A heterojunction-induced defect bi-phase heterostructure composite material, a preparation method thereof and application thereof in a battery

Abstract

The application provides a heterojunction-induced defect dual-phase heterostructure composite material and a preparation method and application in a battery thereof. The application prepares a heterojunction-induced defect dual-phase heterostructure NiS@ZnS / C nanosphere composite material through a simple two-step MOFs derivation method combined with a sulfuration and calcination process, wherein the dual-phase metal sulfides are NiS and ZnS respectively and are encapsulated in a carbon layer. The heterojunction interface between different crystals can induce an internal electric field to accelerate ion diffusion kinetics, improve the conductivity and provide abundant reaction sites for sodium energy storage. The application has high reversible capacity, high specific capacity, stable cycle performance and robust rate performance.

Description

Technical Field

[0001] This invention belongs to the field of battery electrode material technology, specifically relating to a heterojunction-induced defect biphase heterostructure composite material, its preparation method, and its application in batteries. Background Technology

[0002] With the escalating global energy crisis and environmental problems, the development of efficient and clean energy storage systems has become a research hotspot. While lithium-ion batteries are widely used in various energy storage devices, the limited and uneven distribution of lithium resources leads to high production costs, making it difficult to meet the long-term needs of large-scale energy storage. Sodium-ion batteries, due to the abundant and widely distributed nature of sodium resources, low cost, and similar charge-discharge storage mechanisms to lithium-ion batteries, have become one of the most promising alternative technologies for large-scale energy storage, attracting widespread attention from researchers worldwide.

[0003] As a core component of sodium-ion batteries, the performance of the anode material directly determines the battery's specific capacity, cycle life, and rate performance. Transition metal sulfides, due to their suitable interlayer spacing, high theoretical sodium storage capacity, and weak metal-sulfur bond strength, are conducive to sodium ion insertion / extraction and conversion reactions, and are considered highly promising anode materials for sodium-ion batteries.

[0004] However, single transition metal sulfides still face many challenges in practical applications: First, severe volume expansion easily occurs during electrochemical processes, leading to material structure collapse and pulverization, resulting in rapid capacity decay; second, the material itself has poor conductivity and slow ion and electron transport kinetics, affecting the rate performance of the battery; third, the single-phase structure has limited active sites, and the active components are prone to agglomeration during cycling, further reducing the cycle stability of the battery. Researchers have proposed modification strategies such as heterostructure construction, carbon material composites, and defect engineering.

[0005] Metal-organic frameworks (MOFs) are widely used as precursors for preparing metal sulfide and carbon composite electrode materials due to their high specific surface area, controllable pore structure, and abundant metal active sites. MOF derivatization allows for precise control over the morphology, composition, and defect structure of materials. Currently, there are reports on the preparation of single metal sulfides or simple composite sulfides using MOF derivatization; however, these materials still suffer from problems such as weak heterogeneous interface bonding, poor controllability of defect density, and insignificant dual-phase synergistic effects, making it difficult to fully meet the requirements of sodium-ion batteries for high capacity, long cycle life, and excellent rate performance.

[0006] Therefore, developing a novel electrode material with a defective, stable two-phase heterogeneous interface that is tightly integrated with carbon materials, and designing a simple and controllable preparation method, is of great significance for promoting the commercial application of sodium-ion batteries. Summary of the Invention

[0007] The purpose of this invention is to provide a heterojunction-induced defect biphase heterostructure composite material and its preparation method. Ni-MOFs are generated through solvothermal processing, then sulfided into NiS2, followed by in-situ encapsulation of ZIF-8 to form NiS2@ZIF-8. This is combined with a high-temperature calcination process to achieve efficient preparation, resulting in a nickel sulfide@zinc sulfide / carbon (NiS@ZnS / C) composite material. The prepared NiS@ZnS / C composite material consists of uniform nanospheres with a width of 2-2.5 μm, significantly improving cycle stability, lifespan, and battery capacity. Furthermore, the preparation method provided by this invention is simple, reproducible, and suitable for industrial production, which is beneficial for promoting the commercialization of sodium-ion batteries.

[0008] Another objective of this invention is to provide an application of a heterojunction-induced defect biphase heterostructure composite material in batteries, using the aforementioned heterojunction-induced defect biphase heterostructure nickel sulfide@zinc sulfide / carbon (NiS@ZnS / C) composite material as a negative electrode material for sodium-ion batteries.

[0009] The specific technical solution of this invention is as follows:

[0010] This invention provides a heterojunction-induced defect biphase heterostructure composite material, which is a nickel sulfide@zinc sulfide / carbon structure (NiS@ZnS / C) composite material, consisting of rough-surfaced nanospheres with a diameter of 2-2.5 μm. The heterojunction-induced defect biphase heterostructure composite material uses NiS and ZnS as active core phases and an outer carbon layer as a coating shell. The carbon layer is based on MOF calcination-derived carbon, with a shell thickness of 30-50 nm, and is uniformly coated on the surface.

[0011] The method for preparing the above-mentioned heterojunction-induced defect biphase heterostructure composite material provided by the present invention includes the following steps:

[0012] 1) Ni-MOFs precursor and sulfur powder are mixed and calcined under a protective atmosphere to obtain NiS2;

[0013] 2) NiS2 is in situ wrapped with ZIF-8 to obtain NiS2@ZIF-8;

[0014] 3) NiS2@ZIF-8 was calcined to obtain a two-phase heterostructure composite material NiS@ZnS / C with heterojunction-induced defects.

[0015] In step 1), the method for preparing the Ni-MOFs precursor is as follows: organic ligands, surfactants and nickel sources are mixed in a solvent and subjected to a solvothermal reaction to obtain the Ni-MOFs precursor;

[0016] In the preparation method of the Ni-MOFs precursor, the molar ratio of the organic ligand to the nickel source is 1:2-2.3; the concentration of the nickel source in the solvent is 0.04-0.06 mol / L; the amount of nickel source used is 40%-50% of the mass of the surfactant; the organic ligand is 1,3,5-pyromellitic acid; and the surfactant is polyvinylpyrrolidone (PVP). M=58000, K29-32); the surfactant, as a dispersant, can effectively control the morphology of Ni-MOFs and avoid particle agglomeration; the nickel source is a soluble nickel salt, preferably Ni(NO3)2·6H2O or NiSO4·5H2O; the solvent is a mixed solution of water and N,N-dimethylformamide or pure N,N-dimethylformamide, preferably a mixed solution of deionized water and N,N-dimethylformamide in a volume ratio of 1:1; the solvothermal reaction conditions are 150-170℃ for 10-14h, preferably 160℃ for 12h; furthermore, after the solvothermal reaction, the product is washed 3-6 times with water and 1-3 times with ethanol, centrifuged, and then dried at 40-80℃ for 12-15h.

[0017] Preferably, the preparation method of Ni-MOF nanospheres is as follows: 0.15 g of 1,3,5-pyrrolidone, 1.033 g of polyvinylpyrrolidone (PVP M = 58000, K29-32), and 0.432 g of Ni(NO3)2·6H2O are dissolved in 30 mL of a mixed solvent (the volume ratio of water to DMF in the mixed solvent is 1:1). The homogeneous solution is then transferred to a 50 mL autoclave lined with polytetrafluoroethylene and kept in an oven at 160 °C for 12 hours. The sample is then washed three times with deionized water and three times with anhydrous ethanol. After washing, the sample is centrifuged and placed in an oven at 80 °C for 12 hours. The prepared Ni-MOF precursor has the morphology of nanospheres with burrs on the surface and a diameter of 2-3 μm.

[0018] The mass ratio of Ni-MOFs precursor to sulfur powder in step 1) is 1:5-1:10;

[0019] The calcination conditions described in step 1) are: calcination at 350℃ for 2 hours, with a heating rate of 2℃ / min, and calcination in a tube furnace.

[0020] The protective atmosphere mentioned in step 1) is nitrogen or argon.

[0021] Step 2) Specifically: Dissolve NiS2 and the organic ligand in methanol to obtain solution A; dissolve the zinc source in methanol to form solution B; add solution B dropwise to solution A, stir the reaction, and let it stand overnight.

[0022] In step 2), the molar ratio of NiS2 to the organic ligand is 1:10-15;

[0023] In step 2), the concentration of NiS2 in solution A is 1-2 g / L;

[0024] In step 2), the mass ratio of NiS2 to zinc source is 0.1-0.15 : 0.65-1.0.

[0025] In step 2), the volume ratio of solution A to solution B is 2:1;

[0026] In step 2), NiS2 and the organic ligand are dissolved in methanol and sonicated for half an hour to obtain solution A; the zinc source is dissolved in methanol and stirred for 10 minutes to form solution B.

[0027] In step 2), the organic ligand is 2-methylimidazole;

[0028] In step 2), the zinc source is a soluble zinc salt, preferably Zn(NO3)2·6H2O, ZnSO4·5H2O or ZnSO4·7H2O;

[0029] In step 2), the stirring reaction is carried out at 20-70℃ for 4-10 hours, preferably at 25℃ for 4 hours, to conduct an in-situ polymerization reaction;

[0030] In step 2), the standing condition is to stand overnight at 20-70℃, preferably at room temperature of 25℃ overnight.

[0031] The NiS2@ZIF-8 prepared in step 2) is a rough-surfaced nanosphere with a width of 2-3 μm.

[0032] In step 3), the calcination refers to calcination in a high-temperature tubular furnace, with an Ar or N2 atmosphere. The calcination process involves a heating rate of 2°C / min, reaching 650°C, and calcining for 2 hours. During calcination, ZIF-8 undergoes pyrolysis to form a carbon layer and releases gases, while Zn... 2+ With S 2- ZnS is generated by combining with NiS2, which is reduced to NiS, ultimately forming a two-phase heterostructure NiS@ZnS / C with heterojunction-induced defects. After calcination, the product is cooled to room temperature in the furnace and collected, which is the target material.

[0033] This invention employs a two-step MOFs derivatization method combined with sulfidation and calcination processes. The preparation process is simple and controllable, using readily available raw materials, with low cost, and is easy to scale up. By controlling the reaction parameters in each step, the material performance can be optimized. The NiS@ZnS / C material prepared by this invention is a unique heterostructure composite material with heterojunction-induced defects. A stable heterostructure interface is formed between NiS and ZnS, which can construct an internal electric field, significantly promoting the transport of electrons and sodium ions and improving electrode reaction kinetics. At the same time, the synergistic effect of the heterostructure can effectively alleviate the volume expansion of a single sulfide during charge and discharge, enhancing the structural stability of the material. This invention also provides a method for preparing this material and its application in sodium-ion batteries, solving the problems of low specific capacity, poor cycle stability, and complex preparation processes of existing materials. The NiS@ZnS / C composite material provided by this invention, with its rough nanosphere morphology and numerous defects formed during calcination, provides abundant active sites for sodium ion storage, significantly improving the specific capacity of the material. The introduction of the carbon layer further improves the conductivity of the material, while inhibiting the aggregation of active particles and ensuring the long-term cycle stability of the material.

[0034] This invention provides an application of a heterojunction-induced defect biphase heterostructure composite material in batteries. The aforementioned heterojunction-induced defect biphase heterostructure nickel sulfide@zinc sulfide / carbon (NiS@ZnS / C) composite material is used as an active material to prepare a sodium-ion battery anode material. This invention, by controlling the morphology, defect structure, and heterostructure interface, exhibits excellent sodium-ion storage performance and can serve as a high-performance sodium-ion battery anode material. It improves upon the problems of poor conductivity, severe volume expansion, poor cycle stability, and insufficient synergistic effect of heterostructures in transition metal sulfide anode materials.

[0035] The method used to prepare sodium-ion batteries is as follows:

[0036] Nickel sulfide@zinc sulfide / carbon composite material with heterojunction-induced defects was used as the active material. It was mixed with conductive carbon black and PVDF in a ratio of 8:1:1 or 7:2:1 and then magnetically stirred for 6-8 hours to uniformly disperse it in N-methylpyrrolidone (NMP). The uniformly mixed slurry was coated onto copper foil using a coater and placed in a vacuum drying oven at 60-80℃ for 12-24 hours. After drying, it was pressed into a sheet using a tablet press and then cut into a circular electrode sheet with a diameter of 12 mm using a cutting machine. The electrode sheets were then assembled into button batteries in a glove box filled with high-purity argon gas and with water and oxygen values ​​≤0.01 ppm.

[0037] The specific method for assembling the battery is as follows: After adding 1 drop of electrolyte to the positive electrode shell, place the electrode plate, then add 1 drop of electrolyte and place the glass fiber. After adding 3 drops of electrolyte to the glass fiber, place the sodium sheet as the counter electrode, then place two pieces of nickel foam, add 4 drops of electrolyte, cover with the negative electrode shell, press and seal the battery with a hydraulic press, and let it stand for 6-12 hours.

[0038] The inventors discovered that zinc sulfide (ZnS) possesses excellent conductivity and structural stability, while nickel sulfide (NiS) boasts a high specific capacity. However, the volume expansion problem of zinc sulfide alone remains unresolved, leading to particle agglomeration during cycling. Furthermore, cobalt sulfide alone exhibits relatively low specific capacity, making it difficult to simultaneously meet the demands of high energy density and long cycle life. The formation of heterostructures can leverage the synergistic effect between different components to construct an internal electric field that promotes charge transport while mitigating structural stress caused by volume expansion. Carbon composites can effectively enhance material conductivity and provide structural support, inhibiting particle agglomeration. The introduction of defects can increase the number of active sites, lower the ion diffusion barrier, and further optimize electrochemical performance.

[0039] The NiS@ZnS / C heterojunction induced defect biphase heterostructure constructed in this invention is not a simple physical superposition of NiS, ZnS and carbon matrix, but achieves synergistic enhancement of sodium storage performance through interfacial coupling between biphase sulfides and composite modification with carbon matrix. Its core mechanism originates from the lattice and electronic structure regulation induced by the heterojunction, as well as the deep integration of induced defects and heterojunction effect, achieving performance breakthroughs from multiple dimensions such as active sites, mass transfer kinetics and structural stability. Due to inherent differences in lattice parameters, atomic electronegativity, and electron orbital arrangement, NiS and ZnS inevitably undergo lattice distortion when forming a heterojunction. Lattice mismatch directly induces local disorder in the atomic arrangement near the interface, thereby generating numerous intrinsic crystal defects, including S vacancies, Ni / Zn ion vacancies, and interstitial atoms. Simultaneously, the band structure differences between the two-phase sulfides lead to band shifts and rearrangements at the heterojunction, forming continuous interface states and trap levels, among other band structure defects. The introduction of the carbon matrix further exacerbates this defect effect through interfacial bonding, constructing a defect-rich two-phase heterostructure. The improvement in sodium storage performance induced by these heterojunction defects manifests in four aspects: First, defect sites act as additional active sites for sodium storage, breaking through the theoretical capacity limitations of a single NiS or ZnS, significantly increasing the actual sodium storage capacity of the material; second, the multidimensional mass transfer channels formed by lattice distortion and defects effectively reduce Na+ ionization. +The diffusion barrier of the NiS@ZnS / C heterojunction accelerates ion transport kinetics and improves the rate performance of the material. Third, interface defects regulate the overall electronic structure of the material through charge rearrangement, increasing the electronic conductivity at the interface and reducing charge transfer impedance. Simultaneously, the built-in electric field of the heterojunction drives directional electron migration, synergizing with the defect-mediated electron transport path to further optimize charge transport efficiency. Fourth, the synergistic effect of defects and the heterojunction interface effectively disperses volumetric stress during sodium storage, alleviating volume expansion and structural collapse. Furthermore, the spatial confinement effect of the carbon matrix and the bonding constraint of defect sites jointly suppress the aggregation and pulverization of active particles, significantly improving the material's cycle stability. In summary, the defect-induced two-phase heterostructure of NiS@ZnS / C deeply integrates the interface effect of the heterojunction, the activity regulation of defect engineering, and the conductive support of the carbon matrix, achieving simultaneous optimization of sodium storage active sites, ion / electron transport efficiency, and electrode structural stability. Its performance is far superior to single sulfide and defect-free heterojunction systems, fully demonstrating a synergistic effect mechanism that is not simply additive.

[0040] This invention achieves controllable construction and precise size control of the morphology of the NiS@ZnS / C heterojunction-induced defects by precisely controlling the concentration of the reaction precursor, reaction temperature and time, carbon source introduction method, and sulfidation process parameters. This effectively avoids the aggregation of single sulfide nanocrystals and the phase separation of the two-phase sulfides. Simultaneously, through in-situ reaction interfacial bonding, a tight bond is achieved between the NiS@ZnS / C heterojunction and the carbon matrix, constructing a continuous conductive / mass transfer network. The morphology and size characteristics controlled by the specific preparation method contribute multidimensionally to the improvement of sodium storage performance: Firstly, NiS@ZnS… The tight bonding and uniform dispersion of the biphase nanocrystals with the carbon matrix constructs a continuous electronic conductivity network, significantly improving the overall electronic conductivity of the material, reducing charge transfer impedance, and optimizing electrochemical reaction kinetics. Secondly, the uniformity of morphology and size achieved by the specific preparation method of this invention not only ensures the consistency and reversibility of the electrochemical reaction but also provides process feasibility for batch-scale preparation of the material, possessing practical application value. In summary, the specific preparation method of this invention, through precise control of the morphology and size of the NiS@ZnS / C heterostructure, endows the material with abundant active sites, rapid ion / electron transport channels, and a stable electrode structure from the structural design level. This is the core process factor that makes the material of this invention exhibit significant advantages over products obtained by traditional preparation methods in terms of sodium storage capacity, rate performance, and cycle stability. At the same time, this preparation method is simple to operate, has mild conditions, and is highly controllable, making it suitable for industrial promotion.

[0041] When the NiS@ZnS / C material prepared in this invention is used as an anode material for sodium-ion batteries, it exhibits excellent electrochemical performance: It possesses good rate performance, providing a high-quality electrode material choice for the development of high-performance sodium-ion batteries. It has high specific capacity: the synergistic effect of defects and dual-phase active materials, with NiS providing high capacity and ZnS / C improving conductivity and stability, results in an average capacity decay rate of 0.0003% per cycle at 0.1 A / g. It has long cycle life: the nitrogen-doped carbon shell and tight heterogeneous interface effectively suppress volume expansion, with capacity retention exceeding 90% after 500 cycles at 0.5 A / g. It exhibits excellent rate performance: at a high current density of 10 A / g, the specific capacity still reaches 300-350 mAh / g, far exceeding that of traditional sulfide materials (typically below 200 mAh / g). It has good wide-temperature performance: excellent performance from -10 °C to 50 °C.

[0042] Compared with existing technologies, the composite material of this invention is obtained by solvothermal growth of Ni-MOFs followed by sulfidation to generate NiS2, then in-situ encapsulation of ZIF-8, and finally high-temperature calcination to obtain NiS@ZnS / C. This process achieves efficient preparation and is suitable for sodium-ion battery anode systems with high energy density and long cycle life. Through dual innovation in material design and preparation process, this invention provides a new solution for the high performance of sodium-ion battery electrode materials, possessing significant scientific and industrial application value. Attached Figure Description

[0043] Figure 1 SEM image of the Ni-MOF nanosphere precursor material from Example 1;

[0044] Figure 2 The image shows the XRD pattern of the precursor Ni-MOF nanosphere material from Example 1.

[0045] Figure 3 SEM image of NiS2 prepared in Example 1;

[0046] Figure 4 The XRD pattern of NiS2 prepared in Example 1;

[0047] Figure 5 SEM image of NiS2@ZIF-8 prepared in Example 1;

[0048] Figure 6 TEM image of NiS2@ZIF-8 prepared in Example 1;

[0049] Figure 7 SEM image of NiS@ZnS / C prepared in Example 1;

[0050] Figure 8TEM image of NiS@ZnS / C prepared in Example 1;

[0051] Figure 9 HRTEM image of NiS@ZnS / C prepared in Example 1;

[0052] Figure 10 XRD pattern of NiS@ZnS / C prepared in Example 1;

[0053] Figure 11 The refined XRD pattern of the NiS@ZnS / C composite material prepared in Example 1;

[0054] Figure 12 Defect characterization diagrams of the NiS@ZnS / C composite material prepared in Example 1 were generated using electron paramagnetic resonance (EPR) technology.

[0055] Figure 13 SEM image of the precursor NiS2@ZIF-8 nanospheres prepared in Example 2;

[0056] Figure 14 TEM image of NiS2@ZIF-8 nanospheres prepared in Example 2;

[0057] Figure 15 SEM image of the NiS@ZnS / C nanosphere composite material prepared in Example 2;

[0058] Figure 16 SEM image of the precursor NiS2@ZIF-8 nanospheres prepared in Example 3;

[0059] Figure 17 SEM image of the final product NiS@ZnS / C nanosphere composite material prepared in Example 3;

[0060] Figure 18 The XRD pattern of the final product NiS@ZnS / C nanosphere composite material prepared in Example 4;

[0061] Figure 19 SEM image of the final product NiS@ZnS / C nanosphere composite material prepared in Example 4;

[0062] Figure 20 The XRD pattern of the final product NiS@ZnS / C nanosphere composite material prepared in Example 5;

[0063] Figure 21 SEM image of the final product NiS@ZnS / C nanosphere composite material prepared in Example 5;

[0064] Figure 22The NiS@ZnS / C nanosphere composite material prepared in Example 1 was used as a sodium-ion battery anode material at 0.1 mV s. -1 CV test graph at scan speed;

[0065] Figure 23 The charge-discharge curves of the NiS@ZnS / C nanosphere composite material prepared in Example 1 as a sodium-ion battery anode material at a current density of 0.1 A / g are shown.

[0066] Figure 24 The NiS@ZnS / C nanosphere composite material prepared in Example 1 was used as a negative electrode material for a sodium-ion battery at 0.1 A g. -1 Cyclic stability test results at current density;

[0067] Figure 25 The NiS@ZnS / C nanosphere composite material prepared in Example 1 was used as a sodium-ion battery anode material at 0.5 A g. -1 Cyclic stability test results at current density;

[0068] Figure 26 The NiS@ZnS / C nanosphere composite material prepared in Example 1 was used as a negative electrode material for a sodium-ion battery at 2.0 A g. -1 Cyclic stability test results at current density;

[0069] Figure 27 The rate capability diagram of the NiS@ZnS / C composite material prepared in Example 1 as a sodium-ion battery anode material.

[0070] Figure 28 The NiS@ZnS / C composite material prepared in Example 1 was used as the anode material for a sodium-ion battery at 1.0 A g. -1 Cyclic stability test results at current density and high temperature (50°C);

[0071] Figure 29 The NiS@ZnS / C composite material prepared in Example 1 was used as the anode material for a sodium-ion battery at a concentration of 0.5 A g. -1 Cyclic stability test results at current density and at a low temperature of -10°C. Detailed Implementation

[0072] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0073] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0074] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0075] Example 1

[0076] A method for preparing a two-phase heterostructure NiS@ZnS / C composite material with heterojunction-induced defects includes the following steps:

[0077] 1) Preparation of Ni-MOF precursor: 0.15 g of 1,3,5-pyrrolidone, 1.033 g of polyvinylpyrrolidone (PVP, M = 58000, K29-32), and 0.432 g of Ni(NO3)2·6H2O were dissolved in 30 mL of a mixed solvent (a 1:1 volume ratio of water to DMF). The homogeneous solution was then transferred to a 50 mL autoclave lined with polytetrafluoroethylene and dried at 160 °C for 12 hours. The sample was then washed three times with deionized water and three times with anhydrous ethanol. The washed sample was then dried at 80 °C for 12 hours.

[0078] Its SEM image is as follows Figure 1 As shown in the figure, it can be seen that it is a core-shell structured nanosphere with surface burrs, and the width is 2-3 μm. Its XRD pattern is shown in the figure. Figure 2 As shown.

[0079] 2) NiS2 preparation:

[0080] 0.1 g of Ni-MOFs precursor was weighed and mixed with sulfur powder at a mass ratio of 1:10 in a ceramic boat. The mixture was calcined under nitrogen atmosphere at 350 °C for 2 hours at a heating rate of 2 °C / min. After cooling, the black product was collected, and its SEM image is shown below. Figure 3 As shown in the figure, it can be seen that it is a core-shell structured nanosphere with a rough surface. The diameter is 2-3 μm. Its XRD pattern is shown below. Figure 4 As shown.

[0081] 3) Weigh 0.1 g of NiS2 and add it to 100 ml of anhydrous methanol solvent. Then add 0.67 g of 2-methylimidazole to obtain solution A, and sonicate for half an hour. Weigh 0.66 g of ZnSO4·7H2O and add it to 50 ml of anhydrous methanol solvent. Stir for 10 minutes to obtain solution B. Add solution B dropwise to solution A, then stir at room temperature (25°C) for 4 hours, and let it stand overnight at 25°C. Wash three times each with deionized water and anhydrous ethanol, and vacuum dry at 60°C for 12 hours. Collect the black precipitate of precursor NiS2@ZIF-8. Its SEM image is shown below. Figure 5 As shown, the TEM image is as follows Figure 6 As shown in the figure, it can be seen that it is a core-shell structured nanosphere with a rough surface and a diameter of 2-3 μm.

[0082] 4) The dried intermediate product NiS2@ZIF-8 was placed in a ceramic boat and calcined in high-purity argon (99.99%) at 650℃ for 2 hours at a heating rate of 2℃ / min. This yielded the two-phase composite material NiS@ZnS / C with heterojunction-induced defects, as shown in the SEM image below. Figure 7 As shown, the TEM image is as follows Figure 8 As shown in the figure, it can be seen that it is a rough-surfaced nanoparticle with a diameter of 2-2.5 μm and a carbon layer thickness of 30-50 nm.

[0083] The HRTEM image of the NiS@ZnS / C composite material prepared in this embodiment is shown below. Figure 9 As shown, the existence of the two-phase heterostructure is proven; the XRD pattern of the NiS@ZnS / C composite material obtained in this embodiment is shown in the figure. Figure 10 As shown, the refined XRD pattern is as follows: Figure 11 As shown, the obtained product is NiS@ZnS / C. The ERP analysis diagram of the NiS@ZnS / C composite material with heterojunction-induced defects obtained in this embodiment is shown below. Figure 12 As shown in Figure 12, the EPR spectrum is an effective means of detecting unpaired electrons (corresponding to defect sites) in the material. The signal intensity of unpaired electrons directly reflects the defect density, proving the defects in the NiS@ZnS / C nanosphere composite material.

[0084] Example 2 (as a comparison)

[0085] A method for preparing a two-phase heterostructure NiS@ZnS / C composite material with heterojunction-induced defects includes the following steps:

[0086] 1) The preparation of Ni-MOF precursors is the same as in Example 1;

[0087] 2) NiS2 preparation is the same as in Example 1;

[0088] 3) Weigh 0.1 g of NiS2 and add it to 100 ml of anhydrous methanol solvent. Then add 1.34 g of 2-methylimidazole to obtain solution A, and sonicate for half an hour. Weigh 1.32 g of ZnSO4·7H2O and add it to 50 ml of anhydrous methanol solvent. Stir for 10 minutes to obtain solution B. Add solution B dropwise to solution A, stir at room temperature for 4 hours, and let stand overnight. Wash three times each with deionized water and anhydrous ethanol, and dry under vacuum at 60℃ for 12 hours. Collect the black precipitate of precursor NiS2@ZIF-8. Its SEM image is shown below. Figure 13 As shown, the TEM image is as follows Figure 14 As shown in the figure, increasing the amount of 2-methylimidazole and zinc source results in a greater number of small particles loaded on the surface, with a diameter of 2-3 μm.

[0089] 4) The dried intermediate product NiS2@ZIF-8 was placed in a ceramic boat and calcined in high-purity argon (99.99%) at 650℃ for 2 hours at a heating rate of 2℃ / min. This yielded the two-phase composite material NiS@ZnS / C with heterojunction-induced defects, as shown in the SEM image below. Figure 15 As shown in the figure, the surface coating layer is thickened. The increased carbon layer leads to a decrease in the mass percentage of the active material, resulting in a corresponding reduction in capacity contribution.

[0090] Example 3 (as a comparison)

[0091] A method for preparing a two-phase heterostructure NiS@ZnS / C composite material with heterojunction-induced defects includes the following steps:

[0092] 1) The preparation of Ni-MOF precursors is the same as in Example 1;

[0093] 2) NiS2 preparation is the same as in Example 1;

[0094] 3) Weigh 0.1 g of NiS2 and add it to 100 ml of anhydrous methanol solvent. Then add 0.335 g of 2-methylimidazole to obtain solution A, and sonicate for half an hour. Weigh 0.33 g of ZnSO4·7H2O and add it to 50 ml of anhydrous methanol solvent. Stir for 10 minutes to obtain solution B. Add solution B dropwise to solution A, stir at room temperature for 4 hours, and let stand overnight. Wash three times each with deionized water and anhydrous ethanol, and dry under vacuum at 60℃ for 12 hours. Collect the black precipitate of precursor NiS2@ZIF-8. Its SEM image is shown below. Figure 16 As shown in the figure, it can be seen that with the reduction of the amount of 2-methylimidazole and zinc source, the number of small particles on the surface load decreases, and the diameter size is 2-3 μm.

[0095] 4) The dried intermediate product NiS2@ZIF-8 was placed in a ceramic boat and calcined in high-purity argon (99.99%) at 650℃ for 2 hours at a heating rate of 2℃ / min. This yielded a two-phase heterostructure NiS@ZnS / C with heterojunction-induced defects, as shown in the SEM image below. Figure 17 As shown in the figure, the surface coating thickness is reduced. With the reduced thickness of the carbon coating, the material's conductivity is affected, resulting in poor long-cycle performance.

[0096] Example 4 (as a comparison)

[0097] A method for preparing a two-phase heterostructure NiS@ZnS / C composite material with heterojunction-induced defects includes the following steps:

[0098] 1) The preparation of Ni-MOF precursors is the same as in Example 1;

[0099] 2) NiS2 preparation is the same as in Example 1;

[0100] 3) The preparation of NiS2@ZIF-8 was the same as in Example 1;

[0101] 4) The preparation of NiS@ZnS / C was the same as in Example 1, except that the calcination temperature was 550℃. At 550℃, the crystallinity of the material decreased due to insufficient calcination reduction temperature. The XRD pattern of the NiS@ZnS / C composite material obtained in this example is shown below. Figure 18 As shown, its SEM image is as follows: Figure 19 As shown.

[0102] Example 5 (as a comparison)

[0103] A method for preparing a two-phase heterostructure NiS@ZnS / C composite material with heterojunction-induced defects includes the following steps:

[0104] 1) The preparation of Ni-MOF precursors is the same as in Example 1;

[0105] 2) NiS2 preparation is the same as in Example 1;

[0106] 3) The preparation of NiS2@ZIF-8 was the same as in Example 1;

[0107] 4) The preparation of NiS@ZnS / C was the same as in Example 1, except that the calcination temperature was 750℃. Due to the increased calcination reduction temperature, the XRD pattern of the resulting NiS@ZnS / C composite material is shown below. Figure 20 As shown, its SEM image is as follows: Figure 21 As shown, at a calcination temperature of 750°C, the calcination reduction temperature is too high, causing the material morphology to collapse and become unsatisfactory, making it difficult to buffer the volume expansion required during battery cycling.

[0108] Example 6

[0109] The application of a heterojunction-induced defect biphase heterostructure composite material in batteries: The aforementioned heterojunction-induced defect biphase heterostructure nickel sulfide@zinc sulfide / carbon (NiS@ZnS / C) composite material is used as the active material to prepare anode materials for sodium-ion batteries. Specifically:

[0110] Nickel sulfide@zinc sulfide / carbon composite material with heterojunction-induced defects was used as the active material. It was mixed with conductive carbon black and PVDF in a ratio of 7:2:1 and then magnetically stirred for 8 hours to disperse it evenly in N-methylpyrrolidone (NMP). The uniformly mixed slurry was coated onto copper foil using a coater and placed in a vacuum drying oven at 80°C for 24 hours. After drying, it was pressed into a sheet using a tablet press and then cut into a circular electrode sheet with a diameter of 12 mm using a cutting machine. The electrode sheet was then assembled into a button cell in a glove box filled with high-purity argon gas and with water and oxygen values ​​≤0.01 ppm.

[0111] The specific method for assembling the battery is as follows: After adding 1 drop of electrolyte to the positive electrode shell, place the electrode plate, then add 1 drop of electrolyte and place the glass fiber, add 3 drops of electrolyte to the glass fiber and place the sodium plate as the counter electrode, then place two pieces of nickel foam, add 4 drops of electrolyte, cover with the negative electrode shell, press and seal the battery with a hydraulic press, and let it stand for 12 hours.

[0112] Performance testing process: After assembling the sodium-ion half-cell, the following steps were set on the Xinwei tester: first, constant current discharge to 0.3V, then constant current charging to 3.0V, repeating this cycle a certain number of times. The active material loading on the electrode plates was approximately 1.2 mg / cm³. -2 .

[0113] The test results and data are as follows:

[0114] Figure 22 The final product of the heterojunction-induced defect biphase heterostructure prepared in Example 1, a nickel sulfide@zinc sulfide / carbon structure (NiS@ZnS / C) composite material, was shown to perform well as a sodium-ion battery anode material at 0.1 mV s⁻¹. -1 CV test results at this scan rate. At this scan rate, the curves for cycles 2-5 show a high degree of overlap, indicating good cyclic reversibility.

[0115] Figure 23 The charging and discharging curves are for a current density of 0.1 A / g, with average discharge voltages around 1.61 and 0.91 V. The curves for different number of cycles have a high degree of overlap, indicating good reversibility.

[0116] Figure 24 The nickel sulfide@zinc sulfide / carbon structure (NiS@ZnS / C) composite material, the final product of the heterojunction-induced defect biphase heterostructure prepared in Example 1, was used as a sodium-ion battery anode material in 0.1 Ag. -1 The cycling stability test results at current density show good cycling stability. After 60 cycles, the capacity retention is 453.5 mAh / g, and the coulombic efficiency is 97%.

[0117] Figure 25 The NiS@ZnS / C nanosphere composite material prepared in Example 1 was used as a sodium-ion battery anode material at 0.5 A g. -1 Cyclic stability test results at current density: After 500 cycles at 0.5 A / g, capacity retention exceeds 90%. The capacity retention after 500 cycles is 394.5 mAh / g, with a coulombic efficiency of 98.8%.

[0118] Figure 26 The nickel sulfide@zinc sulfide / carbon structure (NiS@ZnS / C) composite material, the final product of the heterojunction-induced defect dual-phase heterostructure prepared in Example 1, was used as a sodium-ion battery anode material at 2.0 Ag. -1 Cyclic stability test results at current density. It exhibits good cycling stability. After 3000 cycles, the capacity retention is 322.9 mAh / g, and the coulombic efficiency is 99.8%.

[0119] Figure 27 The figure shows the rate performance of the nickel sulfide@zinc sulfide / carbon (NiS@ZnS / C) composite material, the final product of the heterojunction-induced defect biphase heterostructure prepared in Example 1, as a sodium-ion battery anode material. As can be seen from the figure, the composite material can withstand a maximum current density of 10.0 A / g, indicating its excellent rate performance. This electrode material can stably withstand multiple rounds of rate cycling tests within a wide current density range of 0.1-10 A / g. Even under harsh conditions of nearly two orders of magnitude current density span and repeated high-low current switching, it still maintains excellent capacity response and highly stable cycling characteristics, fully demonstrating ultrafast sodium-ion diffusion kinetics and efficient charge transfer capabilities. Thanks to the synergistic effect of heterojunction interface, defect enrichment and carbon matrix conductive network, the material can quickly complete ion insertion / extraction and electron conduction during high current charge and discharge, and can effectively resist structural deformation and pulverization caused by repeated rate fluctuations. It achieves a balance between high rate performance and long cycle stability, and has excellent rate adaptability and high power energy storage application potential.

[0120] Figure 28The final product of the heterojunction-induced defect biphase heterostructure prepared in Example 1, a nickel sulfide@zinc sulfide / carbon structure (NiS@ZnS / C) composite material, was used as a sodium-ion battery anode material at 1.0 A g. -1 Cyclic stability test results at current density and high temperature (50°C) show that the composite material has high temperature tolerance, expanding its application scenarios. Even at 50°C, the electrode material can still cycle stably for 180 cycles at a current density of 1.0 A / g, maintaining a capacity of 461.4 mAh / g, demonstrating excellent high-temperature structural stability and electrochemical reliability. Under harsh conditions where high temperatures easily lead to increased electrode side reactions, material structural collapse, and rapid capacity decay, the material still maintains efficient and stable sodium storage behavior, fully demonstrating that its internal heterojunction and defect system can effectively suppress structural deformation and interface instability at high temperatures. It possesses excellent high-temperature adaptability and long-cycle durability, fully meeting the practical application requirements of energy storage devices under high-temperature conditions.

[0121] Figure 29 The final product of the heterojunction-induced defect biphase heterostructure prepared in Example 1, a nickel sulfide@zinc sulfide / carbon structure (NiS@ZnS / C) composite material, was used as a sodium-ion battery anode material at 0.5 A g. -1 Cyclic stability test results at current density and -10°C show that the composite material exhibits high temperature tolerance, expanding its application scenarios. In the extreme environment of -10°C, after 120 cycles at a current density of 0.5 A / g, the electrode material still retains a considerable capacity of 326.8 mAh / g, demonstrating excellent low-temperature sodium storage capability. Low temperatures typically significantly limit sodium ion diffusion kinetics and reduce charge transport efficiency. However, this material, with its optimized electronic conductivity, ion transport channels, and stable interface structure, effectively overcomes the challenge of sluggish kinetics at low temperatures, maintaining good reversibility and cycling stability even under harsh low-temperature conditions, demonstrating excellent wide-temperature adaptability.

[0122] This invention utilizes a simple two-step MOF derivatization method combined with sulfidation and calcination processes to prepare a heterojunction-induced defect-bearing biphase heterostructure NiS@ZnS / C nanosphere composite material, in which the biphase metal sulfides are NiS and ZnS, respectively, and the cubes are encapsulated in a carbon layer. The heterojunction interface between the different crystals can induce an internal electric field to accelerate ion diffusion kinetics, improve conductivity, and provide abundant reaction sites for sodium energy storage. It exhibits high reversible capacity, high specific capacity, stable cycling performance, and robust rate performance.

[0123] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A two-phase heterostructure composite material with heterojunction-induced defects, characterized in that, The heterojunction-induced defect biphase heterostructure composite material is a nickel sulfide@zinc sulfide / carbon structure composite material, which is a rough-surfaced nanosphere with a diameter of 2-2.5 μm; the heterojunction-induced defect biphase heterostructure composite material has NiS and ZnS as active core phases and an outer carbon layer as a coating shell with a thickness of 30-50 nm.

2. A method for preparing a two-phase heterostructure composite material with heterojunction-induced defects as described in claim 1, characterized in that, The preparation method includes the following steps: 1) Ni-MOFs precursor and sulfur powder are mixed and calcined under a protective atmosphere to obtain NiS2; 2) NiS2 is in situ wrapped with ZIF-8 to obtain NiS2@ZIF-8; 3) NiS2@ZIF-8 was calcined to obtain a two-phase heterostructure composite material NiS@ZnS / C with heterojunction-induced defects.

3. The preparation method according to claim 2, characterized in that, In step 1), the method for preparing the Ni-MOFs precursor is as follows: organic ligands, surfactants and nickel sources are mixed in a solvent and subjected to a solvothermal reaction to obtain the Ni-MOFs precursor.

4. The preparation method according to claim 3, characterized in that, The amount of nickel source used is 40%-50% of the mass of the surfactant; the surfactant is polyvinylpyrrolidone.

5. According to the preparation method of claim 2, the mass ratio of Ni-MOFs precursor to sulfur powder in step 1) is 1:5-1:10; the calcination conditions are: calcination at 350°C for 2 hours.

6. The preparation method according to claim 2, characterized in that, In step 2), the molar ratio of NiS2 to the organic ligand is 1:10-15.

7. The preparation method according to claim 2 or 6, characterized in that, In step 2), the mass ratio of NiS2 to zinc source is 0.1-0.15 : 0.65-1.

0.

8. The preparation method according to claim 2 or 6, characterized in that, In step 2), the stirring reaction is carried out at 20-70℃ for 4-10 hours.

9. The preparation method according to claim 2 or 6, characterized in that, In step 3), the calcination atmosphere is Ar or N2 atmosphere, and the calcination is: calcining at 650°C for 2 hours.

10. The application of the heterojunction-induced defect biphase heterostructure composite material as described in claim 1 in a battery, characterized in that, A sodium-ion battery anode material was prepared using a two-phase heterostructure nickel sulfide@zinc sulfide / carbon composite material with heterojunction-induced defects as the active material.

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