Preparation method of positive electrode material, positive electrode material and power battery

Abstract

The invention provides a preparation method of a positive electrode material, the positive electrode material and a power battery, and relates to the technical field of batteries, the preparation method of the positive electrode material comprises the following steps: step S11: adding a dispersant into a mixed slurry, stirring and dispersing to obtain a target slurry, the mixed slurry at least comprising a main active material, carbon black, an adhesive, a solvent and a conductive agent; and S12, preparing the positive electrode material by adopting the target slurry. By adding the specific dispersing agent into the mixed slurry and carrying out optimized stirring and dispersing operation, the CNT conductive agent can be quickly and uniformly dispersed in the slurry, so that the low viscosity, high solid content and good coating performance of the slurry are ensured while the slurry homogenizing time is shortened; the technical problems that the capacity is low due to long-time stirring in a traditional wet-method stirring process and the CNT is not uniformly dispersed in a dry-method stirring process, so that the battery performance is influenced are solved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method for preparing a positive electrode material, a positive electrode material, and a power battery. Background Art

[0002] Battery technology is advancing rapidly. The requirements for fast charging and discharging, long cycle times, high energy density, and high safety are becoming increasingly stringent in power batteries, energy storage batteries, and consumer electronics. In particular, the pursuit of higher energy density has become a key focus for energy storage batteries. Improving battery energy density can effectively reduce battery costs and reduce the footprint of energy storage systems. Increasing the proportion of primary materials and reducing the proportion of auxiliary materials in batteries can fundamentally improve battery energy density. For lithium iron phosphate (LFP) cathodes, replacing conductive carbon black (SP) with a small amount of carbon nanotubes (CNTs) can reduce the amount of conductive additive and further increase the proportion of primary materials. CNTs have excellent conductivity and can form a continuous conductive network in the electrode material, thereby improving the conductivity of lithium batteries. Their addition to the cathode is generally relatively small, typically less than 5%, to effectively improve conductivity, helping to reduce material costs and increase energy density. However, due to their extremely high aspect ratio and strong van der Waals interactions, CNTs are prone to entanglement and agglomeration, posing challenges to their dispersion in the cathode slurry. During fluid flow and shear mixing, CNTs not only experience interparticle attraction, but also internal friction within individual fibers, leading to agglomeration. Therefore, addressing the dispersion of CNTs in the cathode slurry becomes crucial. In existing mixing processes, either increasing the speed for faster CNT dispersion or increasing the mixing time for more uniform CNT mixing is recommended. Both approaches significantly impact machine wear and tear and production capacity.

[0003] To address the above problems, no effective solutions have been proposed yet. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for preparing a positive electrode material, a positive electrode material, and a power battery, so as to solve the problems of low production capacity and machine loss in the prior art method for preparing a positive electrode material.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a positive electrode material is provided. The method comprises: step S11: adding a dispersant to a mixed slurry and performing a stirring and dispersing operation to obtain a target slurry, wherein the mixed slurry comprises at least: a main active material, carbon black, a binder, a solvent, and a conductive agent; and step S12: using the target slurry to prepare the positive electrode material.

[0006] Furthermore, before step S11, the method further includes: step S10: adding LFP, SP, PVDF, NMP, and CNT into a stirring tank for stirring and dispersing to obtain a mixed slurry.

[0007] Further, step S10 includes: step S101: adding LFP, SP, and PVDF into a stirring tank for a first stirring operation and a first dispersion operation to obtain a first slurry, the stirring speed of the first stirring operation is a, the dispersion speed of the first dispersion operation is b, and the time of the first stirring operation is T1, wherein 24.5rpm≤a≤25.5rpm, 299.5rpm≤b≤300.5rpm, and 29.5min≤T1≤30.5min.

[0008] Furthermore, step S10 also includes: step S102: adding NMP to the first slurry to perform a second stirring operation to obtain a second slurry; step S103: adding CNT and NMP to the second slurry to obtain a mixed slurry.

[0009] Furthermore, step S11 includes: step S111: adding PVP to the mixed slurry to perform a third stirring operation and a second dispersion operation to obtain a third slurry; step S112: adding NMP to the third slurry to perform a fourth stirring operation and a third dispersion operation to obtain a fourth slurry; step S113: performing a vacuum degassing operation and a filtering operation on the fourth slurry to obtain a target slurry.

[0010] Further, in step S101, the mass of LFP is m1, the mass of SP is m2, and the mass of PVDF is m3, wherein 3995 g ≤ m1 ≤ 4005 g, 28.85 g ≤ m2 ≤ 28.95 g, and 82.45 g ≤ m3 ≤ 82.55 g, and / or, in step S102, the mass of NMP is m4, wherein 1466.5 g ≤ m4 ≤ 1467.5 g, and / or, in step S103, the mass of CNT is m5, and the mass of NMP is m6, wherein 247.44.5 g ≤ m5 ≤ 247.45 g, 929.5 g ≤ m6 ≤ 930.5 g, and / or, in step S111, the mass of PVP is m7, wherein 4.115 g ≤ m7 ≤ 4.125 g.

[0011] Further, in step S102, the second stirring operation includes: first performing a reverse stirring operation, then performing a first forward stirring operation, and finally performing a second forward stirring operation, wherein the stirring speed of the reverse stirring operation is c, the stirring time of the reverse stirring operation is T2, the stirring speed of the first forward stirring operation is d, the stirring time of the first forward stirring operation is T3, the stirring speed of the second forward stirring operation is e, and the stirring time of the second forward stirring operation is T4, wherein, 9.5rpm≤c≤10.5rpm, 14.5rpm≤d≤15.5rpm, 24.5rpm≤e≤25.5rpm, 29.5min≤T2≤30.5min, 9.5min≤T3≤10.5min, 59.5min≤T4≤60.5min.

[0012] Further, in step S111, the stirring speed of the third stirring operation is f, the speed of the second dispersion operation is i, and the stirring time of the third stirring operation is T5, wherein 24.5 rpm≤f≤25.5 rpm, 2999.5 rpm≤i≤3000.5 rpm, and 29.5 min≤T5≤30.5 min, and / or, in step S112, the stirring speed of the fourth stirring operation is j, the speed of the third dispersion operation is k, and the stirring time of the fourth stirring operation is T6, wherein 24.5 rpm≤j≤25.5 rpm, 2499.5 rpm≤k≤2500.5 rpm, and 39.5 min≤T6≤40.5 min.

[0013] According to another aspect of the present invention, a positive electrode material is provided. The positive electrode material is prepared by a method for preparing a positive electrode material. The method for preparing the positive electrode material is the method for preparing the positive electrode material of the above embodiment.

[0014] According to another aspect of the present invention, a power battery is provided. The power battery includes a positive electrode material. The positive electrode material is made by a preparation method of the positive electrode material. The preparation method of the positive electrode material is the preparation method of the positive electrode material in the above embodiment.

[0015] By applying the technical solution of the present invention, a specific dispersant is added to the mixed slurry and an optimized stirring and dispersing operation is performed, so that the CNT (carbon nanotube) conductive agent can be quickly and evenly dispersed in the slurry, thereby shortening the homogenization time while ensuring the low viscosity, high solid content and good coating performance of the slurry. This solves the technical problems of low production capacity caused by long stirring time in the traditional wet stirring process and uneven CNT dispersion in the dry stirring process, which affects battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 A schematic structural diagram of the process of preparing the positive electrode material according to the present invention is shown;

[0018] Figure 2 Shown is a schematic diagram of the process structure of Comparative Example 1;

[0019] Figure 3 Shown is a schematic diagram of the process structure of Comparative Example 2;

[0020] Figure 4 The schematic diagram of the process structure of Example 1 is shown;

[0021] Figure 5 A comparison chart of the viscosity of each group at a solid content of 61% is shown;

[0022] Figure 6 The static viscosity trend diagram of each group is shown;

[0023] Figure 7 The SEM image of the electrode surface after coating in Comparative Example 1 is shown;

[0024] Figure 8 The SEM image of the electrode surface after coating in Comparative Example 2 is shown;

[0025] Figure 9 The SEM image of the electrode surface after coating in Example 1 is shown. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0028] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way are interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0029] Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in a variety of different forms and should not be interpreted as being limited to the embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of this application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art. In the accompanying drawings, for the sake of clarity, the thickness of layers and regions may be exaggerated, and the same reference numerals are used to represent the same devices, and thus their descriptions will be omitted.

[0030] Combine Figure 1 As shown, according to a specific embodiment of the present invention, a method for preparing a positive electrode material is provided.

[0031] Specifically, if Figure 1 As shown, the method for preparing the positive electrode material includes: step S11: adding a dispersant to the mixed slurry, stirring and dispersing, and obtaining a target slurry, wherein the mixed slurry at least includes: a main active material, carbon black, a binder, a solvent, and a conductive agent; step S12: using the target slurry to prepare the positive electrode material.

[0032] In this embodiment, by adding a specific dispersant to the mixed slurry and performing optimized stirring and dispersing operations, the CNT (carbon nanotube) conductive agent can be quickly and evenly dispersed in the slurry, thereby shortening the homogenization time while ensuring the low viscosity, high solid content and good coating performance of the slurry. This solves the technical problems of low production capacity caused by long-term stirring in the traditional wet stirring process and uneven CNT dispersion in the dry stirring process, which affects battery performance.

[0033] Specifically, through dry premixing and an improved dispersant addition strategy, not only is the use of NMP (N-methylpyrrolidone) solvent reduced, reducing the cost and energy consumption of slurry preparation, but also by precisely controlling the stirring speed and time, effectively avoiding the problems of CNT agglomeration and excessive wear of equipment, thereby significantly improving the preparation efficiency and slurry quality. Compared with existing processes, the embodiments of this application significantly improve the stability and consistency of the slurry, thereby improving the coating quality of the electrode material, and ultimately helping to produce lithium battery positive electrodes with higher energy density and better cycle performance.

[0034] Furthermore, before step S11, the process also includes step S10: adding LFP, SP, PVDF, NMP, and CNT into a stirring tank for stirring and dispersing to obtain a mixed slurry. This process ensures that all components are fully mixed and avoids local aggregation, thereby improving the conductivity and adhesion of the positive electrode material during the battery manufacturing process, significantly improving the battery's charge and discharge efficiency and extending its service life.

[0035] Further, step S10 includes: step S101: adding LFP, SP, and PVDF into a stirring tank for a first stirring operation and a first dispersion operation to obtain a first slurry, the stirring speed of the first stirring operation is a, the dispersion speed of the first dispersion operation is b, and the time of the first stirring operation is T1, wherein 24.5rpm≤a≤25.5rpm, 299.5rpm≤b≤300.5rpm, and 29.5min≤T1≤30.5min.

[0036] Specifically, at the specified stirring speed a and dispersion speed b, LFP, SP and PVDF can be dispersed and combined more evenly. PVDF, as a binder, helps to bond LFP and SP particles together to form a stable slurry structure. CNT, as a conductive agent, can form a conductive network to improve the conductivity of the battery. In this process, LFP, as the main active material, and the uniform dispersion of its particles are crucial to improving the energy density and cycle performance of the battery. By precisely controlling the stirring speed (a), dispersion speed (b) and stirring time (T1), the viscosity and fineness of the final slurry can be effectively controlled. Excessively high or low viscosity and fineness will affect the coating performance of the slurry, and thus affect the quality of the battery electrode. Within the specified parameter range, the viscosity and fineness of the slurry can reach the optimal state suitable for coating, thereby improving the consistency and efficiency of the coating.

[0037] In this example, to verify the effects of stirring speed and time on slurry uniformity, comparative experiments were conducted using different stirring parameters. For example, in the first stirring operation, the stirring speed was adjusted to 25.1 rpm, and the stirring time was shortened to 29.8 minutes. In the first dispersion operation, the dispersion speed was reduced to 299.5 rpm, and the time was extended to 30.2 minutes. These fine-tuning adjustments allow for the evaluation of the subtle effects of stirring speed and time on the performance of the cathode material.

[0038] Furthermore, step S10 also includes: step S102: adding NMP to the first slurry to perform a second stirring operation to obtain a second slurry; step S103: adding CNT and NMP to the second slurry to obtain a mixed slurry.

[0039] Specifically, in step S102, NMP (N-methylpyrrolidone) is added to the first slurry as a solvent and a second stirring operation is performed. NMP can effectively dissolve the PVDF binder, making it easier to form a uniform bond with LFP and SP in the slurry. In addition, the addition of NMP helps to activate the surface of LFP and SP, enhance the interaction between them, and thus form a more stable slurry system. NMP can reduce the viscosity of the slurry, making it smoother in the subsequent coating process and easier to form a uniform coating. Lower viscosity also helps to improve coating speed and efficiency. Through the second stirring operation, NMP is fully mixed with the slurry, promoting further dispersion of LFP, SP and PVDF, reducing agglomeration between particles, and thus obtaining a more uniform second slurry.

[0040] In step S103, CNTs (carbon nanotubes) and additional NMP are added to the second slurry to form a mixed slurry. The addition of CNTs significantly improves the conductive network in the slurry. This is because CNTs have excellent conductivity and a high aspect ratio, and can form a continuous conductive path in the slurry. This not only improves the conductivity of the battery, but also because CNTs can replace part of the SP, thereby reducing the overall use of the conductive agent, further increasing the proportion of LFP, and improving energy density. The addition of CNTs, combined with an appropriate dispersant (such as PVP), can increase the stability of the slurry during standing and transportation, prevent precipitation and agglomeration, and maintain a uniform distribution of the slurry components.

[0041] Furthermore, step S11 includes: step S111: adding PVP to the mixed slurry to perform a third stirring operation and a second dispersion operation to obtain a third slurry; step S112: adding NMP to the third slurry to perform a fourth stirring operation and a third dispersion operation to obtain a fourth slurry; step S113: performing a vacuum degassing operation and a filtering operation on the fourth slurry to obtain a target slurry.

[0042] Specifically, in step S111, PVP (polyvinyl pyrrolidone) is used as a dispersant to enhance the dispersion of CNTs in the slurry. PVP can adsorb on the CNT surface, preventing agglomeration caused by van der Waals forces between CNTs, ensuring uniform distribution of CNTs in the slurry and forming a stable conductive network. Through the third stirring operation and the second dispersion operation, PVP is evenly mixed in the slurry, which helps improve the stability of the slurry during standing and transportation, reducing precipitation and stratification.

[0043] In step S112, NMP is added as a solvent to further dissolve the PVDF and promote uniform dispersion of the various components in the slurry, ensuring the uniformity and stability of the slurry. Through the fourth stirring step and the third dispersion step, the slurry's properties, including viscosity, solids content, and fluidity, can be optimized to better meet coating requirements. This helps improve the controllability and consistency of the coating process.

[0044] In step S113, vacuum degassing removes bubbles from the slurry, preventing voids or uneven coating during the coating process and improving the smoothness and quality of the electrode. Filtration removes undispersed or agglomerated particles and possible impurities from the slurry, ensuring a smooth, defect-free surface after coating, which helps improve battery performance and consistency.

[0045] Further, in step S101, the mass of LFP is m1, the mass of SP is m2, and the mass of PVDF is m3, wherein 3995 g ≤ m1 ≤ 4005 g, 28.85 g ≤ m2 ≤ 28.95 g, and 82.45 g ≤ m3 ≤ 82.55 g, and / or, in step S102, the mass of NMP is m4, wherein 1466.5 g ≤ m4 ≤ 1467.5 g, and / or, in step S103, the mass of CNT is m5, and the mass of NMP is m6, wherein 247.44.5 g ≤ m5 ≤ 247.45 g, 929.5 g ≤ m6 ≤ 930.5 g, and / or, in step S111, the mass of PVP is m7, wherein 4.115 g ≤ m7 ≤ 4.125 g.

[0046] Among them, the main active materials are LFP and SP, the adhesive is PVDF, the solvent is NMP, and the conductive agent is CNT. By strictly controlling the mass (m1, m2, m3) of LFP, SP and PVDF in step S101, the accuracy and consistency of the slurry composition can be ensured, which is crucial for controlling product quality in large-scale production. In steps S102 and S103, the precise addition amount of NMP (m4) and CNT, NMP (m5, m6) helps to optimize the viscosity, solid content and dispersibility of the slurry, which directly affect the performance and production efficiency of the battery. In step S103, precise control of the mass (m5) of CNT is crucial for its dispersion effect in the slurry. Excessive or insufficient CNT may lead to uneven dispersion, affecting the formation of the conductive network. Accurate control of the mass (m7) of PVP in step S111 can ensure that PVP is evenly dispersed in the slurry, give full play to its dispersant function, prevent CNT agglomeration, and further optimize the stability of the slurry.

[0047] Preferably, the mass of LFP is set to 4000 g, the mass of SP is set to 28.9 g, the mass of PVDF is set to 82.5 g, the mass of NMP is set to 1467 g, the mass of CNT is set to 247.45 g, the mass of PVP is set to 4.12 g, and the additional mass of NMP is set to 930 g.

[0048] Preferably, step S101: accurately weigh LFP (m1 = 4000g), SP (m2 = 28.9g), and PVDF (m3 = 82.5g) into a 5L double-helix planetary stirring tank, perform a first stirring operation (25rpm) and a first dispersion operation (300rpm), and the stirring time is 30min. Step S102: accurately add 1467g of NMP to the slurry in step S101, and perform a second stirring operation. The stirring speed and time are fine-tuned according to previous experience and test results to obtain the best dispersion effect. Step S103: accurately weigh CNT conductive slurry (m5 = 247.4g, of which CNT accounts for 6%) and NMP (m6 = 930g), add them to the second slurry, and perform a third stirring operation to ensure that the CNTs are evenly mixed, reduce agglomeration, and improve the conductive properties of the slurry. Step S111: PVP (m7=4.12 g) is precisely added to the mixed slurry, and a fourth stirring operation and a second dispersing operation are performed to further improve the dispersion effect of CNTs and optimize the rheological properties of the slurry to ensure its stability during the coating process.

[0049] Through the above precise control, we obtained the third slurry, whose solid content, viscosity and fineness were optimized. The specific parameters are as follows: solid content: 59.2%; viscosity: 17610mPa·s (at 61% solid content); fineness: 7μm.

[0050] Subsequently, in steps S112 and S113, the target slurry is finally obtained through the fourth stirring operation, the third dispersion operation, the vacuum degassing and the filtration operation, which ensures the purity and consistency of the slurry, playing a vital role in the subsequent coating and battery performance improvement.

[0051] Compared with wet mixing (Group A) and dry mixing (Group B), the improved dry mixing (Group C) achieved a shorter mixing time (220 minutes, excluding the time for adding materials and adjusting viscosity) by precisely controlling the mass of the components, thereby improving production efficiency. At a solid content of 61%, the viscosity of the slurry in Group C was 17610 mPa·s, which was lower than that of the wet mixing (Group A) and was evenly dispersed, indicating that the CNT dispersion in the slurry was excellent. The viscosity change was small, the slurry was stable, and it was not easy to agglomerate during the static process. See the static viscosity change trend chart of each group ( Figure 6 ).

[0052] After coating, the surface of the electrode is smooth and the conductive agent is evenly distributed, see the SEM image of the electrode surface after coating ( Figure 7 、 Figure 9 ). This is beneficial to improving the fast charge and discharge performance and cycle stability of the battery.

[0053] By adjusting the amount of PVP and additional NMP added, the effect of different slurry viscosities on the performance of the cathode material can be explored. For example, if the mass of PVP is increased to 4.13g and the mass of additional NMP is reduced to 929g, the effect of varying slurry viscosity on battery energy density can be studied.

[0054] Further, in step S102, the second stirring operation includes: first performing a reverse stirring operation, then performing a first forward stirring operation, and finally performing a second forward stirring operation, wherein the stirring speed of the reverse stirring operation is c, the stirring time of the reverse stirring operation is T2, the stirring speed of the first forward stirring operation is d, the stirring time of the first forward stirring operation is T3, the stirring speed of the second forward stirring operation is e, and the stirring time of the second forward stirring operation is T4, wherein 9.5rpm≤c≤10.5rpm, 14.5rpm≤d≤15.5rpm, 24.5rpm≤e≤25.5rpm, 29.5min≤T2≤30.5min, 9.5min≤T3≤10.5min, and 59.5min≤T4≤60.5min.

[0055] Preferably, during the second stirring operation, a stirring mode of first reverse rotation and then forward rotation is adopted, with the reverse stirring speed being 10 rpm and the duration set to 30 minutes; the first forward stirring speed being 15 rpm and the duration set to 10 minutes; and the second forward stirring speed being 25 rpm and the duration set to 60 minutes. This stirring mode helps improve the fluidity of the slurry, reduce the generation of bubbles, and enhance the stability of the positive electrode material.

[0056] To further optimize the stirring process, the stirring speed and duration can be adjusted. For example, in the second stirring operation, try reducing the reverse stirring speed to 9.7 rpm, increasing the first forward stirring speed to 14.8 rpm, and maintaining the same forward stirring speed for the second time, but extending the stirring time to 60.5 minutes. These adjustments may affect the properties of the slurry and, therefore, the performance of the cathode material.

[0057] Further, in step S111, the stirring speed of the third stirring operation is f, the speed of the second dispersion operation is i, and the stirring time of the third stirring operation is T5, wherein 24.5 rpm≤f≤25.5 rpm, 2999.5 rpm≤i≤3000.5 rpm, and 29.5 min≤T5≤30.5 min, and / or, in step S112, the stirring speed of the fourth stirring operation is j, the speed of the third dispersion operation is k, and the stirring time of the fourth stirring operation is T6, wherein 24.5 rpm≤j≤25.5 rpm, 2499.5 rpm≤k≤2500.5 rpm, and 39.5 min≤T6≤40.5 min.

[0058] Preferably, in the third stirring operation, the stirring speed is set to 25 rpm and the stirring time is 30 minutes; the second dispersion operation is set to 3000 rpm and the stirring time is also 30 minutes. In the fourth stirring operation, the stirring speed is set to 25 rpm and the stirring time is 40 minutes; the third dispersion operation is set to 2500 rpm and the stirring time is 40 minutes. These stirring and dispersion parameters help eliminate bubbles in the slurry and improve the density and conductivity of the positive electrode material.

[0059] In order to explore the influence of stirring and dispersion parameters on the performance of cathode materials, different experimental conditions can be designed. For example, in the third stirring operation, the stirring speed is adjusted to 25.2 rpm and the stirring time is shortened to 29.9 min; in the second dispersion operation, the dispersion speed is increased to 3001 rpm and the dispersion time remains unchanged. In the fourth stirring operation, the stirring speed is reduced to 24.8 rpm and the stirring time is extended to 40.5 min; in the third dispersion operation, the dispersion speed is reduced to 2499 rpm and the dispersion time is adjusted to 40.2 min. By comparing the performance of cathode materials prepared under different parameters, the optimal process conditions can be found to achieve optimal battery performance.

[0060] According to another aspect of the present invention, a positive electrode material is provided. The positive electrode material is prepared by a method for preparing a positive electrode material. The method for preparing the positive electrode material is the method for preparing the positive electrode material of the above embodiment.

[0061] According to another aspect of the present invention, a power battery is provided. The power battery includes a positive electrode material. The positive electrode material is made by a preparation method of the positive electrode material. The preparation method of the positive electrode material is the preparation method of the positive electrode material in the above embodiment.

[0062] The beneficial effects of the present application will be described below with reference to specific embodiments and comparative examples.

[0063] Example 1

[0064] The preparation method of the positive electrode material of the present application adopts an improved dry process flow, which is named C. Figure 4 As shown, the specific steps include:

[0065] Step 1: Prepare a 5L double-helix planetary mixing tank, add 4000g of LFP, 28.9g of SP, and 82.5g of PVDF, start stirring and dispersing, with a stirring speed of 25rpm, a dispersion speed of 300rpm, and a stirring time of 30min.

[0066] Step 2: Add 1467g of NMP and knead, start stirring, stir in reverse, the speed is 10rpm, and the stirring time is 30min; then stir in forward direction, the speed is 15rpm, and the stirring time is 10min, and then stir in forward direction, the speed is 25rpm, and the stirring time is 60min.

[0067] Step 3: Add 247.4 g of CNT, 4.12 g of polyvinylpyrrolidone (PVP), and 930 g of NMP, start stirring and dispersing, with a stirring speed of 25 rpm, a dispersion speed of 3000 rpm, and a stirring time of 30 min.

[0068] Step 4: Add NMP to adjust the viscosity, start stirring and dispersing, the stirring speed is 25 rpm, the dispersing speed is 2500 rpm, and the stirring time is 40 min; turn on the vacuum to remove bubbles, and the vacuum degree is set to <-85 kPa.

[0069] Step 5: After testing the viscosity, fineness and solid content, discharge the material for coating. Use a 180-mesh double-layer filter to filter the slurry, and then transfer the slurry to the coating machine for coating.

[0070] Comparative Example 1

[0071] The preparation method of the positive electrode material adopts a wet stirring process, and the process flow is named A. Figure 2 As shown, the specific steps include:

[0072] Step 1: Prepare a 5L double-helix planetary stirring tank, put 82.5g of polyvinylidene fluoride (PVDF) into the tank and add 2000g of solvent N-methylpyrrolidone (NMP), start stirring and dispersing, stir slowly first, the stirring speed is 10rpm, the dispersion speed is 500rpm, and the stirring time is 10min; after slow stirring, scrape the material, then stir quickly, the stirring speed is 20rpm, the dispersion speed is 2000rpm, and the stirring time is 360min; the input mass ratio is PVDF / (NMP+PVDF)=4%, and the solid content of the glue is 4%.

[0073] Step 2: Add 28.9g of conductive carbon black (SP), start stirring and dispersing, stir slowly first, the stirring speed is 10rpm, the dispersing speed is 500rpm, and the stirring time is 10min; after slow stirring, scrape the material, then stir quickly, the stirring speed is 20rpm, the dispersing speed is 2000rpm, and the stirring time is 120min.

[0074] Step 3: Add 247.4 g of conductive paste (CNT), start stirring and dispersing, the stirring speed is 20 rpm, the dispersion speed is 2000 rpm, and the stirring time is 60 min; the conductive paste (CNT) is a solid solution, in which CNT accounts for 6% of the solid solution.

[0075] Step 4: Add 4000g of lithium iron phosphate (LFP) and 510g of NMP, start stirring and dispersing, first stir slowly, the stirring speed is 20rpm, the dispersing speed is 500rpm, and the stirring time is 20min; then stir quickly, the stirring speed is 25rpm, the dispersing speed is 2500rpm, and the stirring time is 180min; turn on the circulating water, the temperature is <50℃, if the temperature is greater than 50℃, start slow stirring, the stirring speed is 10rpm, the dispersing speed is 500rpm, and wait until the temperature is less than 40℃ before continuing to stir quickly.

[0076] Step 5: Add NMP to adjust the viscosity, start stirring and dispersing, the stirring speed is 25 rpm, the dispersing speed is 2500 rpm, and the stirring time is 40 min; turn on the vacuum to remove bubbles, and the vacuum degree is set to <-85 kPa.

[0077] Step 6: After testing the viscosity, fineness and solid content, discharge the material for coating. Use a 180-mesh double-layer filter to filter the slurry, and then transfer the slurry to the coating machine for coating.

[0078] Comparative Example 2

[0079] The preparation method of the positive electrode material adopts a dry stirring process, and the process flow is named B. Figure 3 As shown, the specific steps include:

[0080] Step 1: Prepare a 5L double-helix planetary mixing tank, add 4000g of LFP, 28.9g of SP, and 82.5g of PVDF into the tank, start stirring and dispersing, the stirring speed is 25rpm, the dispersion speed is 300rpm, and the stirring time is 30min.

[0081] Step 2: Add 1467g of NMP and knead, start stirring, stir in reverse, the speed is 10rpm, and the stirring time is 30min; then stir in forward direction, the speed is 15rpm, and the stirring time is 30min, and then stir in forward direction, the speed is 25rpm, and the stirring time is 60min.

[0082] Step 3: Add 247.4 g of CNT and 930 g of NMP, start stirring and dispersing, with a stirring speed of 25 rpm, a dispersion speed of 3000 rpm, and a stirring time of 60 min.

[0083] Step 4: Add NMP to adjust the viscosity, start stirring and dispersing, the stirring speed is 25 rpm, the dispersing speed is 2500 rpm, and the stirring time is 40 min; turn on the vacuum to remove bubbles, and the vacuum degree is set to <-85 kPa.

[0084] Step 5: After testing the viscosity, fineness and solid content, discharge the material for coating. Use a 180-mesh double-layer filter to filter the slurry, and then transfer the slurry to the coating machine for coating.

[0085] The solid material ratios for Groups A, B, and C are LFP:PVDF:SP:CNT = 97:2:0.7:0.3; the PVP addition amount is 0.1% of the total solid mass. LFP, PVDF, SP, and PVP are solids, the CNT conductive paste is a solid solution, with CNT accounting for 6% of the solid solution, and NMP is a liquid.

[0086] Among them, the theoretical stirring time of the wet process is 800 minutes (excluding the time for adding materials and adjusting viscosity), and the theoretical stirring time of the dry process is 220 minutes (excluding the time for adding materials and adjusting viscosity). Compared with the wet process, the efficiency of the dry process is improved by 27.5%.

[0087] like Figure 5 As shown in the figure, when the solid content of the three is 61%, the viscosities of groups A, B, and C are 15430mPa·s, 31220mPa·s, and 17610mPa·s, respectively. Generally speaking, under the same solid content, the lower the viscosity, the better the slurry dispersion. From the data, we can see that group A is the most evenly dispersed, followed by group C, and group B has the worst dispersion.

[0088] like Figure 6 The static viscosity change trend of each group shows that the viscosity changes of Groups A and C are the smallest, indicating that the two groups of slurries are relatively evenly dispersed, while the viscosity of Group B changes greatly. This indicates that the particles may re-agglomerate during the static process, causing a large viscosity change.

[0089] Figure 7 、 8 9 are SEM images of the electrode surface after coating of groups A, B and C respectively. It can be seen from the pictures that the SEM images of groups A and C show that the electrode surface is smooth and defect-free, and the large and small iron-lithium particles fill each other to form a high-density electrode, without agglomeration of large and small particles. In addition, the conductive agent and the binder are evenly distributed, showing a good interface effect; while the SEM image of group B shows that the conductive agent is unevenly distributed and agglomerated on the electrode surface. The red area is the agglomerated area of ​​the conductive agent, and the rest of the interface is uneven due to the agglomeration of the conductive agent.

[0090] As shown in Table 1, which compares the viscosity, fineness, and solids content of each group at discharge, the discharge viscosity remained essentially the same. This is because coating requires controlled slurry viscosity to facilitate a smooth coating process. In terms of fineness, Groups A and C had similar finenesses, both around 7, while Group B had a fineness of around 9. Furthermore, fine particles were evident when the discharge passed through the sieve, indicating poor slurry dispersion. Regarding discharge solids, Group C had the highest solids content at 59.2%, Group B had a solids content of 58.5%, and Group A had a solids content of 57%.

[0091] Table 1: Comparison of viscosity, fineness and solid content of each group at discharge

[0092] Group A B C Fineness (μm) 7 9 7 Viscosity (mpa·s) 6170 6450 6280 Solid content 57.0％ 58.5％ 59.2％

[0093] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0094] In addition to the above, it should be noted that references to "one embodiment," "another embodiment," "an embodiment," and the like in this specification refer to specific features, structures, or characteristics described in conjunction with that embodiment as included in at least one embodiment generally described in this application. The appearance of the same expression in multiple places in the specification does not necessarily refer to the same embodiment. Furthermore, when a specific feature, structure, or characteristic is described in conjunction with any embodiment, it is intended that such feature, structure, or characteristic, when implemented in conjunction with other embodiments, also falls within the scope of the present invention.

[0095] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0096] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

[0097] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0098] In addition to the above, it should be noted that references to "one embodiment," "another embodiment," "an embodiment," and the like in this specification refer to specific features, structures, or characteristics described in conjunction with that embodiment as included in at least one embodiment generally described in this application. The appearance of the same expression in multiple places in the specification does not necessarily refer to the same embodiment. Furthermore, when a specific feature, structure, or characteristic is described in conjunction with any embodiment, it is intended that such feature, structure, or characteristic, when implemented in conjunction with other embodiments, also falls within the scope of the present invention.

[0099] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0100] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: include: Step S11: adding a dispersant to the mixed slurry and performing a stirring and dispersing operation to obtain a target slurry, wherein the mixed slurry at least includes: a main active material, carbon black, a binder, a solvent, and a conductive agent; Step S12: preparing a positive electrode material using the target slurry.

2. The method for preparing the positive electrode material according to claim 1, wherein: Before step S11, the method further includes: Step S10: adding LFP, SP, PVDF, NMP, and CNT into a stirring tank for stirring and dispersing to obtain the mixed slurry.

3. The method for preparing the positive electrode material according to claim 2, wherein: The step S10 includes: Step S101: LFP, SP, and PVDF are added to a stirring tank for a first stirring operation and a first dispersion operation to obtain a first slurry. The stirring speed of the first stirring operation is a, the dispersion speed of the first dispersion operation is b, and the time of the first stirring operation is T1, wherein 24.5rpm≤a≤25.5rpm, 299.5rpm≤b≤300.5rpm, and 29.5min≤T1≤30.5min.

4. The method for preparing the positive electrode material according to claim 3, wherein: The step S10 further includes: Step S102: adding NMP to the first slurry and performing a second stirring operation to obtain a second slurry; Step S103: adding CNT and NMP to the second slurry to obtain the mixed slurry.

5. The method for preparing the positive electrode material according to claim 4, wherein: The step S11 includes: Step S111: adding PVP to the mixed slurry to perform a third stirring operation and a second dispersion operation to obtain a third slurry; Step S112: adding NMP to the third slurry to perform a fourth stirring operation and a third dispersion operation to obtain a fourth slurry; Step S113: performing vacuum degassing and filtering operations on the fourth slurry to obtain the target slurry.

6. The method for preparing the positive electrode material according to claim 5, wherein: In the step S101, the mass of LFP is m1, the mass of SP is m2, and the mass of PVDF is m3, wherein 3995g≤m1≤4005g, 28.85g≤m2≤28.95g, and 82.45g≤m3≤82.55g, and / or, in the step S102, the mass of NMP is m4, wherein 1466.5g≤m4≤1467.5g, and / or, in the step S103, the mass of CNT is m5, and the mass of NMP is m6, wherein 247.44.5g≤m5≤247.45g, and 929.5g≤m6 ≤930.5g, and / or, in step S111, the mass of PVP is m7, wherein 4.115g≤m7≤4.125g.

7. The method for preparing the positive electrode material according to claim 4, wherein: In step S102, the second stirring operation includes: first performing a reverse stirring operation, then performing a first forward stirring operation, and finally performing a second forward stirring operation, wherein the stirring speed of the reverse stirring operation is c, the stirring time of the reverse stirring operation is T2, the stirring speed of the first forward stirring operation is d, the stirring time of the first forward stirring operation is T3, the stirring speed of the second forward stirring operation is e, and the stirring time of the second forward stirring operation is T4, wherein 9.5rpm≤c≤10.5rpm, 14.5rpm≤d≤15.5rpm, 24.5rpm≤e≤25.5rpm, 29.5min≤T2≤30.5min, 9.5min≤T3≤10.5min, and 59.5min≤T4≤60.5min.

8. The method for preparing the positive electrode material according to claim 5, wherein: In step S111, the stirring speed of the third stirring operation is f, the speed of the second dispersion operation is i, and the stirring time of the third stirring operation is T5, wherein 24.5 rpm≤f≤25.5 rpm, 2999.5 rpm≤i≤3000.5 rpm, and 29.5 min≤T5≤30.5 min, and / or, in step S112, the stirring speed of the fourth stirring operation is j, the speed of the third dispersion operation is k, and the stirring time of the fourth stirring operation is T6, wherein 24.5 rpm≤j≤25.5 rpm, 2499.5 rpm≤k≤2500.5 rpm, and 39.5 min≤T6≤40.5 min.

9. A positive electrode material, characterized in that The positive electrode material is prepared by a positive electrode material preparation method, and the positive electrode material preparation method is the positive electrode material preparation method according to any one of claims 1 to 8.

10. A power battery, characterized in that: The power battery includes a positive electrode material, and the positive electrode material is prepared by a positive electrode material preparation method, which is the positive electrode material preparation method according to any one of claims 1 to 8.

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