High-entropy doped manganous oxide / metal solid solution heterojunction, preparation method thereof, electrode plate and zinc ion battery

Abstract

The invention belongs to the technical field of zinc ion battery positive electrode materials, and particularly relates to a high-entropy doped manganous oxide / metal solid solution heterojunction, a preparation method thereof, an electrode plate and a zinc ion battery. Manganese acetate tetrahydrate, various metal salts and trimesic acid are used as raw materials to prepare a precursor, the high-entropy manganous oxide / metal solid solution heterojunction is synthesized through high-temperature calcination heat treatment, the chemical formula is shown as Mnx (M1aM2b) y (M3cM4dM5e) zO / IMC, Mn represents a manganese element, and M1-M5 represent doped metal elements different from manganese. According to the invention, by changing the types of doped metal elements, the crystal / electronic structure of the material is optimized, and the regulation and control of product ion / electron transport kinetics are realized, so that the prepared zinc ion battery shows excellent rate capability and cycling stability, and has wide application prospects and important economic values in the field of zinc ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for zinc-ion batteries, and particularly relates to a high-entropy doped manganese oxide / metal solid solution heterojunction, a preparation method thereof, an electrode sheet, and a zinc-ion battery. Background Art

[0002] Zinc-ion batteries (ZIBs) have the advantages of high safety, rich zinc resources, environmental friendliness, wide applications, etc., and are a promising energy storage technology in the post-lithium-ion era. However, the 2+ relatively large ionic radius and high charge density of Zn will generate strong electrostatic repulsion with the host material, resulting in structural collapse and slow kinetics, thus hindering the insertion process and reducing the cycle stability. Therefore, it is urgent to develop cathode materials with high energy density and structural stability. As a representative cathode material, manganese-based oxides have multiple oxidation states with high energy density. Their different crystal structures also provide flexible options for optimizing electrochemical performance. So far, various manganese-based oxides (MnO2, Mn2O3, Mn3O4, and MnO) have been explored for ZIBs. Among them, MnO has the highest theoretical capacity and has the potential to achieve ultra-high energy density. However, the 2+ transport of Zn is hindered by the compact [MnO6] octahedral arrangement in its rock salt (NaCl-type) structure, while the electron transport is inhibited by its wide bandgap and strong electron correlation of the Mn 3d orbitals, which hinders its development.

[0003] The development of multi-scale ion / electron transport channels has received extensive attention. Under the existing research background, new material modification strategies have emerged, mainly including two technical paths: heterostructure construction and ion doping regulation. Specifically, heterostructures accelerate electron migration through external interface modulation, while ion doping optimizes ion migration through internal lattice distortion. However, there are few reports on their synergy. A heterojunction is an interface structure formed between different materials, and its unique electronic properties originate from the interface effect. Metal single-metal oxide heterostructures utilize the difference in electronic structure to achieve unique functions, and their interface effect optimizes charge transfer through a three-layer mechanism: (1) the difference in energy band structure leads to electron-hole separation, improving the charge storage and transport efficiency; (2) electron polarization and charge density gradient induce electron redistribution, activating electrochemically reactive sites; (3) the built-in electric field regulates the ion migration energy barrier, improving carrier kinetics. Although heterojunction engineering has significantly improved the performance of functional materials, its development is hindered by two main bottlenecks: it is difficult to achieve precise nanoscale control of the heterojunction interface, which often leads to local charge accumulation; the mismatch in electron / ion transport capabilities between components (for example, the poor synergy between highly conductive phases and highly ion-diffusive phases) exacerbates concentration polarization. Therefore, the transformation to a synergistic, multi-dimensional modulation strategy is crucial.

[0004] In recent years, an innovative concept of high entropy (i.e., the number of element types ≥ 5) has emerged in the field of doping. Due to lattice distortion and diffusion delay effects, it exhibits high electrochemical activity. By introducing elements with different ionic radii and chemical properties, lattice distortion occurs in the host material, generating defects and unsaturated coordination, thus promoting the transport of charge carriers. This lattice distortion also induces lattice reconstruction, resulting in more continuous ion migration pathways and reduced energy barriers. In addition, the higher activation energy required for multi-element diffusion leads to a diffusion delay effect, which delays atomic migration, effectively inhibits phase transformation, and stabilizes the ion channels during charge and discharge cycles. However, it is necessary to be vigilant against local optimization traps, where single-parameter improvement is difficult to achieve the overall optimal state and may even cause adverse effects. For example, doping with Zn 2+ improves the initial activity of manganese oxide but sacrifices its cycle stability. Therefore, combining heterostructure engineering with high-entropy doping strategies can achieve the synergistic modulation of electronic and crystal structures, which is crucial for optimizing electron / ion transport kinetics. At the same time, elucidating the multi-component cooperation mechanism provides an innovative approach to solving the inherent limitations of manganese-based materials. Summary of the Invention

[0005] Aiming at the problem of limited ion / electron transport in manganese oxide-based zinc-ion batteries, the present invention uses manganese acetate tetrahydrate, various metal salts, and trimesic acid as raw materials to prepare a precursor, and synthesizes a high-entropy doped manganese oxide / metal solid solution heterojunction through high-temperature calcination heat treatment, and successfully applies it as a cathode material for zinc-ion batteries. The results show that lattice distortion is induced by the high-entropy doping strategy, promoting ion transport; the electronic structure is affected by the heterojunction strategy, promoting electron transport. The synergistic effect of the two effectively solves the irreversible phase transformation and structural collapse of MnO during zinc storage, and exhibits excellent cycle stability and rate performance as a cathode material for zinc-ion batteries.

[0006] The object of the present invention is achieved through the following technical solutions: The first aspect of the present invention provides a high-entropy doped manganese oxide / metal solid solution heterojunction, the chemical formula of which is represented as Mn x (M 1a M 2b )y(M 3c M 4d M 5e ) z O / IMC, where Mn represents the manganese element, M1, M2, M3, M4, M5 represent doping metal elements different from manganese, and the doping metal elements are selected from at most five metal elements in the second to fifth periods of the periodic table of elements, 0 ≤ a ≤ 0.025, 0 ≤ b ≤ 0.025, 0 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.1, 0 ≤ e ≤ 0.1.

[0007] Further, M1 and M2 represent substitutional doped metal elements different from manganese, where a + b = y; M3, M4, and M5 represent interstitial doped metal elements different from manganese, where c + d + e = z; 0.8 ≤ x ≤ 1, 0 ≤ y ≤ 0.05, 0 ≤ z ≤ 0.15, and x + y + z = 1.

[0008] Further, in the chemical formula, IMC represents a metal solid solution, which is composed of at least two metal elements among M1, M2, M3, M4, and M5.

[0009] Further, the doped metal elements are selected from at most five elements among magnesium, calcium, cobalt, nickel, copper, zinc, barium, and bismuth elements.

[0010] Further, in the high-entropy doped manganese oxide phase M1, M2, M3, M4, and M5 in the heterojunction are magnesium, zinc, cobalt, nickel, and copper elements respectively, corresponding to the diffraction peaks (111), (200), (220), (311), and (222); the metal solid solution phase is Cu 0.603 Co 0.327 Ni 0.07 , corresponding to the diffraction peaks (111), (200), and (220).

[0011] The second aspect of the present invention provides a method for preparing a high-entropy doped manganese oxide / metal solid solution heterojunction, which is characterized by comprising the following steps: Step 1: Weigh manganese acetate tetrahydrate and polyvinylpyrrolidone respectively and add them to a solvent, stir at room temperature for 0.5 - 2 h to obtain solution a; weigh trimesic acid and add it to the solvent, stir at room temperature for 0.5 - 2 h to obtain solution b; weigh other metal salts and add them to the solvent, stir at room temperature for 0.5 - 2 h to obtain solution c; the solvent is a mixed solution of ethanol and water with a volume ratio of 1:1; Step 2: Slowly pour solution b into solution a and continuously stir at room temperature for 1 - 2 h to obtain suspension d; Step 3: Slowly add solution c to suspension d, continuously stir at room temperature for 2 - 5 h, and let it stand for 12 - 24 h to obtain a precipitate; Step 4: Vacuum filter the obtained precipitate, wash it with ethanol and water 3 - 6 times, and then place the product in a vacuum drying oven at 80 °C and dry it for 10 - 15 h to obtain the heterojunction precursor; Step 5: Heat-treat the precursor obtained in Step 4 under nitrogen to obtain the high-entropy doped manganese oxide / metal solid solution heterojunction.

[0012] Further, the weight-average molecular weight of polyvinylpyrrolidone is 10 - 50 kDa, and the molar ratio of manganese acetate tetrahydrate, metal salts, and trimesic acid is (2 - 3):(0 - 1.5):5.

[0013] Further, in Step 1, the metal salts are copper acetate, cobalt acetate tetrahydrate, nickel acetate tetrahydrate, magnesium acetate, and zinc acetate, and the molar ratio of manganese acetate tetrahydrate, copper acetate, cobalt acetate tetrahydrate, nickel acetate tetrahydrate, magnesium acetate, and zinc acetate is 2.499:(0 - 0.24):(0 - 0.104):(0 - 0.104):(0 - 0.208):(0 - 0.208).

[0014] Further, during the heat treatment in Step 5, the calcination temperature is 600 - 800 °C, the heat preservation time is 2 - 4 h, and the heating rate is 2 - 5 °C / min.

[0015] The third aspect of the present invention provides an electrode sheet, which includes an electrode active material, conductive carbon, a binder, and a dispersion solvent, wherein the electrode active material is the high-entropy doped manganese oxide / metal solid solution heterojunction provided by the first aspect of the present invention.

[0016] The fourth aspect of the present invention provides a zinc-ion battery, which includes 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.

[0017] Advantages of the present invention: Aiming at the problems of limited ion / electron transport in manganese oxide (MnO)-based zinc-ion batteries, the present invention proposes an innovative solution: First, by means of the high-entropy doping strategy, the lattice distortion effect is induced, significantly improving the ion transport ability of the material; Second, the heterojunction structure is used to regulate the electronic energy band structure, effectively enhancing the electron conduction performance. The synergistic effect of the two not only solves the key problems such as irreversible phase change and structure collapse existing in the traditional MnO material during zinc-ion storage, but also enables the positive electrode material to exhibit excellent cycle stability and excellent rate performance. In addition, through the precise ratio design of multiple metal elements, the present invention realizes the synergistic optimization of the crystal structure and electronic structure of the material, providing a new design idea for the development of high-performance positive electrode materials for zinc-ion batteries. This material has the characteristics of simple preparation process and excellent electrochemical performance, showing broad application prospects and significant economic benefits in the field of zinc-ion batteries. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for the description of the embodiments or the prior art; Obviously, the following drawings are some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0019] Figure 1Scanning electron microscope photographs of high-entropy doped manganese oxide / metal solid solution heterojunctions prepared for different embodiments, where: a is for Example 1, b is for Example 2, and c is for Example 3; Figure 2 Scanning electron microscope photograph of the material prepared in Comparative Example 6 of the present invention; Figure 3 XRD Rietveld refinement spectra of the materials prepared in different embodiments and comparative examples of the present invention, where: a is for Example 1, b is for Example 2, c is for Example 3, and d is for Comparative Example 4; Figure 4 Full width at half maximum of the (200) crystal plane of the materials prepared in Examples 1 to 3 and Comparative Example 4 of the present invention; Figure 5 High-resolution XPS spectrum of the high-entropy doped manganese oxide / solid solution heterojunction prepared in Example 1, where: a is the Co 2p orbital, b is the Ni 2p orbital, and c is the Cu 2p orbital; Figure 6 XRD spectra of the materials prepared in different comparative examples, where: a is for Comparative Example 2, b is for Comparative Example 3, c is for Comparative Example 4, and d is for Comparative Example 5; Figure 7 EDS spectrum of the high-entropy doped manganese oxide / metal solid solution heterojunction material prepared in Example 1 of the present invention; Figure 8 Density of states curves of the materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 of the present invention; Figure 9 Bader charge analysis of the high-entropy doped manganese oxide / metal solid solution heterojunction material prepared in Example 1 of the present invention; Figure 10 Adsorption energy values of the materials prepared in Examples 1 to 3 and Comparative Example 1 of the present invention for Zn 2+ ; Figure 11 Zn of the materials prepared in Comparative Example 1 and Example 1 2+ Migration path and energy barrier values, where: a is for Comparative Example 1, b is for Example 1, and c is the energy barrier value; Figure 12 Rate performance curves of the materials prepared in Examples 1 to 3 of the present invention; Figure 13 Stability performance curves of the materials prepared in Examples 1 to 3 of the present invention; Figure 14 Performance curve of the high-loading electrode of the high-entropy doped manganese oxide / metal solid solution heterojunction prepared in Example 1 of the present invention; Figure 15Stability performance curve of the high-loading electrode of the high-entropy doped manganese oxide / metal solid solution heterojunction prepared in Example 1 of the present invention. Detailed implementation mode

[0020] To make the objectives, technical effects and technical solutions of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention; obviously, the described embodiments are part of the embodiments of the present invention. Based on the disclosed embodiments of the present invention, other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] Example 1: This example provides a preparation method of a HE-MnO / IMC high-entropy doped manganese oxide / metal solid solution heterojunction, which includes the following steps: Step 1: Weigh 2.499 mmol of manganese acetate tetrahydrate and 0.15 g of 40 kDa polyvinylpyrrolidone and add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution b; weigh 0.24 mmol of copper acetate, 0.104 mmol of cobalt acetate tetrahydrate, 0.104 mmol of nickel acetate tetrahydrate, 0.208 mmol of zinc acetate, and 0.208 mmol of magnesium acetate and add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution c; Step 2: Slowly pour solution b into solution a and continuously stir at room temperature for 2 h to obtain suspension d; Step 3: Slowly add solution c to suspension d, continuously stir at room temperature for 5 h, and let it stand for 24 h to obtain a precipitate; Step 4: Vacuum filter the obtained precipitate, wash it 6 times with ethanol and water, and then place the product in a vacuum drying oven at 80 °C for 15 h to obtain a heterojunction precursor; Step 5: Heat-treat the precursor obtained in Step 4 under nitrogen, raise the temperature to 700 °C, keep the temperature for 4 h, and the heating rate is 2 °C / min to obtain the HE-MnO / IMC high-entropy doped manganese oxide / metal solid solution heterojunction.

[0022] Example 2: This example provides a preparation method of a ME-MnO / Cu medium-entropy doped manganese oxide / metal solid solution heterojunction, which includes the following steps: Step 1: Weigh 2.499 mmol of manganese acetate tetrahydrate and 0.15 g of 40 kDa polyvinylpyrrolidone respectively, add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution b; weigh 0.24 mmol of copper acetate, 0.208 mmol of zinc acetate, and 0.208 mmol of magnesium acetate respectively, add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution c; Step 2: Slowly pour solution b into solution a, and continuously stir at room temperature for 1 h to obtain suspension d; Step 3: Slowly add solution c to suspension d, continuously stir at room temperature for 4 h, and let it stand for 18 h to obtain a precipitate; Step 4: Vacuum filter the precipitate obtained in Step 3, then wash it 5 times with ethanol and water, and then place the product in a vacuum drying oven at 80 °C and dry for 12 h to obtain the heterojunction precursor; Step 5: Heat-treat the precursor obtained in Step 4 under nitrogen, raise the temperature to 700 °C, keep the temperature for 3 h, and the heating rate is 3 °C / min to obtain the ME-MnO / Cu medium-entropy doped manganese oxide / metal solid solution heterojunction.

[0023] Example 3: This example provides a preparation method of LE-MnO low-entropy manganese oxide, which includes the following steps: Step 1: Weigh 2.499 mmol of manganese acetate tetrahydrate and 0.15 g of 40 kDa polyvinylpyrrolidone respectively, add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution b; weigh 0.208 mmol of zinc acetate and 0.208 mmol of magnesium acetate respectively, add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, and stir at room temperature for 1 h to obtain solution c; Step 2: Slowly pour solution b into solution a, and continuously stir at room temperature for 1 h to obtain suspension d; Step 3: Slowly add solution c to suspension d, continuously stir at room temperature for 4 h, and let it stand for 16 h to obtain a precipitate; Step 4: Vacuum filter the precipitate obtained in Step 3, then wash it 4 times with ethanol and water, and then place the product in a vacuum drying oven at 80 °C and dry for 12 h to obtain a low-entropy doped manganese oxide precursor; Step 5: Heat-treat the precursor obtained in Step 4 under nitrogen, raise the temperature to 700 °C, keep the temperature for 2 h, and the heating rate is 3 °C / min to obtain low-entropy doped manganese oxide of LE-MnO.

[0024] Example 4: This example provides a method for preparing a battery with HE-MnO / IMC as the cathode material, which includes the following steps: A. Preparation of the electrode: Weigh HE-MnO / IMC, Ketjen black, and polyvinylidene fluoride in a mass ratio of 7:2:1, make a slurry using N,N-dimethylformamide, evenly coat it on a stainless steel mesh, and place the stainless steel mesh in a vacuum drying oven at 80 °C and dry for 12 h to obtain an electrode plate with HE-MnO / IMC as the active material.

[0025] B. Preparation of the battery: Select zinc foil as the negative electrode, the HE-MnO / IMC electrode plate 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.

[0026] Example 5: This example provides a method for preparing a battery with ME-MnO / Cu as the cathode material, which includes the following steps: A. Preparation of the electrode: Weigh ME-MnO / Cu, acetylene black, and polytetrafluoroethylene in a mass ratio of 7:2:1, make a slurry using N-methylpyrrolidone, evenly coat it on a stainless steel mesh, and place the stainless steel mesh in a vacuum drying oven at 80 °C and dry for 12 h to obtain an electrode plate with ME-MnO / Cu as the active material.

[0027] B. Preparation of the battery: Select zinc foil as the negative electrode, the ME-MnO / Cu electrode plate 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.

[0028] Example 6: This example provides a method for preparing a battery with LE-MnO as the cathode material, which includes the following steps: A. Preparation of the electrode: Weigh LE-MnO, acetylene black, and polytetrafluoroethylene with a mass ratio of 7:2:1, make a slurry using N-methylpyrrolidone, evenly coat it on a stainless steel mesh, and place the stainless steel mesh in a vacuum drying oven at 80 °C for 12 h to obtain an electrode plate with LE-MnO as the active material.

[0029] B. Preparation of the battery: Select zinc foil as the negative electrode, the LE-MnO electrode plate 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.

[0030] Comparative Example 1: This comparative example provides a preparation method of manganese oxide manganous oxide, which includes the following steps: Step 1: Weigh 2.499 mmol of manganese acetate tetrahydrate and 0.15 g of 40 kDa polyvinylpyrrolidone and add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution b; Step 2: Slowly pour solution b into solution a, continuously stir at room temperature for 2 h to obtain suspension c, and let it stand for 24 h to obtain a precipitate; Step 3: Vacuum filter the precipitate obtained in Step 2, then wash it 6 times with ethanol and water, and then place the product in a vacuum drying oven at 80 °C and dry it for 15 h to obtain a manganous oxide precursor; Step 4: Heat-treat the precursor obtained in Step 3 under nitrogen, raise the temperature to 700 °C, keep the temperature for 4 h, and the heating rate is 2 °C / min to obtain manganous oxide.

[0031] Comparative Example 2: This comparative example provides a preparation method of HE-MnO high-entropy doped manganous oxide, which includes the following steps: Step 1: Weigh 2.499 mmol of manganese acetate tetrahydrate and 0.15 g of 40 kDa polyvinylpyrrolidone respectively and add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1. Stir at room temperature for 2 h to obtain solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1. Stir at room temperature for 2 h to obtain solution b; weigh 0.0315 mmol of copper acetate, 0.0315 mmol of cobalt acetate tetrahydrate, 0.0315 mmol of nickel acetate tetrahydrate, 0.208 mmol of zinc acetate, and 0.208 mmol of magnesium acetate respectively and add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1. Stir at room temperature for 2 h to obtain solution c; Step 2: Slowly pour solution b into solution a and continuously stir at room temperature for 2 h to obtain suspension d; Step 3: Slowly add solution c to suspension d and continuously stir at room temperature for 5 h. Let it stand for 24 h to obtain a precipitate; Step 4: Vacuum filter the obtained precipitate and wash it 6 times with ethanol and water. Then place the product in a vacuum drying oven at 80 °C and dry it for 15 h to obtain a high-entropy doped manganese oxide precursor; Step 5: Heat-treat the precursor obtained in Step 4 under nitrogen. Raise the temperature to 700 °C, keep the temperature for 4 h, and the heating rate is 2 °C / min to obtain HE-MnO / IMC high-entropy doped manganese oxide.

[0032] Comparative Example 3: Step 1: Weigh 0.24 mmol of copper acetate, 0.104 mmol of cobalt acetate tetrahydrate, 0.104 mmol of nickel acetate tetrahydrate, 0.208 mmol of zinc acetate, 0.208 mmol of magnesium acetate, and 0.15 g of 40 kDa polyvinylpyrrolidone and add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1. Stir at room temperature for 2 h to obtain solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1. Stir at room temperature for 2 h to obtain solution b; Step 2: Slowly pour solution b into solution a and continuously stir at room temperature for 5 h to obtain suspension c. Let it stand for 24 h to obtain a precipitate; Step 3: Vacuum filter the precipitate obtained in Step 2, then wash it 6 times with ethanol and water. Then place the product in a vacuum drying oven at 80 °C and dry it for 15 h to obtain an IMC solid solution precursor; Step 4: Heat-treat the precursor obtained in Step 3 under nitrogen, raise the temperature to 700 °C, keep the temperature for 4 h, and the heating rate is 2 °C / min to obtain the product.

[0033] Comparative Example 4: This comparative example provides a method for preparing a heterojunction, which includes the following steps: Step 1: Weigh 2.499 mmol of manganese acetate tetrahydrate and 0.15 g of 40 kDa polyvinylpyrrolidone respectively, add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution b; weigh 0.24 mmol of copper acetate, 0.104 mmol of cobalt acetate tetrahydrate, 0.104 mmol of nickel acetate tetrahydrate, 0.208 mmol of zinc acetate, and 0.208 mmol of magnesium acetate respectively, add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution c; Step 2: Slowly pour solution b into solution a, and continuously stir at room temperature for 2 h to obtain suspension d; Step 3: Slowly add solution c to suspension d, continuously stir at room temperature for 5 h, and let it stand for 24 h to obtain a precipitate; Step 4: Vacuum filter the obtained precipitate, wash it 6 times with ethanol and water, and then place the product in a vacuum drying oven at 80 °C for drying for 15 h to obtain the heterojunction precursor; Step 5: Heat-treat the precursor obtained in Step 4 under nitrogen, raise the temperature to 1000 °C, keep the temperature for 4 h, and the heating rate is 2 °C / min to obtain the heterojunction.

[0034] Comparative Example 5: The present invention provides a method for preparing a heterojunction, which includes the following steps: Step 1: Weigh 2.499 mmol of manganese acetate tetrahydrate, 0.24 mmol of copper acetate, 0.104 mmol of cobalt acetate tetrahydrate, 0.104 mmol of nickel acetate tetrahydrate, 0.208 mmol of zinc acetate, 0.208 mmol of magnesium acetate, and 0.15 g of 40 kDa polyvinylpyrrolidone respectively, add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain solution b; Step 2: Slowly pour Solution b into Solution a, continuously stir at room temperature for 5 h to obtain suspension c, and let it stand for 24 h to obtain a precipitate; Step 3: Vacuum filter the obtained precipitate, wash it 6 times with ethanol and water, and then place the product in a vacuum drying oven at 80 °C for drying for 15 h to obtain the heterojunction precursor; Step 4: Heat-treat the precursor obtained in Step 3 under nitrogen, raise the temperature to 700 °C, keep the temperature for 4 h, and the heating rate is 2 °C / min to obtain the product heterojunction.

[0035] Comparative Example 6: This comparative example provides a method for preparing a heterojunction, which includes the following steps: Step 1: Weigh 2.499 mmol of manganese acetate tetrahydrate and 0.15 g of 270 kDa polyvinylpyrrolidone and add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain Solution a; weigh 5.353 mmol of trimesic acid and add it to 100 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain Solution b; weigh 0.24 mmol of copper acetate, 0.104 mmol of cobalt acetate tetrahydrate, 0.104 mmol of nickel acetate tetrahydrate, 0.208 mmol of zinc acetate, and 0.208 mmol of magnesium acetate and add them to 50 mL of a mixed solvent of ethanol and water with a volume ratio of 1:1, stir at room temperature for 2 h to obtain Solution c; Step 2: Slowly pour Solution b into Solution a, continuously stir at room temperature for 2 h to obtain suspension d; Step 3: Slowly add Solution c to suspension d, continuously stir at room temperature for 5 h, and let it stand for 24 h to obtain a precipitate; Step 4: Vacuum filter the obtained precipitate, wash it 6 times with ethanol and water, and then place the product in a vacuum drying oven at 80 °C for drying for 15 h to obtain the heterojunction precursor; Step 5: Heat-treat the precursor obtained in Step 4 under nitrogen, raise the temperature to 700 °C, keep the temperature for 4 h, and the heating rate is 2 °C / min to obtain the heterojunction.

[0036] Figure 1 Scanning electron microscope photos of the high-entropy doped manganese oxide / metal solid solution heterojunctions prepared for different examples, where: a is Example 1, b is Example 2, and c is Example 3. It shows a pomegranate-like particle morphology. This unique structure increases the contact area between the electrode material and the electrolyte, is conducive to the full infiltration of the electrolyte, and further enhances the ion / electron transport kinetics.

[0037] Figure 2Scanning electron microscope image of the material prepared in Comparative Example 6. Compared with the well-dispersed pomegranate-shaped particle morphology in Example 1, this material shows severe agglomeration. This indicates that when using high molecular weight polyvinylpyrrolidone, the conformation of its long chains is prone to curling, which will lead to a decrease in the steric hindrance efficiency and significantly increase the risk of bridging flocculation, ultimately forming irregular particles that are prone to agglomeration. Such an agglomerated structure may reduce the effective specific surface area and the number of surface active sites of the material, thus being unfavorable for improving its electrochemical performance.

[0038] Figure 3 X-ray Rietveld refinement patterns of the materials prepared in Example 1, Example 2, Example 3 and Comparative Example 1 confirmed the formation of the high-entropy doped manganese oxide / metal solid solution heterojunction; in Step 1, the types of acetates added have an important influence on the formation of the heterojunction. Figure 3 In a of Example 1, a high-entropy doped manganese oxide and a metal solid solution heterojunction containing Cu, Co, and Ni (HE-MnO / IMC) were formed; Figure 3 In b of Example 2, a medium-entropy doped manganese oxide and a Cu single crystal heterojunction (ME-MnO / Cu) were formed; Figure 3 In c of Example 3, a low-entropy doped manganese oxide (LE-MnO) was formed. Figure 3 In d of Comparative Example 1, an undoped manganese oxide (MnO) was formed. The crystal structure difference proves that Cu, Co, Ni, Zn, and Mg will be doped into manganese oxide; at the same time, part of Cu, Co, Ni will be reduced at high temperature to form an intermetallic compound solid solution with a crystal phase structure of Cu 0.603 Co 0.327 Ni 0.07 This is attributed to the entropy stabilization effect driven by thermodynamics during the high-temperature calcination process, which prompts the system to spontaneously evolve towards a low Gibbs free energy and high-entropy state, ultimately forming a heterostructure of high-entropy doped manganese oxide and intermetallic compounds. The coexistence of high-entropy doped manganese oxide and intermetallic compounds in this system is a natural manifestation of reaching thermodynamic equilibrium.

[0039] Table 1

[0040] Table 1 shows Figure 3 The corresponding crystallographic data of X-ray Rietveld refinement. Lattice parameter analysis shows that compared with MnO, the volume of LE-MnO shrinks by 0.19%, which is mainly due to the smaller ionic radii of Zn 2+ and Mg 2+ ions preferentially replacing Mn 2+Lattice sites, corresponding to substitution doping, where the ionic radius mismatch leads to a reduction in bond length and lattice compression. In contrast, ME-MnO / Cu and HE-MnO / IMC exhibit volume expansions of 0.20% and 0.24% compared to LE-MnO, which is due to Cu 2+ 、Co 2+ and Ni 2+ occupying the octahedral interstitial sites, corresponding to interstitial doping, which expands the interlayer spacing.

[0041] Figure 4 Gaussian fitting of the full width at half maximum (FWHM) of the diffraction peak of the manganese(II) oxide (200) crystal plane for different examples and Comparative Example 1, where: a is Example 1, b is Example 2, c is Example 3, and d is Comparative Example 1. Data analysis shows that the FWHM value of LE-MnO on the (200) crystal plane is the largest (0.66°), indicating that Zn 2+ / Mg 2+ substitution doping introduces controllable defects, reducing the crystallinity and increasing the reactivity. In contrast, the FWHM values of ME-MnO / Cu and HE-MnO / IMC are smaller (0.45° and 0.22° respectively), which is in line with the characteristics of interstitial doping and optimized long-range order, facilitating the construction of a three-dimensional electron conduction network through charge compensation. This result further confirms that Zn 2+ and Mg 2+ belong to substitution doping, substituting the Mn sites; Cu 2+ 、Co 2+ and Ni 2+ belong to interstitial doping, entering the lattice interstices.

[0042] Figure 5 High-resolution XPS spectra of the high-entropy doped manganese(II) oxide / metal solid solution heterojunction prepared in Example 1, where: a is the Co 2p orbital, b is the Ni 2p orbital, and c is the Cu 2p orbital. And the valence state distribution of HE-MnO / IMC was further analyzed. It was found through the Co 2p spectrum that the Co element has a mixed valence state of +2 and 0, with proportions of 70.9% and 29.1% respectively; similar phenomena were found in Ni 2p and Cu 2p. This further indicates that part of Co / Ni / Cu is doped into manganese(II) oxide in the form of +2 valence, forming high-entropy doped manganese(II) oxide; part of Co / Ni / Cu precipitates and forms an intermetallic compound solid solution in the form of a single substance, forming a heterojunction with high-entropy doped manganese(II) oxide.

[0043] Figure 6 XRD spectra of the materials prepared in Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5. It was found that Figure 6In Comparative Example 2, by reducing the input amounts of copper salt, cobalt salt, and nickel salt, a single-phase structure containing only high-entropy doped manganese oxide was formed after calcination, without a solid solution heterojunction. This indicates that controlling the salt concentration has an important influence on the synthesis of high-entropy doped manganese oxide / metal solid solution heterojunction.

[0044] Figure 6 In Comparative Example 3, IMC was synthesized without adding manganese salt. Through XRD, it was found that in addition to the characteristic peaks of IMC, there were also impurity peaks of Co / Ni elemental substances, which were different from the single-phase characteristic peaks of the IMC part in Example 1. This further indicates that manganese oxide can accommodate Co / Ni elements to form high-entropy doped manganese oxide.

[0045] Figure 6 In Comparative Example 4, HE-MnO / IMC was synthesized at 1000 °C. It was found that the IMC part shifted towards the characteristic peaks of Co / Ni elemental substances. This is attributed to the increase in calcination temperature, and the Co / Ni elements doped into manganese oxide will further precipitate and be reduced to elemental substances, which will lead to a decrease in the configurational entropy of manganese oxide and loss of the property of high-entropy doping, having an adverse effect on the electrochemical performance. Therefore, the calcination temperature has an important influence on the synthesis of high-entropy doped manganese oxide / metal solid solution heterojunction.

[0046] Figure 6 In Comparative Example 5, all acetates were mixed by the one-pot method, and the relative content of IMC in the obtained heterojunction was significantly higher than that in Example 1. This indicates that during the one-pot synthesis process, the ion exchange reaction was insufficient, resulting in a precursor structure with uneven distribution of metal elements. This non-uniformity causes a decrease in the content of the target metal doped in the MnO matrix in the final product, while the proportion of the metal precipitated to form an independent IMC phase increases. Thus, it can be seen that the preparation method of adding acetates step by step has an important influence on the synthesis of high-entropy doped manganese oxide / metal solid solution heterojunction.

[0047] Figure 7 It is the element mapping diagram of the high-entropy doped manganese oxide heterojunction prepared in Example 1. It shows the uniform distribution of C, Mn, Mg, Cu, Zn, Co, and Ni, as well as rich nanoscale heterointerfaces. Intuitively, it confirms the successful synthesis of high-entropy doping and solid solution heterojunction.

[0048] Figure 8The density of states spectra of the materials prepared in Examples 1-3 and Comparative Examples 1-3. MnO exhibits broadband gap characteristics, confirming its semiconductor characteristics with poor conductivity. IMC exhibits continuous energy levels, proving that it is a good electronic conductor. Continuous energy level distributions are observed in both HE-MnO and HE-MnO / IMC, indicating that the heterojunction and high-entropy doping strategies significantly improve the conductivity of MnO. In addition, HE-MnO / IMC shows a higher density of states near the Fermi level, indicating the presence of a large number of free electrons participating in charge transport, which benefits from the synergistic effect of high-entropy doping and heterojunction engineering and affects the electronic structure of MnO.

[0049] Figure 9 Bader charge analysis of the high-entropy doped manganese oxide / metal solid solution heterojunction prepared in Example 1. It was found that during discharge, the valence states of Co and Ni decreased significantly with the binding of Zn 2+ while the valence state changes of Cu, Zn, and Mg were relatively small. This indicates that Co and Ni are the main active elements in IMC, using redox characteristics to balance charges and promote electron transfer.

[0050] Figure 10 Adsorption energies of the materials prepared in Examples 1-3 and Comparative Example 1 for Zn 2+ The adsorption energy of HE-MnO / IMC for Zn 2+ (-2.06 eV) is significantly higher than that of ME-MnO / Cu (-1.56 eV), LE-MnO (-1.09 eV), and MnO (-0.54 eV). This indicates that the changes in high-entropy doping and heterointerfaces optimize the electronic structure of MnO, enhance the adsorption of Zn 2+ , and accelerate its kinetic behavior. The higher adsorption energy enables the material to effectively capture Zn 2+ in the electrolyte, providing favorable conditions for the subsequent Zn 2+ intercalation reaction.

[0051] Figure 11 Zn 2+ migration paths and energy barrier values of the materials prepared in Comparative Example 1 and Example 1. By comparing the energy barriers for Zn 2+ migration in MnO and HE-MnO / IMC, the influence of the high-entropy doping strategy on the ion migration pathway was further understood. The migration energy barrier of HE-MnO / IMC is much lower than that of MnO, indicating that the doped ions increase the disorder in MnO, which is beneficial to the diffusion of Zn 2+ . In addition, the low energy barrier of HE-MnO / IMC provides driving force for Zn 2+ migration, thus improving the electrochemical performance.

[0052] Figure 12 andFigure 13 The constant current charge-discharge tests of the materials prepared in Examples 1-3 and Comparative Example 1 were carried out under a Neware device, and the voltage window was set to 0.8-1.9 V; the long-term cycle stability test was carried out at a current density of 5.0 A g -1 ; the rate performance test was carried out successively at current densities of 0.2-5.0 A g -1 . It was observed that HE-MnO / IMC had excellent rate performance; and the long-term cycle stability test showed that at a current density of 5.0 A g -1 , the battery still had a capacity retention rate of 92.3% after 10,000 cycles, demonstrating that HE-MnO / IMC with fast ion / electron transport kinetics exhibited the best electrochemical performance and could maintain the material structure stable during fast charge and discharge processes.

[0053] Figure 14 and Figure 15 Performance curves of the high-entropy doped manganese oxide / metal solid solution heterojunction prepared in Example 1 at high loadings. Performance tests were carried out at different mass loadings of 2.5, 6.5 and 9.5 mg cm -2 . At a current density of 0.2 A g -1 , as the loading increased, the areal capacity increased significantly (from 0.68 to 1.60 to 1.74 mAh cm -2 ), and at the same time the energy density also increased correspondingly (from 0.94 to 2.11 to 2.26 mWh cm -2 ), showing good scalability. The long-term cycle test of the 6.5 mg cm -1 electrode at 0.2 Ag -2 showed that the capacity decay was negligible during 80 cycles and the average Coulombic efficiency was 99.1%, confirming its stability.

[0054] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art can still modify the specific embodiments of the present invention or make equivalent replacements. Any such modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of the claims of the present invention pending approval.

Claims

1. A high-entropy doped manganese oxide / metal solid solution heterojunction, characterized in that The chemical formula of the high-entropy doped manganese oxide / metal solid solution heterojunction is expressed as Mn x (M 1a M 2b ) y (M 3c M 4d M 5e ) z O / IMC, where Mn represents the manganese element, and M1, M2, M3, M4, and M5 represent doping metal elements different from manganese. The doping metal elements are selected from at most five metal elements in the second to fifth periods of the periodic table, 0 ≤ a ≤ 0.025, 0 ≤ b ≤ 0.025, 0 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.1, and 0 ≤ e ≤ 0.

1.

2. A high-entropy doped manganese oxide / metal solid solution heterojunction according to claim 1, wherein, M1 and M2 represent substitutional doping metal elements different from manganese, and a + b = y; M3, M4, and M5 represent interstitial doping metal elements different from manganese, and c + d + e = z; 0.8 ≤ x ≤ 1, 0 ≤ y ≤ 0.05, 0 ≤ z ≤ 0.15, and x + y + z = 1.

3. A high-entropy doped manganese oxide / metal solid solution heterojunction according to claim 1, wherein In the chemical formula, IMC represents a metal solid solution, which is composed of at least two metal elements among M1, M2, M3, M4, and M5.

4. A high-entropy doped manganese oxide / metal solid solution heterojunction according to claim 1, wherein, The doping metal elements are selected from at most five elements among magnesium, calcium, cobalt, nickel, copper, zinc, barium, and bismuth elements.

5. A high-entropy doped manganese oxide / metal solid solution heterojunction according to claim 1, characterized in that, In the heterojunction, the high-entropy doped manganese oxide phases M1, M2, M3, M4, and M5 are magnesium, zinc, cobalt, nickel, and copper elements respectively, corresponding to the diffraction peaks (111), (200), (220), (311), and (222); the metal solid solution phase is Cu 0.603 Co 0.327 Ni 0.07 , corresponding to the diffraction peaks (111), (200), and (220).

6. The preparation method of the high-entropy doped manganese oxide / metal solid solution heterojunction according to any one of claims 1 to 5, characterized in that, It includes the following steps: Step 1: Weigh manganese acetate tetrahydrate and polyvinylpyrrolidone respectively and add them to a solvent, stir at room temperature for 0.5 - 2 h to obtain solution a; weigh trimesic acid and add it to the solvent, stir at room temperature for 0.5 - 2 h to obtain solution b; weigh other metal salts and add them to the solvent, stir at room temperature for 0.5 - 2 h to obtain solution c; The solvents are all ethanol and water mixed solutions with a volume ratio of 1:1; Step 2: Slowly pour solution b into solution a, and continuously stir at room temperature for 1 - 2 h to obtain suspension d; Step 3: Slowly add solution c to suspension d, continuously stir at room temperature for 2 - 5 h, and let it stand for 12 - 24 h to obtain a precipitate; Step 4: Vacuum filter the obtained precipitate, wash it with ethanol and water 3 - 6 times, and then place the product in a vacuum drying oven at 80 °C and dry it for 10 - 15 h to obtain a heterojunction precursor; Step 5: Heat-treat the precursor obtained in Step 4 under nitrogen to obtain a high-entropy doped manganese oxide / metal solid solution heterojunction.

7. The preparation method of a high-entropy doped manganese oxide / metal solid solution heterojunction according to claim 6, characterized in that, The weight-average molecular weight of the polyvinylpyrrolidone is 10 - 50 kDa; The molar ratio of the manganese acetate tetrahydrate, metal salts, and trimesic acid is (2 - 3):(0 - 1.5):

5.

8. The preparation method of a high-entropy doped manganese oxide / metal solid solution heterojunction according to claim 6, characterized in that, During the heat treatment process in Step 5, the calcination temperature is 600 - 800 °C, the heat preservation time is 2 - 4 h, and the heating rate is 2 - 5 °C / min.

9. An electrode sheet, the electrode sheet comprising an electrode active material, a conductive carbon, a binder, and a dispersion solvent, characterized in that, The electrode active material is the high-entropy doped manganese oxide / metal solid solution heterojunction according to any one of Claims 1 to 5.

10. A zinc-ion battery, the zinc-ion battery comprising positive and negative electrode plates, an electrolyte, and a battery separator, characterized in that, The positive electrode sheet of the zinc ion battery is the electrode sheet described in Claim 9.

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