first slurry and the first glue solution, and adding PVP dispersant during the mixing process to perform homogenization and dispersion; S42, stirring the mixture of the first slurry and the first glue solution at a first stirring speed to form a first intermediate slurry; S43, stirring the first intermediate slurry at a second stirring speed to form a second intermediate slurry; S44, vacuumizing the second intermediate slurry, and setting the vacuum degree to -88~-92 kpa to complete the preparation of the second slurry; The first stirring speed is less than the second stirring speed.

[0035] Specifically, the first stirring speed is 15-20 rpm for rotation and 800-1000 rpm for dispersion, and the stirring time is 10 min; the second stirring speed is 25-30 rpm for rotation and 2500-3500 rpm for dispersion, and the stirring time is 90-120 min.

[0036] The embodiment also provides a positive electrode slurry made by using the homogenizing process.

[0037] The embodiment also provides a lithium ion battery made by using the positive electrode slurry. The lithium ion battery using the positive electrode slurry has reduced amount of conductive agent, increased proportion of active material, high energy density, stable electrode structure, significantly increased cycle life and improved cycle performance.

[0038] Further, in order to prove the superiority of the homogenizing process, the following embodiments are provided. Embodiment 1 Embodiment 1 uses the new homogenizing process, which is as follows. S11, PVDF (polyvinylidene fluoride) powder and NMP solvent are added to a double planetary stirring tank in a certain proportion, the revolution speed is set to 10-25 rpm, the dispersion speed is 1000-3000 rpm, and the time is 150-300 min, to prepare a positive electrode glue solution with a solid content of 6%-10%; S12, 40-50% of the dispersed glue solution is taken out and stored for standby (marked as glue solution 1), and a composite conductive agent slurry is added to the remaining glue solution, wherein the composite conductive agent slurry includes conductive carbon black SP, carbon nanotube CNT, graphene, dispersant and solvent, and the content ratio of conductive carbon black SP, carbon nanotube CNT and graphene is that the content of conductive carbon black SP is the highest, the content of carbon nanotube CNT is the second, and the content of graphene is the lowest, the revolution speed is 20-30 rpm, the dispersion speed is 2000-3000 rpm, and the time is 90-120 min, to complete the preparation of the conductive glue solution; S13, lithium iron phosphate is added to the conductive glue solution, the solid content of the conductive glue solution is adjusted in advance or a certain amount of NMP solvent is added to control the slurry to a certain solid content (70%-80%) to be mud-like, the revolution speed is 10-15 rpm, the glue is scraped after stirring for 10 min, then the revolution speed is 15-20 rpm, the dispersion speed is 300-600 rpm, and the stirring time is 60-90 min, and the cooling water circulation system is started during the process, to complete the preparation of the first slurry; S14, the remaining glue liquid is added to the first slurry, and a proper amount of NMP solvent and PVP dispersant are added for homogenization and dispersion. First, the rotation speed is 15-20 rpm, the dispersion speed is 800-1000 rpm, the stirring speed is low for 10 minutes, then the material is scraped, and then the rotation speed is 25-30 rpm, the dispersion speed is 2500-3500 rpm, and the high-speed stirring is 90-120 minutes. In the dispersion process, vacuum is extracted, and the vacuum degree is -88~-92 kpa. This step completes the preparation of the second slurry; S15, a certain amount of NMP solvent is added to adjust the viscosity of the second slurry, the rotation speed is 25-30 rpm, the dispersion speed is 2500-3500 rpm, and the stirring is 30 minutes. In the dispersion process, vacuum is extracted, and the vacuum degree is -88~-92 kpa. The slurry viscosity is controlled at 4000-10000 mPa.s, and the solid content is controlled at 55%-65%. The preparation of lithium ion battery lithium iron phosphate positive electrode slurry is completed.

[0039] Comparative Example 1: Comparative Example 1 uses a traditional homogenization process S111, a certain proportion of NMP solvent and PVDF (polyvinylidene fluoride) powder are added to the double planetary stirring tank, the rotation speed is set to 15 rpm, the dispersion speed is 2000 rpm, and the time is 180 minutes. The solid content of the positive electrode PVDF glue liquid is 5%; S112, a certain amount of conductive agent SP and carbon nanotube CNT conductive slurry is added to the PVDF glue liquid, the rotation speed is set to 20 rpm, the dispersion speed is 2500 rpm, and the high-speed dispersion is 120 minutes to prepare the conductive glue liquid; S113, lithium iron phosphate positive electrode material and a proper amount of NMP solvent are added to the conductive glue liquid, and then the rotation speed is set to 25 rpm and the dispersion speed is 2500 rpm for high-speed dispersion for 180 minutes; S114, a certain amount of NMP solvent is added to adjust the viscosity, and the stirring is 40 minutes. In the process, vacuum is extracted, and the slurry viscosity meets the process requirements to complete the slurry preparation.

[0040] Comparative Example 2: S121, a certain proportion of NMP solvent and PVDF (polyvinylidene fluoride) powder are added to the double planetary stirring tank, the rotation speed is set to 15 rpm, the dispersion speed is 2000 rpm, and the time is 180 minutes. The solid content of the positive electrode PVDF glue liquid is 5%; S122, a certain amount of conductive agent SP is added to the PVDF glue liquid, the rotation speed is set to 20 rpm, the dispersion speed is 2500 rpm, and the high-speed dispersion is 120 minutes to prepare the conductive glue liquid; S123, the lithium iron phosphate positive electrode material and the appropriate NMP solvent are added into the conductive glue solution, first slowly stirring for 10 minutes, then setting the revolution speed to 25 rpm, the dispersion speed to 2500 rpm, and high-speed dispersing for 180 minutes; S124, a certain amount of NMP solvent is added to adjust the viscosity, stirring for 40 minutes, and in the process, vacuum is extracted, the slurry viscosity is tested to meet the process requirements, and the slurry preparation is completed.

[0041] It can be understood that Comparative Example 1 and Comparative Example 2 are both traditional homogenizing processes, and Table 1 and Table 2 show the basic performance of lithium ion batteries made by Example 1, Comparative Example 1 and Comparative Example 2. In combination with Table 1 and Table 2, Comparative Example 1 does not add graphene, resulting in that the CNT is not uniformly dispersed, and finally a large amount of NMP solvent is needed to adjust the viscosity, the solid content of the discharge is very low, and the viscosity changes greatly after standing for 48 hours, and the slurry stability is poor; Comparative Example 2 does not add graphene and CNT, the electrode sheet resistivity is large, the slurry stability is general, the battery internal resistance is high, and the rate is poor. Obviously, the above examples of the present application are only examples for clearly illustrating the present application, and are not the limitation of the embodiments of the present application. For ordinary skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, all the embodiments are not required to be exhausted. Any modification, equivalent replacement and improvement made in the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A homogenization process characterized in that, A composite conductive agent slurry is used, the composite conductive agent slurry includes conductive carbon black SP, carbon nanotube CNT and graphene, and the homogenizing process includes the following steps: S1, PVDF powder and NMP solvent are added into a stirring tank according to a certain proportion to prepare a positive electrode glue solution; S2, the positive electrode glue solution prepared in S1 is taken out, 40-50% of which is used as a first glue solution, and the remaining part is used as a second glue solution, and a composite conductive agent slurry is added into the second glue solution to complete preparation of a conductive glue solution; S3, lithium iron phosphate is added into the conductive glue solution to form a first slurry; S4, the first slurry and the first glue solution are mixed, and a PVP dispersant is added during the mixing to perform homogenizing dispersion, thereby forming a second slurry; S5, NMP solvent is added into the second slurry until the viscosity of the second slurry is controlled to be 4000-10000 mPa.s and the solid content is controlled to be 55%-65%, and preparation of a positive electrode slurry is completed.

2. The homogenization process of claim 1, wherein, The content ratio of the conductive carbon black SP, the carbon nanotube CNT and the graphene decreases in turn.

3. The homogenization process of claim 1, wherein, The composite conductive agent slurry further includes a PVP dispersant for homogenizing and dispersing the mixed conductive carbon black SP, the carbon nanotube CNT and the graphene.

4. The homogenization process of claim 1, wherein, The stirring tank is a double-planetary stirring tank.

5. The homogenization process of claim 4, wherein, In step S1, the public rotation speed of the stirring tank is set to 10-25 rpm, the dispersion speed is set to 1000-3000 rpm, and the time is set to 150-300 min, and a positive electrode glue solution with a solid content of 6%-10% is prepared.

6. The homogenization process according to any of claims 1, 4 or 5, characterized in that, In step S3, after lithium iron phosphate is added into the conductive glue solution, the solid content of the conductive glue solution is adjusted to 70%-80% to make the conductive glue solution into a muddy first slurry.

7. The homogenization process of claim 6, wherein, The solid content of the conductive glue solution is controlled by adding NMP solvent into the conductive glue solution, so that the solid content of the conductive glue solution is 70%-80%.

8. The homogenization process of claim 4, wherein, Step S4 specifically includes the following steps: S41, the first slurry and the first glue solution are mixed, and a PVP dispersant is added during the mixing to perform homogenizing dispersion; S42, the mixture of the first slurry and the first glue solution is stirred at a first stirring speed to form a first intermediate slurry; S43, the first intermediate slurry is stirred at a second stirring speed to form a second intermediate slurry; S44, the second intermediate slurry is vacuumized, and the vacuum degree is set to -88~-92 kpa to complete preparation of the second slurry; The first stirring speed is less than the second stirring speed.

9. A positive electrode slurry, characterized by, The homogenizing process is prepared by using any one of claims 1-8.

10. A lithium-ion battery, characterized by, The positive electrode slurry is prepared by using claim 9.

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