A molten salt-assisted synthesis of ultrathin carbon nanosheet supported high-entropy single-atom catalyst and a preparation method and application thereof

Abstract

The application relates to a molten salt-assisted synthesis of an ultrathin carbon nanosheet loaded high-entropy single-atom catalyst as well as a preparation method and application thereof. The preparation method of the ultrathin carbon nanosheet loaded high-entropy single-atom catalyst comprises the following steps: providing ZIF-67 powder; coating the ZIF-67 powder with a dopamine solution to obtain ZIF-67@PDA powder; performing heat treatment on the obtained ZIF-67@PDA powder to obtain dopamine-coated Co organic framework hollow dodecahedrons; then adding soluble metal salt and molten salt and further pyrolyzing under a nitrogen atmosphere; finally performing acid washing and water washing to obtain the high-entropy single-atom catalyst loaded on the ultrathin carbon nanosheet. The preparation method of the ultrathin carbon nanosheet loaded high-entropy single-atom catalyst is energy-saving, adopts a molten salt method process, and has mild reaction conditions; the prepared ultrathin carbon nanosheet has a large specific surface area, provides a larger reaction active surface, and is applied to a lithium-sulfur battery, so that the lithium-sulfur battery exhibits excellent cycle performance.

Description

TECHNICAL FIELD

[0001] The application relates to a new chemical energy material, in particular to a molten salt assisted synthesis of an ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst and a preparation method and application thereof. BACKGROUND

[0002] Lithium-sulfur batteries are considered as the next generation of secondary batteries due to their high theoretical capacity (S: 1675 mAh / g and Li: 3860 mAh / g), sustainability of S, and the lowest reduction potential of Li (-3.04 V vs. standard hydrogen electrode). Despite decades of efforts, lithium-sulfur batteries still suffer from some detrimental issues related to the cathode and anode. For the sulfur cathode, the diffusion of intermediate lithium polysulfides and the slow sulfur redox conversion kinetics lead to poor specific capacity, poor rate capability, and rapid capacity degradation. Therefore, it is urgent to design a kinetic advanced lithium-sulfur battery system with good structure for the lithium polysulfide-inhibited cathode. To solve these problems of the sulfur electrode, it is common to load (pack, attach, mix, epitaxial growth, coat, etc.) elemental sulfur into a nano-reactor material with high specific surface area, high porosity, and good electrical conductivity characteristics to form a composite positive electrode material to limit the dissolution of polysulfides into the electrolyte during the cycle and the various negative effects caused thereby.

[0003] At present, there are various nanoreactors for preparing nanoparticles and nanowires (rods), such as micellar vesicles and carbon nanotubes. The nanoreactor plays an important role in controlling the reaction selectivity and the morphology of the product. With the discovery of graphene, two-dimensional materials have attracted widespread interest in scientific and applied research. At present, the synthesis of two-dimensional materials mainly includes the interface method and the layered crystal exfoliation method. The interface method is limited by low yield, and the layered crystal exfoliation method is limited by the fact that there are very limited layered crystals that can be exfoliated. Therefore, the development of a new type of two-dimensional nanoreactor will open up a new method for the synthesis of two-dimensional materials. SUMMARY

[0004] The molten salt assisted synthesis (MSAS) technology combines the advantages of traditional solid-phase and liquid-phase synthesis methods, and at the same time gives complete kinetic accessibility of catalyst synthesis and controllability of nanocrystal size, morphology and size, becoming an important means for preparing catalysts. In order to further improve the polysulfide adsorption conversion kinetics, more kinds of elements are introduced into the single-atom system, and the rich active sites and synergistic effect between different active sites of the high-entropy single-atom catalytic material exhibit excellent electrochemical performance when used in lithium-sulfur batteries.

[0005] Based on this, the purpose of the present application is to provide a molten salt assisted synthesis of ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst and its preparation method. The uniform liquid nucleation environment formed by molten salt plays a crucial role in improving the reaction rate, reducing the growth barrier of 2D material and improving the yield.

[0006] A molten salt assisted synthesis of ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst preparation method, comprising the following steps:

[0007] S1: dispersing ZIF-67 powder in a tris-hydroxymethyl aminomethane hydrochloride buffer solution, then coating with a dopamine solution, then obtaining the product by centrifugation and drying to obtain ZIF-67@PDA powder;

[0008] S2: heating the obtained ZIF-67@PDA powder to obtain dopamine coated Co organic framework hollow dodecahedron;

[0009] S3: adding a plurality of soluble metal salt solutions and molten salt to the reaction system obtained in step S2, ultrasonic treatment, freeze-drying, and pyrolysis under a nitrogen atmosphere;

[0010] S4: washing with an acid solution and deionized water to remove salt templates and aggregated metal particles to obtain a high-entropy single-atom catalyst loaded on ultra-thin carbon nanosheets.

[0011] The molten salt assisted synthesis of ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst preparation method provided by the present application uses molten salt as a template agent to assist the pyrolysis process. The molten salt can be used as a stripping agent to embed, strip and etch the carbon material of Co-PDA, which leads to the formation of two-dimensional, porous carbon material with rich porous structure (defective carbon). At the same time, these defective carbons (pyridine N and inherent carbon defects) can be used as anchor points for capturing metal atoms. Finally, after leaching the aggregated metal particles, a two-dimensional nanoreactor of ultra-thin carbon nanosheet loaded high-entropy single atoms is obtained.

[0012] Further, in step S1, the nitrogen source in the dopamine solution includes one or more of dopamine, urea, melamine and glycine.

[0013] Further, in step S1, the pH value of the tris-hydroxymethyl aminomethane hydrochloride buffer solution is 7-9.

[0014] Further, in step S1, the mass-volume ratio of the ZIF-67 powder to the tris-hydroxymethyl aminomethane hydrochloride buffer solution is (0.1-0.2) g:(60-80) ml.

[0015] Further, in step S1, the dopamine coating temperature is room temperature, and the stirring time is 10h.

[0016] Further, in step S2, the obtained ZIF-67@PDA powder is dispersed in 20 mL of deionized water, heated to 70-100℃, and kept for 20-50 min.

[0017] Further, in step S3, the soluble metal salt solution includes five or more.

[0018] Further, in step S3, the metal elements in the soluble metal salt solution are selected from at least four of Fe, Ni, Ir, Pd, and Ce, and the soluble metal salt solution is selected from at least one of nitrate, chloride, acetylacetone salt, and acetate.

[0019] Further, the molten salt includes at least one or more of sodium chloride, calcium chloride, and potassium chloride.

[0020] Further, in step S3, the mass ratio of the dopamine-coated cobalt metal organic framework hollow dodecahedron to the soluble metal salt solution is 2:5.

[0021] Further, the mass ratio of the soluble metal salt to the molten salt is 1:3.

[0022] Further, in step S3, the pyrolysis temperature under a nitrogen atmosphere is 600-800℃, the time is 1-3h, and the heating rate is 1℃ / min-10℃ / min.

[0023] It should be noted that the purpose of the pyrolysis process in the present application is to reach the temperature at which the key reactions occur, and to maintain a certain time to ensure the completeness of the reaction. Pyrolysis has a multi-stage heating process, which is determined according to the intermediate reactions of the reactants. The purpose of setting the temperature and time is to ensure the completeness of the reaction. If the process is not properly set, it may cause the morphology of the product to be uneven, and a large amount of raw materials to be lost, etc.

[0024] Specifically, the pyrolysis temperature in the preparation method of the present application is 600-800℃. Exemplarily, the sintering temperature of the heat treatment can be 600℃, 700℃, 800℃, or a range composed of any two of the above values.

[0025] Specifically, the pyrolysis time in the preparation method of the present application is 1-3h. Exemplarily, the sintering time of the first heat treatment can be 1h, 2h, 3h, or a range composed of any two of the above values.

[0026] Specifically, the heating rate of pyrolysis in the preparation method is 1℃ / min-10℃ / min. Exemplarily, the heating rate of the first heat treatment can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min or a range formed by any two of the above values.

[0027] By adopting the heat treatment conditions, the completion degree of the reaction can be improved, thereby facilitating obtaining two-dimensional nanomaterials with stable properties.

[0028] A molten salt-assisted synthesis of an ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst is prepared by the preparation method of the molten salt-assisted synthesis of the ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst.

[0029] Further, the thickness of the molten salt-assisted synthesis of the ultra-thin carbon nanosheet is 0.4-1.2nm.

[0030] Further, the molten salt-assisted synthesis of the ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst comprises metal elements Fe, Co, Ni, Ir and Pd; and the atomic molar ratio of Fe, Co, Ni, Ir and Pd is 0.8:1:0.8:0.6:0.4.

[0031] Alternatively, the molten salt-assisted synthesis of the ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst comprises metal elements Fe, Co, Ni, Ir and Ce, and the atomic molar ratio of Fe, Co, Ni, Ir and Ce is 0.7:1:0.6:0.6:0.4.

[0032] Alternatively, the ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst comprises metal elements Fe, Co, Ni, Pd and Ce, and the atomic molar ratio of Fe, Co, Ni, Pd and Ce is 0.7:1:0.6:0.5:0.5.

[0033] The application further provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active layer arranged on at least one side of the positive electrode current collector, and the positive electrode active layer comprises the ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst prepared by the preparation method of the application or the modified ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst prepared by the preparation method of the application.

[0034] The application further provides a secondary battery comprising the positive electrode sheet of the application.

[0035] The application further provides applications of the ultra-thin carbon nanosheet loaded high-entropy single-atom catalyst in secondary batteries, electrocatalytic materials, lithium-sulfur batteries and lithium metal batteries.

[0036] Specifically, the sulfur powder and the ultra-thin carbon nanosheet loaded high-entropy monatomic catalyst material are weighed according to a mass ratio of 7:3, mixed thoroughly, heated to 155 DEG C, and fused sulfur in a reaction kettle for 12 hours to obtain the ultra-thin carbon nanosheet loaded high-entropy monatomic catalyst material loaded with sulfur as a positive electrode material.

[0037] The obtained ultra-thin carbon nanosheet loaded high-entropy monatomic catalyst material loaded with sulfur, carbon black conductive agent (SuperP) and polyvinylidene fluoride (PVDF) binder are mixed according to a mass ratio of 8:1:1, an appropriate amount of N-methyl pyrrolidone (NMP) is added, and the mixture is ground into a paste in a jade mortar, coated on a current collector aluminum foil, and then placed in a 60 DEG C vacuum drying box for drying for 8 hours, and then cut to prepare an electrode sheet. Then, they are all transferred to an argon-filled glove box for assembly of a button cell, the button cell is CR2032, lithium metal is used as a counter electrode, a separator is a polypropylene microporous membrane Celgard 2400, and an electrolyte is 1 mol / L LiPF6 / EC+DMC+EMC (V / V=1:1:1).

[0038] Compared with the prior art, the present application has the following beneficial effects:

[0039] 1. The present application develops a general molten salt-assisted synthesis of two-dimensional nanoreactor. The uniform liquid nucleation environment formed by molten salt plays a crucial role in improving the reaction rate, reducing the growth barrier of 2D material and improving the yield. In the molten salt-assisted pyrolysis process, metal chloride (e.g., NaCl) can be used as a stripping agent to embed, strip and etch the carbon material of Co-PDA, which leads to the formation of two-dimensional, porous carbon material with rich porous structure (defective carbon). At the same time, these defective carbons (pyridine N and inherent carbon defects) can be used as anchor points for capturing metal atoms. Finally, after leaching the agglomerated metal particles, an ultra-thin carbon nanosheet loaded high-entropy monatomic two-dimensional nanoreactor is obtained.

[0040] 2. Molten salt can induce the formation of high-entropy monatomic and porous graphene-like carbon, which is beneficial to the full exposure of active centers, and the introduction of multiple metal elements can effectively anchor polysulfides and speed up their conversion, thereby effectively inhibiting the shuttle effect and improving the utilization rate of active substances.

[0041] 3. The prior art synthesizes ultra-thin carbon nanosheet loaded high-entropy single atom or high-entropy alloy, the starting point of which is to modify and synthesize on the basis of two-dimensional material (carbon-nitrogen base), and the starting point of the present application is to directly synthesize thin carbon nanosheet loaded high-entropy single atom, thereby omitting the step of purchasing or preparing two-dimensional material; secondly, the prior art high-entropy single atom or high-entropy alloy synthesis is under high-temperature conditions (1000 DEG C), and the present application adopts a molten salt method, the pyrolysis temperature is 600-800 DEG C, the conditions are relatively mild, and the energy consumption is low; the prepared two-dimensional layered nanomaterial has a regular structure and good electrocatalytic performance.

[0042] In order to better understand and implement, the present application will be described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 A preparation process schematic diagram of a molten salt assisted synthesis of ultra-thin carbon nanosheet loaded high-entropy single atom catalyst;

[0044] Figure 2 An SEM image of two-dimensional layered nanosheet prepared in Example 1;

[0045] Figure 3 An SEM image of two-dimensional layered nanosheet prepared in Example 2;

[0046] Figure 4 An SEM image of two-dimensional layered nanosheet prepared in Example 3;

[0047] Figure 5 A TEM image of two-dimensional layered nanosheet prepared in Example 1;

[0048] Figure 6 A lithium-sulfur battery cycle performance diagram of positive electrode material prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0050] In the preparation method of the present application, by controlling the reaction conditions, especially the pyrolysis temperature, different pyrolysis temperatures can make the pore structure of carbon-nitrogen material different, thereby affecting the porosity and pore size distribution, and thereby affecting the reaction sites for polysulfide adsorption conversion. Suitable reaction sites can accelerate the kinetics of polysulfide conversion, reduce the opportunity of lithium polysulfide dissolving in electrolyte, thereby further reducing the amount of lithium polysulfide dissolved in electrolyte, and further improving the cycle stability of lithium-sulfur battery.

[0051] The application discloses a preparation process of a high-entropy single-atom catalyst loaded on an ultrathin carbon nanosheet by means of a molten salt, and the process comprises the following steps:

[0052] S1: dispersing ZIF-67 powder in a tris-hydroxymethyl aminomethane hydrochloride buffer solution with a pH value of 7-9, then coating the ZIF-67 powder by stirring in a dopamine solution at room temperature, and then obtaining a product by centrifugation and drying to obtain ZIF-67@PDA powder;

[0053] S2: adding the obtained ZIF-67@PDA powder into deionized water, heating to 85 DEG C and keeping for 30 min to obtain dopamine-coated Co organic framework hollow dodecahedron;

[0054] S3: adding a plurality of soluble metal salt solutions and molten salt into the reaction system obtained in step S2, performing ultrasonic treatment, and then freeze-drying, and then pyrolyzing at 600-800 DEG C under a nitrogen atmosphere at a temperature rising rate of 1 DEG C / min-10 DEG C / min for 1-3 h;

[0055] S4: washing with an acid solution and deionized water to remove salt templates and aggregated metal particles, and obtaining a high-entropy single-atom catalyst loaded on an ultrathin carbon nanosheet.

[0056] Example 1

[0057] First, the cobalt-based metal-organic framework ZIF-67 was prepared at room temperature by co-precipitation method, and the precursor solution was prepared. 4.516 g (55 mmol) of 2-methylimidazole was weighed and added to 60 ml of water for magnetic stirring and dissolution, denoted as solution A; 0.291 g (1 mmol) of cobalt nitrate hexahydrate was weighed and added to 20 ml of water for magnetic stirring and dissolution; 5 mg of cetyltrimethylammonium bromide (CTAB) was weighed and poured into the cobalt nitrate solution, denoted as solution B. Pour solution B into solution A and react at 300-400 rpm for 1 h. Centrifuge the product obtained after the reaction. The centrifuged product was placed in an oven at 70°C for drying to obtain ZIF-67 powder. The prepared ZIF-67 powder (0.1 g) was dispersed in 70 mL of Tris-HCl buffer solution (pH = 8.5) to form a suspension, and then 20 mL of dopamine (0.1 g) solution was added dropwise to the above suspension, which was continuously stirred at room temperature for 10 h, then the product was obtained by centrifugation and washed with deionized water for 3 times, and then dried at room temperature. The obtained ZIF-67@PDA powder was dispersed in 20 mL of deionized water, heated to 85°C and kept for 30 min to obtain hollow dodecahedron Co-PDA. According to the atomic molar ratio of Fe, Co, Ni, Ir, Pd of 0.8:1:0.8:0.6:0.4, 190 mg of iron nitrate nonahydrate, 146 mg of nickel nitrate hexahydrate, 207 mg of iridium nitrate trihydrate, and 92 mg of palladium nitrate were weighed into a 100 mL beaker, 70 mL of ethanol was added, and stirred for 15 minutes. At this time, the total concentration of metal salts was 10 mmol / L, then 50 mL of sodium chloride was added, and ultrasonic treatment was performed for 1 h, and then freeze-dried; then, further pyrolysis was carried out at 800°C under nitrogen atmosphere, and finally washed with 1 mol HCl solution and deionized water to remove NaCl template and aggregated metal particles. After drying, two-dimensional nanosheet powder was obtained.

[0058] According to the mass ratio of 7:3, sulfur powder and two-dimensional nanosheet powder were weighed, thoroughly mixed, and heated to 155°C to melt sulfur in a reaction kettle for 12 hours to obtain a sulfur-loaded ultra-thin carbon nanosheet-loaded high-entropy single-atom catalyst material positive electrode material 1.

[0059] Example 2

[0060] First, the cobalt-based metal-organic framework ZIF-67 was prepared at room temperature by co-precipitation method, and the precursor solution was configured. 4.516 g (55 mmol) of 2-methylimidazole was weighed and added to 60 ml of water for magnetic stirring and dissolution, denoted as solution A; 0.291 g (1 mmol) of cobalt nitrate hexahydrate was weighed and added to 20 ml of water for magnetic stirring and dissolution; 5 mg of cetyltrimethylammonium bromide (CTAB) was weighed and poured into the cobalt nitrate solution, denoted as solution B. Solution B was poured into solution A and reacted at 300-400 rpm for 1 h. After the reaction, centrifugation was performed. The product obtained by centrifugation was placed in an oven at 70°C for drying to obtain ZIF-67 powder. The prepared ZIF-67 powder (0.1 g) was dispersed in 70 mL of Tris-HCl buffer solution (pH = 8.5) to form a suspension, and then 20 mL of dopamine (0.1 g) solution was added dropwise to the above suspension, which was continuously stirred at room temperature for 10 h, and then the product was obtained by centrifugation and washed three times in deionized water, and then dried at room temperature. The obtained ZIF-67@PDA powder was dispersed in 20 mL of deionized water, heated to 85°C and kept for 30 min to obtain hollow dodecahedron Co-PDA. According to the atomic molar ratio of Fe, Co, Ni, Ir, Pd of 0.8:1:0.8:0.6:0.4, 190 mg of iron nitrate nonahydrate, 146 mg of nickel nitrate hexahydrate, 207 mg of iridium nitrate trihydrate, and 92 mg of palladium nitrate were weighed into a 100 mL beaker, 70 mL of ethanol was added, and stirred for 15 minutes. At this time, the total concentration of metal salts was 10 mmol / L, then 50 mL of sodium chloride was added, and ultrasonic treatment was performed for 1 h, and freeze-drying was performed; then, further pyrolysis was performed at 600°C under nitrogen atmosphere, and finally washed with 1 mol HCl solution and deionized water to remove NaCl template and aggregated metal particles. After drying, two-dimensional nanosheet powder was obtained.

[0061] Example 3

[0062] First, the cobalt-based metal-organic framework ZIF-67 was prepared at room temperature by co-precipitation method, and the precursor solution was prepared. 4.516 g (55 mmol) of 2-methylimidazole was weighed and added to 60 ml of water for magnetic stirring and dissolution, and was recorded as solution A; 0.291 g (1 mmol) of cobalt nitrate hexahydrate was weighed and added to 20 ml of water for magnetic stirring and dissolution; 5 mg of cetyltrimethylammonium bromide (CTAB) was weighed and poured into the cobalt nitrate solution, and was recorded as solution B. Solution B was poured into solution A and reacted at 300-400 rpm for 1 h. After the reaction, centrifugation was performed. The product obtained by centrifugation was placed in an oven at 70°C for drying to obtain ZIF-67 powder. The prepared ZIF-67 powder (0.1 g) was dispersed in 70 mL of Tris-HCl buffer solution (pH = 8.5) to form a suspension, and then 20 mL of dopamine (0.1 g) solution was added dropwise to the above suspension, which was continuously stirred at room temperature for 10 h, and then the product was obtained by centrifugation and washed with deionized water for 3 times, and then dried at room temperature. The obtained ZIF-67@PDA powder was dispersed in 20 mL of deionized water, heated to 85°C and kept for 30 min to obtain hollow dodecahedron Co-PDA. According to the atomic molar ratio of Fe, Co, Ni, Ir, Pd of 0.8:1:0.8:0.6:0.4, 190 mg of iron nitrate nonahydrate, 146 mg of nickel nitrate hexahydrate, 207 mg of iridium nitrate trihydrate, and 92 mg of palladium nitrate were weighed into a 100 mL beaker, 70 mL of ethanol was added, and stirred for 15 minutes. At this time, the total concentration of metal salts was 10 mmol / L. Then 50 mL of sodium chloride was added, ultrasonic treated for 1 h, and freeze-dried. Subsequently, further pyrolysis was carried out at 700°C under nitrogen atmosphere, and finally washed with 1 mol HCl solution and deionized water to remove NaCl template and aggregated metal particles. After drying, two-dimensional nanosheet powder was obtained.

[0063] Comparative Example 1

[0064] CNT-S lithium-sulfur battery positive electrode material

[0065] Sulfur powder and carbon nanotube (CNT) material were weighed according to a mass ratio of 7:3, thoroughly mixed, and heated to 155°C to melt sulfur in a reaction kettle for 12 hours to obtain CNT-S lithium-sulfur battery positive electrode material 4 loaded with sulfur.

[0066] Performance Testing

[0067] The high-entropy single-atom catalyst supported by the ultra-thin carbon nanosheet prepared in Examples 1-3 and Comparative Example 1 was subjected to the following performance tests:

[0068] 1. SEM test

[0069] Figures 2-4The SEM images of the two-dimensional layered nanosheets prepared in Examples 1-3 are shown. It can be seen from the figures that the products obtained by the preparation method of the present invention are all sheet-like nanomaterials. Figure 2 It can be seen that the product prepared in Example 1 is a two-dimensional layered nanosheet. Figure 3 It can be seen that the product prepared in Example 2 is a two-dimensional layered nanosheet. Compared with Example 1, the nanosheet prepared in Example 2 has more pores. Figure 4 It can be seen that the product prepared in Example 3 is a two-dimensional layered nanosheet. Compared with Example 1, Example 3 produces nanofragments.

[0070] 2. TEM test

[0071] Figure 5 This is a TEM image of the two-dimensional layered nanosheets prepared in Example 1. It can be seen from the transmission electron microscopy image that the product prepared in Example 1 is a two-dimensional layered nanosheet.

[0072] 3. Battery performance test

[0073] The prepared cathode material, carbon black conductive agent (Super P), and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was then added and ground into a paste in an agate mortar. The paste was then applied to an aluminum foil current collector, dried in a 60°C vacuum oven for 8 hours, and cut into pieces to prepare the electrodes. The mixture was then transferred to an argon-filled glove box for assembly of a CR2032 coin cell battery with a lithium metal sheet as the counter electrode, a Celgard 2400 polypropylene microporous membrane as the separator, and an electrolyte consisting of 1 mol / L LiPF6 / EC+DMC+EMC (V / V = 1:1:1).

[0074] Figure 6 The lithium-sulfur battery cycle performance diagram of the positive electrode materials prepared in Example 1 and Comparative Example 1. Figure 6 As can be seen from the figure, when tested at a current density of 1C, the battery performance of cathode material 1 prepared in Example 1 is significantly better than that of cathode material 4 prepared in Comparative Example 1. This indicates that the ultrathin carbon nanosheet-supported high-entropy single-atom catalyst prepared by the preparation method of the present invention has excellent electrocatalytic performance. Its application in lithium-sulfur batteries accelerates the kinetics of polysulfide adsorption and conversion, inhibits the shuttle effect, and also improves the conductivity of sulfur, resulting in excellent cycling performance for lithium-sulfur batteries.

[0075] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and the present application also intends to include these modifications and improvements.

Claims

1. A method for preparing a high-entropy single-atom catalyst supported by ultrathin carbon nanosheets assisted by molten salt, characterized in that: The following steps are involved: S1: ZIF-67 powder is dispersed in tris(hydroxymethylaminomethane) hydrochloride buffer solution, then coated with dopamine solution, and the product is obtained by centrifugation and dried to obtain ZIF-67@PDA powder; S2: The obtained ZIF-67@PDA powder was heat-treated to obtain dopamine-coated Co organic framework hollow dodecahedrons; S3: adding a variety of soluble metal salt solutions and molten salts to the reaction system obtained in step S2, performing ultrasonic treatment, freeze-drying, and pyrolysis under a nitrogen atmosphere; S4: Washing with acid solution and deionized water to remove the salt template and aggregated metal particles to obtain a high-entropy single-atom catalyst supported on ultrathin carbon nanosheets; The metal elements in the soluble metal salt solution are selected from at least four of Fe, Ni, Ir, Pd, and Ce, and the soluble metal salt solution is selected from at least one of nitrate, chloride, acetylacetonate, and acetate.

2. The method for preparing a high-entropy single-atom catalyst supported by molten salt-assisted ultrathin carbon nanosheets according to claim 1, characterized in that: In step S1, the pH value of the tris(hydroxymethyl)aminomethane hydrochloride buffer solution is 7-9.

3. The method for preparing a high-entropy single-atom catalyst supported by molten salt-assisted synthesis of ultrathin carbon nanosheets according to claim 2, characterized in that: In step S1, the mass volume ratio of the ZIF-67 powder to the tris(hydroxymethyl)aminomethane hydrochloride buffer solution is (0.1-0.2) g: (60-80) ml.

4. The method for preparing a high-entropy single-atom catalyst supported by molten salt-assisted synthesis of ultrathin carbon nanosheets according to claim 3, characterized in that: In step S3, the molten salt includes at least one or more of sodium chloride, calcium chloride and potassium chloride.

5. The method for preparing a high-entropy single-atom catalyst supported by molten salt-assisted synthesis of ultrathin carbon nanosheets according to claim 4, characterized in that: In step S3, the mass ratio of the dopamine-coated cobalt metal organic framework hollow dodecahedron to the soluble metal salt solution is 2:5; The mass ratio of the soluble metal salt to the molten salt is 1:

3.

6. The method for preparing a high-entropy single-atom catalyst supported by molten salt-assisted synthesis of ultrathin carbon nanosheets according to claim 1, characterized in that: In step S3, the pyrolysis temperature under nitrogen atmosphere is 600-800°C, the time is 1-3 hours, and the heating rate is 1°C / min-10°C / min.

7. A molten salt-assisted synthesis of ultrathin carbon nanosheets loaded with high-entropy single-atom catalysts, characterized by: The method for preparing the ultrathin carbon nanosheet-supported high-entropy single-atom catalyst by molten salt-assisted synthesis is adopted according to any one of claims 1 to 6.

8. The molten salt-assisted synthesis of ultrathin carbon nanosheets supported on high-entropy single-atom catalysts according to claim 7, characterized in that: The ultrathin carbon nanosheet-supported high-entropy single-atom catalyst includes metal elements Fe, Co, Ni, Ir, and Pd; and the atomic molar ratio of Fe, Co, Ni, Ir, and Pd is 0.8:1:0.8:0.6:0.4; Alternatively, the ultrathin carbon nanosheet-supported high-entropy single-atom catalyst includes metal elements Fe, Co, Ni, Ir, and Ce, and the atomic molar ratio of Fe, Co, Ni, Ir, and Ce is 0.7:1:0.6:0.6:0.4; Alternatively, the ultrathin carbon nanosheet-supported high-entropy single-atom catalyst includes metal elements Fe, Co, Ni, Pd, and Ce, and the atomic molar ratio of Fe, Co, Ni, Pd, and Ce is 0.7:1:0.6:0.5:0.5; The thickness of the ultra-thin carbon nanosheet is 0.4-1.2 nm.

9. Use of the molten salt-assisted synthesis of ultrathin carbon nanosheets loaded with high entropy single-atom catalysts according to claim 7 or 8 in positive electrode sheets, secondary batteries, electrocatalytic materials, lithium-sulfur batteries and lithium metal batteries.

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