A nitrogen-doped carbon composite cobalt diselenide nanocubic material, its preparation method, and its application in batteries.

Abstract

This invention provides a nitrogen-doped carbon composite cobalt-nickel diselenide nanocubic material, its preparation method, and its application in batteries. The invention involves dispersing cobalt salt, nickel salt, and hexadecyltrimethylammonium bromide in a solvent and mixing to obtain solution A; dispersing an organic ligand in the solvent and mixing to obtain solution B; pouring solution A into solution B and aging at room temperature to obtain a nanocubic precursor; then mixing with selenium powder and calcining under a protective atmosphere to obtain the CoNiSe2 / NC composite material. Compared with existing technologies, the synergistic effect of Co and Ni in this invention provides more active sites for the reaction and improves conductivity, resulting in a significant improvement in sodium-ion battery performance. Furthermore, the synthesis in this invention is performed at room temperature, simplifying the process; the porous structure design greatly improves the battery's cycle stability, extends its lifespan, and increases and stabilizes its capacity.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery composite material technology, specifically relating to a nitrogen-doped carbon composite cobalt nickel diselenide nanocubic material, its preparation method, and its application in batteries. The prepared binary metal selenide CoNiSe2 / NC is used as a negative electrode material for sodium-ion batteries. Background Technology

[0002] While clean energy sources such as geothermal, wind, and solar power can serve as alternatives, their intermittent nature prevents them from providing a stable and continuous energy supply, highlighting the need to find a substitute with consistent energy output. Lithium-ion batteries offer long lifespan and high rate capability, but resource scarcity and low safety performance hinder large-scale market production. Scientists are therefore searching for lithium alternatives. Sodium-ion batteries (SIBs) are considered a promising rechargeable battery due to their high capacity, abundant sodium content, low cost, and environmental friendliness.

[0003] Sulfonated iron oxides (SIBs) are becoming an important complement to lithium-ion batteries (LIBs), thanks to their wide energy storage capabilities based on the natural abundance and environmental friendliness of sodium resources. Monometallic selenides have been extensively studied and explored by researchers as anode materials for sodium-ion batteries. Binary metal selenides exhibit extraordinary improvements in electrochemical performance compared to monometallic selenides, but only a very small number of binary metal selenides have been studied for use in sodium-ion batteries.

[0004] Sodium-ion battery anode materials based on binary metal selenides have shown good electrochemical performance and should be explored as a promising sodium-ion anode material. Since binary metal selenides can be combined with a wide variety of metals or phases, and can be combined in many novel structures, developing other binary metal selenide combinations and using them as high-performance anode materials for SIBs, exploring sodium storage mechanisms, and performing composite modification of electrode materials are of significant research importance.

[0005] However, these binary metal selenium compounds inevitably face problems such as poor cycle stability and the need to improve high-rate performance. How to improve the performance of binary metal selenium compounds in sodium-ion batteries is a problem we need to address. Summary of the Invention

[0006] This invention provides a nitrogen-doped carbon composite cobalt nickel diselenide nanocube material and its preparation method. First, a nanocube precursor is prepared, and then it is calcined to transform it into CoNiSe2 / NC nanocubes with a three-dimensional porous structure. The preparation method is simple and efficient.

[0007] This invention also provides the application of nitrogen-doped carbon composite cobalt-nickel diselenide nanocube material in batteries. This nitrogen-doped carbon composite cobalt-nickel diselenide nanocube material is used as an active material to prepare the negative electrode of a sodium-ion battery, thereby preparing a sodium-ion battery. The CoNiSe2 / NC composite material prepared by this invention, its polycrystalline structure, and the increased conductivity after carbon coating can significantly improve cycle stability, lifespan, and battery capacity.

[0008] The specific technical solution of this invention is as follows:

[0009] A method for preparing a nitrogen-doped carbon composite cobalt-nickel diselenide nanocubic material includes the following steps:

[0010] 1) Disperse cobalt salt, nickel salt and hexadecyltrimethylammonium bromide in a solvent and mix well to obtain solution A; disperse organic ligand in a solvent and mix well to obtain solution B; add solution A dropwise into solution B and age at room temperature to obtain nanocube precursor;

[0011] 2) The nanocube precursor and selenium powder were mixed and calcined under a protective atmosphere to obtain the CoNiSe2 / NC composite material.

[0012] In step 1), the molar ratio of the cobalt source to the nickel source is 2:1; the molar ratio of the nickel source to hexadecyltrimethylammonium bromide is 45-55:1; the cobalt source is a soluble cobalt salt, preferably Co(NO3)2·6H2O; the nickel source is a soluble nickel source, preferably Ni(NO3)2·6H2O; the concentration of the cobalt source in solution A is 0.05-0.2 mol / L.

[0013] In step 1), the molar ratio of the nickel source to the organic ligand is 1:100-130;

[0014] In step 1), the organic ligand is 2-methylimidazole; in solution B, the concentration of 2-methylimidazole is 0.79 mol / L;

[0015] In step 1), the solvent for both solution A and solution B is deionized water;

[0016] In step 1), the droplets are added drop by drop, with the dropping rate controlled at one drop per second. The dropping rate affects the crystallinity and defect level of the crystal, thus affecting the physicochemical properties of the material, such as specific surface area and porosity. A suitable dropping rate helps to form a regular polyhedral structure.

[0017] In step 1), the room temperature aging process takes 24 hours.

[0018] After aging at room temperature in step 1), the precursor is centrifuged, washed, and dried to obtain a nanocube precursor; specifically: washed with water 3-4 times, washed with ethanol 1-2 times, centrifuged, and dried at 60℃ for 8 hours.

[0019] The nanocube precursor prepared in step 1) is a three-dimensional porous cube with a size of 200-500 nm.

[0020] Preferably, the preparation method of the nanocube precursor in step 1) is as follows: 2 mmol of Co(NO3)2·6H2O, 1 mmol of Ni(NO3)2·6H2O, and 0.022 mmol of CTAB are dispersed in 20 mL of deionized water and stirred vigorously to form solution A. 0.11 mol of 2-methylimidazole is dispersed in 140 mL of deionized water and stirred vigorously to form solution B. Solution A is quickly poured into solution B, and after stirring for 30 s, the contact between the solute and the solution is increased to ensure thorough mixing. After standing and aging at room temperature for 24 h, the product nanocube precursor is obtained by washing and centrifugation.

[0021] The protective atmosphere described in step 2) is a hydrogen-argon mixture, consisting of 95% argon and 5% hydrogen by volume.

[0022] Step 2) The mass ratio of the nanocube precursor to selenium powder is 1:5; the calcination conditions are 600-700℃ for 2 hours, with 700℃ being the preferred temperature.

[0023] Step 1) Preparation of the nanocube precursor CoNi-MOF: The synthesis of CoNi-MOF involves metal ions (Co... 2+ and Ni 2+) The process of self-assembly between metal ions and organic ligands through coordination bonds. In this process, metal ions and organic ligands first form coordination bonds, and then connect to form a crystalline network with a specific topological structure, directly forming CoNi-MOF crystals with specific crystal forms and structures. When the concentrations of reactants such as cobalt salts and nickel salts are within a specific range, the distribution and interaction of ions in the solution are relatively ideal, providing a suitable material basis for the uniform growth of crystals in all directions, which helps to form cubic crystals. Solvents with moderate polarity may allow ions to be uniformly dispersed in the solution, and their interaction with the crystal surface can promote the growth of crystals into a cubic morphology. The long-chain alkyl structure of CTAB can interact with metal ions and organic ligands during the synthesis process, guiding them to arrange and assemble in a specific way, promoting the formation of CoNi-MOFs with specific topological structures and pore sizes. At the same time, it can reduce the surface tension of the synthesis system, allowing metal ions and organic ligands to be better dispersed in the solution, preventing them from agglomerating, and helping to form uniform CoNi-MOFs. The 2-methylimidazolium molecule contains carbon elements, which will undergo a pyrolysis reaction under the high-temperature conditions of synthesizing CoNiSe2. Chemical bonds in the molecule break, generating small carbon-containing molecular fragments, such as hydrocarbon radicals. These fragments further polymerize and condense, gradually forming amorphous carbon or carbon with a certain degree of graphitization as the reaction proceeds, eventually depositing on or around the CoNiSe2 surface to form a carbon layer. Under the influence of high temperature and the reaction system, some nitrogen atoms from 2-methylimidazole enter the CoNiSe2 lattice. Due to the similarity in atomic radius and electronic structure between nitrogen atoms and atoms such as carbon and sulfur, nitrogen atoms can replace some sulfur atoms in the lattice or occupy interstitial positions, thus achieving N doping. In selenization, high-temperature calcination provides the energy required for crystal growth. Initially, the CoNiSe2 generated by the reaction may exist in the form of tiny crystal nuclei. As calcination proceeds, these nuclei continuously absorb surrounding cobalt, nickel, and selenium atoms, growing according to certain crystal structure rules. Different conditions such as temperature and selenium powder dosage affect the crystal growth rate and the final crystal structure, such as crystal size and phase composition.

[0024] The present invention provides a nitrogen-doped carbon composite cobalt nickel diselenide nanocube material, which is prepared by the above method. The nitrogen-doped carbon composite cobalt nickel diselenide nanocube material is referred to as CoNiSe2 / NC composite material, which has a three-dimensional porous cubic structure with a size of 200-500 nm.

[0025] In the preparation method of this invention, the influence of the cobalt-nickel ratio is significant: when the metal ratio changes, the crystal structure may undergo a phase transition or a change in lattice parameters. This is particularly relevant in the preparation of cobalt-nickel selenide (Co... x Ni 1-xWhen selenium (Se2) is used, the crystal structure gradually transforms from a cubic phase to a hexagonal phase as the cobalt-nickel ratio changes. This change in crystal structure directly leads to a change in the morphology of the material, transforming it from nanoparticles to nanosheets. Therefore, this invention controls an appropriate cobalt-nickel ratio. The effect of selenium powder dosage on morphology: Some metal atoms in the system cannot completely combine with selenium, potentially forming impurity phases such as elemental metals or other low-valence selenides. The presence of these impurity phases will damage the crystal structure and morphology of the product, resulting in a rough surface and uneven structure. Furthermore, due to incomplete grain growth, the specific surface area is large, and the surface energy is high. To reduce surface energy, particles are more likely to attract each other and agglomerate, leading to severe agglomeration, poor dispersibility, and an inability to form a regular morphology. Therefore, this invention controls an appropriate selenium dosage. Selenization temperature: When selenization is performed at a lower temperature, the phase transformation may be incomplete, or only some metastable phases may be formed. The crystal structure and morphology of these metastable phases may differ from those of the stable phases, and they may change during subsequent processing, leading to unstable or undesirable morphology of the final product. As the selenization temperature increases, the thermal motion of atoms intensifies, which can overcome the energy barrier in the phase transformation process, allowing the crystal structure to smoothly transform from one phase state to another more stable phase state, thereby obtaining a stable phase product with a specific morphology. Therefore, this invention controls the appropriate selenization calcination temperature.

[0026] Compared to traditional solvothermal synthesis methods, the room-temperature synthesis method of this invention has a simpler operation process, higher safety performance, and can reduce energy consumption and lower costs. Although the thermal motion speed of molecules is slower at room temperature than at high temperatures, this reaction rate is actually more conducive to sufficient time for self-assembly between cobalt ions and ligands for ZIF-67. The lower temperature can reduce the nucleation rate, allowing for the formation of fewer but uniformly sized nuclei in the system. The slower growth rate helps the crystal grow according to a specific crystal structure, reducing the introduction of defects and impurities, and obtaining higher quality products. The three-dimensional network structure of ZIF-67 contains certain voids and channels. The size and chemical environment of these channels allow Ni... + Under certain conditions, it can enter the electrolyte to form a bimetallic MOF, which has a high specific surface area and a unique pore structure that facilitates the rapid adsorption and desorption of electrolyte ions. Ni + The presence of sodium ions can provide additional redox active sites, improving electrochemical performance. Therefore, the synthesized cubic three-dimensional porous structure not only increases the specific surface area but also facilitates the insertion / extraction of sodium ions, thereby improving battery cycle stability.

[0027] The CoNiSe2 / NC composite material prepared by this invention, along with its polycrystalline structure and increased conductivity after carbon coating, can significantly improve cycle stability, lifespan, and battery capacity. Its three-dimensional porous structure design enables it to withstand high current and long-term cycling, reducing the loss of active material during charging and discharging, buffering volume changes during charging and discharging, reducing the shedding of active material during cycling, and facilitating sodium formation / desodium formation during the reaction process. When applied as a negative electrode material for sodium-ion batteries, this material exhibits advantages such as good cycle performance and high energy density.

[0028] This invention provides the application of a nitrogen-doped carbon composite cobalt nickel diselenide nanocube material in batteries, which is used as an active material to prepare the negative electrode of a sodium-ion battery, thereby preparing a sodium-ion battery.

[0029] Specifically, the nitrogen-doped carbon composite cobalt nickel diselenide nanocube material is used as the active material. It is mixed uniformly with conductive carbon black and polyvinylidene fluoride 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 is coated onto copper foil using a coater and placed in a vacuum drying oven at 60-80°C for 12-24 hours. After drying, it is pressed into sheets using a tablet press and then cut into small circular electrode sheets using a cutting machine. The electrode sheets are then assembled into button batteries in a glove box filled with high-purity argon gas and with water and oxygen values ​​≤0.01ppm. The electrolyte is NaPF6+DEGDME, the sodium sheet has a purity of Na≥99.99%, a thickness of 0.5mm, and is rolled and then cut to the size of the electrode sheet.

[0030] 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 6 to 12 hours.

[0031] Transition metal selenides are considered excellent anode materials for sodium-ion batteries (SIBs) due to their stable structure and high theoretical capacity. However, the internal strain caused by sodiumization of transition metal selenides makes sodium-ion batteries unstable at high current densities. This invention improves the conductivity of binary metal selenides by doping with carbon and enhances the stability of the battery during cycling at high current densities by forming a three-dimensional porous cubic structure by doping with another metal element. The nitrogen-doped carbon composite cobalt-nickel diselenide nanocubic material provided by this invention exhibits good cycle stability and high rate performance.

[0032] The CoNiSe2 / NC material provided by this invention, due to the interaction of two metals, can provide more active sites during charge and discharge. The CoNiSe2 / NC composite material, its polycrystalline structure, and the increased conductivity after carbon coating can significantly improve cycle stability, lifespan, and battery capacity. Its three-dimensional porous structure design allows it to withstand high current and long-term cycling, reducing the loss of active material during charge and discharge, buffering volume changes during charge and discharge, reducing the shedding of active material during cycling, and facilitating sodium formation / desodium formation during the reaction process, thereby improving the electrochemical performance of the anode material. Therefore, constructing a CoNiSe2 / NC polycrystalline structure is expected to accelerate reaction kinetics. The multi-component synergistic effect of this invention promotes rapid charge transfer, resulting in excellent rate performance and cycle performance. The interface effect of the binary metal selenide can introduce an internal electric field to improve reaction kinetics, while providing abundant electrochemical reaction sites, thereby improving its reversible capacity and cycle stability.

[0033] Compared with existing technologies, this invention synthesizes a nitrogen-doped carbon composite cobalt-nickel diselenide nanocubic material at room temperature via a simple sedimentation method, in which the binary metal selenide CoNiSe2 is encapsulated within a carbon layer. The synergistic effect of Co and Ni provides more active sites for the reaction and improves conductivity, significantly enhancing the performance of sodium-ion batteries. Furthermore, the three-dimensional porous structure creates buffer spaces to mitigate volume changes. Benefiting from these advantages, the prepared CoNiSe2 / NC composite material exhibits high conductivity at 1 Ag... -1 After 800 cycles at the current density, the display showed 447.5 mAh g. -1 The high reversible capacity, high specific capacity, stable cycle performance, and robust rate performance demonstrate that CoNiSe2 / NC is an excellent and promising SIB anode material. Furthermore, the synthesis in this invention is performed at room temperature, under simple conditions, easy to operate, and with inexpensive and readily available cobalt and nickel sources. The porous structure design significantly improves the battery's cycle stability, extends its lifespan, and increases and stabilizes its capacity. Attached Figure Description

[0034] Figure 1 SEM image of the precursor nanocube prepared in Example 1;

[0035] Figure 2 SEM image of the CoNiSe2 / NC three-dimensional porous cube prepared in Example 1;

[0036] Figure 3 TEM image of the CoNiSe2 / NC three-dimensional porous cube prepared in Example 1;

[0037] Figure 4XRD pattern of the CoNiSe2 / NC three-dimensional porous cube prepared in Example 1;

[0038] Figure 5 Mapping diagram of the three-dimensional porous cube of CoNiSe2 / NC prepared in Example 1;

[0039] Figure 6 HRTEM of the three-dimensional porous cubic CoNiSe2 / NC prepared in Example 1;

[0040] Figure 7 SEM image of CoNiSe2 / NC prepared in Example 2;

[0041] Figure 8 SEM image of CoNiSe2 / NC prepared in Example 3;

[0042] Figure 9 SEM image of CoNiSe2 / NC prepared in Example 4;

[0043] Figure 10 SEM image of CoNiSe2 / NC prepared in Example 5;

[0044] Figure 11 SEM image of CoNiSe2 / NC prepared in Example 6;

[0045] Figure 12 SEM image of CoNiSe2 / NC prepared in Example 7;

[0046] Figure 13 SEM image of CoNiSe2 / NC prepared in Example 8;

[0047] Figure 14 SEM image of CoNiSe2 / NC prepared in Example 9;

[0048] Figure 15 SEM image of CoNiSe2 / NC prepared in Example 10;

[0049] Figure 16 SEM image of CoNiSe2 / NC prepared in Example 11;

[0050] Figure 17 The three-dimensional porous cubic CoNiSe2 / NC material prepared in Example 1 was used as a negative electrode material for a sodium-ion battery in 0.2 Ag. -1 Test graph of charge-discharge curves at current density;

[0051] Figure 18The three-dimensional porous cubic CoNiSe2 / NC material prepared in Example 1 was used as a negative electrode material for a sodium-ion battery in 0.2 Ag. -1 Cyclic performance test graph at current density;

[0052] Figure 19 The three-dimensional porous cubic material of CoNiSe2 / NC prepared in Example 1 was used as a negative electrode material for lithium-ion batteries in 1Ag. -1 Test graph of charge-discharge curves at current density;

[0053] Figure 20 The three-dimensional porous cubic material of CoNiSe2 / NC prepared in Example 1 was used as a negative electrode material for lithium-ion batteries in 1Ag. -1 Cyclic performance test graph at current density;

[0054] Figure 21 The three-dimensional porous cubic material of CoNiSe2 / NC prepared in Example 1 is shown in the test graph of its cycling performance as a lithium-ion battery anode material at current densities of 0.1, 0.2, 0.5, 1, 3, 5, and 10 A. Detailed Implementation

[0055] 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.

[0056] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0057] 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.

[0058] Example 1

[0059] A method for preparing a nitrogen-doped carbon composite cobalt-nickel diselenide nanocubic material includes the following steps:

[0060] 1) Preparation of nanocube precursors:

[0061] 0.592 g of Co(NO3)2·6H2O, 0.296 g of Ni(NO3)2·6H2O, and 0.008 g of CTAB were ultrasonically dispersed in a beaker containing 20 mL of deionized water to form a homogeneous solution, denoted as solution A. 9.08 g of 2-methylimidazole was weighed and added to a beaker containing 140 mL of deionized water, and stirred vigorously to form a homogeneous solution, denoted as solution B. Solution A was poured into solution B and magnetically stirred for 30 s to ensure thorough mixing. The mixture was then aged at room temperature for 24 h. Afterward, it was washed three times with deionized water by centrifugation, twice with ethanol, and vacuum dried at 60 °C for 8 h. The precursor precipitate was collected. Its SEM image is shown below. Figure 1 As shown in the figure, it can be seen that it is a nanocube with a size of 200-500nm.

[0062] 2) Preparation of CoNiSe2 / NC:

[0063] 0.1g of the precursor and selenium powder were weighed and placed in two ceramic boats at a mass ratio of 1:5. The ceramic boat containing the selenium powder was placed at the upwind end and calcined in a mixed gas atmosphere. The heating rate was 4℃ / min, and the temperature was raised to 700℃ for 2 hours. The final product CoNiSe2 / NC was obtained, and its SEM image is shown below. Figure 2 As shown in the image, it can be seen that it is a porous nanocube with a size of 200-500 nm. TEM image as follows. Figure 3 As shown.

[0064] The XRD pattern of the CoNiSe2 / NC composite material obtained in this embodiment is as follows: Figure 4 As shown, the obtained product is CoNiSe2 / NC. Figure 5 The diagram shows the mapping of the material, which indicates that the elements in the composite material are evenly distributed. Figure 6 The image shows the HRTEM image of this material, and the C layer in the image clearly demonstrates successful C doping.

[0065] Example 2 (as a comparison)

[0066] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0067] 1) Preparation of nanocube precursors:

[0068] Take respectively 0.592gCo(NO3)2·6H2O, 0.592g Ni(NO3)2·6H2O, and 0.008g CTAB were ultrasonically dispersed in a beaker containing 20mL of deionized water to form a homogeneous solution, denoted as solution A. 9.08g 2-methylimidazole was weighed and added to a beaker containing 140mL of deionized water, and stirred vigorously to form a homogeneous solution, denoted as solution B. Solution A was poured into solution B and magnetically stirred for 30s to ensure thorough mixing. The mixture was then aged at room temperature for 24h. Afterward, it was washed three times with deionized water by centrifugation, twice with ethanol, and vacuum dried at 60℃ for 8h. The precursor precipitate was collected.

[0069] 2) The preparation of CoNiSe2 / NC was the same as in Example 1. The SEM images of the products prepared in Example 2 are shown below. Figure 7 As shown in the figure, it can be seen that it is spherical with a size of 400-600 nm. After changing the ratio of cobalt salt and nickel salt, the morphology changed from cubic agglomeration to spherical.

[0070] Example 3 (as a comparison)

[0071] A method for preparing nitrogen-nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0072] 1) Preparation of nanocube precursors:

[0073] Take respectively 0.888g Co(NO3)2·6H2O, 0.296g Ni(NO3)2·6H2O, and 0.008g CTAB were ultrasonically dispersed in a beaker containing 20mL of deionized water to form a homogeneous solution, denoted as solution A. 9.08g 2-methylimidazole was weighed and added to a beaker containing 140mL of deionized water, and stirred vigorously to form a homogeneous solution, denoted as solution B. Solution A was poured into solution B and magnetically stirred for 30s to ensure thorough mixing. The mixture was then aged at room temperature for 24h. Afterward, it was washed three times with deionized water by centrifugation, twice with ethanol, and vacuum dried at 60℃ for 8h. The precursor precipitate was collected.

[0074] 2) The preparation of CoNiSe2 / NC was the same as in Example 1; the SEM image of the product prepared in Example 3 is shown below. Figure 8 As shown in the figure, there is no obvious shape.

[0075] Example 4 (as a comparison)

[0076] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0077] 1) Preparation of nanocube precursors:

[0078] Take respectively 1.184gCo(NO3)2·6H2O, 0.296g Ni(NO3)2·6H2O, and 0.008g CTAB were ultrasonically dispersed in a beaker containing 20mL of deionized water to form a homogeneous solution, denoted as solution A. 9.08g 2-methylimidazole was weighed and added to a beaker containing 140mL of deionized water, and stirred vigorously to form a homogeneous solution, denoted as solution B. Solution A was poured into solution B and magnetically stirred for 30s to ensure thorough mixing. The mixture was then aged at room temperature for 24h. Afterward, it was washed three times with deionized water by centrifugation, twice with ethanol, and vacuum dried at 60℃ for 8h. The precursor precipitate was collected.

[0079] 2) The preparation of CoNiSe2 / NC was the same as in Example 1. SEM images of the products prepared in Example 4 are shown below. Figure 9 As shown in the figure, there is no obvious cubic morphology when the cobalt-nickel ratio is 4:1.

[0080] Example 5 (as a comparison)

[0081] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0082] 1) The preparation of the nanocubic precursor is the same as in Example 1;

[0083] 2) Preparation of CoNiSe2 / NC:

[0084] Weigh 0.1g of the precursor and selenium powder according to the mass ratio 1:1 The sample was placed in two separate ceramic boats, with the boat containing selenium powder positioned upwind. Calcination was carried out in a mixed gas atmosphere, with a heating rate of 4℃ / min to a calcination temperature of 700℃, and a calcination time of 2 hours. The final product, CoNiSe2 / NC, was obtained, and its SEM image is shown below. Figure 10 As shown in the figure, it can be seen that the product was not completely selenized due to insufficient selenium powder, and the product formed an irregularly sized nanosphere structure.

[0085] Example 6 (as a comparison)

[0086] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0087] 1) The preparation of the nanocubic precursor is the same as in Example 1;

[0088] 2) Preparation of CoNiSe2 / NC:

[0089] Weigh 0.1g of the precursor and selenium powder according to the mass ratio 1:2The sample was placed in two separate ceramic boats, with the boat containing selenium powder positioned upwind. Calcination was carried out in a mixed gas atmosphere, with a heating rate of 4℃ / min to a calcination temperature of 700℃, and a calcination time of 2 hours. The final product, CoNiSe2 / NC, was obtained, and its SEM image is shown below. Figure 11 As shown in the figure, the insufficient amount of selenium powder resulted in incomplete selenization of the product, leading to an irregularly sized nanosphere structure. Selenium atoms participate in the formation of chemical bonds in the CoNiSe2 crystal; insufficient selenium powder causes incomplete or uneven bond formation. This affects the internal forces and the directionality of crystal growth, preventing the crystal from growing into a cubic shape along a specific crystal axis. Instead, the growth is more balanced in all directions, tending towards a spherical shape.

[0090] Example 7 (as a comparison)

[0091] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0092] 1) The preparation of the nanocubic precursor is the same as in Example 1;

[0093] 2) Preparation of CoNiSe2 / NC:

[0094] Weigh 0.1g of the precursor and selenium powder according to the mass ratio 1:3 The sample was placed in two separate ceramic boats, with the boat containing selenium powder positioned upwind. Calcination was carried out in a mixed gas atmosphere, with a heating rate of 4℃ / min to a calcination temperature of 700℃, and a calcination time of 2 hours. The final product, CoNiSe2 / NC, was obtained, and its SEM image is shown below. Figure 12 As shown in the figure, with the continuous increase of selenium powder, the morphology of the product gradually tends towards a cubic structure. However, due to insufficient selenium powder, the product remains an irregular nanosphere structure. At high temperatures, selenium powder transforms into selenium atoms to participate in the formation of chemical bonds in the CoNiSe2 / NC crystal. Insufficient selenium powder leads to incomplete or uneven formation of chemical bonds. This affects the internal forces and the directionality of crystal growth, preventing the crystal from growing into a cubic shape along a specific crystal axis. Instead, the growth is more balanced in all directions, tending towards a spherical shape.

[0095] Example 8 (as a comparison)

[0096] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0097] 1) The preparation of the nanocubic precursor is the same as in Example 1;

[0098] 2) Preparation of CoNiSe2 / NC:

[0099] Weigh 0.1g of the precursor and selenium powder according to the mass ratio 1:4The sample was placed in two separate ceramic boats, with the boat containing selenium powder positioned upwind. Calcination was carried out in a mixed gas atmosphere, with a heating rate of 4℃ / min to a calcination temperature of 700℃, and a calcination time of 2 hours. The final product, CoNiSe2 / NC, was obtained, and its SEM image is shown below. Figure 13 As shown in the figure, some products have a cubic structure, while others are not selenized and are irregularly shaped spheres.

[0100] Example 9 (as a comparison)

[0101] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0102] 1) The preparation of the nanocubic precursor is the same as in Example 1;

[0103] 2) Preparation of CoNiSe2 / NC:

[0104] Weigh 0.1g of the precursor and selenium powder into two ceramic boats at a mass ratio of 1:5. Place the boat containing the selenium powder at the upwind end and calcine it in a mixed gas atmosphere. The temperature is increased at a rate of 4℃ / min until the calcination temperature is reached. 400℃， The calcination time was 2 hours, and the final product CoNiSe2 / NC was obtained. Its SEM image is shown below. Figure 14 As shown, due to the low calcination temperature, the product was not completely calcined and had no obvious structure.

[0105] Example 10 (as a comparison)

[0106] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0107] 1) The preparation of the nanocubic precursor is the same as in Example 1;

[0108] 2) Preparation of CoNiSe2 / NC:

[0109] Weigh 0.1g of the precursor and selenium powder into two ceramic boats at a mass ratio of 1:5. Place the boat containing the selenium powder at the upwind end and calcine it in a mixed gas atmosphere. The temperature is increased at a rate of 4℃ / min until the calcination temperature is reached. 500℃， The calcination time was 2 hours, and the final product CoNiSe2 / NC was obtained. Its SEM image is shown below. Figure 15 As shown in the figure, its structure is an irregular nanosphere structure.

[0110] Example 11

[0111] A method for preparing nitrogen-doped carbon composite cobalt diselenide nickel includes the following steps:

[0112] 1) The preparation of the nanocubic precursor is the same as in Example 1;

[0113] 2) Preparation of CoNiSe2 / NC:

[0114] 0.1 g of the precursor and selenium powder were weighed and placed in two ceramic boats at a mass ratio of 1:5. The ceramic boat containing the selenium powder was placed at the upwind end and calcined in a mixed gas atmosphere. The temperature was increased at a rate of 4 °C / min to the calcination temperature of 600 °C, and the calcination time was 2 h. The final product CoNiSe2 / NC was obtained, and its SEM image is shown below. Figure 16 As shown, with the continuous increase of calcination temperature, the product transforms into a cubic structure. It can be seen from the figure that some products have a cubic structure.

[0115] Example 12

[0116] The application of a nitrogen-doped carbon composite cobalt-nickel diselenide nanocube material in batteries, wherein the nitrogen-doped carbon composite cobalt-nickel diselenide nanocube material is used as an active material to prepare the negative electrode of a sodium-ion battery, thereby preparing a sodium-ion battery. Specifically:

[0117] The product of Example 1 was used to prepare sodium batteries as anode materials for sodium-ion batteries.

[0118] The cobalt-nickel diselenide nitrogen-doped carbon composite material was used as the active material. It was mixed with conductive carbon black and polyvinylidene fluoride in a ratio of 8:1:1 and then magnetically stirred for 8 hours to disperse it evenly in 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 tablets using a tablet press and then cut into small circular electrode sheets using a cutting machine. The electrode sheets were assembled into button batteries in a glove box filled with high-purity argon gas and with water and oxygen values ​​≤0.01ppm. The electrolyte was NaPF6+DEGDME, the sodium sheet purity was Na≥99.99%, the thickness was 0.5mm, and it was rolled and cut to the size of the electrode sheet.

[0119] The specific method for assembling the battery is as follows: Add one drop of electrolyte to the positive electrode shell, then place the electrode plate. Next, add one drop of electrolyte and place the glass fiber. Add three drops of electrolyte to the glass fiber and place a sodium sheet as the counter electrode. Then, place two pieces of nickel foam, add four more drops of electrolyte, cover with the negative electrode shell, and use a hydraulic press to press and seal the battery. Let it stand for 12 hours.

[0120] Specific testing process: After assembling the sodium-ion half-cell, set the steps on the Xinwei tester, first discharge with constant current to 0.01V, then charge with constant current to 3V, and repeat this cycle a certain number of times.

[0121] Then, the cycle performance and charge / discharge performance of the coin cell were tested at currents of 0.2A and 1A, and the results are as follows: Figure 17 , Figure 18 , Figure 19 , Figure 20As shown in the figure, the battery exhibits a relatively stable charge-discharge platform and cycle performance. The rate capability of the battery was tested at current densities of 0.1, 0.2, 0.5, 1, 3, 5, and 10 A. Figure 21 shows that the material has good rate performance and can withstand larger currents.

[0122] This invention develops anode materials with unique structures using a practical and direct SIB (Synthetic Induction Block) method. Electrode materials with nanostructures are promising candidates. Bimetallic selenides, through the synergistic effect between the two metals, add more active sites for redox reactions, thereby improving the electrochemical performance of the electrode. Employing bimetallic selenides and effectively designing a three-dimensional porous structure effectively mitigates volume expansion and prevents structural pulverization, thus preventing structural collapse of the electrode material. Furthermore, compositing with conductive carbon species effectively reduces the negative impact of poor conductivity. A well-structured carbon-based composite material can improve electronic conductivity and buffer internal stress, which is beneficial to the electrochemical performance of SIBs. Therefore, combining nanostructured CoNiSe2 three-dimensional porous cubes with nitrogen-doped carbon layers is an effective strategy for achieving high-performance SIBs.

[0123] The data underlined above do not meet the requirements of this invention.

[0124] 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 method for preparing a nitrogen-doped carbon composite cobalt-nickel diselenide nanocubic material, characterized in that, The preparation method includes the following steps: 1) Disperse cobalt salt, nickel salt and hexadecyltrimethylammonium bromide in a solvent and mix well to obtain solution A; disperse organic ligand in a solvent and mix well to obtain solution B; pour solution A into solution B and age at room temperature to obtain nanocube precursor; 2) The nanocube precursor and selenium powder were mixed and calcined under a protective atmosphere to obtain the CoNiSe2 / NC composite material; In step 1), the molar ratio of the cobalt source to the nickel source is 2:1; the organic ligand is 2-methylimidazole; Step 2) The mass ratio of the nanocube precursor to selenium powder is 1:5; the calcination conditions are 600-700℃ for 2 hours.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the nickel source to cetyltrimethylammonium bromide is 45-55:

1.

3. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of the nickel source to the organic ligand is 1:100-130.

4. The preparation method according to claim 1 or 2, characterized in that, In step 1), the room temperature aging process takes 24 hours.

5. A nitrogen-doped carbon composite cobalt diselenide nanocube material prepared by the preparation method according to any one of claims 1-4, wherein the nitrogen-doped carbon composite cobalt diselenide nanocube material is a three-dimensional porous cubic structure with a size of 200-500 nm.

6. The application of the nitrogen-doped carbon composite cobalt diselenide nickel nanocubic material as described in claim 5 in a battery.

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