Preparation method and application of blackberry-like heterostructure composite electrode material for potassium-sulfur batteries

Abstract

The present invention discloses a preparation method and application of a blackberry-shaped heterostructure composite electrode material for potassium-sulfur batteries. The TiO2 / Cu MOF heterostructure is used as a sulfur carrier material to prevent the accumulation of polysulfides and improve sulfur utilization. By regulating the ratio of the TiO2 precursor solution to the Cu MOF and the microwave-assisted solvothermal reaction temperature, a blackberry-shaped heterostructure material is constructed. The blackberry-shaped heterostructure achieves a synergistic effect between the TiO2 and Cu MOF, effectively adsorbing, diffusing, and converting polysulfides. During the battery charge and discharge process, the TiO2 can physically capture and adsorb the intermediate polysulfide, while the Cu MOF promotes the bidirectional catalysis of polysulfides. The TiO2 / Cu MOF heterostructure ensures the directional transfer of polysulfides between the TiO2 and Cu MOF. As a sulfur reservoir in potassium-sulfur batteries, the TiO2 / Cu MOF heterostructure ensures a longer and more stable charge and discharge platform, significantly improving the electron transfer of sulfur and the discharge product potassium sulfide, reducing internal resistance, and achieving higher battery specific capacity and cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of composite electrode materials for potassium-sulfur batteries, and in particular to a preparation method and application of a blackberry-shaped heterostructure composite electrode material for potassium-sulfur batteries. Background Art

[0002] Potassium-sulfur battery is a rechargeable battery that uses potassium metal and sulfide as negative and positive electrode materials, with the advantages of high energy density, low cost and environmental friendliness. Potassium-sulfur battery realizes the charge and discharge reaction of the battery through the reversible electrochemical conversion reaction between potassium ions and sulfur, so that each sulfur atom can transfer two electrons. The potassium metal negative electrode has the advantages of high electronic conductivity and ion diffusion rate, and the abundance and wide distribution of potassium resources in the earth's crust make potassium-sulfur batteries more sustainable and economical. However, potassium-sulfur batteries also face some technical challenges, mainly the low conductivity of sulfur, the active material of the positive electrode, and the dissolution shuttle effect of polysulfides, which lead to capacity decay and reduced cycle life of the battery.

[0003] While some existing composite motor materials can improve the specific capacity and cycle performance of potassium-sulfur batteries, they still suffer from low sulfur redox conversion rates during charge and discharge, resulting in low discharge specific capacity and rapid capacity decay during cycling. Therefore, there is an urgent need for electrode materials and preparations for potassium-sulfur batteries that can adsorb, rapidly diffuse, and accelerate the catalytic redox conversion of polysulfides, while suppressing the shuttling effect of polysulfides. Summary of the Invention

[0004] To solve the problems existing in the prior art, the present invention provides a preparation method and application of a blackberry-shaped heterostructure composite electrode material for potassium-sulfur batteries. The process has high process repeatability and is simple. It can be used to prepare positive electrode materials for potassium-sulfur batteries, can bidirectionally catalyze sulfur redox reactions, and can adsorb, diffuse and convert polysulfides and inhibit the shuttle effect of polysulfides, thereby ensuring the electrochemical performance of potassium-sulfur batteries and solving the problems mentioned in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a blackberry-like heterostructure composite electrode material for a potassium-sulfur battery, comprising the following steps:

[0006] S1. Prepare TiO2 precursor solution: prepare TiO2 precursor mixed solution with tetrabutyl titanate, concentrated hydrochloric acid and anhydrous ethanol, and then use ultrasonic vibration for 3h to 8h until the solution becomes homogeneous to form TiO2 precursor solution;

[0007] S2. Preparation of Cu MOF suspension: Dissolve Cu(NO3)2·3H2O and 2,5-pyridinedicarboxylic acid in a mixed solution of N,N-dimethylformamide and methanol, and reflux at 80°C for 12 hours. Collect the obtained Cu MOF suspension;

[0008] S3. Preparation of gel material by microwave-assisted solvothermal reaction: TiO2 precursor solution and Cu MOF suspension were mixed, stirred evenly at room temperature, and then placed in a microwave hydrothermal synthesizer for microwave-assisted solvothermal reaction to synthesize gel material;

[0009] S4. Preparing a TiO2 / Cu MOF heterostructure: The gel-like material prepared in step S3 was washed three times with anhydrous ethanol, immersed in dichloromethane, and replaced with fresh dichloromethane every day for three days, followed by freeze drying for 10 hours to 14 hours to obtain a blackberry-shaped TiO2 / Cu MOF heterostructure;

[0010] S5. Liquid phase infiltration of sulfur: The TiO2 / Cu MOF obtained in step S4 was ground into powder using a ball mill, and then sulfur powder was added. The mixture was heated at 120°C to 180°C for 15h to 30h to obtain a blackberry-shaped TiO2 / Cu MOF / S composite positive electrode material.

[0011] Preferably, in step S1, the volume ratio of tetrabutyl titanate to concentrated hydrochloric acid is 2:1, and the volume ratio of anhydrous ethanol to tetrabutyl titanate is 3:1.

[0012] Preferably, in step S1, when preparing the TiO2 precursor solution, tetrabutyl titanate and concentrated hydrochloric acid are stirred at room temperature for 10 minutes to 30 minutes to obtain a tetrabutyl titanate / hydrochloric acid mixed solution; then, anhydrous ethanol is added dropwise to the tetrabutyl titanate / hydrochloric acid mixed solution, and the dropping speed of anhydrous ethanol is 5 mL / min to 7 mL / min; the mass concentration of concentrated hydrochloric acid is 36%.

[0013] Preferably, in step S2, the molar ratio of Cu(NO3)2·3H2O to 2,5-pyridinedicarboxylic acid is 1:5.

[0014] Preferably, in step S3, the molar ratio of tetrabutyl titanate in the TiO2 precursor solution to Cu(NO3)2·3H2O in the Cu MOF solution is 1:1-30, preferably 1:10-30.

[0015] Preferably, in step S3, the temperature of the microwave-assisted solvothermal reaction is 100-180° C., the time is 20 min-60 min, and the output power of the microwave hydrothermal synthesizer is 800W.

[0016] Preferably, in step S3, the temperature of the microwave-assisted solvent thermal reaction is 140° C. and the time is 40 min.

[0017] Preferably, in step S4, the freeze-drying temperature is -80°C, and the preferred time is 12 hours.

[0018] Preferably, in step S5, the mass ratio of TiO2 / Cu MOF powder to sulfur powder is 1:3.

[0019] On the other hand, to achieve the above-mentioned purpose, the present invention also provides the following technical solution: an application of a blackberry-shaped heterostructure composite electrode material for a potassium-sulfur battery in a positive electrode of a potassium-sulfur battery, wherein a blackberry-shaped TiO2 / Cu MOF / S composite positive electrode material, conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) are stirred evenly with N-methylpyrrolidone (NMP) to form a paste to prepare a blackberry-shaped TiO2 / Cu MOF / S positive electrode composite material electrode.

[0020] Preferably, the mass ratio of the blackberry-shaped TiO2 / Cu MOF / S composite positive electrode material, conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) is 7:2:1; the blackberry-shaped TiO2 / Cu MOF / S positive electrode composite material electrode has a specific capacity of 1184mAh / g, 830mAh / g and 595mAh / g at rates of 0.1C, 0.2C and 0.5C; after 50 cycles at a current density of 0.5C, the capacity retention rate is 92.49% of the original.

[0021] The beneficial effects of the present invention are:

[0022] 1) The present invention utilizes a microwave-assisted solvothermal method to synthesize a blackberry-like TiO2 / Cu MOF heterostructure material. A Cu MOF solution is added to a TiO2 precursor solution to allow the two precursors to be compounded into a system, ultimately forming a blackberry-like heterostructure material.

[0023] 2) Compared with the traditional drying method, the present invention uses freeze-drying to remove the residual organic solvent in TiO2 / Cu MOF, thereby improving the purity and stability of the material.

[0024] 3) The present invention utilizes a TiO2 / Cu MOF heterostructure as a sulfur carrier material, which can prevent the accumulation of polysulfides and improve sulfur utilization. By regulating the ratio of the TiO2 precursor solution to the Cu MOF and the temperature conditions of the microwave-assisted solvent thermal reaction, a blackberry-like heterostructure material is constructed. This blackberry-like heterostructure achieves a synergistic effect between TiO2 and Cu MOF, effectively adsorbing, diffusing, and converting polysulfides. During the battery charge and discharge process, TiO2 can physically capture and adsorb the intermediate polysulfide, Cu MOF can promote the bidirectional catalysis of polysulfides, and the TiO2 / Cu MOF heterostructure can ensure the directional transfer of polysulfides between TiO2 and Cu MOF. As a sulfur storage device for potassium-sulfur batteries, it makes the charge and discharge platform longer and more stable, greatly improves the electron transfer of sulfur and the discharge product potassium sulfide, reduces internal resistance, and thus obtains higher battery specific capacity and cycle stability.

[0025] 4) This invention utilizes a TiO2 / Cu MOF / S composite material as the positive electrode for a potassium-sulfur battery, demonstrating high specific capacity, cycle stability, and coulombic efficiency. The assembled potassium-sulfur battery achieved specific capacities of 1184 mAh / g, 830 mAh / g, and 595 mAh / g at rates of 0.1C, 0.2C, and 0.5C, respectively. After 50 cycles at a current density of 0.5C, the capacity retention rate remained at 92.49% of the original value, demonstrating the material's potential for application in potassium-sulfur batteries. This material also offers advantages such as a simple, repeatable process and easy structural analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is a charge and discharge curve diagram of a potassium-sulfur battery assembled with a blackberry-like heterostructure composite material electrode in Example 1 of the present invention;

[0027] Figure 2 This is a cycle performance curve of a potassium-sulfur battery assembled with a blackberry-like heterostructure composite material electrode in Example 1 of the present invention;

[0028] Figure 3 is a SEM image of the blackberry-like heterostructure composite material in Example 1 of the present invention;

[0029] Figure 4 Schematic diagram of the dynamic diffusion interface of the blackberry-like heterostructure composite material in Example 1 of the present invention;

[0030] Figure 5 1 is a charge and discharge curve diagram of a potassium-sulfur battery assembled with a blackberry-shaped heterostructure composite material electrode in Example 2 of the present invention;

[0031] Figure 6 This is a graph showing the cycling performance of a potassium-sulfur battery assembled with a blackberry-like heterostructure composite material electrode in Example 2 of the present invention;

[0032] Figure 7 is a SEM image of the blackberry-shaped heterostructure composite material in Example 2 of the present invention;

[0033] Figure 8 3 is a charge and discharge curve of a potassium-sulfur battery assembled with a blackberry-like heterostructure composite material electrode in Example 3 of the present invention;

[0034] Figure 9 This is a cycle performance curve of a potassium-sulfur battery assembled with a blackberry-like heterostructure composite material electrode in Example 3 of the present invention;

[0035] Figure 10 is a SEM image of the blackberry-like heterostructure composite material in Example 3 of the present invention;

[0036] Figure 11 is the charge and discharge curve measured for the assembled battery of Comparative Example 1;

[0037] Figure 12 This is the cycle performance curve measured for the battery assembled in Comparative Example 1;

[0038] Figure 13 Schematic diagram of scanning electron microscopy of the composite material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] Example 1

[0041] Preparation of TiO2 / Cu MOF / S composite electrode materials:

[0042] (1) Preparation of TiO2 precursor solution

[0043] 5.6 mL of tetrabutyl titanate and 2.8 mL of 36% concentrated hydrochloric acid were stirred at room temperature for 10 minutes to obtain a tetrabutyl titanate / hydrochloric acid mixed solution; then, 16.8 mL of anhydrous ethanol was added dropwise to the tetrabutyl titanate / hydrochloric acid mixed solution at a rate of 5 mL / min, and ultrasonically vibrated for 3 hours until the solution became homogeneous, thereby forming a TiO2 precursor solution;

[0044] (2) Preparation of Cu MOF suspension

[0045] Copper nitrate trihydrate (Cu(NO3)2·3H2O) and 2,5-pyridinedicarboxylic acid (2,5-PDCA) were dissolved in a mixed solution of N,N-dimethylformamide (DMF) and methanol at a molar ratio of 1:5 and refluxed at 80°C for 12 hours. The resulting CuMOF suspension was collected.

[0046] (3) Solvothermal reaction

[0047] The TiO2 precursor solution and the CuMOF suspension were mixed, with the molar ratio of tetrabutyl titanate in the TiO2 precursor solution to copper nitrate trihydrate in the CuMOF solution being 1:10. After stirring at room temperature, the mixture was placed in a microwave hydrothermal synthesizer and subjected to microwave-assisted solvothermal reaction at 100°C for 20 minutes to synthesize the gel material.

[0048] (4) Washing

[0049] The prepared gel-like material was washed three times with anhydrous ethanol and immersed in dichloromethane, and fresh dichloromethane was replaced every day for three days;

[0050] (5) Freeze-drying

[0051] The gel-like material was freeze-dried for 10 h;

[0052] (6) Preparation of blackberry-like composite electrode materials

[0053] The freeze-dried material was taken out to obtain a blackberry-like TiO2 / Cu MOF heterostructure; after being ground into powder using a ball mill, sulfur powder was added and mixed evenly in a mass ratio of 1:3. The mixture was heated and kept at 120°C for 15 hours to obtain a blackberry-like TiO2 / Cu MOF / S composite electrode material.

[0054] Application: Preparation of potassium-sulfur battery cathode using blackberry-like TiO2 / Cu MOF composite electrode materials

[0055] TiO2 / Cu MOF / S composite electrode material, conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1 with N-methylpyrrolidone (NMP) to form a paste. The paste was then coated on one side of a 9 μm thick aluminum foil with a coating thickness of 0.05 mm. The paste was then dried in a vacuum at 40°C for 15 h to obtain a blackberry-like TiO2 / Cu MOF / S composite electrode.

[0056] A 2025-type button-type potassium-sulfur battery was assembled using potassium metal as the negative electrode, an Al2O3 / polyethylene / Al2O3 ceramic separator, a 1 mol / L potassium hexafluorophosphate solution in ethylene glycol dimethyl ether as the electrolyte, and the blackberry-shaped TiO2 / Cu MOF / S composite material electrode prepared in Example 1 as the positive electrode.

[0057] The charge and discharge curves and cycle performance curves of the battery assembled according to Example 1 are as follows: Figure 1 、 Figure 2 As shown by Figure 1 and Figure 2 The electrochemical test results show that at current densities of 0.1C, 0.2C, and 0.5C, the battery specific capacity can reach 983mAh / g, 798mAh / g, and 587mAh / g, respectively. After 50 cycles at a current density of 0.5C, the capacity retention rate is 85.23% of the original capacity.

[0058] Figure 3 This is a scanning electron microscope photo of the prepared blackberry-like TiO2 / Cu MOF composite material. Figure 3 It can be clearly seen that the blackberry-like structure is present, but the TiO2 nanoparticles are aggregated on the surface of Cu MOF.

[0059] Depend on Figure 4 The blackberry-like TiO2 / Cu MOF heterostructure forms a dynamic diffusion heterointerface, which ensures the directional transfer of polysulfides between TiO2 and Cu MOF. A synergistic effect between TiO2 and CuMOF is achieved at the heterointerface, effectively adsorbing, diffusing, and converting polysulfides. During the battery charge and discharge process, TiO2 physically captures and adsorbs the intermediate polysulfides, while Cu MOF enables bidirectional redox conversion of the polysulfides. The heterointerface improves the regulation from adsorption to conversion, preventing polysulfide accumulation and increasing sulfur utilization. As a sulfur reservoir in potassium-sulfur batteries, the blackberry-like TiO2 / Cu MOF heterostructure provides a longer and smoother charge-discharge platform, significantly improving electron transfer between sulfur and the discharge product potassium sulfide, and reducing internal resistance, thereby achieving higher battery specific capacity and cycling stability.

[0060] Example 2

[0061] Preparation of TiO2 / Cu MOF / S composite electrode materials:

[0062] (1) Preparation of TiO2 precursor solution

[0063] 5.6 mL of tetrabutyl titanate and 2.8 mL of 36% concentrated hydrochloric acid were stirred at room temperature for 20 minutes to obtain a tetrabutyl titanate / hydrochloric acid mixed solution; then, 16.8 mL of anhydrous ethanol was added dropwise to the tetrabutyl titanate / hydrochloric acid mixed solution at a rate of 6 mL / min, and ultrasonically vibrated for 5 hours until the solution became homogeneous, thereby forming a TiO2 precursor solution;

[0064] (2) Preparation of Cu MOF suspension

[0065] Copper nitrate trihydrate (Cu(NO3)2·3H2O) and 2,5-pyridinedicarboxylic acid (2,5-PDCA) were dissolved in a mixed solution of N,N-dimethylformamide (DMF) and methanol at a molar ratio of 1:5 and refluxed at 80°C for 12 hours. The resulting CuMOF suspension was collected.

[0066] (3) Solvothermal reaction

[0067] The TiO2 precursor solution was mixed with the CuMOF suspension, with the molar ratio of tetrabutyl titanate in the TiO2 precursor solution to copper nitrate trihydrate in the CuMOF solution being 1:20. After stirring at room temperature, the mixture was placed in a microwave hydrothermal synthesizer and subjected to microwave-assisted solvothermal reaction at 140°C for 40 minutes to synthesize the gel material.

[0068] (4) Washing

[0069] The prepared gel-like material was washed three times with anhydrous ethanol and immersed in dichloromethane, and fresh dichloromethane was replaced every day for three days;

[0070] (5) Freeze-drying

[0071] The gel-like material was freeze-dried for 12 h;

[0072] (6) Preparation of blackberry-like composite electrode materials

[0073] The freeze-dried material was taken out to obtain a blackberry-shaped TiO2 / Cu MOF heterostructure; after being ground into powder using a ball mill, sulfur powder was added and mixed evenly in a mass ratio of 1:3. The mixture was heated and kept at 150°C for 20 hours to obtain a blackberry-shaped TiO2 / Cu MOF / S composite electrode material.

[0074] Application: Preparation of potassium-sulfur battery cathode using blackberry-like TiO2 / Cu MOF composite electrode material

[0075] TiO2 / Cu MOF / S composite cathode material, conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1 with N-methylpyrrolidone (NMP) and uniformly mixed into a paste. The paste was then coated on one side of a 9 μm thick aluminum foil with a coating thickness of 0.05 mm and dried at 50°C in a vacuum for 20 h to obtain a blackberry-shaped TiO2 / Cu MOF / S composite electrode.

[0076] A 2025-type button-type potassium-sulfur battery was assembled using potassium metal as the negative electrode, an Al2O3 / polyethylene / Al2O3 ceramic separator, a 1 mol / L potassium hexafluorophosphate solution in ethylene glycol dimethyl ether as the electrolyte, and the blackberry-shaped TiO2 / Cu MOF / S composite material electrode prepared in Example 2 as the positive electrode.

[0077] The charge and discharge curves and cycle performance curves of the battery assembled according to Example 2 are as follows: Figure 5 、 Figure 6 As shown by Figure 5 and Figure 6 The electrochemical test results show that at current densities of 0.1C, 0.2C, and 0.5C, the battery specific capacity can reach 1184mAh / g, 830mAh / g, and 595mAh / g, respectively; after 50 cycles at a current density of 0.5C, the capacity retention rate is 92.49% of the original capacity, and after 50 cycles at a current density of 1C, the capacity retention rate is 74.95% of the original capacity.

[0078] Figure 7 This is a scanning electron microscope image of the prepared blackberry-like TiO2 / Cu MOF composite. The blackberry-like morphology is clearly visible in the image. The Cu MOF surface is evenly coated with a layer of TiO2 nanoparticles, maintaining its original shape while avoiding agglomeration. Furthermore, these rough surfaces create more active sites, providing conditions for the effective adsorption of intermediate polysulfides. The Cu MOF promotes bidirectional catalysis of polysulfides. The TiO2 / Cu MOF heterostructure ensures directional transfer of polysulfides between the TiO2 and Cu MOF, thereby limiting the shuttle effect and improving the battery's specific capacity and cycling stability.

[0079] Example 3

[0080] Preparation of TiO2 / Cu MOF / S composite electrode materials:

[0081] (1) Preparation of TiO2 precursor solution

[0082] 5.6 mL of tetrabutyl titanate and 2.8 mL of 36% concentrated hydrochloric acid were stirred at room temperature for 30 minutes to obtain a tetrabutyl titanate / hydrochloric acid mixed solution; then, 16.8 mL of anhydrous ethanol was added dropwise to the tetrabutyl titanate / hydrochloric acid mixed solution at a rate of 7 mL / min, and ultrasonically vibrated for 8 hours until the solution became homogeneous, thereby forming a TiO2 precursor solution;

[0083] (2) Preparation of Cu MOF suspension

[0084] Copper nitrate trihydrate (Cu(NO3)2·3H2O) and 2,5-pyridinedicarboxylic acid (2,5-PDCA) were dissolved in a mixed solution of N,N-dimethylformamide (DMF) and methanol at a molar ratio of 1:5 and refluxed at 80°C for 12 hours. The resulting CuMOF suspension was collected.

[0085] (3) Solvothermal reaction

[0086] The TiO2 precursor solution and the CuMOF suspension were mixed, with the molar ratio of tetrabutyl titanate in the TiO2 precursor solution to copper nitrate trihydrate in the CuMOF solution being 1:30. After stirring at room temperature, the mixture was placed in a microwave hydrothermal synthesizer and subjected to microwave-assisted solvothermal reaction at 180°C for 60 minutes to synthesize the gel material.

[0087] (4) Washing

[0088] The prepared gel-like material was washed three times with anhydrous ethanol and immersed in dichloromethane, and fresh dichloromethane was replaced every day for three days;

[0089] (5) Freeze-drying

[0090] The gel-like material was freeze-dried for 14 h;

[0091] (6) Preparation of blackberry-like composite electrode materials

[0092] The freeze-dried material was taken out to obtain a blackberry-like TiO2 / Cu MOF heterostructure; after being ground into powder using a ball mill, sulfur powder was added and mixed evenly in a mass ratio of 1:3. The mixture was heated and kept at 180°C for 30 hours to obtain a blackberry-like TiO2 / Cu MOF / S composite electrode material.

[0093] Application: Preparation of potassium-sulfur battery cathode using blackberry-like TiO2 / Cu MOF composite electrode materials

[0094] The blackberry-like TiO2 / Cu MOF / S composite cathode material, conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1 with N-methylpyrrolidone (NMP) and uniformly mixed into a paste. The paste was then coated on one side of a 9μm thick aluminum foil with a coating thickness of 0.05mm. The paste was then dried at 60°C in a vacuum oven for 30h to obtain a blackberry-like TiO2 / Cu MOF / S composite electrode.

[0095] A 2025-type button-type potassium-sulfur battery was assembled using potassium metal as the negative electrode, an Al2O3 / polyethylene / Al2O3 ceramic separator, a 1 mol / L potassium hexafluorophosphate solution in ethylene glycol dimethyl ether as the electrolyte, and the blackberry-shaped TiO2 / Cu MOF / S composite material electrode prepared in Example 3 as the positive electrode.

[0096] The charge and discharge curves and cycle performance curves of the battery assembled according to Example 3 are as follows: Figure 8 、 Figure 9 As shown by Figure 8 and Figure 9The electrochemical test results show that at current densities of 0.1C, 0.2C, and 0.5C, the battery specific capacity can reach 952mAh / g, 771mAh / g, and 572mAh / g, respectively. After 50 cycles at a current density of 0.5C, the capacity retention rate is 86.15% of the original capacity.

[0097] Figure 10 This is a scanning electron microscope photo of the prepared blackberry-like TiO2 / Cu MOF composite material. It can be clearly seen from the figure that TiO2 partially wraps the Cu MOF, the morphology becomes irregular, and the adsorption effect on polysulfides is weakened.

[0098] Comparative Example 1

[0099] (1) Preparation of TiO2 precursor solution

[0100] 5.6 mL of tetrabutyl titanate and 2.8 mL of 36% concentrated hydrochloric acid were stirred at room temperature for 20 minutes to obtain a tetrabutyl titanate / hydrochloric acid mixed solution; then, 16.8 mL of anhydrous ethanol was added dropwise to the tetrabutyl titanate / hydrochloric acid mixed solution at a rate of 6 mL / min, and ultrasonically vibrated for 5 hours until the solution became homogeneous, thereby forming a TiO2 precursor solution;

[0101] (2) Preparation of Cu MOF suspension

[0102] Copper nitrate trihydrate (Cu(NO3)2·3H2O) and 2,5-pyridinedicarboxylic acid (2,5-PDCA) were dissolved in a mixed solution of N,N-dimethylformamide (DMF) and methanol at a molar ratio of 1:5 and refluxed at 80°C for 12 hours. The resulting CuMOF suspension was collected.

[0103] (3) Solvothermal reaction

[0104] The TiO2 precursor solution and the CuMOF suspension were mixed, with the molar ratio of tetrabutyl titanate in the TiO2 precursor solution to copper nitrate trihydrate in the CuMOF solution being 1:20. After stirring at room temperature, the mixture was placed in a reactor and subjected to microwave-assisted solvothermal reaction at 140°C for 12 hours to synthesize the material.

[0105] (4) Washing

[0106] The prepared materials were washed three times with anhydrous ethanol, immersed in dichloromethane, and replaced with fresh dichloromethane every day for three days;

[0107] (5) Freeze-drying

[0108] The material was freeze-dried for 12 h;

[0109] (6) Preparation of composite electrode materials

[0110] The freeze-dried material was taken out to obtain TiO2 / Cu MOF material; after being ground into powder using a ball mill, sulfur powder was added and mixed evenly in a mass ratio of 1:3, and heated at 150°C for 20 hours to obtain TiO2 / Cu MOF / S composite electrode material.

[0111] Preparation of potassium-sulfur battery positive electrode using TiO2 / Cu MOF composite electrode material of Comparative Example 1

[0112] TiO2 / Cu MOF / S composite cathode material, conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1 with N-methylpyrrolidone (NMP) and uniformly mixed into a paste. The paste was then coated on one side of a 9 μm thick aluminum foil with a coating thickness of 0.05 mm and dried at 50°C in a vacuum oven for 20 h to obtain a TiO2 / Cu MOF / S composite electrode.

[0113] A 2025-type button-type potassium-sulfur battery was assembled with potassium metal as the negative electrode, Al2O3 / polyethylene / Al2O3 ceramic diaphragm, 1 mol / L potassium hexafluorophosphate solution in ethylene glycol dimethyl ether as the electrolyte, and the TiO2 / Cu MOF / S composite material electrode prepared in the comparative example as the positive electrode.

[0114] The charge and discharge curves and cycle performance curves of the battery assembled according to the comparative example are as follows: Figure 11 、 Figure 12 As shown by Figure 11 and Figure 12 The electrochemical test results show that at current densities of 0.1C, 0.2C, and 0.5C, the battery specific capacity can reach 730mAh / g, 561mAh / g, and 225mAh / g, respectively. After 50 cycles at a current density of 0.5C, the capacity retention rate is 78.86% of the original capacity.

[0115] Through the full demonstration of the comparative examples, that is, using different microwave-assisted solvent thermal reaction temperature conditions, the excellent charge-discharge and cycle performance of the present invention cannot be achieved, and its morphology may obtain other shapes such as sheet shapes, but the blackberry-like morphology of the present invention (avoiding agglomeration) cannot be obtained. Figure 13 As shown, Figure 13 This is a scanning electron microscope photo of the prepared TiO2 / Cu MOF composite material. From the picture, we can see that there are many irregularly shaped TiO2 aggregates, severe stacking, and very few gaps.

[0116] Comparative Example 2

[0117] The protocol steps and reaction parameters were identical to those of Example 2, except that the molar ratio of tetrabutyl titanate in the TiO2 precursor solution to copper nitrate trihydrate in the Cu MOF solution was 1:40. Electrochemical testing of cells assembled according to Comparative Example 2 demonstrated that the battery achieved specific capacities of 755 mAh / g, 582 mAh / g, and 320 mAh / g at current densities of 0.1C, 0.2C, and 0.5C, respectively. After 50 cycles at a current density of 0.5C, the capacity retention was only 81.69% of the original value.

[0118] In summary, the successful preparation of the blackberry-like heterostructure composite materials TiO2 / Cu MOF of Examples 1 and 3 and the blackberry-like heterostructure composite material TiO2 / Cu MOF of Example 2 of the present invention provides an effective solution for the design of positive electrode materials for potassium-sulfur batteries. They can adsorb intermediate polysulfides and promote the bidirectional catalysis of polysulfides. At the same time, the TiO2 / Cu MOF heterostructure can ensure the directional transfer of polysulfides between TiO2 and Cu MOF, thereby limiting the shuttle effect, thereby improving the battery specific capacity and cycle stability. In particular, the blackberry-like heterostructure composite material obtained in Example 2 has excellent battery specific capacity and cycle stability.

[0119] This invention utilizes microwave-assisted solvothermal and freeze-drying methods to prepare a blackberry-like TiO2 / Cu MOF heterostructure. This structure effectively adsorbs, diffuses, and converts polysulfides, limiting the shuttle effect. This synergistic effect between TiO2 and Cu MOF accelerates the bidirectional catalytic conversion of polysulfides and improves the battery's kinetic performance. The TiO2 / Cu MOF / S composite electrode material exhibits high specific capacity, cycle stability, and Coulombic efficiency in potassium-sulfur batteries, providing a new, high-performance cathode material that addresses the shuttle effect in potassium-sulfur batteries.

[0120] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a blackberry-like heterostructure composite electrode material for potassium-sulfur batteries, characterized in that: The steps include: S1. Prepare TiO2 precursor solution: prepare TiO2 precursor mixed solution with tetrabutyl titanate, concentrated hydrochloric acid and anhydrous ethanol, and then use ultrasonic vibration for 3h to 8h until the solution becomes homogeneous to form TiO2 precursor solution; S2. Prepare a CuMOF suspension: dissolve Cu(NO3)2·3H2O and 2,5-pyridinedicarboxylic acid in a mixed solution of N,N-dimethylformamide and methanol, and reflux at 80°C for 12 hours. Collect the obtained CuMOF suspension; S3. Preparation of gel material by microwave-assisted solvothermal reaction: TiO2 precursor solution and CuMOF suspension were mixed, stirred evenly at room temperature, and then placed in a microwave hydrothermal synthesizer for microwave-assisted solvothermal reaction to synthesize gel material; S4. Preparing a TiO2 / CuMOF heterostructure: washing the gel material prepared in step S3 three times with anhydrous ethanol, immersing it in dichloromethane, and replacing it with fresh dichloromethane every day for three days, followed by freeze drying for 10 hours to 14 hours to obtain a blackberry-shaped TiO2 / CuMOF heterostructure; S5. Liquid-phase sulfur infiltration: The TiO2 / CuMOF heterostructure obtained in step S4 is ground into powder using a ball mill, and then sulfur powder is added. The mixture is heated at 120°C to 180°C for 15 to 30 hours to obtain a blackberry-shaped TiO2 / CuMOF / S composite cathode material. In step S3, the molar ratio of tetrabutyl titanate in the TiO2 precursor solution to Cu(NO3)2·3H2O in the CuMOF suspension is 1:1-30; In step S3, the temperature of the microwave-assisted solvent thermal reaction is 100-180° C., and the time is 20 min-60 min.

2. The method for preparing a blackberry-like heterostructure composite electrode material for potassium-sulfur batteries according to claim 1, characterized in that: In step S1, the volume ratio of tetrabutyl titanate to concentrated hydrochloric acid is 2:1, and the volume ratio of anhydrous ethanol to tetrabutyl titanate is 3:

1.

3. The method for preparing a blackberry-like heterostructure composite electrode material for potassium-sulfur batteries according to claim 1, wherein: In step S1, when preparing the TiO2 precursor solution, tetrabutyl titanate and concentrated hydrochloric acid are stirred at room temperature for 10 minutes to 30 minutes to obtain a tetrabutyl titanate / hydrochloric acid mixed solution; Then, anhydrous ethanol is added dropwise to the tetrabutyl titanate / hydrochloric acid mixed solution at a dropping speed of 5 mL / min to 7 mL / min; and the mass concentration of the concentrated hydrochloric acid is 36%.

4. The method for preparing a blackberry-like heterostructure composite electrode material for potassium-sulfur batteries according to claim 1, wherein: In step S2, the molar ratio of Cu(NO3)2·3H2O to 2,5-pyridinedicarboxylic acid is 1:

5.

5. The method for preparing a blackberry-like heterostructure composite electrode material for potassium-sulfur batteries according to claim 1, wherein: In step S3, the temperature of the microwave-assisted solvothermal reaction is 140° C. and the time is 40 minutes.

6. The method for preparing a blackberry-like heterostructure composite electrode material for potassium-sulfur batteries according to claim 1, characterized in that: In step S5, the mass ratio of the TiO2 / CuMOF heterostructure to the sulfur powder is 1:

3.

7. Use of a blackberry-like heterostructure composite electrode material prepared by the method for preparing a blackberry-like heterostructure composite electrode material for a potassium-sulfur battery according to any one of claims 1 to 6 in a positive electrode of a potassium-sulfur battery, characterized in that: The blackberry-shaped TiO2 / CuMOF / S composite cathode material, conductive carbon black and polyvinylidene fluoride were evenly stirred with N-methylpyrrolidone to form a paste to prepare a blackberry-shaped TiO2 / CuMOF / S cathode composite material electrode.

8. The use according to claim 7, characterized in that: The mass ratio of the blackberry-shaped TiO2 / CuMOF / S composite positive electrode material, conductive carbon black and polyvinylidene fluoride is 7:2:1; the blackberry-shaped TiO2 / CuMOF / S positive electrode composite material electrode has a specific capacity of 1184mAh / g, 830mAh / g and 595mAh / g at rates of 0.1C, 0.2C and 0.5C; after 50 cycles at a current density of 0.5C, the capacity retention rate is 92.49% of the original.

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