A thick electrode with high conductivity, high mass transfer structure stability and a preparation method and application thereof

Abstract

This invention relates to the field of lithium-ion battery technology, specifically providing a thick electrode with high conductivity, high mass transfer, and stable structure, as well as its preparation method and application. The method includes: mixing and stirring active material particles, conductive carbon fibers, and a binder until homogeneous, obtaining a mixed powder; wherein the conductive carbon fibers have a multidimensional network structure, with a fiber diameter of 50-500 nm and a specific surface area of ​​50-500 m². 2 / g; Under a first voltage, the mixed powder is electrostatically sprayed onto a current collector, and then electrostatically sprayed again under a second voltage to obtain an electrode with a gradient porosity structure (porosity increases from near the current collector to far away from the current collector), wherein the first voltage > the second voltage; then hot-pressing is performed to obtain a thick electrode with high conductivity, high mass transfer, and stable structure. This invention solves the problems in the prior art where the conductivity, structural stability, and mass transfer efficiency of thick electrodes cannot be synergistically optimized, and the gradient porosity preparation process is cumbersome.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a thick electrode with high conductivity, high mass transfer, and stable structure, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries possess outstanding advantages such as excellent cycle performance, high energy density, and high energy conversion efficiency, making them the most promising electrochemical energy storage devices. With the rapid development of new energy vehicles and energy storage devices, the demand for energy density is increasing year by year. In recent years, thick electrode technology with high active material loading has become a research hotspot. By increasing the electrode coating thickness and active material loading, the proportion of active material in the battery is increased, thereby significantly improving energy density.

[0003] Thick electrodes face numerous challenges in practical applications. For example, during preparation and use, thick electrodes are prone to structural stability issues such as cracking and peeling; the increased electron transport path leads to increased electron transport impedance; electrolyte wetting is difficult, limiting ion transport; and the utilization rate of active materials is low, resulting in poor rate performance.

[0004] To address these issues, existing technologies typically increase the content of conductive agents and binders in the electrode to improve its mass transfer performance. However, traditional conductive agents (such as carbon black) cannot form a continuous multidimensional conductive network in thick electrodes, thus failing to solve the problems of electrode cracking and peeling. Furthermore, thick electrodes prepared using traditional coating processes exhibit a uniform porosity distribution, making it difficult to simultaneously meet the requirements of electron and ion transport.

[0005] Therefore, there is an urgent need to develop a new thick electrode fabrication technology that can simultaneously solve problems such as structural stability, electron transport, and ion transport. Summary of the Invention

[0006] This invention provides a thick electrode with high conductivity, high mass transfer, and stable structure, as well as its preparation method and application. The purpose is to solve the problems in the prior art where the conductivity, structural stability, and mass transfer efficiency of thick electrodes cannot be optimized in a coordinated manner, and the preparation process of gradient porosity is cumbersome.

[0007] To achieve the above objectives, embodiments of the present invention provide a multidimensional conductive carbon fiber for use in thick electrodes of lithium-ion batteries, possessing high conductivity, high structural stability, and excellent mass transfer efficiency. Furthermore, the present invention proposes a synergistic strategy of multidimensional conductive carbon fiber and electrostatic spraying gradient particle size deposition to simultaneously optimize the conductivity, structural stability, and mass transfer efficiency of thick electrodes in lithium-ion batteries. In the preparation of the conductive carbon fiber, a systematic reconstruction is achieved based on microstructure design, multi-scale charge transfer regulation, and interface engineering optimization, rather than simply relying on the superposition of raw material components. Traditional physical mixing methods, such as directly blending conductive agents like graphite, carbon black, carbon nanotubes (CNTs), and carbon fibers with electrode active materials, easily lead to discontinuous conductive networks and significantly increased contact resistance due to random accumulation and strong agglomeration tendency of the conductive phase. Especially inside thick electrodes, such structural defects can form local electronic insulation regions, causing severe polarization and restricting overall electrochemical performance. Therefore, the present invention achieves efficient charge conduction and distribution through multi-scale ordered structural design and interface synergistic optimization, thereby breaking through the core transport bottleneck of thick electrodes.

[0008] One embodiment of the present invention provides a method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure, comprising the following steps: S1: Take active material particles, conductive carbon fibers, and binder, mix and stir evenly to obtain a mixed powder; wherein, the conductive carbon fibers have a multi-dimensional network structure, with a fiber diameter of 50-500 nm and a specific surface area of ​​50-500 m². 2 / g; S2: Under a first voltage, the mixed powder is electrostatically sprayed onto the current collector, and then electrostatically sprayed again under a second voltage to obtain an electrode with a gradient porosity structure; wherein, the first voltage > the second voltage; the gradient porosity structure has the characteristic of increasing porosity from near the current collector to far away from the current collector; the particle size distribution of active materials at different levels of the electrode is precisely controlled by the voltage-particle size charge matching effect, such as depositing small-particle-size active materials (particle size range 50~200nm) in the core layer near the current collector, when small-particle-size particles are stacked, the pore size is smaller and the packing density is higher, thus forming a low-porosity structure; large-particle-size active materials (particle size range 1~10μm) are deposited on the electrode surface layer, when large-particle-size particles are stacked, the pore size is larger and the packing density is lower, thus forming a high-porosity structure.

[0009] S3: The electrode with the gradient porosity structure is subjected to hot pressing to obtain the thick electrode with high conductivity and high mass transfer structure and stable structure.

[0010] Preferably, in step S1, the preparation process of the conductive carbon fiber includes the following steps: S1.1: Add multiple polymer precursors to the solvent in sequence, stir and mix evenly, then add the conductive precursor and ultrasonically disperse evenly to obtain the electrospinning solution; S1.2: Electrospin the electrospinning solution to obtain precursor fibers; S1.3: The precursor fiber is pre-oxidized and then carbonized in an inert atmosphere to obtain the conductive carbon fiber.

[0011] Preferably, in step S1.1, the polymer precursor is selected from at least one of polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), hexafluoropropylene (HFP), polyimide (PI), polyaniline (PANI), polypyrrole (PPy), polyvinylpyrrolidone (PVP), and polylactic acid (PLA); the solvent is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), acetone, and deionized water; and the conductive precursor is selected from at least one of polyaniline, polypyrrole, polythiophene, graphene oxide, and carbon nanotubes.

[0012] Preferably, in step S1.2, the electrospinning process conditions are: voltage 10-50kV, receiving distance 5-25cm, injection speed 0.5-3mL / h, temperature 20-40℃, and relative humidity 20%-60%.

[0013] Preferably, in step S1.3, the pre-oxidation treatment temperature is 150-400℃, the time is 1-4 hours, and the heating rate is 1-5℃ / min; the carbonization treatment temperature is 800-1500℃, the time is 1-6 hours, and the heating rate is 2-10℃ / min; the inert gas is selected from at least one of nitrogen, argon, and helium.

[0014] Preferably, in step S1, the active material particles are selected from at least one of lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM), lithium cobalt oxide (LCO), and lithium manganese oxide (LMO); the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polyacrylate (PAAS); and the mass ratio of active material particles, conductive carbon fiber, and binder is (85-95):(1-8):(1-8).

[0015] Preferably, in step S2, the first voltage is 30~50kV, the second voltage is 20~40kV; the spraying distance of the electrostatic spraying deposition is 1~20cm, the spraying speed is 5~10g / min; and the thickness of the current collector is 10-20μm.

[0016] Preferably, in step S3, the hot pressing temperature is 80~300℃, the hot pressing pressure is 10~80MPa, and the hot pressing time is 10~60min; the total thickness of the thick electrode is 70-500μm. The physicochemical reaction during hot pressing involves the binder (such as polyvinyl alcohol or polyvinylidene fluoride) slightly melting and undergoing plastic flow under the hot pressing temperature conditions. This fluid binder can penetrate into the tiny gaps between the active material particles, conductive carbon fibers, and the current collector, forming a continuous bonding interface, thereby improving the overall bonding strength of the electrode. The uniform pressure generated by hot pressing can effectively release the non-uniform internal stress formed by particle stacking in the precursor, making the particle arrangement more regular and improving the overall density of the electrode structure, significantly reducing the risk of powder shedding during subsequent service, but without changing the porosity gradient characteristics of each region. During hot pressing, the plastic flow of the binder firmly bonds the multidimensional network structure of the conductive carbon fibers to the active material particles, effectively preventing deformation or breakage of the conductive network during subsequent processing and ensuring the continuity and stability of electron conduction. Some binders (such as phenolic resin binders) undergo a slight cross-linking reaction at the hot pressing temperature, forming a more stable multidimensional cross-linked structure, further improving the high-temperature resistance and bonding strength of the binder, and enhancing the stability of the electrode structure. During hot pressing, trace amounts of residual moisture and incompletely decomposed impurities in the precursor decompose or volatilize (e.g., moisture evaporation, and the decomposition of trace organic impurities into CO2 and H2O). The removal of these trace substances does not affect the particle size distribution and porosity structure of the active material; on the contrary, it can reduce internal defects in the electrode and improve the stability of electrode performance.

[0017] Another aspect of the present invention provides a thick electrode with high conductivity, high mass transfer, and stable structure prepared by the above-described preparation method.

[0018] Another embodiment of the present invention provides a secondary battery comprising a thick electrode with high conductivity, high mass transfer, and stable structure prepared by the preparation method described above.

[0019] The above-described solution of the present invention has the following beneficial effects: 1. Enhanced structural stability: The multidimensional support network formed by conductive carbon fibers can effectively consolidate the thick electrode structure, significantly alleviate the problem of electrode cracking, and improve the mechanical strength and cycle stability of the electrode.

[0020] 2. Improved electron transport performance: Conductive carbon fibers construct a continuous multidimensional electron transport network, which shortens the electron transport path, reduces electron transport impedance, and improves the utilization rate of active materials.

[0021] 3. Mass transfer efficiency optimization: Through gradient pore structure design, the small particle active layer near the current collector (core layer) is dense, which is conducive to electron transport; the large particle active layer far from the current collector (surface layer) has high porosity, which is conducive to electrolyte wetting and ion transport.

[0022] 4. Simple preparation process: The core principle of electrostatic spraying gradient deposition is the "voltage-particle size charge matching effect," meaning that smaller active particles have a larger specific surface area and can achieve a higher charge-to-mass ratio at higher voltages, making them easier to be adsorbed and deposited by the current collector. As the voltage decreases, the charge capacity of smaller particles declines, while larger active particles have a relatively better charge-to-mass ratio, thus enabling subsequent deposition. This process requires only one mixing step to complete the gradient structure construction, solving the problems of cumbersome traditional layered powder spreading processes and poor interlayer bonding.

[0023] 5. Environmentally friendly and highly compatible process: Dry electrodes are prepared by electrostatic spraying, with no organic solvents involved in the process, reducing the environmental pressure of the production process and making it suitable for large-scale industrial production. Detailed Implementation

[0024] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0027] This invention addresses existing problems by providing a thick electrode with high conductivity, high mass transfer, and stable structure, along with its preparation method and applications.

[0028] The following will illustrate the points through specific embodiments and comparative examples. Example 1 This embodiment provides a method for fabricating a thick electrode with high conductivity, high mass transfer, and stable structure, specifically including the following steps: (1) Mix 200g of lithium iron phosphate (particle size 50nm~10μm), 10g of conductive carbon fiber and 10g of polyvinylidene fluoride (PVDF), and stir for 4 hours to obtain a uniformly dispersed mixed powder. (2) Use an electrostatic spray gun to spray the mixed powder onto the grounded aluminum foil (15μm), set the distance between the spray gun and the aluminum foil to 16cm, set the first voltage to 40kV, spray to the core layer (close to the current collector) with a thickness of 100μm, and then set the second voltage to 25kV, spray to the surface layer (away from the current collector) with a thickness of 100μm; (3) The coated electrode is isothermally hot-pressed at 120°C for 40 min with a hot-pressing pressure of 50 MPa to finally obtain a thick electrode with gradient porosity. The active layer near the current collector (core layer) is a dense small particle layer, which is conducive to electron transport; the active layer far from the current collector (surface layer) is a large particle layer with high porosity, which is conducive to electrolyte wetting and ion transport.

[0029] The preparation process of the above-mentioned conductive carbon fiber includes the following steps: (1.1) 12g of polyacrylonitrile (PAN), 3g of polyvinylidene fluoride (PVDF), and 1g of polyvinylpyrrolidone (PVP) were added sequentially to 80mL of DMF-acetone mixed solution (3:1), and the mixture was stirred continuously until a homogeneous viscous solution was formed. 5g of carbon nanotubes (CNTs) were ultrasonically dispersed in the above solution to form a homogeneous electrospinning solution; (1.2) Electrospinning the electrospinning solution was performed with a spinning voltage of 20kV, a receiving distance of 15cm, a injection speed of 1mL / h, a temperature of 25℃, and a relative humidity of 40% to obtain precursor fibers. (1.3) The precursor fibers were pre-oxidized in a forced-air drying oven at 250°C for 2 hours at a heating rate of 2°C / min; then carbonized in a high-purity argon atmosphere to convert the polymer into carbon material at 1200°C for 3 hours at a heating rate of 5°C / min, resulting in conductive carbon fibers with a diameter of 400 nm and a specific surface area of ​​210 m². 2 / g.

[0030] With DMF acting as a good solvent, the cohesive forces of the molecular chains of PAN, PVDF, and PVP are disrupted, allowing the polymer chains to stretch and dissolve. Acetone is used to regulate the solvation strength and polarity of the system, promoting the formation of a uniform polymeric entanglement network. PAN forms the main framework, PVDF integrates into the entanglement network through its side chains to regulate the viscoelasticity of the system, and PVP uses its polar lactam groups to form hydrogen bonds with the two matrix polymers, effectively preventing phase separation.

[0031] Example 2 The difference from Example 1 is that lithium iron phosphate is replaced with lithium manganese oxide, while the other steps and parameters are the same as in Example 1.

[0032] Example 3 The difference from Example 1 is that lithium iron phosphate is replaced with lithium cobalt oxide, while the other steps and parameters are the same as in Example 1.

[0033] Example 4 The difference from Example 1 is that the amount of conductive carbon fiber added is 5g, while the rest of the steps and parameters are the same as in Example 1.

[0034] Example 5 The difference from Example 1 lies in the preparation process of the conductive carbon fiber, where the injection rate was adjusted from 1 mL / h to 0.6 mL / h. The remaining spinning, pre-oxidation, and carbonization steps are the same as in Example 1. This example yielded conductive carbon fibers with a diameter of 200 nm and a specific surface area of ​​320 m². 2 / g.

[0035] Comparative Example 1 The difference from Example 1 is that the conductive carbon fiber is replaced with conventional zero-dimensional conductive carbon (Super P), while the other steps and parameters are the same as in Example 1.

[0036] Comparative Example 2 This comparative example provides a method for preparing a thick electrode, which specifically includes the following steps: 200g of lithium iron phosphate (particle size 50nm~10μm), 10g of conductive carbon fiber, 10g of polyvinylidene fluoride (PVDF) and 200mL of N-methylpyrrolidone (NMP) were mixed and stirred for more than 4 hours to obtain a slurry. The slurry was then coated onto the surface of a 15μm aluminum foil current collector with a coating thickness of 200μm. After baking at 170℃ for 2 hours, the slurry was rolled at room temperature under a pressure of 25MPa to obtain a thick electrode.

[0037] Comparative Example 3 The difference from Example 1 is that a single porosity coating method is used, while the other steps and parameters are the same as in Example 1.

[0038] (1) Mix 200g of lithium iron phosphate (particle size 3~10μm), 10g of conductive carbon fiber and 10g of polyvinylidene fluoride (PVDF), and stir for 4 hours to obtain a uniformly dispersed mixed powder. (2) Use an electrostatic spray gun to spray the mixed powder onto a grounded aluminum foil (15μm), set the distance between the spray gun and the aluminum foil to 16cm, set the DC voltage between the nozzle and the aluminum foil to 40kV, and set the coating thickness to 200μm; (3) The coated electrode is isothermally pressed at 120°C for 40 min with a pressing pressure of 50 MPa to finally obtain a single porosity thick electrode.

[0039] The thick electrodes of the above embodiments and comparative examples were tested on the electrode sheets, and the results are shown in Table 1.

[0040] Table 1

[0041] The test results in Table 1 show that: Comparing Examples 1-3, it is evident that using conductive carbon fiber combined with electrostatic spraying to prepare a gradient porosity thick electrode yields a thick electrode with excellent peel strength, electrode resistivity, and liquid absorption capacity. Furthermore, this method is applicable to various mainstream cathode materials. Comparing Examples 1 and 4, it is evident that reducing the proportion of conductive carbon fiber decreases the continuity of the conductive network, leading to a decrease in electrode conductivity and a slight reduction in peel strength, but with minimal impact on electrolyte wetting performance. Comparing Examples 1 and 5, it is evident that the conductive carbon fiber prepared in Example 5 has a smaller diameter and larger specific surface area, which improves the conductivity and electrolyte wetting performance of the thick electrode. However, the excessively fine fibers are prone to agglomeration, slightly reducing structural stability. Comparing Examples 1 and Comparative Example 1, it is evident that using conductive carbon fiber instead of conventional zero-dimensional conductive carbon significantly improves the peel strength and crack resistance of the electrode, and because… The multidimensional electronic conduction network constructed from conductive carbon fibers significantly reduces the resistivity of the electrode. Comparing Example 1 and Comparative Example 2, it can be seen that the performance of the dry electrode prepared by electrostatic spraying is not significantly different from that of the electrode prepared by conventional NMP slurry system. The dry electrode can reduce costs by reducing slurry preparation and drying time, and eliminates the pollution caused by NMP solvent. Comparing Example 1 and Comparative Example 3, it can be seen that the electrostatic spraying method with gradient porosity can greatly improve the liquid absorption capacity of the electrode. This is because the coating near the current collector has a high conductive agent content and low porosity, which facilitates electron transport. The coating on the surface / diaphragm side away from the current collector has a low conductive agent content and high porosity, which facilitates ion transport. The higher ion conductivity can significantly alleviate the concentration polarization of the electrode liquid phase and improve the kinetic performance of the thick electrode. The gradient porosity structure can improve the mass transfer process of the electrode - enhance the electrolyte wetting performance of the electrode.

[0042] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure, characterized in that, Includes the following steps: S1: Take active material particles, conductive carbon fibers, and binder, mix and stir evenly to obtain a mixed powder; wherein, the conductive carbon fibers have a multi-dimensional network structure, with a fiber diameter of 50-500 nm and a specific surface area of ​​50-500 m². 2 / g; S2: Under a first voltage, the mixed powder is electrostatically sprayed onto the current collector, and then electrostatically sprayed under a second voltage to obtain an electrode with a gradient porosity structure; wherein, the first voltage > the second voltage; the gradient porosity structure has the characteristic of increasing porosity from near the current collector to far away from the current collector; S3: The electrode with the gradient porosity structure is subjected to hot pressing to obtain the thick electrode with high conductivity and high mass transfer structure and stable structure.

2. The method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure according to claim 1, characterized in that, In step S1, the preparation process of the conductive carbon fiber includes the following steps: S1.1: Add multiple polymer precursors to the solvent in sequence, stir and mix evenly, then add the conductive precursor and ultrasonically disperse evenly to obtain the electrospinning solution; S1.2: Electrospin the electrospinning solution to obtain precursor fibers; S1.3: The precursor fiber is pre-oxidized and then carbonized in an inert atmosphere to obtain the conductive carbon fiber.

3. The method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure according to claim 2, characterized in that, In step S1.1, the polymer precursor is selected from at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, hexafluoropropylene, polyimide, polyaniline, polypyrrole, polyvinylpyrrolidone, and polylactic acid; the solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, acetone, and deionized water; and the conductive precursor is selected from at least one of polyaniline, polypyrrole, polythiophene, graphene oxide, and carbon nanotubes.

4. The method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure according to claim 2, characterized in that, In step S1.2, the electrospinning process conditions are: voltage 10-50kV, receiving distance 5-25cm, injection speed 0.5-3mL / h, temperature 20-40℃, and relative humidity 20%-60%.

5. The method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure according to claim 2, characterized in that, In step S1.3, the pre-oxidation treatment temperature is 150-400℃, the time is 1-4 hours, and the heating rate is 1-5℃ / min; the carbonization treatment temperature is 800-1500℃, the time is 1-6 hours, and the heating rate is 2-10℃ / min; the inert gas is selected from at least one of nitrogen, argon, and helium.

6. The method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure according to claim 1, characterized in that, In step S1, the active material particles are selected from at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium manganese oxide; the binder is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, and polyacrylate; the mass ratio of active material particles, conductive carbon fiber, and binder is (85-95):(1-8):(1-8).

7. The method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure according to claim 1, characterized in that, In step S2, the first voltage is 30~50kV and the second voltage is 20~40kV; the spraying distance of the electrostatic spraying deposition is 1~20cm and the spraying speed is 5~10g / min; the thickness of the current collector is 10-20μm.

8. The method for preparing a thick electrode with high conductivity, high mass transfer, and stable structure according to claim 1, characterized in that, In step S3, the hot pressing temperature is 80~300℃, the hot pressing pressure is 10~80MPa, and the hot pressing time is 10~60min; the total thickness of the thick electrode is 70-500μm.

9. A thick electrode with high conductivity, high mass transfer, and stable structure prepared by the preparation method according to any one of claims 1 to 8.

10. A secondary battery, characterized in that, This includes thick electrodes with high conductivity, high mass transfer, and stable structure prepared by the preparation method according to any one of claims 1 to 8.

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