A manganese oxide heterojunction with adjustable work function, preparation method thereof, electrode sheet and zinc ion battery

Abstract

The present invention belongs to the field of positive electrode materials for zinc ion batteries, and specifically relates to a manganese oxide heterojunction with adjustable work function, a preparation method thereof, an electrode sheet and a zinc ion battery. The present invention first prepares manganese acetate tetrahydrate, metal acetate, polyvinyl pyrrolidone and trimesic acid into a precursor, and then performs gradient heat treatment on the precursor under a nitrogen atmosphere to obtain a metal element-manganese oxide heterojunction. The metal element-manganese oxide heterojunction provided by the present invention inherits the uniform mixed structure of the two metals in the precursor at the atomic level, giving the heterojunction a rich heterogeneous interface, thereby significantly improving the efficiency of electron transfer. Since the type of metal element will affect the change of work function, and the work function has a negative correlation with adsorption energy, the present invention realizes the heterojunction to H by changing the type of metal element. + / Zn 2+ Regulation of adsorption energy. Electrochemical detection has shown that the heterojunction provided by the present invention can be successfully applied in the field of zinc ion batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of zinc ion electronic positive electrode materials, and specifically relates to a manganese oxide heterojunction with adjustable work function, a preparation method thereof, an electrode sheet and a zinc ion battery. Background Art

[0002] As the demand for energy increases, the development of low-cost and reliable electrochemical energy storage devices has attracted widespread attention. Aqueous secondary batteries have a broader prospect than lithium batteries due to their cheap and safe electrolytes and the promise of excellent rate performance. Among them, zinc metal can provide a high theoretical capacity (820 mAh g -1 ), low redox potential (0.76 V vs. SHE), and environmentally friendly advantages, which make aqueous zinc-ion batteries (AZIBs) close to practical applications. However, there are still huge challenges for high-performance AZIBs, especially for designing cathodes with high energy density and cycle stability. Therefore, the development of high-performance cathode materials is the key to promote the practical application of AZIBs.

[0003] In the research of positive electrode materials, great progress has been made in manganese-based materials, vanadium-based materials, Prussian blue analogs, organic compounds, etc. In particular, manganese-based materials (such as MnO x , MnS, MnSe and MnBO x ), has attracted great interest from researchers due to its advantages such as non-polluting, high natural abundance, and high discharge voltage (1.35 V). However, manganese dissolution, low conductivity, and irreversible phase transition limit the practical capacity and continuous output. In recent years, manganese-based oxides prepared by calcining metal-organic frameworks (MOFs) in inert gas have been shown to have excellent electrochemical performance due to their advantages such as adjustable pore size, inherited conductive carbon skeleton, and suppressed manganese dissolution. However, Zn 2+ The Coulomb repulsion with the matrix lattice is large, resulting in slow reaction kinetics, and the large radius Zn 2+ The insertion of H will cause lattice collapse, resulting in capacity decay. + The embedding of H can reduce the lattice distortion of the material and the ionic radius, making it a potential charge carrier that can improve the rate performance and cycle stability of the material. + An effective strategy for embedding contributions to obtain high energy density and stable AZIB materials is of great significance.

[0004] At present, people have been working on changing the cathode to H + The adsorption energy of H +Contribution of intercalation. A significant linear relationship can be established between adsorption energy and the work function of the material. The lower the work function of the material, the higher the adsorption energy. Specifically, the work function represents the minimum energy required for electrons to escape from the material. The smaller the work function, the higher the electron emission efficiency and the easier it is to adsorb cations. Therefore, by adjusting the work function to increase H + The adsorption energy of H is a feasible method. The formation of heterojunction affects the size of the work function. In a heterojunction, the two materials have different electron affinities and polarizabilities, resulting in a charge transfer layer at the interface. This charge transfer layer causes band bending and energy level movement, affecting the energy distribution and electron mobility, thereby changing the work function of the material. These results verify that building a heterostructure is an effective strategy to adjust the overall work function of the material. It can be seen that the use of manganese-based oxides and heterogeneous metal elements to build a heterojunction can adjust the work function of manganese-based oxides, thereby affecting H + Therefore, it is urgent to explore the relationship between work function and H + The relationship between the intercalation capacity contribution to precisely tune the electrochemical properties of Mn-based cathodes for high-performance aqueous Zn-ion batteries. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for preparing manganese oxide heterojunction energy storage materials based on work function regulation. The method prepares a heterojunction precursor by designing the order of reactant addition and the type of polyvinyl pyrrolidone (PVP), and then obtains a heterojunction after gradient heat treatment of the precursor. The heterojunction provided by the present invention inherits the uniform mixed structure of the two metals in the MOF precursor at the atomic level, giving it a rich heterogeneous interface, thereby significantly improving the efficiency of electron transfer. At the same time, the selection of different metal elements will affect the overall work function change of the heterojunction, thereby regulating H + / Zn 2+ The adsorption energy of H + The heterojunction obtained by the method described in the present invention can be used as the positive electrode material of zinc ion battery, and its performance is verified by electrochemical detection.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A first aspect of the present invention provides a method for preparing a manganese oxide heterojunction with adjustable work function, characterized in that it comprises the following steps:

[0008] Step 1, respectively weighing manganese acetate tetrahydrate and polyvinyl pyrrolidone, then adding them into a mixed solvent of ethanol and water in a volume ratio of 1:1, stirring at room temperature for 0.5-2 h to obtain solution a;

[0009] The weight average molecular weight of the polyvinyl pyrrolidone is 10-100 kDa;

[0010] Step 2: adding trimesic acid to a mixed solvent of ethanol and water in a volume ratio of 1:1, stirring at room temperature for 0.5 to 2 h to dissolve, to obtain a solution b;

[0011] Step 3, slowly pouring the solution b obtained in step 2 into the solution a obtained in step 1, stirring continuously at room temperature, to obtain a suspension c;

[0012] Step 4: weigh a metal acetate and add it to a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 to 2 h to obtain a solution d;

[0013] Step 5: Slowly pour the solution d obtained in step 4 into the suspension c obtained in step 3, continue stirring at room temperature for 2 to 6 hours, and let stand for 12 to 24 hours to obtain a precipitate;

[0014] Step 6: vacuum filter the precipitate obtained in step 5, then wash it with ethanol and water for 5 to 8 times, and then place the product in a vacuum drying oven and dry it for 10 hours to obtain a manganese oxide heterojunction precursor;

[0015] Step 7: Place the precursor obtained in step 6 under nitrogen for gradient heat treatment to obtain a manganese oxide heterojunction.

[0016] Furthermore, in step 1, the mass ratio of manganese acetate tetrahydrate to polyvinyl pyrrolidone is 5:(8-10).

[0017] Furthermore, in step three, the metal acetate is one of copper acetate, cobalt acetate tetrahydrate, nickel acetate tetrahydrate and zinc acetate.

[0018] Furthermore, the molar ratio of manganese acetate tetrahydrate, metal acetate and trimesic acid described in the preparation step is (1-4): (0.1-0.4): (4-8).

[0019] Furthermore, in step seven, the gradient heat treatment comprises the following steps: firstly heating to 200°C, keeping the temperature for 20 min, and heating at a rate of 2-5°C / min; then heating to 600-900°C, keeping the temperature for 2 h, and heating at a rate of 2-5°C / min.

[0020] The second aspect of the present invention provides a manganese oxide heterojunction with adjustable work function, which is prepared by any preparation method in the above technical solutions.

[0021] The third aspect of the present invention is an electrode sheet, which includes an electrode active material, conductive carbon, a binder, and a dispersing solvent. The electrode active material is the manganese oxide heterojunction provided by the second aspect of the present invention.

[0022] Furthermore, the conductive carbon in the electrode sheet is one of Ketjen black and acetylene black; the binder is one of polyvinylidene fluoride and polytetrafluoroethylene; and the dispersing solvent is one of N,N-dimethylformamide and ‌N-methylpyrrolidone.

[0023] A fourth aspect of the present invention is a zinc ion battery, comprising positive and negative electrode sheets, an electrolyte, and a battery separator, wherein the positive electrode sheet of the zinc ion battery is the above-mentioned electrode sheet.

[0024] Beneficial effects of the present invention:

[0025] 1. The heterojunction provided by the present invention inherits the uniform mixed structure of the two metals in the precursor, giving it a rich heterojunction interface and significantly improving the efficiency of electron transfer;

[0026] 2. The present invention changes the type of metal element in the heterojunction, thereby affecting the change of the heterojunction work function. Since the work function has a negative correlation with the adsorption energy, the H + / Zn 2+ Regulation of adsorption energy;

[0027] 3. The CO bond network formed during the carbonization of the precursor is H + The transfer of H + The capacity contribution makes the prepared zinc-ion battery have excellent rate performance and good cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art; obviously, the drawings described below are some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 The scanning electron microscope photographs of the precursor materials prepared in Examples 1 to 4 of the present invention;

[0030] Figure 2 Scanning electron microscope photographs of heterojunction materials prepared in Examples 1 to 4 of the present invention;

[0031] Figure 3The scanning electron microscope photographs of the heterojunction materials prepared in Comparative Examples 1 to 3 of the present invention;

[0032] Figure 4 X-ray diffraction spectrum curves of the heterojunction materials prepared in Examples 1 to 4 of the present invention;

[0033] Figure 5 The ultraviolet photoelectron spectrum curve of the heterojunction material prepared in Examples 1 to 4 of the present invention;

[0034] Figure 6 A simplified diagram of electron transfer and work function values ​​of heterojunction materials prepared in Examples 1 to 4 of the present invention;

[0035] Figure 7 The heterojunction material prepared in Examples 1 to 4 of the present invention is H + The adsorption energy value of

[0036] Figure 8 The heterojunction materials prepared in Examples 1 to 4 of the present invention are Zn 2+ The adsorption energy value of

[0037] Fig. 9 H of the heterojunction material prepared in Examples 1 to 4 of the present invention + Adsorption energy and work function relationship curve;

[0038] Fig.10 The cyclic voltammetry curve of the heterojunction material prepared in Example 1 of the present invention;

[0039] Fig.11 The stability performance curves of the heterojunction materials prepared in Examples 1 to 4 of the present invention;

[0040] Fig.12 The rate performance curves of the heterojunction materials prepared in Examples 1 to 4 of the present invention;

[0041] Fig.13 The discharge platform and dQ / dV curve of the heterojunction material prepared in Examples 1 to 4 of the present invention;

[0042] Fig.14 The Zn of the heterojunction material prepared in Examples 1 to 4 of the present invention 2+ / H + Contribution capacity ratio curve. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical effect and technical solution of the embodiment of the present invention clearer, the technical solution in the embodiment of the present invention is clearly and completely described below in conjunction with the drawings in the embodiment of the present invention; it is obvious that the described embodiment is a part of the embodiment of the present invention. Based on the embodiment disclosed in the present invention, other embodiments obtained by ordinary technicians in this field without making creative work should all fall within the scope of protection of the present invention.

[0044] Embodiment 1: The present invention provides a method for preparing a Cu-MnO manganese oxide heterojunction, comprising the following steps:

[0045] Step 1: Weigh 1 mmol of manganese acetate tetrahydrate and 0.392 g of 45-58 kDa polyvinyl pyrrolidone respectively, add them into 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution a;

[0046] Step 2: Add 4 mmol of trimesic acid to 100 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to dissolve, to obtain solution b;

[0047] Step 3: slowly pour the solution b obtained in step 2 into the solution a obtained in step 1, and continue stirring at room temperature for 10 min to obtain a suspension c;

[0048] Step 4: Weigh 0.1 mmol of copper acetate and add it to 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution d;

[0049] Step 5: Then slowly pour the solution d obtained in step 4 into the suspension c obtained in step 3, continue stirring at room temperature for 2 h, and let it stand for 12 h to obtain a precipitate;

[0050] Step 6: vacuum filter the precipitate obtained in step 5, then wash it with ethanol and water for 5 times, and then place the product in a vacuum drying oven at 70° C. and dry it for 10 h to obtain a manganese oxide heterojunction precursor;

[0051] Step 7: The precursor obtained in step 6 is placed in nitrogen for gradient heat treatment, first heated to 200 °C, kept at this temperature for 20 min, and heated at a rate of 2 °C / min, then heated to 700 °C, kept at this temperature for 2 h, and heated at a rate of 2 °C / min, to obtain a Cu-MnO manganese oxide heterojunction.

[0052] Embodiment 2: The present invention provides a method for preparing a Co-MnO manganese oxide heterojunction, comprising the following steps:

[0053] Step 1: Weigh 4 mmol of manganese acetate tetrahydrate and 1.53 g of 45-58 kDa polyvinyl pyrrolidone respectively, add them into 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution a;

[0054] Step 2: add 8 mmol of trimesic acid to 100 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to dissolve, to obtain solution b;

[0055] Step 3: slowly pour the solution b obtained in step 2 into the solution a obtained in step 1, and continue stirring at room temperature for 10 min to obtain a suspension c;

[0056] Step 4: Weigh 0.4 mmol of cobalt acetate tetrahydrate and add it to 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution d;

[0057] Step 5: Then slowly pour the solution d obtained in step 4 into the suspension c obtained in step 3, continue stirring at room temperature for 3 h, and let it stand for 20 h to obtain a precipitate;

[0058] Step 6: vacuum filter the precipitate obtained in step 5, then wash it with ethanol and water for 6 times, and then place the product in a vacuum drying oven at 70° C. and dry it for 10 h to obtain a manganese oxide heterojunction precursor;

[0059] Step 7: The precursor obtained in step 6 is placed in nitrogen for gradient heat treatment, first heated to 200 °C, kept for 20 min, and heated at a rate of 5 °C / min, then heated to 600 °C, kept for 2 h, and heated at a rate of 3 °C / min, to obtain a Co-MnO manganese oxide heterojunction.

[0060] Embodiment 3: The present invention provides a method for preparing a Ni-MnO manganese oxide heterojunction, comprising the following steps:

[0061] Step 1: Weigh 2 mmol of manganese acetate tetrahydrate and 0.882 g of 30-40 kDa polyvinyl pyrrolidone respectively, add them into 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution a;

[0062] Step 2: Add 6 mmol of trimesic acid to 100 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to dissolve, to obtain solution b;

[0063] Step 3: slowly pour the solution b obtained in step 2 into the solution a obtained in step 1, and continue stirring at room temperature for 10 min to obtain a suspension c;

[0064] Step 4: Weigh 0.2 mmol of nickel acetate tetrahydrate and add it to 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution d;

[0065] Step 5: Then slowly pour the solution d obtained in step 4 into the suspension c obtained in step 3, continue stirring at room temperature for 4 h, and let it stand for 20 h to obtain a precipitate;

[0066] Step 6: vacuum filter the precipitate obtained in step 5, then wash it with ethanol and water for 6 times, and then place the product in a vacuum drying oven at 70° C. and dry it for 10 h to obtain a manganese oxide heterojunction precursor;

[0067] Step 7: The precursor obtained in step 6 is placed in nitrogen for gradient heat treatment, first heated to 200 °C, kept at this temperature for 20 min, and heated at a rate of 5 °C / min, then heated to 800 °C, kept at this temperature for 2 h, and heated at a rate of 5 °C / min, to obtain a Ni-MnO manganese oxide heterojunction.

[0068] Embodiment 4: The present invention provides a method for preparing a Zn-MnO manganese oxide heterojunction, comprising the following steps:

[0069] Step 1: Weigh 3 mmol of manganese acetate tetrahydrate and 1.176 g of 10-16 kDa polyvinyl pyrrolidone respectively, add them into 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution a;

[0070] Step 2: Add 5 mmol of trimesic acid to 100 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to dissolve, to obtain solution b;

[0071] Step 3: slowly pour the solution b obtained in step 2 into the solution a obtained in step 1, and continue stirring at room temperature for 10 min to obtain a suspension c;

[0072] Step 4: Weigh 0.3 mmol of zinc acetate and add it to 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution d;

[0073] Step 5: Slowly pour the solution d obtained in step 4 into the suspension c obtained in step 3, continue stirring at room temperature for 4 h, and let stand for 24 h to obtain a precipitate;

[0074] Step 6: vacuum filter the precipitate obtained in step 5, then wash it with ethanol and water for 6 times, and then place the product in a vacuum drying oven at 70° C. and dry it for 10 h to obtain a manganese oxide heterojunction precursor;

[0075] Step 7: The precursor obtained in step 6 is placed in nitrogen for gradient heat treatment, first heated to 200 °C, kept for 20 min, and heated at a rate of 3 °C / min, then heated to 900 °C, kept for 2 h, and heated at a rate of 5 °C / min, to obtain a Zn-MnO manganese oxide heterojunction.

[0076] Embodiment 5: The present invention provides a method for preparing a battery using Cu-MnO as a positive electrode material, comprising the following steps:

[0077] A. Preparation of electrodes:

[0078] Cu-MnO, Ketjen black and polyvinylidene fluoride in a mass ratio of 7:2:1 were weighed, made into a slurry using N,N-dimethylformamide, and evenly applied on a stainless steel mesh. The stainless steel mesh was placed in a vacuum drying oven at 70 °C and dried for 12 h to obtain an electrode sheet with Cu-MnO as the active material.

[0079] B. Preparation of batteries:

[0080] Zinc foil was selected as the negative electrode, Cu-MnO electrode sheet as the positive electrode, 2 M ZnSO4 and 0.2 M MnSO4 as the electrolyte, and glass fiber as the battery separator to assemble a zinc ion battery.

[0081] Embodiment 6: The present invention provides a method for preparing a battery using Co-MnO as a positive electrode material, comprising the following steps:

[0082] A. Preparation of electrodes:

[0083] Co-MnO, acetylene black and polytetrafluoroethylene in a mass ratio of 7:2:1 were weighed, made into slurry using N-methylpyrrolidone, and evenly spread on a stainless steel mesh. The stainless steel mesh was placed in a vacuum drying oven at 70 °C and dried for 12 h to obtain an electrode sheet with Co-MnO as the active material.

[0084] B. Preparation of batteries:

[0085] Zinc foil was selected as the negative electrode, Co-MnO electrode sheet as the positive electrode, 2 M ZnSO4 and 0.2 M MnSO4 as the electrolyte, and glass fiber as the battery separator to assemble a zinc ion battery.

[0086] Embodiment 7: The present invention provides a method for preparing a battery using Ni-MnO as a positive electrode material, comprising the following steps:

[0087] A. Preparation of electrodes:

[0088] Weigh Ni-MnO, acetylene black and polytetrafluoroethylene in a mass ratio of 7:2:1, use N-methylpyrrolidone to make a slurry, evenly apply it on a stainless steel mesh, and place the stainless steel mesh in a vacuum drying oven at 70 °C and dry it for 12 h to obtain an electrode sheet with Ni-MnO as the active material.

[0089] B. Preparation of batteries:

[0090] Zinc foil was selected as the negative electrode, Ni-MnO electrode sheet as the positive electrode, 2 M ZnSO4 and 0.2 M MnSO4 as the electrolyte, and glass fiber as the battery separator to assemble a zinc ion battery.

[0091] Embodiment 8: The present invention provides a method for preparing a battery using Zn-MnO as a positive electrode material, comprising the following steps:

[0092] A. Preparation of electrodes:

[0093] Weigh Zn-MnO, Ketjen black and polyvinylidene fluoride in a mass ratio of 7:2:1, use N,N-dimethylformamide to make a slurry, evenly apply it on a stainless steel mesh, and place the stainless steel mesh in a vacuum drying oven at 70 °C and dry it for 12 h to obtain an electrode sheet with Zn-MnO as the active material.

[0094] B. Preparation of batteries:

[0095] Zinc foil was selected as the negative electrode, Zn-MnO electrode sheet as the positive electrode, 2 M ZnSO4 and 0.2 M MnSO4 as the electrolyte, and glass fiber as the battery separator to assemble a zinc ion battery.

[0096] Comparative Example 1: The present invention provides a method for preparing a Co-MnO manganese oxide heterojunction, comprising the following steps:

[0097] Step 1: Weigh 4 mmol of manganese acetate tetrahydrate and 1.96 g of 270-400 kDa polyvinyl pyrrolidone respectively, add them into 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution a;

[0098] Step 2: add 8 mmol of trimesic acid to 100 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to dissolve, to obtain solution b;

[0099] Step 3: slowly pour the solution b obtained in step 2 into the solution a obtained in step 1, and continue stirring at room temperature for 10 min to obtain a suspension c;

[0100] Step 4: Weigh 0.4 mmol of cobalt acetate tetrahydrate and add it to 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution d;

[0101] Step 5: Then slowly pour the solution d obtained in step 4 into the suspension c obtained in step 3, continue stirring at room temperature for 3 h, and let it stand for 20 h to obtain a precipitate;

[0102] Step 6: vacuum filter the precipitate obtained in step 5, then wash it with ethanol and water for 6 times, and then place the product in a vacuum drying oven at 70° C. and dry it for 10 h to obtain a manganese oxide heterojunction precursor;

[0103] Step 7: The precursor obtained in step 6 is placed in nitrogen for gradient heat treatment, first heated to 200 °C, kept for 20 min, and heated at a rate of 5 °C / min, then heated to 600 °C, kept for 2 h, and heated at a rate of 3 °C / min, to obtain a Co-MnO manganese oxide heterojunction.

[0104] Comparative Example 2: The present invention provides a method for preparing a Co-MnO manganese oxide heterojunction, comprising the following steps:

[0105] Step 1: Weigh 4 mmol of manganese acetate tetrahydrate and 1.53 g of 45-58 kDa polyvinyl pyrrolidone respectively, add them into 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution a;

[0106] Step 2: add 8 mmol of trimesic acid to 100 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to dissolve, to obtain solution b;

[0107] Step 3: slowly pour the solution b obtained in step 2 into the solution a obtained in step 1, and continue stirring at room temperature for 10 min to obtain a suspension c;

[0108] Step 4: Weigh 0.4 mmol of cobalt acetate tetrahydrate and add it to 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to obtain solution d;

[0109] Step 5: Then slowly pour the solution d obtained in step 4 into the suspension c obtained in step 3, continue stirring at room temperature for 3 h, and let it stand for 20 h to obtain a precipitate;

[0110] Step 6: vacuum filter the precipitate obtained in step 5, then wash it with ethanol and water for 6 times, and then place the product in a vacuum drying oven at 70° C. and dry it for 10 h to obtain a manganese oxide heterojunction precursor;

[0111] Step 7: heat-treat the precursor obtained in step 6 under nitrogen, raise the temperature to 600°C, keep the temperature for 2 h, and raise the temperature at a rate of 3°C / min, so as to obtain a Co-MnO manganese oxide heterojunction.

[0112] Comparative Example 3: The present invention provides a method for preparing a Co-MnO manganese oxide heterojunction, comprising the following steps:

[0113] Step 1: Weigh 4 mmol of manganese acetate tetrahydrate, 0.4 mmol of cobalt acetate tetrahydrate and 1.53 g of 45-58 kDa polyvinyl pyrrolidone respectively, add them into 50 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution a;

[0114] Step 2: add 8 mmol of trimesic acid to 100 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 h to dissolve, to obtain solution b;

[0115] Step 3: slowly pour the solution b obtained in step 2 into the solution a obtained in step 1, continue stirring for 1 h to mix evenly, and let stand for 20 h to obtain a precipitate;

[0116] Step 4: vacuum filter the precipitate obtained in step 3, then wash it with ethanol and water for 6 times, and then place the product in a vacuum drying oven at 70° C. and dry it for 10 h to obtain a manganese oxide heterojunction precursor;

[0117] Step 5: The precursor obtained in step 4 is placed in nitrogen for gradient heat treatment, first heated to 200 °C, kept at this temperature for 20 min, and heated at a rate of 5 °C / min, then heated to 600 °C, kept at this temperature for 2 h, and heated at a rate of 3 °C / min, to obtain a Co-MnO manganese oxide heterojunction.

[0118] Figure 1 The scanning electron microscope images of the precursors prepared in Examples 1 to 4 are shown. The precursors exhibit a bulk structure of accumulated particles, and the use of polyvinyl pyrrolidone with different weight average molecular weights results in differences in the morphology and size of the precursors. The rough surface of the block can be attributed to the etching effect of the acetate added in step 5.

[0119] Figure 2Scanning electron microscope images of manganese oxide heterojunctions prepared in Examples 1 to 4. The heterojunction formed after the precursor is calcined presents a microspherical morphology of particle assembly, which is attributed to the decomposition of the bulk structure of the precursor at high temperature to form microspheres of smaller size. Among them, Cu-MnO has the smallest size, with an average microsphere diameter of about 420 nm. The unique microsphere structure increases the contact area between the electrode material and the electrolyte, which is conducive to the full infiltration of the electrolyte, thereby providing better ion / electron diffusion kinetics. Co-MnO, Ni-MnO and Zn-MnO show microspheres with increased volume, which is attributed to the difference in staged heating conditions. As the temperature increases, the material shows agglomeration to a certain extent. Therefore, temperature control plays an important role in morphology and performance.

[0120] Figure 3 The scanning electron microscope images of Co-MnO prepared in Comparative Examples 1 to 3. In Comparative Example 1, due to the use of polyvinyl pyrrolidone with a weight average molecular weight of up to 270-400 kDa, the calcined particles are wrapped in a larger carbon matrix and no microsphere structure is formed. Therefore, the type of polyvinyl pyrrolidone has a greater influence on the morphology, and a microsphere structure with a larger active area cannot be formed if the range exceeds 10-100 kDa. In Comparative Example 2, the temperature was directly raised to 600°C during the calcination of the precursor, and the gradient temperature was not used, resulting in the failure to pre-remove the adsorbed water and other impurities in the material at a lower temperature, and the heterojunction formed showed an agglomerated irregular block morphology (compared with Example 2). In Comparative Example 3, due to the change in the order of addition of cobalt acetate, the heterojunction finally formed showed a rough block structure, which was attributed to the surface etching effect of the acetate added later. Therefore, the order of addition of acetate, the method of gradient heat treatment, and the type of polyvinyl pyrrolidone selected have a greater influence on the heterojunction morphology.

[0121] Figure 4 The X-ray diffraction patterns of the manganese oxide heterojunctions prepared in Examples 1 to 4 confirm the formation of the heterostructure; in step five, the added acetate, as a Lewis acid, etches the precursor formed by the manganese salt and trimesic acid, and competes with the manganese ions for coordination, forming a bimetallic precursor, which lays the foundation for the formation of a heterojunction after calcination; in addition, since Zn is partially sublimated at high temperature, the peak intensity of Zn is weak.

[0122] Figure 5 and Figure 6 The ultraviolet photoelectron energy spectrum of the manganese oxide heterojunction prepared in Examples 1 to 4 was used to determine the work function value of the material. It was observed that the difference in the type of metal element resulted in the change of the work function of MnO, among which Cu-MnO had the smallest work function value of 4.27 eV.

[0123] Figure 7 and Figure 8 H of the manganese oxide heterojunction prepared in Examples 1 to 4 + and Zn 2+ Adsorption energy, where H + Adsorption energy is higher than Zn 2+ , the manganese oxide heterojunction exhibits resistance to H + Stronger selectivity; in addition, Cu-MnO has the highest H + adsorption energy (-2.77 eV), making it easier to adsorb H + , thus showing better battery performance.

[0124] Fig. 9 The relationship curves between the adsorption energy value and the work function of the manganese oxide heterojunction prepared in Examples 1 to 4 show a negative correlation, which proves that the design of the controllable work function of the manganese oxide heterojunction has a great influence on the H + The adsorption energy and selectivity regulation effect.

[0125] Fig.10 The cyclic voltammetry test of Cu-MnO was performed using a CHI660E electrochemical workstation. During the test, the scan rate was set to 0.2-2.0 mV / s and the voltage window was set to 0.8-1.9 V. The test curve showed two pairs of reversible redox peaks. The high potential region corresponds to H + The low potential region corresponds to the Zn 2+ The embedding / de-embedding reaction of H + The peak current of the reduction peak of the intercalation reaction exceeds that of Zn 2+ , confirming that H + The proportion of intercalation reactions exceeds that of Zn 2+ .

[0126] Fig.11 and Fig.12 The constant current charge and discharge test of the manganese oxide heterojunction prepared in Examples 1 to 4 was carried out under the Neware device, and the voltage window was set to 0.8-1.9 V; the long cycle stability test was carried out at 5.0 A g -1 The rate performance tests were carried out at current densities of 0.2-5.0 A g -1 It was observed that Cu-MnO has excellent rate performance, even back to 0.2 A g -1 At a current density of 5.0A g, the capacity is higher than the initial capacity; and the long cycle stability test shows that at 5.0A g -1 At a current density of 1.34, the battery still has a capacity retention rate of 98.24% after 12,000 cycles, proving that the H +Cu-MnO with high adsorption energy and selectivity exhibits excellent electrochemical performance and can maintain a stable material structure during rapid charging and discharging.

[0127] Fig.13 and Fig.14 Discharge platform curve, dQ / dV curve and H curve of manganese oxide heterojunction prepared in Examples 1 to 4 + / Zn 2+ Capacity contribution ratio curve. Use the dQ / dV curve peak position to segment the discharge platform curve and determine H + / Zn 2+ The capacity contribution ratio is consistent with the characterization and calculation results. + The adsorption energy and selectivity of Cu-MnO showed a high H absorption rate of 73.62% in the performance test. + The capacity contribution successfully confirmed the H + Contribution effectiveness and H + Its excellent properties as a charge carrier provide new insights for the subsequent development of high-performance AZIB cathode materials.

[0128] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art can still modify or make equivalent substitutions to the specific implementations of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A method for preparing a manganese oxide heterojunction with adjustable work function, characterized in that: The following steps are involved: Step 1, respectively weighing manganese acetate tetrahydrate and polyvinyl pyrrolidone, and then adding them to a mixed solvent of ethanol and water in a volume ratio of 1:1, and stirring at room temperature for 0.5 to 2 hours to obtain a solution a; the weight average molecular weight of the polyvinyl pyrrolidone is 10 to 100 kDa; Step 2: adding trimesic acid to a mixed solvent of ethanol and water in a volume ratio of 1:1, stirring at room temperature for 0.5 to 2 h to dissolve, to obtain solution b; Step 3, slowly pouring the solution b obtained in step 2 into the solution a obtained in step 1, stirring continuously at room temperature, to obtain a suspension c; Step 4: weigh a metal acetate and add it to a mixed solvent of ethanol and water in a volume ratio of 1:1, and stir at room temperature for 0.5 to 2 h to obtain a solution d; Step 5: Slowly pour the solution d obtained in step 4 into the suspension c obtained in step 3, continue stirring at room temperature for 2 to 6 hours, and let stand for 12 to 24 hours to obtain a precipitate; Step 6: vacuum filter the precipitate obtained in step 5, then wash it with ethanol and water for 5 to 8 times, and then place the product in a vacuum drying oven and dry it for 10 hours to obtain a manganese oxide heterojunction precursor; Step 7, placing the precursor obtained in step 6 under nitrogen for gradient heat treatment to obtain a manganese oxide heterojunction; The gradient heat treatment comprises the following steps: firstly heating to 200°C, keeping the temperature for 20 min, and heating at a rate of 2-5°C / min; then heating to 600-900°C, keeping the temperature for 2 h, and heating at a rate of 2-5°C / min.

2. The method for preparing a manganese oxide heterojunction with adjustable work function according to claim 1, characterized in that: In step 1, the mass ratio of manganese acetate tetrahydrate to polyvinyl pyrrolidone is 5:(8-10).

3. The method for preparing a manganese oxide heterojunction with adjustable work function according to claim 1, characterized in that: In step 3, the metal acetate is one of copper acetate, cobalt acetate tetrahydrate, nickel acetate tetrahydrate and zinc acetate.

4. The method for preparing a manganese oxide heterojunction with adjustable work function according to claim 1, characterized in that: The molar ratio of manganese acetate tetrahydrate, metal acetate and trimesic acid described in the preparation step is (1 to 4): (0.1 to 0.4): (4 to 8).

5. A manganese oxide heterojunction with adjustable work function, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 4.

6. An electrode sheet, comprising an electrode active material, conductive carbon, a binder, and a dispersing solvent, characterized in that: The electrode active material is the manganese oxide heterojunction according to claim 5.

7. An electrode sheet according to claim 6, characterized in that: The conductive carbon is one of Ketjen black and acetylene black; the binder is one of polyvinylidene fluoride and polytetrafluoroethylene; the dispersing solvent is one of N,N-dimethylformamide and N-methylpyrrolidone.

8. A zinc ion battery, comprising positive and negative electrode sheets, an electrolyte, and a battery separator, characterized in that: The positive electrode sheet of the zinc ion battery is the electrode sheet according to claim 7.

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