Silicon-carbon negative electrode material, preparation method thereof and battery

Abstract

The invention relates to the field of new energy batteries, in particular to a silicon-carbon negative electrode material, a preparation method thereof and a battery, the silicon-carbon negative electrode material comprises silicon-carbon composite particles and a coating layer coating the surfaces of the silicon-carbon composite particles; wherein the silicon-carbon composite particles comprise a porous carbon matrix, a metal catalytic base layer deposited in pores of the porous carbon matrix, a carbon nanotube growing on the metal catalytic base layer, and a nano silicon layer deposited on the surface of the carbon nanotube and the surface of the pores of the porous carbon matrix; the material of the coating layer comprises at least one of a conductive material, a solid electrolyte and a metal oxide. According to the silicon-carbon composite negative electrode material disclosed by the invention, the structural strength of the porous carbon matrix is effectively improved, the deposition uniformity of nano silicon is improved, and the electronic conductivity of the material and the overall fast charging performance and long cycle performance of the material are improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy batteries, and in particular to a silicon-carbon negative electrode material and a preparation method thereof and a battery. Background Art

[0002] With the development of science and technology, the demand for batteries in electronic products is increasing, especially in the fields of electric vehicles, energy storage systems, etc., and the requirements for fast charging capabilities and long cycle performance of batteries are also getting higher and higher. In this context, research and development in the fields of battery manufacturing technology, negative electrode material preparation technology, and coating technology have become particularly important. Among them, the negative electrode material is an important component of the battery, and its performance directly affects the performance of the battery. Graphite has been used as the mainstream negative electrode material for lithium-ion batteries due to its low cost and stable performance. However, with the rapid development of the new energy industry, higher capacity and higher rate performance are regarded as important indicators. The theoretical capacity of graphite is only 372mAh / g, which seriously reduces the application of graphite materials in high energy density lithium-ion batteries.

[0003] The theoretical gram capacity of silicon-based materials is 4200mAh / g, which is more than ten times that of graphite. It can greatly improve the energy density of the battery cell and has gradually become a hot spot and focus of research on negative electrode materials. However, the huge volume expansion of silicon materials during charging and discharging limits its further application. At present, the main method to improve the volume expansion of silicon materials is to deposit silicon in a porous carbon matrix by chemical vapor deposition, and buffer the volume expansion of silicon through the pores in the porous carbon matrix. However, the electronic conductivity and ionic conductivity of the silicon-carbon composite material prepared by chemical vapor deposition are poor, resulting in insufficient kinetic performance of the silicon-carbon composite material, which to a certain extent limits the application of silicon-carbon composite materials. Summary of the invention

[0004] In view of this, the present invention is committed to providing a silicon-carbon negative electrode material and a preparation method and a battery thereof, so as to solve the problem of insufficient kinetic performance of silicon-carbon composite materials in the prior art.

[0005] In order to solve the above technical problems, this application is implemented as follows:

[0006] The present invention provides a silicon-carbon negative electrode material, which comprises silicon-carbon composite particles and a coating layer coated on the surface of the silicon-carbon composite particles;

[0007] The silicon-carbon composite particles include a porous carbon matrix, a metal catalyst layer deposited in the pores of the porous carbon matrix, carbon nanotubes grown on the metal catalyst layer, and a nano-silicon layer deposited on the surface of the carbon nanotubes and the surface of the pores of the porous carbon matrix;

[0008] The coating layer material includes at least one of a conductive material, a solid electrolyte and a metal oxide.

[0009] Optionally, the metal element in the metal catalyst base layer is selected from at least one of Group VIII elements and Group IIB elements; optionally, the metal element in the metal catalyst base layer is selected from at least one of iron, cobalt, nickel and zinc; optionally, based on the total mass of the silicon-carbon negative electrode material, the content of the metal element in the metal catalyst base layer is 0.05 to 1 wt%.

[0010] Optionally, the average D50 of the porous carbon matrix is ​​4 to 10 μm; the pore size of the porous carbon matrix is ​​2 to 50 nm, the porosity of the porous carbon matrix is ​​25 to 90%; the specific surface area of ​​the porous carbon matrix is ​​100 to 3500 m 2 / g.

[0011] Optionally, the carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes; optionally, based on the total mass of the silicon-carbon negative electrode material, the content of the carbon nanotubes is 0.01-0.2 wt%.

[0012] Optionally, the thickness of the nano-silicon layer is 0.5-3 nm; based on the total mass of the silicon-carbon negative electrode material, the content of nano-silicon deposited in the nano-silicon layer is 10-60 wt %.

[0013] Optionally, the coating layer material is a conductive material; optionally, the conductive material includes carbon and / or graphene; optionally, the coating layer thickness is 0.5 to 50 nm; optionally, based on the total mass of the silicon-carbon negative electrode material, the content of the coating layer material is 0.5 to 3 wt%.

[0014] A second aspect of the present invention provides a method for preparing a silicon-carbon negative electrode material, the preparation method comprising the following steps:

[0015] S1, placing the porous carbon substrate in a metal solution for immersion treatment and drying treatment to obtain a first material;

[0016] S2, placing the first material in a first inert atmosphere, introducing a first gaseous carbon source to perform a first deposition treatment, and obtaining a second material;

[0017] S3, placing the second material in a second inert atmosphere, introducing the first gaseous silicon source to perform a second deposition process, and obtaining a third material;

[0018] S4, performing surface coating treatment on the third material.

[0019] Optionally, the solute in the metal solution includes at least one of FeCl2, FeCl3, ZnCl2, NiCl and CoCl2; the solvent in the metal solution includes at least one of water, ethanol, ethylene glycol, benzene and carbon tetrachloride; the first gaseous carbon source includes at least one of methane, ethane, propane, ethylene and acetylene; the first gaseous silicon source includes at least one of monosilane, disilane and chlorosilane; the first inert atmosphere and the second inert atmosphere are each independently selected from nitrogen and / or argon.

[0020] Optionally, in step S1, the conditions of the impregnation treatment include: a temperature of 50-100°C and a time of 30-90 min; in step S2, the introduction rate of the first gaseous carbon source is 0.2-1.0 L / min; the conditions of the first deposition treatment include: a deposition temperature of 500-1200°C and a deposition time of 4-12 h; in step S3, the introduction rate of the first gaseous silicon source is 0.2-1.0 L / min; the conditions of the first deposition treatment include: a deposition temperature of 400-700°C and a deposition time of 2-12 h; in step S4, the surface coating treatment includes at least one of gaseous deposition coating, liquid phase coating and solid phase coating.

[0021] A third aspect of the present invention provides a battery, the battery comprising a negative electrode material, the negative electrode material comprising the above-mentioned silicon-carbon negative electrode material and / or the silicon-carbon negative electrode material prepared according to the above-mentioned method.

[0022] Through the above technical solution, the beneficial technical effects of the present invention are:

[0023] (1) The silicon-carbon negative electrode material of the present invention is prepared by depositing a metal catalyst base layer on the surface of the internal pores of a porous carbon matrix. The metal in the metal catalyst base layer can catalyze the reaction of a gas-phase carbon source to generate carbon nanotubes. The carbon nanotubes run through the pores. The criss-crossed carbon nanotubes can enhance the compressive resistance of the porous carbon matrix and improve the structural stability of the material.

[0024] (2) The present invention deposits silicon in the pores inside the porous carbon matrix by introducing a gaseous silicon source through a vapor deposition method. Due to the presence of carbon nanotubes, nano-silicon is more evenly deposited on the surface of the carbon nanotubes and on the walls of the internal pores. The three-dimensional conductive carbon nanotube network in the pores effectively improves the problem of poor electronic conductivity of nano-silicon, reduces the interface contact resistance between the nano-silicon material and the porous carbon matrix, reduces the electron and ion transfer impedance, and improves the conductivity of the silicon-carbon composite material. At the same time, the three-dimensional conductive structure also effectively improves the volume expansion of the silicon material, and avoids the problem of the silicon material losing electrical contact and activity after volume expansion, thereby greatly improving the long cycle performance of the silicon-carbon composite material.

[0025] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0027] Figure 1 Shown is a schematic diagram of the silicon-carbon negative electrode material in the present invention.

[0028] Description of Reference Numerals

[0029] 1. Coating layer

[0030] 2. Porous carbon matrix

[0031] 3. Pores inside porous carbon matrix

[0032] 4. Carbon Nanotubes

[0033] 5. Nano silicon layer

[0034] 6. Metal catalytic base DETAILED DESCRIPTION

[0035] The present invention discloses a silicon-carbon negative electrode material and a preparation method and a battery. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0036] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0037] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0038] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0040] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0041] In order to solve the problem of insufficient dynamic performance of silicon-carbon composite materials in the prior art, the present invention adopts the following technical solution:

[0042] The present invention provides a silicon-carbon negative electrode material, such as Figure 1 As shown, the silicon-carbon negative electrode material comprises silicon-carbon composite particles and a coating layer coated on the surface of the silicon-carbon composite particles;

[0043] The silicon-carbon composite particles include a porous carbon matrix, a metal catalyst layer deposited in the pores of the porous carbon matrix, carbon nanotubes grown on the metal catalyst layer, and a nano-silicon layer deposited on the surface of the carbon nanotubes and the surface of the pores of the porous carbon matrix;

[0044] The coating layer material includes at least one of a conductive material, a solid electrolyte and a metal oxide.

[0045] The silicon-carbon composite material of the present invention deposits a metal catalytic base layer on the surface of the internal pores of a porous carbon matrix. The metal in the metal catalytic base layer can catalyze the reaction of a gas-phase carbon source to generate carbon nanotubes. The carbon nanotubes run through the pores. The criss-crossed carbon nanotubes can strengthen the compressive resistance of the porous carbon matrix and improve the structural stability of the material. Silicon is deposited in the pores inside the porous carbon matrix. Due to the presence of the carbon nanotubes, nano silicon is more evenly deposited on the surface of the carbon nanotubes and on the pore walls of the internal pores. The three-dimensional conductive carbon nanotube network in the pores effectively improves the problem of poor electronic conductivity of nano silicon, reduces the interface contact resistance between the nano silicon material and the porous carbon matrix, reduces the electron and ion transfer impedance, and improves the conductivity of the silicon-carbon composite material; at the same time, the three-dimensional conductive structure also effectively improves the volume expansion of the silicon material, and avoids the problem of losing electrical contact and activity after the silicon material expands in volume, and improves the long cycle performance of the silicon-carbon composite material.

[0046] According to the present invention, the metal element in the metal catalyst base layer can be selected from at least one of Group VIII elements and Group IIB elements. Exemplarily, the metal element in the metal catalyst base layer can be selected from at least one of iron, cobalt, nickel and zinc.

[0047] According to the present invention, the deposition amount of a suitable metal catalyst base layer helps to increase the content of catalytically grown carbon nanotubes, thereby improving the compaction density and structural strength of the silicon-carbon composite material, and significantly improving the conductivity of the silicon-carbon composite material, thereby improving the kinetic performance and cycle performance of the silicon-carbon composite material.

[0048] In the present invention, if the amount of deposited metal catalyst layer is too low, the amount of catalytically grown carbon nanotubes will be reduced. At this time, the material strength is improved at a low rate, and the conductivity is not significantly improved, resulting in deterioration of the kinetics and cycle performance; if the amount of deposited metal catalyst layer is too high, the amount of catalytically grown carbon nanotubes will increase significantly, resulting in a decrease in the material's gram capacity, and because there are too many carbon nanotubes growing inside the pores, the deposition space of nanosilicon in the pores is limited, and most of the nanosilicon is deposited on the porous carbon surface, resulting in a decrease in the structural strength and conductivity of the material, and the nanosilicon is exposed on the porous carbon surface and directly contacts and reacts with the electrolyte, resulting in a significant deterioration of the kinetics and long cycle performance. In the present invention, based on the total mass of the silicon-carbon negative electrode material, the content of the metal element in the metal catalyst layer is 0.05 to 1wt%. Exemplarily, based on the total mass of the silicon-carbon negative electrode material, the content of the metal element in the metal catalyst base layer can be any value among 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% and 1wt%, or any value within the range composed of any two of the above values.

[0049] According to the present invention, the average D50 of the porous carbon matrix may be 4 to 10 μm. Exemplarily, the average D50 of the porous carbon matrix may be any value among 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm and 10 μm or any value within the range of any two of the above values.

[0050] According to the present invention, the pore size of the porous carbon matrix can be 2 to 50 nm. Exemplarily, the pore size of the porous carbon matrix can be any value among 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm and 50 nm or any value within the range of any two of the above values.

[0051] According to the present invention, the porosity of the porous carbon matrix can be 25-90%. Exemplarily, the porosity of the porous carbon matrix can be any value among 25%, 30%, 40%, 50%, 60%, 70%, 80% and 90%, or any value within the range of any two of the above values.

[0052] According to the present invention, the specific surface area of ​​the porous carbon matrix can be 100 to 3500 m 2 / g. Exemplarily, the specific surface area of ​​the porous carbon matrix can be 100m 2 / g、500m 2 / g、1000m 2 / g、1500m 2 / g, 2000m 2 / g、2500m 2 / g、3000m 2 / g and 3500m 2 / any value in g or any value in the range consisting of any two of the above values.

[0053] According to the present invention, the carbon nanotubes may include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0054] In the present invention, the appropriate content of carbon nanotubes can improve the compaction density and structural strength of the silicon-carbon composite material, and the electrical conductivity of the silicon-carbon composite material is significantly improved, and the dynamic performance and cycle performance of the material are significantly improved. If the carbon nanotube content is too low, the structural strength and electrical conductivity of the silicon-carbon composite material are not well improved, and the dynamic performance and cycle performance of the silicon-carbon composite material will be affected; if the carbon nanotube content is too high, the deposition space of nano-silicon in the pores will be limited, and most of the nano-silicon will be deposited on the porous carbon surface, reducing the structural strength and conductivity of the overall material, and the nano-silicon is exposed on the porous carbon surface and directly contacts and reacts with the electrolyte, thereby affecting the dynamic performance and long cycle performance of the silicon-carbon composite material. In the present invention, based on the total mass of the silicon-carbon negative electrode material, the content of the carbon nanotubes is 0.01 to 0.2wt%. Illustratively, based on the total mass of the silicon-carbon negative electrode material, the content of the carbon nanotubes can be any value among 0.01wt%, 0.02wt%, 0.05wt%, 0.1wt%, 0.15wt% and 0.2wt% or any value within the range formed by any two of the above values.

[0055] According to the present invention, the thickness of the nano silicon layer can be 0.5-3 nm. For example, the thickness of the nano silicon layer can be any value among 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm and 3 nm or any value within the range of any two of the above values.

[0056] In the present invention, the appropriate amount of nano-silicon deposited can increase the gram capacity of the silicon-carbon composite material. If the amount of nano-silicon deposited is too low, the gram capacity of the silicon-carbon composite material will be reduced, affecting the energy density of the material; if the amount of nano-silicon deposited is too high, the nano-silicon grains will grow, thereby reducing the structural strength and electrical conductivity of the silicon-carbon composite material, thereby affecting the dynamics and cycle performance of the material. In the present invention, based on the total mass of the silicon-carbon negative electrode material, the content of nano-silicon deposited in the nano-silicon layer can be 10 to 60wt%. Exemplarily, based on the total mass of the silicon-carbon negative electrode material, the content of nano-silicon deposited in the nano-silicon layer can be any of 10wt%, 20wt%, 30wt%, 40wt%, 50wt% and 60wt% or any value within the range of any two of the above values.

[0057] According to the present invention, the coating layer material is preferably a conductive material; optionally, the conductive material includes carbon and / or graphene.

[0058] In other embodiments, the coating layer material may be a solid electrolyte and / or a metal oxide; wherein the solid electrolyte may be selected from at least one of an oxide solid electrolyte, a sulfide solid electrolyte and a halide solid electrolyte, and the metal oxide may be selected from at least one of aluminum oxide, titanium dioxide, vanadium oxide, zinc oxide, cobalt oxide and zirconium oxide.

[0059] According to the present invention, the surface coating layer of the silicon-carbon material can reduce the direct exposure of the nano-silicon material to the electrolyte and improve the cycle stability. In the present invention, the coating layer thickness can be 0.5 to 50 nm. Exemplarily, the coating layer thickness can be any value among 0.5 nm, 1 nm, 10 nm, 20 nm, 30 nm, 40 nm and 50 nm or any value within the range of any two of the above values.

[0060] Optionally, based on the total mass of the silicon-carbon negative electrode material, the content of the coating layer material is 0.5-3wt%. Exemplarily, based on the total mass of the silicon-carbon negative electrode material, the content of the coating layer material can be any value among 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% and 3wt%, or any value within the range of any two of the above values.

[0061] A second aspect of the present invention provides a method for preparing a silicon-carbon negative electrode material, the preparation method comprising the following steps:

[0062] S1, placing the porous carbon substrate in a metal solution for immersion treatment and drying treatment to obtain a first material;

[0063] S2, placing the first material in a first inert atmosphere, introducing a first gaseous carbon source to perform a first deposition treatment, and obtaining a second material;

[0064] S3, placing the second material in a second inert atmosphere, introducing the first gaseous silicon source to perform a second deposition process, and obtaining a third material;

[0065] S4, performing surface coating treatment on the third material.

[0066] According to the present invention, the solute in the metal solution may include at least one of FeCl2, FeCl3, ZnCl2, NiCl and CoCl2; the solvent in the metal solution may include at least one of water, ethanol, ethylene glycol, benzene and carbon tetrachloride; the first gaseous carbon source may include at least one of methane, ethane, propane, ethylene and acetylene; the first gaseous silicon source may include at least one of monosilane, disilane and chlorosilane; the first inert atmosphere and the second inert atmosphere may be independently selected from nitrogen and / or argon.

[0067] According to the present invention, in step S1, by adjusting the temperature and time of the impregnation treatment, the deposition amount of the metal catalyst base layer inside the pores of the porous carbon matrix can be effectively adjusted. Exemplarily, the conditions of the impregnation treatment may include: a temperature of 50 to 100°C and a time of 30 to 90 minutes; as a preferred embodiment of the present invention, the impregnation treatment of the present invention may be accompanied by a stirring process; exemplarily, the stirring speed may be 100 to 1000 rpm.

[0068] According to the present invention, in step S2, by controlling the flow rate, deposition temperature and deposition time of the first gaseous carbon source, the amount of carbon nanotubes grown in the pores inside the porous carbon matrix can be effectively controlled. Exemplarily, the introduction rate of the first gaseous carbon source can be 0.2 to 1.0 L / min; the conditions of the first deposition treatment can include: a deposition temperature of 500 to 1200°C and a deposition time of 4 to 12 hours.

[0069] According to the present invention, in step S3, by controlling the flow rate, deposition temperature and deposition time of the first gaseous silicon source, the deposition amount of nano-silicon in the pores inside the porous carbon matrix can be effectively controlled. Exemplarily, the introduction rate of the first gaseous silicon source can be 0.2 to 1.0 L / min; the conditions of the first deposition treatment can include: a deposition temperature of 400 to 700°C and a deposition time of 2 to 12 hours.

[0070] According to the present invention, in step S4, the surface coating treatment may include at least one of gaseous deposition coating, liquid phase coating and solid phase coating. Exemplarily, the surface coating treatment material may be a conductive material; the conductive material includes carbon and / or graphene; the gaseous deposition coating step may include: placing the third material to be coated in an inert atmosphere, introducing a second gaseous carbon source for a third deposition treatment; wherein the introduction rate of the third gaseous silicon source may be 0.2 to 1.0 L / min; the conditions of the third deposition treatment may include: a deposition temperature of 400 to 700°C, and a deposition time of 2 to 12 hours.

[0071] A third aspect of the present invention provides a battery, the battery comprising a negative electrode material, the negative electrode material comprising the above-mentioned silicon-carbon negative electrode material and / or the silicon-carbon negative electrode material prepared according to the above-mentioned method.

[0072] The present invention is further described in detail by way of examples. The raw materials used in the examples can be obtained through commercial sources. The average D50 of the porous carbon matrix used in the examples and comparative examples is 8.3 μm; the pore size of the porous carbon matrix is ​​2 nm, the porosity of the porous carbon matrix is ​​50%; the specific surface area of ​​the porous carbon matrix is ​​1500 m 2 / g.

[0073] Example 1

[0074] The preparation method of the silicon-carbon negative electrode material of this embodiment is as follows:

[0075] (1) The porous carbon matrix is ​​placed in a metal solution for immersion treatment to obtain a first material in which a metal catalytic base layer is deposited on the surface of the pores inside the porous carbon matrix, wherein the solute of the metal solution is FeCl2, the solvent is ethanol, the molar concentration is 8%, the immersion temperature is 70°C, and the immersion time is 60 min.

[0076] (2) placing the first material in an inert atmosphere, introducing a first gaseous carbon source for a first deposition treatment, and depositing and growing carbon nanotubes on the metal catalyst substrate to obtain a second material. The inert atmosphere is nitrogen, the first gaseous carbon source is ethylene, the flow rate of ethylene is 0.6 L / min, the time of the first deposition treatment is 8 h, and the temperature is 750° C.

[0077] (3) Switching the first gaseous carbon source to the first gaseous silicon source for a second deposition process to obtain a third material, wherein the first gaseous silicon source is monosilane, the flow rate of monosilane is 0.6 L / min, the second deposition process lasts for 6 h, and the temperature is 450° C.

[0078] (4) Switching the first gaseous silicon source to the second gaseous carbon source for the third deposition process, generating a carbon coating layer, and obtaining the silicon-carbon negative electrode material of this embodiment. The second gaseous carbon source is acetylene, the flow rate of acetylene is 0.5 L / min, the time of the third deposition process is 8 hours, and the temperature is 450°C. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.100wt%, and the content of the coating layer material is 2wt%.

[0079] Example 2

[0080] The preparation method of the silicon-carbon negative electrode material of this embodiment is as follows:

[0081] (1) placing a porous carbon substrate in a metal solution for immersion treatment to obtain a first material in which a metal catalytic base layer is deposited on the surface of the pores inside the porous carbon substrate, wherein the solute of the metal solution is ZnCl2, the solvent is ethanol, the molar concentration is 8%, the immersion temperature is 70°C, and the immersion time is 60 min.

[0082] (2) placing the first material in an inert atmosphere, introducing a first gaseous carbon source for a first deposition treatment, and depositing and growing carbon nanotubes on the metal catalyst substrate to obtain a second material. The inert atmosphere is nitrogen, the first gaseous carbon source is methane, the flow rate of methane is 0.6 L / min, the time of the first deposition treatment is 8 h, and the temperature is 1000° C.

[0083] (3) Switching the first gaseous carbon source to the first gaseous silicon source for a second deposition process to obtain a third material, wherein the first gaseous silicon source is isocyanate, the flow rate of isocyanate is 0.6 L / min, the second deposition process lasts for 6 h, and the temperature is 470°C.

[0084] (4) After the third material and the graphene slurry are mixed and dispersed, they are dried, crushed and sieved to generate a graphene coating layer to obtain the silicon-carbon negative electrode material of this embodiment. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.110wt%, and the coating layer material content is 0.2wt%.

[0085] Example 3

[0086] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (1), the immersion temperature is 50° C. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.030wt%, and the content of the coating layer material is 0.2wt%.

[0087] Example 4

[0088] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (1), the immersion temperature is 100° C. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.190wt%, and the content of the coating layer material is 2wt%.

[0089] Example 5

[0090] The preparation method of the silicon-carbon negative electrode material of this embodiment is the same as that of embodiment 1, except that in step (1), the immersion time is 30 minutes. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.030wt%, and the content of the coating layer material is 2wt%.

[0091] Example 6

[0092] The preparation method of the silicon-carbon negative electrode material of this embodiment is the same as that of embodiment 1, except that in step (1), the immersion time is 90 minutes. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.200wt%, and the content of the coating layer material is 2wt%.

[0093] Example 7

[0094] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (2), the flow rate of ethylene is 0.2 L / min. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.020 wt%, and the content of the coating layer material is 2 wt%.

[0095] Example 8

[0096] The preparation method of the silicon-carbon negative electrode material of this embodiment is the same as that of embodiment 1, except that in step (2), the flow rate of ethylene is 1 L / min. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.200 wt%, and the content of the coating layer material is 2 wt%.

[0097] Example 9

[0098] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (2), the temperature of the first deposition treatment is 500° C. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.010wt%, and the content of the coating layer material is 2wt%.

[0099] Example 10

[0100] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (2), the temperature of the first deposition treatment is 1000° C. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.190wt%, and the content of the coating layer material is 2wt%.

[0101] Embodiment 11

[0102] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (2), the first deposition treatment time is 4 hours. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.020wt%, and the coating layer material content is 2wt%.

[0103] Example 12

[0104] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (2), the first deposition treatment time is 12 hours. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.180wt%, and the coating layer material content is 2wt%.

[0105] Example 13

[0106] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (3), the flow rate of monosilane is 0.2 L / min. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.110 wt%, and the content of the coating layer material is 2 wt%.

[0107] Embodiment 14

[0108] The preparation method of the silicon-carbon negative electrode material of this embodiment is the same as that of embodiment 1, except that in step (3), the flow rate of monosilane is 1 L / min. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.120wt%, and the content of the coating layer material is 2wt%.

[0109] Embodiment 15

[0110] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (3), the temperature of the second deposition treatment is 400° C. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.100wt%, and the content of the coating layer material is 2wt%.

[0111] Example 16

[0112] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (3), the temperature of the second deposition treatment is 650° C. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.110wt%, and the content of the coating layer material is 2wt%.

[0113] Embodiment 17

[0114] The preparation method of the silicon-carbon negative electrode material of this embodiment is generally the same as that of embodiment 1, except that in step (3), the second deposition treatment time is 2 hours. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.120wt%, and the coating layer material content is 2wt%.

[0115] Embodiment 18

[0116] The preparation method of the silicon-carbon negative electrode material of this embodiment is the same as that of embodiment 1, except that in step (3), the second deposition treatment time is 12 hours. Based on the total mass of the silicon-carbon negative electrode material of this embodiment, the carbon nanotube content is 0.110wt%, and the coating layer material content is 2wt%.

[0117] Comparative Example 1

[0118] The preparation method of the silicon-carbon negative electrode material of this comparative example is as follows:

[0119] (1) The porous carbon matrix is ​​placed in a metal solution for immersion treatment to obtain a first material in which a metal catalytic base layer is deposited on the surface of the pores inside the porous carbon matrix, wherein the solute of the metal solution is FeCl2, the solvent is ethanol, the molar concentration is 8%, the immersion temperature is 70°C, and the immersion time is 60 min.

[0120] (2) placing the first material in an inert atmosphere, introducing a first gaseous carbon source for a first deposition treatment, and depositing and growing carbon nanotubes on the metal catalyst substrate to obtain a second material. The inert atmosphere is nitrogen, the first gaseous carbon source is ethylene, the flow rate of ethylene is 0.6 L / min, the time of the first deposition treatment is 8 h, and the temperature is 750° C.

[0121] (3) Switching the first gaseous carbon source to the first gaseous silicon source for a second deposition process to obtain the silicon-carbon negative electrode material of this comparative example. The first gaseous silicon source is monosilane, the flow rate of monosilane is 0.6 L / min, the time of the second deposition process is 6 h, and the temperature is 450° C. Based on the total mass of the silicon-carbon negative electrode material of this comparative example, the carbon nanotube content is 0.120 wt%.

[0122] Comparative Example 2

[0123] The preparation method of the silicon-carbon negative electrode material of this comparative example is as follows:

[0124] (1) Placing the porous carbon substrate in an inert atmosphere, introducing a first gaseous carbon source for a first deposition process, and obtaining a first material, wherein the inert atmosphere is nitrogen, the first gaseous carbon source is ethylene, the flow rate of ethylene is 0.6 L / min, the time of the first deposition process is 8 h, and the temperature is 750° C.

[0125] (3) Switching the first gaseous carbon source to the first gaseous silicon source for a second deposition process to obtain a second material, wherein the first gaseous silicon source is monosilane, the flow rate of monosilane is 0.6 L / min, the second deposition process lasts for 6 hours, and the temperature is 450°C.

[0126] (4) Switch the first gaseous silicon source to the second gaseous carbon source for the third deposition treatment to generate a carbon coating layer to obtain the silicon-carbon negative electrode material of this comparative example. Since the porous carbon matrix of the silicon-carbon negative electrode material of this comparative example is not impregnated with a metal solution, carbon nanotubes cannot be deposited. The second gaseous carbon source is acetylene, and the flow rate of acetylene is 0.5 L / min. The time of the third deposition treatment is 8 hours, and the temperature is 450°C. Based on the total mass of the silicon-carbon negative electrode material of this comparative example, the content of the coating layer material is 2wt%.

[0127] Test Example 1

[0128] The performance of the silicon-carbon negative electrode materials prepared in Examples 1 to 18 and Comparative Examples 1 to 2 was tested. The test results are shown in Table 1.

[0129] Among them, the specific method for testing the performance of silicon-carbon negative electrode materials is as follows:

[0130] 1. Powder compaction density test method

[0131] Using the Sansi Zongheng powder compaction density tester, 1 to 2 g of negative electrode powder was put into a mold with an inner hole diameter of 13 mm. The test pressure was 5t and the pressure holding time was 30s to test the powder compaction density of the negative electrode material.

[0132] 2. Powder metal content test

[0133] Agilent ICP-OES 5800 equipment was used for testing. 0.1-0.2 g of negative electrode powder was digested with 10 mL of HNO3, heated on a graphite heating plate at 180±10°C for 30 min, and then the volume was fixed to 50 mL. The target metal element content was obtained using the calibration curve method.

[0134] 3. Powder gram capacity test

[0135] In a dry argon environment, LiPF6 was added to a solvent mixed with propylene carbonate (PC), ethylene carbonate (EC) and diethyl carbonate (DEC) (weight ratio of about 1:1:1), and the mixture was uniformly mixed to obtain an electrolyte, wherein the concentration of LiPF6 was about 1.15 mol / L. The silicon-carbon negative electrode material, conductive carbon black, binder sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) obtained in the embodiment and the comparative example were added to deionized water according to a weight ratio of about 94.5:1.5:1.5:1.5, stirred to form a slurry, and a coating with a thickness of about 100 μm was formed by coating with a scraper, dried at about 85°C in a vacuum drying oven for about 12 hours, cut into discs with a diameter of about 1 cm by a punch in a dry environment, and a metal lithium sheet was used as a counter electrode in a glove box, and a ceglard composite membrane was selected as the isolation membrane, and an electrolyte was added to assemble a button cell. The battery was charged and discharged using the LAND series battery tester to test its charge and discharge capacity, with a charge and discharge rate of 0.05C and a voltage of 5mV to 2V.

[0136] 4. Powder conductivity test.

[0137] Suzhou Jingge ST2722-SZ four-probe equipment is used, and the four-wire two-terminal method is adopted. The fixed body resistance is determined by measuring the voltage across the two ends of the resistor to be tested and the current flowing through, and the conductivity is calculated in combination with the height and bottom area of ​​the resistor to be tested. A certain amount of powder is added to the test mold, and then the gasket on the mold is placed on the sample; after the sample is loaded, the mold is placed on the workbench of the electronic pressure testing machine, and the pressure is increased to 500kg (159Mpa) at a rate of 5mm / min, constant pressure is applied for 60s, and then the pressure is released to 0; when the sample is constant-pressured to 5000±2kg (about 15-25s after the pressure is increased to 5000kg), the sample pressure is recorded, and the sample deformation height is read, and the value displayed by the resistance tester at this time is recorded, and the electronic conductivity can be calculated using the formula.

[0138] Table 1

[0139]

[0140] Test Example 2

[0141] The silicon-carbon negative electrode materials prepared in Examples 1 to 18 and Comparative Examples 1 to 2 are mixed with activated carbon materials (artificial graphite), single-walled carbon nanotubes, binder polyacrylic acid (PAA) and thickener carboxymethyl cellulose (CMC), wherein the mass ratio of active silicon material to activated carbon material is x%: (100-x)%, the mass sum of active silicon material and activated carbon material, single-walled carbon nanotubes, binder PAA and thickener CMC is 96.7%: 0.1%: 2.8%: 0.4%, and a proper amount of water is added, and kneading is performed at a solid content of about 60-75%. A proper amount of water is added to adjust the viscosity of the slurry to 3000-8000 Pa·S and the solid content to 45-55%, and a negative electrode slurry is prepared. The prepared negative electrode slurry is coated on the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet. The overall gram capacity of the negative electrode sheet of this patent is designed according to 450mAh / g, and the artificial graphite is designed according to 350mAh / g; the calculation method of x is: (450-350) / (silicon gram capacity-350).

[0142] The negative electrode sheet, the positive electrode sheet and the separator are used to prepare a battery cell, wherein the positive electrode sheet uses 622 ternary material as the positive electrode material and a polyethylene porous polymer film as the separator. The preparation method of the battery cell includes: stacking the positive electrode, the separator and the negative electrode in order, so that the separator is between the positive electrode and the negative electrode to play an isolation role. The stacking obtains a bare battery cell. The bare battery cell is placed in an outer package, injected with electrolyte, and packaged. After the process of formation, degassing, trimming and the like, a lithium-ion battery is obtained. The obtained battery cell is subjected to DCR test and high temperature cycle performance test. The specific results are shown in Table 2.

[0143] 1. DCR test:

[0144] At 25°C, discharge at 0.33C to 2.0V, let stand for 5 minutes, charge at 1C for 30 minutes, the voltage is V1 after standing for 5 minutes, discharge at 3C for 10 seconds to get a voltage of V2, then the DCR is (V1-V2) / 3C.

[0145] 2. High temperature cycle performance test:

[0146] The test temperature is 45℃, charge to 3.75V at 1C constant current, charge to 0.05C at constant voltage, and discharge to 2.0V at 1C after standing for 5 minutes. Take the capacity obtained in this step as the initial capacity, perform 1C charge / 1C discharge cycle test, and compare the capacity of each step with the initial capacity to obtain the capacity decay curve. Record the capacity retention rate when cycling 800 times at 45℃ to compare the high temperature cycle performance of the battery.

[0147] Table 2

[0148]

[0149]

[0150] It can be seen from the data in Tables 1 and 2 that the silicon-carbon negative electrode material of the present invention grows carbon nanotubes inside the pores of the porous carbon matrix, which can effectively improve the structural strength and compaction density of the material, and the overall conductivity, kinetics and cycle performance of the material are improved. The coating layer on the surface of the silicon-carbon composite particles can reduce the direct exposure of the nano-silicon material to the electrolyte and improve the cycle stability.

[0151] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A silicon-carbon negative electrode material, characterized in that: The silicon-carbon negative electrode material comprises silicon-carbon composite particles and a coating layer coated on the surface of the silicon-carbon composite particles; The silicon-carbon composite particles include a porous carbon matrix, a metal catalyst layer deposited in the pores of the porous carbon matrix, carbon nanotubes grown on the metal catalyst layer, and a nano-silicon layer deposited on the surface of the carbon nanotubes and the surface of the pores of the porous carbon matrix; The coating layer material includes at least one of a conductive material, a solid electrolyte and a metal oxide.

2. The silicon-carbon negative electrode material according to claim 1, characterized in that: The metal element in the metal catalyst substrate is selected from at least one of Group VIII elements and Group IIB elements; Optionally, the metal element in the metal catalyst base layer is selected from at least one of iron, cobalt, nickel and zinc; Optionally, based on the total mass of the silicon-carbon negative electrode material, the content of the metal element in the metal catalyst substrate is 0.05-1 wt %.

3. The silicon-carbon negative electrode material according to claim 1, characterized in that: The average D50 of the porous carbon matrix is ​​4 to 10 μm; The pore size of the porous carbon matrix is ​​2 to 50 nm, and the porosity of the porous carbon matrix is ​​25 to 90%; The specific surface area of ​​the porous carbon matrix is ​​100 to 3500 m 2 / g.

4. The silicon-carbon negative electrode material according to claim 1, characterized in that: The carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes; Optionally, based on the total mass of the silicon-carbon negative electrode material, the content of the carbon nanotubes is 0.01-0.2 wt %.

5. The silicon-carbon negative electrode material according to claim 1, characterized in that: The thickness of the nano silicon layer is 0.5 to 3 nm; Based on the total mass of the silicon-carbon negative electrode material, the content of nano-silicon deposited in the nano-silicon layer is 10-60wt%.

6. The silicon-carbon negative electrode material according to claim 1, characterized in that: The coating layer material is a conductive material; optionally, the conductive material includes carbon and / or graphene; Optionally, the coating layer has a thickness of 0.5 to 50 nm; Optionally, based on the total mass of the silicon-carbon negative electrode material, the content of the coating layer material is 0.5-3wt%.

7. A method for preparing the silicon-carbon negative electrode material according to claims 1 to 6, characterized in that: The preparation method comprises the following steps: S1, placing the porous carbon substrate in a metal solution for immersion treatment and drying treatment to obtain a first material; S2, placing the first material in a first inert atmosphere, introducing a first gaseous carbon source to perform a first deposition treatment, and obtaining a second material; S3, placing the second material in a second inert atmosphere, introducing the first gaseous silicon source to perform a second deposition process, and obtaining a third material; S4, performing surface coating treatment on the third material.

8. The preparation method according to claim 7, characterized in that: The solute in the metal solution includes at least one of FeCl2, FeCl3, ZnCl2, NiCl and CoCl2; the solvent in the metal solution includes at least one of water, ethanol, ethylene glycol, benzene and carbon tetrachloride; The first gaseous carbon source includes at least one of methane, ethane, propane, ethylene and acetylene; The first gaseous silicon source comprises at least one of monosilane, disilane and chlorosilane; The first inert atmosphere and the second inert atmosphere are each independently selected from nitrogen and / or argon.

9. The preparation method according to claim 7, characterized in that: In step S1, the conditions of the immersion treatment include: a temperature of 50 to 100° C. and a time of 30 to 90 min; In step S2, the introduction rate of the first gaseous carbon source is 0.2 to 1.0 L / min; the conditions of the first deposition treatment include: a deposition temperature of 500 to 1200° C., and a deposition time of 4 to 12 hours; In step S3, the introduction rate of the first gaseous silicon source is 0.2 to 1.0 L / min; the conditions of the first deposition treatment include: a deposition temperature of 400 to 700° C., and a deposition time of 2 to 12 hours; In step S4, the surface coating treatment includes at least one of gaseous deposition coating, liquid phase coating and solid phase coating.

10. A battery, characterized in that: The battery comprises a negative electrode material, and the negative electrode material comprises the silicon-carbon negative electrode material according to any one of claims 1 to 6 and / or the silicon-carbon negative electrode material prepared by the method according to any one of claims 7 to 9.

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