Preparation method and application of iron-cobalt sulfide / nitrogen-doped carbon composite material based on spray drying method

Abstract

The application relates to the field of batteries, in particular to a preparation method of an iron cobalt sulfide / nitrogen-doped carbon composite material based on a spray drying method and application thereof. The method comprises the following steps: mixing a 2-methyl imidazole solution and a cobalt salt solution, then spray drying to obtain purple precursor powder, recrystallizing, exchanging iron ions to obtain Fe / ZIF-67, and finally forming an iron cobalt sulfide / nitrogen-doped carbon composite material derived from a ZIF-67 skeleton through a gas phase sulfuration method. The Fe / ZIF-67 is nanoscale in size and has high structural stability. When the iron cobalt sulfide / nitrogen-doped carbon composite material is used as a sodium ion battery negative electrode material, an internal electric field of an iron cobalt sulfide heterostructure can significantly improve ion diffusion kinetics, and meanwhile, a nitrogen-doped carbon matrix can improve the conductivity of the composite material and effectively relieve the volume change of the iron cobalt sulfide heterojunction in the electrochemical reaction process, so that the iron cobalt sulfide / nitrogen-doped carbon composite material exhibits excellent and stable sodium storage performance.

Description

TECHNICAL FIELD

[0001] The application relates to the field of batteries, in particular to a preparation method of a ZIF-67 skeleton-derived iron-cobalt sulfide / nitrogen-doped carbon composite material based on a spray drying method and application of the ZIF-67 skeleton-derived iron-cobalt sulfide / nitrogen-doped carbon composite material as a negative electrode material of a sodium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in portable energy storage, electric vehicles and other fields due to their high energy density, long service life, high charging and discharging efficiency and small pollution, but the problems of uneven resource distribution and cost increase are gradually highlighted. In contrast, sodium is abundant and has similar chemical properties to lithium, so sodium ion batteries have also been widely studied and are considered to be the most likely replacement for lithium ion batteries. Carbon materials are the most widely studied negative electrode materials for sodium ion batteries. Similar to lithium ion batteries, carbon materials have excellent electrical conductivity and structural stability, making them one of the ideal negative electrode materials. However, the theoretical sodium storage capacity of carbon materials is limited. Therefore, finding new negative electrode materials to improve the performance of sodium ion batteries is a current research hotspot.

[0003] Transition metal sulfides have become the subject of attention as negative electrode materials due to their high theoretical capacity, abundant storage and no pollution. However, these materials have poor electrical conductivity and volume expansion during the sodium storage process, which leads to insufficient rate performance and cycle stability. Research has found that the built-in electric field generated by the coupling of two crystals with different band gaps can promote charge transfer and improve ion transmission rate, and carbon coating not only serves as a fast electron transmission layer but also inhibits the volume change of the material during the charging and discharging process, thereby improving the cycle stability of the material. Therefore, preparing transition metal sulfide heterojunction / carbon composite materials is a modification method that can effectively solve the above problems.

[0004] Currently, there are methods such as solvothermal method, electrospinning method and mechanical ball milling method to prepare transition metal sulfide heterojunction / carbon composite materials. For example, patent CN114094078A uses bismuth source, molybdenum source and sulfur source as raw materials to prepare nitrogen-doped carbon-coated metal sulfide heterostructure p-MoS2 / n-Bi2S3@NC composite electrode material through hydrothermal reaction and calcination process, but there are problems such as complex preparation process, high manufacturing cost and long time consumption. In addition, the capacity retention rate of the sodium ion half-battery composed of the electrode material is also low. In view of the above problems, it is necessary to study a simple and easy-to-operate preparation method that can achieve carbon coating and construct a heterostructure to obtain stable and excellent sodium storage performance. SUMMARY

[0005] In order to solve the problems in the prior art, the application provides a preparation method of ZIF-67 skeleton derived iron cobalt sulfide / nitrogen-doped carbon composite material based on a spray drying method and application of the ZIF-67 skeleton derived iron cobalt sulfide / nitrogen-doped carbon composite material as a negative electrode material of a sodium ion battery. The iron cobalt sulfide / nitrogen-doped carbon composite material is prepared by first preparing ZIF-67 through a spray drying method, then performing iron ion exchange and subsequent gas phase sulfuration to form the ZIF-67 skeleton derived iron cobalt sulfide / nitrogen-doped carbon composite material. When the composite material is used as the negative electrode material of the sodium ion battery, the composite material has excellent rate performance and cycle stability.

[0006] The specific technical scheme of the application is as follows:

[0007] In the first aspect, the application provides a preparation method of ZIF-67 skeleton derived iron cobalt sulfide / nitrogen-doped carbon composite material based on a spray drying method, which comprises the following steps:

[0008] (1) a certain amount of 2-methyl imidazole and cobalt salt are respectively dissolved in deionized water, then the 2-methyl imidazole solution is quickly poured into the cobalt salt solution, and a mixed solution A is obtained after uniform stirring;

[0009] (2) the mixed solution A obtained in step (1) is subjected to spray drying treatment to obtain purple precursor powder B;

[0010] (3) the purple precursor powder B obtained in step (2) is dispersed in an alcohol solvent, and after recrystallization by soaking, an iron salt is added for ion exchange, and the mixture is left to stand for a period of time, and then the intermediate product C, i.e., Fe / ZIF-67, is obtained through centrifugation, washing and drying;

[0011] (4) the intermediate product C obtained in step (3) and sulfur powder are respectively placed at two ends of a porcelain boat, and gas phase sulfuration is performed under an inert atmosphere to obtain the iron cobalt sulfide / nitrogen-doped carbon composite material in nanoscale and in a polyhedral (mainly dodecahedral) morphology.

[0012] In the above steps, the present application mixes 2-methylimidazole and cobalt salt to prepare a mixed solution A, and then sprays and dries the mixed solution A; in the process of spray drying, as the water in the droplets evaporates, the concentration of the metal-ligand complex formed by 2-methylimidazole and cobalt salt in the mixed solution A gradually increases, and the saturation on the surface of the droplets is formed, and the saturation is higher and higher, and finally the precursor spherical particles with a size of several microns are formed. The precursor is an intermediate coordination compound of cobalt and 2-methylimidazole, which has amorphous characteristics, and then nucleates and gradually recrystallizes into a ZIF-67 structure with a polyhedral (mainly dodecahedral) morphology in the process of soaking in an alcohol solvent. Then, by ion exchange with iron ions in an iron salt, a Fe / ZIF-67 material can be formed. Finally, under the protection of an inert atmosphere, a gas phase sulfidation treatment is carried out, and in the process of gas phase sulfidation, the nitrogen-doped carbon framework derived from Fe / ZIF-67 provides a good conductive network, while also serving to limit the agglomeration of metal sulfide particles. At the same time, iron and cobalt react with sulfur to form iron cobalt sulfide, and finally a nanoscale iron cobalt sulfide / nitrogen-doped carbon composite material with a dodecahedral morphology is obtained.

[0013] In the prior art, ZIF-67 materials are usually prepared using a traditional hydrothermal method. The present application finds that the ZIF-67 particles prepared by this method have a relatively large particle size of about 1 μm and exhibit a thin-walled or hollow feature. The present application finds that when prepared by a spray drying method, the particle size of the obtained product is significantly reduced to about 200-400 nm, and the morphology is uniform, regular and compact. Such a material is more suitable as a negative electrode material for sodium ion batteries. Analysis finds that the significant difference is mainly due to the difference in reaction mechanism between the two preparation methods. The core feature of the spray drying method is to atomize the precursor solution into small droplets and solidify the droplets into particles by rapid evaporation at high temperature. In this process, the evaporation rate of the droplets is fast and uniform, avoiding the agglomeration or migration of particles during growth, thereby generating particles with smaller particle size and more compact structure. In addition, the rapid drying mechanism of spray drying effectively suppresses the separation effect of the internal and external components of the material, making the composition distribution of the particles more uniform. In contrast, the hydrothermal method relies on ion diffusion, crystal nucleation and growth in the solution. Due to the relatively long reaction time and the relatively complex reaction kinetics, the particles are prone to agglomeration, resulting in an increase in particle size. In addition, due to the influence of solute internal and external migration during the hydrothermal reaction process, the particle surface is prone to form a thin-walled or hollow structure, and the morphology lacks compactness. This phenomenon reflects the imbalance between ion diffusion and crystal growth rate in the hydrothermal reaction.

[0014] As a preferred, in step (1), the cobalt salt is one or more of cobalt sulfate, cobalt chloride or cobalt acetate.

[0015] It is found in the research process that the type of cobalt salt has a significant impact on the successful completion of spray drying. For example, when cobalt nitrate is used, no powder particles are generated in the spray drying collection unit, only a viscous gel is obtained near the cyclone outlet, indicating that cobalt nitrate is not suitable for the spray drying process system. In contrast, when cobalt sulfate, cobalt chloride or cobalt acetate is selected as the cobalt salt, the spray drying process can be successfully completed, and the particle morphology is good; the reason may be related to the physical and chemical properties of the cobalt salt and the evaporation behavior of the solution in the spray drying process. Cobalt nitrate may have undergone premature chemical reaction or gelation during drying, resulting in the failure of the particles to form normally, while the evaporation and nucleation behavior of cobalt sulfate, cobalt chloride and cobalt acetate is more stable, thereby ensuring the successful formation of the particles.

[0016] Preferably, in step (1), the molar ratio of 2-methylimidazole to cobalt salt is controlled to be 1:(0.25-0.9).

[0017] It is found that the molar ratio of 2-methylimidazole to cobalt salt has a significant impact on the formation of ZIFs. Specifically, an appropriate amount of excess 2-methylimidazole is required during the spray drying synthesis process to effectively complete the deprotonation reaction of ZIFs, ensuring that a pure crystalline phase material is finally obtained. This phenomenon can be attributed to the key role of the ligand in the formation of ZIFs. 2-methylimidazole is not only a structural unit of ZIFs, but also coordinates with cobalt ions through deprotonation in solution, thereby realizing the formation of the framework structure. When the content of 2-methylimidazole is insufficient, the degree of deprotonation is low, resulting in incomplete crystal growth or mixed-phase generation. Excessive 2-methylimidazole can provide sufficient ligand molecules to further drive the deprotonation process and stabilize the framework structure, thereby forming a pure crystalline phase.

[0018] Preferably, in step (3), the mass ratio of the iron salt to the purple precursor powder B is (0.1-0.3):1.

[0019] It is further found that the ratio of the iron salt to the purple precursor powder B has a significant impact on the morphology of the material. In the case of a low Fe content, the framework structure of ZIF-67 remains basically intact, the material morphology is uniform, and the performance is excellent. However, as the Fe content increases, the morphology of the material gradually changes, and phenomena such as partial collapse of the framework or uneven structure may occur, which in turn adversely affects the performance. This indicates that the amount of Fe introduced needs to be strictly controlled to maintain the stability of the framework structure while optimizing the performance of the material. This phenomenon may be related to the substitution behavior of Fe during ion exchange. Appropriate Fe substitution may only affect the local framework structure, while excessive Fe may cause excessive substitution or damage the stability of the metal organic framework, thereby causing changes in the morphology and affecting the performance of the material.

[0020] Preferably, in step (1), the mixing is performed by stirring at room temperature for 5-30 min.

[0021] Preferably, in step (2), the spray drying process is performed at an inlet temperature of 180-200℃, an outlet temperature of 90-110℃, and a feed rate of 5-15 mL / min. -1 .

[0022] The present application finds that too fast a feed rate will hinder the complete formation of particles, increasing the risk of agglomeration; too slow a feed rate may result in irregular particle shapes, prolonging the drying time, increasing energy consumption, and reducing production efficiency. Therefore, controlling the appropriate temperature and feed rate is crucial to ensuring particle quality and improving production efficiency.

[0023] Preferably, in step (3), the alcohol solvent is one or more of ethanol, methanol, and isopropanol.

[0024] Preferably, in step (3), the iron salt is ferric chloride and / or ferric nitrate.

[0025] Preferably, in step (3), the temperature for standing is room temperature, and the time is 1-12 h.

[0026] Preferably, in step (3), the recrystallization time is 0.5-6 h.

[0027] Preferably, in step (4), the mass ratio of intermediate product C to sulfur powder is 1:(3-5), and the temperature for gas-phase sulfuration is 300-500℃, with a holding time of 1-3 h.

[0028] In a second aspect, the present application provides the use of the iron-cobalt sulfide / nitrogen-doped carbon composite material prepared by the above method as a negative electrode material for sodium-ion batteries.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] (1) The present application uses a spray drying method to prepare nanoscale ZIF-67 framework materials, which is simpler, more efficient, and more reproducible than traditional liquid-phase methods, and is more suitable for large-scale production.

[0031] (2) The ZIF-67 framework material synthesized by the present application has a regular morphology, is a dodecahedral-shaped nanoparticle, and has a stable structure, making it more promising as a functional template and precursor for application in the energy storage field.

[0032] (3) The present application uses ZIF-67 as a template, loads iron ions onto ZIF-67 through ion exchange, and then obtains an iron-cobalt sulfide heterojunction through a one-step gas-phase sulfuration method. The built-in electric field of this heterostructure can significantly improve the ion diffusion kinetics.

[0033] (4) The nitrogen-doped carbon matrix formed in the one-step gas-phase sulfidation process is not only conducive to improving the electrical conductivity of the composite material, but also effectively alleviates the volume expansion and contraction of the iron-cobalt sulfide heterojunction during the electrochemical reaction process, which helps to improve the electrochemical stability. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 A scanning electron microscope image of the cobalt sulfide / nitrogen-doped carbon composite material prepared in Comparative Example 1.1;

[0035] Figure 2 A scanning electron microscope image of the iron-cobalt sulfide / nitrogen-doped carbon composite material prepared in Example 1;

[0036] Figure 3 A scanning electron microscope image of ZIF-67 prepared in Example 2.1;

[0037] Figure 4 A battery rate performance graph of the iron-cobalt sulfide / nitrogen-doped carbon composite material prepared in Example 2.2;

[0038] Figure 5 An X-ray diffraction pattern of ZIF-67 prepared in Example 2.3;

[0039] Figure 6 A scanning electron microscope image of Fe / ZIF-67 prepared in Example 3.1;

[0040] Figure 7 A scanning electron microscope image of Fe / ZIF-67 prepared in Example 3.2;

[0041] Figure 8 An X-ray diffraction pattern of the iron-cobalt sulfide / nitrogen-doped carbon composite material prepared in Example 3.2;

[0042] Figure 9 A scanning electron microscope image of Fe / ZIF-67 prepared in Comparative Example 3;

[0043] Figure 10 A scanning electron microscope image of the iron-cobalt sulfide / nitrogen-doped carbon composite material prepared in Example 4.1;

[0044] Figure 11 A battery cycle performance graph of the iron-cobalt sulfide / nitrogen-doped carbon composite material prepared in Example 4.1;

[0045] Figure 12 A scanning electron microscope image of the iron-cobalt sulfide / nitrogen-doped carbon composite material prepared in Example 4.2;

[0046] Figure 13The scanning electron microscope image of the iron cobalt sulfide / nitrogen-doped carbon composite material prepared in Comparative Example 4. DETAILED DESCRIPTION

[0047] The application will be further described below in connection with specific examples, but the application is not limited thereto.

[0048] (I) Comparison between traditional hydrothermal method and spray drying method

[0049] Comparative Example 1.1

[0050] (1) 32 mmol of 2-methylimidazole and 16 mmol of cobalt acetate were respectively dissolved in 50 mL of anhydrous methanol, and after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt acetate solution to obtain a mixed solution A;

[0051] (2) The mixed solution A obtained in step (1) was placed in a polytetrafluoroethylene reaction liner, and after reaction at 60°C for 24 h, centrifugation, washing and drying were performed to obtain an intermediate product B, i.e. a ZIF-67 material;

[0052] (3) The intermediate product B obtained in step (2) and sulfur powder were respectively placed at both ends of a porcelain boat in a mass ratio of 1:4, and gas-phase sulfuration was performed at 500°C for 2 h under a nitrogen atmosphere to obtain a cobalt sulfide / nitrogen-doped carbon composite material.

[0053] Comparative Example 1.2

[0054] (1) 32 mmol of 2-methylimidazole and 8 mmol of cobalt acetate were respectively dissolved in 50 mL of deionized water, and after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt acetate solution to obtain a mixed solution A;

[0055] (2) The mixed solution A obtained in step (1) was placed in a polytetrafluoroethylene reaction liner, and after reaction at 60°C for 24 h, centrifugation, washing and drying were performed to obtain an intermediate product B, i.e. a ZIF-67 material;

[0056] (3) 1 g of the intermediate product B obtained in step (2) was dispersed in anhydrous methanol solvent, and after soaking and recrystallization for 0.5 h, 0.2 mmol of iron chloride was added for ion exchange, and the mixture was left to stand at room temperature for 6 h, followed by centrifugation, washing and drying to obtain an intermediate product C, i.e. Fe / ZIF-67;

[0057] (4) The intermediate product C obtained in step (3) and sulfur powder were respectively placed at both ends of a porcelain boat in a mass ratio of 1:5, and gas-phase sulfuration was performed at 500°C for 3 h under a nitrogen atmosphere to obtain an iron cobalt sulfide / nitrogen-doped carbon composite material.

[0058] Example 1

[0059] (1) Dissolve 32 mmol of 2-methylimidazole and 8 mmol of cobalt acetate in 50 mL of deionized water, stir each at room temperature for 5 min, and then quickly pour the 2-methylimidazole solution into the cobalt acetate solution to obtain mixed solution A;

[0060] (2) The mixed solution A obtained in step (1) is subjected to spray drying to obtain purple precursor powder B. The inlet air temperature of the spray drying process is 190°C, the outlet air temperature is 100°C, and the feed rate is 15 mL / min. -1 ;

[0061] (3) Disperse 1g of purple precursor powder B obtained in step (2) in anhydrous methanol solvent, soak and recrystallize for 0.5h, add 0.2mmol of ferric chloride for ion exchange, let stand at room temperature for 6h, and obtain intermediate product C, namely Fe / ZIF-67, by centrifugation, washing and drying.

[0062] (4) The intermediate product C obtained in step (3) and sulfur powder are placed at both ends of a ceramic boat in a mass ratio of 1:5, and gas-phase sulfurization is carried out at 500°C for 3 hours under a nitrogen atmosphere to obtain iron cobalt sulfide / nitrogen-doped carbon composite material.

[0063] Results Comparison: A comparison of the experimental results of Comparative Example 1.1, Comparative Example 1.2, and Example 1 revealed that the particles prepared by the traditional hydrothermal method in Comparative Example 1.1 had a larger particle size, such as... Figure 1 The particle size shown is approximately 1 μm, exhibiting thin-walled or hollow characteristics. In contrast, the particle size of the particles prepared by spray drying in Example 1 is significantly reduced to approximately 300 nm. Figure 2The two methods, spray drying and hydrothermal drying, exhibit uniform and compact morphology. This significant difference stems primarily from the fundamental differences in their reaction mechanisms. The core characteristic of spray drying lies in atomizing the precursor solution into tiny droplets and then rapidly evaporating them at high temperatures to solidify them into particles. During this process, the droplet evaporation rate is fast and uniform, preventing particle aggregation or migration during growth, resulting in smaller and more compact particles. Furthermore, the rapid drying mechanism of spray drying effectively suppresses the separation effect of internal and external components, leading to a more uniform particle composition distribution. In contrast, hydrothermal drying relies on ion diffusion, crystal nucleation, and growth processes in solution. Due to the longer reaction time and relatively complex reaction kinetics, particle aggregation is more likely, resulting in increased particle size. Additionally, the hydrothermal reaction process is affected by the migration of solute, easily leading to thin-walled or hollow structures on the particle surface, resulting in a lack of compactness. This phenomenon reflects the imbalance between ion diffusion and crystal growth rates in hydrothermal reactions. In summary, spray drying not only demonstrates a significant advantage in particle size control but also effectively improves the uniformity and compactness of particle morphology. The rapid evaporation characteristics of this method provide important support for the optimization of the microstructure of materials, while the traditional hydrothermal method is relatively insufficient in terms of particle size and morphology control due to the limitations of the reaction mechanism.

[0064] (II) Comparison of different cobalt salts

[0065] Example 2.1 (Cobalt acetate)

[0066] (1) Dissolve 32 mmol of 2-methylimidazole and 8 mmol of cobalt acetate in 50 mL of deionized water, stir each at room temperature for 5 min, and then quickly pour the 2-methylimidazole solution into the cobalt acetate solution to obtain mixed solution A;

[0067] (2) The mixed solution A obtained in step (1) is subjected to spray drying to obtain purple precursor powder B. The inlet air temperature of the spray drying process is 200℃, the outlet air temperature is 110℃, and the feed rate is 10mL / min. -1 ;

[0068] (3) Disperse 1g of purple precursor powder B obtained in step (2) in anhydrous methanol solvent, soak and recrystallize for 0.5h, add 0.1mmol of ferric chloride for ion exchange, let stand at room temperature for 3h, and obtain intermediate product C, namely Fe / ZIF-67, by centrifugation, washing and drying.

[0069] (4) The intermediate product C obtained in step (3) and sulfur powder are placed at both ends of a ceramic boat in a mass ratio of 1:5, and gas-phase sulfidation is carried out at 400°C for 3 hours under a nitrogen atmosphere to obtain iron cobalt sulfide / nitrogen-doped carbon composite material.

[0070] Comparative Example 2 (Cobalt Nitrate)

[0071] (1) 32 mmol of 2-methylimidazole and 8 mmol of cobalt nitrate were respectively dissolved in 50 mL of deionized water, after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt nitrate solution to obtain a mixed solution A;

[0072] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain a purple sticky gel material, example 2.2 (cobalt chloride)

[0073] (1) 32 mmol of 2-methylimidazole and 8 mmol of cobalt chloride were respectively dissolved in 50 mL of deionized water, after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt chloride solution to obtain a mixed solution A;

[0074] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain a purple precursor powder B, the spray drying treatment was carried out at an inlet temperature of 200°C, an outlet temperature of 110°C, and a feeding rate of 10 mL / min -1 ;

[0075] (3) 1 g of the purple precursor powder B obtained in step (2) was dispersed in anhydrous methanol solvent, soaked and recrystallized for 0.5 h, then 0.1 mmol of iron chloride was added for ion exchange, and the mixture was placed at room temperature for 3 h, then centrifuged, washed and dried to obtain an intermediate product C, Fe / ZIF-67;

[0076] (4) The intermediate product C obtained in step (3) and sulfur powder were placed at a mass ratio of 1:5 at both ends of a porcelain boat, and gas-phase sulfuration was carried out at 400°C for 3 h under a nitrogen atmosphere to obtain a cobalt sulfide / nitrogen-doped carbon composite material.

[0077] Example 2.3 (cobalt sulfate)

[0078] (1) 32 mmol of 2-methylimidazole and 8 mmol of cobalt sulfate were respectively dissolved in 50 mL of deionized water, after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt sulfate solution to obtain a mixed solution A;

[0079] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain a purple precursor powder B, the spray drying treatment was carried out at an inlet temperature of 200°C, an outlet temperature of 110°C, and a feeding rate of 10 mL / min -1 ;

[0080] (3) 1 g of the purple precursor powder B obtained in step (2) was dispersed in anhydrous methanol solvent, soaked and recrystallized for 0.5 h, then 0.1 mmol of iron chloride was added for ion exchange, and the mixture was placed at room temperature for 3 h, then centrifuged, washed and dried to obtain an intermediate product C, Fe / ZIF-67;

[0081] (4) The intermediate product C obtained in step (3) and sulfur powder were respectively placed at both ends of a porcelain boat in a mass ratio of 1 : 5, and gas-phase sulfuration was carried out at 400°C for 3h under a nitrogen atmosphere to obtain a cobalt sulfide / nitrogen-doped carbon composite material.

[0082] As can be seen from the comparison of the experimental results of Comparative Example 2 and Examples 2.1-2.3, when nitric cobalt is used in Comparative Example 2, powder particles cannot be obtained in the collection unit during the spray drying process, but a viscous gel-like substance is formed near the outlet of the cyclone, indicating that nitric cobalt is not suitable for the spray drying process system. In contrast, when cobalt acetate, cobalt chloride and cobalt sulfate are respectively selected as the cobalt salt in Examples 2.1-2.3, the spray drying process can be successfully completed, and powder materials with good particle morphology can be obtained (as shown in FIG. 2). Figure 3 Therefore, in the present application, the suitable cobalt salt is any one of cobalt sulfate, cobalt chloride or cobalt acetate. This phenomenon may be related to the physical and chemical properties of the cobalt salt and the evaporation behavior of the solution during the spray drying process. Nitric cobalt may have undergone premature chemical reaction or gelation during the drying process, resulting in the failure of the particles to form normally, while the evaporation and nucleation behavior of cobalt sulfate, cobalt chloride and cobalt acetate is more stable, thereby ensuring the successful generation of particles.

[0083] (III) Comparison of different molar ratios of 2-methylimidazole (2-MIM) to cobalt salt

[0084] Example 3.1 (2-methylimidazole: cobalt acetate = 32:8)

[0085] (1) 32 mmol of 2-methylimidazole and 8 mmol of cobalt acetate were respectively dissolved in 50 mL of deionized water, and after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt acetate solution to obtain a mixed solution A;

[0086] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain purple precursor powder B, and the spray drying treatment was carried out at an inlet air temperature of 180°C, an outlet air temperature of 90°C and a feeding rate of 10 mL / min -1 ;

[0087] (3) 1 g of the purple precursor powder B obtained in step (2) was dispersed in anhydrous methanol solvent, soaked and recrystallized for 0.5h, and then 0.1 mmol of iron chloride was added for ion exchange, and the mixture was placed at room temperature for 1h, and then centrifuged, washed and dried to obtain an intermediate product C, i.e. Fe / ZIF-67;

[0088] (4) The intermediate product C obtained in step (3) and sulfur powder were respectively placed at both ends of a porcelain boat in a mass ratio of 1 : 5, and gas-phase sulfuration was carried out at 400°C for 3h under a nitrogen atmosphere to obtain a cobalt sulfide / nitrogen-doped carbon composite material.

[0089] Example 3.2 (2-methylimidazole: cobalt acetate = 32: 16)

[0090] (1) 32 mmol of 2-methylimidazole and 16 mmol of cobalt acetate were respectively dissolved in 50 mL of deionized water, after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt acetate solution to obtain a mixed solution A;

[0091] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain purple precursor powder B, the spray drying treatment was carried out at an inlet air temperature of 180°C, an outlet air temperature of 90°C, and a feeding rate of 10 mL / min -1 ;

[0092] (3) 1 g of the purple precursor powder B obtained in step (2) was dispersed in anhydrous methanol solvent, after soaking and recrystallization for 0.5 h, 0.1 mmol of iron chloride was added for ion exchange, and the mixture was placed at room temperature for 1 h, then centrifuged, washed and dried to obtain intermediate product C, i.e. Fe / ZIF-67;

[0093] (4) The intermediate product C obtained in step (3) and sulfur powder were respectively placed at both ends of a porcelain boat at a mass ratio of 1:4, and gas-phase sulfidation was carried out at 500°C for 2 h under a nitrogen atmosphere to obtain a cobalt sulfide / nitrogen-doped carbon composite material.

[0094] Comparative Example 3 (2-methylimidazole: cobalt acetate = 32:32)

[0095] (1) 32 mmol of 2-methylimidazole and 32 mmol of cobalt acetate were respectively dissolved in 50 mL of deionized water, after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt acetate solution to obtain a mixed solution A;

[0096] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain purple precursor powder B, the spray drying treatment was carried out at an inlet air temperature of 180°C, an outlet air temperature of 90°C, and a feeding rate of 10 mL / min -1 ;

[0097] (3) 1 g of the purple precursor powder B obtained in step (2) was dispersed in anhydrous methanol solvent, after soaking and recrystallization for 0.5 h, 0.1 mmol of iron chloride was added for ion exchange, and the mixture was placed at room temperature for 1 h, then centrifuged, washed and dried to obtain intermediate product C, i.e. Fe / ZIF-67;

[0098] (4) The intermediate product C obtained in step (3) and sulfur powder were respectively placed at both ends of a porcelain boat at a mass ratio of 1:4, and gas-phase sulfidation was carried out at 500°C for 2 h under a nitrogen atmosphere to obtain a cobalt sulfide / nitrogen-doped carbon composite material.

[0099] The influence of the molar ratio of 2-methylimidazole (2-MIM) to cobalt salt on the formation of ZIFs was investigated by adjusting the molar ratio of 2-MIM to cobalt salt in the above cases. As shown in the results of Figure 6 (Example 3.1), Figure 7 (Example 3.2), and Figure 9 (Comparative Example 3), an appropriate amount of excess 2-MIM is required during the synthesis process to effectively complete the deprotonation reaction of ZIFs and ensure the final acquisition of pure crystalline phase materials. This phenomenon can be attributed to the key role of the ligand in the formation of ZIFs. 2-MIM is not only a structural unit of ZIFs, but also coordinates with metal ions (such as cobalt ions) through a deprotonation reaction in solution, thereby realizing the formation of the framework structure. When the content of 2-MIM is insufficient (Comparative Example 3), the degree of deprotonation is low, leading to incomplete crystal growth or the generation of mixed phases. Excessive 2-MIM, on the other hand, can provide sufficient ligand molecules to further drive the deprotonation process and stabilize the framework structure, thereby forming pure crystalline phases.

[0100] (IV) Comparison of different iron contents

[0101] Example 4.1 (purple precursor powder B: mass ratio of iron chloride = 62:1)

[0102] (1) 32 mmol of 2-methylimidazole and 8 mmol of cobalt chloride were respectively dissolved in 50 mL of deionized water, and after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt chloride solution to obtain a mixed solution A;

[0103] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain purple precursor powder B, and the spray drying treatment was carried out at an inlet temperature of 200°C, an outlet temperature of 110°C, and a feeding rate of 10 mL / min -1 ;

[0104] (3) 1 g of the purple precursor powder B obtained in step (2) was dispersed in anhydrous methanol solvent, soaked and recrystallized for 0.5 h, then 0.1 mmol of iron chloride was added for ion exchange, and the mixture was left to stand at room temperature for 6 h. After centrifugation, washing and drying, intermediate product C, Fe / ZIF-67, was obtained;

[0105] (4) The intermediate product C obtained in step (3) and sulfur powder were placed at the two ends of a porcelain boat in a mass ratio of 1:5, and gas-phase sulfidation was carried out at 500°C for 3 h under a nitrogen atmosphere to obtain iron cobalt sulfide / nitrogen-doped carbon composite material.

[0106] Example 4.2 (purple precursor powder B: mass ratio of iron chloride = 31:1)

[0107] (1) 32 mmol of 2-methylimidazole and 8 mmol of cobalt chloride were respectively dissolved in 50 mL of deionized water, and after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt chloride solution to obtain a mixed solution A;

[0108] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain purple precursor powder B, the spray drying treatment was carried out at an inlet temperature of 200°C, an outlet temperature of 110°C, and a feeding rate of 10 mL / min -1 ;

[0109] (3) 1 g of the purple precursor powder B obtained in step (2) was dispersed in anhydrous methanol solvent, and after soaking and recrystallization for 0.5 h, 0.2 mmol of iron chloride was added for ion exchange, and the mixture was placed at room temperature for 6 h, and then centrifuged, washed and dried to obtain an intermediate product C, i.e. Fe / ZIF-67;

[0110] (4) The intermediate product C obtained in step (3) and sulfur powder were respectively placed at both ends of a porcelain boat at a mass ratio of 1:5, and gas-phase sulfidation was carried out at 500°C for 3 h under a nitrogen atmosphere to obtain a cobalt sulfide / nitrogen-doped carbon composite material.

[0111] Comparative Example 4 (mass ratio of purple precursor powder B: iron chloride = 21:1)

[0112] (1) 32 mmol of 2-methylimidazole and 8 mmol of cobalt chloride were respectively dissolved in 50 mL of deionized water, and after stirring at room temperature for 5 min, the 2-methylimidazole solution was quickly poured into the cobalt chloride solution to obtain a mixed solution A;

[0113] (2) The mixed solution A obtained in step (1) was subjected to spray drying treatment to obtain purple precursor powder B, the spray drying treatment was carried out at an inlet temperature of 200°C, an outlet temperature of 110°C, and a feeding rate of 10 mL / min -1 ;

[0114] (3) 1 g of the purple precursor powder B obtained in step (2) was dispersed in anhydrous methanol solvent, and after soaking and recrystallization for 0.5 h, 0.3 mmol of iron chloride was added for ion exchange, and the mixture was placed at room temperature for 6 h, and then centrifuged, washed and dried to obtain an intermediate product C, i.e. Fe / ZIF-67;

[0115] (4) The intermediate product C obtained in step (3) and sulfur powder were respectively placed at both ends of a porcelain boat at a mass ratio of 1:5, and gas-phase sulfidation was carried out at 500°C for 3 h under a nitrogen atmosphere to obtain a cobalt sulfide / nitrogen-doped carbon composite material.

[0116] In the above case, Fe / ZIF-67 material was successfully prepared by introducing iron for ion exchange. It is worth noting that as Figure 10(Example 4.1), Figure 12 (Example 4.2), and Figure 13 As shown by the results of Comparative Example 4, the amount of introduced Fe has a significant impact on the morphology of the material. In the case of a lower Fe content, the framework structure of ZIF-67 remains essentially intact, the material morphology is uniform, and the performance is excellent. However, as the Fe content increases, the morphology of the material gradually changes, and phenomena such as partial collapse of the framework or uneven structure may occur, which in turn adversely affects its performance (Comparative Example 4). This indicates that the amount of introduced Fe needs to be strictly controlled to maintain the stability of the framework structure while optimizing the performance of the material. This phenomenon may be related to the substitution behavior of Fe during the ion exchange process. An appropriate amount of Fe substitution may only affect the local framework structure, while an excessive amount of Fe may cause excessive substitution or damage to the stability of the metal-organic framework, thereby triggering a change in morphology and affecting the performance of the material.

[0117] Performance test

[0118] The final product of all the above comparative examples and examples was mixed with a conductive agent Super P, a binder polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1, and 2 mL of N-methyl pyrrolidone (NMP) solvent to form a homogeneous slurry, which was then evenly coated on a copper current collector. After drying at 60°C for 12 h, the slurry was cut into 1.2 cm diameter round pieces as sodium ion battery electrodes. Then, a glass fiber was used as a separator, and a 1.0 mol·L -1 NaPF6 as a solute, diglyme as a solvent, and a metal sodium sheet as a counter electrode to assemble a liquid half-cell. The assembled sodium ion half-cell was placed in a constant temperature environment at 25°C for 12 h, and then a constant current charge-discharge test was performed in the range of 0.01-3 V.

[0119] Figure 1 For the X-ray diffraction pattern of Example 3.2, the cobalt disulfide (JCPDS No. 89-3056) and iron disulfide (JCPDS No. 89-3057) in the figure confirm the formation of the iron-cobalt sulfide heterojunction after iron ion exchange. Figure 5 For the X-ray diffraction pattern of Example 2.3, the figure shows that ZIF-67 material can be successfully synthesized by a simple spray drying plus short time alcohol soaking process, and the material has a uniform morphology and excellent performance. Figure 3 The scanning electron microscope image of Example 2.3 shows that the prepared ZIF-67 has a uniform polyhedral morphology with an average diameter of about 200 nm.

[0120] Figure 4 For the rate performance test results of Example 2.2, it can be seen from the figure that the sodium ion battery has a discharge capacity of 120 mAh·g -1 , 0.5 Ag -1 , 1 Ag-1 2Ag -1 5Ag -1 And restore 0.2Ag -1 The specific capacity at the current density is 703 mAh g. -1 654mAhg -1 626mAh g -1 587mAh g -1 471mAh g -1 and 741mAh g -1 It exhibits excellent rate performance.

[0121] As shown in Table 1, Examples 4.1-4.2 and Comparative Examples 1 and 4 were prepared in 1 Ag. -1 The first-cycle coulombic efficiency at current density and the reversible capacity and capacity retention after 100 cycles.

[0122] Table 1

[0123]

[0124] Table 1 shows that changing the amount of iron salt introduced has a certain impact on the performance of the electrode material. Examples 4.1-4.2 and Comparative Example 4 show a significant improvement in performance compared to Comparative Example 1. This is attributed to the built-in electric field of the iron-cobalt sulfide heterostructure promoting the migration and diffusion of sodium ions in the material, thereby improving its electrochemical performance. When more iron salt is introduced... Figure 13 The scanning electron microscope (SEM) image of the final product of Comparative Example 4, an iron-cobalt sulfide / nitrogen-doped carbon composite material, reveals significant accumulation, which hinders the activation of active sites and results in inferior electrochemical performance compared to Examples 4.1 and 4.2. It is worth noting that... Figure 11 Example 4.1 shown exhibited the highest capacity retention (99.4%) after 100 cycles. Figure 10 Scanning electron microscopy (SEM) images of the final product, iron-cobalt sulfide / nitrogen-doped carbon composite material, reveal that the product has a uniform polyhedral morphology with a particle size of approximately 200 nm. This stable structure is beneficial for improving its electrochemical stability. Figure 1 The image shown is a scanning electron microscope image of the final product, cobalt iron sulfide / nitrogen-doped carbon composite material, in Comparative Example 1.1. It exhibits a micron-sized hollow polyhedral morphology. This structure is prone to breakage and collapse during charge and discharge, ultimately affecting the electrochemical performance.

[0125] In summary, the preparation condition of the precursor ZIF-67 of the Fe / ZIF-67 of the present application is very simple, compared with the traditional solvothermal method, the present application can be quickly and continuously prepared, and the size of ZIF-67 can be reduced to nanoscale, and the structural stability is enhanced. In addition, under the nitrogen atmosphere, by calcining at a high temperature of 500 DEG C, the target iron cobalt sulfide / nitrogen-doped carbon composite material can be obtained, no other by-products are generated, and the preparation of the material has good economic and utilization benefits. The results of Table 1 show that when the amount of iron salt introduced is 0.1 mmol, the iron cobalt sulfide / nitrogen-doped carbon composite material as a negative material of sodium ion battery exhibits good electrochemical performance, so that it becomes an effective method worthy of consideration in the preparation of sodium ion battery materials.

[0126] The raw materials and equipment used in the present application are conventional raw materials and equipment in the art unless otherwise specified; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0127] The above is only a preferred embodiment of the present application, and does not limit the present application in any way, any simple modification, change and equivalent transformation of the above embodiment according to the technical essence of the present application still belong to the protection scope of the technical solution of the present application.

Claims

1. A method for preparing iron-cobalt sulfide / nitrogen-doped carbon composite based on a spray drying method, characterized by The method comprises the following steps: (1) mixing a 2-methylimidazole aqueous solution into a cobalt salt aqueous solution to obtain a mixed solution A; wherein the cobalt salt is one or more of cobalt sulfate, cobalt chloride and cobalt acetate; the molar ratio of 2-methylimidazole to cobalt salt is 1:(0.25-0.9); (2) The mixed solution A is subjected to spray drying treatment to obtain purple precursor powder B; the inlet air temperature of the spray drying treatment is 180-200 ℃, the outlet air temperature is 90-110 ℃, and the feeding rate is 5-15 mL / min -1 ; (3) dispersing the purple precursor powder B in an alcohol solvent, soaking and recrystallizing, then adding an iron salt for ion exchange, standing, centrifuging, washing and drying to obtain an intermediate product C, i.e. Fe / ZIF-67; wherein the mass ratio of the iron salt to the purple precursor powder B is (21-62):1; (4) performing gas-phase sulfuration of the intermediate product C and sulfur powder under an inert atmosphere to obtain a nanoscale and polyhedral iron cobalt sulfide / nitrogen-doped carbon composite material.

2. The method of claim 1, wherein: In step (1), the mixing is performed at room temperature for 5-30 min.

3. The method of claim 1, wherein: In step (3), the alcohol solvent is one or more of ethanol, methanol and isopropanol.

4. The method of claim 1, wherein: In step (3), the recrystallization is performed for 0.5-6 h.

5. The method of claim 1, wherein: In step (3), the iron salt is ferric chloride and / or ferric nitrate.

6. The method of claim 1, wherein: In step (3), the standing is performed at room temperature for 1-12 h.

7. The method of claim 1, wherein: In step (4), the mass ratio of the intermediate product C to sulfur powder is 1:(3-5).

8. The method of claim 1, wherein: In step (4), the gas-phase sulfuration is performed at a temperature of 300-500 ℃ for 1-3 h.

9. Use of the iron cobalt sulfide / nitrogen-doped carbon composite material prepared by the method of any one of claims 1-8 in preparation of a negative electrode material for a sodium ion battery.

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