Polyhedral nanocage multi-metal hydroxide material as well as preparation method and application thereof

Abstract

The embodiment of the invention relates to a polyhedral nanocage multi-metal hydroxide material and a preparation method and application thereof, and the preparation method comprises the following steps: dissolving a zinc salt and a cobalt salt in methanol to obtain a first solution; dissolving 2-methylimidazole in methanol to obtain a second solution; adding the first solution into the second solution, and uniformly mixing to obtain a third solution; the third solution is subjected to first heat treatment, zinc ions in the zinc salt and cobalt ions in the cobalt salt are coordinated with 2-methylimidazole, and a zeolite imidazate framework structure material ZIFs solution is obtained; the preparation method comprises the following steps: carrying out primary centrifugation, washing and drying treatment on a zeolite imidazate framework structure material ZIFs solution to obtain polyhedral ZIFs powder; and dispersing the polyhedral ZIFs powder in methanol, adding hydrated nickel salt and hydrated ruthenium salt, carrying out secondary heat treatment to hydrolyze nickel ions in the hydrated nickel salt and ruthenium ions in the hydrated ruthenium salt so as to chemically etch the ZIFs, and then carrying out secondary centrifugation, washing and drying treatment to obtain the polyhedral nanocage multi-metal hydroxide material.

Description

Technical Field

[0001] The present invention relates to the field of cathode materials for lithium-oxygen batteries, and particularly to a polyhedral nanocage multi-metal hydroxide material, a preparation method thereof, and an application thereof. Background Art

[0002] Cobalt-nickel-based oxides / hydroxides, as an important chemical raw material, have extensive applications in battery materials, catalysts, electronic materials, chemical engineering fields, etc. In recent years, researchers have made great breakthroughs in the design and synthesis of cobalt-nickel-based oxide / hydroxide electrocatalysts, making such materials show extremely important application potential in the field of energy storage and conversion.

[0003] Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are important processes in energy conversion devices such as metal-air batteries. Although noble metal catalysts are usually used to solve the problem of slow ORR reaction kinetics caused by the multi-electron transfer process, their high cost has brought many obstacles to large-scale popularization and use. Therefore, the development of OER catalysts and ORR catalysts with higher activity has become a research hotspot in the fields of materials, chemistry, and energy. For example, transition metals (Fe, Co, Ni, etc.) with rich reserves are used to develop catalysts to regulate the kinetics of the reaction process. However, traditional preparation methods are difficult to obtain multi-metal hydroxides, and traditional transition metal hydroxides, such as nickel hydroxide and cobalt hydroxide, have disadvantages such as poor stability, small specific surface area, poor conductivity, and low catalytic activity. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and provide a polyhedral nanocage multi-metal hydroxide material, a preparation method thereof, and an application thereof. The polyhedral nanocage multi-metal hydroxide obtained by this preparation method has the high porosity, high specific surface area, and rich gas-liquid diffusion channels of ZIFs, and also has high catalytic activity.

[0005] To achieve the above object, in a first aspect, the present invention provides a preparation method of a polyhedral nanocage multi-metal hydroxide material, and the preparation method includes:

[0006] Dissolve a zinc salt and a cobalt salt in methanol to obtain a first solution; the molar ratio of zinc ions in the zinc salt to cobalt ions in the cobalt salt is [1-8]:[0-1];

[0007] Dissolve 2-methylimidazole in methanol to obtain a second solution;

[0008] Add the first solution to the second solution and mix evenly to obtain a third solution;

[0009] The third solution is subjected to the first heat treatment so that zinc ions in the zinc salt and cobalt ions in the cobalt salt coordinate with 2-methylimidazole to obtain a zeolitic imidazolate framework material ZIFs solution; wherein, the zinc ions coordinate with 2-methylimidazole to form a dodecahedral structure, and the cobalt ions coordinate with 2-methylimidazole to form a tetrahedral framework structure; wherein, the first heat treatment is carried out in an incubator at a temperature of 25°C - 35°C for a time of 22 hours - 26 hours;

[0010] The zeolitic imidazolate framework material ZIFs solution is subjected to the first centrifugation, washing and drying treatments to obtain polyhedral ZIFs powder; the polyhedral ZIFs powder is dodecahedral or a mixture of dodecahedral and octadecahedral;

[0011] The polyhedral ZIFs powder is dispersed in methanol, and then hydrated nickel salt and hydrated ruthenium salt are added for the second heat treatment so that nickel ions in the hydrated nickel salt and ruthenium ions in the hydrated ruthenium salt hydrolyze to generate hydrogen ions. Under the action of the hydrogen ions, the coordination bonds between the ligands and zinc ions and between the ligands and cobalt ions in the ZIFs are broken, thereby chemically etching the ZIFs. At the same time, cobalt ions, nickel ions in the hydrated nickel salt and ruthenium ions in the hydrated ruthenium salt form cobalt hydroxide, nickel hydroxide and ruthenium hydroxide on the surface of the ZIFs through hydrolysis, and then after the second centrifugation, washing and drying treatments, a polyhedral nanocage multi-metal hydroxide material is obtained; wherein, the second heat treatment is carried out in a forced air drying oven at a temperature of 110°C - 130°C for a time of 1 hour - 3 hours.

[0012] Preferably, the zinc salt includes one or more of zinc nitrate hexahydrate, zinc chloride, zinc acetate; the cobalt salt includes one or more of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, cobalt sulfate heptahydrate.

[0013] Preferably, the ratio of the molar number of 2-methylimidazole to the sum of the molar numbers of zinc ions in the zinc salt and cobalt ions in the cobalt salt is 4:1 - 6:1.

[0014] Preferably, the rotation speed of the first centrifugation is 7000 - 9000 revolutions per minute, the cleaning agent for washing is one or more of ethanol, methanol or acetone; drying is carried out in a vacuum drying oven at a temperature of 75°C - 85°C for a time of 22 hours - 26 hours.

[0015] Preferably, the hydrated nickel salt is one or more of nickel chloride hexahydrate, nickel nitrate hexahydrate, nickel sulfate hexahydrate; the hydrated ruthenium salt is ruthenium chloride trihydrate; the molar ratio of nickel ions in the hydrated nickel salt to ruthenium ions in the hydrated ruthenium salt is [1 - 8]:[0 - 1].

[0016] Preferably, the molar ratio of the sum of the moles of nickel ions and ruthenium ions to the polyhedral ZIFs is 1:1 - 3:1.

[0017] Preferably, the rotation speed of the second centrifugation is 7000 - 9000 revolutions per minute, and the cleaning agent for washing is one or more of ethanol, methanol, or acetone; drying is carried out in a vacuum drying oven at a temperature of 75°C - 85°C for 22 - 26 hours.

[0018] In a second aspect, the present invention provides a polyhedral nanocage multi-metal hydroxide material, which is prepared by the preparation method according to any one of the first aspects above.

[0019] In a third aspect, the present invention provides a positive electrode sheet, which includes the polyhedral nanocage multi-metal hydroxide material according to the second aspect.

[0020] In a fourth aspect, the present invention provides a lithium-oxygen battery, which includes the positive electrode sheet according to the third aspect.

[0021] The preparation method of the polyhedral nanocage multi-metal hydroxide material provided by the embodiments of the present invention first adjusts the molar ratio between zinc ions and cobalt ions so that the formed ZIFs are in the shape of dodecahedrons or a mixture of dodecahedrons and octadecahedrons, retaining the advantages of high porosity, high stability, and abundant gas-liquid diffusion channels of ZIFs. Then, through chemical etching, the ZIFs form a cavity structure, obtaining the polyhedral nanocage multi-metal hydroxide material. This polyhedral nanocage multi-metal hydroxide material has a high specific surface area, can expose more active sites, has high catalytic activity, and due to the doping of ruthenium, its conductivity is also improved. In summary, the high stability and high catalytic activity of the polyhedral nanocage multi-metal hydroxide material can reduce the overpotential, thereby reducing battery polarization. Description of the Drawings

[0022] Figure 1 It is a flow chart of the preparation method of the polyhedral nanocage multi-metal hydroxide material provided by the embodiments of the present invention;

[0023] Figure 2 It is a SEM image of ZIF-2:1(Zn / Co) provided in Example 5 of the present invention;

[0024] Figure 3 It is a SEM image of the polyhedral nanocage Co / Ni bimetallic hydroxide (Co1Ni2-OH) material provided in Example 5 of the present invention;

[0025] Figure 4SEM image of the polyhedral nanocage Co / Ni bimetallic hydroxide (Co1Ni4-OH) material provided in Example 6 of the present invention;

[0026] Figure 5 SEM image of the polyhedral nanocage Co / Ni bimetallic hydroxide (Co1Ni8-OH) material provided in Example 7 of the present invention;

[0027] Figure 6 SEM image of the polyhedral nanocage Co / Ni / Ru polymetallic hydroxide (Co4Ni7Ru1-OH) material provided in Example 1 of the present invention;

[0028] Figure 7 SEM image of the polyhedral nanocage Co / Ni / Ru polymetallic hydroxide (Co1Ni3Ru1-OH) material provided in Example 3 of the present invention;

[0029] Figure 8 XRD pattern of ZIF-2:1 (Zn / Co) provided in Example 5 of the present invention;

[0030] Figure 9 XRD patterns of Ni(OH)2 in Example 4, Co1Ni2-OH in Example 5, and Co4Ni7Ru1-OH in Example 1 of the present invention;

[0031] Figure 10 Initial charge-discharge curves of the lithium-oxygen battery provided in Examples 1, 4, and 6 of the present invention;

[0032] Figure 11 Schematic diagram of the formation process of the polyhedral nanocage polymetallic hydroxide material provided in the examples of the present invention. Detailed implementation manners

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0034] The technical solutions of the present invention will be further described in detail below through the accompanying drawings and examples.

[0035] A preparation method of a polyhedral nanocage polymetallic hydroxide material provided in an embodiment of the present invention specifically includes the steps as Figure 1 shown:

[0036] Step 110, dissolving a zinc salt and a cobalt salt in methanol to obtain a first solution;

[0037] Specifically, the zinc salt may specifically include one or more of zinc nitrate hexahydrate, zinc chloride, or zinc acetate. The cobalt salt may specifically include one or more of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, or cobalt sulfate heptahydrate. The molar ratio of zinc ions in the zinc salt to cobalt ions in the cobalt salt may be [1-8]:[0-1], preferably 2:1, 3:1, 4:1, or 8:1.

[0038] Step 120: Dissolve 2-methylimidazole in methanol to obtain a second solution;

[0039] Specifically, the ratio of the number of moles of 2-methylimidazole to the sum of the number of moles of zinc ions in the zinc salt and cobalt ions in the cobalt salt is specifically 4:1 - 6:1, preferably 5:1. The concentration of methanol is specifically 95%.

[0040] The reason for dissolving the metal salts (zinc salt, cobalt salt) and the ligand (2-methylimidazole) separately is mainly to avoid the phenomenon of uneven particle size of the product caused by the direct reaction of solid metal salts and ligands.

[0041] Step 130: Add the first solution to the second solution and mix evenly to obtain a third solution;

[0042] Step 140: Perform a first heat treatment on the third solution to coordinate zinc ions in the zinc salt and cobalt ions in the cobalt salt with 2-methylimidazole to obtain a zeolitic imidazolate framework material ZIFs solution;

[0043] Specifically, the first heat treatment can be carried out in an incubator, the temperature can specifically be 25°C - 35°C, preferably 30°C. The time can specifically be 22 hours - 26 hours, preferably 24 hours.

[0044] Among them, the structure of the zeolitic imidazolate framework material (Zeolitic imidazolate frameworks, ZIFs) formed by the coordination of zinc ions and 2-methylimidazole is a dodecahedron, denoted as ZIF-8. The structure of the zeolitic imidazolate framework material formed by the coordination of cobalt ions and 2-methylimidazole is a tetrahedral framework structure, denoted as ZIF-67. By adjusting the molar ratio between zinc ions and cobalt ions, the exposed crystal planes of ZIF-8 and ZIF-67 are different, so that the structure of the zeolitic imidazolate framework material presents a dodecahedron or a mixed dodecahedron and octahedron. In this way, the advantages of high porosity, high stability, and rich gas-liquid diffusion channels of ZIFs are retained.

[0045] Step 150: Subject the zeolitic imidazolate framework material ZIFs solution to the first centrifugation, washing, and drying treatments to obtain polyhedral ZIFs powder;

[0046] Specifically, the rotation speed of the first centrifugation can be 7,000 - 9,000 revolutions per minute, preferably 8,000 revolutions per minute, and the time can be 6 - 10 minutes, preferably 8 minutes. After centrifugation, the supernatant is removed, and the precipitate is taken for washing. The cleaning agent for washing can specifically be one or more of ethanol, methanol, or acetone. Among them, the concentration of ethanol is specifically 99%, the concentration of methanol is specifically 95%, and the concentration of acetone is specifically 90%. The number of washing times can specifically be 3 - 5 times. Drying can specifically be carried out in a vacuum drying oven, the temperature can be 75°C - 85°C, preferably 80°C; the time can be 22 - 26 hours, preferably 24 hours. The polyhedral ZIFs powder is a dodecahedron or a mixture of dodecahedrons and octadecahedrons.

[0047] Step 160: Disperse the polyhedral ZIFs powder in methanol, then add hydrated nickel salt and hydrated ruthenium salt, and perform a second heat treatment to enable the nickel ions in the hydrated nickel salt and the ruthenium ions in the hydrated ruthenium salt to hydrolyze to produce hydrogen ions. Under the action of the hydrogen ions, the coordination bonds between the ligands and zinc ions, and the ligands and cobalt ions in the ZIFs are broken, thereby chemically etching the ZIFs. At the same time, cobalt ions, nickel ions in the hydrated nickel salt, and ruthenium ions in the hydrated ruthenium salt form cobalt hydroxide, nickel hydroxide, and ruthenium hydroxide on the surface of the ZIFs through hydrolysis. After that, it is further subjected to a second centrifugation, washing, and drying treatment to obtain the polyhedral nanocage multi-metal hydroxide material.

[0048] Specifically, the hydrated nickel salt can specifically be one or more of nickel chloride hexahydrate, nickel nitrate hexahydrate, or nickel sulfate hexahydrate. The hydrated ruthenium salt can specifically be ruthenium chloride trihydrate. The second molar ratio can be [1 - 8]:[0 - 1], preferably 2:1, 3:1, 4:1, or 8:1. And the molar ratio of the sum of the nickel ions in the hydrated nickel salt and the ruthenium ions in the hydrated ruthenium salt to the polyhedral ZIFs can specifically be 1:1 - 3:1, preferably 2:1.

[0049] The second heat treatment can specifically be carried out in a forced-air drying oven, the temperature can be 110°C - 130°C, preferably 120°C; the time is 1 - 3 hours, preferably 2 hours.

[0050] The rotation speed of the second centrifugation can be 7,000 - 9,000 revolutions per minute, preferably 8,000 revolutions per minute, and the time can be 6 - 10 minutes, preferably 8 minutes. After centrifugation, the supernatant is removed, and the precipitate is taken for washing. The cleaning agent for washing can specifically be one or more of ethanol, methanol, or acetone. The number of washing times can specifically be 3 - 5 times. Drying can specifically be carried out in a vacuum drying oven, the temperature can be 75°C - 85°C, preferably 80°C; the time can be 22 - 26 hours, preferably 24 hours.

[0051] The specific chemical reaction equation is as follows:

[0052]

[0053]

[0054] Zn 2+ [2-mlm] n + nH + →→ n[2-mlm]H + + Zn 2+

[0055] Co 2+ [2-mlm] n + nH + → n[2-mlm]H + + Co 2+

[0056]

[0057] Among them, 2-mlm represents a ligand. As Figure 11 shown, in this step, ZIFs are used as a template. Since the hydrated nickel salt and hydrated ruthenium salt are hydrates, after dissolution, they diffuse to the surface of ZIFs and undergo hydrolysis reactions to form corresponding hydroxides and hydrogen ions. H + has a chemical corrosive effect on ZIFs, which can break the coordination bonds between the ligands and metal ions in ZIFs, thereby chemically etching ZIFs. At the same time, cobalt ions, nickel ions in the hydrated nickel salt, and ruthenium ions in the hydrated ruthenium salt form cobalt hydroxide, nickel hydroxide, and ruthenium hydroxide on the surface of ZIFs through hydrolysis.

[0058] In this way, the exposed ZIFs gradually decrease, resulting in a slowdown in the etching rate of the hydrated nickel salt and hydrated ruthenium salt on ZIFs. However, nickel ions and ruthenium ions continue to diffuse into the interior of ZIFs, and the hydrolysis of cobalt ions also proceeds. Therefore, chemical etching still exists. Eventually, a cavity structure is formed inside ZIFs, and a multi-metal hydroxide material is obtained. Zinc ions and ligands are removed in the supernatant after centrifugation. That is to say, this multi-metal hydroxide only has the structure of ZIFs, namely polyhedral nanocages, and is actually an inorganic substance. This makes the multi-metal hydroxide material have the advantages of ZIFs, that is, it has a high specific surface area, can expose more active sites, and due to the doping of ruthenium, its conductivity is improved. In this way, both the difficulty of synthesizing multi-metal hydroxides by traditional preparation methods is overcome, and the problems of poor stability, small specific surface area, poor conductivity, and low catalytic activity of traditional transition metal hydroxides are also solved.

[0059] The preparation method of the polyhedral nanocage multi-metal hydroxide material provided by the embodiments of the present invention first adjusts the molar ratio between zinc ions and cobalt ions so that the formed ZIFs are in the form of dodecahedrons or a mixture of dodecahedrons and octadecahedrons, retaining the advantages of high porosity, high stability and abundant gas-liquid diffusion channels of ZIFs. Then, through chemical etching, the ZIFs form a cavity structure, obtaining the polyhedral nanocage multi-metal hydroxide material. The polyhedral nanocage multi-metal hydroxide material has a high specific surface area, can expose more active sites, has relatively high catalytic activity, and its conductivity is also improved due to the doping of ruthenium. In short, the high stability and high catalytic activity of the polyhedral nanocage multi-metal hydroxide material can reduce the overpotential, thereby reducing battery polarization.

[0060] The polyhedral nanocage multi-metal hydroxide material provided by the present invention can be applied to the production of the positive electrode sheet of a lithium-oxygen battery.

[0061] To better understand the technical solution provided by the present invention, the following uses multiple specific examples to separately illustrate the specific process of preparing the polyhedral nanocage multi-metal hydroxide material by applying the method provided by the above embodiments of the present invention, and the electrochemical properties of the prepared polyhedral nanocage multi-metal hydroxide material.

[0062] Example 1

[0063] In the first step, 0.99 g of zinc nitrate hexahydrate and 0.49 g of cobalt nitrate hexahydrate were weighed according to the first molar ratio of 2:1, dissolved in 40 mL of methanol to obtain a first solution.

[0064] In the second step, 1.64 g of 2-methylimidazole was weighed and dissolved in 40 mL of methanol to obtain a second solution.

[0065] In the third step, the first solution was added to the second solution and mixed evenly to obtain a third solution.

[0066] In the fourth step, the third solution was subjected to the first heat treatment in an incubator at a temperature of 30 °C for 24 hours to coordinate zinc ions and cobalt ions with 2-methylimidazole, obtaining a ZIFs solution, briefly denoted as ZIF-2:1(Zn / Co).

[0067] In the fifth step, the ZIFs solution was centrifuged at a speed of 8000 revolutions per minute for 8 minutes. The centrifuged precipitate was taken, washed 4 times with ethanol, and then dried in a vacuum drying oven at a temperature of 80 °C for 24 hours to obtain ZIFs powder.

[0068] Step 6: Take 0.18 g of ZIFs powder, disperse it in 40 mL of methanol, then add 0.33 g of nickel chloride hexahydrate and 0.04 g of ruthenium chloride trihydrate. After that, conduct the second heat treatment in a forced-air drying oven at a temperature of 120 °C for 2 hours to enable chemical etching of ZIFs by nickel ions and ruthenium ions. Then wash it 4 times with ethanol, and then dry it in a vacuum drying oven at a temperature of 80 °C for 24 hours to obtain a polyhedral nanocage Co / Ni / Ru polymetallic hydroxide material. Since the molar ratio of zinc ions to cobalt ions is 2:1 and the ratio of nickel ions to ruthenium ions is 7:1, during the chemical etching process, nickel ions and ruthenium ions replace the zinc sites. Therefore, for convenience of labeling, the product obtained in this example is briefly denoted as: Co4Ni7Ru1-OH. That is to say, the subscripts of Co, Ni, and Ru do not represent the actual number of atoms, but only represent the ratio between the atoms in the polyhedral nanocage structure. The subscripts of Co, Ni, and Ru in the following examples and comparative examples are obtained based on the same principle and will not be elaborated further.

[0069] After that, use the prepared Co4Ni7Ru1-OH as the positive electrode plate to assemble a lithium-oxygen battery for testing, specifically as follows:

[0070] First, add Co4Ni7Ru1-OH, polyvinylidene fluoride (PVDF), and Ketjenblack (KB) to N-methylpyrrolidone (NMP) according to a mass ratio of 6:2:2, and mix them into a homogeneous slurry by ball milling, and then coat it on carbon paper. After that, place it in a vacuum drying oven at 100 °C and dry it for 12 hours, and then use a punching machine to punch it into a pole piece with a diameter of 13 mm.

[0071] Second, use the pole piece prepared above as the positive electrode, a metal lithium sheet as the negative electrode, and a glass fiber as the separator to assemble a lithium-oxygen battery. Among them, the electrolyte is a mixed solution of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and triethylene glycol dimethyl ether (TEGDME).

[0072] Finally, conduct a constant current charge-discharge test on the assembled lithium-oxygen battery. Test conditions: current density is 0.1 mA / cm 2 , and the cut-off capacity is 0.2 mAh / cm 2 .

[0073] Example 2

[0074] Step 1: Weigh 1.19 g of zinc nitrate hexahydrate and 0.29 g of cobalt nitrate hexahydrate according to a first molar ratio of 4:1, and dissolve them in 40 mL of methanol to obtain a first solution.

[0075] Step 2: Weigh 1.64 g of 2-methylimidazole and dissolve it in 40 mL of methanol to obtain a second solution.

[0076] Step 3: Add the first solution to the second solution and mix evenly to obtain the third solution.

[0077] Step 4: Perform the first heat treatment on the third solution in an incubator at a temperature of 30 °C for 24 hours, so that zinc ions and cobalt ions coordinate with 2-methylimidazole to obtain a ZIFs solution, briefly denoted as ZIF-4:1(Zn / Co).

[0078] Step 5: Centrifuge the ZIFs solution at a speed of 8000 revolutions per minute for 8 minutes. Take the centrifuged precipitate, wash it 4 times with ethanol, and then dry it in a vacuum drying oven at a temperature of 80 °C for 24 hours to obtain ZIFs powder.

[0079] Step 6: Take 0.18 g of ZIFs powder, disperse it in 40 mL of methanol, then add 0.33 g of nickel chloride hexahydrate and 0.04 g of ruthenium chloride trihydrate, and then perform the second heat treatment in a forced-air drying oven at a temperature of 120 °C for 2 hours, so that nickel ions and ruthenium ions chemically etch the ZIF, then wash it 4 times with ethanol, and then dry it in a vacuum drying oven at a temperature of 80 °C for 24 hours to obtain a dodecahedral nanocage Co / Ni / Ru polymetallic hydroxide material, briefly denoted as: Co2Ni7Ru1-OH.

[0080] The assembly and testing of the lithium-oxygen battery are the same as in Example 1.

[0081] Example 3

[0082] Step 1: Weigh 1.19 g of zinc nitrate hexahydrate and 0.29 g of cobalt nitrate hexahydrate according to a first molar ratio of 4:1, dissolve them in 40 mL of methanol to obtain the first solution.

[0083] Step 2: Weigh 1.64 g of 2-methylimidazole and dissolve it in 40 mL of methanol to obtain the second solution.

[0084] Step 3: Add the first solution to the second solution and mix evenly to obtain the third solution.

[0085] Step 4: Perform the first heat treatment on the third solution in an incubator at a temperature of 30 °C for 24 hours, so that zinc ions and cobalt ions coordinate with 2-methylimidazole to obtain a ZIFs solution, briefly denoted as ZIF-4:1(Zn / Co).

[0086] Step 5: Centrifuge the ZIFs solution at a speed of 8000 revolutions per minute for 8 minutes. Take the centrifuged precipitate, wash it 4 times with ethanol, and then dry it in a vacuum drying oven at a temperature of 80 °C for 24 hours to obtain ZIFs powder.

[0087] Step 6: Take 0.18 g of ZIFs powder, disperse it in 40 mL of methanol, then add 0.29 g of nickel chloride hexahydrate and 0.08 g of ruthenium chloride trihydrate. After that, conduct the second heat treatment in a forced-air drying oven at 120 °C for 2 hours to enable the chemical etching of ZIFs by nickel ions and ruthenium ions. Then wash it 4 times with ethanol, and then dry it in a vacuum drying oven at 80 °C for 24 hours to obtain a polyhedral nanocage Co / Ni / Ru polymetallic hydroxide material, briefly denoted as: Co1Ni3Ru1-OH.

[0088] The assembly and testing of the lithium-oxygen battery are the same as in Example 1.

[0089] Example 4

[0090] Step 1: Weigh 1.49 g of zinc nitrate hexahydrate according to a first molar ratio of 5:0, dissolve it in 40 mL of methanol to obtain a first solution.

[0091] Step 2: Weigh 1.64 g of 2-methylimidazole, dissolve it in 40 mL of methanol to obtain a second solution.

[0092] Step 3: Add the first solution to the second solution and mix them evenly to obtain a third solution.

[0093] Step 4: Conduct the first heat treatment on the third solution in a constant-temperature oven at 30 °C for 24 hours to enable the coordination of zinc ions with 2-methylimidazole to obtain a cobalt-free ZIFs solution, briefly denoted as ZIF-8-5:0(Zn / Co).

[0094] Step 5: Centrifuge the cobalt-free ZIFs solution at a speed of 8000 revolutions per minute for 8 minutes. Take the centrifuged precipitate, wash it 4 times with ethanol, and then dry it in a vacuum drying oven at 80 °C for 24 hours to obtain cobalt-free ZIFs powder.

[0095] Step 6: Take 0.18 g of cobalt-free ZIFs powder, disperse it in 40 mL of methanol, then add 0.38 g of nickel chloride hexahydrate. After that, conduct the second heat treatment in a forced-air drying oven at 120 °C for 2 hours to enable the chemical etching of ZIFs by nickel ions. Then wash it 4 times with ethanol, and then dry it in a vacuum drying oven at 80 °C for 24 hours to obtain a polyhedral nanocage Ni metal hydroxide material, briefly denoted as: Ni(OH)2.

[0096] The assembly and testing of the lithium-oxygen battery are the same as in Example 1.

[0097] Example 5

[0098] Step 1: Weigh 0.99 g of zinc nitrate hexahydrate and 0.49 g of cobalt nitrate hexahydrate in a ratio of 2:1 (the first molar ratio), dissolve them in 40 mL of methanol to obtain the first solution.

[0099] Step 2: Weigh 1.64 g of 2-methylimidazole, dissolve it in 40 mL of methanol to obtain the second solution.

[0100] Step 3: Add the first solution to the second solution and mix them evenly to obtain the third solution.

[0101] Step 4: Conduct the first heat treatment on the third solution in an incubator at a temperature of 30 °C for 24 hours, so that zinc ions and cobalt ions coordinate with 2-methylimidazole to obtain a ZIFs solution, abbreviated as ZIF-2:1(Zn / Co).

[0102] Step 5: Centrifuge the ZIFs solution at a speed of 8000 revolutions per minute for 8 minutes. Take the centrifuged precipitate, wash it 4 times with ethanol, and then dry it in a vacuum drying oven at a temperature of 80 °C for 24 hours to obtain ZIF powder.

[0103] Step 6: Take 0.18 g of ZIFs powder, disperse it in 40 mL of methanol, then add 0.38 g of nickel chloride hexahydrate, and then conduct the second heat treatment in a forced-air drying oven at a temperature of 120 °C for 2 hours, so that nickel ions chemically etch the ZIFs, then wash it 4 times with ethanol, and then dry it in a vacuum drying oven at a temperature of 80 °C for 24 hours to obtain a polyhedral nanocage Co / Ni bimetallic hydroxide material, abbreviated as: Co1Ni2-OH.

[0104] Example 6

[0105] Step 1: Weigh 1.19 g of zinc nitrate hexahydrate and 0.29 g of cobalt nitrate hexahydrate in a ratio of 4:1 (the first molar ratio), dissolve them in 40 mL of methanol to obtain the first solution.

[0106] Step 2: Weigh 1.64 g of 2-methylimidazole, dissolve it in 40 mL of methanol to obtain the second solution.

[0107] Step 3: Add the first solution to the second solution and mix them evenly to obtain the third solution.

[0108] Step 4: Conduct the first heat treatment on the third solution in an incubator at a temperature of 30 °C for 24 hours, so that zinc ions and cobalt ions coordinate with 2-methylimidazole to obtain a ZIFs solution, abbreviated as ZIF-4:1(Zn / Co).

[0109] Step 5: Centrifuge the ZIFs solution at a speed of 8000 revolutions per minute for 8 minutes. Take the centrifuged precipitate, wash it 4 times with ethanol, and then dry it in a vacuum drying oven at 80 °C for 24 hours to obtain ZIF powder.

[0110] Step 6: Take 0.18 g of ZIFs powder, disperse it in 40 mL of methanol, then add 0.38 g of nickel chloride hexahydrate, and then conduct the second heat treatment in a forced-air drying oven at 120 °C for 2 hours to allow nickel ions to chemically etch the ZIFs. Then wash it 4 times with ethanol, and then dry it in a vacuum drying oven at 80 °C for 24 hours to obtain a polyhedral nanocage Co / Ni bimetallic hydroxide material, abbreviated as: Co1Ni4-OH.

[0111] The assembly and testing of the lithium-oxygen battery are the same as in Example 1.

[0112] Example 7

[0113] Step 1: Weigh 1.32 g of zinc nitrate hexahydrate and 0.16 g of cobalt nitrate hexahydrate according to a molar ratio of 8:1, dissolve them in 40 mL of methanol to obtain the first solution.

[0114] Step 2: Weigh 1.64 g of 2-methylimidazole and dissolve it in 40 mL of methanol to obtain the second solution.

[0115] Step 3: Add the first solution to the second solution and mix them evenly to obtain the third solution.

[0116] Step 4: Conduct the first heat treatment on the third solution in a constant-temperature oven at 30 °C for 24 hours to allow zinc ions and cobalt ions to coordinate with 2-methylimidazole to obtain a ZIFs solution, abbreviated as ZIF-8:1(Zn / Co).

[0117] Step 5: Centrifuge the ZIFs solution at a speed of 8000 revolutions per minute for 8 minutes. Take the centrifuged precipitate, wash it 4 times with ethanol, and then dry it in a vacuum drying oven at 80 °C for 24 hours to obtain ZIF powder.

[0118] Step 6: Take 0.18 g of ZIFs powder, disperse it in 40 mL of methanol, then add 0.38 g of nickel chloride hexahydrate, and then conduct the second heat treatment in a forced-air drying oven at 120 °C for 2 hours to allow nickel ions to chemically etch the ZIFs. Then wash it 4 times with ethanol, and then dry it in a vacuum drying oven at 80 °C for 24 hours to obtain a polyhedral nanocage Co / Ni bimetallic hydroxide material, abbreviated as: Co1Ni8-OH.

[0119] From Figure 2It can be seen that when the molar ratio of zinc element to cobalt element in zinc salt and cobalt salt is 2:1, a ZIFs template with an octahedral structure can be obtained, and the particle size is 7nm - 800nm.

[0120] Comparison Figure 3 and Figure 2 , through the action of chemical etching, the ZIFs template with an octahedral structure forms a cage structure with a cavity structure.

[0121] Comparison Figure 3 , 4 and 5, through the action of chemical etching, the ZIFs template is chemically etched into bimetallic hydroxides with different morphologies, and the roughness of the particle surface after chemical etching varies. This is because the chemical etching effect mainly depends on the sites where nickel replaces zinc. Due to the different proportions of zinc added, the chemical etching effect is naturally different. When the molar ratio of zinc ion / cobalt ion is 2:1, the obtained product is an octahedron; when the molar ratio of zinc ion / cobalt ion is greater than 2:1, the obtained product is a dodecahedron, that is, the higher the zinc content in the ZIFs template, the more the structure of ZIFs tends to be a dodecahedron.

[0122] Figure 6 and 7 show that the doping of ruthenium does not destroy the structure of the polymetallic hydroxide, and due to the stability of cobalt, ruthenium mainly replaces the sites of zinc.

[0123] From Figure 8 it can be known that the two main peak positions of ZIF-8 are at 7.4° and 12.8° respectively. However, as shown in Figure 9 , no diffraction peak of ZIF-8 can be observed in the spectra of Co1Ni2-OH and Co4Ni7Ru1-OH. It can be concluded that the original crystal structure of ZIF is destroyed by chemical etching. At the same time, due to the increased proportion of nickel content, therefore, in Figure 9 only the diffraction peaks of Ni(OH)2 can be observed in the Co1Ni2-OH and Co4Ni7Ru1-OH samples, and the positions of the three main peaks are 11.3°, 33.7° and 59.0° respectively

[0124] As Figure 10 shown, at a current density of 0.1mA / cm 2 , the cut-off capacity is 0.2mAh / cm 2Under the test conditions, the overpotential of the first cycle of the Ni(OH)2 electrode is about 1.04 V. This is because the stability and catalytic activity of Ni(OH)2 are low, resulting in a relatively high overpotential. The overpotential of Co1Ni4-OH is 0.87 V, and the overpotential of Co4Ni7Ru1-OH is 0.52 V. It can be concluded that compared with the dodecahedral Co1Ni4-OH, the octahedral Co4Ni7Ru1-OH has a larger specific surface area and more exposed active sites, which is beneficial to the catalytic reaction. In addition, due to the excellent catalytic activity of the noble metal ruthenium, the overpotential can be further reduced, indicating that the synergistic catalysis of the three metals is beneficial to reducing polarization.

[0125] Example 8

[0126] First step: Weigh 0.82 g of zinc chloride and 0.24 g of cobalt chloride hexahydrate according to the first molar ratio of 6:1, and dissolve them in 40 mL of methanol to obtain the first solution.

[0127] Second step: Weigh 2.87 g of 2-methylimidazole and dissolve it in 40 mL of methanol to obtain the second solution.

[0128] Third step: Add the first solution to the second solution and mix them evenly to obtain the third solution.

[0129] Fourth step: Perform the first heat treatment on the third solution in an incubator at a temperature of 25 °C for 26 hours, so that zinc ions and cobalt ions coordinate with 2-methylimidazole to obtain the ZIFs solution, abbreviated as ZIF-6:1(Zn / Co).

[0130] Fifth step: Centrifuge the ZIFs solution at a speed of 7000 revolutions per minute for 10 minutes. Take the centrifuged precipitate, wash it 3 times with methanol, and then dry it in a vacuum drying oven at a temperature of 75 °C for 26 hours to obtain the ZIFs powder.

[0131] Sixth step: Take 0.08 g of the ZIFs powder, disperse it in 40 mL of methanol, then add 0.58 g of nickel nitrate hexahydrate and 0.10 g of ruthenium chloride trihydrate, and then perform the second heat treatment in a forced-air drying oven at a temperature of 110 °C for 3 hours, so that nickel ions and ruthenium ions chemically etch the ZIFs. Then wash it 3 times with methanol, and then dry it in a vacuum drying oven at a temperature of 85 °C for 22 hours to obtain the polyhedral nanocage Co / Ni / Ru multi-metal hydroxide material, abbreviated as: Co1Ni4Ru2-OH.

[0132] Example 9

[0133] Step 1: Weigh 0.41 g of zinc chloride and 0.24 g of cobalt(II) chloride hexahydrate according to the first molar ratio of 3:1, and dissolve them in 40 mL of methanol to obtain the first solution.

[0134] Step 2: Weigh 2.29 g of 2-methylimidazole and dissolve it in 40 mL of methanol to obtain the second solution.

[0135] Step 3: Add the first solution to the second solution and mix them evenly to obtain the third solution.

[0136] Step 4: Conduct the first heat treatment on the third solution in an incubator at a temperature of 35 °C for 22 hours, enabling the coordination of zinc ions and cobalt ions with 2-methylimidazole to obtain a ZIFs solution, abbreviated as ZIF-3:1(Zn / Co).

[0137] Step 5: Centrifuge the ZIFs solution at a speed of 9000 revolutions per minute for 6 minutes. Take the centrifuged precipitate, wash it 5 times with acetone, and then dry it in a vacuum drying oven at a temperature of 85 °C for 22 hours to obtain ZIFs powder.

[0138] Step 6: Take 0.16 g of ZIFs powder, disperse it in 40 mL of methanol, then add 1.45 g of nickel(II) nitrate hexahydrate and 0.10 g of ruthenium(III) chloride trihydrate, and then conduct the second heat treatment in a forced-air drying oven at a temperature of 130 °C for 1 hour, enabling the chemical etching of ZIFs by nickel ions and ruthenium ions, then wash it 5 times with acetone, and then dry it in a vacuum drying oven at a temperature of 75 °C for 26 hours to obtain a polyhedral nanocage Co / Ni / Ru polymetallic hydroxide material, abbreviated as: Co3Ni5Ru1-OH.

[0139] Example 10

[0140] Step 1: Weigh 1.47 g of zinc acetate and 0.28 g of cobalt(II) sulfate heptahydrate according to the first molar ratio of 8:1, and dissolve them in 40 mL of methanol to obtain the first solution.

[0141] Step 2: Weigh 3.33 g of 2-methylimidazole and dissolve it in 40 mL of methanol to obtain the second solution.

[0142] Step 3: Add the first solution to the second solution and mix them evenly to obtain the third solution.

[0143] Step 4: Conduct the first heat treatment on the third solution in an incubator at a temperature of 29 °C for 23 hours, enabling the coordination of zinc ions and cobalt ions with 2-methylimidazole to obtain a ZIFs solution, abbreviated as ZIF-8:1(Zn / Co).

[0144] Step 5: Centrifuge the ZIFs solution at a speed of 8500 revolutions per minute for 9 minutes. Take the precipitate after centrifugation, wash it 3 times with acetone, and then dry it in a vacuum drying oven at a temperature of 78 °C for 24 hours to obtain ZIFs powder.

[0145] Step 6: Take 0.25 g of ZIFs powder, disperse it in 40 mL of methanol, then add 2.10 g of nickel sulfate hexahydrate and 0.10 g of ruthenium chloride trihydrate, and then perform a second heat treatment in a forced-air drying oven at a temperature of 125 °C for 3 hours to allow nickel ions and ruthenium ions to chemically etch ZIFs. Then wash it 3 times with acetone, and then dry it in a vacuum drying oven at a temperature of 78 °C for 24 hours to obtain a polyhedral nanocage Co / Ni / Ru polymetallic hydroxide material, abbreviated as: Co9Ni 64 Ru8-OH.

[0146] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a polyhedral nanocage multi-metal hydroxide material, characterized in that: The preparation method comprises: Dissolving a zinc salt and a cobalt salt in methanol to obtain a first solution; wherein the molar ratio of zinc ions in the zinc salt to cobalt ions in the cobalt salt is [1-8]:[0-1]; dissolving 2-methylimidazole in methanol to obtain a second solution; adding the first solution to the second solution and mixing uniformly to obtain a third solution; The third solution is subjected to a first heat treatment, so that the zinc ions in the zinc salt and the cobalt ions in the cobalt salt are coordinated with 2-methylimidazole to obtain a zeolite imidazolate framework material ZIFs solution; wherein the zinc ions are coordinated with the 2-methylimidazole to form a dodecahedral structure, and the cobalt ions are coordinated with the 2-methylimidazole to form a tetrahedral framework structure; wherein the first heat treatment is carried out in a constant temperature oven at a temperature of 25° C. to 35° C. for 22 hours to 26 hours; The zeolite imidazolate framework structure material ZIFs solution is subjected to a first centrifugation, washing and drying process to obtain polyhedral ZIFs powder; the polyhedral ZIFs powder is a dodecahedron or a mixture of dodecahedron and octahedron; The polyhedral ZIFs powder is dispersed in methanol, and then a hydrated nickel salt and a hydrated ruthenium salt are added, and a second heat treatment is performed to hydrolyze the nickel ions in the hydrated nickel salt and the ruthenium ions in the hydrated ruthenium salt to produce hydrogen ions. Under the action of the hydrogen ions, the coordination bonds between the ligands and zinc ions, and between the ligands and cobalt ions in the ZIFs are broken, thereby chemically etching the ZIFs. At the same time, the cobalt ions, the nickel ions in the hydrated nickel salt, and the ruthenium ions in the hydrated ruthenium salt are hydrolyzed to form cobalt hydroxide, nickel hydroxide, and ruthenium hydroxide on the surface of the ZIFs. The material is then subjected to a second centrifugation, washing, and drying treatment to obtain a polyhedral nanocage polymetallic hydroxide material. The second heat treatment is performed in a blast drying oven at a temperature of 110° C. to 130° C. for 1 to 3 hours.

2. The preparation method according to claim 1, characterized in that, The zinc salt includes one or more of zinc nitrate hexahydrate, zinc chloride, and zinc acetate; the cobalt salt includes one or more of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, and cobalt sulfate heptahydrate.

3. The preparation method according to claim 1, characterized in that, The ratio of the mole number of the 2-methylimidazole to the sum of the mole numbers of the zinc ions in the zinc salt and the cobalt ions in the cobalt salt is 4:1-6:

1.

4. The preparation method according to claim 1, wherein, The speed of the first centrifugation is 7000 rpm-9000 rpm, and the washing detergent is one or more of ethanol, methanol or acetone; the drying is carried out in a vacuum drying oven at a temperature of 75° C.-85° C. for 22 hours-26 hours.

5. The preparation method according to claim 1, characterized in that, The hydrated nickel salt is one or more of nickel chloride hexahydrate, nickel nitrate hexahydrate, and nickel sulfate hexahydrate; the hydrated ruthenium salt is ruthenium chloride trihydrate; and the molar ratio of nickel ions in the hydrated nickel salt to ruthenium ions in the hydrated ruthenium salt is [1-8]:[0-1].

6. The preparation method according to claim 1, characterized in that, The molar ratio of the sum of the moles of nickel ions and ruthenium ions to the polyhedral ZIFs is 1:1-3:

1.

7. The preparation method according to claim 1, characterized in that: The rotation speed of the second centrifugation is 7000 - 9000 revolutions per minute, and the cleaning agent for washing is one or more of ethanol, methanol, or acetone; drying is carried out in a vacuum drying oven at a temperature of 75°C - 85°C for 22 - 26 hours.

8. A polyhedral nanocage multi-metal hydroxide material, characterized in that: The polyhedral nanocage multi-metal hydroxide material is prepared by the preparation method described in any one of the above claims 1 - 7.

9. A positive electrode sheet, characterized in that, The positive electrode plate includes the polyhedral nanocage multi-metal hydroxide material described in claim 8.

10. A lithium-oxygen battery, characterized in that, The lithium-oxygen battery includes the positive electrode plate described in claim 9.

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