Preparation method and application of nanosheet-shaped lithium-sulfur battery positive electrode catalytic material

Abstract

The application discloses a preparation method and application of a nanosheet lithium-sulfur battery positive electrode catalytic material, and through hydrothermal synthesis combined with a high-temperature calcination process, In2O3 and CQDs are precisely co-anchored on g-C3N4 nanosheet lattice sites, a "physical confinement-electron / ion dual high-speed transport network-bipolar catalysis" trinity synergistic catalytic system is constructed, the catalytic system relies on two-dimensional hierarchical pores of the g-C3N4 nanosheet to constrain the volume deformation of sulfur; the introduction of CQDs compensates for the inherent defects of poor intrinsic conductivity of pure-phase g-C3N4, and a continuous and efficient electron-ion mixed transport network is constructed; the In2O3 catalytic phase and the rich N active sites on the surface of the g-C3N4 substrate form a functional complementation, efficient anchoring and rapid conversion of LiPSs are realized, and the shuttle effect is inhibited from the root. The application can significantly improve the rate performance and long cycle stability of lithium-sulfur batteries without noble metals and complex processes.

Description

Technical Field

[0002] This invention belongs to the field of lithium-sulfur battery cathode material technology, specifically relating to a method for preparing and applying a nanosheet-like lithium-sulfur battery cathode catalytic material. Background Technology

[0004] With the rapid iteration of the global new energy industry, the market demand for high-energy-density electrochemical energy storage continues to surge. The energy density of traditional commercial lithium-ion batteries has approached the theoretical limit of materials and cannot meet the high-requirement application scenarios such as long driving range of new energy vehicles, long standby time of portable electronic devices, and special energy storage. There is an urgent need to break through the performance of next-generation energy storage technology.

[0005] Lithium-sulfur batteries, with a theoretical specific capacity of 1675 mAh / g and a theoretical energy density of 2600 Wh / kg, far surpass existing lithium-ion battery systems. Furthermore, the core active material, sulfur, is abundant, inexpensive, and environmentally friendly, making it the next-generation high-energy-density energy storage technology with the greatest commercial potential. However, elemental sulfur has poor intrinsic conductivity. During charging and discharging, both sulfur and the final discharge product Li₂S are insulating phases, resulting in extremely slow redox kinetics of polysulfides (LiPSs). A large amount of intermediate products continuously accumulate inside the electrode. When elemental sulfur is fully lithiated during charging and discharging, it undergoes a volume deformation of up to approximately 80%, easily causing the overall structure of the positive electrode to pulverize and collapse, leading to irreversible shedding and deactivation of the active material. Soluble LiPSs induce a "shuttle effect," continuously corroding the lithium metal anode and causing a large amount of irreversible loss of active sulfur. Ultimately, this results in short cycle life and poor rate performance in lithium-sulfur batteries, failing to meet commercial application requirements.

[0006] To address the aforementioned core technical challenges of lithium-sulfur batteries, methods include using porous carbon materials to physically confine LiPSs within the cathode reaction region, utilizing the strong chemisorption of polar metal compounds to fix LiPSs, or introducing highly active catalytic sites into the cathode system to accelerate the redox conversion of LiPSs. However, existing solutions have consistently failed to overcome the inherent limitations of the "single adsorption / single catalysis" approach: the nonpolar carbon matrix and polar LiPSs can only form weak van der Waals forces, failing to achieve a long-term stable anchoring effect; furthermore, the surface of pure carbon materials lacks active sites capable of efficiently catalyzing LiPS conversion, making it difficult to meet the kinetic requirements of rapid liquid-solid phase transitions in LiPSs; simply introducing a metal catalytic phase cannot directionally control the diffusion path of LiPSs, resulting in a large amount of free LiPSs failing to be precisely transported to the surface of the catalytic active sites to complete the reaction, ultimately leading to escape shuttle, thus failing to fundamentally solve the shuttle problem.

[0007] In the prior art, patent document CN201810183323.7 discloses a ZnO-C3N4-CQDs visible light catalytic composite material and its preparation method. Based on the excellent electron storage capacity and upconversion fluorescence performance of CQDs, which can form a water-soluble protection on the material surface, the excellent electron transport properties of ZnO, and the excellent electron migration properties of C3N4, the similar conjugated structure of CQDs and C3N4 can enable them to stably aggregate on the ZnO surface to form a stable three-phase structure. The π–π interaction between the conjugated structure of CQDs and benzene is conducive to the enrichment of benzene on the surface of the composite material. The three work synergistically to efficiently degrade organic gaseous pollutants under visible light. Patent document CN202410022423.7 discloses a method and application for microwave-assisted hydrothermal preparation of g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts. By combining g-C3N4 and CQDs with FeVO4 to form a heterojunction photocatalyst, it effectively solves the shortcomings of g-C3N4, such as rapid recombination of photoinduced charge carriers, low visible light utilization, easy particle aggregation, and few reactive sites. However, the technical solutions in both patent documents only describe the application of g-C3N4 and CQDs composites in the field of photocatalysts. They do not involve related technical solutions for designing lithium-sulfur battery cathode catalyst materials by combining In2O3 catalytic phase and carbon quantum dots (CQDs) with graphitic carbon nitride (g-C3N4), nor do they provide any technical inspiration for precisely co-anchoring the two at the lattice sites of graphitic carbon nitride nanosheets to construct a three-in-one synergistic catalytic system integrating "physical confinement - high-speed electron / ion transport network - bipolar catalysis".

[0008] Patent document CN202410194404.2 discloses a polyanionic cathode composite material, its preparation method, and its application. The composite material includes a core and a coating layer. The core is a polyanionic material, and the coating layer is a high-entropy carbon quantum dot coating layer. By using carbon quantum dots with a specific structure as the coating layer, the abundant tunable electronegativity elements in the carbon quantum dots can synergistically improve the conductivity and interfacial stability of the carbon composite layer, which is beneficial to improving the structural stability and integrity of the electrode material. However, the technical solution of this patent document only involves enhancing the conductivity of the cathode composite material through the high-entropy carbon quantum dot coating layer. It does not involve the relevant technical inspiration of precisely co-anchoring the catalytic phase In2O3 and CQDs on the lattice sites of graphitic carbon nitride nanosheets to construct a three-in-one synergistic catalytic system integrating "physical confinement - high-speed electron / ion transport network - bipolar catalysis". Patent document CN202610478463.1 discloses a method for preparing and applying a cathode catalytic material for lithium-sulfur batteries. It utilizes a three-dimensional porous graphene support with a three-dimensional interconnected hierarchical pore structure to form a strong physical confinement, suppressing the migration and diffusion of LiPSs from a spatial perspective. In2O3 and LiNbO3 are co-loaded in a three-dimensional porous graphene conductive network. By leveraging the stress-induced piezoelectric effect of LiNbO3 during charge-discharge cycles, a dynamic local micro-electric field is constructed in situ. This electric field directionally regulates the migration behavior of LiPSs and strengthens their interaction with the active sites of In2O3, reducing the energy barrier for the conversion of LiPSs into the insoluble discharge product Li2S, thus achieving efficient adsorption and rapid complete conversion of LiPSs. However, the technical solution in this patent document only involves In2O3 and LiNbO3 being co-loaded in a three-dimensional porous graphene conductive network to prepare lithium-sulfur battery cathode catalyst materials. It does not involve the composite design of the catalytic phase In2O3 and CQDs, nor does it provide any technical inspiration for accurately co-anchoring the two at the lattice sites of g-C3N4 nanosheets to construct a three-in-one synergistic catalytic system integrating "physical confinement - high-speed electron / ion transport network - bipolar catalysis".

[0009] Therefore, it is urgent to design cathode catalytic materials with excellent confined anchoring and catalytic capabilities to adsorb and convert LiPSs, fundamentally solving the LiPSs shuttle problem, which is of vital research significance for promoting the practical application of lithium-sulfur batteries. Summary of the Invention

[0011] The technical problem solved by this invention is to overcome the shortcomings of existing technologies and provide a method for preparing and applying nanosheet-like lithium-sulfur battery cathode catalytic materials. This invention breaks through the inherent limitations of the traditional "single adsorption / single catalysis" modification approach, innovatively constructing a precise co-anchoring of the catalytic phase In2O3 and CQDs at two-dimensional g-C3N4 nanosheet lattice sites, building a three-in-one synergistic catalytic system of "physical confinement - high-speed electron / ion transport network - bipolar catalysis". This catalytic system, relying on the two-dimensional hierarchical pore structure of g-C3N4, effectively constrains the volume expansion of sulfur species during charge and discharge, physically confining LiPSs; the in-situ modification of CQDs compensates for the shortcomings of pure-phase g-C... By addressing the inherent poor conductivity of 3N4, the electron transport path was optimized and the surface electron distribution was modulated to construct a multi-channel lithium-ion transport network, significantly improving the overall electron-ion mixed transport efficiency of the reaction system. Finally, by combining the functional complementarity of the high-density nitrogen-rich active sites on the g-C3N4 surface with the catalytic phase In2O3, strong chemical anchoring of LiPSs was achieved, while significantly reducing the reaction energy barrier of the liquid-solid phase transition of LiPSs and accelerating the conversion kinetics. This fundamentally solves the shuttle effect and significantly improves the rate performance and long-cycle stability of lithium-sulfur batteries.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing a nanosheet-like lithium-sulfur battery cathode catalyst material, the specific preparation steps of which are as follows:

[0013] Step S1: Preparation of nano-CQDs materials

[0014] Nano-CQDs materials were prepared by hydrothermal method. Citric acid and urea were dissolved in deionized water, ultrasonically dispersed, and then transferred to an autoclave for hydrothermal reaction at 160~200℃ for 3~7h. The nano-CQDs materials were then obtained by centrifugation, dialysis, and freeze-drying.

[0015] Step S2: Preparation of acid-etched nanosheet g-C3N4 material

[0016] Urea was calcined at 300-700℃ for 2 hours in air to obtain nanosheet g-C3N4 material. Hydrochloric acid was mixed with g-C3N4 material and transferred to a high pressure vessel for hydrothermal treatment at 150-190℃ for 1-5 hours. After centrifugation and drying, acid-etched nanosheet g-C3N4 material was obtained.

[0017] Step S3: Preparation of nanosheet g-C3N4@In2O3@CQDs material

[0018] The nano-CQDs material obtained in step S1, the acid-etched nanosheet g-C3N4 material obtained in step S2, and the catalyst In2O3 are mixed evenly. Then, the mixture is annealed at 200~500℃ for 2h in air atmosphere to obtain nanosheet g-C3N4@In2O3@CQDs material.

[0019] Step S4: Preparation of nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material

[0020] The nanosheet g-C3N4@In2O3@CQDs material obtained in step S3 is mixed evenly with elemental sulfur. The mixture is then transferred to a tube furnace and calcined at 150~160℃ for 4~8h in an oxygen-free atmosphere to finally obtain the nanosheet g-C3N4@In2O3@CQDs@S cathode catalyst material, which is the cathode catalyst material for lithium-sulfur batteries.

[0021] The nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material, relying on the two-dimensional hierarchical pore structure of g-C3N4, effectively constrains the volume expansion during the sulfur charge-discharge process, physically confining LiPSs. In-situ modification of CQDs compensates for the inherent poor conductivity of pure-phase g-C3N4, optimizes electron transport paths, and regulates surface electron distribution, constructing a multi-channel lithium-ion transport network, significantly improving the overall electron-ion mixed transport efficiency of the reaction system. Finally, combining the functional complementarity between the high-density nitrogen-rich active sites on the g-C3N4 surface and the catalytic phase In2O3, it achieves strong chemical anchoring of LiPSs, while significantly reducing the reaction energy barrier of the LiPSs liquid-solid phase transition and accelerating conversion kinetics, fundamentally breaking the shuttle effect and significantly improving the rate performance and long-cycle stability of lithium-sulfur batteries.

[0022] Further specifying, the molar ratio of citric acid and urea in step S1 is 1:0.5~1.2, preferably 1:1.05.

[0023] Further specifying, the hydrothermal reaction temperature in step S1 is 180°C, and the hydrothermal reaction time is 5 hours.

[0024] Further specifying, the mass fraction of hydrochloric acid in step S2 is 1% to 5%, preferably 3%.

[0025] Further specified, in step S3, the mass ratio of the nano-CQDs material and the acid-etched nanosheet g-C3N4 material is 0.1~0.5:1, preferably 0.3:1; the mass ratio of the catalyst In2O3 and the acid-etched nanosheet g-C3N4 material is 0.01~0.05:1, preferably 0.03:1.

[0026] Further specifying, the mass ratio of the nanosheet-like g-C3N4@In2O3@CQDs material to elemental sulfur in step S4 is 3:5~10.

[0027] Further defining the specifics, in step S4, the In2O3 catalytic phase and CQDs in the nanosheet-like g-C3N4@In2O3@CQDs@S catalytic material are precisely co-anchored at the two-dimensional g-C3N4 nanosheet lattice sites, constructing a three-in-one synergistic catalytic system of "physical confinement - high-speed electron / ion transport network - bipolar catalysis".

[0028] Application of nanosheet-shaped lithium-sulfur battery cathode catalyst material prepared by the above method in the preparation of lithium-sulfur battery cathode materials.

[0029] Application of lithium-sulfur battery cathode materials prepared by the above method in the assembly of lithium-sulfur batteries.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] 1. g-C3N4 not only has the advantages of graphite-like structure, light weight, simple preparation and high porosity, but also has a high theoretical N content (57.1 atom%), and plays an important role in energy storage, catalysis and chemical industry. When g-C3N4 nanosheets are used as a carrier for sulfur composite cathode, their multiple advantages can achieve synergistic solutions to the core technical difficulties of lithium-sulfur batteries: (1) The hierarchical pore structure and ultra-large surface space constructed by two-dimensional nanosheets can provide sufficient buffer space for the volume expansion of active material sulfur, and avoid the cathode structure from pulverization and collapse during cycling; (2) The large number of nitrogen-rich active sites distributed in the skeleton can efficiently anchor soluble long-chain LiPSs through strong polar interaction, and inhibit the shuttle loss of LiPSs from both physical confinement and chemical adsorption dimensions, and finally achieve the simultaneous improvement of cycle life and rate performance of lithium-sulfur batteries. It is a highly competitive candidate carrier material to promote the practical application of lithium-sulfur batteries.

[0032] 2. g-C3N4 is rich in nitrogen and has excellent adsorption properties, exhibiting strong binding ability for LiPSs and effectively inhibiting their dissolution. However, directly prepared bulk g-C3N4 generally has a small specific surface area, making increasing its specific surface area a key direction for performance optimization. Activation modification of g-C3N4 with hydrochloric acid can exfoliate bulk g-C3N4 into micro / nano units, simultaneously generating etched pores and particle accumulation pores, significantly increasing the material's specific surface area. With increasing hydrochloric acid concentration, the number of micropores increases, and the specific surface area gradually rises; however, when the acid concentration is too high, the micropores merge into macropores, resulting in a decrease in specific surface area. Multiple experiments verified that the specific surface area of ​​activated g-C3N4 reaches its maximum when the mass fraction of hydrochloric acid is 3%.

[0033] 3. In view of the inherent defect of insufficient intrinsic semiconductor conductivity of g-C3N4 carrier, the present invention performs directional modification on it through in-situ modification of carbon quantum dots: (1) The surface electron distribution of g-C3N4 two-dimensional sheets can be directly controlled, and a continuous high-speed electron transport network can be constructed on the substrate surface, which completely breaks the electron transport barrier and greatly improves the overall electronic conductivity of the electrode; (2) The optimized g-C3N4@CQDs retains and further expands the hierarchical porous structure, providing more low-resistance fast transport paths for lithium ions, significantly reducing the ion diffusion barrier, and simultaneously improving the electrode ion conductivity, which can fully adapt to the fast mass transfer requirements in high-rate charge and discharge scenarios.

[0034] 4. This invention constructs a three-in-one synergistic catalytic system of "physical confinement - ion / electron dual transport network - bipolar catalytic center" by precisely anchoring and co-growing the catalytic phase In2O3 and conductive carbon quantum dots on the lattice sites of g-C3N4 nanosheets, forming a three-layer progressive technical closed loop, fundamentally solving the LiPSs shuttle problem: (1) The first layer relies on the intrinsic advantages of g-C3N4 to complete the basic interception: its two-dimensional hierarchical pore structure with high nitrogen content can buffer the volume expansion of sulfur and avoid the pulverization and collapse of the positive electrode structure. At the same time, the high-density nitrogen-rich sites can anchor L through strong chemical adsorption. iPSs achieves a dual barrier of "physical confinement + chemical adsorption"; (2) The second layer achieves performance gain through carbon quantum dots: while opening up the high-speed electron transport channel of the system and improving the conductivity of the matrix, it further enhances the polar adsorption capacity of the material for LiPSs, and avoids the secondary diffusion and escape of intercepted LiPSs; (3) The third layer completes efficient conversion with the help of In2O3: through the two-step catalytic path of generating LiInS2 active intermediate, the reaction energy barrier of LiPSs to Li2S conversion is greatly reduced, and the excessive accumulation of LiPSs in the electrolyte is reduced from the source. The three work together to achieve a closed-loop control of LiPSs from "passive interception" to "active regulation" to "complete conversion".

[0035] 5. This invention does not rely on high-cost precious metal catalysts or complex structural designs. The target composite sulfur-supported material can be prepared through a simple process of hydrothermal synthesis combined with high-temperature calcination. The entire process avoids cumbersome and delicate special synthesis steps. While achieving a significant improvement in the rate performance and long-cycle stability of lithium-sulfur batteries, it also takes into account the economy and scalability of the preparation process, providing a feasible technical path for the practical development of high-performance lithium-sulfur battery cathode carriers. Attached Figure Description

[0037] Figure 1 The image shows the XRD curve of the nanosheet g-C3N4@In2O3@CQDs obtained in Example 1.

[0038] Figure 2This is an FESEM image of the nanosheet g-C3N4@In2O3@CQDs obtained in Example 1.

[0039] Figure 3 The graph shows a comparison of the rate charge-discharge performance of the catalytic materials prepared in Examples 1-3 and Comparative Examples 1-3. Detailed Implementation

[0041] This invention suppresses the shuttle effect of LiPSs by constructing nanosheet-like g-C3N4@In2O3@CQDs@S, solving the problems of sulfur expansion and poor conductivity, thereby improving its electrochemical performance.

[0042] To better illustrate the above technical solutions, detailed descriptions of specific embodiments will be provided below. However, this should not be construed as limiting the scope of the invention to the following embodiments; all technologies implemented based on the above content of this invention fall within the scope of this invention.

[0043] Example 1

[0044] Step S1: Preparation of nano-CQDs materials

[0045] Nano-sized CQDs were prepared using a hydrothermal method. 1.92 g of citric acid and 0.63 g of urea were dissolved in deionized water and ultrasonically dispersed. The solution was then transferred to an autoclave and hydrothermally reacted at 180 °C for 5 h. After cooling to room temperature, the resulting dark green solution was centrifuged at 10,000 rpm for 30 min. To obtain purer CQDs, the supernatant was dialyzed. The supernatant was treated in pure water using a 1000D dialysis bag for 24 h, followed by freeze-drying to obtain the nano-sized CQDs.

[0046] Step S2: Preparation of acid-etched nanosheet g-C3N4 material

[0047] 10g of urea was calcined at 500℃ for 2h in air atmosphere to obtain nanosheet g-C3N4 material; 3% hydrochloric acid was mixed evenly with g-C3N4 material, transferred to a high pressure vessel and hydrothermally treated at 170℃ for 3h, and then centrifuged and dried to obtain acid-etched nanosheet g-C3N4 material.

[0048] Step S3: Preparation of nanosheet g-C3N4@In2O3@CQDs material

[0049] The 30 mg nano CQDs material obtained in step S1, the 100 mg acid-etched nanosheet g-C3N4 material obtained in step S2, and 3 mg commercial In2O3 were ball-milled at 400 r / min for 8 h to mix them evenly. The mixture was then calcined at 350 °C for 2 h in air atmosphere to obtain nanosheet g-C3N4@In2O3@CQDs material.

[0050] Step S4: Preparation of nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material

[0051] The nanosheet g-C3N4@In2O3@CQDs material obtained in step S3 was mixed with elemental sulfur at a mass ratio of 3:7. The mixture was then transferred to a tube furnace and sintered under nitrogen protection, calcination temperature of 155℃ and holding time of 6h to obtain the nanosheet g-C3N4@In2O3@CQDs@S cathode catalyst material, i.e., lithium-sulfur battery cathode catalyst material.

[0052] Example 2

[0053] Step S1: Preparation of nano-CQDs materials

[0054] Nano-sized CQDs were prepared using a hydrothermal method. 1.92 g of citric acid and 0.3 g of urea were dissolved in deionized water and ultrasonically dispersed. The solution was then transferred to an autoclave and hydrothermally reacted at 160 °C for 3 h. After cooling to room temperature, the resulting dark green solution was centrifuged at 10,000 rpm for 30 min. To obtain purer CQDs, the supernatant was dialyzed. The supernatant was treated in pure water using a 1000D dialysis bag for 24 h, followed by freeze-drying to obtain the nano-sized CQDs.

[0055] Step S2: Preparation of acid-etched nanosheet g-C3N4 material

[0056] 10g of urea was calcined at 300℃ for 2h in air atmosphere to obtain nanosheet g-C3N4 material; 1% hydrochloric acid was mixed evenly with g-C3N4 material, transferred to a high pressure vessel and hydrothermally treated at 150℃ for 1h, and then centrifuged and dried to obtain acid-etched nanosheet g-C3N4 material.

[0057] Step S3: Preparation of nanosheet g-C3N4@In2O3@CQDs material

[0058] The 10 mg nano CQDs material obtained in step S1, the 100 mg acid-etched nanosheet g-C3N4 material obtained in step S2, and 1 mg commercial In2O3 were ball-milled at 400 r / min for 8 h to mix them evenly. The mixture was then calcined at 200 °C for 2 h in air atmosphere to obtain nanosheet g-C3N4@In2O3@CQDs material.

[0059] Step S4: Preparation of nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material

[0060] The nanosheet g-C3N4@In2O3@CQDs material obtained in step S3 was mixed with elemental sulfur at a mass ratio of 3:5. The mixture was then transferred to a tube furnace and sintered under nitrogen protection, calcination temperature of 150℃ and holding time of 4h to obtain the nanosheet g-C3N4@In2O3@CQDs@S cathode catalyst material, i.e., lithium-sulfur battery cathode catalyst material.

[0061] Example 3

[0062] Step S1: Preparation of nano-CQDs materials

[0063] Nano-sized CQDs were prepared using a hydrothermal method. 1.92 g of citric acid and 0.72 g of urea were dissolved in deionized water and ultrasonically dispersed. The solution was then transferred to an autoclave and hydrothermally reacted at 200 °C for 7 h. After cooling to room temperature, the resulting dark green solution was centrifuged at 10,000 rpm for 30 min. To obtain purer CQDs, the supernatant was dialyzed. The supernatant was treated in pure water using a 1000D dialysis bag for 24 h, followed by freeze-drying to obtain the nano-sized CQDs.

[0064] Step S2: Preparation of acid-etched nanosheet g-C3N4 material

[0065] 10g of urea was calcined at 700℃ for 2h in air atmosphere to obtain nanosheet g-C3N4 material; 5% hydrochloric acid was mixed evenly with g-C3N4 material, transferred to an autoclave and hydrothermally treated at 190℃ for 5h, and then centrifuged and dried to obtain acid-etched nanosheet g-C3N4 material.

[0066] Step S3: Preparation of nanosheet g-C3N4@In2O3@CQDs material

[0067] The 50 mg nano CQDs material obtained in step S1, the 100 mg acid-etched nanosheet g-C3N4 material obtained in step S2, and 5 mg commercial In2O3 were ball-milled at 400 r / min for 8 h to mix them evenly. The mixture was then calcined at 500 °C for 2 h in air atmosphere to obtain nanosheet g-C3N4@In2O3@CQDs material.

[0068] Step S4: Preparation of nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material

[0069] The nanosheet g-C3N4@In2O3@CQDs material obtained in step S3 was mixed with elemental sulfur at a mass ratio of 3:10. The mixture was then transferred to a tube furnace and sintered under nitrogen protection, calcination temperature of 160℃ and holding time of 8h to obtain the nanosheet g-C3N4@In2O3@CQDs@S cathode catalyst material, i.e., lithium-sulfur battery cathode catalyst material.

[0070] Comparative Example 1 (nanoflake-like g-C3N4 without acid etching)

[0071] Step S1: Preparation of nano-CQDs materials

[0072] Nano-sized CQDs were prepared using a hydrothermal method. 1.92 g of citric acid and 0.63 g of urea were dissolved in deionized water and ultrasonically dispersed. The solution was then transferred to an autoclave and hydrothermally reacted at 180 °C for 5 h. After cooling to room temperature, the resulting dark green solution was centrifuged at 10,000 rpm for 30 min. To obtain purer CQDs, the supernatant was dialyzed. The supernatant was treated in pure water using a 1000D dialysis bag for 24 h, followed by freeze-drying to obtain the nano-sized CQDs.

[0073] Step S2: Preparation of nanosheet g-C3N4 material

[0074] 10g of urea was calcined at 500℃ for 2h in air atmosphere to obtain nanosheet g-C3N4 material.

[0075] Step S3: Preparation of nanosheet g-C3N4@In2O3@CQDs material

[0076] The 30 mg nano CQDs material obtained in step S1, the 100 mg nanosheet g-C3N4 material obtained in step S2, and 3 mg commercial In2O3 were ball-milled at 400 r / min for 8 h to make them uniformly mixed. The mixture was then calcined at 350 °C for 2 h in air atmosphere to obtain nanosheet g-C3N4@In2O3@CQDs material.

[0077] Step S4: Preparation of nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material

[0078] The nanosheet g-C3N4@In2O3@CQDs material obtained in step S3 was mixed with elemental sulfur at a mass ratio of 3:7. The mixture was then transferred to a tube furnace and sintered under nitrogen protection, calcination temperature of 155℃ and holding time of 6h to obtain the nanosheet g-C3N4@In2O3@CQDs@S cathode catalyst material, i.e., lithium-sulfur battery cathode catalyst material.

[0079] Comparative Example 2 (without nano CQDs material)

[0080] Step S1: Preparation of acid-etched nanosheet g-C3N4 material

[0081] 10g of urea was calcined at 500℃ for 2h in air atmosphere to obtain nanosheet g-C3N4 material; 3% hydrochloric acid was mixed evenly with g-C3N4 material, transferred to a high pressure vessel and hydrothermally treated at 170℃ for 3h, and then centrifuged and dried to obtain acid-etched nanosheet g-C3N4 material.

[0082] Step S2: Preparation of nanosheet g-C3N4@In2O3 material

[0083] The 100 mg acid-etched nanosheet g-C3N4 material and 3 mg commercial In2O3 obtained in step S1 were ball-milled at 400 r / min for 8 h to make them uniformly mixed. The mixture was then calcined at 350 °C for 2 h in air atmosphere to obtain nanosheet g-C3N4@In2O3 material.

[0084] Step S3: Preparation of nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material

[0085] The nanosheet g-C3N4@In2O3 material obtained in step S2 was mixed with elemental sulfur at a mass ratio of 3:7. The mixture was then transferred to a tube furnace and sintered under nitrogen protection, calcination temperature of 155℃ and holding time of 6h to obtain the nanosheet g-C3N4@In2O3@S cathode catalyst material, i.e., lithium-sulfur battery cathode catalyst material.

[0086] Comparative Example 3 (without In2O3)

[0087] Step S1: Preparation of nano-CQDs materials

[0088] Nano-sized CQDs were prepared using a hydrothermal method. 1.92 g of citric acid and 0.63 g of urea were dissolved in deionized water and ultrasonically dispersed. The solution was then transferred to an autoclave and hydrothermally reacted at 180 °C for 5 h. After cooling to room temperature, the resulting dark green solution was centrifuged at 10,000 rpm for 30 min. To obtain purer CQDs, the supernatant was dialyzed. The supernatant was treated in pure water using a 1000D dialysis bag for 24 h, followed by freeze-drying to obtain the nano-sized CQDs.

[0089] Step S2: Preparation of acid-etched nanosheet g-C3N4 material

[0090] 10g of urea was calcined at 500℃ for 2h in air atmosphere to obtain nanosheet g-C3N4 material; 3% hydrochloric acid was mixed evenly with g-C3N4 material, transferred to a high pressure vessel and hydrothermally treated at 170℃ for 3h, and then centrifuged and dried to obtain acid-etched nanosheet g-C3N4 material.

[0091] Step S3: Preparation of nanosheet g-C3N4@CQDs material

[0092] The 30 mg nano CQDs material obtained in step S1 and the 100 mg acid-etched nanosheet g-C3N4 material obtained in step S2 were ball-milled at 400 r / min for 8 h to make them evenly mixed. The mixture was then calcined at 350 °C for 2 h in air atmosphere to obtain nanosheet g-C3N4@CQDs material.

[0093] Step S4: Preparation of nanosheet-like g-C3N4@CQDs@S cathode catalyst material

[0094] The nanosheet g-C3N4@CQDs material obtained in step S3 is mixed with elemental sulfur at a mass ratio of 3:7. The mixture is then transferred to a tube furnace and sintered under nitrogen protection, calcination temperature of 155℃ and holding time of 6h to obtain the nanosheet g-C3N4@CQDs@S cathode catalyst material, i.e., lithium-sulfur battery cathode catalyst material.

[0095] Product performance testing:

[0096] Electrode preparation and coin cell assembly are carried out before electrochemical testing, and then the battery's electrical performance is tested using a charge-discharge test cabinet.

[0097] from Figure 1The XRD results show that the nanosheet g-C3N4@In2O3@CQDs prepared according to the method of Example 1 has a weak diffraction peak at 13.0° and a characteristic diffraction peak with a higher intensity at 27.2°, with no impurity peaks, which confirms that the g-C3N4@In2O3@CQDs material has been successfully synthesized and has high phase purity.

[0098] from Figure 2 The FESEM results show that the g-C3N4@In2O3@CQDs prepared according to the method in Example 1 have a uniform morphology and regular dimensional two-dimensional nanosheet structure. This structure has a dual benefit for lithium-sulfur batteries: it can reserve sufficient space to buffer the volume expansion of sulfur during charge and discharge, avoiding irreversible collapse of the electrode structure; and it can build a low-resistivity electronic pathway based on a continuous two-dimensional network, which can significantly accelerate electron transport inside the electrode and optimize reaction kinetics.

[0099] from Figure 3 The electrical performance test results show that the nanosheet g-C3N4@In2O3@CQDs@S cathode catalyst material prepared in Example 1 of this invention has better rate performance and capacity recovery performance.

[0100] Based on the above system test results, it can be clearly verified that the present invention uses a simple process of hydrothermal synthesis combined with high-temperature calcination to precisely co-anchor the catalytic phase In2O3 and conductive CQDs on the two-dimensional g-C3N4 nanosheet lattice sites, constructing a nanosheet lithium-sulfur battery cathode catalytic system with a triple synergistic mechanism of "physical confinement - electron / ion dual high-speed transport network - bipolar catalysis", thereby suppressing the shuttle effect of LiPSs from the root. The nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalytic material prepared in Example 1 of this invention achieves multifunctional deep coupling: the two-dimensional hierarchical pores of the g-C3N4 nanosheets constrain the volume deformation of sulfur; the introduction of CQDs compensates for the inherent defect of poor intrinsic conductivity of pure-phase g-C3N4, constructing a continuous and efficient electron-ion hybrid transport network; the In2O3 catalytic phase and the abundant N active sites on the surface of the g-C3N4 substrate form functional complementarity, achieving efficient anchoring and rapid conversion of LiPSs, ultimately achieving a simultaneous and significant improvement in the high-rate charge-discharge performance and long-cycle stability of lithium-sulfur batteries. A series of comparative experiments further corroborate the unique advantages of this invention: using only a single functional component (Comparative Examples 1-3) and when the key parameters in the preparation process are not within the optimal range (Examples 2-3), it is impossible to simultaneously achieve long-term suppression of the LiPSs shuttle effect and synergistic improvement in the overall electrochemical performance of the battery.

[0101] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A method for preparing a nanosheet-like lithium-sulfur battery cathode catalyst material, characterized in that... The specific preparation steps are as follows: Step S1: Preparation of nano-CQDs materials Nano-CQDs materials were prepared by hydrothermal method. Citric acid and urea were dissolved in deionized water, ultrasonically dispersed, and then transferred to an autoclave for hydrothermal reaction at 160~200℃ for 3~7h. The nano-CQDs materials were then obtained by centrifugation, dialysis, and freeze-drying. Step S2: Preparation of acid-etched nanosheet g-C3N4 material Urea was calcined at 300-700℃ for 2 hours in air to obtain nanosheet g-C3N4 material. Hydrochloric acid was mixed with g-C3N4 material and transferred to a high pressure vessel for hydrothermal treatment at 150-190℃ for 1-5 hours. After centrifugation and drying, acid-etched nanosheet g-C3N4 material was obtained. Step S3: Preparation of nanosheet g-C3N4@In2O3@CQDs material The nano-CQDs material obtained in step S1, the acid-etched nanosheet g-C3N4 material obtained in step S2, and the catalyst In2O3 are mixed evenly. Then, the mixture is annealed at 200~500℃ for 2h in air atmosphere to obtain nanosheet g-C3N4@In2O3@CQDs material. Step S4: Preparation of nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material The nanosheet g-C3N4@In2O3@CQDs material obtained in step S3 is mixed evenly with elemental sulfur. The mixture is then transferred to a tube furnace and calcined at 150~160℃ for 4~8h in an oxygen-free atmosphere to finally obtain the nanosheet g-C3N4@In2O3@CQDs@S cathode catalyst material, which is the cathode catalyst material for lithium-sulfur batteries. The nanosheet-like g-C3N4@In2O3@CQDs@S cathode catalyst material, relying on the two-dimensional hierarchical pore structure of g-C3N4, effectively constrains the volume expansion during the sulfur charge-discharge process, physically confining LiPSs. In-situ modification of CQDs compensates for the inherent poor conductivity of pure-phase g-C3N4, optimizes electron transport paths, and regulates surface electron distribution, constructing a multi-channel lithium-ion transport network, significantly improving the overall electron-ion mixed transport efficiency of the reaction system. Finally, combining the functional complementarity between the high-density nitrogen-rich active sites on the g-C3N4 surface and the catalytic phase In2O3, it achieves strong chemical anchoring of LiPSs, while significantly reducing the reaction energy barrier of the LiPSs liquid-solid phase transition and accelerating conversion kinetics, fundamentally breaking the shuttle effect and significantly improving the rate performance and long-cycle stability of lithium-sulfur batteries.

2. The method for preparing the nanosheet-like lithium-sulfur battery cathode catalyst material according to claim 1, characterized in that: The molar ratio of citric acid and urea in step S1 is 1:0.5~1.

2.

3. The method for preparing the nanosheet-like lithium-sulfur battery cathode catalyst material according to claim 1, characterized in that: The hydrothermal reaction temperature in step S1 is 180℃, and the hydrothermal reaction time is 5h.

4. The method for preparing the nanosheet-like lithium-sulfur battery cathode catalyst material according to claim 1, characterized in that: The mass fraction of hydrochloric acid in step S2 is 1% to 5%.

5. The method for preparing the nanosheet-like lithium-sulfur battery cathode catalyst material according to claim 1, characterized in that: In step S3, the mass ratio of the nano-CQDs material to the acid-etched nanosheet g-C3N4 material is 0.1~0.5:1; the mass ratio of the catalyst In2O3 to the acid-etched nanosheet g-C3N4 material is 0.01~0.05:

1.

6. The method for preparing the nanosheet-like lithium-sulfur battery cathode catalyst material according to claim 1, characterized in that: In step S4, the mass ratio of the nanosheet-like g-C3N4@In2O3@CQDs material to elemental sulfur is 3:5~10.

7. The method for preparing the nanosheet-like lithium-sulfur battery cathode catalyst material according to claim 1, characterized in that: In step S4, the In2O3 catalytic phase and CQDs in the nanosheet g-C3N4@In2O3@CQDs@S catalytic material are precisely co-anchored at the two-dimensional g-C3N4 nanosheet lattice sites, constructing a three-in-one synergistic catalytic system of "physical confinement - high-speed electron / ion transport network - bipolar catalysis".

8. The application of the nanosheet lithium-sulfur battery cathode catalyst material prepared by the method according to any one of claims 1 to 7 in the preparation of lithium-sulfur battery cathode materials.

9. The application according to claim 8, characterized in that: The lithium-sulfur battery cathode material is used to assemble lithium-sulfur batteries.

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