Silicon-carbon composite material, preparation method and application thereof, and lithium ion battery

Abstract

The application discloses a silicon-carbon composite material and a preparation method, application and lithium ion battery thereof. The preparation method of the silicon-carbon composite material comprises the following steps: S1, performing silicon deposition on pre-lithiated porous carbon by using a chemical vapor deposition method to obtain a first precursor; S2, coating a passivation layer on the surface of the first precursor to obtain a second precursor; S3, adding an alkaline reagent into a mixed solution containing the second precursor, a transition metal salt and a solvent, and drying to obtain a third precursor; S4, performing carbon deposition on the third precursor by using a chemical vapor deposition method to obtain a fourth precursor; and S5, performing a polymerization reaction on a slurry containing the fourth precursor, a phenolic compound and an aldehyde compound, and performing carbonization treatment after drying. The silicon-carbon composite material has good conductivity and mechanical strength, and has excellent swelling inhibition performance, and the obtained lithium ion battery can have excellent initial efficiency, specific capacity, rate performance and cycle performance.

Description

Silicon-carbon composite materials, their preparation methods, applications, and lithium-ion batteries Technical Field

[0001] This invention relates to a silicon-carbon composite material, its preparation method, applications, and lithium-ion batteries. Background Technology

[0002] Silicon-carbon anode materials have attracted widespread attention due to their extremely high specific capacity and volumetric energy density, becoming an important means to rapidly improve battery energy density at present, and are widely used in the 3C and power fields. However, they have significant drawbacks, including low initial efficiency, low single-particle strength, and large lithium intercalation expansion. These three major drawbacks have hindered their widespread application, and currently only about 15% silicon-carbon anode materials can be doped to balance various performance aspects.

[0003] The reasons for these three drawbacks are as follows: When depositing silane on porous carbon with a large pore volume, sufficient filling can easily lead to excessive expansion, while insufficient filling, although mitigating expansion, results in insufficient single-particle strength and low initial efficiency. Furthermore, current acetylene-coated silicon-carbon anode materials suffer from insufficient coating strength due to the difficulty in achieving a thick passivation layer. Even with prolonged passivation to enhance coating strength, it affects the rate capability, failing to meet current end-user requirements. Finally, even if pre-lithiation of large-pore silicon-carbon anode materials is successful, the alloy-like lithium intercalation mechanism of silicon leads to instability after pre-lithiation, resulting in spontaneous combustion, bubble formation during stirring, automatic reduction in initial efficiency during natural placement, and a series of application-related problems.

[0004] If a silicon-carbon anode material that integrates multiple aspects such as single-particle strength, specific capacity, initial efficiency, rate capability, and expansion can be designed, the application of silicon-carbon anodes will grow exponentially and have significant economic value. Summary of the Invention

[0005] To address the aforementioned problems with existing silicon-carbon materials, this invention provides a silicon-carbon composite material, its preparation method, applications, and a lithium-ion battery thereof. The silicon-carbon composite material exhibits good electrical conductivity and mechanical strength, and excellent expansion suppression performance. The lithium-ion battery prepared from it can achieve excellent initial efficiency, specific capacity, rate performance, and cycle performance.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution.

[0007] This invention provides a method for preparing a silicon-carbon composite material, which includes the following steps:

[0008] S1. Silicon deposition was performed on pre-lithiated porous carbon using chemical vapor deposition to obtain the first precursor.

[0009] S2. A passivation layer is coated on the surface of the first precursor to obtain a second precursor;

[0010] S3. Add an alkaline reagent to a mixed solution containing the second precursor, a transition metal salt, and a solvent, and dry to obtain the third precursor.

[0011] S4. Carbon deposition is performed on the third precursor using chemical vapor deposition to grow carbon nanotubes in situ, thus obtaining the fourth precursor.

[0012] S5. The slurry containing the fourth precursor, phenolic compound and aldehyde compound is subjected to polymerization reaction, dried and then carbonized to obtain the silicon-carbon composite material.

[0013] In step S1, the use of pre-lithiated porous carbon can not only improve the initial efficiency but also shrink the pores. During the subsequent silicon deposition process, silicon is deposited into the porous carbon in an adaptive manner, that is, the amount of silicon deposited in the micropores is reduced and the amount in the mesopores is increased. This step can significantly reduce expansion and further nanoscale the deposition of silicon nanoparticles, thereby improving the rate of change.

[0014] In step S1, the pre-lithiated porous carbon can be prepared using conventional methods.

[0015] In some preferred embodiments, the pre-lithiation method includes mixing the porous carbon and a lithium source, followed by heating.

[0016] The lithium source preferably includes one or more of lithium phenyl, lithium chloride, lithium sulfate, lithium carbonate, lithium acetate, lithium bromide, lithium iodide, lithium nitrate, lithium phosphate, lithium sulfate, lithium bisulfite, lithium citrate, and lithium hydride, for example, lithium phenyl.

[0017] The heating temperature is between the melting point and decomposition temperature of the lithium source. At this heating temperature, the lithium source melts but does not undergo a chemical reaction (i.e., it does not decompose), and the molten lithium source then enters the porous carbon.

[0018] In some specific embodiments, the lithium source is phenyl lithium, and the heating temperature is 140-165°C, for example, 150°C.

[0019] The preferred mass ratio of the porous carbon to the lithium source is 1:(0.1-0.6), for example, 1:0.42.

[0020] The pre-lithiation process is preferably carried out under the protection of an inert gas, such as argon. The flow rate of the inert gas is preferably 0.2-5 L / kg. -1 ·min -1 For example, 2L·kg-1 ·min -1 Among them, "L·kg -1 min -1 "" refers to the volume of inert gas introduced per minute relative to one kilogram of porous carbon.

[0021] In this invention, the pre-lithiation process can be carried out in a closed environment.

[0022] In step S1, the temperature of silicon deposition is preferably 400-800°C, for example 500°C.

[0023] In step S1, the silicon deposition time is preferably 4-20 hours, for example, 10 hours.

[0024] In step S1, the silicon source for silicon deposition may include silane, preferably one or more of methylsilane, disilane, propane, and butane.

[0025] In step S1, during the silicon deposition process, the gas flow rate of the silicon source is preferably 0.04-0.4 L·kg⁻¹. -1 min -1 Among them, "L·kg -1 min -1 "" refers to the volume of silicon source introduced per minute relative to one kilogram of pre-lithiated porous carbon.

[0026] In step S1, preferably, the gas source for silicon deposition includes a silicon source and a carrier gas; wherein the volume ratio of the silicon source to the carrier gas is 1:(2-6), for example, 1:4.

[0027] In this invention, in step S2, the passivation layer preferably includes a carbon layer and / or an oxide layer.

[0028] In some preferred embodiments, the passivation layer is a carbon layer. Preferably, the carbon layer is obtained by carbon deposition using chemical vapor deposition.

[0029] The carbon source for the carbon deposition preferably includes one or more of alkynes, alkanes, alkenes, aromatic compounds, and carbohydrates, such as acetylene.

[0030] During the carbon deposition process, the aeration rate of the carbon source is preferably 0.1-10 L·kg⁻¹. -1 ·min -1 For example, 1L·kg -1 ·min -1 Among them, "L·kg -1 min -1 "" refers to the volume of carbon source introduced per minute relative to one kilogram of the first precursor.

[0031] The carbon deposition time is preferably 4-20 hours, for example 10 hours.

[0032] The carbon deposition temperature is preferably 400-800°C, for example 500°C.

[0033] Preferably, after carbon deposition, the process further includes purging with an inert atmosphere and cooling. The inert atmosphere is, for example, nitrogen. The cooling is preferably to -40°C to 100°C, for example, to 25°C.

[0034] In this invention, in step S3, the transition metal salt reacts with a basic reagent to generate nano-transition metal oxides. During the reaction, nano-transition metal oxides are preferentially generated in the mesopores and macropores of the second precursor, and then subsequently generated on the surface.

[0035] In this invention, the transition metal salt can be a soluble salt of a transition metal that is conventional in the art and capable of catalyzing the growth of carbon nanotubes in oxide or elemental form.

[0036] In step S3, the transition metal salt preferably includes one or more of iron salts, nickel salts, and cobalt salts.

[0037] In step S3, the transition metal salt may include divalent and / or trivalent salts of transition metals.

[0038] In some preferred embodiments, in step S3, the transition metal salt includes divalent and trivalent iron salts; wherein the molar ratio of the divalent and trivalent iron salts is preferably (2-4):1.

[0039] In step S3, the transition metal salt preferably includes one or more of transition metal hydrochloride, transition metal nitrate, transition metal sulfate, transition metal acetate, and transition metal citrate.

[0040] In some specific embodiments, the transition metal salt comprises ferrous sulfate and ferric chloride. Preferably, the molar ratio of ferrous sulfate to ferric chloride is (2-4):1.

[0041] In step S3, the content of the transition metal salt is preferably 0.01-0.3 mol / kg, for example 0.06 mol / kg, which is the number of moles of the transition metal element relative to 1 kg of the second precursor in the transition metal salt.

[0042] In step S3, the alkaline reagent may include a weak base reagent and / or a strong base reagent, preferably ammonia.

[0043] The concentration of the ammonia water is preferably 1-10%, for example 5%, where the percentage is the mass of ammonia relative to the total mass of the ammonia water.

[0044] In step S3, the mass ratio of the alkaline reagent to the solvent is preferably (1-1000):100, for example, 1:1.

[0045] In step S3, the mixed solution preferably also includes a complexing agent. Based on the complexing effect of the complexing agent, the nano-sizing and uniformity of the transition metal oxides in the reaction can be maximized, further reducing their agglomeration. Furthermore, when a complexing agent is added, it coats the surface of the second precursor. After carbonization, it retains some oxygen-containing groups, resulting in stronger hydrogen bonds and van der Waals forces with the polar binder, thus strengthening the bonding effect and suppressing powder shedding. When the complexing agent contains metal atoms, its carbonization easily alters the smoothness of the subsequent carbon coating layer, increasing the contact between the subsequent carbon coating layer and the second precursor surface, which is more conducive to improving the strength of the subsequent carbon coating layer. Moreover, the doping of metal atoms in the carbon coating layer has the effect of transforming the carbon material into amorphous carbon, changing the disordered structure of the amorphous carbon material, effectively suppressing the buffer stress and expansion on the surface of the silicon-carbon composite material, and improving the pressure resistance of the silicon-carbon composite material.

[0046] The complexing agent may include organic acids and / or organic acid salts, preferably one or more of acetic acid, citric acid, EDTA and their salts, such as one or more of ferric acetate, sodium acetate, ferric citrate, sodium citrate and EDTA.

[0047] The mass ratio of the complexing agent to the second precursor is preferably 1:(5-1000), for example 1:10.

[0048] In step S3, the solvent is preferably deionized water.

[0049] In step S3, the mass ratio of the second precursor to the solvent is preferably 1:(5-50), for example 1:10.

[0050] In step S3, the addition is preferably carried out under stirring conditions.

[0051] The stirring speed is preferably 100-1000 r / min, for example 300 r / min.

[0052] In step S3, the alkaline reagent is preferably added by dropping, and the dropping rate of the alkaline reagent is 1-1000 mL / min, for example 10 mL / min.

[0053] In step S3, the addition of the alkaline reagent is preferably performed under a protective atmosphere. The protective atmosphere preferably includes one or more of an inert atmosphere, a reducing atmosphere, and a carbon dioxide atmosphere, such as one or more of nitrogen, argon, helium, hydrogen, and carbon monoxide.

[0054] In step S3, the method for preparing the mixed solution may include: immersing the second precursor in a solvent, and then adding a transition metal salt to obtain the mixed solution.

[0055] In step S3, the drying can be carried out using methods conventional in the art, preferably spray drying.

[0056] In step S3, the drying rate can be 0.1-10 kg / h, for example, 1 kg / h.

[0057] In step S3, the drying temperature is preferably 50-300°C, for example 200°C.

[0058] In step S3, the drying can be carried out under a protective atmosphere, such as nitrogen.

[0059] In step S3, the Dv50 particle size of the third precursor can be 4-20 μm, for example 8 μm.

[0060] In step S3, after the addition of the alkaline reagent and before drying, an alcoholysis step is preferably included. The alcoholysis step can further enhance the degree of reaction of the transition metal salt to form a transition metal oxide. Preferably, the alcoholysis temperature is 50-100°C, for example, 90°C; and the alcoholysis time is preferably 0.5-25 h, for example, 5 h.

[0061] In this invention, in step S4, the transition metal oxide in the third precursor and / or the elemental transition metal obtained after reduction can catalyze the in-situ growth of carbon nanotubes. Simultaneously with the in-situ growth of carbon nanotubes, a carbon coating process occurs. At this time, the grown carbon nanotubes can grow by embedding themselves in the carbon layer. Once they protrude from the carbon layer, they facilitate further carbon coating, accelerating the coating speed and thickening the carbon layer. Whether the carbon nanotubes grown in situ are single-walled or multi-walled depends on the loading amount of the transition metal, the uniformity of its distribution, and the nanoscale degree of the transition metal oxide.

[0062] In step S4, the carbon nanotubes may include single-walled carbon nanotubes and / or multi-walled carbon nanotubes. Preferably, the pore size of the multi-walled carbon nanotubes is 5-50 nm; and the pore size of the single-walled carbon nanotubes is preferably 2-20 nm.

[0063] In step S4, prior to carbon deposition, a step of reducing the third precursor may also be included.

[0064] The reduction temperature is preferably 400-800℃, for example 550℃.

[0065] The reduction is preferably carried out in a reducing atmosphere; the reducing atmosphere is preferably hydrogen; and the flow rate of the reducing atmosphere is preferably 0.1-10 L·kg⁻¹. -1 ·min -1 For example, 1L·kg -1 ·min -1 Among them, "L·kg -1 min -1 "" refers to the volume of reducing atmosphere introduced per minute relative to one kilogram of the third precursor.

[0066] The reduction time is preferably 60-300 min, for example 120 min.

[0067] In step S4, the carbon deposition may use carbon sources conventionally used in the art for vapor phase deposition, preferably including one or more of alkynes, alkanes, alkenes, aromatic compounds and carbohydrates, such as acetylene.

[0068] In step S4, during the carbon deposition process, the aeration rate of the carbon source is preferably 0.2-20 L·kg⁻¹. -1 ·min -1 For example, 2L·kg -1 ·min -1 Among them, "L·kg -1 min -1 "" refers to the volume of carbon source introduced per minute relative to each kilogram of the third precursor.

[0069] In step S4, the carbon deposition time is preferably 60-300 min, for example 120 min.

[0070] In step S4, the carbon deposition temperature is preferably 400-800°C, for example 550°C.

[0071] In step S4, the specific surface area of ​​the fourth precursor is preferably 300-400 m². 2 / g, for example, 349m 2 / g.

[0072] In step S4, the Dv50 particle size of the fourth precursor can be 4-20 μm, for example 8.2 μm.

[0073] In this invention, step S5, involving in-situ polymerization and carbonization of phenolic resin on the surface of the fourth precursor, offers the following advantages: First, by utilizing the lance-anchoring effect of carbon nanotubes, the phenolic resin can be directionally induced to solidify on the surface of the fourth precursor with carbon nanotubes through a piling effect; Second, the optional addition of acid to the slurry can transform transition metal oxides and / or transition metals into transition metal salts, which can intensify the polymerization of phenolic resin on its surface, thereby increasing the strength of the coating layer; Third, during the carbonization process, iron ions can catalyze the generation of graphitized carbon, and the shrinkage effect during carbonization improves the conductivity of the outer carbon layer, while also achieving enhanced conductivity. The high tap density of the material reduces porosity and improves strength. Fourthly, based on the unstable behavior of lithium in porous carbon due to its easy diffusion, a lithium hydroxide layer is formed during the polymerization of phenolic resin on the surface of the fourth precursor. This layer can uniformly cover the area between the passivation layer and the phenolic resin layer, thereby shielding the continued leakage of lithium from the porous carbon and inhibiting the free diffusion of lithium. At the same time, during the carbonization of the outer phenolic resin, it decomposes to form a solid electrolyte layer containing lithium oxide with high ionic conductivity, forming an artificial SEI film. This film can not only improve rate performance and thermal cycling performance, but also improve the stability of the obtained silicon-carbon composite material during processing and further enhance the strength of individual particles.

[0074] In step S5, the pH of the slurry can be 1-3, or the pH of the slurry can be 12-14. The pH of the slurry is achieved by adding acid or alkali.

[0075] In step S5, the slurry may further include alkali or acid.

[0076] In some alternative embodiments, the slurry further includes an acid, such as hydrochloric acid, sulfuric acid, or nitric acid.

[0077] In some alternative embodiments, the slurry also includes alkali.

[0078] Preferably, the mass ratio of the alkali to the fourth precursor is (0.1-1):1, for example, 0.4:1.

[0079] The alkali can be a conventional alkali used in the art, preferably an alkali metal hydroxide or ammonia, such as sodium hydroxide.

[0080] In step S5, the solvent in the slurry is, for example, water.

[0081] In step S5, the mass ratio of the fourth precursor to the solvent in the slurry is 1:(5-15), for example, 1:9.

[0082] In step S5, the molar ratio of the phenolic compound to the aldehyde compound is preferably 1:(1-2), for example, 6:7.

[0083] In step S5, the mass ratio of the fourth precursor to the phenolic compound is preferably 100:(0.1-120), more preferably 100:(15-120), for example 100:17, 100:34, 100:68, 100:85, 100:102 or 100:119.

[0084] In step S5, the temperature of the polymerization reaction can be 40-100℃, for example, 80℃.

[0085] In step S5, the polymerization reaction time can be 6-600 min, for example, 300 min.

[0086] In step S5, the polymerization reaction can be carried out in a stirring device, preferably with a stirring speed of 100-1000 r / min, for example 300 r / min.

[0087] In some preferred embodiments, in step S5, the phenolic compound is phenol and the aldehyde compound is formaldehyde.

[0088] In step S5, the drying can be carried out in a manner conventional in the art, preferably spray drying or vacuum drying.

[0089] In step S5, the carbonization process can be a conventional carbonization process in the art, preferably a segmented heat treatment.

[0090] In some preferred embodiments, the carbonization process includes the following stages:

[0091] First stage: Increase the temperature to 150-250℃ at a rate of 1-10℃ / min, and hold for 0.5-5 hours;

[0092] Second stage: Increase the temperature to 600-700℃ at a rate of 0.5-20℃ / min and hold for 5-20 hours.

[0093] In some specific implementations, the carbonization process includes the following stages:

[0094] First stage: Heat to 200℃ at a heating rate of 4℃ / min and hold for 1 hour;

[0095] Second stage: Heat to 600℃ at a heating rate of 4℃ / min and hold for 12 hours.

[0096] In step S5, the carbonization can be carried out under an inert atmosphere, which preferably includes one or more of nitrogen, helium and argon.

[0097] In this invention, step S5 preferably includes an acid pickling step after the carbonization treatment. The acid pickling treatment after carbonization is beneficial for removing transition metals.

[0098] Preferably, the pickling includes a step of washing with hydrochloric acid; the mass ratio of the hydrochloric acid to the product obtained from the carbonization treatment is (1-20):1, for example, 10:1; the concentration of the hydrochloric acid can be 0.1-10 mol / L, for example, 1 mol / L.

[0099] In this invention, the porous carbon can be conventional porous carbon in the art.

[0100] In some embodiments, the porous carbon satisfies one or more of the following conditions: ① specific surface area of ​​1400-2500 m² 2 / g, ② Micropore volume ratio is 60-100%, ③ Mesopore and larger pore volume ratio is 0-40%, ④ Pore volume is 0.6-1.4cm 3 / g.

[0101] In some specific embodiments, the porous carbon satisfies one or more of the following conditions: ① specific surface area of ​​1890 m² 2 / g, ② Micropore volume accounts for 85.3%, ③ Mesopores and larger pore volumes account for 14.7%, ④ Pore volume is 1.32cm³. 3 / g.

[0102] In this invention, the porous carbon can be prepared using methods conventional in the art. The carbon source of the porous carbon may include one or more of resin, sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, hemicellulose, lignin, and pitch, preferably resin, and more preferably phenolic resin.

[0103] In some embodiments, the porous carbon is prepared using phenolic resin as a carbon source.

[0104] In some specific embodiments, the method for preparing the porous carbon includes the following steps:

[0105] (1) Spray-dry the slurry containing phenolic resin to obtain a carbon material precursor;

[0106] (2) Carbonize the carbon material precursor to obtain a porous carbon precursor;

[0107] (3) The porous carbon precursor is activated to obtain porous carbon.

[0108] In step (1), the slurry may further include a curing agent and a solvent; the curing agent is, for example, hexamethylenetetramine, and the solvent is, for example, ethanol. The mass ratio of the phenolic resin to the curing agent is preferably 100:(1-20), for example, 100:6.

[0109] In step (1), the spray drying temperature is preferably 80-200℃, for example 130℃.

[0110] In step (1), the spray drying is preferably performed until the particle size Dv50 is 4-20 μm, for example, 8 μm.

[0111] In step (2), the carbonization method can be a conventional carbonization method in the art, such as segmented heat treatment; preferably, the carbonization includes the following stages:

[0112] First stage: Increase the temperature to 150-250℃ at a rate of 1-10℃ / min, and hold for 0.5-5 hours;

[0113] Second stage: Increase the temperature to 600-700℃ at a rate of 0.5-20℃ / min, and hold for 0.5-5 hours.

[0114] In some specific implementations, the carbonization includes the following stages:

[0115] First stage: Heat to 200℃ at a heating rate of 4℃ / min and hold for 1 hour;

[0116] Second stage: Heat to 652℃ at a heating rate of 4℃ / min and hold for 1 hour.

[0117] In step (2), the carbonization can be carried out under an inert atmosphere, which preferably includes one or more of nitrogen, helium and argon.

[0118] In step (3), the activation method can be a conventional activation pore-forming method in the art, such as alkaline activation or gas activation, preferably gas activation.

[0119] Preferably, the gas activation is carbon dioxide activation or water vapor activation.

[0120] Preferably, the gas activation ventilation rate is 0.2-20 L·kg⁻¹. -1 ·min -1 For example, 2 L·kg -1 ·min -1 Among them, "L·kg -1 min -1 "" refers to the volume of gas activated per minute that is introduced per kilogram of porous carbon precursor.

[0121] The gas activation temperature is preferably 400-1000℃, for example 550℃.

[0122] The gas activation time is preferably 5-20 hours, for example, 9 hours.

[0123] This invention provides a silicon-carbon composite material, which is prepared by the silicon-carbon composite material preparation method described above.

[0124] This invention provides a silicon-carbon composite material, which may include a core-shell structure, the core-shell structure including a core and a shell covering the core, the core including pre-lithiated porous carbon and silicon particles, the silicon particles being distributed within the pores of the pre-lithiated porous carbon; along a direction away from the core, the shell sequentially includes a passivation layer, a solid electrolyte layer and a graphitized carbon layer; wherein carbon nanotubes are distributed in the passivation layer and the solid electrolyte layer, and the carbon nanotubes penetrate the solid electrolyte layer.

[0125] In this invention, the Dv50 particle size of the silicon-carbon composite material can be 8-10 μm, preferably 8-9 μm, for example 8.3 μm, 8.4 μm, 8.5 μm, 8.7 μm or 8.9 μm.

[0126] In this invention, the specific surface area of ​​the silicon-carbon composite material can be 1-2 m². 2 / g, for example, 1.1m 2 / g, 1.2m 2 / g, 1.5m 2 / g or 1.6m 2 / g.

[0127] In this invention, the carbon content of the silicon-carbon composite material can be 50%-60%, for example, 51.8%, 53.1%, 53.8%, 53.9%, 55.3%, 58.1% or 58.7%.

[0128] In this invention, the oxygen content of the silicon-carbon composite material can be 0.2%-1.6%, for example, 0.3%, 0.5%, 0.7%, 0.8%, 1.1% or 1.4%.

[0129] In this invention, the silicon content of the silicon-carbon composite material can be 30%-50%, preferably 35%-45%, for example 35.4%, 36.1%, 39.1%, 40.7%, 40.5%, 41.6%, and 43.5%.

[0130] In this invention, the lithium content of the silicon-carbon composite material can be 4%-5%, for example, 4.3%, 4.4%, 4.5%, 4.6% or 4.8%.

[0131] In this invention, the single-particle strength of the silicon-carbon composite material can be 5-25 MPa, preferably 10-20 MPa, for example 10.4 MPa, 14.3 MPa, 16.6 MPa, 16.9 MPa, 17.2 MPa, 17.5 MPa or 18.2 MPa.

[0132] In this invention, the silicon-carbon composite material that meets the above-mentioned structural, compositional and performance parameters can be prepared by the aforementioned method for preparing silicon-carbon composite materials.

[0133] The present invention also provides an electrode comprising the silicon-carbon composite material as described above.

[0134] This invention provides an application of the silicon-carbon composite material described above as a negative electrode material in lithium-ion batteries.

[0135] The present invention also provides a lithium-ion battery comprising the silicon-carbon composite material as described above.

[0136] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0137] The reagents and raw materials used in this invention are all commercially available.

[0138] The positive and progressive effects of this invention are as follows:

[0139] In the preparation method of the silicon-carbon composite material of this invention, porous carbon is first pre-lithiated and then silicon deposited. A transition metal salt is introduced, which induces in-situ growth of carbon nanotubes during subsequent carbon deposition. Based on this, a graphitized carbon layer is obtained by in-situ polymerization and coating with phenolic resin followed by carbonization. The resulting silicon-carbon composite material exhibits good electrical conductivity and mechanical strength, as well as excellent expansion suppression performance. Lithium-ion batteries prepared using this silicon-carbon composite material can achieve excellent initial efficiency, specific capacity, rate performance, and cycle performance. Attached Figure Description

[0140] Figure 1 is a schematic diagram of the structure of the silicon-carbon composite materials obtained in Examples 1-7.

[0141] Figure label:

[0142] Pre-lithiated porous carbon 1

[0143] Silicon particles 2

[0144] passivation layer 3

[0145] Solid electrolyte layer 4

[0146] Carbon nanotubes 5

[0147] Graphitized carbon layer 6 Detailed Implementation

[0148] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0149] In the following examples and comparative examples, the phenolic resin was purchased from Hubei Hengye Technology Co., Ltd., model 2135.

[0150] In the following examples and comparative examples, the preparation of porous carbon includes the following steps (the total number of steps is denoted as S0):

[0151] (1) Preparation of carbon material precursor: 1 kg of phenolic resin, 2 kg of ethanol, and 60 g of hexamethylenetetramine (HMT) were mixed using a high-speed homogenizer at a speed of 2000 r / min for 60 min. The mixture was then spray-dried at 130 °C until the particle size (Dv50) was 8 μm.

[0152] (2) Carbonization: The spray-dried powder is first cross-linked in a rotary kiln at 10 r / min, followed by carbonization. The initial heating rate is 4℃ / min, reaching 200℃ and holding for 1 hour, primarily to induce cross-linking of the phenolic resin. The subsequent heating rate is 4℃ / min, reaching 652℃ and holding for 1 hour under nitrogen atmosphere protection at a flow rate of 1 L·kg⁻¹. -1 ·min -1 .

[0153] (3) Activation: Porous carbon was obtained by activation in a CO2 atmosphere for 9 hours, wherein the furnace temperature was 550℃ and the gas flow rate was 2L·kg⁻¹. -1 ·min -1 The specific surface area of ​​the obtained porous carbon is 1890 m². 2 / g, microporous pore volume accounts for 85.3%, mesoporous pore volume accounts for 14.7%, and pore volume is 1.32cm. 3 / g.

[0154] Example 1

[0155] S1. Preparation of the first precursor:

[0156] S1-1, Pre-lithiation: 1 kg of porous carbon obtained in step S0 is mixed with phenyl lithium at a mass ratio of 1:0.42, and argon gas is introduced at 150°C at a flow rate of 2 L·kg⁻¹. -1 ·min -1 .

[0157] S1-2. Switch the atmosphere to a silane mixture (20% silane and 80% argon by mass percentage), and deposit at 500°C for 10 hours to form the first precursor. The flow rate of the silane mixture is 2 L·kg⁻¹. -1 ·min -1 .

[0158] S2. Preparation of the second precursor:

[0159] Switch the atmosphere to an acetylene mixture (20% acetylene and 80% argon by mass percentage) at a flow rate of 5 L / kg. -1 ·min -1 After continuing deposition at 500℃ for 10 hours, nitrogen gas was switched to nitrogen gas, and then the temperature was lowered to room temperature (25℃) to obtain the second precursor.

[0160] S3. Preparation of the third precursor:

[0161] S3-1, Deposition of carbon nanotube catalyst: 1 kg of the second precursor was immersed in 10 kg of deionized water. 100 g of sodium citrate complexing agent was added, followed by 0.04 mol of ferrous sulfate and ferric chloride in a 2:1 molar ratio. Then, 1 kg of 5% ammonia solution was added, and the titration was carried out at 10 mL / min. After titration, the solution was ethanolified at 90 °C for 5 h. All of the above deposition steps were carried out under stirring at a speed of 300 r / min, with nitrogen as a protective atmosphere throughout the process.

[0162] S3-2, Drying and Granulation: The product obtained in step S3-1 is spray-dried under a nitrogen atmosphere at a drying rate of 1 kg / h at 200°C to obtain the third precursor with a Dv50 particle size of 8 μm.

[0163] S4. Preparation of the fourth precursor:

[0164] S4-1, Hydrogen reduction: At a temperature of 550℃, with a gas flow rate of 1 L·kg⁻¹ -1 ·min -1 Under these conditions, ventilation was performed for 120 minutes for reduction.

[0165] S4-2. Carbon deposition for in-situ growth of carbon nanotubes: The product obtained from the reduction process above is subjected to carbon deposition (chemical vapor deposition) using acetylene, wherein the acetylene flow rate is 2 L·kg⁻¹. -1 ·min -1 The time was 120 minutes and the temperature was 550℃, resulting in the fourth precursor with a specific surface area of ​​349 m². 2 / g, Dv50 particle size is 8.2μm.

[0166] S5, Carbon coating layer:

[0167] S5-1, Phenolic Resin Polymerization: Take 1 kg of the fourth precursor, adjust the ratio of the fourth precursor to water to 1:9, add 400 g of sodium hydroxide; add 0.018 mol of phenol, and add formaldehyde at a molar ratio of 6:7 for phenol to formaldehyde. Adjust the rotation speed to 300 r / min and the temperature to 80℃ for polymerization reaction, and the polymerization time is 300 min. Spray dry the polymerized particles at 120℃ at a drying rate of 10 kg / h.

[0168] S5-2, Carbonization: The spray-dried powder is placed in a rotary kiln for segmented heat treatment.

[0169] The initial heating rate was 4℃ / min, and the temperature was raised to 200℃ and held for 1 hour to allow the phenolic resin to crosslink.

[0170] The subsequent heating rate was 4℃ / min, and the temperature was raised to 600℃ and held for 12 hours for carbonization.

[0171] The nitrogen atmosphere protection gas supply rate is 1 L·kg. -1 ·min -1 .

[0172] S5-3. Pickling: Use 1mol / L hydrochloric acid, with a volume 10 times that of the cured material, to pickle several times until there is no transition metal on the material surface, and the magnetic foreign matter impurities are below 10ppm.

[0173] Examples 2-7

[0174] Except for the parameters in Table 1, the specific parameters and conditions in Examples 2-7 are the same as in Example 1.

[0175] Figure 1 shows a schematic diagram of the silicon-carbon composite materials obtained in Examples 1-7. The silicon-carbon composite material includes a core-shell structure, comprising a core and an outer shell covering the core. The core includes pre-lithiated porous carbon 1 and silicon particles 2, with the silicon particles 2 distributed within the pores of the pre-lithiated porous carbon 1. Along the direction away from the core, the outer shell sequentially includes a passivation layer 3, a solid electrolyte layer 4, and a graphitized carbon layer 6. Carbon nanotubes 5 are distributed in the passivation layer 3 and the solid electrolyte layer 4, and the carbon nanotubes 5 penetrate the solid electrolyte layer 4.

[0176] Comparative Example 1

[0177] The difference between this comparative example and Example 1 is that steps S3-1, S5-1, and S5-2 are omitted, and in step S4-2, the carbon deposition time is changed to 600 min. All other conditions remain the same as in Example 1. The resulting silicon-carbon composite material is a pre-lithiated composite material without in-situ carbon nanotube growth and without a graphitized carbon layer.

[0178] Comparative Example 2

[0179] The difference between this comparative example and Example 1 is that step S5 is omitted, while the remaining conditions are the same as in Example 1.

[0180] The resulting silicon-carbon composite material is a composite material that has undergone pre-lithiation and in-situ growth of carbon nanotubes but does not have a graphitized carbon layer.

[0181] Comparative Example 3

[0182] The difference between this comparative example and Example 1 is that steps S1-1, S3-1, S5-1 and S5-2 are omitted, and the carbon deposition time in step S4-2 is changed to 600 min. The other conditions are the same as in Example 1.

[0183] The resulting silicon-carbon composite material is a composite material that has not undergone pre-lithiation, has not grown carbon nanotubes, and has no graphitized carbon layer.

[0184] Comparative Example 4

[0185] The difference between this comparative example and Example 1 is that step S3-1 is omitted, while the remaining conditions are the same as in Example 1.

[0186] The resulting silicon-carbon composite material is a pre-lithiated composite material with a graphitized carbon layer that does not grow carbon nanotubes.

[0187] Comparative Example 5

[0188] The difference between this comparative example and Example 1 is that steps S1-1 and S3-1 are omitted, while the remaining conditions are the same as in Example 1.

[0189] The resulting silicon-carbon composite material is a composite material that has not undergone pre-lithiation, has no carbon nanotubes grown, and has a graphitized carbon layer.

[0190] Comparative Example 6

[0191] The difference between this comparative example and Example 1 is that steps S5-1 and S5-2 are replaced with acetylene coating. Specifically, the acetylene coating method involves carbon deposition (chemical vapor deposition) using acetylene, with an acetylene flow rate of 2 L·kg⁻¹. -1 ·min -1 The time was 120 minutes and the temperature was 550°C. All other conditions remained the same as in Example 1.

[0192] The resulting silicon-carbon composite material is a composite material that has undergone pre-lithiation and carbon nanotube growth, and has a conventional carbon coating layer instead of a graphitized carbon layer.

[0193] Comparative Example 7

[0194] The difference between this comparative example and Example 1 is that step S1-1 is omitted, while the remaining conditions are the same as in Example 1.

[0195] The resulting silicon-carbon composite material is a composite material with graphitized carbon layers that has not undergone pre-lithiation, carbon nanotube growth, and has been subjected to graphitization.

[0196] Comparative Example 8

[0197] The difference between this comparative example and Example 1 is that step S5-1 is omitted, while the remaining conditions are the same as in Example 1.

[0198] The resulting silicon-carbon composite material is a composite material that has undergone pre-lithiation and growth of carbon nanotubes, but without a graphitized carbon layer.

[0199] Example 1

[0200] The porous carbon and silicon-carbon composite materials prepared in Examples 1-7 and Comparative Examples 1-8 were tested, as follows:

[0201] (1) Element content test

[0202] Lithium content: 3g of silicon-carbon composite material was dissolved in 20mL of aqua regia as a test sample, and the lithium content was tested using a Thermofisher ICAP 7400DUO.

[0203] Carbon content: The results were obtained using a Nicolet 6700 Fourier transform infrared spectrometer (carbon and oxygen content analyzer).

[0204] Oxygen content: The results were obtained using a Nicolet 6700 Fourier transform infrared spectrometer (carbon and oxygen content analyzer).

[0205] Silicon content = 1 - Carbon content - Oxygen content - Silicon content - Lithium content.

[0206] (2) Particle size Dv50 test

[0207] Add 0.02g of silicon-carbon composite material to a 50mL clean beaker, add 20mL of deionized water, and sonicate for 5min using a 120W ultrasonic cleaner to completely disperse the silicon-carbon composite material particles in the deionized water to obtain the sample dispersion.

[0208] The above sample dispersion was tested using a particle size analyzer (MasterSizer 2000) to obtain the Dv50 particle size of the silicon-carbon composite particles.

[0209] (3) Quality of the internal carbon coating layer

[0210] The mass of the internal carbon coating layer = the weight after coating - the weight before coating, i.e., the mass of the fourth precursor - the mass of the first precursor.

[0211] (4) Specific surface area test

[0212] The measurements were obtained using Bestech NT-8000.

[0213] (5) Single particle strength: The SPFT2000 single particle mechanical property testing system of Yuaneng Technology was used for testing.

[0214] (6) Powder resistivity

[0215] 5MPa Powder Resistivity: Using a PRCD3100, the test mold was placed on the table of the electronic pressure testing machine and connected to the resistivity meter. The electronic pressure testing machine was pressurized to 5MPa, held at constant pressure for 60s, and then depressurized to zero. The deformation height of the sample and the value of the resistivity meter (representing the sample resistance) were recorded. Conductivity was calculated using the following formula: σ=h / (S×R), where: σ is the powder conductivity of the silicon-carbon composite material, in S / cm; h is the deformation height of the sample, in cm; and S is the bottom area of ​​the sample, which is 3.14cm². 2 R is the sample resistance, in Ω. Resistivity = 1 / σ, in Ω·cm.

[0216] 25MPa Powder Resistivity: PRCD3100. Place the test mold on the table of the electronic pressure testing machine and connect it to the resistivity meter. Increase the pressure of the electronic pressure testing machine to 25MPa, maintain the pressure for 60s, then release the pressure to zero. Read the sample deformation height and the resistivity meter reading (sample resistance). Conductivity is calculated using the following formula: σ=h / (S×R), where: σ is the powder conductivity of the silicon-carbon composite material, in S / cm; h is the sample deformation height, in cm; S is the sample bottom area, which is 3.14cm². 2 R is the sample resistance, in Ω. Resistivity = 1 / σ, in Ω·cm.

[0217] Powder resistivity retention rate = 25MPa resistivity (Ω·cm) / 5MPa resistivity (Ω·cm).

[0218] The test results are shown in Tables 1 and 2.

[0219] Example 2

[0220] Preparation of electrodes and lithium-ion batteries

[0221] This embodiment uses the carbon-silicon composite materials provided in Examples 1-7 and Comparative Examples 1-8 as negative electrode materials to assemble lithium-ion batteries. The specific steps are as follows:

[0222] (1) Preparation of negative electrode slurry and electrode sheet:

[0223] The negative electrode formulation was designed as CMC:PAA:SBR:SP:CNTs:silicon-carbon composite material:graphite = 1:3:1:0.1:0.1:15:79.8. The negative electrode slurry preparation process was graphite → CMC → SP → CNTs. After dispersion for 3 hours using a planetary disperser at a rotation speed of 300 rpm and a revolution speed of 1000 rpm, 80% deionized water was injected, and dispersion was carried out for 1 hour at a rotation speed of 500 rpm and a revolution speed of 600 rpm. PAA was then added, and dispersion was carried out for 1 hour at a rotation speed of 500 rpm and a revolution speed of 500 rpm. 20% deionized water was then injected, and finally SBR was added and dispersed for 1 hour at a rotation speed of 300 rpm and a revolution speed of 300 rpm to obtain the negative electrode slurry (solid content 40%). The coated current collector used was an 8 μm thick copper foil, coated on one side only. The active material coating thickness on one side was 40 μm, with a compaction density of 1.7 g / cm³. 3 The coating process involves a coating speed of 40 cm / s followed by drying at 80°C for 400 seconds. The resulting negative electrode slurry forms the negative electrode material layer.

[0224] The method for testing compaction density is as follows: the electrode sheet is stamped into a unit circle, the weight is measured, the weight of the copper foil is subtracted, and the result is divided by the thickness to obtain the compaction density.

[0225] (2) Electrolyte

[0226] Electrolyte formulation: by mass percentage, ethylene carbonate (EC) 10%, propylene carbonate (PC) 15%, diethyl carbonate (DEC) 20%, propylene propylene (PP) 30%, LiPF6 15%, fluoroethylene carbonate (FEC) 6%, propylene sulfite (PS) 2.5%, lithium difluorooxalate borate (LiODFB) 1.5%.

[0227] (3) Diaphragm: The diaphragm was purchased from Enjie (model HSV7).

[0228] (4) Assembly of lithium-ion batteries: Using lithium metal as the counter electrode, with the coating surface of the above negative electrode facing the positive electrode of the button cell, the above separator and electrolyte are used to assemble the CR2032 button cell.

[0229] Electrochemical performance testing

[0230] The button cells prepared above were subjected to electrical performance tests:

[0231] (1) First cycle lithium insertion expansion (%): First, record the thickness of the non-lithium-inserted electrode and the thickness of the copper foil. Disassemble the 1C battery for the first cycle and record the electrode thickness after saturation lithium insertion after the first cycle. First cycle lithium insertion expansion (%) = [(thickness of electrode after saturation lithium insertion - thickness of copper foil) / (thickness of non-lithium-inserted electrode - thickness of copper foil) - 1] × 100.

[0232] (2) 0.8V first efficiency: First, assemble a CR2032 button battery, then use constant voltage discharge method to discharge to 0.000V at 0.1V / h, and then charge to 0.8V at 0.1V / h. Record the charge and discharge capacity, and obtain the first efficiency by discharging capacity / charging capacity.

[0233] (3) 0.8V specific capacity: CCCV cycle charge-discharge was performed with a voltage window of 0V-0.8V. During charging, the voltage was 0.2mA / h, and after reaching 0.8V, it was held at a constant voltage for 5 minutes with a cutoff current of 0.01mA. During discharging, the voltage was 0.2mA / h, and after reaching 0V, it was held at a constant voltage for 5 minutes with a cutoff current of 0.01mA. Specific capacity = discharge capacity / mass of active material, where the mass of active material = mass of silicon-carbon composite material + mass of graphite.

[0234] (4) Number of cycles and cycle retention rate

[0235] 1C battery cycle count: At 25℃, perform CCCV charge and discharge cycles at 1000mA / h until the battery capacity reaches 800mAh. The voltage window is 2.8V-4.2V, and the cutoff current is 10mA. Record the number of cycles.

[0236] 3C battery cycle count: At 25℃, perform CCCV charge and discharge cycles at 3000mA / h until the battery capacity reaches 800mAh, with a voltage window of 2.8V-4.2V and a cutoff current of 10mA. Record the number of cycles.

[0237] 3C battery cycle retention rate = 3C battery cycle count / 1C battery cycle count.

[0238] (5) Number of cycles in the hot box and hot box cycle retention rate

[0239] 1C battery hot box cycle count: At 45℃, perform CCCV charge and discharge cycles at 1000mA / h until the battery capacity reaches 800mAh, the voltage window is 2.8V-4.2V, the cutoff current is 10mA, and the cycle count is recorded.

[0240] 3C battery hot box cycle count: At 45℃, perform CCCV charge and discharge cycles at 3000mA / h until the battery capacity reaches 800mAh, the voltage window is 2.8V-4.2V, the cutoff current is 10mA, and the cycle count is recorded.

[0241] 1C battery thermal chamber cycle retention rate = 1C battery thermal chamber cycle count / 1C battery cycle count.

[0242] 3C battery thermal chamber cycle retention rate = 3C battery thermal chamber cycle count / 1C battery cycle count.

[0243] (6) Number of bubbles

[0244] Number of bubbles per square meter: After the negative electrode slurry mixing is completed and stopped for 20 minutes, open the mixing tank, calculate the cross-sectional area of ​​the mixing tube and the number of bubbles on the surface, and calculate the number of bubbles per square meter, i.e., number of bubbles per square meter = number of bubbles on the surface / cross-sectional area of ​​the mixing tube.

[0245] The test results are shown in Tables 2 and 3.

[0246] Table 1

[0247]

[0248]

[0249] Table 2

[0250]

[0251] Table 3

[0252]

[0253]

[0254] Note: In Tables 1 and 2, " / " indicates that the condition parameter is not involved in the specific experiment.

[0255] In Examples 1-7 of this invention, the obtained silicon-carbon composite material exhibits good electrical conductivity, high mechanical strength, and excellent expansion suppression performance. Specifically, the single-particle strength can reach over 10 MPa, the powder resistivity at 5 MPa can reach below 6.2 Ω·cm, the powder resistivity at 25 MPa can reach below 5.1 Ω·cm, and the powder resistivity retention rate can reach over 0.46. When this composite silicon-carbon material is used as the negative electrode material, the number of bubbles in the negative electrode slurry per unit square meter can be less than 121, and the electrode sheet exhibits excellent expansion suppression performance (the initial lithium insertion expansion can be less than 17%). Furthermore, the prepared lithium-ion battery can achieve excellent initial efficiency, specific capacity, and cycle performance. Specifically, the 1C battery cycle count can exceed 1000 cycles. Based on this, the 0.8V initial efficiency can reach over 93%, the 0.8V specific capacity can reach over 1430 mAh / g, the 3C battery cycle retention rate can reach over 0.6, the 1C battery hot box cycle retention rate can reach over 0.85, and the 3C battery hot box cycle retention rate can reach over 0.6.

[0256] Based on Example 1, the silicon-carbon composite material obtained in Comparative Example 1 has no carbon nanotubes or graphitized carbon layer, and the first-cycle lithium insertion expansion of the electrode is relatively high. Although the prepared lithium-ion battery has comparable first-cycle efficiency at 0.8V and relatively high specific capacity at 0.8V, the cycle count of the 1C battery, the cycle retention rate of the 3C battery, the cycle retention rate of the 1C battery in the hot box, and the cycle retention rate of the 3C battery in the hot box are all significantly worse.

[0257] Based on Example 1, the composite silicon-carbon materials obtained in Comparative Examples 2 and 8 lacked a graphitized carbon layer, resulting in poor first-cycle lithium insertion expansion of the electrode. Although the prepared lithium-ion batteries had a high 0.8V specific capacity, their 0.8V first-cycle efficiency was poor, and the number of 1C battery cycles, 3C battery cycle retention rate, 1C battery hot box cycle retention rate, and 3C battery hot box cycle retention rate all significantly deteriorated.

[0258] Based on Example 1, the silicon-carbon composite material obtained in Comparative Example 3 lacks pre-lithiation, carbon nanotubes, and a graphitized carbon layer. The first-cycle lithium insertion expansion of the electrode is poor, resulting in a significantly worse first-cycle efficiency at 0.8V and a lower 0.8V specific capacity. Furthermore, the number of cycles at 1C, the cycle retention rate at 3C, the hot box cycle retention rate at 1C, and the hot box cycle retention rate at 3C are all significantly worse.

[0259] Based on Example 1, the silicon-carbon composite material obtained in Comparative Example 4 does not have carbon nanotubes, and the first-cycle lithium insertion expansion of the electrode is improved. Although the prepared lithium-ion battery has a high first-cycle efficiency of 0.8V and a high specific capacity of 0.8V, the 1C battery cycle count, 3C battery cycle retention rate, 1C battery hot box cycle retention rate, and 3C battery hot box cycle retention rate of the prepared lithium-ion battery are all significantly reduced.

[0260] Based on Example 1, the silicon-carbon composite material obtained in Comparative Example 5 had no pre-lithiation and no carbon nanotubes. The first-cycle lithium insertion expansion of the electrode was increased, and the first-cycle efficiency of the prepared lithium-ion battery at 0.8V was significantly worse. The 0.8V specific capacity was lower, and the number of cycles of the 1C battery, the cycle retention rate of the 3C battery, the hot box cycle retention rate of the 1C battery, and the hot box cycle retention rate of the 3C battery were all significantly reduced.

[0261] Based on Example 1, the silicon-carbon composite material obtained in Comparative Example 6 uses a conventional carbon layer instead of a graphitized carbon layer, resulting in a higher initial lithium insertion expansion of the electrode. Although the prepared lithium-ion battery has a higher initial efficiency of 0.8V and a higher specific capacity of 0.8V, the number of cycles of the 1C battery, the cycle retention rate of the 3C battery, the hot box cycle retention rate of the 1C battery, and the hot box cycle retention rate of the 3C battery all deteriorate significantly.

[0262] Based on Example 1, the silicon-carbon composite material obtained in Comparative Example 7 did not have pre-lithiation, and the first-cycle lithium insertion expansion of the electrode was relatively high. The first-cycle efficiency of the prepared lithium-ion battery at 0.8V was significantly worse, the specific capacity at 0.8V was lower, and the number of cycles of the 1C battery, the cycle retention rate of the 3C battery, the hot box cycle retention rate of the 1C battery, and the hot box cycle retention rate of the 3C battery were all significantly worse.

[0263] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that, It includes the following steps: S1. Silicon deposition was performed on pre-lithiated porous carbon using chemical vapor deposition to obtain the first precursor. S2. A passivation layer is coated on the surface of the first precursor to obtain the second precursor; S3. An alkaline reagent is added to a mixed solution containing the second precursor, a transition metal salt, and a solvent, and the solution is dried to obtain the third precursor. S4. Carbon deposition is performed on the third precursor using chemical vapor deposition to grow carbon nanotubes in situ, thus obtaining the fourth precursor; S5. A slurry containing the fourth precursor, phenolic compounds, and aldehyde compounds is subjected to a polymerization reaction, dried, and then carbonized to obtain the silicon-carbon composite material.

2. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, In step S1, the pre-lithiation method includes mixing the porous carbon and a lithium source and heating them to obtain the desired result.

3. The method for preparing the silicon-carbon composite material as described in claim 2, characterized in that, It satisfies one or more of the following conditions a, b: a) The lithium source includes one or more of lithium phenyl, lithium chloride, lithium sulfate, lithium carbonate, lithium acetate, lithium bromide, lithium iodide, lithium nitrate, lithium phosphate, lithium sulfate, lithium bisulfite, lithium citrate, and lithium hydride; b) The heating temperature is between the melting point and decomposition temperature of the lithium source; c) The mass ratio of the porous carbon to the lithium source is 1:(0.1-0.6); d) The pre-lithiation process is carried out under the protection of an inert gas.

4. The method for preparing the silicon-carbon composite material as described in claim 3, characterized in that, The lithium source is phenyllithium.

5. The method for preparing the silicon-carbon composite material as described in claim 3, characterized in that, The mass ratio of the porous carbon to the lithium source is 1:0.

42.

6. The method for preparing the silicon-carbon composite material as described in claim 3, characterized in that, The inert gas is argon.

7. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, Step S5 satisfies one or more of the following conditions ag: a) the molar ratio of the phenolic compound to the aldehyde compound is 1:(1-2); b) the mass ratio of the fourth precursor to the phenolic compound is 100:(0.1-120); c) the polymerization temperature is 40-100℃; d) the polymerization time is 6-600 min; e) the phenolic compound is phenol, and the aldehyde compound is formaldehyde; f) the pH of the slurry is 1-3, or the pH of the slurry is 12-14; g) the slurry further includes an alkali or an acid.

8. The method for preparing the silicon-carbon composite material as described in claim 7, characterized in that, The molar ratio of the phenolic compounds to the aldehyde compounds is 6:

7.

9. The method for preparing the silicon-carbon composite material as described in claim 7, characterized in that, The mass ratio of the fourth precursor to the phenolic compound is 100:(15-120).

10. The method for preparing the silicon-carbon composite material as described in claim 7, characterized in that, The mass ratio of the fourth precursor to the phenolic compound is 100:17, 100:34, 100:68, 100:85, 100:102, or 100:

119.

11. The method for preparing the silicon-carbon composite material as described in claim 7, characterized in that, The polymerization reaction was carried out at a temperature of 80°C.

12. The method for preparing the silicon-carbon composite material as described in claim 7, characterized in that, The polymerization reaction took 300 minutes.

13. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, Steps S1 and S2 satisfy one or more of the following conditions af: a) In step S1, the silicon deposition temperature is 400-800℃; b) In step S1, the silicon deposition time is 4-20 h. c. In step S1, the silicon source for silicon deposition includes silane; d. In step S1, during the silicon deposition process, the gas flow rate of the silicon source is 0.04-0.4 L·kg⁻¹. -1 min -1 e. In step S1, the gas source for silicon deposition includes a silicon source and a carrier gas; wherein the volume ratio of the silicon source to the carrier gas is 1:(2-6). f. In step S2, the passivation layer includes a carbon layer and / or an oxide layer.

14. The method for preparing the silicon-carbon composite material as described in claim 13, characterized in that, In step S1, the silicon deposition temperature is 500°C.

15. The method for preparing the silicon-carbon composite material as described in claim 13, characterized in that, In step S1, the silicon deposition time is 10 h.

16. The method for preparing the silicon-carbon composite material as described in claim 13, characterized in that, In step S1, the silane includes one or more of methylsilane, disilane, propane, and butane.

17. The method for preparing the silicon-carbon composite material as described in claim 13, characterized in that, In step S1, the volume ratio of the silicon source to the carrier gas is 1:

4.

18. The method for preparing the silicon-carbon composite material as described in claim 13, characterized in that, In step S2, the carbon layer is obtained by carbon deposition using chemical vapor deposition.

19. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, Steps S3 and S4 satisfy one or more of the following conditions (a): a) In step S3, the transition metal salt includes divalent and / or trivalent salts of transition metals; b) In step S3, the content of the transition metal salt is 0.01-0.3 mol / kg; c) In step S3, the alkaline reagent includes weak and / or strong base reagents; d) In step S3, the mass ratio of the alkaline reagent to the solvent is (1-1000):100; e) In step S3, the mixed solution further includes a complexing agent; wherein the complexing agent includes organic acids and / or organic acid salts; f) In step S3, the alkaline reagent is added by dropping, and the dropping rate of the alkaline reagent is 1-1000 mL / min; g) In step S3, the operation of adding the alkaline reagent is carried out under protective conditions. The process is carried out under the following atmosphere: h) In step S3, after adding the alkaline reagent and before drying, an alcoholysis step is included; i) In step S3, the Dv50 particle size of the third precursor is 4-20 μm; j) In step S4, before carbon deposition, a reduction step of the third precursor is included; k) In step S4, the carbon source for carbon deposition includes one or more of alkynes, alkanes, alkenes, aromatic compounds, and carbohydrates; l) In step S4, during carbon deposition, the gas flow rate of the carbon source is 0.2-20 L·kg⁻¹. -1 ·min -1 m. In step S4, the carbon deposition time is 60-300 min; n. In step S4, the carbon deposition temperature is 400-800℃.

20. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, The transition metal salts include divalent and trivalent iron salts.

21. The method for preparing the silicon-carbon composite material as described in claim 20, characterized in that, The transition metal salts are ferrous sulfate and ferric chloride.

22. The method for preparing the silicon-carbon composite material as described in claim 20, characterized in that, The molar ratio of the divalent and trivalent iron salts is (2-4):

1.

23. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S3, the content of the transition metal salt is 0.06 mol / kg.

24. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S3, the alkaline reagent is ammonia.

25. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S3, the mass ratio of the alkaline reagent to the solvent is 1:

1.

26. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, The complexing agent includes one or more of acetic acid, citric acid, EDTA, and their salts.

27. The method for preparing the silicon-carbon composite material as described in claim 26, characterized in that, The complexing agent includes one or more of ferric acetate, sodium acetate, ferric citrate, sodium citrate, and EDTA.

28. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, The mass ratio of the complexing agent to the second precursor is 1:(5-1000).

29. The method for preparing the silicon-carbon composite material as described in claim 28, characterized in that, The mass ratio of the compound to the second precursor is 1:

10.

30. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S3, the alkaline reagent is added at a rate of 10 mL / min.

31. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S3, the alcoholization temperature is 50-100℃.

32. The method for preparing the silicon-carbon composite material as described in claim 31, characterized in that, In step S3, the alcoholization temperature is 90°C.

33. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S3, the alcoholysis time is 0.5-25 hours.

34. The method for preparing the silicon-carbon composite material as described in claim 33, characterized in that, In step S3, the alcoholysis time is 5 hours.

35. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S3, the Dv50 particle size of the third precursor is 8 μm.

36. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S4, the reduction satisfies one or more of the following conditions ac: a) the reduction temperature is 400-800℃; b) the reduction is carried out in a reducing atmosphere; c) the reduction time is 60-300min.

37. The method for preparing the silicon-carbon composite material as described in claim 36, characterized in that, In step S4, the reducing atmosphere is hydrogen; and / or, the flow rate of the reducing atmosphere is 0.1-10 L·kg⁻¹. -1 ·min -1 .

38. The method for preparing the silicon-carbon composite material as described in claim 37, characterized in that, In step S4, the ventilation rate of the reducing atmosphere is 1 L·kg⁻¹. -1 ·min -1 .

39. The method for preparing the silicon-carbon composite material as described in claim 36, characterized in that, In step S4, the restoration time is 120 minutes.

40. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S4, the carbon source for the carbon deposition is acetylene.

41. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S4, during the carbon deposition process, the aeration rate of the carbon source is 2 L·kg⁻¹. -1 ·min -1 .

42. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S4, the carbon deposition time is 120 minutes.

43. The method for preparing the silicon-carbon composite material as described in claim 19, characterized in that, In step S4, the carbon deposition temperature is 550°C.

44. A silicon-carbon composite material, characterized in that, It is prepared by the method for preparing silicon-carbon composite materials as described in any one of claims 1-43.

45. The silicon-carbon composite material as described in claim 44, characterized in that, The silicon-carbon composite material includes a core-shell structure, comprising a core and an outer shell covering the core. The core comprises pre-lithiated porous carbon and silicon particles, with the silicon particles distributed within the pores of the pre-lithiated porous carbon. Along a direction away from the core, the outer shell sequentially comprises a passivation layer, a solid electrolyte layer, and a graphitized carbon layer. Carbon nanotubes are distributed in the passivation layer and the solid electrolyte layer, and the carbon nanotubes penetrate the solid electrolyte layer.

46. ​​The silicon-carbon composite material as described in claim 45, characterized in that, It meets one or more of the following conditions: a) the Dv50 particle size of the silicon-carbon composite material is 8-10 μm; b) the specific surface area of ​​the silicon-carbon composite material is 1-2 m². 2 / g; c. The carbon content of the silicon-carbon composite material is 50%-60%; d. The oxygen content of the silicon-carbon composite material is 0.2%-1.6%; e. The silicon content of the silicon-carbon composite material is 30%-50%; f. The lithium content of the silicon-carbon composite material is 4%-5%; g. The single particle strength of the silicon-carbon composite material is 5-25 MPa.

47. The silicon-carbon composite material as described in claim 46, characterized in that, The Dv50 particle size of the silicon-carbon composite material is 8-9 μm.

48. The silicon-carbon composite material as described in claim 46, characterized in that, The Dv50 particle size of the silicon-carbon composite material is 8.3 μm, 8.4 μm, 8.5 μm, 8.7 μm or 8.9 μm.

49. The silicon-carbon composite material as described in claim 46, characterized in that, The specific surface area of ​​the silicon-carbon composite material is 1.1 m². 2 / g, 1.2 m 2 / g, 1.5 m 2 / g or 1.6 m 2 / g.

50. The silicon-carbon composite material as described in claim 46, characterized in that, The carbon content of the silicon-carbon composite material is 51.8%, 53.1%, 53.8%, 53.9%, 55.3%, 58.1%, or 58.7%.

51. The silicon-carbon composite material as described in claim 46, characterized in that, The oxygen content of the silicon-carbon composite material is 0.3%, 0.5%, 0.7%, 0.8%, 1.1%, or 1.4%.

52. The silicon-carbon composite material as described in claim 46, characterized in that, The silicon content of the silicon-carbon composite material is 35%-45%.

53. The silicon-carbon composite material as described in claim 46, characterized in that, The silicon content of the silicon-carbon composite material is 35.4%, 36.1%, 39.1%, 40.7%, 40.5%, 41.6%, or 43.5%.

54. The silicon-carbon composite material as described in claim 46, characterized in that, The silicon content of the silicon-carbon composite material is 4.3%, 4.4%, 4.5%, 4.6%, or 4.8%.

55. The silicon-carbon composite material as described in claim 46, characterized in that, The silicon content of the silicon-carbon composite material is such that the strength of a single particle of the silicon-carbon composite material is 10-20 MPa.

56. The silicon-carbon composite material as described in claim 46, characterized in that, The silicon content of the silicon-carbon composite material is such that the single-particle strength of the silicon-carbon composite material is 10.4 MPa, 14.3 MPa, 16.6 MPa, 16.9 MPa, 17.2 MPa, 17.5 MPa or 18.2 MPa.

57. The application of a silicon-carbon composite material as a negative electrode material in a lithium-ion battery as described in any one of claims 44-56.

58. A lithium-ion battery, characterized in that, It includes silicon-carbon composite materials as described in any one of claims 44-56.

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