Spherical hollow multilayer high-entropy metal oxide and preparation method and application thereof

Abstract

The application relates to the technical field of supercapacitors, and particularly discloses a spherical hollow multilayer high-entropy metal oxide as well as a preparation method and application thereof. The spherical hollow multilayer high-entropy metal oxide is prepared by crosslinking metal cation nitrate salt including iron nitrate nonahydrate, zinc nitrate hexahydrate, copper nitrate hexahydrate, cobalt nitrate hexahydrate and nickel nitrate hexahydrate with glucose monohydrate to generate spherical high-entropy metal hydroxide FeZnCuCoNi-HO with a solid core structure, and annealing the metal hydroxide to form the spherical hollow multilayer high-entropy metal oxide. Compared with the prior art, the high-entropy metal oxide is prepared by a low-energy-consumption and simple synthesis method, the problem of volume change of the high-entropy metal oxide as an electrode material in a cycle process is solved, more reaction active sites are provided, the ion diffusion path is improved, the stability of the material is maintained, the specific capacitance of the composite material is improved, and the energy storage performance of the supercapacitor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of supercapacitors, in particular to a spherical hollow multi-layer high-entropy metal oxide and a preparation method and application thereof. BACKGROUND

[0002] High-entropy metal oxides are composed of five or more metal elements in a near-equimolar ratio. Due to their unique "high-entropy effect" and component synergy, they are ideal candidates for supercapacitor electrode materials. Compared with traditional single / dual metal oxides, high-entropy metal oxides not only enable the synergistic redox reaction of multiple metal sites (such as the coupled electron transfer of Fe 3+ / Fe 2+ and Co 3+ / Co 2+ ), but also inhibit grain boundary migration and phase separation through the high-entropy effect, significantly improving the structural stability of the material. In addition, the disordered lattice structure and chemical complexity of high-entropy oxides can induce lattice distortion and electronic structure rearrangement, forming a rich variety of lattice defects (such as oxygen vacancies and metal vacancies) and wide-band characteristics, thereby enhancing electronic conductivity and reducing charge transfer impedance.

[0003] However, the multi-metal precursors of high-entropy oxides are prone to element segregation due to differences in hydrolysis rates, and traditional co-precipitation methods cannot achieve atomic-level mixing. Local composition fluctuations can reduce active site density. Existing methods (such as atomic layer deposition and template etching) rely on precision equipment or expensive templates, making it difficult to achieve kilogram-scale preparation, and high-temperature annealing (> 800°C) results in high energy consumption and severe particle agglomeration. In addition, most high-entropy metal oxides are solid particles or simple core-shell structures, lacking hierarchical mass transfer channels, resulting in long ion diffusion paths and low active site utilization. During electrochemical testing, the severe ion intercalation / deintercalation (such as OH - insertion in transition metal oxides) during charging and discharging induces lattice stress accumulation, and the multi-layer stacked structure is prone to crack propagation, affecting long-term cycle stability.

[0004] To solve the above problems, researchers have attempted to improve the performance of high-entropy metal oxide electrodes through component optimization and structure design. For example, the prior art ("Exploring the charge storage ability of the spinel-type high entropy oxide (MnFeCoNiZn)3O4nanoparticles for supercapacitor applications" DOI: 10.1016 / j.ceja.2025.100708) uses a solution combustion method to prepare spinel-type (MnFeCoNiZn)3O4HEO NPs electrodes. This material has a specific capacitance of 1, 200 F g-1 at 3 A g-1 in 6 M KOH electrolyte, but the preparation process is complex and the specific capacitance is low.-1 The specific capacitance is 288.7 F g -1 , but the specific capacity is still small, mainly due to insufficient exposure of active sites caused by the solid particle structure; and the rate performance is poor (3-30 Ag -1 , the capacity retention rate is only 52%), and the cycle stability is insufficient (the capacity retention rate is 50% after 5000 cycles), indicating that the ion diffusion kinetics is limited and the structure is pulverized due to volume expansion. These limitations highlight the deficiencies of the synthesis strategy in terms of component homogenization and structure regulation. To further improve the performance, the prior art (Electrochemical investigation of synthesized (Mg 0.21 Cr 0.21 Mn 0.21 Fe 0.21 Cu 0.16 )3O4 high entropy oxide for supercapacitor electrode material, DOI: 10.1016 / j.ceramint.2024.11.365) based on the chemical compatibility of alkaline and transition metal elements, synthesized (Mg 0.21 Cr 0.21 Mn 0.21 Fe 0.21 Cu 0.16 )3O4 by sol-gel method, and formed a single-phase spinel structure by optimizing the stoichiometry of the precursor. Microscopic characterization shows that the particle size is uniform (250-500 nm), and the introduction of Mg significantly enhances the structural stability (the capacity retention rate is 86% after 2000 cycles), and the synergistic effect of other metals provides multi-electron redox activity (1 A g -1 The specific capacitance is 241 F g -1 ). However, this technology still has a large gap between the specific capacitance and the theoretical value, and the possible reason is that the high proportion of low-activity Mg in the material leads to insufficient redox site density; although the sol-gel method can regulate the micro-morphology, the calcination temperature is still high, and the ion diffusion path is still limited.

[0005] In view of the deficiencies of the prior art, the present application provides an innovative solution: a preparation method and application of a spherical hollow multi-layer high-entropy metal oxide electrode material. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a spherical hollow multi-layer high-entropy metal oxide and its preparation method and application.

[0007] In order to solve the above technical problems, the present application discloses the following technical solutions:

[0008] In a first aspect, the application discloses a spherical hollow multi-layer high-entropy metal oxide FeZnCuCoNi-O.

[0009] The spherical hollow multi-layer FeZnCuCoNi high-entropy metal oxide is generated by hydrothermal reaction cross-linking of metal cation nitrate salt including iron nitrate nine hydrate, zinc nitrate six hydrate, copper nitrate six hydrate, cobalt nitrate six hydrate and nickel nitrate six hydrate and glucose one hydrate to generate a spherical high-entropy metal hydroxide with a solid core structure, i.e. high-entropy hydroxide precursor FeZnCuCoNi-HO (HEHO); the spherical high-entropy metal hydroxide is annealed to induce metal hydroxide to form the spherical hollow multi-layer high-entropy metal oxide FeZnCuCoNi-O (HEO).

[0010] The molar ratio of the iron nitrate nine hydrate and the zinc nitrate six hydrate is controlled to be (1-2):(1-2) to control the molar ratio of Fe and Zn metal to be (1-2):(1-2); in some embodiments, the molar ratio of the iron nitrate nine hydrate and the zinc nitrate six hydrate is 2:(0.5-1.5), for example, 2:1.

[0011] The molar ratio of the copper nitrate six hydrate, the cobalt nitrate six hydrate and the nickel nitrate six hydrate is controlled to be (3.5-4.5):(4.5-5.5):(5.5-6.5) to control the molar ratio of Cu, Co and Ni to be (3.5-4.5):(4.5-5.5):(5.5-6.5); in some embodiments, the molar ratio of the copper nitrate six hydrate, the cobalt nitrate six hydrate and the nickel nitrate six hydrate is 4:5:6.

[0012] The molar ratio of the copper nitrate six hydrate and the glucose one hydrate is (3.5-4.5):(21.4-23.4), for example, 4:22.4.

[0013] The spherical hollow multi-layer high-entropy metal oxide FeZnCuCoNi-O contains 3-4 layers of spheres, the diameter of the innermost layer of spheres is 0.3-1.5 μm, for example, 0.5, 0.8, 1.1 μm; the diameter of the outermost layer of spheres is 1-4.3 μm, for example, 1.2, 2.2, 4.1 μm; and the thickness of the shell layer in the outermost layer of spheres is 90-200 nm, for example, 125, 139, 149, 165, 178, 187 nm.

[0014] In a second aspect, the application discloses a preparation method of the spherical hollow multi-layer high-entropy metal oxide FeZnCuCoNi-O.

[0015] The method comprises:

[0016] (1) A mixed solution containing ferric nitrate nonahydrate, zinc nitrate hexahydrate, copper nitrate hexahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate and glucose monohydrate is subjected to a hydrothermal reaction, and the obtained reaction product is sequentially washed with deionized water and anhydrous ethanol and dried to obtain a high-entropy hydroxide precursor FeZnCuCoNi-HO (HEHO);

[0017] (2) Subsequently, the HEHO is placed in a muffle furnace to perform calcination annealing to induce crystallization of the inner shell and outer shell of the metal oxide, thereby forming a spherical hollow multi-layer FeZnCuCoNi-O high-entropy oxide (HEO).

[0018] In step (1), the glucose monohydrate, ferric nitrate nonahydrate, zinc nitrate hexahydrate, copper nitrate hexahydrate, cobalt nitrate hexahydrate and nickel nitrate hexahydrate are stirred in deionized water to obtain a mixed solution; the stirring speed is 500-600 rpm, and the stirring time is 30-60 min.

[0019] In step (1), the molar ratio of the ferric nitrate nonahydrate to the zinc nitrate hexahydrate is controlled to be (1-2):(1-2) to control the molar ratio of Fe to Zn metal to be (1-2):(1-2); in some embodiments, the molar ratio of the ferric nitrate nonahydrate to the zinc nitrate hexahydrate is 2:(0.5-1.5), such as 2:1.

[0020] In step (1), the molar ratio of the copper nitrate hexahydrate, the cobalt nitrate hexahydrate and the nickel nitrate hexahydrate is controlled to be (3.5-4.5):(4.5-5.5):(5.5-6.5) to control the molar ratio of Cu, Co and Ni to be (3.5-4.5):(4.5-5.5):(5.5-6.5); in some embodiments, the molar ratio of the copper nitrate hexahydrate, the cobalt nitrate hexahydrate and the nickel nitrate hexahydrate is 4:5:6.

[0021] In step (1), the molar ratio of the copper nitrate hexahydrate to the glucose monohydrate is (3.5-4.5):(21.4-23.4), such as 4:22.4.

[0022] In step (1), the temperature of the hydrothermal reaction is 80-120°C, such as 100°C; the time of the hydrothermal reaction is 5-10 h, such as 400 min.

[0023] In step (1), the temperature of the drying is 60-80°C, and the time of the drying is 12-24 h.

[0024] In step (2), the annealing is to heat at a rate of 0.5-5°C / min to 450-600°C, and calcine at 450-600°C for 0.5-1.5 h; in some embodiments, the calcination temperature is 500-600°C, and the calcination time is 1 h.

[0025] In a third aspect, the present application discloses a high-entropy metal oxide electrode material for supercapacitors.

[0026] The high-entropy metal oxide electrode material for supercapacitors comprises the spherical hollow multilayer high-entropy metal oxide FeZnCuCoNi-O of the first aspect or the spherical hollow multilayer high-entropy metal oxide FeZnCuCoNi-O prepared by the method of the second aspect.

[0027] The specific capacitance of the high-entropy metal oxide electrode material for supercapacitors is 400-700 F g -1 450, 480, 510, 560, 600, 635, 642, 650 F g -1 The capacitance retention rate is 75%-90%, such as 80%, 85%, 87%, and 88%, after 10,000 cycles.

[0028] In the present application, the micro-morphology of the HEHO with different metal proportions is a solid spherical structure with a smooth surface, and the HEO with different metal proportions has a spherical hollow multilayer structure.

[0029] The technical solution provided by the present application is that under hydrothermal conditions, metal cations play the role of cross-linking agent by forming coordination bonds with free glucose molecules, and finally generate amorphous carbon spheres with a solid core structure and hydroxide. Subsequently, annealing treatment is carried out in air, forming a radial directional thermal gradient, which promotes the kinetic preferential combustion and gas release of the peripheral region of the carbon sphere. As the temperature rises, the microsphere particles begin to shrink, and the accumulated metal ions on the outside reach the critical concentration "threshold", which promotes the formation of a rigid shell. Subsequently, the microsphere undergoes a synchronous process of template dissolution and phase transition of hydroxide to oxide, and forms a supplementary structure layer by internal deposition; the internal deposition is realized by gas-driven dissolved metal ions reprecipitating on the gap surface. Gas escape leads to significant surface roughening.

[0030] The technical solution provided by this invention first utilizes free glucose molecules to form coordination bonds, leveraging the multi-coordination characteristics of its hydroxyl and carbonyl groups to promote the in-situ complexation and synergistic distribution of five metal ions: Fe, Zn, Cu, Co, and Ni. This increases the compatibility of multiple cations in the sublattice and reduces the differences in ion diffusion rates, forming a spherical high-entropy metal hydroxide with a solid core structure. Subsequently, combined with an annealing process, the spheres achieve hierarchical migration and crystallization partitioning under a radial thermal gradient, thereby inducing the crystallization of the inner and outer shells of the metal oxide. The constructed spherical hollow multilayer structure provides hierarchical mass transfer channels through its internal cavity and interlayer pores. The interlayer pores shorten the electron / ion diffusion distance, increase the electrolyte contact surface, and expose more active sites. Simultaneously, the formed lattice defects (such as oxygen vacancies) serve as ion adsorption sites, further reducing K0. + Migration barrier, achieving simultaneous optimization of specific capacity and rate performance. Furthermore, this invention can also dynamically adjust the Fe / Zn ratio, utilizing Fe... 3+ The strong redox activity of Zn 2+ The structural stabilizing effect is achieved by constructing and optimizing the electronic structure distribution of metal sites in the formed multi-shell high-entropy metal oxide structure, thereby synergistically improving activity and stability.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0032] This invention utilizes metal cations as crosslinking agents by forming coordination bonds with free glucose molecules. A complexation-adsorption method is used to load metal precursors, improving component homogeneity and preventing multi-element segregation. Furthermore, it avoids the reliance on precision equipment or expensive templates required by traditional methods, achieving gram-scale preparation. Annealing induces the crystallization of the inner and outer shells of the metal oxide, forming a spherical hollow multilayer structure, reducing ion diffusion paths and improving the utilization rate of active sites. Through optimization of Fe...

[0033] 3+ / Zn 2+ The ratio (1:2 to 2:1) was used to select the pentagonal system (FeZnCuCoNi-O) with the best compatibility based on theoretical calculations, suppressing phase separation and utilizing Fe 3+ High redox activity (Fe 3+ / Fe 2+ ) and Zn 2+ Structural stabilizing effect (Zn-O bond energy > 400 kJ mol) -1), and optimizes the supercapacitor energy storage performance. Therefore, compared with the prior art, the high-entropy metal oxide is prepared by a low-energy-consumption and simple synthesis method, the volume change problem of the high-entropy metal oxide as an electrode material in a cycle process is solved, more reaction active sites are provided, the ion diffusion path is improved, the stability of the material is maintained while the specific capacitance of the composite material is improved, the energy storage performance of the supercapacitor is improved, and the high-entropy metal oxide has a wide application prospect in the supercapacitor application field. BRIEF DESCRIPTION OF DRAWINGS

[0034] The above and / or other aspects of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which:

[0035] Figure 1 TEM and EDS spectra of the precursor HEHO of Example 1.

[0036] Figure 2 XRD test graphs of HEO2, HEO1, and HEHO prepared in Example 1, Example 2, and Example 3, and an XRD graph of a CoFe2O4 standard card (CoFe2O4 PDF #22-1086).

[0037] Figure 3 Rietveld refinement result graph of HEO2 prepared in Example 1.

[0038] Figure 4 TEM and EDS spectra of HEO2 prepared in Example 1.

[0039] Figure 5 ICP test result graph of HEO2 prepared in Example 1.

[0040] Figure 6 EPR test graphs of HEO2, HEO1, and HEHO prepared in Example 1, Example 2, and Example 3.

[0041] Figure 7 Charge-discharge curve graph of HEO2 prepared in Example 1.

[0042] Figure 8 Cycle life curve graph of HEO2 prepared in Example 1.

[0043] Figure 9 TEM graph of HEO2 after cycling of Example 1.

[0044] Figure 10 Adsorption energy graphs of HEO2, HEO1, and HEHO prepared in Example 1, Example 2, and Example 3 on OH - ​

[0045] Figure 11 TEM image of HEO1 prepared in Example 2.

[0046] Figure 12 Charge-discharge curve of HEO1 prepared in Example 2.

[0047] Figure 13 Cycle life curve of HEO1 prepared in Example 2.

[0048] Figure 14 TEM image of HEO1 after cycling in Example 2.

[0049] Figure 15 TEM image of HEO0 prepared in Example 3.

[0050] Figure 16 Charge-discharge curve of HEO0 prepared in Example 3.

[0051] Figure 17 Cycle life curve of HEO0 prepared in Example 3.

[0052] Figure 18 TEM image of HEO0 after cycling in Example 3. DETAILED DESCRIPTION

[0053] The present application can be better understood according to the following examples. However, it will be readily apparent to those of ordinary skill in the art that the examples described are for purposes of illustration only and should not be so limited unless otherwise specifically identified in the claims.

[0054] In the following examples, the experimental methods described are routine methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0055] In the present application, the ratio of the amount of substance of Fe and Zn is referred to as Fe / Zn ratio, such as the Fe / Zn ratio of 2:1 in Example 1.

[0056] Example 1: A preparation method of spherical hollow multi-layer high-entropy metal oxide FeZnCuCoNi-O

[0057] Step 1, preparation of spherical high-entropy metal hydroxide, first, 0.625 mmol of zinc nitrate hexahydrate, 1.25 mmol of iron nitrate nonahydrate, 2.5 mmol of copper nitrate hexahydrate, 3.125 mmol of cobalt nitrate hexahydrate, 3.75 mmol of nickel nitrate hexahydrate and 14 mmol of glucose monohydrate were placed in 50 mL of deionized water in a molar ratio of Zn:Fe:Cu:Co:Ni = 1:2:4:5:6, and stirred for 30 min to obtain a mixed solution, then the mixed solution was subjected to hydrothermal reaction at 100 ℃ for 400 min, finally, the reaction product was washed with deionized water and anhydrous ethanol in turn, and then dried at a drying temperature of 60 ℃ for 12 h to obtain spherical high-entropy metal hydroxide ZnFeCuCoNi-HO, abbreviated as HEHO.

[0058] Step 2, preparation of spherical hollow multi-layer high-entropy metal oxide, the HEHO obtained in step 1 was calcined at a heating rate of 1 ℃ min -1 -1 and a calcination temperature of 500 ℃ for 1 h to obtain spherical hollow multi-layer high-entropy metal oxide ZnFeCuCoNi-O, abbreviated as HEO2 because the Fe / Zn ratio is 2:1.

[0059] In order to prove the micro-morphology and element distribution of HEHO, TEM and EDS tests were performed. The test results are shown in Figure 1 , the micro-morphology of HEHO is solid spherical structure, and Zn element, Fe element, Cu element, Co element and Ni element exist at the same time, in addition, the elements are uniformly distributed without segregation.

[0060] In order to prove the composition of HEO2, XRD test was performed, and Rietveld refinement was performed. The XRD test results are shown in Figure 2 , the diffraction peak of HEO2 matches CoFe2O4 with a lattice constant of 8.38 Å, which confirms the formation of cubic spinel structure. At 2 θ values of 30.1 o , 35.4 o , 37.1 o , 43.1 o , 62.6 o , 65.8 o , 75.0 o and 79.0 o , the diffraction peaks correspond to (220), (311), (222), (400), (440), (531), (622) and (444) respectively; the Rietveld refinement results are shown in Figure 3As shown in FIG. 6, the space group of HEO2 is Fd-3m, and the lattice parameter is 8.39 Å. The lattice expansion (+0.01 Å) compared with the theoretical lattice constant 8.38 Å indicates that the average radius of the introduced metal ions is larger than that of the ions in the original lattice, i.e., it proves that the metal ions are successfully doped into the lattice to form a solid solution. The test results show that the high-entropy oxide HEO2 is successfully synthesized in Example 1.

[0061] In order to prove the micro-morphology and element distribution of HEO2, TEM, EDS and ICP tests are performed. The TEM and EDS test results are as shown in FIGS. 7 and 8. Figure 4 As shown in FIG. 7, the micro-morphology of HEO2 is a spherical hollow structure, and the whole sphere has four ordered shell layers, each of which contains Zn, Fe, Cu, Co and Ni metal elements. At the same time, Figure 4 As shown in FIG. 8, the diameter of the innermost sphere in HEO2 is 0.8 μm, the diameter of the outermost sphere is 4.1 μm, and the thickness of the shell layer in the outermost sphere is 125-187 nm. The ICP test results are as shown in FIG. 9. Figure 5 As shown in FIG. 9, the mass percentage of elements in HEO2 is Zn:Fe:Cu:Co:Ni = 12.91:14.92:21.42:22.16:28.59. The test results show that HEO2 has a multi-shell hollow structure, and there is a large gap between the layers, and the metal elements are uniformly distributed in each layer without segregation, which meets the definition of the "multi-principal element" of the high-entropy system. Combined with the XRD diffraction peak and the lattice constant, and the fact that the five elements in the ICP test all reach a significant content (>5%), it can be proved that the high-entropy oxide is successfully synthesized.

[0062] In order to prove the oxygen vacancies (Vo) in HEO2 due to the high-entropy effect, an EPR test is performed. The test results are as shown in FIG. 10. Figure 6 As shown in FIG. 10, the EPR signal at g = 2.003 is attributed to the electrons trapped in Vo. The test results show that the high Fe ratio increases the concentration of Fe 3+ / Fe 2+ redox pairs, and the charge compensation mechanism of Fe 3+ promotes the formation of oxygen vacancies, which is beneficial to provide more high-activity sites for OH - .

[0063] In order to prove the electrochemical performance of HEO2, an electrochemical performance test is performed. The test results are as shown in FIG. 11. Figure 7 As shown in FIG. 11, in the electrolyte of 3 M KOH, in the voltage window of 0-0.5 V, the specific capacitance of HEO2 is 642 F g -1 when the discharge current density is 1 A g -1 .

[0064] In order to prove the cycle stability of HEO2, a cycle stability test is performed. The test results are as shown in FIG. 12.Figure 8 As shown, the capacitance retention of HEO2 is 87.4% and the coulombic efficiency is 100% after 10000 cycles.

[0065] In order to prove the structural stability of HEO2, TEM images of HEO2 after 10000 cycles were tested. The test results are shown in Figure 9 As shown, the spherical morphology of HEO2 is complete after 10000 cycles, and it is still a hollow multi-layer structure.

[0066] In order to prove the influence of Fe and Zn sites in HEO2 on the electrochemical performance, OH - adsorption energy was calculated. The calculation results are shown in Figure 10 As shown, the adsorption energy of Fe site is -1.87 eV, and the initial position of Zn site is placed on the Zn site, and after optimization, OH - will move to the oxygen vacancy (Vo), and the adsorption energy is -2.47 eV. The reason is that Zn 2+ occupies the tetrahedral interstice (A site), and Fe 3+ occupies the octahedral interstice (B site). Vo tends to form near the B site rich in Fe 3+ , but through lattice distortion and electronic coupling, the local electric field of Vo can polarize the adjacent Zn 2+ site, significantly enhancing its adsorption capacity for OH - . Therefore, combined with EPR test, Vo induced by high Fe ratio provides low energy potential well, which strengthens the adsorption of OH - , that is, near Vo, the strong oxidizing property of Fe 3+ promotes the partial charge transfer of OH - (OH - → Fe 3+ ), and Zn 2+ stabilizes the adsorption configuration through electrostatic interaction, forming a “Fe 3+ -OH - -Zn 2+ ” ternary composite structure, which finally enhances the performance of HEO2 in supercapacitor electrochemical energy storage.

[0067] In order to prove the effect of Fe and Zn on the structure and electrochemical performance of the material, examples 2 and 3 are provided, HEO1 prepared by adjusting the ratio of Fe / Zn to 1:1, and HEO0 prepared by adjusting the ratio of Fe / Zn to 1:2.

[0068] Example 2: HEO1

[0069] A method for preparing a spherical hollow multi-layer high-entropy metal oxide with a Fe / Zn ratio of 1:1, the steps not specifically described are the same as in Example 1, the difference is that: 1.25 mmol of zinc nitrate hexahydrate, 1.25 mmol of ferric nitrate nonahydrate, the obtained material is named as HEO1.

[0070] In order to prove the composition of HEO1, XRD test was carried out. The test results are shown in Figure 2 , HEO1 has the characteristic peak of CoFe2O4. The test results show that single-phase CoFe2O4 is successfully synthesized, the sample shows pure spinel phase, no peak splitting and additional weak peak. Compared with Example 1, the peak at 35.5° is slightly lower than the peak at 37.1°, and the change is not obvious, which is caused by the lattice distortion and multiphase competition caused by Fe / Zn balance, and the peak intensity of (311) and secondary phase is close.

[0071] In order to prove the micro-morphology of HEO1, TEM test was carried out. The test results are shown in Figure 11 , the micro-morphology of HEO1 is spherical hollow structure, and there are 3-4 ordered shell layers inside the sphere. Compared with Example 1, the micro-morphology does not change, which proves that the carbon template adsorption balances the ion compatibility and inhibits the phase separation.

[0072] In order to prove the oxygen vacancy (Vo) of HEO1, EPR test was carried out. The test results are shown in Figure 6 , the EPR signal at g = 2.003 is attributed to the electron trapped in Vo. Compared with Example 1, the Vo concentration is increased by 15.3% when the Fe / Zn ratio is 2:1.

[0073] In order to prove the electrochemical performance of HEO1, electrochemical performance test was carried out. The test results are shown in Figure 12 , in the electrolyte of 3M KOH, in the voltage window of 0-0.5V, the specific capacitance is 560 Fg -1 when the discharge current density is 1 Ag -1 . Compared with Example 1, the specific capacitance performance can be improved when the Fe / Zn ratio is 2:1, and the improvement is 14.6%.

[0074] In order to prove the influence of Fe, Zn sites in HEO1 on the electrochemical performance, theoretical calculation of OH - adsorption energy was carried out. The calculation results are shown in Figure 10 , the adsorption energy of Fe site is-1.42 eV, and the adsorption energy of Zn site is-1.08 eV. Compared with Example 1, when the Fe / Zn ratio is 2:1, the adsorption energy of Fe site to OH - increases by-0.45 eV, and the adsorption energy of Zn site to OH -The adsorption energy of HEO1 increases by -1.39 eV, which is conducive to promoting more redox reactions, thereby improving the specific capacitance.

[0075] In order to prove the cycle stability of HEO1, cycle stability test was carried out. The test results are shown in Figure 13 The retention rate of the capacitance of HEO1 is 82.2% and the coulombic efficiency is 100% when the cycle number is 10000 times. Compared with Example 1, it can be known that the cycle performance can be improved when the Fe / Zn ratio is 2:1, and the improvement range is 6.3%.

[0076] In order to prove the structural stability of HEO1, the TEM image of HEO1 after 10000 cycles was tested. The test results are shown in Figure 14 The morphology of HEO1 is kept intact after 10000 cycles. Compared with Example 1, it can be known that the structural stability does not change after the ratio changes.

[0077] From Example 1 and Example 2, it can be known that adjusting the Fe / Zn ratio affects the lattice distortion or phase distribution. Increasing the Fe / Zn ratio (HEO2) optimizes the stability of the spinel structure, and forms a crystal orientation that is more conducive to charge transfer. In the migration process from the Zn site to Vo, the adsorption energy jumps from -1.08 eV to -2.47 eV, indicating that Vo provides a lower energy potential well, which is conducive to improving the electrochemical energy storage performance of supercapacitors.

[0078] Example 3: HEO0

[0079] A method for preparing a spherical hollow multilayer high-entropy metal oxide with a Fe / Zn ratio of 1:2, the steps not specifically described are the same as those in Example 1, and the difference is that 1.25 mmol of zinc nitrate hexahydrate and 0.625 mmol of iron nitrate nonahydrate are used, and the obtained material is named as HEO0.

[0080] In order to prove the composition of HEO0, XRD test was carried out. The test results are shown in Figure 2 HEO0 has the characteristic peak of CoFe2O4. The test results show that single-phase CoFe2O4 is successfully synthesized, and the sample shows pure spinel phase without peak splitting and additional weak peaks. Compared with Example 1, it can be known that the peak at 35.5° is slightly higher than the peak at 37.1°, which is because Zn 2+ occupies the spinel tetrahedral A site, stabilizes the (311) crystal surface, and inhibits the high-angle peak intensity due to lattice expansion. Moreover, the difference in ionic radii between Fe 3+ (0.645 Å) and Zn 2+ (0.74 Å) decreases when the Fe ratio decreases, and the degree of lattice distortion decreases.

[0081] To prove the micro-morphology of HEO0, TEM test was performed. The test results, as shown in Figure 15 FIG. 6, the basic micro-morphology of HEO0 is still spherical hollow structure, and there are 3 ordered shell layers inside the sphere with a size of 1.1-2.2 pm. Compared with Example 1, it can be seen that the micro-morphology change is negligible.

[0082] To prove the oxygen vacancies (Vo) of HEO0, EPR test was performed. The test results, as shown in Figure 6 FIG. 7, the EPR signal at g = 2.003 is attributed to the electrons trapped in Vo. Compared with Example 1, it can be seen that when the Fe / Zn ratio is 2:1, the Vo concentration can be increased by 32.8%. This indicates that when the proportion of Fe increases, the Fe 3+ / Fe 2+ redox pair has a higher concentration, which enhances the ability to generate Vo through charge compensation.

[0083] To prove the electrochemical performance of HEO0, electrochemical performance test was performed. The test results, as shown in Figure 16 FIG. 8, in the voltage window of 0-0.5 V, the specific capacitance is 476 F g -1 when the discharge current density is 1 A g -1 . Compared with Example 1, it can be seen that when the Fe / Zn ratio is 2:1, the specific capacitance performance can be improved by 34.8%.

[0084] To prove the influence of Fe and Zn sites in HEO0 on the electrochemical performance, theoretical calculation of OH - adsorption energy was performed. The calculation results, as shown in Figure 10 FIG. 9, the adsorption energy of Fe site is -1.07 eV, and the adsorption energy of Zn site is -0.79 eV. Compared with Example 1, it can be seen that when the Fe / Zn ratio is 2:1, the adsorption energy of Fe site to OH - increases by -0.8 eV, and the adsorption energy of Zn site to OH - increases by -1.68 eV, which can promote more redox reactions, thereby improving the specific capacitance.

[0085] To prove the cycle stability of HEO0, its cycle stability was tested. The test results, as shown in Figure 17 FIG. 10, when the cycle number is 10000 times, the capacitance retention rate of HEO0 is 75.9%, and the coulombic efficiency is 100%. Compared with Example 1, it can be seen that when the Fe / Zn ratio is 2:1, the cycle performance can be improved by 15.1%.

[0086] To prove the structural stability of HEO0, its TEM image after 10000 cycles was tested. The test results, as shown in Figure 18As shown, the morphology of HEO0 remained intact after 10000 cycles. Compared with Example 1, it can be seen that the structure stability did not change after the ratio change.

[0087] Compared with Example 1, it can be seen that when the Fe / Zn ratio is 1:2, a hollow multi-layer HEO can also be formed, but the structural defects, the adsorption energy of OH - and the electrochemical performance are reduced. The reason is that Zn 2+ occupies the tetrahedral site (A site), and Fe 3+ occupies the octahedral site (B site). Oxygen vacancies (Vo) tend to form near the B site rich in Fe 3+ . When the Fe / Zn ratio decreases, the concentration of the Fe 3+ / Fe 2+ redox pair in the HEO decreases, weakening the ability to generate Vo through charge compensation. The decrease in Vo concentration leads to a lack of sufficient Vo near the Zn site to form a “Zn 2+ -Vo-OH - ” ternary active center. Moreover, the increase in the Zn ratio can lead to the surface being covered by more Zn 2+ , and the active sites exposed by the tetrahedral site (A site) of Zn 2+ are limited. At the same time, the reduction of Vo makes the coordination environment of Fe³⁺ more complete, lacking unsaturated bonds to participate in adsorption.

[0088] From Example 1, Example 2 and Example 3, it can be seen that Fe is the main driving force for the generation of oxygen vacancies (Vo) in HEO. Fe 3+ releases oxygen ions to form Vo through a reduction reaction (Fe 3+ → Fe 2+ ), and a decrease in the Fe ratio directly reduces the concentration of the Fe 3+ / Fe 2+ redox pair, resulting in a significant decrease in the Vo generation rate. Among them, oxygen vacancies are the key factor to improve the adsorption energy. The decrease in the Fe ratio leads to a decrease in the Vo concentration, and the Zn site cannot enhance the adsorption capacity through the “Zn 2+ -Vo-OH - ” ternary active center, thereby affecting the electrochemical performance. Among them, HEO0 exhibits low ion adsorption capacity for OH − , -1.07 eV and -0.79 eV at the Fe site and the Zn site, respectively, which significantly hinders the adsorption of free OH − . HEO1 is -1.42 eV and -1.08 eV at the Fe site and the Zn site, respectively, showing low adsorption energy. After the increase in the Fe ratio, the phenomenon of OH - migration from the Zn site to Vo indicates that the presence of Vo can further optimize OH- The adsorption energy of HEO2 at Fe sites and Zn sites is further improved to -1.87 eV and -2.47 eV, which is beneficial to the capture of OH - , and is more beneficial to the electrochemical reaction, so as to improve the supercapacitor energy storage performance.

[0089] In summary, the technical effects of the application are detected by experiments, and the specific contents are as follows:

[0090] The XRD test of the application shows that HEO0, HEO1 and HEO2 show pure spinel phase without peak splitting and additional weak peaks; the Rietveld refinement shows that the metal is incorporated into the crystal lattice to form a solid solution, indicating that the high-entropy oxide is successfully synthesized.

[0091] The TEM test of the application shows that HEO0, HEO1 and HEO2 have multiple ordered shell layers inside the sphere, the diameter of the innermost sphere is 0.5-1.1 μm, the diameter of the outermost sphere is 1.2-4.1 μm, and the thickness of the shell layer in the outermost sphere is 125-187 nm; the EDS test shows that the metal elements in HEO0, HEO1 and HEO2 are uniformly distributed without segregation.

[0092] The ICP test of the application shows that the content of the five elements in HEO2 is more than 5%, which proves the successful synthesis of high-entropy oxide.

[0093] The EPR test of the application shows that the oxygen vacancy concentration of HEO2 is 15.3% higher than that of HEO1 and 32.8% higher than that of HEO0, and the oxygen vacancy concentration of HEO2 is the highest.

[0094] The TEM test of the application after cycling shows that HEO0, HEO1 and HEO2 are stable in structure and still maintain the spherical hollow multilayer structure.

[0095] The electrochemical performance test of the application shows that in 3 M KOH solution, the voltage window for charging and discharging is 0-0.5 V, the specific capacitance of HEO is 476-642 F g -1 when the discharge current density is 1 A g -1 , and the capacitance retention rate is 75.9%-87.4% after 10000 cycles.

[0096] The application of the application to the Fe and Zn sites to OH -Theoretical calculation of adsorption energy shows that the adsorption energy of Fe site in HEO2 is-1.87 eV, the adsorption energy of Zn site is-2.47 eV; the adsorption energy of Fe site in HEO1 is-1.42 eV, the adsorption energy of Zn site is-1.08 eV; the adsorption energy of Fe site in HEO0 is-1.07 eV, the adsorption energy of Zn site is-0.79 eV, so HEO2 can promote more redox reactions, thereby improving specific capacitance.

[0097] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A supercapacitor electrode material, characterized in that, The application relates to a spherical hollow multilayer high-entropy metal oxide FeZnCuCoNi-O. The spherical hollow multilayer high-entropy metal oxide FeZnCuCoNi-O is prepared by cross-linking metal cation nitrate including iron nitrate nonahydrate, zinc nitrate hexahydrate, copper nitrate hexahydrate, cobalt nitrate hexahydrate and nickel nitrate hexahydrate with glucose monohydrate to generate a spherical high-entropy metal hydroxide with a solid core structure; the spherical high-entropy metal hydroxide is annealed to induce metal hydroxide, and the spherical hollow multilayer high-entropy metal oxide FeZnCuCoNi-O is formed. The molar ratio of the iron nitrate nonahydrate and the zinc nitrate hexahydrate is 2: (1-1.5). The spherical hollow multilayer high-entropy metal oxide FeZnCuCoNi-O contains 3-4 layers of spheres, the diameter of the outermost sphere is 4.1-4.3 microns, and the thickness of the shell in the outermost sphere is 90-200 nm.

2. The supercapacitor electrode material of claim 1, wherein, The molar ratio of the copper nitrate hexahydrate, the cobalt nitrate hexahydrate, the nickel nitrate hexahydrate and the glucose monohydrate is (3.5-4.5):(4.5-5.5):(5.5-6.5):(21.4-23.4).

3. The supercapacitor electrode material of claim 1 or 2, wherein, The preparation method of the spherical hollow multilayer high-entropy metal oxide FeZnCuCoNi-O comprises the following steps: (1) a mixed solution containing iron nitrate nonahydrate, zinc nitrate hexahydrate, copper nitrate hexahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate and glucose monohydrate is subjected to hydrothermal reaction to obtain a spherical high-entropy metal hydroxide; (2) the obtained spherical high-entropy metal hydroxide is annealed to induce metal hydroxide, and the spherical hollow multilayer high-entropy metal oxide FeZnCuCoNi-O is formed; In step (1), the temperature of the hydrothermal reaction is 80-100 DEG C, and the time is 5-10 h; In step (2), the annealing is heating at a rate of 0.5-5 DEG C / min to 450-600 DEG C, and calcining at 450-600 DEG C for 0.5-1.5 h.

4. The supercapacitor electrode material of claim 1, wherein, The specific capacitance of the supercapacitor electrode material is 400-700 F g -1 ; the capacitance retention rate is 75%-90% at 10,000 cycles.

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