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

Abstract

The present application relates to a negative electrode material, a preparation method thereof, a negative electrode sheet, and a secondary battery. The negative electrode material comprises 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, wherein the core of the core-shell structure comprises Fe7Se8, the shell comprises FeSe2, a gap is formed between the core and the shell, and the shell has a porous structure, and a portion of the three-dimensional porous carbon skeleton passes through the porous structure and fills the gap. In this way, the structural stability and cycle stability of the negative electrode material can be significantly improved, thereby significantly improving the capacity and cycle performance of the battery.

Description

Technical Field

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

[0002] Lithium-ion batteries are 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. This mechanism gives lithium-ion batteries a high voltage platform and good electrochemical performance.

[0003] However, lithium-ion batteries still face some challenges in practical applications, among which the problems of electrode material capacity decay and poor cycle stability are more prominent. Especially under high-rate charge and discharge conditions, the structural stability of the electrode material is more seriously threatened, which is more likely to lead to rapid decay of battery capacity and significantly shortened battery life.

[0004] Metal selenides have high theoretical specific capacity and good electrochemical activity. If used as negative electrode materials for batteries, they are expected to significantly increase the battery's storage capacity. In addition, the unique layered structure and good conductivity of metal selenides facilitate the transport of active ions and electrons, thereby improving the battery's rate performance. However, metal selenides suffer from structural instability and even structural collapse during battery charge and discharge, which greatly limits their practical application in negative electrode materials. Summary of the Invention

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

[0006] In a first aspect, an embodiment of the present application provides a negative electrode material, comprising 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;

[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 skeleton passes through the porous structure and fills the gap.

[0008] In conjunction 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 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 skeleton includes oxygen-containing functional groups, and the oxygen-containing functional groups are bonded to at least a portion of the metal selenide composite material through chemical bonds.

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

[0014] S1: dissolving a carbon source, an iron source, and a selenium source in a solvent, adding a complexing agent, and mixing to obtain a mixed solution;

[0015] S2: adding a regulator to the mixed solution, adjusting the mixed solution to alkaline, reacting, and allowing to stand to obtain a composite gel; then freezing the composite gel, and drying it to obtain a porous aerogel precursor;

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

[0017] S4: Under closed oxygen-deficient conditions, 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, wherein 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, thereby obtaining an initial negative electrode material;

[0018] S5: Under the condition of introducing 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 gaps, thereby obtaining the negative electrode material.

[0019] In conjunction with the second aspect of the present application, in an optional implementation manner, step S1 satisfies at least one of the following characteristics:

[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-liquid ratio of the carbon source, the iron source, the selenium source, the complexing agent and 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 mixing time is 2h~3.5h.

[0027] In conjunction with the second aspect of the present application, in an optional implementation manner, step S2 satisfies at least one of the following characteristics:

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

[0029] (2) The pH of the mixed solution after adjustment by the regulator is 8.5-9.5;

[0030] (3) The static treatment time is 12h~16h;

[0031] (4) The freezing temperature is between -70°C and -50°C;

[0032] (5) The freezing treatment time is 24h~36h;

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

[0034] In conjunction with the second aspect of the present application, in an optional implementation manner, step S3 satisfies at least one of the following characteristics:

[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 1h~3h;

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

[0039] In conjunction with the second aspect of the present application, in an optional implementation manner, step S4 satisfies at least one of the following characteristics:

[0040] (1) The closed anoxic conditions are: pressure between 0.1MPa and 0.12MPa; oxygen partial pressure less than or equal to 10 -5 MPa;

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

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

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

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

[0045] In conjunction with the second aspect of the present application, in an optional implementation manner, step S5 satisfies at least one of the following characteristics:

[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 third heat treatment time is 30 min to 50 min.

[0049] In a third aspect, an embodiment of the present application provides a negative electrode sheet, comprising the negative electrode material described in any one of the first aspects or the negative electrode material prepared by the preparation method of the negative electrode material described in any one of the second aspects.

[0050] In a fourth aspect, an embodiment of the present application provides a secondary battery comprising 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 embodiments of the present application provide a negative electrode material, a preparation method thereof, a negative electrode sheet, and a secondary battery, wherein the negative electrode material 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. In the embodiment of the present application, a metal selenide composite material with a core-shell structure is loaded in a three-dimensional porous carbon skeleton, and part of the three-dimensional porous carbon skeleton passes through the porous structure of the core-shell structure shell and fills the gap between the core and 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 cycle, improving the structural stability of the metal selenide during the battery charge and discharge process, and greatly reducing the risk of structural collapse. Moreover, 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, thereby significantly improving the structural stability and cycle stability of the negative electrode material. In addition, there is a gap between the core and shell of the metal selenide composite material, which can form a built-in electric field, 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 cycle performance of the battery.

[0053] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through 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 illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0055] Figure 1 A schematic diagram of a process for preparing a negative electrode material provided in an embodiment of the present application;

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

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

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

[0059] Figure 5 This is another transmission electron microscope image of the negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0060] In order to make the technical solutions and beneficial effects of the present invention more clearly understood, the following is a detailed description of the invention by referring to the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the invention. The experimental methods in the following examples where specific conditions are not specified are generally based on conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

[0061] In the following description, numerous specific details are provided to provide a more thorough understanding of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced without one or more of these details. In other instances, certain technical features known in the art are not described to avoid confusion with the present application; that is, all features of actual embodiments are not described herein, nor are well-known functions and steps described in detail.

[0062] The purpose of the terms used herein is only to describe specific embodiments and is not intended to limit the present application. When used herein, the singular forms "a", "an", and "the" are 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, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0063] In order to fully understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution 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 also have other implementation methods.

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

[0065] In the following examples, if no specific techniques or conditions are specified, the methods are generally carried out according to conventional techniques or conditions described in the literature in the field, or according to the product instructions and the conditions recommended by the manufacturer. The numerical ranges in the following examples are all inclusive.

[0066] In the related art, in the negative electrode materials containing selenide and carbon, the binding method between the active component selenide and the carbon carrier is mostly physical mixing or a simple carbon material coating the selenide. In this way, the binding force between the selenide and the carbon carrier is weak, and the two are easily separated, resulting in poor structural stability and cycle stability of the negative electrode material.

[0067] Based on this, an embodiment of the present application provides a negative electrode material, which 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, and 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.

[0068] In the embodiments of the present application, a metal selenide composite material with a core-shell structure is loaded into a three-dimensional porous carbon skeleton, and part of the three-dimensional porous carbon skeleton passes through the porous structure of the core-shell structure shell to fill the gap between the core and shell, so that a physical interlocking structure is formed between the metal selenide composite material and the three-dimensional porous carbon skeleton. This can significantly inhibit the volume expansion and structural pulverization of the metal selenide during cycling, improve the structural stability of the metal selenide during battery charging and discharging, and greatly reduce the risk of structural collapse. In addition, the highly flexible three-dimensional porous carbon skeleton can provide a buffer space for the volume change of the metal selenide composite material and absorb the stress generated by the volume change, thereby significantly improving the structural stability and cycling stability of the negative electrode material. In addition, the core of the metal selenide composite material includes Fe7Se8. The cubic lattice of Fe7Se8 (space group "Fm3m") has three-dimensional ion diffusion channels, and the interlayer spacing is larger than the lithium ion desolvation ion diameter, allowing rapid insertion and extraction of lithium ions and high theoretical capacity. There is a gap between the core and shell of the metal selenide composite material, which can form a built-in electric field, driving active ions (such as lithium ions or sodium ions, etc.) to enrich the inner core with high theoretical capacity. It can also provide a buffer space for the volume expansion of the inner core, thereby significantly improving the capacity and cycle performance of the battery.

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

[0070] Here, the particle size of the core of the metal selenide composite material may 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 shell can be 5 nm to 8 nm. Keeping the thickness of the metal selenide composite shell within this range, below the critical electron tunneling thickness (approximately 10 nm), allows electrons to be directly injected into the core via quantum tunneling, reducing interfacial charge transfer resistance and facilitating the construction of a core-shell structure with greater structural stability.

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

[0073] In some embodiments, the gap between the outer shell and the inner core of the metal selenide composite material can be 1.2 nm to 5.5 nm. This not only provides a suitable buffer for the volume expansion of the inner core, forming a more structurally stable metal selenide composite material, but also facilitates the passage of part of the three-dimensional porous carbon skeleton through the porous structure to fill the gap, thereby forming a more stable physical interlocking structure 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 outer shell and the core of the metal selenide composite material may be understood as the average size of the gap between the outer shell and the core of the metal selenide composite material.

[0075] In some embodiments, the three-dimensional porous carbon framework includes oxygen-containing functional groups, and the oxygen-containing functional groups are bonded to at least a portion of the metal selenide composite material via chemical bonds.

[0076] In the embodiment 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 cationic anchoring sites, so that iron ions can be evenly and firmly bound to the surface of the three-dimensional porous carbon skeleton to form stable bonding sites. The cationic active sites on the three-dimensional porous carbon skeleton can also interact with the anions (Se2O3) on the surface of the metal selenide composite material through electrostatic interaction. 2- / Se - ) are combined to form a strong interface of "ionic bond bridge" and 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; thereby, the metal selenide composite material and the three-dimensional porous carbon skeleton are stably combined through the physical interlocking structure, and the strong binding force of the chemical bond is increased, the interface bonding is more stable, and the structural stability, conductivity and cycle life of the negative electrode material can be significantly increased.

[0077] This application also provides a method for preparing a negative electrode material. Figure 1 The method for preparing the negative electrode material provided in the embodiment of the present application comprises the following steps:

[0078] S1: dissolving a carbon source, an iron source, and a selenium source in a solvent, adding a complexing agent, and mixing to obtain a mixed solution;

[0079] S2: adding a regulator to the mixed solution, adjusting the mixed solution to alkaline, reacting, and standing to obtain a composite gel; then freezing the composite gel, and drying it to obtain a porous aerogel precursor;

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

[0081] S4: Under closed oxygen-deficient conditions, 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, wherein 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, thereby obtaining an initial negative electrode material;

[0082] S5: Under the condition of introducing carbon source gas, the initial negative electrode material 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 and fills the gaps to obtain a negative electrode material.

[0083] In the embodiment of the present application, an in-situ chemical deposition method is first used to form an intermediate product including an initial three-dimensional carbon network and FeSe2 particles loaded in the initial three-dimensional carbon network; then, under closed oxygen-deficient heat treatment conditions, an anion exchange reaction is performed to cause a deselenization reaction to occur inside the FeSe2 particles to form a metal selenide composite material with a core-shell structure, and at the same time, the initial three-dimensional carbon network is carbonized to form a three-dimensional porous carbon skeleton that wraps the metal selenide composite material; finally, the growth of the three-dimensional porous carbon skeleton is catalyzed so that the three-dimensional porous carbon skeleton passes through the porous structure of the core-shell structure shell and fills the gap between the core and shell. In the negative electrode material prepared 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 skeleton, and part of the three-dimensional porous carbon skeleton passes through the porous structure of the core-shell structure shell and fills the gap between the core and 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 cycle, improving the structural stability of the metal selenide during the battery charge and discharge process, and greatly reducing the risk of structural collapse. Moreover, 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, thereby significantly improving the structural stability and cycle stability of the negative electrode material. In addition, there is a gap between the core and shell of the metal selenide composite material, which can form a built-in electric field, 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 cycle performance of the battery.

[0084] In the embodiment of the present application, a large number of oxygen-containing functional groups (such as carboxyl groups) can be introduced into the three-dimensional porous carbon skeleton through the preparation method of in-situ chemical deposition. These oxygen-containing functional groups can serve as cationic anchoring sites, so that iron ions can be evenly and firmly bound to the surface of the three-dimensional porous carbon skeleton to form stable bonding sites. The cationic active sites on the three-dimensional porous carbon skeleton can also interact with the anions (Se2O3) on the surface of the metal selenide composite material through electrostatic interaction. 2- / Se - ) are combined to form a strong interface of "ionic bond bridge" and a dynamic polarization interface. The polarization electric field accelerates charge transfer, reduces the reaction energy barrier, stabilizes the interface structure, and reduces electrolyte side reactions. As a result, the metal selenide composite material and the three-dimensional porous carbon skeleton are stably combined through the physical interlocking structure, and the strong binding force of the chemical bond is increased, the interface bonding is more stable, and the structural stability, conductivity and cycle life of the negative electrode material can be significantly increased.

[0085] In step S1, a carbon source, an iron source and a selenium source are dissolved in a solvent, and then a complexing agent is added and mixed to obtain a mixed solution.

[0086] The carbon source may include, for example, at least one of methyl cellulose, starch, sucrose, lactic acid, citric acid, carboxymethyl cellulose, and hydroxyethyl cellulose. These types of carbon sources can effectively ensure the formation of a high-quality composite gel in subsequent steps. In some specific embodiments, the carbon source may be methyl cellulose. This is because methyl cellulose helps form a stable and uniform negative electrode structure, improving battery performance. It can also improve the dispersion stability of the negative electrode material, helping to increase the battery's energy density.

[0087] The iron source may include at least one of Fe(NO3)3·9H2O, FeCl3·6H2O, Fe2(SO4)3, and FeSO4·7H2O. In some specific embodiments, the iron source may be Fe(NO3)3·9H2O. - As an inert anion, it can decompose into gas and escape in the subsequent high-temperature preparation process, thereby reducing impurity residues and helping to improve the quality of the final negative electrode material.

[0088] The selenium source can include, for example, at least one of selenourea, selenium dioxide, hydrogen selenide, selenourea, sodium selenosulfate, and carbon diselenide. In some specific embodiments, the selenium source can be selenourea. This is because selenourea can release Se vapor at high temperatures (above approximately 500°C). The rate at which selenourea releases Se vapor matches the rate at which the iron source generates FeO, ensuring a more uniform grain size of the subsequently formed FeSe2, thereby improving the performance of the resulting negative electrode material.

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

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

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

[0092] Controlling the material-liquid ratio of the carbon source, iron source, selenium source, chelating agent and solvent within the above range is conducive to the full dissolution of the raw materials, thereby facilitating a more sufficient and complete reaction in the subsequent reaction, forming a higher quality composite gel, and thereby improving the performance of the final negative electrode material.

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

[0094] In step S2, a regulator is added to the mixed solution, the mixed solution is adjusted to alkaline, and then reacted and allowed to stand to obtain a composite gel; the composite gel is then frozen and dried to obtain a porous aerogel precursor.

[0095] The regulator can include at least one of ammonia, triethylamine, ethylenediamine, urea, ammonium carbonate, pyridine, and hexamethylenetetramine. The regulator in the embodiment of the present application can play a role in adjusting the pH of the solution, adjusting the mixed solution to alkalinity to promote Fe 3+ Hydrolysis generates FeO(OH) or Fe(OH)3 colloids, which form composite gels with carbon sources; on the other hand, the NH3 molecules released by the regulator can react with Fe 3+ Complexation, delaying Fe 3+ The precipitation rate is increased, which promotes more uniform cross-linking and avoids local agglomeration, thereby better inducing the formation of composite gel.

[0096] In some embodiments, the pH of the mixed solution after adjustment by the regulator can be 8.5-9.5, which is conducive to the formation of high-quality composite gel.

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

[0098] In step S2, the composite gel is frozen, and the water in the composite gel forms ice crystals to squeeze the Fe-Se complex, forming directional channels and promoting the uniform distribution of the Fe-Se complex, thereby avoiding particle agglomeration, and thus facilitating the subsequent formation of a metal selenide composite material with a core-shell structure; then, after drying, a structurally stable porous aerogel precursor is obtained. After the porous aerogel precursor is subsequently carbonized, the porous structure can be retained to form a structurally stable three-dimensional porous carbon skeleton, which is beneficial to increasing the specific surface area of ​​the negative electrode material and promoting the penetration of the electrolyte.

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

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

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

[0102] In the actual preparation process, the drying process can be carried out under vacuum conditions, so as to avoid oxidation or destruction of the cross-linked network structure in the composite gel during the drying process.

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

[0104] In the embodiment of the present application, a reducing gas is introduced to perform a first heat treatment, on the one hand, the porous aerogel precursor is partially carbonized to form an initial three-dimensional carbon network, and on the other hand, the Fe 3+ It is reduced to FeO, which reacts with the Se vapor released by the selenium source to form FeSe2 nanoparticles. Under high selenium vapor partial pressure (for example, above 0.05 MPa), selenium atoms are enriched on the FeSe2 surface, forming a relatively complete crystal structure.

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

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

[0107] In some embodiments, the holding time of the first heat treatment may be 1 hour to 3 hours, for example, 1 hour, 2 hours, 3 hours, or any value between any two of the above value ranges.

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

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

[0110] In step S4, the intermediate product is subjected to a second heat treatment under closed oxygen-deficient conditions, 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, and 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 negative electrode material.

[0111] The above-mentioned closed anoxic conditions can be specifically: pressure between 0.1MPa and 0.12MPa; oxygen partial pressure less than or equal to 10 -5 MPa. Under this closed oxygen-deficient condition, it is conducive to the deselenization reaction inside the FeSe2 particles, thereby forming a metal selenide composite material with a core-shell structure of good quality. During the second heat treatment process, the initial three-dimensional carbon network will be completely carbonized to form a three-dimensional porous carbon skeleton, which wraps the metal selenide composite material (also known as heterojunction particles). In the embodiment of the present application, the anion exchange strategy is used in the deselenization process of FeSe2 particles to not only generate the core Fe7Se8 and the shell FeSe2, but also form controllable Se vacancies at the interface, so that Se 2- / Se - It is easier to interact with the cationic sites (such as Fe 2+ , oxygen defects, etc.) to form a strong interaction, thereby further enhancing the bonding stability of the metal selenide composite material and the three-dimensional porous carbon skeleton.

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

[0113] In the actual preparation process, for example, the temperature can be first raised to 700°C~750°C at 2°C / min~5°C / min, 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 of the gas introduced in the above step is turned off, and the system is switched to a closed anoxic system. The internal pressure is generated spontaneously. In the high-temperature anoxic environment, the interior of the FeSe2 particles is partially deselenized to generate Fe7Se8 cores, and the surface retains the FeSe2 shell. Next, the temperature is further raised to 750°C~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 low (10 -5 MPa or less), FeSe2 undergoes further deselenization (7FeSe2→Fe7Se8+6Se). The generated Se vapor is confined within the pores of the three-dimensional porous carbon framework, forming a local dynamic equilibrium and promoting the nucleation and growth of Fe7Se8 within the FeSe2. As the reaction proceeds from the interior of the FeSe2 particle outward, the density of the Fe7Se8 formed internally is higher than that of FeSe2, causing the core region to shrink. However, the shell retains its original volume due to incomplete deselenization of the surface layer, forming a gap between the Fe7Se8 core and the FeSe2 shell, forming a metal selenide composite material with a core-shell structure. The internal pressure of the closed environment during this stage is 0.1MPa-0.12MPa, which maintains the Se vapor partial pressure at approximately 103Pa, higher than the equilibrium decomposition pressure of Fe7Se8 (approximately 102Pa), thereby inhibiting excessive deselenization of Fe7Se8. The Se vapor generated by the deselenization reaction will diffuse outward through the FeSe2 shell, but the Se vapor partial pressure in the closed system is close to dynamic equilibrium. Some Se vapor will escape from the defects in the FeSe2 shell, leaving mesoporous channels. At the same time, the reconstruction of the FeSe2 lattice at high temperature will also introduce pores, thereby making the shell in the metal selenide composite material have a porous structure.

[0114] In the embodiment of the present application, the second heat treatment is carried out in two temperature stages. First, in the 700℃~750℃ stage, the controllable initial deselenization of FeSe2 particles and the formation of core-shell prototypes can be achieved. At this temperature, FeSe2 is partially deselenized to generate Fe7Se8 cores, but the deselenization rate is relatively slow, which is conducive to the formation of a transition shell with appropriate porosity. The incomplete shell allows the initial diffusion of Se vapor and the accumulation of pressure in a closed environment. The core-shell gap formed can provide growth space for subsequent core-shell structures. Then, the temperature is raised to the 750℃~800℃ stage. The high temperature significantly accelerates the deselenization kinetics, which makes it easier to promote the saturation of Se vapor in a closed system and reach the critical Se vapor pressure (10 5The increased internal pressure, on the order of Pa, drives capillary condensation of Se in the pores, forming a local equilibrium. Temperature-sensitive surface diffusion promotes Se migration from the Fe7Se8 core to the inner shell. Simultaneously, high temperatures significantly accelerate Fe atomic migration (the bulk diffusion activation energy of Fe in FeSe2 is approximately 2.5 eV). Above 750°C, Fe atomic diffusion accelerates significantly, completing the core-shell structural reorganization and establishing dynamic equilibrium. This facilitates the formation of a core-shell structure with core-shell separation, effectively improving the quality of the resulting metal selenide composite material.

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

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

[0117] In some embodiments, the shell thickness of the prepared metal selenide composite material can be 5 nm to 8 nm. Controlling the shell thickness of the metal selenide composite material within this range, below the critical electron tunneling thickness (approximately 10 nm), allows electrons to be directly injected into the core via quantum tunneling, reduces interfacial charge transfer resistance, and facilitates the construction of a core-shell structure with greater structural stability.

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

[0119] In some embodiments, the gaps in the resulting metal selenide composite material can be sized between 1.2 nm and 5.5 nm. This not only provides a suitable buffer for the volume expansion of the core, forming a more structurally stable metal selenide composite material, but also facilitates the passage of a portion of the three-dimensional porous carbon skeleton through the porous structure to fill the gaps, forming a more stable physical interlocking structure 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 core of the metal selenide composite material may be understood as the average size of the gap between the outer shell and the core of the metal selenide composite material.

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

[0122] In the embodiment of the present application, the growth of the three-dimensional porous carbon skeleton is catalyzed by the third heat treatment, and the growth orientation of the three-dimensional porous carbon skeleton is limited by the porous structure of the shell of the metal selenide composite material to form an isotropic network, so that the three-dimensional porous carbon skeleton passes through the porous structure and fills the gap. While strengthening the three-dimensional porous carbon skeleton, the three-dimensional porous carbon skeleton can better bridge and fix the metal selenide composite material, thereby forming a physical interlocking structure between the metal selenide composite material and the three-dimensional porous carbon skeleton, which can significantly inhibit the volume expansion and structural pulverization of the metal selenide during the cycle, improve the structural stability of the metal selenide during the battery charge and discharge process, and greatly reduce the risk of structural collapse. Moreover, 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 caused by the volume change, thereby significantly improving the structural stability and cycle stability of the negative electrode material.

[0123] 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 may be 800° C. to 900° C., for example, 800° C., 820° C., 840° C., 860° C., 880° C., 900° C., or any value between any two of the above ranges.

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

[0126] In the actual preparation process, a mixture of carbon source gas (specifically, acetylene) and inert gas (specifically, argon) can be introduced at 800°C~900°C, wherein the volume fraction of the carbon source gas in the mixed gas can be, for example, 1%. 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 decomposition of the carbon source, thereby catalyzing the growth of a three-dimensional porous carbon skeleton.

[0127] An embodiment of the present application further provides a negative electrode sheet, comprising the negative electrode material described in any of the above embodiments or the negative electrode material prepared by the preparation method of the negative electrode material described in any of the above embodiments.

[0128] It should be understood that the beneficial effects of the negative electrode material described in any of the above embodiments or the negative electrode material prepared by the preparation method of the negative electrode material described in any 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, and the active material layer includes the negative electrode material described in any of the above embodiments or the negative electrode material prepared by the preparation method of the negative electrode material described in any of the above embodiments.

[0130] An embodiment of the present application further provides a secondary battery, comprising 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 embodiment are all applicable to this battery. Therefore, the secondary battery in the embodiment of the present application has high capacity and cycle performance.

[0132] In some embodiments, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode described in the above embodiments. During the battery's charge and discharge process, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0133] The technical solution of the present application is further described below with reference to a number of embodiments and comparative examples.

[0134] Example 1

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

[0136] S101: Dissolve 2 g of methylcellulose (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 (chelating agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0137] S102: 5% by mass of NH3·H2O (regulator) is added dropwise to the mixed solution obtained in step S101 until the pH reaches 8.5. The solution gradually forms a gel and is allowed to stand for 12 hours to form a Fe-Se-cellulose composite gel (composite gel). The mixture is then frozen at -50°C for 24 hours (freezing treatment) and vacuum dried to obtain a porous aerogel precursor.

[0138] S103: The porous aerogel precursor obtained in step S102 is subjected to a first heat treatment to obtain an intermediate product; specifically, the temperature is raised to 500°C at a rate of 2°C / min, and 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 maintained for 1 hour. During this period, the methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+It is reduced to FeO, which reacts with the Se vapor released by selenourea to form FeSe2 nanoparticles, resulting in an intermediate product in which FeSe2 nanoparticles are supported within an initial three-dimensional carbon network. Due to the high partial pressure of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the FeSe2 surface, forming a complete crystalline structure.

[0139] S104: Under closed, anoxic conditions, the intermediate product obtained in step S103 is subjected to a second heat treatment to obtain an initial negative electrode material. Specifically, the temperature is first raised to 700°C at a rate of 2°C / min, the system is switched to a closed system, the mixed gas flow is shut off, and the internal pressure is generated spontaneously. In the high-temperature, anoxic environment, FeSe2 is partially deselenized to form a Fe7Se8 core, while the FeSe2 shell is retained on the surface. Next, the temperature is raised to 750°C, and the internal oxygen partial pressure in the closed, anoxic environment decreases, causing a deselenization reaction on the FeSe2 surface: 7FeSe2 → Fe7Se8 + 6Se. The released Se vapor is confined to the pores of the three-dimensional porous carbon framework, forming a local dynamic equilibrium, promoting the nucleation and growth of Fe7Se8 within 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 framework (3DCF).

[0140] S105: 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 800°C for 30 minutes. The initial negative electrode material obtained in step S104 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 (which can be called H-Fe7Se8 / FeSe2@3DCF, wherein H represents hollow, Fe7Se8 represents core, FeSe2 represents shell, and 3DCF represents three-dimensional porous carbon skeleton).

[0141] Example 2

[0142] The method for preparing the negative electrode material in this embodiment includes the following steps:

[0143] S201: Dissolve 3 g of methylcellulose (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 (chelating agent), and stir magnetically for 2.5 h to form a homogeneous mixture;

[0144] S202: 5% by mass of NH3·H2O (regulator) is added dropwise to the mixed solution obtained in step S201 until the pH reaches 9. The solution gradually forms a gel and is allowed to stand for 13 hours to form a Fe-Se-cellulose composite gel (composite gel). The mixture is then 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 a rate of 3°C / min, and 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 maintained for 1.5 hours. During this period, the methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ It is reduced to FeO, which reacts with the Se vapor released by selenourea to form FeSe2 nanoparticles, resulting in an intermediate product in which FeSe2 nanoparticles are supported within an initial three-dimensional carbon network. Due to the high partial pressure of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the FeSe2 surface, forming a complete crystalline structure.

[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 generated spontaneously. In a high-temperature anoxic environment, FeSe2 is partially deselenized to generate Fe7Se8 cores, 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. 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 method for preparing the negative electrode material in this embodiment includes the following steps:

[0150] S301: Dissolve 2.8 g of methylcellulose (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 (chelating agent), and stir magnetically for 3 h to form a homogeneous mixture;

[0151] S302: 5% by mass of NH3·H2O (regulator) was added dropwise to the mixed solution obtained in step S301 until the pH reached 9. The solution gradually formed a gel and was allowed to stand for 14 hours to form a Fe-Se-cellulose composite gel (composite gel). The mixture was then frozen at -60°C for 30 hours (freezing treatment) and vacuum dried to obtain a porous aerogel precursor.

[0152] S303: The porous aerogel precursor obtained in step S302 is subjected to a first heat treatment to obtain an intermediate product; specifically, the temperature is raised to 550°C at a rate of 3.5°C / min, and 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 maintained for 1 hour. During this period, the methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ It is reduced to FeO, which reacts with the Se vapor released by selenourea to form FeSe2 nanoparticles, resulting in an intermediate product in which FeSe2 nanoparticles are supported within an initial three-dimensional carbon network. Due to the high partial pressure of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the FeSe2 surface, forming a complete crystalline structure.

[0153] S304: Under closed anoxic conditions, the intermediate product obtained in step S303 is subjected to a second heat treatment to obtain an initial negative electrode material. Specifically, first, the temperature is raised to 730°C at 3°C / min, the system is switched to a closed system, the mixed gas flow is closed, and the internal pressure is generated spontaneously. In the high-temperature anoxic environment, FeSe2 is partially deselenized to form a Fe7Se8 core, and the FeSe2 shell is retained on the surface. Next, the temperature is raised to 770°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. 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.

[0154] S305: 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 860°C for 30 minutes. The initial negative electrode material obtained in step S304 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.

[0155] Example 4

[0156] The method for preparing the negative electrode material in this embodiment includes the following steps:

[0157] S401: Dissolve 3.5 g of methylcellulose (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 (chelating agent), and stir magnetically for 3 h to form a homogeneous mixture;

[0158] S402: 5% by mass of NH3·H2O (regulator) is added dropwise to the mixed solution obtained in step S401 until the pH reaches 9. The solution gradually forms a gel and is allowed to stand for 12 hours to form a Fe-Se-cellulose composite gel (composite gel). The mixture is then frozen at -50°C for 32 hours (freezing treatment) and vacuum dried to obtain a porous aerogel precursor.

[0159] S403: The porous aerogel precursor obtained in step S402 is subjected to a first heat treatment to obtain an intermediate product; specifically, the temperature is raised to 580°C at a rate of 4°C / min, and 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 maintained for 1 hour. During this period, the methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ It is reduced to FeO, which reacts with the Se vapor released by selenourea to form FeSe2 nanoparticles, resulting in an intermediate product in which FeSe2 nanoparticles are supported within an initial three-dimensional carbon network. Due to the high partial pressure of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the FeSe2 surface, forming a complete crystalline structure.

[0160] S404: Under closed anoxic conditions, the intermediate product obtained in step S403 is subjected to a second heat treatment to obtain an initial negative electrode material; specifically, first, the temperature is raised to 740°C at 4.5°C / min, the system is switched to a closed system, the mixed gas flow is closed, and the internal pressure is generated spontaneously. In the high-temperature anoxic environment, FeSe2 is partially deselenized to form a Fe7Se8 core, and the FeSe2 shell is retained on the surface; next, the temperature is raised to 780°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. 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;

[0161] S405: 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 880°C for 30 minutes. The initial negative electrode material obtained in step S404 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.

[0162] Example 5

[0163] The method for preparing the negative electrode material in this embodiment includes the following steps:

[0164] S501: Dissolve 4 g of methylcellulose (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 (chelating agent), and stir magnetically for 3.5 h to form a homogeneous mixture;

[0165] S502: 5% by mass of NH3·H2O (regulator) is added dropwise to the mixed solution obtained in step S501 until the pH reaches 9.5. The solution gradually forms a gel and is allowed to stand for 16 hours to form a Fe-Se-cellulose composite gel (composite gel). The mixture is then frozen at -70°C for 36 hours (freezing treatment) and vacuum dried 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, the temperature is raised to 600°C at a rate of 5°C / min, and 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 maintained for 1 hour. During this period, the methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ It is reduced to FeO, which reacts with the Se vapor released by selenourea to form FeSe2 nanoparticles, resulting in an intermediate product in which FeSe2 nanoparticles are supported within an initial three-dimensional carbon network. Due to the high partial pressure of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the FeSe2 surface, forming a complete crystalline structure.

[0167] S504: Under closed anoxic conditions, the intermediate product obtained in step S503 is subjected to a second heat treatment to obtain an initial negative electrode material. Specifically, first, the temperature is raised to 750°C at 5°C / min, the system is switched to a closed system, the mixed gas flow is closed, and the internal pressure is generated spontaneously. In a high-temperature anoxic environment, FeSe2 is partially deselenized to generate Fe7Se8 cores, and the FeSe2 shell is retained on the surface. Next, the temperature is raised to 800°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. 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.

[0168] S505: 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 900°C for 50 minutes. The initial negative electrode material obtained in step S504 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.

[0169] Example 6

[0170] The preparation method of the negative electrode material in this embodiment is basically the same as that in Example 1, with the main differences being:

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

[0172] Comparative Example 1

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

[0174] S601: Dissolve 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 (chelating agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0175] S602: The mixed solution obtained in step S601 is subjected to a first heat treatment to obtain Fe7Se8 negative electrode material; specifically, first, the temperature is raised to 700°C at 2°C / min, and a mixed gas of Ar and H2 is introduced, wherein the volume ratio of Ar to H2 is 95:5, and the temperature is kept for 1 hour. During this period, Fe 3+ It is reduced to FeO and reacts with the Se vapor released by selenourea to form FeSe2 nanoparticles; next, it switches to a closed system, turns off the flow of the mixed gas, and uses the internal pressure to self-generate FeSe2 to deselenize Fe7Se8.

[0176] Comparative Example 2

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

[0178] S701: Dissolve 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 (chelating agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0179] S702: The mixed solution obtained in step S701 is subjected to a first heat treatment to obtain FeSe2 negative electrode material; specifically, the temperature is raised to 550°C at a rate of 2°C / min, a mixed gas of Ar and H2 is introduced, wherein the volume ratio of Ar to H2 is 95:5, and the temperature is kept for 1 hour. During this period, FeSe2 3+ It is reduced to FeO and reacts with the Se vapor released by selenourea to form FeSe2 nanoparticles. Due to the high partial pressure of selenium vapor (above 0.05 MPa), selenium 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 comprises the following steps:

[0182] S801: Dissolve 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 (chelating agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0183] S802: The mixed solution obtained in step S801 is subjected to a first heat treatment to obtain FeSe2; specifically, the temperature is raised to 500°C at a rate of 2°C / min, a mixed gas of Ar and H2 is introduced, wherein the volume ratio of Ar to H2 is 95:5, and the temperature is kept for 1 hour. During this period, FeSe2 3+ It is reduced to FeO and reacts with the Se vapor released by selenourea to form FeSe2 nanoparticles. Due to the high partial pressure of selenium vapor (above 0.05 MPa), selenium atoms are enriched on the surface of FeSe2, forming a complete crystal structure.

[0184] S803: The FeSe2 obtained in step S802 is subjected to a second heat treatment. Specifically, first, the temperature is raised to 700°C at a rate of 2°C / min, the system is switched to a closed system, the flow of the mixed gas is closed, and the internal pressure is used to generate the FeSe2 partially in a high-temperature oxygen-deficient environment to generate a Fe7Se8 core, while the FeSe2 shell is retained on the surface; next, the temperature is raised to 750°C, the internal oxygen partial pressure in the closed oxygen-deficient environment becomes low, and a deselenization reaction occurs on the surface of FeSe2: 7FeSe2→Fe7Se8+6Se, which promotes the nucleation and growth of Fe7Se8 inside the FeSe2, forming a negative electrode material with Fe7Se8 as the core and FeSe2 as the shell.

[0185] Comparative Example 4

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

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

[0188] S902: 5% by mass of NH3·H2O (regulator) is added dropwise to the mixed solution obtained in step S901 until the pH reaches 8.5. The solution gradually forms a gel and is allowed to stand for 12 hours. The solution is then frozen at -50°C for 24 hours and vacuum dried to obtain an aerogel precursor.

[0189] S903: 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 800°C for 30 minutes. The aerogel precursor obtained in step S902 is heat-treated to carbonize the aerogel precursor and catalyze the growth of a three-dimensional porous carbon skeleton to obtain a negative electrode material.

[0190] Comparative Example 5

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

[0192] S110: Dissolve 2 g of methylcellulose (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 (chelating agent), and stir magnetically for 2 h to form a homogeneous mixture;

[0193] S111: 5% by mass of NH3·H2O (regulator) is added dropwise to the mixed solution obtained in step S110 until the pH reaches 8.5, and the solution gradually forms a gel. The solution is allowed to stand for 12 hours to form a Fe-Se-cellulose composite gel (composite gel). The solution is then frozen at -50°C for 24 hours and then vacuum dried to obtain a porous aerogel precursor.

[0194] S112: The porous aerogel precursor obtained in step S111 is subjected to a first heat treatment to obtain an intermediate product; specifically, the temperature is raised to 500°C at a rate of 2°C / min and kept at this temperature for 1 hour, during which the methyl cellulose is partially carbonized to form an initial three-dimensional carbon network; Fe 3+ It is reduced to FeO, which reacts with Se vapor released by selenourea to form FeSe2 nanoparticles, obtaining an intermediate product in which FeSe2 nanoparticles are loaded in the initial three-dimensional carbon network;

[0195] S113: The intermediate product obtained in step S112 is subjected to a second heat treatment to obtain an initial negative electrode material. Specifically, the temperature is first raised to 700°C at a rate of 2°C / min while maintaining an open system. Next, the temperature is raised to 750°C while continuing to maintain an open system. During this period, the methyl cellulose is completely carbonized into a three-dimensional porous carbon skeleton.

[0196] S114: introducing Ar and maintaining the temperature at 800° C. for 30 min to perform a third heat treatment on the initial negative electrode material obtained in step S113 to obtain a negative electrode material.

[0197] The negative electrode material prepared in Example 1 was tested and analyzed. Figure 2 is the XRD pattern of the negative electrode material obtained in Example 1, Figure 2 It can be seen that the characteristic peaks in the XRD pattern of the negative electrode material prepared in Example 1 are highly consistent with the standard peak positions of the Fe7Se8 and FeSe2 patterns, and no obvious impurity peaks are detected, indicating that the prepared negative electrode material contains Fe7Se8 and FeSe2. Figure 3 This is a scanning electron microscope image of the negative electrode material obtained in Example 1. Figure 4 A transmission electron microscope image of the negative electrode material prepared in Example 1 is shown. Figure 3 It can be seen that the negative electrode material prepared in Example 1 has a typical core-shell structure, with a clear interface between the core and the shell, and a gap between the core and the shell. This shows that the metal selenide composite material with a core-shell structure was successfully synthesized in the negative electrode material prepared in Example 1. Figure 4 High-resolution transmission electron microscopy images of Figure 4 Clear lattice fringes can be observed, where the lattice spacing of 0.158nm corresponds to the (211) crystal plane of FeSe2 and the lattice spacing of 0.205nm corresponds to the (102) crystal plane of Fe7Se8. Figure 3 and Figure 4 It can be seen that the negative electrode material prepared in Example 1 successfully synthesized a metal selenide composite material with Fe7Se8 as the core and FeSe2 as the shell. Figure 5 This is another transmission electron microscope image of the negative electrode material prepared in Example 1. Figure 5 The high-resolution transmission electron microscope image in the figure mainly shows the three-dimensional porous carbon skeleton structure located in the gap between the core and the shell of the core-shell structure in the negative electrode material. The gap between the core and the shell is interconnected 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] Using a scanning electron microscope, the microscopic dimensions of the core-shell structures comprising Fe7Se8 as the core and FeSe2 as the shell in the negative electrode materials prepared in Examples 1 to 6 and Comparative Example 3 were measured. The average size of the gap between the core and the shell, the average shell thickness, and the average core particle size were determined. The measurement results are shown in Table 1.

[0199] Table 1

[0200]

[0201] As shown in Table 1, the gap between the outer shell and the inner core of the metal selenide composite material in the negative electrode materials prepared in Examples 1 to 6 ranges from 1.2 nm to 5.5 nm. This provides a suitable buffer for the volume expansion of the inner core, resulting in a more structurally stable metal selenide composite material. Furthermore, it allows a portion of the three-dimensional porous carbon skeleton to penetrate the porous structure and fill the gap, resulting in a more stable physical interlocking structure between the metal selenide composite material and the three-dimensional porous carbon skeleton, further enhancing the structural stability of the negative electrode material. The particle size of the inner core of the metal selenide composite material ranges from 6 nm to 10 nm, which helps improve the capacity of the negative electrode material and facilitates the construction of a core-shell structure with greater structural stability. The thickness of the outer shell of the metal selenide composite material ranges from 5 nm to 8 nm. This thickness is below the critical electron tunneling thickness (approximately 10 nm), allowing electrons to be directly injected into the inner core via quantum tunneling, reducing interfacial charge transfer resistance and facilitating the construction of a more structurally stable core-shell structure.

[0202] The negative electrode materials obtained in the above embodiments and comparative examples are made into batteries, and the electrochemical performance of the batteries is tested. The preparation of the battery includes the following steps: using the negative electrode materials obtained in the above embodiments and comparative examples as the working electrode, the metal lithium sheet as the reference electrode, the glass fiber as the diaphragm, and a solution of 1 mol / L LiPF6 dissolved in diethylene glycol dimethyl ether as the electrolyte; dripping 100 μL of electrolyte on the diaphragm, and assembling the half-cell in the order of the positive electrode shell, the working electrode, the diaphragm, the lithium sheet, the gasket, the shrapnel and the negative electrode shell. The assembled half-cell is clamped with insulating tweezers and placed on the packaging machine for sealing. Finally, the packaged battery is taken out of the glove box and left to stand for 12 hours to allow the electrolyte to fully infiltrate before performing relevant electrochemical tests. The specific tests are as follows:

[0203] 1) First cycle discharge capacity and first cycle coulombic efficiency test: The lithium ion button half-cell prepared above was placed in an environment of 26°C and charged at 0.1A. . g -1 The battery was charged at a constant current of 3.0 V at a current density of 1.5 volts. The total capacity during the charge cycle was recorded as the first-cycle charge capacity (C1). The first-cycle discharge cycle followed the charge process until the voltage dropped to 0.01 V. The total capacity during the discharge cycle was recorded as the first-cycle discharge capacity (C2). The first-cycle discharge specific capacity = C2 / active material (negative electrode material) mass, and the first-cycle coulombic efficiency = (C2 / C1) × 100%.

[0204] 2) Cycle life test: The lithium-ion button half-cell prepared above was placed in an environment of 26°C and . g -1 A cycle test was performed under a current density of 3.0 V, wherein the charge cut-off voltage was 3.0 V and the discharge cut-off voltage was 0.01 V; the cycle was repeated 4000 times, and the ratio of the discharge capacity at the end of the 4000 cycles to the initial discharge capacity was used as the capacity retention rate after 4000 cycles.

[0205] 3) Electrochemical impedance spectroscopy: Electrochemical impedance spectroscopy was performed using an electrochemical workstation with a test frequency of 0.01 Hz to 100 kHz. The charge transfer resistance was obtained based on the measured electrochemical impedance spectrum.

[0206] The test results of the above tests are shown in Table 2.

[0207] Table 2

[0208]

[0209] As can be seen from the data in Table 2, relative to Comparative Examples 1 to 5, the first-cycle discharge specific capacity, first-cycle coulomb efficiency, and 4000-cycle capacity retention rate of the battery comprising the negative electrode material obtained in Examples 1 to 6 are significantly improved. This shows that in the negative electrode material prepared in the present application, the metal selenide composite material having a core-shell structure is loaded in a three-dimensional porous carbon skeleton, and part of the three-dimensional porous carbon skeleton passes through the porous structure of the core-shell structure shell and fills the gap between the core and 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 cycle, improving the structural stability of the metal selenide during the battery charge and discharge process, 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 caused by the volume change, so that the structural stability and cycle stability of the negative electrode material can be significantly improved. In addition, there are gaps between the core and shell of the metal selenide composite material, which can form a built-in electric field, drive active ions (such as lithium ions or sodium ions) to enrich the inner core with high theoretical capacity, and provide a buffer space for the volume expansion of the inner core, thereby significantly improving the capacity and cycle performance of the battery.

[0210] Furthermore, from the test results of the charge transfer resistance in Table 2, it can be seen that in the negative electrode material prepared in 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 core-shell structure shell and fills the gap between the core and shell. This special structure allows the gap between the core and shell of the metal selenide composite material to be interconnected with the interconnected three-dimensional porous carbon skeleton, forming 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 to reduce the charge transfer resistance of the battery.

[0211] The negative electrode material prepared in Comparative Example 1 contains only Fe7Se8 material, the negative electrode material prepared in Comparative Example 2 contains only FeSe2 material, and the negative electrode material prepared in Comparative Example 3 contains a material with Fe7Se8 as the core and FeSe2 as the shell. It can be seen from the data in Table 2 that due to the unstable structure of the metal selenide during the battery cycle, it is prone to volume expansion and even structural collapse and structural pulverization. As a result, the first-cycle discharge specific capacity, first-cycle coulomb efficiency and 4000-cycle capacity retention rate of the batteries containing the negative electrode materials prepared in Comparative Examples 1 to 3 are all low, that is, the battery capacity is low and the cycle performance is poor.

[0212] The negative electrode material prepared in Comparative Example 4 contains only carbon material. From the data in Table 2, it can be seen that the first-cycle discharge specific capacity, first-cycle coulombic 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 cycle performance is very poor.

[0213] 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 Fe 3+ The reduction reaction results in incomplete reaction, and the FeSe2 particles formed are uneven in size and have poor crystallinity. Moreover, in the subsequent second heat treatment process, it is not switched to a closed oxygen-deficient environment. Due to the lack of internal pressure regulation, FeSe2 cannot undergo an effective deselenization reaction, that is, it cannot form Fe7Se8 nuclei; in addition, the selenium atoms on the surface of the FeSe2 particles are severely lost, which will also lead to an incomplete crystal structure, and ultimately it is impossible to form a core-shell structure with Fe7Se8 as the core and FeSe2 as the shell. In the third heat treatment process, no carbon source gas is introduced, resulting in incomplete carbonization and growth of the carbon skeleton, and the three-dimensional carbon skeleton formed is loose and has poor conductivity. The FeSe2 particles are not tightly combined with the three-dimensional carbon skeleton, the FeSe2 particles are easy to agglomerate, and the FeSe2 particles and the carbon support are easy to separate, and an effective conductive network cannot be formed, resulting in poor structural stability and cycle stability of the negative electrode material. Therefore, compared with Example 1, the capacity and cycle performance of the battery containing the negative electrode material prepared in Comparative Example 5 are significantly reduced.

[0214] The present invention successfully synthesized an innovative composite material through in-situ chemical deposition technology and anion exchange reaction strategy, 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 hollow Fe7Se8 / FeSe2 nanoparticles anchored inside is its core advantage over 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 carbon supports are mostly physically mixed or simply coated, the interfacial bonding force is weak, and it is easy to fall off. In the negative electrode material of the present invention, the in-situ chemical deposition and anion exchange strategy enable the metal selenide to form a chemical bond cascade with the three-dimensional porous carbon skeleton: the cationic sites on the surface of the three-dimensional porous carbon skeleton interact with the Se in the metal selenide through electrostatic interaction. 2- / Se -The anions combine to form a strong interface of "ionic bond bridge"; the porous shell of the hollow Fe7Se8 / FeSe2 nanoparticles and the three-dimensional network of the carbon skeleton interweave to form a physical interlocking structure. The combination of the two has both 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 the cycle. 2) Anion-cation synergistic activation interface: The three-dimensional porous carbon skeleton can provide local cationic active sites, which interact with the anions (Se 2- / Se - The H-Fe7Se8 / FeSe2@3DCF composite material exhibits excellent electrochemical performance, primarily due to the synergistic effects between its structural design and its components, opening up a new path for the development of high-performance secondary battery electrode materials.

[0215] It should be noted that the negative electrode material embodiments, negative electrode material preparation method embodiments, negative electrode sheet embodiments and secondary battery embodiments provided in this application belong to the same concept; the technical features in the technical solutions recorded in each embodiment can be arbitrarily combined without conflict.

[0216] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations. Various modifications and changes may be made to the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments merely express several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. A negative electrode material, characterized in that It comprises 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 6 nm to 10 nm; (2) The thickness of the shell is 5 nm to 8 nm; (3) The size of the gap is 1.2 nm to 5.5 nm; (4) The three-dimensional porous carbon skeleton includes oxygen-containing functional groups, and the oxygen-containing functional groups are bonded to at least a portion of the metal selenide composite material through chemical bonds.

3. A method for preparing a negative electrode material, characterized in that: The method comprises the following steps: S1: dissolving a carbon source, an iron source, and a selenium source in a solvent, adding a complexing agent, and mixing to obtain a mixed solution; S2: adding a regulator to the mixed solution, adjusting the mixed solution to alkaline, reacting, and allowing to stand to obtain a composite gel; then freezing the composite gel, and drying it to obtain a porous aerogel precursor; S3: Under the condition of introducing a reducing gas, performing a first heat treatment on the porous aerogel precursor to obtain an intermediate product, wherein the intermediate product includes an initial three-dimensional carbon network and FeSe2 particles supported in the initial three-dimensional carbon network; S4: Under closed oxygen-deficient conditions, 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, wherein 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, thereby obtaining an initial negative electrode material; S5: Under the condition of introducing 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 gaps, thereby obtaining the negative electrode material.

4. The method for preparing the negative electrode material according to claim 3, wherein: 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-liquid ratio of the carbon source, the iron source, the selenium source, the complexing agent and 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 mixing time is 2h~3.5h.

5. The method for preparing the negative electrode material according to claim 3, wherein: Step S2 satisfies at least one of the following characteristics: (1) The regulator includes at least one of ammonia, triethylamine, ethylenediamine, urea, ammonium carbonate, pyridine, and hexamethylenetetramine; (2) The pH of the mixed solution after adjustment by the regulator is 8.5-9.5; (3) The static treatment time is 12h~16h; (4) The freezing temperature is between -70°C and -50°C; (5) The freezing treatment time is 24h~36h; (6) Drying is carried out under vacuum conditions.

6. The method for preparing 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, and H2Se; (2) The temperature of the first heat treatment is 500°C to 600°C; (3) The holding time of the first heat treatment is 1h~3h; (4) The heating rate of the first heat treatment is 2°C / min~5°C / min.

7. The method for preparing the negative electrode material according to claim 3, wherein: Step S4 satisfies at least one of the following characteristics: (1) The closed anoxic conditions are: pressure between 0.1MPa and 0.12MPa; oxygen partial pressure less than or equal to 10 -5 MPa; (2) The second heat treatment includes: first, keeping the temperature at 700°C to 750°C for 1.5 hours to 2.5 hours, and then keeping the temperature at 750°C to 800°C for 0.5 hours to 1.5 hours; (3) The particle size of the core is 6 nm to 10 nm; (4) The thickness of the shell is 5 nm to 8 nm; (5) The size of the gap is 1.2 nm to 5.5 nm.

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

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

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

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