Silicon-carbon composite material and preparation method thereof, negative pole piece, battery and application

Abstract

The invention is suitable for the technical field of lithium ion battery materials, and discloses a silicon-carbon composite material and a preparation method thereof, a negative electrode plate, a lithium ion battery and application. The silicon-carbon composite material is of a core-shell structure and comprises an inner core and an outer shell, the inner core comprises porous carbon and a composite body deposited on the porous carbon, the composite body is composed of nanometer silicon, metal, a carbon nanotube and a heteroatom compound, and the shell comprises amorphous carbon; with the mass of the silicon-carbon composite material as the reference, the mass ratio of the shell is 1-5 wt%. According to the silicon-carbon composite material provided by the invention, the electronic and ionic conductivity is improved, the rate capability is improved, the expansion is reduced, and the cycle performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and in particular to a silicon-carbon composite material and a preparation method thereof, a negative electrode sheet, a lithium-ion battery and applications thereof. Background Art

[0002] Silicon-carbon materials are composed of porous carbon, nano-silicon deposited in the pores of the porous carbon, and amorphous carbon coated on the surface of the porous carbon. They can be used as a high-energy-density negative electrode material in high-energy-density batteries. At present, the silicon-carbon specific capacity in silicon-carbon materials is between 1800-2000mAh / g. Although it has a high specific capacity, for batteries with higher energy density, it needs to be further improved while taking into account expansion and circulation. In related technologies, the specific capacity of the material is increased by increasing the amount of silicon deposited, but this will cause more floating silicon in the silicon-carbon material, reduce the rate performance, increase the expansion, and reduce the cycle life. Summary of the Invention

[0003] The purpose of the present invention is to provide a silicon-carbon composite material and its preparation method, negative electrode plate, lithium-ion battery and application, aiming to solve the technical problems of improving the specific capacity of silicon-carbon materials while causing decreased rate performance, increased expansion, and reduced cycle performance.

[0004] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0005] A first aspect of the present invention provides a silicon-carbon composite material, wherein the silicon-carbon composite material has a core-shell structure, comprising a core and an outer shell;

[0006] The inner core includes porous carbon and a composite body deposited on the porous carbon, wherein the composite body is composed of nano-silicon, metal, carbon nanotubes and heteroatom compounds, and the outer shell includes amorphous carbon. Based on the mass of the silicon-carbon composite material, the mass ratio of the outer shell is 1-5wt%.

[0007] It should be noted that by doping carbon nanotubes and doping metals, the electronic and ionic conductivity of silicon-carbon composite materials can be improved, the rate performance can be improved, the expansion can be reduced, and the cycle performance can be improved.

[0008] In one implementation of the present invention, the metal includes at least one of zinc, magnesium, and lithium.

[0009] A second aspect of the present invention provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0010] S1, uniformly mixing porous carbon, carbon nanotubes, an organic metal catalyst, a heteroatom compound, and hydrogen peroxide, performing a hydrothermal reaction, and then filtering and freeze-drying to obtain modified porous carbon;

[0011] S2, transferring the modified porous carbon to a tube furnace, first introducing a reducing mixed gas for treatment, and then introducing a metal sublimation gas for treatment, to obtain a multi-element doped porous carbon;

[0012] S3. After introducing an inert gas into the tubular furnace containing the multi-element doped porous carbon, a silane mixed gas is introduced for treatment, and then a mixed gas of a carbon source gas and a heteroatom gas is introduced for treatment to obtain a silicon-carbon composite material.

[0013] It should be noted that by doping organic metal catalysts in porous carbon, under high temperature conditions (the hydrothermal reaction is carried out under high temperature conditions), the carbon layer spacing can be expanded, the diffusion rate of lithium ions can be increased and the expansion can be reduced, while the silicon storage capacity and specific capacity can be increased. By doping carbon nanotubes and heteroatom compounds, the electronic conductivity of the material can be improved by utilizing the characteristics of carbon nanotubes and heteroatom compounds, and the high strength characteristics of carbon nanotubes can be utilized to reduce expansion. By treating with a reducing mixed gas, the hydrophilic groups on the surface of the material can be reduced, the electronic conductivity of the interface can be improved, and by doping with metal gases, the electronic conductivity of the material can be improved, and the rate performance can be improved.

[0014] In one implementation of the present invention, step S1 satisfies one or more of the following conditions a to e:

[0015] a. In step S1, the porous carbon, the carbon nanotubes, the organometallic catalyst, the heteroatom compound and the hydrogen peroxide are mixed in a mass ratio of 100:(1-5):(1-5):(1-5):(10-20);

[0016] It should be noted that, when carbon nanotubes, organic metal catalysts, heteroatom compounds and hydrogen peroxide are mixed in a mass ratio of 100:(1-5):(1-5):(1-5):(10-20), the electronic conductivity of the material can be improved, the pore volume can be increased, the lithium storage function of the material can be improved, and the specific capacity can be increased; when the amount of carbon nanotubes added is too low, the improvement in the electronic conductivity and the reduction in expansion of the material is low; when the amount of carbon nanotubes added is too high, the initial efficiency is reduced; when the amount of organic metal catalyst added is too low, the pore-forming effect is poor, and the lithium storage capacity is reduced; when the amount of organic metal catalyst added is too high, the pore-forming effect is too high, and the strength of the pore is reduced; when the amount of heteroatom compound added is too low, the improvement in electronic conductivity is limited; when the amount of heteroatom compound added is too high, the tap density is reduced.

[0017] b. In step S1, the concentration of the carbon nanotubes is 1-5wt%;

[0018] c. In the step S1, the organometallic catalyst is at least one of palladium acetate, tetrakistriphenylphosphine palladium, and ditriphenylphosphine palladium dichloride;

[0019] d. In step S1, the heteroatom compound is a purine series heteroatom compound; preferably, the purine series heteroatom compound is at least one of 6-hydroxypurine, adenine, mercaptopurine, 2-amino-6-hydroxypurine, and 8-mercaptoadenine;

[0020] e. In step S1, the hydrothermal reaction temperature is 130-170°C, the pressure is 3-7 MPa, and the time is 1.5-4 h; preferably, the hydrothermal reaction temperature is 150°C, the pressure is 5 MPa, and the time is 2 h.

[0021] In one implementation of the present invention, step S2 satisfies one or more of the following conditions a to d:

[0022] a. In the step S2, the reducing gas mixture is introduced at a temperature of 400-600 ℃ for 30-300min, and the flow rate of the reducing gas mixture is 100-500SCCM;

[0023] b. In step S2, the reducing gas mixture is a mixture of a reducing gas and nitrogen, the reducing gas being at least one of hydrogen and carbon monoxide; preferably, the volume ratio of the reducing gas to the nitrogen is (1-5): 10;

[0024] c. In the step S2, the metal sublimation gas is introduced for treatment at a temperature of 1400-1800°C for 30-300min, and the flow rate of the metal sublimation gas is 10-50SCCM;

[0025] d. In step S2, the metal sublimation gas is a sublimated gas of at least one of zinc, magnesium, and lithium.

[0026] In one implementation of the present invention, step S3 satisfies one or more of the following conditions a to e:

[0027] a. In the step S3, the temperature of the silane mixed gas is 500-700 ℃ for 30-300min, and the flow rate of the silane mixed gas is 50-200SCCM;

[0028] b. In step S3, the silane gas mixture is a mixture of silane gas and nitrogen, the silane gas being at least one of monosilane, disilane, monochlorosilane and methyltrichlorosilane; preferably, the volume ratio of the silane gas to the nitrogen is (1-5): 10;

[0029] c. In step S3, the temperature of the carbon source gas and the heteroatom gas mixture is 650-900°C for 30-300min, and the flow rate of the carbon source gas and the heteroatom gas mixture is 50-200 SCCM;

[0030] d. In step S3, the carbon source gas is at least one of methane, ethane, ethylene, and acetylene, and / or the heteroatom gas is an inorganic heteroatom gas; preferably, the inorganic heteroatom gas is at least one of ammonia, phosphine, and hydrogen sulfide;

[0031] e. In step S3, in the mixed gas of the carbon source gas and the heteroatom gas, the volume ratio of the carbon source gas to the heteroatom gas is 1:1.

[0032] A third aspect of the present invention provides a silicon-carbon composite material, which is prepared using the preparation method of the silicon-carbon composite material according to the second aspect.

[0033] It should be noted that the silicon-carbon composite material prepared by the above-mentioned preparation method can reduce expansion while increasing specific capacity, improve cycle performance, and increase the electronic conductivity of the material, thereby improving rate performance.

[0034] In one implementation of the present invention, the silicon-carbon composite material has a core-shell structure, comprising a core and an outer shell;

[0035] The inner core includes porous carbon and a composite body deposited on the porous carbon, wherein the composite body is composed of nano-silicon, metal, carbon nanotubes and heteroatom compounds, and the outer shell includes amorphous carbon. Based on the mass of the silicon-carbon composite material, the mass ratio of the outer shell is 1-5wt%.

[0036] In one implementation of the present invention, the metal includes at least one of zinc, magnesium, and lithium.

[0037] A fourth aspect of the present invention provides a negative electrode plate comprising the silicon-carbon composite material of the first and third aspects.

[0038] It should be noted that by adopting the above-mentioned silicon-carbon composite material, the specific capacity of the negative electrode plate is increased while the expansion is reduced, the cycle performance is improved, and it has better ionic and electronic conductivity and improved rate performance.

[0039] A fifth aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet of the fourth aspect.

[0040] It should be noted that by adopting the above-mentioned negative electrode plate, the lithium-ion battery has the characteristics of large specific capacity, low expansion, good rate performance and good cycle performance.

[0041] The sixth aspect of the present invention provides an application of a silicon-carbon composite material, wherein the silicon-carbon composite material of the first and third aspects is used as an active material raw material for preparing battery pole pieces, preferably as an active material raw material for lithium-ion battery negative pole pieces.

[0042] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0043] 1) By doping porous carbon with organometallic catalysts, the carbon interlayer spacing can be expanded under high temperature conditions, increasing the diffusion rate of lithium ions and reducing expansion, while increasing silicon storage capacity and specific capacity;

[0044] 2) By doping carbon nanotubes and heteroatom compounds, the electronic conductivity of the material can be improved by utilizing the properties of carbon nanotubes and heteroatom compounds, and the expansion can be reduced by utilizing the high strength properties of carbon nanotubes.

[0045] 3) By treating with a reducing mixed gas, the hydrophilic groups on the surface of the material can be reduced, the electronic conductivity of the interface can be improved, and by doping with metal gas, the electronic conductivity of the material can be increased, thereby improving the rate performance;

[0046] 4) By combining purine series heteroatom compounds with inorganic heteroatom gases (ammonia, phosphine, etc.), after heating and carbonization, the material can have the characteristics of high electronic conductivity and large pore size. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] in:

[0049] Figure 1 This is an SEM image of the silicon-carbon composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below by specific embodiments in conjunction with the accompanying drawings. In the following embodiments, many detailed descriptions are intended to enable the present application to be better understood. However, those skilled in the art can readily appreciate that some of the features may be omitted in different circumstances, or may be replaced by other materials or methods. In some cases, some operations related to the present application are not shown or described in the specification. This is to avoid overwhelm the core of the present application with excessive descriptions, and for those skilled in the art, it is not necessary to describe these related operations in detail. The related operations can be fully understood based on the description in the specification and the general technical knowledge in the art.

[0051] In addition, the features, operations, or characteristics described in the specification may be combined in any appropriate manner to form various embodiments. Furthermore, the steps or actions in the method description may be reordered or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various sequences in the specification and drawings are provided solely for the purpose of clearly describing a particular embodiment and are not intended to be mandatory, unless otherwise specified.

[0052] A first aspect of the present invention provides a silicon-carbon composite material, wherein the silicon-carbon composite material has a core-shell structure, comprising a core and an outer shell;

[0053] The inner core includes porous carbon and a composite body deposited on the porous carbon, wherein the composite body is composed of nano-silicon, metal, carbon nanotubes and heteroatom compounds, and the outer shell includes amorphous carbon. Based on the mass of the silicon-carbon composite material, the mass ratio of the outer shell is 1-5wt%.

[0054] By doping carbon nanotubes and doping metals, the electronic and ionic conductivity of silicon-carbon composites can be improved, the rate performance can be improved, the expansion can be reduced, and the cycle performance can be improved.

[0055] A second aspect of the present invention provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0056] S1, uniformly mixing porous carbon, carbon nanotubes, an organic metal catalyst, a heteroatom compound, and hydrogen peroxide, performing a hydrothermal reaction, and then filtering and freeze-drying to obtain modified porous carbon;

[0057] S2, transferring the modified porous carbon to a tube furnace, first introducing a reducing mixed gas for treatment, and then introducing a metal sublimation gas for treatment, to obtain a multi-element doped porous carbon;

[0058] S3. After introducing an inert gas into the tubular furnace containing the multi-element doped porous carbon, a silane mixed gas is introduced for treatment, and then a mixed gas of a carbon source gas and a heteroatom gas is introduced for treatment to obtain a silicon-carbon composite material.

[0059] By doping porous carbon with organic metal catalysts, under high temperature conditions (the hydrothermal reaction is carried out under high temperature conditions), the carbon layer spacing can be expanded, the diffusion rate of lithium ions can be increased, and expansion can be reduced, while increasing the silicon storage capacity and specific capacity. By doping carbon nanotubes and heteroatom compounds, the electronic conductivity of the material can be improved by utilizing the characteristics of carbon nanotubes and heteroatom compounds, and the high strength characteristics of carbon nanotubes can be utilized to reduce expansion. By treating with a reducing mixed gas, the hydrophilic groups on the surface of the material can be reduced, improving the electronic conductivity of the interface, and by doping with metal gases, the electronic conductivity of the material can be increased, improving the rate performance.

[0060] A third aspect of the present invention provides a silicon-carbon composite material, which is prepared using the preparation method of the silicon-carbon composite material according to the second aspect.

[0061] The silicon-carbon composite material prepared by the above preparation method can reduce expansion while increasing specific capacity, improve cycle performance, and increase the electronic conductivity of the material, thereby improving rate performance.

[0062] A fourth aspect of the present invention provides a negative electrode plate comprising the silicon-carbon composite material of the first and third aspects.

[0063] By adopting the above silicon-carbon composite material, the specific capacity of the negative electrode plate is increased while the expansion is reduced, the cycle performance is improved, and it has better ionic and electronic conductivity and improved rate performance.

[0064] A fifth aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet of the fourth aspect.

[0065] By adopting the above-mentioned negative electrode plate, the lithium-ion battery has the characteristics of large specific capacity, low expansion, good rate performance and excellent cycle performance.

[0066] The sixth aspect of the present invention provides an application of a silicon-carbon composite material, wherein the silicon-carbon composite material of the first and third aspects is used as an active material raw material for preparing battery pole pieces, preferably as an active material raw material for lithium-ion battery negative pole pieces.

[0067] The present application is further described in detail below through specific examples. The following examples are only provided to further illustrate the present application and should not be construed as limiting the present application. It should be noted that if specific conditions are not specified in the examples, the process is carried out according to conventional conditions or the conditions recommended by the product manufacturer; the equipment and reagents used in the examples, for which the manufacturer is not specified, are all conventional products that can be purchased through commercial channels.

[0068] Example 1

[0069] A method for preparing a silicon-carbon composite material comprises the following steps:

[0070] Step S1:

[0071] 100 g of porous carbon was mixed with 100 g of a 3 wt% carboxylated carbon nanotube solution, 3 g of ditriphenylphosphine palladium dichloride, 3 g of 6-hydroxypurine, and 15 g of hydrogen peroxide. The mixture was hydrothermally reacted at 150° C. and 5 MPa for 2 h, filtered, and the resulting material was freeze-dried at −40° C. for 48 h to obtain a modified porous carbon.

[0072] Step S2:

[0073] The modified porous carbon was transferred to a tube furnace, heated to 500°C, and a mixed gas of hydrogen and nitrogen (volume ratio, hydrogen: nitrogen = 3:10) was introduced at a flow rate of 300 SCCM for 150 minutes for surface modification. The temperature was then raised to 1600°C, and metallic zinc gas was introduced at a flow rate of 30 SCCM for 150 minutes to obtain multi-element doped porous carbon.

[0074] Step S3:

[0075] The multi-element doped porous carbon was transferred to a tubular furnace. Argon inert gas was first introduced to exhaust the gas in the tube. Then, it was heated to 600°C and a disilane mixed gas (volume ratio, disilane: nitrogen = 1:5) was introduced at a flow rate of 100 SCCM for 150 minutes. Then, it was heated to 800°C and a ethane and phosphine mixed gas (volume ratio, ethane: phosphine = 1:1) was introduced at a flow rate of 100 SCCM for 150 minutes to obtain a silicon-carbon composite material.

[0076] Example 2

[0077] A method for preparing a silicon-carbon composite material comprises the following steps:

[0078] Step S1:

[0079] 100 g of porous carbon was mixed with 100 g of a 1 wt% carboxylated carbon nanotube solution, 1 g of palladium acetate, 1 g of adenine, and 10 g of hydrogen peroxide. The mixture was hydrothermally reacted at 150° C. and 5 MPa for 2 h. The resulting material was filtered and freeze-dried at -40° C. for 48 h to obtain modified porous carbon.

[0080] Step S2:

[0081] The modified porous carbon was transferred to a tube furnace, heated to 400°C, and a mixed gas of carbon monoxide and nitrogen (volume ratio, carbon monoxide: nitrogen = 1:10) was introduced at a flow rate of 100 SCCM for surface modification for 300 minutes. The temperature was then raised to 1400°C, and metallic magnesium gas was introduced at a flow rate of 10 SCCM for 300 minutes to obtain multi-element doped porous carbon.

[0082] Step S3:

[0083] The multi-element doped porous carbon was transferred to a tubular furnace. First, argon inert gas was introduced to exhaust the gas in the tube. Then, it was heated to 500°C and a silane mixed gas (volume ratio, silane: nitrogen = 1:10) was introduced at a flow rate of 50 SCCM for 300 minutes. Then, it was heated to 650°C and a acetylene and ammonia mixed gas (volume ratio, acetylene: ammonia = 1:1) was introduced at a flow rate of 50 SCCM for 300 minutes to obtain a silicon-carbon composite material.

[0084] Example 3

[0085] A method for preparing a silicon-carbon composite material comprises the following steps:

[0086] Step S1:

[0087] 100 g of porous carbon was mixed with 100 g of a 5 wt% carboxylated carbon nanotube solution, 5 g of tetrakistriphenylphosphine palladium, 5 g of mercaptopurine, and 20 g of hydrogen peroxide. The mixture was hydrothermally reacted at 150° C. and 5 MPa for 2 h, and the resulting material was freeze-dried at −40° C. for 24 h to obtain a modified porous carbon.

[0088] Step S2:

[0089] The modified porous carbon was transferred to a tube furnace, heated to 600°C, and a mixed gas of hydrogen and nitrogen (volume ratio, hydrogen: nitrogen = 5:10) was introduced at a flow rate of 500 SCCM for 30 minutes for surface modification. The temperature was then raised to 1800°C, and metallic lithium gas was introduced at a flow rate of 50 SCCM for 30 minutes to obtain multi-element doped porous carbon.

[0090] Step S3:

[0091] The multi-element doped porous carbon was transferred to a tubular furnace. First, argon inert gas was introduced to exhaust the gas in the tube. Then, it was heated to 700°C and a monochlorosilane mixed gas (volume ratio, monochlorosilane: nitrogen = 5:10) was introduced at a flow rate of 200 SCCM for 30 minutes. Then, it was heated to 900°C and a methane and hydrogen sulfide mixed gas (volume ratio, methane: hydrogen sulfide = 1:1) was introduced at a flow rate of 200 SCCM for 30 minutes to obtain a silicon-carbon composite material.

[0092] Comparative Example 1

[0093] The difference from Example 1 is that the carboxylated carbon nanotube solution, the ditriphenylphosphine palladium dichloride catalyst and 6-hydroxypurine are not added in step S1. Other steps are the same as those in Example 1.

[0094] Comparative Example 2

[0095] The difference from Example 1 is that no ditriphenylphosphine palladium dichloride catalyst is added in step S1, and the other steps are the same as Example 1.

[0096] Comparative Example 3

[0097] The difference from Example 1 is that the carboxylated carbon nanotube solution and 6-hydroxypurine are not added in step S1 . The other steps are the same as those in Example 1.

[0098] Comparative Example 4

[0099] The difference from Example 1 is that in step S1, 100 g of porous carbon, 100 g of 20 wt% carboxylated carbon nanotube solution, 20 g of ditriphenylphosphine palladium dichloride, 20 g of 6-hydroxypurine and 15 g of hydrogen peroxide are mixed evenly. Other steps are the same as in Example 1.

[0100] Comparative Example 5

[0101] The difference from Example 1 is that in step S2, metallic zinc gas is not introduced, but the introduction of a mixed gas of hydrogen and nitrogen is extended for 150 minutes. The rest is the same as in Example 1.

[0102] Comparative Example 6

[0103] The difference from Example 1 is that in step S2, metallic zinc gas is introduced at a flow rate of 200 SCCM for 150 minutes. The rest is the same as Example 1.

[0104] Physical and chemical performance testing and button battery testing

[0105] SEM test: Figure 1 This is a SEM image of the silicon-carbon composite material prepared in Example 1. As can be seen from the figure, the material has a spherical structure with a reasonable and uniform size distribution. The particle size is between 5-10 microns and there is slight adhesion.

[0106] The specific surface area and tap density of the silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-6 were tested according to the method in GB / T 38823-2020 "Silicon Carbon", and the powder resistivity was tested using a powder resistance tester (model ST2742B).

[0107] The silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-6 were respectively used to prepare button batteries according to the following method: using each heteroatom-doped silicon-carbon composite material as the negative electrode material, LA136D binder, SP conductive agent and NMP solvent were added respectively (silicon-carbon composite material: SP conductive agent: LA136D binder: NMP solvent = 95g: 1g: 4g: 220mL), stirred and slurried, and then coated on copper foil. After drying and rolling, each battery negative electrode sheet was obtained. Each battery negative electrode sheet was assembled with a counter electrode (metal lithium sheet), an electrolyte (1 mol / L LiPF6 solution, the solvent was composed of ethylene carbonate and diethyl carbonate (1:1) in a volume ratio of 1:1) and a diaphragm (polypropylene film) in an argon-filled glove box to form a button battery. The button battery was subjected to the following performance test using a Wuhan Blue Electric Battery Tester (model CT2001A):

[0108] 1) First discharge specific capacity and first efficiency: The test conditions are charge and discharge voltage of 0.005V-2.0V and charge and discharge rate of 0.1C;

[0109] 2) Rate performance: Test conditions are 1C / 0.1C;

[0110] 3) Full Charge Expansion Rate: Test the thickness D1 of the negative electrode sheet of each battery after rolling. Then fully charge the button battery to 100% SOC, dissect its negative electrode sheet, and test the thickness D2 of the negative electrode sheet at this time. Calculate the full charge expansion rate according to the following formula: Full Charge Expansion Rate = (D1-D2)÷D1×100%.

[0111] The test results are shown in Table 1 below.

[0112] Table 1

[0113]

[0114] As can be seen from Table 1, compared with comparative examples 1-6, the materials made from the silicon-carbon composite materials in Examples 1-3 are superior to the comparative examples in terms of powder resistance, specific capacity, initial efficiency and full-charge expansion rate. The reason may be that the materials in the examples are doped with carbon nanotubes with high electronic conductivity, and the organic metal catalyst volatilizes to expand the pores and increase the pore volume, thereby improving the specific capacity of the material. At the same time, the large interlayer spacing and low powder electrons improve the rate performance.

[0115] Soft pack battery testing

[0116] The silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-6 were used to prepare soft-pack batteries according to the following method: the silicon-carbon composite materials were doped with artificial graphite (the mass ratio of the silicon-carbon composite material to the artificial graphite was 1:9) as the negative electrode and the positive electrode ternary material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, electrolyte (1.3 mol / L LiPF6, solvent composed of a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1), and separator (celegard 2400) were assembled into 5Ah soft-pack batteries. The following performance tests were performed on each soft-pack battery:

[0117] 1) Liquid absorption capacity: Use a 1mL burette to absorb 1mL of electrolyte, add one drop of electrolyte to the surface of the negative electrode, and time until the electrolyte is completely absorbed. Record the absorption time.

[0118] 2) Electrode sheet surface resistance test: Use an electrode sheet surface resistance tester (model FT-551) to measure the surface area of ​​100cm 2 The negative electrode is placed on the test bench and the resistance is tested under a pressure of 500kg;

[0119] 3) Cycling performance test: The test conditions are charge and discharge voltage range of 2.5~4.2V, temperature of 25±3.0℃, charge and discharge rate of 1.0C / 1.0C, and cycle number of 500 times;

[0120] 4) Rate performance test: The charge capacity retention rate (constant current capacity / (constant current capacity + constant voltage capacity)) at 0.5C, 1C, 2C and 3C is tested respectively.

[0121] The test results are shown in Table 2 below.

[0122] Table 2

[0123]

[0124]

[0125] It can be seen from Table 2 that compared with Comparative Examples 1-6, the soft-pack batteries prepared from the silicon-carbon composite materials in Examples 1-3 have higher liquid absorption capacity and lower electrode sheet surface resistance. The reason is that the silicon-carbon composite materials prepared in Examples 1-3 have higher specific surface area and lower powder resistivity, which shortens the liquid absorption time and reduces the surface resistance.

[0126] Compared with Comparative Examples 1-6, the soft-pack batteries prepared from the silicon-carbon composite materials in Examples 1-3 have better cycle performance. The reason is that the silicon-carbon composite materials prepared in Examples 1-3 have lower expansion and higher specific surface area, which improves the liquid retention performance, reduces the expansion of the soft-pack batteries during the cycle, and improves the cycle performance.

[0127] Compared with comparative examples 1-6, the soft-pack batteries prepared from the silicon-carbon composite materials in Examples 1-3 have better rate performance. The reason is that the silicon-carbon composite material prepared in Example 1 has higher powder conductivity and larger specific surface area, thereby improving the rate performance.

[0128] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material has a core-shell structure, comprising a core and an outer shell; The inner core includes porous carbon and a composite body deposited on the porous carbon, wherein the composite body is composed of nano-silicon, metal, carbon nanotubes and heteroatom compounds, and the outer shell includes amorphous carbon. Based on the mass of the silicon-carbon composite material, the mass ratio of the outer shell is 1-5wt%.

2. The silicon-carbon composite material according to claim 1, wherein The metal includes at least one of zinc, magnesium and lithium.

3. A method for preparing a silicon-carbon composite material, characterized in that: The following steps are involved: S1, uniformly mixing porous carbon, carbon nanotubes, an organic metal catalyst, a heteroatom compound, and hydrogen peroxide, performing a hydrothermal reaction, and then filtering and freeze-drying to obtain modified porous carbon; S2, transferring the modified porous carbon to a tube furnace, first introducing a reducing mixed gas for treatment, and then introducing a metal sublimation gas for treatment, to obtain a multi-element doped porous carbon; S3. After introducing an inert gas into the tubular furnace containing the multi-element doped porous carbon, a silane mixed gas is introduced for treatment, and then a mixed gas of a carbon source gas and a heteroatom gas is introduced for treatment to obtain a silicon-carbon composite material.

4. The method for preparing the silicon-carbon composite material according to claim 3, wherein: Step S1 satisfies one or more of the following conditions a to e: a. In step S1, the porous carbon, the carbon nanotubes, the organometallic catalyst, the heteroatom compound and the hydrogen peroxide are mixed in a mass ratio of 100:(1-5):(1-5):(1-5):(10-20); b. In step S1, the concentration of the carbon nanotubes is 1-5wt%; c. In the step S1, the organometallic catalyst is at least one of palladium acetate, tetrakistriphenylphosphine palladium, and ditriphenylphosphine palladium dichloride; d. In step S1, the heteroatom compound is a purine series heteroatom compound; preferably, the purine series heteroatom compound is at least one of 6-hydroxypurine, adenine, mercaptopurine, 2-amino-6-hydroxypurine, and 8-mercaptoadenine; e. In step S1, the hydrothermal reaction temperature is 130-170°C, the pressure is 3-7 MPa, and the time is 1.5-4 h.

5. The method for preparing the silicon-carbon composite material according to claim 3, wherein: Step S2 satisfies one or more of the following conditions a to d: a. In the step S2, the reducing gas mixture is introduced at a temperature of 400-600 ℃ for 30-300min, and the flow rate of the reducing gas mixture is 100-500SCCM; b. In step S2, the reducing gas mixture is a mixture of a reducing gas and nitrogen, the reducing gas being at least one of hydrogen and carbon monoxide; preferably, the volume ratio of the reducing gas to the nitrogen is (1-5): 10; c. In the step S2, the metal sublimation gas is introduced for treatment at a temperature of 1400-1800°C for 30-300min, and the flow rate of the metal sublimation gas is 10-50SCCM; d. In step S2, the metal sublimation gas is a sublimated gas of at least one of zinc, magnesium, and lithium.

6. The method for preparing the silicon-carbon composite material according to claim 3, wherein: Step S3 satisfies one or more of the following conditions a to e: a. In the step S3, the temperature of the silane mixed gas is 500-700 ℃ for 30-300min, and the flow rate of the silane mixed gas is 50-200SCCM; b. In step S3, the silane gas mixture is a mixture of silane gas and nitrogen, the silane gas being at least one of monosilane, disilane, monochlorosilane and methyltrichlorosilane; preferably, the volume ratio of the silane gas to the nitrogen is (1-5): 10; c. In step S3, the temperature of the carbon source gas and the heteroatom gas mixture is 650-900°C for 30-300min, and the flow rate of the carbon source gas and the heteroatom gas mixture is 50-200 SCCM; d. In step S3, the carbon source gas is at least one of methane, ethane, ethylene, and acetylene, and / or the heteroatom gas is an inorganic heteroatom gas; preferably, the inorganic heteroatom gas is at least one of ammonia, phosphine, and hydrogen sulfide; e. In step S3, in the mixed gas of the carbon source gas and the heteroatom gas, the volume ratio of the carbon source gas to the heteroatom gas is 1:

1.

7. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material is prepared by the preparation method according to any one of claims 3 to 6.

8. A negative electrode plate, characterized in that: Comprising the silicon-carbon composite material as described in claim 1, 2 or 7.

9. A lithium-ion battery, characterized in that: Comprising the negative electrode sheet as claimed in claim 8.

10. An application of a silicon-carbon composite material, characterized in that: The silicon-carbon composite material as claimed in claim 1, 2 or 7 is used as an active material raw material for preparing battery pole pieces, preferably as an active material raw material for lithium-ion battery negative pole pieces.

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