Hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material, preparation method and application thereof

Abstract

This invention provides a hollow polyhedron NiS2 / Cu 7.2 This invention relates to the field of sodium-ion battery electrode materials technology, specifically the S4 sodium battery composite material, its preparation method, and its application. The hollow polyhedral NiS2 / Cu composite material of this invention... 7.2 The S4 sodium battery composite material exhibits a hollow polyhedral morphology and is prepared from nickel nitrate, copper chloride, and sulfur powder through a simple hydrothermal reaction and high-temperature calcination. The hollow polyhedral NiS2 / Cu... 7.2 The S4 sodium battery composite material is used in the negative electrode material of sodium batteries. The assembled half-cell has good rate performance and excellent cycle performance. After 100 cycles at a current density of 0.1 A / g, it has a discharge specific capacity of 566.3 mAh / g, and after 10,000 cycles at a high current density of 10 A / g, it still has a discharge specific capacity of 443.7 mAh / g.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of catalysts, in particular to a hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material, a preparation method therefor, and an application thereof. BACKGROUND

[0002] In recent years, the consumption of fossil energy continues to grow, which is in conflict with the goal of green and sustainable development, and the gradual depletion of fossil energy forces us to find energy storage materials with higher performance. Secondary batteries are considered to be energy storage devices that can be widely used in environmental protection vehicles, power storage and power fields. Among them, lithium ion batteries have been widely used due to their high energy density, high window voltage, light weight and no self-discharge. However, with wider application, the demand for lithium resources is in conflict with its abundance on the earth's surface, so the cost of lithium rises. At this time, sodium ion batteries, which are similar to lithium in terms of chemical properties, make it possible to replace and supplement lithium ion batteries. As a key component of batteries, electrode materials directly affect the performance of sodium ion batteries. The development of electrode materials with excellent performance can make the commercialization of sodium ion batteries possible. Among them, the research on negative electrode materials mainly focuses on intercalation materials based on carbon-based materials, conversion reaction materials based on transition metal oxides / sulfides and alloy reaction materials.

[0003] Compared with oxides, transition metal sulfides have higher electrical conductivity, higher specific capacity based on conversion reaction and higher potential as electrode materials. Nickel sulfide has a wide variety and high theoretical specific capacity, and exhibits high electrochemical reversibility in the application of sodium ion battery negative electrode materials. However, the electrical conductivity of nickel sulfide is low, and the volume expansion and material pulverization caused by the conversion reaction mechanism greatly shorten the long cycle life of the electrode material. Therefore, it is crucial to improve the mechanical stability and electrical conductivity of the material. Generally, special microstructures are constructed to release the cycle strain force, such as hollow structure, yolk shell structure, etc. The existence of heterojunction structure will introduce a built-in electric field, which is generally considered to be a common means to improve the electrical conductivity. The Kirkendall effect refers to the formation of defects in the diffusion process of two metals with different diffusion rates, and then hollow nanoparticles are prepared, so the heterojunction and hollow structure can be introduced by the Kirkendall effect. Therefore, reasonable design of material structure and construction of heterojunction can improve the performance of nickel sulfide in sodium ion batteries, so as to realize its application in the field of sodium ion batteries.

[0004] In summary, the application combines metal ion doping and structure construction, and prepares a corresponding solid polyhedral NiS2 / Cu 7.2S4 composite. According to the Kirkendall diffusion effect, by adjusting the content ratio of different metals, hollow polyhedral NiS2 / Cu 7.2 S4 composite material. The hollow structure is beneficial to release the mechanical stress generated in the cycle process of the material, thereby relieving the inherent volume expansion problem of the sulfide material, ensuring the cycle stability of the material in the sodium storage process, and the NiS2 / Cu 7.2 The existence of S4 heterojunction builds an internal electric field, which promotes electron transmission, improves electrical conductivity, and promotes electron diffusion dynamics, thereby improving the electrochemical performance of the sulfide material. SUMMARY

[0005] In view of the above deficiencies of the prior art, the present application provides a hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material and its preparation method and application, the present application constructs a special hollow polyhedral structure, which is beneficial to release the stress generated in the cycle process of the sulfide material, slows down the volume expansion of the sulfide material in the sodium insertion / desorption process, and improves the cycle stability of the sulfide material; in addition, the NiS2 / Cu 7.2 The existence of S4 heterojunction introduces an internal electric field, accelerates electron diffusion, improves electron diffusion dynamics, and thereby improves the electrochemical performance of the sulfide material.

[0006] To achieve the above-mentioned purpose, the specific technical solutions of the present application are as follows:

[0007] A hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material, which is in the form of a hollow polyhedron and is prepared by the following method: using nickel nitrate, copper chloride and sulfur powder as raw materials, a solid polyhedral NiS2 / Cu 7.2 S4 composite, and then calcining at high temperature to obtain a hollow polyhedral NiS2 / Cu 7.2 S4 (NiS2 / Cu 7.2 S4 is abbreviated as NCSs) sodium battery composite material; the molar ratio of the nickel nitrate, copper chloride and sulfur powder is 2:1:6.

[0008] The present application obtains the corresponding solid polyhedral NiS2 / Cu 7.2 S4 composite, and then according to the Kirkendall diffusion effect, by adjusting the content ratio of different metals, a hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material. The hollow polyhedral NiS2 / Cu 7.2The S4 sodium battery composite material has the best structure and morphology, and the hollow polyhedral structure is beneficial to release the mechanical stress generated by the sulfide material in the cycle process, thereby relieving the inherent volume expansion problem of the sulfide material, and ensuring the cycle stability of the sulfide material in the sodium storage process; in addition, the hollow polyhedral NiS2 / Cu 7.2 The S4 sodium battery composite material has the best structure and morphology, and the hollow polyhedral structure is beneficial to release the mechanical stress generated by the sulfide material in the cycle process, thereby relieving the inherent volume expansion problem of the sulfide material, and ensuring the cycle stability of the sulfide material in the sodium storage process; in addition, the hollow polyhedral NiS2 / Cu 7.2 The existence of the S4 heterojunction constructs a built-in electric field, and the internal electric field can promote electron transmission, improve electrical conductivity, and promote electron diffusion kinetics, thereby improving the electrochemical performance of the sulfide material. The hollow polyhedral NiS2 / Cu 7.2 The S4 sodium battery composite material has good rate performance and excellent cycle performance, and when it is applied to the negative electrode material of a sodium battery, the half battery assembled has a discharge specific capacity of 566.3 mAh / g after 100 cycles at a current density of 0.1 A / g; and still has a discharge specific capacity of 443.7 mAh / g after 10,000 cycles at a large current density of 10 A / g.

[0009] Preferably, the hollow polyhedral NiS2 / Cu 7.2 The diameter of the S4 sodium battery composite material is 300-400 nm.

[0010] The hollow polyhedral NiS2 / Cu 7.2 The preparation method of the S4 sodium battery composite material comprises the following steps:

[0011] S1. A proper amount of polyvinylpyrrolidone (polyvinylpyrrolidone is abbreviated as PVP) is added into ethylene glycol and uniformly dispersed, and then nickel nitrate, copper chloride and sulfur powder are sequentially added into the solution, and after being mixed uniformly, the solution is subjected to hydrothermal reaction at 120-180 DEG C for 10-18 h, and after washing, separation and drying, a solid polyhedral NiS2 / Cu 7.2 S4 composite;

[0012] S2. The solid polyhedral NiS2 / Cu 7.2 The S4 composite is subjected to high-temperature calcination at 450-600 DEG C for 2-3 h in an inert gas atmosphere to obtain a hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material.

[0013] The hollow polyhedral NiS2 / Cu 7.2 The S4 sodium battery composite material is prepared by simple hydrothermal reaction and high-temperature calcination, and in step S1, the solid polyhedral NiS2 / Cu 7.2S4 composite, wherein different kinds of metal salts will affect the external morphology of the final composite; in step S2, the solid polyhedral NiS2 / Cu 7.2 S4 composite is kept at high temperature for a certain period of time, and according to the Kishner effect, different degrees of hollow polyhedral NiS2 / Cu are formed by adjusting the proportion of different kinds of metal sources. 7.2 S4 sodium battery composite material.

[0014] Preferably, in step S1, the molecular weight of the polyvinylpyrrolidone is 58000, the concentration of the polyvinylpyrrolidone in ethylene glycol is 3.3 ~ 15 g / L; the concentration of the nickel nitrate in ethylene glycol is 0.02 ~ 0.18 mol / L.

[0015] Preferably, in step S2, the temperature of the high-temperature calcination is 500 ~ 600 ℃.

[0016] The application also provides the hollow polyhedral NiS2 / Cu 7.2 Application of the S4 sodium battery composite material in a sodium ion battery negative material.

[0017] Compared with the prior art, the application has the following advantages:

[0018] (1) The hollow polyhedral structure constructed in the application can release the mechanical stress generated by the sulfide material in the cycle process, thereby relieving the inherent volume expansion problem of the sulfide material and ensuring the cycle stability of the sulfide material in the sodium storage process; in addition, the hollow polyhedral NiS2 / Cu 7.2 NiS2 / Cu in the S4 composite 7.2 The existence of the S4 heterojunction constructs a built-in electric field, and this internal electric field can promote electron transmission, thereby improving the electrical conductivity and promoting the diffusion dynamics of electrons.

[0019] (2) The hollow polyhedral NiS2 / Cu 7.2 The S4 sodium battery composite material has good rate performance and excellent cycle performance, and when it is applied to a sodium battery negative material, the assembled half battery has a discharge specific capacity of 566.3 mAh / g after 100 cycles at a current density of 0.1 A / g and still has a discharge specific capacity of 443.7 mAh / g after 10000 cycles at a large current density of 10 A / g.

[0020] (3) The hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material, the preparation process is simple, the equipment and devices used are all conventional equipment and devices, and the raw material cost is low, which is conducive to industrial large-scale production. Attached Figure Description

[0021] Figure 1 XRD pattern of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1;

[0022] Figure 2 SEM image of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1;

[0023] Figure 3 TEM image of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1;

[0024] Figure 4 The graph shows the cycling performance of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1 at a current density of 0.1 A / g.

[0025] Figure 5 The graph shows the cycling performance of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1 at a current density of 10 A / g.

[0026] Figure 6 TEM image of the NSs sodium battery material prepared in Comparative Example 1;

[0027] Figure 7 TEM image of the CNSs sodium battery composite material prepared in Comparative Example 2;

[0028] Figure 8 TEM image of the CSs sodium battery material prepared in Comparative Example 3;

[0029] Figure 9 The graph shows the cycling performance of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1 at different current densities.

[0030] Figure 10 Comparison of the cycling performance of the sodium NSs battery material prepared in Comparative Example 1, the sodium CNSs battery composite material prepared in Comparative Example 2, and the sodium CSs battery material prepared in Comparative Example 3 at a current density of 0.1 A / g.

[0031] Figure 11 The graph shows the cycling performance of the hollow spherical NCSs-C sodium battery composite material prepared in Comparative Example 4 at a current density of 10 A / g. Detailed Implementation

[0032] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0033] The present application provides a hollow polyhedral NiS2 / Cu 7.2 The present application provides a hollow polyhedral NiS2 / Cu 7.2 S4 composite, and then high-temperature calcination to obtain a hollow polyhedral NiS2 / Cu 7.2 S4 (NiS2 / Cu 7.2 S4, which is referred to as NCSs) sodium battery composite material; the molar ratio of the nickel nitrate, copper chloride and sulfur powder is 2:1:6.

[0034] The present application provides a hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material has a diameter of 300-400 nm.

[0035] The present application provides a hollow polyhedral NiS2 / Cu 7.2 The present application provides a preparation method of a hollow polyhedral NiS2 / Cu

[0036] S1. A proper amount of polyvinylpyrrolidone is added into ethylene glycol and dispersed uniformly, and then nickel nitrate, copper chloride and sulfur powder are sequentially added into the solution, mixed uniformly, and then subjected to hydrothermal reaction at 120-180°C for 10-18 h. After washing, separation and drying, a solid polyhedral NiS2 / Cu 7.2 S4 composite is obtained.

[0037] S2. The solid polyhedral NiS2 / Cu 7.2 S4 composite obtained in step S1 is subjected to high-temperature calcination at 450-600°C for 2-3 h in an inert gas atmosphere to obtain a hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material.

[0038] In some examples, the concentration of the polyvinylpyrrolidone in the ethylene glycol is 3.3-15 g / L; and the concentration of the nickel nitrate in the ethylene glycol is 0.02-0.18 mol / L.

[0039] In the following specific embodiments, the molecular weight of the polyvinylpyrrolidone is 58000.

[0040] Embodiment 1

[0041] Hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material, the preparation steps are as follows:

[0042] S1. Dissolve 0.4 g of PVP in 50 mL of ethylene glycol, and after ultrasonic stirring to form a solution A, add 2 mmol of nickel nitrate hexahydrate, 1 mmol of copper chloride dihydrate, and 6 mmol of sulfur powder to solution A in sequence and stir until uniform to obtain a mixed solution A; place the mixed solution A in a reaction kettle and heat to 180 ℃ for hydrothermal reaction for 12 h; centrifugally wash the obtained precipitate with deionized water and anhydrous ethanol four times respectively, and then vacuum dry to obtain a solid of a solid NCSs composite material;

[0043] S2. Place the solid NCSs composite material in a tube furnace filled with argon, heat to 600 ℃ at a heating rate of 3 ℃ / min and keep for 3 h to obtain a hollow polyhedral NCSs sodium battery composite material.

[0044] Figure 1 The XRD pattern of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1, from the XRD pattern, it can be seen that the diffraction peaks at 27.1 o ,31.4 o ,35.3 o ,38.8 o , and 45.1 o , respectively, correspond to the (1 1 1), (2 0 0), (2 1 0), (2 1 1) and (2 2 0) faces of NiS2 (JCPDS No. 89-7142); the diffraction peaks at 27.7 o ,32.1 o ,45.9 o , respectively, correspond to the (1 1 1), (2 0 0) and (2 2 0) faces of Cu 7.2 S4 (JCPDS No. 72-1966); the XRD results show that the hollow polyhedral NCSs sodium battery composite material has been successfully synthesized. Figure 2 , Figure 3 are respectively the SEM and TEM images of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1, from Figure 2 , it can be seen from Figure 3 that the hollow polyhedral NCSs sodium battery composite material is in the form of a polyhedron, and the inside is a loose hollow structure, and the diameter is between 300-400 nm.

[0045] Comparative Example 1

[0046] A NSs sodium battery material, the preparation steps are as follows:

[0047] S1. 0.4 g PVP was dissolved in 50 mL ethylene glycol, and after ultrasonic stirring to form a solution A, 3 mmol of nickel nitrate hexahydrate and 6 mmol of sulfur powder were sequentially dissolved in the solution A and stirred to be uniform to obtain a mixed solution A; the mixed solution A was placed in a reaction kettle and heated to 180 ℃ for hydrothermal reaction for 12 h; the obtained precipitate was washed with deionized water and anhydrous ethanol by centrifugation for four times, and then vacuum dried to obtain solid NSs;

[0048] S2. The solid NSs were placed in a tube furnace filled with argon, and heated to 600 ℃ at a heating rate of 3 ℃ / min and kept for 3 h to obtain the NSs sodium battery material.

[0049] Figure 6 The TEM image of the NSs sodium battery material prepared for Comparative Example 1 can be seen that the morphology of the monomer NSs sodium battery material is similar to the hollow polyhedral NCSs sodium battery composite material prepared in Example 1, but there is no obvious hollow structure.

[0050] Comparative Example 2

[0051] A CNSs sodium battery composite material, the preparation steps are as follows:

[0052] S1. 0.4 g PVP was dissolved in 50 mL ethylene glycol, and after ultrasonic stirring to form a solution A, 3 mmol of nickel nitrate hexahydrate and 6 mmol of sulfur powder were sequentially dissolved in the solution A and stirred to be uniform to obtain a mixed solution A; the mixed solution A was placed in a reaction kettle and heated to 180 ℃ for hydrothermal reaction for 12 h; the obtained precipitate was washed with deionized water and anhydrous ethanol by centrifugation for four times, and then vacuum dried to obtain solid NSs;

[0053] S2. The solid NSs were placed in a tube furnace filled with argon, and heated to 600 ℃ at a heating rate of 3 ℃ / min and kept for 3 h to obtain the NSs sodium battery material.

[0054] Figure 7 The TEM image of the CNSs sodium battery composite material prepared for Comparative Example 2 can be seen that when the molar amount of copper chloride is greater than that of nickel nitrate, the morphology of the obtained CNSs sodium battery composite material changes significantly, showing an internal loose porous microsphere structure, and the diameter thereof is about 2-3 μm.

[0055] Comparative Example 3

[0056] A CSs sodium battery material, the preparation steps are as follows:

[0057] S1. 0.4 g PVP was dissolved in 50 mL ethylene glycol, and after ultrasonic stirring to form a solution A, 3 mmol copper chloride dihydrate, 6 mmol sulfur powder were dissolved in the above solution A and stirred to be uniform to obtain a mixed solution A; the mixed solution A was placed in a reaction kettle and heated to 180 ℃ for hydrothermal reaction for 12 h; the obtained precipitate was washed with deionized water and anhydrous ethanol by centrifugation for four times respectively, and then vacuum dried to obtain solid CSs;

[0058] S2. The solid CSs was placed in a tube furnace filled with argon, heated to 600 ℃ at a heating rate of 3 ℃ / min and kept for 3 h to obtain a CSs sodium battery material.

[0059] Figure 8 The TEM image of the CSs sodium battery material prepared for Comparative Example 3 can be seen from the figure, and the morphology of the monomer CSs sodium battery material is similar to that of the CNSs sodium battery composite material prepared in Comparative Example 2, but the interior is more compact than that of the CNSs sodium battery composite material.

[0060] Comparative Example 4

[0061] A NCSs-C sodium battery composite material, the preparation steps are as follows:

[0062] S1. 0.4 g PVP was dissolved in 50 mL ethylene glycol, and after ultrasonic stirring to form a solution A, 2 mmol nickel sulfate hexahydrate, 1 mmol copper chloride dihydrate, 3 mmol thiourea, 3 mmol sulfur sublimation were dissolved in the above solution A and stirred to be uniform to obtain a mixed solution A; the mixed solution A was placed in a reaction kettle and heated to 180 ℃ for hydrothermal reaction for 12 h; the obtained precipitate was washed with deionized water and anhydrous ethanol by centrifugation for four times respectively, and then vacuum dried to obtain solid NCSs-c;

[0063] S2. The solid NCSs-c was placed in a tube furnace filled with argon, heated to 600 ℃ at a heating rate of 3 ℃ / min and kept for 3 h to obtain a hollow spherical NCSs-C sodium battery composite material.

[0064] Application Example

[0065] The materials prepared in Examples 1 and Comparative Examples 1-4, the conductive agent (Super P), and carboxymethyl cellulose (CMC) were mixed evenly at a mass ratio of 7:2:1. An appropriate amount of ultrapure water was added to form a slurry, which was then coated onto copper foil using a doctor blade to form a negative electrode. The coated copper foil was placed in a drying oven and dried at 80 °C for 12 h. The coated copper foil was then cut into small circular pieces with a diameter of 12 mm and assembled into button batteries (CR2032) in a glove box. The negative electrode made of the composite material was used as the working electrode, and a sodium block was used as the counter electrode. Its electrochemical performance was tested. The separator was Whatman GF / A, and the electrolyte system consisted of 1 M NaF6 as the solute and 100% DME as the solvent.

[0066] Electrochemical performance tests were conducted on the assembled button batteries. The testing instrument used for the electrochemical performance tests was the LANHE-CT2001A multi-channel battery testing system manufactured by Wuhan Landian Electronics Co., Ltd. The resting time was 12 hours, the voltage window range was 0.2-2.8 V, the current density range was 100-10000 mA / g, and the cycle number range was 100-10000 times.

[0067] Figure 4 The graph shows the cycling performance of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1 at a current density of 0.1 A / g. Figure 4 As can be seen, the hollow polyhedral NCSs sodium battery composite material still maintains a high discharge specific capacity of 566.3 mAh / g after 100 cycles, indicating that it has good cycle stability. Figure 5 The graph shows the cycling performance of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1 at a current density of 10 A / g. Figure 5 As can be seen, the hollow polyhedral NCSs sodium battery composite material still has a discharge specific capacity of 443.7 mAh / g after 10,000 cycles, reflecting its good rate performance and excellent cycle performance.

[0068] Figure 9 The graph shows the cycling performance of the hollow polyhedral NCSs sodium battery composite material prepared in Example 1 at different current densities. Figure 10 Comparison of the cycling performance of the sodium NSs battery material prepared in Comparative Example 1, the sodium CNSs battery composite material prepared in Comparative Example 2, and the sodium CSs battery material prepared in Comparative Example 3 at a current density of 0.1 A / g; comprehensive comparison. Figure 9 and Figure 10 It can be seen that the hollow polyhedron NiS2 / Cu prepared by this invention 7.2 S4 sodium battery composite material has the best cycle performance.

[0069] Figure 11 The cycle performance graph of the hollow spherical NCSs-C sodium battery composite material prepared for Comparative Example 4 at a current density of 10 A / g is shown in Figure 6, from which it can be seen that the discharge specific capacity of the composite material is attenuated to 208.5 mAh / g after 2000 cycles. Figure 11

[0070] In summary, the present application adjusts the types of raw materials and the ratio therebetween to regulate the micro-morphology and hollow degree of the composite material, so that the hollow polyhedral composite material prepared has the optimal structure and morphology; the hollow polyhedral NiS2 / Cu 7.2 The hollow structure in the NCSs-C sodium battery composite material can relieve the volume expansion problem during the material cycle process, so that it has the optimal cycle stability, in addition, the NiS2 / Cu 7.2 The existence of the NCSs-C heterojunction can introduce a built-in electric field to improve the conductivity and electron diffusion dynamics, which is beneficial to the sodium storage kinetics process. The hollow polyhedral NiS2 / Cu 7.2 The NCSs-C sodium battery composite material is applied to the sodium battery negative material, and the assembled half battery has good rate performance and excellent cycle performance, wherein the discharge specific capacity is 566.3 mAh / g after 100 cycles at a current density of 0.1 A / g, and the discharge specific capacity is 443.7 mAh / g after 10000 cycles at a large current density of 10 A / g.

[0071] The above specific embodiments describe the implementation of the present application in detail, but the present application is not limited to the specific details in the above embodiments. Within the scope of the claims and technical concepts of the present application, the technical solutions of the present application can be modified and changed in many simple ways, and these simple modifications all belong to the protection scope of the present application.​

Claims

1. A hollow polyhedral NiS2 / Cu 7.2 S4 sodium battery composite material characterized by, The hollow polyhedron is prepared by using nickel nitrate, copper chloride and sulfur powder as raw materials, and through a hydrothermal reaction to generate a solid polyhedron of NiS2 / Cu 7.2 S4 composite, and then through high-temperature calcination to obtain a hollow polyhedron of NiS2 / Cu 7.2 S4 sodium battery composite material; the molar ratio of the nickel nitrate, copper chloride and sulfur powder is 2:1:

6.

2. A hollow polyhedral NiS2 / Cu according to claim 1 7.2 S4 sodium battery composite material characterized by, The hollow polyhedron NiS2 / Cu 7.2 The diameter of the S4 sodium battery composite material is 300-400 nm.

3. A hollow polyhedral NiS2 / Cu as claimed in any one of claims 1-2 7.2 A method for preparing a S4 sodium battery composite material, comprising the following steps: S1. A certain amount of polyvinylpyrrolidone is added into ethylene glycol and dispersed uniformly, then nickel nitrate, copper chloride and sulfur powder are sequentially added into the solution, and the mixture is subjected to hydrothermal reaction at 120-180 ℃, and after washing, separation and drying, a solid polyhedral NiS2 / Cu 7.2 S4 composite; S2. The solid polyhedral NiS2 / Cu obtained in step S1 is subjected to high-temperature calcination at 450-600 ℃ under an inert gas atmosphere to obtain hollow polyhedral NiS2 / Cu 7.2 S4. The composite is subjected to high-temperature calcination at 450-600 ℃ under an inert gas atmosphere to obtain hollow polyhedral NiS2 / Cu 7.2 S4. The sodium battery composite material.

4. Hollow polyhedral NiS2 / Cu according to claim 3 7.2 Process for the preparation of a S4 sodium battery composite material, characterized in that, In step S1, the polyvinylpyrrolidone has a molecular weight of 58000, the concentration of the polyvinylpyrrolidone in ethylene glycol is 3.3-15 g / L, and the concentration of the nickel nitrate in ethylene glycol is 0.02-0.18 mol / L.

5. Hollow polyhedral NiS2 / Cu according to claim 3 7.2 Process for the preparation of a S4 sodium battery composite material, characterized in that, In step S1, the hydrothermal reaction is performed for 10-18 h.

6. Hollow polyhedral NiS2 / Cu according to claim 3 7.2 Process for the preparation of a S4 sodium battery composite material, characterized in that, In step S2, the high-temperature calcination is performed at a temperature of 500-600 ℃ for 2-3 h.

7. Hollow polyhedral NiS2 / Cu according to any one of claims 1 to 2 7.2 Use of S4 sodium battery composite in sodium-ion battery anode material.

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