A lithium-sulfur battery positive electrode material, a preparation method thereof and a lithium-sulfur battery

Abstract

The application relates to the technical field of lithium-sulfur batteries, in particular to a lithium-sulfur battery positive electrode material, a preparation method thereof and a lithium-sulfur battery. The lithium-sulfur battery positive electrode material provided by the application comprises sulfur and a framework structure; the sulfur is distributed on the framework structure in a point shape; and the framework structure comprises graphene and Bi2S3 nanoflowers; the graphene is in a sheet shape and is distributed on the surface of the Bi2S3 nanoflowers. The application distributes the sulfur on the framework structure formed by the graphene and the Bi2S3 nanoflowers in a point shape, the graphene is in a sheet shape and is distributed on the surface of the Bi2S3 nanoflowers, the sulfur is uniformly dispersed, the graphene and the Bi2S3 nanoflowers synergistically act, inherent defects of the sulfur are overcome, and the cycle stability, the rate performance and the sulfur utilization rate are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery technology, and in particular to a lithium-sulfur battery cathode material, its preparation method, and a lithium-sulfur battery. Background Technology

[0002] Lithium-sulfur batteries, with their ultra-high theoretical energy density of 2600 Wh / kg, abundant sulfur resources, low cost, and environmental friendliness, are considered one of the most promising next-generation electrochemical energy storage technologies. Lithium-sulfur batteries operate based on the redox reaction between sulfur and lithium. During discharge, S8 gradually transforms into lithium polysulfides and is eventually reduced to Li2S. During charging, the reverse reaction occurs. Their theoretical cathode specific capacity reaches as high as 1675 mAh / g, far exceeding that of existing lithium-ion battery cathode materials.

[0003] However, sulfur has extremely low electronic conductivity (<10). -12 The sulfur content (S / cm) results in low utilization of active materials; secondly, the volume expansion rate of sulfur during charging and discharging is as high as 80%, which can easily damage the electrode structure; in addition, the intermediate product lithium polysulfides can easily trigger the "shuttle effect", which seriously affects battery performance.

[0004] As a key component determining the energy density, cycle life, and safety of batteries, the preparation technology of cathode materials has become a core bottleneck for the industrialization of lithium-sulfur batteries. To overcome these problems, existing technologies often employ loading sulfur onto porous carbon, metal oxides, or other carrier materials to form composite cathode materials, thereby improving the conductivity of sulfur, suppressing volume expansion, and mitigating the shuttle effect. However, existing composite cathode materials are mostly simple composites of a single carrier or two carriers, making it difficult to achieve synergistic effects. Problems such as uneven sulfur dispersion, low sulfur utilization, and insufficient cycle stability persist, making it difficult to simultaneously achieve high sulfur loading and excellent electrochemical performance.

[0005] Therefore, how to develop a lithium-sulfur battery cathode material that can fully leverage the synergistic advantages of each component, effectively address the inherent defects of sulfur, and improve the overall electrochemical performance of the cathode to meet the needs of industrial applications of lithium-sulfur batteries is a problem that urgently needs to be solved by those skilled in the art.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The primary objective of this invention is to provide a lithium-sulfur battery cathode material in which sulfur is distributed in a dotted manner on a framework structure formed by graphene and Bi2S3 nanoflowers. The graphene is in sheet form and distributed on the surface of the Bi2S3 nanoflowers, and the sulfur is uniformly dispersed. The synergistic effect of graphene and Bi2S3 nanoflowers overcomes the inherent defects of sulfur and significantly improves cycle stability, rate performance and sulfur utilization.

[0008] The second objective of this invention is to provide a method for preparing a lithium-sulfur battery cathode material.

[0009] A third objective of this invention is to provide a lithium-sulfur battery.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a lithium-sulfur battery cathode material, comprising: sulfur and a framework structure; The sulfur is distributed in a dotted pattern on the framework structure; the framework structure includes graphene and Bi2S3 nanoflowers, the graphene is in sheet form and distributed on the surface of the Bi2S3 nanoflowers.

[0011] Furthermore, the graphene includes mechanochemical graphene.

[0012] Further, the mass ratio of the sulfur, the graphene, and the Bi2S3 nanoflowers is 1:(0.01~1):(0.01~1). Preferably, the mass ratio of sulfur, graphene and Bi2S3 nanoflowers is 1:(0.4~0.75):(0.01~0.25).

[0013] Secondly, the present invention also provides a method for preparing the lithium-sulfur battery cathode material as described above, comprising the following steps: (a) Bi2S3 nanoflowers were prepared by hydrothermal method; (b) Graphene was prepared by mechanochemical exfoliation; (c) After mixing and grinding sulfur, the graphene and the Bi2S3 nanoflowers, heat treatment is performed to obtain the lithium-sulfur battery cathode material.

[0014] Further, in step (a), the method for preparing the Bi2S3 nanoflowers includes: adjusting the pH of an aqueous solution containing bismuth nitrate and thiourea to alkaline, and then carrying out a hydrothermal reaction to obtain a precipitate; the precipitate is then washed, dried, and calcined in sequence to obtain the Bi2S3 nanoflowers.

[0015] Further, step (a) includes at least one of the following features (1) to (4); (1) The molar ratio of bismuth nitrate to thiourea is 1:(1.5~2.5); (2) Adjust the pH of the aqueous solution containing bismuth nitrate and thiourea to 7.5-13.5; (3) The hydrothermal reaction includes: reacting at 50~280℃ for 1~20h; (4) The calcination includes calcining at 100~500℃ for 1~6h.

[0016] Further, in step (b), the method for preparing the graphene includes: ball milling graphite powder, oxidant and reducing agent to obtain the graphene.

[0017] Furthermore, step (b) includes at least one of the following features (1) to (5); (1) The oxidant includes at least one of potassium permanganate, sodium hypochlorite, potassium hypochlorite, potassium dichromate, manganese dioxide, sodium persulfate and potassium persulfate; (2) The reducing agent includes at least one of aspartic acid, hydrazine hydrate, sodium borohydride, alanine, glutamic acid, thiourea dioxide and lithium aluminum hydride; (3) The mass ratio of the graphite powder, the oxidant and the reducing agent is 1:(0.1~15):(0.1~12); (4) The ball milling includes: ball milling for 1 to 6 hours under the conditions of a rotation speed of 1000 to 7000 rpm and a linear velocity of 0.1 to 250 m / s; (5) After ball milling, the process also includes: acid washing, water washing and drying in sequence.

[0018] Further, in step (c), the heat treatment includes: heat treatment at 100~500℃ for 1~6 hours.

[0019] The present invention also provides a lithium-sulfur battery, comprising the lithium-sulfur battery cathode material as described above.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention distributes sulfur in a dotted pattern on a framework structure formed by graphene and Bi2S3 nanoflowers. The graphene is in sheet form and distributed on the surface of the Bi2S3 nanoflowers, constructing an S / graphene / Bi2S3 nanoflower lithium-sulfur battery cathode material. In this lithium-sulfur battery cathode material, the highly conductive and easily dispersed graphene and the high specific surface area and strong adsorption capacity of Bi2S3 nanoflowers work together to disperse sulfur, facilitate electron transport, and suppress polysulfides. Through the synergistic effect of graphene and Bi2S3 nanoflowers, the inherent defects of sulfur, such as low electronic conductivity, volume expansion, and severe shuttle effect, are effectively improved, significantly enhancing the cycle stability, rate performance, and sulfur utilization rate of lithium-sulfur batteries. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is an X-ray diffraction pattern of the lithium-sulfur battery cathode material of Example 4 of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0024] In some embodiments of the present invention, a lithium-sulfur battery cathode material is provided, comprising: sulfur and a framework structure; Sulfur is distributed in dots on the framework structure; the framework structure includes graphene and Bi2S3 nanoflowers, with graphene in sheet form and distributed on the surface of Bi2S3 nanoflowers.

[0025] Sulfur itself has extremely low electronic conductivity and significant volume expansion during charging and discharging. Furthermore, lithium polysulfides are prone to triggering the "shuttle effect." Existing lithium-sulfur battery cathode materials, which are formed by simple composites of single or two carriers, have poor sulfur dispersion, making it difficult to achieve the synergistic effect of conductivity, physical confinement, and chemical adsorption. This results in poor cycle stability and low sulfur utilization in lithium-sulfur batteries, limiting their industrial application.

[0026] The lithium-sulfur battery cathode material of the present invention uses sulfur as the cathode active component and graphene and Bi2S3 nanoflowers as carriers. By constructing a synergistic system through the composite of the three, the inherent defects of sulfur are improved and the overall electrochemical performance of the cathode material is enhanced. The performance shortcomings of sulfur are solved, and excellent electrochemical performance under high sulfur load is achieved.

[0027] Using graphene as the conductive substrate and Bi2S3 nanoflowers as the functional modification component, sulfur was uniformly loaded into the composite system. Graphene is sheet-like, resembling shredded paper; Bi2S3 nanoflowers have a spherical cage-like structure, similar to a spherical cage, with petal-like structures, thus possessing a high specific surface area; graphene is distributed on the surface of Bi2S3 nanoflowers; while sulfur is amorphous, distributed in dots on the framework structure formed by graphene and Bi2S3; thus, an S / graphene / Bi2S3 nanoflower lithium-sulfur battery cathode material was constructed. In this lithium-sulfur battery cathode material, highly conductive and easily dispersed graphene and high specific surface area and strong adsorption capacity Bi2S3 nanoflowers work together to disperse sulfur, transport electrons, and suppress polysulfides. Through the synergistic effect of graphene and Bi2S3 nanoflowers, the inherent defects of sulfur, such as low electronic conductivity, volume expansion, and severe shuttle effect, are effectively improved, significantly enhancing the cycle stability, rate performance, and sulfur utilization rate of lithium-sulfur batteries.

[0028] In some embodiments of the present invention, graphene has a sheet-like structure. Graphene has a high specific surface area and excellent electrical conductivity.

[0029] In some embodiments of the present invention, the Bi2S3 nanoflowers are Bi2S3 nanoflowers with a three-dimensional (3D) structure. Bi2S3 nanoflowers have a unique three-dimensional structure, a large specific surface area, and abundant active sites. They possess good conductivity and polysulfide adsorption capacity, and can construct efficient transport channels. They complement graphene, and the combination of the two with sulfur can achieve synergistic effects.

[0030] In some embodiments of the present invention, graphene includes mechanochemical graphene (MCG); mechanochemical graphene is graphene obtained by mechanochemical exfoliation.

[0031] Graphene is an ideal cathode carrier due to its high specific surface area and excellent conductivity. However, conventional preparation methods are complex, costly, and prone to agglomeration, limiting its large-scale application. Mechatronic graphene (MCG), prepared by mechatronic exfoliation, retains the inherent advantages of graphene while also possessing the characteristics of simple process, low cost, good dispersibility, and easy composite, effectively solving the application pain points of conventional graphene.

[0032] In some embodiments of the present invention, the mass ratio of sulfur, graphene, and Bi2S3 nanoflowers is 1:(0.01~1):(0.01~1); typically, but not limitingly, for example, the mass ratio of sulfur, graphene, and Bi2S3 nanoflowers can be 1:0.01:0.01, 1:0.3:0.015, 1:0.5:0.02, 1:0.75:0.03, 1:0.1:0.05, 1:0.4:0.15, 1:0.7:0.2, 1:0.8:0.5, 1:1:1, and any value between any two of these.

[0033] In some preferred embodiments of the present invention, the mass ratio of sulfur, graphene and Bi2S3 nanoflowers can be 1:(0.4~0.75):(0.01~0.25); more preferably 1:(0.7~0.8):(0.02~0.04).

[0034] Within the above-mentioned mass ratio of sulfur, graphene, and Bi2S3 nanoflowers, sulfur, as the positive electrode active material, can maintain a high theoretical specific capacity. At the same time, graphene constructs a continuous conductive network to compensate for the low conductivity of sulfur, effectively utilizing the high specific surface area and adsorption effect of Bi2S3 nanoflowers. This improves the low electronic conductivity, volume expansion, and shuttle effect of sulfur. It avoids insufficient conductivity and adsorption due to too little graphene or Bi2S3, while excessive graphene or Bi2S3 dilutes the active material and reduces the energy density.

[0035] In some embodiments of the present invention, a method for preparing the above-mentioned lithium-sulfur battery cathode material is also provided, comprising the following steps: (a) Bi2S3 nanoflowers were prepared by hydrothermal method; (b) Graphene was prepared by mechanochemical exfoliation; (c) After mixing and grinding sulfur, graphene and Bi2S3 nanoflowers, heat treatment is performed to obtain lithium-sulfur battery cathode material.

[0036] In some embodiments of the present invention, step (a) of the preparation method of Bi2S3 nanoflowers includes: adjusting the pH of an aqueous solution containing bismuth nitrate and thiourea to alkaline, and then carrying out a hydrothermal reaction to obtain a precipitate; the precipitate is washed, dried and calcined in sequence to obtain Bi2S3 nanoflowers.

[0037] In some embodiments of the present invention, in step (a), the molar ratio of bismuth nitrate to thiourea is 1:(1.5~2.5); preferably 1:2.

[0038] In some embodiments of the present invention, in step (a), the aqueous solution containing bismuth nitrate and thiourea has a mass concentration of bismuth nitrate of 1 to 200 g / L and a mass concentration of thiourea of ​​0.2 to 70 g / L; typically, but not limitingly, for example, the mass concentration of bismuth nitrate in the aqueous solution containing bismuth nitrate and thiourea can be 1 g / L, 10 g / L, 50 g / L, 100 g / L, 200 g / L and any value between any two thereof, and the mass concentration of thiourea can be 0.2 g / L, 5 g / L, 10 g / L, 30 g / L, 70 g / L and any value between any two thereof.

[0039] In some embodiments of the invention, in step (a), the pH of the aqueous solution containing bismuth nitrate and thiourea is adjusted to 7.5–13.5; typically, but not limitingly, the pH of the aqueous solution containing bismuth nitrate and thiourea can be 7.5, 8.5, 9.5, 10.5, 11.5, 12.5, 13.5, and any value between any two thereof. The aqueous solution containing bismuth nitrate and thiourea is alkaline, and the alkalinity of the solution is further adjusted by ammonium hydroxide (NH4OH).

[0040] In some embodiments of the present invention, in step (a), the hydrothermal reaction includes: reacting at 50~280°C for 1~20 h; typically, but not limitingly, for example, the temperature of the hydrothermal reaction can be 50°C, 70°C, 90°C, 110°C, 130°C, 150°C, 170°C, 190°C, 210°C, 230°C, 250°C, 280°C and any two of these values; the time of the hydrothermal reaction can be 1 h, 5 h, 10 h, 15 h, 20 h and any two of these values.

[0041] In some embodiments of the present invention, step (a) includes washing with acetone, ethanol and deionized water to remove residual impurities.

[0042] In some embodiments of the present invention, in step (a), drying includes drying at 70~90°C for 20~30 hours.

[0043] In some embodiments of the present invention, step (a) includes calcination at 100-500°C for 1-6 hours; typically, but not limitingly, the calcination temperature can be 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 500°C, and any two of these values; the calcination time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, and any two of these values. Calcination improves crystallinity.

[0044] In some embodiments of the present invention, step (b) of the graphene preparation method includes: ball milling graphite powder, oxidant and reducing agent to obtain graphene.

[0045] Using graphite powder as raw material, an oxidant reacts graphite to produce graphite oxide, and a reducing agent reacts graphite oxide to produce graphene, which also has a certain exfoliating agent function; the oxidant and reducing agent are used as auxiliary agents to perform ball milling, during which a mechanochemical exfoliation reaction occurs.

[0046] In some embodiments of the present invention, in step (b), the oxidant includes at least one of potassium permanganate, sodium hypochlorite, potassium hypochlorite, potassium dichromate, manganese dioxide, sodium persulfate, and potassium persulfate; preferably potassium permanganate.

[0047] In some embodiments of the present invention, in step (b), the reducing agent includes at least one of aspartic acid, hydrazine hydrate, sodium borohydride, alanine, glutamic acid, thiourea dioxide, and lithium aluminum hydride; preferably aspartic acid.

[0048] In some embodiments of the present invention, in step (b), the mass ratio of graphite powder, oxidant and reducing agent is 1:(0.1~15):(0.1~12); typically, but not limitingly, for example, the mass ratio of graphite powder, oxidant and reducing agent can be 1:0.1:0.1, 1:1:1, 1:5:5, 1:8:6, 1:12:12, 1:15:12 and any two of these ranges; preferably, the mass ratio of graphite powder, oxidant and reducing agent is 1:(2~5):(0.5~2).

[0049] In some embodiments of the present invention, step (b) includes ball milling for 1 to 6 hours at a rotational speed of 1000 to 7000 rpm and a linear velocity of 0.1 to 250 m / s. Typically, but not limitingly, the rotational speed of the ball mill can be any value between 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm, 6000 rpm, 7000 rpm, and any two of these values; the linear velocity of the ball mill can be a range between 0.1 m / s, 5 m / s, 50 m / s, 100 m / s, 150 m / s, 200 m / s, 250 m / s, and any two of these values; the ball milling time can be any value between 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, and any two of these values; preferably, the ball milling uses a grinding media with a ball-to-powder mass ratio of (8 to 12):1.

[0050] In some embodiments of the present invention, step (b) further includes, after ball milling, acid washing, water washing and drying in sequence; preferably, acid washing includes: using a 5wt% hydrochloric acid (HCl) solution; water washing includes: washing with water until the pH of the filtrate is neutral; drying includes: drying at -25~350℃ for 0.2~48h; wherein, low temperature drying is suitable for cold drying operation.

[0051] In some embodiments of the present invention, in step (c), the mass ratio of sulfur, graphene and Bi2S3 nanoflowers is 1:(0.01~1):(0.01~1); preferably, the mass ratio of sulfur, graphene and Bi2S3 nanoflowers is 1:(0.4~0.75):(0.01~0.25).

[0052] In some embodiments of the present invention, step (c) includes heat treatment at 100-500°C for 1-6 hours; typically, but not limitingly, for example, the temperature of the heat treatment can be 100°C, 200°C, 300°C, 400°C, 500°C and any value between any two thereof; the time of the heat treatment can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours and any value between any two thereof.

[0053] In some embodiments of the present invention, a lithium-sulfur battery is also provided, comprising the above-described lithium-sulfur battery cathode material.

[0054] Using the lithium-sulfur battery cathode material of the present invention in lithium-sulfur batteries is beneficial to improving the cycle stability of lithium-sulfur batteries.

[0055] In some embodiments of the present invention, the lithium-sulfur battery includes a positive electrode sheet, which includes a lithium-sulfur battery positive electrode material in a mass ratio of (7~9):(0.5~1.5):(0.5~1.5), a conductive agent, and a binder; the conductive agent includes, but is not limited to, carbon black; the binder includes, but is not limited to, polyvinylidene fluoride (PVDF).

[0056] In some embodiments of the present invention, lithium-sulfur batteries include button batteries, cylindrical batteries, square batteries, or pouch batteries.

[0057] Example 1 The method for preparing the lithium-sulfur battery cathode material provided in this embodiment includes the following steps: (a) Preparation of Bi2S3 (3D) nanoflowers by hydrothermal method: 19.75 g of bismuth nitrate and 7.61 g of thiourea were dissolved in 1000 mL of distilled water and stirred at room temperature (25 °C) for 20 min to obtain bismuth nitrate solution and thiourea solution; the bismuth nitrate solution and thiourea solution were mixed and stirred for 20 min to obtain a mixed solution; ammonium hydroxide (NH4OH) was slowly added to the mixed solution under stirring until the pH of the mixed solution was 9.5 ± 0.1, and stirred for 10 min; then transferred to a polytetrafluoroethylene-lined stainless steel reactor and subjected to hydrothermal reaction at 160 °C for 10 h to obtain a black precipitate; the black precipitate was washed with acetone, ethanol and deionized water, placed in a hot air oven and dried at 80 °C for 24 h, and the dried precipitate was calcined at 380 °C for 3 h to obtain Bi2S3 (3D) nanoflower powder; (b) Preparation of mechanochemical graphene (MCG) by mechanochemical exfoliation: 1g of graphite powder was used as raw material, and 3.2g of potassium permanganate (KMnO4) and 0.95g of aspartic acid were used as auxiliary agents. The grinding media with a ball-to-powder mass ratio of 10:1 was placed in a planetary ball mill and ball-milled for 1.5h at a speed of 3500rpm and a linear velocity of 36.65m / s to complete the mechanochemical exfoliation reaction. The ball-milled product was washed with a 5wt% hydrochloric acid (HCl) solution. Then it was washed repeatedly with distilled water until the filtrate reached a neutral pH value. Then it was placed in a hot air oven and dried at 95℃ for 16h. After drying, 1g of dried graphene was dispersed in 10mL of distilled water and ultrasonically treated for 5h to obtain a stable brown solution, i.e., mechanochemical graphene (MCG) dispersion. (c) Preparation of lithium-sulfur battery cathode material: Sulfur, mechanochemical graphene (MCG) dispersion and Bi2S3 (3D) nanoflower powder were mixed in a mass ratio of 1:0.75:0.03, placed in a quartz mortar and ground thoroughly with a grinding rod to obtain a mixture; then the mixture was transferred to a quartz crucible and heat-treated at 350°C for 4 h to obtain lithium-sulfur battery cathode material.

[0058] Example 2 The method for preparing the lithium-sulfur battery cathode material provided in this embodiment includes the following steps: (a) Preparation of Bi2S3 (3D) nanoflowers by hydrothermal method: 19.75 g of bismuth nitrate and 7.61 g of thiourea were dissolved in 1000 mL of distilled water and stirred at room temperature (25 °C) for 20 min to obtain bismuth nitrate solution and thiourea solution; the bismuth nitrate solution and thiourea solution were mixed and stirred for 20 min to obtain a mixed solution; ammonium hydroxide (NH4OH) was slowly added to the mixed solution under stirring until the pH of the mixed solution was 9.5 ± 0.1, and stirred for 10 min; then transferred to a polytetrafluoroethylene-lined stainless steel reactor and subjected to hydrothermal reaction at 180 °C for 14 h to obtain a black precipitate; the black precipitate was washed with acetone, ethanol and deionized water, placed in a hot air oven and dried at 80 °C for 24 h, and the dried precipitate was calcined at 480 °C for 3 h to obtain Bi2S3 (3D) nanoflower powder; (b) Preparation of mechanochemical graphene (MCG) by mechanochemical exfoliation: 1g of graphite powder was used as raw material, and 3.2g of potassium permanganate (KMnO4) and 0.95g of aspartic acid were used as auxiliary agents. The grinding media with a ball-to-powder mass ratio of 10:1 was placed in a planetary ball mill and ball-milled for 3h at a speed of 2800rpm and a linear velocity of 29.32m / s to complete the mechanochemical exfoliation reaction. The ball-milled product was washed with a 5wt% hydrochloric acid (HCl) solution. Then it was washed repeatedly with distilled water until the filtrate reached a neutral pH value. Then it was placed in a hot air oven and dried at 95℃ for 16h. After drying, 1g of dried graphene was dispersed in 10mL of distilled water and ultrasonically treated for 5h to obtain a stable brown solution, i.e., mechanochemical graphene (MCG) dispersion. (c) Preparation of lithium-sulfur battery cathode material: Sulfur, mechanochemical graphene (MCG) dispersion and Bi2S3 (3D) nanoflower powder were mixed in a mass ratio of 1:0.5:0.02, placed in a quartz mortar and ground thoroughly with a grinding rod to obtain a mixture; then the mixture was transferred to a quartz crucible and heat-treated at 250°C for 5 h to obtain lithium-sulfur battery cathode material.

[0059] Example 3 The method for preparing the lithium-sulfur battery cathode material provided in this embodiment includes the following steps: (a) Preparation of Bi2S3 (3D) nanoflowers by hydrothermal method: 19.75 g of bismuth nitrate and 7.61 g of thiourea were dissolved in 1000 mL of distilled water and stirred at room temperature (25 °C) for 20 min to obtain bismuth nitrate solution and thiourea solution; the bismuth nitrate solution and thiourea solution were mixed and stirred for 20 min to obtain a mixed solution; ammonium hydroxide (NH4OH) was slowly added to the mixed solution under stirring until the pH of the mixed solution was 9.5 ± 0.1, and stirred for 10 min; then transferred to a polytetrafluoroethylene-lined stainless steel reactor and subjected to hydrothermal reaction at 230 °C for 10 h to obtain a black precipitate; the black precipitate was washed with acetone, ethanol and deionized water, placed in a hot air oven and dried at 80 °C for 24 h, and the dried precipitate was calcined at 420 °C for 2.5 h to obtain Bi2S3 (3D) nanoflower powder; (b) Preparation of mechanochemical graphene (MCG) by mechanochemical exfoliation: 1g of graphite powder was used as raw material, and 3.2g of potassium permanganate (KMnO4) and 0.95g of aspartic acid were used as auxiliary agents. The grinding media with a ball-to-powder mass ratio of 10:1 was placed in a planetary ball mill and ball-milled for 2h at a speed of 4200rpm and a linear velocity of 43.98m / s to complete the mechanochemical exfoliation reaction. The ball-milled product was washed with a 5wt% hydrochloric acid (HCl) solution. Then it was washed repeatedly with distilled water until the filtrate reached a neutral pH value. Then it was placed in a hot air oven and dried at 95℃ for 16h. After drying, 1g of dried graphene was dispersed in 10mL of distilled water and ultrasonically treated for 5h to obtain a stable brown solution, i.e., mechanochemical graphene (MCG) dispersion. (c) Preparation of lithium-sulfur battery cathode material: Sulfur, mechanochemical graphene (MCG) dispersion and Bi2S3 (3D) nanoflower powder were mixed in a mass ratio of 1:0.7:0.2 and placed in a quartz mortar. The mixture was then thoroughly ground with a grinding rod to obtain a mixture. The mixture was then transferred to a quartz crucible and heat-treated at 250°C for 5 h to obtain lithium-sulfur battery cathode material.

[0060] Example 4 The method for preparing the lithium-sulfur battery cathode material provided in this embodiment includes the following steps: (a) Preparation of Bi2S3 (3D) nanoflowers by hydrothermal method: 19.75 g of bismuth nitrate and 7.61 g of thiourea were dissolved in 1000 mL of distilled water and stirred at room temperature (25 °C) for 20 min to obtain bismuth nitrate solution and thiourea solution; the bismuth nitrate solution and thiourea solution were mixed and stirred for 20 min to obtain a mixed solution; ammonium hydroxide (NH4OH) was slowly added to the mixed solution under stirring until the pH of the mixed solution was 9.5 ± 0.1, and stirred for 10 min; then transferred to a polytetrafluoroethylene-lined stainless steel reactor and subjected to hydrothermal reaction at 200 °C for 12 h to obtain a black precipitate; the black precipitate was washed with acetone, ethanol and deionized water, placed in a hot air oven and dried at 80 °C for 24 h, and the dried precipitate was calcined at 440 °C for 4.5 h to obtain Bi2S3 (3D) nanoflower powder; (b) Preparation of mechanochemical graphene (MCG) by mechanochemical exfoliation: 1g of graphite powder was used as raw material, and 3.2g of potassium permanganate (KMnO4) and 0.95g of aspartic acid were used as auxiliary agents. The grinding media with a ball-to-powder mass ratio of 10:1 was placed in a planetary ball mill and ball-milled for 1.5h at a speed of 5500rpm and a linear velocity of 57.59m / s to complete the mechanochemical exfoliation reaction. The ball-milled product was washed with a 5wt% hydrochloric acid (HCl) solution. Then it was washed repeatedly with distilled water until the filtrate reached a neutral pH value. Then it was placed in a hot air oven and dried at 95℃ for 16h. After drying, 1g of dried graphene was dispersed in 10mL of distilled water and ultrasonically treated for 5h to obtain a stable brown solution, namely the mechanochemical graphene (MCG) dispersion. (c) Preparation of lithium-sulfur battery cathode material: Sulfur, mechanochemical graphene (MCG) dispersion and Bi2S3 (3D) nanoflower powder were mixed in a mass ratio of 1:0.4:0.15, placed in a quartz mortar and ground thoroughly with a grinding rod to obtain a mixture; then the mixture was transferred to a quartz crucible and heat-treated at 250°C for 3 h to obtain lithium-sulfur battery cathode material.

[0061] The X-ray diffraction pattern of the lithium-sulfur battery cathode material in this embodiment is as follows: Figure 1 As shown.

[0062] Example 5 The preparation method of the lithium-sulfur battery cathode material provided in this embodiment is the same as that in Example 1, except that in step (c), the mass ratio of sulfur, MCG and Bi2S3 (3D) nanoflower powder is 1:0.48:0.3.

[0063] Example 6 The preparation method of the lithium-sulfur battery cathode material provided in this embodiment is the same as that in Example 1, except that in step (c), the mass ratio of sulfur, MCG and Bi2S3 (3D) nanoflower powder is 1:0.03:0.75.

[0064] Example 7 The preparation method of the lithium-sulfur battery cathode material provided in this embodiment is the same as that in Example 1, except that in step (c), the mass ratio of sulfur, MCG and Bi2S3 (3D) nanoflower powder is 1:1:0.04.

[0065] Example 8 The preparation method of the lithium-sulfur battery cathode material provided in this embodiment is the same as that in embodiment 1, except that in step (b), the graphene is graphene (1 to 10 layers) prepared by vapor deposition or exfoliation and purchased from Maclean's Reagent Network or Aladdin Reagent Network.

[0066] Comparative Example 1 The lithium-sulfur battery cathode material provided in this comparative example is sulfur.

[0067] Comparative Example 2 The method for preparing the lithium-sulfur battery cathode material provided in this comparative example includes the following steps: (a) Preparation of mechanochemical graphene (MCG) by mechanochemical exfoliation: 1g of graphite powder was used as raw material, and 3.2g of potassium permanganate (KMnO4) and 0.95g of aspartic acid were used as auxiliary agents. The grinding media with a ball-to-powder mass ratio of 10:1 was placed in a planetary ball mill and ball-milled for 1.5h at a speed of 3500rpm and a linear velocity of 36.65m / s to complete the mechanochemical exfoliation reaction. The ball-milled product was washed with a 5wt% hydrochloric acid (HCl) solution. Then it was washed repeatedly with distilled water until the filtrate reached a neutral pH value. Then it was placed in a hot air oven and dried at 95℃ for 16h. After drying, 1g of dried graphene was dispersed in 10mL of distilled water and ultrasonically treated for 5h to obtain a stable brown solution, namely the mechanochemical graphene (MCG) dispersion. (b) Preparation of lithium-sulfur battery cathode material: sulfur and mechanical-mechanical graphene (MCG) dispersion were mixed at a mass ratio of sulfur to MCG of 1:0.78, placed in a quartz mortar, and ground thoroughly with a grinding rod to obtain a mixture; the mixture was then transferred to a quartz crucible and heat-treated at 350°C for 4 hours to obtain lithium-sulfur battery cathode material.

[0068] Comparative Example 3 The method for preparing the lithium-sulfur battery cathode material provided in this comparative example includes the following steps: (a) Preparation of Bi2S3 (3D) nanoflowers by hydrothermal method: 19.75 g of bismuth nitrate and 7.61 g of thiourea were dissolved in 1000 mL of distilled water and stirred at room temperature (25 °C) for 20 min to obtain bismuth nitrate solution and thiourea solution; the bismuth nitrate solution and thiourea solution were mixed and stirred for 20 min to obtain a mixed solution; ammonium hydroxide (NH4OH) was slowly added to the mixed solution under stirring until the pH of the mixed solution was 9.5 ± 0.1, and stirred for 10 min; then transferred to a polytetrafluoroethylene-lined stainless steel reactor and subjected to hydrothermal reaction at 160 °C for 10 h to obtain a black precipitate; the black precipitate was washed with acetone, ethanol and deionized water, placed in a hot air oven and dried at 80 °C for 24 h, and the dried precipitate was calcined at 380 °C for 3 h to obtain Bi2S3 (3D) nanoflower powder; (b) Preparation of lithium-sulfur battery cathode material: Sulfur and Bi2S3 (3D) nanoflower powder were mixed at a mass ratio of 1:0.78, placed in a quartz mortar, and ground thoroughly with a grinding rod to obtain a mixture; then the mixture was transferred to a quartz crucible and heat-treated at 350°C for 4 hours to obtain lithium-sulfur battery cathode material.

[0069] Comparative Example 4 The preparation method of the lithium-sulfur battery cathode material provided in this comparative example is the same as that in Example 1, except that in step (a), the preparation method of molybdenum disulfide nanoflowers is as follows: 1.412 g of (NH4)6Mo7O 24 • 4H2O and 0.7g of N2H4CS were dissolved in 60ml of water and stirred for at least 30min to prepare a homogeneous mixed aqueous solution. The solution was then poured into a 50mL reaction vessel and reacted at 180℃ for 6h. After the reaction was completed, the resulting suspension was centrifuged at 7000r / min and washed repeatedly with deionized water and anhydrous ethanol more than 3 times. The precipitate was dried in a blower dryer at 80℃ for 12h to obtain molybdenum disulfide nanoflowers. In step (c), Bi2S3 (3D) nanoflowers were replaced with molybdenum disulfide nanoflowers.

[0070] Test case Coin cells were prepared using the lithium-sulfur battery cathode materials of Examples 1-8 and Comparative Examples 1-4, respectively. The coin cells were placed on a CT2001A Blue Electric testing system for charge-discharge performance testing. The discharge capacity, capacity retention rate after 100 cycles, and rate performance of each battery were measured. The sulfur loading of the lithium-sulfur battery cathode material is shown in Table 1. The charge-discharge rate was 0.1C, and the voltage range was 1.70~2.80V.

[0071] Methods for manufacturing button cells: Following standard slurry preparation procedures, a composite mixture of 80% lithium-sulfur battery cathode material, 10% carbon black, and 10% polyvinylidene fluoride (PVDF) binder was prepared. After uniformly mixing the above components, they were dispersed in N-methyl-2-pyrrolidone (NMP) solvent to form a homogeneous slurry. Subsequently, the slurry was coated onto the surface of aluminum foil using a blade coating method to form a uniform coating. The coated aluminum foil was then placed in an oven and dried overnight at 70°C to ensure complete solvent evaporation and guarantee electrode stability. A lithium-sulfur button cell was assembled using lithium foil as the negative electrode and the aforementioned positive electrode sheet as the positive electrode. A porous insulating membrane was placed between the two electrodes to prevent direct contact while allowing ion transport. The membrane was immersed in an electrolyte composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and ethylene carbonate in a 1:1 mass ratio. The entire assembly process was carried out in an argon-filled glove box to ensure an inert atmosphere. After assembly, the button cell was sealed to prevent electrolyte leakage and ensure the battery's environmental stability.

[0072] Table 1

[0073] As shown in Table 1, the lithium-sulfur battery cathode material of the present invention has a high sulfur loading and high sulfur utilization rate. Using it in lithium-sulfur batteries is beneficial to improving the cycle stability and rate performance of lithium-sulfur batteries.

[0074] Compared with Example 1, Example 7 shows that the total amount of MCG and Bi2S3 nanoflower powder is too high, which affects the insertion and extraction of lithium ions in the cathode material and affects the electrical performance. Compared with Example 1, Example 8 shows that compared with conventional graphene, the sheets are prone to agglomeration. Mechanochemical graphene (MCG) prepared by mechanochemical exfoliation retains the inherent advantages of graphene and has the characteristics of good dispersibility and easy recombination, which is conducive to further improving the performance of lithium-sulfur battery cathode materials.

[0075] The lithium-sulfur battery cathode material in Comparative Example 1 consists only of sulfur, resulting in poor electronic conductivity and affecting capacity utilization and cycle performance. The lithium-sulfur battery cathode material in Comparative Example 2 lacks Bi₂S₃ nanoflowers, leading to poor sulfur dispersion and impacting cycle performance and capacity utilization. The lithium-sulfur battery cathode material in Comparative Example 3 exhibits good sulfur dispersion due to the presence of Bi₂S₃ nanoflowers, but the lack of electronically conductive graphene also severely affects cycle performance. Comparative Example 4, which replaces Bi₂S₃ nanoflowers with other molybdenum disulfide nanoflowers, exhibits performance inferior to Example 1.

[0076] A comparison of Examples 1, 2, and 3 shows that the synergistic effect of graphene and Bi2S3 nanoflowers can simultaneously compensate for each other's shortcomings and significantly improve the cycle stability of lithium-sulfur batteries.

[0077] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A lithium-sulfur battery cathode material, characterized in that, include: Sulfur and skeletal structure; The sulfur is distributed in a dotted pattern on the framework structure; the framework structure includes graphene and Bi2S3 nanoflowers, the graphene is in sheet form and distributed on the surface of the Bi2S3 nanoflowers.

2. The lithium-sulfur battery cathode material according to claim 1, characterized in that, The graphene includes mechanochemical graphene.

3. The lithium-sulfur battery cathode material according to claim 1, characterized in that, The mass ratio of the sulfur, the graphene, and the Bi2S3 nanoflowers is 1:(0.01~1):(0.01~1). Preferably, the mass ratio of sulfur, graphene and Bi2S3 nanoflowers is 1:(0.4~0.75):(0.01~0.25).

4. The method for preparing the lithium-sulfur battery cathode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: (a) Bi2S3 nanoflowers were prepared by hydrothermal method; (b) Graphene was prepared by mechanochemical exfoliation; (c) After mixing and grinding sulfur, the graphene and the Bi2S3 nanoflowers, heat treatment is performed to obtain the lithium-sulfur battery cathode material.

5. The method for preparing the lithium-sulfur battery cathode material according to claim 4, characterized in that, In step (a), the method for preparing the Bi2S3 nanoflowers includes: adjusting the pH of an aqueous solution containing bismuth nitrate and thiourea to alkaline, and then carrying out a hydrothermal reaction to obtain a precipitate; the precipitate is then washed, dried, and calcined in sequence to obtain the Bi2S3 nanoflowers.

6. The method for preparing the lithium-sulfur battery cathode material according to claim 5, characterized in that, Step (a) includes at least one of the following features (1) to (4); (1) The molar ratio of bismuth nitrate to thiourea is 1:(1.5~2.5); (2) Adjust the pH of the aqueous solution containing bismuth nitrate and thiourea to 7.5-13.5; (3) The hydrothermal reaction includes: reacting at 50~280℃ for 1~20h; (4) The calcination includes calcining at 100~500℃ for 1~6h.

7. The method for preparing the lithium-sulfur battery cathode material according to claim 4, characterized in that, In step (b), the method for preparing the graphene includes: ball milling graphite powder, oxidant and reducing agent to obtain the graphene.

8. The method for preparing the lithium-sulfur battery cathode material according to claim 7, characterized in that, Step (b) includes at least one of the following features (1) to (5); (1) The oxidant includes at least one of potassium permanganate, sodium hypochlorite, potassium hypochlorite, potassium dichromate, manganese dioxide, sodium persulfate and potassium persulfate; (2) The reducing agent includes at least one of aspartic acid, hydrazine hydrate, sodium borohydride, alanine, glutamic acid, thiourea dioxide and lithium aluminum hydride; (3) The mass ratio of the graphite powder, the oxidant and the reducing agent is 1:(0.1~15):(0.1~12); (4) The ball milling includes: ball milling for 1 to 6 hours under the conditions of a rotation speed of 1000 to 7000 rpm and a linear velocity of 0.1 to 250 m / s; (5) After ball milling, the process also includes: acid washing, water washing and drying in sequence.

9. The method for preparing the lithium-sulfur battery cathode material according to claim 4, characterized in that, In step (c), the heat treatment includes: heat treatment at 100~500℃ for 1~6 hours.

10. A lithium-sulfur battery, characterized in that, Including the lithium-sulfur battery cathode material as described in any one of claims 1 to 3.

Images