Negative electrode material, preparation method and application thereof, and lithium ion battery

Abstract

The invention discloses a negative electrode material, a preparation method and application thereof, and a lithium ion battery. The negative electrode material comprises porous silicon, organic gel and graphene oxide, wherein the organic gel comprises at least one of self-healing silica gel, polystyrene gel and polyimide aerogel. The negative electrode material can effectively relieve the volume expansion of silicon and improve the conductivity of the negative electrode material.

Description

Technical Field

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

[0002] Silicon-based anode materials have significant advantages such as high specific capacity, low voltage platform, environmental friendliness, and abundant resources. Therefore, silicon-based anode materials are the first choice for the next generation of high specific energy lithium-ion battery anode materials. However, there are some challenges in silicon-based anode materials, including poor conductivity, volume expansion during lithiation-delithiation, severe electrode crushing, significant thickening of solid electrolyte membrane, low Coulombic efficiency, and deterioration of cycle life, all of which lead to the complexity of realizing the full potential of silicon-based anode materials in commercial lithium-ion battery applications.

[0003] At present, the improvement methods of silicon-based negative electrode materials are mainly divided into three categories: nano-sizing, microstructure design and composite design. Usually these three methods can be carried out simultaneously, which can solve the problems faced by silicon, such as powdering caused by volume expansion, unstable SEI film and poor ion and electron conductivity, to a certain extent. Among them, the one-dimensional nano-sizing method has strict requirements on the size of silicon. Only when the size of silicon is reduced to a certain size range can the silicon particles avoid breaking. The two-dimensional structured silicon negative electrode effectively promotes the diffusion of lithium ions, improves the interface charge transfer rate, and brings higher capacity. However, the stress concentration caused by the two-dimensional silicon lithiation process brings structural instability, destroys the two-dimensional structure and produces fractures, resulting in performance deterioration. In addition, it is impossible to alleviate the electrochemical instability caused by volume change. The specific surface area of ​​three-dimensional porous silicon structure materials is usually large, which increases the chemical side reactions on the surface of the material, resulting in a decrease in the first coulomb efficiency and a significant attenuation of capacity. Secondly, the porosity of some porous structures is large, which will greatly reduce the volume energy density of the electrode material and also reduce the conductivity of the material itself. Finally, the preparation process of porous structures is generally relatively complicated, and it is difficult to ensure the consistency of the materials.

[0004] The low tap density of nano- and microstructured silicon materials leads to low volume energy density, and the high specific surface area leads to low initial coulombic efficiency; battery safety issues caused by electrode film expansion, as well as high preparation costs and complex processes, also hinder the practical application of silicon-based negative electrode materials and severely limit the development of high energy density lithium-ion batteries. Summary of the invention

[0005] The present invention is based on the inventors' discovery and understanding of the following facts and problems: At present, silicon-based negative electrode materials have some problems, including poor conductivity, volume expansion during lithiation-delithiation, severe electrode crushing, significant thickening of the solid electrolyte membrane, low Coulomb efficiency, deterioration of cycle life, battery safety issues, high preparation cost and complex process, etc.

[0006] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, the embodiments of the present invention provide a negative electrode material and a preparation method and application thereof, and a lithium-ion battery, which effectively alleviate the volume expansion of silicon and improve the conductivity of the negative electrode material.

[0007] An embodiment of the present invention provides a negative electrode material, including porous silicon, organic gel and graphene oxide, wherein the organic gel includes at least one of self-healing silicon gel, polystyrene gel and polyimide aerogel.

[0008] Advantages and technical effects of the negative electrode material of the embodiment of the present invention: The composite silicon-based negative electrode material includes porous silicon, organic gel and graphene oxide, which can alleviate volume expansion and improve the conductivity of the negative electrode material. Organic gels such as self-healing silicone gel have a protective effect, have excellent impulse response and self-healing ability, alleviate volume expansion, ensure the structural stability of the material, and ensure that the electrode cycle process will not cause the electrode film to crack due to expansion problems, causing the active material to fall off the current collector and cause the battery to fail. When the organic gel is compounded with porous silicon, on the one hand, porous silicon itself has a large number of pore structures, and these pores provide a large specific surface area. When compounded with organic gel, the organic gel can be filled into these pores. The organic gel itself has rich functional groups, and after filling, the pores have active groups distributed inside, which greatly increases the area that can be contacted and reacted; on the other hand, when the organic gel and porous silicon are compounded, new active sites will be generated at the interface between the two, because there is an interaction between the organic gel and the porous silicon, such as chemical bonding or physical adsorption. This interaction changes the arrangement and properties of atoms or molecules in the interface area, forming a new active area, so that the overall surface active area of ​​the material increases. Increasing the surface active area can provide abundant sites for the insertion and extraction of lithium ions, thereby improving the specific capacity of silicon negative electrode materials. Graphene oxide improves the conductivity of negative electrode materials. The organic gel and graphene oxide in the negative electrode material complement each other, and at the same time, the organic gel network skeleton and the graphene oxide network have good ductility, and the negative electrode material has good mechanical strength and self-healing properties. By utilizing the network skeleton of the organic gel, a stronger mechanical framework can be formed, thereby improving the pressure resistance of silicon, and the overall conductivity of the silicon material is improved by compounding graphene oxide with the silicon negative electrode material. Compared with related technologies, the preparation method of the present invention can improve production efficiency while ensuring the quality and stability of the negative electrode material.

[0009] In the embodiment of the present invention, graphene oxide has the advantages of high strength, light weight, high conductivity, strong chemical and thermal stability and good structural flexibility. Graphene oxide can improve the overall conductivity and structural stability of the negative electrode material. By compounding the organic gel, graphene oxide and silicon negative electrode material, a stable framework can also be formed, and the mechanical strength and pressure resistance of the framework can be further improved to adapt to the huge pressure of volume expansion of silicon material during lithiation / delithiation. The prepared porous silicon is a three-dimensional structure. After compounding with the organic gel and graphene oxide, the graphene oxide is a sheet structure. After the composite material is formed, the sheets are interconnected to form a network. On the one hand, the three-dimensional conductive network provides a fast transmission channel for electrons, and the porous structure of the material improves the fast diffusion channel of lithium ions, and can effectively alleviate the volume expansion of silicon materials, and can ensure the overall structural stability of the material. The composite negative electrode material combines the advantages of various characteristics of the material to jointly alleviate the problems existing in silicon itself.

[0010] In some embodiments, the mass ratio of the porous silicon, the organogel and the graphene oxide is 9:1-5:1-5;

[0011] And / or, the particle size of the porous silicon is 500nm-1μm;

[0012] And / or, the particle size of the negative electrode material is 700nm-2μm.

[0013] An embodiment of the present invention provides a method for preparing a negative electrode material, comprising the following steps:

[0014] (1) grinding and mixing magnesium powder and silicon powder, performing an alloying reaction to obtain an alloying reaction product, cooling, and performing vapor-phase dealloying in an ammonia atmosphere to obtain a vapor-phase dealloying product; immersing the vapor-phase dealloying product in hydrochloric acid, washing and drying to obtain porous silicon;

[0015] (2) mixing methyl methacrylate, (3-mercaptopropyl)trimethoxysilane, a first catalyst and a solvent to react; removing the solvent after the reaction, dispersing the product in ethanol, adding hydrochloric acid to react; removing the ethanol after the reaction, extracting with water and chloroform, removing chloroform, and obtaining a hyperbranched fluid;

[0016] (3) reacting 4-(hydroxymethyl)phenylboronic acid and triethanolamine to obtain a nitrogen-containing coordinated borate ester;

[0017] (4) mixing isophorone diisocyanate and polyetheramine to obtain a prepolymer; then mixing the prepolymer, the hyperbranched fluid and the nitrogen-containing coordinated borate to obtain a precursor;

[0018] (5) The precursor, porous silicon and a second catalyst are mixed and reacted, and after the reaction, they are mixed with a graphene oxide aqueous solution for compounding, and dried to obtain a negative electrode material.

[0019] In the embodiment of the present invention, magnesium powder and silicon powder are fully ground and reacted at high temperature to obtain the product of alloying reaction. Gas phase dealloying is carried out in an ammonia atmosphere to achieve gas phase dealloying; the product is immersed in hydrochloric acid for pickling to obtain porous silicon. Methyl methacrylate, (3-mercaptopropyl) trimethoxysilane and the first catalyst are mixed to perform a telomerization reaction to obtain a silane-terminated polymer, ethanol is added as a solvent to fully mix, and then hydrochloric acid is added, heated and concentrated to remove ethanol, and water and chloroform are used for extraction and separation. After the solution removes chloroform, a hyperbranched fluid can be obtained. 4-(Hydroxymethyl)phenylboric acid and triethanolamine react to obtain a nitrogen-containing coordinated borate. Isophorone diisocyanate and polyetheramine are mixed to obtain a prepolymer, and then the prepolymer, hyperbranched fluid and nitrogen-containing coordinated borate are mixed to obtain a precursor. The precursor and porous silicon are mixed and reacted to obtain graphene oxide to obtain a composite comprising a self-healing silica gel organogel, porous silicon and graphene oxide, and the negative electrode material is obtained after drying.

[0020] In some embodiments, in step (1), the mass ratio of the magnesium powder to the silicon powder is 1-3:1;

[0021] And / or, the temperature of the alloying reaction is 400-600°C;

[0022] And / or, the holding time of the alloying reaction is 2-6h;

[0023] And / or, the alloying reaction is carried out under a protective atmosphere;

[0024] And / or, the temperature of the vapor phase dealloying is 700-900°C;

[0025] And / or, the vapor phase dealloying is carried out for a holding time of 4-8 hours;

[0026] And / or, the concentration of the hydrochloric acid is 1-3 mol / L;

[0027] And / or, the temperature of immersing in hydrochloric acid is 40-60°C;

[0028] And / or, the immersion time in hydrochloric acid is 2-6 hours.

[0029] In some embodiments, in step (2), the mass ratio of methyl methacrylate to (3-mercaptopropyl)trimethoxysilane is 1:0.8-1.2;

[0030] and / or, the first catalyst comprises azobisisobutyronitrile;

[0031] and / or, the mass percentage of the first catalyst relative to methyl methacrylate, (3-mercaptopropyl)trimethoxysilane and solvent is 0.1-5%;

[0032] and / or, the reaction temperature for the mixed reaction is 50-70°C;

[0033] And / or, the reaction time of the mixed reaction is 6-24h;

[0034] and / or, the reaction temperature for adding hydrochloric acid to carry out the reaction is 60-80°C;

[0035] And / or, the reaction time of adding hydrochloric acid for reaction is 12-36 hours.

[0036] In some embodiments, in step (3), the molar ratio of 4-(hydroxymethyl)phenylboronic acid to triethanolamine is 1:0.5-2;

[0037] And / or, the reaction temperature is 60-90°C;

[0038] And / or, the reaction time is 1-4h.

[0039] In some embodiments, in step (4), the molar ratio of isophorone diisocyanate to polyetheramine is 1-2:1;

[0040] And / or, the isophorone diisocyanate and the polyetheramine are mixed in a solvent to obtain a mixed solution, wherein the solid content of the mixed solution is 10-25%;

[0041] And / or, the temperature of the mixed reaction is 10-35°C;

[0042] And / or, the mixing reaction time is 10-60min;

[0043] And / or, the mass ratio of the prepolymer, the hyperbranched fluid and the nitrogen-containing coordinated borate ester is 1-5:1-5:1-5.

[0044] In some embodiments, in step (5), the mass ratio of the porous silicon, the precursor and the graphene oxide is 9:1-5:1-5;

[0045] And / or, the mass fraction of the graphene oxide aqueous solution is 10-30%;

[0046] and / or, the second catalyst comprises dibutyltin dilaurate;

[0047] And / or, the mass percentage of the second catalyst relative to the porous silicon is 0.1-4%;

[0048] And / or, the reaction temperature is 60-80°C;

[0049] And / or, the reaction time is 4-8h;

[0050] and / or, mixing with an aqueous solution of graphene oxide and subjecting to ultrasonic treatment;

[0051] And / or, the drying is carried out by spray drying;

[0052] And / or, the drying temperature is 120-160°C.

[0053] The embodiment of the present invention provides an application of a negative electrode material for a lithium ion battery. In the embodiment of the present invention, the negative electrode material can effectively alleviate the volume expansion of silicon and improve the conductivity of the negative electrode material.

[0054] The embodiment of the present invention provides a lithium ion battery, comprising a negative electrode material. In the embodiment of the present invention, the negative electrode material can effectively alleviate the volume expansion of silicon and improve the conductivity of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The negative electrode material of Example 1 is 1Ag -1 Cycling performance diagram under charge and discharge current density.

[0056] Figure 2 The Si@GO of Example 1 is 1Ag -1 Cycling performance diagram under charge and discharge current density.

[0057] Figure 3 The Si@IPO of Example 2 is 1Ag -1 Cycling performance diagram under charge and discharge current density.

[0058] Figure 4 This is a charge and discharge rate performance diagram of the negative electrode material of Example 1. DETAILED DESCRIPTION

[0059] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0060] A negative electrode material according to an embodiment of the present invention comprises porous silicon, organic gel and graphene oxide, wherein the organic gel comprises at least one of self-healing silicon gel, polystyrene gel and polyimide aerogel.

[0061] The negative electrode material of the embodiment of the present invention includes porous silicon, organic gel and graphene oxide, which can alleviate volume expansion and improve the conductivity of the negative electrode material. Organic gels such as self-healing silicone gel have a protective effect, have excellent impulse response and self-healing ability, alleviate volume expansion, ensure the structural stability of the material, and ensure that the electrode cycle process will not cause the electrode film to crack due to expansion problems, causing the active material to fall off the current collector and cause the battery to fail. The organic gel is compounded with porous silicon. On the one hand, porous silicon itself has a large number of pore structures, and these pores provide a large specific surface area. When compounded with organic gel, the organic gel can be filled into these pores. The organic gel itself has rich functional groups. After filling, the pores have active groups distributed inside, which greatly increases the area that can be contacted and reacted; on the other hand, when the organic gel and porous silicon are compounded, new active sites will be generated at the interface between the two, because there is an interaction between the organic gel and the porous silicon, such as chemical bonding or physical adsorption. This interaction changes the arrangement and properties of atoms or molecules in the interface area, forming a new active area, so that the overall surface active area of ​​the material increases. Increasing the surface active area can provide abundant sites for the insertion and extraction of lithium ions, thereby improving the specific capacity of silicon negative electrode materials. Graphene oxide improves the conductivity of negative electrode materials. The organic gel and graphene oxide in the negative electrode material complement each other, and at the same time, the organic gel network skeleton and the graphene oxide network have good ductility, and the negative electrode material has good mechanical strength and self-healing properties. By utilizing the network skeleton of the organic gel, a stronger mechanical framework can be formed, thereby improving the pressure resistance of silicon, and the overall conductivity of the silicon material is improved by compounding graphene oxide with the silicon negative electrode material. Compared with related technologies, the preparation method of the present invention can improve production efficiency while ensuring the quality and stability of the negative electrode material.

[0062] In the embodiment of the present invention, graphene oxide has the advantages of high strength, light weight, high conductivity, strong chemical and thermal stability and good structural flexibility. Graphene oxide can improve the overall conductivity and structural stability of the negative electrode material. By compounding the organic gel, graphene oxide and silicon negative electrode material, a stable framework can also be formed, and the mechanical strength and pressure resistance of the framework can be further improved to adapt to the huge pressure of volume expansion of silicon material during lithiation / delithiation. The prepared porous silicon is a three-dimensional structure. After compounding with the organic gel and graphene oxide, the graphene oxide is a sheet structure. After the composite material is formed, the sheets are interconnected to form a network. On the one hand, the three-dimensional conductive network provides a fast transmission channel for electrons, and the porous structure of the material improves the fast diffusion channel of lithium ions, and can effectively alleviate the volume expansion of silicon materials, and can ensure the overall structural stability of the material. The composite negative electrode material combines the advantages of various characteristics of the material to jointly alleviate the problems existing in silicon itself.

[0063] In some embodiments, the negative electrode material includes porous silicon, organic gel and graphene oxide, and the porous silicon, organic gel and graphene oxide are uniformly dispersed in the negative electrode material; optionally, the organic gel is partially or completely filled in the pores of the porous silicon; optionally, the graphene oxide forms a graphene oxide network in the negative electrode material; the organic gel forms an organic gel network skeleton in the negative electrode material.

[0064] In some embodiments, the organogel comprises a self-healing silicone gel; optionally, the self-healing silicone gel is obtained by reacting a prepolymer, a hyperbranched fluid, and a nitrogen-containing coordinated borate ester.

[0065] In an embodiment of the present invention, the negative electrode material may contain a self-healing silica gel, which contains a dynamic borate-containing polymer as a network skeleton and has a matching mesh size. The network skeleton accurately captures the hyperbranched fluid used as a large-volume solvent through steric hindrance, which not only improves the stability and pressure resistance of the organic gel, but also can effectively inhibit the influence of the volume expansion of the silicon material during the lithiation / delithiation process, thereby improving the pressure resistance of silicon, thereby solving the problem of volume expansion while maintaining the high specific capacity of the silicon material.

[0066] In some embodiments, the mass ratio of the porous silicon, the organic gel and the graphene oxide is 9:1-5 (e.g., 1, 1.5, 2, 3, 4, 5):1-5 (e.g., 1, 1.5, 2, 3, 4, 5). In the embodiments of the present invention, it is beneficial to further alleviate the volume expansion of the negative electrode material silicon and improve the conductivity of the negative electrode material.

[0067] In some embodiments, the porous silicon has a particle size of 500 nm-1 μm, specifically, for example, 500 nm, 700 nm, 900 nm, 1 μm.

[0068] In some embodiments, the particle size of the negative electrode material is 700 nm-2 μm, specifically, for example, 700 nm, 900 nm, 1 μm, 1.5 μm, 2 μm.

[0069] A method for preparing a negative electrode material according to an embodiment of the present invention comprises the following steps:

[0070] (1) grinding and mixing magnesium powder and silicon powder, performing an alloying reaction to obtain an alloying reaction product, cooling, and performing vapor-phase dealloying in an ammonia atmosphere to obtain a vapor-phase dealloying product; immersing the vapor-phase dealloying product in hydrochloric acid, washing and drying to obtain porous silicon;

[0071] (2) mixing methyl methacrylate, (3-mercaptopropyl)trimethoxysilane, a first catalyst and a solvent to react; removing the solvent after the reaction, dispersing the product in ethanol, adding hydrochloric acid to react; removing the ethanol after the reaction, extracting with water and chloroform, removing chloroform, and obtaining a hyperbranched fluid;

[0072] (3) reacting 4-(hydroxymethyl)phenylboronic acid and triethanolamine to obtain a nitrogen-containing coordinated borate ester;

[0073] (4) mixing isophorone diisocyanate and polyetheramine to obtain a prepolymer; then mixing the prepolymer, the hyperbranched fluid and the nitrogen-containing coordinated borate to obtain a precursor;

[0074] (5) The precursor, porous silicon and a second catalyst are mixed and reacted, and after the reaction, they are mixed with a graphene oxide aqueous solution for compounding, and dried to obtain a negative electrode material.

[0075] In the embodiment of the present invention, magnesium powder and silicon powder are fully ground and reacted at high temperature to obtain the product of alloying reaction. Gas phase dealloying is carried out in an ammonia atmosphere to achieve gas phase dealloying; the product is immersed in hydrochloric acid for pickling to obtain porous silicon. Methyl methacrylate, (3-mercaptopropyl) trimethoxysilane and the first catalyst are mixed and poly-reacted to obtain a silane-terminated polymer. Ethanol is added as a solvent to fully mix and then hydrochloric acid is added, heated and concentrated to remove ethanol, and water and chloroform are used for extraction and separation. After the solution removes chloroform, a hyperbranched fluid can be obtained. 4-(Hydroxymethyl)phenylboric acid and triethanolamine react to obtain a nitrogen-containing coordinated borate. Isophorone diisocyanate and polyetheramine are mixed to obtain a prepolymer, and then the prepolymer, hyperbranched fluid and nitrogen-containing coordinated borate are mixed to obtain a precursor. The precursor and porous silicon are mixed and reacted to form a composite graphene oxide to obtain a composite comprising a self-healing silica gel organogel, porous silicon and graphene oxide, and the negative electrode material is obtained after drying.

[0076] In some embodiments, in step (1), the mass ratio of the magnesium powder to the silicon powder is 1-3:1, specifically, for example, 1:1, 9:5, 2:1, 3:1.

[0077] In some embodiments, in step (1), the silicon powder is metallurgical silicon powder.

[0078] In some embodiments, in step (1), the alloying temperature is 400-600°C, specifically, for example, 400°C, 500°C, 600°C; the holding time of the alloying reaction is 2-6h, specifically, for example, 2h, 4h, 6h; the alloying reaction is carried out under a protective atmosphere, optionally, an Ar atmosphere; the alloying reaction is carried out in a tube furnace under a protective atmosphere; the heating rate is 3-7°C / min; the cooling is carried out by natural cooling to room temperature; optionally, grinding is carried out after cooling, and the grinding time is 0.1-2h. In the embodiment of the present invention, grinding and mixing magnesium powder and silicon powder can make their reaction more complete, and then obtain the alloying reaction magnesium silicide product through the alloying reaction.

[0079] In some embodiments, in step (1), the temperature of the gas phase dealloying is 700-900°C, specifically, for example, 700°C, 800°C, 900°C; the holding time of the gas phase dealloying is 4-8h, specifically, for example, 4h, 6h, 8h; the gas phase dealloying is carried out under a protective atmosphere, optionally, Ar atmosphere, optionally, in a tube furnace; after reaching the target temperature, the protective atmosphere is replaced with ammonia and kept warm; the heating rate is 3-7°C / min; grinding is performed after gas phase dealloying. In the embodiment of the present invention, Si and Mg are reacted with NH4+ in ammonia to form a molten salt solution. 3 The difference in reaction activity, Si and Mg are generated after nitridation heat treatment 3 N 2 phase, and then porous silicon is obtained by acid leaching.

[0080] In some embodiments, in step (1), the concentration of the hydrochloric acid is 1-3 mol / L, specifically, for example, 1 mol / L, 2 mol / L, 3 mol / L; the temperature of the hydrochloric acid is 40-60°C, specifically, for example, 40°C, 50°C, 60°C; the time of the hydrochloric acid immersion is 2-6h, specifically, for example, 2h, 4h, 6h; the hydrochloric acid immersion is heated in a water bath. In the embodiment of the present invention, the immersion in the hydrochloric acid can remove the Mg by pickling. 3 N 2 Phase porous silicon is obtained.

[0081] In some embodiments, in step (1), the washing is performed with water, optionally with deionized water, and optionally, the washing is performed three times. In the embodiment of the present invention, water is used for centrifugation to remove excess hydrochloric acid solution.

[0082] In some embodiments, in step (1), the drying is freeze drying, optionally carried out in a freeze dryer, and optionally, the drying time is 12-36 hours. In the embodiments of the present invention, freeze drying is beneficial to ensure the structure and shape of the material itself.

[0083] In some embodiments, in step (2), methyl methacrylate, (3-mercaptopropyl)trimethoxysilane, a first catalyst and a solvent are mixed for reaction; optionally, the mass ratio of methyl methacrylate to (3-mercaptopropyl)trimethoxysilane is 1:0.8-1.2, specifically, for example, 1:0.8, 1:1, 1:1.2; the first catalyst includes azobisisobutyronitrile; the solvent includes anhydrous tetrahydrofuran; the mass percentage of the first catalyst relative to methyl methacrylate, (3-mercaptopropyl)trimethoxysilane and the solvent is 0.1-5%, specifically, for example, 0.1%, 0.5%, 1%, 3%, 5%; the reaction temperature is 50-70°C, specifically, for example, 50°C, 60°C, 70°C; the reaction time is 6-24h, specifically, for example, 6h, 10h, 12h, 24h, optionally, water bath heating is used; the reaction is carried out under anaerobic conditions, optionally, after methyl methacrylate, (3-mercaptopropyl)trimethoxysilane, the first catalyst and the solvent are mixed, oxygen in the solution is removed by three freeze-pump-thaw cycles.

[0084] In some embodiments, in step (2), after the reaction, the solvent is removed, the product is dispersed in ethanol, and hydrochloric acid is added to react; after the reaction, the ethanol is removed, and the mixture is extracted with water and chloroform to remove chloroform to obtain a hyperbranched fluid;

[0085] Optionally, there is no special restriction on the amount of the ethanol and the amount of the hydrochloric acid. For example, in a specific embodiment, the ethanol is 400-600 mL, specifically, for example, 400 mL, 500 mL, 600 mL; the mass fraction of the hydrochloric acid is 37%; the ratio of the ethanol to the hydrochloric acid is 400-600 mL: 10 g;

[0086] Optionally, the reaction temperature for adding hydrochloric acid to react is 60-80°C, specifically, for example, 60°C, 70°C, 80°C; the reaction time for adding hydrochloric acid to react is 12-36h, specifically, for example, 12h, 18h, 24h, 36h.

[0087] In the embodiment of the present invention, methyl methacrylate reacts with (3-mercaptopropyl)trimethoxysilane to obtain a hyperbranched fluid. Ethanol serves as a solvent, and hydrochloric acid can promote the dehydration condensation reaction between the reactive groups and accelerate the reaction rate.

[0088] In some embodiments, in step (3), 4-(hydroxymethyl)phenylboronic acid and triethanolamine are reacted to obtain a nitrogen-containing coordinated borate ester; optionally, the molar ratio of 4-(hydroxymethyl)phenylboronic acid and triethanolamine is 1:0.5-2, specifically, for example, 1:0.5, 1:1, 1:1.5, 1:2; the reaction temperature is 60-90°C, specifically, for example, 60°C, 70°C, 80°C, 90°C; the reaction time is 1-4h, specifically, for example, 1h, 2h, 3h, 4h; 4-(hydroxymethyl)phenylboronic acid and triethanolamine are mixed with a solvent for reaction, and optionally, the solvent includes N,N-dimethylformamide (DMF).

[0089] In some embodiments, in the step (4), isophorone diisocyanate and polyetheramine are mixed and reacted to obtain a prepolymer; optionally, the molar ratio of isophorone diisocyanate to polyetheramine is 1-2:1, specifically, for example, 1:1, 1.5:1, 2:1; the mixing of isophorone diisocyanate and polyetheramine is carried out in a solvent to obtain a mixed solution, and the solid content of the mixed solution is 10-25%, specifically, for example, 10%, 15%, 25%; the polyetheramine includes D2000; the solvent includes N,N-dimethylformamide (DMF); the temperature of the mixing reaction is 10-35°C, specifically, for example, 10°C, 20°C, 35°C, 30°C, 35°C; the time of the mixing reaction is 10-60min, specifically, for example, 10min, 30min, 60min.

[0090] In some embodiments, in the step (4), the prepolymer, the hyperbranched fluid and the nitrogen-containing coordinated borate are mixed to obtain a precursor; optionally, the mass ratio of the prepolymer, the hyperbranched fluid and the nitrogen-containing coordinated borate is 1-5 (for example, 1, 2, 3, 4, 5): 1-5 (for example, 1, 2, 3, 4, 5): 1-5 (for example, 1, 2, 3, 4, 5); the mixing temperature of the three is 50-70°C, specifically, for example, 50°C, 60°C, 70°C; the mixing time is 1-3h, optionally, 2h.

[0091] In some embodiments, in step (5), the mass ratio of the porous silicon, the precursor and the graphene oxide is 9: 1-5 (for example, 1, 2, 3, 4, 5): 1-5 (for example, 1, 2, 3, 4, 5). In the embodiments of the present invention, it is beneficial to improve the conductivity of the silicon material and alleviate the expansion problem. When there are fewer precursors, it is difficult to achieve uniform coating, which is not conducive to improving the ability of the negative electrode material to alleviate expansion; when there are more precursors, the conductivity deteriorates. The less graphene oxide, the smaller the improvement in conductivity; the more graphene oxide, the smaller the proportion of silicon and the lower the battery energy density.

[0092] In some embodiments, in step (5), ultrasonic dispersion is used for mixing with the graphene oxide aqueous solution. Optionally, the ultrasonic dispersion time is 10-50 min.

[0093] In some embodiments, in step (5), the mass fraction of the graphene oxide aqueous solution is 10-30%, optionally, 20%.

[0094] In some embodiments, in step (5), the second catalyst comprises dibutyltin dilaurate.

[0095] In some embodiments, in step (5), the mass percentage of the second catalyst relative to the porous silicon is 0.1-4%, specifically, for example, 0.1%, 1%, 2%, 3%, 4%.

[0096] In some embodiments, in step (5), the reaction temperature is 60-80°C, optionally, 70°C; the reaction time is 4-8h, optionally, 6h.

[0097] In some embodiments, in step (5), the precursor, porous silicon, a second catalyst and a solvent are mixed to react; optionally, the solvent includes N,N-dimethylformamide (DMF).

[0098] In some embodiments, in step (5), after the reaction, the graphene oxide aqueous solution and a solvent are mixed for compounding; optionally, the solvent includes water.

[0099] In some embodiments, in step (5), the drying is performed by spray drying, and the drying temperature is 120-160° C., optionally, 140° C. In the embodiment of the present invention, spray drying is conducive to the continuous production of porous silicon, organic gel and graphene oxide after compounding.

[0100] In some embodiments, in step (5), the precursor, porous silicon and the second catalyst are mixed and reacted, and after the reaction, they are mixed with a graphene oxide aqueous solution for compounding to achieve the compounding of porous silicon, organic gel and graphene oxide to obtain a negative electrode material.

[0101] In some embodiments, in step (5), the porous silicon can be replaced by at least one of nano-silicon and micro-silicon.

[0102] An application of a negative electrode material according to an embodiment of the present invention is used in a lithium-ion battery. In the embodiment of the present invention, the negative electrode material can effectively alleviate the volume expansion of silicon and improve the conductivity of the negative electrode material.

[0103] A lithium-ion battery according to an embodiment of the present invention comprises a negative electrode material. According to the embodiment of the present invention, the negative electrode material can effectively alleviate the volume expansion of silicon and improve the conductivity of the negative electrode material.

[0104] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0105] Example 1

[0106] A method for preparing a negative electrode material comprises the following steps:

[0107] 1) Preparation of porous silicon: Magnesium powder and metallurgical silicon powder were fully ground and mixed in a mass ratio of 2:1 and placed in a tubular furnace. The temperature was raised from room temperature to 500°C at a rate of 5°C / min under Ar atmosphere. After keeping the temperature for 4 hours, an alloying reaction product was obtained, which was then naturally cooled to room temperature.

[0108] The product was taken out and fully ground and mixed for 1 h, then transferred to a tube furnace, and an inert Ar atmosphere was introduced into the tube furnace. The temperature was raised from room temperature to 800 °C at a rate of 5 °C / min. When the target temperature was reached, the Ar atmosphere was replaced with NH 3 atmosphere, and keep warm for 6h;

[0109] The product was taken out and ground, and then the ground sample was immersed in a dilute hydrochloric acid solution with a concentration of 1 mol / L, stirred in a 50°C water bath for 4 hours, and then centrifuged three times with deionized water to wash away the excess hydrochloric acid solution in the sample. The centrifuged sample was then placed in a freeze dryer and low-temperature dried for 24 hours to obtain a porous silicon material.

[0110] 2) Preparation of an organogel precursor: 10 g of methyl methacrylate and 10 g of (3-mercaptopropyl) trimethoxysilane were mixed, and 0.5% (mass percentage relative to methyl methacrylate, (3-mercaptopropyl) trimethoxysilane and solvent anhydrous tetrahydrofuran) of azobisisobutyronitrile and 40 mL of anhydrous tetrahydrofuran were added. The oxygen in the solution was removed by three freeze-pump-thaw cycles, and then reacted at 70 ° C for 24 hours. After the reaction was completed, THF was removed using a rotary evaporator to obtain the product silane-terminated polymer. The silane-terminated polymer was added to a flask with a magnetic stirrer, and 500 mL of ethanol was added as a solvent. Under stirring, 10 g of hydrogen chloride solution (HCl, mass fraction 37%) was added to the solution, heated at 70 ° C for 24 hours, and then concentrated under vacuum to remove ethanol. The product was extracted with water and chloroform, and the two solutions were separated using a separatory funnel. After removing chloroform, a hyperbranched fluid was obtained;

[0111] 4-(Hydroxymethyl)phenylboronic acid (HPBA) and triethanolamine (TEA) were added to 20 ml of N,N-dimethylformamide (DMF) in a molar ratio of 1:1, and heated at 80°C for 2 hours to obtain a nitrogen-containing coordinated borate ester;

[0112] Isophorone diisocyanate and polyetheramine D2000 were mixed with DMF at a molar ratio of 1:1 for 30 minutes to prepare a solution with a solid content of 15%, and DMF was removed to obtain a prepolymer. Finally, a hyperbranched fluid, a nitrogen-containing coordinated borate ester and a prepolymer were mixed at a mass ratio of 3:2:5 to obtain a precursor.

[0113] 3) Porous silicon was added to the precursor, the mass ratio of porous silicon to precursor was 9:2, and then 0.2 g of dibutyltin dilaurate (DBTDL) was added as a catalyst in the solvent DMF and stirred in a water bath at 70°C for 6 hours to obtain a porous silicon and organic gel composite (Si@IPO), and then 20 ml of a 20% by mass graphene oxide (GO) aqueous solution was added, and an appropriate amount of deionized water was added for ultrasonic dispersion for 30 minutes. The mass ratio of the porous silicon and organic gel composite to graphene oxide was 11:2, that is, the mass ratio of porous silicon, precursor, and graphene oxide was 9:2:2. The composite solution was spray dried at a spray drying temperature of 140°C to obtain a negative electrode material (Si@IPO-GO).

[0114] Example 2

[0115] The preparation method is the same as that of Example 1, except that in step 3), the mass ratio of porous silicon, precursor, and graphene oxide is 9:4:2.

[0116] Example 3

[0117] The preparation method is the same as that of Example 1, except that in step 3), the mass ratio of porous silicon, precursor, and graphene oxide is 9:2:4.

[0118] Comparative Example 1

[0119] The preparation method is the same as that in Example 1, except that step 2) is omitted, and in step 3), porous silicon is added to 20 ml of a 20% by mass graphene oxide aqueous solution, ultrasonically dispersed for 30 minutes, and the solution is spray-dried to obtain a negative electrode material (Si@GO), and the proportion of graphene oxide in the negative electrode material is the same as that in the negative electrode material of Example 1.

[0120] Comparative Example 2

[0121] The preparation method is the same as that of Example 1, except that in step 3), graphene oxide is omitted to obtain a negative electrode material (Si@IPO), and the proportion of the organic gel in the negative electrode material is the same as that in Example 1.

[0122] Comparative Example 3

[0123] The preparation method is the same as that of Example 1, except that steps 2) and 3) are omitted, and the porous silicon material in step 1) is used as the negative electrode material.

[0124] The resistivity of the negative electrode material was tested using a four-probe tester, and the results are shown in Table 1.

[0125] Table 1

[0126] sample <![CDATA[Resistivity (ρ) Ωcm -1 > Example 1 (Si@IPO-GO) 99.56 Example 2 150.32 Example 3 87.38 Comparative Example 1 (Si@GO) 180.50 Comparative Example 2 (Si@IPO) 268.40 Comparative Example 3 220.56

[0127] It can be seen from Table 1 that the conductivity of the negative electrode materials of the embodiments of the present invention is improved, and the resistivity of the negative electrode materials Si@IPO-GO of embodiments 1-3 is lower than 160Ωcm -1 , indicating that the negative electrode material obtained by composite of porous silicon, organic gel and graphene oxide has improved conductivity.

[0128] By comparing Example 1, Comparative Example 1 and Comparative Example 3, it can be seen that the resistivity of Si@IPO-GO in Example 1 is lower than the resistivity of Si@GO in Comparative Example 1 and the resistivity of porous silicon in Comparative Example 3. This is because the porous silicon and graphene oxide in Comparative Example 1 are only physically composited, and Comparative Example 3 is only porous silicon, while in Example 1, porous silicon, graphene oxide and IPO organogel are composited, and graphene oxide can form a three-dimensional conductive network in the negative electrode material, providing a fast transmission channel for electrons, further improving the overall conductivity of the silicon material.

[0129] By comparing Example 1, Example 2 and Example 3, it can be seen that the resistivity of Si@IPO in Example 2 is higher than the resistivity of Si@IPO-GO in Example 1 and the resistivity of porous silicon in Example 3. This is because the organic gel causes the conductive performance to deteriorate.

[0130] Figure 1 The negative electrode material Si@IPO-GO of Example 1 is 1Ag -1 Electrochemical cycle performance diagram under charge and discharge current density, the first efficiency of the negative electrode material of Example 1 is 78.3%, at 1Ag -1 At the current density, the reversible specific capacity after 300 cycles is 924 mAh g -1 . Figure 2 The negative electrode material Si@GO of Comparative Example 1 is 1Ag -1Cyclic performance diagram under charge and discharge current density, the reversible specific capacity after 300 cycles is 807 mAh g -1 . Figure 3 The negative electrode material Si@IPO of Comparative Example 2 is 1Ag -1 Cyclic performance diagram under charge and discharge current density. After 300 cycles, the reversible specific capacity is only 638 mAh g -1 The negative electrode material of Example 1 has a higher reversible specific capacity. This is because the negative electrode material of Example 1 includes porous silicon, organic gel and graphene oxide. The porous silicon has a three-dimensional structure. The sheets of graphene oxide are interconnected to form a network. The organic gel can be filled into the pores, so that the pores have active groups distributed inside, and new active sites are generated at the interface, providing abundant sites for the insertion and extraction of lithium ions, thereby improving the specific capacity of the silicon negative electrode material, alleviating volume expansion, improving the conductivity of the negative electrode material, and improving the cycle performance.

[0131] Figure 4 The charge and discharge rate performance diagram of the negative electrode material Si@IPO-GO of Example 1, from 0.1Ag -1 , 0.2Ag -1 , 0.5Ag -1 , 1Ag -1 , 2Ag -1 Back to 0.1Ag -1 The specific capacity of the negative electrode material Si@IPO-GO is still 1252mAhg -1 The negative electrode material of the present invention has good rate performance.

[0132] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0133] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that: The invention comprises porous silicon, organic gel and graphene oxide, wherein the organic gel comprises at least one of self-healing silicon gel, polystyrene gel and polyimide aerogel.

2. The negative electrode material according to claim 1, characterized in that The mass ratio of the porous silicon, the organic gel and the graphene oxide is 9:1-5:1-5; And / or, the particle size of the porous silicon is 500nm-1μm; And / or, the particle size of the negative electrode material is 700nm-2μm.

3. A method for preparing the negative electrode material according to claim 1 or 2, characterized in that: The following steps are involved: (1) grinding and mixing magnesium powder and silicon powder, performing an alloying reaction to obtain an alloying reaction product, cooling, and performing vapor-phase dealloying in an ammonia atmosphere to obtain a vapor-phase dealloying product; immersing the vapor-phase dealloying product in hydrochloric acid, washing and drying to obtain porous silicon; (2) mixing methyl methacrylate, (3-mercaptopropyl)trimethoxysilane, a first catalyst and a solvent to react; removing the solvent after the reaction, dispersing the product in ethanol, adding hydrochloric acid to react; removing the ethanol after the reaction, extracting with water and chloroform, removing chloroform, and obtaining a hyperbranched fluid; (3) reacting 4-(hydroxymethyl)phenylboronic acid and triethanolamine to obtain a nitrogen-containing coordinated borate ester; (4) mixing isophorone diisocyanate and polyetheramine to obtain a prepolymer; then mixing the prepolymer, the hyperbranched fluid and the nitrogen-containing coordinated borate to obtain a precursor; (5) The precursor, porous silicon and a second catalyst are mixed and reacted, and after the reaction, they are mixed with a graphene oxide aqueous solution for compounding, and dried to obtain a negative electrode material.

4. The method for preparing the negative electrode material according to claim 3, characterized in that: In the step (1), the mass ratio of the magnesium powder to the silicon powder is 1-3:1; And / or, the temperature of the alloying reaction is 400-600°C; And / or, the holding time of the alloying reaction is 2-6h; And / or, the alloying reaction is carried out under a protective atmosphere; And / or, the temperature of the vapor phase dealloying is 700-900°C; And / or, the vapor phase dealloying holding time is 4-8h; And / or, the concentration of the hydrochloric acid is 1-3 mol / L; And / or, the temperature of immersing in hydrochloric acid is 40-60°C; And / or, the immersion time in hydrochloric acid is 2-6 hours.

5. The method for preparing the negative electrode material according to claim 3, characterized in that: In the step (2), the mass ratio of methyl methacrylate to (3-mercaptopropyl)trimethoxysilane is 1:0.8-1.2; and / or, the first catalyst comprises azobisisobutyronitrile; and / or, the mass percentage of the first catalyst relative to methyl methacrylate, (3-mercaptopropyl)trimethoxysilane and solvent is 0.1-5%; and / or, the reaction temperature for the mixed reaction is 50-70°C; And / or, the reaction time of the mixed reaction is 6-24h; and / or, the reaction temperature for adding hydrochloric acid to carry out the reaction is 60-80°C; And / or, the reaction time of adding hydrochloric acid for reaction is 12-36 hours.

6. The method for preparing the negative electrode material according to claim 3, characterized in that: In the step (3), the molar ratio of 4-(hydroxymethyl)phenylboric acid to triethanolamine is 1:0.5-2; And / or, the reaction temperature is 60-90°C; And / or, the reaction time is 1-4h.

7. The method for preparing the negative electrode material according to claim 3, characterized in that: In the step (4), the molar ratio of isophorone diisocyanate to polyetheramine is 1-2:1; And / or, the isophorone diisocyanate and the polyetheramine are mixed in a solvent to obtain a mixed solution, wherein the solid content of the mixed solution is 10-25%; And / or, the temperature of the mixed reaction is 10-35°C; And / or, the mixing reaction time is 10-60min; And / or, the mass ratio of the prepolymer, the hyperbranched fluid and the nitrogen-containing coordinated borate ester is 1-5:1-5:1-5.

8. The method for preparing the negative electrode material according to claim 3, characterized in that: In the step (5), the mass ratio of the porous silicon, the precursor and the graphene oxide is 9:1-5:1-5; And / or, the mass fraction of the graphene oxide aqueous solution is 10-30%; and / or, the second catalyst comprises dibutyltin dilaurate; And / or, the mass percentage of the second catalyst relative to the porous silicon is 0.1-4%; And / or, the reaction temperature is 60-80°C; And / or, the reaction time is 4-8h; and / or, mixing with an aqueous solution of graphene oxide and subjecting to ultrasonic treatment; And / or, the drying is carried out by spray drying; And / or, the drying temperature is 120-160°C.

9. An application of a negative electrode material, characterized in that: For lithium-ion batteries, the negative electrode material includes the negative electrode material according to claim 1 or 2 or the negative electrode material prepared by the preparation method according to any one of claims 3-8.

10. A lithium ion battery, characterized in that: The invention comprises a negative electrode material, wherein the negative electrode material comprises the negative electrode material according to claim 1 or 2 or the negative electrode material prepared by the preparation method according to any one of claims 3 to 8.

Images