Negative electrode material and preparation method thereof, negative electrode plate and secondary battery

Abstract

The invention relates to a negative electrode material and a preparation method thereof, a negative electrode plate and a secondary battery, the negative electrode material comprises a metal selenide composite material and a three-dimensional porous carbon skeleton, and the metal selenide composite material is loaded in the three-dimensional porous carbon skeleton; the metal selenide composite material is of a core-shell structure, an inner core of the core-shell structure comprises Fe7Se8, a shell of the core-shell structure comprises FeSe2, a gap is formed between the inner core and the shell, the shell is of a porous structure, and part of the three-dimensional porous carbon skeleton penetrates through the porous structure to be filled in the gap. Therefore, the structural stability and the cycle stability of the negative electrode material can be remarkably improved, so that the capacity and the cycle performance of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a negative electrode material, a preparation method thereof, a negative electrode sheet, and a secondary battery. Background Art

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and low self-discharge rate. The working principle of lithium-ion batteries is based on the reversible insertion and extraction of lithium ions between the positive and negative electrode materials, which endows lithium-ion batteries with a high voltage platform and good electrochemical performance.

[0003] However, in practical applications, lithium-ion batteries still face some challenges. Among them, problems such as capacity decay of electrode materials and poor cycle stability are more prominent. Especially under high-rate charge and discharge conditions, the structural stability of electrode materials is more severely threatened, which is more likely to cause rapid decay of battery capacity and significant shortening of battery life.

[0004] Metal selenides have high theoretical specific capacity and good electrochemical activity. If used as the negative electrode material of a battery, it is expected to significantly improve the storage capacity of the battery. In addition, the unique layered structure and good conductivity of metal selenides are beneficial to the transport of active ions and electrons, which is conducive to improving the rate performance of the battery. However, metal selenides have problems of unstable structure and even easy collapse during the charge and discharge process of the battery, which greatly limits the practical application of metal selenides as negative electrode materials. Summary of the Invention

[0005] In view of this, embodiments of the present application provide a negative electrode material, a preparation method thereof, a negative electrode sheet, and a secondary battery to solve at least one problem in the background art.

[0006] In a first aspect, embodiments of the present application provide a negative electrode material, including a metal selenide composite material and a three-dimensional porous carbon framework, wherein the metal selenide composite material is loaded in the three-dimensional porous carbon framework;

[0007] The metal selenide composite material has a core-shell structure. The core of the core-shell structure includes Fe7Se8, the shell includes FeSe2, there is a gap between the core and the shell, the shell has a porous structure, and part of the three-dimensional porous carbon framework passes through the porous structure and fills the gap.

[0008] Combined with the first aspect of the present application, in an optional embodiment, the negative electrode material satisfies at least one of the following characteristics:

[0009] (1) The particle size of the core is 6 nm to 10 nm;

[0010] (2) The thickness of the outer shell is 5 nm to 8 nm;

[0011] (3) The size of the gap is 1.2 nm to 5.5 nm;

[0012] (4) The three-dimensional porous carbon framework includes oxygen-containing functional groups, and the oxygen-containing functional groups are chemically bonded to at least part of the metal selenide composite material.

[0013] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode material, and the method includes the following steps:

[0014] S1: Dissolve a carbon source, an iron source, and a selenium source in a solvent, and then add a complexing agent. After mixing, a mixed solution is obtained;

[0015] S2: Add a regulator to the mixed solution, adjust the mixed solution to be alkaline, and then react. After standing, a composite gel is obtained; then the composite gel is subjected to a freezing treatment, and after drying, a porous aerogel precursor is obtained;

[0016] S3: Under the condition of introducing a reducing gas, perform a first heat treatment on the porous aerogel precursor to obtain an intermediate product, and the intermediate product includes an initial three-dimensional carbon network and FeSe2 particles loaded in the initial three-dimensional carbon network;

[0017] S4: Under a closed and oxygen-deficient condition, perform a second heat treatment on the intermediate product, so that the initial three-dimensional carbon network forms a three-dimensional porous carbon framework, and a deselenization reaction occurs inside the FeSe2 particles to form a metal selenide composite material with a core-shell structure. The core of the core-shell structure includes Fe7Se8, the outer shell includes FeSe2, there is a gap between the core and the outer shell, and the outer shell has a porous structure to obtain an initial negative electrode material;

[0018] S5: Under the condition of introducing a carbon source gas, perform a third heat treatment on the initial negative electrode material to catalyze the growth of the three-dimensional porous carbon framework, so that the three-dimensional porous carbon framework passes through the porous structure and fills the gap to obtain the negative electrode material.

[0019] In combination with the second aspect of the present application, in an optional embodiment, step S1 satisfies at least one of the following features:

[0020] (1) The carbon source includes at least one of methyl cellulose, starch, sucrose, lactic acid, citric acid, carboxymethyl cellulose, and hydroxyethyl cellulose;

[0021] (2) The iron source includes at least one of Fe(NO3)3·9H2O, FeCl3·6H2O, Fe2(SO4)3, and FeSO4·7H2O;

[0022] (3) The selenium source includes at least one of selenourea, selenium dioxide, hydrogen selenide, selenourea, sodium selenosulfate, and carbon diselenide;

[0023] (4) The solvent includes at least one of deionized water, ethanol, ethylene glycol, glycerol, dimethyl sulfoxide, and ammonia water;

[0024] (5) The complexing agent includes at least one of citric acid, oxalic acid, tartaric acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, and polyvinylpyrrolidone;

[0025] (6) The material ratio of the carbon source, the iron source, the selenium source, the complexing agent to the solvent is (2 - 4) g : (1.5 - 4.5) g : (0.8 - 1.2) g : (0.5 - 1) g : (50 - 70) ml;

[0026] (7) The time of the mixing treatment is 2 h to 3.5 h.

[0027] Combining with the second aspect of the present application, in an alternative embodiment, step S2 satisfies at least one of the following features:

[0028] (1) The regulator includes at least one of ammonia water, triethylamine, ethylenediamine, urea, ammonium carbonate, pyridine, and hexamethylenetetramine;

[0029] (2) The pH of the mixed solution after being regulated by the regulator is 8.5 to 9.5;

[0030] (3) The time of the standing treatment is 12 h to 16 h;

[0031] (4) The temperature of the freezing treatment is -70°C to -50°C;

[0032] (5) The time of the freezing treatment is 24 h to 36 h;

[0033] (6) The drying treatment is carried out under vacuum conditions.

[0034] Combining with the second aspect of the present application, in an alternative embodiment, step S3 satisfies at least one of the following features:

[0035] (1) The reducing gas includes at least one of H2, NH3, CH4, CO, and H2Se;

[0036] (2) The temperature of the first heat treatment is 500°C to 600°C;

[0037] (3) The holding time of the first heat treatment is 1 h to 3 h;

[0038] (4) The heating rate of the first heat treatment is 2 °C / min to 5 °C / min.

[0039] Combining with the second aspect of the present application, in an alternative embodiment, step S4 satisfies at least one of the following features:

[0040] (1) The airtight and anoxic condition is: the pressure is between 0.1 MPa and 0.12 MPa; the oxygen partial pressure is less than or equal to 10 -5 MPa;

[0041] (2) The second heat treatment includes: first holding at 700 °C to 750 °C for 1.5 h to 2.5 h, and then holding at 750 °C to 800 °C for 0.5 h to 1.5 h;

[0042] (3) The particle size of the inner core is 6 nm to 10 nm;

[0043] (4) The thickness of the outer shell is 5 nm to 8 nm;

[0044] (5) The size of the gap is 1.2 nm to 5.5 nm.

[0045] Combining with the second aspect of the present application, in an alternative embodiment, step S5 satisfies at least one of the following features:

[0046] (1) The carbon source gas includes at least one of methane, ethane, ethylene, and acetylene;

[0047] (2) The temperature of the third heat treatment is 800 °C to 900 °C;

[0048] (3) The time of the third heat treatment is 30 min to 50 min.

[0049] In a third aspect, an embodiment of the present application provides a negative electrode sheet, which includes the negative electrode material according to any one of the first aspect or the negative electrode material prepared by the preparation method of the negative electrode material according to any one of the second aspect.

[0050] In a fourth aspect, an embodiment of the present application provides a secondary battery, which includes the negative electrode sheet described in the third aspect.

[0051] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0052] The negative electrode material, its preparation method, negative electrode sheet and secondary battery provided by the embodiments of the present application. The negative electrode material includes a metal selenide composite material and a three-dimensional porous carbon framework. Among them, the metal selenide composite material is loaded in the three-dimensional porous carbon framework; the metal selenide composite material has a core-shell structure. The core of the core-shell structure includes Fe7Se8, and the shell includes FeSe2. There is a gap between the core and the shell, and the shell has a porous structure. Part of the three-dimensional porous carbon framework passes through the porous structure and fills the gap. In the embodiments of the present application, the metal selenide composite material with a core-shell structure is loaded in the three-dimensional porous carbon framework, and part of the three-dimensional porous carbon framework passes through the porous structure of the shell of the core-shell structure and fills the gap between the core and the shell, so that a physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon framework, thereby significantly inhibiting the volume expansion and structural pulverization of the metal selenide during the cycling process, improving the structural stability of the metal selenide during the charge and discharge process of the battery, greatly reducing the risk of structural collapse, and the three-dimensional porous carbon framework with high flexibility can provide a buffer space for the volume change of the metal selenide composite material and absorb the stress generated by the volume change. Therefore, the structural stability and cycling stability of the negative electrode material can be significantly improved. In addition, there is a gap between the core and the shell of the metal selenide composite material, which can form a built-in electric field to drive the active ions (such as lithium ions or sodium ions, etc.) to enrich in the core with a high theoretical capacity, and can also provide a buffer space for the volume expansion of the core, thereby significantly improving the capacity and cycling performance of the battery.

[0053] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0055] Figure 1 It is a schematic flow chart of a preparation method of a negative electrode material provided by an embodiment of the present application;

[0056] Figure 2 It is an XRD diagram of the negative electrode material prepared in Example 1;

[0057] Figure 3 It is a scanning electron microscope image of the negative electrode material prepared in Example 1;

[0058] Figure 4 It is a transmission electron microscope image of the negative electrode material prepared in Example 1;

[0059] Figure 5 It is another transmission electron microscope image of the negative electrode material prepared in Example 1. Detailed implementation manners

[0060] To make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following provides a detailed description by combining the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally in accordance with conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0061] In the following description, numerous specific details are given to provide a more thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the present application may be practiced without one or more of these details. In other instances, in order to avoid obscuring the present application, some well-known technical features have not been described; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.

[0062] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present application. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, specify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of the related listed items.

[0063] To thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may have other implementation manners.

[0064] Unless otherwise defined, the technical and scientific terms used in the present application have the same meanings as those in the technical and scientific fields to which the present application belongs.

[0065] For those not noted with specific techniques or conditions in the following embodiments, they are generally in accordance with the conventional techniques or conditions described in the literature in the relevant field, or in accordance with the conditions recommended in the product specifications and by the manufacturers. The numerical ranges in the following embodiments include the endpoint values.

[0066] In the related art, in the anode material containing selenide and carbon, the binding mode between the active component selenide and the carbon carrier is mostly physical mixing or simply coating the selenide with a carbon material. In this way, the binding force between the selenide and the carbon carrier is weak, and the two are prone to detachment, resulting in poor structural stability and cycling stability of the anode material.

[0067] Based on this, an embodiment of the present application provides an anode material, which includes a metal selenide composite material and a three-dimensional porous carbon framework. Among them, the metal selenide composite material is loaded in the three-dimensional porous carbon framework; the metal selenide composite material has a core-shell structure, the core of the core-shell structure includes Fe7Se8, the shell includes FeSe2, there is a gap between the core and the shell, the shell has a porous structure, and part of the three-dimensional porous carbon framework passes through the porous structure and fills the gap.

[0068] In the embodiment of the present application, the metal selenide composite material with a core-shell structure is loaded in the three-dimensional porous carbon framework, and part of the three-dimensional porous carbon framework passes through the porous structure of the shell of the core-shell structure and fills the gap between the core and the shell, so that a physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon framework, thereby significantly suppressing the volume expansion and structural pulverization of the metal selenide during cycling, improving the structural stability of the metal selenide during the charge and discharge process of the battery, greatly reducing the risk of structural collapse, and the three-dimensional porous carbon framework with high flexibility can provide a buffer space for the volume change of the metal selenide composite material and absorb the stress generated by the volume change. Therefore, the structural stability and cycling stability of the anode material can be significantly improved. In addition, the core of the metal selenide composite material includes Fe7Se8, and the cubic lattice (space group "Fm3m") of Fe7Se8 has a three-dimensional ion diffusion channel, and the layer spacing is greater than the diameter of the lithium ion desolvated ion, allowing the rapid insertion and extraction of lithium ions, and the theoretical capacity is high. There is a gap between the core and the shell of the metal selenide composite material, which can form a built-in electric field to drive the active ions (such as lithium ions or sodium ions, etc.) to enrich in the core with a high theoretical capacity, and can also provide a buffer space for the volume expansion of the core, thereby significantly improving the capacity and cycling performance of the battery.

[0069] In some embodiments, the particle size of the core of the metal selenide composite material can be 6nm to 10nm. This is beneficial to improving the capacity of the anode material and at the same time beneficial to constructing a core-shell structure with higher structural stability.

[0070] Here, the particle size of the core of the metal selenide composite material can be understood as the average particle size of the core of the metal selenide composite material.

[0071] In some embodiments, the thickness of the metal selenide composite material shell can be 5 nm to 8 nm. Controlling the thickness of the metal selenide composite material shell within the above range, which is lower than the critical thickness of electron tunneling (about 10 nm), allows electrons to be directly injected into the core through quantum tunneling, can reduce the interfacial charge transfer resistance, and is also conducive to constructing a core-shell structure with higher structural stability.

[0072] Here, the thickness of the metal selenide composite material shell can be understood as the average thickness of the metal selenide composite material shell.

[0073] In some embodiments, the size of the gap between the shell and the core of the metal selenide composite material can be 1.2 nm to 5.5 nm. In this way, on the one hand, it can provide a suitable buffer space for the volume expansion of the core, forming a more stable metal selenide composite material; on the other hand, it is conducive to part of the three-dimensional porous carbon skeleton passing through the porous structure and filling in the gap, so that a more stable physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon skeleton, thereby further improving the structural stability of the negative electrode material.

[0074] Here, the size of the gap between the shell and the core of the metal selenide composite material can be understood as the average size of the gap between the shell and the core of the metal selenide composite material.

[0075] In some embodiments, the three-dimensional porous carbon skeleton includes oxygen-containing functional groups, and the oxygen-containing functional groups are chemically bonded to at least part of the metal selenide composite material.

[0076] In the embodiments of the present application, by introducing oxygen-containing functional groups (such as carboxyl groups) on the three-dimensional porous carbon skeleton, in the actual preparation process, these oxygen-containing functional groups can serve as cation anchoring sites, enabling iron ions to be uniformly and firmly bound to the surface of the three-dimensional porous carbon skeleton, forming stable bonding sites. The cation active sites on the three-dimensional porous carbon skeleton can also be combined with the anions (Se 2- / Se - ) on the surface of the metal selenide composite material through electrostatic interaction to form a strong interface of "ionic bond bridge", forming a dynamic polarization interface. The polarization electric field accelerates charge transfer, reduces the reaction energy barrier, stabilizes the interface structure, and reduces the side reaction between the negative electrode material and the electrolyte; thus, on the basis of the stable combination between the metal selenide composite material and the three-dimensional porous carbon skeleton through the physical interlocking structure, the strong binding force of chemical bonds is increased, the interface binding is more stable, and further, the structural stability, conductivity and cycle life of the negative electrode material can be significantly increased.

[0077] The embodiments of the present application also provide a preparation method for a negative electrode material. Please refer to Figure 1 , and the preparation method for the negative electrode material provided by the embodiments of the present application includes the following steps:

[0078] S1: Dissolve a carbon source, an iron source and a selenium source in a solvent, then add a complexing agent. After mixing, a mixed solution is obtained.

[0079] S2: Add a regulator to the mixed solution. After adjusting the mixed solution to be alkaline, carry out a reaction. After standing, a composite gel is obtained. Then, the composite gel is subjected to a freezing treatment and then dried to obtain a porous aerogel precursor.

[0080] S3: Under the condition of introducing a reducing gas, carry out a first heat treatment on the porous aerogel precursor to obtain an intermediate product, which includes an initial three-dimensional carbon network and FeSe2 particles loaded in the initial three-dimensional carbon network.

[0081] S4: Under a closed and oxygen-deficient condition, carry out a second heat treatment on the intermediate product, so that the initial three-dimensional carbon network forms a three-dimensional porous carbon skeleton, and a deselenization reaction occurs inside the FeSe2 particles to form a metal selenide composite material with a core-shell structure. The core of the core-shell structure includes Fe7Se8, the shell includes FeSe2, there is a gap between the core and the shell, and the shell has a porous structure to obtain an initial anode material.

[0082] S5: Under the condition of introducing a carbon source gas, carry out a third heat treatment on the initial anode material to catalyze the growth of the three-dimensional porous carbon skeleton, so that the three-dimensional porous carbon skeleton passes through the porous structure and fills the gap to obtain an anode material.

[0083] In the embodiments of the present application, first, an intermediate product including an initial three-dimensional carbon network and FeSe2 particles loaded in the initial three-dimensional carbon network is formed by an in-situ chemical deposition method; then, under the condition of airtight and oxygen-deficient heat treatment, through an anion exchange reaction, a deselenization reaction occurs inside the FeSe2 particles to form a metal selenide composite material with a core-shell structure. At the same time, the initial three-dimensional carbon network is carbonized to form a three-dimensional porous carbon skeleton wrapping the metal selenide composite material; finally, the three-dimensional porous carbon skeleton is catalyzed to grow, so that the three-dimensional porous carbon skeleton passes through the porous structure of the outer shell of the core-shell structure and fills the gap between the core and the shell. In the negative electrode material prepared in the embodiments of the present application, the metal selenide composite material with a core-shell structure is loaded in the three-dimensional porous carbon skeleton, and part of the three-dimensional porous carbon skeleton passes through the porous structure of the outer shell of the core-shell structure and fills the gap between the core and the shell, so that a physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon skeleton, thereby significantly inhibiting the volume expansion and structural pulverization of the metal selenide during the cycling process, improving the structural stability of the metal selenide during the charge and discharge process of the battery, greatly reducing the risk of structural collapse, and the three-dimensional porous carbon skeleton with high flexibility can provide a buffer space for the volume change of the metal selenide composite material and absorb the stress generated by the volume change. Therefore, the structural stability and cycling stability of the negative electrode material can be significantly improved. In addition, there is a gap between the core and the shell of the metal selenide composite material, which can form a built-in electric field to drive active ions (such as lithium ions or sodium ions, etc.) to enrich in the core with a high theoretical capacity, and can also provide a buffer space for the volume expansion of the core, thereby significantly improving the capacity and cycling performance of the battery.

[0084] In the embodiments of the present application, through the in-situ chemical deposition preparation method, a large number of oxygen-containing functional groups (such as carboxyl groups) can be introduced onto the formed three-dimensional porous carbon skeleton. These oxygen-containing functional groups can serve as cation anchoring sites, enabling iron ions to bind uniformly and firmly on the surface of the three-dimensional porous carbon skeleton to form stable bonding sites. The cation active sites on the three-dimensional porous carbon skeleton can also combine with anions (Se 2- / Se - )on the surface of the metal selenide composite material through electrostatic interaction to form a strong interface of "ionic bond bridge", forming a dynamic polarization interface. The polarization electric field accelerates charge transfer, reduces the reaction energy barrier, stabilizes the interface structure, and reduces side reactions of the electrolyte; thus, on the basis of the stable combination between the metal selenide composite material and the three-dimensional porous carbon skeleton through the physical interlocking structure, the strong binding force of chemical bonds is increased, the interface binding is more stable, and further, the structural stability, conductivity, and cycling life of the negative electrode material can be significantly increased.

[0085] In step S1, the carbon source, iron source, and selenium source are dissolved in a solvent, and then a complexing agent is added. After mixing, a mixed solution is obtained.

[0086] Among them, the carbon source can, for example, include at least one of methyl cellulose, starch, sucrose, lactic acid, citric acid, carboxymethyl cellulose, and hydroxyethyl cellulose. These types of carbon sources can better ensure the formation of a composite gel with higher quality in subsequent steps. In some specific embodiments, the carbon source can be methyl cellulose. Because methyl cellulose helps to form a stable and uniform negative electrode structure, improve battery performance, and methyl cellulose can improve the dispersion stability of the negative electrode material, which helps to improve the battery energy density.

[0087] The iron source can, for example, include at least one of Fe(NO3)3·9H2O, FeCl3·6H2O, Fe2(SO4)3, and FeSO4·7H2O. In some specific embodiments, the iron source can be Fe(NO3)3·9H2O. Because NO3 - is an inert anion and can decompose into gas and escape during subsequent high-temperature preparation processes, thereby reducing impurity residues and being beneficial to improving the quality of the finally prepared negative electrode material.

[0088] The selenium source can, for example, include at least one of selenourea, selenium dioxide, hydrogen selenide, selenium urea, sodium selenosulfate, and carbon diselenide. In some specific embodiments, the selenium source can be selenourea. Because, under high-temperature conditions (above about 500 °C), selenourea can release Se vapor. The rate of Se vapor release from selenourea matches the rate of FeO formation from the iron source, which can ensure that the grain size of the subsequently formed FeSe2 is more uniform, and thus can better improve the performance of the finally prepared negative electrode material.

[0089] The solvent can, for example, include at least one of deionized water, ethanol, ethylene glycol, glycerol, dimethyl sulfoxide, and ammonia water.

[0090] The complexing agent can, for example, include at least one of citric acid, oxalic acid, tartaric acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, and polyvinylpyrrolidone.

[0091] In some embodiments, the material ratio of the carbon source, iron source, selenium source, complexing agent to the solvent can be (2 - 4) g : (1.5 - 4.5) g : (0.8 - 1.2) g : (0.5 - 1) g : (50 - 70) ml, for example, it can be 2 g : 1.5 g : 0.8 g : 0.5 g : 50 ml, 3 g : 2 g : 0.9 g : 0.6 g : 50 ml, 2.8 g : 2.5 g : 1 g : 0.8 g : 60 ml, 3.5 g : 4 g : 1.1 g : 0.9 g : 65 ml, 4 g : 4.5 g : 1.2 g : 1 g : 70 ml or any other ratio within the above range.

[0092] Controlling the material ratio of the carbon source, iron source, selenium source, complexing agent to the solvent within the above range is conducive to the full dissolution of the raw materials, thereby facilitating more sufficient and complete subsequent reactions, forming a composite gel with higher quality, and further improving the performance of the finally formed anode material.

[0093] Furthermore, the mixing time in step S1 can be 2h to 3.5h, for example, it can be 2h, 2.5h, 3h, 3.5h or any value between any two of the above numerical ranges. In actual preparation, for example, magnetic stirring can be used for the mixing treatment.

[0094] In step S2, a regulator is added to the mixed solution. After adjusting the mixed solution to be alkaline, a reaction is carried out. After standing, a composite gel is obtained; then the composite gel is subjected to freezing treatment and then dried to obtain a porous aerogel precursor.

[0095] Among them, the regulator can include, for example, at least one of ammonia water, triethylamine, ethylenediamine, urea, ammonium carbonate, pyridine, hexamethylenetetramine. On the one hand, the regulator in the embodiments of the present application can play a role in adjusting the pH of the solution, adjusting the mixed solution to be alkaline to promote the hydrolysis of Fe 3+ to generate FeO(OH) or Fe(OH)3 colloid and form a composite gel with the carbon source; on the other hand, the NH3 molecules released by the regulator can complex with Fe 3+ to delay the precipitation rate of Fe 3+ and promote more uniform crosslinking, avoid local agglomeration, and thus better induce the formation of the composite gel.

[0096] In some embodiments, the pH of the mixed solution adjusted by the regulator can be 8.5 to 9.5. This is conducive to forming a composite gel of high quality.

[0097] In some embodiments, the standing time can be 12h to 16h, for example, it can be 12h, 13h, 14h, 15h, 16h or any value between any two of the above numerical ranges. This is conducive to improving the quality of the formed composite gel.

[0098] In step S2, by subjecting the composite gel to freezing treatment, the water in the composite gel forms ice crystals to squeeze the Fe-Se composite, forming oriented pores and promoting the uniform distribution of the Fe-Se composite, avoiding particle agglomeration, and thus being conducive to the subsequent formation of a metal selenide composite material with a core-shell structure; then after drying, a porous aerogel precursor with a stable structure is obtained. After carbonizing the porous aerogel precursor, the porous structure can be retained, forming a stable three-dimensional porous carbon skeleton, which is conducive to increasing the specific surface area of the anode material and promoting the penetration of the electrolyte.

[0099] In some embodiments, the temperature of the freezing treatment can be -70°C to -50°C. For example, it can be -70°C, -60°C, -50°C, or any value between any two of the above numerical ranges.

[0100] In some embodiments, the time of the freezing treatment is 24h to 36h. For example, it can be 24h, 28h, 32h, 36h, or any value between any two of the above numerical ranges.

[0101] Controlling at least one of the temperature and time of the freezing treatment within the above ranges is beneficial to improving the quality of the obtained porous aerogel precursor.

[0102] In the actual preparation process, the drying treatment can be carried out under vacuum conditions. This can avoid the cross-linked network structure in the composite gel from being oxidized or damaged during the drying treatment.

[0103] In step S3, under the condition of introducing a reducing gas, the porous aerogel precursor is subjected to a first heat treatment to obtain an intermediate product, which includes an initial three-dimensional carbon network and FeSe2 particles loaded in the initial three-dimensional carbon network.

[0104] In the embodiments of the present application, by introducing a reducing gas and performing the first heat treatment, on the one hand, partial carbonization of the porous aerogel precursor forms an initial three-dimensional carbon network, and on the other hand, Fe 3+ in the porous aerogel precursor is reduced to FeO, and FeO reacts with the Se vapor released from the selenium source to generate FeSe2 nanoparticles. Under a high selenium vapor partial pressure (for example, higher than 0.05 MPa), selenium atoms are enriched on the surface of FeSe2, and a relatively complete crystal structure can be formed.

[0105] Exemplarily, the reducing gas can include at least one of H2, NH3, CH4, CO, and H2Se. In the actual preparation process, a mixed gas of a reducing gas and an inert gas can be introduced. Specifically, the volume ratio of the inert gas to the reducing gas can be, for example, 95:5. The inert gas can be, for example, at least one of argon, nitrogen, and helium.

[0106] In some embodiments, the temperature of the first heat treatment can be 500°C to 600°C. For example, it can be 500°C, 550°C, 600°C, or any value between any two of the above numerical ranges.

[0107] In some embodiments, the heat preservation time of the first heat treatment can be 1h to 3h. For example, it can be 1h, 2h, 3h, or any value between any two of the above numerical ranges.

[0108] In some embodiments, the heating rate of the first heat treatment can be 2 °C / min to 5 °C / min. For example, it can be 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, or any value between any two of the above numerical ranges.

[0109] Controlling at least one of the temperature, holding time, and heating rate of the first heat treatment within the above ranges is beneficial to the formation of a high-quality initial three-dimensional carbon network and FeSe2 particles.

[0110] In step S4, under a closed and oxygen-deficient condition, the intermediate product is subjected to a second heat treatment, so that the initial three-dimensional carbon network forms a three-dimensional porous carbon skeleton, and a deselenization reaction occurs inside the FeSe2 particles to form a metal selenide composite material with a core-shell structure. The core of the core-shell structure includes Fe7Se8, the shell includes FeSe2, there is a gap between the core and the shell, the shell has a porous structure, and the initial anode material is obtained.

[0111] The above-mentioned closed and oxygen-deficient condition can specifically be: the pressure is between 0.1 MPa and 0.12 MPa; the oxygen partial pressure is less than or equal to 10 -5 MPa. Under this closed and oxygen-deficient condition, it is beneficial to the occurrence of the deselenization reaction inside the FeSe2 particles, thereby forming a metal selenide composite material with a better quality core-shell structure. During the second heat treatment process, the initial three-dimensional carbon network will be completely carbonized to form a three-dimensional porous carbon skeleton, wrapping the metal selenide composite material (which can also be called a heterojunction particle). In the embodiments of the present application, an anion exchange strategy is adopted during the deselenization process of FeSe2 particles, not only generating the core Fe7Se8 and the shell FeSe2, but also forming controllable Se vacancies at the interface, making Se 2- / Se - more likely to combine with the cation sites (such as Fe 2+ and oxygen defects, etc.) on the three-dimensional porous carbon skeleton to form a strong interaction, thereby further enhancing the binding stability between the metal selenide composite material and the three-dimensional porous carbon skeleton.

[0112] In some embodiments, the second heat treatment can include: first holding at 700 °C to 750 °C for 1.5 h to 2.5 h, and then holding at 750 °C to 800 °C for 0.5 h to 1.5 h.

[0113] In the actual preparation process, for example, it can be first heated from 2°C / min to 5°C / min to 700°C to 750°C. For example, it can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C or any value between any two of the above numerical ranges. Next, the flow rate of the gas introduced in the above step is closed, and it is switched to a closed anoxic system. Using the self-generated internal pressure, in a high-temperature anoxic environment, partial deselenization occurs inside the FeSe2 particles to form a Fe7Se8 core, and the FeSe2 shell is retained on the surface. Next, it is further heated to 750°C to 800°C. For example, it can be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C or any value between any two of the above numerical ranges. The internal oxygen partial pressure in the closed anoxic environment becomes lower (10 -5 MPa or less), and FeSe2 further undergoes a deselenization reaction (7FeSe2 → Fe7Se8 + 6Se). The generated Se vapor is confined in the pores of the three-dimensional porous carbon skeleton to form a local dynamic equilibrium, promoting the nucleation and growth of Fe7Se8 inside FeSe2. Since the reaction proceeds from the inside to the outside of the FeSe2 particles, the density of the Fe7Se8 formed inside is higher than that of FeSe2, resulting in the contraction of the core region, while the shell layer retains its original volume due to incomplete deselenization on the surface, thus forming a void between the Fe7Se8 inner core and the FeSe2 shell layer, forming a metal selenide composite material with a core-shell structure. The internal pressure in the closed environment at this stage is 0.1 MPa to 0.12 MPa, maintaining the Se vapor partial pressure at about 103 Pa, which is higher than the equilibrium decomposition pressure of Fe7Se8 (about 102 Pa), thereby being able to inhibit the excessive deselenization of Fe7Se8. The Se vapor generated by the deselenization reaction will diffuse outward through the FeSe2 shell layer, but the Se vapor partial pressure in the closed system is close to dynamic equilibrium, and part of the Se vapor will escape from the defects of the FeSe2 shell layer, leaving mesoporous channels. At the same time, the lattice reconstruction of FeSe2 at high temperature will also introduce pores, so that the outer shell of the metal selenide composite material has a porous structure.

[0114] In the embodiments of the present application, the second heat treatment is carried out in two temperature stages. First, in the 700°C to 750°C stage, controllable initial deselenization of FeSe2 particles and the formation of the core-shell prototype can be achieved. At this temperature, partial deselenization of FeSe2 generates a Fe7Se8 core, but the deselenization rate is relatively slow, which is beneficial to the formation of a transition shell layer with appropriate porosity. The incomplete shell layer allows the preliminary diffusion of Se vapor and the pressure accumulation in the closed environment. The formed core-shell gap can provide growth space for the subsequent core-shell structure. Then, when heated to the 750°C to 800°C stage, the high temperature significantly accelerates the deselenization kinetics, making it easier to promote the saturation of Se vapor in the closed system and reach the critical Se vapor pressure (10 5(at the Pa order of magnitude), the increased internal pressure drives the capillary condensation of Se in the pores to form a local equilibrium. The temperature-sensitive surface diffusion promotes the migration of Se from the Fe7Se8 core to the inside of the shell. At the same time, at high temperatures, the migration of Fe atoms can be significantly accelerated (the activation energy of the bulk diffusion of Fe in FeSe2 is about 2.5 eV). Above 750 °C, the diffusion of Fe atoms is significantly accelerated, completing the restructuring of the core-shell structure and the establishment of dynamic equilibrium, and it is easier to form a core-shell structure with separated core and shell, thereby effectively improving the quality of the obtained metal selenide composite material.

[0115] In some embodiments, the particle size of the inner core of the obtained metal selenide composite material can be 6 nm to 10 nm. This is beneficial to improving the capacity of the negative electrode material and is also conducive to constructing a core-shell structure with higher structural stability.

[0116] Here, the particle size of the inner core of the metal selenide composite material can be understood as the average particle size of the inner core of the metal selenide composite material.

[0117] In some embodiments, the thickness of the outer shell of the obtained metal selenide composite material can be 5 nm to 8 nm. Controlling the thickness of the outer shell of the metal selenide composite material within the above range, which is lower than the critical thickness of electron tunneling (about 10 nm), allows electrons to be directly injected into the core through quantum tunneling, can reduce the interfacial charge transfer resistance, and is also conducive to constructing a core-shell structure with higher structural stability.

[0118] Here, the thickness of the outer shell of the metal selenide composite material can be understood as the average thickness of the outer shell of the metal selenide composite material.

[0119] In some embodiments, the size of the gap of the obtained metal selenide composite material can be 1.2 nm to 5.5 nm. In this way, on the one hand, it can provide a suitable buffer space for the volume expansion of the inner core, forming a more stable metal selenide composite material; on the other hand, it is beneficial for part of the three-dimensional porous carbon skeleton to pass through the porous structure and fill the gap, so that a more stable physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon skeleton, thereby further improving the structural stability of the negative electrode material.

[0120] Here, the size of the gap between the outer shell and the inner core of the metal selenide composite material can be understood as the average size of the gap between the outer shell and the inner core of the metal selenide composite material.

[0121] In step S5, under the condition of introducing a carbon source gas, the initial negative electrode material is subjected to a third heat treatment to catalyze the growth of the three-dimensional porous carbon skeleton, so that the three-dimensional porous carbon skeleton passes through the porous structure and fills the gap, obtaining the negative electrode material.

[0122] In the embodiments of the present application, through the third heat treatment, the growth of the three-dimensional porous carbon framework is catalyzed. The growth orientation of the three-dimensional porous carbon framework is confined by the porous structure of the outer shell of the metal selenide composite material, forming an isotropic network, so that the three-dimensional porous carbon framework fills the gaps through the porous structure. Thus, while strengthening the three-dimensional porous carbon framework, it can enable the three-dimensional porous carbon framework to better bridge and fix the metal selenide composite material. Furthermore, a physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon framework, which can significantly inhibit the volume expansion and structural pulverization of the metal selenide during the cycling process, improve the structural stability of the metal selenide during the charge and discharge process of the battery, greatly reduce the risk of structural collapse, and the three-dimensional porous carbon framework with high flexibility can provide a buffer space for the volume change of the metal selenide composite material and absorb the stress generated due to the volume change. Therefore, the structural stability and cycling stability of the negative electrode material can be significantly improved.

[0123] Among them, the carbon source gas may include, for example, at least one of methane, ethane, ethylene, and acetylene.

[0124] In some embodiments, the temperature of the third heat treatment can be 800°C to 900°C, for example, it can be 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, or any value between any two of the above numerical ranges.

[0125] In some embodiments, the time of the third heat treatment can be 30 min to 50 min, for example, it can be 30 min, 40 min, 50 min, or any value between any two of the above numerical ranges.

[0126] In the actual preparation process, a mixed gas of a carbon source gas (specifically, acetylene for example) and an inert gas (specifically, argon for example) can be introduced at 800°C to 900°C. Among them, the volume fraction of the carbon source gas in the mixed gas can be 1%, for example. At this temperature, part of the Se on the surface of the metal selenide composite material volatilizes, and the exposed Fe atoms can catalyze the cracking of the carbon source, thereby catalyzing the growth of the three-dimensional porous carbon framework.

[0127] The embodiments of the present application also provide a negative electrode sheet, which includes the negative electrode material described in any one of the above embodiments or the negative electrode material prepared by the preparation method of the negative electrode material described in any one of the above embodiments.

[0128] It should be understood that the beneficial effects of the negative electrode material described in any one of the above embodiments or the negative electrode material prepared by the preparation method of the negative electrode material described in any one of the above embodiments are applicable to the negative electrode sheet in the embodiments of the present application.

[0129] In some embodiments, the negative electrode sheet includes a negative electrode current collector and an active material layer located on the negative electrode current collector. The active material layer includes the negative electrode material described in any one of the above embodiments or the negative electrode material prepared by the preparation method of the negative electrode material described in any one of the above embodiments.

[0130] An embodiment of the present application also provides a secondary battery, including the negative electrode sheet described in the above embodiment.

[0131] It should be understood that the beneficial effects of the negative electrode sheet in the above embodiments are all applicable to this battery. Therefore, the secondary battery in the embodiments of the present application has high capacity and cycling performance.

[0132] In some embodiments, the secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The negative electrode sheet is the negative electrode sheet described in the above embodiment. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows active ions to pass through.

[0133] The technical solution of the present application will be further described below in conjunction with multiple embodiments and comparative examples.

[0134] Example 1

[0135] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0136] S101: Dissolve 2 g of methyl cellulose (carbon source), 1.5 g of Fe(NO3)3·9H2O (iron source), and 0.8 g of selenourea (selenium source) in 50 mL of deionized water (solvent), add 0.5 g of citric acid (complexing agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0137] S102: Dropwise add NH3·H2O (regulator) with a mass fraction of 5% to the mixture obtained in step S101 until pH = 8.5. The solution gradually forms a gel, and stands for 12 h to form a Fe-Se-cellulose composite gel (composite gel); then freeze at -50 °C for 24 h (freezing treatment) and then vacuum dry to obtain a porous aerogel precursor;

[0138] S103: Perform a first heat treatment on the porous aerogel precursor obtained in step S102 to obtain an intermediate product; specifically, heat up to 500 °C at a rate of 2 °C / min, and introduce a mixed gas of Ar and H2 (reducing gas), where the volume ratio of Ar to H2 is 95:5, and keep it at a constant temperature for 1 h. During this period, methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+It is reduced to FeO, reacts with the Se vapor released by selenourea to generate FeSe2 nanoparticles, and an intermediate product with FeSe2 nanoparticles loaded in the initial three-dimensional carbon network is obtained. Due to the high partial pressure condition of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the surface of FeSe2, and a complete crystal structure can be formed;

[0139] S104: Under a closed and oxygen-deficient condition, the intermediate product obtained in step S103 is subjected to a second heat treatment to obtain an initial negative electrode material; specifically, first, it is heated to 700 °C at a rate of 2 °C / min, switched to a closed system, the flow rate of the mixed gas is closed, and the internal pressure is self-generated. In a high-temperature and oxygen-deficient environment, part of the selenium in FeSe2 is removed to generate an Fe7Se8 core, and an FeSe2 shell layer is retained on the surface layer; next, the temperature is raised to 750 °C, and the internal oxygen partial pressure in the closed and oxygen-deficient environment becomes lower, and a deselenization reaction occurs on the surface layer of FeSe2: 7FeSe2 → Fe7Se8 + 6Se. The removed Se vapor is confined in the pores of the three-dimensional porous carbon skeleton to form a local dynamic equilibrium, which promotes the nucleation and growth of Fe7Se8 inside FeSe2, and a void is formed between the Fe7Se8 inner core and the FeSe2 shell layer, thereby forming a metal selenide composite material with a core-shell structure, and the FeSe2 shell layer has a porous structure. During this period, methyl cellulose is completely carbonized into a three-dimensional porous carbon skeleton (3DCF);

[0140] S105: A mixed gas of C2H2 (carbon source) and Ar (inert gas) is introduced, where the volume fraction of C2H2 in the mixed gas is 1%, and it is kept at 800 °C for 30 min. The initial negative electrode material obtained in step S104 is subjected to a third heat treatment to catalyze the growth of the three-dimensional porous carbon skeleton, so that the three-dimensional porous carbon skeleton passes through the porous structure of the outer shell of the metal selenide composite material and fills the gap between the Fe7Se8 inner core and the FeSe2 shell layer, and a negative electrode material (which can be called H-Fe7Se8 / FeSe2@3DCF, where H represents hollow, Fe7Se8 represents the inner core, FeSe2 represents the outer shell, and 3DCF represents the three-dimensional porous carbon skeleton) is prepared.

[0141] Example 2

[0142] In this example, the preparation method of the negative electrode material includes the following steps:

[0143] S201: Dissolve 3 g of methyl cellulose (carbon source), 2 g of Fe(NO3)3·9H2O (iron source), and 0.9 g of selenourea (selenium source) in 50 mL of deionized water (solvent), add 0.6 g of citric acid (complexing agent), and stir magnetically for 2.5 h to form a homogeneous mixed solution;

[0144] S202: 5% by mass of NH3·H2O (regulator) is added to the mixed solution obtained in step S201 until the pH value is 9, and the solution gradually forms a gel, and is allowed to stand for 13 hours to form a Fe-Se-cellulose composite gel (composite gel); then, the mixture is frozen at -60°C for 28 hours (freezing treatment) and vacuum dried to obtain a porous aerogel precursor;

[0145] S203: The porous aerogel precursor obtained in step S202 is subjected to a first heat treatment to obtain an intermediate product; specifically, the temperature is raised to 520°C at 3°C / min, a mixed gas of Ar and H2 (reducing gas) is introduced, wherein the volume ratio of Ar to H2 is 95:5, and the temperature is kept for 1.5 hours, during which the methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ It is reduced to FeO, and reacts with the Se vapor released by selenourea to generate FeSe2 nanoparticles, and obtains an intermediate product in which FeSe2 nanoparticles are loaded in the initial three-dimensional carbon network. Due to the high partial pressure of selenium vapor (above 0.05MPa), selenium atoms are enriched on the surface of FeSe2, and a complete crystal structure can be formed;

[0146] S204: Under closed anoxic conditions, the intermediate product obtained in step S203 is subjected to a second heat treatment to obtain an initial negative electrode material; specifically, first, the temperature is raised to 710°C at 2.5°C / min, the system is switched to a closed system, the mixed gas flow is closed, and the internal pressure is used to generate the FeSe2 partially deselenized to generate the Fe7Se8 core in a high-temperature anoxic environment, and the FeSe2 shell is retained on the surface; next, the temperature is raised to 750°C, the internal oxygen partial pressure in the closed anoxic environment becomes low, and a deselenization reaction occurs on the surface of FeSe2: 7FeSe2→Fe7Se8+6Se, and the released Se vapor is confined in the pores of the three-dimensional porous carbon skeleton, forming a local dynamic equilibrium, promoting the nucleation and growth of Fe7Se8 inside the FeSe2, and forming a gap between the Fe7Se8 core and the FeSe2 shell, thereby forming a metal selenide composite material with a core-shell structure, and the FeSe2 shell has a porous structure. During this period, the methyl cellulose is completely carbonized into a three-dimensional porous carbon skeleton;

[0147] S205: A mixed gas of C2H2 (carbon source) and Ar (inert gas) is introduced, wherein the volume fraction of C2H2 in the mixed gas is 1%, and the mixture is kept at 820°C for 30 minutes. The initial negative electrode material obtained in step S204 is subjected to a third heat treatment to catalyze the growth of a three-dimensional porous carbon skeleton, so that the three-dimensional porous carbon skeleton passes through the porous structure of the metal selenide composite material shell and fills the gap between the Fe7Se8 core and the FeSe2 shell, thereby obtaining a negative electrode material.

[0148] Example 3

[0149] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0150] S301: Dissolve 2.8 g of methyl cellulose (carbon source), 2.5 g of Fe(NO3)3·9H2O (iron source), and 1.0 g of selenourea (selenium source) in 60 mL of deionized water (solvent), add 0.8 g of citric acid (complexing agent), and stir magnetically for 3 h to form a homogeneous mixed solution;

[0151] S302: Drop 5% NH3·H2O (regulator) by mass fraction into the mixed solution obtained in step S301 until pH = 9. The solution gradually forms a gel, stands for 14 h to form a Fe-Se-cellulose composite gel (composite gel); then freeze at -60 °C for 30 h (freezing treatment) and then vacuum dry to obtain a porous aerogel precursor;

[0152] S303: Perform a first heat treatment on the porous aerogel precursor obtained in step S302 to obtain an intermediate product; specifically, heat up to 550 °C at a rate of 3.5 °C / min, and introduce a mixed gas of Ar and H2 (reducing gas), where the volume ratio of Ar to H2 is 95:5, and keep it at this temperature for 1 h. During this period, methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ is reduced to FeO and reacts with the Se vapor released from selenourea to generate FeSe2 nanoparticles, obtaining an intermediate product with FeSe2 nanoparticles loaded in the initial three-dimensional carbon network. Due to the high partial pressure condition of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the surface of FeSe2, and a complete crystal structure can be formed;

[0153] S304: Under a closed and oxygen-deficient condition, perform a second heat treatment on the intermediate product obtained in step S303 to obtain the initial negative electrode material; specifically, first, heat up to 730 °C at a rate of 3 °C / min, switch to a closed system, close the flow rate of the mixed gas, and use the internal pressure to generate itself. In a high-temperature and oxygen-deficient environment, FeSe2 is partially deselenized to form a Fe7Se8 core, and a FeSe2 shell layer is retained on the surface layer; next, when the temperature rises to 770 °C, the internal oxygen partial pressure in the closed and oxygen-deficient environment becomes lower, and a deselenization reaction occurs on the surface layer of FeSe2: 7FeSe2 → Fe7Se8 + 6Se. The released Se vapor is confined in the pores of the three-dimensional porous carbon skeleton to form a local dynamic equilibrium, which promotes the nucleation and growth of Fe7Se8 inside FeSe2, forming a void between the Fe7Se8 core and the FeSe2 shell layer, thereby forming a metal selenide composite material with a core-shell structure, and the FeSe2 shell layer has a porous structure. During this period, methyl cellulose is completely carbonized into a three-dimensional porous carbon skeleton;

[0154] S305: Introduce a mixed gas of C2H2 (carbon source) and Ar (inert gas), where the volume fraction of C2H2 in the mixed gas is 1%. Keep it at 860 °C for 30 min to conduct the third heat treatment on the initial anode material obtained in step S304, catalyze the growth of the three-dimensional porous carbon framework, and enable the three-dimensional porous carbon framework to pass through the porous structure of the metal selenide composite shell and fill the gap between the Fe7Se8 core and the FeSe2 shell layer to obtain the anode material.

[0155] Example 4

[0156] The preparation method of the anode material in this example includes the following steps:

[0157] S401: Dissolve 3.5 g of methyl cellulose (carbon source), 4 g of Fe(NO3)3·9H2O (iron source), and 1.1 g of selenourea (selenium source) in 65 mL of deionized water (solvent), add 0.9 g of citric acid (complexing agent), and stir magnetically for 3 h to form a homogeneous mixed solution;

[0158] S402: Dropwise add NH3·H2O (regulator) with a mass fraction of 5% to the mixed solution obtained in step S401 until pH = 9. The solution gradually forms a gel, and stand for 12 h to form an Fe-Se-cellulose composite gel (composite gel); then freeze at -50 °C for 32 h (freezing treatment) and then vacuum dry to obtain a porous aerogel precursor;

[0159] S403: Conduct the first heat treatment on the porous aerogel precursor obtained in step S402 to obtain an intermediate product; specifically, heat it to 580 °C at a rate of 4 °C / min, introduce a mixed gas of Ar and H2 (reducing gas), where the volume ratio of Ar to H2 is 95:5, and keep it for 1 h. During this period, methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ is reduced to FeO and reacts with the Se vapor released by selenourea to generate FeSe2 nanoparticles, obtaining an intermediate product with FeSe2 nanoparticles loaded on the initial three-dimensional carbon network. Due to the high partial pressure condition of Se vapor (above 0.05 MPa), selenium atoms are enriched on the surface of FeSe2, and a complete crystal structure can be formed;

[0160] S404: Under airtight and oxygen-deficient conditions, perform a second heat treatment on the intermediate product obtained in step S403 to obtain the initial anode material. Specifically, first, heat it to 740 °C at a rate of 4.5 °C / min, switch to an airtight system, close the flow rate of the mixed gas, and utilize the self-generated internal pressure. In a high-temperature and oxygen-deficient environment, FeSe2 partially de-selenizes to form a Fe7Se8 core, and a FeSe2 shell layer is retained on the surface. Next, when the temperature rises to 780 °C, the internal oxygen partial pressure in the airtight and oxygen-deficient environment becomes lower, and a de-selenization reaction occurs on the surface of FeSe2: 7FeSe2 → Fe7Se8 + 6Se. The escaped Se vapor is confined in the pores of the three-dimensional porous carbon skeleton to form a local dynamic equilibrium, promoting the nucleation and growth of Fe7Se8 inside FeSe2, and forming a void between the Fe7Se8 core and the FeSe2 shell layer, thereby forming a metal selenide composite material with a core-shell structure, and the FeSe2 shell layer has a porous structure. During this period, methyl cellulose is completely carbonized into a three-dimensional porous carbon skeleton;

[0161] S405: Introduce a mixed gas of C2H2 (carbon source) and Ar (inert gas), where the volume fraction of C2H2 in the mixed gas is 1%. Keep it at 880 °C for 30 min, perform a third heat treatment on the initial anode material obtained in step S404 to catalyze the growth of the three-dimensional porous carbon skeleton, so that the three-dimensional porous carbon skeleton fills the gap between the Fe7Se8 core and the FeSe2 shell layer through the porous structure of the outer shell of the metal selenide composite material, and obtain the anode material.

[0162] Example 5

[0163] The preparation method of the anode material in this example includes the following steps:

[0164] S501: Dissolve 4 g of methyl cellulose (carbon source), 4.5 g of Fe(NO3)3·9H2O (iron source), and 1.2 g of selenourea (selenium source) in 70 mL of deionized water (solvent), add 1 g of citric acid (complexing agent), and magnetically stir for 3.5 h to form a homogeneous mixed solution;

[0165] S502: Dropwise add NH3·H2O (regulator) with a mass fraction of 5% to the mixed solution obtained in step S501 until pH = 9.5. The solution gradually forms a gel, stand for 16 h to form a Fe-Se-cellulose composite gel (composite gel); then freeze at -70 °C for 36 h (freezing treatment) and then vacuum dry to obtain a porous aerogel precursor;

[0166] S503: The porous aerogel precursor obtained in step S502 is subjected to a first heat treatment to obtain an intermediate product; specifically, it is heated to 600 °C at a rate of 5 °C / min, and a mixed gas of Ar and H2 (reducing gas) is introduced, where the volume ratio of Ar to H2 is 95:5, and it is held for 1 h. During this period, methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ is reduced to FeO and reacts with the Se vapor released by selenourea to generate FeSe2 nanoparticles, obtaining an intermediate product with FeSe2 nanoparticles loaded in the initial three-dimensional carbon network. Due to the high partial pressure condition of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the surface of FeSe2, and a complete crystal structure can be formed;

[0167] S504: Under a closed and oxygen-deficient condition, the intermediate product obtained in step S503 is subjected to a second heat treatment to obtain an initial anode material; specifically, first, it is heated to 750 °C at a rate of 5 °C / min, switched to a closed system, the flow rate of the mixed gas is closed, and the internal pressure is self-generated. In a high-temperature and oxygen-deficient environment, FeSe2 is partially deselenized to form a Fe7Se8 core, and a FeSe2 shell layer is retained on the surface layer; next, the temperature is raised to 800 °C, and the internal oxygen partial pressure in the closed and oxygen-deficient environment becomes low. A deselenization reaction occurs on the surface layer of FeSe2: 7FeSe2 → Fe7Se8 + 6Se. The released Se vapor is restricted in the pores of the three-dimensional porous carbon skeleton to form a local dynamic equilibrium, promoting the nucleation and growth of Fe7Se8 inside FeSe2, and forming a void between the Fe7Se8 inner core and the FeSe2 shell layer, thereby forming a metal selenide composite material with a core-shell structure, and the FeSe2 shell layer has a porous structure. During this period, methyl cellulose is completely carbonized into a three-dimensional porous carbon skeleton;

[0168] S505: A mixed gas of C2H2 (carbon source) and Ar (inert gas) is introduced, where the volume fraction of C2H2 in the mixed gas is 1%, and it is held at 900 °C for 50 min. The initial anode material obtained in step S504 is subjected to a third heat treatment to catalyze the growth of the three-dimensional porous carbon skeleton, so that the three-dimensional porous carbon skeleton fills the gap between the Fe7Se8 inner core and the FeSe2 shell layer through the porous structure of the metal selenide composite material shell, and the anode material is prepared.

[0169] Example 6

[0170] The preparation method of the anode material in this example is basically the same as that in Example 1, and the main difference is that:

[0171] The carbon source methyl cellulose in step S101 is replaced with starch, and the iron source Fe(NO3)3·9H2O in step S101 is replaced with FeCl3·6H2O.

[0172] Comparative Example 1

[0173] The preparation method of the negative electrode material in this comparative example includes the following steps:

[0174] S601: Dissolve 1.5 g of Fe(NO3)3·9H2O (iron source), 0.8 g of selenourea (selenium source) in 50 mL of deionized water (solvent), add 0.5 g of citric acid (complexing agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0175] S602: Perform a first heat treatment on the mixture obtained in step S601 to obtain the Fe7Se8 negative electrode material; specifically, first, heat it to 700 °C at a rate of 2 °C / min, and introduce a mixed gas of Ar and H2, where the volume ratio of Ar to H2 is 95:5, and keep it at this temperature for 1 h. During this period, Fe 3+ is reduced to FeO and reacts with the Se vapor released from selenourea to form FeSe2 nanoparticles; next, switch to a closed system, turn off the flow of the mixed gas, and use the self-generated internal pressure to cause the FeSe2 to deselenize to form Fe7Se8.

[0176] Comparative Example 2

[0177] The preparation method of the negative electrode material in this comparative example includes the following steps:

[0178] S701: Dissolve 1.5 g of Fe(NO3)3·9H2O (iron source), 0.8 g of selenourea (selenium source) in 50 mL of deionized water (solvent), add 0.5 g of citric acid (complexing agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0179] S702: Perform a first heat treatment on the mixture obtained in step S701 to obtain the FeSe2 negative electrode material; specifically, heat it to 550 °C at a rate of 2 °C / min, and introduce a mixed gas of Ar and H2, where the volume ratio of Ar to H2 is 95:5, and keep it at this temperature for 1 h. During this period, Fe 3+ is reduced to FeO and reacts with the Se vapor released from selenourea to form FeSe2 nanoparticles. Due to the high partial pressure condition of the Se vapor (above 0.05 MPa), Se atoms are enriched on the surface of FeSe2 to form a complete crystal structure.

[0180] Comparative Example 3

[0181] The preparation method of the negative electrode material in this comparative example includes the following steps:

[0182] S801: Dissolve 1.5 g of Fe(NO3)3·9H2O (iron source), 0.8 g of selenourea (selenium source) in 50 mL of deionized water (solvent), add 0.5 g of citric acid (complexing agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0183] S802: Perform a first heat treatment on the mixture obtained in step S801 to obtain FeSe2. Specifically, heat it at a rate of 2 °C / min to 500 °C, and introduce a mixed gas of Ar and H2, where the volume ratio of Ar to H2 is 95:5, and keep it at this temperature for 1 h. During this period, Fe 3+ is reduced to FeO and reacts with the Se vapor released from selenourea to form FeSe2 nanoparticles. Due to the high partial pressure condition of the Se vapor (above 0.05 MPa), Se atoms are enriched on the surface of FeSe2, forming a complete crystal structure;

[0184] S803: Perform a second heat treatment on the FeSe2 obtained in step S802. Specifically, first, heat it at a rate of 2 °C / min to 700 °C, switch to a closed system, close the flow rate of the mixed gas, and utilize the self-generated internal pressure. In a high-temperature and oxygen-deficient environment, part of the Se in FeSe2 is removed to form a Fe7Se8 core, and a FeSe2 shell layer is retained on the surface layer. Next, raise the temperature to 750 °C. The internal oxygen partial pressure in the closed oxygen-deficient environment becomes lower, and a deselenization reaction occurs on the surface layer of FeSe2: 7FeSe2 → Fe7Se8 + 6Se, promoting the nucleation and growth of Fe7Se8 inside FeSe2, forming a negative electrode material with a Fe7Se8 core and a FeSe2 shell.

[0185] Comparative Example 4

[0186] The preparation method of the negative electrode material in this comparative example includes the following steps:

[0187] S901: Dissolve 2 g of methylcellulose (carbon source) in 50 mL of deionized water (solvent), add 0.5 g of citric acid (complexing agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0188] S902: Dropwise add NH3·H2O (regulator) with a mass fraction of 5% to the mixture obtained in step S901 until the pH reaches 8.5. The solution gradually forms a gel and is left standing for 12 h; then it is frozen at -50 °C for 24 h and then vacuum dried to obtain an aerogel precursor;

[0189] S903: Introduce a mixed gas of C2H2 (carbon source) and Ar (inert gas), where the volume fraction of C2H2 in the mixed gas is 1%, and keep it at 800 °C for 30 min to perform a heat treatment on the aerogel precursor obtained in step S902, so that the aerogel precursor is carbonized and catalyzes the growth of a three-dimensional porous carbon skeleton to prepare the negative electrode material.

[0190] Comparative Example 5

[0191] The preparation method of the negative electrode material in this comparative example includes the following steps:

[0192] S110: Dissolve 2 g of methyl cellulose (carbon source), 1.5 g of Fe(NO3)3·9H2O (iron source), and 0.8 g of selenourea (selenium source) in 50 mL of deionized water (solvent), add 0.5 g of citric acid (complexing agent), and stir magnetically for 2 h to form a homogeneous mixed solution;

[0193] S111: Dropwise add NH3·H2O (regulator) with a mass fraction of 5% to the mixed solution obtained in step S110 until pH = 8.5. The solution gradually forms a gel, and stand for 12 h to form a Fe-Se-cellulose composite gel (composite gel); then freeze at -50 °C for 24 h and then vacuum dry to obtain a porous aerogel precursor;

[0194] S112: Perform a first heat treatment on the porous aerogel precursor obtained in step S111 to obtain an intermediate product; specifically, heat it to 500 °C at a rate of 2 °C / min and hold for 1 h. During this period, part of the methyl cellulose is carbonized to form an initial three-dimensional carbon network; Fe 3+ is reduced to FeO and reacts with the Se vapor released from selenourea to generate FeSe2 nanoparticles, obtaining an intermediate product with FeSe2 nanoparticles loaded in the initial three-dimensional carbon network;

[0195] S113: Perform a second heat treatment on the intermediate product obtained in step S112 to obtain an initial anode material; specifically, first, heat it to 700 °C at a rate of 2 °C / min and maintain an open system; next, raise the temperature to 750 °C and continue to maintain an open system. During this period, the methyl cellulose is completely carbonized into a three-dimensional porous carbon skeleton;

[0196] S114: Introduce Ar, hold at 800 °C for 30 min, perform a third heat treatment on the initial anode material obtained in step S113 to prepare the anode material.

[0197] Test and analyze the anode material prepared in the above Example 1. Figure 2 is the XRD pattern of the anode material prepared in Example 1. From Figure 2 it can be seen that the characteristic peaks in the XRD pattern of the anode material prepared in Example 1 highly coincide with the standard peak positions of the Fe7Se8 and FeSe2 patterns, and no obvious impurity peaks are detected. Thus, it is indicated that the prepared anode material contains Fe7Se8 and FeSe2. Figure 3 is the scanning electron microscope image of the anode material prepared in Example 1, Figure 4 is a transmission electron microscope image of the anode material prepared in Example 1. From Figure 3 it can be seen that the anode material prepared in Example 1 has a typical core-shell structure, the interface between the core and the shell is distinct, and there is a gap between the core and the shell. Thus, it is indicated that a metal selenide composite material with a core-shell structure has been successfully synthesized in the anode material prepared in Example 1. Combining withFigure 4 The high-resolution transmission electron microscope images in Figure 4 show clear lattice fringes. Among them, the lattice spacing of 0.158 nm corresponds to the (211) crystal plane of FeSe2, and the lattice spacing of 0.205 nm corresponds to the (102) crystal plane of Fe7Se8. From Figure 3 and Figure 4 , it can be seen that a metal selenide composite material with Fe7Se8 as the core and FeSe2 as the shell is successfully synthesized in the negative electrode material prepared in Example 1. Figure 5 Figure 9 is another transmission electron microscope image of the negative electrode material prepared in Example 1. Figure 5 The high-resolution transmission electron microscope images in it mainly show the three-dimensional porous carbon skeleton structure in the gap between the core and the shell of the core-shell structure in the negative electrode material. Among them, the gap between the core and the shell communicates with the interconnected porous carbon skeleton to form a highly open pore system, which can provide rich channels for the transmission of active ions and electrons, promote the diffusion of active ions and electrons, and thus help reduce the charge transfer resistance.

[0198] A scanning electron microscope was used to measure the microscopic sizes of the core-shell structure with Fe7Se8 as the core and FeSe2 as the shell in the negative electrode materials prepared in Examples 1 to 6 and Comparative Example 3, and the average size of the gap between the core and the shell, the average size of the shell thickness, and the average size of the core particle size were obtained. The measurement results are shown in Table 1.

[0199] Table 1

[0200] As can be seen from Table 1, in the negative electrode materials prepared in Examples 1 to 6, the size range of the gap between the shell and the core of the metal selenide composite material is between 1.2 nm and 5.5 nm; in this way, on the one hand, it can provide a suitable buffer space for the volume expansion of the core to form a more stable metal selenide composite material; on the other hand, it is beneficial for part of the three-dimensional porous carbon skeleton to pass through the porous structure and fill the gap, so that a more stable physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon skeleton, thereby further improving the structural stability of the negative electrode material. The particle size range of the core of the metal selenide composite material is between 6 nm and 10 nm; in this way, it is beneficial to improve the capacity of the negative electrode material and at the same time beneficial to construct a core-shell structure with higher structural stability. The thickness range of the shell of the metal selenide composite material is between 5 nm and 8 nm; this thickness range is lower than the critical thickness of electron tunneling (about 10 nm), allowing electrons to be directly injected into the core through quantum tunneling, which can reduce the interfacial charge transfer resistance and is also beneficial to construct a core-shell structure with higher structural stability.

[0201] The anode materials obtained in the above-mentioned examples and comparative examples were made into batteries, and the electrochemical performance of the batteries was tested. Among them, the preparation of the battery included the following steps: The anode materials obtained in the above-mentioned examples and comparative examples were used as the working electrode, a lithium metal sheet was used as the reference electrode, glass fiber was used as the separator, and a solution of 1 mol / L LiPF6 dissolved in diglyme was used as the electrolyte; 100 μL of the electrolyte was dropped on the separator, and a half-cell was assembled in the order of the positive electrode case, the working electrode, the separator, the lithium sheet, the gasket, the shrapnel, and the negative electrode case. The assembled half-cell was clamped with insulated tweezers and placed on a packaging machine for sealing. Finally, the packaged battery was taken out of the glove box and left to stand for 12 h. After the electrolyte was fully infiltrated, relevant electrochemical tests were carried out. The specific tests are as follows:

[0202] 1) First-cycle discharge specific capacity and first-cycle Coulombic efficiency test: The above-prepared lithium-ion button half-cell was placed in an environment of 26 °C, and at a current density of 0.1 A . g -1 the battery was charged at a constant current. The charging cut-off voltage was 3.0 V, and the total capacity during the charging process was recorded as the first-cycle charging capacity C1. The first-cycle discharge immediately followed the charging process until the voltage dropped to 0.01 V, and the total capacity during the discharge process was recorded as the first-cycle discharge capacity C2. The first-cycle discharge specific capacity = C2 / mass of the active material (anode material), and the first-cycle Coulombic efficiency = (C2 / C1) × 100%.

[0203] 2) Cycle life test: The above-prepared lithium-ion button half-cell was placed in an environment of 26 °C and subjected to a cycle test at a current density of 3 A . g -1 where the charging cut-off voltage was 3.0 V and the discharging cut-off voltage was 0.01 V; the cycle was repeated 4,000 times, and the ratio of the discharge capacity at the end of 4,000 cycles to the first discharge capacity was used as the capacity retention rate after 4,000 cycles.

[0204] 3) Electrochemical impedance spectroscopy test: An electrochemical workstation was used to perform an electrochemical impedance spectroscopy test. The test frequency was 0.01 Hz to 100 kHz, and the charge transfer resistance was obtained based on the measured electrochemical impedance spectroscopy.

[0205] The test results of the above tests are shown in Table 2.

[0206] Table 2

[0207] As can be seen from the data in Table 2, compared with Comparative Examples 1 to 5, the first-cycle discharge specific capacity, first-cycle Coulombic efficiency, and capacity retention rate after 4000 cycles of the batteries containing the anode materials prepared in Examples 1 to 6 are all significantly improved. This shows that in the anode material prepared in this application, the metal selenide composite material with a core-shell structure is loaded on the three-dimensional porous carbon framework, and part of the three-dimensional porous carbon framework passes through the porous structure of the core-shell structure shell and fills the gap between the core and the shell, so that a physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon framework, thereby significantly suppressing the volume expansion and structural pulverization of the metal selenide during the cycling process, improving the structural stability of the metal selenide during the charge and discharge process of the battery, greatly reducing the risk of structural collapse, and the three-dimensional porous carbon framework with high flexibility can provide a buffer space for the volume change of the metal selenide composite material and absorb the stress generated by the volume change. Therefore, the structural stability and cycling stability of the anode material can be significantly improved. In addition, there is a gap between the core and the shell of the metal selenide composite material, which can form a built-in electric field to drive the active ions (such as lithium ions or sodium ions) to enrich in the core with high theoretical capacity, and can also provide a buffer space for the volume expansion of the core, thereby significantly improving the capacity and cycling performance of the battery.

[0208] Furthermore, as can be seen from the test results of the charge transfer resistance in Table 2, in the anode material prepared in this application, the metal selenide composite material with a core-shell structure is loaded on the three-dimensional porous carbon framework, and part of the three-dimensional porous carbon framework passes through the porous structure of the core-shell structure shell and fills the gap between the core and the shell. This special structure enables the gap between the core and the shell of the metal selenide composite material to communicate with the interconnected three-dimensional porous carbon framework, forming a highly open pore system, which can provide rich channels for the transport of active ions and electrons, promote the diffusion of active ions and electrons, and thus is conducive to reducing the charge transfer resistance of the battery.

[0209] The anode material prepared in Comparative Example 1 only contains Fe7Se8 material, the anode material prepared in Comparative Example 2 only contains FeSe2 material, and the anode material prepared in Comparative Example 3 contains a material with Fe7Se8 as the core and FeSe2 as the shell. As can be seen from the data in Table 2, due to the unstable structure of the metal selenide during the battery cycling process, problems such as volume expansion, even structural collapse, and structural pulverization are likely to occur, resulting in lower first-cycle discharge specific capacity, first-cycle Coulombic efficiency, and capacity retention rate after 4000 cycles of the batteries containing the anode materials prepared in Comparative Examples 1 to 3, that is, the capacity of the battery is low and the cycling performance is poor.

[0210] The negative electrode material prepared in Comparative Example 4 only contains carbon materials. It can be seen from the data in Table 2 that the initial discharge specific capacity, initial Coulomb efficiency, and capacity retention rate after 4000 cycles of the battery containing the negative electrode material prepared in Comparative Example 4 are all at the lowest level, that is, the capacity of the battery is very low and the cycling performance is very poor.

[0211] In Comparative Example 5, during the preparation of the negative electrode material, no reducing gas was introduced during the first heat treatment of the porous aerogel precursor, which affected the reduction reaction of Fe 3+ , resulting in incomplete reaction, uneven particle size and poor crystallinity of the formed FeSe2 particles. Moreover, during the subsequent second heat treatment process, the environment was not switched to a closed and oxygen-deficient environment. Due to the lack of internal pressure regulation, effective deselenization reaction of FeSe2 could not occur, that is, Fe7Se8 nuclei could not be formed; in addition, serious loss of selenium atoms on the surface of FeSe2 particles would also lead to incomplete crystal structure, and finally a core-shell structure with Fe7Se8 as the core and FeSe2 as the shell could not be formed. During the third heat treatment process, no carbon source gas was introduced, resulting in incomplete carbonization and growth of the carbon skeleton, the formed three-dimensional carbon skeleton was loose and had poor conductivity, and the FeSe2 particles were not tightly combined with the three-dimensional carbon skeleton. The FeSe2 particles were prone to agglomeration, and it was easy for the FeSe2 particles and the carbon carrier to separate from each other, and an effective conductive network could not be formed, resulting in poor structural stability and cycling stability of the negative electrode material. Therefore, compared with Example 1, the capacity and cycling performance of the battery containing the negative electrode material prepared in Comparative Example 5 were significantly reduced.

[0212] Through the in-situ chemical deposition technology and anion exchange reaction strategy, the present invention successfully synthesized an innovative composite material, namely a metal selenide composite material with a core-shell structure anchored on a three-dimensional porous carbon skeleton (3DCF) (which can be called a hollow Fe7Se8 / FeSe2 nanoparticle composite material), and named it H-Fe7Se8 / FeSe2@3DCF. In the H-Fe7Se8 / FeSe2@3DCF composite material, the synergistic effect between the three-dimensional porous carbon skeleton and the internally anchored hollow Fe7Se8 / FeSe2 nanoparticles is the core advantage that differentiates it from traditional selenide composite materials. The specific differences and innovations are reflected in the following aspects: 1) Dynamic ionic bonding and structural interlocking: In traditional selenide composite materials, the active components and the carbon carrier are mostly physically mixed or simply coated, with weak interfacial binding force and easy detachment. In the negative electrode material of the present invention, the in-situ chemical deposition and anion exchange strategies enable the metal selenide to form chemical bond cascades with the three-dimensional porous carbon skeleton: the cationic sites on the surface of the three-dimensional porous carbon skeleton are electrostatically attracted to Se 2- / Se -Anion binding forms a strong interface of "ionic bond bridge"; the porous shell of hollow Fe7Se8 / FeSe2 nanoparticles interpenetrates with the three-dimensional network of the carbon skeleton to form a physical interlocking structure. The combination of the two combines the strong binding force of chemical bonds and the stability of physical interlocking, which can significantly inhibit the volume expansion and structural pulverization of metal selenides during cycling. 2) Anion-cation synergistic activation interface: The three-dimensional porous carbon skeleton can provide local cation active sites, which form a dynamic polarization interface with the anions (Se 2- / Se - ) on the surface of the metal selenide. The polarization electric field accelerates charge transfer and reduces the reaction energy barrier; the anion-cation interaction stabilizes the interface structure and can also avoid side reactions between the material and the electrolyte. The H-Fe7Se8 / FeSe2@3DCF composite material exhibits excellent electrochemical performance, which is mainly attributed to the synergistic effect between its structural design and composition, opening up a new path for the development of high-performance secondary battery electrode materials.

[0213] It should be noted that the negative electrode material embodiments, the preparation method embodiments of the negative electrode material, the negative electrode sheet embodiments and the secondary battery embodiments provided in this application belong to the same concept; among the technical features in the technical solutions recorded in each embodiment, they can be arbitrarily combined without conflict.

[0214] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners. Without departing from the scope of the present disclosure, various deformations and changes can be made on the basis of the above embodiments. Similarly, the technical features of the above embodiments can also be arbitrarily combined to form other embodiments of the present invention that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present invention and do not limit the protection scope of the present invention patent.

Claims

1. A negative electrode material, characterized in that, It includes a metal selenide composite material and a three-dimensional porous carbon skeleton, wherein the metal selenide composite material is loaded in the three-dimensional porous carbon skeleton; The metal selenide composite material has a core-shell structure. The core of the core-shell structure includes Fe7Se8, the shell includes FeSe2, there is a gap between the core and the shell, the shell has a porous structure, and part of the three-dimensional porous carbon skeleton passes through the porous structure and fills the gap.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material satisfies at least one of the following characteristics: (1) The particle size of the core is 6nm to 10nm; (2) The thickness of the shell is 5nm to 8nm; (3) The size of the gap is 1.2nm to 5.5nm; (4) The three-dimensional porous carbon skeleton includes oxygen-containing functional groups, and the oxygen-containing functional groups are chemically bonded to at least part of the metal selenide composite material.

3. A method for preparing a negative electrode material, characterized in that, The method includes the following steps: S1: Dissolve a carbon source, an iron source, and a selenium source in a solvent, and then add a complexing agent. After mixing, a mixed solution is obtained; S2: Add a regulator to the mixed solution. After adjusting the mixed solution to be alkaline, react, and after standing, a composite gel is obtained; then the composite gel is subjected to freeze treatment, and after drying, a porous aerogel precursor is obtained; S3: Under the condition of introducing a reducing gas, perform a first heat treatment on the porous aerogel precursor to obtain an intermediate product, and the intermediate product includes an initial three-dimensional carbon network and FeSe2 particles loaded in the initial three-dimensional carbon network; S4: Under a closed and oxygen-deficient condition, perform a second heat treatment on the intermediate product, so that the initial three-dimensional carbon network forms a three-dimensional porous carbon skeleton, and a deselenization reaction occurs inside the FeSe2 particles to form a metal selenide composite material with a core-shell structure. The core of the core-shell structure includes Fe7Se8, the shell includes FeSe2, there is a gap between the core and the shell, the shell has a porous structure, and an initial negative electrode material is obtained; S5: Under the condition of introducing a carbon source gas, perform a third heat treatment on the initial negative electrode material to catalyze the growth of the three-dimensional porous carbon skeleton, so that the three-dimensional porous carbon skeleton passes through the porous structure and fills the gap to obtain the negative electrode material.

4. The method for preparing a negative electrode material according to claim 3, characterized in that, Step S1 satisfies at least one of the following characteristics: (1) The carbon source includes at least one of methyl cellulose, starch, sucrose, lactic acid, citric acid, carboxymethyl cellulose, and hydroxyethyl cellulose; (2) The iron source includes at least one of Fe(NO3)3·9H2O, FeCl3·6H2O, Fe2(SO4)3, and FeSO4·7H2O; (3) The selenium source includes at least one of selenourea, selenium dioxide, hydrogen selenide, selenourea, sodium selenosulfate, and carbon diselenide; (4) The solvent includes at least one of deionized water, ethanol, ethylene glycol, glycerol, dimethyl sulfoxide, and ammonia water; (5) The complexing agent includes at least one of citric acid, oxalic acid, tartaric acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, and polyvinylpyrrolidone; (6) The material ratio of the carbon source, the iron source, the selenium source, the complexing agent to the solvent is (2-4) g : (1.5-4.5) g : (0.8-1.2) g : (0.5-1) g : (50-70) ml; (7) The time of the mixing treatment is 2 h to 3.5 h.

5. The preparation method of the negative electrode material according to claim 3, characterized in that, Step S2 satisfies at least one of the following characteristics: (1) The regulator includes at least one of ammonia water, triethylamine, ethylenediamine, urea, ammonium carbonate, pyridine, hexamethylenetetramine; (2) The pH of the mixed solution after being regulated by the regulator is 8.5 to 9.5; (3) The time of the standing treatment is 12 h to 16 h; (4) The temperature of the freezing treatment is -70 °C to -50 °C; (5) The time of the freezing treatment is 24 h to 36 h; (6) The drying treatment is carried out under vacuum conditions.

6. The preparation method of the negative electrode material according to claim 3, wherein, Step S3 satisfies at least one of the following characteristics: (1) The reducing gas includes at least one of H2, NH3, CH4, CO, H2Se; (2) The temperature of the first heat treatment is 500 °C to 600 °C; (3) The heat preservation time of the first heat treatment is 1 h to 3 h; (4) The heating rate of the first heat treatment is 2 °C / min to 5 °C / min.

7. The preparation method of the negative electrode material according to claim 3, characterized in that, Step S4 satisfies at least one of the following characteristics: (1) The described airtight and oxygen-deficient condition is as follows: the pressure is between 0.1 MPa and 0.12 MPa; the oxygen partial pressure is less than or equal to 10 -5 MPa; (2) The second heat treatment includes: first heat preserving at 700 °C to 750 °C for 1.5 h to 2.5 h, and then heat preserving at 750 °C to 800 °C for 0.5 h to 1.5 h; (3) The particle size of the inner core is 6 nm to 10 nm; (4) The thickness of the outer shell is 5 nm to 8 nm; (5) The size of the gap is 1.2 nm to 5.5 nm.

8. The preparation method of the negative electrode material according to claim 3, characterized in that, Step S5 satisfies at least one of the following characteristics: (1) The carbon source gas includes at least one of methane, ethane, ethylene, acetylene; (2) The temperature of the third heat treatment is 800 °C to 900 °C; (3) The time of the third heat treatment is 30 min to 50 min.

9. A negative electrode sheet, characterized in that, The negative electrode material prepared by the preparation method of the negative electrode material described in claim 1 or 2 or the negative electrode material described in any one of claims 3 to 8.

10. A secondary battery, characterized in that, Including the negative electrode sheet described in claim 9.

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