Nitrogen-doped carbon composite cobalt-nickel diselenide nanocube material and preparation method and application thereof in battery

Abstract

The invention provides a nitrogen-doped carbon composite cobalt nickel diselenide nanocube material and a preparation method and application thereof in a battery. Cobalt salt, nickel salt and hexadecyl trimethyl ammonium bromide are dispersed in a solvent and evenly mixed, and a solution A is obtained; dispersing an organic ligand in a solvent, and uniformly mixing to obtain a solution B; pouring the solution A into the solution B, and aging at room temperature to obtain a nanocube precursor; and mixing the CoNiSe2 / NC composite material with selenium powder, and calcining in a protective atmosphere to obtain the CoNiSe2 / NC composite material. Compared with the prior art, due to the mutual synergistic effect of Co and Ni, more active sites are provided for the reaction, and the conductivity is improved, so that the performance of the sodium-ion battery is remarkably improved. In addition, synthesis is carried out at room temperature, and conditions are simple; the design of the porous structure greatly improves the cycling stability of the battery, prolongs the service life, and increases and stabilizes the capacity.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials for sodium ion batteries, and specifically relates to a nitrogen-doped carbon composite cobalt nickel diselenide nanocube material and a preparation method thereof and application in batteries, and the prepared binary metal selenide CoNiSe 2 / NC is used as a negative electrode material for sodium ion batteries to make sodium ion batteries. Background Art

[0002] Although clean energy sources such as geothermal, wind, and solar energy can be used as alternatives, they cannot provide stable and lasting energy due to their intermittent shortcomings, indicating the need to find an alternative with stable energy output. Lithium-ion batteries have long life and high rate performance, but their resource shortage and low safety performance cannot meet the market's large-scale production. Scientists are looking for alternatives to lithium. Sodium-ion batteries (SIBs) are considered a promising secondary battery due to their high capacity, rich sodium content, low cost, and environmental protection.

[0003] SIBs are becoming an important supplement to lithium-ion batteries (LIBs), thanks to their extensive energy storage based on the natural abundance of sodium resources and environmental friendliness. Monometallic selenides have been extensively studied and explored as anode materials for sodium-ion batteries. Binary metal selenides have shown extraordinary improvements in electrochemical performance compared to monometallic selenides, but only very few binary metal selenides have been studied for use in sodium-ion batteries.

[0004] The 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 variety of metals or phases and can be combined in many novel structures, it is of great research significance to develop other binary metal selenide combinations and use them as high-performance anode materials for SIBs, explore the sodium storage mechanism, and composite modification of electrode materials.

[0005] However, this type of binary metal selenide material inevitably faces the problem of poor cycle stability and the need to improve high-rate performance. How to improve the performance of binary metal selenide materials for sodium-ion batteries is a problem that needs to be solved. Summary of the invention

[0006] The present invention provides a nitrogen-doped carbon composite cobalt nickel diselenide nanocube material and a preparation method thereof, first preparing a nanocube precursor, and then calcining it to convert it into CoNiSe with a three-dimensional porous structure. 2 / NC nanocubes, the preparation method is simple and efficient.

[0007] The present invention also provides an application of a nitrogen-doped carbon composite cobalt nickel diselenide nanocube material in a battery, wherein the nitrogen-doped carbon composite cobalt nickel diselenide nanocube material is used as an active material to prepare a negative electrode of a sodium ion battery, thereby preparing a sodium ion battery. 2 / NC composite materials and their polycrystalline structure and increased conductivity after carbon coating can greatly improve the cycle stability, service life and battery capacity.

[0008] The specific technical solutions of the present invention are as follows:

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

[0010] 1) Dispersing cobalt salt, nickel salt and hexadecyltrimethylammonium bromide in a solvent and mixing them to obtain solution A; dispersing an organic ligand in a solvent and mixing them to obtain solution B; dripping solution A into solution B drop by drop and aging at room temperature to obtain a nanocube precursor;

[0011] 2) Mix the nanocube precursor and selenium powder and calcine under a protective atmosphere to obtain CoNiSe 2 / NC composite materials.

[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(NO 3 ) 2 6H 2 O; the nickel source is a soluble nickel source, preferably Ni(NO 3 ) 2 6H 2 O; 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 solvents of solution A and solution B are both deionized water;

[0016] In step 1), the dripping is controlled to be one drop per second. The dripping speed affects the crystallinity and defect degree of the crystal, and further affects the physical and chemical properties of the material such as specific surface area and porosity. A suitable dripping speed helps to form a regular polyhedral structure.

[0017] In step 1), the room temperature aging time is 24 hours;

[0018] In step 1), after aging at room temperature, centrifugation, washing, and drying are performed to obtain a nanocube precursor; specifically, washing with water 3 to 4 times, washing with ethanol 1 to 2 times, centrifugation, and drying at 60° C. for 8 hours;

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

[0020] Preferably, the preparation method of the nanocube precursor in step 1) is: 2 mmol of Co(NO 3 ) 2 6H 2 O, 1mmol Ni(NO 3 ) 2 6H 2 O, 0.022mmol CTAB was dispersed in 20mL deionized water and stirred vigorously to form solution A, 0.11mol 2-methylimidazole was dispersed in 140mL deionized water and stirred vigorously to form solution B, solution A was quickly poured into solution B, and after stirring for 30s, the contact between the solute and the solution was increased to make them fully mixed, and then the product nanocube precursor was washed and centrifuged after standing and aging at room temperature for 24h.

[0021] The protective atmosphere in step 2) is a hydrogen-argon mixture, which is 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 condition is 600-700°C for 2h, preferably 700°C.

[0023] Step 1) Preparation of nanocube precursor CoNi-MOF synthesis is metal ion (Co 2+ and Ni 2+) and organic ligands through coordination bonds to self-assemble. 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 in a specific range, the distribution and interaction of ions in the solution are ideal, which can provide a suitable material basis for the uniform growth of crystals in all directions and help to form cubes. Solvents with moderate polarity may make ions evenly dispersed in the solution, and the interaction with the crystal surface can promote the growth of crystals into a cubic form. 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 manner, promoting the formation of CoNi-MOF with a specific topological structure and pore size, and at the same time reducing the surface tension of the synthetic system, so that metal ions and organic ligands are better dispersed in the solution, preventing them from agglomerating, and helping to form a uniform CoNi-MOF. 2-Methylimidazole molecules contain carbon elements, which are used in the synthesis of CoNiSe 2 Under high temperature conditions, pyrolysis occurs. The chemical bonds in the molecules break, generating small molecular fragments containing carbon, such as hydrocarbon free radicals. These small molecular fragments further polymerize and condense, gradually forming amorphous carbon or carbon with a certain degree of graphitization as the reaction proceeds, and finally deposited on the CoNiSe 2 Under the action of high temperature and reaction system, some nitrogen atoms in 2-methylimidazole will enter CoNiSe 2 Since nitrogen atoms have similar atomic radius and electronic structure to carbon, sulfur and other atoms, nitrogen atoms can replace some sulfur atoms in the lattice or occupy interstitial positions in the lattice, thereby achieving N doping. In selenization, high-temperature calcination provides the energy required for crystal growth. Initially, the CoNiSe generated by the reaction 2 It may exist in the form of tiny crystal nuclei. As calcination proceeds, these crystal nuclei continuously absorb surrounding cobalt, nickel and selenium atoms and grow according to certain crystal structure rules. Different conditions such as temperature and amount of selenium powder will affect the growth rate of the crystal and the final crystal structure, such as the size of the crystal and the composition of the crystal phase.

[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 CoNiSe 2 / NC composite material is a three-dimensional porous cubic structure with a size of 200-500nm.

[0025] In the preparation method of the present invention, the influence of the ratio of cobalt to nickel: when the ratio of metals changes, the crystal structure may undergo a phase transition or a change in lattice parameters.x Ni 1-x Se 2 ), with the change of the cobalt-nickel ratio, the crystal structure will gradually change from the cubic phase to the hexagonal phase. This change in the crystal structure will directly lead to a change in the morphology of the material, from nano-particles to nano-sheets. Therefore, the present invention controls a suitable cobalt-nickel ratio. Effect of selenium powder dosage on morphology: Some metal atoms in the system cannot be completely combined with selenium, and may form impurity phases such as metal elements or other low-valent selenides. The presence of these impurity phases will destroy the crystal structure and morphology of the product, making the product surface rough and the structure uneven. In addition, due to incomplete grain growth, large specific surface area, and high surface energy, the particles are more likely to attract each other and agglomerate in order to reduce the surface energy, resulting in serious product agglomeration, poor dispersibility, and inability to form a regular morphology. Therefore, the present invention controls a suitable amount of selenium. Selenization temperature: When selenization is performed at a lower temperature, the phase transition may be incomplete, or only some metastable phases can be formed. The crystal structure and morphology of these metastable phases may be different from those of the stable phases, and they may change in the subsequent processing process, resulting in unstable or unexpected morphology of the final product. As the selenization temperature continues to increase, the thermal motion of atoms intensifies, which can overcome the energy barriers in the phase transition process and make the crystal structure smoothly transform from one phase to another more stable phase, thereby obtaining a stable phase product with a specific morphology. Therefore, the present invention controls the appropriate selenization calcination temperature.

[0026] Compared with the traditional solvent thermal synthesis method, the method of synthesis at room temperature of the present invention has a simpler operation process and higher safety performance. In addition, it can reduce energy consumption and reduce costs. Although the thermal motion speed of molecules at room temperature is slower than that at high temperature, for ZIF-67, this reaction rate is more conducive to sufficient time for cobalt ions and ligands to self-assemble. Lower temperatures can reduce the nucleation rate, so that fewer but uniformly sized crystal nuclei can be formed in the system. The slow growth rate helps the crystals grow according to a specific crystal structure, reduces the introduction of defects and impurities, and obtains higher quality products. The three-dimensional network structure of ZIF-67 has certain gaps and channels. The size and chemical environment of these channels make Ni + Under certain conditions, it can enter the electrolyte to form a bimetallic MOF with a high specific surface area and unique pore structure, which is conducive to the rapid adsorption and desorption of electrolyte ions. + The presence of can provide additional redox active sites and improve the electrochemical performance. Therefore, the synthesized cubic three-dimensional porous structure can not only increase the specific surface area but also be more conducive to the insertion / deinsertion of sodium ions, thereby improving the battery cycle stability.

[0027] CoNiSe prepared by the present invention 2 / NC composite material and its polycrystalline surface structure and increased conductivity after carbon coating can greatly improve the cycle stability, service life and battery capacity. The design of its three-dimensional porous structure enables it to withstand long cycles with large currents, reduce the loss of active substances during the charge and discharge process, buffer the volume change during the charge and discharge process, reduce the shedding of active materials during the cycle, and is beneficial to the sodiumization / de-sodiumization during the reaction process. This material is used in sodium ion battery negative electrode materials and has the advantages of good cycle performance and high energy density.

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

[0029] Specifically, the nitrogen-doped carbon composite cobalt nickel diselenide nanocube material is an active material, which is evenly mixed with conductive carbon black and polyvinylidene fluoride in a ratio of 8:1:1 or 7:2:1, and then evenly dispersed in N-methylpyrrolidone (NMP) by magnetic stirring for 6 to 8 hours, and the mixed slurry is coated on a copper foil by a coater, and placed in a vacuum drying oven at 60 to 80° C. After drying for 12 to 24 hours, it is pressed by a tablet press, and then cut into a small circular electrode sheet by a sheet cutter; the prepared electrode sheet is assembled into a button battery in a glove box filled with high-purity argon and the water oxygen value is ≤0.01ppm; the electrolyte is NaPF 6 +DEGDME, the purity of the sodium sheet is Na≥99.99%, the thickness is 0.5mm, and it is cut into the size of the electrode sheet after rolling.

[0030] The specific method of assembling the battery is: add 1 drop of electrolyte on the positive electrode shell of the battery and place the electrode sheet, then add 1 drop of electrolyte and place the glass fiber, add 3 drops of electrolyte on the glass fiber and place the sodium sheet as the counter electrode, then place two pieces of foam nickel, then add 4 drops of electrolyte, cover the negative electrode shell, press and seal the battery with a hydraulic press, and leave it for 6 to 12 hours.

[0031] Transition metal selenides are considered to be excellent negative electrode materials for SIBs due to their stable structure and high theoretical capacity. However, transition metal selenides make sodium ion batteries unstable at high current densities due to internal strain caused by sodiumization. The present invention improves the conductivity of binary metal selenides by doping carbon, and improves the stability of the battery cycle at high current density by doping another metal element to form a three-dimensional porous cubic structure. The nitrogen-doped carbon composite cobalt nickel diselenide nanocube material provided by the present invention has good cycle stability and high rate performance.

[0032] The CoNiSe provided by the present invention 2Since the / NC material has two metal interactions, it can provide more active sites during the charge and discharge process. 2 The / NC composite material and its polycrystalline surface structure and increased conductivity after carbon coating can greatly improve the cycle stability, service life and battery capacity. The design of its three-dimensional porous structure enables it to withstand long cycles with large currents, reduce the loss of active materials during charge and discharge, buffer the volume change during charge and discharge, reduce the shedding of active materials during the cycle, and facilitate the sodium / de-sodiumization during the reaction process, thereby improving the electrochemical performance of the negative electrode material. Therefore, by constructing CoNiSe 2 The / NC polycrystalline face structure is expected to accelerate the reaction kinetics. The multi-component synergistic effect of the present invention promotes the rapid transfer of charge, resulting in excellent rate performance and cycle performance. The interface effect of binary metal selenides 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 the prior art, the present invention prepares a nitrogen-doped carbon composite cobalt nickel diselenide nanocube material by a simple precipitation method at room temperature, wherein the binary metal selenide CoNiSe 2 The synergistic effect of Co and Ni provides more active sites for the reaction and improves the conductivity, which significantly improves the performance of sodium ion batteries. In addition, the three-dimensional porous structure constructs a buffer space to reduce volume changes. Benefiting from these advantages, the prepared CoNiSe 2 / NC composites in 1Ag -1 After 800 cycles at the same current density, the current density was 447.5 mAh g -1 The high reversible capacity, high specific capacity, stable cycling performance and robust rate performance indicate that CoNiSe 2 / NC is an excellent and promising negative electrode material for SIBs. Moreover, the present invention is synthesized at room temperature, the conditions are simple, the operation is easy, and the cobalt source and nickel source are cheap and easy to obtain; the design of the porous structure greatly improves the cycle stability of the battery, increases the service life, and increases and stabilizes the capacity. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0036] Figure 3 CoNiSe prepared in Example 1 2 / TEM image of NC three-dimensional porous cube;

[0037] Figure 4 CoNiSe prepared in Example 1 2 / XRD pattern of NC three-dimensional porous cube;

[0038] Figure 5 CoNiSe prepared in Example 1 2 / Mapping diagram of NC three-dimensional porous cube;

[0039] Figure 6 CoNiSe prepared in Example 1 2 HRTEM of 3D porous cubic blocks of NC;

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

[0041] Figure 8 CoNiSe prepared in Example 3 2 / SEM image of NC;

[0042] Fig. 9 CoNiSe prepared in Example 4 2 / SEM image of NC;

[0043] Fig.10 CoNiSe prepared in Example 5 2 / SEM image of NC;

[0044] Fig.11 CoNiSe prepared in Example 6 2 / SEM image of NC;

[0045] Fig.12 CoNiSe prepared in Example 7 2 / SEM image of NC;

[0046] Fig.13 CoNiSe prepared in Example 8 2 / SEM image of NC;

[0047] Fig.14 CoNiSe prepared in Example 9 2 / SEM image of NC;

[0048] Fig.15 CoNiSe prepared in Example 10 2 / SEM image of NC;

[0049] Fig.16 CoNiSe prepared in Example 112 / SEM image of NC;

[0050] Fig.17 CoNiSe prepared in Example 1 2 Three-dimensional porous cubic materials of NC as anode materials for sodium-ion batteries at 0.2Ag -1 The charge and discharge curve test diagram under current density;

[0051] Fig.18 CoNiSe prepared in Example 1 2 Three-dimensional porous cubic materials of NC as anode materials for sodium-ion batteries at 0.2Ag -1 Cyclic performance test diagram under current density;

[0052] Fig.19 CoNiSe prepared in Example 1 2 Three-dimensional porous cubic materials of NC as negative electrode materials for lithium-ion batteries at 1Ag -1 The charge and discharge curve test diagram under current density;

[0053] Fig. 20 CoNiSe prepared in Example 1 2 Three-dimensional porous cubic materials of NC as negative electrode materials for lithium-ion batteries at 1Ag -1 Cyclic performance test diagram under current density;

[0054] Fig.21 CoNiSe prepared in Example 1 2 / NC three-dimensional porous cubic block material as lithium-ion battery negative electrode material at current densities of 0.1, 0.2, 0.5, 1, 3, 5, and 10A. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0057] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0058] Example 1

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

[0060] 1) Preparation of nanocube precursor:

[0061] Take 0.592g of Co(NO 3 ) 2 6H 2 O,0.296gNi(NO 3 ) 2 6H 2 O and 0.008g CTAB were ultrasonically dispersed in a beaker containing 20mL of deionized water to form a uniform solution, which was recorded 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 uniform solution, which was recorded as solution B. Solution A was poured into solution B and magnetically stirred for 30s to mix it thoroughly. Then aged at room temperature for 24h. Then, it was centrifuged and washed 3 times with deionized water, washed twice with ethanol, and vacuum dried at 60°C for 8h to collect the precursor precipitate product. Its SEM picture is as follows Figure 1 As shown, it can be seen from the figure that it is a nanocube with a size of 200-500nm.

[0062] 2) CoNiSe 2 / NC preparation:

[0063] Weigh 0.1g of the precursor and selenium powder in a mass ratio of 1:5 and place them in two porcelain boats. The porcelain boat containing selenium powder is placed at the upwind port and calcined in a mixed gas flow atmosphere at a heating rate of 4℃ / min to a calcination temperature of 700℃ for 2h to obtain the product CoNiSe. 2 / NC, its SEM picture is as follows Figure 2 As shown in the figure, it can be seen that it is a porous nanocube with a size of 200-500nm. Figure 3 shown.

[0064] The CoNiSe obtained in this example 2 XRD patterns of / NC composites are shown in Figure 4 As shown, it is proved that the obtained product is CoNiSe 2 / NC. Figure 5 This is the mapping diagram of the material. From the diagram, we can see that the elements in the composite material are evenly distributed. Figure 6 This is the HRTEM image of the material. The C layer in the image is a good proof of the successful doping of C.

[0065] Example 2 (for comparison)

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

[0067] 1) Preparation of nanocube precursor:

[0068] Take separately 0.592g Co(NO 3 ) 2 6H 2 O,0.592gNi(NO 3 ) 2 6H 2 O and 0.008g CTAB were ultrasonically dispersed in a beaker containing 20mL of deionized water to form a uniform solution, which was recorded 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 uniform solution, which was recorded as solution B. Solution A was poured into solution B and magnetically stirred for 30s to mix it thoroughly. Then it was aged at room temperature for 24h. Then it was centrifuged and washed 3 times with deionized water, washed 2 times with ethanol, and vacuum dried at 60℃ for 8h to collect the precursor precipitate product.

[0069] 2) CoNiSe 2 The preparation of / NC is the same as that of Example 1. The SEM image of the product prepared in Example 2 is as follows Figure 7 As shown in the figure, it can be seen that it is spherical, with a size of 400-600nm. After changing the ratio of cobalt salt and nickel salt, it is found that the morphology changes from cubic agglomeration to spherical.

[0070] Example 3 (for comparison)

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

[0072] 1) Preparation of nanocube precursor:

[0073] Take separately 0.888g Co(NO 3 ) 2 6H 2 O,0.296gNi(NO 3 ) 2 6H 2 O and 0.008g CTAB were ultrasonically dispersed in a beaker containing 20mL of deionized water to form a uniform solution, which was recorded 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 uniform solution, which was recorded as solution B. Solution A was poured into solution B and magnetically stirred for 30s to mix it thoroughly. Then it was aged at room temperature for 24h. Then it was centrifuged and washed 3 times with deionized water, washed 2 times with ethanol, and vacuum dried at 60℃ for 8h to collect the precursor precipitate product.

[0074] 2) CoNiSe 2 / NC was prepared in the same manner as in Example 1; the SEM image of the product prepared in Example 3 is as follows Figure 8 As shown, it can be seen from the figure that there is no obvious morphology.

[0075] Example 4 (for comparison)

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

[0077] 1) Preparation of nanocube precursor:

[0078] Take separately 1.184g Co(NO 3 ) 2 6H 2 O,0.296gNi(NO 3 ) 2 6H 2 O and 0.008g CTAB were ultrasonically dispersed in a beaker containing 20mL of deionized water to form a uniform solution, which was recorded 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 uniform solution, which was recorded as solution B. Solution A was poured into solution B and magnetically stirred for 30s to mix it thoroughly. Then it was aged at room temperature for 24h. Then it was centrifuged and washed 3 times with deionized water, washed 2 times with ethanol, and vacuum dried at 60℃ for 8h to collect the precursor precipitate product.

[0079] 2) CoNiSe 2 The preparation of / NC is the same as that of Example 1. The SEM image of the product prepared in Example 4 is as follows Fig. 9 As shown in the figure, it can be seen that there is no obvious cubic morphology when the cobalt-nickel ratio is 4:1.

[0080] Example 5 (for comparison)

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

[0082] 1) Preparation of nanocube precursor is the same as in Example 1;

[0083] 2) CoNiSe 2 / NC preparation:

[0084] Weigh 0.1g of precursor and selenium powder according to the mass ratio 1:1 The powders were placed in two porcelain boats, with the porcelain boat containing selenium powder placed at the upper wind port, and calcined in a mixed gas flow atmosphere at a heating rate of 4°C / min to a calcination temperature of 700°C for 2 hours to obtain the product CoNiSe. 2 / NC, its SEM picture is as follows Fig.10 As shown in the figure, it can be seen that the product is not completely selenized due to insufficient amount of selenium powder, and the product is a nanosphere structure of irregular size.

[0085] Example 6 (for comparison)

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

[0087] 1) Preparation of nanocube precursor is the same as in Example 1;

[0088] 2) CoNiSe 2 / NC preparation:

[0089] Weigh 0.1g of precursor and selenium powder according to the mass ratio 1:2 The powders were placed in two porcelain boats, with the porcelain boat containing selenium powder placed at the upper wind port, and calcined in a mixed gas flow atmosphere at a heating rate of 4°C / min to a calcination temperature of 700°C for 2 hours to obtain the product CoNiSe. 2 / NC, its SEM picture is as follows Fig.11 As shown in the figure, it can be seen that the product is not completely selenized due to the small amount of selenium powder, and the product is an irregular nanosphere structure. Selenium atoms participate in the formation of chemical bonds in CoNiSe2 crystals, and insufficient selenium powder makes the formation of chemical bonds incomplete or uneven. This will affect the internal forces of the crystal and the directionality of crystal growth, so that the crystal cannot grow into a square shape along a specific crystal axis direction, but grows more evenly in all directions, approaching a spherical shape.

[0090] Example 7 (for comparison)

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

[0092] 1) Preparation of nanocube precursor is the same as in Example 1;

[0093] 2) CoNiSe 2 / NC preparation:

[0094] Weigh 0.1g of precursor and selenium powder according to the mass ratio 1:3 The powders were placed in two porcelain boats, with the porcelain boat containing selenium powder placed at the upper wind port, and calcined in a mixed gas flow atmosphere at a heating rate of 4°C / min to a calcination temperature of 700°C for 2 hours to obtain the product CoNiSe. 2 / NC, its SEM picture is as follows Fig.12As shown in the figure, it can be seen that as the amount of selenium powder increases, the morphology of the product gradually tends to a cubic block structure, but due to insufficient amount of selenium powder, the product is still an irregular nanosphere structure. At high temperature, selenium powder will become selenium atoms to participate in the formation of chemical bonds in CoNiSe2 / NC crystals. Insufficient selenium powder makes the formation of chemical bonds incomplete or uneven. This will affect the internal forces of the crystal and the directionality of crystal growth, so that the crystal cannot grow into a square shape along a specific crystal axis direction, but grows more evenly in all directions, approaching a spherical shape.

[0095] Example 8 (for comparison)

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

[0097] 1) Preparation of nanocube precursor is the same as in Example 1;

[0098] 2) CoNiSe 2 / NC preparation:

[0099] Weigh 0.1g of precursor and selenium powder according to the mass ratio 1:4 The powders were placed in two porcelain boats, with the porcelain boat containing selenium powder placed at the upper wind port, and calcined in a mixed gas flow atmosphere at a heating rate of 4°C / min to a calcination temperature of 700°C for 2 hours to obtain the product CoNiSe. 2 / NC, its SEM picture is as follows Fig.13 As shown in the figure, it can be seen that some products have a cubic structure, and some products have not been selenized and have an irregular spherical structure.

[0100] Example 9 (for comparison)

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

[0102] 1) Preparation of nanocube precursor is the same as in Example 1;

[0103] 2) CoNiSe 2 / NC preparation:

[0104] Weigh 0.1g of precursor and selenium powder in a mass ratio of 1:5 and place them in two porcelain boats respectively. The porcelain boat containing selenium powder is placed at the upwind port and calcined in a mixed gas flow atmosphere. The heating rate is 4℃ / min to the calcination temperature. 400℃， The calcination time is 2h, and the final product CoNiSe is obtained. 2 / NC, its SEM picture is as follows Fig.14 As shown, due to the low calcination temperature, the product was not calcined completely and had no obvious structure.

[0105] Example 10 (for comparison)

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

[0107] 1) Preparation of nanocube precursor is the same as in Example 1;

[0108] 2) CoNiSe 2 / NC preparation:

[0109] Weigh 0.1g of precursor and selenium powder in a mass ratio of 1:5 and place them in two porcelain boats respectively. The porcelain boat containing selenium powder is placed at the upwind port and calcined in a mixed gas flow atmosphere. The heating rate is 4℃ / min to the calcination temperature. 500℃， The calcination time is 2h, and the final product CoNiSe is obtained. 2 / NC, its SEM picture is as follows Fig.15 As shown in the figure, it can be seen that its structure is an irregular nanosphere structure.

[0110] Embodiment 11

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

[0112] 1) Preparation of nanocube precursor is the same as in Example 1;

[0113] 2) CoNiSe 2 / NC preparation:

[0114] Weigh 0.1g of the precursor and selenium powder in a mass ratio of 1:5 and place them in two porcelain boats. The porcelain boat containing selenium powder is placed at the upwind port and calcined in a mixed gas flow atmosphere at a heating rate of 4℃ / min to a calcination temperature of 600℃ for 2h to obtain the product CoNiSe. 2 / NC, its SEM picture is as follows Fig.16 As shown, with the continuous increase of calcination temperature, the product changes to a cubic structure. It can be seen from the figure that some products have a cubic structure.

[0115] Example 12

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

[0117] The product of Example 1 is used as a negative electrode material for sodium ion batteries to prepare sodium batteries:

[0118] Cobalt diselenide nickel nitrogen-doped carbon composite material is used as the active material. It is mixed with conductive carbon black and polyvinylidene fluoride in a ratio of 8:1:1, and then magnetically stirred for 8 hours to evenly disperse it in NMP. The mixed slurry is coated on copper foil with a coater, placed in a vacuum drying oven at 80°C, and pressed with a tablet press after drying for 24 hours. It is then cut into a small circular electrode sheet with a sheet cutter; the prepared electrode sheet is assembled into a button battery in a glove box filled with high-purity argon and with a water-oxygen value of ≤0.01ppm; the electrolyte is NaPF 6 +DEGDME, the purity of the sodium sheet is Na≥99.99%, the thickness is 0.5mm, and it is cut into the size of the electrode sheet after rolling.

[0119] The specific method of assembling the battery is as follows: add 1 drop of electrolyte on the positive electrode shell of the battery and place the electrode sheet, then add 1 drop of electrolyte and place the glass fiber, add 3 drops of electrolyte on the glass fiber and place the sodium sheet as the counter electrode, then place two pieces of foam nickel, add 4 drops of electrolyte, cover the negative electrode shell, press and seal the battery with a hydraulic press, and leave it for 12 hours.

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

[0121] Then the cycle performance and charge-discharge performance of the button battery were tested at currents of 0.2A and 1A. The results are as follows: Fig.17 , Fig.18 , Fig.19 , Fig. 20 As shown in the figure, it can be seen that there is a relatively stable charge and discharge platform and cycle performance. The battery rate was tested at current densities of 0.1, 0.2, 0.5, 1, 3, 5, and 10A. It can be seen from Figure 21 that the material has good rate performance and can withstand larger currents.

[0122] The present invention develops negative electrode materials with unique structures through a practical and direct SIBs method. Electrode materials with nanostructures are promising candidate materials. Bimetallic selenides, the synergistic effect between the two metals adds more active sites for redox reactions, thereby improving the electrochemical performance of the electrode. The use of bimetallic selenide material form and the effective design of a three-dimensional porous structure can effectively reduce the volume expansion phenomenon of the material and prevent the structural pulverization of the material, thereby preventing the structural collapse of the electrode material. In addition, composites with conductive carbon species can effectively reduce the negative effects of poor conductivity. Reasonable structural carbon-based composite materials can improve electronic conductivity and buffer internal stress, which is beneficial to the electrochemical performance of SIBs. Therefore, nanostructured CoNiSe 2The combination of three-dimensional porous cubes and nitrogen-doped carbon layers is an effective strategy to achieve high-performance SIBs.

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

[0124] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present 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 comprises the following steps: 1) Dispersing cobalt salt, nickel salt and hexadecyltrimethylammonium bromide in a solvent and mixing them to obtain solution A; dispersing an organic ligand in a solvent and mixing them to obtain solution B; pouring solution A into solution B and aging at room temperature to obtain a nanocube precursor; 2) The nanocube precursor and selenium powder are mixed and calcined under a protective atmosphere to obtain a CoNiSe2 / NC composite material.

2. The preparation method according to claim 1, characterized in that: In step 1), the molar ratio of the cobalt source to the nickel source is 2:

1.

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

1.

4. 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.

5. The preparation method according to claim 1 or 4, characterized in that: In step 1), the organic ligand is 2-methylimidazole.

6. The preparation method according to claim 1 or 2, characterized in that: In step 1), the room temperature aging time is 24 hours.

7. The preparation method according to claim 1, characterized in that: Step 2) The mass ratio of the nanocube precursor to selenium powder is 1:

5.

8. The preparation method according to claim 1, characterized in that: Step 2) calcination conditions are 600-700°C for 2h.

9. A nitrogen-doped carbon composite cobalt nickel diselenide nanocube material prepared by the preparation method according to any one of claims 1 to 8, wherein the nitrogen-doped carbon composite cobalt nickel diselenide nanocube material is a three-dimensional porous cubic structure with a size of 200-500 nm.

10. Use of the nitrogen-doped carbon composite cobalt nickel diselenide nanocube material according to claim 9 in a battery.

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