Nickel-copper sulfide with core-shell structure, preparation method of nickel-copper sulfide and supercapacitor based on nickel-copper sulfide

Abstract

The invention discloses core-shell structure nickel-copper sulfide, a preparation method thereof and a supercapacitor based on the core-shell structure nickel-copper sulfide, and belongs to the technical field of supercapacitor electrode materials. The method comprises the following steps: uniformly mixing a solution containing nickel ions and copper ions with a ligand to obtain a turbid liquid; carrying out plasma activation treatment on the turbid liquid, carrying out gradient heating and heat preservation, centrifugally collecting precipitates, washing and drying to obtain spherical Ni-Cu bimetal MOF powder; the preparation method comprises the following steps: dissolving spherical Ni-Cu bimetal MOF powder, and dispersing to obtain a precursor suspension; and under an inert atmosphere, injecting a dissolving solution containing thioacetamide and thiourea into the precursor suspension, uniformly mixing, vulcanizing, centrifuging, washing, drying and calcining to obtain the nickel-copper sulfide with the core-shell structure. Experiments prove that the nickel-copper sulfide with the core-shell structure can solve the problems that an existing MOF derivative sulfide electrode material is limited in specific surface area and insufficient in capacitive performance, and a preparation process is prone to causing structural damage.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor electrode material technology, specifically relating to core-shell structured nickel copper sulfide, its preparation method, and supercapacitors based thereon. Background Technology

[0002] Supercapacitors, as high-power energy storage devices, are widely used in new energy vehicles, smart grids, and other fields. Their performance hinges on the electrode materials. Among these, MOF-derived sulfides, due to their porous structure and highly active metal sites, have become an important research direction for supercapacitor cathode materials. However, current technologies have significant shortcomings: The performance of single-metal MOF-derived sulfides is limited. Traditionally, single-metal precursors such as Ni-MOF and Co-MOF are often used. However, during coordination self-assembly, the single valence state of the metal ions easily leads to pore aggregation, resulting in a specific surface area of ​​less than 1300 m². 2 / g, and relying solely on a single-component redox pair to store charge, the specific capacitance is often less than 900 F / g, making it difficult to meet high energy density requirements; the vulcanization process easily damages the material structure. Currently, most vulcanizing agents use a single agent (such as thiourea, sodium sulfide), S 2- The release rate is difficult to control. Too rapid a release can lead to excessive etching of the MOF framework, causing core-shell structure collapse; too slow a release results in incomplete sulfidation, leaving unreacted metal ions and reducing electrochemical activity, with stability often below 80% after 10,000 cycles. Furthermore, the preparation process is neither economically efficient nor environmentally friendly. Some processes rely on high-temperature, high-pressure reactors, temperatures exceeding 200°C, or the use of toxic solvents (such as DMF), requiring complex purification processes to remove residual impurities. This not only results in high energy consumption and cost but also environmental pollution, hindering large-scale application.

[0003] Therefore, developing a MOF-derived sulfide preparation technology that can simultaneously optimize pore structure, enhance active sites, and achieve environmentally friendly and economical processes has become a key direction for breaking through the performance bottleneck of supercapacitor electrode materials. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a core-shell structured nickel-copper sulfide, a method for preparing the same, and a supercapacitor based thereon, so as to solve the technical problems of limited specific surface area, insufficient capacitance performance, and structural damage caused by the preparation process of existing MOF-derived sulfide electrode materials.

[0005] To achieve the above objectives, the present invention employs the following technical solution: The first aspect of this invention discloses a method for preparing core-shell structured nickel-copper sulfide, comprising the following steps: 1) Mix the solution containing nickel and copper ions with the ligand to obtain a suspension; subject the suspension to plasma activation treatment, gradient heating and heat preservation, centrifuge to collect the precipitate, wash, dry, and obtain spherical Ni-Cu bimetallic MOF powder. The ligand is isophthalic acid or 2,5-dihydroxyterephthalic acid; 2) Dissolve and disperse the spherical Ni-Cu bimetallic MOF powder obtained in step 1) to obtain a precursor suspension; under an inert atmosphere, inject a solution containing thioacetamide and thiourea into the precursor suspension, mix, sulfide, centrifuge, wash, dry, and calcine to obtain core-shell structured nickel copper sulfide.

[0006] Preferably, in step 1), the solution containing nickel ions and copper ions is a solution of nickel nitrate tetrahydrate and copper nitrate pentahydrate, or a solution of nickel chloride and copper chloride.

[0007] Preferably, in step 1), the molar ratio of nickel ions, copper ions and ligands is 1:(0.3~0.6):(1.2~1.8).

[0008] Preferably, in step 1), after mixing the solution containing nickel ions and copper ions with the ligand, the pH value is adjusted to 6.8~7.5 to obtain a suspension.

[0009] Preferably, in step 1), the plasma activation treatment specifically involves treating for 10 to 15 minutes at a power of 150 to 200 W.

[0010] Preferably, in step 1), the gradient heating and holding process specifically involves: heating to 150-160°C at a rate of 2-3°C / min and holding for 8-10 h, then heating to 180-190°C at a rate of 2-3°C / min and holding for 10-12 h.

[0011] Preferably, in step 2), diethylene glycol is used for dissolution.

[0012] Preferably, in step 2), after dissolving the spherical Ni-Cu bimetallic MOF powder, it is ultrasonically crushed for 25-30 min.

[0013] Preferably, in step 2), sodium dodecylbenzenesulfonate or oleic acid is used for dispersion.

[0014] Preferably, in step 2), the inert atmosphere flow rate is 50~60 mL / min.

[0015] Preferably, during the process of injecting the solution containing thioacetamide and thiourea into the precursor suspension, the mass ratio of thioacetamide, thiourea and spherical Ni-Cu bimetallic MOF powder is (2.0~2.8):(1.0~1.5):1.

[0016] Preferably, in step 2), the injection rate is 0.5~0.8 mL / min.

[0017] Preferably, in step 2), after injecting the precursor suspension, the mixture is stirred at a stirring rate of 250-300 r / min.

[0018] Preferably, in step 2), the vulcanization process is as follows: first, heat the temperature at 80°C for 5 hours, and then heat it to 110~120°C and heat it for 7~12 hours.

[0019] In a second aspect, the present invention discloses a core-shell structured nickel-copper sulfide obtained by the above preparation method.

[0020] A third aspect of the present invention discloses the application of the above-described core-shell structured nickel-copper sulfide in the preparation of supercapacitors.

[0021] A fourth aspect of the present invention discloses a supercapacitor containing the aforementioned core-shell structure of nickel copper sulfide.

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing core-shell structured nickel-copper sulfide. Using nickel and copper ions as bimetallic sources, spherical Ni-Cu bimetallic MOFs are prepared via a "plasma pretreatment-gradient heating solvothermal" process. Then, using this MOF as a precursor and thioacetamide and thiourea as composite sulfiding agents, core-shell structured nickel-copper sulfide is prepared via a "rate-controlled sulfidation-segmented calcination" process. This method achieves bimetallic synergy and synchronous control of process parameters, breaking through the performance bottlenecks of traditional single-metal or stepwise processes. Traditional MOF-derived sulfides often use a single metal source, which easily leads to pore aggregation due to a single coordination environment; or the stepwise preparation and sulfidation of MOFs easily damage the pre-constructed pore structure. In this invention, Ni... 2+ With Cu 2+ The formation of a bimetallic coordination system allows for the regulation of the MOF self-assembly process and the suppression of excessive grain growth. Simultaneously, plasma pretreatment and gradient-heating solvothermal processes work synergistically to activate ligand active sites while ensuring uniform pore development, achieving a synergistic effect of high specific surface area and structural integrity from a mechanistic perspective. Secondly, the process mechanism better aligns with the core requirements of high energy and long lifespan for supercapacitors. Traditional vulcanization processes often use a single vulcanizing agent, which is prone to problems due to sulfur dioxide (S). 2- Uneven release rates lead to incomplete sulfidation or excessive damage to the core-shell structure; this invention uses thioacetamide (low-temperature slow-release S...). 2- The composite vulcanizing agent, composed of thiourea (high-temperature sulfur supplementation), has a release rate precisely matched to the vulcanization process of the MOF precursor. This allows for the construction of a gradient structure of "dense inner vulcanization core - porous outer vulcanization shell," preserving charge storage sites while enhancing electron transport efficiency. Furthermore, the bimetallic redox pair (Ni...) 2+ / Ni3+ / Ni 4+ With Cu + / Cu 2+ / Cu 3+ This invention introduces additional pseudocapacitance, resulting in superior electrochemical activity compared to single metal sulfides. Thirdly, its economic and environmental benefits are significantly improved through optimized process mechanisms. Existing MOF preparation processes rely on high-temperature, high-pressure equipment or toxic solvents, and subsequent sulfidation requires complex post-treatment. The metal salts and ligands used in this invention are all conventional reagents; N-methylpyrrolidone is recyclable and reusable; the decomposition products of the composite sulfiding agent leave no toxic residues and can be purified simply by water washing. Simultaneously, the process parameters are mild (maximum calcination temperature 380℃), requiring no special high-pressure equipment, thus reducing energy consumption and pollution from a mechanistic perspective, lowering production costs, and making it more suitable for large-scale industrial production. Performance testing results show that the specific surface area of ​​a single Ni-MOF-derived nickel sulfide (Comparative Example 1) is only 1245 m². 2 / g, the specific capacitance at 1 A / g is 865 F / g; while the specific surface area of ​​the core-shell structured nickel-copper sulfide prepared in this invention (Example 3) reaches 1982 m². 2 With a specific capacitance of 1356 F / g at 1 A / g and a capacitance retention of 93.8% after 10,000 cycles, and an internal resistance as low as 0.48 Ω, it provides a new path for the industrialization of high-performance supercapacitor electrode materials. Detailed Implementation

[0023] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in the event of any conflict, the definitions in this specification shall prevail.

[0024] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0025] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0026] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0027] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0028] This invention provides a method for preparing core-shell structured nickel-copper sulfide, comprising the following steps: Step 1: Preparation of spherical Ni-Cu bimetallic MOFs Ligands were added to a solution containing nickel and copper ions and mixed well. The pH was adjusted to 6.8-7.5 to obtain a suspension. The suspension was then activated by plasma, heated in a gradient and held at that temperature, and the precipitate was collected by centrifugation, washed, and vacuum dried to obtain spherical Ni-Cu bimetallic MOF powder. The solution containing nickel and copper ions is nickel nitrate tetrahydrate (Ni(NO3)2). 4H2O) and copper nitrate pentahydrate (Cu(NO3)2) A solution of 5H2O, or nickel chloride (NiCl2). 6H2O) and copper chloride (CuCl2) The solution contains 2H2O; the molar ratio of nickel ions, copper ions, and ligands is 1:(0.3~0.6):(1.2~1.8); the ligands include, but are not limited to, isophthalic acid or 2,5-dihydroxyterephthalic acid; the plasma activation treatment specifically involves treating for 10~15 min at a power of 150~200 W; the gradient heating and holding specifically involves heating to 150~160℃ at a rate of 2~3℃ / min and holding for 8~10 h, then heating to 180~190℃ at a rate of 2~3℃ / min and holding for 10~12 h; Step 2: Preparation of core-shell structured nickel-copper sulfide The spherical Ni-Cu bimetallic MOF powder obtained in step one was dissolved in a solvent, ultrasonically crushed for 25-30 min, and dispersed to obtain a uniform black precursor suspension. Under an inert atmosphere, a solution of thioacetamide (TAA) and thiourea (CS(NH2)2) was injected into the uniform black precursor suspension at a rate of 0.5-0.8 mL / min, mixed at a stirring rate of 250-300 r / min, sulfided, centrifuged, washed, dried, and calcined to obtain core-shell structured nickel-copper sulfide. The solvent includes, but is not limited to, diethylene glycol; the dispersant used for dispersion includes, but is not limited to, sodium dodecylbenzenesulfonate (SDBS) or oleic acid; the inert atmosphere flow rate is 50~60 mL / min; the mass ratio of thioacetamide (TAA), thiourea (CS(NH2)2), and spherical Ni-Cu bimetallic MOF powder is (2.0~2.8):(1.0~1.5):1; the vulcanization step is as follows: first, heat at 80℃ for 5 h, then heat to 110~120℃ and heat for 7~12 h. This invention also provides a method for preparing a supercapacitor based on the above-mentioned core-shell structure nickel-copper sulfide. NiCuS@MOF-1, carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) are weighed in a mass ratio of (85~88):(8~10):(4~5) and mixed with NMP to obtain a uniform electrode slurry. The slurry is coated onto a nickel foam current collector using a coating method, vacuum dried, cut into discs, and pressed to obtain the positive electrode of the supercapacitor. A button-type supercapacitor is assembled in an argon-protected glove box using KOH as the electrolyte and activated carbon as the negative electrode. After the electrolyte has fully wetted the electrode material, the supercapacitor is obtained.

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading this description, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0030] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under standard conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications in the art, unless otherwise stated.

[0031] Example 1: Step 1: Preparation of spherical Ni-Cu bimetallic MOFs Weigh 0.92 g of nickel nitrate tetrahydrate (Ni(NO3)2) 4H2O) and 0.38 g copper nitrate pentahydrate (Cu(NO3)2) Add 5H₂O and N-methylpyrrolidone (NMP) to 90 mL of a magnetic stirrer at 350 r / min for 35 min, maintaining a constant temperature of 30°C in a water bath to ensure complete dissolution and form a light blue-green mixed metal salt solution. Then, weigh 0.71 g of isophthalic acid (H₂IPC) and add it to 60 mL of the mixed metal salt solution, continuing stirring for 2 h. During stirring, add 0.5 mL of diethylamine dropwise in three portions, 20 min apart, adjusting the pH to 7.0 to promote coordination between the ligand and metal ions, forming a light blue suspension. Transfer this suspension to a low-temperature plasma reactor, introduce argon gas at a flow rate of 20 mL / min, and treat at 150 W for 10 min. Utilize plasma active species to activate the metal ions and ligand surfaces, improving subsequent self-assembly efficiency. Then, transfer the pretreated suspension to a 150 W low-temperature plasma reactor. A high-pressure reactor containing 1 mL of polytetrafluoroethylene was sealed and placed in an oven. The heating program was set as follows: the temperature was increased to 160 °C at a rate of 3 °C / min and held for 8 h, then increased to 190 °C at a rate of 2 °C / min and held for 12 h, for a total reaction time of 20 h, in order to achieve stepwise coordination self-assembly. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The precipitate was collected by centrifugation at 8500 r / min for 12 min. It was washed twice with NMP and three times with anhydrous ethanol to remove unreacted raw materials. The precipitate was placed in a vacuum drying oven and dried at 75 °C and 0.08 MPa for 11 h to obtain dark blue spherical Ni-Cu bimetallic MOF powder, denoted as NiCu-MOF-1.

[0032] Step 2: Preparation of core-shell structured nickel-copper sulfide (NiCuS) Weigh 0.15 g NiCu-MOF-1 and add it to 45 mL of diethylene glycol. First, treat the mixture with an ultrasonic homogenizer (350 W) for 30 min, then transfer it to a magnetic stirrer and stir at 280 r / min for 20 min. During stirring, add 0.3 mL of oleic acid as a dispersant to form a uniform black suspension. Separately, weigh 0.32 g thioacetamide (TAA) and 0.21 g thiourea (CS(NH2)2) and add them to 40 mL of deionized water. Stir in a 50℃ water bath for 25 min until completely dissolved to obtain S. 2-A slow-release composite sulfiding agent solution was prepared. Under nitrogen protection, the composite sulfiding agent solution was injected into 35 mL of precursor suspension at a rate of 0.5 mL / min using a constant flow pump, while the stirring rate was increased to 300 r / min. After the addition was completed, stirring was continued for 8 min, and the suspension was observed to turn grayish-black. The mixture was transferred to a 150 mL reactor and kept at 80℃ for 5 h, then heated to 120℃ and kept at 120℃ for 7 h. The sulfidation reaction rate was controlled to avoid over-sulfidation and damage to the core-shell structure. After cooling, the mixture was centrifuged at 9500 r / min for 15 min, and the precipitate was collected and washed 4 times with deionized water and 2 times with anhydrous ethanol. Then, it was dried at 60℃ for 6 h to obtain primary NiCuS powder. The primary powder was placed in a tube furnace, and the air in the furnace was replaced with high-purity nitrogen at a flow rate of 60 mL / min for 35 min. The calcination program was set as follows: the temperature was increased to 280℃ at a rate of 5℃ / min and held for 2 h. h, then raise the temperature to 380℃ at a rate of 3℃ / min and hold for 1.5 h. After cooling, core-shell structured NiCuS powder is obtained, denoted as NiCuS@MOF-1.

[0033] Step 3: Electrode and Device Assembly 44.0 mg NiCuS@MOF-1, 4.0 mg carbon nanotubes (CNTs), and 2.0 mg polyvinylidene fluoride (PVDF) were weighed and added to 300 μL NMP. The mixture was stirred for 9 h to form a uniform electrode slurry. The slurry was coated onto a 100 μm thick nickel foam current collector using a coating method. The coated current collector was placed in a vacuum drying oven and dried at 105 °C for 12 h. After drying, it was cut into 12 mm diameter discs and pressed at 15 MPa for 50 s using a tablet press to obtain the positive electrode of the supercapacitor. A button-type supercapacitor was assembled in an argon-protected glove box using 1 mol / L KOH as the electrolyte and activated carbon as the negative electrode. After assembly, the capacitor was left to stand outside the glove box for 16 h to allow the electrolyte to fully wet the electrode material, thus obtaining the supercapacitor.

[0034] Example 2: Step 1: Preparation of spherical Ni-Cu bimetallic MOFs Weigh 0.85 g of nickel nitrate tetrahydrate (Ni(NO3)2) 4H2O) and 0.45 g copper nitrate pentahydrate (Cu(NO3)2) Add 5 H₂O and N-methylpyrrolidone (NMP) to 80 mL of N-methylpyrrolidone (NMP). Turn on the magnetic stirrer and set the speed to 350 r / min. Stir for 35 min, and maintain the temperature at 30℃ in a constant temperature water bath during this period to ensure complete dissolution of the solid, forming a light blue-green mixed metal salt solution. Then, weigh 0.71 g of isophthalic acid (H₂IPC) and add it to 50 mL of the mixed metal salt solution. Continue stirring for 2 h. During stirring, add 0.5 mL of diethylamine dropwise in three batches at 20 min intervals. Adjust the pH of the solution to 7.0 to promote coordination between the ligand and the metal ions, forming a light blue suspension. Transfer the suspension to a low-temperature plasma reactor, introduce argon gas at a flow rate of 20 mL / min, and treat for 10 min at a power of 150 W. Utilize plasma active species to activate the metal ions and ligand surfaces, improving the subsequent self-assembly efficiency. Then, transfer the pretreated suspension to a 150 W low-temperature plasma reactor. A high-pressure reactor containing 1 mL of polytetrafluoroethylene was sealed and placed in an oven. The heating program was set as follows: the temperature was increased to 150 °C at a rate of 2 °C / min and held for 10 h, then increased to 180 °C at a rate of 3 °C / min and held for 10 h, for a total reaction time of 20 h, in order to achieve stepwise coordination self-assembly. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The precipitate was collected by centrifugation at 8500 r / min for 12 min. It was washed twice with NMP and three times with anhydrous ethanol to remove unreacted raw materials. The precipitate was placed in a vacuum drying oven and dried at 75 °C and 0.08 MPa for 11 h to obtain dark blue spherical Ni-Cu bimetallic MOF powder, denoted as NiCu-MOF-2.

[0035] Step 2: Preparation of core-shell structured nickel-copper sulfide (NiCuS) Weigh 0.15 g NiCu-MOF-2 and add it to 45 mL diethylene glycol. First, treat the mixture with an ultrasonic homogenizer (350 W) for 30 min, then transfer it to a magnetic stirrer and stir at 280 r / min for 20 min. During stirring, add 0.3 mL oleic acid as a dispersant to form a uniform black suspension. Separately, weigh 0.40 g thioacetamide (TAA) and 0.15 g thiourea (CS(NH2)2) and add them to 40 mL deionized water. Stir in a 50℃ water bath for 25 min until completely dissolved to obtain S. 2-A slow-release composite sulfiding agent solution was prepared. Under nitrogen protection, the composite sulfiding agent solution was injected into 30 mL of precursor suspension at a rate of 0.5 mL / min using a constant flow pump, while the stirring rate was increased to 300 r / min. After the addition was completed, stirring was continued for 8 min, and the suspension was observed to turn grayish-black. The mixture was transferred to a 150 mL reactor and kept at 80℃ for 5 h, then heated to 110℃ and kept at 12 h. The sulfidation reaction rate was controlled to avoid over-sulfidation and damage to the core-shell structure. After cooling, the mixture was centrifuged at 9500 r / min for 15 min, and the precipitate was collected and washed 4 times with deionized water and 2 times with anhydrous ethanol. Then, it was dried at 60℃ for 6 h to obtain primary NiCuS powder. The primary powder was placed in a tube furnace, and the air in the furnace was replaced with high-purity nitrogen at a flow rate of 60 mL / min for 35 min. The calcination program was set as follows: the temperature was increased to 280℃ at a rate of 5℃ / min and held for 2 h. h, then raise the temperature to 380℃ at a rate of 3℃ / min and hold for 1.5 h, then cool to obtain core-shell structured NiCuS powder, and obtain the product NiCuS@MOF-2.

[0036] The corresponding supercapacitor was prepared using the method obtained in Example 1.

[0037] Example 3: Step 1: Preparation of spherical Ni-Cu bimetallic MOFs Weigh 0.92 g of nickel nitrate tetrahydrate (Ni(NO3)2) 4H2O) and 0.38 g copper nitrate pentahydrate (Cu(NO3)2) Add 5H₂O and N-methylpyrrolidone (NMP) to 90 mL of N-methylpyrrolidone (NMP). Turn on the magnetic stirrer and set the speed to 350 r / min. Stir for 35 min, and maintain the temperature at 30℃ in a constant temperature water bath during this period to ensure complete dissolution of the solid, forming a light blue-green mixed metal salt solution. Then, weigh 0.71 g of isophthalic acid (H₂IPC) and add it to 65 mL of the mixed metal salt solution. Continue stirring for 2 h. During stirring, add 0.5 mL of diethylamine dropwise in three batches at 20 min intervals. Adjust the pH of the solution to 7.0 to promote coordination between the ligand and the metal ions, forming a light blue suspension. Transfer the suspension to a low-temperature plasma reactor, introduce argon gas at a flow rate of 20 mL / min, and treat for 15 min at a power of 200 W. Utilize plasma active species to activate the metal ions and ligand surfaces, improving the subsequent self-assembly efficiency. Then, transfer the pretreated suspension to a 150°C... A high-pressure reactor containing 1 mL of polytetrafluoroethylene was sealed and placed in an oven. The heating program was set as follows: the temperature was increased to 160 °C at a rate of 3 °C / min and held for 8 h, then increased to 190 °C at a rate of 2 °C / min and held for 12 h, for a total reaction time of 20 h, in order to achieve stepwise coordination self-assembly. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The precipitate was collected by centrifugation at 8500 r / min for 12 min. It was washed twice with NMP and three times with anhydrous ethanol to remove unreacted raw materials. The precipitate was placed in a vacuum drying oven and dried at 75 °C and 0.08 MPa for 11 h to obtain dark blue spherical Ni-Cu bimetallic MOF powder, denoted as NiCu-MOF-3.

[0038] Step 2: Preparation of core-shell structured nickel-copper sulfide (NiCuS) Weigh 0.15 g NiCu-MOF-3 and add it to 45 mL of diethylene glycol. First, treat the mixture with an ultrasonic homogenizer (350 W) for 25 min, then transfer it to a magnetic stirrer and stir at 280 r / min for 20 min. During stirring, add 0.2 mL of sodium dodecylbenzenesulfonate (SDBS) dropwise as a dispersant to form a uniform black suspension. Separately, weigh 0.32 g thioacetamide (TAA) and 0.21 g thiourea (CS(NH2)2) and add them to 40 mL of deionized water. Stir in a 50℃ water bath for 25 min until completely dissolved to obtain S. 2-A slow-release composite sulfiding agent solution was prepared. Under nitrogen protection, the composite sulfiding agent solution was injected into 40 mL of precursor suspension at a rate of 0.5 mL / min using a constant flow pump, while the stirring rate was increased to 300 r / min. After the addition was completed, stirring continued for 8 min, and the suspension was observed to turn grayish-black. The mixture was transferred to a 150 mL reactor and kept at 80℃ for 5 h, then heated to 120℃ and kept at 120℃ for 7 h. The sulfidation reaction rate was controlled to avoid over-sulfidation and damage to the core-shell structure. After cooling, the mixture was centrifuged at 9500 r / min for 15 min, and the precipitate was collected and washed 4 times with deionized water and 2 times with anhydrous ethanol. Then, it was dried at 60℃ for 6 h to obtain primary NiCuS powder. The primary powder was placed in a tube furnace, and the air in the furnace was replaced with high-purity nitrogen at a flow rate of 60 mL / min for 35 min. The calcination program was set as follows: the temperature was increased to 280℃ at a rate of 5℃ / min and held for 2 h. h, then raise the temperature to 400℃ at a rate of 3℃ / min and hold for 2 h, and after cooling, obtain core-shell structured NiCuS powder, and obtain the product NiCuS@MOF-3.

[0039] The corresponding supercapacitor was prepared using the method obtained in Example 1.

[0040] Example 4: Step 1: Preparation of spherical Ni-Cu bimetallic MOFs Weigh 0.92 g of nickel nitrate tetrahydrate (Ni(NO3)2) 4H2O) and 0.38 g copper nitrate pentahydrate (Cu(NO3)2) 5H₂O was added together with 90 mL of N-methylpyrrolidone (NMP). A magnetic stirrer was turned on and the speed was set to 350 r / min. The mixture was stirred for 35 min, and the temperature was controlled at 30℃ during the process to ensure complete dissolution of the solid, forming a light blue-green mixed metal salt solution. Then, 0.68 g of 2,5-dihydroxyterephthalic acid was weighed and added to 55 mL of the mixed metal salt solution. The mixture was stirred for another 2 h. During the stirring process, 0.5 mL of diethylamine was added dropwise in three portions, 20 min apart, to adjust the pH of the solution to 7.2 to promote coordination between the ligand and the metal ions, forming a light blue suspension. The suspension was then transferred to a low-temperature plasma reactor, and argon gas was introduced at a flow rate of 20 mL / min. The reactor was set to 150 W and treated for 10 min to activate the metal ions and ligand surfaces using plasma active species, thereby improving the subsequent self-assembly efficiency. The pretreated suspension was then transferred to a 150 W low-temperature plasma reactor. A high-pressure reactor containing 1 mL of polytetrafluoroethylene was sealed and placed in an oven. The heating program was set as follows: the temperature was increased to 160 °C at a rate of 3 °C / min and held for 8 h, then increased to 190 °C at a rate of 2 °C / min and held for 12 h, for a total reaction time of 20 h, in order to achieve stepwise coordination self-assembly. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The precipitate was collected by centrifugation at 8500 r / min for 12 min. It was washed twice with NMP and three times with anhydrous ethanol to remove unreacted raw materials. The precipitate was placed in a vacuum drying oven and dried at 75 °C and 0.08 MPa for 11 h to obtain dark blue spherical Ni-Cu bimetallic MOF powder, denoted as NiCu-MOF-4.

[0041] Step 2: Preparation of core-shell structured nickel-copper sulfide (NiCuS) Weigh 0.15 g NiCu-MOF-4 and add it to 45 mL of diethylene glycol. First, treat the mixture with an ultrasonic homogenizer (350 W) for 30 min, then transfer it to a magnetic stirrer and stir at 280 r / min for 20 min. During stirring, add 0.3 mL of oleic acid as a dispersant to form a uniform black suspension. Separately, weigh 0.32 g thioacetamide (TAA) and 0.21 g thiourea (CS(NH2)2) and add them to 40 mL of deionized water. Stir in a 50℃ water bath for 25 min until completely dissolved to obtain S. 2-A slow-release composite sulfiding agent solution was prepared. Under nitrogen protection, the composite sulfiding agent solution was injected into 33 mL of precursor suspension at a rate of 0.5 mL / min using a constant flow pump, while the stirring rate was increased to 300 r / min. After the addition was completed, stirring was continued for 8 min, and the suspension was observed to turn grayish-black. The mixture was transferred to a 150 mL reactor and kept at 70℃ for 6 h, then heated to 110℃ and kept at 110℃ for 8 h. The sulfidation reaction rate was controlled to avoid over-sulfidation and damage to the core-shell structure. After cooling, the mixture was centrifuged at 9500 r / min for 15 min, and the precipitate was collected and washed 4 times with deionized water and 2 times with anhydrous ethanol. Then, it was dried at 60℃ for 6 h to obtain primary NiCuS powder. The primary powder was placed in a tube furnace, and the air in the furnace was replaced with high-purity nitrogen at a flow rate of 60 mL / min for 35 min. The calcination program was set as follows: the temperature was increased to 280℃ at a rate of 5℃ / min and held for 2 h. h, then raise the temperature to 380℃ at a rate of 3℃ / min and hold for 1.5 h, then cool to obtain core-shell structured NiCuS powder, thus obtaining the product NiCuS@MOF-4.

[0042] The supercapacitor was prepared according to the method obtained in Example 1, except that carbon nanotubes (CNTs) were replaced with conductive carbon black, and the amounts of NiCuS@MOF-1, conductive carbon black and polyvinylidene fluoride (PVDF) added were 42.5 g, 5 g and 2.5 g, respectively.

[0043] Example 5: Step 1: Preparation of spherical Ni-Cu bimetallic MOFs Weigh 0.88 g of nickel chloride (NiCl2) 6H2O) and 0.35 g copper chloride (CuCl2) Add 2H₂O and N-methylpyrrolidone (NMP) to 90 mL of a magnetic stirrer at 350 r / min for 35 min, maintaining a constant temperature of 30°C in a water bath to ensure complete dissolution and form a light blue-green mixed metal salt solution. Then, weigh 0.71 g of isophthalic acid (H₂IPC) and add it to 62 mL of the mixed metal salt solution, continuing stirring for 2 h. During stirring, add 0.5 mL of diethylamine in three 20-min increments, adjusting the pH to 7.0 to promote coordination between the ligand and metal ions, forming a light blue suspension. Transfer this suspension to a low-temperature plasma reactor, introduce argon gas at a flow rate of 20 mL / min, and treat at 150 W for 10 min. Utilize plasma active species to activate the metal ions and ligand surfaces, improving subsequent self-assembly efficiency. Then, transfer the pretreated suspension to a 150 W low-temperature plasma reactor. A high-pressure reactor containing 1 mL of polytetrafluoroethylene was sealed and placed in an oven. The heating program was set as follows: the temperature was increased to 160 °C at a rate of 3 °C / min and held for 8 h, then increased to 190 °C at a rate of 2 °C / min and held for 12 h, for a total reaction time of 20 h, in order to achieve stepwise coordination self-assembly. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The precipitate was collected by centrifugation at 8500 r / min for 12 min. The precipitate was washed twice with NMP and three times with anhydrous ethanol to remove unreacted raw materials. The precipitate was placed in a vacuum drying oven and dried at 75 °C and 0.08 MPa for 11 h to obtain dark blue spherical Ni-Cu bimetallic MOF powder, denoted as NiCu-MOF-5.

[0044] Step 2: Preparation of core-shell structured nickel-copper sulfide (NiCuS) Weigh 0.15 g NiCu-MOF-5 and add it to 45 mL of diethylene glycol. First, treat the mixture with an ultrasonic homogenizer (350 W) for 30 min, then transfer it to a magnetic stirrer and stir at 280 r / min for 20 min. During stirring, add 0.3 mL of oleic acid as a dispersant to form a uniform black suspension. Separately, weigh 0.32 g thioacetamide (TAA) and 0.21 g thiourea (CS(NH2)2) and add them to 40 mL of deionized water. Stir in a 50℃ water bath for 25 min until completely dissolved to obtain S. 2-A slow-release composite sulfiding agent solution was prepared. Under nitrogen protection, the composite sulfiding agent solution was injected into 37 mL of precursor suspension at a rate of 0.8 mL / min using a constant flow pump, while the stirring rate was increased to 250 r / min. After the addition was completed, stirring was continued for 8 min, and the suspension was observed to turn grayish-black. The mixture was transferred to a 150 mL reactor and heated to 80℃ for 5 h, then heated to 120℃ and held for 7 h. The sulfidation reaction rate was controlled to avoid over-sulfidation and damage to the core-shell structure. After cooling, the mixture was centrifuged at 9500 r / min for 15 min, and the precipitate was collected and washed 4 times with deionized water and 2 times with anhydrous ethanol. Then, it was dried at 60℃ for 6 h to obtain primary NiCuS powder. The primary powder was placed in a tube furnace, and the air in the furnace was replaced with high-purity argon at a flow rate of 50 mL / min for 35 min. The calcination program was set to increase the temperature to 280℃ at a rate of 5℃ / min and hold for 2 h. h, then raise the temperature to 380℃ at a rate of 3℃ / min and hold for 1.5 h, then cool to obtain core-shell structured NiCuS powder, and obtain the product NiCuS@MOF-5.

[0045] The corresponding supercapacitor was prepared using the method obtained in Example 1.

[0046] Comparative Example 1: Unlike Example 1, in Step 1, only 1.25 g of nickel nitrate tetrahydrate was used as the metal source (without copper nitrate pentahydrate), and in Step 2, only 0.5 g of thiourea was used as the sulfiding agent (without thioacetamide). The remaining parameters remained unchanged, resulting in the product NiS@MOF-Comparative 1.

[0047] The corresponding supercapacitor was prepared using the method obtained in Example 1.

[0048] Comparative Example 2: Unlike Example 1, only the low-temperature plasma pretreatment was omitted in step one and the solvothermal temperature was directly maintained at 180°C for 20 h (without gradient heating). In step two, only 0.5 g of thioacetamide (thiourea-free) was used as the sulfiding agent, and the other parameters remained unchanged, resulting in the product NiCuS@MOF-Comparative 2.

[0049] The corresponding supercapacitor was prepared using the method obtained in Example 1.

[0050] Comparative Example 3: Unlike Example 1, the vulcanizing agent was changed to a single 0.55 g TAA (thiourea-free), while the other parameters remained unchanged, resulting in the product NiCuS@MOF-Comparative 3.

[0051] Performance testing was performed using the following methods: 1. Specific surface area: 100 mg of active material (Examples 1-5, Comparative Examples 1-3) was degassed under vacuum at 120℃ for 4 h to remove impurities; using a fully automated specific surface area analyzer, with liquid nitrogen (-196℃) as the adsorption environment and high-purity nitrogen as the adsorbate, the specific surface area was determined at P / P... o Adsorption-desorption isotherms were measured in the 0.05–0.3 m² range. Specific surface area (m²) was calculated using the BET multilayer adsorption model. 2 / g).

[0052] 2. Specific capacitance: Using CHI 660E, constant current charge-discharge (GCD) was performed on each group of supercapacitors in the 0~2.7 V window and at a current density of 1 A / g. The specific capacitance (F / g) was calculated according to the formula C=It / (mΔV), where I is the current, t is the discharge time, m is the mass of the active material, and ΔV is the discharge voltage range.

[0053] 3. Cyclic stability: Using the Blue Electric testing system, each group of supercapacitors was cycled 10,000 times at a current density of 1 A / g and a V window of 0~2.7 V; according to (C 10000 Calculate the capacity retention rate by multiplying (C0) by 100%, where C is the capacity retention rate. 10000 C0 is the capacitance of the 10,000th test, and C0 is the initial capacitance.

[0054] 4. Internal Resistance: Using Autolab PGSTAT302N, with the device in open-circuit state, apply a 5 mV AC signal at 10... 5 ~10 -2 Measure the AC impedance (EIS) in the Hz frequency range; read the value at the intersection of the high-frequency region of the Nyquist spectrum and the real axis, which is the equivalent series internal resistance (Ω).

[0055] 5. Rate performance: Using an electrochemical workstation, GCD was performed sequentially at current densities of 0.5 A / g, 1 A / g, 2 A / g, 5 A / g, and 10 A / g within the 0~2.7 V window. The third specific capacitance at each density was taken. The rate performance (%) was calculated as (C 10 A / g / C 0.5 A / g)×100%.

[0056] Table 1 Performance Test Results

[0057] The performance differences between Examples 1-5 and Comparative Examples 1-3 are shown in Table 1. The core reasons are the bimetallic synergistic effect, the control effect of process parameters on material structure, and the difference in interface charge transport efficiency.

[0058] The difference in specific surface area is essentially due to the synergistic effect of bimetallic doping and processing on the pore structure. Comparative Example 1 shows a single Ni-MOF-derived nickel sulfide, Ni 2+When a single metal ion coordinates with a ligand, the self-assembled pores tend to aggregate, resulting in a specific surface area of ​​only 1245 m². 2 / g; Comparative Example 2, due to the omission of plasma pretreatment and the use of single-step solvothermal treatment, had poor suspension homogeneity and incomplete MOF channel development, with a specific surface area of ​​1386 m². 2 / g; Comparative Example 3, due to the use of a single sulfiding agent, exhibits significantly inferior specific capacitance, internal resistance, and rate performance compared to Examples 1-5. In contrast, the Ni-Cu bimetallic systems of Examples 1-5 show Cu... 2+ The introduction of plasma can alter the coordination environment between metal ions and ligands, inhibiting excessive MOF grain growth. Furthermore, plasma pretreatment can activate active sites on the ligand surface, promoting uniform pore formation. In particular, Example 3 further optimizes pore connectivity by increasing plasma power and extending the treatment time, achieving a specific surface area of ​​1982 m². 2 / g provides ample space for charge storage.

[0059] The advantages in specific capacitance and cycle stability stem from the optimized electronic structure resulting from bimetallic synergy and composite sulfidation. In contrast, single NiS in Comparative Example 1 lacks the electronic modulation of Cu, relying solely on Ni. 2+ / Ni 3+ / Ni 4+ The single-component redox pair exhibits a specific capacitance of only 865 F / g at 1 A / g; furthermore, the sulfidation of a single thiourea readily leads to numerous grain boundary defects in the sulfidation products, resulting in a capacity retention of only 75.8% after 10,000 cycles. In Examples 1-5, Cu... 2+ The introduction of Ni 2+ This creates a synergistic electronic effect, lowering the energy barrier for d-orbital electron transitions in metal ions. Simultaneously, the composite sulfurizing agent (TA + thiourea) can achieve S... 2- Slow release avoids excessive sulfidation that could damage the core-shell structure; TAA releases S at low temperatures. 2- An inner sulfide core is formed, and thiourea is used to supplement sulfur at high temperature to construct an outer sulfide shell, forming a "core-shell" gradient structure. This retains the porous characteristics of MOFs while enhancing the conductivity of the sulfides. For example, in Example 1, the specific capacitance reaches 1285 F / g, and the cycle retention rate is 91.5%. Essentially, it is a bimetallic pair (Ni... 2- / Ni 3+ / Ni 4+ With Cu + / Cu 2+ / Cu 3+ It works synergistically with the core-shell structure to enhance charge storage and structural stability.

[0060] The difference in internal resistance and rate performance depends on the rationality of the ion transport channels. In Comparative Example 1, the agglomeration of single NiS pores and in Comparative Example 2, the disordered pore structure both resulted in high ion diffusion resistance in the electrolyte, with internal resistances reaching 0.98 Ω and 0.82 Ω, respectively, and capacity ratios of only 56.3% and 65.8% for 10 A / g and 0.5 A / g, respectively. Examples 1-5 constructed a multi-level pore structure of "micropore-mesopore" through gradient heating solvothermal treatment and segmented calcination: micropores were used for charge storage, mesopores served as ion transport channels, and the CNT conductive network further reduced electron transport resistance. In Example 3, due to the increased final calcination temperature to 400℃, the crystallinity of the sulfide was optimized, the ion transport path was smoother, the internal resistance decreased to 0.48 Ω, and the rate performance reached 81.2%, meeting the high power requirements of supercapacitors.

[0061] In summary, the synergistic effect of Ni-Cu bimetallic synthesis, controlled composite sulfidation rate, and optimized process parameters simultaneously improve performance in terms of pore structure construction, electron transport, and structural stability, which is the core reason why the embodiments are superior to the comparative examples.

[0062] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing core-shell structured nickel-copper sulfide, characterized in that, Includes the following steps: 1) Mix the solution containing nickel and copper ions with the ligand to obtain a suspension; subject the suspension to plasma activation treatment, gradient heating and heat preservation, centrifuge to collect the precipitate, wash, dry, and obtain spherical Ni-Cu bimetallic MOF powder. The ligand is isophthalic acid or 2,5-dihydroxyterephthalic acid; 2) Dissolve and disperse the spherical Ni-Cu bimetallic MOF powder obtained in step 1) to obtain a precursor suspension; under an inert atmosphere, inject a solution containing thioacetamide and thiourea into the precursor suspension, mix, sulfide, centrifuge, wash, dry, and calcine to obtain core-shell structured nickel copper sulfide.

2. The method for preparing core-shell structured nickel-copper sulfide according to claim 1, characterized in that, In step 1), the solution containing nickel ions and copper ions is a solution of nickel nitrate tetrahydrate and copper nitrate pentahydrate, or a solution of nickel chloride and copper chloride.

3. The method for preparing core-shell structured nickel-copper sulfide according to claim 1, characterized in that, In step 1), the molar ratio of nickel ions, copper ions and ligands is 1:(0.3~0.6):(1.2~1.8).

4. The method for preparing core-shell structured nickel-copper sulfide according to claim 1, characterized in that, In step 1), the solution containing nickel and copper ions is mixed with the ligand, and the pH value is adjusted to 6.8-7.5 to obtain a suspension.

5. The method for preparing core-shell structured nickel-copper sulfide according to claim 1, characterized in that, In step 1), the plasma activation treatment specifically involves treating the plasma for 10 to 15 minutes at a power of 150 to 200 W.

6. The method for preparing core-shell structured nickel-copper sulfide according to claim 1, characterized in that, In step 1), the gradient heating and holding process is as follows: the temperature is increased to 150-160℃ at a rate of 2-3℃ / min and held for 8-10 h, and then increased to 180-190℃ at a rate of 2-3℃ / min and held for 10-12 h.

7. The method for preparing core-shell structured nickel-copper sulfide according to claim 1, characterized in that, During the process of injecting the solution containing thioacetamide and thiourea into the precursor suspension, the mass ratio of thioacetamide, thiourea and spherical Ni-Cu bimetallic MOF powder is (2.0~2.8):(1.0~1.5):

1.

8. The core-shell structured nickel-copper sulfide obtained by the preparation method according to any one of claims 1 to 7.

9. The application of the core-shell structured nickel-copper sulfide as described in claim 8 in the preparation of supercapacitors.

10. A supercapacitor, characterized in that, It contains the core-shell structure of nickel-copper sulfide as described in claim 8.

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