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

Abstract

The application relates to a negative electrode material and a preparation method thereof and a lithium ion battery, wherein the negative electrode material comprises hollow carbon and silicon material between the hollow carbon, the hollow carbon comprises a hollow core and a carbon shell layer, the carbon shell layer has holes, and the carbon shell layer comprises a plurality of single-layer graphene, and the plurality of single-layer graphene are arranged in a stacked mode along the radial direction of the hollow carbon. In the negative electrode material, the hollow carbon has the hollow core in the inside and the holes on the surface of the carbon shell layer, so that the negative electrode material can reserve sufficient space to bear the expansion stress of lithium intercalation, thereby improving the anti-expansion performance and cycle performance of the negative electrode material; further, the silicon material is filled between the hollow carbon, the space utilization of the negative electrode material is improved, and the capacity of the negative electrode material is also improved.

Description

Technical Field

[0001] This application belongs to the field of negative electrode material technology, specifically, it relates to negative electrode materials and their preparation methods, and lithium-ion batteries. Background Technology

[0002] Porous carbon anode materials are among the most critical materials for improving the cycle expansion performance of lithium-ion batteries. Existing commonly used porous carbon anode materials achieve lithium loading and suppress the resulting volume expansion through their large internal cavities or porous structures. These porous carbon materials are often synthesized through simple high-temperature carbonization. The porous structure formed directly through high-temperature carbonization has a discontinuous graphite lattice structure. This structure reduces the mechanical properties of the carbon material itself and the van der Waals forces between carbon particles due to the π-π stacking of graphite. This results in the pores and gaps between particles being unable to withstand the expansion stress of lithium intercalation. Therefore, additional binders need to be added to the anode material, which to some extent reduces the energy density of the porous carbon anode material. Simultaneously, porous carbon anode materials often require thick pore walls to provide sufficient mechanical strength, which also reduces carbon utilization efficiency and is detrimental to capacity utilization.

[0003] Therefore, there is an urgent need for a high-capacity, low-expansion anode material. Summary of the Invention

[0004] In order to overcome the above-mentioned defects, this application provides an anode material and its preparation method, as well as a lithium-ion battery. The anode material of this application can improve the carbon utilization efficiency in the material, further improve the capacity and cycle capability of the material, and also has excellent anti-expansion performance.

[0005] In a first aspect, embodiments of this application provide a negative electrode material, characterized in that the negative electrode material includes hollow carbon and silicon material located between the hollow carbons, the hollow carbon includes a hollow core and a carbon shell, the carbon shell has pores, the carbon shell includes a plurality of monolayer graphenes, and the plurality of monolayer graphenes are stacked along the radial direction of the hollow carbon.

[0006] In some embodiments, layered graphite is disposed between the hollow carbon atoms.

[0007] In some embodiments, at least a portion of the pores penetrate the carbon shell.

[0008] In some embodiments, the median particle size of the hollow carbon is 5 nm to 200 nm.

[0009] In some embodiments, the number of graphene layers in the carbon shell is 4 to 15.

[0010] In some embodiments, the thickness of the carbon shell is 1.2 nm to 5.2 nm.

[0011] In some embodiments, the carbon shell is shown in a Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532 nm, at 1300 nm. -1 Up to 1400 -1 D band was observed and at 1500 -1 ~1600 -1 The peak intensity I of the G band and the D band was observed. D And the peak intensity I of the G-band G The ratio between I G / I D Greater than 0.5.

[0012] In some embodiments, the average pore size of the hollow core is 3.8 nm to 198.8 nm.

[0013] In some embodiments, the average pore diameter is 0.42 nm to 2 nm.

[0014] In some embodiments, the distance between adjacent hollow carbon atoms is 0 nm to 40 nm.

[0015] In some embodiments, the sphericity of the hollow carbon is 0.6 to 1.

[0016] In some embodiments, the silicon material accounts for 5% to 80% of the mass of the anode material.

[0017] In some embodiments, the median particle size of the silicon material is 1 nm to 15 nm.

[0018] In some embodiments, the silicon material includes at least one of crystalline silicon and amorphous silicon.

[0019] In some embodiments, the hollow carbon has an elastic modulus of 0.1 TPa to 0.8 TPa.

[0020] In some embodiments, the hollow carbon has a tensile strength of 15 GPa to 110 GPa.

[0021] In some embodiments, the porosity of the hollow carbon is 65% to 96%.

[0022] In some embodiments, the porosity of the negative electrode material is 7% to 50%.

[0023] In some embodiments, the π-π packing van der Waals forces between adjacent hollow carbon atoms are 1 kJ / mol to 50 kJ / mol.

[0024] Secondly, embodiments of this application provide a method for preparing a negative electrode material, comprising the following steps: A mixture of silicon-oxygen raw material containing supported metal catalyst particles and a carbon source is subjected to a first heat treatment to catalyze the graphitization of the carbon source, thereby obtaining a first precursor. The first precursor is etched to obtain the second precursor, wherein the etchant used in the etching process is an oxidizing acid; At least a portion of the silicon-oxygen raw material in the second precursor is reduced to silicon material to obtain the negative electrode material.

[0025] In some embodiments, the silicon-oxygen raw material supported on metal catalyst particles is prepared by the following method: The mixture containing silicon-oxygen raw materials and metal salt catalysts is subjected to a third heat treatment in a reducing atmosphere to obtain silicon-oxygen raw materials loaded with metal catalyst particles.

[0026] In some embodiments, the silicon-oxygen raw material includes at least one of silicon dioxide and silicon monoxide.

[0027] In some embodiments, the median particle size of the silicon-oxygen raw material is 5 nm to 200 nm.

[0028] In some embodiments, the metal salt catalyst comprises Fe 3+ Co 2+ Ni 2+ Cu 2+ and Au 3+ At least one of them.

[0029] In some embodiments, the metal salt catalyst includes at least one of Fe(NO3)3, FeCl3, Co(NO3)2, CoCl2, Ni(NO3)2, NiCl2, Cu(NO3)2, CuCl2, and HAuCl4.

[0030] In some embodiments, the mass ratio of the silicon-oxygen raw material to the metal salt catalyst is 1:(0.08~5.00).

[0031] In some embodiments, the mixture containing silicon-oxygen raw materials and metal salt catalysts also includes a solvent.

[0032] In some embodiments, the mixture containing silicon-oxygen raw materials and metal salt catalysts further includes a solvent, which includes at least one of methanol, ethanol, propanol, and water.

[0033] In some embodiments, the mixture containing silicon-oxygen raw materials and metal salt catalysts further includes a solvent, wherein the amount of solvent added is 50 to 1000 times the total mass of the silicon-oxygen raw materials and metal salt catalysts.

[0034] In some embodiments, the mixture containing silicon-oxygen raw materials and metal salt catalysts further includes steps of drying and grinding the mixture before undergoing a second heat treatment.

[0035] In some embodiments, the reducing atmosphere includes at least one of hydrogen and ammonia.

[0036] In some embodiments, the flow rate of the reducing atmosphere is 10 sccm to 150 sccm.

[0037] In some embodiments, the temperature of the second heat treatment is 400°C to 1000°C.

[0038] In some embodiments, the holding time for the second heat treatment is 5 min to 30 min.

[0039] In some embodiments, the heating rate of the second heat treatment is 100°C / h to 1200°C / h.

[0040] In some embodiments, the carbon source includes a gaseous carbon source and a solid carbon source.

[0041] In some embodiments, the carbon source includes a gaseous carbon source and a solid carbon source, wherein the gaseous carbon source includes at least one of methane, ethane, and acetylene.

[0042] In some embodiments, the carbon source includes a gaseous carbon source and a solid carbon source, wherein the solid carbon source includes at least one selected from pitch, glucose, sucrose, cellulose, glycine, alanine, and phenylalanine.

[0043] In some embodiments, the carbon source includes a gaseous carbon source and a solid carbon source, wherein the mass ratio of the solid carbon source to the metal catalyst particles is 1:(10~10000).

[0044] In some embodiments, the carbon source includes a gaseous carbon source and a solid carbon source, wherein the flow rate of the gaseous carbon source is 10 sccm to 250 sccm.

[0045] In some embodiments, the temperature of the first heat treatment is 600°C to 1000°C.

[0046] In some embodiments, the holding time for the first heat treatment is 1 min to 30 min.

[0047] In some embodiments, prior to subjecting the mixture of silicon-oxygen feedstock containing supported metal catalyst particles and carbon source to a first heat treatment, the method further includes introducing hydrogen gas into the mixture of silicon-oxygen feedstock containing supported metal catalyst particles and carbon source.

[0048] In some embodiments, prior to subjecting the mixture of silicon-oxygen raw material containing supported metal catalyst particles and carbon source to a first heat treatment, the method further includes: introducing hydrogen gas into the mixture of silicon-oxygen raw material containing supported metal catalyst particles and carbon source, wherein the hydrogen gas flow rate is 10 sccm to 90 sccm.

[0049] In some embodiments, the oxidizing acid includes at least one of sulfuric acid, nitric acid, and hydrogen peroxide.

[0050] In some embodiments, the oxidizing acid includes a mixture of sulfuric acid and nitric acid.

[0051] In some embodiments, the oxidizing acid includes a mixture of sulfuric acid and nitric acid, wherein the concentration of sulfuric acid in the mixture is 0.1 mol / L to 4 mol / L.

[0052] In some embodiments, the oxidizing acid includes a mixture of sulfuric acid and nitric acid, wherein the concentration of nitric acid in the mixture is 0.1 mol / L to 4 mol / L.

[0053] In some embodiments, the etching process takes 2 hours to 24 hours.

[0054] In some embodiments, before at least a portion of the silicon-oxygen raw material in the second precursor is reduced to silicon material, the method further includes: performing solid-liquid separation on the second precursor, and subjecting the resulting solid to a first water wash and a first drying step.

[0055] In some embodiments, reducing at least a portion of the silicon-oxygen raw material in the second precursor to silicon material includes the step of mixing the second precursor with a reducing agent and then subjecting it to a third heat treatment.

[0056] In some embodiments, the reducing agent includes at least one of metallic magnesium and metallic aluminum.

[0057] In some embodiments, the mass ratio of the second precursor to the reducing agent is (1.25~2.00):1.

[0058] In some embodiments, the third heat treatment is performed in an inert gas atmosphere.

[0059] In some embodiments, the third heat treatment is carried out in an inert gas atmosphere, the inert gas including at least one of nitrogen and argon.

[0060] In some embodiments, the temperature of the third heat treatment is 600°C to 800°C.

[0061] In some embodiments, the holding time for the third heat treatment is 0.5 h to 5 h.

[0062] In some embodiments, the third heat treatment of the second precursor and reducing agent further includes inerting the material obtained from the third heat treatment.

[0063] In some embodiments, the third heat treatment of the second precursor and the reducing agent further includes inerting the material obtained from the third heat treatment, wherein the inerting gas includes ammonia.

[0064] In some embodiments, the third heat treatment of the second precursor and reducing agent further includes: inerting the material obtained from the third heat treatment, and then subjecting the inerted material to acid washing, a second water washing, and a second drying.

[0065] Thirdly, embodiments of this application provide a lithium-ion battery, the lithium-ion battery comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method described in the second aspect.

[0066] The technical solution of this application has at least the following beneficial effects: In the negative electrode material of this application, the hollow carbon has a hollow core located inside the carbon shell and pores located on the surface of the carbon shell. The presence of the hollow core and pores makes the hollow carbon a porous hollow shell. The carbon shell includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. Therefore, the carbon shell has excellent elastic modulus and tensile strength, which helps it not break during deformation and can recover its shape after shrinkage. This structure can reserve sufficient space for the expansion of the filled silicon material. When the silicon material expands and compresses the hollow carbon, the hollow carbon discharges internal gas or electrolyte through the pores on the carbon shell to form deformation to withstand the expansion stress of lithium insertion. When the silicon material delithiates and shrinks, the deformed hollow carbon absorbs gas or electrolyte through the pores on the carbon shell and recovers its shape, thereby improving the expansion resistance and cycle performance of the negative electrode material. Furthermore, the filling of silicon material between the hollow carbons increases the utilization space of the negative electrode material and also increases the capacity of the negative electrode material. The anode material of this application can improve the carbon utilization efficiency in the material, further improve the capacity and cycle capability of the material, and also has excellent anti-expansion properties.

[0067] This application involves subjecting a mixture of silicon-oxygen raw material containing catalyst-supported metal particles and a carbon source to a first heat treatment. During the first heat treatment, the carbon source undergoes graphitization and decomposition to generate carbon atoms. Some of these carbon atoms can dissolve inside the catalyst metal particles. Once the dissolution reaches saturation, they precipitate on the catalyst surface. The precipitated carbon atoms grow to form a carbon shell. Other carbon atoms can grow along the surface of the metal particles under the catalytic action of the catalyst metal particles to form a carbon shell, thus creating a structure in which the catalyst metal particles are encapsulated within the carbon shell. Since the silicon-oxygen raw material has poor catalytic ability for the carbon source material, it is distributed outside the carbon shell and dispersed between the metal particles encapsulated in the carbon shell, thereby obtaining the first precursor. The first precursor is then etched to remove the catalyst metal particles inside the carbon shell, forming a hollow core. Simultaneously, the oxidizing acid from the etching process reacts with the defects in the carbon shell to form CO, C=O, CN, and CS bonds, creating pores and resulting in porous hollow carbon (the second precursor). Finally, at least a portion of the silicon-oxygen raw material in the second precursor is reduced to silicon to obtain the anode material. In the preparation method of this application, under the first heat treatment conditions, the carbon source is catalytically grown into a shell structure using metal catalyst particles. Further etching creates a hollow core and porous carbon shell, increasing the material's resistance to expansion. Finally, this application eliminates the need for etching the silicon-oxygen raw material, directly reducing its reduction to silicon and increasing the anode material's capacity. Attached Figure Description

[0068] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0069] Figure 1 This is a schematic diagram of the structure of the negative electrode material in this application; Figure 2 This is a schematic diagram of the structure of hollow carbon. Figure 3 This is a flowchart illustrating the preparation process of the negative electrode material in this application; Figure 4 This is a diagram illustrating the preparation process of the first precursor obtained by subjecting silicon-oxygen raw materials and carbon sources supported on metal catalyst particles to a first heat treatment in this application. Figure 5 The preparation process of the silicon-oxygen feedstock supported on metal catalyst particles as described in this application Figure 1 ; Figure 6 The preparation process of the silicon-oxygen feedstock supported on metal catalyst particles as described in this application Figure 2 ; Figure 7 This is a diagram illustrating the process of etching the first precursor to obtain the second precursor in this application. Figure 8 This diagram illustrates the preparation process of obtaining the negative electrode material by mixing the second precursor and the reducing agent followed by a third heat treatment. Figure 9 This is a schematic diagram of the simulated structure of the negative electrode material of this application.

[0070] In the attached image: 10- Anode material; 1-Hollow carbon; 11-Hollow kernel; 12-Carbon shell; 13-hole; 14-Monolayer graphene; 2-Silicon materials. Detailed Implementation

[0071] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0072] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0073] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0074] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0075] This application provides a negative electrode material 10, such as Figure 1 As shown, the negative electrode material 10 includes hollow carbon 1 and silicon material 2 located between the hollow carbon 1. The hollow carbon 1 includes a hollow core 11 and a carbon shell 12. The carbon shell 12 has pores 13 and includes a plurality of monolayer graphene 14. The plurality of monolayer graphene 14 are stacked along the radial direction of the hollow carbon 1.

[0076] In the above scheme, the hollow carbon 1 in the negative electrode material 10 of this application has a hollow core 11 located inside the carbon shell 12 and a hole 13 located on the surface of the carbon shell 12. The presence of the hollow core 11 and the hole 13 makes the hollow carbon 1 a porous hollow shell. The carbon shell 12 includes a plurality of monolayer graphene 14, which are stacked along the radial direction of the hollow carbon 1. Therefore, the carbon shell 12 has excellent elastic modulus and tensile strength, which helps to prevent cracking and shrinkage to restore the shape when deformation occurs. This structure can reserve enough space for the expansion of the filled silicon material 2. When the silicon material 2 expands and compresses the hollow carbon 1, the hollow carbon 1 discharges internal gas / electrolyte through the pores 13 on the shell to form deformation to withstand the expansion stress of lithium intercalation; when the silicon material delithiates and shrinks, the deformed hollow carbon 1 absorbs gas / electrolyte through the pores 13 on the shell and restores its shape, so that the negative electrode material 10 can reserve enough space to withstand the expansion stress of lithium intercalation, thereby improving the expansion resistance and cycle performance of the negative electrode material 10; furthermore, the silicon material 2 is filled between the hollow carbon 1, which increases the utilization space of the negative electrode material 10 and also increases the capacity of the negative electrode material 10.

[0077] Schematic diagram of hollow carbon 1 (see reference) Figure 2 Multiple single-layer graphene 14 in the carbon shell layer 12 are stacked, with the stacking direction along the radial direction of the hollow carbon 1. That is, the length direction of the graphene sheet is consistent with the extension direction of the carbon shell layer 12 and perpendicular to the radial direction of the hollow carbon 1. The thickness direction of the graphene sheet (i.e. the stacking direction) is perpendicular to the extension direction of the carbon shell layer and consistent with the radial direction of the hollow carbon.

[0078] In some embodiments, layered graphite is disposed between the hollow carbon 1s. The presence of the layered graphite structure can strengthen the conductive network of the negative electrode material 10, thereby improving the conductivity of the negative electrode material 10.

[0079] In some embodiments, at least some of the pores 13 penetrate the carbon shell 12, giving the negative electrode material 10 a larger pore volume, which is beneficial to improving the anti-expansion performance of the negative electrode material.

[0080] In some embodiments, the hollow carbon 1 includes graphite, that is, the negative electrode material 10 of this application includes hollow graphite particles with holes 13 on them. The holes 13 penetrate the graphite particles and communicate with the hollow part of the graphite particles. The spaces between the graphite particles are filled with silicon material 2.

[0081] In some embodiments, the median particle size of hollow carbon 1 is 5 nm to 200 nm. Specifically, the median particle size of hollow carbon 1 can be, for example, 5 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm and 200 nm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0082] In some embodiments, the thickness of the carbon shell 12 is 1.2 nm to 5.2 nm. Specifically, the thickness of the carbon shell 12 can be, for example, 1.2 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 5 nm and 5.2 nm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0083] In some embodiments, the number of graphene layers in the carbon shell 12 is 4 to 15. Specifically, the number of graphene layers in the carbon shell 12 can be, for example, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 layers, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0084] In this application, the thickness of the carbon shell 12 is 1.2 nm to 5.2 nm, and the number of graphene layers in the carbon shell 12 is 4 to 15, indicating that the carbon shell 12 in this application has both a certain rigidity and a certain elasticity, and can resist the volume expansion caused by lithium intercalation in the material.

[0085] In some embodiments, the negative electrode material is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532 nm, at 1300 cm⁻¹. -1 Up to 1400 -1 D band was observed and at 1500 -1 ~1600 -1 The peak intensity I of the G band and the D band was observed. D And the peak intensity I of the G-band G The ratio between I G / I D Greater than 0.5. Specifically, I G / I D The values ​​can be 0.6, 0.7, 0.8, and 0.9, or other values ​​within the above range, which are not limited herein. Within the above-defined range, it indicates that the graphitization degree of the negative electrode material of this application is relatively high, resulting in strong π-π stacking van der Waals forces between the hollow carbon atoms. This structure can resist the expansion stress generated by lithium intercalation, thereby leveraging the ability of the pores between the hollow carbon atoms to intercalate lithium and improving the carbon utilization efficiency.

[0086] In some embodiments, the average pore size of the hollow core 11 is 3.8 nm to 198.8 nm. Specifically, the average pore size of the hollow core 11 can be, for example, 3.8 nm, 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm and 198.8 nm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0087] In some embodiments, the average pore size of the pore 13 is 0.42 nm to 2 nm. Specifically, the average pore size of the pore 13 can be 0.42 nm, 0.5 nm, 1 nm, 1.5 nm, 1.8 nm and 2 nm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0088] In some embodiments, the distance between adjacent hollow carbons 1 is 0 nm to 40 nm. Specifically, the distance between adjacent hollow carbons 1 can be, for example, 0.34 nm, 1 nm, 5 nm, 10 nm, 20 nm, 30 nm and 40 nm, etc. Of course, it can also be other values ​​within the above range. This application does not limit it here. In the negative electrode material 10 of this application, the distance between adjacent hollow carbons 1 is relatively close, which is beneficial to reduce the formation of bulk lithium during the lithium intercalation process and the leakage of silicon material 2 during the lithium delithiation process.

[0089] In some embodiments, the sphericity of the hollow carbon 1 is 0.6 to 1.0. Specifically, the sphericity of the hollow carbon 1 can be 0.6, 0.7, 0.8, 0.9, and 1.0, etc., and of course, it can also be other values ​​within the above range. This application does not impose any limitations on this. The hollow carbon 1 of this application has a high sphericity, which is beneficial to improving the processing performance of the material.

[0090] In some embodiments, the mass percentage of silicon material 2 in the negative electrode material 10 is 5% to 80%. Specifically, the mass percentage of silicon material 2 in the negative electrode material 10 can be, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80%, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0091] In some embodiments, the median particle size of silicon material 2 is 1 nm to 15 nm. For example, the median particle size of silicon material 2 can be 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 14 nm and 15 nm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0092] In some embodiments, the silicon material 2 includes at least one of crystalline silicon and amorphous silicon.

[0093] In some embodiments, the elastic modulus of hollow carbon 1 is 0.1 TPa to 0.8 TPa. Specifically, the elastic modulus of hollow carbon 1 can be, for example, 0.1 TPa, 0.2 TPa, 0.3 TPa, 0.4 TPa, 0.5 TPa, 0.6 TPa, 0.7 TPa and 0.8 TPa, etc. Of course, it can also be other values ​​within the above range. This application does not limit it here. If the elastic modulus is too small, the hollow carbon is easy to collapse. If the elastic modulus is too large, the rigidity of the hollow carbon increases, making it difficult to provide space for lithium intercalation expansion.

[0094] In some embodiments, the tensile strength of hollow carbon 1 is 15 GPa to 110 GPa. Specifically, the tensile strength of hollow carbon 1 can be, for example, 15 GPa, 30 GPa, 50 GPa, 60 GPa, 80 GPa, 100 GPa, and 110 GPa, etc., and of course, other values ​​within the above range are also possible, which are not limited herein. Within the above range, the hollow carbon 1 of this application has superior mechanical properties. This is because the shell thickness of the hollow carbon 1 of this application is relatively thin, the degree of graphitization is high, and the close distance between the hollow carbon 1 particles gives it strong π-π stacking van der Waals forces, thereby giving the gap structure between the hollow carbon 1 particles good stability. This stability can resist the expansion stress generated by lithium intercalation, thereby giving full play to the ability of interparticle porosity lithium intercalation and improving carbon utilization efficiency. If the tensile strength of hollow carbon 1 is too low, the hollow carbon is easy to break during lithium intercalation expansion; if the tensile strength is too high, it is difficult to provide space for lithium intercalation expansion.

[0095] In some embodiments, the porosity of hollow carbon 1 is 65% to 96%. Specifically, the porosity of hollow carbon 1 can be, for example, 65%, 70%, 75%, 80%, 85%, 90%, and 96%, etc. Of course, it can also be other values ​​within the above range. This application does not limit it here. It can be understood that the porosity of hollow carbon 1 refers to the volume ratio of hollow core 11 and pore 13 in hollow carbon 1.

[0096] In some embodiments, the porosity of the negative electrode material 10 is 7% to 50%. Specifically, the porosity of the negative electrode material 10 can be, for example, 7%, 10%, 15%, 20%, 30%, 40%, and 50%, etc., and of course, other values ​​within the above range are also possible. This application does not impose any limitations on this. It can be understood that the porosity of the negative electrode material 10 refers to the volume percentage of the voids between the pores 13 and the hollow carbon 1 in the negative electrode material 10. The negative electrode material 10 of this application has a relatively large porosity, which gives the negative electrode material 10 excellent resistance to expansion.

[0097] In some embodiments, the π-π packing van der Waals force between adjacent hollow carbon 1s is 1 kJ / mol to 50 kJ / mol. Specifically, the π-π packing van der Waals force between adjacent hollow carbon 1s is 1 kJ / mol, 5 kJ / mol, 10 kJ / mol, 20 kJ / mol, 30 kJ / mol, 40 kJ / mol, and 50 kJ / mol, etc. Of course, other values ​​within the above range are also possible, and this application does not impose any limitations. The hollow carbon 1s of this application have strong π-π packing van der Waals forces, which enable the gaps between the hollow carbon 1s to withstand the expansion stress of lithium intercalation, and no additional binder is required, thereby improving the energy density of the negative electrode material 10.

[0098] This application also provides a method for preparing the above-mentioned negative electrode material 10, such as... Figure 3 The diagram shown is a flowchart of the preparation process of the negative electrode material 10 of this application, which includes the following steps: A mixture of silicon-oxygen raw material containing supported metal catalyst particles and a carbon source is subjected to a first heat treatment to catalytically graphitize the carbon source, thereby obtaining a first precursor.

[0099] The first precursor is etched to obtain the second precursor. The etchant used in the etching process includes an oxidizing acid.

[0100] At least a portion of the silicon-oxygen raw material in the second precursor is reduced to silicon material to obtain anode material 10.

[0101] In the above scheme, this application performs a first heat treatment on a mixture of silicon-oxygen raw material containing catalyst metal particles and a carbon source. During the first heat treatment, the carbon source is graphitized and cracked to produce carbon atoms. Some of the carbon atoms can dissolve inside the catalyst metal particles. After the dissolution reaches saturation, they precipitate on the catalyst surface. The precipitated carbon atoms grow to form a carbon shell 12. Other carbon atoms can grow along the surface of the metal particles under the catalytic action of the catalyst metal particles to form a carbon shell 12, thereby forming a structure in which the catalyst metal particles are encapsulated inside the carbon shell 12. Since the silicon-oxygen raw material has poor catalytic ability for the carbon source material, the silicon-oxygen raw material is distributed outside the carbon shell 12 and dispersed between the metal particles encapsulated by the carbon shell 12, thus obtaining the first precursor. The first precursor is then etched to remove the catalyst metal particles inside the carbon shell, forming a hollow core 11. Simultaneously, the oxidizing acid from the etching process reacts with the defects in the carbon shell 12 via a redox reaction, gradually stripping away carbon atoms to form pores 13. Upon termination of the redox reaction, CO, C=O, CN, and CS bonds are formed at the pore edges, creating a porous hollow carbon 1 (i.e., the second precursor). Finally, at least a portion of the silicon-oxygen raw material in the second precursor is reduced to silicon material to obtain the anode material 10. In the preparation method of this application, under the first heat treatment conditions, the carbon source is catalytically grown into a shell structure using metal catalyst particles. This shell structure has a large pore volume and lithium intercalation capability. Further etching ensures that the carbon shell 12 structure has a hollow core 11 and pores 13, thereby increasing the material's resistance to expansion. Finally, this application eliminates the need for etching the silicon-oxygen raw material, directly reducing it to silicon material 2, thus reducing waste of silicon-oxygen raw materials while increasing the capacity of the anode material 10.

[0102] The preparation method of this application is described in detail below with reference to the embodiments: Step S100, as follows Figure 4 As shown, a mixture of silicon-oxygen raw material containing supported metal catalyst particles and a carbon source is subjected to a first heat treatment to catalytically graphitize the carbon source, thereby obtaining a first precursor.

[0103] In some implementations, the carbon source includes a gaseous carbon source and a solid carbon source.

[0104] In some embodiments, the gaseous carbon source includes at least one of methane, ethane, and acetylene.

[0105] In some embodiments, the solid carbon source includes at least one selected from pitch, glucose, sucrose, cellulose, glycine, alanine, and phenylalanine. When a solid carbon source is used for the first heat treatment, the poorer uniformity of the solid carbon source compared to the gaseous carbon source leads to localized carbon source excess, thereby forming a layered graphite structure between the hollow carbon 1s. The presence of this layered graphite structure strengthens the conductive network of the negative electrode material 10, thereby improving the conductivity of the negative electrode material 10.

[0106] In some embodiments, the mass ratio of solid carbon source to metal catalyst particles is 1:(10~10000). Specifically, the mass ratio can be, for example, 1:10, 1:50, 1:100, 1:500, 1:1000, 1:500, 1:1000, 1:5000, and 1:10000, or other values ​​within the above range. This application does not impose any limitations on these values. Within the above-defined range, a higher amount of metal catalyst particles is beneficial for the formation of a thinner shell structure on the surface of the metal catalyst particles from the carbon source. If the mass ratio of solid carbon source to metal catalyst particles is greater than 1:10, it will lead to the formation of excessive amorphous carbon, which is detrimental to the improvement of material performance. If the mass ratio of solid carbon source to metal catalyst particles is less than 1:10000, the amount of carbon source added is too small, and the carbon source cannot completely coat the metal catalyst particles.

[0107] In some embodiments, the flow rate of the gaseous carbon source is 10 sccm to 250 sccm. Specifically, the flow rate of the gaseous carbon source is 10 sccm, 30 sccm, 50 sccm, 100 sccm, 150 sccm, 200 sccm, and 250 sccm, etc. Of course, other values ​​within the above range are also possible, and this application does not impose any limitations on them. It is understood that increasing the flow rate of the gaseous carbon source will increase the number and thickness of the graphene layers in the carbon shell 11, thereby increasing the tensile strength and elastic modulus of the carbon shell 11. If the flow rate is greater than 250 sccm, the carbon shell grows faster, has more defects, and both the tensile modulus and elastic modulus will decrease.

[0108] In some embodiments, the temperature of the first heat treatment is 600°C to 1000°C. Specifically, the temperature of the first heat treatment can be, for example, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, and 1000°C, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0109] In some embodiments, the holding time of the first heat treatment is 1 min to 30 min. Specifically, the holding time of the first heat treatment can be, for example, 1 min, 5 min, 10 min, 20 min and 30 min, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0110] In some embodiments, hydrogen gas is introduced during the first heat treatment process, with a flow rate of 10 ccm to 290 sccm. For example, the flow rate can be 10 sccm, 30 sccm, 50 sccm, 80 sccm, and 90 sccm, or other values ​​within the aforementioned range. This application does not impose any limitations on these values. Controlling the hydrogen flow rate within the above range can slow down carbon source decomposition, reduce the concentration of decomposed carbon atoms, thereby slowing down the rate of graphene layer formation and reducing the defect site content, thus controlling the Ig of the negative electrode material. D / I G Greater than 0.5.

[0111] In some embodiments, the silicon-oxygen feedstock supported on metal catalyst particles is prepared by the following method: A mixture containing silicon-oxygen raw materials and metal salt catalysts is subjected to a second heat treatment in a reducing atmosphere to obtain silicon-oxygen raw materials loaded with metal catalyst particles. Specifically, such as... Figure 5 As shown, the mixture containing silicon-oxygen raw materials and metal salt catalysts includes the following steps: The solvent, silicon-oxygen raw material and metal salt catalyst are mixed to obtain a mixture. The mixture is then dried and ground to obtain a silicon-oxygen raw material loaded with metal catalyst particles. It can be understood that the material obtained after drying is a blocky solid, which needs to be ground into powder for later use.

[0112] In this step, such as Figure 6 As shown, by reducing catalyst metal ions in a mixture containing silicon-oxygen raw materials and metal salt catalysts to catalyst metal nanoparticles in a reducing atmosphere, on the one hand, the silicon-oxygen raw material acts as a template agent, providing loading sites for the metal salt catalyst; on the other hand, the silicon-oxygen raw material acts as a dispersant, restricting the fusion of metal nanoparticles during the reduction and growth of catalyst metal ions into metal nanoparticles, thus giving the catalyst metal nanoparticles a relatively uniform and controllable size. Of course, this application can also obtain silicon-oxygen raw materials loaded with metal catalyst particles through other conventional methods. For example, metal catalyst particles can be directly mixed with silicon-oxygen raw materials using dry or wet processes. This application does not impose any limitations here, wherein the metal catalyst particles include at least one of iron, cobalt, nickel, copper, gold, iron alloys, cobalt alloys, nickel alloys, copper alloys, and gold alloys.

[0113] In some embodiments, the silicon-oxygen raw material includes at least one of silicon dioxide and silicon monoxide.

[0114] In some embodiments, the median particle size of the silicon-oxygen raw material is 5 nm to 200 nm. Specifically, the median particle size of the silicon-oxygen raw material can be, for example, 5 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm and 200 nm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0115] In some embodiments, the metal salt catalyst includes Fe 3+ Co 2+ Ni 2+ Cu 2+ and Au 3+ At least one of the following. For example, the metal salt catalyst includes at least one of Fe(NO3)3, FeCl3, Co(NO3)2, CoCl2, Ni(NO3)2, NiCl2, Cu(NO3)2, CuCl2 and HAuCl4.

[0116] In some embodiments, the mass ratio of silicon-oxygen raw material to metal salt catalyst is 1:(0.08~5). Specifically, the mass ratio of silicon-oxygen raw material to metal salt catalyst can be 1:0.08, 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4 and 1:5, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0117] In some embodiments, the solvent includes at least one of methanol, ethanol, propanol, and water.

[0118] In some embodiments, the amount of solvent added is 50 to 1000 times the total mass of the silicon-oxygen raw material and the metal salt catalyst. Specifically, the amount of solvent added is 50, 100, 200, 500, 700, 800, 900, and 1000 times the total mass of the silicon-oxygen raw material and the metal salt catalyst, etc. Of course, other values ​​within the above range are also possible, and this application does not limit them.

[0119] In some embodiments, the mixing method includes at least one of grinding and ultrasonication. For example, the ultrasonic power is 40 W to 50 W, and the ultrasonic power can be, for example, 40 W, 42 W, 45 W, 48 W, and 50 W, etc., or other values ​​within the above range, which are not limited herein. The ultrasonic holding time is 0.5 h to 5 h, and the ultrasonic holding time can be, for example, 0.5 h, 1 h, 2 h, 3 h, 4 h, and 5 h, etc., or other values ​​within the above range, which are not limited herein. Within the above range, sufficient mixing of the silicon-oxygen raw material and the metal salt catalyst can be ensured, which is beneficial for forming a silicon-oxygen material with uniformly loaded metal salt catalyst particles.

[0120] In some implementations, the drying method includes evaporative drying.

[0121] In some embodiments, the reducing atmosphere includes at least one of hydrogen and ammonia.

[0122] In some embodiments, the flow rate of the reducing atmosphere is 10 sccm to 150 sccm. Specifically, the flow rate of the reducing atmosphere can be, for example, 10 sccm, 30 sccm, 50 sccm, 80 sccm, 100 sccm, 120 sccm and 150 sccm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0123] In some embodiments, the temperature of the second heat treatment is 400°C to 1000°C. Specifically, the temperature of the second heat treatment can be, for example, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, and 1000°C, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0124] In some embodiments, the holding time of the second heat treatment is 5 min to 30 min. Specifically, the holding time of the second heat treatment can be, for example, 5 min, 10 min, 15 min, 20 min, 25 min and 30 min, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0125] In some embodiments, the heating rate of the second heat treatment is 100℃ / h to 1200℃ / h. Specifically, the heating rate of the second heat treatment is 100℃ / h, 300℃ / h, 500℃ / h, 800℃ / h, 1000℃ / h, and 1200℃ / h, etc. Of course, other values ​​within the above range are also possible, and this application does not limit them.

[0126] Step S200, such as Figure 7As shown, the first precursor is etched to obtain the second precursor. The etchant used in the etching process includes an oxidizing acid. The second precursor includes hollow carbon 1, which includes a hollow core 11 and a carbon shell 12. The carbon shell 12 has pores 13, and the spaces between the hollow carbon 1 are filled with silicon-oxygen material.

[0127] In some embodiments, the oxidizing acid includes at least one of sulfuric acid, nitric acid, and hydrogen peroxide. On one hand, using the oxidizing acid, the catalyst metal particles inside the carbon shell 12 can be etched away, thereby forming a hollow core 11. On the other hand, the oxidizing acid can react with the defects in the hollow carbon 1 through redox reactions to form bonds such as CO, C=O, CN, and CS, forming pores 13. For example, for metal catalyst particles made of materials that are difficult to corrode, such as iron, cobalt, iron alloys, and cobalt alloys, a mixed acid of sulfuric acid and nitric acid is used as the etchant for etching. If necessary, heat treatment can be performed during the etching process to improve the corrosion effect.

[0128] In some embodiments, the concentration of sulfuric acid in the mixed acid is 0.1 mol / L to 4 mol / L. Specifically, the concentration of sulfuric acid in the mixed acid is 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L, etc. Of course, other values ​​within the above range are also possible, and this application does not limit them.

[0129] In some embodiments, the concentration of nitric acid in the mixed acid is 0.1 mol / L to 4 mol / L. Specifically, the concentration of nitric acid in the mixed acid is 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L, etc. Of course, other values ​​within the above range are also possible, and this application does not limit them.

[0130] In some embodiments, the etching process takes 2 hours to 24 hours. Specifically, the etching process takes 2 hours, 5 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, and 24 hours, etc. Of course, other values ​​within the above range are also possible, and this application does not limit them.

[0131] In some embodiments, the material obtained after etching is a solid-liquid mixture, and the material obtained after etching needs to be separated into solid and liquid phases. The obtained solid is then subjected to a first water wash and a first drying to obtain a second precursor. The second precursor includes hollow carbon 1. A hollow core 11 is etched into the interior of the shell structure of hollow carbon 1, and holes 13 are etched into the surface of the shell structure of hollow carbon 1, which can reserve sufficient space to withstand the expansion stress of lithium intercalation, thereby improving the expansion resistance of the negative electrode material 10.

[0132] In some implementations, solid-liquid separation can be, for example, centrifugation or filtration.

[0133] In some implementations, the first water wash is performed at least once, preferably 3 to 10 times.

[0134] In some embodiments, the temperature of the first drying is 50°C to 80°C. Specifically, the temperature of the first drying can be 50°C, 60°C, 70°C, and 80°C, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0135] In some embodiments, the first drying time is 6 h to 24 h. Specifically, the first drying time is 6 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h and 24 h, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0136] Step S300: At least a portion of the silicon-oxygen raw material in the second precursor is reduced to silicon material to obtain the negative electrode material 10, specifically, as follows: Figure 8 As shown, after mixing with a reducing agent in the second precursor and undergoing a third heat treatment, the silicon-oxygen raw material in the second precursor can be reduced to silicon material 2. The simulated structure of the resulting negative electrode material 10 is shown below. Figure 9 As shown.

[0137] In some embodiments, the reducing agent includes at least one of magnesium powder and aluminum powder. Under the reducing action of the reducing agent, the silicon-oxygen raw material in the second precursor is reduced to silicon material 2, without the need to etch away the silicon-oxygen raw material, thereby increasing the capacity of the negative electrode material 10 while reducing resource waste.

[0138] In some embodiments, the mass ratio of the second precursor to the reducing agent is (1.25~2.00):1. Specifically, the mass ratio of the second precursor to the reducing agent can be 1.25:1, 1.50:1, 1.75:1, and 2.00:1, etc., and of course, other values ​​within the above range are also possible, which are not limited herein. Within the above range, the silicon-oxygen raw material can be reduced to silicon material 2 as much as possible, thereby improving the capacity of the negative electrode material 10.

[0139] In some embodiments, the third heat treatment is carried out in an inert gas atmosphere.

[0140] In some embodiments, the inert gas includes at least one of nitrogen and argon.

[0141] In some embodiments, the temperature of the third heat treatment is 600°C to 800°C. Specifically, the temperature of the third heat treatment can be 600°C, 630°C, 650°C, 680°C, 700°C, 730°C, 750°C, 780°C, 790°C, and 800°C, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0142] In some embodiments, the holding time of the third heat treatment is 0.5 h to 5 h. Specifically, the holding time of the third heat treatment can be 0.5 h, 1 h, 2 h, 3 h, 4 h and 5 h, etc., and of course it can also be other values ​​within the above range. This application does not limit it here.

[0143] In some embodiments, the process after the third heat treatment further includes: inertizing the material obtained from the third heat treatment to inertize the silicon material 2, reduce the oxidation of the silicon material 2, and increase the capacity of the material.

[0144] In some embodiments, the inerting gas includes ammonia.

[0145] In some embodiments, the inerting process further includes the steps of acid washing, a second water washing, and a second drying of the inerting material.

[0146] In some implementations, the pickling agent includes hydrochloric acid.

[0147] In some embodiments, the pickling time is 2 h to 24 h. Specifically, the pickling time can be, for example, 2 h, 5 h, 8 h, 10 h, 12 h, 15 h, 18 h and 24 h, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0148] In some implementations, the second water wash is performed 5 to 10 times.

[0149] In some implementations, the second drying method includes freeze drying.

[0150] Thirdly, this application provides a lithium-ion battery, which includes the above-described negative electrode material 10 or the negative electrode material 10 prepared by the above-described preparation method.

[0151] Those skilled in the art will understand that the methods for preparing lithium-ion batteries described above are merely examples. Other methods commonly used in the art can be employed without departing from the disclosure of this application.

[0152] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the main claims.

[0153] Example 1 (1) In 800 mL of methanol, 1 g of SiO2 was added first, followed by 2.10 g of Co(NO3)2·6H2O to obtain a mixed solution. The mixed solution was then sonicated at 40 W for 4 h. Next, the sonicated mixed solution was evaporated and dried for 12 h to obtain a blocky solid. Finally, the blocky solid was ground into powder to obtain the supported catalyst Co. 2+ Silica SiO2@Co.

[0154] (2) The SiO2@Co powder in (1) is placed in a CVD tube furnace and heated to 800℃ at a heating rate of 1200℃ / h in an H2 environment with a flow rate of 90 sccm. Then it is kept at the temperature for 20 min to reduce SiO2@Co to form silicon dioxide SiO2-CoNPs powder loaded with cobalt nanoparticles.

[0155] (3) Under high temperature conditions of 800℃, the flow rate of H2 was adjusted to 10 sccm, and methane with a flow rate of 150 sccm was introduced. After 10 min, H2 and methane were turned off, and Ar gas was introduced to cool down to room temperature, thus obtaining silicon dioxide SiO2-Co@GNPs powder loaded with multilayer graphite-encapsulated cobalt nanoparticles.

[0156] (4) SiO2-Co@GNPs powder was placed in a mixed acid solution of 1 mol / L sulfuric acid and 1 mol / L nitric acid and etched for 8 h. After centrifugation, silica SiO2-MGNPs precipitate loaded with porous hollow graphite was obtained. After washing with water several times, it was dried for 8 h to obtain SiO2-MGNPs powder.

[0157] (5) SiO2-MGNPs powder and magnesium powder were mixed at a mass ratio of 1.5 and placed in a high-temperature tube furnace. A high-temperature reduction reaction was carried out at 650℃ in an Ar atmosphere for 2 hours, and then cooled to room temperature. Next, ammonia gas was introduced for 1 hour and then the ammonia gas was turned off. Ar gas was then introduced for 0.5 hours and then the Ar gas was turned off. The mixed powder was then taken out. Finally, the mixed powder was acid-washed in 1 mol / L hydrochloric acid for 2 hours, centrifuged and washed with water, and freeze-dried to obtain Si-MGNPs powder.

[0158] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0159] Example 2 Unlike Example 1, Co(NO3)2·6H2O in step (1) is replaced with Cu(NO3)2.

[0160] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0161] Example 3 Unlike Example 1, Co(NO3)2·6H2O in step (1) is replaced with Fe(NO3)3.

[0162] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0163] Example 4 Unlike Example 1, Co(NO3)2·6H2O in step (1) is replaced with NiCl2.

[0164] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0165] Example 5 Unlike Example 1, steps (1) and (2) were omitted. Instead, 1g of silica, 0.43g of cobalt nanoparticles, and 800ml of methanol were mixed and ultrasonicated at 40W for 4 hours. After drying, silica SiO2-CoNPs powder loaded with cobalt nanoparticles was obtained. The obtained SiO2-CoNPs were then subjected to steps (3) to (5) in Example 1.

[0166] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0167] Example 6 (1) In 800 mL of methanol, 1 g of SiO2 was added, followed by 2.10 g of Co(NO3)2·6H2O and 20 mg of phenylalanine (Phe) to obtain a mixed solution. The mixed solution was then sonicated at 40 W for 4 h. Next, the sonicated mixed solution was evaporated and dried for 12 h to obtain a blocky solid. Finally, the blocky solid was ground into powder to obtain the supported catalyst Co. 2+ Silicon dioxide SiO2@Co-Phe with solid carbon source phe.

[0168] (2) Place the SiO2@Co-Phe powder from (1) into a CVD tube furnace, and heat it to 800℃ at a rate of 1200℃ / h in an H2 environment with a flow rate of 90 sccm. Then keep it at that temperature for 20 min to reduce SiO2@Co to form silica SiO2-CoNPs powder loaded with cobalt nanoparticles (the solid carbon source Phe has already begun to decompose during this process).

[0169] (3) Under high temperature conditions of 800℃, the flow rate of H2 was adjusted to 10 sccm to continue the pyrolysis process of Phe. After 10 min, H2 was turned off and Ar gas was introduced to cool down to room temperature to obtain silicon dioxide SiO2-Co@GNPs powder loaded with multilayer graphite-encapsulated cobalt nanoparticles.

[0170] (4) SiO2-Co@GNPs powder was placed in a mixed acid solution of 1 mol / L sulfuric acid and 1 mol / L nitric acid and etched for 8 h. After centrifugation, silica SiO2-MGNPs precipitate loaded with porous hollow graphite was obtained. After washing with water several times, it was dried for 8 h to obtain SiO2-MGNPs powder.

[0171] (5) SiO2-MGNPs powder and magnesium powder were mixed at a mass ratio of 1.5 and placed in a high-temperature tube furnace. A high-temperature reduction reaction was carried out at 650℃ in an Ar atmosphere for 2 hours, and then cooled to room temperature. Next, ammonia gas was introduced for 1 hour and then the ammonia gas was turned off. Ar gas was then introduced for 0.5 hours and then the Ar gas was turned off. The mixed powder was then taken out. Finally, the mixed powder was acid-washed in 1 mol / L hydrochloric acid for 2 hours, centrifuged and washed with water, and freeze-dried to obtain Si-MGNPs powder.

[0172] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0173] Example 7 Unlike Example 1, the methane flow rate was 8 sccm and the inlet holding time was 5 min.

[0174] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0175] Example 8 Unlike Example 1, the methane flow rate was 10 sccm and the inlet holding time was 30 min.

[0176] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0177] Example 9 Unlike Example 1, the methane flow rate was 50 sccm and the inlet holding time was 20 min.

[0178] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0179] Example 10 Unlike Example 1, the methane flow rate was 250 sccm and the inlet holding time was 1 min.

[0180] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0181] Example 11 Unlike Example 1, the methane flow rate was 300 sccm and the inlet holding time was 10 min.

[0182] The negative electrode material prepared in this embodiment includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores and includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell, the thickness of the carbon shell, the average pore size of the hollow core, the average pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0183] Comparative Example 1 (1) Mix 1g of SiO2 powder with 0.5g of asphalt powder evenly, then place the mixed powder in a high-temperature box furnace, heat it to 800℃ at a heating rate of 1200℃ / h under N2 atmosphere, and then maintain the constant temperature for 10min for carbonization to form carbon-encapsulated silicon dioxide SiO2-C powder.

[0184] (2) SiO2-C powder was placed in a mixed acid solution of 1 mol / L sulfuric acid and 1 mol / L nitric acid and etched for 8 h. After centrifugation, porous carbon-coated silicon dioxide SiO2-MCNPs precipitate was obtained. Then, the SiO2-MCNPs precipitate was placed in 20 wt% hydrofluoric acid to etch silicon dioxide for 8 h to obtain porous hollow carbon MCNPs powder.

[0185] (3) MGNPs powder, SiO2, and magnesium powder were mixed in a mass ratio of 1:2:2 and placed in a high-temperature tube furnace. A high-temperature reduction reaction was carried out at 650℃ in an N2 atmosphere for 2 hours, and then cooled to room temperature. Next, ammonia gas was introduced for 1 hour and then the ammonia gas was turned off. Then N2 was introduced for 0.5 hours and then the N2 was turned off. The mixed powder was then taken out. Finally, the mixed powder was acid-washed in 1 mol / L hydrochloric acid for 2 hours, centrifuged and washed with water, and freeze-dried to obtain Si-MCNPs powder.

[0186] The negative electrode material prepared in this comparative example includes hollow carbon and silicon material located between the hollow carbon layers. The hollow carbon includes a hollow core and a carbon shell layer with pores. The carbon shell layer is amorphous carbon. The graphene layer number of the carbon shell layer, the thickness of the carbon shell layer, the pore size of the hollow core, the pore size, and the porosity and thickness of the negative electrode material are shown in Table 1.

[0187] Comparative Example 2 Unlike Example 1, the mixed acid solution of 1 mol / L sulfuric acid and 1 mol / L nitric acid in step (4) was replaced with HF.

[0188] The negative electrode material prepared in this comparative example includes graphite particles and silicon material located between the graphite particles. The graphite particles include a solid metal core and a graphite shell on the surface of the solid metal core. The test parameters of the negative electrode material are shown in Table 1.

[0189] Performance testing (1) Use BET pore distribution to test the pore volume of the hollow core and pores, and calculate the porosity of the hollow carbon and the porosity of the negative electrode material. Before testing the porosity of the hollow carbon, the silicon material in the negative electrode material needs to be etched away using HF.

[0190] (2) Before etching the silicon material in the negative electrode material, test the mass M1 of the negative electrode material. After etching the silicon material with HF, test the mass M2 of the negative electrode material. (M2-M1) / M2 is the mass ratio of silicon material in the negative electrode material.

[0191] (3) High-resolution transmission electron microscopy was used to test the number of graphene layers in the carbon shell, the thickness of the carbon shell, and the distance between adjacent hollow carbons.

[0192] (4) After etching the silicon material in the negative electrode material with HF, the sphericity and median particle size of the hollow carbon were tested by a laser particle size analyzer.

[0193] (5) After etching the silicon material in the negative electrode material with HF, the elastic modulus and tensile strength of the hollow carbon were tested using a nanoindenter.

[0194] (6) The π-π packing van der Waals forces between hollow carbon atoms were tested using a dual polarization interferometer.

[0195] (7) Test method for the average pore size of hollow cores: The average pore size of 200 hollow cores in the hollow carbon in the transmission electron microscope image is calculated by mathematical statistics.

[0196] (8) Test method for average pore diameter: After etching the silicon material in the negative electrode material with HF, the average pore diameter is tested using a Micromeritics ASAP 2460 fully automatic surface area and porosity analyzer. The gas used in the test is CO2.

[0197] (9) Test method for median particle size of silicon material: Mathematical statistics are performed on the diameter of silicon material in transmission electron microscopy images.

[0198] (10) The following methods were used to test the electrochemical performance of the negative electrode material: The prepared silicon-carbon anode material, conductive agent, and binder were mixed in a solvent at a mass ratio of 94:1:5 to form a slurry (solid content 50%), which was then coated onto a copper foil current collector and vacuum dried to obtain the anode sheet. Then, using conventional production processes, the anode sheet, a ternary cathode sheet prepared using traditional mature processes, a 1 mol / L LiPF6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v=1:1:1) electrolyte, a Celgard 2400 separator, and a battery casing were assembled into an 18650 cylindrical single-cell battery. Charge-discharge tests of the cylindrical battery were conducted on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd., under the following conditions: constant current charge-discharge at 0.2 C at room temperature, with charge-discharge voltage limited to 2.75~4.2V. The test results are shown in Tables 1 and 2.

[0199] Table 1. Parameter test results of the negative electrode materials in each embodiment and comparative example

[0200] Table 2. Parameter test results of the negative electrode materials in each embodiment and comparative example.

[0201] As shown in Tables 1 and 2, in the preparation methods of Examples 1 to 11 of this application, under the first heat treatment condition, the carbon source is catalytically grown into a carbon shell 12 by metal catalyst particles. Further etching treatment is performed to make the interior of the carbon shell 12 structure have a hollow core 11 and pores 13 on the carbon shell 12, thereby giving the material a large pore volume and lithium intercalation capability, thereby increasing the material's anti-expansion performance. Moreover, in the preparation method of this application, there is no need to etch the silicon-oxygen raw material, but to directly reduce the silicon-oxygen raw material to silicon material, which reduces the waste of silicon-oxygen raw material and improves the capacity of the negative electrode material.

[0202] In Examples 1 and 8-11, the thickness of the generated carbon shell 12 (i.e., the number of graphene layers in the carbon shell 12) is controlled by adjusting the flow rate of the gas phase carbon source in step (3) and the holding time of the first heat treatment. In Example 8, the flow rate of the gas phase carbon source is too small, resulting in a thinner carbon shell 12, which reduces the tensile strength of the hollow carbon 1 and causes a decrease in the cycle performance and anti-expansion performance of the negative electrode material 10. In Example 11, the flow rate of the gas phase carbon source is too large, resulting in a thicker carbon shell 12, which increases the tensile strength of the hollow carbon 1 but reduces its flexibility. The gaps between the hollow carbon 1 decrease, resulting in a decrease in the amount of silicon material 2, thereby reducing the capacity of the negative electrode material 10.

[0203] In the negative electrode material prepared in Comparative Example 1, since no catalyst metal particles were added, the resulting hollow carbon was amorphous carbon, which did not have a continuous graphite lattice structure. This resulted in poor mechanical properties of the obtained negative electrode material, which in turn led to poor resistance to expansion and cycle stability.

[0204] In Comparative Example 2, HF etching was used. The carbon shell can isolate HF, resulting in the absence of hollow cores and pores in the hollow carbon. Furthermore, the silicon content in the material is reduced due to HF etching, which leads to a poor specific capacity. Although the lack of hollow cores and pores will cause the material to expand in volume, the overall volume expansion is relatively small because the amount of silicon in the negative electrode material obtained in this comparative example is very small.

[0205] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes hollow carbon and silicon material located between the hollow carbons. The hollow carbon includes a hollow core and a carbon shell. The carbon shell has pores, at least some of which penetrate the carbon shell. The carbon shell includes multiple monolayer graphenes, which are stacked along the radial direction of the hollow carbon. The number of graphene layers in the carbon shell is 4 to 15.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following features (1) to (11): (1) Layered graphite is disposed between the hollow carbon atoms; (2) The median particle size of the hollow carbon is 5 nm to 200 nm; (3) The thickness of the carbon shell is 1.2 nm to 5.2 nm; (4) The Raman spectrum of the negative electrode material obtained by Raman spectroscopy using a measuring light source with a wavelength of 532 nm is shown at 1300 cm⁻¹. -1 Up to 1400 cm -1 D bands were observed at 1500 cm. -1 ~1600 cm -1 The peak intensity I of the G band and the D band was observed. D And the peak intensity I of the G-band G The ratio between I G / I D Greater than 0.5; (5) The average pore size of the hollow core is 3.8 nm to 198.8 nm; (6) The average pore diameter of the pore is 0.42 nm to 2 nm; (7) The distance between adjacent hollow carbon atoms is 0 nm to 40 nm; (8) The sphericity of the hollow carbon is 0.6~1; (9) The silicon material accounts for 5% to 80% of the mass of the anode material; (10) The median particle size of the silicon material is 1 nm to 15 nm; (11) The silicon material includes at least one of crystalline silicon and amorphous silicon.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following features (1) to (5): (1) The elastic modulus of the hollow carbon is 0.1 TPa ~ 0.8 TPa; (2) The tensile strength of the hollow carbon is 15 GPa to 110 GPa; (3) The porosity of the hollow carbon is 65%~96%; (4) The porosity of the negative electrode material is 7%~50%; (5) The π-π packing van der Waals force between adjacent hollow carbons is 1 kJ / mol to 50 kJ / mol.

4. A method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: A mixture of silicon-oxygen raw material containing supported metal catalyst particles and a carbon source is subjected to a first heat treatment to catalyze the graphitization of the carbon source, thereby obtaining a first precursor. The first precursor is etched to obtain the second precursor, wherein the etchant used in the etching process is an oxidizing acid; At least a portion of the silicon-oxygen raw material in the second precursor is reduced to silicon material to obtain the negative electrode material.

5. The preparation method according to claim 4, characterized in that, The silicon-oxygen raw material supported on metal catalyst particles is prepared by the following method: The mixture containing silicon-oxygen raw materials and metal salt catalysts is subjected to a second heat treatment in a reducing atmosphere to obtain silicon-oxygen raw materials loaded with metal catalyst particles.

6. The preparation method according to claim 5, characterized in that, The preparation method includes at least one of the following features (1) to (14): (1) The silicon-oxygen raw material includes at least one of silicon dioxide and silicon monoxide; (2) The median particle size of the silicon-oxygen raw material is 5 nm to 200 nm; (3) The metal salt catalyst includes Fe 3+ Co 2+ Ni 2+ Cu 2+ and Au 3+ At least one of them; (4) The metal salt catalyst includes at least one of Fe(NO3)3, FeCl3, Co(NO3)2, CoCl2, Ni(NO3)2, NiCl2, Cu(NO3)2, CuCl2 and HAuCl4; (5) The mass ratio of the silicon-oxygen raw material to the metal salt catalyst is 1:(0.08~5.00); (6) The mixture containing silicon-oxygen raw materials and metal salt catalysts also includes a solvent; (7) The mixture containing silicon-oxygen raw materials and metal salt catalysts also includes a solvent, wherein the solvent includes at least one of methanol, ethanol, propanol and water; (8) The mixture containing silicon-oxygen raw materials and metal salt catalysts also includes a solvent, wherein the amount of solvent added is 50 to 1000 times the total mass of the silicon-oxygen raw materials and metal salt catalysts; (9) The mixture containing silicon-oxygen raw materials and metal salt catalyst further includes the steps of drying and grinding the mixture before the second heat treatment; (10) The reducing atmosphere includes at least one of hydrogen and ammonia; (11) The flow rate of the reducing atmosphere is 10 sccm ~ 150 sccm; (12) The temperature of the second heat treatment is 400℃~1000℃; (13) The holding time for the second heat treatment is 5 min to 30 min; (14) The heating rate of the second heat treatment is 100℃ / h ~ 1200℃ / h.

7. The preparation method according to claim 4, characterized in that, The preparation method includes at least one of the following features (1) to (9): (1) The carbon source includes a gaseous carbon source and a solid carbon source; (2) The carbon source includes a gaseous carbon source and a solid carbon source, wherein the gaseous carbon source includes at least one of methane, ethane and acetylene; (3) The carbon source includes a gaseous carbon source and a solid carbon source, wherein the solid carbon source includes at least one of pitch, glucose, sucrose, cellulose, glycine, alanine and phenylalanine; (4) The carbon source includes a gaseous carbon source and a solid carbon source, and the mass ratio of the solid carbon source to the metal catalyst particles is 1:(10~10000). (5) The carbon source includes a gaseous carbon source and a solid carbon source, and the flow rate of the gaseous carbon source is 10 sccm ~ 250 sccm; (6) The temperature of the first heat treatment is 600℃~1000℃; (7) The holding time for the first heat treatment is 1 min to 30 min; (8) Before subjecting the mixture of silicon-oxygen raw material containing supported metal catalyst particles and carbon source to the first heat treatment, the method further includes: introducing hydrogen gas into the mixture of silicon-oxygen raw material containing supported metal catalyst particles and carbon source; (9) Before subjecting the mixture of silicon-oxygen raw material containing supported metal catalyst particles and carbon source to the first heat treatment, the method further includes: introducing hydrogen gas into the mixture of silicon-oxygen raw material containing supported metal catalyst particles and carbon source, wherein the flow rate of hydrogen gas is 10 sccm to 90 sccm.

8. The preparation method according to claim 4, characterized in that, The preparation method includes at least one of the following features (1) to (6): (1) The oxidizing acid includes at least one of sulfuric acid and nitric acid; (2) The oxidizing acid includes a mixture of sulfuric acid and nitric acid; (3) The oxidizing acid includes a mixed acid of sulfuric acid and nitric acid, wherein the concentration of sulfuric acid in the mixed acid is 0.1 mol / L to 4 mol / L; (4) The oxidizing acid includes a mixed acid of sulfuric acid and nitric acid, wherein the concentration of nitric acid in the mixed acid is 0.1 mol / L to 4 mol / L; (5) The etching process takes 2 hours to 24 hours; (6) Before at least a portion of the silicon-oxygen raw material in the second precursor is reduced to silicon material, the process further includes: solid-liquid separation of the second precursor, and first washing and first drying of the resulting solid.

9. The preparation method according to claim 4, characterized in that, Reducing at least a portion of the silicon-oxygen raw material in the second precursor to silicon material includes the step of mixing the second precursor with a reducing agent and then performing a third heat treatment, wherein the preparation method includes at least one of the following features (1) to (9): (1) The reducing agent includes at least one of metallic magnesium and metallic aluminum; (2) The mass ratio of the second precursor to the reducing agent is (1.25~2.00):1; (3) The third heat treatment is carried out in an inert gas atmosphere; (4) The third heat treatment is carried out in an inert gas atmosphere, wherein the inert gas includes at least one of nitrogen and argon; (5) The temperature of the third heat treatment is 600℃~800℃; (6) The heat treatment holding time for the third heat treatment is 0.5 h to 5 h; (7) The process of subjecting the second precursor and reducing agent to a third heat treatment further includes: subjecting the material obtained from the third heat treatment to an inert treatment; (8) The process of subjecting the second precursor and reducing agent to a third heat treatment further includes: subjecting the material obtained from the third heat treatment to an inert treatment, wherein the inert treatment gas includes ammonia. (9) The process of subjecting the second precursor and reducing agent to a third heat treatment further includes: inertizing the material obtained from the third heat treatment, and then subjecting the inertized material to acid washing, a second water washing, and a second drying.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode material according to any one of claims 1 to 3 or the negative electrode material prepared by the preparation method according to any one of claims 4 to 9.

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