Vulcanized polyacrylonitrile dry-method electrode as well as preparation method and application thereof

Abstract

The invention belongs to the field of lithium ion batteries, and discloses a sulfurized polyacrylonitrile dry-method electrode and a preparation method and application thereof.The sulfurized polyacrylonitrile dry-method electrode comprises a dry-method self-supporting film and a current collector, and the dry-method self-supporting film comprises sulfurized polyacrylonitrile, a composite conductive agent and a composite binder; the electrode constructed through collaborative optimization of a dry process and a composite binder system has the advantages that the chemical stability and cycle durability of the material can be remarkably improved through a low-porosity compact microstructure; the composite binder not only enhances the interface bonding strength of electrode components, but also constructs an efficient charge transfer channel, accelerates charge transfer dynamics, reduces polarization loss, and improves the SPAN utilization rate, the battery rate capability and the energy output efficiency; the surface load gt can be conveniently prepared by a multi-layer calendering dry process; the high-load electrode with the thickness of 15 mg cm <-2 > avoids the problems of non-uniform dispersion and out-of-control thickness in wet-process high-load preparation, does not need an organic solvent, and can be tightly laminated with flexible current collectors such as carbon-coated aluminum foil and carbon fiber cloth.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a sulfurized polyacrylonitrile dry electrode, its preparation method, and its application. Background Technology

[0002] With the rapid development of industries such as electronic devices and electric vehicles, the market demand for high-performance lithium-ion batteries is becoming increasingly urgent. Sulphurized polyacrylonitrile (SPAN), with its unique molecular structure and excellent electrochemical performance, has shown great application potential in the energy storage field, becoming one of the most competitive electrode materials. However, SPAN faces significant challenges in practical applications – its initial lithium intercalation process involves dramatic volume expansion. This problem stems from the simultaneous reduction reaction of sulfur groups and nitrogen-containing carbon skeletons in the PAN matrix. This volume change disrupts the reversibility of the material's structure, accelerating the mechanical degradation of the electrode, and this phenomenon is more pronounced under high load conditions. Traditional wet slurry processes further exacerbate this predicament. This process prepares the electrode by dispersing active materials, conductive additives, and polymer binders with solvents. While it can achieve coating uniformity, structural defects easily arise during the solvent drying stage: problems such as binder migration and conductive additive aggregation are particularly evident under high load scenarios. These defects, combined with the volume expansion effect of SPAN itself, lead to the loss of mechanical integrity and failure of effective electron transport channels in high-load SPAN wet electrodes during cycling, ultimately causing complete electrode failure.

[0003] In contrast, dry electrode manufacturing offers a new approach to solving these problems. This process eliminates the need for solvents, avoiding binder migration and conductive additive aggregation, while also imparting good structural integrity and mechanical robustness to the electrode, creating favorable conditions for achieving high-load SPAN electrodes. Unfortunately, current SPAN dry electrode fabrication generally follows mature inorganic material processes, primarily employing a single binder—polytetrafluoroethylene (PTFE). Due to its completely fluorine-containing, nonpolar molecular structure, PTFE exhibits almost negligible intrinsic ionic conductivity. In densely packed dry electrodes, this poor affinity leads to interfacial resistance and continuous lithium ion (Li) ionization. + The disruption of the transport pathway leads to slower charge transfer kinetics, reduced utilization of active materials under high areal loading, and severely impaired high-rate performance.

[0004] Therefore, developing dry electrode fabrication technology that adapts to SPAN characteristics and has excellent performance is of great practical significance and has broad application prospects for promoting the development of high-performance lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a dry-process electrode of vulcanized polyacrylonitrile, its preparation method and application, so as to overcome the technical bottlenecks of poor structural stability, low utilization rate of active materials and insufficient conductivity of existing dry-process electrodes of vulcanized polyacrylonitrile.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a vulcanized polyacrylonitrile dry electrode, comprising a dry self-supporting membrane and a current collector, wherein the dry self-supporting membrane comprises vulcanized polyacrylonitrile, a composite conductive agent, and a composite binder. The composite conductive agent includes at least three of the following: Super P, Ketjen Black, acetylene black, carbon nanotubes, and graphene. The composite adhesive comprises at least two of polytetrafluoroethylene (PTFE), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(styrene sulfonic acid) (PSS), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyimide (PI), and polyvinyl butyral (PVB).

[0007] Preferably, the mass ratio of the vulcanized polyacrylonitrile, the composite conductive agent, and the composite binder is 90-95:0.5-5:3-6, and more preferably 90:5:5.

[0008] Preferably, the composite conductive agent comprises acetylene black, carbon nanotubes, and graphene in a mass ratio of 3-6:1-4:1-3.

[0009] Preferably, the composite adhesive comprises polytetrafluoroethylene (PTFE), poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(styrene sulfonic acid) (PSS) in a mass ratio of 2-6:2:2-6.

[0010] Preferably, the thickness of the vulcanized polyacrylonitrile dry electrode is 40-500 μm.

[0011] Preferably, the current collector is one of carbon-coated aluminum foil, titanium mesh, stainless steel mesh, and carbon fiber cloth.

[0012] The dry self-supporting membrane in this invention is on one side or both sides of the current collector.

[0013] In a second aspect, the present invention provides a method for preparing a dry-process sulfurized polyacrylonitrile electrode, comprising: (1) The vulcanized polyacrylonitrile, composite conductive agent and composite binder are dry mixed, stirred and fibrillated to obtain a dry mixture. (2) After the dry mixture is preheated, it is repeatedly rolled to obtain a dry self-supporting membrane; (3) The dry self-supporting membrane is combined with the current collector by roller pressing to obtain the vulcanized polyacrylonitrile dry electrode.

[0014] Preferably, the dry mixing is a stepwise mixing: first, vulcanized polyacrylonitrile and composite conductive agent are premixed, then composite binder is added, and the mixture is mixed in a centrifuge to fibrillate the components in the composite binder to obtain the dry mixture.

[0015] Preferably, the rolling temperature in step (2) is 80-100℃, the initial roller spacing is set to 450-550μm, the roller speed is 3-6rpm, and the roller spacing is reduced by 20-50μm after each rolling.

[0016] Preferably, the temperature of the roll forming process in step (3) is 80-95℃ and the forming rate is 1.5-2.5m / min.

[0017] Thirdly, the present invention provides a lithium metal battery comprising the above-mentioned sulfurized polyacrylonitrile dry electrode and electrolyte.

[0018] Fourthly, the present invention provides an application of the above-mentioned sulfurized polyacrylonitrile dry electrode in the preparation of lithium metal batteries.

[0019] This invention utilizes a specific ratio of composite binder to vulcanized polyacrylonitrile (SPAN) and a composite conductive agent, mixed using a dry process, and then combined with a current collector to obtain a vulcanized polyacrylonitrile dry electrode. This electrode exhibits a uniform and dense microstructure, significantly improving chemical stability and cycle durability. This is due to the following aspects of the composite binder system: the fibrous structure of PTFE forms a robust three-dimensional network, enhancing the bonding strength between the active material, the composite conductive agent, and the current collector within the electrode, effectively suppressing the volume expansion and shedding of SPAN during charge and discharge; PEDOT and PSS not only act as binder components to improve interfacial bonding and ensure electrode structural integrity to enhance cycle stability, but as highly conductive polymers themselves, they can directly construct a continuous conductive network within the electrode, compensating for the insufficient intrinsic electronic conductivity of SPAN, thereby effectively reducing charge transfer resistance and improving the electrode's rate performance and charge / discharge efficiency. The synergistic effect of these three components ensures the electrode's structural integrity, cycle stability, and excellent electron transport efficiency.

[0020] The advantages and beneficial effects of this invention are: (1) The dry electrode of vulcanized polyacrylonitrile (SPAN) prepared by the present invention has low porosity, which confirms that a uniform and dense microstructure is formed inside the electrode. This structure can effectively inhibit the chemical structure damage of SPAN during electrode preparation and electrochemical cycling, and significantly improve the chemical stability and cycle durability of the material.

[0021] (2) The dry-process sulfurized polyacrylonitrile electrode prepared in this invention not only enhances the interfacial bonding strength between the various components of the electrode by adopting a composite binder system, but also constructs an efficient charge transport channel, significantly accelerates the charge transfer kinetics process inside the electrode, effectively reduces polarization loss, and thus greatly improves the electrochemical utilization rate of SPAN active material.

[0022] (3) The dry process of the present invention can conveniently prepare materials with a surface loading of >15 mg / cm³ through multilayer calendering technology. 2 The high-load electrode solves the problems of uneven dispersion and uncontrolled thickness that are easily encountered in the traditional wet process for high-load preparation. At the same time, the process does not require the use of organic solvents, avoiding the risk of liquid corrosion to the current collector. It can be directly and tightly pressed with flexible current collectors such as carbon-coated aluminum foil, carbon fiber cloth, and carbon nanotube paper. It is especially suitable for new battery structures such as flexible batteries, tandem batteries, and micro energy storage devices, providing key technical support for the development of high-energy-density and multifunctional lithium-ion batteries. Attached Figure Description

[0023] Figure 1 The electronic conductivity comparison diagram shows the SPAN dry electrode prepared in Examples 1-3 and Comparative Examples 1-3.

[0024] Figure 2 This is a comparison chart of porosity between Example 1 and Comparative Example 3.

[0025] Figure 3 The graphs show the cyclic performance test results for Example 1 and Comparative Examples 2-3. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0027] Example 1 This embodiment provides a dry-process sulfurized polyacrylonitrile electrode, its preparation method, and its application, including the following steps: Step 1: Place the vulcanized polyacrylonitrile (SPAN), acetylene black, carbon nanotubes, graphene, and PTFE powder in a vacuum drying oven and dry them at 80°C for 12 hours.

[0028] Step 2: Add the dried vulcanized polyacrylonitrile (SPAN), acetylene black, carbon nanotubes, and graphene to the feed hopper of the air jet mill, and set the milling parameters as follows: working pressure 0.6 MPa, feed rate 10 g / min, and classifier speed 8000 rpm. Mill each raw material for 30 minutes, and collect the product through a 300-mesh sieve.

[0029] Step 3: Weigh each component according to the ratio of SPAN: composite conductive agent (acetylene black: carbon nanotube: graphene = 5:3:2): composite binder (PEDOT: PSS: PTFE = 6:2:2) = 90:5:5.

[0030] Step 4: Pour the SPAN, acetylene black, carbon nanotubes and graphene weighed in step (3) into a high-speed disperser for premixing. Set the speed to 3000 rpm and disperse for 30 minutes to obtain mixed powder.

[0031] Step 5: Add the mixed powder from step (4) into a centrifugal mixer and add the components of the composite binder weighed in step (3) (PEDOT:PSS:PTFE=6:2:2). Set the rotation speed to 1500 rpm and the centrifugal force to 1000 g. Mix for 1 hour to obtain a uniform, lumpy, plastic dry mixture.

[0032] Step 6: Wrap the dry mixture in plastic wrap and preheat it in a 60℃ oven for 30 minutes. Place the preheated mixture into a heated roller mill, set the roller temperature to 90℃, the initial roller spacing to 500μm, and the roller speed to 5rpm. Repeat the rolling process multiple times, reducing the roller spacing by 20-50μm after each rolling process. Finally, control the electrode film thickness to 200μm. After rolling, a dry self-supporting membrane is obtained.

[0033] Step 7: Cut the dry self-supporting membrane to a suitable size, and put the dry self-supporting membrane and carbon-coated aluminum foil into a sheet laminator. Set the lamination temperature to 90℃ and the lamination rate to 2m / min. After lamination, a vulcanized polyacrylonitrile dry electrode is obtained.

[0034] Step 8: The above-mentioned sulfurized polyacrylonitrile dry electrode is rolled and cut to obtain a circular electrode sheet with a diameter of 10 mm. The circular electrode sheet is the positive electrode, and the 14 cm × 500 μm lithium metal is the negative electrode. It is matched with a Celgard separator and an electrolyte of 1 M LiPF6 in DEC:EC:FEC=9:9:2 Vol% is used. The electrode is assembled into a 2032 type button cell in an argon glove box with a water and oxygen content of less than 0.01 ppm.

[0035] Example 2 This embodiment refers to Example 1 to provide a dry-process sulfurized polyacrylonitrile electrode, its preparation method and application. The difference between this embodiment and Example 1 is that the ratio of PEDOT:PSS:PTFE=4:2:4 is used instead of PEDOT:PSS:PTFE=6:2:2 in Example 1. The other raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0036] Example 3 This embodiment provides a dry-process sulfurized polyacrylonitrile electrode and its preparation method and application, referring to Embodiment 1. The difference between this embodiment and Embodiment 1 is that the ratio of PEDOT:PSS:PTFE=2:2:6 is used instead of PEDOT:PSS:PTFE=6:2:2 in Embodiment 1, while the other raw material ratios and preparation methods are strictly consistent with Embodiment 1.

[0037] Comparative Example 1 This embodiment provides a vulcanized polyacrylonitrile dry electrode and its preparation method and application, with reference to Embodiment 1. The difference from Embodiment 1 is that PTFE binder is used instead of the composite binder (PEDOT:PSS:PTFE=6:2:2) in Embodiment 1, while the other raw material ratios and preparation methods are strictly consistent with Embodiment 1.

[0038] Comparative Example 2 This embodiment refers to Example 1 to provide a vulcanized polyacrylonitrile dry electrode and its preparation method and application. The difference from Example 1 is that a composite binder (PEDOT:PSS=6:4) is used instead of the composite binder (PEDOT:PSS:PTFE=6:2:2) in Example 1. The other raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0039] Comparative Example 3 This embodiment provides a dry-process sulfurized polyacrylonitrile electrode, its preparation method, and its application, with reference to Embodiment 1. The difference from Embodiment 1 is that a wet process is used instead of the dry process in Embodiment 1. The wet process includes the following steps: Step 1: Stainless polyacrylonitrile (SPAN) is ball-milled and filtered through a 300-mesh sieve to collect the powder for later use.

[0040] Step 2: Prepare 10% aqueous solutions of poly(3,4-ethylenedioxythiophene) (PEDOT), poly(styrene sulfonic acid) (PSS), and polytetrafluoroethylene (PTFE).

[0041] Step 3: Weigh the components according to the following ratio: SPAN: composite conductive agent (acetylene black: carbon nanotube: graphene = 5:3:2): composite binder (PEDOT: PSS: PTFE = 6:2:2) = 90:5:5.

[0042] Step 4: Mix the SPAN, composite conductive agent, composite binder and appropriate amount of deionized water described in Step 3, stir and disperse, and finally sieve to obtain electrode slurry.

[0043] Step 5: The electrode slurry described in Step 4 is coated onto carbon-coated aluminum foil with a coating thickness of 1500 μm and a coating speed of 10 m / min. Then, the active slurry is dried at 90°C with a wind frequency of 60 Hz to obtain a wet-process thick electrode of vulcanized polyacrylonitrile (SPAN).

[0044] Performance testing Performance tests were performed on the electrodes prepared in the examples and comparative examples, as well as the assembled 2032 model button cells: Electrode peel force test: The provided organic electrode was cut into dimensions of 61 mm wide and 75 mm long, and the electrode peel force was recorded. The test results are shown in Table 1.

[0045] Diaphragm resistance: The diaphragm resistance was recorded using an ACCFILM diaphragm resistance tester. The test results are shown in Table 1.

[0046] Electronic conductivity test: The resistance was recorded using a four-probe tester, and the electronic conductivity was calculated. The results are as follows: Figure 1 As shown.

[0047] The porosity of the electrodes prepared in Example 1 and Comparative Example 3 was tested: the porosity of the electrode sheets could be accurately determined using a three-dimensional X-ray microscope. Results Figure 2 As shown.

[0048] Cycle stability tests were conducted on the batteries prepared in Example 1 and Comparative Examples 2-3: activation was performed twice at 0.1C, followed by cycle performance testing at 0.5C. The test results are as follows: Figure 3 As shown.

[0049] Table 1 Performance test results of the examples and comparative examples

[0050] (1) By analyzing Table 1 and Figure 1-3Analysis of the test data shows that, compared with the SPAN dry electrodes of Examples 2-3 and Comparative Examples 1-2, the SPAN dry electrode of Example 1 exhibits core structural and interfacial advantages such as low porosity, high peel strength, and low membrane resistance. Low porosity ensures the integrity of the electrode structure and its service stability, reducing the risk of active material shedding during cycling. High peel strength improves the reliability of the interface between the electrode and the current collector, avoiding performance degradation caused by interface peeling during charging and discharging. Low membrane resistance effectively reduces electron transport impedance, synergistically optimizes ion diffusion channels, and significantly improves electrode conductivity and ion transport efficiency. In electrochemical performance testing, the SPAN dry electrode of Example 1 not only achieved a 13 mAh·cm⁻¹ electrochemical conductivity... -2 The electrode exhibits a high areal capacity (far exceeding the areal capacity level of conventional dry-process electrodes) and demonstrates superior capacity retention during long-term cycling. This performance fully verifies the synergistic effect of the preparation process used in Example 1 (emphasizing composite conductive agents and optimized dry-process electrode technology) on improving electrode structure and electrochemical performance. Its overall performance significantly surpasses the technical level of existing SPAN dry-process electrodes, providing key technical support for the development of high-energy-density, long-cycle-stability lithium-ion batteries.

[0051] (2) Comparing the proportions of each component of the composite adhesive in Example 1 and Examples 2-3, increasing the proportion of PEDOT can enhance the π-π conjugation with graphene, significantly improve electron transport efficiency, and meet the demand for fast conductivity in high-rate scenarios; increasing the proportion of PTFE can enhance mechanical strength through the fibrous winding structure, increase peeling force, suppress the volume change of vulcanized polyacrylonitrile, and improve long-cycle stability, but the insulation will cause the film resistance to increase and the electronic conductivity to decrease.

[0052] (3) Comparing the binders of Example 1 with those of Comparative Examples 1-2, the composite binder of Example 1 showed better performance. The fibrous structure of PTFE can form a tough three-dimensional network, enhancing the bonding strength between the active material, composite conductive agent, and current collector inside the electrode, effectively suppressing the volume expansion and shedding of SPAN during charging and discharging; at the same time, the bonding properties of PEDOT and PSS can further improve the interfacial bonding force, ensure the integrity of the electrode structure, and prolong cycle stability. In addition, as highly conductive polymers, PEDOT and PSS can construct a continuous conductive network inside the electrode, making up for the deficiency of SPAN's own insufficient electronic conductivity, reducing charge transfer resistance, and improving the electrode rate performance and charge-discharge efficiency.

[0053] (4) Comparison of the core processes and performance of Example 1 (dry process) and Comparative Example 3 (wet process) (e.g.) Figure 2 and Figure 3As shown in the figure, the two methods exhibit significant differences in electrode microstructure and service performance: the porosity of the dry electrode is only 10.3%, far lower than the 28.7% of the wet electrode. This low-porosity architecture not only endows the dry electrode with higher packing density and superior mechanical strength, but also effectively suppresses the volume expansion, active material shedding, and structural collapse of the electrode during charge-discharge cycles. In electrochemical performance testing, the dry electrode of Example 1 demonstrated excellent capacity retention during long-term cycling with no significant capacity decay; while the wet electrode of Comparative Example 3, due to its high porosity, suffered from insufficient electrode structural stability, resulting in a continuous increase in interfacial impedance during cycling. Simultaneously, the interfacial side reactions between the electrolyte and electrode materials intensified, ultimately leading to a significant capacity decay trend. This comparative result fully verifies the technical advantages of the dry process in constructing stable electrode microstructures, optimizing interfacial interactions, and improving electrochemical cycling stability, providing a more promising process route for the preparation of high-performance lithium-ion battery electrodes.

[0054] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A dry-process electrode made of vulcanized polyacrylonitrile, characterized in that, It includes a dry self-supporting membrane and a current collector, wherein the dry self-supporting membrane comprises vulcanized polyacrylonitrile, a composite conductive agent, and a composite binder; The composite conductive agent includes at least three of the following: Super P, Ketjen Black, acetylene black, carbon nanotubes, and graphene. The composite adhesive includes at least two of polytetrafluoroethylene, poly(3,4-ethylenedioxythiophene), poly(styrene sulfonic acid), sodium carboxymethyl cellulose, styrene-butadiene rubber, polyimide, and polyvinyl butyral.

2. The dry-process sulfurized polyacrylonitrile electrode according to claim 1, characterized in that, The mass ratio of vulcanized polyacrylonitrile, conductive agent, and composite binder is 90-95:0.5-5:3-6.

3. The dry-process sulfurized polyacrylonitrile electrode as described in claim 1, characterized in that, The composite conductive agent comprises acetylene black, carbon nanotubes, and graphene in a mass ratio of 3-6:1-4:1-3.

4. The dry-process sulfurized polyacrylonitrile electrode according to claim 1, characterized in that, The composite adhesive comprises polytetrafluoroethylene, poly(3,4-ethylenedioxythiophene), and poly(styrene sulfonic acid) in a mass ratio of 2-6:2:2-6.

5. The dry-process sulfurized polyacrylonitrile electrode according to claim 1, characterized in that, The thickness of the vulcanized polyacrylonitrile dry electrode is 40-500 μm.

6. The dry-process sulfurized polyacrylonitrile electrode according to claim 1, characterized in that, The current collector is one of the following: carbon-coated aluminum foil, titanium mesh, stainless steel mesh, or carbon fiber cloth.

7. A method for preparing a dry-process sulfurized polyacrylonitrile electrode as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) The vulcanized polyacrylonitrile, composite conductive agent and composite binder are dry mixed, stirred and fibrillated to obtain a dry mixture. (2) After the dry mixture is preheated, it is repeatedly rolled to obtain a dry self-supporting membrane; (3) The dry self-supporting membrane is combined with the current collector by roller pressing to obtain the vulcanized polyacrylonitrile dry electrode.

8. The preparation method according to claim 7, wherein the dry mixing is a stepwise mixing: first, vulcanized polyacrylonitrile and composite conductive agent are premixed, then composite binder is added, and the mixture is mixed in a centrifuge to fibrillate the components in the composite binder to obtain the dry mixture.

9. A lithium metal battery, characterized in that, Includes the vulcanized polyacrylonitrile dry electrode and electrolyte as described in any one of claims 1-6.

10. The application of a sulfurized polyacrylonitrile dry electrode as described in any one of claims 1-6 in the preparation of lithium metal batteries.

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