A pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material and preparation method thereof

Abstract

The present invention belongs to the technical field of inorganic / carbon composite material synthesis, and relates to a pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material and a preparation method thereof. The composite material is a pomegranate-like three-dimensional nanosphere structure formed by a shell coating a number of cores, and there are voids between the cores and between the shell and the cores. The shell is nitrogen-doped carbon, and the cores are tin-nickel alloys. The preparation method comprises the following steps: using a hydrothermal method to co-precipitate a divalent nickel salt, a tetravalent tin salt and an alkali to synthesize nanospheres; using the self-polymerization reaction of dopamine to coat polydopamine on the surface of the nanospheres to obtain a precursor; annealing the precursor under a mixed atmosphere of inert and reducing, and performing pyrolysis and reduction during the annealing process to obtain the product. Using the composite material provided by the present invention as the anode material of a lithium / sodium ion battery, the prepared lithium / sodium ion battery has excellent cycle stability and rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic / carbon composite material synthesis, and relates to a pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material and a preparation method thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to increase the understanding of the overall background of the present invention, and does not necessarily be regarded as an admission or imply in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Although tin-based materials have a high specific capacity, they have defects such as large volume expansion during ion insertion / extraction and easy pulverization of the electrode, resulting in poor electrochemical stability and rate performance. According to the inventor's research and understanding, in order to solve the problem of volume change of tin-based materials during the electrochemical process, they can be compounded with carbon materials, which can improve the electrode conductivity and stabilize the electrode structure, reduce the pulverization and shedding of the electrode. For example, the patent number CN 112510177 A prepared a Sn / C composite material, but its composite electrode materials are stacked, and the initial Coulomb efficiency is only 57%, with poor performance. By compounding with other metal elements or other metal oxides and introducing this part of inactive metal, the volume expansion can be alleviated to a certain extent, ensuring the stability of the electrode structure and being beneficial to the long-term cycle stability of the electrode. For example, CN 109378462 B prepared a Co 3 Sn 2 / SnO 2 composite material. Compared with single materials, its capacity has been greatly improved, but its stability cannot meet the requirements of lithium-ion batteries, and its preparation process is complex and difficult to synthesize. Summary of the Invention

[0004] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material and a preparation method thereof. Using the composite material provided by the present invention as the negative electrode material of a lithium / sodium ion battery, the prepared lithium / sodium ion battery has excellent cycle stability and rate performance.

[0005] In order to achieve the above purpose, the technical solution of the present invention is as follows:

[0006] On the one hand, a pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material, the composite material is a three-dimensional nanosphere structure in the shape of a pomegranate formed by an outer shell covering a number of inner cores, there are gaps between the inner cores and between the outer shell and the inner cores, the outer shell is nitrogen-doped carbon, and the inner cores are tin-nickel alloys.

[0007] Compared with traditional single tin-based electrode materials, due to the introduction of inactive metal Ni in the Sn-Ni bimetallic alloy anode material, metal Ni as a "buffer body" can buffer the volume change during ion insertion / extraction, prevent the structure from collapsing, stabilize the electrode structure, and the synergistic effect between the two metals improves the activity of the metal alloy, making it more conducive to electrochemical reactions. In addition, by designing and constructing a pomegranate-like multi-core-shell structured alloy nanocomposite, the large voids between the multi-core alloy particles and between the multi-core-shell can effectively buffer and adapt to the volume change, while providing fast ion and electron transport channels. The nanomaterial increases the specific surface area and provides abundant reaction sites. In addition, the coating of nitrogen-doped carbon alleviates the volume expansion and reduces the self-aggregation of the electrode material. The doping of heteroatom nitrogen improves the conductivity to a certain extent, which is beneficial to charge transfer and provides a certain capacity. Therefore, the nanocomposite prepared by the present invention combines the above advantages and accelerates the reaction kinetics of lithium / sodium ion batteries, showing excellent cycle stability and rate performance.

[0008] On the other hand, a preparation method of a pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material includes the following steps:

[0009] Using the hydrothermal method, divalent nickel salt, tetravalent tin salt and alkali are co-precipitated to synthesize NiSn(OH) 6 nanospheres; using the self-polymerization reaction of dopamine to coat poly-dopamine on the surface of NiSn(OH) 6 nanospheres to obtain NiSn(OH) 6 @PDA nanosphere precursors;

[0010] Under an inert and reducing mixed atmosphere, the NiSn(OH) 6 @PDA nanosphere precursors are annealed, and pyrolysis and reduction are carried out during the annealing process to obtain the product.

[0011] By controlling the co-precipitation synthesis of NiSn(OH) 6 nanospheres by the hydrothermal method, and synergistic annealing treatment can reduce the size of the alloy particles, and obtain the coating of nitrogen-doped carbon shell, which stabilizes the electrode structure while preventing its self-aggregation and electrode pulverization, and improves the lithium / sodium storage performance.

[0012] In the third aspect, an application of the above pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material as a negative electrode of a lithium ion battery or a negative electrode of a sodium ion battery.

[0013] When applied to the negative electrode material of a lithium ion battery, it can exhibit excellent cycle stability, rate performance and fast reaction kinetics. When applied to the negative electrode material of a sodium ion battery, it shows excellent electrochemical performance.

[0014] Fourth aspect, an ion battery, which is a lithium-ion battery or a sodium-ion battery, and the active material in the negative electrode of the lithium-ion battery or the sodium-ion battery is the above-mentioned pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material.

[0015] The beneficial effects of the present invention are as follows:

[0016] In the present invention, a pomegranate-like multi-core-shell structure Sn-Ni@NC alloy composite material is designed and prepared by hydrothermal method and annealing and other easy-to-operate methods. The synergy of the bimetals provides rich redox reaction sites. The coating of the nitrogen atom-doped carbon shell increases the specific surface area and lattice spacing, which speeds up the ion and electron transport rates to a certain extent and reduces the agglomeration of the electrode material. The alloy composite material gives full play to the advantages of each component. The most important pomegranate-like multi-core-shell structure can effectively inhibit volume expansion and structure collapse, which is beneficial to the stability of the electrode material structure. When applied to the negative electrode materials of lithium-ion batteries and sodium-ion batteries, it shows excellent cycle stability and rate performance. Description of the Drawings

[0017] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0018] Figure 1 Transmission electron microscope image of the core-shell structure NiSn(OH) 6 @PDA nanosphere precursor prepared in Example 1 of the present invention;

[0019] Figure 2 X-ray powder diffraction pattern of the pomegranate-like multi-core-shell structure Sn-Ni@NC alloy composite material prepared in Example 2 of the present invention;

[0020] Figure 3 Pomegranate-like multi-core-shell structure Sn-Ni@NC alloy composite material prepared in Example 2 of the present invention. a is the scanning electron microscope image at low magnification, b is the scanning electron microscope image at high magnification, c is the transmission electron microscope image at low magnification, and d is the transmission electron microscope image at high magnification;

[0021] Figure 4 Cycling performance graph of the pomegranate-like multi-core-shell structure Sn-Ni@NC alloy composite material prepared in Example 2 of the present invention when applied to a lithium-ion battery at a current density of 2.0 A g -1 ;

[0022] Figure 5 Cycling performance graph of the pomegranate-like multi-core-shell structure Sn-Ni@NC alloy composite material prepared in Example 2 of the present invention when applied to a sodium-ion battery. (a) At a current density of 0.05 - 1.0 A g -1Rate performance plots at different current densities and (b) cycling performance plots at 1.0 A g -1 Cycling performance plots at different current densities;

[0023] Figure 6 X-ray powder diffraction patterns of Sn-Ni@NC-2h, Sn-Ni@NC-4h, and Sn-Ni@NC-6h obtained at different calcination times in Example 3 of the present invention;

[0024] Figure 7 Transmission electron microscope images of (a,d) Sn-Ni@NC-2h, (b,e) Sn-Ni@NC-4h, and (c,f) Sn-Ni@NC-6h obtained at different calcination times in Example 3 of the present invention;

[0025] Figure 8 Cycling performance plots of Example 8 of the present invention at (a) 0.2 A g -1 and rate performance plots at (b) 0.05 - 1.0 A g -1 current density; Detailed Description of the Invention

[0026] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] As introduced in the background art, there are disadvantages in the prior art such as complex preparation methods, easy collapse of structures, and poor cycling stability. To solve the above technical problems, the present invention proposes a pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material and a preparation method.

[0029] A typical embodiment of the present invention provides a pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material. The composite material is a three-dimensional nanosphere structure in the shape of a pomegranate formed by a shell coating a number of cores. There are voids between the cores and between the shell and the cores. The shell is nitrogen-doped carbon, and the cores are tin-nickel alloys.

[0030] The present invention effectively inhibits volume expansion and structural collapse through the synergy of tin-nickel alloy and the influence of microtopography, which is beneficial to the stability of the electrode material structure. When applied to the anode materials of lithium-ion batteries and sodium-ion batteries, it exhibits excellent cycle stability and rate performance.

[0031] In some embodiments, the tin-nickel alloy includes Ni 2.67 Sn 2 , Ni 3 Sn, Sn.

[0032] In some embodiments, the diameter of the nanospheres is 400 - 500 nm.

[0033] In some embodiments, the thickness of the outer shell is 60 - 70 nm.

[0034] In some embodiments, the diameter of the inner core is not greater than 200 nm.

[0035] Another embodiment of the present invention provides a method for preparing a pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material, including the following steps:

[0036] Using the hydrothermal method to co-precipitate divalent nickel salt, tetravalent tin salt and alkali to synthesize NiSn(OH) 6 nanospheres; using the self-polymerization reaction of dopamine to coat the surface of NiSn(OH) 6 nanospheres with polydopamine to obtain NiSn(OH) 6 @PDA nanosphere precursor;

[0037] Under an inert and reducing mixed atmosphere, annealing the NiSn(OH) 6 @PDA nanosphere precursor, and performing pyrolysis and reduction during the annealing process to obtain the product.

[0038] The present invention controls the particle size of NiSn(OH) 6 nanospheres by the hydrothermal method for co-precipitation synthesis. The synergy of annealing treatment can reduce the size of alloy particles, and obtain the coating of nitrogen-doped carbon shell, which stabilizes the electrode structure while preventing its self-aggregation and electrode pulverization, and improves the lithium / sodium storage performance.

[0039] The divalent nickel salt described in the present invention is a compound containing divalent nickel ions, such as nickel dichloride, nickel nitrate, nickel sulfate, nickel acetate, etc.

[0040] The tetravalent tin salt described in the present invention is a compound containing tetravalent tin ions, such as tin tetrachloride, tin(IV) nitrate, tin(IV) sulfate, etc.

[0041] The hydrothermal method described in the present invention is a reaction method in a closed container, using water as a solvent and generating high temperature and high pressure conditions after heating.

[0042] In some embodiments, the molar ratio of the divalent nickel salt to the tetravalent tin salt is 1:0.9 to 1.1.

[0043] In some embodiments, the base is sodium hydroxide, potassium hydroxide or ammonia water.

[0044] In some embodiments, the temperature of the hydrothermal method is 100 to 140 °C, and the reaction time is 6 to 14 h.

[0045] In some embodiments, the process of obtaining the NiSn(OH) 6 @PDA nanosphere precursor is as follows: Disperse the NiSn(OH) 6 nanospheres into a solution with a pH of 8.0 to 9.0, add dopamine hydrochloride, and stir. Dopamine can undergo self-polymerization to form polydopamine under the weak alkaline condition of pH 8.0 to 9.0.

[0046] The thickness of the polydopamine (PDA) shell is to some extent determined by the addition amount of dopamine hydrochloride or the stirring time. In one or more embodiments, the mass ratio of the NiSn(OH) 6 @PDA nanosphere precursor to dopamine hydrochloride is 80 to 120:20 to 80.

[0047] In one or more embodiments, the stirring time is 8 to 24 h.

[0048] When the above conditions are satisfied simultaneously, obtaining the NiSn(OH) 6 @PDA nanosphere precursor can better prepare the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material. Especially when the mass ratio of the NiSn(OH) 6 @PDA nanosphere precursor to dopamine hydrochloride is 80 to 120:40 and the stirring time is 15 to 17 h, the effect is better.

[0049] In some embodiments, in the mixed atmosphere, the volume fraction of the reducing gas is 5 to 10%. The reducing gas is hydrogen, CO, etc. When hydrogen is used as the reducing gas, the performance of the obtained material is better.

[0050] The annealing treatment refers to a heat treatment process of heating to a set temperature at a certain rate, holding the temperature, and then cooling at a certain rate.

[0051] In some embodiments, during the annealing treatment, the temperature is raised to 550 to 750 °C. Preferably, it is 640 to 660 °C.

[0052] In some embodiments, during the annealing treatment, the heating rate is 1 to 3 °C / min. Preferably, it is 1.5 to 2.5 °C / min.

[0053] In some embodiments, the annealing treatment time is 2 to 8 h. Preferably, it is 4.5 to 5.5 h. The annealing treatment time described in the present invention refers to the holding time after heating to the set temperature, excluding the heating-up time and the cooling-down time.

[0054] The third embodiment of the present invention provides an application of the above-mentioned pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material as a negative electrode of a lithium-ion battery or a sodium-ion battery.

[0055] Specifically, a battery negative electrode is generally obtained by mixing an active material, a conductive material (such as acetylene black, graphene, etc.), a binder material (such as polyvinylidene fluoride, carboxymethyl cellulose, etc.) with a solvent to form a slurry, and then coating the slurry onto a current collector and drying. At this time, when the active material is replaced with the above-mentioned pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material, a battery negative electrode can be obtained, and this battery negative electrode can be used to prepare a lithium-ion battery or a sodium-ion battery.

[0056] In a fourth aspect, an ion battery, the ion battery is a lithium-ion battery or a sodium-ion battery, and the active material in the negative electrode of the lithium-ion battery or the sodium-ion battery is the above-mentioned pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material.

[0057] An ion battery is composed of a positive electrode, a separator, an electrolyte, and a negative electrode. When the positive electrode is a lithium sheet and the electrolyte is an electrolyte containing lithium ions (such as LiPF 6 、LiClO 4 etc.), it is a lithium-ion battery. When the positive electrode is a sodium sheet and the electrolyte is an electrolyte containing sodium ions (such as NaPF 6 、NaClO 4 etc.), it is a sodium-ion battery.

[0058] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with specific embodiments.

[0059] Example 1

[0060] Preparation of NiSn(OH) 6 @PDA nanospheres includes the following process steps:

[0061] (1) Synthesize NiSn(OH) 6Nanospheres: Nickel acetate tetrahydrate and tin chloride pentahydrate were used as the nickel source and tin source, respectively, with a molar ratio of 1:1, 0.15 mol each. The solvent was 30 mL of secondary water, and the substance providing the alkaline condition was 16 mL of concentrated ammonia water (analytical grade). Through a hydrothermal reaction carried out in a high-pressure reactor at a hydrothermal temperature of 120 °C for 10 h. After filtering and washing three times each with secondary water and absolute ethanol, it was dried in a vacuum drying oven at 65 °C for 4 h to obtain NiSn(OH) 6 nanospheres.

[0062] (2) Under normal temperature conditions, 100 mL of the pre-prepared buffer solution with a pH ≈ 8.5 was taken, and 100 mg of NiSn(OH) 6 nanosphere precursor was added and ultrasonically dispersed for 2 h. After the ultrasonic dispersion ended, it was cooled to room temperature (about 20 °C).

[0063] (3) 40 mg of dopamine hydrochloride was added, and the stirring time was 16 h. The mass of dopamine hydrochloride added and the stirring time determined the thickness of the PDA coating layer to a certain extent. Finally, it was centrifuged and washed three times each with secondary water and absolute ethanol, and the vacuum drying conditions were 65 °C and a drying time of 4 h to prepare NiSn(OH) 6 nanospheres coated with polydopamine. It can be seen from its transmission electron microscope image that the NiSn(OH) 6 @PDA nanospheres have uniform sizes of about 400 - 500 nm, and the PDA thickness is about 60 - 70 nm, as shown in Figure 1 .

[0064] Example 2

[0065] Preparation of a pomegranate-like multi-core-shell structured Sn-Ni@NC alloy composite material, including the following process steps:

[0066] Take about 100 mg of NiSn(OH) 6 @PDA, after evacuating three times, in an Ar / H 2 (volume fraction 95%: 5%) gas atmosphere, the calcination temperature was 650 °C, the heating rate was 2 °C / min, the annealing time was 5 h, and the cooling rate was 5 °C / min to prepare a pomegranate-like multi-core-shell structured Sn-Ni@NC alloy composite material. Its characterization shows that the X-ray powder diffraction pattern is shown in Figure 2 , and it can be obtained that the main components of the alloy in the Sn-Ni@NC alloy composite material are Ni 2.67 Sn 2 , Ni 3 Sn and Sn, respectively, as shown in It is indicated by "◆". Through observation of scanning electron microscope images and transmission electron microscope images, the Sn-Ni@NC alloy composite material has relatively uniform size, about 400 - 500 nm, the thickness of the nitrogen-doped carbon shell is about 60 - 70 nm, and the size of the Sn-Ni alloy particles is within 200 nm, as shown in Figure 3 .

[0067] Electrochemical performance test:

[0068] The pomegranate-like multi-core-shell structured Sn-Ni@NC obtained in this example is used as the anode material for lithium / sodium ion batteries. The anode material, acetylene black, and sodium carboxymethyl cellulose are added to secondary water in a mass ratio of 7:2:1 and ball-milled for 3 - 6 h, then coated on a copper foil, vacuum dried, and cut into anode sheets with a diameter of 12 mm.

[0069] Assemble a lithium-ion battery. The positive electrode used is a lithium sheet, the battery separator is a Celgard 2300 polymer membrane, and the main component of the electrolyte is LiPF 6 . At a current density of 2.0 A g –1 , the discharge specific capacity is 330.7 mAh g after 1000 charge-discharge cycles, as shown in -1 , see Figure 4 .

[0070] Assemble a sodium-ion battery. The positive electrode used is a self-made sodium sheet, the battery separator is glass fiber (Whatman GF / F), and the main component of the electrolyte is NaClO 4 . At a current density of 1.0 A g -1 , the cycling performance graph (the specific capacity is 150.3 mAh g after 200 cycles -1 ), and the rate performance graph at different current densities (at 0.05, 0.1, 0.2, 0.5, and 1.0 A g -1 , its reversible specific capacities are 425.2, 309.5, 264.9, 228.1, and 177.4 mAh g -1 ), see Figure 5 .

[0071] Example 3

[0072] Take about 100 mg of NiSn(OH) 6 @PDA. After evacuating three times, in Ar / H 2In an atmosphere of (volume fraction 95%: 5%) gas, the calcination temperature is 650 °C, the heating rate is 2 °C / min, the annealing time is 2 h, and the cooling rate is 5 °C / min. When the heating rate and the calcination temperature are the same, the annealing time is changed to 4 h and 6 h respectively, and a pomegranate-like multi-core-shell structured Sn-Ni@NC alloy composite material is prepared, which is denoted as Sn-Ni@NC-2h, Sn-Ni@NC-4h and Sn-Ni@NC-6h respectively.

[0073] The three obtained nanocomposites were characterized, and the X-ray powder diffraction pattern is shown in Figure 6 , and it can be obtained that the main components of the alloy in the Sn-Ni@NC nanocomposite are Ni 2.67 Sn 2 , Ni 3 Sn and Sn, respectively represented by "◆". Observed by transmission electron microscopy, the size of the Sn-Ni@NC alloy composite material is relatively uniform, about 400 - 500 nm, and the thickness of the nitrogen-doped carbon shell is about 60 - 70 nm. The size of the Sn-Ni alloy particles in Sn-Ni@NC-2h is larger, and with the increase of the calcination time, the nano-alloy particles gradually decrease, as shown in Figure 7 , where (a, d) are the transmission electron microscopy images of Sn-Ni@NC-2h, (b, e) are those of Sn-Ni@NC-4h, and (c, f) are those of Sn-Ni@NC-6h.

[0074] Electrochemical performance test:

[0075] The steps for assembling the lithium-ion battery are the same as those in Example 2.

[0076] At a current density of 0.2 A g –1 , charge-discharge cycle tests were carried out on Sn-Ni@NC-2h, Sn-Ni@NC-4h and Sn-Ni@NC-6h. After 100 cycles, their discharge specific capacities were 377.7 mAh g -1 , 451.8 mAh g -1 and 598.4 mAh g -1 , as shown in Figure 8 . The rate performance of Sn-Ni@NC-6h at different current densities is better than that of Sn-Ni@NC-4h and Sn-Ni@NC-2h, as shown in Figure 8 .

[0077] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Preparation method of pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material, Characterized in that, Comprising the following steps: The NiSn(OH) nanospheres are synthesized by co-precipitation of divalent nickel salt, tetravalent tin salt and alkali through a hydrothermal method; wherein, the temperature of the hydrothermal method is 100-140 °C, the reaction time is 6-14 h; the molar ratio of the divalent nickel salt to the tetravalent tin salt is 1:0.9-1.1; the alkali is sodium hydroxide, potassium hydroxide or ammonia water; 6 ​ Using the self-polymerization reaction of dopamine to coat the surface of NiSn(OH) 6 nanospheres with polydopamine to obtain NiSn(OH) 6 @PDA nanosphere precursors; Under an inert and reducing mixed atmosphere, NiSn(OH) 6 @PDA nanosphere precursors are annealed, and pyrolysis and reduction are carried out during the annealing process to obtain the product; during annealing, the temperature is raised to 640-660 °C; the annealing time is 2-8 h; The tin-nickel alloy includes Ni 2.67 Sn 2 , Ni 3 Sn, Sn.

2. The preparation method of the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 1, Characterized in that, Obtaining NiSn(OH) 6 The process of the @PDA nanosphere precursor is as follows: Disperse NiSn(OH) 6 nanospheres into a solution with a pH of 8.0 - 9.0, add dopamine hydrochloride, and stir; dopamine can self-polymerize to form polydopamine under the weak alkaline condition of pH 8.0 - 9.

0.

3. The preparation method of the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 2, Characterized in that, NiSn(OH) 6 The mass ratio of the PDA nanosphere precursor to dopamine hydrochloride is 80-120:20-80.

4. The preparation method of the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 2, Characterized in that, The stirring time is 8-24 h.

5. The preparation method of the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 1, Characterized in that, In the mixed atmosphere, the volume fraction of the reducing gas is 5-10%; During the annealing treatment, the heating rate is 1-3 °C / min; During the annealing treatment, the cooling rate is 2-10 °C / min.

6. The preparation method of the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 1, Characterized in that, During the annealing treatment, the heating rate is 1.5-2.5 °C / min.

7. The preparation method of the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 1, Characterized in that, The annealing treatment time is 4.5-5.5 h.

8. The preparation method of the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 1, Characterized in that, During the annealing treatment, the cooling rate is 4-6 °C / min.

9. The pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material prepared by the preparation method according to claim 1, Characterized in that, The composite material is a pomegranate-like three-dimensional nanosphere structure formed by a shell coating a number of cores. There are voids between the cores and between the shell and the cores. The shell is nitrogen-doped carbon, and the core is a tin-nickel alloy; the tin-nickel alloy includes Ni 2.67 Sn 2 、Ni 3 Sn, Sn.

10. The pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 9, Characterized in that, The diameter of the nanospheres is 400-500 nm; The thickness of the outer shell is 60-70 nm; The diameter of the inner core is not more than 200 nm.

11. Application of the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material according to claim 9 or 10 or the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material obtained by the preparation method according to any one of claims 1-8 as a negative electrode of a lithium-ion battery or a sodium-ion battery.

12. The application according to claim 11, Characterized in that, The battery negative electrode is formed by mixing an active material, a conductive material, a binder and a solvent to form a slurry, coating the slurry on a current collector, and drying.

13. An ion battery, the ion battery is a lithium-ion battery or a sodium-ion battery, Characterized in that, The active material in the negative electrode of the lithium-ion battery or sodium-ion battery is the pomegranate-like nitrogen-doped carbon-coated tin-nickel alloy composite material described in claim 9 or 10; the tin-nickel alloy includes Ni 2.67 Sn 2 , Ni 3 Sn, Sn.

14. The ion battery according to claim 13, Characterized in that, It is composed of a positive electrode, a separator, an electrolyte and a negative electrode.

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