Preparation method of lithium battery positive pole piece precursor

Abstract

The invention belongs to the technical field of lithium battery manufacturing, and particularly discloses a lithium battery positive pole piece precursor preparation method which comprises the following steps: mixing an active substance, a conductive agent, a binder and a solvent to prepare positive pole slurry; the positive electrode slurry passes through an electromagnetic slurry magnetic separator, and magnetic foreign matter particles contained in the slurry are removed; and coating a metal current collector with the positive electrode slurry subjected to magnetic separation treatment to obtain a lithium battery positive electrode plate precursor. According to the method, the magnetic separation step is added between the slurry preparation step and the coating step, and the electromagnetic slurry magnetic separator with relatively high magnetic field intensity is adopted, so that the existing magnetic foreign matters in the raw materials and the magnetic foreign matters newly generated in the slurry preparation step are effectively removed, and the quality of the positive pole piece of the lithium battery and the overall performance of the battery are improved.

Description

A method for preparing a lithium battery positive electrode precursor Technical Field

[0001] This invention relates to the field of lithium battery manufacturing technology, specifically to a method for preparing a lithium battery positive electrode precursor. Background Technology

[0002] With the development of science and technology, especially the development of new energy technologies in recent years, lithium batteries have become a major type of electrochemical energy storage device. The positive electrode is a component of a lithium battery, and its performance greatly affects the performance and quality of the battery. The positive electrode preparation process mainly includes steps such as slurry preparation, coating, drying, and rolling. The slurry preparation step involves preparing a positive electrode slurry from active materials and conductive agents; the coating step involves coating the positive electrode slurry onto a metal current collector to obtain the lithium battery positive electrode precursor (i.e., the wet electrode); the drying step involves drying the lithium battery positive electrode precursor to obtain a dry electrode; and the rolling step involves rolling the dried electrode to obtain the lithium battery positive electrode.

[0003] In the preparation of lithium-ion battery cathode precursors, magnetic foreign matter (such as tiny particles of iron, nickel, cobalt, and their alloys, which are not effective components of the cathode material) is a harmful impurity that must be strictly controlled. If the residual amount of magnetic foreign matter is large, the final lithium-ion battery may cause problems such as local electrochemical corrosion and catalytic electrolyte decomposition during cycling. In extreme cases, it may even lead to internal micro-short circuits, thereby affecting the cycle life and safety of the lithium-ion battery.

[0004] Furthermore, during the preparation and transportation of the slurry, wear particles generated by metal equipment such as agitators, pumps, and valves due to long-term operation can directly mix into the slurry as a secondary source of pollution. These magnetic foreign objects, newly generated and introduced during the process, are permanently embedded inside the electrode coating after the slurry is coated and dried, making them difficult to remove effectively through subsequent finished product testing, thus becoming a potential hazard affecting the safety and reliability of lithium batteries.

[0005] Currently, the industry mainly relies on high-standard screening and testing of upstream raw materials, or the use of relatively simple permanent magnet separators with weak magnetic force, to control magnetic foreign objects. Magnetic separation is a common method for removing magnetic foreign objects from powder materials, but due to the high viscosity of the positive electrode slurry, the weak magnetic properties of the magnetic impurities, and the limited magnetic force of permanent magnet separators, this method is not very effective. Existing electromagnetic slurry magnetic separators are bulky and limited by production line installation space, and there are no successful application cases in the industry.

[0006] Therefore, developing an efficient, online magnetic foreign matter removal technology that meets the requirements of small installation space for both existing magnetic foreign matter in raw materials and newly generated magnetic foreign matter during the preparation of lithium battery positive electrode precursors has become an urgent technical problem to be solved in order to improve the quality of high-end lithium battery products. Summary of the Invention

[0007] The purpose of this invention is to improve the preparation method of lithium battery positive electrode precursor, thereby removing magnetic foreign matter already present in the raw materials and newly generated during the preparation process of the electrode precursor, thus improving the quality of the lithium battery positive electrode and the overall performance of the battery.

[0008] To achieve the above objectives, this invention discloses a method for preparing a lithium battery positive electrode precursor. The method includes the following steps: Step S100, preparing a positive electrode slurry; Step S200, passing the positive electrode slurry through an electromagnetic slurry magnetic separator to remove magnetic foreign particles contained in the slurry; Step S300, coating the magnetically separated positive electrode slurry onto a metal current collector to obtain the lithium battery positive electrode precursor. This method adds a magnetic separation step between the slurry preparation and coating steps, and employs an electromagnetic slurry magnetic separator. The electromagnetic slurry magnetic separator generates a strong and controllable magnetic field, effectively removing both magnetic foreign particles in the raw materials and newly generated magnetic foreign particles during slurry preparation and transportation, thereby producing high-quality lithium battery positive electrode sheets.

[0009] Further, in step S200, the electromagnetic slurry magnetic separator used includes a magnetic separation channel through which the positive electrode slurry can pass and an electromagnetic coil arranged around the magnetic separation channel. A magnetically conductive medium is provided within the magnetic separation channel. The electromagnetic coil generates a magnetic field when energized, and the magnetically conductive medium adsorbs magnetic particles in the positive electrode slurry when magnetized by the magnetic field generated by the electromagnetic coil. The positive electrode slurry produced in step S100 can be conveyed to the magnetic separation channel. When the electromagnetic coil is energized, it generates a strong magnetic field, thereby magnetizing the magnetically conductive medium. As the slurry passes through the magnetic separation channel, the magnetically conductive medium can fully contact the slurry, adsorbing and effectively removing magnetic foreign matter from the slurry. This electromagnetic slurry magnetic separator can remove magnetic foreign matter from the slurry while it passes through. The magnetic separation channel and the magnetically conductive medium are located within the space enclosed by the electromagnetic coil, resulting in a high magnetic field strength that is easy to control, and a good demagnetizing effect on the positive electrode slurry.

[0010] Furthermore, the magnetically conductive medium includes a vertical connecting shaft installed within the magnetic separation channel and several magnetically conductive mesh sheets disposed on the vertical connecting shaft. The magnetic separation channel is connected to a feed pipe and a discharge pipe, which are respectively connected to both ends of the magnetic separation channel. With the above structure, the feed pipe and discharge pipe can be connected to the slurry input pipe and slurry output pipe, respectively. When the electromagnetic coil is energized, a magnetic field is generated, thereby magnetizing the magnetically conductive mesh sheets and attracting magnetic foreign matter in the slurry passing through.

[0011] Furthermore, the electromagnetic slurry magnetic separator also includes a housing and a heat exchanger. The electromagnetic coil is installed inside the housing. The heat exchanger has a cooling medium channel and a thermally conductive insulating oil channel for heat exchange. The heat exchanger has a cooling medium inlet and a cooling medium outlet connected to the cooling medium channel, and a thermally conductive insulating oil inlet and a thermally conductive insulating oil outlet connected to the thermally conductive insulating oil channel. The thermally conductive insulating oil inlet is connected to the inner cavity of the housing through a first section of the thermally conductive insulating oil circulation pipeline, and the thermally conductive insulating oil outlet is connected to the inner cavity of the housing through a second section of the thermally conductive insulating oil circulation pipeline, thus forming a closed loop. With the above structure, the cooling medium inlet and cooling medium outlet can be connected to a cooling medium supply device. After absorbing the heat dissipated by the electromagnetic coil inside the housing, the thermally conductive insulating oil enters the heat exchanger through the thermally conductive insulating oil circulation pipeline, completes heat exchange with the cooling medium, and then returns to the housing, thereby achieving oil cooling of the electromagnetic coil inside the housing and ensuring that the electromagnetic slurry magnetic separator can continuously provide a high magnetic field strength.

[0012] Furthermore, the inner diameter of the magnetic cavity in the magnetic separation channel is ≤150mm, and the magnetic field strength within the magnetic separation channel is ≥3000GS. Through optimized design of the inner diameter of the magnetic cavity and the magnetic field strength, and by adopting a more reasonable excitation structure and a more effective heat dissipation method, the electromagnetic slurry magnetic separator achieves a compact overall structure while maintaining key separation performance, significantly reducing the overall size of the machine and thus lowering the installation space requirements. The smaller size of the electromagnetic slurry magnetic separator better meets the space requirements of production line installation, while simultaneously improving the removal efficiency of magnetic foreign matter in the slurry with a higher magnetic field strength.

[0013] Further, step S100 specifically includes: step S110, initially mixing the positive electrode active material and the conductive agent; step S120, adding a binder solution composed of a binder and a solvent to the mixture obtained in step S110, and stirring to form a homogeneous slurry. The binder is polyvinylidene fluoride, and the solvent is N-methylpyrrolidone. The initial mixing and stirring steps ensure that the prepared positive electrode slurry has stable performance and uniform dispersion, which is beneficial for improving the uniformity and consistency of the electrode in the subsequent coating process, ultimately improving the energy density and cycle performance of the lithium battery. Using polyvinylidene fluoride as the binder and N-methylpyrrolidone as the solvent ensures that the slurry forms a good bonding structure and conductive network during the drying process after coating, improving the mechanical strength and electrochemical performance of the electrode.

[0014] Furthermore, the positive electrode active material in step S100 is selected from lithium cobalt oxide, ternary materials, or lithium iron phosphate; the conductive agent includes carbon black, Super P, or carbon nanotubes. Lithium cobalt oxide has a high energy density, ternary materials have good overall performance, lithium iron phosphate is beneficial for improving the safety and cycle life of lithium batteries, and conductive agents such as carbon black, Super P, and carbon nanotubes can improve the conductivity of the electrode and reduce the internal resistance of the battery. By selecting the above-mentioned positive electrode active material and conductive agent, the electrochemical performance of the positive electrode can be improved.

[0015] Furthermore, in step S300, a slot extrusion coating method is used for coating. The slot extrusion coating method can achieve high-precision coating control, ensuring that the wet coating thickness is uniform and consistent.

[0016] In summary, the beneficial effects of this invention are as follows: This invention improves the preparation method of lithium battery positive electrode precursor by adding a magnetic separation step between the slurry preparation and coating steps, and by using an electromagnetic slurry magnetic separator with a large magnetic field strength, controllable magnetic field and small size, effectively removing existing magnetic foreign matter in the raw materials as well as newly generated magnetic foreign matter in the slurry preparation and other steps, thereby improving the quality of lithium battery positive electrode and the overall performance of the battery. Attached Figure Description

[0017] Figure 1 is a flowchart of an embodiment of the lithium battery positive electrode precursor preparation method of the present invention; Figure 2 is an external view of an embodiment of the electromagnetic slurry magnetic separator used in the lithium battery positive electrode precursor preparation method of the present invention; Figure 3 is a structural principle diagram of the electromagnetic slurry magnetic separator shown in Figure 2.

[0018] In the diagram: 1. Magnetic separation channel, 2. Electromagnetic coil, 3. Magnetic medium, 301. Vertical connecting shaft, 302. Magnetic mesh, 4. Feed pipe, 5. Discharge pipe, 6. Feed valve, 7. Discharge valve, 8. Shell, 9. Heat exchanger, 10. Cooling medium inlet, 11. Cooling medium outlet, 12. Thermal insulating oil inlet, 13. Thermal insulating oil outlet. Detailed Implementation

[0019] Referring to Figure 1, this invention discloses a method for preparing a lithium battery positive electrode precursor. The method mainly includes the following steps: Step S100, mixing active material, conductive agent, binder, and solvent to form a positive electrode slurry; Step S200, passing the positive electrode slurry through an electromagnetic slurry magnetic separator to remove magnetic foreign particles contained in the slurry; Step S300, coating the magnetically separated positive electrode slurry onto a metal current collector to obtain the lithium battery positive electrode precursor. Example 1

[0020] The material preparation stage involves preparing the materials used to fabricate the positive electrode sheet for lithium batteries. These mainly include active materials, conductive agents, binders, and current collectors. Active materials include lithium cobalt oxide (LCO), ternary materials (NCM / NCA), or lithium iron phosphate (LFP), selected according to the battery type. Conductive agents can be selected from carbon black, Super P (super carbon black), carbon nanotubes, etc., to improve electronic conductivity. The binder uses polyvinylidene fluoride (PVDF), dissolved in N-methylpyrrolidone (NMP) solvent to prepare a binder solution. The current collector uses aluminum foil.

[0021] The material should be stored in a dry environment. Active substances and aluminum foil need to be pre-dried to remove moisture. Vacuum ovens can be used for pre-drying.

[0022] Step S100 involves mixing the active material, conductive agent, binder, and solvent to form a positive electrode slurry. The equipment used can be a planetary mixer or a twin-screw mixer. The specific operation of this step is as follows: The positive electrode active material and conductive agent are initially mixed. The resulting mixture is then added to a binder solution composed of the binder and solvent, and stirred to form a homogeneous slurry. During stirring, bubble generation must be avoided; vacuum degassing can be used if necessary. The particle size distribution and conductivity of the slurry are then checked to ensure no agglomeration. A laser particle size analyzer can be used to check the particle size distribution.

[0023] Step S200 involves passing the positive electrode slurry through an electromagnetic slurry magnetic separator to remove magnetic foreign particles. Referring to Figures 2 and 3, the electromagnetic slurry magnetic separator used in this step includes a magnetic separation channel 1 through which the positive electrode slurry can pass and an electromagnetic coil 2 surrounding the magnetic separation channel 1. A magnetically conductive medium 3 is provided within the magnetic separation channel 1. The electromagnetic coil 2 generates a magnetic field when energized, and the magnetically conductive medium 3 adsorbs magnetic foreign particles in the positive electrode slurry when magnetized by the magnetic field generated by the electromagnetic coil 2. The magnetically conductive medium 3 includes a vertical connecting shaft 301 installed within the magnetic separation channel 1 and several magnetically conductive meshes 302 mounted on the vertical connecting shaft 301. The magnetic separation channel 1 is connected to a feed pipe 4 and a discharge pipe 5, which are respectively connected to both ends of the magnetic separation channel 1, and each pipe is equipped with a feed valve 6 and a discharge valve 7. Opening the feed valve 6 and the discharge valve 7 allows the slurry to pass through the magnetic separation channel 1. The electromagnetic coil 2 is energized to generate a magnetic field, which can magnetize the magnetic mesh 302 and attract magnetic foreign objects in the slurry. After a period of use, the vertical connecting shaft 301 and the magnetic mesh 302 can be disassembled as a whole, cleaned, and reused.

[0024] Referring to Figures 2 and 3, the electromagnetic slurry magnetic separator has been further improved. The improved electromagnetic slurry magnetic separator also includes a housing 8 and a heat exchanger 9. The electromagnetic coil 2 is installed inside the housing 8. The heat exchanger 9 has a cooling medium channel and a thermally conductive insulating oil channel for heat exchange. The heat exchanger 9 is provided with a cooling medium inlet 10 and a cooling medium outlet 11 that connect to the cooling medium channel. The heat exchanger 9 is also provided with a thermally conductive insulating oil inlet 12 and a thermally conductive insulating oil outlet 13 that connect to the thermally conductive insulating oil channel. The thermally conductive insulating oil inlet 12 is connected to the inner cavity of the housing 8 through a first section of the thermally conductive insulating oil circulation pipeline, and the thermally conductive insulating oil outlet 13 is connected to the inner cavity of the housing 8 through a second section of the thermally conductive insulating oil circulation pipeline, thus forming a closed loop. The cooling medium inlet 10 and the cooling medium outlet 11 can be connected to a cooling medium supply device. After absorbing the heat dissipated by the electromagnetic coil 2 within the housing 8, the thermally conductive insulating oil enters the heat exchanger 9 through the thermally conductive insulating oil circulation pipeline. There, it exchanges heat with the cooling medium before returning to the housing 8, thus providing oil cooling for the electromagnetic coil 2 within the housing 8 and ensuring that the electromagnetic slurry magnetic separator can continuously provide a high magnetic field strength. A thermally conductive insulating oil circulation pump can be installed on the thermally conductive insulating oil circulation pipeline to enhance the circulation of the thermally conductive insulating oil and improve the cooling effect on the electromagnetic coil 2.

[0025] Because adsorbing magnetic foreign matter in the positive electrode slurry requires a high magnetic field strength, and the production line space is limited, the electromagnetic slurry magnetic separator cannot be too large, and its external dimensions must meet the installation space requirements. The electromagnetic slurry magnetic separator with the above-described structure can be manufactured in a smaller size. By setting up an oil circulation cooling device (including the aforementioned heat-conducting insulating oil circulation pipeline, heat exchanger, etc.), without increasing the size of the electromagnetic slurry magnetic separator and ensuring good heat dissipation of the electromagnetic coils 2, the magnetic field strength can be enhanced by selecting high-performance electromagnetic materials, setting more electromagnetic coils 2 inside the housing 8, and optimizing the overall structure. Preferably, the inner diameter of the magnetic cavity of the magnetic separation channel 1 is ≤150mm, and the magnetic field strength within the magnetic separation channel 1 is ≥3000GS. When using this electromagnetic slurry magnetic separator, the following precautions should be taken: 1. Clean the magnetic medium 3 regularly, avoiding contamination during cleaning; 2. Regularly check the magnetic content before and after magnetic separation. The magnetic content after magnetic separation should be lower than before. If any abnormality occurs, find the cause and handle it promptly.

[0026] Step S300 involves coating the magnetically separated positive electrode slurry onto a metal current collector to obtain the lithium battery positive electrode precursor. This step employs a slot extrusion coating method. During the coating process, it is crucial to prevent slurry overflow that could cause burrs. The coating thickness and surface uniformity are monitored online during the coating process, and the coating gap and pressure are adjusted promptly to avoid missed areas or thickness fluctuations.

[0027] After obtaining the lithium battery positive electrode precursor, subsequent processing can be carried out according to the lithium battery positive electrode production process. For example, in step S400, the lithium battery positive electrode precursor is dried to obtain a dried electrode. This step uses segmented heating and drying, which includes an initial stage, a main drying stage, and a final stage where the drying temperature increases sequentially. The equipment used in this step can be a multi-layer conveyor oven or a vertical oven. During the drying process, the drying rate and humidity need to be controlled to avoid cracking or edge curling.

[0028] Step S500 involves rolling the dried electrode sheet to obtain the positive electrode sheet for a lithium battery. This step can be performed using a roll press; some materials require heated rollers to reduce internal stress. An online thickness gauge is used for real-time feedback during rolling to ensure thickness consistency. Example 2

[0029] Based on Example 1, this embodiment further illustrates the optional subsequent steps for preparing a complete electrode from the precursor, including steps S600 and S700.

[0030] Step S600 involves slitting the rolled lithium battery positive electrode sheet into strips, and then cutting these strips into individual electrode sheets. The cutting step uses laser cutting or die punching to shape the strips into individual sheets, such as square or round ones. The cut sheets must be burr-free to prevent short circuits after being manufactured into lithium batteries.

[0031] Step S700 involves welding the metal tabs to the metal current collector of the single electrode sheet; aluminum tabs are used, and the welding method is ultrasonic welding or laser welding. The welding process must meet the requirements of weld tensile testing, and metallographic inspection of the weld quality is also required to avoid incomplete welding or overheating.

[0032] The core of this invention is the addition of a magnetic separation step between the slurry preparation and coating steps. We previously experimented with using permanent magnet slurry magnetic separators, but tests showed that their demagnetization effect was not ideal. After a period of research, trial production, and testing, we developed an electromagnetic slurry magnetic separator with a sufficiently strong magnetic field and a sufficiently small size to remove magnetic foreign matter from the slurry. Trial use has shown that the electromagnetic slurry magnetic separator has a significant demagnetization effect, fully meeting the production line requirements. Below are two sets of measured data: Table 1: Test data on the demagnetization effect of the permanent magnet slurry magnetic separator.

[0033] Tests show that the iron removal effect of permanent magnet slurry magnetic separator is not obvious, especially when the content of magnetic foreign matter in the positive electrode slurry is low, the demagnetization effect is almost zero.

[0034] Table 2: Test data on the demagnetization effect of electromagnetic slurry magnetic separator

[0035] Tests show that electromagnetic slurry magnetic separators have a significant demagnetizing effect on magnetic foreign objects, especially for positive electrode slurries with a high content of magnetic foreign objects, where the removal rate is significantly improved.

[0036] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium battery positive electrode precursor, characterized in that, The method includes the following steps: step S100, preparing a positive electrode slurry; step S200, passing the positive electrode slurry through an electromagnetic slurry magnetic separator to remove magnetic foreign particles contained in the slurry; step S300, coating the magnetically separated positive electrode slurry onto a metal current collector to obtain a lithium battery positive electrode precursor.

2. The method for preparing the lithium battery positive electrode precursor as described in claim 1, characterized in that, In step S200, the electromagnetic slurry magnetic separator used includes a magnetic separation channel (1) through which the positive electrode slurry can pass and an electromagnetic coil (2) arranged around the magnetic separation channel (1). The magnetic separation channel (1) is provided with a magnetic medium (3). The electromagnetic coil (2) is used to generate a magnetic field when energized, and the magnetic medium (3) is used to adsorb magnetic particles in the positive electrode slurry when magnetized by the magnetic field generated by the electromagnetic coil (2).

3. The method for preparing the lithium battery positive electrode precursor as described in claim 2, characterized in that, The magnetic medium (3) includes a vertical connecting shaft (301) installed in the magnetic separation channel (1) and several magnetic mesh sheets (302) on the vertical connecting shaft (301). The magnetic separation channel (1) is connected to a feed pipe (4) and a discharge pipe (5). The feed pipe (4) and the discharge pipe (5) are respectively connected to the two ends of the magnetic separation channel (1).

4. The method for preparing the lithium battery positive electrode precursor as described in claim 2, characterized in that, The electromagnetic slurry magnetic separator also includes a housing (8) and a heat exchanger (9). The electromagnetic coil (2) is installed inside the housing (8). The heat exchanger (9) has a cooling medium channel and a thermally conductive insulating oil channel that can exchange heat. The heat exchanger (9) is provided with a cooling medium inlet (10) and a cooling medium outlet (11) that connect to the cooling medium channel. The heat exchanger (9) is provided with a thermally conductive insulating oil inlet (12) and a thermally conductive insulating oil outlet (13) that connect to the thermally conductive insulating oil channel. The thermally conductive insulating oil inlet (12) is connected to the inner cavity of the housing (8) through the first section of the thermally conductive insulating oil circulation pipeline. The thermally conductive insulating oil outlet (13) is connected to the inner cavity of the housing (8) through the second section of the thermally conductive insulating oil circulation pipeline, thereby forming a closed loop.

5. The method for preparing a lithium battery positive electrode precursor as described in any one of claims 2 to 4, characterized in that, The inner diameter of the magnetic cavity of the magnetic separation channel (1) is ≤150mm, and the magnetic field strength in the magnetic separation channel (1) is ≥3000GS.

6. The method for preparing the lithium battery positive electrode precursor as described in claim 1, characterized in that, The step S100 specifically includes: step S110, preliminarily mixing the positive electrode active material and the conductive agent; step S120, adding a binder solution composed of a binder and a solvent to the mixture obtained in step S110, and stirring to form a homogeneous slurry, wherein the binder is polyvinylidene fluoride and the solvent is N-methylpyrrolidone.

7. The method for preparing the lithium battery positive electrode precursor according to claim 6, characterized in that, The positive electrode active material in step S100 is selected from lithium cobalt oxide, ternary materials or lithium iron phosphate; the conductive agent includes carbon black, Super P or carbon nanotubes.

8. The method for preparing the lithium battery positive electrode precursor as described in claim 1, characterized in that, In step S300, the coating is performed using a slot extrusion coating method.

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