A sulfur-doped nickel-cobalt-selenium composite material, a preparation method therefor and applications thereof

Abstract

The application relates to the technical field of supercapacitor electrode materials, in particular to a sulfur-doped nickel cobalt selenide composite material and a preparation method and application thereof. The preparation method comprises the following steps: taking SeO2 as a selenium source, taking hydrazine hydrate as a strong reducing agent, mixing a SeO2 ethylene glycol solution with the hydrazine hydrate and a NiCo-PBA@NiCo-LDH multi-level core-shell precursor, and performing a selenization reaction to obtain NiCoSe2; mixing the NiCoSe2 with sulfur powder, and performing calcination treatment to obtain the sulfur-doped nickel cobalt selenide composite material. Through the synergistic effect of the multi-level core-shell structure and the hetero-doping, the sulfur-doped nickel cobalt selenide composite material is endowed with excellent electrochemical energy storage performance, and the problems of poor rate performance and decreased cycle stability caused by the insufficient intrinsic electrochemical activity and large volume change in the charging and discharging process of the transition metal selenide as a supercapacitor electrode material are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of supercapacitor electrode materials technology, specifically to a sulfur-doped nickel-cobalt selenide composite material, its preparation method, and its application. Background Technology

[0002] Supercapacitors exhibit unique advantages in energy storage due to their rapid charge-discharge capabilities and ultra-long cycle life; however, their relatively low energy density remains a core bottleneck restricting their development. Therefore, developing novel electrode materials that can significantly improve energy storage density while maintaining high power and long lifespan has become a cutting-edge focus in this field.

[0003] Metal-organic frameworks (MOFs) have attracted widespread attention in the field of electrochemical energy storage due to their unique structural advantages. Among them, Prussian blue analogues (PBAs), as important members of the MOF family, possess three-dimensional open-channel structures, mild synthesis conditions, and tunable composition, and are often used as precursors or templates for constructing hierarchical nanostructures. Using PBAs as sacrificial templates, through hydrothermal / solvothermal methods or chemical transformation strategies, transition metal compounds (such as oxides, sulfides, selenides, and phosphides) with higher electrochemical activity can be derived. This strategy retains the original morphological characteristics of PBAs while endowing the materials with richer redox active sites. In recent years, transition metal selenides have shown superior electrochemical activity compared to their corresponding oxides or sulfides due to intermetallic synergistic effects and high conductivity, becoming one of the hot topics in electrode material research. Converting PBA-based precursors into bimetallic selenides through selenization reactions is an effective way to improve the intrinsic reactivity of materials. However, selenide materials obtained solely through phase transformation suffer from insufficient intrinsic electrochemical activity, limited exposure of active sites, and sluggish redox reaction kinetics. Furthermore, the large volume changes during charge and discharge easily lead to structural stress accumulation and mechanical failure, making it difficult to balance rate performance and cycle stability. Consequently, their capacity retention at high current densities and structural stability during long cycles still need improvement, making it difficult to meet the application requirements of high-performance energy storage devices. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a sulfur-doped nickel-cobalt selenide composite material, its preparation method, and its applications. Using a NiCo-PBA@NiCo-LDH hierarchical core-shell precursor as the structural unit, this invention constructs a sulfur-doped nickel-cobalt selenide composite material with a unique hierarchical structure through a multi-step controllable synthesis via solvothermal selenization and vapor deposition sulfur doping. Through the synergistic effect of the hierarchical core-shell structure and heterogeneous doping, this invention effectively improves the specific surface area, charge transport kinetics, and structural stability of the sulfur-doped nickel-cobalt selenide composite material, giving it high specific capacitance, excellent rate performance, and long cycle life. This effectively solves the problems of insufficient intrinsic electrochemical activity and poor rate performance and decreased cycle stability caused by large volume changes during charge and discharge when transition metal selenides are used as electrode materials for supercapacitors. Therefore, this invention has broad application prospects as a high-performance supercapacitor electrode material.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a method for preparing a sulfur-doped nickel-cobalt selenide composite material, comprising the following steps: Preparation of S1 and NiCoSe2: Using SeO2 as the selenium source and hydrazine hydrate as a strong reducing agent, the ethylene glycol solution of SeO2 was mixed with hydrazine hydrate and NiCo-PBA@NiCo-LDH multilevel core-shell precursor. The hydrazine hydrate reduced the Se in SeO2 from +4 to -2 valence. Subsequently, NiCoSe2 was obtained through a selenization reaction.

[0006] Preparation of S2 and S@NiCoSe2: NiCoSe2 is mixed with sulfur powder and calcined. During the calcination process, sulfur atoms diffuse into the NiCoSe2 lattice to form an S-Se solid solution, thus obtaining a sulfur-doped nickel-cobalt selenide composite material.

[0007] Preferably, the mass ratio of SeO2 to NiCo-PBA@NiCo-LDH multilevel core-shell precursor is 1~3:1. When the mass ratio of SeO2 to NiCo-PBA@NiCo-LDH multilevel core-shell precursor is less than 1:1, the selenium source supply is insufficient, the selenization reaction is incomplete, the precursor conversion is incomplete, and impurities such as NiCo-LDH are easily retained, leading to reduced product purity and fewer electrochemical active sites. When the mass ratio of SeO2 to NiCo-PBA@NiCo-LDH multilevel core-shell precursor is greater than 3:1, the selenium source is excessive, the reaction is too violent, and the strong reducing environment destroys the integrity of the multilevel core-shell structure, causing the PBA core to collapse and the outer shell to detach, resulting in a decrease in specific surface area and ultimately deteriorating electrochemical performance.

[0008] More preferably, the mass ratio of SeO2 to NiCo-PBA@NiCo-LDH multilevel core-shell precursor is 2:1.

[0009] Preferably, the selenization reaction is carried out under solvothermal conditions at 160°C to 180°C for 4 to 8 hours; more preferably, the reaction is carried out at 180°C for 6 hours.

[0010] Preferably, the mass ratio of NiCoSe2 to sulfur powder is 1:1 to 5. When the mass ratio is less than 1:1, the sulfur source supply is insufficient, the sulfur doping is inadequate, the doping effect is limited, and the sulfur atoms are only limited to surface physical adsorption or very shallow chemical adsorption, making it difficult to enter the selenide lattice to achieve effective doping and failing to induce sufficient lattice distortion and electronic structure regulation. When the mass ratio is greater than 1:5, the sulfur source is severely excessive, and during the high-temperature vapor deposition process, a large number of sulfur atoms excessively replace selenium atoms in the lattice, destroying the stability of the NiCoSe2 lattice structure, leading to lattice collapse, phase lattice transformation, and ultimately the formation of nickel cobalt sulfides.

[0011] More preferably, the mass ratio of NiCoSe2 to sulfur powder is 1:3.

[0012] Preferably, the calcination treatment conditions are as follows: in an inert atmosphere, the temperature is increased to 450℃~550℃ at a rate of 1~5℃ / min, and held at 450℃~500℃ for 1h~3h; more preferably, the temperature is increased to 500℃ at a rate of 2℃ / min, and held at 500℃ for 2h.

[0013] Preferably, the NiCo-PBA@NiCo-LDH multilevel core-shell precursor is prepared according to the following steps: Preparation of S1, NiCo-PBA@NiCo-LDH multilevel core-shell precursor: NiCo-PBA, a nickel-cobalt Prussian blue analog, was dispersed in Tris buffer, mixed with dopamine, and subjected to a coating reaction to form a polydopamine-modified layer. At this point, NiCo-PBA was coated within the polydopamine-modified layer, yielding NiCo-PBA@PDA. The pH of the Tris buffer was 8.5.

[0014] S2. Soluble nickel salt, soluble cobalt salt, hexamethylenetetramine, and trisodium citrate are dissolved together in water to obtain a mixed aqueous solution. NiCo-PBA@PDA is dispersed in the mixed aqueous solution to obtain a NiCo-PBA@PDA dispersion. Subsequently, a nickel-cobalt layered double hydroxide is grown on the surface of NiCo-PBA@PDA through a hydrothermal reaction to obtain the NiCo-PBA@NiCo-LDH hierarchical core-shell precursor. Hexamethylenetetramine and trisodium citrate jointly provide alkaline conditions, with hexamethylenetetramine acting as a precipitant and trisodium citrate as a complexing agent.

[0015] Preferably, the mass ratio of the nickel-cobalt Prussian blue analog NiCo-PBA to dopamine is 1:0.8 to 1.2. When the mass ratio is below 1:0.8, insufficient dopamine prevents the formation of a complete coating layer on the NiCo-PBA surface. The exposed PBA surface directly serves as a heterogeneous nucleation site during subsequent LDH growth, resulting in severe disordered stacking in the exposed area. When the mass ratio is above 1:1.2, the thick and dense organic PDA layer acts as an electronic insulator, severely hindering electron transfer from the external circuitry to the PBA core or shell.

[0016] More preferably, the mass ratio of the nickel cobalt Prussian blue analog NiCo-PBA to dopamine is 1:1.

[0017] Preferably, the coating reaction is carried out under the following conditions: stirring at room temperature and at a pH of 8.0-9.0 for at least 24 hours in a light-protected environment. More preferably, the pH is 8.5.

[0018] Preferably, the mass concentration of the NiCo-PBA@PDA dispersion is 0.5 g / L to 0.7 g / L, and the Ni in the mixed aqueous solution... 2+ With Co 2+ The molar ratio is 2~4:1, and the mass ratio of hexamethylenetetramine, trisodium citrate and Ni(NO3)2·6H2O is 49:22:65.

[0019] More preferably, Ni 2+ With Co 2+ The molar ratio is 3:1.

[0020] Preferably, the hydrothermal reaction conditions are: reacting at 110℃~120℃ for 6h~12h, more preferably, reacting at 110℃ for 12h.

[0021] Preferably, when preparing the mixed solution, the soluble nickel salt is selected from nickel nitrate hexahydrate; the soluble cobalt salt is selected from cobalt nitrate hexahydrate.

[0022] Preferably, the nickel-cobalt Prussian blue analogue NiCo-PBA is prepared by the following steps: dissolving a soluble nickel salt, a soluble citrate, and a soluble cobalt cyanide salt together in water, and allowing them to stand for reaction to obtain NiCo-PBA.

[0023] Preferably, in the preparation of NiCo-PBA, the soluble nickel salt is selected from Ni(NO3)2·6H2O, the soluble cobalt cyanide salt is selected from K3[Co(CN)6], and the soluble citrate is selected from sodium citrate; and the molar ratio of Ni(NO3)2·6H2O to K3[Co(CN)6] is 1:1~1.5, and the molar ratio of Ni(NO3)2·6H2O to trisodium citrate is 1:2~3.

[0024] More preferably, the molar ratio of Ni(NO3)2·6H2O to K3[Co(CN)6] is 1:1.25, and the molar ratio of Ni(NO3)2·6H2O to trisodium citrate is 1:2.5.

[0025] A second objective of this invention is to provide a sulfur-doped nickel-cobalt selenide composite material prepared by the above-described preparation method.

[0026] A third objective of this invention is to provide the application of the above-mentioned sulfur-doped nickel-cobalt selenide composite material in the preparation of supercapacitor electrode materials.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a method for preparing a sulfur-doped nickel-cobalt selenide composite material. Using SeO2 as the selenium source and hydrazine hydrate as a strong reducing agent, an ethylene glycol solution of SeO2 is mixed with hydrazine hydrate and a NiCo-PBA@NiCo-LDH multi-level core-shell precursor. Following a selenization reaction, NiCoSe2 is obtained. NiCoSe2 is then mixed with sulfur powder and calcined to obtain the sulfur-doped nickel-cobalt selenide composite material. This invention, through the synergistic effect of the multi-level core-shell structure and heterogeneous doping, endows the sulfur-doped nickel-cobalt selenide composite material with excellent electrochemical energy storage performance. This effectively solves the problems of insufficient intrinsic electrochemical activity and poor rate performance and decreased cycle stability caused by large volume changes during charge and discharge when transition metal selenides are used as electrode materials for supercapacitors.

[0028] In this process, the selenization reaction transforms the NiCo-PBA@NiCo-LDH hierarchical core-shell precursor in situ into NiCoSe2 while maintaining its microstructure. Sulfur doping introduces sulfur atoms with higher electronegativity and smaller atomic radius into the NiCoSe2 selenide lattice, which already has relatively good intrinsic conductivity, through vapor deposition. This induces controllable lattice distortion and vacancy defects, while simultaneously achieving lattice regulation and fine modulation of electronic structure. This optimizes the electronic structure of the sulfur-doped nickel-cobalt selenide composite material and enhances its intrinsic conductivity. It also alleviates volume strain during the charging and discharging process, significantly improving the structural stability and reversibility of the sulfur-doped nickel-cobalt selenide composite material.

[0029] 2. In the preparation method of the present invention, the nickel-cobalt Prussian blue analog NiCo-PBA provides a regular three-dimensional pore structure as an electron transport framework; the polydopamine modification layer serves as an interface connection layer and heterogeneous nucleation site, guiding the uniform growth of nickel-cobalt layered double hydroxide (NiCo-LDH nanosheets) on the surface of NiCo-PBA@PDA, thus constructing a stable NiCo-PBA@NiCo-LDH multi-level core-shell precursor, effectively suppressing the stacking of NiCo-LDH nanosheets; this "core-shell-shell" structure effectively shortens the ion / electron transport path, improves the utilization rate of active materials, and suppresses structural collapse during charging and discharging.

[0030] 3. This invention also provides a sulfur-doped nickel-cobalt selenide composite material, which uses NiCo-PBA as the core framework, polydopamine as the interface bonding layer, and sulfur-doped nickel-cobalt selenide as the active shell, achieving synergistic optimization of structural stability and electrochemical activity. This sulfur-doped nickel-cobalt selenide composite material exhibits excellent rate performance and good cycling stability. This is due to the synergistic effect of the hierarchical core-shell structure and heterogeneous doping. The hierarchical structure provides abundant electrochemical active sites and electrolyte wetting channels, while sulfur doping endows the sulfur-doped nickel-cobalt selenide composite material with optimized electronic structure and enhanced ion transport kinetics. The synergistic effect of these two factors enables the sulfur-doped nickel-cobalt selenide composite material to maintain a high specific capacitance (1720 F / g) while exhibiting excellent rate performance (high capacity retention at a high current density of 10 A / g) and outstanding cycling stability (84% capacity retention after 10,000 cycles). Attached Figure Description

[0031] Figure 1 The infrared spectra of NiCo-PBA, NiCo-PBA@NiCo-LDH multilevel core-shell precursor, NiCoSe2, and S@NiCoSe2 are from Example 2.

[0032] Figure 2 The X-ray diffraction patterns are of NiCoSe2 and S@NiCoSe2 from Example 2.

[0033] Figure 3 This is a scanning electron microscope image of NiCoSe2 from Example 2.

[0034] Figure 4 This is a scanning electron microscope image of S@NiCoSe2 from Example 2.

[0035] Figure 5 The images shown are scanning electron microscope (SEM) images and elemental distribution diagrams of S@NiCoSe2 from Example 2, where a is a scanning electron microscope image, b is Ni, c is Co, d is C, e is Se, and f is S.

[0036] Figure 6The cyclic voltammogram is for S@NiCoSe2 in Example 2.

[0037] Figure 7 The discharge curve of S@NiCoSe2 under constant current charge and discharge in Example 2 is shown.

[0038] Figure 8 The image shows the cyclic stability of S@NiCoSe2 in Example 2. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased on the market or prepared by existing methods.

[0041] The structural design and performance regulation of electrode materials are crucial. Prussian blue analogues (PBAs), as typical metal-organic framework materials, are easy to synthesize and possess regular three-dimensional porous structures, often serving as ideal models for constructing hierarchical nanostructures. Using PBAs as a core to epitaxially grow layered hydrogen hydroxides (LDHs) with high theoretical capacity is a common strategy for improving the performance of composite materials. However, the disordered growth and severe stacking of LDH nanosheets at heterogeneous interfaces greatly limit the exposure and utilization of active sites. Introducing mussel-inspired polydopamine (PDA) as an interface layer is an effective solution to this problem. PDAs can form a strongly adhesive and uniform coating layer on the PBA surface through their abundant functional groups, and serve as ideal nucleation sites to guide the orderly and uniform growth of LDHs, thereby effectively suppressing stacking, enhancing structural integrity, and improving ion transport kinetics. To further improve the conductivity and reactivity of materials, converting the aforementioned precursors into transition metal selenides (such as NiCoSe2) is a promising approach. Bimetallic selenides can leverage the synergistic effect between different metals to provide richer redox reactions and higher specific volumes. Nevertheless, their capacity retention at high rates and long-term cycling stability still need to be improved.

[0042] Furthermore, existing doping strategies for optimizing the intrinsic properties of electrode materials through anion doping mainly follow the mainstream paradigm of "introducing elements with better intrinsic conductivity into matrices with relatively poor conductivity." This strategy utilizes the high conductivity and electrochemical activity of elements such as selenium (Se) and phosphorus (P) to enhance the performance of matrices with insufficient intrinsic conductivity, such as sulfides and oxides, aiming to improve their electrochemical performance through the introduction of heteroatoms or defect engineering. For example, Cao Y, et al. (Se-doped cobalt-nickel sulfide hollow nanospheres with heterostructure and engineered defects as high-performance electrode for supercapacitors, J. Energy Storage 2024, 100: 113755.) This study systematically explored the key role of selenium doping in improving material conductivity, increasing charge storage capacity, and optimizing overall electrochemical performance by controlling the selenium doping level to construct heterointerfaces and defects in MOF-derived hollow cobalt-nickel sulfides. Wang M, et al. (In situ P-doping induced Sevacancies enhance the supercapacitor performance of NiCo2Se4, CrystEngComm2024, 26: 2197-2206.) This study successfully prepared NiCo2Se4 electrode materials with optimized electronic structures and achieved high energy densities by using a strategy of inducing selenium vacancy defects through phosphorus doping. However, this strategy always focuses on the doping logic of "compensating for inferiority with superiority," that is, using guest elements with better conductivity to modify host materials with poorer conductivity.

[0043] To address the problems existing in the prior art, this invention provides a method for preparing sulfur-doped nickel-cobalt selenide composite material, comprising the following steps: using SeO2 as a selenium source and hydrazine hydrate as a strong reducing agent, mixing an ethylene glycol solution of SeO2 with hydrazine hydrate and a NiCo-PBA@NiCo-LDH multilevel core-shell precursor, and performing a selenization reaction to obtain NiCoSe2; mixing NiCoSe2 with sulfur powder and calcining it to obtain sulfur-doped nickel-cobalt selenide composite material.

[0044] This invention achieves synergistic design of the structure and composition of sulfur-doped nickel-cobalt selenide composite materials through multi-step precise control of "template construction - shell growth - selenization conversion - sulfur doping". Specifically, the NiCo-PBA template, a nickel-cobalt Prussian blue analogue, provides abundant active sites and a porous structure; the PDA coating layer enhances structural stability and provides anchoring points for subsequent growth; the NiCo-LDH shell further increases the electrochemical active area; the selenization process significantly improves the intrinsic conductivity of the sulfur-doped nickel-cobalt selenide composite material; and sulfur doping effectively controls the electronic structure of the sulfur-doped nickel-cobalt selenide composite material, introducing additional redox activity and mitigating volume strain during charge and discharge. Benefiting from the synergistic effect of the multi-level core-shell structure and heteroelement doping, the sulfur-doped nickel-cobalt selenide composite material prepared in this invention exhibits excellent energy storage performance: a specific capacitance as high as 1720 F / g at a current density of 1 A / g, and maintaining a high capacity retention even at a high current of 10 A / g.

[0045] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will provide a detailed description in conjunction with specific embodiments: Example 1 A method for preparing a sulfur-doped nickel-cobalt selenide composite material includes the following steps: S1. Nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.291 g) and trisodium citrate (TSC, 0.735 g) were dissolved together in 160 mL of ultrapure water. The mixture was stirred at room temperature for 30 min until completely dissolved. Potassium hexacyanocobalaminate (K3[Co(CN)6], 0.416 g) was then added, and the mixture was stirred for another 5 min before being allowed to stand for 24 h. After the reaction was completed, the product was collected by centrifugation and washed three times with ultrapure water and anhydrous ethanol, and dried overnight at 70 °C to obtain NiCo-PBA.

[0046] S2. NiCo-PBA (0.08 g) was uniformly dispersed in 100 mL of Tris buffer solution at pH 8.5. After sonication for 30 min, dopamine (0.08 g) was added, and the reaction was continuously stirred in the dark for 24 h. After the reaction was completed, the product was collected by centrifugation and washed with ultrapure water and ethanol to obtain NiCo-PBA@PDA.

[0047] NiCo-PBA@PDA (0.03 g) was dispersed in 50 mL of ultrapure water and sonicated for 30 min. Then, nickel nitrate hexahydrate (0.131 g) and cobalt nitrate hexahydrate (0.044 g) were added sequentially and stirred for another 10 min. Then, hexamethylenetetramine (HMTA, 0.098 g) and trisodium citrate (0.044 g) were added and stirred until homogeneous to obtain a suspension. The suspension was transferred to a hydrothermal reactor and reacted at 110 °C for 12 h. After natural cooling, the product was collected by centrifugation, washed and dried to obtain the NiCo-PBA@NiCo-LDH multilevel core-shell precursor.

[0048] S3. Selenium dioxide (SeO2, 0.1g) was dissolved in 30mL of ethylene glycol and sonicated for 1h. Then, hydrazine hydrate (3mL) was added dropwise and stirred for 5min to obtain a mixed solution. NiCo-PBA@NiCo-LDH multilevel core-shell precursor (0.05g) was added to the mixed solution and stirred at room temperature for 30min. The mixture was then transferred to a reaction vessel and reacted at 180℃ for 6h. After the reaction was completed, the black product was collected by centrifugation, washed and dried to obtain NiCoSe2.

[0049] S4. Take NiCoSe2 (100mg) and sulfur powder (100mg, mass ratio 1:1) and place them upstream and downstream of the ceramic boat in the tubular furnace, respectively. Under the protection of nitrogen atmosphere, heat to 500℃ at a rate of 2℃ / min and hold for 2h. After naturally cooling to room temperature, collect the downstream product to obtain sulfur-doped nickel-cobalt selenide composite material, denoted as S@NiCoSe2.

[0050] The electrochemical performance of the sulfur-doped nickel-cobalt selenide composite material prepared in Example 1 was tested. The specific capacitance values ​​of the prepared S@NiCoSe2 at current densities of 1A / g, 2A / g, 5A / g, 8A / g and 10A / g were 1473F / g, 1361F / g, 1129F / g, 976F / g and 884F / g, respectively.

[0051] Example 2 A method for preparing a sulfur-doped nickel-cobalt selenide composite material includes the following steps: S1. Nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.291 g) and trisodium citrate (TSC, 0.735 g) were dissolved together in 160 mL of ultrapure water. The mixture was stirred at room temperature for 30 min until completely dissolved. Potassium hexacyanocobalaminate (K3[Co(CN)6], 0.416 g) was then added, and the mixture was stirred for another 5 min before being allowed to stand for 24 h. After the reaction was completed, the product was collected by centrifugation and washed three times with ultrapure water and anhydrous ethanol, and dried overnight at 70 °C to obtain NiCo-PBA.

[0052] S2. NiCo-PBA (0.08 g) was uniformly dispersed in 100 mL of Tris buffer solution at pH 8.5. After sonication for 30 min, dopamine (0.08 g) was added, and the reaction was continuously stirred in the dark for 24 h. After the reaction was completed, the product was collected by centrifugation and washed with ultrapure water and ethanol to obtain NiCo-PBA@PDA.

[0053] NiCo-PBA@PDA (0.03 g) was dispersed in 50 mL of ultrapure water and sonicated for 30 min. Then, nickel nitrate hexahydrate (0.131 g) and cobalt nitrate hexahydrate (0.044 g) were added sequentially, and the mixture was stirred for another 10 min. Then, hexamethylenetetramine (HMTA, 0.098 g) and trisodium citrate (0.044 g) were added, and the mixture was stirred until homogeneous to obtain a suspension. The suspension was transferred to a hydrothermal reactor and reacted at 110 °C for 12 h. After natural cooling, the product was collected by centrifugation, washed, and dried to obtain the NiCo-PBA@NiCo-LDH multilevel core-shell precursor.

[0054] S3. Selenium dioxide (SeO2, 0.1g) was dissolved in 30mL of ethylene glycol and sonicated for 1h. Then, hydrazine hydrate (3mL) was added dropwise and stirred for 5min to obtain a mixed solution. NiCo-PBA@NiCo-LDH multilevel core-shell precursor (0.05g) was added to the mixed solution and stirred at room temperature for 30min. The mixture was then transferred to a reaction vessel and reacted at 180℃ for 6h. After the reaction was completed, the black product was collected by centrifugation, washed and dried to obtain NiCoSe2.

[0055] S4. Take NiCoSe2 (100 mg) and sulfur powder (300 mg, mass ratio 1:3) and place them upstream and downstream of the ceramic boat in a tubular furnace, respectively. Under nitrogen atmosphere protection, heat to 500 °C at a rate of 2 °C / min and hold for 2 h; after natural cooling to room temperature, collect the downstream product to obtain sulfur-doped nickel-cobalt selenide composite material, denoted as S@NiCoSe2.

[0056] The electrochemical performance of the sulfur-doped nickel-cobalt selenide composite material prepared in Example 2 was tested. The specific capacitance values ​​of the prepared S@NiCoSe2 at current densities of 1A / g, 2A / g, 5A / g, 8A / g and 10A / g were 1720F / g, 1549F / g, 1219F / g, 1004F / g and 885F / g, respectively.

[0057] Example 3 A method for preparing a sulfur-doped nickel-cobalt selenide composite material includes the following steps: S1. Nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.291 g) and trisodium citrate (TSC, 0.735 g) were dissolved together in 160 mL of ultrapure water. The mixture was stirred at room temperature for 30 min until completely dissolved. Potassium hexacyanocobalaminate (K3[Co(CN)6], 0.416 g) was then added, and the mixture was stirred for another 5 min before being allowed to stand for 24 h. After the reaction was completed, the product was collected by centrifugation and washed three times with ultrapure water and anhydrous ethanol, and dried overnight at 70 °C to obtain NiCo-PBA.

[0058] S2. NiCo-PBA (0.08 g) was uniformly dispersed in 100 mL of Tris buffer solution at pH 8.5. After sonication for 30 min, dopamine (0.08 g) was added, and the reaction was continuously stirred in the dark for 24 h. After the reaction was completed, the product was collected by centrifugation and washed with ultrapure water and ethanol to obtain NiCo-PBA@PDA.

[0059] NiCo-PBA@PDA (0.03 g) was dispersed in 50 mL of ultrapure water and sonicated for 30 min. Then, nickel nitrate hexahydrate (0.131 g) and cobalt nitrate hexahydrate (0.044 g) were added sequentially, and the mixture was stirred for 10 min. Next, hexamethylenetetramine (HMTA, 0.098 g) and trisodium citrate (0.044 g) were added, and stirring continued until homogeneous, resulting in a suspension. The suspension was transferred to a hydrothermal reactor and reacted at 110 °C for 12 h. After natural cooling, the product was collected by centrifugation, washed, and dried to obtain the NiCo-PBA@NiCo-LDH multilevel core-shell precursor.

[0060] S3. Selenium dioxide (SeO2, 0.1g) was dissolved in 30mL of ethylene glycol and sonicated for 1h. Then, hydrazine hydrate (3mL) was added dropwise and stirred for 5min to obtain a mixed solution. NiCo-PBA@NiCo-LDH multilevel core-shell precursor (0.05g) was added to the mixed solution and stirred at room temperature for 30min. The mixture was then transferred to a reaction vessel and reacted at 180℃ for 6h. After the reaction was completed, the black product was collected by centrifugation, washed and dried to obtain NiCoSe2.

[0061] S4. Place 100 mg of NiCoSe2 and 500 mg of sulfur powder (mass ratio 1:5) upstream and downstream of a ceramic boat in a tubular furnace, respectively. Under nitrogen atmosphere protection, heat to 500 °C at a rate of 2 °C / min and maintain for 2 h. After natural cooling to room temperature, collect the downstream product to obtain sulfur-doped nickel-cobalt selenide composite material, denoted as S@NiCoSe2.

[0062] The electrochemical performance of the sulfur-doped nickel-cobalt selenide composite material prepared in Example 3 was tested. The specific capacitance values ​​of the prepared S@NiCoSe2 at current densities of 1A / g, 2A / g, 5A / g, 8A / g and 10A / g were 1300F / g, 974F / g, 951F / g, 795F / g and 711F / g, respectively.

[0063] Example 4 A method for preparing a sulfur-doped nickel-cobalt selenide composite material is the same as that in Example 2, except that the calcination at 500°C for 2 hours in S4 is replaced with calcination at 450°C for 3 hours to obtain the sulfur-doped nickel-cobalt selenide composite material.

[0064] like Figure 1 As shown: 2180cm -1 The presence of the C≡N characteristic peak at 627 cm⁻¹ confirms the complete preservation of the PBA core framework; -1 The new peak appearing at 765 cm⁻¹ is attributed to the MO / M-OH vibration in LDH, marking the successful formation of the PBA@NiCo-LDH precursor. Following the selenization reaction, the peak at 765 cm⁻¹... -1 The characteristic vibrational peak of the Ni / Co-Se bond was observed at 1386 cm⁻¹, confirming the successful conversion to NiCoSe₂. This peak remained in the final sample and underwent a slight shift, indicating that the sulfur doping process adjusted the local bonding environment while maintaining the host structure. Furthermore, at 1386 cm⁻¹... -1 With 1348cm -1 The characteristic double peaks at the location correspond to residual nitrate species. The continuous evolution of the above spectral characteristics systematically confirms the complete phase transformation process from PBA to PBA@NiCo-LDH, then to NiCoSe2, and finally S@NiCoSe2.

[0065] XRD analysis was performed on S@NiCoSe2 from Example 2 to verify its crystal structure evolution, and the results are as follows: Figure 2 As shown, the diffraction peaks of S@NiCoSe2 are in good agreement with the standard cards for NiS (PDF#75-0613) and CoS (PDF#70-2864), indicating the successful synthesis of the target crystalline phase. Compared with undoped NiCoSe2, the diffraction pattern of S@NiCoSe2 shows significant changes, with its characteristic diffraction peaks shifting noticeably to higher angles. This systematic shift is attributed to the partial substitution of selenium (Se, atomic radius 1.98 Å) atoms by sulfur (S, atomic radius 1.84 Å), which has a smaller atomic radius, thereby causing lattice contraction. Simultaneously, no obvious impurity phase peaks were observed in the spectrum, indicating that S@NiCoSe2 possesses good crystallinity and phase purity. These results collectively confirm that the crystal structure of NiCoSe2 has been successfully controlled and modified through a sulfur doping strategy.

[0066] To further elucidate the structural evolution mechanism during the sulfidation process, the present invention systematically characterized the NiCoSe2 and S@NiCoSe2 from Example 2 using scanning electron microscopy (SEM), such as... Figure 3 and Figure 4 As shown, during the sulfidation process, the regular cubic NiCoSe2 transforms into an irregular polyhedral or spherical structure, and the overall particle size decreases significantly. This morphological transformation is accompanied by stress release and surface reconstruction within the crystal. Simultaneously, a well-developed mesoporous network forms within S@NiCoSe2. This hierarchical porous structure facilitates electrolyte wetting and ion transport, and provides abundant active interfaces for electrochemical reactions.

[0067] To further investigate the influence of elemental composition and distribution on structural evolution, this invention employs energy-dispersive spectroscopy (EDS) to perform surface scan analysis on S@NiCoSe2 from Example 2. The elemental distribution is as follows: Figure 5 As shown, Ni, Co, Se, and S are all uniformly distributed within the observed range, without obvious elemental segregation or phase separation. This confirms that the sulfidation process was successful and formed a homogeneous S@NiCoSe2. The distribution results of these elements provide important evidence for understanding the structural evolution of materials at the atomic scale and for subsequent optimization of their ion transport and structural stability.

[0068] To further investigate the electrochemical energy storage behavior of S@NiCoSe2, cyclic voltammetry (CV) tests were conducted on the S@NiCoSe2 of Example 2 at different scan rates, as follows: Figure 6 As shown in the figure, all curves exhibit distinct redox peaks within the potential window of 0V to 0.6V, indicating that S@NiCoSe2 exhibits typical pseudocapacitive behavior in alkaline electrolytes. With increasing scan rate, the redox peaks shift slightly, mainly due to electrode polarization and the limitation of electron transfer by the internal resistance of S@NiCoSe2; despite this, the CV curves remain highly similar in shape, indicating that S@NiCoSe2 possesses good reaction reversibility and structural stability.

[0069] The S@NiCoSe2 from Example 2 was subjected to a galvanostatic charge-discharge (GCD) test to further evaluate its electrochemical performance. The results are as follows: Figure 7As shown, S@NiCoSe2 exhibits typical charge-discharge plateaus at different current densities, indicating that its energy storage process is mainly controlled by diffusion. Notably, S@NiCoSe2 demonstrates excellent electrochemical performance: its GCD curve maintains minimal deformation even as the current density increases from 1 A / g to 10 A / g, indicating good structural stability and reaction kinetics. Furthermore, the high symmetry of the GCD curve and the coulombic efficiency of 81% at 1 A / g further confirm its highly reversible redox reaction and excellent electrochemical reversibility.

[0070] Long-term cycling stability tests were conducted on the S@NiCoSe2 from Example 2, and the results are as follows: Figure 8 As shown, after 10,000 continuous charge-discharge cycles at a high current density of 10 A / g, its specific capacitance retention rate still reaches 84%, demonstrating excellent cycle stability. The coulombic efficiency remains at a high level (approximately 98% or higher) throughout the cycle, indicating that S@NiCoSe2 exhibits good electrochemical reversibility during repeated redox processes.

[0071] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

Claims

1. A method for preparing a sulfur-doped nickel-cobalt selenide composite material, characterized in that, Includes the following steps: Using SeO2 as the selenium source and hydrazine hydrate as a strong reducing agent, an ethylene glycol solution of SeO2 was mixed with hydrazine hydrate and NiCo-PBA@NiCo-LDH multilevel core-shell precursor, and then subjected to a selenization reaction to obtain NiCoSe2. NiCoSe2 was mixed with sulfur powder and calcined to obtain a sulfur-doped nickel-cobalt selenide composite material.

2. The preparation method according to claim 1, characterized in that, The mass ratio of SeO2 to NiCo-PBA@NiCo-LDH multilevel core-shell precursor is 1~3:1, and the mass-volume ratio of SeO2 to hydrazine hydrate is 0.1g:3mL.

3. The preparation method according to claim 1, characterized in that, The selenization reaction conditions are: solvothermal reaction at 160℃~180℃ for 4h~8h.

4. The preparation method according to claim 1, characterized in that, The mass ratio of NiCoSe2 to sulfur powder is 1:1~5.

5. The preparation method according to claim 1, characterized in that, The calcination conditions are as follows: in an inert atmosphere, heat at 450℃~500℃ for 1h~3h.

6. The preparation method according to claim 1, characterized in that, The NiCo-PBA@NiCo-LDH multi-level core-shell precursor was prepared according to the following steps: The nickel cobalt Prussian blue analog NiCo-PBA was dispersed in Tris buffer, mixed with dopamine, and then coated to obtain NiCo-PBA@PDA. Soluble nickel salt, soluble cobalt salt, hexamethylenetetramine and trisodium citrate are dissolved together in water to obtain a mixed aqueous solution; NiCo-PBA@PDA was dispersed in a mixed aqueous solution to obtain a NiCo-PBA@PDA dispersion, which was then subjected to a hydrothermal reaction to obtain a NiCo-PBA@NiCo-LDH multilevel core-shell precursor.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the nickel cobalt Prussian blue analog NiCo-PBA to dopamine is 1:0.8~1.

2.

8. The preparation method according to claim 6, characterized in that, The mass concentration of the NiCo-PBA@PDA dispersion is 0.5 g / L~0.7 g / L, and in the mixed aqueous solution, Ni... 2+ With Co 2+ The molar ratio is 2~4:1, and the mass ratio of hexamethylenetetramine, trisodium citrate and Ni(NO3)2·6H2O is 49:22:

65.

9. A sulfur-doped nickel-cobalt selenide composite material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the sulfur-doped nickel-cobalt selenide composite material of claim 9 in the preparation of supercapacitor cathode materials.

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