Preparation method of cobalt-based oxide and application of cobalt-based oxide in preparation of positive electrode material of lithium-sulfur battery

Abstract

The invention discloses a preparation method of a cobalt-based oxide and application of the cobalt-based oxide in preparation of a positive electrode material of a lithium-sulfur battery, and relates to the technical field of battery materials. The invention aims to solve the problems of insufficient active sites, limited catalytic efficiency, high cost, poor stability and poor synergistic effect with a sulfur positive electrode of the existing lithium-sulfur battery positive electrode electrocatalyst. The method comprises the following steps: 1, preparing a precursor solution; 2, coprecipitation reaction; 3, collecting and drying; and 4, calcining. The cobalt-based oxide is used for preparing the positive electrode material of the lithium-sulfur battery, and the cobalt-based oxide remarkably improves the adsorption and catalytic conversion capability on polysulfide, remarkably reduces the nucleation and decomposition energy barrier of Li2S and efficiently inhibits the shuttle effect of the polysulfide, so that the discharge capacity and cycle stability of the lithium-sulfur battery are improved. The method is simple in process, simple and convenient in procedure and method operation, low in cost and beneficial to realization of industrial large-scale production, and has remarkable economic advantages.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a method for preparing a cobalt-based oxide and application of the cobalt-based oxide in preparing a positive electrode material for a lithium-sulfur battery. Background Art

[0002] As the global demand for clean energy continues to increase, efficient and safe energy storage technologies are crucial to ensuring the stability and security of energy supply. Lithium-sulfur batteries, as a promising energy storage technology, have a theoretical specific energy of up to 2600W·h / kg, which is more than six times the theoretical energy density of lithium cobalt oxide graphite batteries. This gives them huge application potential in areas with extremely high energy density requirements, such as electric vehicles, drones, and aerospace. However, the research on lithium-sulfur batteries involves many key technical difficulties, such as the shuttle effect of polysulfides, volume changes of the sulfur positive electrode and lithium negative electrode, and slow reaction kinetics of the sulfur positive electrode. Solving these problems will promote the development of related disciplines such as battery materials science and electrochemistry, promote the research and development of new electrode materials and electrolyte materials, and the innovation of lithium-sulfur battery preparation processes, and provide reference and technical support for the development of other types of batteries.

[0003] In order to solve the polysulfide shuttle effect, current research is mainly carried out from the aspects of cathode material modification, electrolyte optimization, and diaphragm modification. In terms of cathode material modification, by introducing carrier materials with high specific surface area and good conductivity, such as carbon nanotubes, graphene, etc., polysulfides can be physically adsorbed to a certain extent. However, due to the weak interaction between carbon materials and polysulfides, it is difficult to effectively suppress the shuttle effect. At the same time, the development of catalytically active cathode materials can accelerate the redox reaction kinetics of polysulfides, promote their rapid conversion to final products, and reduce accumulation in the electrolyte, which is an effective way to improve the performance of lithium-sulfur batteries. At present, the research on cathode catalysts for lithium-sulfur batteries is developing from single material optimization to multi-dimensional innovations such as heterojunction synergy, single-atom precision control, and biomimetic structure design.

[0004] Transition metal oxides have attracted widespread attention in the field of lithium-sulfur battery cathode catalysts due to their unique electronic structure and catalytic activity. Among them, cobalt-based oxides are considered to be highly promising cathode catalyst materials for lithium-sulfur batteries due to their certain adsorption and catalytic conversion capabilities for polysulfides. However, traditional cobalt-based oxides still have some problems in practical applications, such as insufficient active sites, limited catalytic efficiency, and poor synergy with sulfur cathodes. As a result, their suppression of the polysulfide shuttle effect is less than ideal, and they cannot fully meet the high performance requirements of lithium-sulfur batteries.

[0005] Therefore, the development of a cobalt-based oxide catalyst with high activity, high stability and the ability to effectively inhibit the polysulfide shuttle effect and its preparation method are of great practical significance for promoting the practical application of lithium-sulfur batteries. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems of insufficient active sites, limited catalytic efficiency, high cost, poor stability and poor synergy with the sulfur positive electrode of existing lithium-sulfur battery positive electrode electrocatalysts, and to provide a method for preparing cobalt-based oxides and their application in preparing lithium-sulfur battery positive electrode materials.

[0007] A method for preparing a cobalt-based oxide, comprising six elements: Fe, Co, Ni, Mn, Zn, and O, and having a multi-layer hollow spherical shell morphology with a "gas port," wherein the outer shell has a diameter of 1 to 3 μm and a wall thickness of 60 nm to 70 nm, and the inner shell has a decreasing diameter and thickness, and the shell is composed of polycrystalline nanoparticles. The preparation method is specifically carried out in the following steps:

[0008] 1. Preparation of precursor solution:

[0009] C6H 12 O6·H2O, Fe(NO3)2·9H2O, Zn(NO3)2·6H2O, Ni(NO3)2·6H2O, Co(NO3)2·6H2O, and Mn(NO3)2·4H2O were added to deionized water and stirred until completely dissolved to obtain a clear solution A;

[0010] 2. Coprecipitation reaction:

[0011] The transparent solution A is transferred to a polytetrafluoroethylene-lined stainless steel autoclave, and the polytetrafluoroethylene-lined stainless steel autoclave is then transferred to a high-temperature oven for hydrothermal reaction at 170°C to 190°C for a period of time to obtain product B;

[0012] 3. Collection and drying:

[0013] Product B was vacuum filtered to collect the black fluffy precipitate, which was then dried in an oven to obtain product C;

[0014] 4. Calcination treatment:

[0015] The product C is placed in a high-temperature ceramic boat, which is then transferred to a muffle furnace or a tube furnace. The temperature is then raised to 500° C. to 550° C. in an air atmosphere and kept warm for a period of time to obtain a cobalt-based oxide.

[0016] A cobalt-based oxide is used to prepare a positive electrode material for a lithium-sulfur battery, which is specifically completed by the following steps:

[0017] Multi-walled carbon nanotubes, sulfur, and cobalt-based oxide are mixed and ground uniformly in a mass ratio of 2:7:1, and then melted at 150°C to 160°C for 10 hours to 12 hours to obtain a composite material; the composite material, conductive carbon black, and polyvinylidene fluoride are mixed in N-methylpyrrolidone in a mass ratio of 8:1:1 to obtain a uniform suspension; the uniform suspension is dropped onto a carbon cloth, and then vacuum-dried at 60°C to 70°C for 10 hours to 12 hours to obtain a lithium-sulfur battery positive electrode material, wherein the sulfur loading amount is 1 mg / cm2 to 2 mg / cm2;

[0018] The volume ratio of the total mass of the composite material, conductive carbon black and polyvinylidene fluoride to N-methylpyrrolidone is 100 mg:2300 μL.

[0019] Beneficial effects of the present invention:

[0020] 1. High catalytic activity:

[0021] The multi-layer hollow spherical shell morphology of a cobalt-based oxide of the present invention has a high specific surface area and multiple adjustable shell spaces, shell composition, shell thickness, and porosity, providing a large number of adsorption sites and active sites. Furthermore, the novel cobalt-based oxide comprises six elements: Fe, Co, Ni, Mn, Zn, and O. Fe, Co, Ni, and Mn primarily occupy the octahedral body-center positions in the spinel structure, while Zn primarily occupies the tetrahedral body-center position. The synergistic effect of these elements significantly and cleverly optimizes the electronic structure, thereby enhancing the catalytic activity of the material.

[0022] 2. Good charge conduction ability:

[0023] The cobalt-based oxide of the present invention is composed of six elements: Fe, Co, Ni, Mn, Zn, and O. Among them, Fe, Co, Ni, and Mn mainly occupy the octahedral body center position in the spinel structure. The electron exchange between each atom can form a fast transfer channel of electrons and spin states, thereby significantly improving the charge conduction ability of the material (the conductivity is 0.48mS·cm -1 );

[0024] 3. Alleviate structural collapse caused by volume expansion:

[0025] The cobalt-based oxide of the present invention has a multi-layer hollow spherical shell morphology, with multiple shells arranged sequentially from the outside to the inside, and each shell has its own corresponding inner cavity. As the sulfur cathode host of a lithium-sulfur battery, the multi-layer hollow structure provides a buffer space for the volume change of the electrode material during the charge and discharge reaction, preventing the structure from collapsing due to stress accumulation.

[0026] 4. Good electrochemical performance:

[0027] The cobalt-based oxide of the present invention is used in the positive electrode material of lithium-sulfur batteries. The cobalt-based oxide significantly improves the adsorption and catalytic conversion capabilities of polysulfides, while significantly reducing the nucleation and decomposition energy barriers of Li2S, effectively suppressing the shuttle effect of polysulfides, thereby improving the discharge capacity and cycle stability of lithium-sulfur batteries.

[0028] The lithium-sulfur battery positive electrode material prepared by the present invention is used to assemble a lithium-sulfur battery. During the charge and discharge process, the low-valent metal ions (Co 2+ 、Fe 2+ 、Ni 2+ 、Mn 2+ 、Mn 3+ ) dominates the reduction reaction of the sulfur cathode, while high-valent metal ions (Co 3+ 、Fe 3+ 、Ni 3+ 、Mn 4+ ) dominates the oxidation process. Among them, since 92% of Ni atoms occupy octahedral positions, Ni 2+ It plays a key role in affecting the deposition of Li2S. During the discharge process, when the discharge reaches 2.11V, some Co 2+ 、Fe 2+ 、Ni 2+ 、Mn 2+ 、Mn 3+ Begins to be oxidized to Co 3+ 、Fe 3+ 、Ni 3+ 、Mn 4+ ; With the increase of discharge depth (2.10V and 1.70V), more low-valent metal ions are oxidized to high-valent ions; during the charging process, part of Co 3+ 、Fe 3+ 、Ni 3+ 、Mn 4+ Gradually reduced to Co 2+ 、Fe 2+ 、Ni 2+ 、Mn 2+ 、Mn 3 + , and finally returned to its initial state at 2.80 V. Among them, Co occupying the octahedral center 3+ It plays an important role in the decomposition of Li2S. During the entire redox reaction, the valence state of the Zn atom remains unchanged;

[0029] The lithium-sulfur battery cathode material prepared by the present invention is used to assemble a lithium-sulfur battery. At a current density of 0.1C, the battery capacity can reach 1263.2mAhg -1; In the process of increasing the current density from 0.1 to 5.0C, 1238.4, 1045.5, 949.7, 871.9, 802.7 and 622.3 mAh g were achieved respectively -1 When the current density was switched back to 0.2 and 0.1C, the capacity recovered to 984.9 and 1059.0 mAh g -1 , indicating that it can withstand high current density while maintaining good structural stability and electrochemical reversibility; during the charge and discharge process, the cobalt-based oxide exhibits strong adsorption capacity and high catalytic conversion ability for the intermediate product lithium polysulfide, while significantly reducing the nucleation and decomposition energy barriers of Li2S; at a current density of 0.5C, after 300 cycles, the capacity retention rate is 92.8%; at a current density of 2.0C, it still shows excellent cycle performance during 1500 cycles, with a capacity decay rate of only 0.042% per cycle;

[0030] 5. The preparation process is easy to achieve large-scale production:

[0031] The cobalt-based oxide of the present invention uses precursors that are abundant on Earth, is environmentally friendly, and has low cost. The oxide has a simple preparation process, simple and convenient procedures and methods, and is low-cost, facilitating industrial-scale production and offering significant economic advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a scanning electron microscope image of a cobalt-based oxide prepared in Example 1;

[0033] Figure 2 This is a transmission electron microscope image of a cobalt-based oxide prepared in Example 1;

[0034] Figure 3 for Figure 2 A local magnified image of

[0035] Figure 4 A high-resolution transmission electron microscope image of a cobalt-based oxide prepared in Example 1;

[0036] Figure 5 A selected electron diffraction image of a cobalt-based oxide prepared in Example 1;

[0037] Figure 6 This is a Rietveld refined X-ray diffraction spectrum of a cobalt-based oxide prepared in Example 1;

[0038] Figure 7 A high-angle annular dark-field scanning transmission electron microscope image of a cobalt-based oxide prepared in Example 1 and corresponding element mapping images of Fe, Co, Ni, Mn, Zn, and O;

[0039] Figure 8 The atomic percentage of a cobalt-based oxide prepared in Example 1 obtained by energy dispersive spectroscopy measured by a scanning electron microscope system;

[0040] Figure 9 a, e, g are the X-ray absorption near-edge structure spectra of the K-edge of Co, Ni, and Zn elements; b, f, h are the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectrum; c is the octahedral occupancy of Co element in Co3O4 in a cobalt-based oxide prepared in Example 1 and comparative sample 1 prepared in Comparative Example 1; d is a schematic diagram of the redistribution of Co element in the process of forming a cobalt-based oxide prepared in Example 1; i, j, k are the k of Co, Ni, and Zn elements 2 The wavelet transform signal of the weighted extended edge X-ray absorption fine structure;

[0041] Figure 10 a, b, c are comparisons of the X-ray absorption near-edge structure spectra of the Co, Ni, and Zn elements of a cobalt-based oxide prepared in Example 1 and the theoretical calculation results; d, e, f are the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectrum comparison diagram; g is a Bader charge distribution diagram of a cobalt-based oxide and Co3O4 prepared in Example 1;

[0042] Figure 11 a is Figure 9 a is a local enlarged image; b is a cobalt-based oxide prepared in Example 1 and the average oxidation valence state of the Co element in Comparative Example 1; c is the relationship between the number of d orbital vacancies and the average oxidation valence state; d is Figure 9 a Co3O4, Comparative Example 1, and a cobalt-based oxide prepared in Example 1;

[0043] Figure 12 Extended edge X-ray absorption fine structure spectra of the Co element K-edge of a cobalt-based oxide prepared in Co3O4, Comparative Example 1, and Example 1 and their fitting curves;

[0044] Figure 13 Extended edge X-ray absorption fine structure spectra of Ni K-edge of Ni foil, NiO, and a cobalt-based oxide prepared in Example 1 and their fitting curves;

[0045] Figure 14 Extended edge X-ray absorption fine structure spectra of the K-edge of Zn element of Zn foil, ZnO, and a cobalt-based oxide prepared in Example 1 and their fitting curves;

[0046] Figure 15a is the X-ray absorption near-edge structure spectrum of Fe K-edge; b is the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectroscopy;

[0047] Figure 16 The extended edge X-ray absorption fine structure spectrum of the Fe element K edge of Fe3O4 and a cobalt-based oxide prepared in Example 1 and its fitting curve;

[0048] Figure 17 a is the X-ray absorption near-edge structure spectrum of the K-edge of Mn element; b is the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectroscopy;

[0049] Figure 18 The extended edge X-ray absorption fine structure spectrum of the K-edge of the Mn element of Mn2O3 and a cobalt-based oxide prepared in Example 1 and the fitting curve thereof;

[0050] Figure 19 K is the element of Fe and Mn 2 The wavelet transform signal of the weighted extended edge X-ray absorption fine structure;

[0051] Figure 20 a, b are comparisons of the X-ray absorption near-edge structure spectra of the Fe and Mn elements of a cobalt-based oxide prepared in Example 1 and the theoretical calculation results; c, d are the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectrum comparison map;

[0052] Figure 21 This is a scanning electron microscope image of comparative sample 1 prepared in comparative example 1;

[0053] Figure 22 This is a scanning electron microscope image of comparative sample 2 prepared in comparative example 2;

[0054] Figure 23 X-ray diffraction spectra of a cobalt-based oxide prepared in Example 1, comparative sample 1 prepared in Comparative Example 1, and comparative sample 2 prepared in Comparative Example 2;

[0055] Figure 24 for Figure 23 A local magnified image of

[0056] Figure 25 The atomic percentage obtained by energy dispersive spectroscopy measured by a scanning electron microscope system in Comparative Example 1;

[0057] Figure 26 The atomic percentage obtained by energy dispersive spectroscopy measured by scanning electron microscope system in Comparative Example 2;

[0058] Figure 27 XPS spectra of a cobalt-based oxide prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0059] Figure 28 The octahedral ratio of Co element in Co3O4 in a novel cobalt-based oxide prepared in Example 1 and comparative sample 2 prepared in Comparative Example 1;

[0060] Figure 29 The electrical conductivity of a cobalt-based oxide prepared in Example 1, comparative sample 1 prepared in Comparative Example 1, and comparative sample 2 prepared in Comparative Example 2;

[0061] Figure 30 a is the total state density of a cobalt-based oxide prepared in Example 1, comparative sample 1 prepared in Comparative Example 1, and comparative sample 2 prepared in Comparative Example 2; b is the partial state density of a cobalt-based oxide prepared in Example 1; c is the partial state density of a cobalt-based oxide prepared in Example 1, comparative sample 1, and comparative sample 2 in Co Oct and Co Tet Adsorption energy of Li2S4; d is a cobalt-based oxide prepared in Example 1 adsorbed on Co Oct (Left) and Co Tet (right) The optimized structure of Li2S4; e, f are Co in a cobalt-based oxide prepared in Example 1 Oct -O and Co Tet -O d / p energy band center diagram; g is the calculated Co in a cobalt-based oxide prepared in Example 1 Oct and Co Tet Gibbs free energy curve of sulfur reduction reaction;

[0062] Figure 31 Co in Comparative Example 1 Oct -O and Co Tet -Schematic diagram of the d / p band center of O;

[0063] Figure 32 For the Co in Comparative Example 2 Oct -O and Co Tet -Schematic diagram of the d / p band center of O;

[0064] Figure 33 a is the constant current charge and discharge curve of different positive electrodes measured at 0.1C; b is ΔE and Q from the constant current charge and discharge curve L / Q H c is the rate performance curve; d and e are the cycle performance curves at 0.5C and 2.0C, respectively; f is a radar chart comparing the catalytic performance with previously reported catalysts;

[0065] Figure 34 The charge and discharge curves of the three positive electrodes at different current rates;

[0066] Figure 35 The sulfur loading of the three cathodes at 0.5C is 5 mg cm -2 Cycle performance curve;

[0067] Figure 36 a is the CV curve of Li2S6 symmetric battery using different electrodes; b is the peak current response obtained from a and Co Oct c is the constant potential discharge curve of Li2S deposited on different electrode surfaces; d is the nucleation and growth rate of Li2S; e is the comparison between the dimensionless transient model and the theoretical model of a cobalt-based oxide prepared in Example 1; f, g are the lithium-sulfur batteries with different positive electrodes at 0.1mV s –1 CV curves and Tafel slopes at scan rates; h is the relationship between the polarization potential and the normalized charge / discharge time of the three batteries;

[0068] Figure 37 Comparison between the dimensionless transient model and the theoretical model of the electrodes of comparative example 1 and comparative example 2;

[0069] Figure 38 The Li2S dissolution test results of three electrodes;

[0070] Figure 39 For the three positive electrodes corresponding to the reduction of S8 to Li2S n , Li2S n Reduction to Li2S, and oxidation of Li2S to Li2S n The Tafel slope of

[0071] Figure 40 The constant current intermittent titration technical curves of three positive electrodes;

[0072] Figure 41 Electrochemical impedance spectroscopy of three positive electrodes;

[0073] Figure 42 This is the ex-situ XPS spectrum of a cobalt-based oxide positive electrode prepared in Example 1 during the charge and discharge process at different potentials. DETAILED DESCRIPTION

[0074] Specific embodiment 1: This embodiment provides a method for preparing a cobalt-based oxide, wherein the cobalt-based oxide comprises six elements: Fe, Co, Ni, Mn, Zn, and O, and has a multi-layer hollow spherical shell morphology with a "gas port", wherein the outer spherical shell has a diameter of 1 to 3 μm and a wall thickness of 60 nm to 70 nm, and the inner spherical shell has a diameter and thickness that decrease in descending order, and the spherical shell is composed of polycrystalline nanoparticles; the preparation method is specifically completed in the following steps:

[0075] 1. Preparation of precursor solution:

[0076] C6H 12 O6·H2O, Fe(NO3)2·9H2O, Zn(NO3)2·6H2O, Ni(NO3)2·6H2O, Co(NO3)2·6H2O, and Mn(NO3)2·4H2O were added to deionized water and stirred until completely dissolved to obtain a clear solution A;

[0077] 2. Coprecipitation reaction:

[0078] The transparent solution A is transferred to a polytetrafluoroethylene-lined stainless steel autoclave, and the polytetrafluoroethylene-lined stainless steel autoclave is then transferred to a high-temperature oven for hydrothermal reaction at 170°C to 190°C for a period of time to obtain product B;

[0079] 3. Collection and drying:

[0080] Product B was vacuum filtered to collect the black fluffy precipitate, which was then dried in an oven to obtain product C;

[0081] 4. Calcination treatment:

[0082] The product C is placed in a high-temperature ceramic boat, which is then transferred to a muffle furnace or a tube furnace. The temperature is then raised to 500° C. to 550° C. in an air atmosphere and kept warm for a period of time to obtain a cobalt-based oxide.

[0083] Specific embodiment 2: This embodiment differs from the specific embodiment 1 in that: the C6H 12 The mass ratio of O6·H2O to deionized water is (20g-30g):250mL. The other steps are the same as those in the first embodiment.

[0084] Specific embodiment 3: This embodiment differs from specific embodiments 1 or 2 in that the mass ratio of Fe(NO3)2·9H2O to deionized water in step 1 is (0.4g-0.6g):250mL. The other steps are the same as specific embodiments 1 or 2.

[0085] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the mass ratio of Zn(NO3)2·6H2O to deionized water in step 1 is (1.5g-2.0g):250mL. The other steps are the same as specific embodiments 1 to 3.

[0086] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the mass ratio of Ni(NO3)2·6H2O to deionized water in step 1 is (3.3g-4.0g):250mL. The other steps are the same as specific embodiments 1 to 4.

[0087] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the mass ratio of Co(NO3)2·6H2O to deionized water in step 1 is (7g-7.5g):250mL. The other steps are the same as specific embodiments 1 to 5.

[0088] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the mass ratio of Mn(NO3)2·4H2O to deionized water in step 1 is (8.5g-9.5g):250mL. The other steps are the same as specific embodiments 1 to 6.

[0089] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the hydrothermal reaction time in step 2 is 6 to 7 hours; the drying temperature in step 3 is 70°C to 90°C, and the drying time is 10 to 14 hours. The other steps are the same as specific embodiments 1 to 7.

[0090] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the heating rate in step 4 is 1°C / min to 5°C / min and the holding time in step 4 is 1h to 2h. The other steps are the same as specific embodiments 1 to 8.

[0091] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that a cobalt-based oxide is used to prepare a positive electrode material for a lithium-sulfur battery, which is specifically completed by the following steps:

[0092] Multi-walled carbon nanotubes, sulfur, and cobalt-based oxide are mixed and ground uniformly in a mass ratio of 2:7:1, and then melted at 150°C to 160°C for 10 hours to 12 hours to obtain a composite material; the composite material, conductive carbon black, and polyvinylidene fluoride are mixed in N-methylpyrrolidone in a mass ratio of 8:1:1 to obtain a uniform suspension; the uniform suspension is dropped onto a carbon cloth, and then vacuum-dried at 60°C to 70°C for 10 hours to 12 hours to obtain a lithium-sulfur battery positive electrode material, wherein the sulfur loading amount is 1 mg / cm2 to 5 mg / cm2;

[0093] The volume ratio of the total mass of the composite material, conductive carbon black and polyvinylidene fluoride to N-methylpyrrolidone is 100 mg: 2300 μL. The other steps are the same as those of the first to ninth embodiments.

[0094] The following examples are used to verify the beneficial effects of the present invention:

[0095] Example 1: A method for preparing a cobalt-based oxide is specifically completed by the following steps:

[0096] 1. Preparation of precursor solution:

[0097] 25g C6H 12 O6·H2O, 0.505g Fe(NO3)2·9H2O, 1.86g Zn(NO3)2·6H2O, 3.635g Ni(NO3)2·6H2O, 7.275g Co(NO3)2·6H2O and 8.95g Mn(NO3)2·4H2O were added to 250mL deionized water and stirred until completely dissolved to obtain a clear solution A;

[0098] 2. Coprecipitation reaction:

[0099] The transparent solution A was transferred to a polytetrafluoroethylene-lined stainless steel autoclave, and then the polytetrafluoroethylene-lined stainless steel autoclave was transferred to a high-temperature oven for hydrothermal reaction at 180°C for 400 minutes to obtain product B;

[0100] 3. Collection and drying:

[0101] Product B was vacuum filtered to collect the black fluffy precipitate, which was then dried in an oven at 80°C for 12 h to obtain product C.

[0102] 4. Calcination treatment:

[0103] The product C is placed in a high-temperature ceramic boat, which is then transferred to a muffle furnace, and then heated to 500° C. in an air atmosphere and kept at this temperature for 1 hour to obtain a cobalt-based oxide.

[0104] The heating rate in step 4 is 1°C / min.

[0105] Comparative Example 1: The preparation method of comparative sample 1 is specifically completed according to the following steps:

[0106] 1. Preparation of precursor solution:

[0107] 5g C6H 12 O6·H2O, 2.02g Fe(NO3)2·9H2O, 14.54g Ni(NO3)2·6H2O, and 29.1g Co(NO3)2·6H2O were added to 250mL deionized water and stirred until completely dissolved to obtain a transparent solution A;

[0108] 2. Coprecipitation reaction:

[0109] The transparent solution A was transferred to a polytetrafluoroethylene-lined stainless steel autoclave, and then the polytetrafluoroethylene-lined stainless steel autoclave was transferred to a high-temperature oven for hydrothermal reaction at 180°C for 400 minutes to obtain product B;

[0110] 3. Collection and drying:

[0111] Product B was vacuum filtered to collect the black fluffy precipitate, which was then dried in an oven at 80°C for 12 h to obtain product C.

[0112] 4. Calcination treatment:

[0113] Product C was placed in a high-temperature ceramic boat, which was then transferred to a muffle furnace. The temperature was then raised to 500° C. in an air atmosphere and kept at this temperature for 1 hour to obtain comparative sample 1.

[0114] Comparative Example 2: The preparation method of comparative sample 2 is specifically completed according to the following steps:

[0115] 1. Preparation of precursor solution:

[0116] 25g C6H 12 O6·H2O and 43.65g Co(NO3)2·6H2O were added to 250mL deionized water and stirred until completely dissolved to obtain a clear solution A;

[0117] 2. Coprecipitation reaction:

[0118] The transparent solution A was transferred to a polytetrafluoroethylene-lined stainless steel autoclave, and then the polytetrafluoroethylene-lined stainless steel autoclave was transferred to a high-temperature oven for hydrothermal reaction at 180°C for 400 minutes to obtain product B;

[0119] 3. Collection and drying:

[0120] Product B was vacuum filtered to collect the black fluffy precipitate, which was then dried in an oven at 80°C for 12 h to obtain product C.

[0121] 4. Calcination treatment:

[0122] Product C was placed in a high-temperature ceramic boat, which was then transferred to a muffle furnace. The temperature was then raised to 500° C. in an air atmosphere and kept at this temperature for 1 hour to obtain comparative sample 2.

[0123] Figure 1 This is a scanning electron microscope image of a cobalt-based oxide prepared in Example 1;

[0124] Figure 2 This is a transmission electron microscope image of a cobalt-based oxide prepared in Example 1;

[0125] Figure 3 for Figure 2 A local magnified image of

[0126] Figure 4 A high-resolution transmission electron microscope image of a cobalt-based oxide prepared in Example 1;

[0127] Figure 5 A selected electron diffraction image of a cobalt-based oxide prepared in Example 1;

[0128] from Figure 1-5 It can be seen that the cobalt-based oxide prepared in Example 1 has a multi-layer hollow spherical shell morphology with "air vents"; the diameter of the outer spherical shell is 1 to 3 μm, and the wall thickness is 70 nm; the diameter and thickness of the inner spherical shell decrease in order; the spherical shell is composed of polycrystalline nanoparticles, and its (220) crystal plane spacing is 0.29 nm, and the (311) crystal plane spacing is 0.25 nm.

[0129] Figure 6 This is a Rietveld refined X-ray diffraction spectrum of a cobalt-based oxide prepared in Example 1;

[0130] like Figure 6 As shown, the XRD spectrum of the cobalt-based oxide prepared in Example 1 was Rietveld refined using GSAS-II software. The refinement results show that the cobalt-based oxide shows excellent consistency with the cubic spinel structure (space group is Fd-3m), and the lattice parameters are Matching the characteristic AB2O4 phase. The obtained reliability R factor (R wp =6.92%, R p =5.42%) is lower than the 10% threshold for reliable refinement, verifying that the cobalt-based oxide has a spinel single-phase structure with Fd-3m space group (JCPDS#80-1536).

[0131] Figure 7 A high-angle annular dark-field scanning transmission electron microscope image of a cobalt-based oxide prepared in Example 1 and corresponding element mapping images of Fe, Co, Ni, Mn, Zn, and O;

[0132] Figure 8 The atomic percentage of a cobalt-based oxide prepared in Example 1 obtained by energy dispersive spectroscopy measured by a scanning electron microscope system;

[0133] like Figure 7 and 8 As shown, the six elements Fe, Co, Ni, Mn, Zn and O are evenly distributed in the oxide and the atomic percentage of each element is Fe:Co:Ni:Mn:Zn:O=3.25:13.42:7.63:6.79:11.32:57.58.

[0134] Figure 9 a, e, g are the X-ray absorption near-edge structure spectra of the K-edge of Co, Ni, and Zn elements; b, f, h are the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectrum; c is the octahedral occupancy of Co element in Co3O4 in a cobalt-based oxide prepared in Example 1 and comparative sample 1 prepared in Comparative Example 1; d is a schematic diagram of the redistribution of Co element in the process of forming a cobalt-based oxide prepared in Example 1; i, j, k are the k of Co, Ni, and Zn elements 2 The wavelet transform signal of the weighted extended edge X-ray absorption fine structure;

[0135] Figure 10 a, b, c are comparisons of the X-ray absorption near-edge structure spectra of the Co, Ni, and Zn elements of a cobalt-based oxide prepared in Example 1 and the theoretical calculation results; d, e, f are the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectrum comparison diagram; g is a Bader charge distribution diagram of a cobalt-based oxide and Co3O4 prepared in Example 1;

[0136] Figure 9 a, e, g are the X-ray absorption near-edge structure spectra of the K-edge of Co, Ni, and Zn elements; b, f, h are the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectrum; c is the octahedral occupancy of Co element in Co3O4 in a cobalt-based oxide prepared in Example 1 and comparative sample 1 prepared in Comparative Example 1; d is a schematic diagram of the redistribution of Co element in the process of forming a cobalt-based oxide prepared in Example 1; i, j, k are the k of Co, Ni, and Zn elements 2 The wavelet transform signal of the weighted extended edge X-ray absorption fine structure;

[0137] Figure 10 a, b, c are comparisons of the X-ray absorption near-edge structure spectra of the Co, Ni, and Zn elements of a cobalt-based oxide prepared in Example 1 and the theoretical calculation results; d, e, f are the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectrum comparison diagram; g is a Bader charge distribution diagram of a cobalt-based oxide and Co3O4 prepared in Example 1;

[0138] Figure 11 a is Figure 9 a is a local enlarged image; b is a cobalt-based oxide prepared in Example 1 and the average oxidation valence state of the Co element in Comparative Example 1; c is the relationship between the number of d orbital vacancies and the average oxidation valence state; d is Figure 9a Co3O4, Comparative Example 1, and a cobalt-based oxide prepared in Example 1;

[0139] Figure 12 Extended edge X-ray absorption fine structure spectra of the Co element K-edge of a cobalt-based oxide prepared in Co3O4, Comparative Example 1, and Example 1 and their fitting curves;

[0140] Figure 13 Extended edge X-ray absorption fine structure spectra of Ni K-edge of Ni foil, NiO, and a cobalt-based oxide prepared in Example 1 and their fitting curves;

[0141] Figure 14 Extended edge X-ray absorption fine structure spectra of the K-edge of Zn element of Zn foil, ZnO, and a cobalt-based oxide prepared in Example 1 and their fitting curves;

[0142] Figure 15 a is the X-ray absorption near-edge structure spectrum of Fe K-edge; b is the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectroscopy;

[0143] Figure 16 The extended edge X-ray absorption fine structure spectrum of the Fe element K edge of Fe3O4 and a cobalt-based oxide prepared in Example 1 and its fitting curve;

[0144] Figure 17 a is the X-ray absorption near-edge structure spectrum of the K-edge of Mn element; b is the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectroscopy;

[0145] Figure 18 The extended edge X-ray absorption fine structure spectrum of the K-edge of the Mn element of Mn2O3 and a cobalt-based oxide prepared in Example 1 and the fitting curve thereof;

[0146] Figure 19 K is the element of Fe and Mn 2 The wavelet transform signal of the weighted extended edge X-ray absorption fine structure;

[0147] Figure 20 a, b are comparisons of the X-ray absorption near-edge structure spectra of the Fe and Mn elements of a cobalt-based oxide prepared in Example 1 and the theoretical calculation results; c, d are the corresponding K 2 Weighted Fourier transform-extended edge X-ray absorption fine structure spectrum comparison map;

[0148] from Figure 9-20It can be seen that by conducting X-ray absorption fine structure (XAFS) tests on the five elements Fe, Co, Ni, Mn, and Zn in this new type of cobalt-based oxide, their positional occupancy in the oxide and how to regulate the geometric configuration and electronic structure were determined. The experimental results show that with the incorporation of more metal cations, the position of Co cations is redistributed, resulting in an increase in the proportion of Co cations at the octahedral body center position. At the same time, it can be concluded that Fe, Co, Ni, and Mn mainly occupy the octahedral body center position in the spinel structure, while Zn mainly occupies the tetrahedral body center position. By comparing the R space spectrum, the change in bond length can be seen, indicating that with the continuous incorporation of metal elements, the electronic structure and coordination environment of the oxide change, thereby affecting the catalytic performance. By fitting the extended edge X-ray absorption fine structure spectrum, the average coordination numbers of Fe, Co, Ni, Mn, and Zn were found to be 5.76, 5.68, 5.84, 5.50, and 4.10, respectively. Near-edge simulation, fine structure calculation, and wavelet transform analysis were performed on these five metal elements to further verify the successful incorporation of the five metal elements. At the same time, Fe, Co, Ni, and Mn mainly occupy the octahedral body-centered positions in the spinel structure, while Zn mainly occupies the tetrahedral body-centered positions. In order to further understand the charge transfer process within the oxide, Bader charge calculations were performed. Doping metal atoms can significantly increase the Co bridging oxygen atoms. Oct The Bader charge of the cation and Co Tet The Bader charge of the cation is reduced. Tet and Ni Oct The Bader charge of Co in Co3O4 is lower than that of the corresponding Co Tet and Co Oct Besides, the Bader charges of Mn and Fe cations show an increasing trend relative to the original Co sites in Co3O4. These results suggest that multi-atom doping helps to transfer electrons from Fe to Co3O4 via bridging oxygen atoms. Oct / Co Oct / Mn Tet The cation is directly transferred to the adjacent Co Tet / Zn Tet / Ni Oct XAFS measurements and Bader charge calculations provide a deeper understanding of the geometric changes and electron redistribution mechanisms of this novel cobalt-based oxide after formation, contributing to a deeper understanding of its catalytic mechanism.

[0149] Figure 21 This is a scanning electron microscope image of comparative sample 1 prepared in comparative example 1;

[0150] from Figure 21It can be seen that the structure of Comparative Example 1 has a similar spherical morphology to the cobalt-based oxide prepared in Example 1.

[0151] Figure 22 This is a scanning electron microscope image of comparative sample 2 prepared in comparative example 2;

[0152] like Figure 22 As shown, Comparative Example 2 is a nanosheet structure.

[0153] Figure 23 X-ray diffraction spectra of a cobalt-based oxide prepared in Example 1, comparative sample 1 prepared in Comparative Example 1, and comparative sample 2 prepared in Comparative Example 2;

[0154] Figure 24 for Figure 23 A local magnified image of

[0155] from Figure 23 and 24 As can be seen, the cobalt-based oxide prepared in Example 1, Comparative Examples 1, and Comparative Examples 2 all exhibited a spinel structure of the Co₃O₄ phase, corresponding to the Co₃O₄ JCPDS #80-1536 standard card. As the metal element content increases, the XRD spectrum exhibits a shift toward smaller angles, indicating lattice expansion in the novel cobalt-based oxide prepared in Example 1 and Comparative Example 1.

[0156] Figure 25 The atomic percentage obtained by energy dispersive spectroscopy measured by a scanning electron microscope system in Comparative Example 1;

[0157] Figure 26 The atomic percentage obtained by energy dispersive spectroscopy measured by scanning electron microscope system in Comparative Example 2;

[0158] from Figure 25 and 26 As can be seen from the figure, the atomic percentages of the elements in Comparative Example 1 are Fe:Co:Ni:O=5.38:22.45:14.01:58.16. The atomic percentages of the elements in Comparative Example 2 are Co:O=32.63:67.37.

[0159] Figure 27 XPS spectra of a cobalt-based oxide prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0160] like Figure 27 As shown, Fe, Co, and Ni on the surface of the material all exhibit mixed valence states of +2 and +3, and Mn exhibits mixed valence states of +2, +3, and +4. Furthermore, through content analysis, it can be obtained that in a cobalt-based oxide prepared in Example 1, these four metal elements all tend to occupy octahedral body-centered sites.

[0161] Figure 28 The octahedral ratio of Co element in Co3O4 in a novel cobalt-based oxide prepared in Example 1 and comparative sample 2 prepared in Comparative Example 1;

[0162] pass Figure 28 It can be seen that with the continuous addition of more metal elements, Co Oct The proportion of is increasing.

[0163] Figure 29 The electrical conductivity of a cobalt-based oxide prepared in Example 1, comparative sample 1 prepared in Comparative Example 1, and comparative sample 2 prepared in Comparative Example 2;

[0164] like Figure 29 As shown, the conductivity of the cobalt-based oxide prepared in Example 1 is the largest among the three samples, indicating that the conductivity is improved to a certain extent with the continuous addition of metal elements.

[0165] Figure 30 a is the total state density of a cobalt-based oxide prepared in Example 1, comparative sample 1 prepared in Comparative Example 1, and comparative sample 2 prepared in Comparative Example 2; b is the partial state density of a cobalt-based oxide prepared in Example 1; c is the partial state density of a cobalt-based oxide prepared in Example 1, comparative sample 1, and comparative sample 2 in Co Oct and Co Tet Adsorption energy of Li2S4; d is a cobalt-based oxide prepared in Example 1 adsorbed on Co Oct (Left) and Co Tet (right) The optimized structure of Li2S4; e, f are Co in a cobalt-based oxide prepared in Example 1 Oct -O and Co Tet -O d / p energy band center diagram; g is the calculated Co in a cobalt-based oxide prepared in Example 1 Oct and Co Tet Gibbs free energy curve of the upper sulfur reduction reaction;

[0166] Figure 31 Co in Comparative Example 1 Oct -O and Co Tet -Schematic diagram of the d / p band center of O;

[0167] Figure 32 For the Co in Comparative Example 2 Oct -O and Co Tet -Schematic diagram of the d / p band center of O;

[0168] In order to gain a deeper understanding of the intrinsic mechanism of the excellent catalytic ability of a cobalt-based oxide prepared in Example 1, density functional theory calculations were used to study the structure and electronic properties of the oxide. Figure 30-32 As shown, the oxide exhibits more electronic states near the Fermi level, indicating that the incorporation of Mn, Fe, Ni, and Zn greatly improves the electrical conductivity and exhibits excellent electron transport capacity. In this oxide, Co is the primary active site for chemical catalysis, with its d orbital energy level center (-0.36 eV) closest to the Fermi level. The d orbital energy levels of Mn and Fe (-1.17 eV and -1.12 eV) are next, acting synergistically with Co. The d orbital energy center of Zn (-3.07 eV) is the lowest, acting as an "electron warehouse" for other elements. The d orbital energy center of Ni (-1.73 eV) is energetically between the 3d orbitals of Zn and Fe / Co / Mn, reducing the energy barrier for electron transfer between Mn / Fe / Co and Zn. The adsorption energy of Li2S4 can be calculated and it can be concluded that the adsorption energy of Co atoms occupying the octahedral center to Li2S4 (-2.94 eV) is 1.40 times stronger than that of Co atoms occupying the tetrahedral center to Li2S4, indicating that Co Oct By comparing the d orbital energy level center of the Co atom and the p orbital energy level center of the O atom in the two sites, the higher dp difference reflects the decrease in Co-O covalency and increase in polarity. Oct Always show better performance than the corresponding Co Tet A larger difference indicates that Co Oct -O bond has weak covalency and thus stronger polarity, which is beneficial to improve the adsorption and catalytic performance of lithium polysulfide. It can also be observed by Gibbs free energy calculation that Co Oct The above analysis shows that the synergistic effect of Fe, Ni, Mn, and Zn atoms significantly enhances the adsorption capacity of Co atoms on polysulfides, effectively reducing the shuttle effect of lithium polysulfides, thereby improving the performance of lithium-sulfur batteries.

[0169] Table 1 shows the peak positions (eV) of a cobalt-based oxide prepared in Example 1, Comparative Example 1, and Comparative Example 2 obtained based on XPS fitting results;

[0170] Table 1

[0171]

[0172] Application in lithium-sulfur batteries:

[0173] I. 20 mg of multi-walled carbon nanotubes (MWCNTs), 70 mg of sulfur, and 10 mg of the cobalt-based oxide prepared in Example 1 were mixed and ground uniformly in a mass ratio of 2:7:1, and then melted at 155°C for 12 hours to obtain a composite material; the composite material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to obtain a uniform suspension; the uniform suspension was dropwise added to a carbon cloth (CC) with a diameter of 13 mm, and then vacuum dried at 60°C for 12 hours to obtain a lithium-sulfur battery positive electrode material with a sulfur loading of 1.5 mg / cm2;

[0174] The volume ratio of the total mass of the composite material, conductive carbon black and polyvinylidene fluoride to N-methylpyrrolidone is 100 mg:2300 μL.

[0175] II. The cobalt-based oxide prepared in Example 1 described in I was replaced with Comparative Sample 1 prepared in Comparative Example 1, and the other steps and parameters were exactly the same as in I to obtain a lithium-sulfur battery positive electrode material;

[0176] III. The cobalt-based oxide prepared in Example 1 described in I was replaced with Comparative Sample 2 prepared in Comparative Example 2, and the other steps and parameters were exactly the same as in I to obtain a positive electrode material for a lithium-sulfur battery;

[0177] IV. The sulfur loading in Ⅰ was adjusted to 5 mg / cm2, and the other steps and parameters were exactly the same as Ⅰ to obtain a lithium-sulfur battery positive electrode material.

[0178] Assembly of lithium-sulfur batteries:

[0179] A CR2032 coin-type lithium-sulfur battery was assembled using the positive electrode of the lithium-sulfur battery prepared in Example 1 (or Comparative Example 1 or Comparative Example 2), lithium foil as the negative electrode, and a single layer of polypropylene (Celgard 2400) as the separator. The electrolyte used was 30 μL of 1.0 M lithium bis(trifluoromethane)sulfonyl imide (LiTFSI) in a DOL / DME (volume ratio of 1:1) mixed solution containing 2 wt% LiNO3. The ratio of electrolyte to sulfur was 20 μL per milligram.

[0180] Electrochemical performance test:

[0181] The charge and discharge performance of the assembled lithium-sulfur battery was tested using the same test conditions. Galvanostatic charge and discharge (GCD) tests were performed on a LANCT battery test system at room temperature within a voltage range of 1.7 to 2.8 V at different rates. Cyclic voltammetry (CV) measurements were performed between 1.7 and 2.8 V using a VMP3 multi-channel electrochemical workstation (BioLogic, France).

[0182] Figure 33 a is the constant current charge and discharge curve of different positive electrodes measured at 0.1C; b is ΔE and Q from the constant current charge and discharge curve L / Q H c is the rate performance curve; d and e are the cycle performance curves at 0.5C and 2.0C, respectively; f is a radar chart comparing the catalytic performance with previously reported catalysts;

[0183] Figure 34 The charge and discharge curves of the three positive electrodes at different current rates;

[0184] Figure 35 The sulfur loading of the three cathodes at 0.5C is 5 mg cm -2 Cycle performance curve;

[0185] like Figures 33-35 As shown, through the GCD test, it can be seen that a cobalt-based oxide prepared in Example 1 has the highest discharge specific capacity and also exhibits the best rate performance and reversibility under different current rate conditions. In addition, as a positive electrode catalyst, the oxide exhibits a maximum capacity retention rate of 92.8% in a 0.5C cycle performance test and a minimum capacity decay rate of 0.042% in a 2.0C long cycle test. It also has excellent cycle performance under conditions of high sulfur loading and poor electrolyte. At the same time, compared with the popular lithium-sulfur battery positive electrode catalysts in recent years, the catalytic performance of the oxide is extremely competitive.

[0186] Symmetrical battery test:

[0187] 4 mg of the mixture of cobalt-based oxide and polyvinylidene fluoride prepared in Example 1 (mass ratio of 8:1) was coated on a carbon cloth with a diameter of 13 mm to prepare a single electrode. The same two electrodes as above were used, blank PP was used as a separator, and 0.25 M Li2S6 (20 μL) solution was used as the electrolyte. A 2032-size battery was assembled in an argon-filled glove box. Cyclic voltammetry (CV) curves were obtained on a VMP3 electrochemical workstation (BioLogic, France) at 5 mVs -1 The CV test was carried out at a scan rate of -1 V and a voltage range of 1 V. For comparison, a symmetrical battery with Comparative Example 1 and Comparative Example 2 as electrodes was tested.

[0188] Figure 36 a is the CV curve of Li2S6 symmetric battery using different electrodes; b is the peak current response obtained from a and Co Octc is the constant potential discharge curve of Li2S deposited on different electrode surfaces; d is the nucleation and growth rate of Li2S; e is the comparison between the dimensionless transient model and the theoretical model of a cobalt-based oxide prepared in Example 1; f, g are the lithium-sulfur batteries with different positive electrodes at 0.1mV s –1 CV curves and Tafel slopes at scan rates; h is the relationship between the polarization potential and the normalized charge / discharge time of the three batteries;

[0189] Figure 37 Comparison between the dimensionless transient model and the theoretical model of the electrodes of comparative example 1 and comparative example 2;

[0190] Figure 38 The Li2S dissolution test results of three electrodes;

[0191] Figure 39 For the three positive electrodes corresponding to the reduction of S8 to Li2S n , Li2S n Reduction to Li2S, and oxidation of Li2S to Li2S n The Tafel slope of

[0192] Figure 40 The constant current intermittent titration technical curves of three positive electrodes;

[0193] Figure 41 Electrochemical impedance spectroscopy of three positive electrodes;

[0194] like Figures 36-41 As shown, the role of octahedral Co cations in promoting the conversion of lithium polysulfide was explored through CV tests, Li2S nucleation and dissolution tests, and constant current intermittent titration techniques. Through the above tests, it can be concluded that with the increase in the octahedral occupancy of Co, the oxide accelerates the catalytic conversion of lithium polysulfide, is beneficial to the nucleation and dissolution of Li2S, and has the smallest polarization voltage during the entire redox reaction, indicating that the addition of the oxide can prolong the life of the battery. For the electrochemical impedance test, it can be seen that the lithium-sulfur battery assembled with the oxide-modified sulfur positive electrode has the smallest charge transfer resistance, indicating that the oxide is beneficial to accelerating charge transfer and accelerating the reaction. Through the above test analysis, it can be seen that a cobalt-based oxide prepared in Example 1 is beneficial to catalyze the reaction of lithium-sulfur batteries, which promotes the application and development of lithium-sulfur batteries.

[0195] Figure 42 This is the ex-situ XPS spectrum of a cobalt-based oxide positive electrode prepared in Example 1 during charge and discharge at different potentials;

[0196] In order to further determine the role of each metal element in the oxide, ex situ XPS testing was used to explore the role of each metal in the reaction, such as Figure 42 The results show that the four metal cations of Fe, Co, Ni and Mn all play a catalytic role in the entire reaction, but the Co cation plays a key role in the oxidation of Li2S, and the Ni cation plays a key role in the formation of Li2S. This is due to the redistribution of metal cations in the oxide caused by the continuous incorporation of metal elements.

[0197] Table 2 shows the variation of the content of each metal element in the ex-situ XPS spectrum of the positive electrode of S / Example 1 with the depth of discharge and charge.

[0198] Table 2

[0199]

[0200] StepⅠ:Pristine~Dis.2.11V;

[0201] StepⅡ:Dis.2.11V~Dis.2.10V;

[0202] StepⅢ:Dis.2.10V~Dis.1.70V;

[0203] StepⅣ:Dis.1.70V~Cha.2.21V;

[0204] StepⅤ:Cha.2.21V~Cha.2.37V;

[0205] StepVI: Cha.2.37V~Cha.2.80V.

[0206] The above embodiments are only some of the embodiments of the present invention. In actual applications, the raw material ratios, reaction conditions, etc. can be appropriately adjusted according to specific needs. The scope of protection of the present invention is not limited to the above embodiments, but also includes various modifications and improvements based on the technical solution of the present invention.

Claims

1. A method for preparing a cobalt-based oxide, characterized in that The cobalt-based oxide comprises six elements, namely Fe, Co, Ni, Mn, Zn and O, and has a multi-layer hollow spherical shell morphology with a "gas hole". The outer shell has a diameter of 1 to 3 μm and a wall thickness of 60 nm to 70 nm. The inner shell has a diameter and thickness that decrease in descending order. The shell is composed of polycrystalline nanoparticles. The preparation method is specifically completed in the following steps:

1. Preparation of precursor solution: C6H 12 O6·H2O, Fe(NO3)2·9H2O, Zn(NO3)2·6H2O, Ni(NO3)2·6H2O, Co(NO3)2·6H2O, and Mn(NO3)2·4H2O were added to deionized water and stirred until completely dissolved to obtain a clear solution A; 2. Coprecipitation reaction: The transparent solution A is transferred to a polytetrafluoroethylene-lined stainless steel autoclave, and the polytetrafluoroethylene-lined stainless steel autoclave is then transferred to a high-temperature oven for hydrothermal reaction at 170°C to 190°C for a period of time to obtain product B; 3. Collection and drying: Product B was vacuum filtered to collect the black fluffy precipitate, which was then dried in an oven to obtain product C; 4. Calcination treatment: The product C is placed in a high-temperature ceramic boat, which is then transferred to a muffle furnace or a tube furnace. The temperature is then raised to 500° C. to 550° C. in an air atmosphere and kept warm for a period of time to obtain a cobalt-based oxide.

2. The method for preparing a cobalt-based oxide according to claim 1, wherein C6H as described in step 1 12 The mass ratio of O6·H2O to the volume of deionized water is (20g~30g):250mL.

3. The method for preparing a cobalt-based oxide according to claim 1, wherein The mass ratio of Fe(NO3)2·9H2O described in step 1 to the volume ratio of deionized water is (0.4g~0.6g):250mL.

4. The method for preparing a cobalt-based oxide according to claim 1, wherein The mass ratio of Zn(NO3)2·6H2O described in step 1 to the volume ratio of deionized water is (1.5g~2.0g):250mL.

5. The method for preparing a cobalt-based oxide according to claim 1, wherein The mass ratio of Ni(NO3)2·6H2O described in step 1 to the volume ratio of deionized water is (3.3g~4.0g):250mL.

6. The method for preparing a cobalt-based oxide according to claim 1, wherein The mass ratio of Co(NO3)2·6H2O described in step 1 to the volume ratio of deionized water is (7g~7.5g):250mL.

7. The method for preparing a cobalt-based oxide according to claim 1, characterized in that The mass ratio of Mn(NO3)2·4H2O described in step 1 to the volume ratio of deionized water is (8.5g-9.5g):250mL.

8. The method for preparing a cobalt-based oxide according to claim 1, wherein The time of the hydrothermal reaction in step 2 is 6 hours to 7 hours; the drying temperature in step 3 is 70° C. to 90° C., and the drying time is 10 hours to 14 hours.

9. The method for preparing a cobalt-based oxide according to claim 1, characterized in that The heating rate in step 4 is 1°C / min to 5°C / min; the insulation time in step 4 is 1h to 2h.

10. Use of a cobalt-based oxide prepared by the preparation method according to any one of claims 1 to 9, characterized in that A cobalt-based oxide is used to prepare a positive electrode material for a lithium-sulfur battery, which is specifically completed by the following steps: Multi-walled carbon nanotubes, sulfur, and cobalt-based oxide are mixed and ground uniformly in a mass ratio of 2:7:1, and then melted at 150°C to 160°C for 10 hours to 12 hours to obtain a composite material; the composite material, conductive carbon black, and polyvinylidene fluoride are mixed in N-methylpyrrolidone in a mass ratio of 8:1:1 to obtain a uniform suspension; the uniform suspension is dropped onto a carbon cloth, and then vacuum-dried at 60°C to 70°C for 10 hours to 12 hours to obtain a lithium-sulfur battery positive electrode material, wherein the sulfur loading amount is 1 mg / cm2 to 5 mg / cm2; The volume ratio of the total mass of the composite material, conductive carbon black and polyvinylidene fluoride to N-methylpyrrolidone is 100 mg:2300 μL.

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