Secondary battery and preparation method thereof, energy storage system and electric equipment

Abstract

The invention relates to the field of energy storage, provides a secondary battery and a preparation method thereof, an energy storage system and electric equipment, and at least can improve the battery rate of the secondary battery. The preparation method comprises the steps that carbon-containing graphite is prepared, the carbon-containing graphite comprises a graphite matrix and carbon particles, through holes are formed in the graphite matrix, and the carbon particles are adsorbed to the surface of the graphite matrix or located in the through holes; mixing a nitrogen source material, a sulfur source material and carbon-containing graphite, and carrying out heat treatment, so that the graphite matrix is doped with nitrogen atoms and sulfur atoms; the negative electrode material comprises carbon-containing graphite, tin oxide particles and carbon nanotubes, the multiple carbon nanotubes are interwoven to form a three-dimensional network, and the tin oxide particles are located in the through holes, on the surface of the graphite matrix and in the three-dimensional network; providing a positive plate and a diaphragm; and sequentially stacking the negative plate, the diaphragm and the positive plate, winding or laminating to obtain a battery cell assembly, putting the battery cell assembly into a battery shell, injecting an electrolyte into the battery shell, and packaging to obtain the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a secondary battery and a preparation method thereof, an energy storage system and electrical equipment. Background Art

[0002] With the rapid development of the energy storage market, energy storage battery cells are undergoing rapid upgrades. Currently, battery cell products are trending towards larger capacity and higher energy density. The performance of a battery cell depends primarily on the performance of the positive electrode material and the negative electrode material. Graphite has traditionally been used as the negative electrode material, but traditional graphite negative electrode materials in lithium-ion batteries suffer from low diffusion rates and poor rate performance. Volume expansion leads to rupture of the SEI membrane, limiting cycle life.

[0003] On this basis, in addition to developing positive and negative electrode materials with higher specific capacity, in the design of battery cells, the purpose of improving the energy density of the battery cells is often achieved by increasing the electrode coating surface density and increasing the compaction density. However, this will significantly increase the electrochemical internal resistance of the electrode, especially for the negative electrode. The increase in the electrochemical internal resistance of the electrode will increase the risk of lithium plating in the battery cell during charging, resulting in battery cell capacity attenuation.

[0004] At present, how to reduce the electrochemical internal resistance function of the electrode by changing the performance of the electrode, that is, improving the capacity of the positive and negative electrode materials, remains to be solved. Summary of the Invention

[0005] The embodiments of the present application provide a secondary battery and a preparation method thereof, an energy storage system, and an electrical device, which are at least beneficial for increasing the capacity of the secondary battery and reducing the electrochemical internal resistance of the electrode.

[0006] According to some embodiments of the present application, on the one hand, an embodiment of the present application provides a method for preparing a secondary battery, comprising: preparing a negative electrode sheet, wherein the negative electrode sheet comprises a stacked negative electrode current collector and a negative electrode active layer, wherein the negative electrode active layer comprises a negative electrode material, and the method for preparing the negative electrode material comprises: preparing carbon-containing graphite, wherein the carbon-containing graphite comprises a graphite matrix and carbon particles, wherein the graphite matrix has through-holes, and the carbon particles are adsorbed on the surface of the graphite matrix or located in the through-holes; mixing a nitrogen source material, a sulfur source material and the carbon-containing graphite and heat-treating the mixture so that the graphite matrix is ​​doped with nitrogen atoms. and sulfur atoms; mixing the carbon-containing graphite, tin source material and carbon nanotube particles, and calcining them to form the negative electrode material, wherein the negative electrode material includes the carbon-containing graphite, tin oxide particles and carbon nanotubes, a plurality of the carbon nanotubes are interwoven to form a three-dimensional network, and the tin oxide particles are located in the through-holes, on the surface of the graphite matrix and in the three-dimensional network; providing a positive electrode sheet and a separator; stacking the negative electrode sheet, the separator and the positive electrode sheet in sequence, and obtaining a battery core assembly by winding or laminating, placing the battery core assembly in a battery shell, injecting an electrolyte into the battery shell, and encapsulating it to obtain a secondary battery.

[0007] In some embodiments, the process steps of mixing the carbon-containing graphite, tin source material and carbon nanotube particles and performing a calcination treatment include: dissolving the tin source material in alcohol and water to prepare a mixed solution, and mixing and stirring for 5 minutes to 20 minutes; adding the carbon-containing graphite doped with nitrogen atoms and sulfur atoms to the mixed solution, continuing to stir for 10 minutes to 40 minutes, and then centrifuging to separate the precipitate; performing a first calcination treatment on the precipitate to oxidize the tin source material into tin oxide particles; after mixing the calcined precipitate with carbon nanotube particles, performing a second calcination treatment in an atmosphere of catalytic gas.

[0008] In some embodiments, the molar ratio of the carbon-containing graphite, the tin source material, and the carbon nanotube particles is 1:(0.005-0.007):(0.01-0.2).

[0009] In some embodiments, the catalytic gas is a mixed gas of acetylene and hydrogen, and the flow ratio of the acetylene to the hydrogen is 1:(1.8-2.2).

[0010] In some embodiments, in the mixed solution, the mass ratio of alcohol to water is 1:(1.8-2.2); and the molar ratio of the tin source material to the alcohol is 1:(48-52).

[0011] In some embodiments, the size of the tin oxide particles is 30 nm to 50 nm; and the microscopic morphology of the tin oxide particles is rod-shaped.

[0012] In some embodiments, a method for preparing carbon-containing graphite includes: preparing a graphite matrix having through holes; dispersing a metal organic material in a solvent to form a first mixed solution; immersing the graphite matrix in the first mixed solution and performing a hydrothermal reaction to decompose the metal organic material into the carbon particles, followed by centrifugal separation and drying to obtain the carbon-containing graphite; the molar ratio of the graphite matrix to the metal organic material is 1:(0.018~0.022).

[0013] In some embodiments, the graphite matrix is ​​prepared by a template method; the preparation steps include: mixing graphite and colloidal microspheres in a mass ratio of (2 to 4): 1, adding them to ethanol and ultrasonically dispersing them for 2 hours to 3 hours, then drying them, and calcining them in an inert gas atmosphere to remove the colloidal microspheres.

[0014] In some embodiments, the process steps of mixing the nitrogen source material, the sulfur source material and the carbon-containing graphite and performing heat treatment include: dissolving the nitrogen source material and the sulfur source material in ethanol at a mass ratio of 1: (0.9 to 1.1), ultrasonically stirring for 20 minutes to 50 minutes to obtain a second mixed solution; immersing the carbon-containing graphite in the second mixed solution, ultrasonically stirring for 20 minutes to 40 minutes, then drying, and calcining under an inert gas atmosphere for 1 hour to 3 hours.

[0015] According to some embodiments of the present application, another aspect of the embodiments of the present application provides a secondary battery, comprising: a battery shell, wherein the battery shell has a cavity, and the cavity has an electrolyte; a battery cell assembly, wherein the battery cell assembly is located in the cavity and immersed in the electrolyte; the battery cell assembly includes a positive electrode sheet, a separator and a negative electrode sheet, wherein the negative electrode sheet includes a stacked negative electrode current collector and a negative electrode active layer; the negative electrode active layer includes a negative electrode material, and the negative electrode material includes carbon-containing graphite, tin oxide particles and carbon nanotubes, the carbon-containing graphite includes a graphite matrix doped with nitrogen atoms and sulfur atoms and carbon particles, the graphite matrix has through-holes, and the carbon particles are adsorbed on the surface of the graphite matrix or located in the through-holes; a plurality of the carbon nanotubes are interwoven to form a three-dimensional network; the tin oxide particles are located in the through-holes, on the surface of the graphite matrix and in the three-dimensional network.

[0016] In some embodiments, the carbon particles are metal organic framework materials, and the carbon particles have first mesopores therein; and the three-dimensional network has second mesopores therein.

[0017] In some embodiments, the size of the first mesopore is smaller than the size of the through-hole.

[0018] In some embodiments, the through-holes have a size ranging from 350 nm to 450 nm.

[0019] According to some embodiments of the present application, another aspect of the embodiments of the present application provides an energy storage system, including: a secondary battery prepared by the method for preparing a secondary battery as described in any one of the above embodiments or a secondary battery as described in the above embodiments.

[0020] According to some embodiments of the present application, on the other hand, embodiments of the present application provide an electrical device, including: a secondary battery prepared by the method for preparing a secondary battery as described in any of the above embodiments, a secondary battery as described in the above embodiments, or an energy storage system as described in the above embodiments.

[0021] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0022] The present invention provides a method for preparing a secondary battery, comprising a negative electrode material comprising carbon-containing graphite, tin oxide particles, and carbon nanotubes. Multiple carbon nanotubes are interwoven to form a three-dimensional network, with tin oxide particles located within through-holes, on the surface of a graphite matrix, and within the three-dimensional network. The carbon-containing graphite comprises a graphite matrix with through-holes and carbon particles, and the graphite matrix is ​​doped with nitrogen and sulfur atoms. The through-hole graphite matrix and multi-walled carbon nanotubes can form multi-level pores, accelerating ion transport. The carbon particles coated on the surface of the graphite matrix synergistically enhance conductivity with the multi-walled carbon nanotubes. The tin oxide particles and multi-walled carbon nanotubes form an integrated "buffer-conductor" interface, mitigating volume expansion while increasing specific capacity. The synergistic effect of nitrogen and sulfur diatomic doping enhances the conductivity and interfacial wettability of the electrode material, improving electronic conductivity and interfacial wettability, lowering the lithium ion insertion energy barrier, and inhibiting lithium dendrite growth. This increases the capacity of the secondary battery while reducing the internal resistance of the negative electrode sheet.

[0023] Among them, the buffer system includes: carbon nanotubes have high elasticity and flexibility, and the three-dimensional network structure they form can provide physical support for tin oxide particles. When volume expansion occurs, the carbon nanotubes can absorb stress through their own deformation, inhibiting the pulverization or agglomeration of tin oxide particles. Tin oxide particles can be evenly loaded on the surface of carbon nanotubes or embedded in the intertube spaces of carbon nanotubes. The confinement effect of carbon nanotubes prevents excessive migration of tin oxide particles during expansion and maintains the integrity of the electrode structure. The interface between carbon nanotubes and tin oxide is adsorbed and bonded through chemical bonds or physical bonds, which enhances the stability of the interface and avoids interface peeling caused by volume changes.

[0024] The conductive system includes: The high conductivity of carbon nanotubes creates a three-dimensional network structure within the composite material, improving electron transport efficiency and compensating for the poor conductivity of tin oxide particles. The graphite matrix, carbon particles, and carbon nanotube conductive network shorten the ion transport path and enhance reaction kinetics. When microcracks develop in the tin oxide during cycling, the carbon nanotubes maintain contact with the conductive substrate through wrapping or coating, preventing deactivation of the active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] One or more embodiments are exemplified by the figures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 A flow chart of a method for preparing a secondary battery provided in one embodiment of the present application;

[0027] Figure 2 A schematic structural diagram of a graphite matrix formed in a method for preparing a secondary battery provided in one embodiment of the present application;

[0028] Figure 3 A schematic structural diagram of forming carbon-containing graphite in a method for preparing a secondary battery provided in one embodiment of the present application;

[0029] Figure 4 A partially enlarged view of forming a negative electrode material in a method for preparing a secondary battery provided in one embodiment of the present application;

[0030] Figure 5 A schematic structural diagram of a cell assembly formed in a method for preparing a secondary battery provided in one embodiment of the present application.

[0031] Description of reference numerals:

[0032] 100. Graphite matrix; 101. Through-hole; 102. Carbon particles; 105. Carbon nanotubes; 106. Tin oxide particles; 110. Nitrogen-sulfur co-doped graphite matrix; 120. Carbon coating; 1. Positive electrode; 2. Negative electrode; 3. Diaphragm. DETAILED DESCRIPTION

[0033] As can be seen from the background art, the capacity and electrochemical internal resistance of current secondary batteries are poor.

[0034] Research has found that SnO2, as a high-capacity material, can increase the capacity of secondary batteries. However, during the charge and discharge process, the volume of the tin oxide particles expands, and this large expansion can easily lead to structural pulverization, which in turn leads to rapid capacity decay. Therefore, its stability must be improved by combining it with carbon.

[0035] On this basis, the introduction of multi-walled carbon nanotubes or porous carbon coatings can improve conductivity and structural stability. However, the conductivity and structural stability of carbon-coated or doped modified graphite are still insufficient. Conventional composite materials (such as SnO2 / graphite) have poor interfacial bonding and are prone to peeling and failure during cycling. Therefore, it is necessary to improve the conductivity of graphite and the bonding between the SnO2 / graphite interface to promote the further development of lithium-ion batteries.

[0036] The embodiments of the present application provide a method for preparing a secondary battery, wherein a graphite matrix with through-holes and multi-walled carbon nanotubes are provided to form multi-level pores, thereby accelerating ion transport. Carbon particles coated on the surface of the graphite matrix synergistically enhance the conductivity with the multi-walled carbon nanotubes. Tin oxide particles and multi-walled carbon nanotubes are combined to form an integrated "buffer-conductor" interface to alleviate volume expansion while increasing specific capacity. Nitrogen and sulfur diatomic doping creates a synergistic effect, improving the bonding between the SnO2 / graphite interface while increasing conductivity, thereby increasing the capacity of the secondary battery while reducing the internal resistance of the negative electrode.

[0037] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0038] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0039] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0040] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0041] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0042] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0043] In the accompanying drawings corresponding to the embodiments of the present application, the thickness and area of ​​the layers are exaggerated for better understanding and ease of description. When describing a component (such as a layer, film, region or substrate) on another component or on the surface of another component, the component can be "directly" located on the surface of the other component, or there can be a third component between the two components. On the contrary, when describing a component on the surface of another component or when another component is formed or provided on the surface of a component, it means that there is no third component between the two components. In addition, when describing a component as "approximately" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a partial edge of the entire surface.

[0044] In the description of the embodiments of the present application, when a component "includes" another component, unless otherwise specified, other components are not excluded, and other components may be further included. In addition, when a component such as a layer, film, region, or plate is referred to as being "on / located on" another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therebetween. In addition, when a component such as a layer, film, region, or plate is "directly located on" another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it means that no other components are located therebetween.

[0045] The terms used herein in the description of the various embodiments are intended only to describe the specific embodiments and are not intended to be limiting. As used in the description of the various embodiments and the appended claims, "part" is intended to include the plural form unless the context clearly indicates otherwise. A component includes a layer, film, region, or plate.

[0046] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0047] According to some embodiments of the present application, on the one hand, the embodiments of the present application provide a method for preparing a secondary battery, which is used to prepare a secondary battery, can improve the capacity of the secondary battery and reduce the electrochemical internal resistance of the electrode.

[0048] Figure 1 A flow chart of a method for preparing a secondary battery provided in one embodiment of the present application.

[0049] refer to Figure 1 , the preparation method includes: preparing a negative electrode sheet, the negative electrode sheet includes a stacked negative electrode current collector and a negative electrode active layer, the negative electrode active layer includes a negative electrode material. The preparation method of the negative electrode material includes: preparing carbon-containing graphite, the carbon-containing graphite includes a graphite matrix and carbon particles, the graphite matrix has through-holes, and the carbon particles are adsorbed on the surface of the graphite matrix or located in the through-holes. The preparation method of the negative electrode material includes: mixing a nitrogen source material, a sulfur source material and carbon-containing graphite and heat-treating the graphite matrix so that the graphite matrix is ​​doped with nitrogen atoms and sulfur atoms. The preparation method of the negative electrode material includes: mixing carbon-containing graphite, a tin source material and carbon nanotube particles and calcining them to form a negative electrode material, the negative electrode material includes carbon-containing graphite, tin oxide particles and carbon nanotubes, a plurality of carbon nanotubes are interwoven to form a three-dimensional network, and the tin oxide particles are located in the through-holes, on the surface of the graphite matrix and in the three-dimensional network.

[0050] The preparation method includes: providing a positive electrode sheet and a separator; stacking the negative electrode sheet, separator and positive electrode sheet in sequence, obtaining a battery cell assembly by winding or laminating, placing the battery cell assembly into a battery shell, injecting electrolyte into the battery shell, and encapsulating to obtain a secondary battery.

[0051] The present invention provides a method for preparing a secondary battery by preparing a negative electrode material comprising carbon-containing graphite, tin oxide particles, and carbon nanotubes. The carbon nanotubes are interwoven to form a three-dimensional network, with the tin oxide particles located within through-holes, on the surface of the graphite matrix, and within the three-dimensional network. The carbon-containing graphite comprises a graphite matrix with through-holes and carbon particles, and the graphite matrix is ​​doped with nitrogen and sulfur atoms. The through-hole graphite matrix and multi-walled carbon nanotubes form multi-level pores, accelerating ion transport. The carbon particles coated on the surface of the graphite matrix synergistically enhance conductivity with the multi-walled carbon nanotubes. The tin oxide particles and multi-walled carbon nanotubes form an integrated "buffer-conductor" interface, mitigating volume expansion while increasing specific capacity. The nitrogen and sulfur diatomic doping creates a synergistic effect, enhancing the conductivity and interfacial wettability of the electrode material. This can improve electronic conductivity and interfacial wettability, reduce the lithium ion insertion barrier, inhibit lithium dendrite growth, and increase the capacity of the secondary battery while reducing the internal resistance of the negative electrode sheet.

[0052] Among them, the buffer system includes: carbon nanotubes have high elasticity and flexibility, and the three-dimensional network structure they form can provide physical support for tin oxide particles. When volume expansion occurs, the carbon nanotubes can absorb stress through their own deformation, inhibiting the pulverization or agglomeration of tin oxide particles. Tin oxide particles can be evenly loaded on the surface of carbon nanotubes or embedded in the intertube spaces of carbon nanotubes. The confinement effect of carbon nanotubes prevents excessive migration of tin oxide particles during expansion and maintains the integrity of the electrode structure. The interface between carbon nanotubes and tin oxide is adsorbed and bonded through chemical bonds or physical bonds, which enhances the stability of the interface and avoids interface peeling caused by volume changes.

[0053] The conductive system includes: The high conductivity of carbon nanotubes creates a three-dimensional network structure within the composite material, improving electron transport efficiency and compensating for the poor conductivity of tin oxide particles. The graphite matrix, carbon particles, and carbon nanotube conductive network shorten the ion transport path and enhance reaction kinetics. When microcracks develop in the tin oxide during cycling, the carbon nanotubes maintain contact with the conductive substrate through wrapping or coating, preventing deactivation of the active material.

[0054] The method for preparing the secondary battery provided in the above embodiment will be described in detail below with reference to the accompanying drawings.

[0055] Figure 2 A schematic structural diagram of a graphite matrix formed in a method for preparing a secondary battery provided in one embodiment of the present application.

[0056] refer to Figure 2 The method for preparing the negative electrode material includes: preparing a graphite substrate 100, wherein the graphite substrate 100 has a through hole 101.

[0057] In some embodiments, a template method is used to prepare the graphite substrate 100. Using a template as a carrier to prepare the graphite substrate 100 allows for precise control of the size, shape, structure, and properties of the graphite substrate 100; integrates the synthesis and assembly steps within the graphite substrate 100, and addresses the dispersion stability issues of the graphite substrate 100. The synthesis process is relatively simple, and many methods are suitable for mass production.

[0058] The steps of preparing the graphite substrate 100 using the template method include: mixing graphite and colloidal microspheres in a mass ratio of (2-4):1, adding them to ethanol for ultrasonic dispersion for 2-3 hours, and then drying them; and calcining them in an inert gas atmosphere to remove the colloidal microspheres. The remaining pores of the colloidal microspheres are the through-holes 101. The inert gas is Ar / H2.

[0059] The mechanism of preparing the graphite matrix 100 by the template method is as follows: (1) colloidal microspheres self-assemble to form a template with an opal-like structure, for example, a three-dimensional polyhedron; (2) the precursor of the substance to be synthesized, i.e., graphite particles, is filled in the gaps of the template and the graphite particles are solidified; (3) the template is removed to obtain the graphite matrix 100. The through-holes 101 in the graphite matrix 100 are the narrow openings left by the removal of the colloidal microspheres.

[0060] In some embodiments, the colloidal microspheres can be silicon dioxide (SiO 2 ), polystyrene (PS), or polymethyl methacrylate (PMMA).

[0061] In some embodiments, the colloidal microspheres are removed by calcination in an Ar / H2 atmosphere (400°C to 500°C, 2h).

[0062] Figure 3 A schematic structural diagram of forming carbon-containing graphite in a method for preparing a secondary battery provided in one embodiment of the present application.

[0063] refer to Figure 3 , the preparation method of the negative electrode material includes: preparing carbon-containing graphite.

[0064] In some embodiments, a method for preparing carbon-containing graphite includes: preparing a graphite matrix 100, wherein the graphite matrix 100 has through holes 101; dispersing a metal organic material in a solvent to form a first mixed solution; immersing the graphite matrix 100 in the first mixed solution and performing a hydrothermal reaction to decompose the metal organic material into carbon particles 102, followed by centrifugal separation and drying to obtain carbon-containing graphite; wherein the metal organic material decomposes into carbon particles 102 in the hydrothermal reaction; and the molar ratio of the graphite matrix 100 to the metal organic material is 1:(0.018~0.022).

[0065] In some embodiments, the metal-organic material may be a metal-organic framework (MOF), and the MOF material may be isoreticular MOFs (IRMOFs), zeolite-imidazolate frameworks (ZIFs), materials of the Institute Lavoisier (MILs), and pocket-channel frameworks (PCNs). IRMOFs may be MOF-5, ZIFs may be ZIF-6, ZIF-7, or ZIF-8, and MILs may be MIL-100 or MIL-101.

[0066] Taking ZIF-8 as an example of a metal organic material, in some embodiments, the preparation method includes: preparing a precursor solution of ZIF-8 precursor: dissolving zinc nitrate and 2-methylimidazole in methanol at a molar ratio of 1:4 and stirring for 30 minutes. The resulting graphite substrate 100 is immersed in the precursor solution for hydrothermal reaction, centrifuged, and then washed and dried. Under argon protection, the temperature is increased at 5°C / min to 700°C to 900°C, maintained at this temperature for 2 hours, and dried to produce porous carbon-coated graphite (ZIF-8-C@G), i.e., carbon-containing graphite.

[0067] The mechanism of forming carbon-containing graphite is as follows: when the temperature reaches 600℃, ZIF-8 begins to decompose and carbonize, and the Zn 2+ At high temperatures, it is reduced to metallic Zn. Metallic Zn has a low boiling point (907°C) and readily volatilizes into vapor and escapes from the carbon framework at typical carbonization temperatures. During this volatilization process, some Zn may react with residual carbon or nitrogen to form intermediates such as ZnO or Zn3N2, leading to complete Zn volatilization. ZIF-8 undergoes cracking, devolatilization, and aromatization at high temperatures. As the temperature increases, the carbon-containing fragments gradually reorganize and condense, forming a disordered, defect-rich, nitrogen-doped carbon framework with high specific surface area and porosity. This is because the imidazole ligands contain nitrogen, and after carbonization, some nitrogen atoms are retained and doped into the carbon matrix. With further increases in temperature, ZIF-8 carbonizes into porous carbon with a graphitic phase structure. Higher calcination temperatures lead to more pronounced particle agglomeration, with nanoparticles coalescing to form distinct aggregates, namely carbon particles. Carbonized samples exhibit higher specific surface areas and a greater proportion of mesopores and macropores.

[0068] Among them, pores with a diameter less than 2nm are called micropores; pores with a diameter greater than 50nm are called macropores; and pores with a diameter between 2nm and 50nm are called mesopores (or mesopores). The first mesopore and the second mesopore mentioned below refer to pores with a diameter between 2nm and 50nm.

[0069] The method for preparing the negative electrode material includes: preparing a nitrogen-sulfur co-doped graphite substrate 110 .

[0070] In some embodiments, the process steps of mixing a nitrogen source material, a sulfur source material, and carbon-containing graphite and heat-treating the mixture include: dissolving the nitrogen source material and the sulfur source material in ethanol at a mass ratio of 1: (0.9 to 1.1), ultrasonically stirring for 20 to 50 minutes to obtain a second mixed solution; immersing the carbon-containing graphite in the second mixed solution, ultrasonically stirring for 20 to 40 minutes, drying, and calcining under an inert gas atmosphere for 1 to 3 hours.

[0071] The mass ratio of the nitrogen source material, the sulfur source material and the carbon-containing graphite is 1:(0.9-1.1):(8-12).

[0072] Nitrogen-sulfur co-doped graphite matrix 110 refers to a functional material in which nitrogen atoms and sulfur atoms are introduced into the graphite lattice to replace some carbon atoms or form a specific functionalized structure, thereby regulating its electronic, optical and chemical properties. The doped N and S atoms act as electron-attracting atoms, attracting nearby C atoms and polarizing oxygen functional groups, and are more active in anchoring sulfur and polysulfides. At the same time, the highly developed defects and edges and the porous structure derived from the chemical activation of graphene not only achieve a high sulfur loading in a well-dispersed amorphous state, but also act as a polysulfide reservoir to alleviate the shuttle effect. The doping atoms are nitrogen atoms and sulfur atoms.

[0073] The nitrogen species in nitrogen-doped carbon materials are mainly divided into four types, namely graphitic nitrogen (graphitic N), pyridinic nitrogen (pyridinic N), pyrrolic nitrogen (pyrrolic N) and pyridinic nitrogen oxide. For example, the nitrogen-doped graphite matrix 100 provided in the embodiment of the present application is graphitic nitrogen that replaces the carbon atoms of the graphite matrix to form sp 2 Hybrid structure, that is, the nitrogen species is graphitic nitrogen.

[0074] In some embodiments, the nitrogen source material can be one or more of a nitrogen-rich polymer, a biomass derivative, a metal organic framework, a small molecule nitrogen-containing compound, a nitrogen-containing inorganic salt, or a nitrogen-containing ionic liquid. The nitrogen-rich polymer can be selected from one or more of polyacrylonitrile (PAN), polypyrrole (PPy), polyaniline (PANI), polyimide (PI), or melamine-formaldehyde resin. The biomass derivative can be selected from one or more of chitosan / chitin, protein (such as gelatin, silk fibroin), or algae / bacterial cellulose. The metal organic framework can be selected from one or more of ZIF-8, ZIF-67 (cobalt-based), or UiO-66-NH2 (zirconium-based, amino-containing). The small molecule nitrogen-containing compound can be selected from one or more of urea (CO(NH2)2), melamine (C3H6N6), dicyandiamide (C2H4N4), or ammonia. The nitrogen-containing inorganic salt can be selected from ammonium chloride or ammonium nitrate. The nitrogen-containing ionic liquid may be 1-ethyl-3-methylimidazolium dicyanamide salt.

[0075] In some embodiments, the sulfur source material can be one or more of a sulfur-rich polymer, a biomass raw material, an inorganic sulfide, or an organic small molecule sulfur source. The sulfur-rich polymer can be selected from one or more of polythiophene, polybenzothiophene, or sulfide polyacrylonitrile. The biomass raw material can be selected from one or more of garlic / onion extract or wool / keratin. The inorganic sulfide can be selected from one or more of sulfur powder, sulfuric acid, or potassium sulfide. The organic small molecule sulfur source can be selected from thiourea, 2-thiophenecarboxylic acid, carbon disulfide, or 4,4'-dimethyldiphenyl disulfide.

[0076] In some embodiments, the nitrogen source material can be composed of polyaniline, and the sulfur source material can be composed of 4,4'-dimethyldiphenyl disulfide. A specific example is: PANI (polyaniline) and DBDS (4,4'-dimethyldiphenyl disulfide) are dissolved in an ethanol solution at a mass ratio of 1:1 and ultrasonically stirred for 30 minutes. The mixture is then dried under vacuum at 60°C for 12 hours with a carbon-coated graphite substrate. A secondary carbonization step is then performed in an Ar atmosphere (500°C to 600°C for 1 to 3 hours) to obtain a nitrogen-sulfur co-doped graphite substrate 110.

[0077] In some embodiments, not only the carbon atoms in the graphite matrix are substituted by nitrogen atoms or sulfur atoms, but also part of the carbon atoms in the carbon particles may be substituted by nitrogen atoms or sulfur atoms.

[0078] Figure 4 A partially enlarged view of forming a negative electrode material in a method for preparing a secondary battery provided in one embodiment of the present application.

[0079] It should be noted that the microscopic size of the graphite matrix and the through-holes is relatively large, and the subsequently formed tin oxide particles and carbon nanotubes are all microscopic morphologies, that is, in the same field of view, multiple tin oxide particles and carbon nanotubes can be seen, but only a small part of the graphite matrix and a small part of the through-holes can be seen.

[0080] refer to Figure 4 , the preparation method of the negative electrode material includes: preparing the negative electrode material.

[0081] In some embodiments, the process steps of mixing carbon-containing graphite, tin source material and carbon nanotube (CNT) particles and performing a calcination treatment include: dissolving the tin source material in alcohol and water to prepare a mixed solution, and stirring the mixture for 5 minutes to 20 minutes; adding the nitrogen-sulfur co-doped graphite matrix 110 to the mixed solution, continuing to stir for 10 minutes to 40 minutes, and then centrifuging to separate the precipitate; performing a first calcination treatment on the precipitate to oxidize the tin source material into tin oxide particles 106; after mixing the calcined precipitate with carbon nanotube particles, performing a second calcination treatment in an atmosphere of catalytic gas to load the carbon nanotubes 105 on the carbon-containing graphite.

[0082] In some embodiments, the carbon nanotube particles may be single-walled carbon nanotube (SWCNTs) particles or multi-walled carbon nanotube (MWCNTs) particles.

[0083] In some embodiments, the molar ratio of the carbon-containing graphite, the tin source material, and the carbon nanotube particles is 1:(0.005-0.007):(0.01-0.2).

[0084] In some embodiments, the catalytic gas is a mixture of acetylene and hydrogen, and the flow ratio of acetylene to hydrogen is 1:(1.8-2.2).

[0085] In some embodiments, in the mixed solution, the mass ratio of alcohol to water is 1:(1.8-2.2); and the molar ratio of the tin source material to the alcohol is 1:(48-52).

[0086] In some embodiments, the size of the tin oxide particles 106 is 30 nm to 50 nm; the microscopic morphology of the tin oxide particles 106 is rod-shaped.

[0087] It should be noted that micromorphology in chemistry refers to the appearance and structural characteristics of a substance at the microscopic scale. Micromorphology in chemistry can be studied and described using various experimental techniques and theoretical calculations, such as optical microscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and X-ray irradiation.

[0088] In some embodiments, the carbon particles are further carbonized and coated to form a carbon coating layer 120. The carbon coating layer 120 is located on the nitrogen-sulfur co-doped graphite substrate 110 and within the through-holes 101, and the SnO2 nanoparticles are loaded on the carbon coating layer 120. The carbon coating layer 120 has micropores and mesopores.

[0089] Specifically, SnCl2·2H2O was dissolved in a mixture of water and ethanol (2:1), mixed with the carbonaceous graphite doped with nitrogen and sulfur atoms prepared above, and ultrasonically stirred for 30 minutes. The mixture was dried in a vacuum oven at 60°C and calcined in air (300°C for 2 hours) to obtain a micron-sized rod-shaped SnO2 material. The SnO2-loaded sample and MWNTs were placed in a tube furnace, and an acetylene / hydrogen mixture (650°C to 750°C, C2H2:H2=1:2) was introduced into the surface of the mixture to catalytically grow carbon nanotubes on the SnO2 surface, forming a G@SnO2@MWNTs composite structure. The G@SnO2@MWNTs composite structure was used as the negative electrode material.

[0090] The microscopic morphology of G@SnO2@MWNTs is characterized by a graphite matrix with a stacked, layered structure, intersected by vertical channels. These channels are covered with ZIF-8-derived carbon layers, which are then surface-loaded with SnO2 nanoparticles and CNTs. The carbon coating is a carbon material with a complex interweaving of micropores and mesopores. The SnO2 nanoparticles are entangled or encapsulated by the CNTs, partially embedded in the interstices between the carbon layers of the graphite matrix.

[0091] Figure 5 A schematic structural diagram of a cell assembly formed in a method for preparing a secondary battery provided in one embodiment of the present application.

[0092] refer to Figure 5 The negative electrode material, adhesive, conductive agent and the remaining water provided in the above embodiment are stirred to form a negative electrode coating slurry.

[0093] In some embodiments, the conductive agent may be selected from at least one or more of carbon nanotubes (CNTs) and conductive carbon black (SPs).

[0094] In some embodiments, the binder may be selected from at least one or more of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA).

[0095] The negative electrode material: conductive agent (such as SP): binder (such as SBR and CMC) is stirred and coated on the negative electrode current collector with a mass ratio of (7.6-8.4): (0.8-1.2): (0.8-1.2), and dried at 80° C. for 24 hours to obtain a negative electrode sheet 2.

[0096] After forming the negative electrode sheet, the method further includes: die-cutting a portion of the negative electrode current collector according to preset parameters so that the end of the negative electrode current collector forms a negative electrode tab; and cutting the negative electrode current collector to form multiple identical negative electrode sheets.

[0097] The positive electrode sheet 1 includes a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode current collector can be an aluminum foil.

[0098] The diaphragm 3 can be located between the positive electrode and the negative electrode to prevent short circuit problems caused by physical contact between the positive electrode and the negative electrode, while allowing ions to be conducted through the electrolyte and hindering electron transmission, so that ions and electrons form a circuit during the charge and discharge process of the battery.

[0099] The separator 3 may be any one of a microporous membrane, a modified microporous membrane, a non-woven fabric separator, and a composite separator. The separator may be coated with polyvinylidene fluoride (PVDF) material to provide the separator with excellent adhesion and flexibility.

[0100] refer to Figure 5 The preparation method includes: winding or laminating the positive electrode sheet 1, the negative electrode sheet 2 and the separator 3.

[0101] In some embodiments, the winding process involves passing the separator, positive electrode sheet, and negative electrode sheet through a winding machine to form a single core. The order is to wrap the positive electrode sheet with the negative electrode sheet, and then separate the positive and negative electrodes with the separator. The stacking process involves stacking the separator, positive electrode sheet, and negative electrode sheet in sequence, and then rolling and cutting them into a single battery cell.

[0102] The preparation method also includes: welding the tabs to the adapter, connecting the other end of the adapter to the terminal post; and engaging the top cover with the battery case. The adapter is located in the cavity, and the terminal post passes through the top cover.

[0103] Among them, the adapter plate includes at least a first adapter plate and a second adapter plate, the pole includes a positive pole pole and a negative pole pole, the first adapter plate is electrically connected to the positive pole tab and the positive pole pole of the positive pole plate respectively, and the second adapter plate is electrically connected to the negative pole tab and the negative pole pole of the negative pole plate respectively.

[0104] The present invention provides a method for preparing a secondary battery by preparing a negative electrode material comprising carbon-containing graphite, tin oxide particles 106, and carbon nanotubes. Multiple carbon nanotubes are interwoven to form a three-dimensional network, with the tin oxide particles 106 located within through-holes 101, on the surface of the graphite matrix, and within the three-dimensional network. The carbon-containing graphite comprises a graphite matrix with through-holes and carbon particles, and the graphite matrix is ​​doped with nitrogen and sulfur atoms. The through-hole graphite matrix and multi-walled carbon nanotubes form multi-level pores, accelerating ion transport. The carbon particles coated on the graphite matrix synergistically enhance conductivity with the multi-walled carbon nanotubes. The tin oxide particles and multi-walled carbon nanotubes form an integrated "buffer-conductor" interface, mitigating volume expansion and increasing specific capacity. The nitrogen and sulfur diatomic doping creates a synergistic effect, enhancing the conductivity and interfacial wettability of the electrode material. This can improve electronic conductivity and interfacial wettability, lower the lithium ion insertion barrier, inhibit lithium dendrite growth, and increase the capacity of the secondary battery while reducing the internal resistance of the negative electrode sheet.

[0105] Among them, the buffer system includes: carbon nanotubes have high elasticity and flexibility, and the three-dimensional network structure they form can provide physical support for tin oxide particles. When volume expansion occurs, the carbon nanotubes can absorb stress through their own deformation, inhibiting the pulverization or agglomeration of tin oxide particles. Tin oxide particles can be evenly loaded on the surface of carbon nanotubes or embedded in the intertube spaces of carbon nanotubes. The confinement effect of carbon nanotubes prevents excessive migration of tin oxide particles during expansion and maintains the integrity of the electrode structure. The interface between carbon nanotubes and tin oxide is adsorbed and bonded through chemical bonds or physical bonds, which enhances the stability of the interface and avoids interface peeling caused by volume changes.

[0106] The conductive system includes: The highly conductive carbon nanotubes 105 form a three-dimensional network within the composite material, improving electron transport efficiency and compensating for the poor conductivity of the tin oxide particles. The graphite matrix, carbon particles, and carbon nanotube conductive network shorten the ion transport path and enhance reaction kinetics. If microcracks develop in the tin oxide during cycling, the carbon nanotubes maintain contact with the conductive substrate through wrapping or coating, preventing deactivation of the active material.

[0107] According to some embodiments of the present application, on the other hand, embodiments of the present application provide a secondary battery, which is prepared using the secondary battery preparation method provided by the above embodiments, and has the same or corresponding technical features as the above embodiments. Please refer to the above embodiments and will not go into details here.

[0108] The secondary battery includes: a battery shell having a cavity therein, and an electrolyte therein; a battery cell assembly, the battery cell assembly being located in the cavity and immersed in the electrolyte; the battery cell assembly including a wound positive electrode sheet, a separator and a negative electrode sheet, wherein the negative electrode sheet comprises a stacked negative electrode current collector and a negative electrode active layer; the negative electrode active layer comprises a negative electrode material, and the negative electrode material comprises carbon-containing graphite, tin oxide particles and carbon nanotubes, the carbon-containing graphite comprising a graphite matrix doped with nitrogen atoms and sulfur atoms and carbon particles, the graphite matrix having through-holes, and the carbon particles being adsorbed on the surface of the graphite matrix or located in the through-holes; a plurality of carbon nanotubes are interwoven to form a three-dimensional network; the tin oxide particles are located in the through-holes, on the surface of the graphite matrix and in the three-dimensional network.

[0109] In some embodiments, the carbon particles are metal organic framework materials, and the carbon particles have first mesopores and the three-dimensional network has second mesopores.

[0110] In some embodiments, the size of the first mesopores is smaller than the size of the through-pores.

[0111] In some embodiments, the size of the through hole 101 ranges from 350 nm to 450 nm, and the size of the through hole 101 can be 350 nm, 360 nm, 370 nm, 380 nm, 390 nm, 400 nm, 410 nm, 420 nm, 430 nm, 440 nm, or 450 nm.

[0112] According to some embodiments of the present application, another aspect of the embodiments of the present application provides an energy storage system, including: a secondary battery prepared by the method for preparing a secondary battery as in any of the above embodiments or a secondary battery as in the above embodiments.

[0113] According to some embodiments of the present application, on the other hand, embodiments of the present application provide an electrical device, including: a secondary battery prepared by the method for preparing a secondary battery as in any of the above embodiments, a secondary battery as in the above embodiments, or an energy storage system as in the above embodiments.

[0114] The beneficial effects of the embodiments of the present application will be further illustrated below in combination with examples and comparative examples.

[0115] Example 1:

[0116] (1) Preparation of negative electrode materials: 1.1 Graphite and polystyrene were mixed in a mass ratio of 3:1, added to ethanol and ultrasonically dispersed for 2 h, dried, and calcined at 450°C in an Ar / H2 atmosphere for 2 h to remove the polystyrene, thereby obtaining a graphite matrix having through pores.

[0117] 1.2 Preparation of the ZIF-8 precursor solution: Dissolve zinc nitrate and 2-methylimidazole in methanol at a molar ratio of 1:4 and stir for 30 minutes. Immerse the resulting graphite substrate in the precursor solution for a hydrothermal reaction. Centrifuge, rinse, and dry. Under argon protection, heat the solution at a rate of 5°C / min to 500°C and maintain for 2 hours to produce porous carbon-coated graphite (ZIF-8-C@G). The molar ratio of graphite substrate to 2-methylimidazole is 1:0.02.

[0118] 1.3 PANI (polyaniline) and DBDS (4,4'-dimethyldiphenyl disulfide) were dissolved in an ethanol solution at a mass ratio of 1:1 and ultrasonically stirred for 30 minutes. The mixture was then dried at 60°C in a vacuum oven with the carbon-coated graphite substrate for 12 hours. A secondary carbonization reaction was performed in an Ar atmosphere (500°C for 2 hours) to obtain a nitrogen-sulfur co-doped graphite substrate. The mass ratio of PANI (polyaniline):DBDS (4,4'-dimethyldiphenyl disulfide) to the graphite substrate was 1:1:10.

[0119] 1.4 SnCl2·2H2O was dissolved in a mixture of water and ethanol (2:1) and mixed with the nitrogen-sulfur co-doped graphite matrix prepared above. The mixture was ultrasonically stirred for 30 minutes, dried in a vacuum oven at 60°C, and calcined in air (300°C for 2 hours) to obtain a micron-sized rod-shaped SnO2 material. The SnO2-loaded sample and MWNTs were placed in a tube furnace. An acetylene / hydrogen mixture (700°C, C2H2:H2 = 1:2) was introduced over the surface of the mixture to catalytically grow carbon nanotubes on the SnO2 surface, forming a G@SnO2@MWNTs composite structure. The G@SnO2@MWNTs composite structure served as the anode material. The molar ratio of carbon-containing graphite, tin source material, and carbon nanotube particles was 1:0.006:0.03.

[0120] (2) Forming a negative electrode sheet: The negative electrode material: conductive agent (SP): binder (SBR and CMC) were stirred and coated on the negative electrode current collector at a mass ratio of 8:1:1, and dried at 80°C for 24 hours to obtain a negative electrode sheet.

[0121] Example 2: The difference from Example 1 is that graphite and polystyrene are mixed in a mass ratio of 2:1.

[0122] Example 3: The difference from Example 1 is that graphite and polystyrene are mixed in a mass ratio of 4:1.

[0123] Example 4: The difference from Example 1 is that the diameter of the polystyrene is 500 nm.

[0124] Example 5: The difference from Example 1 is that the diameter of the polystyrene is 800 nm.

[0125] Example 6: The difference from Example 1 is that the molar ratio of graphite matrix to 2-methylimidazole is 1:0.018.

[0126] Example 7: The difference from Example 1 is that the molar ratio of graphite matrix to 2-methylimidazole is 1:0.022.

[0127] Example 8: The difference from Example 1 is that the mass ratio of PANI (polyaniline): DBDS (4,4'-dimethyldiphenyl disulfide) to graphite matrix is ​​1:0.9:8.

[0128] Example 9: The difference from Example 1 is that the mass ratio of PANI (polyaniline): DBDS (4,4'-dimethyldiphenyl disulfide) to graphite matrix is ​​1:1.1:12.

[0129] Example 10: The difference from Example 1 is that the molar ratio of carbon-containing graphite, tin source material and carbon nanotube particles is 1:0.006:0.012.

[0130] Example 11: The difference from Example 1 is that the molar ratio of carbon-containing graphite, tin source material and carbon nanotube particles is 1:0.006:0.2.

[0131] Example 12: The difference from Example 1 is that the carbon nanotube particles are single-walled carbon nanotube particles.

[0132] Comparative Example 1: The difference from Example 1 is that there are no through holes in the graphite matrix.

[0133] Comparative Example 2: The difference from Example 1 is that: step 1.2 is omitted, that is, no carbon coating layer is formed.

[0134] Comparative Example 3: The difference from Example 1 is that: Step 1.3 is omitted, and the graphite matrix is ​​not doped with nitrogen and sulfur atoms.

[0135] Comparative Example 4: The difference from Example 1 is that the graphite matrix is ​​only doped with nitrogen atoms.

[0136] Comparative Example 5: The difference from Example 1 is that the graphite matrix is ​​only doped with sulfur atoms.

[0137] Comparative Example 6: The difference from Example 1 is that: Step 1.4 is omitted, and SnO2 materials and carbon nanotubes with micron-scale rod-like structures are not formed.

[0138] Comparative Example 7: The difference from Example 1 is that in step 1.4, only SnO2 material with a micron-scale rod-like structure is formed.

[0139] Comparative Example 8: The difference from Example 1 is that only carbon nanotubes are formed in step 1.4.

[0140] Comparative Example 9: The difference from Example 1 is that graphite and polystyrene are mixed in a mass ratio of 5:1.

[0141] Comparative Example 10: The difference from Example 1 is that graphite and polystyrene are mixed in a mass ratio of 1:1.

[0142] Comparative Example 11: The difference from Example 1 is that the diameter of the polystyrene is 300 nm.

[0143] Comparative Example 12: The difference from Example 1 is that the diameter of the polystyrene is 1000 nm.

[0144] Comparative Example 13: The difference from Example 1 is that the molar ratio of the graphite matrix to 2-methylimidazole is 1:0.01.

[0145] Comparative Example 14: The difference from Example 1 is that the molar ratio of the graphite matrix to 2-methylimidazole is 1:0.3.

[0146] Comparative Example 15: The difference from Example 1 is that the mass ratio of PANI (polyaniline): DBDS (4,4'-dimethyldiphenyl disulfide) to graphite matrix is ​​1:0.9:5.

[0147] Comparative Example 16: The difference from Example 1 is that the mass ratio of PANI (polyaniline): DBDS (4,4'-dimethyldiphenyl disulfide) to graphite matrix is ​​1:0.9:15.

[0148] Comparative Example 17: The difference from Example 1 is that the molar ratio of carbon-containing graphite, tin source material and carbon nanotube particles is 1:0.006:0.25.

[0149] Comparative Example 18: The difference from Example 1 is that the molar ratio of carbon-containing graphite, tin source material and carbon nanotube particles is 1:0.006:0.005.

[0150] The internal resistance, charge and discharge efficiency, and capacity retention rate of the secondary batteries corresponding to Examples 1 to 12 and Comparative Examples 1 to 18 were tested, as well as the resistivity and contact angle of the negative electrode sheets corresponding to Examples 1 to 12 and Comparative Examples 1 to 18 were tested.

[0151] Charge and discharge test process: Place the secondary battery under test in a 25°C environment, charge it to 3.65V at a current of 0.5C, then charge it at a constant voltage until the current drops to 0.05C, and then discharge it to 2.5V at a current of 0.5C. Repeat these steps 100 times to test the capacity retention rate and charge and discharge efficiency of the secondary battery.

[0152] The test results are shown in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] The data in Table 1 show that carbon coating and multi-porous structure design accelerate electrolyte infiltration, provide lithium ion adsorption sites, and form a high-speed ion transport path. Nitrogen and sulfur dual doping improves electronic conductivity and interface wettability, reduces the lithium ion insertion energy barrier, and inhibits lithium dendrite growth.

[0157] The data of Example 1, Example 3 to Example 4, and Comparative Examples 9 to Comparative Examples 10 in Table 1 show that when the proportion of graphite in graphite and polystyrene is relatively large, the structure of the graphite matrix formed is stable but the performance improvement is limited; when the proportion of graphite is relatively small, the through-pores of the graphite matrix formed are too dense, resulting in a serious decrease in stability, and thus the capacity retention rate is poor.

[0158] The data of Example 1, Example 5 to Example 6, and Comparative Examples 11 to Comparative Examples 12 in Table 1 show that if the diameter of PS is too small, the through holes in the graphite matrix formed cannot penetrate each film layer, that is, no through holes can be formed; if the diameter of PS is too large, the through holes in the graphite matrix formed will be too large, resulting in poor stability of the through structure and easy collapse during circulation.

[0159] The data of Example 1, Example 7 to Example 8, and Comparative Examples 13 to Comparative Example 14 in Table 1 show that when the content of 2-methylimidazole is low, that is, when the content of the graphite matrix is ​​high, the content of porous carbon in the negative electrode material of the negative electrode sheet is low and the conductivity is poor; when the content of the graphite matrix is ​​low and the content of the porous carbon is high, the thickness is thicker, which blocks the diffusion of lithium ions.

[0160] The data of Example 1, Example 9-Example 10, and Comparative Example 15-Comparative Example 16 in Table 1 show that when the nitrogen source and sulfur source are more, that is, when the nitrogen-sulfur mixture is more, dense defect areas will be formed, which may generate micropores or amorphous domains, affecting ion diffusion; when the nitrogen source and sulfur source are less doped, isolated defects will be introduced, slightly disturbing the sp 2 The carbon network has less impact on performance improvement.

[0161] The data from Examples 1, 11-12, and Comparative Examples 17-18 in Table 1 demonstrate that while a low SnO2 content allows for uniform dispersion on the MWNT surface, the loading is insufficient, resulting in limited active sites. High SnO2 content leads to SnO2 agglomeration, blocking the pores of the MWNTs and reducing conductivity.

[0162] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined in the claims.

Claims

1. A method for preparing a secondary battery, characterized in that: include: A negative electrode sheet is prepared, wherein the negative electrode sheet includes a stacked negative electrode current collector and a negative electrode active layer, wherein the negative electrode active layer includes a negative electrode material, and the preparation method of the negative electrode material includes: Prepare carbon-containing graphite, wherein the carbon-containing graphite includes a graphite matrix and carbon particles, wherein the graphite matrix has through holes, The carbon particles are adsorbed on the surface of the graphite substrate or located in the through holes; mixing a nitrogen source material, a sulfur source material and the carbon-containing graphite and subjecting the mixture to heat treatment so that the graphite matrix is ​​doped with nitrogen atoms and sulfur atoms; The carbon-containing graphite, tin source material and carbon nanotube particles are mixed and calcined to form the negative electrode material, wherein the negative electrode material includes the carbon-containing graphite, tin oxide particles and carbon nanotubes, a plurality of the carbon nanotubes are interwoven to form a three-dimensional network, and the tin oxide particles are located in the through-holes, on the surface of the graphite matrix and in the three-dimensional network; A positive electrode sheet and a separator are provided; the negative electrode sheet, separator and positive electrode sheet are stacked in sequence, a battery core assembly is obtained by winding or laminating, the battery core assembly is placed in a battery shell, an electrolyte is injected into the battery shell, and then encapsulated to obtain a secondary battery.

2. The method for preparing a secondary battery according to claim 1, wherein: The process steps of mixing the carbon-containing graphite, tin source material and carbon nanotube particles and calcining the mixture include: Dissolve the tin source material in alcohol and water to prepare a mixed solution, and stir for 5 to 20 minutes; adding the carbon-containing graphite doped with nitrogen atoms and sulfur atoms into the mixed solution, continuing stirring for 10 minutes to 40 minutes, and then centrifuging to separate the precipitate; performing a first calcination treatment on the precipitate to oxidize the tin source material into tin oxide particles; The calcined precipitate is mixed with carbon nanotube particles and then subjected to a second calcination treatment in an atmosphere of a catalytic gas.

3. The method for preparing a secondary battery according to claim 2, wherein: The molar ratio of the carbon-containing graphite, the tin source material and the carbon nanotube particles is 1: (0.005-0.007): (0.01-0.2).

4. The method for preparing a secondary battery according to claim 2, wherein: The catalytic gas is a mixed gas of acetylene and hydrogen, and the flow ratio of the acetylene to the hydrogen is 1:(1.8-2.2).

5. The method for preparing a secondary battery according to claim 2, wherein: In the mixed solution, the mass ratio of alcohol to water is 1:(1.8-2.2); and the molar ratio of the tin source material to the alcohol is 1:(48-52).

6. The method for preparing a secondary battery according to claim 1, wherein: The size of the tin oxide particles is 30nm to 50nm; the microscopic morphology of the tin oxide particles is rod-shaped.

7. The method for preparing a secondary battery according to claim 1, wherein: The preparation method of the carbon-containing graphite comprises: preparing a graphite matrix having through-holes therein; dispersing the metal organic material in a solvent to form a first mixed solution; Immersing the graphite substrate in the first mixed solution and performing a hydrothermal reaction to decompose the metal organic material into the carbon particles, followed by centrifugal separation and drying to obtain the carbon-containing graphite; The molar ratio of the graphite matrix to the metal organic material is 1:(0.018-0.022).

8. The method for preparing a secondary battery according to claim 7, wherein: The graphite matrix is ​​prepared by a template method, and the preparation steps include: mixing graphite and colloidal microspheres in a mass ratio of (2-4):1, adding them into ethanol for ultrasonic dispersion for 2-3 hours, then drying, and calcining in an inert gas atmosphere to remove the colloidal microspheres.

9. The method for preparing a secondary battery according to claim 1, wherein: The process steps of mixing the nitrogen source material, the sulfur source material and the carbon-containing graphite and heat treating the mixture include: Dissolve the nitrogen source material and the sulfur source material in ethanol at a mass ratio of 1: (0.9-1.1), and stir ultrasonically for 20-50 minutes to obtain a second mixed solution; The carbon-containing graphite is immersed in the second mixed solution, ultrasonically stirred for 20 minutes to 40 minutes, dried, and calcined under an inert gas atmosphere for 1 hour to 3 hours.

10. A secondary battery, characterized in that: include: A battery case, wherein the battery case has a cavity therein, and the cavity contains an electrolyte; A battery cell assembly, wherein the battery cell assembly is located in the cavity and immersed in the electrolyte; the battery cell assembly includes a positive electrode sheet, a separator and a negative electrode sheet, wherein the negative electrode sheet includes a stacked negative electrode current collector and a negative electrode active layer; the negative electrode active layer includes a negative electrode material, and the negative electrode material includes carbon-containing graphite, tin oxide particles and carbon nanotubes, the carbon-containing graphite includes a graphite matrix doped with nitrogen atoms and sulfur atoms and carbon particles, the graphite matrix has through-holes, and the carbon particles are adsorbed on the surface of the graphite matrix or located in the through-holes; a plurality of the carbon nanotubes are interwoven to form a three-dimensional network; the tin oxide particles are located in the through-holes, on the surface of the graphite matrix and in the three-dimensional network.

11. The secondary battery according to claim 10, wherein The carbon particles are metal organic framework materials, and the carbon particles have first mesopores; the three-dimensional network has second mesopores.

12. The secondary battery according to claim 11, wherein The size of the first mesopore is smaller than that of the through hole.

13. The secondary battery according to claim 10 or 12, characterized in that: The size of the through-holes ranges from 350 nm to 450 nm.

14. An energy storage system, characterized in that: include: A secondary battery prepared by the method for preparing a secondary battery according to claims 1 to 9, or a secondary battery according to any one of claims 10 to 13.

15. An electrical device, characterized in that: include: A secondary battery prepared by the method for preparing a secondary battery according to claims 1 to 9, a secondary battery according to any one of claims 10 to 13, or an energy storage system according to claim 14.

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