A transition metal high-entropy oxide, a preparation method and application thereof

Abstract

The application discloses a transition metal high-entropy oxide, a preparation method and application thereof, and a chemical formula of the transition metal high-entropy oxide is represented as La 1‑x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3(0

Description

Technical Field

[0001] This invention relates to a high-entropy transition metal oxide, its preparation method, and its application, particularly a high-entropy transition metal oxide with excellent electrochemical energy storage performance, its preparation method, and its application in supercapacitors, belonging to the field of supercapacitors. Background Technology

[0002] With the continuous development and utilization of new energy sources, efficient, clean, and low-cost new energy conversion and storage systems will play an increasingly important role. Electrochemical supercapacitors are a new type of energy storage device, and due to their advantages such as high power density, long cycle life, and high safety, they are gradually being widely used in many advanced technology fields, including new energy. However, compared to commercially available lithium-ion batteries and fuel cells, which have high energy density, supercapacitors have a much lower energy density, which seriously hinders their practical application. Electrode materials are the core of supercapacitors' energy storage capabilities; therefore, the key to developing high-energy-density supercapacitors is to develop electrode materials that combine high energy density and high power density.

[0003] Supercapacitors can be mainly classified into two categories based on their energy storage mechanism: electric double-layer capacitors and pseudocapacitive supercapacitors. The charge storage mechanism of electric double-layer capacitors is similar to that of traditional electrostatic capacitors, which is a purely electrostatic adsorption physical process. In this type of electrochemical system, when the external power supply provides a sufficient charging voltage, electrons and ions will be oriented at the electrode / electrolyte interface, thereby generating a capacitor layer with a thickness of nanometers to achieve energy storage. Compared with electric double-layer supercapacitors, pseudocapacitive supercapacitors have a much larger specific capacitance, and therefore the energy density of the device is higher.

[0004] Energy storage processes based on pseudocapacitance mechanisms include: (1) ions in the electrolyte deposit on the electrode surface at a potential higher than the Nernst potential, a process called underpotential deposition; (2) ions in the electrolyte adsorb onto the electrode surface and undergo charge transfer with the electrode, resulting in a reversible redox reaction, a process called redox capacitance; (3) small-radius ions in the electrode solution (such as Li) + Na + OH - Intercalation pseudocapacitance refers to the transfer process that occurs within the electrode material, involving insertion and extraction without altering the material's microstructure. In actual electrochemical reactions, multiple charge storage mechanisms typically work together; therefore, supercapacitors are also known as hybrid energy storage devices.

[0005] Anion-intercalated electrode materials have attracted much attention due to their ability to achieve high specific capacitance with relatively low specific surface area. Among them, ABO3-type oxides with perovskite structures are the most widely studied. Since Mefford et al. proposed the mechanism of electrochemical energy storage in LaMnO3 electrode materials using oxygen ion intercalation behavior in 2014, various ABO3-type perovskite structure transition metal oxide supercapacitor electrode materials have been reported. For example, LaFeO oxide... 3-δ The specific capacitance of SrCoO3 is approximately 200 F / g, while that of SrCoO3 oxide is approximately 170 F / g (F. Xiao et al. Materials Chemistry and Pgysics, 2005, 94221-225; A. Rai et al. Solid State Ionics, 2014, 262, 230-233). Various techniques have been used to improve the energy storage performance of these materials. For example, doping the A-site of ABO3 oxides can improve conductivity and enhance energy storage capacity, or fabricating nanofiber structures can further increase specific capacitance. For instance, the specific capacitance of LaNiO3 oxide nanofibers can reach 1200 F / g (X. Liu et al. Applied Surface Science, 2016, 384, 92-98); SrCoO3 oxide... 2+ Ion A-site doped LaMnO 3-δ This can increase the specific capacitance of the material from 180 F / g to 230 F / g. Although there have been many research reports on anion intercalation electrode materials based on ABO3 type oxides, when these materials are used to assemble supercapacitors, the energy density of the device at a power density of 1000 W / kg is often less than 50 Wh / kg, which cannot meet the requirements of practical applications for both high power density and high energy density.

[0006] High-entropy oxides of transition metals are a novel oxide system developed in recent years. These materials break away from the traditional design concept of doped oxides, with atoms of five or more elements occupying the same lattice site in equimolar or near-equimolar amounts. They exhibit excellent performance in energy storage devices, thus attracting widespread attention from researchers both domestically and internationally. Due to their high configurational entropy, high-entropy materials enable atoms of multiple elements to form solid solutions with a single crystal structure. This ensures the uniform distribution of atoms of various elements in the same lattice site of the crystal and suppresses phase separation, ultimately forming a structurally stable solid solution. Therefore, based on the principle of maximum entropy, by designing the material composition and structure, different atoms of multiple elements occupying the same lattice site can work synergistically, facilitating electron migration and transport, and developing electrode materials with high specific capacity. For example, Y. Yin et al. prepared a high-entropy oxide (Fe) with a spinel structure using the sol-gel method. 0.2 Co 0.2 Cr 0.2 Mn 0.2 Ni 0.2 The 3O4 cathode material exhibits a specific capacity of 332.2 F / g when charged and discharged at a current density of 0.3 A / g (Y. Yin et al., Dalton Transactons, 2023, 52, 9005); Z. Meng et al. developed a hollow spherical perovskite-type high-entropy oxide La(Co) with a multilayer structure. 0.2 Mn 0.2 Fe 0.2 Ni 0.2 Cu 0.2 O3 cathode material exhibits a specific capacitance of 625 F / g, and retains 88% of its capacitance after 10,000 charge-discharge cycles (Z. Meng et al., Chemical Engineering Journal, 457, 2023, 141242). Another example is the La-type perovskite high-entropy oxide anode material with a core-shell structure, prepared by H. Nan et al. using a self-assembly solvothermal method. 0.7 Bi 0.3 (Mn 0he.7-x Fe 0.3 Cu xO3, under a current density of 0.5 A / g, can achieve a specific capacitance of 480.95 C / g, with a working window voltage of -1.0 to 0 V (H. Nan et al., Chemical Engineering Journal, 452, 2023, 139501); In addition, the literature "Preparation and Electrical Performance Study of Lanthanide Perovskite High Entropy Oxides" (Guo Meng, Preparation and Electrical Performance Study of Lanthanide Perovskite High Entropy Oxides, 2022, Master's Thesis of Taiyuan University of Technology, DOI: 10.27352 / d.cnki.gylgu.2022.000928; M. Guo et al., Journal of Advanced Ceramics, 2022, 11(5), 742-753) prepared the electrode material La(Cr) of perovskite transition metal high entropy oxide supercapacitors by precipitation method. 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 O3 and Al 3+ Electrode materials for doped perovskite-type high-entropy oxide supercapacitors: La(CrFeMnCoNiAl) x ) 1 / (5+x) O3 has a maximum specific capacitance of 353.65 F / g, but after 2000 charge-discharge cycles, the specific capacitance retention rate is only about 86%. Although there are many reports on high-entropy oxide supercapacitor electrode materials, the specific capacitance of these reported materials is still not within the ideal range suitable for practical applications, which makes the energy density of supercapacitors based on high-entropy oxide electrode materials still not high.

[0007] The energy storage process of high-entropy oxide electrode materials is mainly based on the reversible redox reaction of transition metal ions and the insertion and extraction transfer of oxygen ions within the electrode material. Therefore, the energy-carrying ions (e.g., OH-) can store energy. - H + Li + The kinetics of diffusion and migration of ions (such as electrons) within materials play a crucial role in their energy storage performance. In high-entropy materials, due to the diverse elements and significant differences in atomic size, local lattice distortion is substantial, hindering the diffusion and migration of energetic ions. This results in the charging and discharging processes of electrochemical energy storage occurring only at or near the electrode surface, preventing the full utilization of the electrode material. This may be a significant reason why the specific capacitance of high-entropy materials is not yet very high. Overcoming the hindrance of lattice distortion to the diffusion and migration of energetic ions and designing high-entropy materials with excellent energy storage performance is a critical technical challenge that urgently needs to be addressed in the development of supercapacitors with both high power density and high energy density. Summary of the Invention

[0008] An object of the present invention is to overcome the deficiencies in the prior art. A transition metal high-entropy oxide La is prepared by a citric acid sol-gel method 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3 is further compounded with nano-silver to prepare a transition metal high-entropy oxide supercapacitor electrode material La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3:yAg (wherein 0 < x < 0.3, 0 < y < 4). The transition metal high-entropy oxide La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3 or La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3:yAg is used as the positive electrode of a supercapacitor and assembled into a supercapacitor together with an activated carbon negative electrode, realizing the device application of the material. The specific capacitance of this transition metal high-entropy oxide electrode material can reach more than 4000 F / g, and the energy density of the corresponding supercapacitor exceeds 100 Wh / kg when the power density is 1200 W / kg. The material and device also exhibit excellent charge-discharge cycle stability and Coulombic efficiency, and after 5000 charge-discharge cycles, the specific capacitance retention rate of the material and the device can reach more than 95%.

[0009] The technical scheme of the present invention is as follows:

[0010] A transition metal high-entropy oxide, the chemical formula of which is represented as: La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3, wherein 0 < x < 0.3; the crystal structure of the transition metal high-entropy oxide has symmetry with a space group of R-3c; Sr 2+Ion doping promotes the transformation of BO6 octahedra with shared vertices to BO6 octahedra with shared edges, thereby forming larger ion diffusion channels within the crystal. In the electrochemical energy storage process, it can overcome the hindrance of energy-carrying ion diffusion and migration caused by the crystal structure distortion caused by multiple atoms occupying the same lattice site. This ensures that the electrochemical reaction during charging and discharging does not only occur on the surface and near the surface of the electrode material. By enhancing the bulk diffusion of energy-carrying ions, the metal ions inside the material can also play a role in energy storage.

[0011] A method for preparing a high-entropy oxide of a transition metal includes the following steps:

[0012] (1) Using La(NO3)3·6H2O, Sr(NO3)2, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O and a 50% (w / w) Mn(NO3)2 solution as raw materials, the above raw materials and reagents are dispersed and dissolved in deionized water according to the stoichiometric ratio. The mixture is stirred under a magnetic stirrer until all the metal salts are dissolved in the deionized water. Then, citric acid monohydrate C6H8O7·H2O is added to the obtained nitrate solution, and a certain amount of ethylene glycol is added at the same time. The molar ratio of C6H8O7·H2O to metal ions is 1.5:1, and the volume ratio of ethylene glycol to nitrate solution is 3:50.

[0013] (2) Continue stirring until the solution is uniform and free of precipitate. Then, transfer the obtained solution to a constant temperature water bath and continue stirring under a water bath temperature of 90°C until the solution forms a uniform and transparent sol. Then, transfer the sol to an oven at a temperature of 180°C for heat treatment for 8-15 hours to form a dry gel precursor.

[0014] (3) After grinding the dry gel precursor, it is transferred to a tube furnace for heating and reaction in an oxygen atmosphere at a temperature within the range of 600-900℃ for 4-8 hours.

[0015] (4) Cooling with the furnace to obtain the transition metal high-entropy oxide.

[0016] Further, in step (1), the molar ratio of C6H8O7·H2O to metal ions is 1.5:1.

[0017] Furthermore, in step (1), the volume ratio of ethylene glycol to nitrate solution is 3:50.

[0018] Further, in step (3), the heating rate is 2℃ / min, and the temperature is maintained at 200℃ for 0.5-2h and at 400℃ for 1-3h.

[0019] Further, the transition metal high-entropy oxide is used as an active material for a positive electrode material of a supercapacitor. A supercapacitor is assembled by using the transition metal high-entropy oxide as the positive electrode material and a negative electrode using activated carbon as an active material.

[0020] Further, a hydrothermal method is used to prepare the transition metal high-entropy transition metal oxide La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3 is compounded with nano-Ag to prepare the composite material La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3:yAg, the process thereof is as follows: weighing AgNO3 and the La prepared by the foregoing citric acid sol-gel method according to the stoichiometry 1- x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3:yAg powder, adding deionized water and stirring, wherein the ratio of the powder to deionized water is approximately that 40 ml of deionized water is added into 150 mg of the powder, simultaneously adding 16-20 mg of polyvinylpyrrolidone (PVP) and 5-10 ml of ethylene glycol, stirring for 30 minutes, finally transferring the solution into a 100 mL reaction kettle with a polytetrafluoroethylene liner, and heating in an oven at 160°C for 3-8 hours. After repeated centrifugation, washing with water and drying, La represented by the chemical formula is obtained 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3:yAg composite material.

[0021] The foregoing transition metal high-entropy oxide with the chemical formula La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3 (0<x<0.3), or the chemical formula La 1-x Sr x (Cr0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3:yAg(0<x<0.3, 0<y<4) composite material, which is used as an active material to fabricate an electrode serving as the positive electrode of a supercapacitor. The electrode fabrication process is as follows: nickel foam is used as a current collector, the active material, conductive carbon black, and a binder (e.g., polyvinylidene fluoride PVDF) are dispersed in an N-methylpyrrolidone solution with a mass percentage of 15% PVDF at a mass ratio of 7:1.5:1.5 to form a uniform and stable coating. The coating is uniformly applied onto the surface of the nickel foam by a doctor blade method, dried at 50°C, and finally left to stand under a pressure of 10 MPa for 2 minutes to prepare a positive electrode sheet.

[0022] Using activated carbon as the negative electrode active material of the supercapacitor, the activated carbon is dispersed in an N-methylpyrrolidone solution with a mass percentage of 15% PVDF, a uniform and stable coating is prepared with a mass ratio of activated carbon to PVDF of 85:15, the coating is applied onto the surface of the current collector by the doctor blade method, dried at 50°C, and finally left to stand under a pressure of 10 MPa for 2 minutes to prepare a negative electrode sheet.

[0023] The positive and negative electrodes satisfy m + / m - =(C - ×ΔV - ) / (C + ×ΔV + ) to assemble a supercapacitor, where m respectively represents the coating mass of the active material on the positive and negative electrodes of the capacitor, C respectively represents the specific capacitance of the single positive and negative electrodes, and ΔV represents the window voltage of the single electrode of the positive and negative electrode materials. First, the positive / negative electrode sheets are respectively immersed in a KOH electrolyte with a concentration of 6 mol / L for 24 hours for activation, then tabs are welded on the two electrodes as lead-out electrodes, the two electrodes are symmetrically and closely attached to both sides of an ionic diaphragm, then the electrodes and the ionic diaphragm are sealed with hard plastic, and the electrolyte is injected therein to prepare the supercapacitor.

[0024] The present invention is based on the "maximum entropy principle", that is: by increasing the configurational entropy of the material, atoms of multiple different elements occupy the same lattice site of the material, suppress phase separation, and form a solid solution phase with stable structure. Five equimolar transition metal atoms are introduced into the B-site of the ABO3-type oxide to prepare a high-entropy transition metal oxide. Due to the synergistic effect between electron-donating atoms and electron-accepting atoms among these five metal atoms, such materials can obtain high pseudocapacitance. Meanwhile, the present invention uses Sr 2+ ion doping to regulate the electrochemical energy storage performance of high-entropy oxides, and the effect of this technology is different from that of Sr in conventional perovskite-type oxides2+ Ion doping. For traditional perovskite-type oxide materials (e.g., LaMnO3) with only one type of transition metal atom at the B-site, Sr 2+ ion doping regulates the valence of B-site metal atoms on the one hand, and increases the carrier concentration of the material on the other hand, enhances the electrical conductivity of the material, and can improve the energy storage capacity of the material. However, the crystal structure of the material generally does not change, so this enhancement effect is relatively small. In contrast, in the present invention, Sr is doped into high-entropy oxide materials 2+ ions to trigger the transformation of vertex-sharing BO6 octahedra to edge-sharing BO6 octahedra, thereby forming large ion diffusion channels in the crystal, which overcomes the hindrance to the diffusion and migration of energy-carrying ions caused by local lattice distortion induced by multi-atom co-occupation at the same site, so that the electrochemical reaction during charge and discharge does not only occur on the surface and near-surface of the electrode material. By enhancing the bulk diffusion of energy-carrying ions, the metal ions inside the material can also contribute to energy storage. In addition, the present invention further enhances the energy storage capacity of the material by compounding transition metal high-entropy oxide with nano-Ag. Therefore, the transition metal high-entropy oxide supercapacitor electrode material and the composite material thereof with nano-Ag of the present invention realize an electrode material with ultra-high energy storage performance through the synergistic effect of multiple technical means including entropy regulation, crystal structure regulation, electronic state regulation and interface regulation.

[0025] Beneficial effects of the present invention include:

[0026] (1) The present invention provides a supercapacitor electrode material with high specific capacitance and good charge-discharge cycle stability. Examples show that the transition metal high-entropy oxide La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3 (0<x<0.3) as the active material of the electrode, when charged and discharged at 1 A / g, the specific capacity of the material can reach 3086 F / g; after 5000 cycles of charge and discharge at a current density of 10 A / g, the retention rate of specific capacitance reaches 90.63%, and the Coulombic efficiency is 99.23%. The electrode material of ABO3 perovskite high-entropy transition metal oxide supercapacitor La(Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3 prepared by precipitation method reported in the literature "Preparation and Electrical Properties of Lanthanide Perovskite High-Entropy Oxides", and B-site Al 3+ doped perovskite high-entropy transition metal oxide La(CrFeMnCoNiAl x )1 / (5+x) O3 has a maximum specific capacitance of only 353.65 F / g, and its specific capacitance decays to about 86% after 2000 charge-discharge cycles. In contrast, the specific capacitance of the material provided by this invention is more than 8-17 times that reported in the literature, and the material's charge-discharge cycle stability is also much better, resulting in unexpected technical effects.

[0027] (2) The method for preparing high-entropy transition metal oxides provided by the present invention is simple to operate and has low production cost;

[0028] (3) The high-entropy transition metal oxide provided by this invention is used as an active material in the positive electrode of a supercapacitor and assembled with an anode material of activated carbon to form a supercapacitor. When the power density of the device is 1780 W / kg, the energy density reaches 80 Wh / kg, which is more than 10 times the energy density of currently commercially available supercapacitors. Therefore, the high-entropy transition metal oxide supercapacitor provided by this invention has both high power density and high energy density, and the device has good charge-discharge cycle stability and high coulombic efficiency. Attached Figure Description

[0029] Figure 1 High-entropy oxides La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 X-ray diffraction patterns of O3 (x = 0.05, 0.10, 0.15, 0.20), with insets showing the crystal structure of the material;

[0030] Figure 2 High-entropy oxides La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Scanning electron microscope image of O3;

[0031] Figure 3 :La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic voltammetry curves of the O3 electrode measured at different voltage scan rates;

[0032] Figure 4 :La 0.90 Sr0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The charging and discharging curves of the O3 electrode at different current densities are shown in the inset, which shows the specific capacitance (SC) values ​​of charging and discharging at different current densities.

[0033] Figure 5 :La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic stability of the O3 electrode at a current density of 10 A / g;

[0034] Figure 6 High-entropy oxides La(Cr) 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 X-ray diffraction pattern of O3;

[0035] Figure 7 :La(Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic stability of the O3 electrode at a current density of 10 A / g;

[0036] Figure 8 Composite material La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 X-ray diffraction pattern of O3:yAg; HEO in the figure refers to high-entropy oxides;

[0037] Figure 9 :La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic voltammetry curves of the O3:Ag electrode at different voltage scan rates;

[0038] Figure 10 :La 0.90 Sr0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The charge-discharge curves of the O3:Ag electrode at different current densities are shown in the inset, which shows the specific capacitance (SC) values ​​of the charge-discharge at different current densities.

[0039] Figure 11 :La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic stability of O3:Ag electrode under charge-discharge conditions at a current density of 10 A / g;

[0040] Figure 12 High-entropy oxide supercapacitors La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Energy density of O3 / / C at different power densities;

[0041] Figure 13 High-entropy oxide supercapacitors La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic stability and coulombic efficiency of O3 / / C under charge-discharge at a current density of 10 A / g;

[0042] Figure 14 Supercapacitor La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Energy density of O3:Ag / / C at different power densities;

[0043] Figure 15 Supercapacitor La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2Cyclic stability and coulombic efficiency of O3:Ag / / C under charge and discharge at a current density of 10A / g. Detailed implementation method:

[0044] Example 1: High-entropy transition metal oxide La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Preparation of O3 (x = 0.05, 0.10, 0.15, 0.20) supercapacitor electrode materials

[0045] The process steps are as follows: Using La(NO3)3·6H2O, Sr(NO3)2, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, and a 50% (w / w) Mn(NO3)2 solution as raw materials, firstly, the above raw materials and reagents are dispersed and dissolved in deionized water according to the stoichiometric ratio. The mixture is stirred for ten minutes under a magnetic stirrer. After all the metal salts have dissolved in the deionized water, citric acid monohydrate (C6H8O7·H2O) is added to the obtained nitrate solution, along with a certain amount of ethylene glycol. The molar ratio of C6H8O7·H2O to metal ions is 1.5:1, and the volume ratio of ethylene glycol to the solution is 3:50. Continue stirring until the solution is homogeneous and free of precipitate. Transfer the resulting solution to a constant-temperature water bath and continue stirring at 90°C until a homogeneous and transparent sol is formed. Transfer the sol to an oven at 180°C and heat-treat for 12 hours to form a dry gel precursor. Grind the dry gel precursor and transfer it to a tube furnace. React at 850°C for 5 hours in an oxygen atmosphere. The heating rate is 2°C / min, and the temperature is maintained at 200°C for 30 minutes, 400°C for 2 hours, and finally at the final reaction temperature for 5 hours. After furnace cooling, grind the resulting high-entropy transition metal oxide nanoparticles.

[0046] like Figure 1 The transition metal high-entropy oxide La shown 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The X-ray diffraction pattern of O3 (x = 0.05, 0.10, 0.15, 0.20) shows that all diffraction peaks correspond to the peak positions on the standard card PDF 86-1664, indicating that a pure-phase high-entropy oxide material was prepared by the citric acid sol-gel method without phase separation. Furthermore, the high-entropy oxide La... 1-xSr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The crystal structure of O3 has symmetry characteristics with space group R-3c, such as... Figure 1 As shown in the inner illustration.

[0047] like Figure 2 The high-entropy oxide La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The scanning electron microscope image of O3 shows that the particle size distribution of the nanocrystals of the nanoparticles is in the range of 10-200 nm.

[0048] Example 2: Fabrication of a high-entropy oxide electrode

[0049] Using nickel foam as the current collector, a transition metal high-entropy oxide was coated onto the nickel foam sheet to fabricate an electrode. The fabrication process was as follows: transition metal high-entropy oxide powder, conductive carbon black, and polyvinylidene fluoride (PVDF) binder were dispersed in a 7:1.5:1.5 mass ratio in an N-methylpyrrolidone solution containing 15% PVDF to form a uniform and stable coating. This coating was then uniformly coated onto the surface of the nickel foam using a blade coating method and dried at 50°C. Finally, the electrode was allowed to stand at 10 MPa for 2 minutes to form the positive electrode sheet. The mass density of the active material on the electrode sheet was 3 mg / cm³. 2 The surface area of ​​the electrode sheet is 1 cm². 2 .

[0050] Example 3: High-entropy oxide La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Energy storage performance test of O3

[0051] The dried electrode sheet was activated by immersing it in 6 mol / L NaOH electrolyte for 24 h and used as the working electrode. Together with the Hg / HgO reference electrode and the platinum sheet counter electrode, it was fixed in an electrolytic cell containing electrolyte to form a three-electrode system for cyclic voltammetry scanning and charge-discharge performance testing.

[0052] like Figure 3 La shown 0.90 Sr 0.10 (Cr0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic voltammetry curves of the O3 electrode at different voltage scan rates show that high-entropy oxides mainly achieve energy storage through reversible redox reactions of transition metal ions, exhibiting obvious pseudocapacitive characteristics.

[0053] like Figure 4 La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The charge-discharge curves of the O3 electrode at different current densities are shown in the inset, where the specific capacitance (SC) values ​​are the values ​​of charge and discharge at different current densities. This indicates that the specific capacitance of the material is as high as 3086 F / g when the charge-discharge current density is 1 A / g.

[0054] like Figure 5 The high-entropy oxide La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The cycle stability of the O3 electrode under charge-discharge at a current density of 10 A / g shows that after 5000 charge-discharge cycles, the specific capacitance retention rate reaches 90.63%.

[0055] Example 4: High-entropy oxide La(Cr) 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Preparation of O3

[0056] In order to react with Sr 2+ The effect of ion doping on the regulation of the structure of high-entropy oxides was also demonstrated by our preparation of Sr-free oxides using the citric acid sol-gel method. 2+ Ion-doped high-entropy oxides La(Cr) 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2The process steps for obtaining nitrate solution (NO3) are as follows: Using La(NO3)3·6H2O, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O, along with a 50% (w / w) Mn(NO3)2 solution, the raw materials are first dispersed and dissolved in deionized water according to stoichiometric ratios. The solution is stirred for ten minutes using a magnetic stirrer until all metal salts are dissolved in the deionized water. Then, citric acid monohydrate (C6H8O7·H2O) is added to the resulting nitrate solution, along with a certain amount of ethylene glycol. The molar ratio of C6H8O7·H2O to metal ions is 1.5:1, and the volume ratio of ethylene glycol to the solution is 3:50. Continue stirring until the solution is homogeneous and free of precipitate. Transfer the resulting solution to a constant-temperature water bath and stir continuously at 90°C until a homogeneous and transparent sol is formed. Transfer the sol to an oven at 180°C and heat-treat for 12 hours to form a dry gel precursor. Grind the dry gel precursor and transfer it to a tube furnace. React at 850°C for 5 hours in an oxygen atmosphere. The heating rate is 2°C / min, and the temperature is maintained at 200°C for 30 minutes, 400°C for 2 hours, and finally at the final reaction temperature for 5 hours. After cooling in the furnace, grind the solution to obtain a Sr-free product. 2+ Ion-doped high-entropy transition metal oxide nanopowders.

[0057] like Figure 6 The image shows the absence of Sr. 2+ Ion-doped high-entropy oxides La(Cr) 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The X-ray diffraction pattern of O3 shows that all diffraction peaks correspond to the peak positions on the standard card PDF 89-2470, indicating that a pure-phase high-entropy oxide material was also prepared via the citric acid sol-gel method. This material has an orthogonal symmetric crystal structure, indicating that the BO6 octahedra are connected by oxygen atoms sharing vertices, and the crystal has a space group of Pnma symmetry, which is consistent with Sr 2+ Ion-doped high-entropy oxide La 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 O3 is significantly different.

[0058] The method in Implementation Example 2 was used to create a product without Sr. 2+ Ion-doped high-entropy oxides of transition metals La(Cr) 0.2 Fe 0.2 Mn0.2 Co 0.2 Ni 0.2 The electrode of O3 was used to test La(Cr) using the method in Example 3. 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The charge-discharge cycle stability of the O3 electrode at a current density of 10 A / g is as follows: Figure 7 As shown, after 5000 charge-discharge cycles, the specific capacitance retention rate is only 67.1%, which is much lower than that of Sr. 2+ Ion-doped high-entropy oxide La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 )O3.

[0059] Example 5: Composite material La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Preparation of O3:yAg (y = 0.5, 1.0, 1.5, 2.0, 2.5, 3.0)

[0060] First, La was prepared according to the method in Example 1. 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 O3 high-entropy oxide powder was obtained, and then a hydrothermal method was used to realize the transition metal high-entropy oxide La. 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 O3 and nano-Ag composites. The preparation process of the composite material is as follows: AgNO3 and La2O3 prepared using the citric acid sol-gel method are weighed at a molar ratio of y:1. 0.9 Sr 0.1 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2150 mg of O3 powder was added to 40 mL of deionized water and stirred. Simultaneously, 20 mg of polyvinylpyrrolidone (PVP) and 5 mL of ethylene glycol were added, and the mixture was stirred for 30 minutes. Finally, the solution was transferred to a 100 mL polytetrafluoroethylene-lined reactor and heated in an oven at 160 °C for 5 hours. After repeated centrifugation and washing with water, the product was dried to obtain the chemical formula La. 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 O3:yAg composite material.

[0061] like Figure 8 The high-entropy oxide La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 La, a composite material of O3 and nano-Ag. 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The X-ray diffraction pattern of O3:yAg shows that in addition to the diffraction peaks of high entropy oxide (HEO), diffraction peaks of nano-metal Ag can also be observed. The X-ray diffraction peaks of nano-metal Ag correspond to the card in PDF87-0717.

[0062] Implementation Example 6: Composite Material La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Electrode fabrication of O3:Ag

[0063] Using nickel foam as the current collector, the composite material La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2O3:Ag was coated onto the surface of nickel foam to form an electrode. The manufacturing process was as follows: The composite material, conductive carbon black, and polyvinylidene fluoride (PVDF) binder were dispersed in a 7:1.5:1.5 mass ratio in a 15% N-methylpyrrolidone (PVDF) solution to form a uniform and stable coating. This coating was then uniformly coated onto the nickel foam surface using a blade coating method and dried at 50°C. Finally, it was allowed to stand at 10 MPa for 2 minutes to form the positive electrode sheet. The mass density of the active material on the electrode sheet was 3 mg / cm³. 2 The surface area of ​​the electrode sheet is 1 cm². 2 .

[0064] Implementation Example 7: Composite Material La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Energy storage performance test of O3:Ag

[0065] The dried electrode sheet was activated by immersing it in 6 mol / L NaOH electrolyte for 24 hours and used as the working electrode. Together with the Hg / HgO reference electrode and the platinum sheet counter electrode, it was fixed in an electrolytic cell containing electrolyte to form a three-electrode system for cyclic voltammetry scanning and charge-discharge performance testing.

[0066] like Figure 9 La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic voltammetry curves of the O3:Ag electrode measured at different voltage scan rates indicate that the composite material also exhibits significant pseudocapacitive characteristics. In addition to the reversible redox reactions of the transition metal oxides, Ag also undergoes significant reversible redox reactions during the energy storage process of the composite material, and the two reactions mutually promote each other. Figure 3 and Figure 9 The test results show that, at the same voltage scan rate, the current response of the composite material electrode is much greater than that of the transition metal high-entropy oxide electrode without composite nano-Ag.

[0067] like Figure 10 La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2The charge-discharge curves of the O3:Ag electrode at different current densities are shown, with the inset plots representing the specific capacitance (SC) values ​​at different current densities. This indicates that the specific capacitance of the material reaches as high as 4866 F / g at a charge-discharge current density of 1 A / g. (Comparison) Figure 4 and Figure 10 The test results of the composite material La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The specific capacity of the O3:Ag electrode is higher than that of the high-entropy oxide La without composite nano-Ag. 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The O3 electrode increased by 1780 F / g.

[0068] like Figure 11 La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The cycle stability of the O3:Ag electrode under charge-discharge at a current density of 10 A / g shows that after 5000 charge-discharge cycles, the specific capacitance retention rate reaches 96.8%.

[0069] Implementation Example 8: High-entropy oxide La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 O3 / / C supercapacitor

[0070] With high-entropy oxide La 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2The O3 electrode serves as the positive electrode of the supercapacitor, and the activated carbon electrode serves as the negative electrode, forming a supercapacitor. The high-entropy oxide electrode is fabricated using the method described in Example 2. The activated carbon electrode is prepared by dispersing activated carbon in a PVDF solution containing 15% N-methylpyrrolidone by mass, resulting in a uniform and stable coating with a PVDF mass ratio of 85:15. This coating is then applied to the surface of the current collector using a scraping method, dried at 50°C, and finally allowed to stand at 10 MPa for 2 minutes to form the negative electrode sheet.

[0071] The selection of positive and negative electrodes should be based on the mass of the active material satisfying m + / m - =(C - ×ΔV - ) / (C + ×ΔV + The following formulas are used to assemble a supercapacitor: m represents the coating mass of the positive and negative electrode active materials, C represents the specific capacitance of a single positive and negative electrode, and ΔV represents the window voltage of a single positive and negative electrode. First, the positive and negative electrode sheets are immersed in a 6 mol / L KOH electrolyte for 24 hours for activation. Then, tabs are welded onto the two electrodes as lead-out electrodes. The two electrodes are symmetrically attached to both sides of an ion-exchange membrane. The electrodes and the ion-exchange membrane are then sealed with hard plastic, and electrolyte is injected to prepare the supercapacitor.

[0072] like Figure 12 The high-entropy oxide supercapacitor La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The energy density of O3 / / C at different power densities indicates that when the power density is 1780W / kg, the energy density reaches 80Wh / kg.

[0073] like Figure 13 The high-entropy oxide supercapacitor La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic stability and coulombic efficiency of O3 / / C at a current density of 10 A / g were measured. The results showed that after 5000 charge-discharge cycles, the specific capacitance retention reached 84.96% and the coulombic efficiency was 99.23%.

[0074] Implementation Example 9: Composite Material La 0.90 Sr0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 O3:Ag / / C supercapacitor

[0075] La composite material 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 A supercapacitor is assembled using an O3:Ag electrode as the positive electrode and an activated carbon electrode as the negative electrode. The composite material electrode is fabricated using the method described in Example 2. The activated carbon electrode is prepared by dispersing activated carbon in an N-methylpyrrolidone solution containing 15% PVDF by mass, resulting in a uniform and stable coating with a PVDF mass ratio of 85:15. This coating is then applied to the surface of the current collector using a scraping method, dried at 50°C, and finally allowed to stand at 10 MPa for 2 minutes to form the negative electrode sheet.

[0076] The selection of positive and negative electrodes should be based on the mass of the active material satisfying m + / m - =(C - ×ΔV - ) / (C + ×ΔV + The following formulas are used to assemble a supercapacitor: m represents the coating mass of the positive and negative electrode active materials, C represents the specific capacitance of a single positive and negative electrode, and ΔV represents the window voltage of a single positive and negative electrode. First, the positive and negative electrode sheets are immersed in a 6 mol / L KOH electrolyte for 24 hours for activation. Then, tabs are welded onto the two electrodes as lead-out electrodes. The two electrodes are symmetrically attached to both sides of an ion-exchange membrane. The electrodes and the ion-exchange membrane are then sealed with hard plastic, and electrolyte is injected to prepare the supercapacitor.

[0077] like Figure 14 The supercapacitor La shown 0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 The energy density of O3:Ag / / C at different power densities indicates that when the power density is 1200W / kg, its energy can be as high as 102Wh / kg.

[0078] like Figure 15 The supercapacitor La shown0.90 Sr 0.10 (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 Cyclic stability and coulombic efficiency of O3:Ag / / C under a current density of 10A / g were measured, indicating that after 5000 charge-discharge cycles, the specific capacitance retention reached 95.49% and the coulombic efficiency reached 99.96%.

Claims

1. A high-entropy transition metal oxide, characterized in that, The chemical formula of this high-entropy transition metal oxide is La. 1-x Sr x (Cr 0.2 Fe 0.2 Mn 0.2 Co 0.2 Ni 0.2 O3, where 0 < x < 0.3; the crystal structure of this high-entropy transition metal oxide has a space group of R-3c symmetry; This transition metal high-entropy oxide is produced by doping Sr. 2+ Ions promote the transformation of BO6 octahedra with shared vertices into BO6 octahedra with shared edges, thereby forming larger ion diffusion channels within the material lattice. In the electrochemical energy storage process, this can overcome the hindrance to the diffusion and migration of energy-carrying ions caused by the distortion of the crystal structure due to multiple atoms occupying the same lattice site. This ensures that the electrochemical reactions during charging and discharging do not only occur on and near the surface of the electrode material. By enhancing the bulk diffusion of energy-carrying ions, metal ions inside the material can also play a role in energy storage. The preparation method of the high-entropy transition metal oxide includes the following steps: (1) Using La(NO3)3·6H2O, Sr(NO3)2, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O and a 50% (w / w) Mn(NO3)2 solution as raw materials, the above raw materials and reagents are dispersed and dissolved in deionized water according to the stoichiometric ratio. The mixture is stirred under a magnetic stirrer until all the metal salts are dissolved in the deionized water. Then, citric acid monohydrate C6H8O7∙H2O is added to the obtained nitrate solution. The molar ratio of C6H8O7∙H2O to the metal ions is 1.5:

1. At the same time, a certain amount of ethylene glycol is added. The volume ratio of ethylene glycol to the nitrate solution is 3:

50. (2) Continue stirring until the solution is uniform and free of precipitate. Then, transfer the obtained solution to a 90 ℃ constant temperature water bath and continue stirring until the solution forms a uniform and transparent sol. Then, transfer the sol to an oven and heat-treat it at 180 ℃ for 8-15 hours to form a dry gel precursor. (3) After grinding the dry gel precursor, it is transferred to a tube furnace for heating and reaction in an oxygen atmosphere at a temperature within the range of 600-900 °C for 4-8 h. (4) Cool with the furnace to obtain the transition metal high entropy oxide.

2. The high-entropy transition metal oxide according to claim 1, characterized in that, In step (3), the heating rate is 2 °C / min.

3. The high-entropy transition metal oxide according to claim 2, characterized in that, In step (3), the heating temperature is raised to 200 ℃ and kept at 0.5-2 h, and then kept at 400 ℃ for 1-3 h.

4. An application of the high-entropy transition metal oxide as described in claim 1, characterized in that, This high-entropy transition metal oxide is used as a reactive material for the positive electrode material of supercapacitors.

5. The application according to claim 4, characterized in that, A supercapacitor is assembled using this high-entropy transition metal oxide as the positive electrode material and activated carbon as the negative electrode material.

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