Montmorillonite modified graphite / sulfurized polyacrylonitrile composite positive electrode powder and preparation method and application thereof

Abstract

The invention relates to the technical field of positive electrode materials, in particular to montmorillonite modified graphite / sulfurized polyacrylonitrile composite positive electrode powder as well as a preparation method and application thereof. The preparation method comprises the following steps: dispersing polyacrylonitrile, graphite and montmorillonite in a volatile solvent, carrying out ultrasonic treatment, and evaporating the solvent to obtain a precursor; and physically mixing the precursor with sulfur, and performing high-temperature vulcanization in a nitrogen atmosphere to obtain the montmorillonite modified graphite / vulcanized polyacrylonitrile composite positive electrode powder. According to the invention, the sulfurized polyacrylonitrile is more uniformly limited in the montmorillonite and the graphite, so that the agglomeration phenomenon and side reaction of the sulfurized polyacrylonitrile in the synthesis process are reduced, the batch stability of the synthesis process is improved, the conductivity of the positive electrode material is increased, and the internal impedance of the battery is reduced; the charge-discharge performance of the vulcanized polyacrylonitrile is improved.

Description

Technical Field

[0001] This invention relates to the field of cathode material technology, and in particular to a montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder, its preparation method, and its application. Background Technology

[0002] Novel energy storage devices have become an effective solution for addressing the fossil fuel crisis and environmental pollution. Among them, lithium-sulfur batteries have a theoretical specific capacity of 1675 mAh g⁻¹. -1 Because it involves an electrochemical reaction process with 16 electrons, it is far superior to lithium-ion batteries using lithium iron phosphate (approximately 170 mAh g⁻¹). -1 The theoretical energy density of lithium-sulfur batteries is as high as 2600 Wh / kg. -1 This is several times higher than that of currently commercial lithium-ion batteries. Furthermore, compared to ordinary lithium-ion battery cathode materials, sulfur has advantages such as abundant natural reserves, environmental friendliness, and low cost. However, lithium-sulfur batteries face problems such as the polysulfide shuttle effect, lithium anode dendrite formation, and slow kinetic processes, which are difficult to solve. To address these issues, sulfurized polyacrylonitrile cathodes, as a novel organic cathode for lithium-sulfur batteries, have attracted widespread attention due to their unique chemical structure and excellent electrochemical performance. In this cathode, the active material sulfur is covalently bonded to the carbon skeleton in the form of short-chain sulfur. Unlike traditional lithium-sulfur batteries that can only use ether-based electrolytes, the covalent sulfur chains of sulfurized polyacrylonitrile can be charged and discharged in both ether-based and ester-based electrolytes, where energy conversion between sulfur and lithium sulfide occurs through a solid-solid conversion mechanism. This is completely different from the working mechanism in ether-based electrolytes, and polysulfides do not form during charging and discharging, thus fundamentally avoiding the "shuttle effect" of polysulfides. Therefore, it shows great promise for application in high-energy-density secondary metal sulfur batteries.

[0003] Vulcanized polyacrylonitrile (PAB) is polymerized from polyacrylonitrile (PA) and sulfur powder at a specific temperature. The polymerization process involves the cyclization of PAB and the sulfur-involved vulcanization reaction. Significant structural changes occur during the polymerization of PAB at temperatures between 330-460℃. Excessively high temperatures exacerbate the pyrolysis of PAB, reducing the amount of PAB bound to sulfur and resulting in a low specific capacity of the cathode. The cyclization and vulcanization reactions involved in the polymerization of PAB are both parallel and continuous, making it difficult to produce stable vulcanized PAB products by controlling temperature, heating time, vapor pressure, or molecular weight. The molecular structure of vulcanized PAB is highly complex, with existing studies revealing multiple structures. The electrode reaction mechanism of vulcanized PAB is closely related to its molecular structure; therefore, studying the electrode reaction mechanism helps inferring its molecular structure. Due to the structural diversity of vulcanized PAB, researchers still debate its specific structure, making the controllable synthesis of high-performance vulcanized PABs with stable structures extremely difficult. In addition, issues such as significant capacity decay at high sulfur content, poor compatibility with ester electrolytes, and poor rate performance due to poor conductivity and ion migration of the cathode material limit the charge / discharge rate and cycle stability of the battery, thus affecting the improvement of energy density.

[0004] To address these issues, researchers have proposed methods using composites with other functional materials, including inorganic material composites and polymer modification. Some inorganic materials can effectively promote electrochemical reactions and physically confine lithium-ion conduction during the formation of sulfurized polyacrylonitrile (PPI), thus controlling the preparation of PPI cathode materials. Alternatively, composites of some polymers with PPI can improve electrolyte compatibility and reduce side reactions. However, achieving stable positive and negative electrode cycling and suppressing side reactions while maintaining a high lithium-ion conduction rate beneficial to cycle stability is difficult, leading to battery performance instability and hindering further electrode material design. Therefore, it is necessary to select materials that can simultaneously promote electrolyte compatibility and ion conduction rate to form the positive electrode with PPI. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder, its preparation method, and its applications.

[0006] The first objective of this invention is to provide a method for preparing montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder, comprising the following steps: Polyacrylonitrile, graphite and montmorillonite were dispersed in a volatile solvent, and after ultrasonic treatment, the solvent was evaporated to obtain the precursor. The precursor was physically mixed with sulfur and then vulcanized at high temperature in a nitrogen atmosphere to obtain the montmorillonite-modified graphite / vulcanized polyacrylonitrile composite cathode powder.

[0007] Furthermore, the ratio of polyacrylonitrile to montmorillonite is 10:(1-2), and the mass ratio of polyacrylonitrile to graphite is 10:(1-3).

[0008] Furthermore, during the high-temperature vulcanization process, the precursor and sulfur are physically mixed in a ratio of 1:(2-4).

[0009] Furthermore, during the high-temperature vulcanization process, the mixture of precursor and sulfur is sealed and then heated to 250-400℃ at a rate of 1-10℃ / min, held for 1-6 hours, and then annealed at 200-310℃ for 1-5 hours.

[0010] Furthermore, the volatile solvents are water, ethanol, acetone, and dimethyl sulfoxide, and the mixture is ultrasonically treated at room temperature for 1-12 hours.

[0011] Furthermore, the mass percentages of the montmorillonite components are as follows: SiO2 65-70%, Al2O3 15-25%, MgO 4-8%, Fe2O3 <4%, CaO <2%, and other elements <1%.

[0012] A second objective of this invention is to provide a montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder prepared by the method described above.

[0013] A third objective of this invention is to provide a positive electrode sheet for lithium-sulfur batteries, comprising the above-mentioned montmorillonite-modified graphite / sulfurized polyacrylonitrile composite positive electrode powder.

[0014] Further, montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder, acetylene black, and binder are physically mixed, stirred in water, and uniformly ground to obtain a composite slurry. The composite slurry is then coated onto the surface of a carbon-coated aluminum foil and subsequently vacuum dried to obtain the cathode sheet.

[0015] Furthermore, the adhesive is sodium carboxymethyl cellulose and styrene-butadiene rubber, and the mass ratio of montmorillonite-modified graphite / vulcanized polyacrylonitrile composite cathode powder, acetylene black, sodium carboxymethyl cellulose and styrene-butadiene rubber is (7-8):(2-1):0.5:0.5; the composite slurry coating thickness is 10-25 μm.

[0016] The unique multidimensional pores and wettability of clay mineral materials enable high ion conductivity, suppress lithium anode dendrite formation, and exhibit good compatibility with electrolytes. Montmorillonite, with its two-dimensional channels, can effectively composite cathode materials and improve battery charge-discharge performance; graphite, with its high conductivity, can promote electron transfer during the reaction process. By constructing an artificial layer that fixes soluble polysulfides and regulates lithium-ion flux, the problems of lithium dendrite growth and polysulfide shuttle are effectively alleviated. The lithiophilic extended-layer lithium montmorillonite promotes the desolvation process of lithium ions and has a moderate adsorption capacity for polysulfides, effectively suppressing polysulfide shuttle.

[0017] This invention utilizes montmorillonite and graphite to co-confine and sulfidate polyacrylonitrile (PAC) cathode materials, resulting in a more stable PAC cathode material. This method effectively improves the batch stability of the cathode material, reduces agglomeration and side reactions during the synthesis of PAC, and addresses the problems of unstable synthesis and poor rate performance of traditional PAC cathodes, significantly improving electrochemical performance. Simultaneously, the montmorillonite used in this invention, after ultrasonic dispersion in ethanol, increases the interlayer spacing, enhancing ion transport capacity compared to un-ultrasonicized montmorillonite. This improves the cathode's conductivity, reduces battery impedance, and enhances the charge-discharge performance of PAC. The addition of montmorillonite with a wider interlayer spacing, along with graphite, synergistically regulates the electron cloud distribution of the PAC cathode, increasing the sulfur-sulfur bond content. Higher sulfur-sulfur bond content promotes increased discharge specific capacity, improves the cathode's electronic conductivity, and reduces capacity decay caused by unstable PAC cathodes, thus improving the cycle stability of lithium-sulfur batteries. This allows the battery to undergo 500 charge-discharge cycles, and the rate performance of the battery is significantly improved simultaneously, promoting the application of lithium-sulfur batteries under different conditions. Due to the addition of montmorillonite and graphite, the internal impedance of the battery is significantly reduced. This is because the electron transport capability of graphite effectively reduces charge transfer resistance, and the increased interlayer spacing of montmorillonite increases ion channels and improves the ion diffusion rate.

[0018] The cathode material prepared by this invention can be used in ester-based electrolytes or ether-based electrolytes, and exhibits excellent electrochemical performance in both electrolytes. Attached Figure Description

[0019] Figure 1 X-ray diffraction patterns of Comparative Example 1, Example 1, and Example 2; Figure 2 This is a scanning electron microscope image of Comparative Example 1; Figure 3 This is a scanning electron microscope image of Example 1; Figure 4 This is a scanning electron microscope image of Example 2; Figure 5 A comparison of charge-discharge curves for different positive electrodes; Figure 6 For different positive electrodes at 1.0 A g -1 The following is a cycle performance curve; Figure 7 For different positive electrodes at 0.5 A g -1 -10.0 A g -1 The rate performance curve at the following rates; Figure 8 Cyclic performance curves of different cathodes in ether electrolytes; Figure 9 These are electrochemical impedance spectroscopy spectra of different cathodes. Detailed Implementation

[0020] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0021] Example 1: (1) Preparation of precursors: Take 1 g of polyacrylonitrile, 0.1 g of graphite, and 0.1 g of montmorillonite, disperse them in 100 ml of ethanol, and mix for 30 minutes. Then, sonicate at room temperature for 8 hours to fully mix the cathode material and exfoliate the montmorillonite. Subsequently, evaporate the ethanol solvent using a rotary evaporator and collect the montmorillonite-modified graphite / polyacrylonitrile powder.

[0022] (2) High-temperature vulcanization: Montmorillonite-modified graphite / polyacrylonitrile powder was physically mixed with sulfur at a ratio of 1:4, and then placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 400℃ at a rate of 2℃ / min and held for 4 hours. Subsequently, it was annealed at 300℃ for 3 hours to obtain montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder. The conductivity of the cathode powder was tested, and the specific results are shown in Table 1.

[0023] (3) Preparation of cathode materials for lithium-sulfur batteries In a typical preparation method, acetylene black is used as a conductive agent, and sodium carboxymethyl cellulose and styrene-butadiene rubber are used as binders. Montmorillonite-modified graphite / vulcanized polyacrylonitrile composite cathode powder, acetylene black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are physically mixed in a ratio of 7:2:0.5:0.5, stirred in water, and uniformly ground. The mixture is then coated onto the surface of carbon-coated aluminum foil and vacuum dried at 60 °C for 8 h to obtain a sulfur cathode.

[0024] (4) Electrochemical testing: In an argon-filled glove box, a lithium metal sheet was used as the counter electrode, and the separator was Celgard 2500. The ester electrolyte was 1 mol / L LiPF6 dissolved in EC:DEC = 1:1 V%. The ether electrolyte was 1 mol / L LiTFSI dissolved in DME:DOL = 1:1 V%, with 1% LiNO3 added. CR2025 coin cells were used. Electrochemical testing was performed at 1 A g… -1 Constant current charge-discharge tests were conducted at current densities ranging from 1.7 to 2.8 V, with voltage ranges of 1.7–2.8 V. Rate tests were performed at current densities of 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 A g. -1 Constant current charge-discharge tests were performed at a rate of [missing value]. AC impedance testing was conducted at open-circuit voltage, with a frequency range of 0.01-100000 Hz and an amplitude of 0.05 mV.

[0025] After assembling the positive electrode into a lithium-sulfur battery, using an ester-based electrode solution, at a concentration of 1.0 A g... -1 Charge-discharge tests were conducted at a current density of 0.2 A g. -1 After two activation cycles, the concentration becomes 1.0 A g. -1 Discharge, the first discharge specific capacity was 1482 mAh g. -1 After 500 cycles, the discharge specific capacity is 993.3 mAh g. -1 The decay rate is 0.066% per lap. See Table 2 for specific data.

[0026] Example 2: (1) Preparation of precursors: Take 1 g of polyacrylonitrile, 0.3 g of graphite, and 0.2 g of montmorillonite, disperse them in 200 ml of ethanol, and mix for 60 minutes. Then, sonicate at room temperature for 12 hours to thoroughly mix the cathode material and exfoliate the montmorillonite. Subsequently, evaporate the ethanol solvent using a rotary evaporator and collect the montmorillonite-modified graphite / polyacrylonitrile powder.

[0027] (2) High-temperature vulcanization: Montmorillonite-modified graphite / polyacrylonitrile powder was physically mixed with sulfur at a ratio of 1:4, and then placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 330°C at a rate of 2°C / min and held for 6 hours. Subsequently, it was annealed at 280°C for 5 hours to obtain montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder. The conductivity of the cathode powder was tested, and the specific results are shown in Table 1.

[0028] (3) Preparation of cathode materials for lithium-sulfur batteries In a typical preparation method, acetylene black is used as a conductive agent, and sodium carboxymethyl cellulose and styrene-butadiene rubber are used as binders. Montmorillonite-modified graphite / vulcanized polyacrylonitrile composite cathode powder, acetylene black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are physically mixed in a ratio of 7:2:0.5:0.5, stirred in water, and uniformly ground. The mixture is then coated onto the surface of carbon-coated aluminum foil (a 12 mm diameter disc) and vacuum dried at 60 °C for 8 h to obtain a sulfur cathode.

[0029] (4) Electrochemical testing: In an argon-filled glove box, a lithium metal sheet was used as the counter electrode, and the separator was Celgard 2500. The ester electrolyte was 1 mol / L LiPF6 dissolved in EC:DEC = 1:1 V%. The ether electrolyte was 1 mol / L LiTFSI dissolved in DME:DOL = 1:1 V%, with 1% LiNO3 added. CR2025 coin cells were used. Electrochemical testing was performed at 1 A g… -1 Constant current charge-discharge tests were conducted at current densities ranging from 1.7 to 2.8 V, with voltage ranges of 1.7–2.8 V. Rate tests were performed at current densities of 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 A g. -1 Constant current charge-discharge tests were performed at a rate of [missing value]. AC impedance testing was conducted at open-circuit voltage, with a frequency range of 0.01-100000 Hz and an amplitude of 0.05 mV.

[0030] After assembling the positive electrode into a lithium-sulfur battery, using an ester-based electrode solution, at a concentration of 1.0 A g... -1 Charge-discharge tests were conducted at a current density of 0.2 A g. -1 After two activation cycles, the concentration becomes 1.0 A g. -1 Discharge, the first discharge specific capacity was 1224.3 mAh g. -1 After 500 cycles, the discharge specific capacity is 1057.7 mAh g. -1 The decay rate is 0.027% per lap. See Table 2 for specific data.

[0031] Comparative Example 1: (1) High-temperature vulcanization: Polyacrylonitrile powder was physically mixed with sulfur at a ratio of 1:3, then sealed and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 350°C at 3°C / min and maintained for 6 hours. Subsequently, it was annealed at 300°C for 3 hours to obtain sulfurized polyacrylonitrile cathode powder. The conductivity of the cathode powder was tested, and the specific results are shown in Table 1.

[0032] (2) Preparation of lithium-sulfur battery cathode: Vulcanized polyacrylonitrile, acetylene black, sodium carboxymethyl cellulose and styrene-butadiene rubber were physically mixed in a ratio of 7:2:0.5:0.5, stirred in water and ground evenly, coated onto the surface of carbon-coated aluminum foil, and then vacuum dried at 80 °C for 8 h to obtain sulfur cathode.

[0033] (3) Electrochemical testing: In an argon-filled glove box, a lithium metal sheet was used as the counter electrode, and the separator was Celgard 2500. The ester electrolyte was 1 mol / L LiPF6 dissolved in EC:DEC = 1:1 V%. The ether electrolyte was 1 mol / L LiTFSI dissolved in DME:DOL = 1:1 V%, with 1% LiNO3 added. CR2025 coin cells were used. Electrochemical testing was performed at 1 A g… -1 Constant current charge-discharge tests were conducted at current densities ranging from 1.7 to 2.8 V, with voltage ranges of 1.7–2.8 V. Rate tests were performed at current densities of 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 A g. -1 Constant current charge-discharge tests were performed at a rate of [missing value]. AC impedance testing was conducted at open-circuit voltage, with a frequency range of 0.01-100000 Hz and an amplitude of 0.05 mV.

[0034] After assembling the positive electrode into a lithium-sulfur battery, using an ester-based electrode solution, at a concentration of 1.0 A g... -1 Charge-discharge tests were conducted at a current density of 0.2 A g. -1 After two activation cycles, the concentration becomes 1.0 A g. -1 Discharge, the first discharge specific capacity was 1136.7 mAh g. -1 After 500 cycles, the discharge specific capacity is 716.7 mAh g. -1 The decay rate is 0.074% per lap. See Table 2 for specific data.

[0035] Table 1. Conductivity performance of the examples and comparative examples

[0036] Table 2 Electrochemical performance of the examples and comparative examples

[0037] Table 1 shows the conductivity test results. By comparison, the conductivity of Examples 1 and 2 after adding graphite and montmorillonite was significantly higher than that of the comparative example, indicating that the method can effectively improve the conductivity of the electrode material.

[0038] Figure 1The X-ray diffraction patterns of Comparative Example 1, Example 1, and Example 2 show that Comparative Example 1 only has diffraction peaks of sulfurized polyacrylonitrile, while Example 1 and Example 2 contain sulfurized polyacrylonitrile, montmorillonite, and graphite.

[0039] Figure 2 The image shown is a scanning electron microscope image of Comparative Example 1, which mainly consists of vulcanized polyacrylonitrile with a spherical structure. Figure 3 The scanning electron microscope image of Example 1 shows that the spherical structure of the sulfurized polyacrylonitrile is encapsulated inside montmorillonite and graphite, proving its confinement effect. Figure 4 The scanning electron microscope image of Example 2 shows that sulfurized polyacrylonitrile with a spherical structure is distributed on the surface of montmorillonite and graphite, which also proves its confinement effect.

[0040] Figure 5 The comparison of charge-discharge curves for different positive electrodes shows that Examples 1 and 2 have higher capacities and smaller polarization during the charging and discharging processes, while the comparative example has lower capacities and larger polarization during the charging and discharging processes. This indicates that the addition of montmorillonite and graphite can promote electrochemical reactions in both examples.

[0041] Figure 6 For different positive electrodes at 1.0 A g -1 The cycle performance curves show that the discharge specific capacity of the comparative example is lower than that of Examples 1 and 2, and the decay per cycle of 0.074% is also higher, indicating that its electrochemical performance is unstable. However, Example 1 has a higher initial capacity, and Example 2 has higher stability after cycling, which proves its advantage in cycle performance at higher current densities.

[0042] Figure 7 For different positive electrodes at 0.5 A g -1 -10.0 A g -1 The rate performance curves of Examples 1 and 2 show that the comparative example not only has a lower initial discharge specific capacity, but also a faster capacity decrease at high rates. In contrast, Examples 1 and 2 show a lower capacity at 10.0 A g. -1 It can achieve higher specific capacity at high rates, and even when it recovers to 0.5 A g, it can still achieve higher specific capacity. -1 It can still maintain a high discharge specific capacity, which proves that the addition of graphite and montmorillonite effectively improves the conductivity, enabling it to maintain excellent electrochemical performance at high rates.

[0043] Figure 8 The cycling performance curves of different cathodes in ether electrolytes are shown. It can be seen that the comparative example, at 1.0 A g, exhibits better performance in ether electrolytes. -1The capacity decreases faster during charging and discharging at the current density, while Examples 1 and 2 still have higher specific capacity after 200 cycles. This proves that the composite cathode with added graphite and montmorillonite can maintain excellent electrochemical performance in different electrolyte systems.

[0044] Figure 9 The comparison of electrochemical impedance spectroscopy for different cathodes shows that the first semicircle representing charge transfer impedance in Examples 1 and 2 is smaller than that in the comparative example, indicating that the electron transport rate of the composite cathode is significantly improved after the addition of graphite and montmorillonite.

[0045] For any points not covered above, existing technologies shall apply.

[0046] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder, characterized in that, Includes the following steps: Polyacrylonitrile, graphite and montmorillonite were dispersed in a volatile solvent, and after ultrasonic treatment, the solvent was evaporated to obtain the precursor. The precursor was physically mixed with sulfur and then vulcanized at high temperature in a nitrogen atmosphere to obtain the montmorillonite-modified graphite / vulcanized polyacrylonitrile composite cathode powder.

2. The preparation method according to claim 1, characterized in that, The ratio of polyacrylonitrile to montmorillonite is 10:(1-2), and the mass ratio of polyacrylonitrile to graphite is 10:(1-3).

3. The preparation method according to claim 1, characterized in that, During the high-temperature vulcanization process, the precursor and sulfur are physically mixed in a ratio of 1:(2-4).

4. The preparation method according to claim 1, characterized in that, During the high-temperature vulcanization process, the mixture of precursor and sulfur is sealed and then heated to 250-400℃ at a rate of 1-10℃ / min, held for 1-6 hours, and then annealed at 200-310℃ for 1-5 hours.

5. The preparation method according to claim 1, characterized in that, The volatile solvents are water, ethanol, acetone, and dimethyl sulfoxide. The mixture is ultrasonically treated at room temperature for 1-12 hours.

6. The preparation method according to claim 1, characterized in that, The mass percentage of montmorillonite components is as follows: SiO2 65-70%, Al2O3 15-25%, MgO 4-8%, Fe2O3 <4%, CaO <2%, and other elements <1%.

7. A montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder prepared by the preparation method according to any one of claims 1-6.

8. A positive electrode sheet for lithium-sulfur batteries, characterized in that, Including the montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder as described in claim 7.

9. A positive electrode sheet for lithium-sulfur batteries, characterized in that, Montmorillonite-modified graphite / sulfurized polyacrylonitrile composite cathode powder, acetylene black, and binder are physically mixed, stirred in water, and uniformly ground to obtain a composite slurry. The composite slurry is coated onto the surface of carbon-coated aluminum foil and then vacuum dried to obtain the cathode sheet.

10. The positive electrode sheet for a lithium-sulfur battery as described in claim 9, characterized in that, The adhesive is sodium carboxymethyl cellulose and styrene-butadiene rubber. The mass ratio of montmorillonite-modified graphite / vulcanized polyacrylonitrile composite cathode powder, acetylene black, sodium carboxymethyl cellulose and styrene-butadiene rubber is (7-8):(2-1):0.5:0.5; the coating thickness of the composite slurry is 10-25 μm.

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