Preparation and application of high-performance phase inversion method sulfidized polyacrylonitrile positive electrode material

Abstract

This invention discloses the preparation and application of a high-performance sulfurized polyacrylonitrile (PAB) cathode material based on a phase inversion method, relating to the field of high-performance lithium-sulfur battery cathode materials. This invention combines a spray phase inversion method with a heat treatment process to form core-shell structured microspheres with high sulfur content. The core is an S8 microsphere, and the outer shell is selenium-doped sulfurized PAB (S7Se / PAN). The tightly packed microsphere structure significantly improves the tap density of the material, enabling it to be used to manufacture practical sulfur cathodes with high active material loading. Electrochemical testing results show that this core-shell composite cathode material exhibits high energy density and excellent cycle stability and rate performance.

Description

Technical Field

[0001] This invention relates to the field of high-performance lithium-sulfur battery cathode materials, and in particular to the preparation and application of a high-performance sulfurized polyacrylonitrile cathode material based on the phase inversion method. Background Technology

[0002] Traditional sulfur cathode materials suffer from the dissolution and shuttle effect of soluble polysulfides in ether-based electrolyte systems, leading to poor battery cycle stability and low coulombic efficiency. Although existing studies have attempted to suppress polysulfide dissolution through methods such as loading porous carbon materials and modifying with polar compounds, these methods typically struggle to simultaneously achieve high sulfur loading, high tap density, and a stable electrode / electrolyte interface.

[0003] Sulphurized polyacrylonitrile (SPAN) cathode materials effectively circumvent polysulfide dissolution issues due to their unique solid-solid conversion mechanism, but traditional preparation methods still present several key challenges. In SPAN materials prepared by conventional pyrolysis methods, the sulfur content typically cannot exceed 50 wt%. Excessive sulfur loading leads to instability in the polyacrylonitrile framework structure, affecting conductivity and electrochemical performance. Furthermore, traditional SPAN materials generally have low tap density (<1.0 g / cm³). While the porous structure facilitates electrolyte wetting, it reduces the electrode's volumetric energy density. Simultaneously, under high sulfur content conditions, the cathode-electrolyte interface formed by the SPAN cathode in the carbonate electrolyte is predominantly organic, lacking sufficient mechanical strength and prone to cracking during cycling, triggering continuous side reactions and impacting battery cycle life. Existing methods for improving the performance of sulphurized polyacrylonitrile still have significant limitations. For example, elemental doping can improve conductivity, but its effect on improving interface stability under high sulfur content is limited; while nanostructure design optimizes electrode / electrolyte contact, the preparation process is complex, and the improvement in tap density is limited.

[0004] Therefore, it is essential to develop a simple preparation method for a high-sulfur-content sulfurized polyacrylonitrile cathode material, which is of great significance for promoting the practical application of sulfur cathodes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying high-performance sulfurized polyacrylonitrile (SPAN) cathode materials based on phase inversion, addressing the problems of poor electrochemical stability, insufficient cycle life, and sluggish interfacial reaction kinetics in existing SPAN-based cathode materials under high sulfur content conditions. This invention significantly improves the energy density, cycle stability, and rate performance of SPAN-based cathode materials by optimizing the material structure and interfacial chemistry.

[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is a high-performance vulcanized polyacrylonitrile cathode material (S8@S7Se / PAN composite material), wherein the high-performance vulcanized polyacrylonitrile cathode material has a core-shell structure, the core being S8 (cyclooctasulfide) microspheres and the outer shell being S7Se / PAN composite material (selenium-doped vulcanized polyacrylonitrile). The sulfur content of the high-performance vulcanized polyacrylonitrile cathode material is greater than 60 wt%.

[0007] The introduction of S8 microspheres in elemental form increases the content of electrochemically active materials available for the electrode. The S7Se / PAN shell selectively blocks the contact between the electrolyte and the active sulfur core, improving the interfacial stability of the cathode material. The selenized polymer backbone exhibits excellent electron transport properties and ionic conductivity, assisting S8 in the solid-phase transformation of electrochemical processes. The closely packed microsphere structure significantly improves its tap density, enabling the fabrication of practical sulfur cathodes with high active material loading.

[0008] Furthermore, the tap density of the high-performance vulcanized polyacrylonitrile cathode material is 1.8~2.2 g / cm³. 3 The average particle size is 4~6 μm.

[0009] Preferably, the sulfur content of the high-performance vulcanized polyacrylonitrile cathode material is 60-70 wt%, more preferably 67.4 wt%.

[0010] The second technical solution of the present invention: a phase inversion method for preparing the above-mentioned high-performance vulcanized polyacrylonitrile cathode material, comprising the following steps: S8 microspheres were mixed with PAN (polyacrylonitrile) and solvent to prepare S8@PAN precursor by spray phase inversion method; The S8@PAN precursor is mixed with S7Se powder and then subjected to heat treatment to obtain the S8@S7Se / PAN composite material, which is the high-performance vulcanized polyacrylonitrile cathode material.

[0011] The core principle of the phase inversion method is to regulate the phase separation behavior of polymer systems through the exchange of solvents and non-solvents, thereby precisely controlling the microstructure and pore structure of the material. The advantage of this method is that it can achieve homogeneous composite of multiple components in a one-step process and optimize the microstructure and macroscopic properties of the material. This invention achieves uniform loading of high sulfur content through the phase inversion method and forms a more stable interface layer in situ on the material surface.

[0012] Furthermore, the solvent includes N,N-dimethylformamide (DMF).

[0013] Furthermore, the molecular weight (M) of the PAN w The concentration is 150,000-230,000 g / mol.

[0014] Furthermore, the mass ratio of the S8 microspheres to the PAN is 1:2.

[0015] Furthermore, the ratio of PAN to solvent is 1 g: 50 mL.

[0016] Furthermore, the mass ratio of the S8@PAN precursor to the S7Se powder is 1:4.

[0017] Furthermore, the parameters of the spray phase inversion method include: a spray pressure of 0.1~0.5 MPa.

[0018] Furthermore, the coagulation bath used in the spray phase inversion method is water.

[0019] The steps of the spray phase inversion method include: injecting a mixed solution obtained by mixing S8 microspheres with PAN and solvent into a water coagulation bath, inducing phase inversion by utilizing the difference in solubility to form S8@PAN precursor microspheres, and obtaining well-dispersed S8@PAN precursor microsphere powder after freeze-drying.

[0020] Furthermore, the water temperature is 25 °C to ensure uniform particle size distribution of the S8@PAN precursor microspheres.

[0021] Furthermore, the heat treatment temperature is 350~450 ℃, and the time is 3~5 hours.

[0022] Furthermore, the heating rate of the heat treatment is 5~10 °C / min.

[0023] Furthermore, the heat treatment is performed under a nitrogen atmosphere.

[0024] During the heat treatment process, an S7Se / PAN shell with a conductive network is generated through a gas-phase vulcanization reaction, ultimately yielding the S8@S7Se / PAN composite material.

[0025] Furthermore, the preparation steps of the S8 microspheres include: dissolving sodium thiosulfate (Na2S2O3) and polyvinylpyrrolidone (PVP K30) in water, adding hydrochloric acid solution dropwise, and reacting for 2 hours to obtain the S8 microspheres.

[0026] Furthermore, the ratio of sodium thiosulfate, polyvinylpyrrolidone, water, and hydrochloric acid solution is 5 g: 0.5 g: 500 mL: 4 mL.

[0027] Furthermore, the concentration of the hydrochloric acid solution is 37 wt%.

[0028] Furthermore, the preparation steps of the S7Se powder include: mixing sulfur (S) powder and selenium (Se) powder, keeping them at 280 °C for 4 hours for co-melting, and then cooling to obtain the S7Se powder.

[0029] Furthermore, the molar ratio of the sulfur powder to the selenium powder is 7:1.

[0030] The third technical solution of the present invention: the application of the above-mentioned high-performance sulfurized polyacrylonitrile cathode material in the preparation of lithium-sulfur battery cathodes.

[0031] The fourth technical solution of the present invention: a method for preparing a lithium-sulfur battery cathode, comprising the following steps: The above-mentioned high-performance vulcanized polyacrylonitrile cathode material is mixed with a conductive agent and a binder to obtain an electrode slurry; the electrode slurry is coated on a current collector, dried, and then pressed into a sheet to obtain the lithium-sulfur battery cathode.

[0032] Furthermore, the adhesive comprises polyacrylic acid (PAA) and guar gum (GG).

[0033] Furthermore, the mass ratio of the polyacrylic acid to the guar gum is 1:1.

[0034] Furthermore, the mass ratio of the high-performance vulcanized polyacrylonitrile cathode material, the conductive agent, and the binder is 8:1:1.

[0035] Furthermore, the areal loading of sulfur in the positive electrode of the lithium-sulfur battery is ≥3 mg / cm³. 2 .

[0036] Preferably, the areal loading of sulfur in the positive electrode of the lithium-sulfur battery is 3.1~6.0 mg / cm³. 2 .

[0037] The fifth technical solution of the present invention: a lithium-sulfur battery cathode prepared according to the above preparation method.

[0038] The sixth technical solution of the present invention: a lithium-sulfur battery, using the above-mentioned lithium-sulfur battery positive electrode as the positive electrode.

[0039] Furthermore, the negative electrode of the lithium-sulfur battery is lithium, and the electrolyte is a 1 M LiPF6 solution.

[0040] The electrolyte solvent is EC (ethylene carbonate) and DMC (dimethyl carbonate).

[0041] The present invention discloses the following technical effects: This invention presents a high-sulfur-selenium-content sulfurized polyacrylonitrile (SPAN) cathode material prepared via a phase inversion method. Compared to traditional micron-scale continuous SPAN materials, this method enhances the tap density of the material through the difference in solubility at the solvent / non-solvent interface during the phase inversion process and the densification characteristics of the microsphere structure. Simultaneously, the S7Se / PAN shell selectively blocks contact between the electrolyte and the active sulfur core, exhibiting excellent interfacial stability and long cycle life in lithium storage performance tests. This synthesis strategy is simple, easy to scale up, and provides a feasible solution for the large-scale preparation of high-performance lithium-sulfur battery cathode materials. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 SEM image of the S8@S7Se / PAN composite material prepared in Example 1 of this invention; Figure 2 TEM image of the S8@S7Se / PAN composite material prepared in Example 1 of this invention; Figure 3 EDS elemental mapping diagram of the S8@S7Se / PAN composite material prepared in Example 1 of this invention; Figure 4 The XRD pattern of the S8@S7Se / PAN composite material prepared in Example 1 of this invention; Figure 5 The Raman spectrum of the S8@S7Se / PAN composite material prepared in Example 1 of this invention; Figure 6 The graph shows the cycle performance of lithium-sulfur batteries assembled using the S8@S7Se / PAN composite material prepared in Example 1 or the conventional SPAN prepared in Comparative Example 1. Figure 7 The rate performance diagrams show lithium-sulfur batteries assembled using the S8@S7Se / PAN composite material prepared in Example 1 or the conventional SPAN prepared in Comparative Example 1. Detailed Implementation

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0046] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0047] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0050] In the following embodiments and comparative examples of the present invention, room temperature refers specifically to 20-30°C.

[0051] Unless otherwise specified, all raw materials used in the following embodiments and comparative examples of this invention are commercially available products. Specifically, the molecular weight (M) of PAN is... w The value is 150,000 g / mol.

[0052] Example 1 The high-performance vulcanized polyacrylonitrile cathode material (i.e., S8@S7Se / PAN composite material) was prepared based on the phase inversion method, and the steps are as follows: (1) Preparation of S8 microspheres Dissolve 5 g Na2S2O3 and 0.5 g PVP K30 in 500 mL of deionized water, slowly add 4 mL of concentrated hydrochloric acid (37 wt%), stir at room temperature for 2 h, centrifuge and wash, and then vacuum dry at 60 ℃ for 12 h to obtain S8 microspheres.

[0053] (2) Preparation of S8@PAN precursor by spray phase inversion method The S8 microspheres prepared in step (1) were added to 10 mL of DMF at a mass ratio of 1:2 (0.1 g:0.2 g), and ultrasonically dispersed for 2 h to ensure complete dissolution, resulting in a mixed solution. The mixed solution was then sprayed into a deionized water coagulation bath at 25 °C using a high-pressure spray device (nozzle diameter 0.5 mm, pressure 0.3 MPa) to induce phase separation and form S8@PAN core-shell microspheres. After freeze-drying, S8@PAN precursor microsphere powder was obtained.

[0054] (3) Preparation of S8@S7Se / PAN by gas-phase sulfidation reaction S powder and Se powder were mixed and co-melted at 280 °C for 4 hours, then cooled to obtain S7Se powder. The S8@PAN precursor microsphere powder prepared in step (2) was ball-milled with S7Se powder at a mass ratio of 1:4 for 30 min. The mixture was heated to 350 °C at a heating rate of 5 °C / min under N2 atmosphere, held for 210 min, and then naturally cooled to obtain S8@S7Se / PAN.

[0055] Testing revealed that the overall sulfur content of the S8@S7Se / PAN composite material prepared in this embodiment was 67.4 wt%, and the tap density (measured using a ZS-102 tap density meter) was 2.2 g / cm³. 3 .

[0056] Comparative Example 1 PAN and sulfur powder were mixed and ground at a mass ratio of 1:4, and then co-melted at 350 °C for 4 hours. After cooling, conventional SPAN powder was obtained with a sulfur content of 44 wt% and a tap density of 1.80 g / cm³. 3 .

[0057] Test Example 1 Characterization data: Figure 1 The image shows the SEM image of the S8@S7Se / PAN composite material prepared in Example 1. It can be seen that the S8@S7Se / PAN composite material prepared in Example 1 exhibits uniform spherical particles with an average particle size of 5 μm. The surface is dense and crack-free, which conforms to the characteristics of a core-shell structure.

[0058] Figure 2The TEM image shows the S8@S7Se / PAN composite material prepared in Example 1, indicating that the shell (S7Se / PAN) thickness is 200±20 nm.

[0059] Figure 3 The image shows the EDS elemental mapping of the S8@S7Se / PAN composite material prepared in Example 1. It can be seen that the S element is concentrated in the core region of the microsphere, while the C and N elements uniformly cover the outer shell, proving the successful composite of the sulfur core and the S7Se / PAN shell.

[0060] Figure 4 The XRD pattern of the S8@S7Se / PAN composite material prepared in Example 1 shows that an amorphous diffraction peak appears near 25°, corresponding to the disordered carbon skeleton of the vulcanized polyacrylonitrile. Furthermore, no crystalline peaks of elemental S or S7Se (PDF#23-0603) were detected, indicating that sulfur and selenium have been completely doped into the PAN matrix.

[0061] Figure 5 The Raman spectrum of the S8@S7Se / PAN composite material prepared in Example 1, with a characteristic peak position of 307 cm⁻¹. -1 (CS), 387 cm -1 (S-Se), 470 / 926 cm -1 (SS) confirmed the covalent bond between S7Se and PAN; D peak (1325 cm⁻¹) -1 ) and G peak (1532 cm) -1 The strength ratio (ID / IG=0.98) indicates that the material has a high degree of graphitization, which is beneficial for electron conduction.

[0062] Application Example 1 The preparation steps for the positive electrode of a lithium-sulfur battery are as follows: The positive electrode material, conductive carbon black (Super P), and polyacrylic acid (PAA) / guar gum (GG) binder (mass ratio 0.5:0.5) were mixed at a mass ratio of 8:1:1. The mixture was then prepared with deionized water and coated onto aluminum foil. The mixture was vacuum dried at 120 °C for 12 h, with the sulfur surface loading controlled at 5.0 mg / cm³. 2 Then, it is stamped on a tablet press to obtain the positive electrode sheet for lithium-sulfur batteries.

[0063] The assembly steps for lithium-sulfur batteries are as follows: In a glove box with H2O / O2 < 0.1 ppm, CR2032 coin cells were assembled using lithium metal as the negative electrode, the aforementioned lithium-sulfur battery positive electrode sheet as the positive electrode, and commercially available 1 M LiPF6 (EC:DMC = 1:1, v / v) electrolyte. The assembled cells were subjected to constant current charge-discharge tests at 25°C from 0.1 to 5 C (1 C = 1672 mA / g), with a voltage window of 1.0–3.0 V. The test results are as follows: Figures 6-7 As shown.

[0064] Figure 6 The graph shows the cycle performance (at 0.2 C) of lithium-sulfur batteries assembled using the S8@S7Se / PAN composite material prepared in Example 1 or the conventional SPAN prepared in Comparative Example 1. The S8@S7Se / PAN composite material achieved an initial discharge capacity of 1193.6 mAh / g at 0.2 C, retaining 49% of its capacity (588.7 mAh / g) after 500 cycles. In contrast, the conventional SPAN exhibited an initial discharge capacity of only 1084.8 mAh / g at 0.2 C, which decreased to 17.1 mAh / g after 500 cycles, verifying the improved stability brought about by the core-shell structure of the S8@S7Se / PAN composite material.

[0065] Figure 7 The rate performance diagrams of lithium-sulfur batteries assembled using the S8@S7Se / PAN composite material prepared in Example 1 or the conventional SPAN prepared in Comparative Example 1 show that Example 1 still provides a capacity of 278.4 mAh / g at a high rate of 5 C, which is 2.29 times that of Comparative Example 1 (121.5 mAh / g). After the current is restored to 0.1 C, the capacity of Example 1 recovers to 1097 mAh / g, demonstrating the high reversibility of the S8@S7Se / PAN composite material structure prepared in Example 1.

[0066] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-performance vulcanized polyacrylonitrile cathode material, characterized in that, The high-performance vulcanized polyacrylonitrile cathode material has a core-shell structure, with an S8 microsphere core and an S7Se / PAN composite material shell. The sulfur content of the high-performance vulcanized polyacrylonitrile cathode material is greater than 60 wt%.

2. The high-performance vulcanized polyacrylonitrile cathode material as described in claim 1, characterized in that, The tap density of the high-performance vulcanized polyacrylonitrile cathode material is 1.8~2.2 g / cm³. 3 The average particle size is 4~6 μm.

3. A phase inversion method for preparing high-performance vulcanized polyacrylonitrile cathode material as described in any one of claims 1 to 2, characterized in that, Includes the following steps: S8 microspheres were mixed with PAN and solvent to prepare S8@PAN precursor by spray phase inversion method; The S8@PAN precursor is mixed with S7Se powder and then subjected to heat treatment to obtain the S8@S7Se / PAN composite material, which is the high-performance vulcanized polyacrylonitrile cathode material.

4. The phase inversion method for preparing the high-performance vulcanized polyacrylonitrile cathode material as described in claim 3, characterized in that, The solvent includes N,N-dimethylformamide.

5. The phase inversion method for preparing the high-performance vulcanized polyacrylonitrile cathode material as described in claim 3, characterized in that, The parameters of the spray phase inversion method include: spray pressure of 0.1~0.5 MPa.

6. The phase inversion method for preparing the high-performance vulcanized polyacrylonitrile cathode material as described in claim 3, characterized in that, The heat treatment is performed at a temperature of 350~450 ℃ for 3~5 hours.

7. The application of the high-performance sulfurized polyacrylonitrile cathode material as described in any one of claims 1 to 2 in the preparation of lithium-sulfur battery cathodes.

8. A method for preparing a lithium-sulfur battery cathode, characterized in that, Includes the following steps: The high-performance vulcanized polyacrylonitrile cathode material according to any one of claims 1 to 2 is mixed with a conductive agent and a binder to obtain an electrode slurry; the electrode slurry is coated on a current collector, dried, and then pressed into a sheet to obtain the lithium-sulfur battery cathode.

9. A lithium-sulfur battery cathode prepared by the preparation method according to claim 8.

10. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery cathode as described in claim 9 is used as the cathode.

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