A composite material with a hollow four-shell structure and its preparation method and application

Abstract

The present invention belongs to the field of new energy materials, and relates to negative electrode materials for lithium-ion batteries, and specifically relates to a composite material with a hollow four-shell structure, and its preparation method and application. The composite material with a hollow four-shell structure is composed of reduced graphene oxide and Zn 0.5 Mn 0.5 The composite material is composed of micronized spheres and graphene sheets with a hollow four-shell structure. The hollow four-shell structure consists of four shells from the outside to the inside, with gaps between each shell. The hollow four-shell structure formed by the present invention provides sufficient ion and electron transmission channels and free space due to the large space and gaps between the shells, thereby alleviating volume expansion stress and structural collapse during lithium storage. At the same time, the complex internal hollow structure provides abundant reaction sites. The present invention provides a negative electrode material with excellent electrochemical performance for lithium-ion batteries, showing excellent cycle stability, rate performance, and high specific capacity.

Description

Technical Field

[0001] The present invention belongs to the field of new energy materials and relates to negative electrode materials for lithium-ion batteries, and in particular to a composite material with a hollow four-shell structure and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Lithium-ion batteries (Li-ion batteries) have achieved tremendous success in chemical energy storage systems due to their high energy density and long cycle life, particularly driving the development of portable electronic devices, wearable devices, and electric vehicles, greatly facilitating our daily lives. However, commercial Li-ion battery graphite anodes, despite minimal volume change, only deliver low theoretical specific capacity and suffer from severe capacity fading. Therefore, developing high-efficiency Li-ion batteries with higher energy density and longer cycle life is of great significance. Among them, transition metal oxides (TMOs) have demonstrated great potential as advanced anode materials for next-generation Li-ion batteries due to their low cost, simple synthesis methods, and high theoretical specific capacity. However, TMOs typically suffer from low intrinsic conductivity and severe capacity fading, and are prone to large volume changes during prolonged Li-ion insertion / deinsertion, which limits their electrochemical performance. To circumvent the shortcomings of current TMO Li-ion battery anode materials, complex internal structures can be designed and synthesized to mitigate the volume expansion effect, and composited with carbon materials such as graphene to improve their conductivity and cycling stability. However, the inventors have found that the negative electrode materials synthesized so far still have problems such as poor stability, large volume expansion stress and low specific capacity when used in lithium-ion batteries, which seriously hinder the large-scale application of lithium-ion batteries. Summary of the Invention

[0004] In order to address the deficiencies of the prior art, the present invention aims to provide a composite material with a hollow four-shell structure, a preparation method thereof, and an application thereof. Due to its unique hollow four-shell structure and diversified elemental composition, the present invention is conducive to the transport of ions and electrons during the electrode reaction of lithium-ion batteries, giving it excellent cycle stability and rate performance.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] On the one hand, a composite material with a hollow four-shell structure is prepared by reducing graphene oxide (RGO) and trimetallic oxide Zn 0.5 Mn 0.5Co2O4 composite material is formed, and the composite material is composed of micron balls with a hollow four-shell structure and a graphene sheet structure. The hollow four-shell structure is composed of four shell layers from the outside to the inside, and there is a gap between each shell layer.

[0007] Compared with the existing single metal oxide or double metal oxide electrode materials, the trimetallic oxide Zn 0.5 Mn 0.5 Co2O4 is composed of three transition metal elements: zinc, manganese and cobalt. It has a rich valence electron configuration and a variety of different oxidation states. Through the synergistic effect between the three transition metals, zinc, manganese and cobalt, the active sites of the metal oxide are increased, which is more conducive to the occurrence of electrochemical reactions and accelerates the transmission of ions and electrons during the electrode reverse process.

[0008] At the same time, the hollow four-shell structure formed by the present invention provides sufficient ion and electron transmission channels and free space to alleviate the problems of large volume expansion stress and structural collapse during lithium storage due to the large space and gaps between the shells. At the same time, the complex internal hollow structure provides abundant reaction sites. Compounding with carbon materials such as graphene is one of the main methods to alleviate the volume change and material accumulation of lithium-ion battery negative electrode materials during lithium ion insertion and extraction. Therefore, the composite material provided by the present invention can accelerate the charge transfer rate and has rich redox potentials. It can also increase the specific surface area, expose more active sites, improve reaction kinetics, and show excellent cycle stability, rate performance and high specific capacity.

[0009] In another aspect, a method for preparing a composite material having a hollow four-shell structure comprises the following steps:

[0010] Amorphous solid sphere Zn–Mn–Co precursors were obtained by dissolving divalent zinc salt, divalent manganese salt and divalent cobalt salt in anhydrous ethanol and performing solvothermal reaction.

[0011] The Zn-Mn-Co precursor is calcined in air to obtain a crystalline hollow four-shell structure of Zn 0.5 Mn 0.5 Co2O4 powder;

[0012] Zn 0.5 Mn 0.5 Co2O4 powder and graphene oxide dispersion were mixed uniformly by stirring and subjected to hydrothermal reaction to obtain a composite material with a hollow four-shell structure, namely a composite material of trimetallic zinc manganese cobalt oxide / reduced graphene oxide (Zn 0.5 Mn 0.5 Co2O4 / RGO).

[0013] The hollow four-shell composite material prepared by the present invention using solvent thermal, calcination and hydrothermal methods has uniform size, good dispersion and high structural stability, so that the structure is not easily collapsed or damaged during the insertion and deinsertion of lithium ions, thereby having good electrochemical lithium storage performance.

[0014] In a third aspect, a composite material having the hollow four-shell structure is used in a lithium-ion battery.

[0015] In a fourth aspect, a negative electrode for a lithium-ion battery includes an active component, a current collector, a conductive agent, and a binder, wherein the active component is the composite material of the hollow four-shell structure.

[0016] In a fifth aspect, a lithium-ion battery comprises a positive electrode, the above-mentioned negative electrode of the lithium-ion battery and a secondary electrolyte.

[0017] The beneficial effects of the present invention are:

[0018] 1. The hollow four-shell composite material provided by the present invention contains trimetallic zinc-manganese-cobalt oxide and reduced graphene oxide. Due to its rich valence electron configuration, multiple different oxidation states and synergistic effects between multiple metal ions, the activity of the metal oxide is improved, showing excellent lithium storage performance.

[0019] 2. The present invention adopts heat treatment methods such as solvent thermal method, calcination method and hydrothermal method to prepare trimetallic zinc manganese cobalt oxide / reduced graphene oxide composite material with a hollow four-shell structure. The synthesis method is simple, easy to operate, safe and efficient.

[0020] 3. The hollow four-shell composite material provided by the present invention has a special hollow four-shell structure, with a large internal space and structural stability, which is conducive to sufficient penetration of the electrolyte and sufficient charge transfer channels. The structure is not easy to collapse and break during the insertion and deinsertion of lithium ions, shortening the diffusion path of ions and electrons, which is conducive to the occurrence of electrochemical reactions.

[0021] 4. The hollow four-shell structure composite material provided by the present invention, through compounding with graphene material, alleviates the volume change and aggregation problems of the negative electrode material during the electrochemical reaction and improves the conductivity and stability.

[0022] 5. The hollow four-shell structure composite material provided by the present invention is used as a negative electrode material for lithium-ion batteries and exhibits excellent rate performance, cycle stability and high specific capacity in electrochemical performance tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 The hollow four-shell structure Zn prepared in Example 1 of the present invention 0.5 Mn 0.5 Electron microscope images of Co2O4, (a) is a scanning electron microscope image (SEM); (b) is a transmission electron microscope image (TEM);

[0025] Figure 2 The hollow four-shell structure Zn prepared in Example 1 of the present invention 0.5 Mn 0.5 Electron microscopy images of Co2O4 / RGO composite materials, (a) is a scanning electron microscopy image (SEM); (b) is a transmission electron microscopy image (TEM);

[0026] Figure 3 The hollow four-shell structure Zn prepared in Example 1 of the present invention 0.5 Mn 0.5 Co2O4 and Zn 0.5 Mn 0.5 X-ray diffraction pattern (XRD) of Co2O4 / RGO composite material, the ordinate is the relative diffraction intensity, and the abscissa is the 2θ diffraction angle;

[0027] Figure 4 The hollow four-shell structure Zn prepared in Example 3 of the present invention 0.5 Mn 0.5 Co2O4 / RGO composites have a high conductivity and good stability in the range of 0.1~5A·g –1 Rate performance charge and discharge curve at current density;

[0028] Figure 5 The hollow four-shell structure Zn prepared in Example 4 of the present invention 0.5 Mn 0.5 The Co2O4 / RGO composite material was heated at a current density of 2 A·g –1 The cycle performance curve below. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0030] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0031] As introduced in the background technology, the existing technology has disadvantages such as complex preparation method, simple internal structure, large volume expansion stress, low capacity and poor cycle stability. In order to solve the above technical problems, the present invention proposes a composite material with a hollow four-shell structure and its preparation method and application.

[0032] A typical embodiment of the present invention provides a composite material with a hollow four-shell structure, which is composed of reduced graphene oxide and Zn 0.5 Mn 0.5 Co2O4 composite material is formed, and the composite material is composed of micron balls with a hollow four-shell structure and a graphene sheet structure. The hollow four-shell structure is composed of four shell layers from the outside to the inside, and there is a gap between each shell layer.

[0033] The hollow four-shell structure composite material provided by the present invention contains trimetallic zinc-manganese-cobalt oxide and reduced graphene oxide. Due to its rich valence electron configuration, multiple different oxidation states and synergistic effects between multiple metal ions, the activity of the metal oxide is improved. At the same time, through compounding with graphene materials, the aggregation and structural collapse problems of negative electrode materials are alleviated, the conductivity and cycle stability are improved, and excellent electrochemical performance is exhibited.

[0034] In some examples of this embodiment, the diameter of the microspheres is 1.5-2 μm.

[0035] In some examples of this embodiment, the thickness of the outer two shells is 70-80 nm, and the thickness of the inner two shells is 20-30 nm.

[0036] In some examples of this embodiment, the composite material has a spinel structure.

[0037] Another embodiment of the present invention provides a method for preparing a composite material having a hollow four-shell structure, comprising the following steps:

[0038] Amorphous solid sphere Zn–Mn–Co precursors were obtained by dissolving divalent zinc salt, divalent manganese salt and divalent cobalt salt in anhydrous ethanol and performing solvothermal reaction.

[0039] The Zn–Mn–Co precursor was calcined in air to obtain a crystalline hollow four-shell Zn 0.5Mn 0.5 Co2O4 powder;

[0040] Zn 0.5 Mn 0.5 Co2O4 and graphene oxide dispersion are uniformly mixed by stirring and subjected to a hydrothermal reaction to obtain the product.

[0041] The present invention adopts solvent thermal method, calcination method and hydrothermal method to synthesize the composite material of hollow four-shell structure, which has uniform size and stable structure. In addition, there is a synergistic effect between different metal ions such as zinc, manganese and cobalt, which increases the number of reactive sites and makes it have excellent lithium storage performance. In addition, the hydrothermal method (i.e., hydrothermal reaction) can reduce graphene oxide to reduced graphene oxide, and can better combine reduced graphene oxide with Zn 0.5 Mn 0.5 Co2O4 composite.

[0042] The divalent zinc salt described in the present invention refers to a compound containing divalent zinc ions, such as zinc acetate, zinc chloride, etc.

[0043] The divalent manganese salt described in the present invention refers to a compound containing divalent manganese ions, such as manganese acetate, manganese chloride, etc.

[0044] The divalent cobalt salt described in the present invention refers to a compound containing divalent cobalt ions, such as cobalt acetate, cobalt chloride, etc.

[0045] In some examples of this embodiment, the molar ratio of the divalent zinc salt, the divalent manganese salt, and the divalent cobalt salt is 1:0.8 to 1:1.8 to 2.2.

[0046] In some examples of this embodiment, the volume ratio of the total molar amount of the divalent zinc salt, the divalent manganese salt and the divalent cobalt salt to anhydrous ethanol is 1.0-2.0:50-60, mmol:mL.

[0047] In some examples of this embodiment, the solvothermal reaction temperature is 160-180° C., the reaction time is 8-12 hours, and the ratio of the volume of anhydrous ethanol to the volume of the reactor is 0.4-0.6:1.

[0048] In some examples of this embodiment, the calcination temperature of the Zn—Mn—Co precursor is 450-600°C.

[0049] In some examples of this embodiment, the hydrothermal reaction temperature is 180-200° C., and the time is 14-18 hours.

[0050] In some examples of this embodiment, the hydrothermal reaction is followed by freeze-drying.

[0051] The preferred steps of the present invention are:

[0052] (1) adding zinc salt, manganese salt and cobalt salt to an organic solvent, anhydrous ethanol, and stirring until a clear and transparent solution is formed;

[0053] (2) subjecting the clear and transparent solution obtained in step (1) to a solvothermal reaction, and naturally cooling to room temperature to obtain a light pink precipitate;

[0054] (3) The light pink precipitate obtained in step (2) was centrifuged with anhydrous ethanol, washed, dried, ground and collected, and then calcined in air to obtain a hollow four-shell structure of Zn 0.5 Mn 0.5 Co2O4 black powder;

[0055] (4) The sample obtained in step (3) was dispersed in a graphene oxide dispersion, subjected to a hydrothermal reaction, naturally cooled to room temperature, centrifuged with deionized water, washed, and freeze-dried to obtain Zn 0.5 Mn 0.5 Co2O4 / RGO composite material.

[0056] Specifically, in step (1), the stirring time is 2 to 5 hours, preferably 3 hours.

[0057] In step (2), the reaction conditions of the solvent thermal process are: reaction at 160-180° C. for 8-12 h, and more preferably, the solvent thermal conditions are preferably reaction at 170° C. for 10 h.

[0058] In step (3), the centrifugation condition is to use anhydrous ethanol and centrifuge for washing 2 to 4 times, and the centrifugation condition is preferably to use anhydrous ethanol and centrifuge for 3 times.

[0059] In step (3), the calcination temperature is 450-600° C. and the calcination time is 2-6 hours; more preferably, the calcination temperature is 550° C. for 4 hours.

[0060] In step (4), the reaction conditions of the hydrothermal process are: reaction at 180-200°C for 14-18 hours, and more preferably the hydrothermal conditions are reaction at 180°C for 16 hours; the centrifugal conditions are using deionized water and centrifuging and washing 2-4 times, and the centrifugal conditions are preferably using deionized water and centrifuging 3 times.

[0061] A third embodiment of the present invention provides a use of the composite material having the hollow four-shell structure described above in the preparation of a lithium-ion battery.

[0062] A fourth embodiment of the present invention provides a lithium-ion battery negative electrode, comprising an active component, a current collector, a conductive agent, and a binder, wherein the active component is the composite material of the hollow four-shell structure.

[0063] A fifth embodiment of the present invention provides a lithium-ion battery comprising a positive electrode, a secondary electrolyte, and the above-mentioned negative electrode of the lithium-ion battery.

[0064] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0065] Example 1

[0066] 0.325 mmol Zn(CH3COO)2·2H2O, 0.325 mmol Mn(CH3COO)2·4H2O, and 0.65 mmol Co(CH3COO)2·4H2O were added to 50 mL of anhydrous ethanol and magnetically stirred for 3 h until completely dissolved, forming a clear, transparent purple-red solution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined container and placed in a reactor. The solution was then solvothermally reacted at 180°C for 10 h. After cooling to room temperature, the resulting precipitate was collected by centrifugation and washed three times with anhydrous ethanol. The product was then dried in a forced-air drying oven at 50°C for 10 h to obtain light pink solid spheres of the Zn–Mn–Co precursor. The prepared Zn–Mn–Co precursor powder was placed in a tube furnace and calcined at 550°C for 4 h in air at a heating rate of 1°C min. –1 , and obtain black Zn 0.5 Mn 0.5 Co2O4 powder. 60mg Zn 0.5 Mn 0.5 Co2O4 powder was dispersed in 20 mL of graphene oxide dispersion (2 mg mL –1 ) was stirred evenly, transferred to a 50 mL polytetrafluoroethylene liner and placed in a reactor, and then hydrothermally reacted at 180 ° C for 16 hours. After cooling naturally to room temperature, it was washed several times with deionized water and the product Zn was collected. 0.5 Mn 0.5 Co2O4 / RGO hydrogel was then freeze-dried to obtain a hollow four-shell structure of Zn 0.5 Mn 0.5 Co2O4 / RGO composite material.

[0067] The Zn obtained in this example 0.5 Mn 0.5 The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Co2O4 are shown in Figure 1 (a) and Figure 1 (b) Zn 0.5 Mn 0.5 The SEM and TEM images of Co2O4 / RGO composites are shown in Figure 2. Figure 2 (a) and Figure 2 (b). Figure 1 and Figure 2 It shows that the trimetallic oxide Zn prepared in this example 0.5 Mn 0.5 Co2O4 and Zn 0.5 Mn 0.5 The Co2O4 / RGO composite material is a hollow four-shell structure, wherein the diameter of the microspheres of the hollow four-shell structure is about 1.5-2 μm, the thickness of the outer two-layer shell is about 70-80 nm, and the thickness of the inner two-layer shell is about 20-30 nm. The hollow four-shell structure of Zn obtained in this embodiment 0.5 Mn 0.5 Co2O4 and Zn 0.5 Mn 0.5 The X-ray powder diffraction pattern (XRD) of Co2O4 / RGO is as follows Figure 3 As shown, it is proved to be a spinel structure with good crystallinity.

[0068] Example 2

[0069] 0.325 mmol Zn(CH3COO)2·2H2O, 0.3 mmol Mn(CH3COO)2·4H2O, and 0.65 mmol Co(CH3COO)2·4H2O were added to 60 mL of anhydrous ethanol and stirred magnetically for 3 h until completely dissolved, forming a clear, transparent purple-red solution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined container and placed in a reactor, where it was solvothermally reacted at 160°C for 12 h. After cooling to room temperature, the resulting precipitate was collected by centrifugation and washed three times with anhydrous ethanol. The product was then dried in a forced-air drying oven at 50°C for 10 h to obtain pale pink Zn–Mn–Co precursor solid spheres. The prepared Zn–Mn–Co precursor powder was placed in a tube furnace and calcined at 550°C for 4 h in air at a heating rate of 1°C min. –1 , and obtain black Zn 0.5 Mn 0.5 Co2O4 powder. 60mg Zn 0.5 Mn 0.5 Co2O4 powder was dispersed in 20 mL of graphene oxide dispersion (2 mg mL –1 ) was stirred evenly, transferred to a polytetrafluoroethylene liner with a capacity of 50 mL and placed in a reactor, and then hydrothermally reacted at 200°C for 18 hours. After cooling naturally to room temperature, it was washed several times with deionized water and the product Zn was collected. 0.5 Mn 0.5 Co2O4 / RGO hydrogel was then freeze-dried to obtain a hollow four-shell structure of Zn 0.5 Mn 0.5Co2O4 / RGO composite material.

[0070] Example 3

[0071] 0.3 mmol Zn(CH3COO)2·2H2O, 0.3 mmol Mn(CH3COO)2·4H2O, and 0.6 mmol Co(CH3COO)2·4H2O were added to 50 mL of anhydrous ethanol and stirred magnetically for 3 h until completely dissolved, forming a clear, transparent purple-red solution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined container and placed in a reactor, where it was subjected to a solvothermal reaction at 170°C for 8 h. After cooling to room temperature, the synthesized precipitate was collected by centrifugation and washed three times with anhydrous ethanol. The product was then dried in a forced air drying oven at 50°C for 10 h to obtain light pink solid spheres of the Zn–Mn–Co precursor. The prepared Zn–Mn–Co precursor powder was placed in a tube furnace and calcined at 450°C for 4 h in air at a heating rate of 1°C·min. –1 , and obtain black Zn 0.5 Mn 0.5 Co2O4 powder. 60mg Zn 0.5 Mn 0.5 Co2O4 powder was dispersed in 20 mL of graphene oxide dispersion (2 mg mL –1 ) was stirred evenly, transferred to a 50 mL polytetrafluoroethylene liner and placed in a reactor, and then hydrothermally reacted at 180 ° C for 14 h. After cooling naturally to room temperature, it was washed several times with deionized water and the product Zn was collected. 0.5 Mn 0.5 Co2O4 / RGO hydrogel was then freeze-dried to obtain a hollow four-shell structure of Zn 0.5 Mn 0.5 Co2O4 / RGO composite material.

[0072] The hollow four-shell structure of Zn obtained in this embodiment 0.5 Mn 0.5 Co2O4 / RGO composite material is used as the negative electrode material of lithium-ion battery. The active material, Ketjen black and sodium carboxymethyl cellulose are added to deionized water in a mass ratio of 7:2:1 and mixed evenly by ball milling. Then it is coated on copper foil and vacuum dried to obtain the negative electrode of lithium-ion battery. The positive electrode used is a lithium sheet. The separator used is a high-strength thin-film polyolefin porous membrane. The secondary electrolyte model is LB-064, in which the electrolyte is lithium hexafluorophosphate and the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate (volume ratio of 1:1). The lithium-ion battery is assembled. After electrochemical test verification, the lithium-ion battery showed excellent rate performance. It was tested at different current densities of 0.1~5A·g –1The rate performance under the condition of Figure 4 As shown, at 0.1, 0.2, 0.5, 1, 2 and 5 A·g –1 At current densities of 1176.8, 992.3, 870.3, 757.4, 645.6, and 446.8 mA·h·g, respectively. –1 discharge capacity.

[0073] Example 4

[0074] 0.3 mmol Zn(CH3COO)2·2H2O, 0.3 mmol Mn(CH3COO)2·4H2O, and 0.6 mmol Co(CH3COO)2·4H2O were added to 50 mL of anhydrous ethanol and stirred magnetically for 3 h until completely dissolved, forming a clear, transparent purple-red solution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined container and placed in a reactor. The solution was then solvothermally reacted at 180°C for 10 h. After cooling to room temperature, the precipitate was collected by centrifugation and washed three times with anhydrous ethanol. The product was then dried in a forced-air drying oven at 50°C for 10 h to obtain light pink solid spheres of the Zn–Mn–Co precursor. The prepared Zn–Mn–Co precursor powder was placed in a tube furnace and calcined at 550°C for 4 h in air at a heating rate of 1°C min. –1 , and obtain black Zn 0.5 Mn 0.5 Co2O4 powder. 60mg Zn 0.5 Mn 0.5 Co2O4 powder was dispersed in 20 mL of graphene oxide dispersion (2 mg mL –1 ) was stirred evenly, transferred to a 50 mL polytetrafluoroethylene liner and placed in a reactor, and then hydrothermally reacted at 180 ° C for 16 hours. After cooling naturally to room temperature, it was washed several times with deionized water and the product Zn was collected. 0.5 Mn 0.5 Co2O4 / RGO hydrogel was then freeze-dried to obtain a hollow four-shell structure of Zn 0.5 Mn 0.5 Co2O4 / RGO composite material.

[0075] The hollow four-shell structure of Zn obtained in this embodiment 0.5 Mn 0.5 Co2O4 / RGO was used as the negative electrode material for lithium-ion batteries. The active material, Ketjen black, and sodium carboxymethyl cellulose were added to deionized water at a mass ratio of 8:1:1 and mixed evenly by ball milling. The mixture was then coated on copper foil and the lithium-ion battery was assembled in sequence. Electrochemical tests showed that the lithium-ion battery exhibited excellent cycle stability. At 2A·g–1 The discharge capacity of the battery is 623.6 mA·h·g after 500 cycles of charge and discharge at a high current density. –1 See Figure 5 .

[0076] Example 5

[0077] 0.325 mmol Zn(CH3COO)2·2H2O, 0.325 mmol Mn(CH3COO)2·4H2O, and 0.65 mmol Co(CH3COO)2·4H2O were added to 60 mL of anhydrous ethanol and stirred magnetically for 3 h until completely dissolved, forming a clear, transparent purple-red solution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined container and placed in a reactor. The solution was then solvothermally reacted at 180°C for 12 h. After cooling to room temperature, the precipitate was collected by centrifugation and washed three times with anhydrous ethanol. The product was then dried in a forced-air drying oven at 50°C for 10 h to obtain pale pink Zn–Mn–Co precursor solid spheres. The prepared Zn–Mn–Co precursor powder was placed in a tube furnace and calcined at 450°C for 4 h in air at a heating rate of 1°C min. –1 , and obtain black Zn 0.5 Mn 0.5 Co2O4 powder. 60mg Zn 0.5 Mn 0.5 Co2O4 powder was dispersed in 20 mL of graphene oxide dispersion (2 mg mL –1 ) was stirred evenly, transferred to a 50 mL polytetrafluoroethylene liner and placed in a reactor, and then hydrothermally reacted at 190 ° C for 14 h. After cooling naturally to room temperature, it was washed several times with deionized water and the product Zn was collected. 0.5 Mn 0.5 Co2O4 / RGO hydrogel was then freeze-dried to obtain a hollow four-shell structure of Zn 0.5 Mn 0.5 Co2O4 / RGO composite material.

[0078] The hollow four-shell structure of Zn obtained in this embodiment 0.5 Mn 0.5 Co2O4 / RGO was used as the negative electrode material for lithium-ion batteries. The active material, acetylene black, and sodium carboxymethyl cellulose were added to deionized water in a mass ratio of 7:2:1 and mixed evenly by ball milling. Then, they were coated on copper foil and lithium-ion batteries were assembled in sequence.

[0079] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A composite material with a hollow four-shell structure, characterized in that: Reduced graphene oxide and trimetallic Zn oxide 0.5 Mn 0.5 Co2O4 composite material is formed, the composite material is composed of micron spheres with a hollow four-shell structure and a graphene sheet structure, the hollow four-shell structure is composed of four shell layers from the outside to the inside, and there is a gap between each shell layer; The preparation method of the composite material with a hollow four-shell structure comprises the following steps: Amorphous solid sphere Zn–Mn–Co precursors were obtained by dissolving divalent zinc salt, divalent manganese salt and divalent cobalt salt in anhydrous ethanol and performing solvothermal reaction. The Zn–Mn–Co precursor was calcined in air to obtain a crystalline hollow four-shell Zn 0.5 Mn 0.5 Co2O4 powder; Zn 0.5 Mn 0.5 Co2O4 and graphene oxide dispersion are uniformly mixed by stirring and subjected to a hydrothermal reaction to obtain the product.

2. The composite material of the hollow four-shell structure according to claim 1, characterized in that: The diameter of the microspheres is 1.5–2 μm; or, the thickness of the outer two shells is 70–80 nm; Alternatively, the thickness of the inner two shells is 20–30 nm.

3. The composite material of the hollow four-shell structure according to claim 1, characterized in that: The composite material has a spinel structure.

4. A method for preparing the composite material of the hollow four-shell structure according to claim 1, characterized in that: The steps include: Amorphous solid sphere Zn–Mn–Co precursors were obtained by dissolving divalent zinc salt, divalent manganese salt and divalent cobalt salt in anhydrous ethanol and performing solvothermal reaction. The Zn–Mn–Co precursor was calcined in air to obtain a crystalline hollow four-shell Zn 0.5 Mn 0.5 Co2O4 powder; Zn 0.5 Mn 0.5 Co2O4 and graphene oxide dispersion are uniformly mixed by stirring and subjected to a hydrothermal reaction to obtain the product.

5. The method for preparing a composite material with a hollow four-shell structure as claimed in claim 4, characterized in that: Zn 0.5 Mn 0.5 Co2O4 has a spinel structure.

6. The method for preparing the composite material of the hollow four-shell structure according to claim 4, characterized in that: The molar ratio of zinc salt, manganese salt and cobalt salt is 1:0.8~1:1.8~2.2; Alternatively, the volume ratio of the total molar amount of the divalent zinc salt, the divalent manganese salt and the divalent cobalt salt to anhydrous ethanol is 1.0-2.0:50-60, mmol:mL; Alternatively, the solvothermal reaction temperature is 160–180 °C and the time is 8–12 h; Alternatively, the calcination temperature of the Zn–Mn–Co precursor is 450–600 °C; Alternatively, the hydrothermal reaction temperature is 180-200 °C and the time is 14-18 h.

7. Use of the composite material with a hollow four-shell structure according to any one of claims 1 to 3 in the preparation of a lithium-ion battery.

8. A lithium ion battery negative electrode, comprising an active component, a current collector, a conductive agent and a binder, characterized in that: The active ingredient is the composite material of the hollow four-shell structure according to any one of claims 1 to 3.

9. A lithium-ion battery, characterized in that: The lithium-ion battery comprises a positive electrode, a secondary electrolyte and the negative electrode of the lithium-ion battery according to claim 8.

10. The lithium-ion battery according to claim 9, wherein: The positive electrode is a lithium sheet.

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