Carbon-silicon composite material, preparation method thereof, negative electrode sheet and lithium ion battery

Abstract

The present disclosure relates to a carbon-silicon composite material, a preparation method thereof, a negative electrode sheet and a lithium ion battery. The method comprises the following steps: S1, mixing a silicon source with an organic solvent, and performing a crushing treatment to obtain a nano-silicon slurry; S2, contacting the nano-silicon slurry with a first carbon source to perform a first in-situ coating reaction, and obtaining a primary coated nano-silicon slurry, wherein the first carbon source comprises an organic acid; S3, contacting the primary coated nano-silicon slurry with a second carbon source to perform a second in-situ coating reaction, and obtaining a secondary coated nano-silicon slurry, wherein the second carbon source comprises an organic amine; S4, contacting the secondary coated nano-silicon slurry with a carbonizable binder and a third carbon source to perform a third in-situ coating reaction, and obtaining a carbon-silicon composite material precursor, wherein the third carbon source comprises a graphite-based carbon source; and S5, performing a calcination treatment on the carbon-silicon composite material precursor under an inert atmosphere. A carbon-silicon composite material with high initial coulombic efficiency and cycle stability is prepared.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of lithium ion batteries, in particular, to a carbon-silicon composite material, a preparation method thereof, a negative electrode sheet and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have become the ideal chemical power source for modern communication, portable electronic products and hybrid electric vehicles, etc. due to their high specific energy, long charge-discharge life, no memory effect, low self-discharge rate, fast charging, no pollution, wide working temperature range and safety and reliability. The currently commercialized negative electrode material is graphite, with a theoretical specific capacity of 372 mAh·g -1 , which cannot meet the needs of high energy density batteries, and therefore it is necessary to develop high-capacity negative electrode active materials.

[0003] Silicon has attracted extensive research due to its high theoretical specific capacity (4200 mA h g -1 ), low working voltage and other characteristics, and it is abundant in the earth's crust, low in cost and environmentally friendly, and is one of the most potential next-generation lithium ion battery negative electrode materials. However, the huge volume expansion and contraction (volume change rate close to 300%) of silicon during charging and discharging will cause the pulverization and structural damage of silicon, leading to the separation of the battery materials and the current collector, resulting in rapid capacity decay, which seriously affects the cycle performance and service life of the battery. SUMMARY

[0004] The purpose of the present disclosure is to provide a carbon-silicon composite material, a preparation method thereof, a negative electrode sheet and a lithium ion battery. The carbon-silicon composite material with high first coulomb efficiency and stable cycle performance is prepared by a method comprising silicon nanocrystallization and silicon-carbon compounding.

[0005] To achieve the above purpose, the first aspect of the present disclosure provides a method for preparing a carbon-silicon composite material, comprising the following steps:

[0006] S1, mixing a silicon source with an organic solvent and performing a crushing treatment to obtain a nano-silicon slurry;

[0007] S2, contacting the nano-silicon slurry with a first carbon source to perform a first in-situ coating reaction to obtain a primary coated nano-silicon slurry, the first carbon source comprising an organic acid;

[0008] S3, contacting the primary coated nano-silicon slurry with a second carbon source to perform a second in-situ coating reaction to obtain a secondary coated nano-silicon slurry, the second carbon source comprising an organic amine;

[0009] S4, contacting the secondary coated nano-silicon slurry with a carbonizable binder and a third carbon source to perform a third in-situ coating reaction to obtain a carbon-silicon composite material precursor, the third carbon source comprising a graphite-based carbon source.

[0010] S5, baking the carbon-silicon composite material precursor under an inert atmosphere.

[0011] Optionally, in step S1, the silicon source is a silicon powder; optionally, the silicon powder comprises single crystal silicon and / or polycrystalline silicon; optionally, the particle size of the silicon powder ranges from 1 μm to 10 μm.

[0012] Optionally, the organic solvent is selected from one or more of an alcohol organic solvent, a hydrocarbon organic solvent, and a benzene organic solvent.

[0013] Preferably, the alcohol organic solvent is selected from one or more of ethanol, propanol, and isopropanol.

[0014] The hydrocarbon organic solvent is selected from one or more of hexane, cyclohexane, and isooctane.

[0015] The benzene organic solvent is selected from one or more of benzene, toluene, and xylene.

[0016] Preferably, the weight of the silicon source is 3 g to 20 g, preferably 5 g to 15 g, relative to 100 mL of the organic solvent.

[0017] Optionally, in step S1, the crushing treatment comprises sand mill mechanical crushing treatment; preferably, the sand mill mechanical crushing treatment is performed under an inert atmosphere in a sand mill at a speed of 2000 r / min to 2500 r / min for 4 to 50 h, preferably 6 to 20 h.

[0018] Preferably, the D50 particle size of the solid nanosilicon in the nanosilicon slurry obtained via the crushing treatment ranges from 5 nm to 150 nm, preferably from 30 nm to 100 nm.

[0019] Optionally, in step S2, the weight ratio of the first carbon source to the silicon source is 1:0.2 to 5, preferably 1:0.5 to 5.

[0020] Preferably, the organic acid comprises one or more of a hydroxyl-containing organic carboxylic acid and a hydroxyl-containing carboxylic acid ester.

[0021] Optionally, the hydroxyl-containing organic carboxylic acid is selected from one or more of tartaric acid, citric acid, lactobionic acid, malic acid, and glutamic acid.

[0022] Preferably, the hydroxyl-containing carboxylic acid ester comprises ascorbic acid.

[0023] Preferably, the organic acid is selected from one or more of citric acid, tartaric acid, and malic acid.

[0024] Optionally, in step S2, the conditions of the first in-situ coating reaction include: a reaction temperature of 15-60°C, and a reaction time of 0.25-4h; preferably, the reaction temperature is 20-30°C, and the reaction time is 0.5-2h; optionally, the stirring rate is 200-600r / min, preferably 300-450r / min.

[0025] Optionally, in step S3, the weight ratio of the second carbon source to the first carbon source is 0.1-2:1, preferably 0.3-1.2:1, and further preferably 0.4-1:1.

[0026] Preferably, the organic amine is selected from one or more of melamine and its ammonium salt, dopamine and its ammonium salt, and hexamethylenetetramine and its ammonium salt; preferably, the organic amine is selected from one or both of dopamine and melamine.

[0027] Optionally, in step S3, the conditions of the second in-situ coating reaction include: a reaction temperature of 15-60°C, and a reaction time of 0.25-4h; preferably, the reaction temperature is 20-30°C, and the reaction time is 0.5-2h; optionally, the stirring rate is 200-600r / min, preferably 300-450r / min.

[0028] Optionally, in step S4, the weight ratio of the carbonizable binder to the silicon source is 0.1-2:1, preferably 0.1-1:1.

[0029] Optionally, the carbonizable binder is selected from one or more of pitch, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose.

[0030] Preferably, in step S4, the weight ratio of the third carbon source to the silicon source is 4-50:1, preferably 6-40:1.

[0031] Optionally, the graphite-based carbon source is selected from one or more of natural graphite, artificial graphite, and flake graphite; preferably, the graphite-based carbon source is selected from one or more of natural graphite and artificial graphite having a quasi-spherical structure.

[0032] Optionally, in step S4, the conditions of the third in-situ coating reaction include: a reaction temperature of 15-60°C, and a reaction time of 0.25-4h; preferably, the reaction temperature is 20-30°C, and the reaction time is 0.5-2h; optionally, the stirring rate is 200-600r / min, preferably 300-400r / min.

[0033] Preferably, step S4 further comprises spray drying the mixed slurry obtained from the third in-situ coating reaction to obtain the carbon-silicon composite precursor; preferably, the spray drying process is performed under the following conditions: the feeding temperature is 120-220°C, the outlet temperature is 80-120°C, the carrier gas flow rate is 10-100 L / min, the inlet pressure is 0.1-0.6 MPa, and the carrier gas is selected from one or more of nitrogen and argon.

[0034] Preferably, the feeding temperature is 140-180°C, the outlet temperature is 80-100°C, the carrier gas flow rate is 30-60 L / min, and the inlet pressure is 0.2-0.4 MPa.

[0035] Optionally, in step S5, the calcination process is performed under the following conditions: the calcination temperature is 600-1100°C, and the calcination time is 0.5-6 h; preferably, the calcination temperature is 800-1000°C, and the calcination time is 1-3 h.

[0036] Optionally, the heating rate is 1-10°C / min, preferably 3-5°C / min.

[0037] The inert atmosphere is selected from one or more of argon and nitrogen.

[0038] The second aspect of the present disclosure provides a carbon-silicon composite prepared by the method according to the first aspect of the present disclosure.

[0039] The third aspect of the present disclosure provides a carbon-silicon composite, which comprises nano-silicon and a multi-layer hetero-carbon coating layer coated on the surface of the silicon matrix; the multi-layer hetero-carbon coating layer comprises a first carbon coating layer, a second carbon coating layer, and a third carbon coating layer arranged in a stacked manner from the surface of the nano-silicon outward; the second carbon coating layer contains nitrogen.

[0040] Optionally, based on the total weight of the carbon-silicon composite, the content of silicon in the carbon-silicon composite is 1-20 wt%, the content of carbon is 80-97 wt%, the content of nitrogen is 0.1-2 wt%, and the content of oxygen is 1-10 wt%.

[0041] Preferably, the content of silicon in the carbon-silicon composite is 1-10 wt%, the content of carbon is 80-90 wt%, the content of nitrogen is 0.1-0.5 wt%, and the content of oxygen is 3-10 wt%.

[0042] Optionally, the first carbon coating layer is an organic acid carbon coating layer, the second carbon coating layer is an organic amine carbon coating layer, and the third carbon coating layer is a graphite-based carbon coating layer.

[0043] Preferably, in the carbon-silicon composite material, the total thickness of the multilayer heterogeneous carbon coating layer is 10 nm to 150 nm, and more preferably 20 nm to 100 nm;

[0044] Preferably, the thickness of the first carbon coating layer is 5 nm to 40 nm, the thickness of the second carbon coating layer is 5 nm to 40 nm, and the thickness of the third carbon coating layer is 10 nm to 50 nm.

[0045] Optionally, the average particle size of the carbon-silicon composite material is 1 μm to 50 μm, and the BET specific surface area is 1 m². 2 / g~50m 2 / g; preferably, the average particle size of the carbon-silicon composite material is 3μm to 30μm, and the BET specific surface area is 1m². 2 / g~10m 2 / g.

[0046] This disclosure provides a fourth aspect of a negative electrode sheet, comprising the carbon-silicon composite material described in the second or third aspect of this disclosure.

[0047] This disclosure provides a fifth aspect of a lithium-ion battery, including the negative electrode sheet described in the fourth aspect of this disclosure.

[0048] Through the above technical solution, this disclosure provides a carbon-silicon composite material and its preparation method, a negative electrode sheet and a lithium-ion battery. This disclosure first reduces the volume effect of silicon by nano-sizing the silicon source, reserving sufficient expansion space for the shrinkage and expansion of silicon particles. Then, multiple heterogeneous carbon coating layers are coated on the outside of the nano-silicon. The multiple heterogeneous carbon coating layers provide sufficient strength and space for the expansion of silicon, thereby improving its cycle stability performance, and at the same time providing structural support for the rate performance of the material.

[0049] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0050] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0051] Figure 1 A TEM image of the carbon-silicon composite material prepared in Example 1 of this disclosure;

[0052] Figure 2 SEM image of the carbon-silicon composite material prepared in Example 1 of this disclosure;

[0053] Figure 3XRD spectrum of the carbon-silicon composite material prepared in Preparation Example 1 of the present disclosure;

[0054] Figure 4 First charge-discharge curve of the carbon-silicon composite material prepared in Preparation Example 1 of the present disclosure;

[0055] Figure 5 Charge-discharge cycle curve of the carbon-silicon composite material prepared in Preparation Example 1 of the present disclosure;

[0056] Figure 6 Rate capability cycle curve of the carbon-silicon composite material prepared in Preparation Example 1 of the present disclosure. DETAILED DESCRIPTION

[0057] The detailed description of the specific embodiments of the present disclosure is described below. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present disclosure, and are not intended to limit the present disclosure.

[0058] In the present disclosure, any matter or item not mentioned, except for the explicitly described content, directly applies the content known in the art without any change. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solution or technical idea formed thereby is deemed to be part of the original disclosure or description of the present disclosure, and should not be deemed as new content not disclosed or anticipated herein, unless the combination is deemed to be obviously unreasonable by the person skilled in the art.

[0059] All features disclosed in the present disclosure can be combined in any manner, and these combinations should be understood as disclosed or described in the present disclosure, and should be deemed to be specifically disclosed and described in the present disclosure, unless the combination is deemed to be obviously unreasonable by the person skilled in the art. The numerical points disclosed in the present specification, unless otherwise specified, not only include the numerical points specifically disclosed in the embodiments, but also include the endpoints of the numerical ranges in the specification, and the ranges formed by any combination of these numerical points should be deemed to be the ranges disclosed or described in the present disclosure.

[0060] The technical and scientific terms in the present disclosure are subject to the definitions given thereto, and the terms not given definitions are understood according to the usual meanings in the art.

[0061] The term "nanosilicon" is defined as silicon with an average particle size (D50 particle size) of 5 nm to 500 nm.

[0062] The term "inert gas" is defined as a gas that does not have a perceptible effect on the electrochemical performance of the composite material.

[0063] The term "soluble" means soluble in the solvent used at the time.

[0064] The first aspect of the present disclosure provides a method for preparing a carbon-silicon composite material, comprising the following steps:

[0065] S1, mixing a silicon source with an organic solvent, performing a crushing treatment to obtain a nano-silicon slurry;

[0066] S2, contacting the nano-silicon slurry with a first carbon source to perform a first in-situ coating reaction, obtaining a primary coated nano-silicon slurry combined with an organic acid, the first carbon source comprising an organic acid;

[0067] S3, contacting the primary coated nano-silicon slurry with a second carbon source to perform a second in-situ coating reaction, obtaining a secondary coated nano-silicon slurry obtained by a second in-situ reaction of an organic amine and an organic acid, the second carbon source comprising an organic amine;

[0068] S4, contacting the secondary coated nano-silicon slurry with a carbonizable binder and a third carbon source to perform a third in-situ coating reaction, obtaining a carbon-silicon composite material precursor, the third carbon source comprising a graphite-based carbon source;

[0069] S5, performing a calcination treatment on the carbon-silicon composite material precursor under an inert atmosphere.

[0070] The present disclosure provides a method for preparing a carbon-silicon composite material, which first nanocrystallizes a silicon source to reduce the volume effect of silicon, reserves sufficient expansion space for the shrinkage and expansion of silicon particles, then coats multiple heterogeneous carbon coating layers on the outside of the nano-silicon, provides sufficient strength and space for the expansion of silicon by using the multiple heterogeneous carbon coating layers, thereby improving the cycle stability performance, and at the same time providing structural support for the rate performance of the material.

[0071] According to the present disclosure, the first carbon source is an organic carboxylic acid or carboxylic acid ester containing a hydroxyl group, and the present disclosure discloses that the organic carboxylic acid or carboxylic acid ester containing a hydroxyl group can react with the reactive silicon sites generated after the crushing of silicon, uniformly cover the surface of silicon, and obtain in-situ coated nano-silicon; after adding the second carbon source, the organic amine can also react with the organic carboxylic acid or carboxylic acid ester containing a hydroxyl group in-situ to form a secondary coating on silicon; and after adding the binder and the graphite-based carbon source, a third coating can be formed, and finally a multiple heterogeneous carbon coating layer can be formed on the surface of the nano-silicon.

[0072] In an embodiment, in step S1, the silicon source is a simple substance silicon powder; optionally, the simple substance silicon powder comprises single crystal silicon and / or polycrystalline silicon; optionally, the particle size of the simple substance silicon powder ranges from 1 μm to 10 μm; and optionally, the organic solvent is selected from one or more of an alcohol organic solvent, a hydrocarbon organic solvent and a benzene organic solvent;

[0073] Preferably, the alcohol organic solvent is selected from one or more of ethanol, isopropyl alcohol and propanol;

[0074] The hydrocarbon organic solvent is selected from one or more of hexane, cyclohexane and isooctane;

[0075] The benzene organic solvent is selected from one or more of benzene, toluene and xylene;

[0076] Preferably, the organic solvent is selected from one or both of isopropyl alcohol and ethanol.

[0077] In a preferred embodiment, in step S1, the weight of the silicon source is 3g-20g, preferably 5g-15g, relative to 100mL of the organic solvent. Preferably, the solid content of the nanosilicon slurry obtained in step S1 is 2wt%-20wt%, preferably 3wt%-15wt% by weight of silicon.

[0078] In an embodiment, in step S1, the breaking treatment is performed by sanding mechanical breaking treatment; preferably, the sanding mechanical breaking treatment is performed in an inert atmosphere, and the sanding machine is operated at a speed of 2000r / min-2500r / min. The sanding device used in the present disclosure is a device of conventional structure in the art.

[0079] In a preferred embodiment, the average particle size (D50) of the solid nanosilicon in the nanosilicon slurry obtained by the breaking treatment is 5nm-150nm, preferably 30nm-100nm.

[0080] In an embodiment, in step S2, the weight ratio of the first carbon source to the silicon source is 1:0.2-5, preferably 1:0.5-5.

[0081] In a preferred embodiment, the organic acid comprises one or more of a hydroxyl-containing organic carboxylic acid and a hydroxyl-containing carboxylic acid ester;

[0082] Optionally, the hydroxyl-containing organic carboxylic acid is selected from one or more of tartaric acid, citric acid, lactobionic acid, malic acid and ascorbic acid;

[0083] Preferably, the hydroxyl-containing carboxylic acid ester comprises ascorbic acid;

[0084] Preferably, the organic acid is selected from one or more of citric acid, tartaric acid and malic acid.

[0085] In a specific embodiment, in step S2, the conditions of the primary in-situ coating reaction include a reaction temperature of 15°C-60°C and a reaction time of 0.25h-4h; preferably, the reaction temperature is 20°C-30°C and the reaction time is 0.5h-2h; optionally, the stirring rate is 200r / min-600r / min, preferably 300r / min-450r / min.

[0086] In an embodiment, the weight ratio of the second carbon source to the first carbon source in step S3 is 0.1-2:1, preferably 0.3-1.2:1, and further preferably 0.4-1:1.

[0087] In a preferred embodiment, the organic amine is selected from one or more of melamine and its ammonium salt, dopamine and its ammonium salt, and hexamethylenetetramine and its ammonium salt; preferably, the organic amine is selected from one or more of dopamine and melamine. The primary coated nanometer silicon slurry of the present disclosure uses an organic carboxylic acid containing hydroxyl group and a carboxylic acid ester containing hydroxyl group as the first carbon source. The abundant alcohol hydroxyl group and carboxyl hydroxyl group in the first carbon source have a strong binding force with the phenolic hydroxyl group and amino group in the organic amine (e.g., dopamine) of the second carbon source, so that the organic amine is uniformly distributed on the surface of the nanometer silicon precursor, thereby improving the secondary in-situ coating effect.

[0088] In a specific embodiment, the conditions of the secondary in-situ coating reaction in step S3 include a reaction temperature of 15-60°C and a reaction time of 0.25-4h; preferably, the reaction temperature is 20-30°C and the reaction time is 0.5-2h; optionally, the stirring rate is 200-600r / min, and preferably 300-450r / min.

[0089] In an embodiment, the weight ratio of the carbonizable binder to the silicon source in step S4 is 0.1-2:1, and preferably 0.1-1:1.

[0090] Optionally, the carbonizable binder is selected from one or more of pitch, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose.

[0091] Preferably, the weight ratio of the third carbon source to the silicon source in step S4 is 4-50:1, and preferably 6-40:1.

[0092] Optionally, the graphite-based carbon source is selected from one or more of natural graphite, artificial graphite, and flake graphite; preferably, the graphite-based carbon source is selected from one or more of natural graphite and artificial graphite having a spherical structure.

[0093] In an embodiment, the conditions of the tertiary in-situ coating reaction in step S4 include a reaction temperature of 15-60°C and a reaction time of 0.25-4h; preferably, the reaction temperature is 20-30°C and the reaction time is 0.5-2h; optionally, the stirring rate is 200-600r / min, and preferably 300-400r / min.

[0094] In one embodiment, step S4 further comprises: performing a solvent removal treatment on the mixed slurry obtained from the third in-situ coating reaction to obtain the carbon-silicon composite material precursor.

[0095] In the present disclosure, the solvent removal treatment can be performed by using methods conventionally selected in the art, and preferably by using a spray drying treatment. In one embodiment, the spray drying treatment is performed under conditions including: a feed temperature of 120-220°C, an outlet temperature of 80-120°C, a carrier gas flow rate of 10-100 L / min, an inlet pressure of 0.1-0.6 MPa, and the carrier gas being selected from one or more of nitrogen and argon.

[0096] Preferably, the feed temperature is 140-180°C, the outlet temperature is 80-100°C, the carrier gas flow rate is 30-60 L / min, and the inlet pressure is 0.2-0.4 MPa.

[0097] In one embodiment, in step S5, the calcination treatment is performed under conditions including: a calcination temperature of 600-1100°C, and a calcination time of 0.5-6 h; preferably, the calcination temperature is 800-1000°C, and the calcination time is 1-3 h; optionally, the heating rate is 1-10°C / min, and preferably 3-5°C / min.

[0098] The inert atmosphere is selected from one or more of argon and nitrogen.

[0099] The present disclosure provides, in a second aspect, a carbon-silicon composite material prepared by the method according to the first aspect of the present disclosure.

[0100] The present disclosure provides, in a third aspect, a carbon-silicon composite material, which comprises nano-silicon and a multi-layer hetero-carbon coating layer coated on the surface of the silicon matrix; the multi-layer hetero-carbon coating layer comprises a first carbon coating layer, a second carbon coating layer, and a third carbon coating layer arranged in a stacked manner from the surface of the nano-silicon outward; and the second carbon coating layer comprises nitrogen.

[0101] In one embodiment, the nano-silicon can be in a form conventionally selected in the art, which can be a nanoparticle, a nanowire, or a nanosheet.

[0102] In one embodiment, the multi-layer hetero-carbon coating layer comprises carbon, nitrogen, and oxygen.

[0103] In one preferred embodiment, the first carbon coating layer in the multi-layer hetero-carbon coating layer is an organic acid carbon coating layer, the second carbon coating layer is an organic amine carbon coating layer, and the third carbon coating layer is a graphite-based carbon coating layer.

[0104] In one specific embodiment, the content of silicon in the carbon-silicon composite material is 1-20 wt%, the content of carbon is 80-97 wt%, the content of nitrogen is 0.1-2 wt%, and the content of oxygen is 1-10 wt%, based on the total weight of the carbon-silicon composite material.

[0105] Preferably, the content of silicon in the carbon-silicon composite material is 1-10 wt%, the content of carbon is 80-90 wt%, the content of nitrogen is 0.1-0.5 wt%, and the content of oxygen is 3-10 wt%.

[0106] In one preferred embodiment, the total thickness of the multi-layered heterogeneous carbon coating layer in the carbon-silicon composite material is 10-150 nm, preferably 20-100 nm.

[0107] Preferably, the thickness of the first carbon coating layer is 5-40 nm, the thickness of the second carbon coating layer is 5-40 nm, and the thickness of the third carbon coating layer is 10-50 nm.

[0108] In one specific embodiment, the average particle size of the carbon-silicon composite material is 1-50 μm, and the BET specific surface area is 1-50 m 2 / g. 2 Preferably, the average particle size of the carbon-silicon composite material is 3-30 μm, and the BET specific surface area is 1-10 m 2 / g. 2 / g.

[0109] In one embodiment, the secondary particle size of the carbon-silicon composite material can be 1-50 μm. The secondary particle size is related to the dry form of the coated and modified nanosilicon obtained in different steps and the operating conditions, such as the use of different types of spray dryers and different operating conditions, which can obtain products with different secondary particle sizes. These are all known in the art, and those skilled in the art can select appropriate equipment and operating conditions according to actual needs.

[0110] The fourth aspect of the present disclosure provides a negative electrode tab comprising the carbon-silicon composite material of the second aspect or the third aspect of the present disclosure.

[0111] In one specific embodiment, the negative electrode tab is prepared by a method comprising the following steps:

[0112] The carbon-silicon composite material, the negative electrode conductive material, and the binder are mixed in a weight ratio of 70-95:2-10:3-20 to obtain a negative electrode slurry. The slurry is coated on a copper foil and dried to obtain a negative electrode tab.

[0113] In one embodiment, the negative active material is selected from one or more of acetylene black, carbon nanotube and graphene.

[0114] The binder is selected from one or more of sodium carboxymethyl cellulose, polystyrene butadiene copolymer (SBR) and lithium carboxymethyl cellulose.

[0115] The specific operations and conditions in the process of preparing the negative electrode tab in the present disclosure are the conventional operations and conditions in the art.

[0116] The fifth aspect of the present disclosure provides a lithium ion battery comprising the negative electrode tab of the fourth aspect of the present disclosure.

[0117] In the present disclosure, the positive electrode, electrolyte and separator used in the lithium ion battery can all be various substances conventionally adapted in the art, and the present disclosure does not have a particular limitation thereon. For example, the separator can be selected from any one of polyethylene film and polypropylene film and polyethylene and polypropylene composite film. And the composition of the lithium ion battery provided by the present disclosure is the conventional composition mode in the art.

[0118] The present disclosure is further illustrated in detail by the following examples. The raw materials used in the examples can be obtained by commercial channels.

[0119] The carbon coating layer structure on the silicon surface was characterized by transmission electron microscopy (TEM). The model of the TEM used was JEM-2100 (Japan Electron Corporation), and the transmission electron microscopy test conditions were: acceleration voltage of 200 kV.

[0120] Instrument and method of elemental analysis: carbon content was tested on a TA5000 thermal analyzer, and the test conditions were: air atmosphere, temperature rising speed of 10 ℃ / min, and temperature range of room temperature (25 ℃) to 1000 ℃; nitrogen element and oxygen element content was tested on an ON5500 nitrogen oxygen analyzer of Gangyan Nanke Detection Technology Co., Ltd., and the carrier gas was high-purity helium.

[0121] Instrument and method of particle size test: British Mastersizer 3000 particle size analyzer was used to determine the average particle size of the nano-silicon after sand milling, and the parameter setting was: shading degree of 5.99%. British Mastersizer 2000 particle size analyzer was used to determine the average particle size of the finished material, and the parameter setting was: shading degree of 10%.

[0122] Instrument and method of XPS test: X-ray photoelectron spectroscopy analysis was tested on the ESCA Lab 250 X-ray photoelectron spectrometer of Thermo Scientific Company, the excitation source was monochromatic Al Kα X-ray, the energy was 1486.6 eV, the power was 150 W, the penetration energy used for narrow scanning was 30 eV, the base vacuum during analysis test was 6.5 x 10-10 mbar, data processing was carried out on Thermo Avantage software, and quantitative analysis was carried out in the analysis module by using sensitivity factor method. The sample was dried at a temperature of 150 DEG C and 1 standard atmosphere in a helium atmosphere for 3 hours before testing.

[0123] Electrochemical test instrument: CT3002A battery test system of Wuhan Blue Electronic Co., Ltd.

[0124] Sand mill model: VB0.6Q nano sand mill of Suzhou Weiguan Nanometer Technology Co., Ltd.

[0125] Spray dryer model: B-290 of BUCHI Company in Switzerland, containing B-295 inert gas circulation device, nitrogen gas was used as carrier gas for spray drying.

[0126] Preparation example 1

[0127] (1) 75 g of elemental silicon powder (single crystal silicon, silicon purity is 99.999%, particle size range is 2 μm-10 μm) was added into 1500 mL of ethanol solution, and after sand milling in a sand mill at a speed of 2200 r / min under nitrogen protection for 8 h, a nano silicon slurry was obtained, the weight of elemental silicon powder was 5 g relative to 100 mL of organic solvent, and the average particle size D50 of solid nano silicon in the obtained nano silicon slurry was 29.1 nm;

[0128] (2) 40 mL of the nano silicon slurry prepared in step (1) (silicon mass was 2 g) was added into 1.0 g of ascorbic acid (first carbon source) and stirred to dissolve and disperse, the weight ratio of the first carbon source to the silicon source was 1:2, and the one-time in-situ coating reaction conditions included a reaction temperature of 25 DEG C, a reaction time of 2 h, and a stirring speed of 450 r / min, to obtain an ascorbic acid primary coated nano silicon slurry;

[0129] (3) 0.5 g of dopamine hydrochloride (second carbon source) was added into the ascorbic acid primary coated nano silicon slurry prepared in step (2), the weight ratio of the second carbon source to the first carbon source was 0.5:1, and the stirring was continued at room temperature for 1 h at a stirring speed of 450 r / min, to obtain a nano silicon slurry coated by in-situ reaction of dopamine and ascorbic acid;

[0130] (4) Take 1.0 g of pitch, 0.4 g of carboxymethyl cellulose (total 1.4 g of carbonizable binder, weight ratio of carbonizable binder to silicon source is 0.7:1), add to the nano-silicon slurry prepared in step (3), continue stirring at room temperature for 1 h, then add 20 g of artificial graphite (third carbon source, weight ratio of third carbon source to silicon source is 10:1) and further mix, reaction temperature is 30°C, reaction time is 3 h, stirring rate is 300 r / min, after uniform stirring, spray drying, feed temperature is 160°C, outlet temperature is 80°C, carrier gas flow rate is 40 L / min, inlet pressure is 0.2 MPa, carrier gas is nitrogen, to obtain a silicon-carbon coated precursor;

[0131] (5) Put the obtained silicon-carbon coated precursor into a ceramic boat, heat to 900°C at a rate of 5°C / min under an argon atmosphere in a tube furnace, then keep for 3 h, and naturally cool to room temperature, to obtain a silicon-carbon coated material. -1

[0132] The TEM photo of the silicon-carbon coated material obtained in this preparation example is shown in Figure 1 It can be seen that the silicon-carbon coated material of this preparation example has a multi-layer heterogeneous carbon coating layer with clear boundaries, which includes 3 layers of carbon coating layers from inside to outside, and the thickness range of each layer of carbon coating layer and the total thickness range of the carbon coating layer are listed in Table 1.

[0133] The SEM photo of the silicon-carbon coated material obtained in this preparation example is shown in Figure 2 It can be seen that the silicon-carbon coated material obtained in this preparation example is spherical, with regular particle size and dense coating.

[0134] The XRD spectrum of the silicon-carbon coated material obtained in this preparation example is shown in Figure 3 It can be seen that the silicon-carbon coated material obtained in this preparation example contains characteristic peaks of graphite and silicon, without other impurity peaks, and the nano-silicon and graphite in the prepared silicon-carbon coated material maintain the material's physicochemical characteristics, which is beneficial to maintaining the material's electrochemical intrinsic properties.

[0135] Comparative Example 1

[0136] This comparative example refers to the method in Preparation Example 1 to prepare a nano-carbon silicon composite material, which is different from Preparation Example 1 in that this comparative example does not add dopamine hydrochloride in step (3), and the rest of the process is the same as Preparation Example 1, to prepare an ascorbic acid coated silicon-carbon coated material.

[0137] Comparative Example 2

[0138] This comparative example refers to the method in Preparation Example 1 to prepare a nano-carbon silicon composite material, which is different from Preparation Example 1 in that this comparative example does not include step (2) and does not add an organic acid, and the rest of the process is the same as Preparation Example 1, to prepare a dopamine hydrochloride coated silicon-carbon coated material.​

[0139] Comparative Example 3

[0140] The comparative example was prepared by the method in Preparation Example 1, except that the comparative example did not include step (2) and step (3), and neither ascorbic acid nor dopamine hydrochloride was added.

[0141] Comparative Example 4

[0142] The comparative example was prepared by the method in Preparation Example 1, except that steps (2) to (4) were combined, i.e., ascorbic acid, dopamine hydrochloride and pitch and carboxymethyl cellulose were added to the nanosilicon slurry obtained in step (1) and then in-situ coated, the coating conditions being: a reaction temperature of 25°C, a reaction time of 2h, a stirring rate of 450r / min, and after uniform stirring, spray drying, a feed temperature of 160°C, an outlet temperature of 85°C, a carrier gas flow rate of 40L / min, an inlet pressure of 0.2MPa, and a carrier gas of nitrogen, to obtain a coated precursor; then the same step (5) as in Preparation Example 1 was performed to obtain a silicon-carbon coated material.

[0143] Preparation Example 2

[0144] (1) 75g of elemental silicon powder (single crystal silicon, silicon purity of 99.999%, particle size range of 2μm-10μm) was added to 1500mL of isopropyl alcohol solution, and after sanding in a sand mill at a speed of 2300r / min for 8h under nitrogen protection, a nanosilicon slurry was obtained, the weight of the elemental silicon powder being 5g relative to 100mL of organic solvent, and the average particle size D50 of the solid nanosilicon in the obtained nanosilicon slurry being 42.7nm;

[0145] (2) 40mL of the nanosilicon slurry prepared in step (1) (silicon mass of 2g) was added to 2.0g of citric acid (first carbon source) and stirred to dissolve and disperse, the weight ratio of the first carbon source to the silicon source being 1:1, and the conditions for the one-step in-situ coating reaction including a reaction temperature of 25°C, a reaction time of 1h, and a stirring rate of 450r / min, to obtain a citric acid primary coated nanosilicon slurry;

[0146] (3) 2.0g of dopamine hydrochloride (second carbon source) was added to the citric acid primary coated nanosilicon slurry prepared in step (2), the weight ratio of the second carbon source to the first carbon source being 1:1, and the stirring was continued at room temperature (25°C) for 1h at a stirring rate of 450r / min, to obtain a nanosilicon slurry coated with dopamine and citric acid by in-situ reaction;

[0147] (4) Take 2.0 g of pitch (carbonizable binder 2.0 g, weight ratio of carbonizable binder to silicon source is 1:1) and add the nano-silicon slurry prepared in step (3), continue to stir at room temperature for 1 h, then add 20 g of artificial graphite (third carbon source, weight ratio of third carbon source to silicon source is 10:1) and further mix, the reaction temperature is 25℃, the reaction time is 1 h, the stirring rate is 300 r / min, after uniform stirring, spray drying is performed, the feeding temperature is 160℃, the outlet temperature is 80℃, the carrier gas flow rate is 50 L / min, the inlet pressure is 0.2 MPa, the carrier gas is nitrogen, and a silicon-carbon coated precursor is obtained;

[0148] (5) The obtained silicon-carbon coated precursor is placed into a ceramic boat, and is heated to 900℃ at a rate of 5℃ / min under an argon atmosphere in a tube furnace, and then is kept for 3 h, and is naturally cooled to room temperature, and a silicon-carbon coated material is obtained. -1

[0149] Preparation Example 3

[0150] (1) 75 g of elemental silicon powder (single crystal silicon, silicon purity is 99.999%, particle size range is 2 μm-10 μm) is added into 1500 mL of ethanol solution, and is ground in a sand mill under nitrogen protection at a rotation speed of 2200 r / min for 8 h, and then is taken out, to obtain a nano-silicon slurry, the weight of the elemental silicon powder is 5 g relative to 100 mL of organic solvent, and the average particle size D50 of the solid nano-silicon in the obtained nano-silicon slurry is 29.1 nm;

[0151] (2) 40 mL of the nano-silicon slurry prepared in step (1) (the mass of silicon is 2 g) is taken and added into 2.0 g of L-malic acid (first carbon source) to be fully stirred, dissolved and dispersed, and the weight ratio of the first carbon source to the silicon source is 1:1, and the one-time in-situ coating reaction conditions include that the reaction temperature is 30℃, the reaction time is 2 h, and the stirring rate is 500 r / min, to obtain a malic acid primary coated nano-silicon slurry;

[0152] (3) 1.0 g of dopamine hydrochloride (second carbon source) is added into the malic acid primary coated nano-silicon slurry prepared in step (2), the weight ratio of the second carbon source to the first carbon source is 0.5:1, and the stirring is continued at room temperature for 1 h, and the stirring rate is 500 r / min, to obtain a nano-silicon slurry coated by in-situ reaction of dopamine and malic acid;

[0153] ​(4) Take 2.0g of asphalt (2.0g of carbonizable binder, the weight ratio of carbonizable binder to silicon source is 1:1) and add it to the nano-silicon slurry prepared in step (3). After stirring at room temperature for 1h, add 18g of artificial graphite (third carbon source, the weight ratio of third carbon source to silicon source is 9:1) and mix further. The reaction temperature is 30℃, the reaction time is 2h, the stirring rate is 500r / min, and after stirring evenly, spray dry. The feed temperature is 140℃, the outlet temperature is 75℃, the carrier gas flow rate is 40L / min, the inlet pressure is 0.2MPa, and the carrier gas is nitrogen to obtain silicon-carbon coated precursor.

[0154] (5) The obtained silicon-carbon coated precursor was placed in a ceramic boat and heated in a tube furnace at 5°C for 5 min under an argon atmosphere. -1 The temperature was increased to 900℃ at a certain rate, then held for 3 hours, and then naturally cooled to room temperature to obtain silicon-carbon coated material.

[0155] Preparation Example 4

[0156] (1) 75g of elemental silicon powder (monocrystalline silicon, silicon purity of 99.999%, particle size range of 2μm~10μm) was added to 1500mL of ethanol solution, and milled in a sand mill at a speed of 2200r / min for 9h under nitrogen protection to obtain nano-silicon slurry. The weight of elemental silicon powder relative to 100mL of organic solvent was 5g, and the particle size range of solid nano-silicon in the obtained nano-silicon slurry was 27nm.

[0157] (2) Take 40 mL of the nano-silicon slurry (silicon mass is 2 g) prepared in step (1) and add 2.0 g of citric acid (first carbon source) and stir thoroughly to dissolve and disperse. The weight ratio of the first carbon source to the silicon source is 1:1. The conditions for the first in-situ coating reaction include: reaction temperature of 25℃, reaction time of 2 h, and stirring rate of 450 r / min to obtain citric acid primary coated nano-silicon slurry.

[0158] (3) Add 1.0g of melamine (second carbon source) to the citric acid primary coated nano-silicon slurry prepared in step (2). The weight ratio of the second carbon source to the first carbon source is 0.5:1. Continue stirring at room temperature for 1h at a stirring rate of 500r / min to obtain the nano-silicon slurry coated by the in-situ reaction of melamine and citric acid.

[0159] (4) Take 0.5g sodium carboxymethyl cellulose and 2.0g asphalt (a total of 2.5g of carbonizable binder, with a weight ratio of 1.25:1 between the carbonizable binder and the silicon source) and add them to the nano-silicon slurry prepared in step (3). After stirring at room temperature for 1 hour, add 12g artificial graphite (the third carbon source, with a weight ratio of 6:1 between the third carbon source and the silicon source) and mix further. The reaction temperature is 25℃, the reaction time is 2 hours, the stirring rate is 300r / min, and after stirring evenly, spray dry. The feed temperature is 160℃, the outlet temperature is 85℃, the carrier gas flow rate is 50L / min, the inlet pressure is 0.3MPa, and the carrier gas is nitrogen to obtain the silicon-carbon coated precursor.

[0160] (5) The obtained silicon-carbon coated precursor was placed in a ceramic boat and heated in a tube furnace at 5°C for 5 min under an argon atmosphere. -1 The temperature was increased to 900℃ at a certain rate, then held for 3 hours, and then naturally cooled to room temperature to obtain silicon-carbon coated material.

[0161] Preparation Example 5

[0162] This preparation example follows the method in Preparation Example 1, but differs from Preparation Example 1 in that the proportion of raw materials added is changed, specifically including:

[0163] In step (2), take 20 mL of the nano-silicon slurry (silicon mass is 1 g) prepared in step (1) and add 2 g of ascorbic acid (first carbon source) and stir thoroughly to dissolve and disperse. The weight ratio of the first carbon source to the silicon source is 1:0.5. Perform an in-situ coating reaction to obtain ascorbic acid primary coated nano-silicon slurry.

[0164] In step (3), 1g of dopamine hydrochloride (second carbon source) is added to the ascorbic acid primary coated nano-silica slurry prepared in step (2). The weight ratio of the second carbon source to the first carbon source is 1:2, i.e. 0.5:1. Secondary in-situ coating is carried out to obtain nano-silica slurry coated by in-situ reaction of dopamine and ascorbic acid.

[0165] In step (4), 1g of asphalt and 1g of carboxymethyl cellulose (a total of 2g of carbonizable binder, with a weight ratio of 2:1 between the carbonizable binder and the silicon source) are added to the nano-silicon slurry prepared in step (3). After stirring at room temperature for 1 hour, 40g of artificial graphite (a third carbon source, with a weight ratio of 40:1 between the third carbon source and the silicon source) is added and mixed further to obtain a silicon-carbon coated precursor.

[0166] The remaining process is the same as in Preparation Example 1, and silicon-carbon coated material is obtained.

[0167] Preparation Example 6

[0168] This preparation example follows the method in Preparation Example 1, but differs from Preparation Example 1 in that the proportion of raw materials added is changed, specifically including:

[0169] In step (2), 40 mL of the nanosilicon slurry prepared in step (1) (2 g of silicon) was added to 0.25 g of ascorbic acid (first carbon source) and stirred to dissolve and disperse, the weight ratio of the first carbon source to the silicon source being 1:8, to perform a primary in-situ coating reaction to obtain ascorbic acid primary coated nanosilicon slurry;

[0170] In step (3), 0.1 g of dopamine hydrochloride (second carbon source) was added to the ascorbic acid primary coated nanosilicon slurry prepared in step (2), the weight ratio of the second carbon source to the first carbon source being 0.4:1, to perform a secondary in-situ coating to obtain dopamine and ascorbic acid in-situ reaction coated nanosilicon slurry;

[0171] In step (4), 0.5 g of pitch and 0.5 g of carboxymethyl cellulose (1 g of carbonizable binder in total, the weight ratio of the carbonizable binder to the silicon source being 0.5:1) were added to the nanosilicon slurry prepared in step (3), and 12 g of artificial graphite (third carbon source, the weight ratio of the third carbon source to the silicon source being 6:1) was further mixed after stirring at room temperature for 1 h to obtain a silicon-carbon coated precursor;

[0172] The remaining process was the same as that of Preparation Example 1 to obtain a silicon-carbon coated material.

[0173] Preparation Example 7

[0174] This preparation example refers to the method in Preparation Example 1, and is different from Preparation Example 1 in that the process conditions are changed, specifically including:

[0175] In step (1), the sand mill was taken out after sand milling at a speed of 2500 r / min for 50 h to obtain nanosilicon slurry, and the average particle size D50 of the solid nanosilicon in the obtained nanosilicon slurry was 42.7 nm;

[0176] In step (2), the conditions of the primary in-situ coating reaction included a reaction temperature of 30℃, a reaction time of 4 h, and a stirring rate of 600 r / min to obtain ascorbic acid primary coated nanosilicon slurry;

[0177] In step (3), the conditions of the secondary in-situ coating reaction included a reaction temperature of 30℃, a reaction time of 4 h, and a stirring rate of 600 r / min to obtain dopamine and ascorbic acid in-situ reaction coated nanosilicon slurry;

[0178] In step (4), the conditions of the tertiary in-situ coating reaction included a reaction temperature of 30℃, a reaction time of 4 h, and a stirring rate of 600 r / min, and after uniform stirring, spray drying was performed with a feed temperature of 180℃, an outlet temperature of 100℃, a carrier gas flow rate of 60 L / min, an inlet pressure of 0.4 MPa, and nitrogen as the carrier gas to obtain a silicon-carbon coated precursor;

[0179] In step (5), the obtained silicon-carbon coated precursor was placed in a porcelain boat, and was heated to 1100℃ at a rate of 5℃ / min under an argon atmosphere in a tube furnace, and then was kept for 3h, and was naturally cooled to room temperature to obtain a silicon-carbon coated material. -1 -1

[0180] Preparation Example 8

[0181] The present preparation example refers to the method in Preparation Example 1, and is different from Preparation Example 1 in that the process conditions are changed, specifically including:

[0182] In step (1), the sand mill was taken out after sand milling at a speed of 2500r / min for 52h to obtain a nano-silicon slurry, and the average particle size D50 of the solid nano-silicon in the obtained nano-silicon slurry was 33.9nm;

[0183] In step (2), the conditions of the first in-situ coating reaction included a reaction temperature of 30℃, a reaction time of 0.25h, and a stirring speed of 600r / min, and an ascorbic acid primary coated nano-silicon slurry was obtained;

[0184] In step (3), the conditions of the second in-situ coating reaction included a stirring speed of 600r / min at 30℃ for 12h, and a dopamine and ascorbic acid in-situ reaction coated nano-silicon slurry was obtained;

[0185] In step (4), the conditions of the third in-situ coating reaction included a reaction temperature of 30℃, a reaction time of 12h, and a stirring speed of 600r / min, and after uniform stirring, spray drying was performed with a feed temperature of 220℃, an outlet temperature of 120℃, a carrier gas flow rate of 50L / min, an inlet pressure of 0.5MPa, and nitrogen as the carrier gas, and a silicon-carbon coated precursor was obtained;

[0186] In step (5), the obtained silicon-carbon coated precursor was placed in a porcelain boat, and was heated to 1200℃ at a rate of 5℃ / min under an argon atmosphere in a tube furnace, and then was kept for 3h, and was naturally cooled to room temperature to obtain a silicon-carbon coated material.

[0187] The composition content, structure characteristics and other data of the products obtained in the above preparation examples and comparative examples are listed in Table 1 below.

[0188] Table 1

[0189]

[0190] In Table 1, the symbol “ / ” in the carbon coating layer thickness indicates that the layering boundary is not clear, or there is no obvious layering.

[0191] The following test examples are used to illustrate the electrochemical performance of the nano-carbon silicon composite material provided by the preparation examples and comparative examples of the present disclosure. ​​

[0192] Test Examples 1-8

[0193] The nano-carbon silicon composite materials prepared in Examples 1-8 were mixed with acetylene black and a binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1) at a mass ratio of 8:1:1 to form a slurry. This slurry was then coated onto copper foil and dried to obtain an electrode sheet. The prepared electrode sheet was used as the positive electrode, and a lithium metal sheet as the negative electrode. A Celgard 2400 type separator was selected. 1 mol L -1 A button half-cell was assembled in a glove box using LiPF6 electrolyte (a mixed solvent with a volume ratio of ethylene carbonate: dimethyl carbonate: diethyl carbonate = 1:1:1). Charge-discharge tests were conducted on the battery using a Blue Electric system. Parameters were set as follows: current density 100 mA g. -1 The voltage range is 0.01 to 2.0V.

[0194] Comparative test examples 1-4

[0195] The test was conducted according to the method of Test Example 1, except that the nano-silicon carbon composite material obtained in the preparation example was replaced with the products obtained in Comparative Preparation Examples 1 to 4.

[0196] The test results of the above test cases and the comparison test cases are listed in Table 2 below.

[0197] Table 2

[0198]

[0199] The initial charge-discharge curve of Test Example 1 (using the composite material obtained in Preparation Example 1) is shown below. Figure 4 As shown, the charge-discharge cycle curves are as follows: Figure 5 As shown, by Figure 5 It can be seen that the charge and discharge lines are highly overlapping and difficult to distinguish in the attached figure, indicating that the composite material obtained in Preparation Example 1 has good performance and stable charge and discharge performance.

[0200] The rate performance cycling curve of Test Example 1 (using the composite material obtained in Preparation Example 1) is shown below. Figure 6 As shown (including charging and discharging at 0.1C / 0.2C / 0.5C / 1.0C / 2.0C, with the charging and discharging voltage limited to 0.01V~2.0V), the figure shows that the silicon-carbon coated composite material provided in this disclosure has good rate performance; and Figure 5 The high degree of overlap between the charging and discharging curves at different current densities further demonstrates the stable performance of the composite material.

[0201] Comparing test example 1 with comparative test examples 1-4, the composite material prepared by comparative examples 1-4 is not prepared according to the method provided in the present disclosure, and compared with comparative test examples 1-4, test example 1 uses the composite material obtained from practical preparation example 1, and test example 1 obtains higher initial coulombic efficiency and cycle capacity retention rate;

[0202] Comparing test example 5 with test example 6, the composite material used in test example 5 is prepared according to the addition ratio provided in the present disclosure during the preparation process, and compared with test example 6, test example 5 can achieve higher initial coulombic efficiency and cycle capacity retention rate;

[0203] Comparing test example 1 with test example 7, the composite material used in test example 1 is prepared according to the optimized conditions provided in the present disclosure during the preparation process, and compared with test example 7, test example 1 can achieve higher initial coulombic efficiency and cycle capacity retention rate.

[0204] Comparing test example 7 with test example 8, test example 7 uses the composite material prepared by example 7, and compared with test example 8 which uses the composite material prepared by example 8, on the basis of good cycle stability, the initial charge specific capacity and initial coulombic efficiency of test example 7 are significantly higher than those of test example 8.

[0205] The above describes the preferred embodiments of the present disclosure, but the present disclosure is not limited to the specific details in the above embodiments, and various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0206] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0207] In addition, various different embodiments of the present disclosure can also be combined in any manner, as long as they do not deviate from the idea of the present disclosure, and they should also be considered as disclosed in the present disclosure.

Claims

1. A method of producing a carbon-silicon composite material, characterized by, The method comprises the following steps: S1, mixing a silicon source with an organic solvent and performing a crushing treatment to obtain a nano-silicon slurry; S2, contacting the nano-silicon slurry with a first carbon source to perform a first in-situ coating reaction, thereby obtaining a primary coated nano-silicon slurry, wherein the first carbon source comprises an organic acid; and the organic acid comprises one or more of a hydroxyl-containing organic carboxylic acid and a hydroxyl-containing carboxylic acid ester; S3, contacting the primary coated nano-silicon slurry with a second carbon source to perform a second in-situ coating reaction, thereby obtaining a secondary coated nano-silicon slurry, wherein the second carbon source comprises an organic amine; S4, contacting the secondary coated nano-silicon slurry with a carbonizable binder and a third carbon source to perform a third in-situ coating reaction, thereby obtaining a carbon-silicon composite material precursor, wherein the third carbon source comprises a graphite-based carbon source; S5, performing a calcination treatment on the carbon-silicon composite material precursor under an inert atmosphere.

2. The method of claim 1, wherein, In step S1, the silicon source is a silicon powder.

3. The method of claim 2, wherein, The silicon powder comprises single crystal silicon and / or polycrystalline silicon.

4. The method of claim 2, wherein, The particle size of the silicon powder ranges from 1 μm to 10 μm.

5. The method of claim 1, wherein, The organic solvent is selected from one or more of an alcohol organic solvent, a hydrocarbon organic solvent, and a benzene organic solvent.

6. The method of claim 5, wherein, The alcohol organic solvent is selected from one or more of ethanol, propanol, and isopropanol. The hydrocarbon organic solvent is selected from one or more of hexane, cyclohexane, and isooctane. The benzene organic solvent is selected from one or more of benzene, toluene, and xylene.

7. The method of claim 1, wherein, In step S1, the weight of the silicon source relative to 100 mL of the organic solvent ranges from 3 g to 20 g.

8. The method of claim 7, wherein, In step S1, the weight of the silicon source relative to 100 mL of the organic solvent ranges from 5 g to 15 g.

9. The method of claim 1, wherein, In step S1, the crushing treatment is performed by a sand mill mechanical crushing treatment.

10. The method of claim 9, wherein, The sand mill mechanical crushing treatment is performed under an inert atmosphere in a sand mill at a speed of 2000 r / min to 2500 r / min for 4 to 50 h.

11. The method of claim 10, wherein, The sand mill mechanical crushing treatment is performed for 6 to 20 h.

12. The method of claim 1, wherein, In step S1, the D50 particle size of the solid nano-silicon in the nano-silicon slurry obtained by the crushing treatment ranges from 5 nm to 150 nm.

13. The method of claim 12, wherein, In step S1, the D50 particle size of the solid nano-silicon in the nano-silicon slurry obtained by the crushing treatment ranges from 30 nm to 100 nm.

14. The method of claim 1, wherein, In step S2, the weight ratio of the first carbon source to the silicon source ranges from 1:0.2 to 5.

15. The method of claim 14, wherein, In step S2, the weight ratio of the first carbon source to the silicon source ranges from 1:0.5 to 5.

16. The method of claim 1, wherein, In step S2, the hydroxyl-containing organic carboxylic acid is selected from one or more of tartaric acid, citric acid, lactobionic acid, malic acid, and glutamic acid.

17. The method of claim 1, wherein, In step S2, the hydroxyl-containing carboxylic acid ester comprises ascorbic acid.

18. The method of claim 1, wherein, In step S2, the organic acid is selected from one or more of citric acid, tartaric acid, and malic acid.

19. The method of claim 1, wherein, In step S2, the conditions of the first in-situ coating reaction include a reaction temperature of 15°C to 60°C and a reaction time of 0.25 h to 4 h.

20. The method of claim 19, wherein, The one-time in-situ coating reaction in step S2 has a reaction temperature of 20-30℃ and a reaction time of 0.5-2h.

21. The method of claim 1, wherein, The one-time in-situ coating reaction in step S2 has a stirring rate of 200-600r / min.

22. The method of claim 1, wherein, The one-time in-situ coating reaction in step S2 has a stirring rate of 300-450r / min.

23. The method of claim 1, wherein, The weight ratio of the second carbon source to the first carbon source in step S3 is 0.1-2:

1.

24. The method of claim 23, wherein, The weight ratio of the second carbon source to the first carbon source in step S3 is 0.3-1.2:

1.

25. The method of claim 24, wherein, The weight ratio of the second carbon source to the first carbon source in step S3 is 0.4-1:

1.

26. The method of claim 1, wherein, The organic amine in step S3 is selected from one or more of melamine and its ammonium salt, dopamine and its ammonium salt, and hexamethylenetetramine and its ammonium salt.

27. The method of claim 26, wherein, The organic amine in step S3 is selected from one or more of dopamine and melamine.

28. The method of claim 1, wherein, The secondary in-situ coating reaction in step S3 has a reaction temperature of 15-60℃ and a reaction time of 0.25-4h.

29. The method of claim 28, wherein, The secondary in-situ coating reaction in step S3 has a reaction temperature of 20-30℃ and a reaction time of 0.5-2h.

30. The method of claim 28, wherein, The secondary in-situ coating reaction in step S3 has a stirring rate of 200-600r / min.

31. The method of claim 30, wherein, The secondary in-situ coating reaction in step S3 has a stirring rate of 300-450r / min.

32. The method of claim 1, wherein, The weight ratio of the carbonizable binder to the silicon source in step S4 is 0.1-2:

1.

33. The method of claim 32, wherein, The weight ratio of the carbonizable binder to the silicon source in step S4 is 0.1-1:

1.

34. The method of claim 1, wherein, The carbonizable binder in step S4 is selected from one or more of pitch, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose.

35. The method of claim 1, wherein, The weight ratio of the third carbon source to the silicon source in step S4 is 4-50:

1.

36. The method of claim 35, wherein, The weight ratio of the third carbon source to the silicon source in step S4 is 6-40:

1.

37. The method of claim 1, wherein, The graphite-based carbon source in step S4 is selected from one or more of natural graphite, artificial graphite, and flake graphite.

38. The method of claim 37, wherein, The graphite-based carbon source in step S4 is selected from one or more of natural graphite and artificial graphite with a spherical structure.

39. The method of claim 1, wherein, The tertiary in-situ coating reaction in step S4 has a reaction temperature of 15-60℃ and a reaction time of 0.25-4h.

40. The method of claim 39, wherein, The tertiary in-situ coating reaction in step S4 has a reaction temperature of 20-30℃ and a reaction time of 0.5-2h.

41. The method of claim 1, wherein, The tertiary in-situ coating reaction in step S4 has a stirring rate of 200-600r / min.

42. The method of claim 41, wherein, The tertiary in-situ coating reaction in step S4 has a stirring rate of 300-400r / min.

43. The method of claim 1, wherein, Step S4 further comprises spray drying the mixed slurry obtained from the tertiary in-situ coating reaction to obtain the carbon-silicon composite material precursor.

44. The method of claim 43, wherein, The spray drying treatment has the following conditions: the feed temperature is 120-220 DEG C, the outlet temperature is 80-120 DEG C, the carrier gas flow rate is 10-100 L / min, the inlet pressure is 0.1-0.6 MPa, and the carrier gas is selected from one or more of nitrogen and argon.

45. The method of claim 44, wherein, The spray drying treatment has the following conditions: the feed temperature is 140-180 DEG C, the outlet temperature is 80-100 DEG C, the carrier gas flow rate is 30-60 L / min, the inlet pressure is 0.2-0.4 MPa.

46. The method of claim 1, wherein, In step S5, the calcination treatment has the following conditions: the calcination temperature is 600-1100 DEG C, and the calcination time is 0.5-6 h. The inert atmosphere is selected from one or more of argon and nitrogen.

47. The method of claim 46, wherein, In step S5, the calcination treatment has the following conditions: the calcination temperature is 800-1000 DEG C, and the calcination time is 1-3 h.

48. The method of claim 46, wherein, In step S5, the calcination treatment has the following conditions: the temperature increase rate is 1-10 DEG C / min.

49. The method of claim 48, wherein, In step S5, the calcination treatment has the following conditions: the temperature increase rate is 3-5 DEG C / min.

50. The carbon-silicon composite material prepared by the method of any one of claims 1-49.

51. The carbon-silicon composite of claim 50, wherein, The carbon-silicon composite material comprises nanosilicon and a multi-layer hetero-carbon coating layer covering the surface of the nanosilicon; the multi-layer hetero-carbon coating layer comprises a first carbon coating layer, a second carbon coating layer and a third carbon coating layer arranged in a stack from the surface of the nanosilicon outward; and the second carbon coating layer contains nitrogen.

52. The carbon-silicon composite of claim 51, wherein, The content of silicon in the carbon-silicon composite material is 1-20 wt%, the content of carbon is 80-97 wt%, the content of nitrogen is 0.1-2 wt%, and the content of oxygen is 1-10 wt%.

53. The carbon-silicon composite of claim 52, wherein, The content of silicon in the carbon-silicon composite material is 1-10 wt%, the content of carbon is 80-90 wt%, the content of nitrogen is 0.1-0.5 wt%, and the content of oxygen is 3-10 wt%.

54. The carbon-silicon composite of claim 51, wherein, The first carbon coating layer is an organic acid carbon coating layer, the second carbon coating layer is an organic amine carbon coating layer, and the third carbon coating layer is a graphite-like carbon coating layer.

55. The carbon-silicon composite of claim 54, wherein, The total thickness of the multi-layer hetero-carbon coating layer in the carbon-silicon composite material is 10-150 nm.

56. The carbon-silicon composite of claim 55, wherein, The total thickness of the multi-layer hetero-carbon coating layer in the carbon-silicon composite material is 20-100 nm.

57. The carbon-silicon composite of claim 55, wherein, The thickness of the first carbon coating layer is 5-40 nm, the thickness of the second carbon coating layer is 5-40 nm, and the thickness of the third carbon coating layer is 10-50 nm.

58. The carbon-silicon composite of claim 51, wherein, The average particle size of the carbon-silicon composite material is 1 μm to 50 μm, and the BET specific surface area is 1 m 2 / g to 50 m 2 / g.

59. The carbon-silicon composite of claim 58, wherein, The average particle size of the carbon-silicon composite material is 3-30 μm, and the BET specific surface area is 1-10 m 2 / g. 2 / g.

60. A negative electrode sheet characterized by comprising: The carbon-silicon composite material of any one of claims 51-59.

61. A lithium-ion battery, characterized in that, The negative electrode sheet of claim 60.

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