Copper heptasulfide / cobalt octasulfide / carbon composite material, preparation method and application thereof, and rechargeable battery

Abstract

The invention provides a copper heptasulfide / cobalt octasulfide / carbon composite material, a preparation method and application thereof, and a rechargeable battery, a nanosphere Cu7S4 / Co9S8 / C composite material composed of hollow nano blocks is prepared through a room temperature sedimentation method and an annealing process, a bimetallic sulfide Cu7S4 / Co9S8 and carbon form a heterojunction, and the preparation method is simple and efficient. Compared with the prior art, the composite electrode material shows multiple advantages in the charging and discharging process of the sodium ion battery through multi-component collaborative design and nanostructure optimization, and the product shows high reversible capacity of 305mAh g <-1 >, high specific capacity, stable cycle performance and steady rate capability after 1000 cycles under the current density of 3Ag <-1 >.

Description

Technical Field

[0001] This invention belongs to the field of battery material preparation, specifically involving a copper tetrasulfide / cobalt octasulfide / carbon composite material, its preparation method and application, and rechargeable batteries. The prepared binary metal sulfide Cu7S4 / Co9S8 / C is used as a negative electrode material for sodium-ion batteries in the manufacture of rechargeable batteries. Background Technology

[0002] As the global energy structure transitions towards a low-carbon model, safe, low-cost, and sustainable energy storage technologies have become crucial for driving the large-scale application of renewable energy. Lithium-ion batteries, due to their high energy density and mature technology, have dominated the portable electronic device and electric vehicle markets for the past three decades. However, the uneven global distribution of lithium resources (approximately 70% of reserves are concentrated in the "Lithium Triangle" region of South America), rising mining costs, and volatile lithium metal prices pose significant challenges to the large-scale energy storage application of lithium-ion batteries.

[0003] Against this backdrop, sodium-ion batteries have attracted widespread attention due to their significant cost advantages and resource sustainability. Sodium, as the sixth most abundant element in the Earth's crust (abundance of approximately 2.3%), is widely distributed and its extraction cost is only one-tenth that of lithium. Therefore, sodium-ion batteries have broad application prospects.

[0004] However, the industrialization of sodium-ion batteries still faces multiple technical bottlenecks, due to the radius of sodium ions... Compared to lithium-ion The 35% increase in sodium ion content leads to sluggish diffusion kinetics in electrode materials and easily causes lattice distortion, affecting the performance and lifespan of sodium-ion batteries. The large-scale use of sodium-ion batteries still faces challenges.

[0005] Therefore, it is essential to provide a material that can improve the performance of sodium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a copper tetrasulfide / cobalt octasulfide / carbon composite material and its preparation method. A hollow nanosphere Cu7S4 / Co9S8 / C composite material composed of nanobulbs is prepared by a simple room temperature sedimentation method and annealing process. The bimetallic sulfides Cu7S4 / Co9S8 form a heterojunction and are encapsulated by carbon. The preparation method of this invention is simple and efficient.

[0007] Another objective of this invention is to provide an application of a copper tetrasulfide / cobalt octasulfide / carbon composite material as an active material in the preparation of a sodium-ion battery anode, thereby preparing a sodium-ion battery.

[0008] The final objective of this invention is to provide a rechargeable battery that uses a copper tetrasulfide / cobalt octasulfide / carbon composite material as the active material to prepare a sodium-ion battery negative electrode, thereby making a rechargeable battery.

[0009] The specific technical solution of this invention is as follows:

[0010] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0011] 1) Preparation of Cu / Co-PBA precursor by room temperature sedimentation method;

[0012] 2) Cu / Co-PBA precursor and sulfur powder were sulfidated and annealed in a reducing atmosphere to obtain Cu7S4 / Co9S8 / C composite material.

[0013] The preparation method of the Cu / Co-PBA precursor in step 1) is as follows:

[0014] Copper source and oxalic acid are dispersed in water and stirred to form solution A; cobalt source and oxalic acid are dispersed in water and stirred to form solution B; solutions A and B are mixed and stirred, and then allowed to settle at room temperature to obtain the Cu / Co-PBA precursor.

[0015] In the preparation method of the Cu / Co-PBA precursor, the molar ratio of the copper source to the cobalt source is 1-5:2; preferably 1:1; the copper source is a soluble copper source, preferably CuSO4·5H2O; the cobalt source is a soluble copper source, preferably K3[Co(CN)6]; the molar ratio of the copper source to oxalic acid in solution A is 1:10; the molar ratio of the cobalt source to oxalic acid in solution B is 1:10; the concentration of the copper source in solution A is 0.04 mol / L; the concentration of the cobalt source in solution B is 0.04 mol / L; the stirring time for forming solution A is 1 h; the stirring time for forming solution B is 1 h; the mixing and stirring of solution A and solution B is carried out for 6 h; the water is deionized water; the settling time at room temperature is 12 h; after the reaction, the mixture is centrifuged, washed 4-6 times with water and 1-2 times with ethanol, centrifuged, and dried at 40-80℃ for 12-15 h;

[0016] The prepared Cu / Co-PBA precursor is a polyhedral nanomaterial with a size of 500-700 nm.

[0017] Preferably, the preparation method of Cu / Co-PBA precursor is as follows: 2 mmol CuSO4·5H2O and 20 mmol oxalic acid are dispersed in 50 mL deionized water and stirred for 1 h to form solution A; 2 mmol K3[Co(CN)6] and 20 mmol oxalic acid are dispersed in 50 mL deionized water and stirred for 1 h to form solution B; then solutions A and B are mixed and stirred at room temperature for 6 h, and finally settled at room temperature for 12 h, collected by centrifugation, and washed with deionized water and ethanol to obtain Cu / Co-PBA precursor.

[0018] In step 2), during the sulfurization annealing, the mass ratio of Cu / Co-PBA precursor to sulfur powder is 1:6-10, with a preferred ratio of 1:6.

[0019] In step 2), the temperature of the vulcanization annealing is 500-550℃, preferably 500℃; the vulcanization annealing time is 2h, the heating rate is 2℃ / min, and the vulcanization annealing is carried out in a tube furnace.

[0020] The reducing atmosphere mentioned in step 2) is a mixture of hydrogen and argon, with hydrogen comprising 5% and argon comprising 95%.

[0021] The present invention provides a copper tetrasulfide heptacobalt / cobalt octacobalt / carbon composite material, which is prepared by the above method. It is a hollow nanosphere Cu7S4 / Co9S8 / C composite material composed of nanobulbs. The size of the spherical structure is 500-700nm, which greatly improves the service life, cycle stability and battery capacity.

[0022] Prussian blue analogues (PBAs) are cubic framework structures formed by bridging two transition metal ions with cyanide (CN-). In Cu / Co-PBAs, Cu... 2+ and Co 3+ A three-dimensional network is formed through cyanide coordination. The room-temperature sedimentation method utilizes the slow reaction between metal ions and ligands in solution to form crystals through nucleation and growth. In the aqueous solution system, a copper source provides copper ions, while potassium cobalt cyanide provides cobalt ions and cyanide ions. Oxalic acid plays a role in complexation and pH adjustment. During the reaction, the copper source releases Cu. 2+ Potassium cobalt cyanide (K3[Co(CN)6]) provides [Co(CN)6]. 3- Complex ions. The two are bridged by cyanide ions (Cu). 2+ -NC-Co 3 +The formation of a Cu / Co-PBA framework structure involves oxalic acid, which participates in the chemical environment regulation of the reaction system, influencing the nucleation and growth process. Oxalic acid (H₂C₂O₄), as a weak acid, adjusts the solution pH, inhibits excessively rapid hydrolysis of metal ions, and may also control the ion release rate through complexation, thus affecting crystal growth kinetics. The reaction is slow at room temperature; extending the reaction time is beneficial for crystal perfection. Shorter times may lead to amorphous or small particles; therefore, this invention controls an appropriate reaction time. Copper source: Different copper source anions affect ionic strength and coordination environment; therefore, this invention uses copper sulfate. High copper source concentration results in a fast nucleation rate, potentially generating smaller, agglomerated particles; low concentrations favor growth, resulting in larger, more dispersed products. Therefore, this invention controls an appropriate concentration. Potassium cobalt cyanide: Its concentration affects the formation rate of the PBA structure. High concentrations rapidly form a large number of crystal nuclei, resulting in small, easily agglomerated products; low concentrations allow for more complete nucleus growth, potentially increasing the size of the nuclei. The oxalic acid used in this invention slows down the reaction rate through complexation, allowing for more complete crystal nucleus growth and potentially resulting in products with larger sizes and more regular morphologies. By changing the amount and method of addition, the morphology of the product can be controlled, such as changing from spherical to cubic shapes. It can also affect the dispersibility of particles and reduce agglomeration. Therefore, this invention involves mixing oxalic acid separately with copper sources and cobalt salts to obtain solutions, ultimately achieving the desired morphology.

[0023] The present invention provides an application of a copper tetrasulfide / cobalt octasulfide / carbon composite material, wherein the copper tetrasulfide / cobalt octasulfide / carbon composite material is used as an active material to prepare a sodium-ion battery anode.

[0024] The present invention provides a rechargeable battery that uses a sodium-ion battery negative electrode prepared by a composite material of copper tetrasulfide / cobalt octasulfide / carbon as the active material, and then makes a rechargeable battery.

[0025] The specific application process is as follows: The above-prepared copper tetrasulfide / cobalt octasulfide / carbon composite material is used as the active material. It is mixed evenly with conductive carbon black and PVDF in a ratio of 8:1:1 or 7:2:1. After being magnetically stirred for 6-8 hours, it is evenly dispersed in N-methylpyrrolidone (NMP). The evenly mixed slurry is coated onto copper foil using a coater and placed in a vacuum drying oven at 60-80℃. After drying for 12-24 hours, it is pressed into tablets using a tablet press and then cut into small circular electrode sheets using a cutting machine. The electrode sheets are assembled into button batteries in a glove box filled with high-purity argon gas and with water and oxygen values ​​≤0.01ppm. The electrolyte is NaPF6+DEGDME, the purity of the sodium sheet is Na≥99.99%, the thickness is 0.5mm, and it is rolled and cut to the size of the electrode sheet.

[0026] The specific method for assembling the battery is as follows: After adding 1 drop of electrolyte to the positive electrode shell, place the electrode plate, then add 1 drop of electrolyte and place the glass fiber, add 3 drops of electrolyte to the glass fiber and place the sodium plate as the counter electrode, then place two pieces of nickel foam, add 4 drops of electrolyte, cover with the negative electrode shell, press and seal the battery with a hydraulic press, and let it stand for 6 to 12 hours.

[0027] Transition metal chalcogenides are considered excellent anode materials for sodium induction binning (SIB) due to their high theoretical specific capacity and low manufacturing cost. However, the poor rate performance and cycling performance of transition metal chalcogenides always lead to low conductivity during the conversion reaction. This invention utilizes a hollow nanosphere composite material composed of nanobulks. The heterogeneous interface between Cu7S4 and Co9S8 crystals can induce an internal electric field to accelerate ion diffusion kinetics, improve conductivity, and provide abundant reaction sites for sodium energy storage. This results in high reversible capacity, high specific capacity, stable cycling performance, and robust rate performance.

[0028] The Cu7S4 / Co9S8 / C porous nanobulb nanosphere composite material provided by this invention significantly increases the specific surface area of ​​the electrode during charge and discharge by reducing the particle size of the material. This not only provides abundant active sites for sodium ions but also shortens the ion diffusion path, effectively mitigating the problem of large sodium ion radii. This leads to a problem of sluggish diffusion kinetics. Composite electrode materials, through multi-component synergistic design and nanostructure optimization, exhibit multiple advantages during the charge-discharge process of sodium-ion batteries. First, Cu7S4 and Co9S8, as high-capacity sulfide active materials, broaden the sodium-ion storage sites through heterojunction coupling effects. For example, the layered structure of Cu7S4 provides fast ion channels, while the cubic crystal framework of Co9S8 enhances structural stability, synergistically achieving high specific capacity. Second, the introduction of a carbon matrix constructs a three-dimensional conductive network, increasing the electronic conductivity of the composite material to 10. -2 The S / cm level significantly reduces charge transfer impedance and suppresses sulfide volume expansion during charge and discharge, thereby improving cycle stability. Mechanistically, this involves a synergistic redox reaction between Cu and Co metals (Cu... 0 / Cu + and Co 2+ / Co 3+ The carbon matrix provides multiple electron transfer pathways, while the confinement effect of the carbon matrix inhibits the aggregation of active particles, thus jointly improving the reaction reversibility and structural durability of the composite electrode.

[0029] Compared with existing technologies, the advantages of this invention are that it prepares a hollow nanosphere Cu7S4 / Co9S8 / C composite material through a simple room temperature precipitation method and annealing process, wherein the bimetallic sulfide Cu7S4 / Co9S8 forms a heterojunction with carbon. Furthermore, the difference in band structure between Cu7S4 and Co9S8 can induce the formation of an internal electric field, accelerating the diffusion kinetics of sodium ions at the heterojunction (increasing the diffusion coefficient to 10⁻¹⁰ cm⁻¹). 2 The carbon coating not only acts as a physical barrier to reduce direct contact between the active material and the electrolyte, mitigating the "shuttle effect" caused by polysulfide dissolution, but also enhances the interfacial sodium ion adsorption capacity through surface functional groups (such as CS bonds), thereby alleviating capacity decay. Benefiting from these advantages, the prepared Cu7S4 / Co9S8 / C composite material exhibits excellent rate performance at 3Ag. -1 After 1000 cycles at current density, the display showed 499mAh g. -1 The high reversible capacity, high specific capacity, stable cycle performance, and robust rate performance demonstrate that Cu7S4 / Co9S8 / C is an excellent and promising SIB anode material. Furthermore, the copper source, cobalt source, and oxalic acid used in this invention are inexpensive and readily available; the carbon coating significantly improves the battery's cycle stability, extends its lifespan, and increases and stabilizes its capacity. Attached Figure Description

[0030] Figure 1 SEM image of Cu / Co PBA nanopolyhedral material, the precursor precipitate of Example 1;

[0031] Figure 2 SEM image of the Cu7S4 / Co9S8 / C nanosphere composite material prepared in Example 1;

[0032] Figure 3 TEM image of the composite material Co9S8 / Cu7S4 / C prepared in Example 1;

[0033] Figure 4 HRTEM image of the composite material Co9S8 / Cu7S4 / C prepared in Example 1;

[0034] Figure 5 The XRD pattern of the composite material Co9S8 / Cu7S4 / C prepared in Example 1;

[0035] Figure 6 The image shows the XRD pattern of the Cu / Co PBA nanopolyhedral material, the precursor precipitate from Example 1.

[0036] Figure 7 SEM image of Cu / Co PBA nanopolyhedral material, the precursor precipitate prepared in Example 2;

[0037] Figure 8 SEM image of the Co9S8 / Cu7S4 / C composite material prepared in Example 2;

[0038] Figure 9 SEM image of Cu / Co PBA nanopolyhedral material, the precursor precipitate prepared in Example 3;

[0039] Figure 10 SEM image of the composite material Co9S8 / Cu7S4 / C prepared in Example 3;

[0040] Figure 11 SEM image of Cu / Co PBA nanopolyhedral material, the precursor precipitate prepared in Example 4;

[0041] Figure 12 SEM image of the composite material Co9S8 / Cu7S4 / C prepared in Example 4;

[0042] Figure 13 SEM image of Cu / Co PBA nanopolyhedral material, the precursor precipitate prepared in Example 5;

[0043] Figure 14 SEM image of the composite material Co9S8 / Cu7S4 / C prepared in Example 5;

[0044] Figure 15 SEM image of Cu / Co PBA nanopolyhedral material, the precursor precipitate prepared in Example 6;

[0045] Figure 16 SEM image of the Co9S8 / Cu7S4 / C composite material prepared in Example 6;

[0046] Figure 17 SEM image of the composite material Co9S8 / Cu7S4 / C prepared in Example 7;

[0047] Figure 18 SEM image of the Co9S8 / Cu7S4 / C composite material prepared in Example 8;

[0048] Figure 19 SEM image of the Co9S8 / Cu7S4 / C composite material prepared in Example 9;

[0049] Figure 20 SEM image of the composite material Co9S8 / Cu7S4 / C prepared in Example 10;

[0050] Figure 21 SEM image of the composite material Co9S8 / Cu7S4 / C prepared in Example 11;

[0051] Figure 22 The composite material Co9S8 / Cu7S4 / C prepared in Example 1 was used as the anode material for a sodium-ion battery in 0.5 Ag. -1 Cyclic stability test results at current density;

[0052] Figure 23 The composite material Co9S8 / Cu7S4 / C prepared in Example 1 was used as the anode material for a sodium-ion battery in 3Ag... -1 Constant current charge-discharge curves at current density;

[0053] Figure 24 The composite material Co9S8 / Cu7S4 / C prepared in Example 1 was used as the anode material for a sodium-ion battery in 0.5 Ag. -1 Cyclic stability test results at current density;

[0054] Figure 25 Rate capability diagram of the composite material Co9S8 / Cu7S4 / C prepared in Example 1 as a negative electrode material for sodium-ion batteries. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0057] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0058] Example 1

[0059] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0060] 1) Preparation of Cu / Co PBA precursor: 2 mmol CuSO4·5H2O and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution A; then 2 mmol K3[Co(CN)6] and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution B; then solutions A and B were mixed and stirred at room temperature for 6 h, and finally settled at room temperature for 12 h, collected by centrifugation, washed 6 times with water and 2 times with ethanol, and dried at 60℃ for 12 h to obtain Cu / Co-PBA nanomaterial precursor.

[0061] Its SEM image is as follows Figure 1 As shown in the figure, it has a polyhedral structure with a size of 600 nm.

[0062] 2) Preparation of Cu7S4 / Co9S8 / C:

[0063] The dried Cu / Co-PBA nanomaterial precursor and sulfur powder were placed in a ceramic boat at a mass ratio of 1:6 and calcined in a hydrogen-argon atmosphere with a hydrogen gas fraction of 5% and an argon gas fraction of 95%. The calcination temperature was 500℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 2 As shown in the image, it can be seen that it is a hollow spherical structure composed of nanobulbs. TEM image as follows. Figure 3 As shown.

[0064] The HRTEM of the Cu7S4 / Co9S8 / C composite material obtained in this embodiment is as follows: Figure 4 As shown, the obtained product is a complex of Cu7S4 and Co9S8, as illustrated in the XRD pattern. Figure 5 As shown, the obtained product is Cu7S4 / Co9S8 / C. The XRD pattern of the Cu / Co PBA precursor material obtained in this embodiment is shown below. Figure 6 As shown in the figure, the successful preparation of the precursor can be illustrated.

[0065] Example 2 (as a comparison)

[0066] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0067] 1) Preparation of the precursor: 4 mmol CuSO4·5H2O and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution A; then 2 mmol K3[Co(CN)6] and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution B; solutions A and B were then mixed and stirred at room temperature for 6 h, and finally allowed to settle at room temperature for 12 h. The mixture was collected by centrifugation, washed 5 times with water and 2 times with ethanol, and dried at 70℃ for 12 h to obtain Cu / Co-PBA nanomaterials. Its SEM image is shown below. Figure 7 As shown in the figure, the morphology has changed and become uneven.

[0068] 2) Preparation of Cu7S4 / Co9S8 / C:

[0069] The dried precursor Cu / Co-PBA nanomaterials and sulfur powder were placed in a ceramic boat at a mass ratio of 1:6 and calcined in a hydrogen-argon atmosphere with a hydrogen gas fraction of 5% and an argon gas fraction of 95%. The calcination temperature was 500℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 8 As shown in the figure, there is basically no morphology, which is inconsistent with the morphology of the precursor.

[0070] Example 3 (as a comparison)

[0071] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0072] 1) Preparation of precursors: 6 mmol CuSO4·5H2O and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution A; then 2 mmol K3[Co(CN)6] and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution B; solutions A and B were then mixed and stirred at room temperature for 6 h, and finally allowed to settle at room temperature for 12 h. The mixture was collected by centrifugation, washed 5 times with water and 2 times with ethanol, and dried at 60℃ for 13 h to obtain Cu / Co-PBA nanomaterials. Its SEM image is shown below. Figure 9 As shown in the figure, it can be seen that it has a polyhedral structure, but there is adhesion between the polyhedra, and the size is about 600nm.

[0073] 2) Preparation of Cu7S4 / Co9S8 / C:

[0074] The dried precursor product Cu / Co-PBA nanomaterials were mixed with sulfur powder at a mass ratio of 1:6 in a ceramic boat and calcined in a hydrogen-argon atmosphere with a hydrogen integral of 5% and an argon integral of 95%. The calcination temperature was 500℃, the calcination time was 2 h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 10 As shown in the figure, some parts retain the original structure of the polyhedron, while most of them have become rubble-like and have not been assembled into a hollow sphere.

[0075] Example 4 (as a comparison)

[0076] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0077] 1) Preparation of precursors: 3 mmol CuSO4·5H2O and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution A; then 3 mmol K3[Co(CN)6] and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution B; solutions A and B were then mixed and stirred at room temperature for 6 h, and finally allowed to settle at room temperature for 12 h. The mixture was collected by centrifugation, washed 5 times with water and 2 times with ethanol, and dried at 80℃ for 12 h to obtain Cu / Co-PBA nanomaterials. Its SEM image is shown below. Figure 11 As shown in the figure, it can be seen that it has a polyhedral structure, but the size varies, ranging from 300 to 600 nm.

[0078] 2) Preparation of Cu7S4 / Co9S8 / C:

[0079] The dried precursor Cu / Co-PBA nanomaterials and sulfur powder were placed in a ceramic boat at a mass ratio of 1:6 and calcined in a hydrogen-argon atmosphere with a hydrogen gas integral of 5% and an argon gas integral of 95%. The calcination temperature was 500℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 12 As shown in the figure, most of the material is in the form of gravel, while a small portion is in the form of long, needle-like structures, with varying shapes and sizes.

[0080] Example 5 (as a comparison)

[0081] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0082] 1) Preparation of the precursor: 3 mmol CuSO4·5H2O and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution A; then 6 mmol K3[Co(CN)6] and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution B; solutions A and B were then mixed and stirred at room temperature for 6 h, and finally allowed to settle at room temperature for 12 h. The mixture was collected by centrifugation, washed 5 times with water and 2 times with ethanol, and dried at 70℃ for 12 h to obtain Cu / Co-PBA nanomaterials. Its SEM image is shown below. Figure 13 As shown in the figure, it can be seen that it is a polyhedral structure, but the sizes are different and there is adhesion. The size ranges from 300 to 800 nm.

[0083] 2) Preparation of Cu7S4 / Co9S8 / C:

[0084] The dried precursor Cu / Co-PBA nanomaterials and sulfur powder were placed in a ceramic boat at a mass ratio of 1:6 and calcined in a hydrogen-argon atmosphere with a hydrogen gas fraction of 5% and an argon gas fraction of 95%. The calcination temperature was 500℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 14 As shown in the figure, the structure collapsed after calcination and did not form a hollow sphere.

[0085] Example 6 (as a comparison)

[0086] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0087] 1) Preparation of the precursor: 3 mmol CuSO4·5H2O and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution A; then 9 mmol K3[Co(CN)6] and 20 mmol oxalic acid were dispersed in 50 mL deionized water and stirred for 1 h to form solution B; solutions A and B were then mixed and stirred at room temperature for 6 h, and finally allowed to settle at room temperature for 12 h. The mixture was collected by centrifugation, washed 6 times with water and 2 times with ethanol, and dried at 60℃ for 14 h to obtain Cu / Co-PBA nanomaterials. Its SEM image is shown below. Figure 15 As shown in the figure, most of them have clustered together, with only a very small number of parts still exhibiting a polyhedral structure of varying sizes.

[0088] 2) Preparation of Cu7S4 / Co9S8 / C:

[0089] The dried precursor Cu / Co-PBA nanomaterials and sulfur powder were placed in a ceramic boat at a mass ratio of 1:6 and calcined in a hydrogen-argon atmosphere with a hydrogen gas fraction of 5% and an argon gas fraction of 95%. The calcination temperature was 500℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 16 As shown in the figure, the agglomeration is more thorough after calcination, resulting in a blocky structure.

[0090] By comparison Figure 1 and Figures 7-16 It can be seen that as the ratio between cobalt and copper sources changes, an excess of either copper or cobalt source will make it easier for the material to aggregate during the sedimentation process at room temperature, resulting in a non-uniform morphology and a tendency to form blocky agglomerates.

[0091] Example 7 (as a comparison)

[0092] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0093] 1) Preparation of the precursor: Same as in Example 1;

[0094] 2) Preparation of Cu7S4 / Co9S8 / C:

[0095] The dried precursor product and sulfur powder were placed in a porcelain boat at a mass ratio of 1:6 and calcined in an argon atmosphere at a temperature of 500℃ for 2 hours at a heating rate of 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 17 As shown in the figure, the material agglomerates after calcination, destroying its original morphology.

[0096] Example 8 (as a comparison)

[0097] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0098] 1) Preparation of the precursor: Same as in Example 1;

[0099] 2) Preparation of Cu7S4 / Co9S8 / C:

[0100] The dried precursor product and sulfur powder were placed in a porcelain boat at a mass ratio of 1:6 and calcined in a flowing hydrogen-argon atmosphere. The hydrogen gas fraction was 5%, the argon gas fraction was 95%, the calcination temperature was 300℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 18 As shown in the figure, a small portion of the precursor retains the same morphology.

[0101] Example 9 (as a comparison)

[0102] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0103] 1) Preparation of the precursor: Same as in Example 1;

[0104] 2) Preparation of Cu7S4 / Co9S8 / C:

[0105] The dried precursor product and sulfur powder (mass ratio 1:6) were placed in a ceramic boat and calcined in a flowing hydrogen-argon atmosphere. The hydrogen gas fraction was 5%, the argon gas fraction was 95%, the calcination temperature was 400℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 19 As shown in the figure, the precursor morphology has collapsed and has not formed a hollow spherical structure.

[0106] Example 10 (as a comparison)

[0107] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0108] 1) Preparation of the precursor: Same as in Example 1;

[0109] 2) Preparation of Cu7S4 / Co9S8 / C:

[0110] The dried precursor product and sulfur powder were placed in a porcelain boat at a mass ratio of 1:6 and calcined in a flowing hydrogen-argon atmosphere. The hydrogen gas fraction was 5%, the argon gas fraction was 95%, the calcination temperature was 600℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 20 As shown in the figure, it can be seen that it has all become a block structure.

[0111] Example 11 (as a comparison)

[0112] A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material includes the following steps:

[0113] 1) Preparation of the precursor: Same as in Example 1;

[0114] 2) Preparation of Cu7S4 / Co9S8 / C:

[0115] The dried precursor product and sulfur powder were placed in a porcelain boat at a mass ratio of 1:6 and calcined in a flowing hydrogen-argon atmosphere. The hydrogen gas fraction was 5%, the argon gas fraction was 95%, the calcination temperature was 700℃, the calcination time was 2h, and the heating rate was 2℃ / min. The final product Cu7S4 / Co9S8 / C was obtained, and its SEM image is shown below. Figure 21 As shown in the figure, it can be seen that everything has become a blocky structure with varying sizes.

[0116] Example 12

[0117] An application of a copper tetrasulfide / cobalt octasulfide / carbon composite material as an active material in the preparation of a sodium-ion battery anode, and subsequently in the preparation of a sodium-ion rechargeable battery, is detailed below:

[0118] Example 1 describes the preparation of sodium batteries using the product, copper tetrasulfide / cobalt octasulfide / carbon composite material, as a negative electrode material for sodium-ion batteries. Specifically:

[0119] The copper tetrasulfide / cobalt octasulfide / carbon composite material prepared in Example 1 was used as the active material. It was mixed with conductive carbon black and PVDF in a ratio of 7:2:1 and then magnetically stirred for 8 hours to disperse it evenly in NMP. The uniformly mixed slurry was coated onto copper foil using a coater and placed in a vacuum drying oven at 80°C for 24 hours. After drying, it was pressed into tablets using a tablet press and then cut into small circular electrode sheets using a cutting machine. The electrode sheets were assembled into button batteries in a glove box filled with high-purity argon gas and with water and oxygen values ​​≤0.01ppm. The electrolyte was NaPF6+DEGDME, the sodium sheet purity was Na≥99.99%, the thickness was 0.5mm, and it was rolled and cut to the size of the electrode sheet.

[0120] The specific method for assembling the battery is as follows: Add one drop of electrolyte to the positive electrode shell, then place the electrode plate. Next, add one drop of electrolyte and place the glass fiber. Add three drops of electrolyte to the glass fiber and place a sodium sheet as the counter electrode. Then, place two pieces of nickel foam, add four more drops of electrolyte, cover with the negative electrode shell, and use a hydraulic press to press and seal the battery. Let it stand for 6–12 hours.

[0121] Specific testing procedure: After assembling the sodium-ion half-cell, the following steps were set on the Xinwei tester: first, constant current discharge to 0.1V, then constant current charging to 3V, repeating this cycle a certain number of times. The active material load on the electrode plates was approximately 1.0 mg / cm³. -2 .

[0122] The test results and data are as follows:

[0123] Figure 22 The composite material Co9S8 / Cu7S4 / C prepared in Example 1 is shown to be effective as a sodium-ion battery anode material in 0.5 Ag.-1 Cyclic stability test results at current density; stable cycling for over 300 cycles at this current density, with capacity remaining stable at 564 mAh g. -1 It exhibits good cyclic stability.

[0124] Figure 23 The composite material Co9S8 / Cu7S4 / C prepared in Example 1 is shown to be used as a negative electrode material for sodium-ion batteries in 3Ag. -1 Cyclic stability test results at current density; after more than 1000 cycles at this current density, the capacity remains at 499 mAh g. -1 It exhibits good cyclic stability.

[0125] Figure 24 The current density is 0.5Ag. -1 The charge-discharge curves show an average discharge voltage of around 1.7V. The second and third curves have a high degree of overlap, indicating good reversibility.

[0126] Figure 25 The graph shows the rate capability of the Co9S8 / Cu7S4 / C composite material prepared in Example 1 as the anode material for a sodium-ion battery. As can be seen from the graph, this composite material exhibits good rate performance. Furthermore, it still maintains high capacity after two cycles of high-current rate cycling, indicating good electrochemical performance.

[0127] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a copper tetrasulfide / cobalt octasulfide / carbon composite material, characterized in that, The preparation method includes the following steps: 1) Preparation of Cu / Co-PBA precursor by room temperature sedimentation method; 2) Cu / Co-PBA precursor and sulfur powder were sulfidated and annealed in a reducing atmosphere to obtain Cu7S4 / Co9S8 / C composite material.

2. The preparation method according to claim 1, characterized in that, The preparation method of the Cu / Co-PBA precursor in step 1) is as follows: Copper source and oxalic acid are dispersed in water and stirred to form solution A; cobalt source and oxalic acid are dispersed in water and stirred to form solution B; solutions A and B are mixed and stirred, and then allowed to settle at room temperature to obtain the Cu / Co-PBA precursor.

3. The preparation method according to claim 2, characterized in that, In the preparation method of the Cu / Co-PBA precursor, the molar ratio of the copper source to the cobalt source is 1-5:2; the cobalt source is K3[Co(CN)6].

4. The preparation method according to claim 2 or 3, characterized in that, In solution A, the molar ratio of copper source to oxalic acid is 1:10; in solution B, the molar ratio of cobalt source to oxalic acid is 1:

10.

5. The preparation method according to claim 2 or 3, characterized in that, The settling time at room temperature was 12 hours.

6. The preparation method according to claim 1, characterized in that, In step 2), during the sulfurization annealing, the mass ratio of Cu / Co-PBA precursor to sulfur powder is 1:6-10.

7. The preparation method according to claim 1 or 6, characterized in that, In step 2), the temperature of the vulcanization annealing is 500-550℃, and the vulcanization annealing time is 2 hours.

8. A copper tetrasulfide heptacobalt / cobalt octacobalt / carbon composite material, prepared by the preparation method according to any one of claims 1-7, is a Cu7S4 / Co9S8 / C composite material composed of hollow nanoblocks, with the size of the spherical structure being 500-700 nm.

9. The application of the copper tetrasulfide heptasulfide / cobalt octasulfide / carbon composite material according to claim 8, characterized in that, Sodium-ion batteries are prepared by using them as active materials to prepare anodes for sodium-ion batteries.

10. A rechargeable battery, characterized in that, The rechargeable battery is made using the sodium-ion battery negative electrode as described in claim 9.

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