Preparation method of electrode plate and battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a preparation method of an electrode pole piece and a battery, and the preparation method of the electrode pole piece comprises the following steps: mixing an electrode active material, a pore forming agent and a magnetic inorganic matter to form a mixture; attaching the mixture to a current collector; applying a magnetic field to the current collector attached with the mixture; and removing the pore-forming agent and the magnetic inorganic matter in the mixture. The internal tortuosity of the pole piece can be reduced, and the electrochemical performance of the battery prepared from the pole piece can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a method for preparing an electrode pole piece and a battery. Background Art

[0002] As an advanced manufacturing process, dry electrode technology has broad application prospects due to its significant advantages such as energy saving, cost reduction, high efficiency and environmental protection.

[0003] The preparation process of dry electrodes includes dry spray deposition, polymer fiberization, and melt extrusion. Among them, the melt extrusion method combines material mixing and molding, which not only ensures the uniformity and quality of electrode materials, but also is environmentally friendly and easy to scale up.

[0004] The thickness of the pole piece prepared by melt extrusion can reach several hundred microns, but its dynamic performance is severely limited during the charge and discharge cycle. In the existing technical solutions, the main purpose of pore formation in the pole piece is to increase the porosity. During the degreasing process, the pore former is removed, thereby increasing the porosity of the pole piece. However, this process does not reduce the tortuosity of the lithium ion transmission channel inside the pole piece (the path is longer), resulting in limited dynamics.

[0005] Reducing the tortuosity of the electrode is of great significance for improving the performance of lithium-ion batteries. Existing studies have shown that low-tortuosity electrodes can promote lithium ion diffusion and reduce concentration polarization, and the effective ion conductivity is inversely proportional to the tortuosity of the electrode. In order to improve the permeability of the electrolyte and the migration rate of ions, the design of electrode structures with low tortuosity has become a key principle in the design of porous electrodes. The pores in the electrode in the existing technical solutions can only increase the porosity of the electrode, but cannot reduce the tortuosity of the electrode.

[0006] Therefore, it is necessary to further improve the internal structure of the electrode and reduce the tortuosity of the lithium ion transmission channel, so as to effectively improve the charging and discharging performance of the battery and meet application scenarios with higher performance requirements. Summary of the invention

[0007] In order to overcome the above-mentioned defects, the present invention proposes a method for preparing an electrode plate and a battery, which can reduce the tortuosity inside the electrode plate and thus improve the electrochemical performance of the battery.

[0008] In a first aspect, the present invention provides a method for preparing an electrode sheet, comprising:

[0009] Mixing the electrode active material, the pore-forming agent and the magnetic inorganic substance to form a mixture;

[0010] attaching the mixture to a current collector;

[0011] applying a magnetic field to the current collector to which the mixture is attached;

[0012] The pore former and the magnetic inorganic material are removed from the mixture.

[0013] Furthermore, the magnetic inorganic substance is at least one of magnetic nylon particles, magnetic nylon rods and magnetic nylon sheets.

[0014] Furthermore, the magnetic nylon particles have a fineness of 125-12500 mesh.

[0015] Furthermore, the weight ratio of the electrode active material, the pore-forming agent and the magnetic inorganic material is (40-60): (30-50): (2-8).

[0016] Further, applying a magnetic field to the current collector to which the mixture is attached comprises:

[0017] A magnetic field perpendicular to the current collector is applied to the current collector to which the mixture is attached.

[0018] Furthermore, applying a magnetic field to the current collector to which the mixture is attached further comprises:

[0019] The magnetic field is applied for a preset time period.

[0020] Furthermore, the preset duration is 30-90s.

[0021] Further, attaching the mixture to a current collector comprises:

[0022] The mixture is attached to a current collector by heat pressing.

[0023] Further, attaching the mixture to the current collector by hot pressing comprises:

[0024] The mixture is extruded at 150-200° C. and 50-150 MPa to form a film and adhere to the current collector.

[0025] Further, the removing of the pore former and the magnetic inorganic substance in the mixture comprises:

[0026] The mixture is calcined at high temperature to remove the pore former and magnetic inorganic substances.

[0027] Furthermore, the high temperature calcination includes 800-1000° C. for 1-5 hours.

[0028] Furthermore, the pore-forming agent includes one or more of polypropylene, paraffin and stearic acid.

[0029] Furthermore, when the pore-forming agent contains paraffin, the removing of the pore-forming agent from the mixture further comprises:

[0030] The current collector to which the mixture is attached is immersed in an organic solvent to remove the paraffin wax.

[0031] Furthermore, the organic solvent includes at least one of n-heptane, 2-methyloctane and 3-methyloctane.

[0032] Furthermore, the pore-forming agent comprises polypropylene, paraffin wax and stearic acid, wherein the mass ratio of the polypropylene, paraffin wax and stearic acid is (40-60):(30-50):(2-6).

[0033] Furthermore, the surface of the magnetic inorganic substance is coated with a polydopamine film.

[0034] In a second aspect, the present invention provides an electrode plate prepared by the method described in the first aspect.

[0035] In a third aspect, the present invention provides a lithium-ion battery comprising the electrode plate as described in the second aspect.

[0036] The above one or more technical solutions of the present invention have at least one or more of the following beneficial effects:

[0037] In the technical solution of the present invention, a self-sacrificial magnetic inorganic substance is introduced, which can be arranged in a directional manner under the action of a magnetic field, thereby forming an ordered structure in the electrode material. This ordered structure is of great significance for improving the performance of the electrode material.

[0038] At the same time, the magnetic inorganic substance can volatilize during the calcination process and will not pollute other components of the electrode material. The volatilized magnetic substance leaves pores inside the electrode material. These pores and the holes formed by the pore-forming agent significantly improve the channels for lithium ion transmission, help improve the transmission efficiency of lithium ions and effectively reduce the tortuosity inside the pole piece, thereby improving the overall performance of the battery.

[0039] The preparation process of the invention is simple and easy to control, which is beneficial to reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The disclosure of the present invention will become more easily understood with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the figures are used to represent similar components, among which:

[0041] Figure 1 It is a schematic flow chart of main steps of a method for preparing an electrode sheet according to an embodiment of the present invention;

[0042] Figure 2 It is a schematic diagram of the process of preparing a dry-process electrode sheet with low tortuosity according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] Some embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0044] The present invention proposes a method for preparing an electrode plate, referring to Figure 1 ,include:

[0045] S1, mixing an electrode active material, a pore-forming agent and a magnetic inorganic substance to form a mixture;

[0046] S2, attaching the mixture to a current collector;

[0047] S3, applying a magnetic field to the current collector to which the mixture is attached;

[0048] S4, removing the pore-forming agent and the magnetic inorganic substance from the mixture.

[0049] The present invention mixes a magnetic inorganic substance with an electrode active substance and a pore-forming agent, and then coats the mixture on the surface of the current collector. After applying a magnetic field, the magnetic inorganic substance is arranged in a directional manner under the guidance of the external magnetic field. Finally, the pore-forming agent and the magnetic inorganic substance are removed. The pore-forming agent forms a hole-like cavity in the pole piece, thereby increasing the porosity of the pole piece. The magnetic inorganic substance forms a channel-like void, thereby reducing the tortuosity of the electrode. In addition, the magnetic inorganic substance and the pore-forming agent also form voids of different sizes and gradients, which are helpful for the rapid deintercalation of lithium ions, thereby improving the rate performance.

[0050] The present invention firstly fully mixes the magnetic inorganic substance with the electrode active substance and the pore-forming agent. The preparation of the mixture needs to ensure that each component is evenly distributed so as to achieve ideal performance during the coating process.

[0051] Next, the mixture is evenly coated on the surface of the current collector. During the coating process, the coating thickness and uniformity need to be controlled to ensure the subsequent performance of the electrode.

[0052] After coating, a magnetic field is applied to the mixture. At this time, the magnetic inorganic material begins to be oriented under the guidance of the external magnetic field. The oriented arrangement of the magnetic inorganic material helps to further increase the porosity of the electrode and reduce the tortuosity.

[0053] Subsequently, the pore former and the magnetic inorganic material are removed. In this process, the pore former forms pore-like cavities in the electrode, thereby increasing the porosity of the electrode. The formation of these pores facilitates the transport of lithium ions within the electrode, thereby improving the performance of the electrode.

[0054] In addition, after the removal of the magnetic inorganic material, channel-like voids are formed. The distribution and size of these voids help reduce the tortuosity of the electrode, making the lithium ion insertion and extraction process smoother. At the same time, the magnetic inorganic material and the pore-forming agent also jointly form voids with different size gradients, which help lithium ions to quickly extract and extract in different states, thereby improving the rate performance of the electrode.

[0055] Therefore, the present invention prepares an electrode material with high porosity, low tortuosity and excellent rate performance by mixing magnetic inorganic substances and pore-forming agents and guiding the magnetic field.

[0056] In one embodiment, the magnetic inorganic substance is a magnetic nylon material, specifically, at least one of magnetic nylon particles, magnetic nylon rods and magnetic nylon sheets.

[0057] Magnetic nylon particles are zero-dimensional materials, magnetic nylon rods are one-dimensional materials, and magnetic nylon sheets are two-dimensional materials.

[0058] Magnetic nylon particles are a zero-dimensional material characterized by their amorphous or small particle structure.

[0059] Magnetic nylon rods are one-dimensional materials with a long strip structure and obvious directionality.

[0060] Magnetic nylon sheet is a two-dimensional material with a thin sheet structure and a layered structure.

[0061] In one embodiment, the magnetic nylon particles have a fineness of 125-12500 mesh.

[0062] In one embodiment, the weight ratio of the electrode active material, the pore-forming agent and the magnetic inorganic material is (40-60): (30-50): (2-8).

[0063] In one embodiment, the weight ratio of the electrode active material, the pore-forming agent and the magnetic inorganic material is 55:42:(2-8).

[0064] In one embodiment, in step S1, the electrode active material, the pore-forming agent and the magnetic inorganic material are mixed in a ball mill or a mixer for 30-120 minutes until the materials are uniform.

[0065] In one embodiment, in step S2, attaching the mixture to a current collector comprises:

[0066] S21, attaching the mixture to a current collector by hot pressing.

[0067] The key parameters of hot pressing are providing temperature and pressure. In one embodiment, attaching the mixture to the current collector by hot pressing comprises:

[0068] The mixture is extruded at 150-200° C. and 50-150 MPa to form a film and adhere to the current collector.

[0069] In one application scenario, the film is extruded through a single screw extruder at high temperature and hot pressing (150-200°C, 50-150MPa).

[0070] In one embodiment, in step S3, applying a magnetic field to the current collector to which the mixture is attached comprises:

[0071] A magnetic field perpendicular to the current collector is applied to the current collector to which the mixture is attached.

[0072] In one embodiment, applying a magnetic field to the current collector to which the mixture is attached further comprises: applying the magnetic field for a preset time period to align the magnetic inorganic substances in a directional manner.

[0073] In one embodiment, the preset duration is 30-90s.

[0074] The arrangement of magnetic inorganic substances needs to be guided by the magnetic field. Specifically, the role of the magnetic field is to make the magnetic inorganic substances align along the direction of the magnetic lines of force. In order to achieve the goal of fully directional arrangement of all magnetic inorganic substances, only by ensuring sufficient magnetic application time can we ensure that each magnetic inorganic substance has enough time to be guided by the magnetic field and finally arranged in place. This process is like "cultivating" the arrangement of magnetic inorganic substances in a magnetic field. The longer the time, the better the arrangement effect. However, the longer the time, the higher the energy consumption.

[0075] Therefore, in order to achieve a fully oriented arrangement of the magnetic inorganic substances, it is necessary to apply a magnetic field on the current collector for a sufficient period of time and ensure that the magnetic field strength is moderate and evenly distributed, so that each magnetic inorganic substance can be guided and arranged in place.

[0076] In one embodiment, in step S4, removing the pore-forming agent and the magnetic inorganic substance in the mixture comprises:

[0077] S41, calcining at high temperature to remove the pore former and magnetic inorganic matter in the mixture.

[0078] In one embodiment, the high temperature calcination includes 800-1000° C. for 1-5 hours.

[0079] During the high temperature calcination process (800-1000℃), the magnetic inorganic substances are volatilized and removed to form a directional lithium ion transmission channel. Usually, the pore former can also be removed at high temperature.

[0080] In one embodiment, the pore-forming agent includes one or more of polypropylene, paraffin and stearic acid.

[0081] In one embodiment, the pore-forming agent includes polypropylene, paraffin wax and stearic acid, wherein the mass ratio of the polypropylene, paraffin wax and stearic acid is (40-60):(30-50):(2-6).

[0082] In one embodiment, when the pore-forming agent contains paraffin, the removing of the pore-forming agent from the mixture further comprises:

[0083] The current collector to which the mixture is attached is immersed in an organic solvent to remove the paraffin wax.

[0084] In a specific embodiment of the electrode manufacturing, when the pore former component includes paraffin wax, the process of removing the pore former from the mixture involves the following steps:

[0085] First, the current collector with the mixture attached is immersed in an organic solvent to effectively remove the paraffin. The necessity of this step lies in the characteristics of paraffin. When paraffin decomposes at high temperatures, it will produce flammable gases, and the presence of these gases may cause safety hazards. Therefore, in order to improve the safety of the production process, the paraffin is first thoroughly removed by dissolving it in an organic solvent.

[0086] Through the above steps, paraffin is effectively removed from the mixture, thereby avoiding the generation of combustible gas during high-temperature calcination.

[0087] This method of pre-removing paraffin significantly improves the safety of the entire process.

[0088] After the paraffin is completely removed, the current collector will undergo a subsequent high-temperature calcination step.

[0089] High temperature calcination is intended to remove the remaining pore formers in the mixture and ensure that the current collector achieves the desired pore structure and performance.

[0090] By removing the paraffin wax in advance, not only the safety of the process is improved, but also more favorable conditions are created for the subsequent high-temperature calcination process, thus ensuring the smooth progress of the entire battery manufacturing process.

[0091] In one embodiment, the organic solvent for dissolving paraffin includes at least one of n-heptane, 2-methyloctane and 3-methyloctane.

[0092] In one application scenario, the organic solvent is n-heptane, which is used to dissolve paraffin.

[0093] In one embodiment, the surface of the magnetic inorganic material is coated with a polydopamine film.

[0094] In an alkaline environment, a layer of polydopamine is deposited on the surface of the magnetic inorganic material by utilizing the self-polymerization reaction of dopamine.

[0095] In a specific embodiment of pole piece manufacturing, the following process is included:

[0096] 1. Dissolve the dopamine monomer in a suitable solvent. The commonly used solvent is Tris buffer. The pH value of Tris buffer is controlled between 7 and 9. This pH range can ensure the stability and activity of the dopamine monomer in the solution.

[0097] 2. Disperse the magnetic inorganic material in the prepared dopamine solution to ensure that the nanoparticles are evenly dispersed and avoid agglomeration, thereby ensuring the uniformity and effectiveness of subsequent reactions.

[0098] 3. Under alkaline conditions, dopamine molecules will spontaneously undergo oxidative polymerization to form a polydopamine (PDA) layer and attach to the surface of the magnetic inorganic material.

[0099] Under alkaline conditions, dopamine molecules will spontaneously undergo oxidative polymerization. This process is spontaneous and does not require additional catalysts or initiators. Through oxidative polymerization, dopamine molecules gradually form a polydopamine (PDA) layer. This polymer layer has high adhesion and can be tightly attached to the surface of the magnetic inorganic material. Through this process, the polydopamine layer can be tightly attached to the surface of the magnetic inorganic material to form a uniform and stable protective film. The polydopamine layer can maintain the stability of the magnetic inorganic material, inhibit the agglomeration of the magnetic inorganic material, and ensure good dispersion, thereby ensuring its directional arrangement in subsequent applications. Moreover, the polydopamine layer can be converted into gas volatilization during subsequent high-temperature calcination, such as above 800°C.

[0100] In one application scenario, the mass ratio of polydopamine or dopamine to the magnetic inorganic material can be selected to be 1:(1-10).

[0101] It should be pointed out that although the various steps in the above embodiments are described in a specific order, those skilled in the art can understand that in order to achieve the effects of the present invention, different steps do not have to be performed in such an order. They can be performed simultaneously (in parallel) or in other orders. These changes are within the scope of protection of the present invention.

[0102] By the following examples, refer to Figure 2 , illustrating the process of preparing dry electrode sheets with low tortuosity.

[0103] Example 1

[0104] Lithium iron phosphate, magnetic nylon rod, and glue (the mass ratio of polypropylene: paraffin: stearic acid is 50:46:4) are mixed in a stirring tank until the materials are uniform, wherein the mass ratio of lithium iron phosphate, magnetic nylon rod, and glue is 55:2:42.

[0105] After being heated at 180°C by a single screw extruder and extruded at 100 MPa to form a film attached to the copper foil, a magnetic field perpendicular to the aluminum foil was applied for 30 seconds to orient the magnetic inorganic matter. The pole piece was then immersed in n-heptane at 50°C for 3 hours to remove part of the paraffin. Finally, it was calcined at 950°C in an Ar / H2 atmosphere for 2 hours to remove the remaining organic matter and the magnetic nylon rod.

[0106] Example 2

[0107] Lithium iron phosphate, magnetic nylon rod, and glue (the mass ratio of polypropylene: paraffin: stearic acid is 50:46:4) are mixed in a stirring tank until the materials are uniform, wherein the mass ratio of lithium iron phosphate, magnetic nylon rod, and glue is 55:4:42.

[0108] After being heated at 180°C by a single screw extruder and extruded at 100 MPa to form a film attached to the copper foil, a magnetic field perpendicular to the aluminum foil was applied for 30 seconds to orient the magnetic inorganic matter. The pole piece was then immersed in n-heptane at 50°C for 3 hours to remove part of the paraffin. Finally, it was calcined at 950°C in an Ar / H2 atmosphere for 2 hours to remove the remaining organic matter and the magnetic nylon rod.

[0109] Comparative Example 1

[0110] Lithium iron phosphate, magnetic nylon rod, and glue (the mass ratio of polypropylene: paraffin: stearic acid is 50:46:4) are mixed in a stirring tank until the materials are uniform, wherein the mass ratio of lithium iron phosphate, magnetic nylon rod, and glue is 55:10:42.

[0111] After being heated at 180°C by a single screw extruder and extruded at 100 MPa to form a film attached to the copper foil, a magnetic field perpendicular to the aluminum foil was applied for 30 seconds to orient the magnetic inorganic matter. The pole piece was then immersed in n-heptane at 50°C for 3 hours to remove part of the paraffin. Finally, it was calcined at 950°C in an Ar / H2 atmosphere for 2 hours to remove the remaining organic matter and the magnetic nylon rod.

[0112] Comparative Example 2

[0113] Lithium iron phosphate and glue (the mass ratio of polypropylene: paraffin: stearic acid is 50:46:4) are mixed in a stirring tank until the materials are uniform, wherein the mass ratio of lithium iron phosphate to glue is 55:42.

[0114] After being heated at 180°C by a single screw extruder and extruded at 100 MPa to form a film attached to an aluminum foil, the electrode was then immersed in n-heptane at 50°C for 3 hours to remove part of the paraffin, and finally calcined at 950°C in an Ar / H2 atmosphere for 2 hours to remove the remaining organic matter.

[0115] Example 3

[0116] Lithium titanate, magnetic nylon rod, and glue (the mass ratio of polypropylene: paraffin: stearic acid is 50:46:4) are mixed in a stirring tank until the materials are uniform, wherein the mass ratio of lithium titanate, magnetic nylon rod, and glue is 60:2.3:42.

[0117] After being heated at 200°C by a single screw extruder and extruded at 110 MPa to form a film attached to the copper foil, a magnetic field perpendicular to the copper foil was applied for 30 seconds to orient the magnetic inorganic matter. The pole piece was then immersed in n-heptane at 50°C for 3 hours to remove part of the paraffin. Finally, it was calcined at 1000°C in an Ar / H2 atmosphere for 2 hours to remove the remaining organic matter and magnetic nylon rods.

[0118] Example 4

[0119] Lithium titanate, magnetic nylon rod, and glue (the mass ratio of polypropylene: paraffin: stearic acid is 50:46:4) are mixed in a stirring tank until the materials are uniform, wherein the mass ratio of lithium titanate, magnetic nylon rod, and glue is 60:4:42.

[0120] After being heated at 200°C by a single screw extruder and extruded at 110 MPa to form a film attached to the copper foil, a magnetic field perpendicular to the copper foil was applied for 30 seconds to orient the magnetic inorganic matter. The pole piece was then immersed in n-heptane at 50°C for 3 hours to remove part of the paraffin. Finally, it was calcined at 1000°C in an Ar / H2 atmosphere for 2 hours to remove the remaining organic matter and magnetic nylon rods.

[0121] Comparative Example 3

[0122] Lithium titanate, magnetic nylon rod, and glue (the mass ratio of polypropylene: paraffin: stearic acid is 50:46:4) are mixed in a stirring tank until the materials are uniform, wherein the mass ratio of lithium titanate, magnetic nylon rod, and glue is 60:10:42.

[0123] After being heated at 200°C by a single screw extruder, it is extruded into a film at 110MPa and attached to the copper foil. During this process, a magnetic field perpendicular to the copper foil is applied for 30s to orient the magnetic inorganic matter. Then the pole piece is immersed in n-heptane at 50°C for 3h to remove part of the paraffin. Finally, it is calcined at 1000°C in Ar / H2 atmosphere for 2h to remove the remaining organic matter and magnetic nylon rods.

[0124] Comparative Example 4

[0125] Lithium titanate and glue (the mass ratio of polypropylene: paraffin: stearic acid is 50:46:4) are mixed in a stirring tank until the materials are uniform, wherein the mass ratio of lithium titanate to glue is 60:42.

[0126] After being heated at 200°C by a single screw extruder and extruded at 110 MPa to form a film attached to the copper foil, the electrode was then immersed in n-heptane at 50°C for 3 hours to remove part of the paraffin, and finally calcined at 1000°C in an Ar / H2 atmosphere for 2 hours to remove the remaining organic matter.

[0127] Example 5

[0128] Lithium titanate, magnetic nylon sheet and glue (polypropylene: paraffin: stearic acid mass ratio is 40:50:2) are mixed in a weight ratio of 40:8:30, and mixed in a stirring tank until the materials are uniform.

[0129] The film is heated at 150℃ and extruded at 150MPa by a single screw extruder and attached to the copper foil. During this process, a magnetic field perpendicular to the copper foil is applied for 50s to orient the magnetic inorganic matter. Then the pole piece is immersed in n-heptane at 50℃ for 3h to remove part of the paraffin. Finally, it is calcined at 800℃ in Ar / H2 atmosphere for 5h to remove the remaining organic matter and magnetic nylon sheet.

[0130] Example 6

[0131] Lithium titanate, magnetic nylon particles (the particle size of the magnetic nylon particles is 12500 mesh and the particle size is 1 μm) and glue (the mass ratio of polypropylene: paraffin: stearic acid is 60:30:6) are mixed in a weight ratio of 50:5:50, mixed in a stirring tank until the materials are uniform, heated at 190°C by a single screw extruder and extruded at 50 MPa to form a film attached to a copper foil. In this process, a magnetic field perpendicular to the copper foil is applied for 90 seconds to orient the magnetic inorganic matter. After that, the pole piece is immersed in n-heptane at 50°C for 3 hours to remove part of the paraffin wax, and finally calcined at 1000°C in an Ar / H2 atmosphere for 1 hour to remove the remaining organic matter and magnetic nylon particles.

[0132] The present invention also provides a battery pole piece, which is prepared by the above method.

[0133] The present invention also provides a lithium ion battery, comprising an electrode plate prepared by the above method.

[0134] The electrode plates prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to ionic impedance tests and cycle tests. The specific test methods are as follows:

[0135] Ionic impedance test method: The electrode is cut into 16mm diameter discs by a cutting machine, two discs are placed on both sides of the celgard2025 separator, and 20μl of electrolyte (1molLiPF6EC / DMC (3:7v:v)) is added to assemble into a button cell, and an EIS test is performed (frequency: 0.01-10 6Hz, voltage: 0.05V). The intersection of the extended line of the low frequency region of the EIS curve and the horizontal axis minus 1 / 3 of the intersection of the extended line of the high frequency region curve and the horizontal axis is the ionic impedance R. i .

[0136] Cycle test method: The electrode is cut into discs with a diameter of 14 mm by a cutting machine. One disc is placed on one side of the celgard2025 separator and a lithium sheet with a diameter of 15.7 mm is placed on the other side. 20 μl of electrolyte (1 mol LiPF6EC / DMC (3:7 v:v)) is added dropwise to assemble a button half-cell. A constant current cycle test is performed (after 5 cycles of activation at 0.01C, a constant current test at 0.33C) is performed, and the number of cycles when the capacity drops to 80% is recorded.

[0137] The test results are shown in Table 1.

[0138] Table 1 Comparison of electrode appearance and electrical properties of different examples

[0139]

[0140] After an in-depth study of the data of Examples 1-2 and Comparative Examples 1-2 in Table 1, it can be seen that the introduction of magnetic inorganics has a significant effect on the battery performance compared with Example 1 and Comparative Example 2. Specifically, by adding magnetic inorganics, the ionic impedance is reduced from 9.8Ω / cm2 (Comparative Example 2 does not add magnetic inorganics) to 5.4Ω / cm2 (Example 1). This change is quite significant. Magnetic inorganics can effectively reduce the transmission resistance of ions in the electrolyte, thereby improving the overall performance of the battery. At the same time, the cycle life of the battery is also increased from 53 cycles to 87 cycles. This improvement can be attributed to the optimization of the pole piece structure by magnetic inorganics. The addition of magnetic inorganics reduces the tortuosity of the pole piece and reduces obstacles in the ion transmission process, thereby extending the service life of the battery.

[0141] As can be seen from Examples 1 and 2, as the amount of magnetic inorganic substances added is further increased, the electrochemical performance of the battery is further improved. Specifically, the kinetic performance of the pole piece is enhanced, and the ionic impedance is further reduced to 2.7Ω / cm2. This change further increases the cycle life of the battery from 87 cycles to 106 cycles. This shows that the appropriate addition of magnetic inorganic substances plays an important role in improving battery performance.

[0142] However, this does not mean that the addition of magnetic nylon rods can be increased at will. As shown in the data of Comparative Example 1, when the content of magnetic nylon rods continues to increase, the quality of the pole piece is difficult to guarantee. In this case, the pole piece has serious cracking, which directly affects the performance and stability of the battery. Therefore, when adding magnetic inorganic substances, its content needs to be strictly controlled to ensure the overall performance and reliability of the battery.

[0143] The above technical effects are also applicable to negative electrode materials. Adding magnetic inorganic substances (Examples 3-6) to the negative electrode active material can improve the electrochemical performance of the battery, but the amount added must be moderate. If the amount added is too much, not only will the performance not be improved, but the pole piece will also crack and become unusable.

[0144] Combining the above embodiments and experimental data, it can be seen that the present invention introduces a self-sacrificing magnetic material that can be arranged in a directional manner under the action of a magnetic field, thereby forming an ordered structure in the electrode material. This ordered structure is of great significance for improving the performance of the electrode material.

[0145] At the same time, the magnetic substance can volatilize during the calcination process and will not pollute other components of the electrode material. The volatilized magnetic substance leaves pore cavities inside the electrode material. The holes formed by these pore cavities and the pore-forming agent cavities significantly improve the channels for lithium ion transmission and help improve the transmission efficiency of lithium ions. The introduction of this self-sacrificial magnetic substance can effectively reduce the tortuosity inside the pole piece. Tortuosity refers to the degree of tortuosity of the path when lithium ions are transmitted inside the pole piece. Reducing the tortuosity means that the lithium ion transmission path is more direct, thereby reducing the transmission resistance and improving the overall performance of the battery.

[0146] In terms of process, the present invention has the advantage of being easy to scale up. Since the self-sacrificial magnetic material (magnetic inorganic material) can volatilize during the calcination process, no additional waste will remain in the production process, especially in the electrode material, which is conducive to large-scale production. In addition, the process flow is simple and easy to control, which is conducive to reducing production costs.

[0147] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for preparing an electrode sheet, It is characterized in that include: Mixing the electrode active material, the pore-forming agent and the magnetic inorganic substance to form a mixture; attaching the mixture to a current collector; applying a magnetic field to the current collector to which the mixture is attached; The pore former and the magnetic inorganic material are removed from the mixture.

2. The method according to claim 1, It is characterized in that The magnetic inorganic substance is at least one of magnetic nylon particles, magnetic nylon rods and magnetic nylon sheets.

3. The method according to claim 2, It is characterized in that The magnetic nylon particles have a fineness of 125-12500 meshes.

4. The method according to claim 1, It is characterized in that The weight ratio of the electrode active material, the pore-forming agent and the magnetic inorganic material is (40-60): (30-50): (2-8).

5. The method according to claim 1, It is characterized in that The step of applying a magnetic field to a current collector to which the mixture is attached comprises: A magnetic field perpendicular to the current collector is applied to the current collector to which the mixture is attached.

6. The method according to claim 1 or 5, It is characterized in that The step of applying a magnetic field to the current collector to which the mixture is attached further comprises: The magnetic field is applied for a preset time period.

7. The method according to claim 6, It is characterized in that The preset duration is 30-90s.

8. The method according to claim 1, It is characterized in that The attaching the mixture to the current collector comprises: The mixture is attached to a current collector by heat pressing.

9. The method according to claim 8, It is characterized in that The step of attaching the mixture to the current collector by hot pressing comprises: The mixture is extruded at 150-200° C. and 50-150 MPa to form a film and adhere to the current collector.

10. The method according to claim 1, It is characterized in that The removing of the pore former and the magnetic inorganic substance in the mixture comprises: The mixture is calcined at high temperature to remove the pore former and magnetic inorganic substances.

11. The method according to claim 10, It is characterized in that The high temperature calcination includes 800-1000° C. for 1-5 hours.

12. The method according to claim 1, It is characterized in that The pore-forming agent includes one or more of polypropylene, paraffin and stearic acid.

13. The method according to claim 12, It is characterized in that When the pore-forming agent contains paraffin, the step of removing the pore-forming agent from the mixture further comprises: The current collector to which the mixture is attached is immersed in an organic solvent to remove the paraffin wax.

14. The method according to claim 13, It is characterized in that The organic solvent includes at least one of n-heptane, 2-methyloctane and 3-methyloctane.

15. The method according to claim 12, It is characterized in that The pore-forming agent comprises polypropylene, paraffin wax and stearic acid, wherein the mass ratio of the polypropylene, paraffin wax and stearic acid is (40-60):(30-50):(2-6).

16. The method according to claim 1, It is characterized in that The surface of the magnetic inorganic substance is coated with a polydopamine film.

17. An electrode plate, It is characterized in that Prepared by the method according to any one of claims 1 to 16.

18. A lithium ion battery, It is characterized in that Comprising the electrode plate as described in claim 17.

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