A modified silicon-carbon composite material, a preparation method and application thereof

Abstract

The application provides a modified silicon-carbon composite material and a preparation method and application thereof, wherein the modified silicon-carbon composite material comprises a core and a shell; the core comprises a material containing silicon elements; and the shell is coated on at least part of the outer surface of the core and comprises a carbon layer doped with slow-release capsule lithium powder. The modified silicon-carbon composite material provided by the application effectively improves the conductivity of the silicon-carbon material by arranging the carbon layer doped with slow-release capsule lithium powder on the surface of the material containing silicon elements, significantly improves the performance of the material under high rate conditions and the initial coulomb efficiency, and overcomes the poor conductivity of the silicon material in the related art. Meanwhile, the slow-release capsule lithium powder can slowly release active lithium in the charging and discharging process, forms a stable silicon-attracting lithium-conducting layer on the surface layer of the silicon-carbon material, and assists the synthesis of an outer SEI film, so that the cycle stability of the silicon-carbon material can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon-carbon materials and secondary batteries, in particular to a modified silicon-carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] The silicon-carbon composite material is used for lithium ion batteries, and has the following advantages: high specific capacity, the specific capacity of conventional silicon-carbon can reach 1620 mAh / g, which can significantly improve the energy density of the battery.

[0003] However, the inventors have found that the silicon-carbon composite material used in lithium ion batteries still has the following defects:

[0004] (1) Significant volume expansion (more than 300%) occurs during charging and discharging, leading to pulverization of the electrode material and separation of the active material, thereby causing a decrease in electrochemical stability;

[0005] (2) Due to the poor electrical conductivity of silicon material and other reasons, its performance under high rate conditions is limited, resulting in insufficient rate performance, and it is difficult to simultaneously consider high initial efficiency and fast charging performance;

[0006] (3) The initial coulombic efficiency and cycle performance of silicon-based negative electrode materials are generally low, which is difficult to meet the actual application requirements;

[0007] (4) Although the composite of silicon-carbon material and carbon material can alleviate the problem of volume expansion to a certain extent, there is still a problem of how to further improve the electrical conductivity and cycle stability of the material.

[0008] Among them, in order to solve the problems of poor rate performance, low initial efficiency, insufficient cycle stability and unable to consider fast charging of silicon-carbon material, the related technology one discloses a carbon nanotube graphene / silicon-carbon composite material, which includes silicon-carbon secondary particles and a graphene layer coated on the surface of the silicon-carbon secondary particles. The composite material is connected by carbon nanotubes modified by silane coupling agent, which can improve the conductivity of silicon material while utilizing the elasticity and stability of the matrix to effectively inhibit the volume change of silicon material during the process of deintercalating lithium ions, and improve the cycle stability of the material. However, the technology still has the problem of how to further improve the energy density and power density of the material. The related technology two provides a preparation method of lithium ion battery negative electrode silicon-carbon material, which includes uniformly dispersing nano-silicon powder, graphite, binder, conductive agent and dispersing agent in deionized water, and then performing steps such as spray drying, molding, pitch coating and carbonization. The method improves the surface conductivity of silicon-carbon by formula optimization, inhibits the expansion of silicon, at the same time, reduces the specific surface area of silicon-carbon, reduces the surface defects of particles, reduces the side reaction between electrolyte and silicon-carbon particle surface, and improves the cycle life of the material. However, the technology still faces the problem of how to further optimize the ratio of nano-silicon powder, graphite, binder, conductive agent and dispersing agent to improve the stability and uniformity of the silicon-carbon mixed slurry.

[0009] Therefore, there is an urgent need for a modification of silicon-carbon composite material, which at least has higher rate performance, initial efficiency and cycle stability while considering fast charging performance. SUMMARY

[0010] In order to solve the problems of poor rate performance, low initial efficiency and insufficient cycle stability of silicon-carbon material in the related technology and unable to consider fast charging, one purpose of the present application is to provide a modified silicon-carbon composite material, which effectively improves the conductivity of silicon-carbon material by setting a carbon layer doped with slow-release lithium powder on the surface of the material containing silicon element, significantly improves the performance of the material under high rate conditions and the initial coulomb efficiency, and overcomes the problem of poor conductivity of silicon material in the related technology. At the same time, the slow-release lithium powder can slowly release active lithium during charging and discharging, form a stable silicon-friendly lithium-conducting layer on the surface layer of the silicon-carbon material, and assist the synthesis of the outer SEI film, effectively alleviate the volume expansion problem of silicon material during charging and discharging, improve the electrochemical stability of the material, and further improve the cycle stability of the silicon-carbon material.

[0011] Another purpose of the present application is to provide a preparation method of a modified silicon-carbon composite material.

[0012] Another purpose of the present application is to provide another preparation method of a modified silicon-carbon composite material.

[0013] Another purpose of the present application is to provide a negative electrode material.

[0014] Another purpose of the present application is to provide a negative electrode sheet.

[0015] Yet another object of the present application is to provide a secondary battery.

[0016] To achieve the above object, a first aspect of the present application provides a modified silicon-carbon composite material, comprising:

[0017] a core, the core comprising a material containing silicon elements;

[0018] an outer shell, the outer shell being coated on at least part of the outer surface of the core, the outer shell comprising a carbon layer doped with slow-release capsule lithium powder.

[0019] The modified silicon-carbon composite material described in the present application can at least bring the following beneficial effects:

[0020] 1. By arranging a carbon layer doped with slow-release capsule lithium powder on the surface layer of the material containing silicon elements, the conductivity of the silicon-carbon material is effectively improved, the performance of the material under high rate conditions is significantly improved, and the problem of poor conductivity of silicon materials in the prior art is overcome.

[0021] 2. The slow-release capsule lithium powder can slowly release active lithium during charging and discharging, form a stable silicon-philic lithium-conducting layer on the surface layer of the silicon-carbon material, effectively alleviate the volume expansion problem of the silicon material during charging and discharging, improve the electrochemical stability of the material; at the same time, the silicon-philic lithium-conducting layer can form a stable SEI film during the cycle process, effectively block the direct contact between the electrolyte and the silicon-carbon material, reduce the occurrence of side reactions, prolong the cycle life of the material, and solve the problem of insufficient cycle performance of the silicon-based negative electrode material in the prior art.

[0022] 3. The structural design of the modified silicon-carbon material realizes the conventional compounding while comprehensively improving the electronic conductivity and ionic conductivity of the silicon-carbon material, and significantly improves the first coulomb efficiency of the silicon-carbon battery.

[0023] In some embodiments, the slow-release capsule lithium powder includes at least one of slow-release capsule lithium powder with polyethylene glycol as the wall material, slow-release capsule lithium powder with polyvinylidene fluoride as the wall material, and slow-release capsule lithium powder with polymethyl methacrylate as the wall material.

[0024] In some embodiments, the mass content of the slow-release capsule lithium powder in the modified silicon-carbon composite material is 4-8%.

[0025] In some embodiments, the mass content of the carbon layer doped with slow-release capsule lithium powder in the modified silicon-carbon composite material is 4.8-16%.

[0026] In some embodiments, the material containing silicon elements includes a material containing both silicon elements and carbon elements.

[0027] In some embodiments, the material containing silicon elements includes at least one of silicon carbide, porous carbon loaded with silicon elements, silicon oxide compound, and nanosilicon-carbon composite material.

[0028] In some embodiments, in the porous carbon loaded with silicon elements, the silicon elements are loaded in at least part of the pores of the porous carbon.

[0029] In some embodiments, the carbon layer forming raw material in the carbon layer doped with the slow-release capsule lithium powder includes graphene.

[0030] A second aspect of the present application provides a preparation method of a modified silicon-carbon composite material, including:

[0031] adding a first silicon source, a first carbon source, and a first conductive agent into a first solvent to obtain a first mixed slurry;

[0032] mixing the slow-release capsule lithium powder with the first mixed slurry and first drying to obtain a first composite material powder;

[0033] mixing the first composite material powder with graphene and dispersing in a first dispersing agent to obtain a first mixed dispersion liquid;

[0034] first calcining and first cooling the first mixed dispersion liquid to obtain the modified silicon-carbon composite material.

[0035] The preparation method of the modified silicon-carbon material described in the present application has at least the following beneficial effects in addition to the beneficial effects of the modified silicon-carbon material described in the present application:

[0036] By coating the graphene material on the outer layer, the conductivity and mechanical properties of the material are further enhanced, and the overall performance of the silicon-carbon composite material is improved.

[0037] In some embodiments, the first silicon source includes at least one of silicon carbide, elemental silicon, carbon-coated silicon oxide material, nanosilicon-carbon composite material, and silicon oxide compound.

[0038] In some embodiments, the D10 particle size of the first silicon source is 2-3 μm.

[0039] In some embodiments, the first carbon source includes at least one of carbon nanotubes and high specific surface area carbon black (BET specific surface area of 600-1500 m 2 / g of carbon black), and optionally carbon nanotubes with a length of 5-15 μm and a diameter of 20-60 nm.

[0040] In some embodiments, the first conductive agent includes at least one of conductive carbon black, carbon nanotubes, and mesoporous alumina.

[0041] In some embodiments, the first solvent comprises at least one of ethanol, water.

[0042] In some embodiments, the first dispersant comprises at least one of polyether ether ketone, and aqueous dispersant for carbon nanotubes.

[0043] In some embodiments, the mass ratio of the first silicon source, the first carbon source, and the first conductive agent is (70-80):(10-20):(5-10).

[0044] In some embodiments, in the process of obtaining the first composite material powder, the amount of the slow-release capsule lithium powder is 5-10% of the mass of the first silicon source.

[0045] In some embodiments, the mass ratio of the first composite material powder and graphene is (90-95):(5-10).

[0046] In some embodiments, the first calcination is performed at a temperature of 600-800℃ for 2-4h.

[0047] In some embodiments, the first drying comprises spray drying.

[0048] In some embodiments, the method for preparing the modified silicon-carbon composite material further comprises a step of coating the first mixed dispersion liquid on a first support before the first calcination.

[0049] A third aspect of the present application provides another method for preparing a modified silicon-carbon composite material, comprising:

[0050] adding a second silicon source, a second carbon source, a second conductive agent, and a second dispersant into a second solvent to obtain a second mixed slurry;

[0051] mixing the slow-release capsule lithium powder with graphene, and then dispersing in a third dispersant to obtain a second mixed dispersion liquid;

[0052] mixing the second mixed slurry and the second mixed dispersion liquid, and then performing a second drying to obtain a second composite material powder;

[0053] performing a second calcination and a second cooling on the second composite material powder to obtain the silicon-carbon composite material.

[0054] The method for preparing the modified silicon-carbon material described in the present application has at least the following beneficial effects in addition to the beneficial effects of the modified silicon-carbon material described in the present application:

[0055] By coating the graphene material on the outer layer, the conductivity and mechanical properties of the material are further enhanced, and the overall performance of the silicon-carbon composite material is improved.

[0056] In some embodiments, the second silicon source comprises at least one of silicon carbide, elemental silicon, carbon-coated silicon-oxygen material, nanosilicon-carbon composite.

[0057] In some embodiments, the D10 particle size of the second silicon source is 2-3 μm.

[0058] In some embodiments, the second carbon source comprises at least one of carbon nanotube, carbon black with BET specific surface area of 600-1500 m 2 / g, optionally carbon nanotube with length of 5-15 μm and diameter of 20-60 nm.

[0059] In some embodiments, the second conductive agent comprises at least one of conductive carbon black, carbon nanotube, mesoporous alumina.

[0060] In some embodiments, the second solvent comprises at least one of ethanol, water.

[0061] In some embodiments, the second dispersant comprises at least one of polyether ether ketone, polyethylene glycol, polyvinylpyrrolidone.

[0062] In some embodiments, the third dispersant comprises at least one of polyether ether ketone, aqueous dispersant for carbon nanotube.

[0063] In some embodiments, the mass ratio of the second silicon source, the second carbon source, the second conductive agent and the second dispersant is (70-80):(10-20):(5-10):(5-10).

[0064] In some embodiments, in the process of obtaining the second mixed dispersion, the mass amount of the slow-release encapsulated lithium powder is 5-10% of the mass of the second silicon source.

[0065] In some embodiments, in the process of obtaining the second mixed dispersion, the mass ratio of the slow-release encapsulated lithium powder and the graphene is (90-95):(5-10).

[0066] In some embodiments, the temperature of the second calcination is 600-800 °C, and the time of the second calcination is 2-4 h.

[0067] In some embodiments, the second drying comprises spray drying.

[0068] In some embodiments, the method for preparing the modified silicon-carbon composite further comprises a step of placing the second composite powder on a second support before the second calcination.

[0069] The fourth aspect of the present application provides a negative material, comprising the modified silicon-carbon composite material according to the first aspect of the present application, or the modified silicon-carbon composite material prepared by the preparation method of the modified silicon-carbon composite material according to the second aspect of the present application, or the modified silicon-carbon composite material prepared by the preparation method of the modified silicon-carbon composite material according to the third aspect of the present application.

[0070] The fifth aspect of the present application provides a negative electrode sheet, comprising the negative material according to the present application.

[0071] The sixth aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the negative electrode sheet is the negative electrode sheet according to the present application.

[0072] The negative material, the negative electrode sheet and the secondary battery according to the present application have at least the beneficial effects of the modified silicon-carbon negative material and the preparation method of the modified silicon-carbon negative material according to the present application.

[0073] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0074] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings, wherein:

[0075] In this regard:

[0076] Figure 1 A structural schematic diagram of the modified silicon-carbon composite material according to an exemplary embodiment of the present application.

[0077] Figure 2 A flow chart of the preparation method of the modified silicon-carbon composite material according to an exemplary embodiment of the present application.

[0078] Figure 3 A flow chart of the preparation method of the modified silicon-carbon composite material according to another exemplary embodiment of the present application.

[0079] Figure 4 A CP-SEM image of the modified silicon-carbon composite material prepared in Example 1.

[0080] Figure 5 An EDX image of the modified silicon-carbon composite material prepared in Example 1.

[0081] Figure 6 A comparison chart of the rate charging of the batteries corresponding to the materials of Example 1 and Comparative Examples 1-3.

[0082] Reference Signs:

[0083] 1 - Core; 101 - Material containing silicon element; 2 - Shell; 201 - Carbon layer; 202 - Sustained-release capsule lithium powder. DETAILED DESCRIPTION

[0084] Embodiments of the present application are described in detail below with reference to examples illustrated in the accompanying drawings. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

[0085] In the present application, the disclosure of numerical ranges includes disclosure of all values and further subdivided ranges within the entire range, including the endpoints and subranges given for these ranges.

[0086] In the present application, the raw materials, equipment, etc. involved, if not specifically stated, are raw materials, equipment that can be made by commercial means or known methods; the methods involved, if not specifically stated, are conventional methods.

[0087] The term "and / or" is used when referring to a list of two or more items, means that any of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression "A and / or B" is intended to mean A or B or a combination of A and B, i.e., only A, only B, or a combination of A and B.

[0088] In the present application, D10 particle size refers to the particle size value corresponding to the cumulative distribution of 10% in the particle size distribution curve of the powder or particulate material.

[0089] In the present application, room temperature refers to 20-30°C.

[0090] The inventors found that due to the poor electrical conductivity of silicon materials, the performance of silicon materials under high rate conditions is limited, etc. Therefore, the present application aims to develop a modified silicon-carbon composite material, which releases active lithium slowly in the charging and discharging process through sustained-release capsule lithium powder in the inner layer, and assists the synthesis of SEI film in the outer layer, which can effectively improve the cycle stability of silicon-carbon materials, and make the modified silicon-carbon composite material can simultaneously consider the initial efficiency and fast charging performance, etc.

[0091] A modified silicon-carbon composite material and a preparation method of the modified silicon-carbon composite material are described below with reference to the accompanying drawings.

[0092] <Modified silicon-carbon composite material>

[0093] Figure 1 A structure diagram of the modified silicon-carbon composite material shown in an exemplary embodiment of the present application.

[0094] As Figure 1As shown, the modified silicon-carbon composite material of the embodiments of the present application includes a core 1 and a shell 2. The core 1 includes a material 101 containing silicon elements. The shell 2 is coated on at least part of the outer surface of the core 1, and the shell 2 includes a carbon layer doped with slow-release capsule lithium powder.

[0095] It can be understood that the carbon layer doped with slow-release capsule lithium powder includes slow-release capsule lithium powder 202 and carbon layer 201, and only the slow-release capsule lithium powder 202 is doped in the carbon layer 201, as shown. Figure 1

[0096] The modified silicon-carbon composite material of the embodiments of the present application can at least bring the following beneficial effects:

[0097] 1. By arranging the carbon layer doped with slow-release capsule lithium powder on the surface layer of the material containing silicon elements, the conductivity of the silicon-carbon material is effectively improved, the performance of the material under high rate conditions is significantly improved, and the problem of poor conductivity of silicon material in the prior art is overcome.

[0098] 2. The slow-release capsule lithium powder can slowly release active lithium during charging and discharging, form a stable silicon-philic lithium-conducting layer on the surface layer of the silicon-carbon material, effectively alleviate the volume expansion problem of the silicon material during charging and discharging, improve the electrochemical stability of the material, and at the same time, the silicon-philic lithium-conducting layer can form a stable SEI film during the cycle process, effectively block the direct contact of the electrolyte with the silicon-carbon material, reduce the occurrence of side reactions, prolong the cycle life of the material, and solve the problem of insufficient cycle performance of the silicon-based negative electrode material in the prior art.

[0099] 3. The structural design of the modified silicon-carbon material realizes the conventional compounding while comprehensively improving the electronic conductivity and ionic conductivity of the silicon-carbon material, and significantly improves the first coulomb efficiency of the silicon-carbon battery.

[0100] In the embodiments of the present application, the slow-release capsule lithium powder 202 includes a capsule core and a capsule wall, the capsule core is lithium powder, and the capsule wall coats the capsule core. The wall material referred to in the present application refers to the wall material of the capsule wall.

[0101] In some embodiments, the slow-release capsule lithium powder 202 includes at least one of the slow-release capsule lithium powder with the wall material of polyethylene glycol, the slow-release capsule lithium powder with the wall material of polyvinylidene fluoride, the slow-release capsule lithium powder with the wall material of polymethyl methacrylate, etc. The selection of the slow-release capsule lithium powder with the above wall materials can improve the chemical stability and structural controllability of the composite material. The three materials of polyethylene glycol, polyvinylidene fluoride and polymethyl methacrylate can effectively isolate the contact between lithium powder and moisture, and at the same time, the internal structure can be designed as a controllable microporous structure to slowly release the lithium powder material.

[0102] ​In some embodiments, the content of the slow-release capsule lithium powder 202 in the modified silicon-carbon composite material is 4-8%, including but not limited to 4.5%, 5%, 6%, 7%, 7.5%, or 8%, etc. The content of the slow-release capsule lithium powder in the modified silicon-carbon composite material in the above range can effectively realize the slow lithiation process of the lithium powder and the silicon-carbon composite material, and realize the slow prelithiation of the silicon-carbon composite material.

[0103] In some embodiments, the content of the carbon layer doped with the slow-release capsule lithium powder in the modified silicon-carbon composite material is 4.8-16%, including but not limited to 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, etc. The content of the carbon layer doped with the slow-release capsule lithium powder in the modified silicon-carbon composite material in the above range can effectively improve the lithium supplement efficiency, and the outer coating layer of the coating material can improve the mechanical strength of the overall material and alleviate the volume expansion in the charging and discharging process.

[0104] In the embodiments of the present application, the slow-release capsule lithium powder is doped in the carbon layer instead of being doped in the core or being independently arranged between the core and the carbon layer, the purpose being to form a silicon-philic lithium guide layer in the silicon-carbon material core in the charging process, thereby effectively supplementing lithium to the silicon-carbon material.

[0105] In some embodiments, the material containing silicon elements includes at least one of silicon carbide, porous carbon loaded with silicon elements, silicon oxide compounds (for example, silicon monoxide, etc.), nano silicon carbide composite materials, etc.

[0106] In some embodiments, in the porous carbon loaded with silicon elements, the silicon elements are loaded in at least part of the pores of the porous carbon. The porous carbon loaded with silicon elements is selected as the material containing silicon elements, which can provide a pore structure for the deposition of the Si material and facilitate the later prelithiation process.

[0107] As an optional example, the material containing silicon elements includes a material containing both silicon elements and carbon elements. The selection of such a material can improve the electronic conductivity of the Si-based material.

[0108] In some embodiments, the carbon layer forming raw material in the carbon layer doped with the slow-release capsule lithium powder includes graphene. The carbon layer formed by the graphene material can further enhance the electrical conductivity and mechanical properties of the material, and improve the overall performance of the silicon-carbon composite material.

[0109] <Method for preparing a modified silicon-carbon composite material>

[0110] The preparation of the modified silicon-carbon composite material in the embodiments of the present application can be used to prepare the modified silicon-carbon composite material in the embodiments of the present application.

[0111] Figure 2 A flow chart of a method for preparing a modified silicon-carbon composite material is shown in an example embodiment of the present application.

[0112] As shown in the figure, the method for preparing the modified silicon-carbon composite material includes the following steps: Figure 2

[0113] S101, adding a first silicon source, a first carbon source and a first conductive agent into a first solvent to obtain a first mixed slurry.

[0114] In the embodiments of the present application, the first silicon source and the first carbon source are used to form a material containing silicon elements in the core, and the first conductive agent can alleviate the volume expansion of the silicon material and increase the electronic conductivity of the silicon material.

[0115] In some embodiments, the first silicon source includes at least one of silicon carbide, elemental silicon, carbon-coated silicon-oxygen material, nanosilicon-carbon composite material, silicon oxide compound (for example, silicon monoxide, etc.), and the like.

[0116] It should be noted that all the carbon-coated silicon-oxygen materials involved in the present application can be conventional carbon-coated silicon-oxygen materials.

[0117] In some embodiments, the D10 particle size of the first silicon source is 2-3 μm, such as 2.25 μm, 2.5 μm or 2.75 μm, etc. The D10 particle size of the first silicon source is 2-3 μm, which can effectively improve the pre-lithiation efficiency in the later stage.

[0118] As an optional example, the first silicon source is silicon carbide with a D10 particle size of 2-3 μm.

[0119] As another optional example, the first silicon source is nanosilicon powder.

[0120] In some embodiments, the first carbon source includes at least one of carbon nanotubes, high specific surface carbon black, etc., and can be carbon nanotubes, and further can be carbon nanotubes with a length of 5-15 μm and a diameter of 20-60 nm.

[0121] For example, the carbon nanotubes in the first carbon source include at least one of oligomeric wall CNT tubes, multi-walled carbon nanotubes, etc.

[0122] For example, the BET specific surface area of the high specific surface carbon black is 600-1500 m 2 / g, including but not limited to 700 m 2 / g, 800 m 2 / g, 900 m 2 / g, 1000 m 2 ​ / g, 1100 m 2 / g, 1200 m 2 / g, 1300 m 2 / g or 1400 m 2 / g, etc.

[0123] In some embodiments, the first conductive agent includes, but is not limited to, at least one of conductive carbon black, carbon nanotube, mesoporous alumina, etc.

[0124] In some embodiments, the first solvent includes, but is not limited to, at least one of ethanol, water, etc.

[0125] As an optional example, the first solvent is a mixed solvent of anhydrous ethanol and water mixed at a volume ratio of 4:1 to 6:1.

[0126] In some embodiments, the mass ratio of the first silicon source, the first carbon source, and the first conductive agent is (70-80):(10-20):(5-10), including but not limited to 75:15:10, 70:20:10, 75:20:5, 80:15:5, or 80:10:10, etc.

[0127] In some embodiments, the method for preparing the modified silicon-carbon composite material further includes a step of stirring the first silicon source, the first carbon source, and the first conductive agent after being added to the first solvent. Optionally, the stirring time is 4-6h, including but not limited to 4.5h, 5h, or 5.5h, etc.

[0128] S102, mixing the slow-release capsule lithium powder with the first mixed slurry obtained in step S101, and first drying to obtain a first composite material powder.

[0129] In some embodiments, in the process of obtaining the first composite material powder, the mass amount of the slow-release capsule lithium powder is 5-10% of the mass of the first silicon source, including but not limited to 6%, 7%, 8%, or 9%, etc.

[0130] In some embodiments, the way of mixing the slow-release capsule lithium powder with the first mixed slurry obtained in step S101 includes, but is not limited to, ultrasonic dispersion, stirring, etc., and is optionally ultrasonic dispersion.

[0131] When the way of mixing the slow-release capsule lithium powder with the first mixed slurry obtained in step S101 is ultrasonic dispersion, the ultrasonic dispersion time is 1-2h, for example, 1.5h, etc.

[0132] In some embodiments, the first drying includes spray drying.

[0133] For example, the first drying temperature is 90-130°C, including but not limited to 100°C, 110°C, or 120°C, etc.

[0134] For example, the first drying rate is 0.2-1.0 L / h, including but not limited to 0.4 L / h, 0.6 L / h, or 0.8 L / h, etc.

[0135] S103, dispersing the first composite material powder obtained in step S102 in the first dispersant after mixing with graphene to obtain a first mixed dispersion.

[0136] In some embodiments, the mass ratio of the first composite material powder to graphene is (90-95):(5-10), including but not limited to 91:9, 92:8, 93:7, or 94:6, etc.

[0137] In some embodiments, the first dispersant includes but is not limited to at least one of polyether ether ketone (PEEK), water-based dispersant for carbon nanotubes, etc., and is optionally polyether ether ketone. 19 H 14 F2O3), water-based dispersant for carbon nanotubes, etc., and is optionally polyether ether ketone.

[0138] For example, in the second dispersant, the water-based dispersant for carbon nanotubes includes but is not limited to at least one of polyvinylpyrrolidone (PVP), ammonium persulfate (APS), carboxymethyl cellulose (CMC), etc.

[0139] In some embodiments, the way of dispersing the first composite material powder obtained in step S102 in the first dispersant after mixing with graphene includes but is not limited to ultrasonic dispersion, stirring, etc., and is optionally ultrasonic dispersion.

[0140] When the way of dispersing the first composite material powder obtained in step S102 in the first dispersant after mixing with graphene is ultrasonic dispersion, the ultrasonic dispersion time is 2-4h, for example, 3h, etc.

[0141] S104, performing first calcination and first cooling on the first mixed dispersion obtained in step S104 to obtain the modified silicon-carbon composite material.

[0142] In some embodiments, the first calcination temperature is 600-800°C, including but not limited to 650°C, 700°C, or 750°C, etc.

[0143] In some embodiments, the first calcination time is 2-4h, including but not limited to 2.5h, 3h, or 3.5h, etc.

[0144] In some embodiments, the first calcination is performed in an inert gas atmosphere.

[0145] For example, inert gases include, but are not limited to, at least one of nitrogen, helium, argon, etc.

[0146] In some embodiments, the method for preparing the modified silicon-carbon composite material further includes the step of coating the first mixed dispersion onto a first support before the first calcination.

[0147] In the embodiments of this application, the function of the first support is to support the first mixed dispersion so that it can undergo the first calcination in calcination equipment such as a tube furnace or a muffle furnace.

[0148] For example, the first support is made of a material with stable physicochemical properties at the first calcination temperature, such as aluminum or copper. Optionally, the first support is a current collector.

[0149] like Figure 2 The method for preparing the modified silicon-carbon material shown, in addition to having the beneficial effects of the modified silicon-carbon material of the embodiments of this application, also has at least the following beneficial effects:

[0150] By coating the outer layer with graphene, the conductivity and mechanical properties of the material are further enhanced, thus improving the overall performance of the silicon-carbon composite material.

[0151] In the embodiments of this application, during the initial charge-discharge process and battery cycling of the modified silicon-carbon composite material, active lithium is encapsulated using a graphene carbon layer / ester coating layer. Due to the protection of the carbon layer, the wall of the slow-release capsule lithium powder gradually dissolves, and active lithium is gradually precipitated, thereby compensating for lithium ion loss during cycling and increasing battery life. The conductive network structure of the first conductive agent (carbon nanotubes or carbon nanotubes and conductive carbon black) is three-dimensional, and the graphene material is coated on the outer layer to form a dense carbon layer coating structure. Compared with soft-pack batteries prepared with conventional lithium iron phosphate, the modified silicon-carbon composite material has an initial coulombic efficiency ≥87%, a capacity retention rate ≥96% at 4C rate, and an expected capacity retention rate ≥80% after 2000 cycles.

[0152] Figure 3 A flowchart illustrating a method for preparing a modified silicon-carbon composite material, as shown in another exemplary embodiment of this application.

[0153] like Figure 3 As shown, the preparation method of this modified silicon-carbon composite material includes the following steps:

[0154] S201. Add the second silicon source, the second carbon source, the second conductive agent, and the second dispersant to the second solvent to obtain the second mixed slurry.

[0155] In the embodiments of the present application, the second silicon source and the second carbon source are used to form the material containing silicon element in the core, the second conductive agent functions as the CNT material with high aspect ratio to relieve the volume expansion of the silicon material and increase the electronic conductivity of the silicon material, and the second dispersing agent functions to uniformly disperse the second silicon source, the second carbon source and the second conductive agent in the second solvent.

[0156] In some embodiments, the second silicon source includes, but is not limited to, at least one of silicon carbide, elemental silicon, carbon-coated silicon-oxygen material, nanosilicon-carbon composite material, silicon-oxygen compound (e.g., silicon monoxide, etc.), and the like.

[0157] In some embodiments, the D10 particle size of the second silicon source is 2-3 μm, such as 2.25 μm, 2.5 μm, 2.75 μm, or the like. The D10 particle size of 2-3 μm of the second silicon source can effectively improve the pre-lithiation efficiency in the later stage.

[0158] As an optional example, the second silicon source is silicon carbide with a D10 particle size of 2-3 μm.

[0159] As another optional example, the second silicon source is nanosilicon powder.

[0160] In some embodiments, the second carbon source includes at least one of carbon nanotube, carbon black with a BET specific surface area of 600-1500 m 2 / g, and optionally, the carbon nanotube has a length of 5-15 μm and a diameter of 20-60 nm.

[0161] For example, the carbon nanotube in the second carbon source includes, but is not limited to, at least one of multi-walled carbon nanotube, oligo-walled carbon nanotube, and the like.

[0162] For example, the BET specific surface area of the high specific surface area carbon black includes, but is not limited to, 700 m 2 / g, 800 m 2 / g, 900 m 2 / g, 1000 m 2 / g, 1100 m 2 / g, 1200 m 2 / g, 1300 m 2 / g, or 1400 m 2 / g, or the like.

[0163] In some embodiments, the second conductive agent includes, but is not limited to, at least one of conductive carbon black, carbon nanotube, mesoporous alumina, and the like, and optionally, the carbon nanotube, and further optionally, the carbon nanotube has a length of 5-15 μm and a diameter of 20-60 nm.

[0164] In some embodiments, the second dispersant includes, but is not limited to, at least one of polyether ether ketone, polyethylene glycol, polyvinylpyrrolidone, and the like.

[0165] In some embodiments, the average molecular weight of the polyethylene glycol in the second dispersant is 4000-10000 Da.

[0166] In some embodiments, the average molecular weight of the polyvinylpyrrolidone in the second dispersant is 40000-100000 Da.

[0167] In some embodiments, the mass ratio of the second silicon source, the second carbon source, the second conductive agent, and the second dispersant is (70-80):(10-20):(5-10):(5-10), including but not limited to 70:15:7.5:7.5, 70:15:5:10, 75:10:7.5:7.5, 75:10:10:5, or 80:10:5:5, and the like.

[0168] In some embodiments, the second solvent includes, but is not limited to, at least one of ethanol, water, and the like.

[0169] As an optional example, the second solvent is a mixed solvent of anhydrous ethanol and water mixed at a volume ratio of 4:1 to 6:1.

[0170] In some embodiments, the method for preparing the modified silicon-carbon composite material further includes a step of stirring the second silicon source, the second carbon source, the second conductive agent, and the second dispersant after being added into the second solvent. Optionally, the stirring time is 4-6h, including but not limited to 4.5h, 5h, or 5.5h, and the like.

[0171] S202, mixing the slow-release capsule lithium powder with graphene, and then dispersing in a third dispersant to obtain a second mixed dispersion liquid.

[0172] In some embodiments, in the process of obtaining the second mixed dispersion liquid, the mass amount of the slow-release capsule lithium powder is 5-10% of the mass of the second silicon source, including but not limited to 6%, 7%, 8%, or 9%, and the like.

[0173] In some embodiments, in the process of obtaining the second mixed dispersion liquid, the mass ratio of the slow-release capsule lithium powder to the graphene is (90-95):(5-10), including but not limited to 91:9, 92:8, 93:7, or 94:6, and the like.

[0174] In some embodiments, the third dispersant includes, but is not limited to, at least one of polyether ether ketone, a water-based dispersant for carbon nanotubes, and the like, and is optionally polyether ether ketone.

[0175] Exemplarily, the third dispersant in which the carbon nanotubes are dispersed with the aqueous dispersant includes but is not limited to at least one of polyvinylpyrrolidone (PVP), ammonium persulfate (APS), carboxymethyl cellulose (CMC), and the like.

[0176] In some embodiments, the manner of mixing the slow-release lithium powder and graphene after mixing and dispersing in the third dispersant includes but is not limited to ultrasonic dispersion, stirring, and the like, and is optionally ultrasonic dispersion.

[0177] When the manner of mixing the slow-release lithium powder and graphene after mixing and dispersing in the third dispersant is ultrasonic dispersion, the ultrasonic dispersion time is 2-4h, such as 3h, and the like.

[0178] S203, mixing the second mixed slurry obtained in step S201 and the second mixed dispersion liquid obtained in step S202, and then performing second drying to obtain a second composite material powder.

[0179] In some embodiments, when the second mixed slurry obtained in step S201 and the second mixed dispersion liquid obtained in step S202 are mixed, the mass ratio of the second mixed slurry to the second mixed dispersion liquid is (90-95):(5-10), including but not limited to 91:9, 92:8, 93:7, or 94:6, and the like, and is optionally 94:6.

[0180] In some embodiments, the manner of mixing the second mixed slurry obtained in step S201 and the second mixed dispersion liquid obtained in step S202 includes but is not limited to ultrasonic dispersion, stirring, and the like, and is optionally ultrasonic dispersion.

[0181] When the manner of mixing the second mixed slurry obtained in step S201 and the second mixed dispersion liquid obtained in step S202 is ultrasonic dispersion, the ultrasonic dispersion time is 2-4h, such as 3h, and the like.

[0182] In some embodiments, the second drying includes at least one of spray drying, nitrogen gas calcination in a tube furnace, and the like.

[0183] Exemplarily, the second drying temperature is 90-130℃, including but not limited to 100℃, 110℃, or 120℃, and the like.

[0184] Exemplarily, the second drying rate is 0.2-1.0L / h, including but not limited to 0.4 L / h, 0.6L / h, or 0.8 L / h, and the like.

[0185] S204, performing second calcination and second cooling on the second composite material powder obtained in step S203 to obtain the silicon-carbon composite material.

[0186] In some embodiments, the second calcination is performed at a temperature of 600-800°C, including but not limited to 650°C, 700°C, or 750°C, etc.

[0187] In some embodiments, the second calcination is performed for a time period of 2-4h, including but not limited to 2.5h, 3h, or 3.5h, etc.

[0188] In some embodiments, the second calcination is performed under an inert gas atmosphere.

[0189] Exemplarily, the inert gas includes at least one of nitrogen, helium, argon, etc.

[0190] In some embodiments, the method for preparing the modified silicon-carbon composite material further comprises a step of placing the second composite material powder on a second support before the second calcination.

[0191] In the embodiments of the present application, the second support serves to support the second composite material powder so as to perform the second calcination in a calcination device such as a tube furnace or a muffle furnace.

[0192] Exemplarily, the second support is made of a material that is stable in physical and chemical properties at the temperature of the second calcination, such as aluminum or copper. Alternatively, the second support is a current collector.

[0193] As shown in the method for preparing the modified silicon-carbon material, in addition to the beneficial effects of the modified silicon-carbon material of the embodiments of the present application, the method also has at least the following beneficial effects: Figure 3 By coating the graphene material on the outer layer, the electrical conductivity and mechanical properties of the material are further enhanced, and the overall performance of the silicon-carbon composite material is improved.

[0194] In the embodiments of the present application, during the first charge and discharge process and the battery cycle process of the modified silicon-carbon composite material, due to the protection of the carbon layer, the wall of the lithium powder capsule is gradually dissolved, and the active lithium is gradually precipitated, thereby making up for the loss of lithium ions during the cycle process, increasing the battery life, the conductive network structure of the first conductive agent (carbon nanotubes or carbon nanotubes and conductive carbon black) is three-dimensional, the graphene material is coated on the outer layer to form a dense carbon layer coating structure. In the soft pack battery prepared by the modified silicon-carbon composite material and the conventional lithium iron phosphate, the first coulombic efficiency is ≥87%, the capacity retention rate at 4C rate is ≥96%, and the capacity retention rate is expected to be ≥80% after 2000 cycles.

[0195] <Anode material>

[0196] The anode material of the embodiments of the present application includes the modified silicon-carbon composite material described in the embodiments of the present application, or includes the modified silicon-carbon composite material prepared by the method for preparing the modified silicon-carbon material described in the embodiments of the present application.

[0197] Figure 2 ​The modified silicon-carbon composite material prepared by the method for preparing a modified silicon-carbon composite material, or the modified silicon-carbon composite material prepared by the method for preparing a modified silicon-carbon composite material according to the present application Figure 3 The modified silicon-carbon composite material prepared by the method for preparing a modified silicon-carbon composite material.

[0198] In some embodiments, the mass content of the modified silicon-carbon composite material in the negative electrode material is 2-20%, including but not limited to 2%, 5%, 7%, 10%, 12%, 15% or 18%, etc.

[0199] It should be noted that, in some embodiments, the negative electrode material of the embodiments of the present application can further include at least one of a negative electrode binder, a negative electrode conductive agent, a negative electrode thickening agent, etc. The specific substance selection and amount of the negative electrode binder, the negative electrode conductive agent, the negative electrode thickening agent, etc. are not limited and can be any substance selection and amount of the negative electrode binder, the negative electrode conductive agent, the negative electrode thickening agent, etc. for secondary batteries, especially lithium ion batteries, which are well known in the art.

[0200] <Negative electrode sheet>

[0201] The negative electrode sheet of the embodiments of the present application includes the negative electrode material of the embodiments of the present application.

[0202] In some embodiments, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode material is arranged on at least one surface of the negative electrode current collector.

[0203] In the embodiments of the present application, the specific material and thickness of the negative electrode current collector are not limited and can be any negative electrode current collector for secondary batteries, especially lithium ion batteries, which are well known in the art.

[0204] <Secondary battery>

[0205] The secondary battery of the embodiments of the present application includes a positive electrode sheet, a negative electrode sheet and a separator, and the negative electrode sheet is the negative electrode sheet of the embodiments of the present application.

[0206] In the embodiments of the present application, the specific selection of the positive electrode sheet, the separator, etc. is not limited and can be any positive electrode sheet, separator, etc. for secondary batteries, especially lithium ion batteries, which are well known in the art.

[0207] The negative electrode material, the negative electrode sheet and the secondary battery of the embodiments of the present application at least have the beneficial effects of the modified silicon-carbon negative electrode material and the method for preparing a modified silicon-carbon negative electrode material of the embodiments of the present application.

[0208] Some features of the present technology are further illustrated in the following non-limiting examples.

[0209] I. Examples and Comparative Examples

[0210] Example 1

[0211] The preparation method of the modified silicon-carbon composite material of the embodiment comprises the following steps:

[0212] (1) Commercial SiC, carbon nanotubes, conductive carbon black (Super P) and polyethylene glycol are mixed according to a mass ratio of 75:15:5:5, and then added into a mixed solution of anhydrous ethanol and deionized water, wherein the volume ratio of the anhydrous ethanol and the deionized water is 5:1, and stirring is performed for 5 h to obtain a mixed slurry.

[0213] The D10 particle size of the commercial SiC is 3 μm; the length of the carbon nanotubes is 10 μm, and the diameter is 40 nm; the specific surface area of the conductive carbon black is 2500 m 2 / g; the polyethylene glycol is PEG-200-800DA; and the mass of the mixed solution of the anhydrous ethanol and the deionized water is 5% of the mass of the commercial SiC.

[0214] (2) The slow-release capsule lithium powder is mixed into the graphene material, and then added into an aqueous solution containing polyether ether ketone as a dispersant, and ultrasonic dispersion is performed at an ultrasonic frequency of 80 Hz for 3 h to obtain a mixed dispersion liquid.

[0215] The slow-release capsule lithium powder is slow-release capsule lithium powder with a wall material of polyethylene glycol (PEG-200-800DA), and the mass of the slow-release capsule lithium powder added is 5% of the mass of the commercial SiC; the mass ratio of the slow-release capsule lithium powder to the graphene is 93:7; the mass of the aqueous solution containing polyether ether ketone as a dispersant added is 2% of the mass of the commercial SiC; and the solid content of the polyether ether ketone in the aqueous solution containing polyether ether ketone as a dispersant is 30%.

[0216] (3) The mixed slurry obtained in step (1) and the mixed dispersion liquid obtained in step (2) are mixed according to a mass ratio of 94:6 and ultrasonic treatment is performed at an ultrasonic frequency of 80 Hz for 2 h to obtain a composite slurry.

[0217] (4) The composite slurry obtained in step (3) is treated by a spray drying method, the drying temperature is 110°C, and the drying rate is 0.5 L / h to obtain a composite material powder.

[0218] (5) The composite material powder obtained in step (4) is placed on an aluminum foil, and then calcined under a nitrogen atmosphere, the calcination temperature is 700°C, the holding time is 3 h, and natural cooling is performed to room temperature (25°C) to obtain the modified silicon-carbon composite material of the embodiment.

[0219] The structure characteristics of the modified silicon-carbon composite material of the embodiment are that a silicon-favorable lithium-conducting layer with a thickness of 3 μm is formed on the surface of the silicon-carbon material, the content of negative ions in the lithium-conducting layer is 20%, the conductive network structure of the conductive agent is three-dimensional, and the graphene material is coated on the outer layer to form a dense carbon layer coating structure. The first coulombic efficiency of the composite material is 90.8%, the capacity retention rate at 4C rate is 96.12%, and the capacity retention rate after 1500 cycles is 80%.

[0220] Embodiment 2

[0221] The preparation method of the modified silicon-carbon composite material of the embodiment comprises the following steps:

[0222] (1) The nanometer silicon powder, carbon nanotubes and conductive carbon black (Super P) are mixed according to the mass ratio of 72:18:10, and then added into a mixed solution of anhydrous ethanol and deionized water, wherein the volume ratio of anhydrous ethanol to deionized water is 4:1, and stirred for 6 h to obtain a mixed slurry.

[0223] The D10 particle size of the nanometer silicon powder is 150 nm; the length of the carbon nanotubes is 12 μm, and the diameter is 30 nm; and the specific surface area of the conductive carbon black (Super P) is 2000 m 2 / g.

[0224] (2) The slow-release capsule lithium powder is added into the mixed slurry obtained in step (1), and ultrasonic treatment is performed at an ultrasonic frequency of 80 Hz for 2 h to obtain a composite slurry.

[0225] The slow-release capsule lithium powder is a slow-release capsule lithium powder with a wall material of polymethyl methacrylate, and the added mass of the slow-release capsule lithium powder is 6% of the mass of the nanometer silicon powder.

[0226] (3) The composite slurry obtained in step (2) is treated by a spray drying method, the drying temperature is 120°C, and the drying rate is 0.8 L / h to obtain a composite material powder.

[0227] (4) The composite material powder obtained in step (3) is mixed with the graphene material according to the mass ratio of 91:9, and then added into an aqueous solution containing polyvinylpyrrolidone as a dispersant, and ultrasonic dispersion is performed at an ultrasonic frequency of 80 Hz for 4 h to obtain a mixed dispersion liquid.

[0228] The added mass of the aqueous solution containing polyvinylpyrrolidone as a dispersant is 2% of the mass of the nanometer silicon powder, and the solid content of the polyvinylpyrrolidone in the aqueous solution containing polyvinylpyrrolidone as a dispersant is 25%; the polyvinylpyrrolidone is PVP K-30.

[0229] (5) The mixed dispersion liquid obtained in step (4) is brush coated on an aluminum foil, and then calcined under an argon atmosphere, with a calcination temperature of 750 DEG C and a holding time of 2.5 h, and naturally cooled to room temperature (25 DEG C), to obtain the modified silicon-carbon composite material of the present example.

[0230] According to the EDX element analysis and SEM structure characterization test, the structural characteristics of the modified silicon-carbon composite material of the present example are as follows: in the first charge-discharge process of the silicon-carbon material, the active lithium is coated by the graphene carbon layer / ester coating layer, and in the battery cycle process, due to the protection of the graphene layer, the ester coating gradually dissolves, and the active lithium gradually precipitates, thereby making up for the loss of lithium ions in the cycle process, increasing the battery life, and the conductive network structure of the conductive agent is in a three-dimensional shape, and the graphene material is coated in the outer layer to form a dense carbon layer coating structure. In the soft pack battery prepared by the conventional lithium iron phosphate, the first coulombic efficiency is 90.5%, the capacity retention rate at 4C rate is 96.10%, and the capacity retention rate after 1500 cycles is 80%.

[0231] Example 3

[0232] The present example is basically the same as example 1, except that:

[0233] In step (2), the added mass of the slow-release capsule lithium powder is 7.5% of the mass of the commercial SiC.

[0234] Example 4

[0235] The present example is basically the same as example 1, except that:

[0236] In step (2), the added mass of the slow-release capsule lithium powder is 10% of the mass of the commercial SiC.

[0237] Example 5

[0238] The present example is basically the same as example 1, except that:

[0239] The commercial SiC is replaced by nano-silicon powder with a D10 particle size of 150 nm, and in step (1):

[0240] The nano-silicon powder, carbon nanotubes, conductive carbon black (Super P) and polyethylene glycol are mixed according to a mass ratio of 80:10:5:5.

[0241] Example 6

[0242] The present example is basically the same as example 1, except that:

[0243] In step (1): the commercial SiC, carbon nanotubes, conductive carbon black (Super P) and polyethylene glycol are mixed according to a mass ratio of 70:20:5:5.

[0244] Example 7

[0245] This example is basically the same as Example 2, except that:

[0246] The nano-silicon powder is replaced by commercial SiC with a D10 particle size of 3 μm, and in step (1):

[0247] Commercial SiC, carbon nanotubes, and conductive carbon black (Super P) are mixed in a mass ratio of 75:15:5.

[0248] Example 8

[0249] This example is basically the same as Example 1, except that:

[0250] In step (2), the mass ratio of slow-release capsule lithium powder to graphene is 95:5.

[0251] Example 9

[0252] This example is basically the same as Example 1, except that:

[0253] In step (2), the mass ratio of slow-release capsule lithium powder to graphene is 90:10.

[0254] Example 10

[0255] This example is basically the same as Example 1, except that:

[0256] Commercial SiC is replaced by silicon monoxide, and:

[0257] In step (1), the carbon nanotubes are replaced by a high specific surface area carbon black material with a BET specific surface area of 874 m 2 / g; and the conductive carbon black (Super P) is replaced by a mesoporous alumina material;

[0258] In step (2), the slow-release capsule lithium powder is a slow-release capsule lithium powder with a wall material of polyvinylidene fluoride, and the polyether ether ketone is replaced by polyvinylpyrrolidone (PVP K-10);

[0259] In step (4), the drying temperature is 130°C, and the drying rate is 0.2 L / h;

[0260] In step (5), the composite material powder obtained in step (4) is directly calcined under a nitrogen atmosphere, with a calcination temperature of 800°C and a holding time of 2 h.

[0261] Example 11

[0262] This example is basically the same as Example 2, except that:

[0263] The nano-silicon powder is replaced by a nano-silicon-carbon composite material, and:

[0264] In step (1), the carbon nanotubes are replaced by a high specific surface carbon black material having a BET specific surface area of 874 m 2 / g; and the conductive carbon black (Super P) is replaced by a mesoporous alumina material;

[0265] In step (2), the slow-release capsule lithium powder is a mixture of slow-release capsule lithium powder having a wall material of polymethyl methacrylate and slow-release capsule lithium powder having a wall material of polyethylene glycol (PEG-10) at a mass ratio of 1:1;

[0266] In step (3), the drying temperature is 90°C, and the drying rate is 1 L / h;

[0267] In step (4), the polyvinylpyrrolidone is replaced by polyether ether ketone.

[0268] In step (5), the calcination temperature is 600°C, and the holding time is 4h.

[0269] Comparative Example 1

[0270] The material of this comparative example is SiC with a D10 particle size of 3 pm.

[0271] Comparative Example 2 (lithium supplement group 1)

[0272] The material of this comparative example is nano-lithium powder lithium supplement.

[0273] The preparation method of the material of this comparative example is:

[0274] Commercial silicon-carbon, nano-lithium powder, and polyvinylidene fluoride (PVDF) are weighed according to the matching ratio of commercial silicon-carbon (Tianmu Pioneer SC2A type silicon-carbon): nano-lithium powder: PVDF = 92wt%: 7wt%: 1wt%, then PVDF is added to the solvent N-methyl pyrrolidone (NMP), and then commercial silicon-carbon and nano-lithium powder are added in sequence, pre-mixed for 6h, and finally dried by ultrasonic assistance (40KHz / 30min).

[0275] Comparative Example 3 (lithium supplement group 2)

[0276] The material of this comparative example uses lithium polyacrylate (Li-PAA) to supplement lithium.

[0277] The preparation method of the material of this comparative example is:

[0278] The commercial silicon carbon, Li-PAA and conductive carbon black (Super P) were weighed according to the blending ratio of commercial silicon carbon: Li-PAA: conductive carbon black = 92wt%: 7wt%: 1wt%, and then they were pre-mixed in a mixed solvent of deionized water and anhydrous ethanol mixed at a mass ratio of 1:1 for 6h to obtain a composite slurry; then, the obtained composite slurry was treated by a spray drying method, the drying temperature was 120°C, and the drying rate was 0.8L / h to obtain a composite material powder.

[0279] The commercial silicon carbon was Tianmu Pioneer SC2A type silicon carbon.

[0280] Comparative Example 4

[0281] The material of the present comparative example was graphite, specifically artificial graphite.

[0282] II. Performance Test

[0283] 1. Material Characterization

[0284] (1) Surface Analysis

[0285] The test method was to test the modified silicon carbon composite material prepared in Example 1 by cross section polishing-scanning electron microscope (CP-SEM, Cross Section Polisher-Scanning Electron Microscope), and the test results are shown in Figure 4 .

[0286] As shown in Figure 4 , the SEM backscattered electron image shows that the inside is the main body of Si material (the atomic number of Si element is higher than that of C element, so it is displayed as a bright color area in the backscattered electron image), and the outer layer is a carbon element coating material. By line scanning element of the cross section of the spherical material: the central spherical part is Si element, and the outer surface is carbon element coating. Since the amount of Li element is small, and there is a coating on the outer layer, the element of the capsule lithium powder cannot be detected.

[0287] (2) Element Distribution

[0288] The element distribution of the modified silicon carbon composite material prepared in Example 1 was tested by X-ray energy spectrometer (EDX), and the test results are shown in Figure 5 .

[0289] As can be seen from Figure 5 , the C content gradually increases, indicating that the modified silicon carbon composite material prepared in Example 1 is a material with a ladder coating.

[0290] 2. Electrochemical Performance

[0291] The modified silicon-carbon composite materials prepared in each example and the materials of Comparative Examples 1-4 were used as negative active materials to assemble lithium ion batteries.

[0292] The method for preparing a lithium ion battery comprises the following steps:

[0293] (1) Preparation of a positive electrode sheet:

[0294] Lithium iron phosphate (LFP), conductive carbon black (Super P, referred to as SP), multi-walled carbon nanotubes, and polyvinylidene fluoride (PVDF) were prepared into a positive electrode sheet in a wet process at LFP:SP:multi-walled carbon nanotubes:PVDF=96wt%:2wt%:0.5wt%:1.5%, including material pre-mixing and coating, and rolling.

[0295] (2) Preparation of a negative electrode sheet:

[0296] The negative active material, SP, single-walled carbon nanotubes (SWCNT), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR) were prepared into a negative electrode sheet in a semi-dry process at negative active material:SP:SWCNT:PAA:SBR=95.5wt%:0.9wt%:0.06wt%:2.5wt%:1.04wt%, including material pre-mixing and coating, and rolling.

[0297] The negative active material is composed of SiC and artificial graphite, and the mass ratio of SiC to artificial graphite is 9:1.

[0298] (3) Preparation of an electrolyte: commercial electrolyte (manufacturer: Tianci; model: TC-CN-009A).

[0299] (4) Selection of a separator: Tianci 7+1.5 single-side ceramic separator, wherein 7 is the thickness of the base film polyethylene (PE) film in microns, and 1.5 is the single-side coating thickness of the ceramic coating aluminum oxide in microns.

[0300] (5) Assembly: stack assembly.

[0301] The electrochemical performance of each lithium ion battery was tested, and the testing method was as follows:

[0302] First coulombic efficiency: 25±2℃Ch:CC-CV 0.33CDch:CC 1C+0.1C+0.01C; 2.75-3.65V. First coulombic efficiency=first discharge capacity / first charge capacity.

[0303] 4C rate capacity retention: 25±2℃ Ch: CC-CV 1 CD ch: CC; 2.75-3.65V; 1C / 1.5C / 2C / 2.5C / 3C / 4C; 2.75-3.65V. Capacity retention = 4C constant current discharge capacity / 1C constant current discharge capacity.

[0304] Cycle performance: 25±2℃ Ch: CC-CV 0.5C, Dch: CC 1C; 2.75-3.65V. Cycle retention = cycle X cycle discharge capacity / initial cycle discharge capacity.

[0305] High temperature storage performance: 25±2℃ Ch: CC-CV 0.33C / Dch: CC 0.33C storage: 45±2℃, rest for 30 days to test capacity retention, capacity recovery.

[0306] Capacity retention = first cycle discharge capacity after 30 days storage under high temperature (45±2℃) condition / constant capacity discharge capacity at room temperature (25±2℃).

[0307] Capacity recovery = third cycle discharge capacity after 30 days storage under high temperature (45±2℃) condition / constant capacity discharge capacity at room temperature (25±2℃).

[0308] The electrochemical performance test results are shown in Table 1.

[0309] Table 1. Electrochemical performance test results

[0310]

[0311] Note: "-" in Table 1 represents no relevant data before the filing date; the cycle performance takes "1500@80%SOH" of Example 1 as an example, which means that the battery can be cycled 1500 times under the state of health (80%SOH).

[0312] As can be seen from Table 1, the modified silicon carbon in each Example 1 can improve the coulombic efficiency, 4C rate and cycle performance to different degrees compared with the conventional silicon carbon (Comparative Example 1), the conventional lithium supplement group 1 (Comparative Example 2) and the conventional lithium supplement group 2 (Comparative Example 3), and also improves the high temperature storage performance of the silicon carbon material, which can achieve the same or better effect as graphite (Comparative Example 4).

[0313] Figure 6 The capacity retention of the batteries corresponding to the materials of Example 1, Comparative Examples 1-3 at different rates. From Figure 6 As can be seen, the modified silicon carbon (Example 1) can improve the 4C rate performance compared with the conventional silicon carbon (Comparative Example 1) and the conventional lithium supplement group (Comparative Example 2 and Comparative Example 3).

[0314] In this application, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present application. The illustrative appearances of the terms "in one embodiment", "in some embodiments", "in an example", "in a specific example" or "in some examples", as used within this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Also, the terms "first", "second", and the like can be used merely as labels to distinguish between different elements, and do not necessarily indicate a relative importance or a chronological order of described features. By using the term "a plurality" it is meant at least two, for example two, three or four, unless explicitly stated otherwise.

[0315] Furthermore, the terms "first", "second", etc. are used herein only to describe different features, and do not imply a relative importance or a chronological order of described features. By using the term "a plurality" it is meant at least two, for example two, three or four, unless explicitly stated otherwise.

[0316] Although the embodiments of the present application have been shown and described above, it is to be understood that the above-described embodiments are merely illustrative of the application, and that changes, modifications, substitutions and variations can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. A method for preparing a modified silicon-carbon composite material, characterized in that, include: A first silicon source, a first carbon source, and a first conductive agent are added to a first solvent to obtain a first mixed slurry; The sustained-release capsule lithium powder is mixed with the first mixed slurry and then dried to obtain the first composite material powder. The first composite material powder is mixed with graphene and then dispersed in a first dispersant to obtain a first mixed dispersion. The first mixed dispersion was subjected to a first calcination and a first cooling to obtain the modified silicon-carbon composite material; The sustained-release capsule lithium powder includes at least one of the following: sustained-release capsule lithium powder with polyethylene glycol as the wall material, sustained-release capsule lithium powder with polyvinylidene fluoride as the wall material, and sustained-release capsule lithium powder with polymethyl methacrylate as the wall material. The first calcination temperature is 600-800℃, and the first calcination time is 2-4h.

2. The preparation method according to claim 1, characterized in that, The first silicon source includes at least one of silicon carbide, elemental silicon, carbon-coated silicon-oxygen material, nano-silicon-carbon composite material, and silicon oxide compound; And / or, the D10 particle size of the first silicon source is 2-3 μm; And / or, the first carbon source includes carbon nanotubes with a BET specific surface area of ​​600-1500 m². 2 At least one of the carbon black in / g; And / or, the first conductive agent includes at least one of conductive carbon black, carbon nanotubes, and mesoporous alumina; And / or, the first solvent includes at least one of ethanol and water; And / or, the first dispersant includes at least one of polyetheretherketone, carbon nanotubes, and aqueous dispersants; And / or, the mass ratio of the first silicon source, the first carbon source, and the first conductive agent is (70-80):(10-20):(5-10); And / or, the mass amount of the sustained-release capsule lithium powder is 5-10% of the mass of the first silicon source; And / or, the mass ratio of the first composite material powder to graphene is (90-95):(5-10); And / or, the first drying includes spray drying; And / or, the method for preparing the modified silicon-carbon composite material further includes the step of coating the first mixed dispersion onto the first support before the first calcination.

3. The preparation method according to claim 2, characterized in that, The first carbon source is a carbon nanotube with a length of 5-15 μm and a diameter of 20-60 nm.

4. A method for preparing a modified silicon-carbon composite material, characterized in that, include: A second silicon source, a second carbon source, a second conductive agent, and a second dispersant are added to a second solvent to obtain a second mixed slurry; The sustained-release capsule lithium powder was mixed with graphene and then dispersed in a third dispersant to obtain a second mixed dispersion. The second mixed slurry and the second mixed dispersion are mixed and then subjected to a second drying process to obtain the second composite material powder. The second composite material powder is subjected to a second calcination and a second cooling to obtain the silicon-carbon composite material. The sustained-release capsule lithium powder includes at least one of the following: sustained-release capsule lithium powder with polyethylene glycol as the wall material, sustained-release capsule lithium powder with polyvinylidene fluoride as the wall material, and sustained-release capsule lithium powder with polymethyl methacrylate as the wall material. The second calcination temperature is 600-800℃, and the second calcination time is 2-4 hours.

5. The preparation method according to claim 4, characterized in that, The second silicon source includes at least one of silicon carbide, elemental silicon, carbon-coated silicon-oxygen materials, nano-silicon-carbon composite materials, and silicon oxide compounds; And / or, the DO1 particle size of the second silicon source is 2-3 μm; And / or, the second carbon source includes carbon nanotubes with a BET specific surface area of ​​600-1500 m². 2 At least one of the carbon black in / g; And / or, the second conductive agent includes at least one of conductive carbon black, carbon nanotubes, and mesoporous alumina; And / or, the second solvent includes at least one of ethanol and water; And / or, the second dispersant comprises at least one of polyetheretherketone, polyethylene glycol, and polyvinylpyrrolidone; And / or, the third dispersant includes at least one of polyetheretherketone and a water-based dispersant for carbon nanotubes; And / or, the mass ratio of the second silicon source, the second carbon source, the second conductive agent and the second dispersant is (70-80):(10-20):(5-10):(5-10); And / or, the mass amount of the sustained-release capsule lithium powder is 5-10% of the mass of the second silicon source; And / or, the mass ratio of the sustained-release capsule lithium powder to the graphene is (90-95):(5-10); And / or, the second drying includes spray drying; And / or, the method for preparing the modified silicon-carbon composite material further includes the step of placing the second composite material powder on a second support before the second calcination.

6. The preparation method according to claim 5, characterized in that, The second carbon source is a carbon nanotube with a length of 5-15 μm and a diameter of 20-60 nm.

7. A modified silicon-carbon composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 3, or by the preparation method according to any one of claims 4 to 6.

8. A negative electrode material, characterized in that, Including the modified silicon-carbon composite material as described in claim 7.

9. A negative electrode sheet, characterized in that, Includes the negative electrode material as described in claim 8.

10. A secondary battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The negative electrode is the negative electrode as described in claim 9.

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