Negative active material, preparation method thereof and lithium ion battery

Abstract

The invention relates to a negative active material, a preparation method thereof and a lithium ion battery. The negative electrode active material is used for the lithium ion battery, the negative electrode active material comprises a silicon-carbon compound, the silicon-carbon compound comprises an inner layer and an outer layer, the inner layer is a winding type carbon nanotube which is a three-dimensional network formed by winding and interweaving multiple layers of filamentous fibers, nano silicon particles are embedded in the winding type carbon nanotube, and the outer layer is a three-dimensional network formed by winding and interweaving multiple layers of filamentous fibers. The outer layer is a graphene layer, and the thickness of the graphene layer is 1 nm to 10 nm. The winding type carbon nano tube is used as loofah sponge, and the graphene layer is used as loofah peel. The silicon-carbon compound is formed by depositing nano silicon on the winding type carbon nano tube and growing graphene in situ, the prepared silicon-carbon compound is uniform and controllable in particle size and higher in compression resistance, tensile resistance, electric conductivity and heat conductivity, and low expansion, long circulation and low-temperature rate performance of the lithium ion battery can be realized.

Description

Technical Field

[0001] The present invention discloses a negative electrode active material for a lithium - ion battery, a method for preparing the negative electrode active material, and a lithium - ion battery including the negative electrode active material. Background Art

[0002] In recent years, with the increasingly wide application range of lithium - ion batteries, lithium - ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of lithium - ion batteries, higher requirements are also put forward for their energy density, cycle performance, and safety performance.

[0003] Silicon - based materials have received attention because of their capacity far higher than that of carbon - based materials, because higher capacity means that higher energy density can be achieved. However, silicon - based materials will undergo huge volume changes (>300%) during charge - discharge processes. This change will cause material structure damage and particle pulverization, and then lead to rapid attenuation of the electrode capacity and even electrode failure. Therefore, silicon - based materials are often used in combination with carbon - based materials in the production of current electrode sheets. However, the current silicon - carbon composite materials still have problems such as high expansion and short cycle life. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a negative electrode active material, a preparation method thereof, and a lithium - ion battery, and the negative electrode active material exhibits improved cycle life characteristics and improved compressive and tensile low - expansion characteristics.

[0005] In a first aspect, the present invention provides a negative electrode active material, comprising: a silicon - carbon composite, including an inner layer and an outer layer. The inner layer is a wound carbon nanotube, which is a three - dimensional network formed by the winding and interlacing of multiple filamentous fibers, and nano - silicon particles are embedded on the wound carbon nanotube. The outer layer is a graphene layer, and the thickness of the graphene layer is 1 nm to 10 nm.

[0006] In some embodiments, the graphene layer is formed by in - situ growth, and the thickness of the graphene layer is 2 nm to 7 nm.

[0007] In some embodiments, the particle size D50 of the silicon - carbon composite is 1 μm to 20 μm, preferably 5 μm to 15 μm.

[0008] In some embodiments, the particle size D50 of the nano - silicon is 5 nm to 500 nm, preferably 10 nm to 300 nm.

[0009] In some embodiments, the pore size between the diameters of the wound carbon nanotubes is 20 nm to 100 nm, preferably 40 nm to 60 nm.

[0010] In some embodiments, the diameter of the wound carbon nanotubes is 1 nm to 20 nm, preferably 5 nm to 15 nm.

[0011] In some embodiments, the negative electrode active material further includes at least one of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, or silicon oxide.

[0012] In a second aspect, the present invention provides a method for preparing a negative electrode active material for a lithium-ion battery, the negative electrode active material including a silicon-carbon composite, and the formation of the silicon-carbon composite includes the following steps:

[0013] S11. Preparation of a carbonaceous framework: Add a catalyst into a fluidized bed reactor; convert liquid nitrogen into gas through a vaporizer and continuously input it into the reactor, and heat the reactor to a temperature of 600 °C to 800 °C; introduce an excessive amount of carbon source gas into the fluidized bed reactor, and pyrolyze it at high temperature to generate carbon atoms; when the carbon atom concentration accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes; form wound carbon nanotube microspheres by heat preservation for 1 h to 4 h;

[0014] S12. Deposition of nano-silicon: Use the wound carbon nanotube microspheres as the carbonaceous framework, cool down to 400 °C to 550 °C, introduce silane gas, pyrolyze the silane gas, deposit particles inside the carbonaceous framework, and stop charging silane after heat preservation for 1 h to 20 h;

[0015] S13. In-situ growth and coating of graphene: Heat up to 600 °C to 1200 °C, introduce hydrogen and a carbon source, and perform in-situ growth and coating of graphene by heat preservation at high temperature for 1 h to 5 h;

[0016] S14. After the growth is completed, close the carbon source gas, cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite, which includes an inner layer and an outer layer. The inner layer is wound carbon nanotubes, which is a three-dimensional network formed by the winding and interweaving of multiple filamentous fibers, and nano-silicon particles are embedded on the wound carbon nanotubes. The outer layer is a graphene layer, and the thickness of the graphene layer is 1 nm to 10 nm.

[0017] In a third aspect, the present invention provides a method for preparing a negative electrode active material, the negative electrode active material including a silicon-carbon composite, and the formation of the silicon-carbon composite includes the following steps:

[0018] S21. After adding the wound carbon nanotubes into a silo, transport them into a chemical vapor deposition furnace under positive pressure, and use the wound carbon nanotubes as the carbonaceous framework for depositing nano-silicon;

[0019] S22, nitrogen is introduced into the vapor deposition furnace to replace the air, the temperature inside the fluidized bed is raised to 400° C. to 550° C., silane gas is introduced to crack the silane gas, and nano-silicon is deposited inside the carbonaceous skeleton. After keeping the temperature for 1 to 20 hours, the introduction of silane is stopped;

[0020] S23, raising the temperature to 600° C. to 1200° C., introducing hydrogen and a carbon source, and maintaining the temperature at high temperature for 1 h to 5 h to perform in-situ growth and coating of graphene;

[0021] S24. After the growth is completed, the carbon source gas is turned off, and the temperature is lowered to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite, which includes an inner layer and an outer layer. The inner layer is a wound carbon nanotube, which is a three-dimensional network formed by winding and interweaving multiple layers of filamentous fibers, and nano-silicon particles are embedded in the wound carbon nanotube. The outer layer is a graphene layer, and the thickness of the graphene layer is 1nm to 10nm.

[0022] In some embodiments, the carbon source gas includes at least one of methane, ethane, propane, ethylene, acetylene or ethanol; in some embodiments, the catalyst in S11 includes Fe 2 O 3 1.3Al 2 O 3 0.1MoO 3 、FeCoAlMo 0.1 O 4.3 or NiAlMgO 3.5 At least one of .

[0023] In a fourth aspect, the present invention provides a lithium ion battery, comprising a negative electrode, a positive electrode, an electrolyte and a separator;

[0024] The negative electrode comprises the negative electrode active material described in the first aspect, or comprises the negative electrode active material obtained according to the preparation method of the second aspect;

[0025] The positive electrode includes a positive electrode active material.

[0026] In some embodiments, the electrolyte includes LiPO 2 F 2 , LiBF 4 、Li(FSO 2 ) 2 N, at least one of lithium tetrafluoromethanesulfonate, lithium difluorobis(oxalato)phosphate or lithium bis(oxalato)borate.

[0027] In some embodiments, based on 100 parts by mass of the electrolyte, if the LiPO 2 F 2 , then the LiPO 2 F 2The content is 0.01 to 0.5 parts by mass;

[0028] If including the LiBF 4 , then the content of the LiBF 4 is 0.01 to 0.5 parts by mass;

[0029] If including the Li(FSO 2 ) 2 N, then the content of the Li(FSO 2 ) 2 N is 0.01 to 3.5 parts by mass;

[0030] If including the lithium tetrafluoromethanesulfonate, then the content of the lithium tetrafluoromethanesulfonate is 0.01 to 0.5 parts by mass;

[0031] If including the lithium difluorobis(oxalate)phosphate, then the content of the lithium difluorobis(oxalate)phosphate is 0.01 to 1.2 parts by mass;

[0032] If including the lithium bis(oxalate)borate, then the content of the lithium bis(oxalate)borate is 0.01 to 0.8 parts by mass.

[0033] Advantageous effects of the present invention: The negative electrode active material for a lithium ion battery according to the embodiment can exhibit improved cycle life characteristics and improved compressive and tensile low expansion characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below with reference to the accompanying drawings in conjunction with the embodiments.

[0035] Figure 1 is a schematic structural diagram of the silicon-carbon composite in the negative electrode active material of the present invention.

[0036] Figure 2 is a schematic flow chart of an embodiment of the method of the present invention.

[0037] Figure 3 is a schematic flow chart of another embodiment of the method of the present invention.

[0038] Figures 4 to 5 are all electron micrographs of the carbon nanotubes of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The embodiments of the present invention will be described in detail below. However, these embodiments are exemplary, the present invention is not limited thereto, and the present invention is defined by the scope of the claims.

[0040] Silicon-carbon composite

[0041] Such as Figure 1As shown, the negative electrode active material for a lithium-ion battery according to an embodiment of the present invention includes a silicon-carbon composite.

[0042] The silicon-carbon composite 100 includes an inner layer and an outer layer. The inner layer is a wound carbon nanotube 1, which is a three-dimensional network formed by the winding and interweaving of multiple layers of filamentous fibers, and nano-silicon particles 2 are embedded on the wound carbon nanotube 1. The outer layer is a graphene layer 3, and the thickness of the graphene layer 3 is 1 nm to 10 nm.

[0043] Among them, the silicon-carbon composite 100 presents a kind of "loofah structure", as Figure 4 and Figure 5 shown. Its wound carbon nanotube 1 is shaped like the structure of a "loofah sponge", and the graphene layer 3 represents the "loofah peel".

[0044] In the present invention, wound carbon nanotube microspheres or wound carbon nanotubes are used to replace traditional porous carbon as the deposited carbonaceous skeleton. Its outer layer is coated with in-situ grown graphene, replacing the previous amorphous carbon coating method, thereby constructing a network fiber structure similar to a dried loofah capsule. By using carbon nanotubes and graphene to replace the currently commonly used graphite and amorphous carbon, higher electrical conductivity, flexibility, mechanical strength, and thermal conductivity are achieved. The outer coating of graphene effectively reduces the direct contact between the exposed silicon and the electrolyte, inhibits the repeated growth of the SEI film, and thus significantly improves the cycle life and first efficiency of the lithium battery. In addition, the voids in the internal carbonaceous skeleton provide a necessary buffer space for the expansion of silicon, which not only improves the energy density of the material, but also extends the service life, improves the fast charging performance, and optimizes the performance of the battery in high and low temperature environments.

[0045] In the present invention, the thickness of the graphene layer is 1 nm to 10 nm. When the thickness of the graphene layer is greater than 10 nm, the defects of expansion can be increased. In particular, when the thickness of the graphene layer is in the range of 2 nm to 7 nm, improved cycle life characteristics and improved expansion inhibition effects can be obtained.

[0046] In the present invention, the particle size (D50) of the nano-silicon can be in the nano size, and the particle size (D50) of the nano-silicon can be 5 nm to 500 nm. When the particle size (D50) of the nano-silicon is greater than the nano size, the defects of expansion can be increased. In particular, when the particle size (D50) of the nano-silicon is in the range of 10 nm to 300 nm, improved cycle life characteristics and improved expansion inhibition effects can be obtained. The particle size (D50) refers to the diameter of the particles with a cumulative volume of 50% by volume in the particle size distribution, and can be measured by a Malvern particle size analyzer.

[0047] In the present invention, the particle size D50 of the silicon-carbon composite is 1 μm to 20 μm, preferably 5 μm to 15 μm. Improved cycle life characteristics and an improved effect of suppressing swelling can be obtained.

[0048] In the present invention, the diameter of the wound carbon nanotubes is 1 nm to 20 nm, preferably 5 nm to 15 nm. The intertubular pores of the wound carbon nanotubes are 20 nm to 100 nm, preferably 40 nm to 60 nm. The carbon nanotubes have high strength and flexibility. The voids inside the hollow tubular structure of the carbon nanotubes provide the necessary buffer space, rebound support, and elastic space for the expansion and contraction of the nanosilicon, strengthening the compressive and tensile properties of the material and maintaining the stability of the material structure.

[0049] In the present invention, the negative electrode active material further includes at least one of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, or silicon oxides. When these substances and the silicon-carbon composite are used as active materials simultaneously (mixed or layered), improved cycle life characteristics and an improved effect of suppressing swelling can be further obtained.

[0050] Preparation of silicon-carbon composite

[0051] In the present invention, the specific implementation process of the silicon-carbon composite includes the following two methods:

[0052] The first is as Figure 2 shown and may specifically include the following steps:

[0053] S11. Preparation of the carbonaceous skeleton: Add a catalyst into the fluidized bed reactor; liquid nitrogen is converted into gas through a vaporizer and continuously input into the reactor, and the temperature in the reactor is raised to 600 °C to 800 °C by heating; an excessive amount of carbon source gas is introduced into the fluidized bed reactor and cracked at high temperature to generate carbon atoms; when the carbon atom concentration accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes; by maintaining the temperature for 1 h to 4 h, wound carbon nanotube microspheres are formed.

[0054] The above catalyst includes at least one of Fe 2 O 3 ·1.3Al 2 O 3 ·0.1MoO 3 、FeCoAlMo 0.1 O 4.3 or NiAlMgO 3.5 。

[0055] The diameter of the above wound carbon nanotube microspheres is 1 nm to 20 nm, and the intertubular pores of the wound carbon nanotubes are 20 nm to 100 nm.

[0056] The total time for the growth and heat preservation of the above carbon nanotubes is maintained at 1 h to 4 h.

[0057] S12. Deposition: Using the above-mentioned wound carbon nanotube microspheres as a carbonaceous skeleton, cooling the temperature to 400°C to 550°C, introducing silane gas, cracking the silane gas, depositing particles inside the carbonaceous skeleton, and stopping the injection of silane after heat preservation for 1 h to 20 h;

[0058] S13. In-situ growth and coating of graphene: Heating the temperature to 600°C to 1200°C, introducing hydrogen and a carbon source, and performing in-situ growth and coating of graphene by heat preservation at a high temperature for 1 h to 5 h;

[0059] The above carbon source gas includes one or more of methane, ethane, ethanol, ethylene, and propylene.

[0060] S14. After the growth is completed, close the carbon source gas, and cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes wound carbon nanotubes as the loofah sponge and a graphene layer as the loofah peel, and the wound carbon nanotubes are embedded with nano-silicon.

[0061] S15. Screen, demagnetize, remove impurities by pickling, wash with water, dry, and package the silicon-carbon composite.

[0062] The second method is as Figure 3 shown, and specifically includes the following steps:

[0063] S21. After the wound carbon nanotube powder is added to the silo as a carbonaceous skeleton, it is then added to the chemical vapor deposition furnace by positive pressure transportation; using the wound carbon nanotubes as the deposited carbonaceous skeleton;

[0064] The wound carbon nanotube powder can be obtained commercially, with a diameter of 1 nm to 20 nm, and the radial pores of the wound carbon nanotube powder are 20 nm to 100 nm.

[0065] S22. The above chemical vapor deposition furnace is filled with nitrogen to displace the air, the internal temperature of the fluidized bed is raised to 400°C to 550°C, silane gas is introduced, the silane gas is cracked, particles are deposited inside the carbonaceous skeleton, and after heat preservation for 1 h to 20 h, the injection of silane is stopped;

[0066] S23. Heat the temperature to 600°C to 1200°C, introduce hydrogen and a carbon source gas, and perform in-situ growth and coating of graphene by heat preservation at a high temperature for 1 h to 5 h;

[0067] The above carbon source gas includes one or more of methane, ethane, ethanol, ethylene, and propylene.

[0068] S24. After the growth is completed, the carbon source gas is turned off, and the temperature is reduced to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite of the "loofah structure", which includes entangled carbon nanotubes as the loofah sponge and graphene layers as the loofah skin, and the entangled carbon nanotubes are embedded with nano-silicon.

[0069] S25. Screen, demagnetize and package the silicon-carbon composite.

[0070] In the present invention, entangled carbon nanotubes are used to replace the existing porous carbon as the carbonaceous skeleton for depositing nano-silicon, and in-situ grown graphene is used to coat the outer layer instead of the existing amorphous carbon coating to form a silicon-carbon composite with a net fiber structure similar to a dried loofah, which has the following advantages:

[0071] 1) The extremely high specific surface areas of carbon nanotubes and graphene provide more space for the deposition of nano-silicon, increasing the specific capacity of the silicon-carbon composite. The coating of graphene on the outer layer can reduce the direct contact between the exposed silicon and the electrolyte, inhibiting the repeated formation of the SEI film. The hollow tubular structure of the internal carbon nanotubes provides a buffer space and a resilient support for the expansion and contraction of silicon. Its excellent flexibility, mechanical strength and thermal conductivity strengthen the compressive and tensile properties of the matrix, maintaining the structural stability of the material, thus ensuring the high capacity density, high initial efficiency and long cycle life of the lithium battery.

[0072] 2) The high conductivity of carbon nanotubes and graphene, and the sponge void structure of carbon nanotubes provide a fast channel for lithium-ion transmission, improving the fast charging performance and ensuring the low-temperature rate performance of the battery.

[0073] 3) By adjusting the aspect ratio of carbon nanotubes and the density of carbon nanotubes in the microspheres, the proportion and conductivity of the deposited silicon can be adjusted to meet the conductivity and capacity density requirements of fast charging type and high specific capacity type battery materials; using carbon nanotube powder instead of porous carbon powder as the carbon skeleton, it has a larger specific surface area, can deposit more nano-silicon within the same volume, has a higher silicon-carbon element ratio and a higher specific capacity.

[0074] Lithium-ion battery

[0075] Another embodiment of the present invention provides a lithium-ion battery, which includes: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte and a separator.

[0076] In the positive electrode active material layer, the positive electrode active material can be a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound), and in particular, one or more composite oxides of metals selected from cobalt, manganese, nickel and their combinations and lithium. More specifically, a compound represented by one of the following chemical formulas can be used. Li a A 1-b X b D2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5);

[0077] Li a A 1-b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0078] Li a E 1-b X b O 2-c D c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0079] Li a E 2-b X b O 4-c D c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0080] Li a Ni 1-b-c Co b X c D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 ≤ α ≤ 2);

[0081] Li a Ni 1-b-c Co b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α < 2);

[0082] Li a Ni 1-b-c Co b X c O 2-α T 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α < 2);

[0083] Li a Ni 1-b-c Mn b X c D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α ≤ 2);

[0084] Li a Ni1-b-c Mn b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α < 2);

[0085] Li a Ni 1-b-c Mn b X c O 2-α T 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α < 2);

[0086] Li a Ni b E c G d O 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1);

[0087] Li a Ni b Co c Mn d G e O 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1);

[0088] Li a NiG b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1)Li a CoG b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0089] Li a Mn 1-b G b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 2 G b O 4 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0090] Li a Mn 1-g G g PO 4(0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); QO 2 ; QS 2 ; LiQS 2 ; V 2 O 5 ; LiV 2 O 5 ; LiZO 2 ;

[0091] LiNiVO 4 ; Li (3-f) J 2 (PO 4 ) 3 (0 ≤ f ≤ 2); Li (3-f) Fe 2 (PO 4 ) 3 (0 ≤ f ≤ 2); Li a FePO 4 (0.90 ≤ a ≤ 1.8).

[0092] In the chemical formula, A is selected from Ni, Co, Mn, and combinations thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from O, F, S, P, and combinations thereof; E is selected from Co, Mn, and combinations thereof. T is selected from F, S, P, and combinations thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from Ti, Mo, Mn, and combinations thereof; Z is selected from Cr, V, Fe, Sc, Y, and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0093] The compound can have a coating on its surface or can be mixed with another compound having a coating. The coating can include at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, hydroxyoxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compound used for the coating can be amorphous or crystalline. The coating elements included in the coating can include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. By using these elements in the compound, the coating can be provided in a manner that has no adverse effect on the performance of the positive electrode active material. For example, the method can include any coating method such as spraying, dip coating, etc., but since it is well known in the relevant field, it is not described in more detail.

[0094] In the positive electrode, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 90 wt% to 98 wt%.

[0095] In an embodiment of the present invention, the positive electrode active material layer may further include a binder and a conductive material. Here, based on the total amount of the positive electrode active material layer, the binder and the conductive material may be included in an amount of 1 wt% to 5 wt% respectively.

[0096] The binder improves the binding performance between the positive electrode active material particles and between the positive electrode active material particles and the current collector, and examples thereof may be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0097] The conductive material is included to provide electrode conductivity, and any conductive material may be used as the conductive material unless it causes a chemical change, and examples of the conductive material may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0098] The current collector may be aluminum foil, nickel foil, or a combination thereof, but is not limited thereto.

[0099] The negative electrode includes a current collector and a negative electrode active material layer provided on the current collector and including a negative electrode active material.

[0100] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the negative electrode active material may be included in an amount of 95 wt% to 99 wt%.

[0101] In an embodiment of the present invention, the negative electrode active material layer includes a binder and an optional conductive material. In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the content of the binder may be 1 wt% to 5 wt%. When the negative electrode active material layer includes a conductive material, the negative electrode active material layer includes 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0102] The binder improves the adhesion performance between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder may use a non-aqueous binder, an aqueous binder, or a combination thereof.

[0103] The non-aqueous binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0104] The aqueous binder may be styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene-propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, polyacrylic acid, or a combination thereof.

[0105] When the aqueous binder is used as the negative electrode binder, a cellulose compound may be further used as a thickener to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li. Based on 100 parts by weight of the negative electrode active material, the thickener may be included in an amount of 0.1 part by weight to 3 parts by weight.

[0106] A conductive material is included to provide electrode conductivity, and any conductive material may be used as the conductive material unless it causes a chemical change, and examples of the conductive material may include carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metallic materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0107] The current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0108] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0109] The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0110] The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, or an aprotic solvent.

[0111] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. Additionally, alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include: nitriles, such as R-CN (where R is a hydrocarbon group having a linear, branched or cyclic structure with C2 to C20 and may include double bonds, aromatic rings or ether bonds), etc.; amides, such as dimethylformamide, etc.; dioxolanes, such as 1,3-dioxolane, etc.; sulfolane, etc.

[0112] The organic solvents can be used alone or in a mixture, and when the organic solvents are used in a mixture, the mixture ratio can be controlled according to the desired battery performance.

[0113] The carbonate solvents may include a mixture of cyclic carbonates and linear (chain) carbonates. The cyclic carbonate and the linear carbonate are mixed together in a mass ratio of 1:1 to 1:9, which can provide enhanced electrolyte performance.

[0114] In some embodiments, the electrolyte includes LiPO 2 F 2 、LiBF 4 、Li(FSO 2 ) 2 N, lithium tetrafluoromethanesulfonate, lithium difluoro bis(oxalato)phosphate or lithium bis(oxalato)borate, at least one of which can further improve the cycle life characteristics and low expansion characteristics of the silicon-carbon composite of the present invention.

[0115] In some embodiments, based on 100 parts by mass of the electrolyte, the content of LiPO 2 F 2 is 0.01 part by mass to 0.5 part by mass; or the content of LiBF 4 is 0.01 part by mass to 0.5 part by mass; or the content of Li(FSO 2 ) 2 N is 0.01 part by mass to 3.5 part by mass; or the content of lithium tetrafluoromethanesulfonate is 0.01 part by mass to 0.5 part by mass; or the content of lithium difluoro bis(oxalato)phosphate is 0.01 part by mass to 1.2 part by mass; or the content of lithium bis(oxalato)borate is 0.01 part by mass to 0.8 part by mass.

[0116] As an electrolyte salt, such as LiPF 6 , a lithium salt can be used at a concentration in the range of about 0.1 M to about 2.0 M. When the lithium salt is included in the above concentration range, the electrolyte can have excellent performance and lithium ion mobility due to appropriate or optimal electrolyte conductivity and viscosity.

[0117] The separator can be a porous substrate; or can be a composite porous substrate.

[0118] The porous substrate can be a substrate including pores, and lithium ions can move through the pores. The porous substrate can, for example, include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, or a multilayer thereof (such as a polyethylene / polypropylene bilayer separator, a polyethylene / polypropylene / polyethylene trilayer separator, and a polypropylene / polyethylene / polypropylene trilayer separator).

[0119] The composite porous substrate can have a form including a porous substrate and a functional layer on the porous substrate. From the perspective of ensuring additional functions, the functional layer can be, for example, at least one selected from a heat-resistant layer and a bonding layer. For example, the heat-resistant layer can include a heat-resistant resin and optionally can include a filler.

[0120] In some embodiments, the bonding layer can include a binder resin and optionally can include a filler.

[0121] The filler can be an organic filler and / or an inorganic filler.

[0122] There is no particular limitation on the form of the lithium ion battery, and various conventionally known forms of batteries such as cylindrical, flat wound square, laminated square, coin type, flat wound laminated type, and laminated composite type can be adopted.

[0123] Examples and comparative examples are listed below to illustrate the present invention more specifically, but the present invention is not limited to the following examples.

[0124] [1] Preparation of silicon-carbon composite

[0125] Example 1-1

[0126] S11. Preparation of carbonaceous framework: Add 3.5 g of catalyst Fe 2 O 3 ·1.3Al 2 O 3 ·0.1MoO 3Liquid nitrogen is converted into gas by a vaporizer and continuously input into the reactor. The temperature inside the reactor is raised to 600 °C by heating. An excessive amount of ethylene gas (25 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms. When the concentration of carbon atoms accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes. By maintaining the temperature for 3 h, entangled carbon nanotube microspheres are formed.

[0127] S12. Deposition: Using the above-mentioned entangled carbon nanotube microspheres as a carbonaceous framework, the temperature is lowered to 500 °C, and 5 kg of silane gas is introduced to crack the silane gas, depositing particles inside the carbonaceous framework. After maintaining the temperature for 1 h, the introduction of silane is stopped.

[0128] S13. In-situ growth and coating of graphene: The temperature is raised to 600 °C, argon and methane (0.015 L / min) are introduced, and the temperature is maintained at high temperature for 1 h for in-situ growth and coating of graphene.

[0129] S14. After the growth is completed, the carbon source gas is turned off, and the temperature is lowered to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes entangled carbon nanotubes as the loofah sponge and a graphene layer as the loofah peel. Nano-silicon is embedded on the entangled carbon nanotubes. The obtained silicon-carbon composite has a D50 particle size of 3 μm, a graphene layer thickness of 1 nm, an inter-pore diameter of 30 nm for the entangled carbon nanotubes, and a diameter of 1 nm for the entangled carbon nanotubes.

[0130] Example 1-2

[0131] S11. Preparation of carbonaceous framework: 10 g of catalyst Fe 2 O 3 ·1.3Al 2 O 3 ·0.1MoO 3 is added into the fluidized bed reactor. Liquid nitrogen is converted into gas by a vaporizer and continuously input into the reactor. The temperature inside the reactor is raised to 800 °C by heating. An excessive amount of propylene gas (75 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms. When the concentration of carbon atoms accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes. By maintaining the temperature for 1 h, entangled carbon nanotube microspheres are formed.

[0132] S12. Deposition: Using the above-mentioned entangled carbon nanotube microspheres as a carbonaceous framework, the temperature is lowered to 500 °C, and 5 kg of silane gas is introduced to crack the silane gas, depositing particles inside the carbonaceous framework. After maintaining the temperature for 20 h, the introduction of silane is stopped.

[0133] S13. In-situ growth and coating of graphene: Heat up to 1200 °C, introduce argon and ethanol (0.75 L / min), keep the temperature at a high level for 4 h for in-situ growth and coating of graphene;

[0134] S14. After the growth is completed, turn off the carbon source gas, cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes wound carbon nanotubes as the loofah sponge and graphene layers as the loofah peel, and the wound carbon nanotubes are embedded with nano-silicon. The obtained silicon-carbon composite has a D50 particle size of 20 μm, the thickness of the graphene layer is 10 nm, the pore size between the wound carbon nanotubes is 30 nm, and the diameter of the wound carbon nanotubes is 20 nm.

[0135] Examples 1-3

[0136] S11. Preparation of carbonaceous framework: Add 80 g of catalyst Fe 2 O 3 ·1.3Al 2 O 3 ·0.1MoO 3 ; Liquid nitrogen is converted into gas through a vaporizer and continuously input into the reactor, and the temperature in the reactor is raised to 700 °C by heating; Excessive ethylene gas (25 L / min) is introduced into the fluidized bed reactor and cracked at a high temperature to generate carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, carbon atoms precipitate and grow into carbon nanotubes; By keeping the temperature for 4 h, a microsphere of wound carbon nanotubes is formed.

[0137] S12. Deposition: Take the above-mentioned microsphere of wound carbon nanotubes as the carbonaceous framework, cool down to 400 °C, introduce 5.3 Kg of silane gas, crack the silane gas, deposit particles inside the carbonaceous framework, and stop charging silane after keeping the temperature for 8 h;

[0138] S13. In-situ growth and coating of graphene: Heat up to 1000 °C, introduce argon and ethanol (0.75 L / min), keep the temperature at a high level for 4 h for in-situ growth and coating of graphene;

[0139] S14. After the growth is completed, turn off the carbon source gas, cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes wound carbon nanotubes as the loofah sponge and graphene layers as the loofah peel, and the wound carbon nanotubes are embedded with nano-silicon. The obtained silicon-carbon composite has a D50 particle size of 5 μm, the thickness of the graphene layer is 2 nm, the pore size between the wound carbon nanotubes is 30 nm, and the diameter of the wound carbon nanotubes is 5 nm.

[0140] Examples 1-4

[0141] S11. Preparation of carbonaceous framework: Add 10 g of catalyst Fe into the fluidized bed reactor. 2 O 3 ·1.3Al 2 O 3 ·0.1MoO 3 ; Liquid nitrogen is converted into gas through a vaporizer and continuously input into the reactor. The temperature in the reactor is raised to 700 °C by heating; Excessive propylene gas (75 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, carbon atoms precipitate and grow into carbon nanotubes; By maintaining the temperature for 2 h, a wound carbon nanotube microsphere is formed.

[0142] S12. Deposition: Use the above-mentioned wound carbon nanotube microsphere as the carbonaceous framework, cool down to 500 °C, introduce 5 Kg of silane gas, crack the silane gas, deposit particles inside the carbonaceous framework, and stop charging silane after maintaining the temperature for 4 h.

[0143] S13. In-situ growth coating of graphene: Raise the temperature to 1000 °C, introduce argon and ethanol (0.75 L / min), and maintain the temperature at high temperature for 4 h for in-situ growth coating of graphene.

[0144] S14. After the growth is completed, close the carbon source gas, cool down to room temperature in the atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes wound carbon nanotubes as the loofah sponge and graphene layers as the loofah peel, and nano-silicon is embedded on the wound carbon nanotubes. The obtained silicon-carbon composite has a D50 particle size of 8 μm, a graphene layer thickness of 3 nm, an inter-pore diameter of 30 nm for the wound carbon nanotubes, and a diameter of 9 nm for the wound carbon nanotubes.

[0145] Examples 1 - 5

[0146] S11. Preparation of carbonaceous framework: Add 50 g of catalyst NiAlMgO into the fluidized bed reactor. 3.5 ; Liquid nitrogen is converted into gas through a vaporizer and continuously input into the reactor. The temperature in the reactor is raised to 700 °C by heating; Excessive propylene gas (75 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, carbon atoms precipitate and grow into carbon nanotubes; By maintaining the temperature for 1.5 h, a wound carbon nanotube microsphere is formed.

[0147] S12. Deposition: Use the above-mentioned wound carbon nanotube microsphere as the carbonaceous framework, cool down to 500 °C, introduce 5 Kg of silane gas, crack the silane gas, deposit particles inside the carbonaceous framework, and stop charging silane after maintaining the temperature for 4 h.

[0148] S13. In-situ growth and coating of graphene: Heat up to 1000 °C, introduce argon and ethanol (0.75 L / min), keep the temperature at a high level for 5 h, and conduct in-situ growth and coating of graphene.

[0149] S14. After the growth is completed, turn off the carbon source gas, cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes intertwined carbon nanotubes as the loofah sponge and graphene layers as the loofah skin, and nano-silicon is embedded on the intertwined carbon nanotubes. The obtained silicon-carbon composite has a D50 particle size of 10 μm, a graphene layer thickness of 4 nm, an inter-tube pore size of 30 nm for the intertwined carbon nanotubes, and a diameter of 11 nm for the intertwined carbon nanotubes.

[0150] Examples 1-6

[0151] S11. Preparation of carbonaceous framework: Add 10 g of catalyst NiAlMgO into the fluidized bed reactor. 3.5 ; Liquid nitrogen is converted into gaseous state through a vaporizer and continuously input into the reactor. The temperature inside the reactor is raised to 700 °C by heating; Excessive methane gas (50 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, carbon atoms precipitate and grow into carbon nanotubes; By keeping the temperature for 2 h, microspheres of intertwined carbon nanotubes are formed.

[0152] S12. Deposition: Take the above-mentioned microspheres of intertwined carbon nanotubes as the carbonaceous framework, cool down to 500 °C, introduce 8 Kg of silane gas, crack the silane gas, deposit particles inside the carbonaceous framework, and stop charging silane after keeping the temperature for 8 h.

[0153] S13. In-situ growth and coating of graphene: Heat up to 1000 °C, introduce argon and ethanol (0.75 L / min), keep the temperature at a high level for 5 h, and conduct in-situ growth and coating of graphene.

[0154] S14. After the growth is completed, turn off the carbon source gas, cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes intertwined carbon nanotubes as the loofah sponge and graphene layers as the loofah skin, and nano-silicon is embedded on the intertwined carbon nanotubes. The obtained silicon-carbon composite has a D50 particle size of 12 μm, a graphene layer thickness of 5 nm, an inter-tube pore size of 30 nm for the intertwined carbon nanotubes, and a diameter of 13 nm for the intertwined carbon nanotubes.

[0155] Examples 1-7

[0156] S11. Preparation of carbonaceous framework: Add 7 g of catalyst Fe 2 O 3 ·1.3Al 2 O3 ·0.1MoO 3 ; Liquid nitrogen is converted into gas through a vaporizer and continuously input into the reactor. The temperature inside the reactor is raised to 700 °C by heating. Excessive ethylene gas (25 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms. When the carbon atom concentration accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes. By maintaining the temperature for 3 h, wound carbon nanotube microspheres are formed.

[0157] S12. Deposition: Using the above-mentioned wound carbon nanotube microspheres as a carbonaceous framework, the temperature is lowered to 500 °C, and 20 Kg of silane gas is introduced to crack the silane gas, and particles are deposited inside the carbonaceous framework. After maintaining the temperature for 10 h, the silane gas injection is stopped;

[0158] S13. In-situ growth and coating of graphene: The temperature is raised to 1000 °C, argon and methane (0.015 L / min) are introduced, and the temperature is maintained at a high temperature for 5 h for in-situ growth and coating of graphene;

[0159] S14. After the growth is completed, the carbon source gas is turned off, and the temperature is lowered to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes wound carbon nanotubes as the loofah sponge and graphene layers as the loofah skin, and nano-silicon is embedded on the wound carbon nanotubes. The obtained silicon-carbon composite: the particle size D50 is 15 μm, the thickness of the graphene layer is 6 nm, the pore size between the diameters of the wound carbon nanotubes is 30 nm, and the diameter of the wound carbon nanotubes is 15 nm.

[0160] Examples 1-8

[0161] S11. Preparation of carbonaceous framework: Add 50 g of catalyst NiAlMgO to the fluidized bed reactor 3.5 ; Liquid nitrogen is converted into gas through a vaporizer and continuously input into the reactor. The temperature inside the reactor is raised to 700 °C by heating. Excessive propylene gas (75 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms. When the carbon atom concentration accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes. By maintaining the temperature for 3 h, wound carbon nanotube microspheres are formed.

[0162] S12. Deposition: Using the above-mentioned wound carbon nanotube microspheres as a carbonaceous framework, the temperature is lowered to 500 °C, and 5 Kg of silane gas is introduced to crack the silane gas, and particles are deposited inside the carbonaceous framework. After maintaining the temperature for 4 h, the silane gas injection is stopped;

[0163] S13. In-situ growth and coating of graphene: The temperature is raised to 1000 °C, argon and ethanol (0.75 L / min) are introduced, and the temperature is maintained at a high temperature for 5 h for in-situ growth and coating of graphene;

[0164] S14. After the growth is completed, close the carbon source gas, and cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with the "loofah structure", which includes the intertwined carbon nanotubes as the loofah sponge and the graphene layer as the loofah peel. The intertwined carbon nanotubes are embedded with nano-silicon. The obtained silicon-carbon composite has a D50 particle size of 10 μm, the thickness of the graphene layer is 4 nm, the pore size between the intertwined carbon nanotubes is 40 nm, and the diameter of the intertwined carbon nanotubes is 11 nm.

[0165] Examples 1-9

[0166] S11. Preparation of the carbonaceous framework: Add 70 g of the catalyst NiAlMgO into the fluidized bed reactor 3.5 ; Liquid nitrogen is converted into gaseous state through the vaporizer and continuously input into the reactor. The temperature in the reactor is raised to 700 °C by heating; Excessive propylene gas (75 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to generate carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes; By maintaining the temperature for 3.5 h, intertwined carbon nanotube microspheres are formed.

[0167] S12. Deposition: Take the above-mentioned intertwined carbon nanotube microspheres as the carbonaceous framework, cool down to 500 °C, introduce 5 Kg of silane gas, crack the silane gas, deposit particles inside the carbonaceous framework, and stop charging silane after maintaining the temperature for 4 h;

[0168] S13. In-situ growth and coating of graphene: Raise the temperature to 1000 °C, introduce argon and ethanol (0.75 L / min), and maintain the temperature at high temperature for 5 h for in-situ growth and coating of graphene;

[0169] S14. After the growth is completed, close the carbon source gas, and cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with the "loofah structure", which includes the intertwined carbon nanotubes as the loofah sponge and the graphene layer as the loofah peel. The intertwined carbon nanotubes are embedded with nano-silicon. The obtained silicon-carbon composite has a D50 particle size of 10 μm, the thickness of the graphene layer is 4 nm, the pore size between the intertwined carbon nanotubes is 50 nm, and the diameter of the intertwined carbon nanotubes is 11 nm.

[0170] Examples 1-10A

[0171] S11. Preparation of the carbonaceous framework: Add 100 g of the catalyst NiAlMgO into the fluidized bed reactor 3.5; Liquid nitrogen is converted into gas through a vaporizer and continuously input into the reactor, and the temperature inside the reactor is raised to 700 °C by heating; Excessive propylene gas (75 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to generate carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes; By maintaining the temperature for 4 h, wound carbon nanotube microspheres are formed.

[0172] S12. Deposition: Using the above-mentioned wound carbon nanotube microspheres as the carbonaceous framework, the temperature is lowered to 500 °C, and 5 kg of silane gas is introduced to crack the silane gas, and particles are deposited inside the carbonaceous framework. After maintaining the temperature for 4 h, the silane gas injection is stopped;

[0173] S13. In-situ growth and coating of graphene: The temperature is raised to 1000 °C, argon and ethanol (0.75 L / min) are introduced, and the temperature is maintained at high temperature for 5 h for in-situ growth and coating of graphene;

[0174] S14. After the growth is completed, the carbon source gas is turned off, and the temperature is lowered to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes wound carbon nanotubes as the loofah sponge and graphene layers as the loofah peel, and nano-silicon is embedded on the wound carbon nanotubes. The obtained silicon-carbon composite: the particle size D50 is 10 μm, the thickness of the graphene layer is 4 nm, the inter-pore diameter of the wound carbon nanotubes is 60 nm, and the diameter of the wound carbon nanotubes is 11 nm.

[0175] Example 1-10B

[0176] Adopt the second preparation method

[0177] S21. After the wound carbon nanotube powder (commercial grade NC7000) is added to the silo as the carbonaceous framework, it is then positively pressured and fed into the chemical vapor deposition furnace; The wound carbon nanotubes are used as the deposited carbonaceous framework;

[0178] S22. Nitrogen is introduced into the above-mentioned chemical vapor deposition furnace to displace the air, the temperature inside the fluidized bed is raised to 400 °C, and silane gas is introduced to crack the silane gas, and particles are deposited inside the carbonaceous framework. After maintaining the temperature for 1 h, the silane gas injection is stopped;

[0179] S23. The temperature is raised to 600 °C, hydrogen and methane are introduced, and the temperature is maintained at high temperature for 1 h for in-situ growth and coating of graphene;

[0180] S24. After the growth is completed, the methane gas is turned off, and the temperature is lowered to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite: the particle size D50 is 12.5 μm, the thickness of the graphene layer is 4 nm, the inter-pore diameter of the wound carbon nanotubes is 55 nm, and the diameter of the wound carbon nanotubes is 9.5 nm.

[0181] Example 1-10C

[0182] The second preparation method is adopted

[0183] S21. After the wound carbon nanotube powder (commercial grade NC7000) is added to the silo as the carbonaceous skeleton, it is then added to the chemical vapor deposition furnace by positive pressure conveying; the wound carbon nanotube is used as the deposited carbonaceous skeleton;

[0184] S22. Nitrogen is introduced into the above chemical vapor deposition furnace to displace the air, the temperature inside the fluidized bed is raised to 550 °C, silane gas is introduced, the silane gas is cracked, particles are deposited inside the carbonaceous skeleton, and after holding for 20 h, the charging of silane is stopped;

[0185] S23. The temperature is raised to 1200 °C, hydrogen and methane are introduced, and it is held at a high temperature for 5 h for in-situ growth and coating of graphene;

[0186] S24. After the growth is completed, the methane gas is turned off, and it is cooled to room temperature in an atmosphere of nitrogen and hydrogen to obtain a silicon-carbon composite: the particle size D50 is 14.5 μm, the thickness of the graphene layer is 7 nm, the inter-tube pore of the wound carbon nanotube is 50 nm, and the diameter of the wound carbon nanotube is 12.5 nm.

[0187] Example 1-10D

[0188] The second preparation method is adopted

[0189] S21. After the wound carbon nanotube powder (commercial grade NC7000) is added to the silo as the carbonaceous skeleton, it is then added to the chemical vapor deposition furnace by positive pressure conveying; the wound carbon nanotube is used as the deposited carbonaceous skeleton;

[0190] S22. Nitrogen is introduced into the above chemical vapor deposition furnace to displace the air, the temperature inside the fluidized bed is raised to 500 °C, silane gas is introduced, the silane gas is cracked, particles are deposited inside the carbonaceous skeleton, and after holding for 5 h, the charging of silane is stopped;

[0191] S23. The temperature is raised to 800 °C, hydrogen and methane are introduced, and it is held at a high temperature for 4 h for in-situ growth and coating of graphene;

[0192] S24. After the growth is completed, the methane gas is turned off, and it is cooled to room temperature in an atmosphere of nitrogen and hydrogen to obtain a silicon-carbon composite: the particle size D50 is 11.5 μm, the thickness of the graphene layer is 6 nm, the inter-tube pore of the wound carbon nanotube is 53 nm, and the diameter of the wound carbon nanotube is 8.5 nm.

[0193] Comparative Example 1-1 Coating of Conventional Porous Carbon and Amorphous Carbon

[0194] S11. The porous carbon fired from coconut shell is used, and the preparation method refers to CN114408919B.

[0195] S12. Deposition: Using the porous carbon obtained by firing the above coconut shell as the carbonaceous framework, cooling the temperature to 500 °C, introducing 5 Kg of silane gas, cracking the silane gas, depositing particles inside the carbonaceous framework, and stopping the injection of silane after heat preservation for 4 h;

[0196] S13. Amorphous carbon coating: The preparation method refers to CN117913239A;

[0197] Obtain a silicon-carbon composite: The particle size D50 is 5 μm.

[0198] Comparative Example 1-2 Conventional porous carbon, graphene coating

[0199] S11. Using the porous carbon obtained by firing the coconut shell, the preparation method refers to CN114408919B.

[0200] S12. Deposition: Using the above wound carbon nanotube microspheres as the carbonaceous framework, cooling the temperature to 500 °C, introducing 5 Kg of silane gas, cracking the silane gas, depositing particles inside the carbonaceous framework, and stopping the injection of silane after heat preservation for 4 h;

[0201] S13. In-situ growth and coating of graphene: Heating up to 1000 °C, introducing argon and methane (0.015 L / min), and heat preserving for 4 h at high temperature for in-situ growth and coating of graphene;

[0202] S14. After the growth is completed, turn off the carbon source gas, and cool down to room temperature in the atmosphere of nitrogen and hydrogen to obtain a silicon-carbon composite: The particle size D50 is 4.7 μm, and the thickness of the graphene layer is 1 nm.

[0203] Comparative Example 1-3 Carbon nanotube framework, amorphous carbon coating

[0204] S11. Preparation of the carbonaceous framework: Add 100 g of catalyst NiAlMgO to the fluidized bed reactor 3.5 ; Liquid nitrogen is converted into gaseous state through a vaporizer and continuously input into the reactor, and the temperature inside the reactor is raised to 700 °C through heating; Excessive propylene gas (75 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to generate carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, carbon atoms precipitate and grow into carbon nanotubes; By heat preserving for 4 h, wound carbon nanotube microspheres are formed.

[0205] S12. Deposition: Using the porous carbon obtained by firing the above coconut shell as the carbonaceous framework, cooling the temperature to 500 °C, introducing 5 Kg of silane gas, cracking the silane gas, depositing particles inside the carbonaceous framework, and stopping the injection of silane after heat preservation for 4 h;

[0206] S13. Amorphous carbon coating: The preparation method refers to CN117913239A;

[0207] Obtain a silicon-carbon composite: The particle size D50 is 5.9 μm, the intertubular pores of the coiled carbon nanotubes are 30 nm, and the diameter of the coiled carbon nanotubes is 8 nm.

[0208] For Comparative Examples 1-4, the graphene layer is too thick

[0209] S11. Preparation of the carbonaceous framework: Add 3.5 g of Fe catalyst to the fluidized bed reactor 2 O 3 ·1.3 Al 2 O 3 ·0.1 MoO 3 ; Liquid nitrogen is converted into gas through a vaporizer and continuously input into the reactor. The temperature in the reactor is raised to 700 °C by heating; Excess ethylene gas (25 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, carbon atoms precipitate and grow into carbon nanotubes; By maintaining the temperature for 3 h, coiled carbon nanotube microspheres are formed.

[0210] S12. Deposition: Use the above-mentioned coiled carbon nanotube microspheres as the carbonaceous framework, cool down to 500 °C, introduce 5 kg of silane gas, crack the silane gas, deposit particles inside the carbonaceous framework, and stop charging silane after maintaining the temperature for 4 h;

[0211] S13. In-situ growth coating of graphene: Raise the temperature to 1000 °C, introduce argon and methane (0.015 L / min), and maintain the temperature at high temperature for 10 h for in-situ growth coating of graphene;

[0212] After the growth is completed, close the carbon source gas, cool down to room temperature in the atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes coiled carbon nanotubes as the loofah sponge and a graphene layer as the loofah skin, and nano-silicon is embedded on the coiled carbon nanotubes. Obtain a silicon-carbon composite: The particle size D50 is 3 μm, the thickness of the graphene layer is 12 nm, the intertubular pores of the coiled carbon nanotubes are 30 nm, and the diameter of the coiled carbon nanotubes is 1 nm.

[0213] For Comparative Examples 1-5, the graphene layer is too thin

[0214] S11. Preparation of the carbonaceous framework: Add 3.5 g of Fe catalyst to the fluidized bed reactor 2 O 3 ·1.3 Al 2 O 3 ·0.1 MoO 3; Liquid nitrogen is converted into gas by a vaporizer and continuously input into the reactor, and the temperature in the reactor is raised to 700 °C by heating; Excessive ethylene gas (25 L / min) is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms; When the carbon atom concentration accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes; By maintaining the temperature for 3 h, wound carbon nanotube microspheres are formed.

[0215] S12. Deposition: Using the above-mentioned wound carbon nanotube microspheres as a carbonaceous skeleton, cooling the temperature to 500 °C, introducing 5 Kg of silane gas, cracking the silane gas, depositing particles inside the carbonaceous skeleton, and stopping the injection of silane after maintaining the temperature for 4 h;

[0216] S13. In-situ growth and coating of graphene: Heating the temperature to 1200 °C, introducing argon and methane (0.015 L / min), and maintaining the temperature at high temperature for 0.5 h for in-situ growth and coating of graphene;

[0217] S14. After the growth is completed, turn off the carbon source gas, cool down to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite with a "loofah structure", which includes wound carbon nanotubes as the loofah sponge and graphene layers as the loofah peel, and nano-silicon is embedded on the wound carbon nanotubes. Obtain the silicon-carbon composite: the particle size D50 is 3 μm, the thickness of the graphene layer is 0.5 nm, the pore size between the diameters of the wound carbon nanotubes is 30 nm, and the diameter of the wound carbon nanotubes is 1 nm.

[0218] [2] Fabrication of lithium-ion battery

[0219] Preparation of the positive electrode plate: Mix lithium cobaltate, conductive agent Super-P carbon black, binder polyvinylidene fluoride, and solvent N-methylpyrrolidone evenly according to a weight ratio of 97:2:1 to obtain a positive electrode active film layer slurry, and the solid content of the slurry is 73%; Then, evenly coat the positive electrode active film layer slurry on the aluminum foil, and then through drying, cold pressing, and slitting, obtain the positive electrode plate.

[0220] Preparation of the negative electrode plate: Dissolve artificial graphite and the silicon-carbon material obtained in the above examples and comparative examples (mass ratio 90:10), conductive agent Super-P carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) in deionized water according to a weight ratio of 98:0.5:1.5, mix evenly and prepare a negative electrode active film layer slurry; Evenly coat the negative electrode slurry on the copper foil, and through drying, cold pressing, and slitting, obtain the negative electrode plate.

[0221] Separator: Use a polypropylene film as the separator.

[0222] Preparation of the electrolyte: In an argon atmosphere glove box (H 2 O <0.1 ppm, O 2(<0.1 ppm), the organic solvents ethylene carbonate (EC) / propylene carbonate (PC) / propyl propionate (PP) / ethyl propionate (EP) are mixed evenly according to the mass ratio of 2:1.1:2.3:0.5, and 12.5% LiPF 6 lithium salt is dissolved in the organic solvent, then 12% fluoroethylene carbonate, 2% 1,3-propane sultone, and additive A are added to obtain the electrolyte. Additive A is selected from LiPO 2 F 2 、LiBF 4 、Li(FSO 2 ) 2 N, lithium tetrafluoromethanesulfonate, lithium difluorobis(oxalate)phosphate or lithium bis(oxalate)borate, or at least one of them.

[0223] The electrolyte additives A used in the following batteries are as follows:

[0224]

[0225]

[0226] Preparation of the wound structure battery core: The negative electrode sheet, the positive electrode sheet and the separator prepared above are wound together to form a wound structure battery core (abbreviation: core).

[0227] Preparation of the lithium ion battery: After the wound structure battery core prepared is hot-pressed and shaped, it is packaged with an aluminum-plastic film, baked to remove moisture, and then the electrolyte is injected, and the obtained battery core is formed to obtain the lithium ion battery.

[0228] [Examples 2-1 to 2-10]

[0229] The silicon-carbon composites in Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-5 are respectively used to make lithium ion batteries, and the electrolyte used is EL-0.

[0230] [Examples 2-11 to 2-23]

[0231] In Example 2-11, the electrolyte EL-0 is replaced with EL-1, and the lithium ion battery is made in the same way as in Example 2-1.

[0232] In Examples 2-12 to 2-17, the electrolytes EL-1 to EL-6 are used to replace EL-0, and the lithium ion batteries are made in the same way as in Example 2-5.

[0233] In Examples 2-18 to 2-23, the electrolyte EL-7 is used, and the lithium ion batteries are made in the same way as in Examples 2-12 to 2-17.

[0234] [Comparative Examples 2-1 to 2-5]

[0235] Lithium-ion batteries were fabricated using the silicon-carbon composites in Comparative Examples 1-1 to 1-5 respectively, and the electrolyte used was EL-0.

[0236] [3] Battery performance test

[0237] <Low-temperature rate performance>

[0238] After injecting the electrolyte into the lithium-ion batteries fabricated in the examples and comparative examples, they were left standing at 25 °C for 5 hours. Then, they were charged at a constant current of 0.2C to a cell voltage of 3.8V at 25 °C, and after that, they were subjected to an aging treatment at 60 °C for 12 hours. Then, they were discharged at a constant current of 0.2C to a cell voltage of 3.0V at 25 °C. After that, CC-CV charging was carried out at a constant current of 0.2C (the upper limit of the cell voltage was 4.5V; this 0.2C charge-discharge was repeated three times).

[0239] Next, in an environment at 25 °C, a constant current charge-discharge of 0.2C was carried out between a cell voltage of 4.5 - 3.0V, and the discharge capacity at this time was defined as C0. After that, similarly, CC-CV charging was carried out at a constant current of 0.2C, and in an environment at -20 °C, a discharge was carried out at a constant current of 0.5C to 3.0V, and the discharge capacity at this time was defined as C1. Then, as the rate performance, the capacity retention rate represented by ΔC = (C1 / C0) × 100 (%) was calculated and evaluated according to the following criteria. The larger the value of the capacity retention rate ΔC, the higher the discharge capacity at low temperature and high current, and the lower the internal resistance.

[0240] A+: The capacity retention rate ΔC is 85% or more;

[0241] A: The capacity retention rate ΔC is 80% or more and less than 85%;

[0242] B: The capacity retention rate ΔC is 70% or more and less than 80%;

[0243] C: The capacity retention rate ΔC is 60% or more and less than 70%;

[0244] D: The capacity retention rate ΔC is 50% or more and less than 60%;

[0245] E: The capacity retention rate ΔC is less than 50%.

[0246] <Swelling inhibition>

[0247] In an environment with a temperature of 25°C, the manufactured lithium-ion battery is left standing for 5 hours with the electrodes immersed in the electrolyte. Then, in an environment with a temperature of 25°C, the standing lithium-ion battery is charged by the constant current method at a rate of 0.2C until the battery voltage reaches 3.8V. Next, in an environment with a temperature of 60°C, the charged lithium-ion battery is subjected to an aging treatment for 12 hours. Subsequently, in an environment with a temperature of 25°C, the lithium-ion battery that has undergone the aging treatment is discharged by the constant current method at a rate of 0.2C until the battery voltage reaches 3.0V. Then, the discharged lithium-ion battery is disassembled, and the value obtained by subtracting the thickness of the current collector from the overall thickness of the negative electrode is measured and taken as the thickness (d0) of the negative electrode before cycling.

[0248] Next, the lithium-ion battery is assembled again. In an environment with a temperature of 25°C, the assembled lithium-ion battery is subjected to charge and discharge operations for 500 cycles under the conditions of a battery voltage of 4.5V to 3.0V and a charge and discharge rate of 1C. Finally, in an environment with a temperature of 25°C, the lithium-ion battery after 50 cycles is charged at a rate of 1C. Then, the charged lithium-ion battery is disassembled, the negative electrode is taken out, and the value obtained by subtracting the thickness of the current collector from the overall thickness of the negative electrode is measured and taken as the thickness (d1) of the negative electrode after cycling. Then, the change rate of the thickness d1 of the negative electrode after cycling with respect to the thickness d0 of the negative electrode before cycling is calculated and taken as the expansion of the negative electrode after cycling = {(d1 - d0) / d0} × 100 (%). The evaluation is carried out according to the following criteria. The smaller the expansion of the negative electrode after cycling, the longer the life of the lithium-ion battery, that is, even if the charge and discharge cycles are repeated, the negative electrode composite material layer can maintain its structure.

[0249] A+: The expansion of the negative electrode after cycling is less than 10%;

[0250] A: The expansion of the negative electrode after cycling is 10% or more and less than 15%;

[0251] B: The expansion of the negative electrode after cycling is 15% or more and less than 20%;

[0252] C: The expansion of the negative electrode after cycling is 20% or more and less than 30%;

[0253] D: The expansion of the negative electrode after cycling is 30% or more and less than 40%;

[0254] E: The expansion of the negative electrode after cycling is 40% or more.

[0255] <Cycling characteristics>

[0256] After injecting the electrolyte into the fabricated lithium-ion battery, it is left standing at a temperature of 25°C for 5 hours. Next, it is charged to a battery voltage of 3.8V by the constant current method at a temperature of 25°C and 0.2C. Then, an aging treatment is carried out at a temperature of 60°C for 12 hours. Then, it is discharged to a battery voltage of 3.0V by the constant current method at a temperature of 25°C and 0.2C. Then, CC-CV charging (with an upper limit of battery voltage 4.5V) is carried out by the constant current method of 0.2C, and CC discharging is carried out to 3.0V by the constant current method of 0.2C.

[0257] Then, in an environment at a temperature of 25°C, charge and discharge operations are carried out for 800 cycles at a charge-discharge rate of 1.0C with a battery voltage of 4.5 - 3.0V. Then, the capacity of the first cycle, that is, the initial discharge capacity X1, and the discharge capacity X2 of the 800th cycle are measured, and the capacity change rate shown by ΔC=(X2 / X1)×100(%) is calculated and evaluated according to the following criteria. The larger the value of the capacity change rate ΔC, the more excellent the cycle characteristics.

[0258] A+: ΔC is 90% or more;

[0259] A: ΔC is 85% or more and less than 90%;

[0260] B: ΔC is 80% or more and less than 85%;

[0261] C: ΔC is 75% or more and less than 80%;

[0262] D: ΔC is 70% or more and less than 75%;

[0263] E: ΔC is less than 70%.

[0264] The battery performance test is shown in Table 1:

[0265] [Table 1]

[0266]

[0267]

[0268] In the present invention, the wound carbon nanotube microspheres or the wound carbon nanotubes are used to replace the traditional porous carbon as the deposited carbonaceous skeleton. Its outer layer is coated with in-situ grown graphene, replacing the previous amorphous carbon coating method, thereby constructing a network fiber structure similar to the "loofah structure". Not only the compressive and tensile properties of the matrix are enhanced, and the stability of the material structure is maintained, but the lithium-ion battery using it has obtained unexpectedly low expansion, low-temperature rate performance, and cycle life.

[0269] The inventor of the present invention also found that particularly in the following situations, further improved effects are obtained:

[0270] 1) When the thickness of the graphene layer is 2 nm to 7 nm, the expansion can be further suppressed;

[0271] 2) When the intertubular pores of the wound carbon nanotubes have a diameter of 40 nm to 60 nm, the expansion can also be further suppressed;

[0272] 3) When the electrolyte system includes at least one of LiPO 2 F 2 , LiBF 4 , Li(FSO 2 ) 2 N, lithium tetrafluoromethanesulfonate, lithium difluoro(oxalato)phosphate or lithium bis(oxalato)borate, the low expansion, low temperature rate performance and cycle life characteristics can be further significantly improved.

[0273] It should be noted that the present invention is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same structure and the same effect within the technical scope of the present invention are included in the technical scope of the present invention. In addition, within the scope not departing from the gist of the present invention, various modifications that can be conceived by those skilled in the art to the embodiments and other embodiments constructed by combining some constituent elements of the embodiments are also included in the scope of the present invention.

Claims

1. A negative electrode active material, characterized in that: include: The silicon-carbon composite comprises an inner layer and an outer layer. The inner layer is a wound carbon nanotube, which is a three-dimensional network formed by winding and interweaving multiple layers of filamentous fibers, and the wound carbon nanotube is embedded with nano silicon particles. The outer layer is a graphene layer, and the thickness of the graphene layer is 1nm to 10nm.

2. The negative electrode active material according to claim 1, characterized in that: The graphene layer is formed by in-situ growth, and the thickness of the graphene layer is 2nm to 7nm.

3. The negative electrode active material according to claim 1, characterized in that: The particle size D50 of the silicon-carbon composite is 1 μm to 20 μm, preferably 5 μm to 15 μm.

4. The negative electrode active material according to claim 1, characterized in that: The inter-diameter pores of the entangled carbon nanotubes are 20 nm to 100 nm, preferably 40 nm to 60 nm.

5. The negative electrode active material according to claim 1, characterized in that: The particle size D50 of the nano-silicon is 5 nm to 500 nm, preferably 10 nm to 300 nm.

6. The negative electrode active material according to claim 1, characterized in that: The diameter of the entangled carbon nanotube is 1 nm to 20 nm, preferably 5 nm to 15 nm.

7. The negative electrode active material according to claim 1, characterized in that: The negative electrode active material further comprises at least one of artificial graphite, natural graphite, hard carbon, mesophase carbon microbeads, or silicon oxide.

8. A method for preparing a negative electrode active material, characterized in that: The negative electrode active material includes a silicon-carbon composite, and the formation of the silicon-carbon composite includes the following steps: S11, preparation of carbonaceous skeleton: adding a catalyst into a fluidized bed reactor; liquid nitrogen is converted into gaseous state through a gasifier and continuously input into the reactor, and the temperature in the reactor is heated to 600° C. to 800° C.; excess carbon source gas is introduced into the fluidized bed reactor and cracked at high temperature to produce carbon atoms; when the concentration of carbon atoms accumulates to a supersaturated state, the carbon atoms precipitate and grow into carbon nanotubes; By keeping the temperature for 1 to 4 hours, entangled carbon nanotube microspheres are formed; S12, depositing nano-silicon: using the entangled carbon nanotube microspheres as a carbon skeleton, cooling to 400° C. to 550° C., introducing silane gas to decompose the silane gas, and depositing particles inside the carbon skeleton. After keeping the temperature for 1 to 20 hours, stop introducing silane; S13, graphene in-situ growth coating: heating to 600° C. to 1200° C., introducing hydrogen and carbon source, and maintaining the temperature at high temperature for 1 h to 5 h to perform graphene in-situ growth coating; S14. After the growth is completed, the carbon source gas is turned off, and the temperature is lowered to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite, which includes an inner layer and an outer layer. The inner layer is a wound carbon nanotube, which is a three-dimensional network formed by winding and interweaving multiple layers of filamentous fibers, and nano-silicon particles are embedded in the wound carbon nanotube. The outer layer is a graphene layer, and the thickness of the graphene layer is 1nm to 10nm.

9. A method for preparing a negative electrode active material, characterized in that: The negative electrode active material includes a silicon-carbon composite, and the formation of the silicon-carbon composite includes the following steps: S21, after adding the wound carbon nanotubes into the silo, the wound carbon nanotubes are added into the vapor deposition furnace through positive pressure conveying, so that the wound carbon nanotubes serve as the carbon skeleton for depositing nano-silicon; S22, nitrogen is introduced into the vapor deposition furnace to replace the air, the temperature inside the fluidized bed is raised to 400° C. to 550° C., silane gas is introduced to crack the silane gas, and nano-silicon is deposited inside the carbonaceous skeleton. After keeping the temperature for 1 to 20 hours, the introduction of silane is stopped; S23, raising the temperature to 600° C. to 1200° C., introducing hydrogen and a carbon source, and maintaining the temperature at high temperature for 1 h to 5 h to perform in-situ growth and coating of graphene; S24. After the growth is completed, the carbon source gas is turned off, and the temperature is lowered to room temperature in an atmosphere of nitrogen and hydrogen to obtain the silicon-carbon composite, which includes an inner layer and an outer layer. The inner layer is a wound carbon nanotube, which is a three-dimensional network formed by winding and interweaving multiple layers of filamentous fibers, and nano-silicon particles are embedded in the wound carbon nanotube. The outer layer is a graphene layer, and the thickness of the graphene layer is 1nm to 10nm.

10. The method for preparing the negative electrode active material according to claim 8, characterized in that: The carbon source gas includes at least one of methane, ethane, propane, ethylene, acetylene or ethanol; or / and the catalyst in S11 includes Fe2O3·1.3Al2O3·0.1MoO3, FeCoAlMo 0.1 O 4.3 or NiAlMgO 3.5 At least one of .

11. A lithium ion battery, characterized in that: It includes a negative electrode, a positive electrode, an electrolyte and a separator; The negative electrode comprises the negative electrode active material according to any one of claims 1 to 7, or comprises the negative electrode active material obtained by the preparation method according to any one of claims 8 to 10; The positive electrode includes a positive electrode active material.

12. The lithium-ion battery according to claim 11, characterized in that: The electrolyte includes at least one of LiPO2F2, LiBF4, Li(FSO2)2N, lithium tetrafluoromethanesulfonate, lithium difluorobis(oxalato)phosphate or lithium bis(oxalato)borate.

13. The lithium-ion battery according to claim 12, characterized in that: Based on 100 parts by mass of the electrolyte, if the LiPO2F2 is included, the content of the LiPO2F2 is 0.01 to 0.5 parts by mass; If the LiBF4 is included, the content of the LiBF4 is 0.01 to 0.5 parts by mass; If the Li(FSO2)2N is included, the content of the Li(FSO2)2N is 0.01 to 3.5 parts by mass; If the lithium tetrafluoromethanesulfonate is included, the content of the lithium tetrafluoromethanesulfonate is 0.01 to 0.5 parts by mass; If the lithium difluorobis(oxalate)phosphate is included, the content of the lithium difluorobis(oxalate)phosphate is 0.01 to 1.2 parts by mass; If the lithium bis(oxalate)borate is included, the content of the lithium bis(oxalate)borate is 0.01 to 0.8 parts by mass.

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