Lithium ion battery negative electrode plate preparation method based on electric field regulation and control and gradient electrode plate

Abstract

The invention provides a lithium ion battery negative electrode plate preparation method based on electric field regulation and control and a gradient electrode plate, and the preparation method comprises the following steps: coating a negative electrode current collector with negative electrode slurry to obtain a first electrode plate; applying a pulsed electric field to the upper surface and the lower surface of the first pole piece to obtain a second pole piece; and baking the second pole piece to obtain the dry lithium ion battery negative pole piece. The negative electrode slurry particles are directionally arranged to form a gradient structure through pulse electric field regulation and control, the ion transmission path is optimized, the problem of transmission path extension caused by a thick pole piece is effectively relieved, and the method has the advantages of improving the ion transmission performance, reducing the interface resistance and improving the comprehensive electrochemical performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a method for preparing a lithium-ion battery negative electrode sheet based on electric field regulation and a gradient electrode sheet. Background Technology

[0002] Lithium-ion batteries, as a representative of new energy sources, are widely used in energy storage, electric vehicles, and other fields. With the continuous development of new energy technologies, there is an urgent need for high-energy-density lithium-ion batteries. Currently, methods to improve the energy density of lithium-ion batteries mainly include material innovation, cell weight reduction, and innovation in battery pack systems. From a design perspective, the ideal way to improve energy density is to reduce the proportion of inactive components and increase the thickness of the lithium-ion battery electrode sheets, which can significantly increase the load of active materials, thereby improving the battery's energy density. However, in practical applications, increasing the thickness of the negative electrode sheet leads to a proportional increase in the electron and ion transport distance and resistance. This results in poor electrode conductivity, lower lithium intercalation capacity of thicker electrodes, and further lower usable capacity and rate performance of the battery.

[0003] Patent application number 2024204893461 discloses a fast-charging negative electrode. In this electrode, a first graphite layer is coated on both sides of the current collector; a second graphite layer is coated on top of the first graphite layer, and the porosity of the second graphite layer is higher than that of the first graphite layer. Multiple vertically extending linear lithium-ion diffusion channels are arrayed on the top surface of the second graphite layer, giving the electrode a gradient pore structure with high surface porosity and low tortuosity, and low internal porosity, thus balancing rate performance and energy density. However, the aforementioned fast-charging negative electrode exhibits abrupt changes in longitudinal porosity, making it difficult to achieve a porosity gradient. Summary of the Invention

[0004] This invention provides a method for preparing lithium-ion battery negative electrode sheets based on electric field control and a gradient electrode sheet, which can be used to solve the problem of abrupt changes in longitudinal porosity of electrode sheets in the prior art, making it difficult to achieve a gradient change in porosity.

[0005] In a first aspect, the present invention provides a method for preparing a lithium-ion battery negative electrode based on electric field modulation, comprising: The negative electrode slurry is coated onto the negative electrode current collector to obtain the first electrode sheet; A pulsed electric field is applied to the upper and lower surfaces of the first electrode to obtain the second electrode; The second electrode is baked to obtain a dry lithium-ion battery negative electrode.

[0006] For example, the step of coating the negative electrode slurry onto the negative electrode current collector to obtain the first electrode includes: A negative electrode slurry consisting of 95wt%-96.5wt% graphite, 0.8wt%-1.5wt% conductive carbon black, 1.0wt%-1.2wt% sodium carboxymethyl cellulose, and 1.1wt%-2.2wt% styrene-butadiene rubber is coated onto a negative electrode current collector to obtain the first electrode.

[0007] Optionally, the solid content of the negative electrode slurry ranges from 45% to 55%; And / or, the pH range of the negative electrode slurry is 6-7; And / or, the viscosity range of the negative electrode slurry is 3000 mPa·s-6000 mPa·s; And / or, the coating thickness of the negative electrode slurry ranges from 150 μm to 350 μm; And / or, the negative electrode current collector is copper foil, carbon-coated copper foil, porous copper foil, or porous carbon-coated copper foil.

[0008] Optionally, applying a pulsed electric field to the upper and lower surfaces of the first electrode to obtain the second electrode includes: At least one metal mesh is disposed at corresponding positions above the upper surface and below the lower surface of the first electrode to apply a pulsed electric field of 10V / cm-15V / cm to the coated negative electrode slurry, thereby obtaining the second electrode; wherein the negative electrode current collector is connected to the negative terminal of the external power supply, and each metal mesh is connected to the positive terminal of the external power supply.

[0009] Optionally, the corresponding position is any distance between each metal mesh and the coated negative electrode slurry in a direction perpendicular to the upper surface of the first electrode sheet, ranging from 10mm to 15mm.

[0010] Optionally, the metal mesh is made of nickel.

[0011] Optionally, the aperture of the metal mesh ranges from 50 μm to 100 μm.

[0012] Optionally, at least one pair of the metal meshes is located between the coating die and the oven; And / or, at least one pair of the metal meshes are located in the heating zone inside the oven near the coating die.

[0013] Optionally, the duty cycle of the pulsed electric field ranges from 30% to 70%, and the frequency ranges from 0.5 Hz to 2 Hz.

[0014] In a second aspect, the present invention provides a gradient electrode sheet, which is prepared by the lithium-ion battery negative electrode sheet preparation method described in the first aspect.

[0015] This invention provides a method for preparing a lithium-ion battery negative electrode sheet and a gradient electrode sheet based on electric field control. In the method, the graphite is positively charged. Under the action of an electric field, small graphite particles aggregate towards the current collector, while large particles are difficult to migrate due to steric hindrance. This results in a gradient distribution of the electrode sheet's porosity, with lower porosity near the current collector and higher porosity further away, which is beneficial for electrolyte wetting and improves the battery's rate performance. By controlling the negative electrode slurry particles with a pulsed electric field to form a gradient structure, the electron / ion transport path is optimized, effectively alleviating the problem of extended transport paths caused by thick electrodes. This method has the advantages of improving ion transport performance, reducing interfacial resistance, and enhancing the overall electrochemical performance of the battery. Attached Figure Description

[0016] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic flowchart illustrating a method for preparing a lithium-ion battery negative electrode based on electric field modulation, provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a lithium-ion battery anode preparation device based on electric field modulation, provided for an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In one embodiment, such as Figure 1 As shown, this embodiment provides a method for preparing a lithium-ion battery negative electrode based on electric field modulation, including: Step 101: Coat the negative electrode slurry onto the negative electrode current collector to obtain the first electrode.

[0020] In practical applications, the negative electrode slurry can be understood as a mixture consisting of active materials, conductive agents, binders, and solvents. Its main function is to provide the basic structure for lithium-ion intercalation and deintercalation. Specifically, the negative electrode slurry can be prepared by mixing using stirring equipment, such as a planetary mixer or a high-speed disperser, to achieve uniform mixing, primarily to ensure that the slurry has good flowability and coating performance. Furthermore, the coating process can be achieved using methods such as slot coating, blade coating, or roller coating, the specific choice depending on process requirements and equipment conditions. The aim is to form a uniform slurry layer on the negative electrode current collector.

[0021] For example, a negative electrode slurry consisting of 95wt%-96.5wt% graphite, 0.8wt%-1.5wt% conductive carbon black, 1.0wt%-1.2wt% sodium carboxymethyl cellulose, and 1.1wt%-2.2wt% styrene-butadiene rubber is coated onto a negative electrode current collector to obtain a first electrode sheet.

[0022] Specifically, graphite refers to the main component of the active material, which can be made from artificial or natural graphite. The purpose is to ensure a high active material loading to improve energy density, while avoiding excessive proportions that could lead to deterioration of the fluidity of the negative electrode slurry.

[0023] Conductive carbon black can be understood as an additive used to construct continuous electron conduction paths, forming an effective three-dimensional conductive network between active material particles. Too low a content of conductive carbon black results in insufficient conductivity, while too high a content will crowd out the active material and may affect the rheological properties of the slurry. Conductive carbon black can be achieved through conductive carbon black particles of different morphologies, ensuring stable electron transport paths under pulsed electric fields and avoiding localized current concentrations that could affect particle rearrangement.

[0024] In practical applications, sodium carboxymethyl cellulose is a key component used as a thickener and dispersant (water-based binder). It can be achieved using sodium carboxymethyl cellulose of different molecular weights. Its purpose is to provide just the right amount of bonding strength to maintain the suspension stability of the slurry and prevent particles from settling or agglomerating during coating.

[0025] In addition, styrene-butadiene rubber can be understood as an elastic binder, which can be achieved by adjusting the degree of polymerization or crosslinking of styrene-butadiene rubber. The purpose is to enhance the mechanical flexibility of the electrode and reduce the risk of coating cracking.

[0026] Specifically, the above technical solution ensures optimized rheological properties and stability of the slurry by precisely limiting the proportion range of each component in the negative electrode slurry, thereby forming a highly uniform initial structure during the coating process. The graphite proportion is controlled within the range of 95wt%-96.5wt%, ensuring a high active material loading to improve energy density while avoiding excessive proportions that could lead to deterioration of slurry fluidity and incomplete conductive networks, thus maintaining structural consistency in the thickness direction of the coated first electrode. The conductive carbon black proportion is set within the range of 0.8wt%-1.5wt%, and its appropriate addition effectively constructs a continuous electron conduction path, avoiding the problems of insufficient graphite conductivity due to a low proportion or excessive proportions crowding out the space of the active material due to a high proportion. The sodium carboxymethyl cellulose proportion is maintained within the range of 1.0wt%-1.2wt%, providing just the right amount of binding strength to prevent particle sedimentation or agglomeration during coating, while avoiding excessively sticky negative electrode slurry caused by a high proportion. The proportion of styrene-butadiene rubber (SBR) was adjusted to the range of 1.1wt%-2.2wt%. Its supplementary effect enhanced the mechanical flexibility of the electrode and effectively buffered stress changes during drying, reducing the risk of coating cracking. This combination synergistically optimized the viscosity, solid content, and dispersibility of the slurry, resulting in a first electrode with uniform thickness and a dense internal structure during the coating process. Consequently, when a pulsed electric field is applied, the electric field can precisely drive the directional migration of active particles, promoting a smooth gradient change in porosity from the surface to the interior, ultimately achieving a synergistic improvement in high energy density and fast charge / discharge performance.

[0027] The aforementioned parameters provide the foundation for the precise guidance of particle alignment by subsequent pulsed electric field modulation, in order to achieve the goal of balancing high energy density and excellent rate performance.

[0028] This embodiment further proposes that the solid content of the negative electrode slurry is in the range of 45%-55%; and / or, the pH value of the negative electrode slurry is in the range of 6-7; and / or, the viscosity of the negative electrode slurry is in the range of 3000mPa.s-6000mPa.s; and / or, the coating thickness of the negative electrode slurry is in the range of 150μm-350μm; and / or, the negative electrode current collector is copper foil, carbon-coated copper foil, porous copper foil, or porous carbon-coated copper foil.

[0029] In practical applications, solid content refers to the percentage of solid particles in the slurry by mass relative to the total slurry mass. This can be achieved by adjusting the proportions of solid components such as graphite and conductive carbon black. pH value can be understood as the acid-base balance of the slurry system, and is typically maintained within a neutral range by adding appropriate buffers or adjusting the solvent ratio.

[0030] Specifically, viscosity refers to the flow characteristics of the slurry under external force, which can be controlled by changing the amount of sodium carboxymethyl cellulose or styrene-butadiene rubber. Furthermore, coating thickness refers to the thickness of the slurry layer covering the negative electrode current collector, which can be precisely controlled by setting the parameters of the coating equipment.

[0031] By limiting the key parameters of the negative electrode slurry, problems such as uneven coating or wet film defects caused by deviations in slurry characteristics can be effectively avoided. For example, when a pulsed electric field is applied, appropriate solid content and viscosity ensure that active particles are oriented under the action of the electric field, thereby forming a continuous gradient pore distribution, which can effectively ensure the uniformity of the negative electrode slurry coating and avoid sagging or orange peel phenomena. Within this range of solid content, a balance between coating efficiency and drying efficiency is ensured, and a suitable liquid phase environment is provided for particle migration under the action of the electric field. At the same time, a reasonable pH range ensures the stability of the binder molecular structure and prevents the decrease in slurry dispersibility from affecting the coating quality. In addition, the optimized design of coating thickness not only increases the loading of active materials but also reduces ion transport resistance, providing a fundamental support for the performance improvement of thick electrode sheets. On this basis, the selection of different types of negative electrode current collectors can further enhance the conductive network and interface bonding. In particular, carbon coating or porous structures significantly enhance the adhesion between the current collector and the active layer, thereby supporting the overall integrity of the gradient electrode. Through the above technical solutions, the internal transport performance of thick electrode sheets can be effectively improved under high energy density targets.

[0032] Step 102: Apply a pulsed electric field to the upper and lower surfaces of the first electrode to obtain the second electrode.

[0033] Applying a pulsed electric field to the first electrode can be understood as a technique that uses electric field force to drive the directional migration of particles in the negative electrode slurry. Specifically, the pulsed electric field can be achieved through a high-voltage power supply in conjunction with the electrode system. For example, a square wave pulse signal generator can be used to generate the electric field, and its frequency and duty cycle can be adjusted according to actual needs. As a preferred embodiment, the electric field direction can be set perpendicular to the electrode surface to promote the formation of a gradient distribution of particles along the electric field direction. In addition, the electrode system can adopt a flat plate electrode or a porous electrode structure, the purpose of which is to generate a uniform electric field distribution within the slurry layer, thereby achieving controllable particle migration.

[0034] For example, such as Figure 2 As shown, at least one metal mesh 2 is provided at corresponding positions above the upper surface and below the lower surface of the first electrode to apply a pulsed electric field of 10V / cm-15V / cm to the coated negative electrode slurry to obtain the second electrode; wherein the negative electrode current collector is connected to the negative terminal of the external power supply, and each metal mesh 2 is connected to the positive terminal of the external power supply.

[0035] Specifically, the corresponding position refers to any distance between each metal mesh 2 and the coated negative electrode slurry in the direction perpendicular to the upper surface of the first electrode sheet, ranging from 10mm to 15mm. In practical applications, this distance range is selected based on the requirement for uniform electric field distribution and to avoid excessively strong local electric fields caused by excessive proximity. By reasonably setting the positions of the metal mesh 2 and the negative electrode slurry, it is ensured that the electric field can uniformly cover the entire slurry layer, thereby achieving precise control of particle migration.

[0036] The metal mesh 2 can be made of nickel, with a pore size ranging from 50μm to 100μm. In practical applications, the material selection for the metal mesh 2 needs to balance conductivity and corrosion resistance, while the pore size design directly affects the uniformity of the electric field distribution and the effect of particle migration. By optimizing the structural parameters of the metal mesh 2, the precision of electric field control can be effectively improved.

[0037] By setting metal mesh 2 on the upper and lower surfaces of the first electrode, a symmetrical electric field application structure is formed, avoiding local intensity differences caused by a unilateral electric field. When applying a pulsed electric field of 10V / cm-15V / cm, this intensity range is optimized. Insufficient field strength (<10V / cm): the electric field force is insufficient to overcome the viscous resistance of the slurry, resulting in insignificant migration of graphite particles (especially small particles) and failure to form an effective porosity gradient; excessive field strength (>15V / cm): may damage the electrochemical stability of the slurry, causing water electrolysis and bubble generation, or leading to excessively rapid particle migration and dense aggregation, which in turn damages the integrity of the electrode structure. The negative electrode current collector, acting as the cathode, attracts positively charged active material particles, promoting particle enrichment towards the current collector, thereby forming a low-porosity layer in the region near the current collector. At the same time, the metal mesh, acting as the anode, guides the directional flow of ions, working synergistically with the current collector to strengthen the electric field gradient inside the slurry, prompting the particles to form a continuously distributed pore structure in the vertical direction.

[0038] Based on this, such as Figure 2 As shown, at least one pair of metal meshes can be disposed between the coating die 1 and the oven 3, or located in the heating area of ​​the oven 3 near the coating die 1. This arrangement can make full use of the space in the preparation process and ensure seamless connection between electric field control and subsequent drying processes, thereby improving overall production efficiency.

[0039] The above technical solution achieves a smooth transition from high surface porosity to low internal porosity, effectively solving the problems of uneven electric field distribution and abrupt changes in porosity, and providing a reliable technical guarantee for improving the performance of lithium-ion battery anode sheets.

[0040] This embodiment further proposes that the corresponding position is any distance between each metal mesh 2 and the coated negative electrode slurry in a direction perpendicular to the upper surface of the first electrode sheet, ranging from 10mm to 15mm.

[0041] Specifically, the corresponding position refers to the precise distance range between the metal mesh 2 and the negative electrode slurry in the vertical direction. In practical applications, this distance range can be achieved using a precision displacement stage or a spacing adjustment device. The purpose is to ensure that the electric field force can act uniformly on the slurry surface, avoiding abnormal electric field strength caused by improper distance, thereby achieving a smooth transition of particles under the action of the electric field.

[0042] By placing the metal mesh 2 within a range of 10mm-15mm from the coated negative electrode slurry, the problem of uneven electric field distribution was effectively solved. Furthermore, the precise vertical positioning ensured that the electric field accurately guided the charged particles to migrate directionally along the thickness direction. If the metal mesh 2 is too close, slurry splashing or localized overheating may occur; conversely, if the distance is too far, the electric field will attenuate significantly, failing to effectively drive particle alignment. Experimental verification showed that this distance range achieves a good balance between electric field strength and uniformity, allowing the particles to form a continuous gradient structure under the influence of the electric field. This results in a gradual distribution of porosity from the surface to the interior, significantly improving the battery's rate performance and energy density.

[0043] Furthermore, by combining the above scheme with the application of the pulsed electric field, the position of the metal mesh 2 is precisely controlled, thereby optimizing the effect of the electric field on the negative electrode slurry and providing a reliable guarantee for the formation of an ideal gradient pore structure.

[0044] This embodiment further proposes that the metal mesh is made of nickel.

[0045] Specifically, the metal mesh, as a key component for applying the pulsed electric field, can be made of materials with good electrical conductivity and chemical stability. In practical applications, nickel is chosen as the material for the metal mesh due to its excellent corrosion resistance and low redox activity, in order to ensure the uniformity of the electric field distribution and avoid contamination of the negative electrode slurry.

[0046] Nickel-based metal meshes maintain stable physical and chemical properties under pulsed electric fields, effectively avoiding discontinuous porosity gradients caused by material limitations. By placing the nickel mesh at corresponding positions on the upper and lower surfaces of the first electrode, uniform transmission of the electric field in the vertical direction is ensured, allowing particles in the negative electrode slurry to form an ordered arrangement under the influence of the electric field. This arrangement not only facilitates a continuous porosity gradient from the surface to the interior but also significantly improves the electrode's conductivity and lithium intercalation capability. Furthermore, the high corrosion resistance of nickel ensures the stability of the pulsed electric field parameters, thereby optimizing the electrochemical performance of thick electrodes and providing reliable technical support for the fabrication of high-energy-density electrodes.

[0047] This embodiment further proposes that the aperture range of the metal mesh 2 is 50μm-100μm.

[0048] Specifically, the aperture of the metal mesh 2 refers to the maximum inscribed circle diameter of each mesh opening. In practical applications, the metal mesh 2 can be made of woven or perforated metal mesh, the purpose of which is to ensure that the pulsed electric field can act uniformly and stably on the coated negative electrode slurry. By limiting the aperture to between 50μm and 100μm, the problems of excessive electric field concentration caused by too small an aperture or electric field dispersion caused by too large an aperture can be effectively avoided.

[0049] This embodiment optimizes the directional migration and arrangement of particles in the slurry by precisely controlling the pore size range of the metal mesh 2, enabling the electric field energy to effectively penetrate the negative electrode slurry layer. The pore size range of the metal mesh is designed with the typical size characteristics of graphite particles in the negative electrode slurry in mind. A pore size smaller than 50 μm can hinder slurry flow and cause localized particle accumulation or coating defects; conversely, a pore size larger than 100 μm weakens the ability to directionally control the slurry particles. Therefore, this specific pore size range not only ensures the uniformity of the electric field distribution but also promotes the orderly rearrangement of particles under pulsed action, ultimately achieving a gradual transition from high porosity on the upper surface to low porosity inside, constructing a gradient electrode structure that balances high energy density and fast charging performance. Furthermore, this design, combined with the technique of applying a pulsed electric field, further enhances the overall performance of the negative electrode.

[0050] This embodiment further proposes that at least one pair of metal meshes 2 are located between the coating die and the oven; and / or, at least one pair of metal meshes 2 are located in the heating area of ​​the oven 3 near the coating die 1.

[0051] The position of the metal mesh 2 is arranged reasonably to ensure that the electric field can be applied when the negative electrode slurry is in a highly fluid state. The position between the coating die 1 and the oven 3 refers to the area where the negative electrode slurry has just been coated but has not yet entered the baking stage. Its purpose is to take advantage of the high water content and strong particle fluidity of the slurry so that the electric field can fully drive the directional migration of the active material.

[0052] The heating area near the coating die head 1 inside the oven 3 refers to the area in the oven where the temperature is low and the slurry is still moderately moist. In this area, the negative electrode slurry still has good fluidity, and the particles can still migrate effectively under the action of the electric field, avoiding uneven drying in some areas due to rapid heating.

[0053] In detail, this embodiment places the metal mesh 2 between the coating die 1 and the oven 3, allowing the pulsed electric field to be applied immediately after the negative electrode slurry is coated. At this time, the slurry has the strongest fluidity, and the electric field can effectively guide the active materials such as graphite to oriented alignment, thereby initially establishing a gradient distribution of porosity. Simultaneously, placing the metal mesh 2 in the heating area of ​​the oven 3 near the coating die 1 utilizes the lower temperature of this area to maintain a moderately moist state of the slurry, allowing the electric field to continuously regulate particle alignment during the initial baking stage and preventing uneven drying caused by rapid heating. This positioning not only ensures a smooth transition of porosity from the surface to the interior but also enhances the adaptability of the process, allowing for flexible selection of the electric field application timing based on the production line layout, thereby stabilizing the formation of a gradient porosity structure and improving the ion transport efficiency and structural stability of the electrode. Furthermore, the combination of the metal mesh arrangement and the pulsed electric field application process further optimizes the porosity distribution of the negative electrode sheet, solving the problem of abrupt porosity changes caused by premature slurry drying, and improving the rate performance and energy density of the battery.

[0054] This embodiment further proposes that the duty cycle of the pulsed electric field is in the range of 30%-70%, and the frequency range is 0.5Hz-2Hz.

[0055] In practical applications, the duty cycle refers to the ratio of the electric field's on-time to the total cycle time, which can be achieved by adjusting the on / off time of the power supply output signal. Setting the duty cycle within the range of 30%-70% balances the particle migration driving force and slurry stability, avoiding structural defects caused by insufficient or excessive on-time. Frequency refers to the number of electric field changes per unit time, which can be adjusted by controlling the period of the power supply output signal. Limiting the frequency to the range of 0.5Hz-2Hz ensures that the particles have sufficient time to respond to the electric field force, while guaranteeing production efficiency and migration effect.

[0056] Specifically, by applying a pulsed electric field with specific parameters to the first electrode, the directional migration process of graphite particles in the negative electrode slurry can be precisely controlled. Setting the electric field duration within a duty cycle range of 30%-70% avoids both insufficient driving force for particle migration due to an excessively low duty cycle and excessive particle aggregation or localized drying of the slurry due to an excessively high duty cycle. In other words, a balance is achieved between ensuring sufficient driving force for migration and allowing for relaxation of the slurry structure (preventing excessively dense particle packing). Simultaneously, applying the pulsed electric field within a frequency range of 0.5Hz-2Hz effectively matches the response characteristics of the particles in the slurry, enabling the particles to gradually rearrange under the influence of the electric field, forming a porosity gradient distribution that smoothly transitions from the surface to the interior. Too low a frequency results in near-DC; too high a frequency leaves the particles insufficient time to respond. 1Hz is the preferred frequency for achieving stable and controllable directional migration of the particles. The above parameter settings not only optimize the ion transport path, but also significantly improve the conductivity and lithium intercalation capability of the thick electrode, thereby solving the problems of unstable electric field effect and abrupt or discontinuous porosity distribution.

[0057] The above technical solution ensures that the electric field can effectively drive the directional migration of graphite particles in the negative electrode slurry, while avoiding structural defects caused by improper parameters. This achieves a gradient structure with high surface porosity and low internal porosity, thereby improving the ion transport efficiency and rate performance of the thick electrode.

[0058] Step 103: Bake the second electrode to obtain a dry lithium-ion battery negative electrode.

[0059] The baking process can be understood as a technical means of removing solvents from the negative electrode slurry and solidifying its structure through heating. Specifically, baking can be achieved through a hot air circulating oven, infrared heating equipment, or microwave heating equipment, and its temperature and time parameters need to be optimized according to the characteristics and thickness of the slurry. For example, extending the baking time at a lower temperature can reduce particle rebound, thereby maintaining the stability of the porosity gradient.

[0060] In summary, this embodiment provides a method for preparing lithium-ion battery negative electrode sheets based on electric field control. In a slurry system with pH 6-7, the oxygen-containing functional groups (such as carboxyl-COOH) at the edges of graphite particles give their surfaces a weak positive charge. When a pulsed electric field is applied, and the current collector copper foil is set as the negative electrode and the upper metal mesh as the positive electrode, the weakly positively charged graphite particles (especially small-sized particles) migrate and accumulate towards the current collector under the drive of the electric field force, forming a low-porosity dense layer near the current collector side. This macroscopically assists in the formation of a continuous gradient structure from the current collector to the electrode surface, with porosity increasing from low to high (20%-25%→40%-45%). The pulse mode (duty cycle 30%-70%, frequency 0.5Hz-2Hz) can effectively suppress side reactions such as water electrolysis that may be caused by a continuous DC electric field, and allow the slurry to recover its viscosity during the pulse interval, thereby achieving controllable and orderly migration of particles, and finally constructing a gradient electrode that can synergistically optimize electron and ion transport paths.

[0061] A first electrode is formed by coating a negative electrode slurry onto a negative electrode current collector, providing an initial uniform structure for subsequent electric field modulation and ensuring the slurry layer possesses plasticity. Further, a pulsed electric field is applied to the upper and lower surfaces of the first electrode, using the electric field force to drive the particles in the slurry to migrate directionally in the vertical direction, thereby forming a continuous porosity gradient from the surface to the interior. This process effectively reduces the tortuosity of ion transport and enhances the connectivity of the conductive network. Specifically, the application of the pulsed electric field causes the particles to rearrange in a wet slurry state, providing the necessary conditions for the construction of the gradient structure. Therefore, by baking the second electrode, the electric field-modulated gradient structure is rapidly solidified, preventing particle rebound and maintaining the stability of the pore distribution. As a preferred embodiment, the above three technical features work together closely: the coating step lays the foundation structure, the pulsed electric field application step enables particle rearrangement to form a gradient, and the baking step locks in the structure. Together, they ensure a smooth transition in porosity, thereby improving the conductivity and ion transport efficiency of the thick electrode, solving the problem of increased electron and ion transport distance and resistance caused by increased thickness, and achieving a gradient change in porosity.

[0062] The innovation of this embodiment lies in actively constructing a porosity gradient structure during the coating process through electric field modulation to optimize electron and ion transport paths. Compared to the existing technology that achieves abrupt porosity changes through multi-layer coating, this embodiment can achieve a continuous porosity gradient from the surface to the interior within a single slurry layer, thereby reducing ion transport tortuosity and enhancing the connectivity of the conductive network. Furthermore, this method drives the directional migration of particles through a pulsed electric field and combines it with a rapid curing process to lock the gradient structure, solving the problem of decreased conductivity and lithium intercalation capability caused by thick electrodes, while simultaneously achieving a smooth transition of porosity.

[0063] To further understand the present invention, the method for preparing lithium-ion battery anode sheets based on electric field modulation provided by the present invention will be described in detail below with reference to embodiments. The scope of protection of the present invention is not limited by the following embodiments. Example 1 The negative electrode slurry is composed of graphite (96.5 wt%), conductive carbon black (0.8 wt%), sodium carboxymethyl cellulose (1.2 wt%), and styrene-butadiene rubber (1.5 wt%). The slurry has a pH of 6.5, a solid content of 52%, and a viscosity of 4500 mPa·s. It is coated by slot extrusion coating, with a coating thickness of 0.3 mm. A nickel mesh is placed 10 mm above the coated negative electrode slurry. The current collector copper foil is connected to the negative electrode, and the nickel mesh is connected to the positive electrode. The electric field parameters are: DC 12V, corresponding to a field strength of 12 V / cm based on a 10 mm electrode spacing; pulse frequency 1 Hz, duty cycle 50%, and duration 90 seconds.

[0064] Results: Electrolyte wetting time 30h (battery); 1C initial efficiency 93.50%; 5C / 1C capacity ratio 86%; near-copper foil porosity 23%; far-copper foil porosity 43%.

[0065] Example 2 The negative electrode slurry composition consists of graphite (95.5 wt%), conductive carbon black (1.4 wt%), sodium carboxymethyl cellulose (1.1 wt%), and styrene-butadiene rubber (1.9 wt%). The solid content is 48%, and the viscosity is 5000 mPa·s. The coating thickness of the negative electrode slurry is 250 μm. The electric field parameters are: DC 9 V, pulse frequency 0.8 Hz, duty cycle 40%, and action time 100 seconds. The remaining parameters are the same as in Example 1.

[0066] Results: Near-copper foil porosity 28%; Far-copper foil porosity 38%; 5C / 1C volume ratio 78%.

[0067] Even when the parameters are at the lower limit of the range, a gradient can still be formed, but the performance improvement is less than that of Example 1, which proves the effectiveness of the lower limit of the parameter range and the necessity of optimization.

[0068] Example 3 Electric field parameters: DC 16V, pulse frequency 1.5 Hz, duty cycle 60%, duration 80 seconds, remaining parameters are the same as in Example 1.

[0069] Results: Near-copper foil porosity 21%; Far-copper foil porosity 46%; 5C / 1C volume ratio 84%. The parameters are at the upper limit of the range, forming a more significant gradient, but the mechanical strength of the electrode needs to be considered, proving the effectiveness of the upper limit of the parameter range.

[0070] Comparative Example 1 The negative electrode slurry and coating parameters are the same as in Example 1.

[0071] Electric field parameters: DC 12V constant DC, duration 90 seconds.

[0072] Results: Electrolyte wetting time 36h (battery) (16.7% higher than Example 1); 1C initial efficiency 92.80% (0.70% lower than Example 1); 5C / 1C capacity ratio 71% (15% lower than Example 1); Porosity near copper foil 32%; Porosity far from copper foil 32% (no gradient porosity formed); Electrode appearance: Fine cracks are visible on the side near copper foil.

[0073] Constant DC leads to excessive densification near the foil end, causing microcracks, and the rate performance is lower than that of pulsed mode (86%), demonstrating the outstanding advantages of pulsed electric field in preventing structural defects and ensuring overall performance.

[0074] In another embodiment, this embodiment also discloses a gradient electrode sheet, which is prepared by a lithium-ion battery negative electrode sheet preparation method based on electric field modulation.

[0075] In this embodiment, by combining electric field modulation with the coating process and using a pulsed electric field to drive the directional migration of particles, a continuous gradient change in porosity along the thickness direction is achieved. Compared with the abrupt porosity change caused by multi-layer coating in the prior art, this reduces the tortuosity of ion transport and enhances the connectivity of the conductive network, thereby optimizing the electron and ion transport performance of the thick electrode.

[0076] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing a lithium-ion battery negative electrode based on electric field modulation, characterized in that, include: The negative electrode slurry is coated onto the negative electrode current collector to obtain the first electrode sheet; A pulsed electric field is applied to the upper and lower surfaces of the first electrode to obtain the second electrode; The second electrode is baked to obtain a dry lithium-ion battery negative electrode.

2. The method for preparing a lithium-ion battery negative electrode sheet according to claim 1, characterized in that, The process of coating the negative electrode slurry onto the negative electrode current collector to obtain the first electrode sheet includes: A negative electrode slurry consisting of 95wt%-96.5wt% graphite, 0.8wt%-1.5wt% conductive carbon black, 1.0wt%-1.2wt% sodium carboxymethyl cellulose, and 1.1wt%-2.2wt% styrene-butadiene rubber is coated onto a negative electrode current collector to obtain the first electrode.

3. The method for preparing a lithium-ion battery negative electrode sheet according to claim 1, characterized in that, The solid content of the negative electrode slurry ranges from 45% to 55%. And / or, the pH range of the negative electrode slurry is 6-7; And / or, the viscosity range of the negative electrode slurry is 3000 mPa·s-6000 mPa·s; And / or, the coating thickness of the negative electrode slurry ranges from 150 μm to 350 μm; And / or, the negative electrode current collector is copper foil, carbon-coated copper foil, porous copper foil, or porous carbon-coated copper foil.

4. The method for preparing a lithium-ion battery negative electrode sheet according to claim 1, characterized in that, The process of applying a pulsed electric field to the upper and lower surfaces of the first electrode to obtain the second electrode includes: At least one metal mesh is disposed at corresponding positions above the upper surface and below the lower surface of the first electrode to apply a pulsed electric field of 10V / cm-15V / cm to the coated negative electrode slurry, thereby obtaining the second electrode; wherein the negative electrode current collector is connected to the negative terminal of the external power supply, and each metal mesh is connected to the positive terminal of the external power supply.

5. The method for preparing a lithium-ion battery negative electrode sheet according to claim 4, characterized in that, The corresponding position is any distance between each metal mesh and the coated negative electrode slurry, in a direction perpendicular to the upper surface of the first electrode sheet, ranging from 10mm to 15mm.

6. The method for preparing a lithium-ion battery negative electrode sheet according to claim 4, characterized in that, The metal mesh is made of nickel.

7. The method for preparing a lithium-ion battery negative electrode sheet according to claim 4, characterized in that, The aperture of the metal mesh ranges from 50μm to 100μm.

8. The method for preparing a lithium-ion battery negative electrode sheet according to claim 4, characterized in that, At least one pair of the metal meshes is located between the coating die and the oven; And / or, at least one pair of the metal meshes are located in the heating zone inside the oven near the coating die.

9. The method for preparing a lithium-ion battery negative electrode sheet according to claim 1, characterized in that, The duty cycle of the pulsed electric field ranges from 30% to 70%, and the frequency ranges from 0.5 Hz to 2 Hz.

10. A gradient electrode sheet, characterized in that, The gradient electrode sheet is prepared by the lithium-ion battery negative electrode sheet preparation method according to any one of claims 1-9.

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