Nitrogen-doped carbon-encapsulated sheet stack microrod-like bismuth material, and preparation method and application thereof

Abstract

The application provides a nitrogen-doped carbon-encapsulated sheet layer stacked microrod-shaped bismuth material and a preparation method and application thereof. The microrod-shaped bismuth matrix is tightly stacked by a plurality of sandwiched nanosheet units, the inside of the sheet layer is metal bismuth, and the outside is a nitrogen-doped carbon shell. The nitrogen-doped carbon-encapsulated sheet layer stacked microrod-shaped bismuth material is obtained by sintering and carbonization of the sheet layer stacked structure containing the microrod-shaped bismuth oxybromide coated with dopamine. The nanosheet units of the material are stacked to form a microstructure, and the nitrogen-doped carbon is tightly encapsulated outside, so that when the material is used as a negative electrode of a sodium ion battery, the transmission path of sodium ions can be effectively shortened to realize fast charging and discharging, direct contact between electrolyte and metal bismuth can be prevented, and the volume expansion of the material during the sodium intercalation / deintercalation process can be fully relieved, thereby greatly improving the rate performance and cycle stability of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion battery electrode materials, and particularly relates to a nitrogen-doped carbon-encapsulated sheet layer stacked microrod bismuth material and a preparation method and application thereof. BACKGROUND

[0002] Sodium ion batteries have great application potential in the fields of medium and low speed electric vehicles, large-scale energy storage and low temperature due to their abundant sodium resources, low cost and excellent low temperature performance.

[0003] Metal bismuth is a material with stable physical and chemical properties, and has abundant reserves, easy-to-obtain raw materials, low price and environmental protection. In addition, when it is used as a negative electrode of a sodium ion battery, the theoretical mass capacity and the theoretical volume capacity are 385 mAh / g and 3773 mAh / cm 3 , respectively, which has great application value in sodium ion batteries. However, when metal bismuth is used as a negative electrode material of a sodium ion battery, the insertion of sodium ions will cause a volume expansion of about 352%, and this significant volume expansion will seriously affect the material structure, cause irreversible structural collapse, make the material lose physical connection between materials and between the material and the current collector, and even fall off from the current collector, finally leading to the failure of the battery.

[0004] Patent CN118016826A discloses a bismuth-carbon composite active material and a preparation method thereof, which comprises the following steps: mixing a bismuth-containing compound with a heat-carbonizable organic matter to obtain a precursor; and then heating the precursor to convert the bismuth-containing compound into bismuth elemental particles and the heat-carbonizable organic matter into hard carbon, thereby obtaining the bismuth-carbon composite active material. The material has a wide source, a simple method, is green and pollution-free, and provides a possibility for large-scale production. At least part of the hard carbon in the bismuth-carbon composite material prepared by the method is coated on the surface of the bismuth elemental particles to form a hard carbon coating layer, or is intercalated between the bismuth elemental particles to form a hard carbon filling layer, which can alleviate the volume expansion of the sodium ion battery during charging and discharging. However, the relatively low bismuth content in the material limits the mass specific capacity of the material, and the structure in which only part of the hard carbon coats the bismuth elemental particles is also not conducive to the rate performance of the material at a larger current density; the capacity of the material is only 332 mAh / g after 450 cycles at a current density of 0.4 A / g, and the maximum current density in the rate performance test is only 5 A / g. Patent CN116111063A discloses a multi-layer nitrogen-doped carbon-coated bismuth material, a preparation method and application thereof, which comprises the following steps: preparing bismuth alginate gel balls by using sodium alginate, urea and bismuth nitrate pentahydrate, and then performing calcination and dopamine hydrochloride coating in two steps after freeze-drying, and drying to obtain the multi-layer nitrogen-doped carbon-coated bismuth material. The material has a uniform morphology, and the bismuth metal is uniformly dispersed to avoid re-aggregation during the preparation process, thereby improving the stability of the structure. However, the high carbon content in the material reduces the mass specific capacity and volume specific capacity of the material; at the same time, the small nano-scale structure has a higher production cost and is prone to produce more by-products during the cycle process, which is not conducive to commercial application; the capacity of the material is only 136 mAh / g after 1000 cycles at a current density of 1 A / g, and the maximum current density in the rate performance test is only 10 A / g. In the paper "Integrating Bi@C Nanospheres in Porous Hard Carbon Frameworks for Ultrafast Sodium Storage, Adv. Mater. 2022, 34, 2202673", a micro-sized bismuth-carbon composite material and a preparation method thereof are disclosed, which comprises the following steps: synthesizing bismuth / organic micro-rods by using bismuth nitrate pentahydrate and trimesic acid under solvothermal reaction conditions, and then directly sintering and reducing the bismuth / organic micro-rods in an argon atmosphere to obtain the micro-sized bismuth-carbon composite material. The material places the metal bismuth particles in the hard carbon framework, thereby effectively improving the cycle stability of the material.However, the hard carbon skeleton of the material has a high carbon content, and the content of elemental bismuth is only 79.8 wt.%, which reduces the capacity of the material; and part of the metal bismuth particles are exposed on the surface of the microrod, which limits the rate performance of the material at a larger current density; the capacity of the material is only 305 mAh / g after 5000 cycles at a current density of 5 A / g, and the maximum current density in the rate performance test is 80 A / g. Therefore, it is necessary to further optimize the carbon encapsulation method, limit the volume expansion of metal bismuth during sodium storage, increase the size of the material and the content of metal bismuth, design a more reasonable micro-nano composite structure, and fully utilize the high theoretical mass and volume specific capacity of metal bismuth, so as to ultimately obtain a metal bismuth-based sodium ion battery negative electrode material with high specific capacity, long cycle stability and excellent rate performance, thereby promoting its commercial application.

[0005] Patent CN115986090A discloses a nitrogen-doped bismuth / carbon composite microsphere material and its preparation method and application. It should be noted that both the present application and the product of the patent are bismuth-based materials in terms of chemical properties, but the design and invention ideas and results are completely different, and there are great differences in material design and synthesis, material structure and morphology, and electrochemical performance.

[0006] The existing solutions mostly use simple surface coating or mix bismuth with carbon materials to form a composite. These methods indeed alleviate the volume expansion of bismuth negative electrode material to some extent and improve the cycle stability, but still cannot solve the problem of rapid capacity decay of bismuth during long-term cycling, especially at a high current density, which greatly limits its commercial application. SUMMARY

[0007] The present application is made in view of the above-mentioned problems, and in order to solve at least one of the above-mentioned technical problems, the present application proposes a nitrogen-doped carbon-encapsulated sheet layer-stacked microrod-shaped bismuth material and its preparation method and application. Benefiting from the microrod structure formed by the close stacking of nanosheet units, the material has a small specific surface area and a high tap density, the short sodium ion migration path and the protection of the carbon layer effectively improve the rate performance and cycle stability of the material, and the high bismuth content of the microrod also ensures its high mass specific capacity.

[0008] In a first aspect, the present application provides a nitrogen-doped carbon-encapsulated sheet layer-stacked microrod-shaped bismuth material, which comprises a microrod-shaped bismuth matrix formed by the close stacking of a plurality of nanosheet units, and the inside of the nanosheet unit is metal bismuth and the outside is an encapsulation layer of nitrogen-doped amorphous carbon.

[0009] In any embodiment, the mass fraction of elemental bismuth in the microrod is 80% to 94%.

[0010] In any embodiment, the microrod-shaped bismuth matrix is a sheet layer-stacked bromine-oxygen bismuth microrod.

[0011] In any embodiment, the nitrogen in the external nitrogen-doped structure is one or more of graphitic nitrogen, pyridinic nitrogen, and pyrrolic nitrogen.

[0012] In any embodiment, the micro-rod-like structure of the material has an average cross-sectional width of 4-6 μm and an average length of 8-12 μm.

[0013] In any embodiment, the nitrogen-doped carbon-encapsulated micro-rod-like bismuth material has a specific surface area of 54-70 m 2 2 / g; and a tap density of 1.62-1.67 g / cm 3 .

[0014] In a second aspect, a method for preparing a nitrogen-doped carbon-encapsulated micro-rod-like bismuth material is provided, comprising the following steps:

[0015] S10: synthesizing bismuth oxybromide micro-rods having a layered structure;

[0016] S20: dispersing the micro-rods in S10 and dopamine hydrochloride in a tris(hydroxymethyl)aminomethane aqueous solution to obtain dopamine-coated micro-rods;

[0017] S30: obtaining the nitrogen-doped carbon-encapsulated micro-rod-like bismuth material by sintering and carbonizing the micro-rods in S20.

[0018] In any embodiment, S10 comprises:

[0019] S11: continuously stirring a mixture of bismuth nitrate pentahydrate and trimesic acid in a methanol solution at room temperature;

[0020] S12: performing a hydrothermal reaction on the stirred mixture in a sealed autoclave;

[0021] S13: washing the reaction product obtained in S12 with methanol and drying to obtain bismuth / organic micro-rods;

[0022] S14: continuously stirring a mixture of the bismuth / organic micro-rods in S13 and potassium bromide in a mixture of water and ethylene glycol at room temperature;

[0023] S15: washing the reaction product in S14 with water and ethanol and drying to obtain bismuth oxybromide micro-rods having a layered structure.

[0024] ​In any embodiment, the mass ratio of the bismuth nitrate pentahydrate to the trimesic acid is 2:1, the stirring time is 10 min; the hydrothermal reaction is incubated at 120 DEG C for 35 min; the mass ratio of the bismuth / organic microrod to the potassium bromide is 1:3, the volume ratio of water to ethylene glycol is 1:1, and the stirring time is 5 h.

[0025] In any embodiment, the S20 comprises:

[0026] S21: dissolving the bromine-oxygen bismuth microrod containing the laminar stacking structure and the dopamine hydrochloride in the aqueous solution of tris(hydroxymethyl) aminomethane, and continuously stirring magnetically at room temperature;

[0027] S22: washing the reactant obtained in S21 with water, and obtaining the dopamine-encapsulated bromine-oxygen bismuth microrod containing the laminar stacking structure after drying.

[0028] In any embodiment, the concentration of the tris(hydroxymethyl) aminomethane dissolved in the aqueous solution is 10 x 10 -3 M; the mass ratio of the bromine-oxygen bismuth microrod containing the laminar stacking structure to the dopamine hydrochloride is 1:0.6, and the stirring time is 4 h.

[0029] In any embodiment, the sintering carbonization mode in S30 is that the dopamine-encapsulated bromine-oxygen bismuth microrod containing the laminar stacking structure obtained in S20 is placed in a tube furnace, heated to 450 DEG C at a heating rate of 2 DEG C / min to 5 DEG C / min under a mixed atmosphere of hydrogen and argon V H2 / V Ar = 20 / 100 mL / min, and incubated for 3 h; then, the nitrogen-doped carbon-encapsulated laminar stacking microrod-shaped bismuth material is obtained after natural cooling.

[0030] In a third aspect, the application provides an application of the nitrogen-doped carbon-encapsulated laminar stacking microrod-shaped bismuth material as a negative electrode material of a sodium ion battery.

[0031] The application has the following beneficial effects:

[0032] 1) The nitrogen-doped carbon-encapsulated laminar stacking microrod-shaped bismuth material provided by the application has low cost, all raw materials are conventional materials, the preparation process is simple, the cycle is short, the yield is considerable, and there is no by-product;

[0033] 2) The nitrogen-doped carbon-encapsulated laminar stacking microrod-shaped bismuth material provided by the application has excellent crystallinity, stability, and more active sites and moderate specific surface area;

[0034] 3) The method uses bismuth salt as a bismuth source and dopamine as a carbon source and nitrogen source, and the required materials are simple and low in cost. The target product is prepared by a hydrothermal-liquid phase structure construction-carbonization reduction method, so that the bismuth-carbon structure is more compact, and the material morphology is more uniform, overcoming the problems of material disintegration and poor uniformity caused by unstable bismuth-carbon combination interface in the traditional carbon coating method.

[0035] 4) The nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material provided by the application has a microrod structure as a whole, is reasonably stacked by nanosheets inside, and is encapsulated by nitrogen-doped amorphous carbon outside, improves the space utilization, and has a high volume specific capacity. As a sodium ion battery negative electrode material, the material can provide a higher sodium storage capacity in a limited space of a battery system, and has a wide commercial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Figure A is a scanning electron microscope (SEM) image of the bismuth / organic microrod in the application, Figure B is a scanning electron microscope (SEM) image of the bismuth oxybromide microrod containing sheet layer stacked structure, and Figure C is a scanning electron microscope (SEM) image of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material.

[0037] Figure 2 Figure is an X-ray diffraction spectrum (XRD) of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in the application.

[0038] Figure 3 Figure is a transmission electron microscope (TEM) image, X-ray energy spectrum analysis (EDS) image and electron diffraction image of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in the application.

[0039] Figure 4 Figure is a thermogravimetric analysis (TGA) of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in the application, wherein the content of metallic bismuth is 91wt.%.

[0040] Figure 5 Figure is an XPS-Bi4f, XPS-C1s and XPS-N1s spectrum of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in the application.

[0041] Figure 6 Figure is a tap density test result graph of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in the application.

[0042] Figure 7 Figure is a specific surface and porosity analysis (BET) test curve graph of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in the application.

[0043] Figure 8is a cyclic voltammetry (CV) test curve graph when the nitrogen-doped carbon-encapsulated sheet layer-stacked microrod-shaped bismuth material of the present application is used as a negative electrode material of a sodium ion battery.

[0044] Figure 9 is a cycle performance graph at a current density of 1 A / g when the nitrogen-doped carbon-encapsulated sheet layer-stacked microrod-shaped bismuth material of the present application is used as a negative electrode material of a sodium ion battery.

[0045] Figure 10 is a cycle performance graph at a current density of 5 A / g when the nitrogen-doped carbon-encapsulated sheet layer-stacked microrod-shaped bismuth material of the present application is used as a negative electrode material of a sodium ion battery.

[0046] Figure 11 is a rate performance graph when the nitrogen-doped carbon-encapsulated sheet layer-stacked microrod-shaped bismuth material of the present application is used as a negative electrode material of a sodium ion battery.

[0047] Figure 12 is a cycle performance graph at a large current density of 10 A / g when the nitrogen-doped carbon-encapsulated sheet layer-stacked microrod-shaped bismuth material of the present application is used as a negative electrode material of a sodium ion battery. DETAILED DESCRIPTION

[0048] Hereinafter, specific embodiments of the nitrogen-doped carbon-encapsulated sheet layer-stacked microrod-shaped bismuth material of the present application, a method of preparing the same, and applications thereof are disclosed in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters that are well known, repeated descriptions of substantially the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0049] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0051] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0052] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0053] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0054] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0055] The nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material has a microrod bismuth matrix, the microrod is stacked by a plurality of nanosheet bismuth, and the outside is tightly encapsulated by nitrogen-doped amorphous carbon. Due to the microrod structure formed by reasonable stacking of nanosheets, the material has more excellent kinetic diffusion performance and exhibits extremely excellent rate performance. The encapsulation of the external nitrogen-doped carbon layer can effectively alleviate the volume expansion of the material, thereby improving the cycle stability. The micrometer structure has higher tap density and smaller specific surface area than the nanometer structure, and is more suitable for practical application of sodium ion batteries.

[0056] A nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material, comprising:

[0057] The microrod bismuth matrix is tightly stacked by a plurality of sandwiched nanosheet units, the inside of the nanosheet is metal bismuth, and the outside is nitrogen-doped amorphous carbon. The type of nitrogen in the nitrogen-doped structure is graphite nitrogen, pyridine nitrogen, and pyrrole nitrogen.

[0058] In some embodiments, the mass fraction of elemental bismuth in the microrod is 80% to 94%.

[0059] In some embodiments, the external encapsulated carbon layer is amorphous carbon.

[0060] In some embodiments, the overall microrod structure of the material has an average width of 4 μm to 6 μm and an average length of 8 μm to 12 μm in cross section.

[0061] Since bismuth will undergo a significant volume expansion of about 352% during the cycle process when used as a negative electrode material for sodium ion batteries, the size of bismuth nanoparticles directly affects the mass fraction of bismuth after the material is compounded with carbon. When the bismuth-carbon composite material is used as a negative electrode for sodium ion batteries, the sodium storage function is mainly realized by bismuth. If the mass fraction of bismuth is reduced, the battery capacity will be reduced; on the contrary, if the bismuth content is too high, the overall expansion rate of the material will increase, thereby causing the material to crack during the cycle process and leading to battery failure.

[0062] In some embodiments, the specific surface area of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material is 54 m 2 / g to 70 m 2 / g; and the tap density of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material is 1.62 to 1.67 g / cm3 .

[0063] The nanosheet layering of bismuth can reduce the adverse effects of volume expansion, and the encapsulation of external amorphous carbon makes the material have better mechanical properties and a more stable structure during the cycle process.

[0064] A moderate specific surface area can reduce the occurrence of side reactions and the loss of electrolyte during the cycle process of the battery. Under the condition of a certain volume, if the material structure is loose, the specific surface area is relatively large. However, too large specific surface area will lead to more electrolyte consumption and side reactions in sodium ion battery materials, thereby adversely affecting the performance of the battery. On the contrary, if the material structure is more compact and the specific surface area is small, it is not conducive to the contact and infiltration of electrolyte with the material, which hinders the electrochemical reaction and also has a negative impact on the performance of the material.

[0065] In a second aspect, a preparation method of a nitrogen-doped carbon-encapsulated sheet-layer-stacked microrod-shaped bismuth material is provided, comprising the following steps:

[0066] S10: Synthesizing bromine-oxygen bismuth microrods containing a sheet-layer-stacked structure;

[0067] S20: Dispersing the bromine-oxygen bismuth microrods containing a sheet-layer-stacked structure in S10 and dopamine hydrochloride in a tris(hydroxymethyl)aminomethane aqueous solution to obtain dopamine-encapsulated bromine-oxygen bismuth microrods containing a sheet-layer-stacked structure;

[0068] S30: Obtaining a nitrogen-doped carbon-encapsulated sheet-layer-stacked microrod-shaped bismuth material by sintering and carbonizing the dopamine-encapsulated bromine-oxygen bismuth microrods containing a sheet-layer-stacked structure in S20.

[0069] The present application first designs a microrod-shaped bismuth / organic composite material with a smooth surface and a solid structure, and then obtains sheet-layer bismuth oxybromide by oxidizing and reducing potassium bromide. This method effectively converts the dense structure of the material into a rod-shaped structure stacked by sheet layers without changing the overall rod structure of the material. Then, a dopamine coating method is used to obtain a carbon layer during the subsequent carbonization process, further improving the protective properties of the carbon layer. The material synthesized by the above design idea has a sandwiched nanosheet unit, in which the sandwiched part is a metal bismuth sheet, and the outside is a carbon layer. The overall morphology of the material is a rod-shaped structure, and the bismuth content is higher. In terms of electrochemical performance, the material has significantly improved rate performance, cycle performance and specific capacity when used in sodium ion batteries, thanks to the short ion migration path of the sandwiched nanosheet unit, the protection of the carbon layer and the high bismuth content.

[0070] In some embodiments, the S10 comprises:

[0071] S11: Dissolving bismuth nitrate pentahydrate and trimesic acid in a methanol solution to obtain a mixed solution;

[0072] S12: continuously stirring the mixed solution at room temperature by magnetic force;

[0073] S13: performing a hydrothermal reaction on the stirred mixed solution in a sealed autoclave;

[0074] S14: cleaning the reaction product obtained in S13 with methanol, and drying to obtain bismuth / organic micro-rods;

[0075] S15: dissolving the bismuth / organic micro-rods obtained in S14 in a mixed solution of potassium bromide, water and ethylene glycol;

[0076] S16: continuously stirring the mixed solution at room temperature by magnetic force;

[0077] S17: cleaning the reaction product obtained in S16 with water and ethanol, and drying to obtain bismuth oxybromide micro-rods with a laminar stacking structure.

[0078] In some embodiments, the mass ratio of bismuth nitrate pentahydrate to trimesic acid is 2:1, the bismuth nitrate pentahydrate and the trimesic acid are dissolved in a methanol solution, the magnetic stirring time of the mixed solution is 10 min, the hydrothermal reaction is performed at 120°C for 35 min, the mass ratio of the bismuth / organic micro-rods to potassium bromide is 1:3, the volume ratio of water to ethylene glycol is 1:1, and the magnetic stirring time of the bismuth / organic micro-rods and the potassium bromide in the mixed solution of water and ethylene glycol is 5 h.

[0079] In some embodiments, S20 comprises:

[0080] S21: dissolving tris(hydroxymethyl)aminomethane in an aqueous solution, and controlling the concentration to be 10×10 -3 M;

[0081] S22: dissolving the bismuth oxybromide micro-rods with a laminar stacking structure and dopamine hydrochloride in the tris(hydroxymethyl)aminomethane aqueous solution;

[0082] S23: continuously stirring the mixed solution at room temperature by magnetic force;

[0083] S24: cleaning the reaction product obtained in S23 with water, and drying to obtain the bismuth oxybromide micro-rods with a laminar stacking structure coated with dopamine on the outside.

[0084] In some embodiments, the mass ratio of the bismuth oxybromide micro-rods with a laminar stacking structure to dopamine hydrochloride is 1:0.6, and the stirring time of the bismuth oxybromide micro-rods with a laminar stacking structure and dopamine hydrochloride in the tris(hydroxymethyl)aminomethane aqueous solution is 4 h.

[0085] In some embodiments, the sintering carbonization method in S30 is as follows: the dopamine-encapsulated bismuth microrod material with a layered stack structure obtained in S20 is placed in a tube furnace, heated to 400-450°C at a heating rate of 2-5°C / min under a mixed atmosphere of hydrogen and argon, and kept at this temperature for 2-3h, and then naturally cooled to obtain the nitrogen-doped carbon-encapsulated layered stack microrod bismuth material.

[0086] In a third aspect, the application provides the use of the nitrogen-doped carbon-encapsulated layered stack microrod bismuth material as a negative electrode material for a sodium ion battery.

[0087] Examples

[0088] The following describes the examples of the present application. The examples described below are exemplary and are intended only to explain the present application, and should not be construed as limiting the present application. If a specific technique or condition is not specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained commercially.

[0089] The following further describes the preparation method of the nitrogen-doped carbon-encapsulated layered stack microrod bismuth material in the present application through specific examples and experimental data:

[0090] Example 1

[0091] A preparation method of a nitrogen-doped carbon-encapsulated layered stack microrod bismuth material, comprising the following steps:

[0092] S10: 2.5g of bismuth nitrate pentahydrate and 1.25g of trimesic acid were added to 100ml of methanol, stirred at room temperature for 10min, and then the mixed solution was transferred to a 200ml sealed Teflon-lined stainless steel autoclave, which was kept at 120°C for 40min, and then naturally cooled and collected by centrifugation with methanol three times. The collected sample was dried in an electric heating air drying oven at 60°C overnight to obtain bismuth / organic microrods. 0.8g of the dried bismuth / organic microrods were dissolved in a mixed solution of 400ml of water and 400ml of ethylene glycol, and then 2.4g of KBr was added, and stirred magnetically for 5h, and then collected by centrifugation with water and ethanol three times, and the collected sample was dried in an electric heating air drying oven at 60°C overnight to obtain bromine-oxygen bismuth microrod material with a layered stack structure.

[0093] S20: 800ml of tris solution (10×10 -3M) 1 g of bismuth oxybromide microrods with lamellar stacking structure was added into M), and 0.6 g of dopamine hydrochloride was added after magnetic stirring for 2 min, followed by magnetic stirring for 4 h. The collected sample was dried in an electric heating air drying oven at 60°C overnight. The dopamine-coated bismuth oxybromide microrods with lamellar stacking structure were obtained.

[0094] S30: The dopamine-coated bismuth oxybromide microrods with lamellar stacking structure were placed in a tube furnace and calcined and reduced under a hydrogen-argon mixed atmosphere. The calcination was performed at a temperature of 450°C with a temperature rising rate of 5°C / min, and the holding time was 2 h. After cooling, the nitrogen-doped carbon-encapsulated lamellar stacking microrod-like bismuth material was obtained.

[0095] S40: The nitrogen-doped carbon-encapsulated lamellar stacking microrod-like bismuth material obtained was used as a sodium ion battery negative electrode material for assembly and characterization of a button cell. The button cell was cycled 3000, 14000 and 20000 times at current densities of 1 A / g, 5 A / g and 10 A / g, respectively, and the rate performance test was performed at different current densities of 0.1 A / g to 200 A / g.

[0096] Example 2: The difference from Example 1 is that the mass ratio of bismuth nitrate pentahydrate to trimesic acid in S10 is 1:1, and the other steps are the same as those in Example 1. The nitrogen-doped carbon-encapsulated lamellar stacking microrod-like bismuth material obtained has an average width of 3 μm and an average length of 8 μm in cross section, a mass fraction of bismuth of 90%, and a specific surface area of 65 m 2 / g.

[0097] Example 3: The difference from Example 1 is that the volume ratio of water to ethylene glycol in S10 is 1:2, and the other steps are the same as those in Example 1. The nitrogen-doped carbon-encapsulated lamellar stacking microrod-like bismuth material obtained has an average width of 4 μm and an average length of 9 μm in cross section, a mass fraction of bismuth of 80%, and a specific surface area of 58 m 2 / g.

[0098] Example 4: The difference from Example 1 is that the volume ratio of water to ethylene glycol in S10 is 2:1, and the other steps are the same as those in Example 1. The nitrogen-doped carbon-encapsulated lamellar stacking microrod-like bismuth material obtained has an average width of 2 μm and an average length of 6 μm in cross section, a mass fraction of bismuth of 92%, and a specific surface area of 70 m 2 / g.

[0099] Example 5: The difference from Example 1 is that the mass ratio of the bromine-oxygen bismuth microrod with a laminated structure and dopamine hydrochloride in S20 is 1:1, and the other steps are the same as Example 1. A nitrogen-doped carbon-encapsulated laminated microrod-shaped bismuth material is prepared, the average width of the microrod cross section is 5 μm, the average length is 10 μm, the mass fraction of bismuth is 85%, and the specific surface area is 68 m 2 / g.

[0100] Example 6: The difference from Example 1 is that the mass ratio of the bromine-oxygen bismuth microrod with a laminated structure and dopamine hydrochloride in S20 is 1:2, and the other steps are the same as Example 1. A nitrogen-doped carbon-encapsulated laminated microrod-shaped bismuth material is prepared, the average width of the microrod cross section is 6 μm, the average length is 12 μm, the mass fraction of bismuth is 83%, and the specific surface area is 65 m 2 / g.

[0101] Example 7: The difference from Example 1 is that the heating temperature in S30 is 450°C, and the holding time is 5 h, and the other steps are the same as Example 1. A nitrogen-doped carbon-encapsulated laminated microrod-shaped bismuth material is prepared, the average width of the microrod cross section is 4 μm, the average length is 9 μm, the mass fraction of bismuth is 93%, and the specific surface area is 56 m 2 / g.

[0102] Example 8: The difference from Example 1 is that the mass ratio of the bromine-oxygen bismuth microrod with a laminated structure and dopamine hydrochloride in S20 is 1:0.4, and the magnetic stirring is 3 h, the heating temperature in S30 is 450°C, and the holding time is 5 h, and the other steps are the same as Example 1. A nitrogen-doped carbon-encapsulated laminated microrod-shaped bismuth material is prepared, the average width of the microrod cross section is 6 μm, the average length is 8 μm, the mass fraction of bismuth is 94%, and the specific surface area is 54 m 2 / g.

[0103] Comparative Example 1: The difference from Example 1 is that the bismuth / organic microrod in S10 is directly calcined and reduced in S30, and then the obtained material is assembled into a button cell as a negative electrode material for a sodium ion battery. After 10,000 cycles at a current density of 5 A / g, the capacity is only 91 mAh / g, and the retention rate is 54.2%; after 5,000 cycles at a current density of 10 A / g, the capacity is only 33 mAh / g, and the retention rate is 30.8%, which is much lower than that of Example 1.

[0104] The following Figures 1 to 12 The nitrogen-doped carbon-encapsulated laminated microrod-shaped bismuth material of the present application is described in detail.

[0105] Figure 1A is a scanning electron microscope (SEM) image of the bismuth / organic microrod in the present application, B is a scanning electron microscope (SEM) image of the bismuth oxybromide microrod containing the laminar stacking structure, and C is a scanning electron microscope (SEM) image of the laminar stacking microrod-like bismuth material encapsulated by nitrogen-doped carbon; the three groups of scanning electron microscope images intuitively show that the laminar stacking microrod-like bismuth material encapsulated by nitrogen-doped carbon is formed by gradually constructing a laminar stacking structure from a solid bismuth / organic microrod, and the average width of the cross section of the microrod is 4 μm to 6 μm, and the average length is 8 μm to 12 μm.

[0106] Figure 2 is an X-ray diffraction (XRD) image of the laminar stacking microrod-like bismuth material encapsulated by nitrogen-doped carbon in Example 1 of the present application, wherein 22.5°, 27.2°, 38.0°, 39.6°, 44.6°, 46.0°, 48.7°, 56.0°, 59.3, 62.2°, 64.5°, 67.4°, and 70.8° correspond to the (003), (012), (104), (110), (015), (113), (202), (024), (107), (116), (122), (018), and (214) crystal planes of metallic bismuth, respectively, showing good crystallinity of the bismuth matrix.

[0107] Figure 3 is a transmission electron microscope (TEM) image, an X-ray energy spectrum analysis (EDS) image, and an electron diffraction image of the laminar stacking microrod-like bismuth material encapsulated by nitrogen-doped carbon in the present application, Figure 3 showing that the material is composed of Bi elements as a whole; in combination with Figure 1 the scanning electron microscope image, it is shown that the C and N elements are uniformly distributed on the surface of the material.

[0108] Figure 4 is a thermogravimetric analysis (TGA) image of the laminar stacking microrod-like bismuth material encapsulated by nitrogen-doped carbon in Example 1 of the present application, showing that the bismuth content of the material is 91 wt.%. When the laminar stacking microrod-like bismuth material encapsulated by nitrogen-doped carbon is used as the negative electrode of a sodium ion battery, the sodium storage function is mainly realized by bismuth. If the mass fraction of bismuth decreases, the capacity of the battery will decrease; on the contrary, if the bismuth content is too high, the overall expansion rate of the material will increase, thereby causing the material to break during the cycle process, resulting in failure of the battery.

[0109] Figure 5 is an XPS-C1 s, XPS-N1 s, and XPS-Bi4f spectrum of the laminar stacking microrod-like bismuth material encapsulated by nitrogen-doped carbon in Example 1 of the present application, Figure 5The C, N, Bi three element fine spectrum of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material is shown, and the fine spectrum clearly shows the bonding mode of each element and the type of nitrogen in the nitrogen-doped structure, which is graphitic-N, pyridinic-N and pyrrolic-N, respectively.

[0110] Figure 6 The tap density test result graph of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in the application is shown, and the tap density of the material is 1.64g / cm after 2.134g of powder sample is placed in the JZ-1 type powder tap density instrument and vibrated for 1h. 3 The higher tap density indicates that the material can provide higher capacity in limited space.

[0111] Figure 7 The specific surface and porosity analysis (BET) test curve graph of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in the application is shown, which shows that the specific surface area of the material is 63.44m 2 / g, and the pore width classification is mesoporous.

[0112] Figure 8 The CV test curve graph of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in Example 1 of the application as the negative material of the sodium ion battery is shown. Figure 6 The cathode peak in the middle corresponds to the sodium process of bismuth at 0.63V and 0.49V; the anode peak is located at 0.61V and 0.75V, corresponding to the desodium process of Na3Bi to NaBi and NaBi to Bi.

[0113] Figure 9 The cycle performance graph of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in Example 1 of the application as the negative material of the sodium ion battery at a current density of 1A / g is shown. The first three circles are 0.1A / g small current activation, and the fourth circle is 1A / g current density. The discharge specific capacity of the fourth circle is 396mAh / g, and the capacity is 381mAh / g after 3000 cycles, with a retention rate of up to 96.2%, showing excellent cycle stability.

[0114] Figure 10 The cycle performance graph of the nitrogen-doped carbon encapsulated sheet layer stacked microrod bismuth material in Example 1 of the application as the negative material of the sodium ion battery at a current density of 5A / g is shown. The first three circles are 0.1A / g small current activation, and the fourth circle is 4A / g current density. The discharge specific capacity of the fourth circle is 378mAh / g, and the capacity is 362mAh / g after 14000 cycles, with a retention rate of up to 95.8%, showing excellent cycle stability.

[0115] Figure 11 is the rate performance chart of the nitrogen-doped carbon-encapsulated sheet layer stacked microrod bismuth material of embodiment 1 as the negative electrode material of the sodium ion battery, when the current density is increased from 0.5 A / g (at this time the discharge specific capacity is 375 mAh / g) to 120 A / g (at this time the discharge specific capacity is 305 mAh / g), the capacity retention rate is 81.3%, even at a super-high current density of 200 A / g, the capacity is still 141 mAh / g, at this time it only takes 5.5 seconds to complete a charge-discharge process, and then it can still recover to 1 A / g and stabilize the cycle, the material exhibits very good rate performance and has very broad application prospects.

[0116] Figure 12 is the cycle performance chart of the nitrogen-doped carbon-encapsulated sheet layer stacked microrod bismuth material of embodiment 1 as the negative electrode material of the sodium ion battery at a large current density of 10 A / g, after 20000 cycles, the capacity is still 286 mAh / g, relative to the capacity of 334 mAh / g at the fourth cycle of the initial cycle, the capacity retention rate is 85.6%, and the cycle stability is excellent.

[0117] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A nitrogen-doped carbon-encapsulated, layered, stacked micron-shaped bismuth material, characterized in that, The material comprises a micron-sized rod-shaped bismuth matrix, which is composed of multiple tightly stacked sandwich nanosheet units. The nanosheet units contain metallic bismuth internally and are encapsulated by a nitrogen-doped amorphous carbon layer externally. The mass fraction of elemental bismuth in the micron-shaped rods is 80%–94%. The overall micron-shaped rod structure of the material has an average cross-sectional width of 4 μm–6 μm and an average length of 8 μm–12 μm. The nitrogen-doped carbon-encapsulated stacked micron-shaped bismuth material has a specific surface area of ​​54 m². 2 / g~70m 2 / g; the tap density of the nitrogen-doped carbon-encapsulated layered stacked micron-shaped bismuth material is 1.62–1.67 g / cm³. 3 .

2. The method for preparing a nitrogen-doped carbon-encapsulated, sheet-stacked micron-shaped bismuth material as described in claim 1, comprising the following steps: S10: Synthesize bismuth oxybromooxymicron rods containing a layered stacked structure; S20: Disperse the microrods in S10 and dopamine hydrochloride in an aqueous solution of tris(hydroxymethyl)aminomethane to obtain microrods externally coated with dopamine; S30: Nitrogen-doped carbon-encapsulated sheet-stacked micron rod-shaped bismuth material is obtained by sintering and carbonizing the micron rods in S20; S10 includes: S11: A mixed solution of bismuth nitrate pentahydrate and pyromellitic acid dissolved in methanol solution is continuously magnetically stirred at room temperature; S12: The stirred mixture is subjected to a hydrothermal reaction in a sealed autoclave; S13: The reactants obtained in S12 were washed with methanol and dried to obtain bismuth / organic microrods; S14: Dissolve the bismuth / organic microrods of S13 with potassium bromide in a mixed solution of water and ethylene glycol and stir continuously with magnetic force at room temperature; S15: Wash the reactants of S14 with water and ethanol, and dry them to obtain bismuth oxybromotriene microrods with a layered stacked structure. The mass ratio of bismuth nitrate pentahydrate to trimesic acid is 2:1; the hydrothermal reaction is carried out at 120°C for 35 minutes; the mass ratio of bismuth / organic microrods to potassium bromide is 1:3; the sintering temperature is 400–450°C, and the holding time is 2–3 hours.

3. The preparation method according to claim 2, characterized in that, The bismuth nitrate pentahydrate and trimesic acid were stirred for 10 min; the volume ratio of water to ethylene glycol was 1:1, and the stirring time was 5 h.

4. The preparation method according to claim 2, characterized in that, S20 includes: S21: Dissolve bismuth oxybromotrione microrods containing a layered stacked structure and dopamine hydrochloride in an aqueous solution of tris(hydroxymethyl)aminomethane and stir continuously with magnetic force at room temperature; S22: The reactants obtained in S21 are washed with water and dried to obtain bismuth oxybromobismuth microrods with a layered stacked structure and externally coated with dopamine.

5. The preparation method according to claim 2, characterized in that, The concentration of the tris(hydroxymethyl)aminomethyl in aqueous solution is 10 × 10⁻⁶. -3 M; The mass ratio of the bismuth oxybromotrione microrods containing the layered stacked structure to dopamine hydrochloride is 1:0.6, and the stirring time is 4 hours.

6. The preparation method according to claim 2, characterized in that, The sintering and carbonization method in S30 is as follows: the bismuth oxybromotriene microrods with dopamine-coated outer layer and layered stacked structure obtained in S20 are placed in a tube furnace and heated to 450°C at a heating rate of 2°C / min to 5°C / min under a mixed atmosphere of hydrogen and argon, and held for 3 hours. Then, after natural cooling, a nitrogen-doped carbon-encapsulated, sheet-stacked micron-shaped bismuth material is obtained.

7. The application of the nitrogen-doped carbon-encapsulated layered stacked micron rod-shaped bismuth material according to claim 1 or the nitrogen-doped carbon-encapsulated layered stacked micron rod-shaped bismuth material obtained by the preparation method according to any one of claims 2-6 as a negative electrode material for sodium-ion batteries.

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