Nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries and preparation method thereof

Abstract

The present invention relates to the technical field of battery materials, and in particular to a nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries and a preparation method thereof. The preparation method comprises preparing a mixture powder of dodecyl sulfonate and a nitrogen source, carbonizing under inert gas conditions, washing the carbonized product, and vacuum drying to obtain a nitrogen-sulfur co-doped hard carbon negative electrode material. The introduction of nitrogen atoms in the negative electrode material prepared by the present invention can change the surface charge distribution of the carbon material, improve the electronic conductivity, and at the same time increase the active sites, and promote the capacitive adsorption behavior of the carbon material for sodium / potassium ions; the introduction of sulfur atoms can increase the hard carbon interlayer spacing, reduce the sodium / potassium ion diffusion energy barrier, enhance the diffusion kinetics behavior, and synergistically improve the sodium / potassium storage performance of the hard carbon material. The above-mentioned negative electrode material can be used to prepare sodium / potassium ion batteries with high specific capacity, excellent rate performance and long cycle stability, and the preparation method is simple in process, controllable in large quantities, low in cost, and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a nitrogen-sulfur co-doped hard carbon negative electrode material for a sodium / potassium ion battery and a preparation method thereof. Background Art

[0002] Sodium- and potassium-ion batteries (SIBs) share similar operating mechanisms to lithium-ion batteries and, due to their resource reserves, exhibit significant potential for large-scale energy storage. However, due to the large ionic radius of sodium and potassium, their carbon anode materials face challenges such as low specific capacity, sluggish kinetics, and poor cycling performance, hindering their practical application.

[0003] From the perspective of reaction mode, the potassium storage pathways of carbon materials can be mainly divided into two types. One is a diffusion-controlled reaction in the form of reversible intercalation and deintercalation of potassium ions in the carbon layer; the other is a pseudocapacitive-controlled reaction in the form of reversible adsorption and desorption of potassium ions on the surface of the carbon material or in the micropores. Improving either of these two reaction modes can effectively improve the potassium storage performance of the carbon material. Increasing the carbon interlayer spacing is an effective way to improve the diffusion-controlled reaction, while increasing the active sites or defect level on the surface of the carbon material is an effective way to enhance the pseudocapacitive-controlled reaction. Therefore, in order to improve the potassium storage performance of non-graphite carbon materials, the mainstream solutions are as follows: (1) Introducing heteroatoms such as sulfur, phosphorus, and iodine with atomic radii larger than carbon to further increase the carbon interlayer spacing, broaden the potassium ion transmission channel and potassium ion storage space, and thus improve its potassium storage capacity and potassium ion intercalation kinetics; (2) Introducing heteroatoms such as boron and nitrogen with atomic radii close to carbon atoms to improve the electronic structure and defect behavior of the carbon material surface, thereby increasing the potassium storage active sites and enhancing pseudocapacitive behavior.

[0004] However, the heteroatom-doped carbon materials reported so far are limited by the need to add additional dopants, low doping efficiency and low product yield, resulting in a large waste of raw materials and high production costs, which are far from meeting the needs of industrialization. Therefore, in order to obtain heteroatom-doped carbon materials with higher yield and higher doping efficiency, it is necessary to select materials with higher carbon content as carbon sources. In addition, since the atomic radius of sulfur atoms, phosphorus atoms, etc. is larger than that of carbon atoms, the doping efficiency of sulfur-doped or phosphorus-doped carbon materials is often lower. In addition, the dopants generally used for sulfur or phosphorus doping are expensive and have toxic side effects. Organic substances, such as mercaptans, polythiophenes, diphenyl disulfide, dibenzyl disulfide, triphenylphosphine, etc., cannot meet the requirements of industrial application of heteroatom-doped carbon materials. Therefore, it is necessary to find a low-cost, green inorganic, environmentally friendly carbon source containing sulfur or phosphorus atoms. These heteroatoms have a bonding effect with the carbon atoms themselves in the carbon source structure, and can remain stable even during the later high-temperature heat treatment process, thereby effectively improving the heteroatom doping efficiency and the doping efficiency during the carbonization process to meet industrialization requirements. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the existing technology and propose a nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries and a preparation method thereof. The prepared nitrogen-sulfur co-doped carbon material has a rich pore structure and a high specific surface area. When used as the negative electrode of a sodium / potassium ion battery, the material can exhibit excellent sodium / potassium storage performance under the dual effects of increasing the carbon layer spacing and enhancing the pseudocapacitance contribution.

[0006] To achieve the above objectives, the present invention adopts the following specific technical solutions:

[0007] The method for preparing a nitrogen-sulfur co-doped hard carbon negative electrode material for a sodium / potassium ion battery provided by the present invention comprises the following steps:

[0008] S1. Weighing dodecyl sulfonate and a nitrogen source, mixing and grinding to obtain a mixture powder;

[0009] S2. carbonizing the mixture powder under inert gas conditions to obtain a carbonized product;

[0010] S3. Washing and vacuum drying the carbonized product to obtain a nitrogen-sulfur co-doped hard carbon negative electrode material.

[0011] Furthermore, in step S1, the dodecyl sulfonate is selected from at least one of sodium dodecyl sulfonate, potassium dodecyl sulfonate, calcium dodecyl sulfonate, sodium dodecylbenzenesulfonate, potassium dodecylbenzenesulfonate and calcium dodecylbenzenesulfonate, the nitrogen source is selected from at least one of melamine, dicyandiamide and urea, and the mass ratio of the dodecyl sulfonate to the nitrogen source is 2:1 to 8:1.

[0012] Furthermore, in step S1, dodecyl sulfonate and a nitrogen source are placed in a ball mill and ball-milled to obtain a mixture powder, with the ball-milling time being 2 to 4 hours and the rotation speed being 300 to 600 rpm / min.

[0013] Furthermore, in step S2, the inert gas is at least one of nitrogen, argon, and a hydrogen-argon mixture; the carbonization temperature is 800-1200°C, the heating rate is 2-5°C / min, and the carbonization time is 1-5h.

[0014] Furthermore, in step S3, the carbonized product is washed with a dilute acid solution, deionized water and ethanol, wherein the dilute acid solution is at least one of dilute hydrochloric acid, dilute sulfuric acid and dilute nitric acid; the vacuum drying temperature is 80-100° C., and the drying time is 8-12 hours.

[0015] The nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries provided by the present invention is prepared by the above-mentioned preparation method. The nitrogen-sulfur co-doped hard carbon negative electrode material is formed by chemically doping nitrogen and sulfur atoms in the hard carbon material, and the hard carbon material has a porous micron tube structure.

[0016] Furthermore, the nitrogen atom doping amount is 2-5 wt%, the sulfur atom doping amount is 1-4 wt%; the microtube length is 1-10 μm, the diameter is 0.5-1 μm, and the BET specific surface area is 400-800 m 2 ·g -1 .

[0017] The present invention can achieve the following technical effects:

[0018] The introduction of nitrogen atoms into the nitrogen-sulfur co-doped hard carbon negative electrode material prepared by the present invention can change the surface charge distribution of the carbon material, improve its electronic conductivity, and at the same time increase active sites, promoting the capacitive adsorption behavior of the carbon material for sodium / potassium ions. The introduction of sulfur atoms can increase the interlayer spacing of the hard carbon, reduce the diffusion energy barrier of sodium / potassium ions, and enhance the diffusion kinetics, thereby synergistically improving the sodium / potassium storage performance of the hard carbon material. The above-mentioned negative electrode material can be used to make sodium / potassium ion batteries with high specific capacity, excellent rate performance and long cycle stability. The preparation method provided by the present invention is simple in process, controllable in large quantities, low in cost, and environmentally friendly, and has broad prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the X-ray diffraction pattern of the nitrogen-sulfur co-doped hard carbon negative electrode material prepared according to Example 1 of the present invention.

[0020] Figure 2 This is an X-ray photoelectron spectroscopy analysis diagram of nitrogen element in the nitrogen-sulfur co-doped hard carbon negative electrode material prepared according to Example 1 of the present invention.

[0021] Figure 3 This is an X-ray photoelectron spectroscopy analysis diagram of sulfur element in the nitrogen-sulfur co-doped hard carbon negative electrode material prepared according to Example 1 of the present invention.

[0022] Figure 4 This is a transmission electron microscope image of the nitrogen-sulfur co-doped hard carbon negative electrode material prepared according to Example 1 of the present invention.

[0023] Figure 5 This is a cycle performance diagram of a potassium ion battery assembled with nitrogen-sulfur co-doped hard carbon negative electrode material prepared according to Example 1 of the present invention. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, identical modules are denoted by identical reference numerals. In the case of identical reference numerals, their names and functions are also identical. Therefore, their detailed description will not be repeated.

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0026] An embodiment of the present invention provides a method for preparing a nitrogen-sulfur co-doped hard carbon negative electrode material for a sodium / potassium ion battery, comprising the following steps:

[0027] S1. Weigh lauryl sulfonate and a nitrogen source, mix them, and grind them to obtain a mixture powder.

[0028] The dodecyl sulfonate is selected from at least one of sodium dodecyl sulfonate, potassium dodecyl sulfonate, calcium dodecyl sulfonate, sodium dodecylbenzene sulfonate, potassium dodecylbenzene sulfonate and calcium dodecylbenzene sulfonate; the nitrogen source is selected from at least one of melamine, dicyandiamide and urea; and the mass ratio of the dodecyl sulfonate to the nitrogen source is 2:1 to 8:1.

[0029] The dodecyl sulfonate and the nitrogen source are placed in a ball mill and ball-milled to obtain powder. The ball-milling time is 2 to 4 hours and the rotation speed is 300 to 600 rpm / min.

[0030] S2. Carbonizing the mixture powder under inert gas conditions to obtain a carbonized product.

[0031] The inert gas is at least one of nitrogen, argon, and hydrogen-argon mixed gas. The carbonization temperature is 800-1200° C., the heating rate is 2-5° C. / min, and the carbonization time is 1-5 hours.

[0032] S3. Washing and vacuum drying the carbonized product to obtain a nitrogen-sulfur co-doped hard carbon negative electrode material.

[0033] The carbonized product is washed with a dilute acid solution, deionized water and ethanol, wherein the dilute acid solution is at least one of dilute hydrochloric acid, dilute sulfuric acid and dilute nitric acid; the vacuum drying temperature is 80-100° C., and the drying time is 8-12 hours.

[0034] The sodium / potassium ion battery nitrogen-sulfur co-doped hard carbon negative electrode material provided by the embodiment of the present invention is prepared by the above-mentioned preparation method. The prepared negative electrode material is formed by chemically doping nitrogen and sulfur atoms in the hard carbon material. The hard carbon material has a porous micron tube structure; the nitrogen atom doping amount is 2-5wt%, the sulfur atom doping amount is 1-4wt%; the micron tube length is 1-10μm, the diameter is 0.5-1μm, and the BET specific surface area is 400-800m 2 ·g -1 .

[0035] The nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries and its preparation method provided by the present invention are described below with reference to specific embodiments.

[0036] Example 1

[0037] Sodium dodecyl sulfate and melamine were weighed in a mass ratio of 6:1, placed in a ball mill and ball milled at a speed of 500 rpm / min for 3 hours to obtain a mixture powder. The above powder was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min in a nitrogen atmosphere and kept warm for 2 hours. The obtained carbonized product was washed repeatedly three times with an appropriate amount of dilute hydrochloric acid solution (concentration of 0.5 mol / L), deionized water and ethanol to fully remove impurities, and placed in a vacuum oven at 80°C for 12 hours. The dried black product was marked as NSC-1, and the physical and chemical properties of the sample were tested and analyzed.

[0038] The NSC-1 material prepared in this example was assembled with potassium to form a button-type potassium ion battery. The material characterization and electrochemical performance of the battery are shown in Figure 2. Figures 1 to 5 shown.

[0039] Figure 1 is the X-ray diffraction pattern of the nitrogen-sulfur co-doped hard carbon negative electrode material prepared in this embodiment, Figure 1 Comparing the diffraction pattern with the standard, it can be seen that NSC-1 has a typical amorphous carbon structure.

[0040] Figure 2 This is an X-ray photoelectron spectroscopy analysis of nitrogen element in the nitrogen-sulfur co-doped hard carbon negative electrode material prepared in this embodiment. Figure 3 This is the X-ray photoelectron spectrum analysis diagram of sulfur element in nitrogen-sulfur co-doped hard carbon negative electrode material. Figure 2 and Figure 3 It can be seen that the nitrogen atoms in NSC-1 exist in three forms: graphitic nitrogen, pyridinic nitrogen and pyrrolic nitrogen, and the sulfur atoms exist in three forms: CSC and C-SO x-C exists in two chemical bond forms.

[0041] Figure 4 This is a transmission electron microscope image of the nitrogen-sulfur co-doped hard carbon negative electrode material prepared in this embodiment. Figure 4 It can be seen that the material has a loose and porous micron-tubular structure.

[0042] Figure 5 This is a graph showing the cycle performance of a potassium ion battery assembled with the nitrogen-sulfur co-doped hard carbon negative electrode material prepared in this embodiment. Figure 5 It can be seen that NSC-1 negative electrode material has a high -1 After 600 cycles at the same current density, the potassium storage capacity can still be maintained at 105.2 mAh g -1 , showing good long-term cycle stability.

[0043] Example 2

[0044] Sodium dodecyl sulfate and melamine were weighed in a mass ratio of 8:1, placed in a ball mill and ball milled at a speed of 500 rpm / min for 3 hours to obtain a mixture powder. The above powder was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min in a nitrogen atmosphere and kept warm for 2 hours. The obtained carbonized product was washed repeatedly three times with an appropriate amount of dilute hydrochloric acid solution (concentration of 0.5 mol / L), deionized water and ethanol to fully remove impurities, and placed in a vacuum oven and dried at 80°C for 12 hours. The dried black product was marked as NSC-2, and the physical and chemical properties of the sample were tested and analyzed.

[0045] The NSC-2 material prepared in this example was assembled with potassium sheets into a button-type potassium ion battery. -1 After 600 cycles at the same current density, the potassium storage capacity can still be maintained at 125.2 mAh g -1 .

[0046] Example 3

[0047] Sodium dodecylbenzenesulfonate and melamine were weighed in a mass ratio of 6:1, placed in a ball mill and ball milled at a speed of 500 rpm / min for 3 hours to obtain a mixture powder. The above powder was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min in a nitrogen atmosphere and kept warm for 2 hours. The obtained carbonized product was washed repeatedly three times with an appropriate amount of dilute hydrochloric acid solution (concentration of 0.5 mol / L), deionized water and ethanol to fully remove impurities, and placed in a vacuum oven at 80°C for 12 hours. The dried black product was marked as NSC-3, and the physical and chemical properties of the sample were tested and analyzed.

[0048] The NSC-3 material prepared in this example was assembled with potassium sheets into a button-type potassium ion battery.-1 After 600 cycles at the same current density, the potassium storage capacity can still be maintained at 115.2 mAh g -1 .

[0049] Example 4

[0050] Sodium dodecyl sulfate and melamine were weighed in a mass ratio of 6:1, placed in a ball mill and ball milled at a speed of 500 rpm / min for 3 hours to obtain a mixture powder. The above powder was placed in a tube furnace and heated to 800°C at a heating rate of 2°C / min in a nitrogen atmosphere and kept warm for 2 hours. The obtained carbonized product was washed repeatedly three times with an appropriate amount of dilute hydrochloric acid solution (concentration of 0.5 mol / L), deionized water and ethanol to fully remove impurities, and placed in a vacuum oven and dried at 80°C for 12 hours. The dried black product was marked as NSC-4, and the physical and chemical properties of the sample were tested and analyzed.

[0051] The NSC-4 material prepared in this example was assembled with potassium sheets into a button-type potassium ion battery. -1 After 600 cycles at the same current density, the potassium storage capacity can still be maintained at 110.5 mAh g -1 .

[0052] Example 5

[0053] Sodium dodecyl sulfate and melamine were weighed in a mass ratio of 6:1, placed in a ball mill and ball milled at a speed of 500 rpm / min for 3 hours to obtain a mixture powder. The above powder was placed in a tube furnace and heated to 1200°C at a heating rate of 5°C / min in a nitrogen atmosphere and kept warm for 2 hours. The obtained carbonized product was washed repeatedly three times with an appropriate amount of dilute hydrochloric acid solution (concentration of 0.5 mol / L), deionized water and ethanol to fully remove impurities, and placed in a vacuum oven at 80°C for 12 hours. The dried black product was marked as NSC-5, and the physical and chemical properties of the sample were tested and analyzed.

[0054] The NSC-5 material prepared in this example was assembled with potassium sheets into a button-type potassium ion battery. -1 After 600 cycles at the same current density, the potassium storage capacity can still be maintained at 95.5 mAh g -1 .

[0055] Comparative Example 1

[0056] Weigh a certain mass of sodium dodecyl sulfate, place it in a ball mill and mill it at a speed of 500rpm / min for 3h to obtain a mixture powder. The above powder is placed in a tube furnace and heated to 800℃ at a heating rate of 5℃ / min in a nitrogen atmosphere and kept warm for 2h. The obtained carbonized product is washed repeatedly 3 times with an appropriate amount of dilute hydrochloric acid solution (concentration of 0.5mol / L), deionized water and ethanol to fully remove impurities, and placed in a vacuum oven and dried at 80℃ for 12h. The dried black product is marked as SC-1, and the physical and chemical properties of the sample are tested and analyzed.

[0057] The SC-1 material prepared in this example was assembled with potassium sheets into button-type potassium ion batteries. -1 After 600 cycles at the same current density, the potassium storage capacity can still be maintained at 55.5 mAh g -1 .

[0058] The present invention uses sodium dodecyl sulfonate (C 12 H 25 A nitrogen-sulfur co-doped hard carbon material was obtained by high-temperature calcination under inert gas conditions using SO3Na (52.87% carbon content, 11.75% sulfur content) as the sulfur and carbon sources and melamine (66.67% nitrogen content) as the nitrogen source. Because melamine decomposes and releases gases at high temperatures (above 355°C), the resulting nitrogen-sulfur co-doped carbon material possesses a rich pore structure and a high specific surface area. When used as the negative electrode for sodium / potassium ion batteries, this material exhibits excellent sodium / potassium storage performance, thanks to the dual effects of increasing the carbon interlayer spacing and enhancing pseudocapacitance.

[0059] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0060] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0061] The above specific embodiments of the present invention do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries, characterized in that: The steps include: S1. Weighing dodecyl sulfonate and a nitrogen source, mixing and grinding to obtain a mixture powder; wherein the mass ratio of the dodecyl sulfonate to the nitrogen source is 2:1 to 8:1; S2, carbonizing the mixture powder under inert gas conditions to obtain a carbonized product; the carbonization temperature is 800° C., and the carbonization time is 2 h; S3. Washing and vacuum drying the carbonized product to obtain a nitrogen-sulfur co-doped hard carbon negative electrode material having a porous micron tube structure.

2. The method for preparing the nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries according to claim 1, characterized in that: In step S1, the dodecyl sulfonate is selected from at least one of sodium dodecyl sulfonate, potassium dodecyl sulfonate, calcium dodecyl sulfonate, sodium dodecylbenzene sulfonate, potassium dodecylbenzene sulfonate and calcium dodecylbenzene sulfonate; and the nitrogen source is selected from at least one of melamine, dicyandiamide and urea.

3. The method for preparing the nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries according to claim 1, characterized in that: In step S1, the dodecyl sulfonate and the nitrogen source are placed in a ball mill and ball milled for 2 to 4 hours at a rotation speed of 300 to 600 rpm / min.

4. The method for preparing the nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries according to claim 1, characterized in that: In step S2, the inert gas is at least one of nitrogen, argon, and a hydrogen-argon mixture, and the carbonization heating rate is 2-5°C / min.

5. The method for preparing the nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries according to claim 1, characterized in that: In step S3, the carbonized product is washed with a dilute acid solution, deionized water and ethanol, wherein the dilute acid solution is at least one of dilute hydrochloric acid, dilute sulfuric acid and dilute nitric acid; the vacuum drying temperature is 80-100° C., and the drying time is 8-12 hours.

6. A nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The sodium / potassium ion battery nitrogen-sulfur co-doped hard carbon negative electrode material is formed by chemically doping nitrogen and sulfur atoms in a hard carbon material, and the hard carbon material has a porous micron tube structure.

7. The nitrogen-sulfur co-doped hard carbon negative electrode material for sodium / potassium ion batteries according to claim 6, characterized in that: The nitrogen atom doping amount is 2 to 5 wt%, and the sulfur atom doping amount is 1 to 4 wt%. The microtube has a length of 1 to 10 μm, a diameter of 0.5 to 1 μm, and a BET specific surface area of ​​400 to 800 m 2 ·g -1 .

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