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

Abstract

The invention relates to a silicon-carbon composite material capable of improving the cycling stability of a battery, a preparation method of the silicon-carbon composite material, a negative pole piece and a lithium ion battery. The carbon-silicon composite particle comprises a silicon-carbon inner core and a carbon coating layer, nano-silicon is attached in holes and / or on the surface of a porous carbon matrix to form the silicon-carbon inner core, and the carbon coating layer is coated on at least part of the surface of the inner core; the porous carbon matrix and the carbon coating layer are both doped with halogen. According to the silicon-carbon composite material, the electron conductivity of the silicon-carbon composite material is improved by doping the halogen in the porous carbon matrix inside the silicon-carbon composite material and the carbon coating layer outside the silicon-carbon composite material; and meanwhile, the porous carbon matrix, the inner core composed of the nano silicon and the carbon coating layer are mutually matched and have synergistic interaction, so that the volume expansibility and defects of the silicon-carbon composite material are reduced, and the cycle stability is improved.

Description

Technical Field

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

[0002] Silicon-carbon materials are novel materials formed through a composite process of nano-silicon and porous carbon. They combine the high capacity of silicon with the electrical conductivity and structural stability of carbon, offering unique advantages in the battery field. Silicon's theoretical specific capacity is as high as 4200 mAh / g, over 10 times that of traditional graphite, significantly increasing battery energy density. Therefore, silicon-carbon materials are suitable for use as high-energy-density anode materials in high-energy-density batteries. However, current silicon-carbon materials used in batteries suffer from poor cycling stability. Summary of the Invention

[0003] Based on this, it is necessary to provide a silicon-carbon composite material and its preparation method, a negative electrode sheet and a lithium-ion battery that can improve the cycle stability of the battery.

[0004] In one aspect of the present application, a silicon-carbon composite material is provided, comprising a porous carbon matrix and carbon-silicon composite particles, wherein the carbon-silicon composite particles comprise a silicon-carbon core and a carbon coating layer, wherein the nano-silicon is attached to the pores and / or surface of the porous carbon matrix to form a silicon-carbon core, and the carbon coating layer is coated on at least a portion of the surface of the core; and both the porous carbon matrix and the carbon coating layer are doped with halogen.

[0005] The above-mentioned silicon-carbon composite material is prepared by doping halogens in the porous carbon matrix inside the silicon-carbon composite material and in the carbon coating layer outside the silicon-carbon composite material. The halogens in the porous carbon matrix optimize the ion migration path, reduce the interface defects of the porous carbon matrix, and thus improve the ionic conductivity of the silicon-carbon composite material; the halogens in the carbon coating layer form polar covalent bonds with silicon and carbon, and inhibit the expansion of silicon through the rigid constraint of chemical bonds, thereby reducing the expansibility of the silicon-carbon composite material; at the same time, the porous carbon matrix has a high pore volume, which leaves room for the expansion of silicon, further reducing the expansibility of the silicon-carbon composite material; the carbon-silicon composite particles are attached to the porous carbon matrix, and the carbon coating layer is coated on at least part of the surface of the silicon-carbon core, so that silicon and carbon are fully in contact, the interface performance is improved, and the cycle stability performance is enhanced; the porous carbon matrix, the silicon-carbon core and the carbon coating layer cooperate with each other and synergistically enhance the effect, reduce the powder resistivity, expansibility and defects of the silicon-carbon composite material, and improve the ionic conductivity and cycle stability of the silicon-carbon composite material.

[0006] In some embodiments, the silicon-carbon composite material satisfies at least one of the following conditions:

[0007] (1) The halogen includes at least one of a fluorine atom and a chlorine atom;

[0008] (2) The mass content of halogen in the porous carbon matrix accounts for 0.5% to 2% of the silicon-carbon composite material;

[0009] (3) The mass content of halogen in the carbon coating layer to the silicon-carbon composite material is 0.5% to 2%;

[0010] (4) The porous carbon matrix has a network structure, and the average pore size of the porous carbon matrix is ​​1 μm to 10 μm;

[0011] (5) The particle size of the carbon-silicon composite particles is 3µm to 12µm;

[0012] (6) The thickness of the carbon coating layer is 10 nm to 100 nm;

[0013] (7) The silicon-carbon core comprises porous nano-silicon;

[0014] (8) The mass ratio of the porous carbon matrix, the silicon-carbon core, and the carbon coating layer is 50-59:40-45:1-5.

[0015] In some embodiments, the silicon-carbon composite material satisfies at least one of the following conditions:

[0016] (1) The particle size of the silicon-carbon composite material is 5µm to 15µm;

[0017] (2) The powder compaction density of the silicon-carbon composite material is 0.93 g / cm 3 ~1.2 g / cm 3 ;

[0018] (3) The specific surface area of ​​the silicon-carbon composite material is 3.0 m 2 / g ~4.0m 2 / g;

[0019] (4) The powder resistivity of the silicon-carbon composite material is 0.8Ω•cm~1.2Ω•cm;

[0020] (5) The gas production of the silicon-carbon composite material is 0.02 mL / mg to 0.06 mL / mg.

[0021] The second aspect of the present application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0022] The carbon source and the halide are mixed in a solvent for solidification, and then activated with halogen atom gas to obtain a porous carbon matrix;

[0023] The porous carbon matrix is ​​subjected to chemical vapor deposition in a mixed reaction gas of silane gas and organic halogenated carbon source gas to prepare a silicon-carbon composite material.

[0024] In some embodiments, the method for preparing the silicon-carbon composite material satisfies at least one of the following conditions:

[0025] (1) The steps of mixing a carbon source and a halide in a solvent for solidification include:

[0026] subjecting a carbon source, a halide, and an oxidant to oxidative crosslinking treatment in a solvent to obtain a halogen-doped carbon gel; and then curing the halogen-doped carbon gel;

[0027] (2) The carbon source includes at least one of dopamine, pyridine, thiophene and isocyanate;

[0028] (3) The halogenated compound includes at least one of fluoroethylene carbonate, hexafluoroisopropanol, hexafluoroisopropyl ether, hexafluoroacetylacetonate, hexafluoroacetylacetonate, hexachloroacetone, hexachlorodisilane, hexachlorocyclohexane and hexachlorobenzene.

[0029] In some embodiments, when performing the oxidative crosslinking treatment, a carbon source, a halide solution, and an oxidant solution are mixed in a mass ratio of 100:100-500:1-5, the mass content of the halide in the halide solution is 0.5%-2%, and the mass concentration of the oxidant in the oxidant solution is 10%-30%;

[0030] Optionally, the oxidant solution includes at least one of hydrogen peroxide, ammonium persulfate solution, ferric chloride solution and sodium hypochlorite solution.

[0031] In some embodiments, the activation treatment satisfies at least one of the following conditions:

[0032] (1) The halogen atom gas includes at least one of chlorine and fluorine;

[0033] (2) The flow rate of the halogen atom gas is 10 SCCM to 100 SCCM;

[0034] (3) first heating the solidified halogen-doped carbon gel to 800°C~1200°C and then introducing the halogen atom gas to react for 30min~300min, then heating the solidified halogen-doped carbon gel to 900°C~1100°C and activating it for 1h~6h;

[0035] Optionally, the curing temperature is 400° C. to 600° C., and the curing time is 1 to 6 hours.

[0036] In some embodiments, the chemical vapor deposition satisfies at least one of the following conditions:

[0037] (1) The silane gas includes at least one of monosilane, dichlorosilane, trichlorosilane and silicon tetrachloride;

[0038] (2) The organic halogenated carbon source gas includes a halogenated alkane gas, and optionally includes at least one of monofluoromethane gas, difluoromethane gas, trifluoromethane gas, tetrafluoromethane gas, monochloromethane gas, dichloromethane gas, trichloromethane gas, and tetrachloromethane gas;

[0039] (3) The temperature of the chemical vapor deposition is 500°C to 700°C;

[0040] (4) The pressure of the chemical vapor deposition is 0.05 MPa to 0.15 MPa;

[0041] (5) The flow rate of the organic halogenated carbon source gas is 0.5 g / min to 2 g / min;

[0042] (6) The flow rate of the silane gas is 0.5 g / min to 2 g / min;

[0043] (7) The volume ratio of the silane gas to the organic halogenated carbon source gas is 0.5 to 2:1;

[0044] (8) The chemical vapor deposition time is 10 min to 100 min.

[0045] The third aspect of the present application provides a negative electrode plate, comprising the silicon-carbon composite material described in the first aspect, or the silicon-carbon composite material prepared by the preparation method described in the second aspect.

[0046] The fourth aspect of the present application provides a lithium-ion battery comprising the negative electrode sheet described in the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a SEM (scanning electron microscope) image of the silicon-carbon composite material prepared in Example 1. DETAILED DESCRIPTION

[0048] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0050] When silicon-carbon materials are used in battery negative electrodes, they have high energy density and good compatibility with battery systems. When used in lithium batteries, the low reaction potential with lithium can increase the voltage platform and can adapt to multiple needs. However, when silicon-carbon materials are used in batteries, they expand too much and have poor cycle stability. After long-term cycling, the internal resistance of the battery increases and the capacity decays rapidly. Some researchers have tried to dope metal ions into silicon-carbon materials or wrap solid electrolyte films on the surface of silicon-carbon materials to improve the ionic conductivity of silicon-carbon materials, thereby improving the cycle stability of the battery, but the improvement effect is not ideal. The inventors of this application have taken a different approach and tried to start from the expansion properties of silicon-carbon materials, and improve the cycle stability by focusing on solving the expansion problem of silicon-carbon materials.

[0051] Based on this, one embodiment of the present application provides a silicon-carbon composite material, including a porous carbon matrix and carbon-silicon composite particles, the carbon-silicon composite particles including a silicon-carbon core and a carbon coating layer, the nano-silicon attached to the pores and / or surface of the porous carbon matrix to form the core, the carbon coating layer coating at least part of the surface of the core; the porous carbon matrix and the carbon coating layer are both doped with halogen.

[0052] The above-mentioned silicon-carbon composite material is prepared by doping halogens in the porous carbon matrix inside the silicon-carbon composite material and in the carbon coating layer outside the silicon-carbon composite material. The halogens in the porous carbon matrix optimize the ion migration path, reduce the interface defects of the porous carbon matrix, and thus improve the ionic conductivity of the silicon-carbon composite material; the halogens in the carbon coating layer form polar covalent bonds with silicon and carbon, and inhibit the expansion of silicon through the rigid constraint of chemical bonds, thereby reducing the expansibility of the silicon-carbon composite material; at the same time, the porous carbon matrix has a high pore volume, which leaves room for the expansion of silicon, further reducing the expansibility of the silicon-carbon composite material; the carbon-silicon composite particles are attached to the porous carbon matrix, and the carbon coating layer is coated on at least part of the surface of the silicon-carbon core, so that silicon and carbon are fully in contact, the interface performance is improved, and the cycle stability performance is enhanced; the porous carbon matrix, the silicon-carbon core and the carbon coating layer cooperate with each other and synergistically enhance the effect, reduce the powder resistivity, expansibility and defects of the silicon-carbon composite material, and improve the ionic conductivity and cycle stability of the silicon-carbon composite material.

[0053] In some embodiments, the halogen includes at least one of a fluorine atom and a chlorine atom.

[0054] In some embodiments, the halogen content in the porous carbon matrix is ​​0.5% to 2% by weight of the silicon-carbon composite material. At this weight content, the ionic conductivity of the silicon-carbon composite material can be further improved.

[0055] In some embodiments, the mass content of the halogen in the carbon coating layer is 0.5% to 2% of the silicon-carbon composite material, which can further improve the ionic conductivity of the silicon-carbon composite material.

[0056] In some embodiments, the porous carbon matrix has a network structure, and the average pore size of the porous carbon matrix is ​​1-10µm. At this pore size, the porous carbon matrix has a stable structure and a high pore volume, forming a robust three-dimensional network structure, further improving the cyclic stability of the silicon-carbon composite material.

[0057] Furthermore, the average pore size of the porous carbon matrix is ​​preferably 4µm to 8µm.

[0058] In some embodiments, the carbon-silicon composite particles have a particle size of 3µm to 12µm.

[0059] In some embodiments, in the silicon-carbon composite material, the mass ratio of the porous carbon matrix, the silicon-carbon core, and the carbon coating layer is 50-59:40-45:1-5.

[0060] Furthermore, in the silicon-carbon composite material, the mass content of the silicon-carbon core is 40% to 45%.

[0061] Furthermore, in the silicon-carbon composite material, the mass content of the carbon coating layer is 1% to 5%.

[0062] Furthermore, in the silicon-carbon composite material, the mass content of the porous carbon matrix is ​​50%~59%, and the mass content of the porous carbon matrix is ​​50%~59%.

[0063] In some embodiments, in the silicon-carbon composite material, the mass content of the silicon-carbon core is 40% to 45%, and the mass content of the carbon coating layer is 1% to 5%.

[0064] In some embodiments, the silicon carbon core comprises porous nano-silicon.

[0065] In some embodiments, the silicon-carbon core comprises porous nano-silicon doped with halogen. Using halogen-doped porous nano-silicon as the core material can further reduce the powder resistivity of the silicon-carbon composite material and improve the electronic conductivity of the silicon-carbon composite material.

[0066] In some embodiments, the thickness of the carbon coating layer is 10 nm to 100 nm. Within this thickness range, the carbon coating layer can significantly restrain the rigidity of the silicon-carbon core, further reducing the expansion of the silicon-carbon composite material.

[0067] In some embodiments, the particle size of the silicon-carbon composite material is 5 μm to 15 μm, preferably 5 μm to 10 μm.

[0068] In some embodiments, the powder compaction density of the silicon-carbon composite material is 0.93 g / cm 3 ~1.2 g / cm 3 .

[0069] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 3.0 m 2 / g ~4.0m 2 / g.

[0070] In some embodiments, the powder resistivity of the silicon-carbon composite material is 0.8 Ω•cm to 1.2 Ω•cm.

[0071] In some embodiments, the gas production of the silicon-carbon composite material is 0.02 ml / mg to 0.06 ml / mg.

[0072] The second aspect of the present application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0073] The carbon source and the halide are mixed in a solvent for solidification, and then activated with halogen atom gas to obtain a porous carbon matrix;

[0074] The porous carbon matrix is ​​subjected to chemical vapor deposition in a mixed reaction gas of silane gas and organic halogenated carbon source gas to prepare a silicon-carbon composite material.

[0075] In the above preparation method, the carbon source and the halide are mixed in a solvent for solidification, and then halogen atom gas is used for activation treatment to obtain a porous carbon matrix with high pore volume, thereby reducing the expansion of the silicon-carbon composite material; the activation treatment with halogen atom gas can increase the pore volume and further reduce the expansion of the silicon-carbon composite material; at the same time, halogens are introduced into the porous carbon matrix by halides and halogen atom gases, the ion migration path is optimized, the interface defects of the porous carbon matrix are reduced, and the ionic conductivity of the silicon-carbon composite material is improved; silane gas and organic halogenated carbon source gas are simultaneously introduced into the porous carbon matrix for chemical vapor deposition, which not only allows silicon and carbon to fully contact, improves the silicon-carbon contact interface, and enhances the storage performance of the silicon-carbon composite material, but also forms a halogen-doped carbon coating on the silicon surface. The halogen in the carbon coating forms polar covalent bonds with silicon and carbon, and suppresses the expansion of silicon through the rigid constraint of the chemical bond, thereby reducing the expansion of the silicon-carbon composite material; the above preparation method reduces the expansion and powder resistivity of the silicon-carbon composite material, and improves the electronic conductivity and cycle stability of the silicon-carbon composite material.

[0076] It can be understood that during chemical vapor deposition, the reaction gas is a mixture of silane gas and organic halogenated carbon source gas, which is conducive to the formation of carbon-silicon composite particles in which a carbon coating layer is coated on at least part of the surface of the silicon-carbon core; if the silane gas and the organic halogenated carbon source gas are deposited separately, carbon-silicon composite particles cannot be formed.

[0077] Furthermore, silane gas and organic halogenated carbon source gas are introduced simultaneously, which can achieve uniform halogen doping.

[0078] Furthermore, the halide is an organic halide, which has a lower boiling point and is beneficial for reducing residue after carbonization.

[0079] In some embodiments, the step of mixing the carbon source and the halide in a solvent for solidification comprises:

[0080] A carbon source, a halide, and an oxidant are oxidatively crosslinked in a solvent to obtain a halogen-doped carbon gel; the halogen-doped carbon gel is then solidified. The carbon source, halide, and oxidant are oxidatively crosslinked in a solvent. Oxidative crosslinking promotes the formation of a three-dimensional network structure and a high-pore volume structure, thereby further reducing the expansion of the silicon-carbon composite material.

[0081] Understandably, the principle of oxidative cross-linking is that the oxygen free radical -O- in the oxidant undergoes a cross-linking reaction with -C- in the carbon source to form a -COC- structure, thereby achieving pore formation.

[0082] In some embodiments, the carbon source includes at least one of dopamine, pyridine, thiophene, and isocyanate.

[0083] In some embodiments, the halogenated compound comprises at least one of fluoroethylene carbonate, hexafluoroisopropanol, hexafluoroisopropyl ether, hexafluoroacetoacetone, hexafluoroacetoacetone, hexachloroacetone, hexachlorodisilane, hexachlorocyclohexane, and hexachlorobenzene. These organic halides have low boiling points and leave no residue after carbonization.

[0084] In some embodiments, during the oxidative crosslinking treatment, the carbon source, the halide solution, and the oxidant solution are mixed in a mass ratio of 100:100-500:1-5, the mass content of the halide in the halide solution is 0.5%-2%, and the mass concentration of the oxidant in the oxidant solution is 10%-30%.

[0085] Furthermore, the oxidant solution includes at least one of hydrogen peroxide, ammonium persulfate solution, ferric chloride solution and sodium hypochlorite solution.

[0086] As an example, the mass concentration of the oxidant solution can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, and 30%, or can be within a range consisting of any two of the above values. The mass concentration of the oxidant is preferably 5% to 15%.

[0087] As an example, the mass content of the halide in the halide solution can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% and 2.0%, or can be within a range consisting of any two of the above points as end values. The mass content of the halide in the halide solution is preferably 0.5% to 1.5%.

[0088] Furthermore, in the oxidative crosslinking treatment, the mass ratio of the carbon source, the halide solution, and the oxidant solution is preferably 100:300-500:3-5.

[0089] In some embodiments, the temperature of the oxidative crosslinking treatment is 50°C to 100°C.

[0090] In some embodiments, the oxidative crosslinking treatment is performed for 1 h to 6 h.

[0091] In some embodiments, during the activation process, the halogen atom gas includes at least one of chlorine gas and fluorine gas.

[0092] In some embodiments, during the activation process, the flow rate of the halogen atom gas is 10 SCCM to 100 SCCM.

[0093] In some embodiments, during the activation treatment, the cured halogen-doped carbon gel is first heated to 800°C~1200°C and then a halogen atom gas is introduced to react for 30min~300min, and then the cured halogen-doped carbon gel is heated to 900°C~1100°C and activated for 1h~6h.

[0094] In some embodiments, the curing temperature is 400° C. to 600° C., and the curing time is 1 to 6 hours.

[0095] In some embodiments, during chemical vapor deposition, the silane gas includes at least one of dichlorosilane, trichlorosilane, and silicon tetrachloride.

[0096] In some embodiments, during chemical vapor deposition, the organic halocarbon source gas comprises a haloalkane gas.

[0097] In some embodiments, in chemical vapor deposition, the organic halogenated carbon source gas includes at least one of monofluoromethane gas, difluoromethane gas, trifluoromethane gas, tetrafluoromethane gas, monochloromethane gas, dichloromethane gas, trichloromethane gas, and tetrachloromethane gas.

[0098] In some embodiments, during chemical vapor deposition, the chemical vapor deposition temperature is 500° C. to 700° C.

[0099] In some embodiments, during chemical vapor deposition, the pressure of chemical vapor deposition is 0.05 MPa to 0.15 MPa. Depositing nano-silicon and carbon at this pressure can improve the completeness of carbon coating on silicon and reduce gas production.

[0100] As an example, the pressure of chemical vapor deposition can be 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.10 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, and 0.15 MPa, or can be within a range consisting of any two of the above values. The pressure of chemical vapor deposition is preferably 0.1 MPa to 0.15 MPa.

[0101] In some embodiments, during chemical vapor deposition, the flow rate of the organic halogenated carbon source gas is 0.5 g / min to 2 g / min.

[0102] In some embodiments, during chemical vapor deposition, the flow rate of the silane gas is 0.5 g / min to 2 g / min.

[0103] In some embodiments, the volume ratio of silane gas to organic halogenated carbon source gas during chemical vapor deposition is 0.5 to 2:1. This allows a halogen-doped amorphous carbon coating to be formed on the silicon surface, thereby increasing the electron transfer rate of the silicon-carbon composite material, reducing its irreversible capacity, lowering polarization, increasing initial efficiency, and reducing DCR (direct current resistance).

[0104] As an example, in chemical vapor deposition, the volume ratio of silane gas to organic halogenated carbon source gas is 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, and 2.0:1, or it can be within a range consisting of any two of the above points as end values. The volume ratio of silane gas to organic halogenated carbon source gas is preferably 1 to 2:1. At this ratio, when the silicon-carbon composite material is used as a battery negative electrode, the cycle stability is better and the impedance and DC resistance are lower.

[0105] In some embodiments, in the chemical vapor deposition, the chemical vapor deposition time is 10 min to 100 min.

[0106] As an example, the time for chemical vapor deposition is 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min and 100 min, or it can be within the range consisting of any two of the above point values ​​as end values. The time for chemical vapor deposition is preferably 10 min to 50 min. The halogen atom-doped amorphous carbon coating layer obtained within this time range has a higher electron transfer rate, better conductivity, and is more lower than the impedance of the silicon-carbon composite material.

[0107] The third aspect of the present application provides a negative electrode plate, comprising the silicon-carbon composite material of the first aspect, or the silicon-carbon composite material prepared by the preparation method of the second aspect.

[0108] In some embodiments, the negative electrode sheet includes a negative electrode active layer, which includes a silicon-carbon composite material and optionally includes a binder and a conductive agent.

[0109] Furthermore, the adhesive includes LA136D adhesive.

[0110] Furthermore, the conductive agent includes carbon black conductive agent Super P.

[0111] In some embodiments, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode active layer is disposed on one or both surfaces of the negative electrode current collector.

[0112] In some embodiments, the negative electrode sheet is prepared by adding a binder, a conductive agent and a solvent to a silicon-carbon composite material, stirring to form a negative electrode slurry, coating the negative electrode slurry on a negative electrode collector such as copper foil, and drying and rolling to obtain a negative electrode sheet.

[0113] The fourth aspect of the present application provides a lithium-ion battery comprising the negative electrode sheet of the third aspect.

[0114] In some embodiments, a lithium-ion battery includes a positive electrode sheet, the aforementioned negative electrode sheet, an electrolyte, and a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and the electrolyte is used to soak the positive electrode sheet, the separator, and the negative electrode sheet.

[0115] In some embodiments, in the electrolyte, the electrolyte is LiPF6 (lithium hexafluorophosphate), the solvent is a mixture of EC (ethylene carbonate) and DEC (diethyl carbonate), the concentration of the electrolyte is 1.3 mol / L, and the volume ratio of EC and DEC is 1:1.

[0116] In some embodiments, the separator is a polyethylene film (PE), a polypropylene film (PP) or a polyethylene propylene composite film (PEP).

[0117] In order to make the technical solutions and advantages of this application more concise and clear, this application is illustrated with the following specific examples, but this application is by no means limited to these examples. The embodiments described below are only preferred embodiments of this application and can be used to describe this application. They should not be understood as limiting the scope of this application. It should be pointed out that any modifications, equivalent replacements, and improvements made within the spirit and principles of this application should be included in the scope of protection of this application.

[0118] In order to better illustrate the present application, the present application is further described below in conjunction with the embodiments. The following are specific embodiments.

[0119] Example 1

[0120] A method for preparing a silicon-carbon composite material comprises the following steps:

[0121] S1: 100 g dopamine was dissolved in 300 g 1 wt% fluoroethylene carbonate solution, and then 3 g hydrogen peroxide (20 wt%) was added and mixed evenly. The mixture was oxidatively cross-linked at 80 °C for 3 h, and the halogen-doped carbon gel was obtained after filtration.

[0122] S2: The halogen-doped carbon gel was cured at 500°C for 2 h, then heated to 950°C and introduced with chlorine gas at a flow rate of 50 SCCM for 150 min, and then heated to 1000°C for activation for 3 h to prepare a porous carbon matrix.

[0123] S3: 100 g of the porous carbon substrate was transferred to a fluidized bed for fluidized bed chemical vapor deposition. At a temperature of 600 ° C and a pressure of 0.1 MPa, silicon dichloride and carbon trifluoride gas were introduced at a volume ratio of 1:1 at a mixed flow rate of 1 g / min for 50 minutes to prepare a silicon-carbon composite material.

[0124] The prepared silicon-carbon composite material includes a porous carbon matrix and deposited nano-silicon thereon to form a composite core and a carbon coating layer, wherein the carbon coating layer is coated on the surface of the silicon-carbon core, the porous carbon matrix is ​​doped with fluorine and chlorine, and the carbon coating layer is doped with fluorine and chlorine, wherein the mass content of fluorine and chlorine in the porous carbon matrix accounts for 1% of the silicon-carbon composite material; the mass content of fluorine and chlorine in the carbon coating layer accounts for 1% of the silicon-carbon composite material; the porous carbon matrix accounts for 50% of the mass of the silicon-carbon composite material, the nano-silicon accounts for 45% of the mass of the silicon-carbon composite material, and the carbon coating layer accounts for 5% of the mass of the silicon-carbon composite material; the average pore size of the porous carbon matrix is ​​8µm; the particle size of the carbon-silicon composite particles is 5µm, and the thickness of the carbon coating layer is 50 nm.

[0125] Example 2

[0126] A method for preparing a silicon-carbon composite material comprises the following steps:

[0127] S1: 100 g of pyridine was dissolved in 100 g of 2 wt% hexafluoroisopropanol solution, and then 1 g of 20 wt% ammonium persulfate oxidant was added and mixed evenly. The mixture was oxidatively cross-linked at 50 °C for 6 h, and the halogen-doped carbon gel was obtained after filtration.

[0128] S2: The halogen-doped carbon gel was cured at 400°C for 6 h, then heated to 800°C and introduced with fluorine gas at a flow rate of 10 SCCM for 300 min, and then heated to 900°C for activation for 6 h to prepare a porous carbon matrix.

[0129] S3: 100 g of the porous carbon substrate was transferred to a fluidized bed for fluidized bed chemical vapor deposition. At a temperature of 500 ° C and a pressure of 0.05 MPa, trichlorosilane and carbon difluoride gas (volume ratio 0.5:1) were introduced simultaneously at a flow rate of 0.5 g / min for 100 minutes to prepare a silicon-carbon composite material.

[0130] Example 3

[0131] A method for preparing a silicon-carbon composite material comprises the following steps:

[0132] S1: 100 g of thiophene was dissolved in 500 g of 0.5 wt% hexafluoroisopropyl ether solution, and then 5 g of 10 wt% ferric chloride oxidant was added for oxidative crosslinking at 100 °C for 1 h. After filtration, the halogen-doped carbon gel was obtained;

[0133] S2: The halogen-doped carbon gel was cured at 600°C for 1 hour, then heated to 1200°C and introduced with bromine gas at a flow rate of 100 SCCM for 30 minutes, and then heated to 1100°C for activation for 1 hour to prepare a porous carbon matrix;

[0134] S3: 100 g of porous carbon was transferred to a fluidized bed for fluidized bed chemical vapor deposition. At a temperature of 700 ° C and a pressure of 0.15 MPa, silicon tetrachloride and carbon monofluoride gas (volume ratio 2:1) were introduced simultaneously at a flow rate of 2 g / min for 10 minutes to prepare a silicon-carbon composite material.

[0135] Example 4

[0136] Example 4 is substantially the same as Example 1, except that in S1, the mass concentration of the fluoroethylene carbonate solution is 2%.

[0137] Example 5

[0138] Example 5 is substantially the same as Example 1, except that in S3, the volume ratio of dichlorosilane gas to carbon trifluoride gas is 0.5:1.

[0139] Example 6

[0140] Example 6 is substantially the same as Example 1, except that in S3, the time for simultaneously introducing trichlorosilane and carbon difluoride gases is 100 minutes.

[0141] Example 7

[0142] Example 7 is substantially the same as Example 1, except that in S1, an equal mass of hexachloroacetone is used instead of hexafluoroisopropanol.

[0143] Comparative Example 1

[0144] Comparative Example 1 is substantially the same as Example 1, except that in S1, fluoroethylene carbonate and hydrogen peroxide are omitted.

[0145] Comparative Example 2

[0146] Comparative Example 2 is basically the same as Example 1, except that: in S3, 100 g of the porous carbon matrix is ​​transferred to a fluidized bed, and dichlorosilane is introduced at a flow rate of 1 g / min for 50 minutes under normal pressure and a temperature of 500°C. Then the temperature is raised to 800°C, and carbon trifluoride gas is introduced at a flow rate of 1 g / min for 50 minutes to prepare a silicon-carbon composite material.

[0147] Comparative Example 3

[0148] Comparative Example 3 is substantially the same as Example 1, except that in S1, ethylene carbonate of equal mass is used instead of fluoroethylene carbonate.

[0149] The silicon-carbon composite materials prepared in the examples and comparative examples were tested for micromorphology and physical and chemical properties. The specific tests are as follows:

[0150] (1) Micromorphology

[0151] The silicon-carbon composite material prepared in Example 1 was subjected to electron microscopy (SEM test), and the test results are as follows: Figure 1 As shown. Figure 1 It can be seen from the figure that the composite material prepared in Example 1 has a granular structure with a uniform size distribution and a particle size of 5 μm to 10 μm.

[0152] (2) Physical and chemical properties

[0153] The physical and chemical properties of the silicon-carbon composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were tested, wherein the powder compaction density and specific surface area were tested according to the national standard GBT-38823-2020 "Silicon Carbon"; the powder resistivity was tested using a four-probe tester; the gas production was tested by adding mlg of powdered silicon-carbon composite material to deionized water to form a slurry with a mass concentration of 10%, soaking it at 45°C for 48 hours, and testing its gas production V1, and calculating the gas production per unit mass as V1 / m1×100%; the test results are shown in Table 1.

[0154] Table 1

[0155]

[0156] As can be seen in Table 1, the gas production per unit mass of the silicon-carbon composite materials produced in Examples 1-3 is significantly lower than that of Comparative Examples 1-2, and the powder resistivity of the silicon-carbon composite materials produced in Examples 1-3 is lower than that of Comparative Examples 1-2. This is because Examples 1-3 use negative pressure deposition of nano-silicon and carbon to improve the coating integrity of the material and reduce gas production, and the doping of the core material with halogen atoms improves the electronic conductivity of the material, thereby reducing the powder resistivity of the silicon-carbon composite material.

[0157] (3) Electrical performance test

[0158] (3.1) Button battery electrical performance test:

[0159] The silicon-carbon composite materials prepared in each example and comparative example were used as negative electrode materials for lithium-ion batteries and assembled into button cells. The specific preparation method for the negative electrode material was as follows: 15g of LA136D binder, 15g of carbon black conductive agent Super P, and 300mL of double-distilled water were added to 80g of the silicon-carbon composite material, stirred to form a slurry, and coated onto copper foil. The slurry was then dried and rolled to form a negative electrode sheet. A metallic lithium sheet served as the positive electrode. The electrolyte employed a LiPF6 / EC+DEC solution, with LiPF6 as the electrolyte and a 1:1 volume ratio of EC (ethylene carbonate) and DEC (diethyl carbonate) as the solvent. The electrolyte concentration was 1.3 mol / L. The separator employed a composite film of polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP). The button cells were assembled in an argon-filled glove box. Electrochemical performance was measured on a Wuhan Landian CT2001A battery tester over a charge and discharge voltage range of 0.005V to 1.5V at a charge and discharge rate of 0.1C. The button cells' initial discharge capacity and efficiency were measured. Cycling stability (0.2C / 0.2C, 100 cycles) was also tested, as was the expansion of the negative electrode sheet at a full charge (100% SOC). The button cells were dissected and tested for negative electrode sheet expansion. The test results are shown in Table 2 below.

[0160] Table 2

[0161]

[0162] As can be seen from Tables 1 and 2, the specific capacity, DCR (direct current resistance), expansion and cycle stability of the silicon-carbon composite materials prepared in each embodiment are better than those of the comparative examples. The reason is that the electron transfer rate of the material is improved by coating the surface of the material with halogen atom-doped amorphous carbon and the defects of the core are reduced, thereby reducing its irreversible capacity and polarization, improving the initial efficiency and reducing the DCR.

[0163] (3.2) Soft pack battery electrical performance test:

[0164] The silicon-carbon composite materials in each embodiment and each comparative example were mixed with 92% artificial graphite as the negative electrode, and the negative electrode sheets were prepared by slurry mixing and coating. 1 / 3 Co 1 / 3 Mn 1 / 3 A 2Ah soft-pack battery was prepared using LiPF6 (the solvent was EC+DEC+DMC (dimethyl carbonate), the volume ratio of EC, DEC and DMC was 1:1:1, and the electrolyte concentration was 1.1 mol / L) as the electrolyte and Celgard2400 membrane as the separator.

[0165] The HPPC rate performance test was conducted on the soft-pack battery. The rate performance of the soft-pack battery was tested over a charge and discharge voltage range of 2.5 to 4.2 V at a temperature of 25 ± 3.0°C. The battery was charged at 3C to test its resistance at different states of charge (SOC) (90%, 70%, 50%, 30%, and 10%), and discharged at 4.0C. The test results are shown in Table 3 below.

[0166] Table 3

[0167]

[0168] As shown in Table 3 above, the impedance of the soft-pack batteries made of the silicon-carbon composite materials in each embodiment is significantly lower than that of the comparative example, resulting in a shorter charging time. Because the battery charging process requires the migration of lithium ions, the silicon-carbon composite materials made in each embodiment reduce the impedance and DCR, thus shortening the charging time.

[0169] The above soft-pack battery was subjected to a cycle stability performance test: the conditions were: charge and discharge current 1C / 1C, voltage range 2.5V ~ 4.2V, cycle number 500 times, and its charging DC resistance (50% SOC, 1.0C) was tested 500 times. The test results are shown in Table 4.

[0170] Table 4

[0171]

[0172] Combining the data in Tables 1 and 2, it can be seen that the silicon-carbon composite materials produced in Examples 1-7 have low expansion and low powder resistivity, thereby reducing the lithium ions consumed by the SEI (solid electrolyte interface) during charge and discharge, thereby improving cycling performance. As shown in Table 4, the battery retention rate of Examples 1-7 exceeded 93.45% after 500 cycles, demonstrating significantly better cycling stability than Comparative Examples 1-3.

[0173] In addition, a comparison of Example 1 with Examples 4-7 shows that when the carbon source, halide solution, and oxidant are subjected to oxidative crosslinking treatment, the halide mass content in the halide solution is 0.5% to 2%, corresponding to better battery cycle stability. When depositing the carbon coating layer, the volume ratio of silane gas to organic halogenated carbon source gas is 1 to 2:1, or the deposition time is 10 min to 50 min. The halogen atom-doped amorphous carbon coating layer has a higher electron transfer rate and better conductivity, and can also reduce the impedance of the silicon-carbon composite material, thereby further improving the battery's cycle stability.

[0174] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0175] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A silicon-carbon composite material, characterized in that: The invention comprises a porous carbon matrix and carbon-silicon composite particles, wherein the carbon-silicon composite particles comprise a silicon-carbon core and a carbon coating layer, the nano-silicon is attached to the pores and / or surface of the porous carbon matrix to form the silicon-carbon core, and the carbon coating layer is coated on at least part of the surface of the core; the porous carbon matrix and the carbon coating layer are both doped with halogen.

2. The silicon-carbon composite material according to claim 1, wherein At least one of the following conditions is met: (1) The halogen includes at least one of a fluorine atom and a chlorine atom; (2) The mass content of halogen in the porous carbon matrix accounts for 0.5% to 2% of the silicon-carbon composite material; (3) The mass content of halogen in the carbon coating layer to the silicon-carbon composite material is 0.5% to 2%; (4) The porous carbon matrix has a network structure, and the average pore size of the porous carbon matrix is ​​1 μm to 10 μm; (5) The particle size of the carbon-silicon composite particles is 3µm to 12µm; (6) The thickness of the carbon coating layer is 10 nm to 100 nm; (7) The silicon-carbon core comprises porous nano-silicon; (8) The mass ratio of the porous carbon matrix, the silicon-carbon core, and the carbon coating layer is 50-59:40-45:1-5.

3. The silicon-carbon composite material according to any one of claims 1 to 2, characterized in that At least one of the following conditions is met: (1) The particle size of the silicon-carbon composite material is 5µm to 15µm; (2) The powder compaction density of the silicon-carbon composite material is 0.93 g / cm 3 ~1.2 g / cm 3 ; (3) The specific surface area of ​​the silicon-carbon composite material is 3.0 m 2 / g ~4.0m 2 / g; (4) The powder resistivity of the silicon-carbon composite material is 0.8Ω•cm~1.2Ω•cm; (5) The gas production of the silicon-carbon composite material is 0.02 mL / mg to 0.06 mL / mg.

4. A method for preparing a silicon-carbon composite material, characterized in that: The following steps are involved: The carbon source and the halide are mixed in a solvent for solidification, and then activated with halogen atom gas to obtain a porous carbon matrix; The porous carbon matrix is ​​subjected to chemical vapor deposition in a mixed reaction gas of silane gas and organic halogenated carbon source gas to prepare a silicon-carbon composite material.

5. The method for preparing the silicon-carbon composite material according to claim 4, wherein: At least one of the following conditions is met: (1) The steps of mixing a carbon source and a halide in a solvent for solidification include: subjecting a carbon source, a halide, and an oxidant to oxidative crosslinking treatment in a solvent to obtain a halogen-doped carbon gel; and then curing the halogen-doped carbon gel; (2) The carbon source includes at least one of dopamine, pyridine, thiophene and isocyanate; (3) The halogenated compound includes at least one of fluoroethylene carbonate, hexafluoroisopropanol, hexafluoroisopropyl ether, hexafluoroacetylacetonate, hexafluoroacetylacetonate, hexachloroacetone, hexachlorodisilane, hexachlorocyclohexane and hexachlorobenzene.

6. The method for preparing the silicon-carbon composite material according to claim 5, wherein: When performing the oxidative crosslinking treatment, a carbon source, a halide solution, and an oxidant solution are mixed in a mass ratio of 100:100-500:1-5, wherein the mass content of the halide in the halide solution is 0.5%-2%, and the mass concentration of the oxidant in the oxidant solution is 10%-30%; Optionally, the oxidant solution includes at least one of hydrogen peroxide, ammonium persulfate solution, ferric chloride solution and sodium hypochlorite solution.

7. The method for preparing the silicon-carbon composite material according to any one of claims 4 to 6, wherein: The activation treatment satisfies at least one of the following conditions: (1) The halogen atom gas includes at least one of chlorine and fluorine; (2) The flow rate of the halogen atom gas is 10 SCCM to 100 SCCM; (3) first heating the solidified halogen-doped carbon gel to 800°C~1200°C and then introducing the halogen atom gas to react for 30min~300min, then heating the solidified halogen-doped carbon gel to 900°C~1100°C and activating it for 1h~6h; Optionally, the curing temperature is 400° C. to 600° C., and the curing time is 1 to 6 hours.

8. The method for preparing the silicon-carbon composite material according to any one of claims 4 to 6, wherein: The chemical vapor deposition satisfies at least one of the following conditions: (1) The silane gas includes at least one of monosilane, dichlorosilane, trichlorosilane and silicon tetrachloride; (2) The organic halogenated carbon source gas includes a halogenated alkane gas, and optionally includes at least one of monofluoromethane gas, difluoromethane gas, trifluoromethane gas, tetrafluoromethane gas, monochloromethane gas, dichloromethane gas, trichloromethane gas, and tetrachloromethane gas; (3) The temperature of the chemical vapor deposition is 500°C to 700°C; (4) The pressure of the chemical vapor deposition is 0.05 MPa to 0.15 MPa; (5) The flow rate of the organic halogenated carbon source gas is 0.5 g / min to 2 g / min; (6) The flow rate of the silane gas is 0.5 g / min to 2 g / min; (7) The volume ratio of the silane gas to the organic halogenated carbon source gas is 0.5 to 2:1; (8) The chemical vapor deposition time is 10 min to 100 min.

9. A negative electrode plate, characterized in that: The silicon-carbon composite material comprises the silicon-carbon composite material according to any one of claims 1 to 3, or the silicon-carbon composite material prepared by the preparation method according to any one of claims 4 to 8.

10. A lithium ion battery, characterized in that: Including the negative electrode sheet according to claim 9.

Images