A rare earth metal single-atom supported nitrogen-doped three-dimensional carbon carrier, a preparation method therefor, and an application thereof

Abstract

The present application relates to a kind of rare earth metal single atom load nitrogen-doped three-dimensional carbon carrier and its preparation method and application.The rare earth metal single atom load nitrogen-doped three-dimensional carbon carrier has the three-dimensional carbon skeleton structure of first carbon nanosheet and second conductive carbon interweave formation, in the three-dimensional carbon skeleton structure, first carbon nanosheet is connected by second conductive carbon between;The three-dimensional carbon skeleton structure is doped with nitrogen element;The rare earth metal single atom is loaded on the nitrogen element and forms stable coordination.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion secondary batteries, and particularly relates to a rare earth metal single-atom supported nitrogen-doped three-dimensional carbon carrier and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of new energy technology, the demand for high-performance energy storage batteries for portable electronic devices, power batteries and energy storage systems is increasingly urgent. Lithium-sulfur batteries have high theoretical specific capacity (about 1675 mAh g -1 ), high energy density (about 2675 Wh kg -1 ), abundant raw material sources, low cost and environmental friendliness, and have become one of the research hotspots of new energy storage batteries. However, the discharge process of lithium-sulfur batteries in an organic electrolyte system generates soluble lithium polysulfide intermediates, which shuttle to the negative electrode side and metal lithium under the action of concentration gradient and electric field, causing active material loss and metal lithium negative electrode failure, affecting battery capacity and cycle performance, and greatly hindering the commercialization of lithium-sulfur batteries. Therefore, constructing a high-conductive positive electrode structure with high-efficiency catalytic sites can achieve effective adsorption and catalysis of lithium polysulfide, promote the fast reaction kinetics of lithium-sulfur batteries, thereby effectively inhibiting the shuttle effect and realizing high specific capacity and long cycle life.

[0003] By designing and preparing high-polarity materials as sulfur carriers, effective adsorption and catalytic conversion of sulfur and polysulfides can be achieved, such as transition metal oxides (M x O y ), nitrides (M x N y ), sulfides (M x S y ), phosphides (M x P y ), etc., which play an important role in improving the performance of lithium-sulfur batteries. However, due to the relatively low specific surface area of such materials, to achieve good catalytic effect, a large proportion is required in the electrode and special structure design is needed, which to some extent reduces the content of active materials and affects the performance of battery energy density.

[0004] Single-atom catalysts have the characteristics of nearly 100% atom utilization efficiency, atomic size structure and high catalytic activity, and are widely used in electrocatalysis and other fields. Among them, the most studied is M-N xThe single-atom catalytic structure design is mainly focused on the coordination configuration of (M=Fe, Co, Ni, Cu, Zn, etc.). In recent years, single-atom catalysts have also attracted widespread attention in lithium-sulfur batteries. For single-atom catalysts that adsorb and catalyze the reaction of the positive electrode, the structure and component design need to be further optimized to improve the electrical conductivity of the structure and the content of single atoms, and the understanding of single-atom catalysis needs to be deepened, so as to effectively utilize the active material and improve the comprehensive performance of the battery.

[0005] The rare earth metal single atom has rich electronic orbital characteristics, and when it is applied in a lithium-sulfur battery, its orbital hybridization theory has a potential catalytic conversion effect on polysulfides. In order to realize the application of the rare earth metal single atom in the lithium-sulfur battery, a preparation method of a rare earth metal single atom catalyst loaded on a nitrogen-doped three-dimensional carbon carrier with high electrical conductivity and high specific surface area needs to be developed, so as to effectively catalyze the bidirectional conversion of sulfur and sulfides in the lithium-sulfur battery, and thus a high-performance lithium-sulfur battery is obtained. SUMMARY

[0006] In view of the above technical problems, the purpose of the present application is to provide a rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier and a preparation method thereof and an application thereof in a lithium-sulfur battery.

[0007] In a first aspect, the present application provides a rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier, wherein the rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier has a three-dimensional carbon skeleton structure formed by first carbon nanosheets and second conductive carbons interwoven, and the first carbon nanosheets are connected through the second conductive carbons in the three-dimensional carbon skeleton structure.

[0008] The three-dimensional carbon skeleton structure is doped with nitrogen elements.

[0009] The rare earth metal single atom is loaded on the nitrogen elements and forms a stable coordination with the nitrogen elements.

[0010] Preferably, the mass percentage of the rare earth metal single atom in the rare earth metal single atom catalyst loaded nitrogen-doped three-dimensional carbon carrier is 0.5-5wt%, and more preferably 1-4wt%.

[0011] Preferably, the specific surface area of the rare earth metal single atom catalyst loaded nitrogen-doped three-dimensional carbon carrier is 400-800m 2 g -1 , and the pore volume is 1.6-2.5cm 3 g -1 .

[0012] In a second aspect, the present application provides a preparation method of the above-mentioned rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier, and the preparation method comprises the following steps:

[0013] (1) dispersing g-C3N4 and the second conductive carbon in a buffer solution to obtain a mixed dispersion solution, and then adding dopamine hydrochloride to make it polymerize on the surface of g-C3N4 and the second conductive carbon to form polydopamine, and separating to obtain a rare earth metal monatomic supported nitrogen-doped three-dimensional carbon carrier precursor powder;

[0014] (2) dispersing the rare earth metal monatomic supported nitrogen-doped three-dimensional carbon carrier precursor powder in water, adding a rare earth metal nitrate to make the polydopamine adsorb rare earth metal ions, filtering, first washing, first freeze-drying, then high-temperature calcination, acid washing, second washing and second drying to obtain the rare earth metal monatomic supported nitrogen-doped three-dimensional carbon carrier.

[0015] Preferably, the second conductive carbon is at least one of a carbon nanotube, conductive carbon black, mesoporous carbon, carbon nanofiber, graphene oxide powder or dispersion, and preferably a dispersion of carbon nanotubes and graphene oxide.

[0016] Preferably, the mass ratio of g-C3N4 to the second conductive carbon is 10-40:1, and preferably 20-30:1; and the mass ratio of g-C3N4 to dopamine hydrochloride is 1:1-5, and preferably 1:1-3.

[0017] Preferably, the rare earth metal nitrate is at least one of a nitrate or nitrate hydrate of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.

[0018] Preferably, the mass ratio of g-C3N4 to the rare earth metal nitrate or nitrate hydrate is 5-0.9:1, and preferably 5-1:1.

[0019] The adsorption of the polydopamine to the rare earth metal ions is performed under stirring at room temperature, and the stirring time is 6-24h.

[0020] Preferably, the high-temperature calcination is performed in an Ar / H2 mixed atmosphere, the calcination temperature is 700-1000℃, and preferably 850-1000℃, the holding time is 1-3h, and the heating rate is 1-5℃ / min.

[0021] In a third aspect, the present application provides a lithium-sulfur battery, which comprises a sulfur positive electrode, a separator, an electrolyte and a metal lithium negative electrode; wherein the sulfur positive electrode is a composite positive electrode material obtained by heat-treating and compounding the above-mentioned rare earth metal monatomic supported nitrogen-doped three-dimensional carbon carrier and sulfur.

[0022] Advantages

[0023] The rare earth metal monatomic nitrogen-doped three-dimensional carbon carrier provided by the application has simple and easy-to-implement preparation, low cost, rich pore structure and excellent conductivity, can effectively load active substances and improve reaction kinetics, and realizes high active substance utilization rate and comprehensive electrochemical performance.

[0024] The rare earth metal monatomic nitrogen-doped three-dimensional carbon carrier for lithium-sulfur batteries provided by the application has simple and easy-to-implement preparation, and can be used to prepare catalysts composed of different types of rare earth metal monatomics or double monatomics and multiple monatomics, and is suitable for quantitatively preparing lithium-sulfur batteries. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 XRD patterns of the carrier materials prepared in Examples 1-4 and Comparative Examples 1 and 4 of the application;

[0026] Figure 2 TEM image of 3D CeSA-NC prepared in Example 1 of the application;

[0027] Figure 3 HAADF-STEM image of 3D CeSA-NC prepared in Example 1 of the application;

[0028] Figure 4 XANES function curve and Fourier transform EXAFS function curve of CeL3 edge of 3D CeSA-NC prepared in Example 1 of the application;

[0029] Figure 5 Battery cycle performance chart of the carrier materials prepared in Example 1 and Comparative Example 1 of the application as a positive electrode;

[0030] Figure 6 Lithium-sulfur battery first circle specific capacity-voltage chart of the carrier materials prepared in Example 1 and Comparative Example 1 of the application as a positive electrode;

[0031] Figure 7 Battery cycle performance chart of the carrier material prepared in Comparative Example 4 of the application as a positive electrode. DETAILED DESCRIPTION

[0032] The application will be further described below through the following embodiments, and it should be understood that the following embodiments are only used to illustrate the application, but not to limit the application.

[0033] Firstly, the present application provides a rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier. The rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier has a three-dimensional carbon skeleton structure formed by first carbon nanosheets and second conductive carbons interwoven, the first carbon nanosheets are connected by the second conductive carbons, the three-dimensional carbon skeleton structure is doped with nitrogen elements, and the rare earth metal single atoms are loaded on the nitrogen elements and form stable coordination with the nitrogen elements. The connection between the first carbon nanosheets and the second conductive carbons presents the form of local physical "welding" points.

[0034] In some embodiments, the mass percentage of the rare earth metal single atoms in the rare earth metal single atom catalyst loaded nitrogen-doped three-dimensional carbon carrier can be controlled to be 0.5-5wt%, preferably 1-4wt%. If the mass percentage of the rare earth metal single atoms is less than 0.5wt%, the effective catalytic effect cannot be achieved; if the mass percentage of the rare earth metal single atoms is more than 5wt%, the agglomeration is easily caused, so that the single atom state of the rare earth metal cannot be guaranteed.

[0035] In some embodiments, the specific surface area of the rare earth metal single atom catalyst loaded nitrogen-doped three-dimensional carbon carrier is 400-800m 2 g -1 , and the pore volume is 1.6-2.5cm 3 g -1 .

[0036] Different from the simple carbon accumulation form, the first carbon nanosheets in the nitrogen-doped three-dimensional carbon carrier provided by the present application are connected by the second conductive carbons, and the connection presents the form of local "welding" points, so that the overall transmission of electrons of the material is easier, and the material has excellent conductivity; at the same time, the high specific surface area can uniformly load the rare earth metal single atoms and can be applied in lithium-sulfur batteries, effectively adsorbs and catalyzes the conversion of active sulfur, inhibits the shuttle effect, and improves the reaction kinetics.

[0037] Hereinafter, the preparation method of the rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier provided by the present application is exemplarily described. The preparation method can include the following steps:

[0038] (1) dispersing g-C3N4 and second conductive carbons in a buffer solution to obtain a mixed dispersion liquid, then adding hydrochloric acid dopamine to polymerize polydopamine on the surfaces of the g-C3N4 and the second conductive carbons, and separating to obtain a rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier precursor powder;

[0039] (2) dispersing the rare earth metal single atom supported nitrogen-doped three-dimensional carbon carrier precursor powder in water, adding a rare earth metal nitrate to enable the polydopamine to adsorb rare earth metal ions, filtering, first washing, and then first freeze-drying, followed by high-temperature calcination, acid washing, second washing, and second drying to obtain the rare earth metal single atom supported nitrogen-doped three-dimensional carbon carrier.

[0040] In the present application, g-C3N4 is used as a soft template to promote the formation of a nitrogen-doped three-dimensional carbon carrier. As an example, the g-C3N4 can be prepared by using urea as a raw material, heating to 550°C in a muffle furnace, and maintaining the temperature for 2 hours. The g-C3N4 is yellow g-C3N4 powder.

[0041] The second conductive carbon serves as a conductive agent. In some embodiments, the second conductive carbon can be at least one of carbon nanotubes (including surface-functionalized carbon nanotubes), conductive carbon black, mesoporous carbon, carbon nanofibers, graphene oxide powder or a dispersion liquid, and preferably a dispersion liquid of carbon nanotubes and graphene oxide.

[0042] In some embodiments, the mass ratio of the g-C3N4 to the second conductive carbon can be 10-40:1, and preferably 20-30:1. The g-C3N4 serves as a soft template and plays a role in loading dopamine hydrochloride. After the dopamine hydrochloride coats the g-C3N4, the first carbon nanosheet is formed by sintering. The volume of the nanosheet is much larger than that of the second conductive carbon such as carbon fibers. By controlling the mass ratio range of the two, an excellent three-dimensional structure can be ensured, and too much or too little will affect the specific surface area and other properties of the material.

[0043] In some embodiments, the buffer solution can be a Tris-buffer buffer solution.

[0044] In some embodiments, the mass ratio of the g-C3N4 to the dopamine hydrochloride can be 1:1-5, and preferably 1:1-3. By controlling the appropriate mass ratio of the two, an effective coating effect can be ensured. Too much dopamine hydrochloride will cause waste, and too little will not achieve the best use of the template effect of g-C3N4.

[0045] In some embodiments, the method of polymerizing dopamine hydrochloride on the surface of g-C3N4 and the second conductive carbon to form polydopamine can be stirring polymerization, and the reaction time can be 3-12 hours, and preferably 3-8 hours.

[0046] In some embodiments, the rare earth metal nitrate can be at least one of a nitrate or a nitrate hydrate of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0047] In some embodiments, the mass ratio of the g-C3N4 and the rare earth metal nitrate or nitrate hydrate can be 5-0.9:1, preferably 5-1:1. Too much rare earth metal nitrate will easily lead to agglomeration and failure to form single atoms; too little will result in too low a content of single atoms.

[0048] In some embodiments, the adsorption of the rare earth metal ions by the polydopamine can be carried out under stirring at room temperature, and the stirring time at room temperature can be 6-24 h.

[0049] The drying method will affect the uniformity of the single atoms in the material. The use of freeze-drying can promote the uniformity of the prepared single atoms, and the use of direct vacuum heat drying is prone to form agglomeration, hindering the formation of single atoms.

[0050] High-temperature calcination can stabilize the structure and form single atoms. In some embodiments, the high-temperature calcination can be carried out in an Ar / H2(5% H2) mixed atmosphere, the calcination temperature can be 700-1000℃, preferably 850-1000℃, the holding time can be 1-3 h, and the heating rate can be 1-5℃ / min. Too low a calcination temperature will result in incomplete carbonization; too high a calcination temperature will cause partial volatilization and side reactions.

[0051] The use of acid washing can dissolve uncoordinated metal or metal oxide impurities.

[0052] The order of sample addition, drying method, and substance content ratio during the preparation process are all related to the conductivity of the final material, the uniformity and content of the rare earth metal single atoms, and whether it can play a high-efficiency catalytic effect. Different sample addition sequences will affect the formation of local "welding" points, thereby affecting the conductivity. Adding g-C3N4 and then the second conductive carbon, and then adding polydopamine is conducive to the formation of welding points; adding g-C3N4 and then directly adding polydopamine, and then adding the second conductive carbon is not conducive to the formation of welding points. The substance content ratio will affect the content of the prepared rare earth metal single atoms, which will directly affect the adsorption and catalytic activity of sulfur in lithium-sulfur batteries. The substance content ratio is equivalent to the amount of rare earth metal nitrate. Too much will easily agglomerate and fail to form single atoms, and too little will result in a low content of single atoms, both of which will weaken the adsorption and catalytic ability of the material.

[0053] The rare earth metal single atom catalyst supported nitrogen-doped three-dimensional carbon provided by the application has high conductivity, can effectively adsorb and catalyze the bidirectional conversion of lithium polysulfide intermediates in the reaction, has excellent redox reaction kinetics, and the preparation process of the composite carrier material is simple, the catalytic performance is excellent, and it is suitable for high-performance lithium-sulfur batteries.

[0054] The application further provides a lithium-sulfur battery, comprising: a sulfur positive electrode, a diaphragm, an electrolyte and a metal lithium negative electrode; wherein the sulfur positive electrode is a composite positive electrode material obtained by heat-treating a sulfur and the rare earth metal monatomic atom-loaded nitrogen-doped three-dimensional carbon carrier.

[0055] As an example, the preparation method of the sulfur positive electrode can comprise the following steps: uniformly mixing the rare earth metal monatomic atom-loaded nitrogen-doped three-dimensional carbon carrier and sulfur, vacuum sealing into a quartz tube, heat-treating at 155 DEG C for 12 hours, then heating to 300 DEG C for 2 hours, uniformly mixing the obtained powder with conductive carbon and a binder, coating on the surface of an aluminum foil, vacuum drying to obtain the sulfur positive electrode.

[0056] In some embodiments, the diaphragm used for assembling the battery in the lithium-sulfur battery can be a commercial porous polymer diaphragm, and the electrolyte can be a mixed solution of 1M LiTFSI and 0.2M LiNO3 dissolved in DOL / DME (volume ratio 1:1); wherein the lithium-sulfur battery is assembled in an argon glove box (water and oxygen content is less than 0.1 ppm).

[0057] The following examples are further provided to illustrate the application in detail. It should also be understood that the following examples are only used to further illustrate the application, and cannot be understood as limiting the protection scope of the application. Some non-essential improvements and adjustments made by those skilled in the art according to the above content of the application are within the protection scope of the application. The specific process parameters in the following examples are only one example in the appropriate range, i.e. those skilled in the art can select within the appropriate range according to the description herein, and are not limited to the specific values in the following examples. If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art.

[0058] Unless otherwise specified, the carrier material prepared in the application is used as a lithium-sulfur battery positive electrode, and the battery is tested by constant current charge-discharge and cycle performance characterization at room temperature (25 DEG C), the voltage range is 1.8-2.8V, and the rate is 0.2C.

[0059] Example 1

[0060] The preparation method of the rare earth metal monatomic atom-loaded nitrogen-doped three-dimensional carbon carrier provided in the embodiment comprises the following steps:

[0061] (1) 0.9691 g of tris-hydroxymethyl aminomethane hydrochloride was dissolved in deionized water to prepare 800 mL of 10 mM Tris-buffer solution; 0.4 g of g-C3N4 and 0.15 g of carbon nanotube (CNT) dispersion liquid (containing 10 wt% of carbon nanotubes) were added to the above Tris-buffer solution, and a uniform dispersion liquid was obtained by ultrasonic treatment; 0.8 g of dopamine hydrochloride was added under stirring, and stirred at room temperature for 3 h; after filtration, the filter cake was washed with deionized water to obtain PDA@g-C3N4-CNT composite (rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier precursor powder);

[0062] (2) The PDA@g-C3N4-CNT material obtained above was dispersed again in 300 mL of deionized water to obtain a uniform dispersion liquid solution, and then 0.4330 g of Ce(NO3)3·6H2O was added, and stirred at room temperature for 12 h, so that Ce 3+ was fully adsorbed on the nitrogen sites on the surface of PDA, and the filter cake was freeze-dried to obtain Ce 3+ -PDA@g-C3N4-CNT powder; the powder sample was placed in a 1M hydrochloric acid solution under an Ar / H2 (5% H2) mixed gas atmosphere, and reacted at 1000℃ for 1 h at a heating rate of 2℃ / min; after cooling, the powder sample was stirred in a 1M hydrochloric acid solution at room temperature for 6 h to remove uncoordinated metals or metal oxides, and then washed and dried to obtain a Ce single atom loaded nitrogen-doped three-dimensional porous carbon carrier (3D CeSA-NC).

[0063] The 3D CeSA-NC prepared in Example 1 was used for heat treatment with sulfur to obtain a composite positive electrode material, and then a battery was prepared for electrochemical performance test.

[0064] Example 2

[0065] The preparation method of the rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier provided in this example refers to Example 1, and the main difference is that the second conductive carbon is graphene oxide, and the amount of Ce(NO3)3·6H2O added is 0.2165 g.

[0066] Example 3

[0067] The preparation method of the rare earth metal single atom loaded nitrogen-doped three-dimensional carbon carrier provided in this example refers to Example 1, and the main difference is that the rare earth metal nitrate is La(NO3)3·6H2O, and the high-temperature calcination time is 2 h, to obtain a La single atom loaded nitrogen-doped three-dimensional porous carbon carrier (3D LaSA-NC).

[0068] Example 4

[0069] The preparation method of the carrier material provided in the example is refer to example 1, the main difference is that the rare earth metal nitrate is Sm(NO3)3·6H2O, the amount of addition is 0.4440g, the stirring time at room temperature is 8h, and the Sm monatomic loaded nitrogen doped three-dimensional porous carbon carrier (3D SmSA-NC) is obtained.

[0070] Comparative example 1

[0071] The preparation method of the carrier material provided in the example is refer to example 1, the main difference is that the rare earth metal nitrate is Sm(NO3)3·6H2O, the amount of addition is 0.4440g, the stirring time at room temperature is 8h, and the Sm monatomic loaded nitrogen doped three-dimensional porous carbon carrier (3D SmSA-NC) is obtained.

[0072] The 3D-NC prepared in comparative example 1 is used for heat treatment with sulfur to obtain a composite positive electrode material, and then a battery is prepared for electrochemical performance test.

[0073] Comparative example 2

[0074] The preparation method of the carrier material provided in the example is refer to example 1, the main difference is that the rare earth metal nitrate is Sm(NO3)3·6H2O, the amount of addition is 0.4440g, the stirring time at room temperature is 8h, and the Sm monatomic loaded nitrogen doped three-dimensional porous carbon carrier (3D SmSA-NC) is obtained.

[0075] The 3D NC prepared by this method does not have stable local "welding" points, and the first carbon nanosheet and the second conductive carbon are in a physical stacking form, and the conductivity is weaker than that of the nitrogen doped three-dimensional porous carbon structure described in comparative example 1.

[0076] Comparative example 3

[0077] The preparation method of the carrier material provided in the example is refer to example 1, the main difference is that in step (2), the drying method of the filter cake is vacuum heat drying.

[0078] The 3D CeSA-NC prepared by this method still has agglomeration phenomenon even after acid treatment, which is caused by direct vacuum drying treatment.

[0079] Comparative example 4

[0080] The preparation method of the carrier material provided by the present comparative example refers to Example 1, and the main difference is that in step (2), the rare earth metal nitrate is replaced by 0.4039 g of Fe(NO3)3·9H2O to obtain a 3d transition metal Fe single atom loaded nitrogen-doped three-dimensional porous carbon carrier (3D FeSA-NC).

[0081] Figure 1 The XRD patterns of the carrier materials prepared in Examples 1-4 and Comparative Examples 1 and 4 of the present application are shown in the figure. As can be seen from the figure, the carrier materials prepared in Examples 1-4 belong to graphite carbon (002) crystal face and (101) crystal face, and there are no Ce, La or Sm metal phase characteristic peaks, indicating that Ce, La or Sm exists in the form of single atoms, and the content of Ce single atoms is 2.23%, 1.36% respectively. The carrier material prepared in Comparative Example 1 belongs to graphite carbon (002) crystal face and (101) crystal face. The carrier material prepared in Comparative Example 4 belongs to graphite carbon (002) crystal face and (101) crystal face, and there is no Fe metal phase characteristic peak.

[0082] Figure 2 The TEM image of the 3D CeSA-NC prepared in Example 1 of the present application is shown in the figure. As can be seen from the figure, the carrier material prepared in Example 1 exhibits a three-dimensional structure of carbon nanotubes and carbon nanosheets interwoven.

[0083] Figure 3 The HAADF-STEM image of the 3D CeSA-NC prepared in Example 1 of the present application is shown in the figure. As can be seen from the figure, there are obvious bright spots corresponding to Ce single atoms (CeSAs) in the material, proving the successful preparation of CeSAs.

[0084] Figure 4 The XANES function curve and the Fourier transform EXAFS function curve of the CeL3 edge of the 3D CeSA-NC prepared in Example 1 of the present application are shown in the figure. As can be seen from the figure, the product prepared in Example 1 of the present application has single atom form of loaded metal Ce.

[0085] Figure 5 The battery cycle performance graph of the carrier materials prepared in Example 1 and Comparative Example 1 of the present application as the positive electrode is shown in the figure. As can be seen from the figure, the carrier material prepared in Example 1 has a first discharge specific capacity of 1225 mAh g -1 at 0.2C, which is much higher than 1130 mAh g -1 of Comparative Example 1 and 1089 mAh g -1 of Comparative Example 4, and the capacity retention rate after 160 cycles is 76.1%, indicating that Ce single atoms effectively accelerate the reaction kinetics, and the performance is much better than that of 3d transition metal single atom catalysts.

[0086] Figure 6The first cycle specific capacity-voltage graph of the lithium-sulfur battery with the support material prepared in Example 1 and Comparative Example 1 as the positive electrode. As can be seen from the graph, the charge-discharge curve of the battery with the support material prepared in Example 1 as the positive electrode maintains the standard curve of lithium-sulfur batteries, and has a higher discharge specific capacity compared to the comparative sample, indicating the effectiveness of Ce single atoms in the bidirectional catalysis process.

[0087] Figure 7 The cycle performance graph of the battery with the support material prepared in Comparative Example 4 as the positive electrode. As can be seen from the graph, the first discharge specific capacity of the battery at 0.2C reaches 1089 mAh g -1 , and the capacity retention rate after 160 cycles is 67.8%.

[0088] Although the content of the present application has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as limiting the present application. Various modifications and alternatives to the present application will be apparent to those skilled in the art after reading the above content. Therefore, the scope of protection of the present application should be defined by the appended claims.

Claims

1. A rare earth metal single atom catalyst supported on a nitrogen-doped three-dimensional carbon support, characterized in that: The rare earth metal single atom catalyst-loaded nitrogen-doped three-dimensional carbon support has a three-dimensional carbon skeleton structure formed by interweaving first carbon nanosheets and second conductive carbon, wherein the first carbon nanosheets are connected by the second conductive carbon. The three-dimensional carbon skeleton structure is doped with nitrogen; The rare earth metal single atom in the rare earth metal single atom catalyst-supported nitrogen-doped three-dimensional carbon carrier is supported on the nitrogen element and forms a stable coordination therewith.

2. The rare earth metal single atom catalyst supported on a nitrogen-doped three-dimensional carbon support according to claim 1, characterized in that: The mass percentage of the rare earth metal single atom in the rare earth metal single atom catalyst-supported nitrogen-doped three-dimensional carbon carrier is 0.5 to 5 wt %.

3. The rare earth metal single atom catalyst supported on a nitrogen-doped three-dimensional carbon support according to claim 1, wherein: The mass percentage of the rare earth metal single atom in the rare earth metal single atom catalyst-supported nitrogen-doped three-dimensional carbon carrier is 1 to 4 wt %.

4. The rare earth metal single atom catalyst supported on a nitrogen-doped three-dimensional carbon support according to claim 1, wherein: The specific surface area of ​​the rare earth metal single atom catalyst supported on the nitrogen-doped three-dimensional carbon support is 400 to 800 m 2 g -1 , pore volume is 1.6~2.5 cm 3 g -1 .

5. A method for preparing a nitrogen-doped three-dimensional carbon support supported by a rare earth metal single atom catalyst according to claim 1, characterized in that: The preparation method comprises the following steps: (1) g-C3N4 and a second conductive carbon are dispersed in a buffer solution to obtain a mixed dispersion, and then dopamine hydrochloride is added to polymerize the g-C3N4 and the second conductive carbon to form polydopamine, and rare earth metal single atom catalyst-loaded nitrogen-doped three-dimensional carbon support precursor powder is separated; (2) The rare earth metal single atom catalyst loaded nitrogen-doped three-dimensional carbon support precursor powder is dispersed in water, rare earth metal nitrate is added to allow the polydopamine to adsorb rare earth metal ions, filtered, washed for the first time, and then freeze-dried for the first time, followed by high-temperature calcination, acid washing, a second washing, and a second drying to obtain the rare earth metal single atom catalyst loaded nitrogen-doped three-dimensional carbon support.

6. The preparation method according to claim 5, characterized in that The second conductive carbon is at least one of carbon nanotubes, conductive carbon black, mesoporous carbon, carbon nanofibers, and graphene oxide powder or dispersion.

7. The preparation method according to claim 5, characterized in that The mass ratio of the g-C3N4 to the second conductive carbon is 10-40:1; the mass ratio of the g-C3N4 to dopamine hydrochloride is 1:1-5.

8. The preparation method according to claim 7, characterized in that The mass ratio of the g-C3N4 to the second conductive carbon is 20-30:1; the mass ratio of the g-C3N4 to dopamine hydrochloride is 1:1-3.

9. The preparation method according to claim 5, characterized in that The rare earth metal nitrate is at least one of the nitrates or nitrate hydrates of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

10. The preparation method according to claim 9, characterized in that The mass ratio of g-C3N4 to rare earth metal nitrate or nitrate hydrate is 5-0.9:1; The polydopamine adsorption of rare earth metal ions is carried out under stirring at room temperature, and the stirring time at room temperature is 6-24 hours.

11. The preparation method according to claim 10, characterized in that: The mass ratio of the g-C3N4 to the rare earth metal nitrate or nitrate hydrate is 5-1:

1.

12. The preparation method according to claim 5, wherein The high-temperature calcination is carried out in an Ar / H2 mixed atmosphere, the calcination temperature is 700-1000°C, the holding time is 1-3 h, and the heating rate is 1-5°C / min.

13. The preparation method according to claim 12, characterized in that The calcination temperature is 850-1000℃.

14. A lithium-sulfur battery, characterized in that: The lithium-sulfur battery comprises a sulfur positive electrode, a separator, an electrolyte and a metallic lithium negative electrode; wherein the sulfur positive electrode is a composite positive electrode material obtained by heat-treating the rare earth metal single-atom catalyst loaded nitrogen-doped three-dimensional carbon support according to claim 1 and sulfur.

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