A gradient pore hierarchical nitrogen-doped carbon-coated composite sodium supplementing agent, a preparation method thereof and application thereof

Abstract

The present application relates to the field of battery, especially to a gradient pore hierarchical nitrogen-doped carbon-coated composite sodium supplement agent and its preparation method and application, comprising: a composite sodium supplement agent core and a coating layer coated on the surface of the composite sodium supplement agent core; wherein the composite sodium supplement agent core comprises: an inorganic sodium supplement phase and an organic sodium supplement phase; the coating layer comprises from inside to outside: an inner dense amorphous carbon layer, a middle mesoporous carbon layer and an outer macroporous carbon layer. The present application innovatively designs a gradient pore carbon coating structure from inside to outside, the inner dense amorphous carbon layer realizes efficient isolation protection, the middle mesoporous carbon layer solves the problem of ion transmission obstruction, and the outer macroporous carbon layer improves the electronic conduction and volume buffering capacity, completely solving the inherent contradiction between the denseness of the traditional carbon coating layer and ion transmission, realizing the synergy and unity of "isolation protection-ion transmission-electronic conduction".

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium supplement agent, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, due to their abundant raw materials, low cost, and environmental friendliness, have broad application prospects in large-scale energy storage, portable electronic devices, and other fields, making them a research hotspot in the field of new energy materials in recent years. However, during the first charge and discharge process of sodium-ion batteries, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode. This process consumes a large number of active sodium ions, resulting in low initial coulombic efficiency and excessively rapid reversible capacity decay, which seriously restricts the commercialization process of sodium-ion batteries.

[0003] Sodium replenishers are key materials for solving the aforementioned sodium ion loss problem, and their performance directly determines the electrochemical performance of sodium-ion batteries. Currently, mainstream sodium replenishers are mainly divided into two categories: inorganic and organic. Inorganic sodium replenishers have the advantages of high stability and sufficient sodium replenishment capacity, but suffer from drawbacks such as poor conductivity, high decomposition potential, and slow reaction kinetics. Organic sodium replenishers have high reactivity and moderate decomposition potential, but are prone to deliquescence and oxidation, and lack structural stability, making them difficult to store and use for long periods. To balance the stability and reactivity of sodium replenishers, organic-inorganic composite sodium replenishers have become a research focus, achieving improved sodium replenishment efficiency and structural stability through the synergistic effect of the inorganic and organic phases.

[0004] Carbon coating is currently the most common modification method to improve the performance of sodium supplements. Its core function is to isolate external air, moisture, and electrolyte, protect the active phase of the sodium supplement, and improve conductivity. However, traditional multi-stage carbon coating technology has an inherent contradiction—the trade-off between density and ion transport: on the one hand, a dense carbon coating layer can effectively isolate external substances, inhibit the deliquescence and oxidation of the active phase of sodium supplementation, and improve material stability. However, the dense structure will seriously hinder the diffusion of sodium ions and electron conduction, resulting in insufficient decomposition of the sodium supplement, high residual amount, and a significant reduction in sodium supplementation efficiency. On the other hand, a porous carbon coating layer has a rich pore structure, which is conducive to the rapid transport of sodium ions and electrolyte penetration, and improves reaction kinetics. However, excessive porosity will lead to insufficient stability of the carbon layer structure, making it impossible to achieve effective isolation and protection. Moreover, during battery charging and discharging, the volume expansion of the material can easily lead to cracking and failure of the carbon layer, shortening the battery cycle life.

[0005] In existing technologies, most carbon-coated sodium replenishing agents employ a single dense carbon layer, a single porous carbon layer, or a simple composite of both carbon layers. These methods fail to address the conflict between density and ion transport in their structural design, making it difficult to simultaneously achieve a synergistic balance between "efficient isolation and protection, rapid ion transport, and excellent electronic conduction." Furthermore, existing carbon coatings are mostly single-doped or undoped structures, resulting in insufficient catalytic activity and an inability to effectively reduce the decomposition activation energy of the sodium replenishing component, further limiting the improvement of sodium replenishment efficiency.

[0006] Therefore, there is an urgent need to innovate the carbon coating structure design, break through the performance bottleneck of traditional carbon coating, and develop a high-performance organic-inorganic composite sodium supplement. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium supplement agent, its preparation method, and its application.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A first aspect of the present invention is to provide a gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium replenisher, comprising: a composite sodium replenisher core and a coating layer coating the surface of the composite sodium replenisher core;

[0010] The core of the composite sodium supplement includes an inorganic sodium supplement phase and an organic sodium supplement phase; the inorganic sodium supplement phase has high sodium supplementation capacity and structural stability, and the organic sodium supplement phase has high reactivity and a suitable decomposition potential; the two work synergistically to balance sodium supplementation efficiency and structural stability.

[0011] The coating layer comprises, from the inside out, an inner dense amorphous carbon layer, a middle mesoporous carbon layer, and an outer macroporous carbon layer.

[0012] Preferably, the mass ratio of the inorganic sodium-supplementing phase to the organic sodium-supplementing phase is 1:(0.2-5).

[0013] Preferably, the inorganic sodium-supplementing phase includes at least one of Na2CO3, Na2Se, and NaN3; the organic sodium-supplementing phase includes at least one of disodium iminodiacetate, sodium oxalate, and sodium benzoate.

[0014] Preferably, the total thickness of the coating layer is 55-150 nm, and the mass of the coating layer is 5-20% of the composite sodium supplement.

[0015] Preferably, the inner dense amorphous carbon layer is an inner Pt-doped dense amorphous carbon layer, the middle mesoporous carbon layer is a middle N / S co-doped mesoporous carbon layer, and the outer macroporous carbon layer is an outer graphene quantum dot-doped macroporous carbon layer.

[0016] More preferably, the inner Pt-doped dense amorphous carbon layer has a pore size of <5nm and a thickness of 5-20nm, and the doping amount of platinum nanoparticles is 0.1-1wt%, with a particle size of 1-3nm. The core function of this layer is to isolate and protect, effectively blocking air, moisture and electrolyte, and inhibiting the deliquescence, oxidation and side reactions of the core sodium-supplemented active phase. At the same time, the platinum nanoparticles exert a trace amount of highly efficient catalytic effect, helping to reduce the residual decomposition activation energy of the sodium-supplemented component and improve the completeness of the decomposition of the sodium-supplemented component.

[0017] The middle layer of NS co-doped mesoporous carbon has a pore size of 5-50 nm, a thickness of 20-50 nm, a nitrogen doping amount of 5-10 at%, and a sulfur doping amount of 2-5 at%. This layer serves as a fast sodium ion transport channel, effectively solving the problem of sodium ion diffusion being hindered by the inner dense carbon layer, and achieving full contact between the electrolyte and the core sodium-supplementing active phase. At the same time, the active sites formed by NS co-doping can enhance electrochemical catalytic activity, further reduce the decomposition activation energy of the sodium-supplementing component, optimize the decomposition potential, and improve reaction kinetics performance.

[0018] The outer graphene quantum dot-doped macroporous carbon layer has a pore size of 50-200 nm and a thickness of 30-80 nm, with a graphene quantum doping amount of 2-5 wt% and a particle size of 5-10 nm. This layer is tightly coupled with the outer three-dimensional conductive network, which can significantly improve the electronic conductivity of the composite sodium supplement. The graphene quantum dots have a high specific surface area and excellent catalytic activity, which can synergistically enhance the catalytic effect with the middle NS co-doped structure, achieving a deep integration of the conductive and catalytic functions of the carbon coating layer. In addition, the macroporous structure can also buffer the volume expansion of the material during charging and discharging, avoid carbon layer cracking, and extend the cycle life of the material.

[0019] A second aspect of the present invention is to provide a method for preparing the above-mentioned gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium supplementer, the steps of which include:

[0020] S1. After ball milling and mixing the inorganic sodium-supplementing phase and the organic sodium-supplementing phase, vacuum drying is performed and heat treatment is carried out at 200-400℃ for 1-3 hours under an inert atmosphere. After treatment, the mixture is ground and sieved to obtain the core of the composite sodium supplement.

[0021] S2. The core of the composite sodium supplement is dispersed in ethanol, and Pt nanoparticle sol, phenolic resin and nano SiO2 template are added to react. After the reaction is completed, the core is dried and carbonized at 600-800℃ for 2-4 hours under an inert atmosphere. After carbonization, the template is removed by HF and washed and dried to obtain an inner Pt-doped dense amorphous carbon layer.

[0022] S3. Place the product from step S2 in a CVD furnace, introduce nitrogen, sulfur and carbon sources, deposit at 700-900℃ for 1-3 hours and then cool to obtain a middle layer of NS co-doped mesoporous carbon layer.

[0023] S4. Disperse the product of step S3 in ethanol, add graphene quantum dot solution and polystyrene microsphere template to react, dry after reaction and deposit in CVD furnace at 800-1000℃ for 1-2h. After deposition, remove template with toluene and wash and dry to obtain the gradient pore hierarchical nitrogen-doped carbon-coated composite sodium supplement agent.

[0024] Preferably, the mass ratio of the composite sodium supplement core to the nano-SiO2 template is 1:(0.05-0.2), and the mass ratio of the composite sodium supplement core to the polystyrene microsphere template is 1:(0.1-0.3).

[0025] Preferably, in step S3, the molar ratio of the nitrogen source, the sulfur source and the carbon source is (3-5):(1-2):10; the nitrogen source includes at least one of pyridine and ammonia; the sulfur source includes at least one of carbon disulfide and thiourea; and the carbon source includes at least one of acetylene and methane.

[0026] A third aspect of the present invention is to provide a positive electrode sodium supplementation additive, comprising: the above-mentioned gradient pore hierarchical nitrogen-doped carbon-coated composite sodium supplementation agent or the gradient pore hierarchical nitrogen-doped carbon-coated composite sodium supplementation agent prepared by the above preparation method; wherein the amount of the gradient pore hierarchical nitrogen-doped carbon-coated composite sodium supplementation agent added is 3-15% of the mass of the positive electrode active material.

[0027] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0028] This invention innovatively designs a gradient porous carbon coating structure from the inside out. The inner dense amorphous carbon layer provides efficient isolation and protection, the middle mesoporous carbon layer solves the problem of ion transport obstruction, and the outer macroporous carbon layer enhances electron conduction and volume buffering capacity. This completely resolves the inherent contradiction between the density and ion transport of traditional carbon coatings, achieving a synergistic unity of "isolation and protection, ion transport, and electron conduction." This invention employs a hierarchical doping system of Pt nanoparticles, N / S dual elements, and graphene quantum dots, enabling the carbon coating layer to simultaneously possess four functions: "isolation and protection, ion transport, electron conduction, and catalytic decomposition." Among these, the co-doping of Pt nanoparticles and N / S, and the synergistic effect of graphene quantum dots, can reduce the activation energy of sodium supplementation component decomposition and improve sodium supplementation efficiency. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of a gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium supplement agent in one embodiment of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0033] Example

[0034] This embodiment provides a method for preparing a gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium supplement, the steps of which include:

[0035] S1. Weigh 10g Na2CO3 and 10g disodium iminodiacetate, add 50mL anhydrous ethanol, and ball mill in a ball mill for 5h to mix evenly; place the slurry in a vacuum drying oven at 70℃ and dry for 4h to obtain the core precursor; place the precursor in a tube furnace and heat treat at 300℃ for 2h under Ar atmosphere, cool and grind, and pass through a 300-mesh sieve to obtain the composite sodium supplement core.

[0036] S2. Take 10g of the composite sodium supplement core and disperse it in 30mL of anhydrous ethanol. Sonicate for 15min. Add 5mL of Pt nanoparticle sol and 2g of phenolic resin and stir for 2h. Add 1g of nano SiO2 template and continue stirring for 2h. Dry at 70℃ for 3h. Place the precursor in a tube furnace and carbonize at 700℃ for 3h under Ar atmosphere. Remove the SiO2 template by soaking in dilute HF solution for 12h. Wash with deionized water until neutral and vacuum dry to obtain an inner Pt-doped dense amorphous carbon layer.

[0037] S3. Place the inner coating product into a CVD furnace, introduce an Ar atmosphere, heat to 800℃, and hold for 30 min; introduce pyridine, carbon disulfide, and acetylene in a molar ratio of 4:1:10, control the gas flow rate at 50 sccm, and the furnace pressure at 0.1 MPa, and deposit for 2 h; cool to room temperature to obtain the middle layer NS co-doped mesoporous carbon layer.

[0038] S4. Take 10g of the middle layer coated product and disperse it in 30mL of anhydrous ethanol. Sonicate for 15min. Add 10mL of graphene quantum dot solution and 2g of polystyrene microsphere template. Stir for 2h and dry at 70℃ for 3h. Place in a CVD furnace and heat to 900℃ under Ar atmosphere. Hold for 30min. Introduce acetylene and deposit for 1.5h. Soak in toluene for 24h to remove the template. Wash with deionized water and vacuum dry to obtain a gradient pore hierarchical nitrogen-doped carbon-coated composite sodium supplementer.

[0039] Comparative Example 1

[0040] This comparative example provides a sodium supplement agent, with a carbon coating layer that is a single, dense, amorphous carbon layer (100 nm thick, without any doping), and all other aspects are the same as in Example 1.

[0041] Comparative Example 2

[0042] This comparative example provides another sodium supplement agent, with a carbon coating layer consisting of a single mesoporous carbon layer (pore size 20 nm, N-doped only, doping amount 8 at%), and all other aspects being the same as in Example 1.

[0043] Comparative Example 3

[0044] This comparative example provides another sodium supplement agent. The carbon coating layer is undoped, and the remaining gradient channel structure is the same as in Example 1, that is, only the gradient channels are retained and the hierarchical doping system is removed.

[0045] Detection Examples

[0046] The sodium supplement agent described in Examples 1-3 and the positive electrode slurry were used to prepare positive electrode sheets, with the sodium supplement agent addition amount being 3.5% in each case. These were then matched with hard carbon negative electrodes to prepare soft-pack sodium-ion batteries for electrochemical testing. The results are shown in Table 1.

[0047] Table 1

[0048]

[0049] Comparative examples and Comparative Examples 1-3 show that the gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium supplementer prepared by the present invention is significantly superior to the traditional carbon-coated sodium supplementer in terms of decomposition potential, initial coulombic efficiency, cycle stability, and complete decomposition of sodium supplementing components. This fully demonstrates that the gradient-channel structure and hierarchical doping system of the present invention can effectively solve the performance trade-off problem of traditional carbon coating, achieve multiple functional synergy, and have excellent electrochemical performance and industrial application prospects.

[0050] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium replenisher, characterized in that, include: The core of the compound sodium supplement and the coating layer covering the surface of the core of the compound sodium supplement; The core of the composite sodium supplement includes: an inorganic sodium supplement phase and an organic sodium supplement phase; The coating layer comprises, from the inside out, an inner dense amorphous carbon layer, a middle mesoporous carbon layer, and an outer macroporous carbon layer.

2. The gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium replenisher according to claim 1, characterized in that, The mass ratio of the inorganic sodium-supplementing phase to the organic sodium-supplementing phase is 1:(0.2-5).

3. The gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium replenisher according to claim 1, characterized in that, The inorganic sodium-supplementing phase includes at least one of Na2CO3, Na2Se, and NaN3; the organic sodium-supplementing phase includes at least one of disodium iminodiacetate, sodium oxalate, and sodium benzoate.

4. The gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium replenisher according to claim 1, characterized in that, The total thickness of the coating layer is 55-150 nm, and the mass of the coating layer is 5-20% of the composite sodium supplement.

5. The gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium replenisher according to claim 1, characterized in that, The inner dense amorphous carbon layer is an inner Pt-doped dense amorphous carbon layer, the middle mesoporous carbon layer is a middle N / S co-doped mesoporous carbon layer, and the outer macroporous carbon layer is an outer graphene quantum dot-doped macroporous carbon layer.

6. The gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium replenisher according to claim 5, characterized in that, The inner Pt-doped dense amorphous carbon layer has a pore size of <5nm and a thickness of 5-20nm, and the doping amount of platinum nanoparticles is 0.1-1wt%, with a particle size of 1-3nm. The intermediate NS co-doped mesoporous carbon layer has a pore size of 5-50 nm, a thickness of 20-50 nm, and a nitrogen doping amount of 5-10 at% and a sulfur doping amount of 2-5 at%. The outer graphene quantum dot-doped macroporous carbon layer has a pore size of 50-200 nm and a thickness of 30-80 nm, the doping amount of the graphene quantum dots is 2-5 wt%, and the particle size of the graphene quantum dots is 5-10 nm.

7. A method for preparing a gradient-channel hierarchical nitrogen-doped carbon-coated composite sodium supplement agent as described in any one of claims 1-6, characterized in that the step... include: S1. After ball milling and mixing the inorganic sodium-supplementing phase and the organic sodium-supplementing phase, vacuum drying is performed and heat treatment is carried out at 200-400℃ for 1-3 hours under an inert atmosphere. After treatment, the mixture is ground and sieved to obtain the core of the composite sodium supplement. S2. The core of the composite sodium supplement is dispersed in ethanol, and Pt nanoparticle sol, phenolic resin and nano SiO2 template are added to react. After the reaction is completed, the core is dried and carbonized at 600-800℃ for 2-4 hours under an inert atmosphere. After carbonization, the template is removed by HF and washed and dried to obtain an inner Pt-doped dense amorphous carbon layer. S3. Place the product from step S2 in a CVD furnace, introduce nitrogen, sulfur and carbon sources, deposit at 700-900℃ for 1-3 hours and then cool to obtain a middle layer of NS co-doped mesoporous carbon layer. S4. Disperse the product of step S3 in ethanol, add graphene quantum dot solution and polystyrene microsphere template to react, dry after reaction and deposit in CVD furnace at 800-1000℃ for 1-2h. After deposition, remove template with toluene and wash and dry to obtain the gradient pore hierarchical nitrogen-doped carbon-coated composite sodium supplement agent.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the composite sodium supplement core to the nano-SiO2 template is 1:(0.05-0.2), and the mass ratio of the composite sodium supplement core to the polystyrene microsphere template is 1:(0.1-0.3).

9. The preparation method according to claim 7, characterized in that, In step S3, the molar ratio of the nitrogen source, the sulfur source and the carbon source is (3-5):(1-2):10; The nitrogen source includes at least one of pyridine and ammonia; the sulfur source includes at least one of carbon disulfide and thiourea; and the carbon source includes at least one of acetylene and methane.

10. A positive electrode sodium supplement additive, characterized in that, include: The gradient-pore hierarchical nitrogen-doped carbon-coated composite sodium supplement agent as described in any one of claims 1-6 or the gradient-pore hierarchical nitrogen-doped carbon-coated composite sodium supplement agent prepared by the preparation method described in any one of claims 7-9; wherein the amount of the gradient-pore hierarchical nitrogen-doped carbon-coated composite sodium supplement agent added is 3-15% of the mass of the positive electrode active material.

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