Silicon-carbon composite negative electrode material, preparation method thereof and secondary battery

Abstract

The embodiment of the application relates to a silicon-carbon composite negative electrode material, a preparation method thereof and a secondary battery, and the silicon-carbon composite negative electrode material is in a core-shell structure, comprising a silicon-carbon inner core, a carbon coating layer, an interface compatibility layer and a solid-state electrolyte layer which are sequentially coated on the silicon-carbon inner core from inside to outside; the silicon-carbon inner core comprises porous carbon and a silicon-based material in the pores of the porous carbon; the interface compatibility layer comprises 2,2,2 trifluoroacetamide; and the solid-state electrolyte layer comprises a polymer electrolyte. In this way, the cycle stability, cycle life and rate performance of the silicon-carbon composite negative electrode material can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a silicon-carbon composite anode material, its preparation method, and a secondary battery. Background Technology

[0002] Traditional graphite anode materials have dominated the development of lithium-ion batteries, with a theoretical specific capacity of approximately 372 mAh / g, and possess mature fabrication processes and relatively low costs. However, the specific capacity of graphite anodes is gradually approaching its theoretical limit, making it difficult to meet the development needs of future high-energy-density batteries. Therefore, exploring novel high-specific-capacity anode materials has become a current research hotspot.

[0003] Silicon-based materials, due to their unique physicochemical properties, have shown great application potential in the field of lithium-ion battery anode materials. Silicon possesses an extremely high theoretical specific capacity, reaching approximately 4200 mAh / g, far exceeding that of graphite anodes. This means that lithium-ion batteries using silicon-based anode materials can store more energy, thereby significantly improving the battery's energy density and enabling longer driving ranges for electric vehicles and longer-lasting power support for portable electronic devices.

[0004] Despite the numerous advantages of silicon-based materials, they still face a series of severe challenges in practical applications. First, silicon-based materials undergo significant volume changes during charge and discharge. These drastic changes generate enormous stress within the electrode material, leading to cracking or even pulverization, thus significantly reducing battery cycle stability. Second, the large volume changes during charge and discharge also trigger the continuous rupture and regeneration of the solid electrolyte interface (SEI) film on the negative electrode surface. This process results in the continuous consumption of electrolyte and active lithium ions, thereby shortening the battery's cycle life. Summary of the Invention

[0005] In view of this, the present application provides a silicon-carbon composite anode material, its preparation method, and a secondary battery to solve at least one problem existing in the background art.

[0006] In a first aspect, embodiments of this application provide a silicon-carbon composite anode material, wherein the silicon-carbon composite anode material has a core-shell structure, including a silicon-carbon core, and a carbon coating layer, an interface compatibility layer, and a solid electrolyte layer that sequentially coat the silicon-carbon core from the inside out;

[0007] The silicon-carbon core comprises porous carbon and silicon-based material located in the pores of the porous carbon; the interface compatibility layer comprises 2,2,2-trifluoroacetamide; and the solid electrolyte layer comprises a polymer electrolyte.

[0008] In conjunction with the first aspect of this application, in an alternative embodiment, the silicon-carbon core satisfies at least one of the following characteristics:

[0009] (1) The porous carbon includes at least one of porous graphite, porous hard carbon, and porous soft carbon;

[0010] (2) The silicon-based material includes pre-lithiated silicon-based material;

[0011] (3) The silicon-based material includes silicon-oxygen materials; optionally, the chemical formula of the silicon-oxygen material is SiO2. x Where 0.8 ≤ x ≤ 1.2;

[0012] (4) The particle size D50 of the porous carbon is 6μm to 24μm;

[0013] (5) The pore size of the porous carbon is 50 nm to 1.2 μm;

[0014] (6) The mass ratio of the porous carbon to the silicon-based material is 100:(2-30).

[0015] In conjunction with the first aspect of this application, in an alternative embodiment, the solid electrolyte layer satisfies at least one of the following characteristics:

[0016] (1) The polymer electrolyte includes at least one of polyvinylidene fluoride-hexafluoropropylene, hexafluorobutyl methacrylate-polyethylene glycol methacrylate, and polyacrylamide-polyacrylonitrile-polyvinyl alcohol;

[0017] (2) The solid electrolyte layer further includes an ion conductor material; optionally, the mass ratio of the polymer electrolyte to the ion conductor material is (0.5–3.5):(0.1–0.5); optionally, the ion conductor material includes Li6PS5I, LiTaO3, Li7La3Zr2O7, Li3LaTiO3, LiAlTi(PO4)3, Li 10 GeP2S 12 At least one of LiCF3SO3.

[0018] In conjunction with the first aspect of this application, in an optional embodiment, the silicon-carbon composite anode material satisfies at least one of the following characteristics:

[0019] (1) The thickness of the carbon coating layer is 2nm to 30nm;

[0020] (2) The thickness of the interface compatibility layer is 5nm to 20nm;

[0021] (3) The thickness of the solid electrolyte layer is 5nm to 20nm.

[0022] Secondly, embodiments of this application provide a method for preparing a silicon-carbon composite anode material, the method comprising the following steps:

[0023] S1: Carbon coating treatment is performed on silicon-carbon material to obtain a first coated negative electrode material with a carbon coating layer; the silicon-carbon material includes porous carbon and silicon-based material located in the pores of the porous carbon;

[0024] S2: The first coated negative electrode material is contacted with a mixed solution containing 2,2,2 trifluoroacetamide, and after drying, an interfacial compatibility layer is formed on the surface of the first coated negative electrode material to obtain the second coated negative electrode material.

[0025] S3: Coat the surface of the second coated negative electrode material with a polymer electrolyte to form a solid electrolyte layer on the surface of the second coated negative electrode material, thereby obtaining the silicon-carbon composite negative electrode material.

[0026] In conjunction with the second aspect of this application, in an optional embodiment, step S1 satisfies at least one of the following features:

[0027] (1) The porous carbon includes at least one of porous graphite, porous hard carbon, and porous soft carbon;

[0028] (2) The silicon-based material includes silicon-oxygen materials; optionally, the chemical formula of the silicon-oxygen material is SiO2. x Where 0.8 ≤ x ≤ 1.2;

[0029] (3) The thickness of the carbon coating layer is 2nm to 30nm;

[0030] (4) The particle size D50 of the porous carbon is 6μm to 24μm;

[0031] (5) The pore size of the porous carbon is 50 nm to 1.2 μm;

[0032] (6) The mass ratio of the porous carbon to the silicon-based material is 100:(2-30).

[0033] In conjunction with the second aspect of this application, in an optional embodiment, step S2 satisfies at least one of the following features:

[0034] (1) The mixed solution further includes a first solvent, wherein the mass ratio of the first coated negative electrode material, the 2,2,2-trifluoroacetamide and the first solvent is (80-180):(0.4-1.2):100; optionally, the first solvent includes at least one of acetone, cyclohexanone, methyl ethyl ketone, ethyl acetate and tetrahydrofuran;

[0035] (2) The method of contacting the first coated negative electrode material with the mixed solution includes immersion treatment or spray treatment;

[0036] (3) The thickness of the interface compatibility layer is 5nm to 20nm.

[0037] In conjunction with the second aspect of this application, in an optional embodiment, step S3 satisfies at least one of the following features:

[0038] (1) The polymer electrolyte includes at least one of polyvinylidene fluoride-hexafluoropropylene, hexafluorobutyl methacrylate-polyethylene glycol methacrylate, and polyacrylamide-polyacrylonitrile-polyvinyl alcohol;

[0039] (2) The method of coating the polymer electrolyte onto the surface of the second coated negative electrode material includes liquid phase coating or mechanical fusion coating;

[0040] (3) While coating the surface of the second coated negative electrode material with a polymer electrolyte, an ion conductor material is added; optionally, the mass ratio of the polymer electrolyte, the ion conductor material, and the second coated negative electrode material is (0.5-3.5):(0.1-0.5):100; optionally, the ion conductor material includes Li6PS5I, LiTaO3, Li7La3Zr2O7, Li3LaTiO3, LiAlTi(PO4)3, Li 10 GeP2S 12 At least one of LiCF3SO3;

[0041] (4) The thickness of the solid electrolyte layer is 5nm to 20nm.

[0042] In conjunction with the second aspect of this application, in an optional embodiment, the silicon-based material in step S1 includes a pre-lithiated silicon-based material; optionally, the pre-lithiated silicon-based material is prepared by mixing and sintering a silicon-based material and a lithium source, wherein the molar ratio of lithium in the lithium source to the silicon-based material is 1:6 to 20; optionally, the particle size D50 of the silicon-based material is 50 nm to 300 nm.

[0043] Thirdly, embodiments of this application provide a secondary battery, including a negative electrode sheet, wherein the negative electrode sheet comprises the silicon-carbon composite negative electrode material as described in any one of the first aspects or the silicon-carbon composite negative electrode material prepared by the method described in any one of the second aspects.

[0044] Compared with the prior art, the embodiments of this application have the following beneficial effects:

[0045] The silicon-carbon composite anode material, its preparation method, and the secondary battery provided in this application embodiment are core-shell structures, including a silicon-carbon core and a carbon coating layer, an interface compatibility layer, and a solid electrolyte layer that sequentially coat the silicon-carbon core from the inside out. The silicon-carbon core includes porous carbon and silicon-based materials located in the pores of the porous carbon. The interface compatibility layer includes 2,2,2-trifluoroacetamide. The solid electrolyte layer includes a polymer electrolyte. In this embodiment, the porous carbon in the silicon-carbon core can suppress the expansion of silicon-based materials during charging and discharging. The carbon coating layer covering the silicon-carbon core can suppress the expansion of the silicon-carbon core and improve the conductivity of the silicon-carbon composite anode material. The interface compatibility layer located between the carbon coating layer and the solid electrolyte layer can not only reduce the binding energy of lithium near the surface of the silicon-carbon core and promote the diffusion of lithium ions, but also improve the compatibility between the carbon coating layer and the solid electrolyte layer, thus improving the problem of poor compatibility between the carbon coating layer and the solid electrolyte layer. The solid electrolyte layer, including the polymer electrolyte, has high mechanical strength, thermal stability and interface stability, can construct continuous lithium ion conduction channels, and reduce side reactions between the silicon-carbon composite anode material and the electrolyte. It can also effectively suppress lithium dendrite growth and silicon-carbon core volume expansion, thereby effectively improving the cycle stability, cycle life and rate performance of the silicon-carbon composite anode material.

[0046] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0047] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0048] Figure 1 This is a schematic diagram of the structure of a silicon-carbon composite anode material provided in an embodiment of this application;

[0049] Figure 2 A schematic flowchart illustrating a method for preparing a silicon-carbon composite anode material provided in this application embodiment;

[0050] Figure 3 This is a schematic flowchart illustrating a method for preparing spherical porous artificial graphite, as provided in an embodiment of this application. Detailed Implementation

[0051] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0052] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0053] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0054] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0055] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0056] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0057] This application provides a silicon-carbon composite anode material, such as... Figure 1As shown, the silicon-carbon composite anode material has a core-shell structure, including a silicon-carbon core 100, and a carbon coating layer 200, an interface compatibility layer 300, and a solid electrolyte layer 400 that sequentially coat the silicon-carbon core 100 from the inside out; the silicon-carbon core 100 includes porous carbon 101 and silicon-based material 102 located in the pores of the porous carbon 101; the interface compatibility layer 300 includes 2,2,2-trifluoroacetamide; and the solid electrolyte layer 400 includes a polymer electrolyte.

[0058] In this embodiment, the porous carbon 101 in the silicon-carbon core 100 can suppress the expansion of the silicon-based material 102 during charging and discharging. The carbon coating layer 200 covering the silicon-carbon core 100 can suppress the expansion of the silicon-carbon core 100 and improve the conductivity of the silicon-carbon composite anode material. The interface compatibility layer 300 located between the carbon coating layer 200 and the solid electrolyte layer 400 can not only reduce the binding energy of lithium near the surface of the silicon-carbon core and promote the diffusion of lithium ions, but also improve the compatibility between the carbon coating layer 200 and the solid electrolyte layer 400, thus improving the problem of poor compatibility between the carbon coating layer 200 and the solid electrolyte layer 400. The solid electrolyte layer 400, including the polymer electrolyte, has high mechanical strength, thermal stability and interface stability. It can construct a continuous lithium ion conduction channel and reduce the side reactions between the silicon-carbon composite anode material and the electrolyte. It can also effectively suppress the growth of lithium dendrites and the volume expansion of the silicon-carbon core 100, thereby effectively improving the cycle stability, cycle life and rate performance of the silicon-carbon composite anode material.

[0059] It should be noted that, in the embodiments of this application, the carbon coating layer 200 substantially covers the entire surface of the silicon-carbon core 100. Here, "substantially" can be understood as meaning that, within the permissible deviations of the process in this art, the carbon coating layer 200 covers the entire surface of the silicon-carbon core 100. Similarly, within the permissible deviations of the process in this art, the interface compatibility layer 300 substantially covers the entire surface of the carbon coating layer 200, and the solid electrolyte layer 400 substantially covers the surface of the interface compatibility layer 300.

[0060] In this embodiment of the application, the porous carbon 101 in the silicon-carbon core 100 may include at least one of porous graphite, porous hard carbon, and porous soft carbon.

[0061] Furthermore, the porous carbon 101 may include spherical porous carbon. Because spherical porous carbon has a higher specific surface area, porosity, and a more uniform pore size distribution, it is beneficial for the uniform filling of the silicon-based material 102, improving the structural stability and compaction density of the silicon-carbon core 100, and thus contributing to the improvement of the capacity and cycle stability of the silicon-carbon composite anode material. For example, the spherical porous carbon 101 may include at least one of spherical porous artificial graphite, spherical porous hard carbon, and spherical porous soft carbon.

[0062] In some embodiments, the particle size D50 of the porous carbon 101 can be 6 μm to 24 μm, for example, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, or any value between any two of the above ranges. Controlling the particle size D50 of the porous carbon 101 within the above range, while ensuring the structural stability of the porous carbon 101, is beneficial to increasing the specific surface area of ​​the silicon-carbon core 100, thereby providing more active ion insertion and extraction sites, and shortening the transport path of active ions, which in turn helps to improve the capacity, cycle stability, cycle life, and rate performance of the silicon-carbon composite anode material.

[0063] In some embodiments, the pore size of porous carbon 101 can be 50 nm to 1.2 μm, for example, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.1 μm, 1.2 μm, or any value between any two of the above ranges. Controlling the pore size of porous carbon 101 within the above range ensures the structural stability of porous carbon 101 while providing sufficient space for the filling and expansion of silicon-based material 102, and is conducive to promoting the transport of active ions, thereby improving the capacity, cycle stability, cycle life, and rate performance of silicon-carbon composite anode materials.

[0064] In this embodiment, the silicon-based material 102 located in the pores of the porous carbon 101 may include silicon and / or silicon-oxygen materials. In some specific embodiments, the silicon-based material 102 includes silicon-oxygen materials; optionally, the chemical formula of the silicon-oxygen material is SiO. x , where 0.8≤x≤1.2.

[0065] Although silicon has a high theoretical energy density, its active material utilization rate is relatively poor, and its production cost is high. In contrast, silicon-oxygen materials have a higher energy density, higher active material utilization rate, and are more inexpensive. Therefore, using silicon-oxygen materials in silicon-based material 102 is beneficial for improving the overall performance of silicon-carbon composite anode materials and reducing costs.

[0066] In some embodiments, the silicon-based material 102 may include a pre-lithiated silicon-based material. While improving the capacity of the silicon-carbon composite anode material, the pre-lithiated silicon-based material can also play a role in lithium replenishment, such as replenishing the active lithium ions consumed in the formation of the SEI film, effectively improving the battery's initial coulombic efficiency. Furthermore, the pre-lithiated silicon-based material can reduce the volume expansion of the silicon-based material and stabilize the SEI film, thereby effectively reducing the battery's internal resistance and capacity decay.

[0067] For the silicon-carbon core 100, when the mass ratio of porous carbon 101 to silicon-based material 102 is too large, it is detrimental to improving the capacity of the silicon-carbon composite anode material; when the mass ratio of porous carbon 101 to silicon-based material 102 is too small, it is detrimental to improving the cycle stability and cycle life of the silicon-carbon composite anode material. Therefore, in some embodiments, the mass ratio of porous carbon 101 to silicon-based material 102 can be 100:(2-30), for example, 100:2, 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, or any value between any two of the above ranges. This is beneficial to improving the overall performance of the silicon-carbon composite anode material.

[0068] In some embodiments, the polymer electrolyte in the solid electrolyte layer 400 may include at least one of polyvinylidene fluoride-hexafluoropropylene, hexafluorobutyl methacrylate-polyethylene glycol methacrylate, and polyacrylamide-polyacrylonitrile-polyvinyl alcohol.

[0069] The polymer electrolyte in this embodiment is a composite solid electrolyte composed of two or more polymer blends or copolymers. It has higher mechanical strength, thermal stability and interfacial stability, which helps to better suppress lithium dendrite growth and silicon-carbon core 100 volume expansion, reduce side reactions between the anode material and the electrolyte, and thus better improve the cycle stability, cycle life and rate performance of the silicon-carbon composite anode material.

[0070] In some embodiments, please refer to Figure 1 The solid electrolyte layer 400 may also include an ion conductor material 401. The ion conductor material 401 dispersed in the solid electrolyte layer 400 can promote the transport of active ions, construct a better lithium ion conduction channel, and make the lithium ion deintercalation / intercalation reversibility better, thereby further improving the cycle stability, cycle life and rate performance of the silicon-carbon composite anode material.

[0071] For example, the ionic conductor material 401 may include Li6PS5I, LiTaO3, Li7La3Zr2O7, Li3LaTiO3, LiAlTi(PO4)3, Li 10 GeP2S 12 At least one of LiCF3SO3.

[0072] In some specific embodiments, the mass ratio of the polymer electrolyte to the ion conductor material 401 can be (0.5–3.5):(0.1–0.5), for example, 0.5:0.1, 0.5:0.2, 0.5:0.4, 0.5:0.5, 1.5:0.2, 2.5:0.2, 2.5:0.3, 3.5:0.1, 3.5:0.3, 3.5:0.5, or any value within any two of the above ranges. This is beneficial for balancing the mechanical strength, thermal stability, interfacial stability, and ion conduction performance of the solid electrolyte layer 400, thereby better improving the overall performance of the silicon-carbon composite anode material.

[0073] In this embodiment, when the thickness of the carbon coating layer 200 is too small, its effect on suppressing the expansion of the silicon-carbon core 100 and improving the conductivity of the anode material is limited; when the thickness of the carbon coating layer 200 is too large, it will prolong the transport path of active ions, affecting the migration of active ions in the anode material, and is also detrimental to the size control of the silicon-carbon composite anode material. Therefore, in some specific embodiments, the thickness of the carbon coating layer 200 can be 2nm to 30nm, for example, it can be 2nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, or any value between any two of the above ranges. This is beneficial to improving the overall performance of the silicon-carbon composite anode material.

[0074] In this embodiment, when the thickness of the interface compatibility layer 300 is too small, its effect on promoting lithium-ion diffusion in the anode material and improving the compatibility between the carbon coating layer 200 and the solid electrolyte layer 400 is limited. When the thickness of the interface compatibility layer 300 is too large, it prolongs the transport path of active ions, affecting their migration in the anode material and hindering the size control of the silicon-carbon composite anode material. Therefore, in some specific embodiments, the thickness of the interface compatibility layer 300 can be 5nm to 20nm, for example, 5nm, 10nm, 15nm, 20nm, or any value between any two of the above ranges. This is beneficial for improving the overall performance of the silicon-carbon composite anode material.

[0075] In this embodiment, when the thickness of the solid electrolyte layer 400 is too small, its effect on suppressing lithium dendrite growth and the volume expansion of the silicon-carbon core 100 is limited; when the thickness of the solid electrolyte layer 400 is too large, it prolongs the transport path of active ions, affecting the migration of active ions in the anode material, and is also detrimental to the size control of the silicon-carbon composite anode material. Therefore, in some specific embodiments, the thickness of the solid electrolyte layer 400 can be 5nm to 20nm, for example, 5nm, 10nm, 15nm, 20nm, or any value between any two of the above ranges. This is beneficial for improving the overall performance of the silicon-carbon composite anode material.

[0076] This application also provides a method for preparing a silicon-carbon composite anode material. Please refer to [link / reference]. Figure 2 The preparation method of the silicon-carbon composite anode material provided in this application includes the following steps:

[0077] S1: Carbon coating treatment is performed on silicon-carbon material to obtain a first coated negative electrode material with a carbon coating layer; the silicon-carbon material includes porous carbon and silicon-based material located in the pores of the porous carbon;

[0078] S2: The first coated negative electrode material is contacted with a mixed solution containing 2,2,2 trifluoroacetamide. After drying, an interfacial compatibility layer is formed on the surface of the first coated negative electrode material to obtain the second coated negative electrode material.

[0079] S3: Coat the surface of the second coated negative electrode material with a polymer electrolyte to form a solid electrolyte layer on the surface of the second coated negative electrode material, thereby obtaining a silicon-carbon composite negative electrode material.

[0080] In this embodiment, the porous carbon in the silicon-carbon material (which can be referred to as the silicon-carbon core) can suppress the expansion of the silicon-based material during charging and discharging. First, carbon coating is applied to the surface of the silicon-carbon core, which can suppress the expansion of the silicon-carbon core and improve the conductivity of the silicon-carbon composite anode material. Then, an interface compatibility layer and a solid electrolyte layer are sequentially formed on the carbon coating layer. The interface compatibility layer located between the carbon coating layer and the solid electrolyte layer can not only reduce the binding energy of lithium near the surface of the silicon-carbon core and promote the diffusion of lithium ions, but also improve the compatibility between the carbon coating layer and the solid electrolyte layer, thus improving the problem of poor compatibility between the carbon coating layer and the solid electrolyte layer. The solid electrolyte layer, including the polymer electrolyte, has certain mechanical strength, thermal stability and interface stability, which can construct a continuous lithium ion conduction channel and reduce the side reactions between the silicon-carbon composite anode material and the electrolyte. It can also effectively suppress the growth of lithium dendrites and the volume expansion of the silicon-carbon core, thereby effectively improving the cycle stability, cycle life and rate performance of the prepared silicon-carbon composite anode material.

[0081] In step S1, the porous carbon in the silicon-carbon material may include at least one of porous graphite, porous hard carbon, and porous soft carbon.

[0082] Furthermore, porous carbon can include spherical porous carbon. Because spherical porous carbon has a higher specific surface area, porosity, and more uniform pore size distribution, it is beneficial for the uniform filling of silicon-based materials, improving the stability and compaction density of the silicon-carbon core structure, and thus contributing to the improvement of the capacity, cycle stability, and cycle life of silicon-carbon composite anode materials. For example, spherical porous carbon can include at least one of spherical porous artificial graphite, spherical porous hard carbon, and spherical porous soft carbon.

[0083] In some embodiments, porous carbon includes spherical porous artificial graphite; please refer to [reference needed]. Figure 3 The preparation method of spherical porous artificial graphite includes the following steps:

[0084] S11: The carbon raw material is ball-milled to obtain powder material.

[0085] Optionally, the carbon raw material includes at least one of petroleum coke, metallurgical coke, pitch coke, anthracite, coal tar pitch, and coal tar; further, the particle size D50 of the powder material can be 0.2 μm to 0.7 μm. This is beneficial for controlling the particle size of the final formed spherical porous graphite.

[0086] S12: The powder material is placed in an acid solution, stirred, and then filtered, washed, and dried to obtain purified powder.

[0087] Optionally, the molar concentration of the acid solution can be 2.5 mol / L to 6 mol / L; the acid solution may include hydrochloric acid solution and / or nitric acid solution; the stirring temperature can be 60℃ to 80℃, and the time can be 3h to 5h.

[0088] S13: The purified powder is mixed with dispersant and binder, ball-milled, and then spray-dried and granulated to obtain spherical granular material.

[0089] Optionally, the mass ratio of purified powder to binder is 100:(1-5); exemplarily, the binder may include at least one selected from polyvinyl alcohol, sodium carboxymethyl cellulose, and polyvinyl butyral. Optionally, the mass ratio of purified powder to dispersant may be 1:(10-15); exemplarily, the dispersant may include water and / or alcohols, wherein alcohols may include, for example, ethanol. Optionally, the rotation speed of the fourth ball milling treatment may be 500 r / min to 800 r / min, and the time may be 3 h to 6 h.

[0090] S14: Under a protective gas atmosphere, spherical particulate materials are graphitized to obtain spherical porous artificial graphite.

[0091] Optionally, the temperature for graphitization can be 2600℃~3000℃, the heating rate can be 2℃ / min~5℃ / min, and the time can be 5h~8h.

[0092] In some embodiments, the particle size D50 of the porous carbon can be 6 μm to 24 μm, for example, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, or any value between any two of the above ranges. Controlling the particle size D50 of the porous carbon within the above range, while ensuring the stability of the porous carbon structure, is beneficial to increasing the specific surface area of ​​the silicon-carbon core, thereby providing more active ion insertion and extraction sites, and shortening the transport path of active ions, which in turn helps to improve the capacity, cycle stability, cycle life, and rate performance of the silicon-carbon composite anode material.

[0093] In some embodiments, the pore size of the porous carbon can be 50 nm to 1.2 μm, for example, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.1 μm, 1.2 μm, or any value between any two of the above ranges. Controlling the pore size of the porous carbon within the above range ensures the stability of the porous carbon structure while providing sufficient space for the filling and expansion of silicon-based materials, and facilitates the transport of active ions, thereby improving the capacity, cycle stability, cycle life, and rate performance of silicon-carbon composite anode materials.

[0094] In step S1, the silicon-based material in the silicon-carbon material may include silicon and / or silicon-oxygen materials. In some specific embodiments, the silicon-based material includes silicon-oxygen materials; optionally, the chemical formula of the silicon-oxygen material is SiO. x Where 0.8 ≤ x ≤ 1.2. Silicon-oxygen materials have high energy density, high utilization rate of active materials, and relatively low cost. Therefore, using silicon-oxygen materials in silicon-based materials is beneficial to improving the overall performance and reducing the cost of silicon-carbon composite anode materials.

[0095] In some embodiments, the silicon-based material in step S1 includes a pre-lithiated silicon-based material.

[0096] In the actual preparation process, the pre-lithiated silicon-based material can be prepared by mixing and sintering silicon-based material and lithium source. The molar ratio of lithium to silicon-based material in the lithium source can be 1:6 to 20. Optionally, the particle size D50 of the silicon-based material can be 50 nm to 300 nm.

[0097] Specifically, silicon-based materials and lithium sources can be mixed, and then subjected to ball milling and sintering to obtain pre-lithiated silicon-based materials. The lithium source can include, for example, at least one of lithium hydroxide, lithium chloride, lithium oxalate, lithium bromide, lithium silicate, lithium powder, lithium carbonate, and lithium aluminate. The ball milling speed can be 300 r / min to 600 r / min, and the time can be 1 h to 3 h. The sintering temperature can be 450℃ to 600℃, and the heating rate can be 2℃ / min to 6℃ / min. This is beneficial for improving the quality of the obtained pre-lithiated silicon-based materials.

[0098] In some embodiments, the mass ratio of porous carbon to silicon-based material can be 100:(2-30), for example, 100:2, 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, or any value between any two of the above ranges. This is beneficial for improving the overall performance of silicon-carbon composite anode materials.

[0099] In the actual preparation process, step S1, which involves preparing silicon-carbon materials and carbon coating them, may include: mixing porous carbon and silicon-based materials, ball milling the mixture, and then depositing carbon in a carbon source gas atmosphere. The ball milling speed can be 700 r / min to 1000 r / min, and the milling time can be 5 h to 7 h. The gaseous carbon source may include at least one of methane, ethane, propane, acetylene, propyne, butyne, and ethylene. The carbon deposition temperature can be 300℃ to 650℃, and the carbon deposition time can be 5 min to 30 min.

[0100] It is understood that the thickness of the carbon coating layer can be controlled by the deposition time. In some embodiments, the thickness of the carbon coating layer formed in step S1 can be 2 nm to 30 nm, for example, 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, or any value between any two of the above ranges. This is beneficial for improving the overall performance of silicon-carbon composite anode materials.

[0101] In step S2, the method of contacting the first coated negative electrode material with the mixed solution containing 2,2,2-trifluoroacetamide includes impregnation or spraying.

[0102] In some embodiments, a spray drying method can be used to form the interfacial compatibility layer. Specifically, a mixed solution containing 2,2,2-trifluoroacetamide can be sprayed onto the surface of the first coated negative electrode material and dried to form the interfacial compatibility layer.

[0103] In some other embodiments of this application, an impregnation method can be used to form the interfacial compatibility layer. Specifically, the first coated negative electrode material can be added to a mixed solution containing 2,2,2-trifluoroacetamide for impregnation treatment. Next, the solvent in the mixed solution is removed by stirring at 40°C to 70°C for 10 min to 45 min, and then maintained at 80°C to 90°C for 30 min to 60 min, thereby forming an interfacial compatibility layer on the surface of the first coated negative electrode material.

[0104] The aforementioned mixed solution includes 2,2,2-trifluoroacetamide and a first solvent, wherein the first solvent may include, for example, at least one selected from acetone, cyclohexanone, methyl ethyl ketone, ethyl acetate, and tetrahydrofuran. In some specific embodiments, the mass ratio of the first coated negative electrode material, 2,2,2-trifluoroacetamide, and the first solvent may be (80–180):(0.4–1.2):100. This is beneficial for improving the quality and integrity of the formed interfacial compatibility layer.

[0105] The thickness of the interfacial compatibility layer formed in step S2 can be 5 nm to 20 nm, for example, 5 nm, 10 nm, 15 nm, 20 nm, or any value between any two of the above ranges. This is beneficial for improving the overall performance of silicon-carbon composite anode materials.

[0106] In step S3, the polymer electrolyte is coated on the surface of the second coated negative electrode material by liquid phase coating or mechanical fusion coating.

[0107] In some embodiments, a ball milling method can be used to form a solid electrolyte layer. Specifically, the second coated negative electrode material and the polymer electrolyte can be mixed and then ball-milled to form a solid electrolyte layer on the surface of the second coated negative electrode material.

[0108] In some other embodiments of this application, a liquid-phase coating process can be used to form a solid electrolyte layer. Specifically, a polymer electrolyte can be added to a second solvent and stirred evenly at 35°C to 65°C to obtain a mixture. Then, a second coated negative electrode material is added to the mixture, stirred evenly, degassed, and then dried to form a solid electrolyte layer on the surface of the second coated negative electrode material.

[0109] For example, the polymer electrolyte may include at least one of polyvinylidene fluoride-hexafluoropropylene, hexafluorobutyl methacrylate-polyethylene glycol methacrylate, and polyacrylamide-polyacrylonitrile-polyvinyl alcohol. The second solvent may include at least one of ethanol, N-methylpyrrolidone, acetonitrile, and N,N-dimethylformamide.

[0110] The polymer electrolyte in this embodiment is a composite solid electrolyte composed of two or more polymer blends or copolymers, which has higher mechanical strength, thermal stability and interfacial stability. Therefore, it is beneficial for the formed solid electrolyte layer to better suppress lithium dendrite growth and silicon-carbon core volume expansion, reduce side reactions between the anode material and the electrolyte, and thus better improve the cycle stability, cycle life and rate performance of the silicon-carbon composite anode material.

[0111] In some embodiments, while coating the surface of the second coated anode material with a polymer electrolyte, an ion conductor material is also added to disperse the ion conductor material in the solid electrolyte layer, thereby constructing a better lithium-ion conduction channel, which can further improve the cycle stability, cycle life and rate performance of the silicon-carbon composite anode material.

[0112] For example, ionic conductor materials may include Li6PS5I, LiTaO3, Li7La3Zr2O7, Li3LaTiO3, LiAlTi(PO4)3, Li 10 GeP2S 12 At least one of LiCF3SO3;

[0113] In some embodiments, the mass ratio of the polymer electrolyte, the ion conductor material, and the second coated negative electrode material can be (0.5–3.5):(0.1–0.5):100, for example, 0.5:0.1:100, 0.5:0.3:100, 2:0.1:100, 2:0.5:100, 2:0.3:100, 3.5:0.1:100, 3.5:0.3:100, 3.5:0.5:100, or any other ratio within the above range. This is beneficial for improving the quality and integrity of the formed solid electrolyte layer.

[0114] The thickness of the solid electrolyte layer formed in step S3 can be 5 nm to 20 nm, for example, 5 nm, 10 nm, 15 nm, 20 nm, or any value between any two of the above ranges. This is beneficial for improving the overall performance of the silicon-carbon composite anode material.

[0115] This application also provides a secondary battery, including a negative electrode sheet, which includes the silicon-carbon composite negative electrode material described in any of the foregoing embodiments or the silicon-carbon composite negative electrode material prepared by the preparation method of the silicon-carbon composite negative electrode material described in any of the foregoing embodiments.

[0116] It should be understood that the beneficial effects of the silicon-carbon composite anode material described in any of the foregoing embodiments, or the silicon-carbon composite anode material prepared by the preparation method including the silicon-carbon composite anode material described in any of the foregoing embodiments, are applicable to the secondary battery.

[0117] In some embodiments, the secondary battery can be a lithium-ion secondary battery. Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0118] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes the silicon-carbon composite negative electrode material described in any of the foregoing embodiments or the silicon-carbon composite negative electrode material prepared by the preparation method of the silicon-carbon composite negative electrode material described in any of the foregoing embodiments.

[0119] Furthermore, the negative electrode active material layer also includes a conductive agent and a binder. The mass ratio of the silicon-carbon composite negative electrode material, the conductive agent, and the binder can be (96-99):(0.3-7.5):(0.3-4).

[0120] For example, the preparation method of the negative electrode sheet may include: first, mixing and stirring silicon-carbon composite negative electrode material, negative electrode conductive agent and negative electrode binder in a mass ratio of (96-99):(0.3-7.5):(0.3-4), adding N-methylpyrrolidone (NMP) and mixing evenly to obtain a negative electrode coating with a solid content (mass fraction) of 40%-60%, a viscosity of 1 Pa·s-6 Pa·s and a fineness of less than 40 μm; next, coating the negative electrode coating onto a negative electrode current collector (specifically, for example, copper foil), drying and rolling to obtain a negative electrode sheet.

[0121] The aforementioned negative electrode conductive agent may include, for example, at least one of conductive carbon black, graphene, and carbon nanotubes. The negative electrode binder may include, for example, at least one of polyacrylate-acrylate, polyacrylate-acrylonitrile, polyacrylate-butadiene-acrylonitrile, polyacrylate-acrylate-acrylonitrile-styrene, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, and polyvinylidene fluoride.

[0122] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one surface of the positive current collector. The positive active material layer includes a positive active material, a positive conductive agent, and a positive binder, wherein the mass ratio of the positive active material, the positive conductive agent, and the positive binder can be 100:(0.8-4.8):(0.5-3.2).

[0123] For example, the positive electrode active material may include at least one of lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, lithium iron manganese phosphate, and lithium iron phosphate. The positive electrode conductive agent may include at least one of conductive carbon black, graphene, and carbon nanotubes. The positive electrode binder may include at least one of polyacrylate-acrylate, polyacrylate-acrylonitrile, polyacrylate-butadiene-acrylonitrile, polyacrylate-acrylate-acrylonitrile-styrene, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, and polyvinylidene fluoride.

[0124] The preparation method of the positive electrode can be understood by referring to the preparation method of the negative electrode described above, and will not be repeated here.

[0125] In some embodiments, the preparation method of a secondary battery may include: winding or stacking a negative electrode sheet, a separator, and a positive electrode sheet to obtain a single bare cell; packaging the single bare cell (specifically, for example, an aluminum-plastic film, an aluminum-steel shell, etc.); and then drying, injecting electrolyte, encapsulating, forming, and capacity testing to obtain the secondary battery. The separator and electrolyte can be any separator and electrolyte well known to those skilled in the art, and this application does not impose any limitations.

[0126] The technical solution of this application will be further described below with reference to several embodiments and comparative examples.

[0127] Example 1

[0128] The preparation method of the silicon-carbon composite anode material in this embodiment includes the following steps:

[0129] S101: First, the petroleum coke is mechanically ball-milled. By adjusting the ball-milling parameters, the particle size of the raw material is controlled to be 0.2 μm to obtain graphitized micro powder. Next, the ball-milled graphitized micro powder is placed in a 3 mol / L hydrochloric acid solution and heated at 60°C to remove impurities. After stirring for 3 hours, it is filtered, washed until the filtrate is neutral, and dried to obtain the raw material powder. Next, the purified raw material powder is mixed with a dispersant and a binder at a mass ratio of 1:12:0.03 and stirred at 600 r / The mixture was dispersed and mixed by ball milling at a speed of min for 4.5 hours. Next, the ball-milled slurry was filtered and then sent to a spray granulator for atomization, granulation and drying to obtain spherical particles with uniform particle size and regular surface. Finally, the obtained spherical particles were placed in a medium-frequency induction graphitization furnace and graphitized at a high temperature of 2850℃ for 7 hours by introducing a protective gas (nitrogen). After the material was cooled and sieved, spherical porous artificial graphite with a particle size D50 of 6μm and a pore size of 50nm was obtained.

[0130] S102: Li and SiO in lithium hydroxide (lithium source) are weighed at a molar ratio of 1:18 and placed in a ball mill. The mixture is ball-milled at 450 r / min for 1.5 h to mix evenly. The evenly mixed powder is placed in a box-type atmosphere furnace and sintered at 550°C for 5 h at a heating rate of 3°C to obtain a pre-lithiated silicon-oxygen material. The spherical porous artificial graphite and the pre-lithiated silicon-oxygen material obtained in step S101 are ball-milled at 800 r / min for 6 h at a mass ratio of 100:2 to mix evenly. The mixture is then placed in a vapor deposition furnace. The temperature of the deposition furnace is controlled at 500°C, and acetylene (gaseous carbon source) is introduced to perform carbon deposition for 15 min to obtain a carbon-silicon based composite anode material with a carbon layer (a first coated anode material with a carbon coating layer). The thickness of the carbon coating layer is 16 nm.

[0131] S103: In a sealed container, add 0.5 parts by mass of 2,2,2-trifluoroacetamide (pre-curing agent) to 100 parts by mass of acetone, then add 100 parts by mass of the first coated negative electrode material with carbon coating layer from step S102, stir and impregnate, then stir at 45°C for 15 min to remove acetone solvent, and then keep at 85°C for 30 min to form an interface compatibility layer with a thickness of 12 nm on the surface of the carbon coating layer, thus obtaining the second coated negative electrode material;

[0132] S104: Polyvinylidene fluoride-hexafluoropropylene (polymer electrolyte), LiAlTi(PO4)3 (ion conductor material), and nitrile butadiene solvent are vigorously stirred at 45°C until homogeneous. The second coated anode material from step S103 is then added, stirred until homogeneous, degassed, and vacuum dried to form a solid electrolyte layer on the surface of the second coated anode material, thus obtaining a graphite-silicon-based solid anode composite material (silicon-carbon composite anode material). The mass ratio of polyvinylidene fluoride-hexafluoropropylene, LiAlTi(PO4)3, nitrile butadiene, and the second coated anode material is 0.5:0.1:45:100, and the thickness of the solid electrolyte layer is 5 nm.

[0133] Example 2

[0134] The preparation of the silicon-carbon composite anode material in this embodiment is basically the same as in Example 1, except that:

[0135] 1) In step S101, by adjusting the ball milling parameters, the particle size of the raw material is controlled to be 0.7 μm, and the particle size D50 of the obtained spherical porous artificial graphite is 24 μm and the pore size is 1.2 μm.

[0136] 2) In step S102, the mass ratio of spherical porous artificial graphite to pre-lithiated silicon oxide material is adjusted to 100:30; the carbon deposition time is adjusted to 30 min; and the thickness of the carbon coating layer is 30 nm.

[0137] 3) In step S104, the conductor filler is adjusted to a mass ratio of 1:1 of LiAlTi(PO4)3 and Li 10 GeP2S 12 A mixture of polyvinylidene fluoride-hexafluoropropylene, LiAlTi(PO4)3 and Li 10 GeP2S 12 The mass ratio of the mixture, nitrile butadiene, and the second coated negative electrode material is 0.5:0.5:45:100, and the thickness of the solid electrolyte layer formed is 7 nm.

[0138] Example 3

[0139] The preparation of the silicon-carbon composite anode material in this embodiment is basically the same as in Example 1, except that:

[0140] 1) In step S101, by adjusting the ball milling parameters, the particle size of the raw material is controlled to be 0.45 μm, and the particle size D50 of the obtained spherical porous artificial graphite is 15 μm and the pore size is 625 nm.

[0141] 2) In step S102, the mass ratio of spherical porous artificial graphite to pre-lithiated silicon oxide material is adjusted to 100:15; the temperature of the deposition furnace is adjusted to 600℃.

[0142] 3) In step S104, the conductor filler is adjusted to a mass ratio of 1:1 of LiAlTi(PO4)3 and Li 10 GeP2S 12 A mixture of polyvinylidene fluoride-hexafluoropropylene, LiAlTi(PO4)3 and Li 10 GeP2S 12 The mass ratio of the mixture, nitrile butadiene, and the second coated negative electrode material is 3.5:0.1:45:100, and the thickness of the solid electrolyte layer formed is 18 nm.

[0143] Example 4

[0144] The preparation of the silicon-carbon composite anode material in this embodiment is basically the same as in Example 1, except that:

[0145] 1) In step S102, the mass ratio of spherical porous artificial graphite to pre-lithiated silicon oxide material is adjusted to 100:3; the carbon deposition time is adjusted to 5 min; and the thickness of the carbon coating layer is 2 nm.

[0146] 2) In step S104, the mass ratio of polyvinylidene fluoride-hexafluoropropylene, LiAlTi(PO4)3, nitrile butadiene, and the second coated negative electrode material is 3.5:0.5:65:100, and the thickness of the solid electrolyte layer formed is 20nm.

[0147] Example 5

[0148] The preparation of the silicon-carbon composite anode material in this embodiment is basically the same as in Example 1, except that:

[0149] 1) In step S102, the molar ratio of Li to SiO in lithium hydroxide is adjusted to 1:15; the mass ratio of spherical porous artificial graphite to pre-lithiated silicon-oxygen material is adjusted to 100:4; and the temperature of the deposition furnace is adjusted to 540℃.

[0150] 2) In step S103, the mass of 2,2,2-trifluoroacetamide is adjusted to 0.8 parts; the mass of the first coated negative electrode material with carbon coating is adjusted to 80 parts; the stirring time for removing acetone solvent is adjusted to 20 min; and the thickness of the formed interfacial compatibility layer is 20 nm.

[0151] 3) In step S104, the polymer electrolyte is adjusted to hexafluorobutyl methacrylate-polyethylene glycol methacrylate; the conductor filler is adjusted to Li3LaTiO3; and the temperature of vigorous stirring is adjusted to 55℃.

[0152] The mass ratio of hexafluorobutyl methacrylate-polyethylene glycol methacrylate, Li3LaTiO3, nitrile butadiene, and the second coated negative electrode material is 1.5:0.3:65:100, and the thickness of the solid electrolyte layer formed is 12nm.

[0153] Example 6

[0154] The preparation of the silicon-carbon composite anode material in this embodiment is basically the same as in Example 1, except that:

[0155] 1) In step S102, the molar ratio of Li to SiO in lithium hydroxide is adjusted to 1:15; the mass ratio of spherical porous artificial graphite to pre-lithiated silicon-oxygen material is adjusted to 100:5; and the temperature of the deposition furnace is adjusted to 540℃.

[0156] 2) In step S103, the mass of 2,2,2-trifluoroacetamide is adjusted to 0.8 parts; the mass of the first coated negative electrode material with carbon coating is adjusted to 180 parts; the stirring time for removing acetone solvent is adjusted to 20 min; and the thickness of the formed interfacial compatibility layer is 12 nm.

[0157] 3) In step S104, the polymer electrolyte is adjusted to hexafluorobutyl methacrylate-polyethylene glycol methacrylate; the conductor filler is adjusted to Li3LaTiO3; and the temperature of vigorous stirring is adjusted to 55℃.

[0158] The mass ratio of hexafluorobutyl methacrylate-polyethylene glycol methacrylate, Li3LaTiO3, nitrile butadiene, and the second coated negative electrode material is 1.2:0.3:65:100, and the thickness of the solid electrolyte layer formed is 10nm.

[0159] Example 7

[0160] The preparation of the silicon-carbon composite anode material in this embodiment is basically the same as in Example 1, except that:

[0161] 1) In step S102, the molar ratio of Li to SiO in lithium hydroxide is adjusted to 1:15; the mass ratio of spherical porous artificial graphite to pre-lithiated silicon-oxygen material is adjusted to 100:6; and the temperature of the deposition furnace is adjusted to 540℃.

[0162] 2) In step S103, the mass of 2,2,2-trifluoroacetamide is adjusted to 0.4 parts; the mass of the first coated negative electrode material with carbon coating is adjusted to 180 parts; the stirring time for removing acetone solvent is adjusted to 20 min; and the thickness of the formed interfacial compatibility layer is 5 nm.

[0163] 3) In step S104, the polymer electrolyte is adjusted to a mixture of polyvinylidene fluoride-hexafluoropropylene and polyacrylamide-polyacrylonitrile-polyvinyl alcohol with a mass ratio of 1:1; the conductor filler is adjusted to Li3LaTiO3; and the temperature of vigorous stirring is adjusted to 55℃.

[0164] The mass ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylamide-polyacrylonitrile-polyvinyl alcohol mixture, Li3LaTiO3, butyronitrile, and the second coated negative electrode material is 1.5:0.1:65:100, and the thickness of the solid electrolyte layer formed is 11nm.

[0165] Example 8

[0166] The preparation of the silicon-carbon composite anode material in this embodiment is basically the same as in Example 1, except that:

[0167] 1) In step S102, the molar ratio of Li to SiO in lithium hydroxide is adjusted to 1:15; the mass ratio of spherical porous artificial graphite to pre-lithiated silicon-oxygen material is adjusted to 100:7; and the temperature of the deposition furnace is adjusted to 540℃.

[0168] 2) In step S103, the mass of 2,2,2-trifluoroacetamide is adjusted to 1.2 parts; the mass of the first coated negative electrode material with carbon coating is adjusted to 180 parts; the stirring time for removing acetone solvent is adjusted to 20 min; and the thickness of the formed interfacial compatibility layer is 17 nm.

[0169] 3) In step S104, the polymer electrolyte is adjusted to a mixture of polyvinylidene fluoride-hexafluoropropylene and polyacrylamide-polyacrylonitrile-polyvinyl alcohol with a mass ratio of 1:1; the conductor filler is adjusted to Li3LaTiO3; and the temperature of vigorous stirring is adjusted to 55℃.

[0170] The mass ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylamide-polyacrylonitrile-polyvinyl alcohol mixture, Li3LaTiO3, nitrile butadiene, and the second coated negative electrode material is 1.8:0.15:65:100, and the thickness of the solid electrolyte layer formed is 15nm.

[0171] Example 9

[0172] The preparation of the negative electrode material in this embodiment is basically the same as in Example 1, except that:

[0173] No conductive filler LiAlTi(PO4)3 was added in step S104.

[0174] Comparative Example 1

[0175] The preparation of the negative electrode material in this comparative example is basically the same as in Example 1, except that:

[0176] The step of preparing spherical porous artificial graphite in step S101 is omitted, and the step of mixing spherical porous artificial graphite and pre-lithiated silicon oxide material in step S102 is omitted. Instead, carbon deposition is performed directly on the surface of the pre-lithiated silicon oxide material to form a carbon coating layer.

[0177] Comparative Example 2

[0178] The preparation of the negative electrode material in this comparative example is basically the same as in Example 1, except that:

[0179] In step S102, after mixing the spherical porous artificial graphite and the pre-lithiated silicon-oxygen material, no carbon deposition was performed, that is, no carbon coating layer was formed on the surface of the silicon-carbon core. In step S103, an interface compatibility layer was directly formed on the surface of the silicon-carbon core.

[0180] Comparative Example 3

[0181] The preparation of the negative electrode material in this comparative example is basically the same as in Example 1, except that:

[0182] The step of forming an interfacial compatibility layer on the surface of the carbon coating layer in step S103 is omitted, and a solid electrolyte layer is directly formed on the surface of the carbon coating layer in step S104.

[0183] The negative electrode materials obtained in the above embodiments and comparative examples were used to make lithium-ion batteries, and the performance of the batteries was tested.

[0184] The preparation method of the lithium-ion battery is as follows: The negative electrode material, conductive agent (conductive carbon black), and binder (polyacrylic acid-acrylate-acrylonitrile-styrene) prepared in the above embodiments and comparative examples are mixed and stirred at a mass ratio of 96.4:3:2.4. NMP is added to obtain a negative electrode slurry with a solid content of 50%, a viscosity of 3 Pa·s, and a fineness of less than 40 μm. The negative electrode slurry is coated onto copper foil, dried, and rolled to obtain the negative electrode (negative electrode sheet). Lithium nickel cobalt manganese oxide (LiNi) is then added... 0.86 Co 0.07 Mn 0.07 O2), conductive agent conductive carbon black, binder polyacrylic acid-acrylate-acrylonitrile-styrene are mixed with NMP at a mass ratio of 97.8:1.2:1.0 and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on aluminum foil, dried, rolled, and then die-cut and welded to obtain a positive electrode (positive electrode sheet). Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1, and then 1 mol / L LiPF6 is added and mixed evenly to prepare an electrolyte. The negative electrode is slit and die-cut to remove some blank foil. The negative electrode, separator, and positive electrode are wound to obtain a bare cell. The bare cell is packaged, dried, injected with electrolyte, encapsulated, formed, and tested for capacity to obtain a lithium-ion battery.

[0185] The performance tests for lithium-ion batteries are as follows:

[0186] (1) Rate performance test: After the lithium-ion battery was left to stand at 25℃ for 2 days, it was first discharged at 0.5C to 2.8V, and then charged at a constant current of 1.0C to 4.25V. Then it was discharged at 1C, 2C, 3C and 4C rates respectively. The discharge capacity at 1C rate was recorded as C1, the discharge capacity at 2C rate was recorded as C2, the discharge capacity at 3C rate was recorded as C3, and the discharge capacity at 4C rate was recorded as C4. The discharge capacity at 2C rate was (C2 / C1)*100%, the discharge capacity at 3C rate was (C3 / C1)*100%, and the discharge capacity at 4C rate was (C4 / C1)*100%. It can be understood that the higher the discharge capacity at higher rates, the better the rate performance of the lithium-ion battery.

[0187] (2) Cyclic performance test: After the lithium-ion battery is left to stand for 2 days at 25°C, it is first discharged to 2.8V at 0.5C, and then charged to 4.25V at a constant current of 1.0C. This charge and discharge cycle is carried out until the discharge capacity is 80% of the initial discharge capacity. The number of cycles at the cutoff point is recorded.

[0188] (3) Impedance test: At 25°C, the lithium-ion battery was charged at a constant current of 0.5C to 4.25V, then charged at a constant voltage of 4.25V until the current < 0.05C, left to stand for 5 minutes, and then discharged at 1C for 48 minutes to 20% SOC. Then, the lithium-ion battery was subjected to electrochemical impedance test on an electrochemical workstation. The test frequency range was 100000Hz~0.01Hz, and the signal amplitude was 5mV.

[0189] The results of the above tests are shown in Table 1.

[0190] Table 1

[0191]

[0192] As can be seen from the data in Table 1, compared to Comparative Examples 1 to 3, the batteries containing the silicon-carbon composite anode materials prepared in Examples 1 to 9 all exhibited reduced impedance, improved rate performance at 2C, 3C, and 4C, and increased cycle count. Compared to Example 1, in Comparative Example 1, the pre-lithiated silicon-oxygen material was not filled into the porous carbon; that is, the core of the anode material was silicon-based. Because the silicon-based material lacked the constraint of porous carbon, its volume expansion during charging and discharging was not well suppressed, easily leading to cracking or even pulverization of the anode material, resulting in a significant reduction in both cycle performance and rate performance. Compared to Example 1, in Comparative Example 2, since no carbon coating layer was formed on the surface of the silicon-carbon core, the expansion of the silicon-carbon core and the conductivity of the anode material could not be suppressed through the carbon coating layer. Therefore, the rate performance and cycle performance of the corresponding battery were reduced, and the impedance of the corresponding battery increased significantly. Compared to Example 1, in Comparative Example 3, no interface compatibility layer was formed on the surface of the carbon coating layer. Therefore, it could not reduce the binding energy of lithium near the surface of the silicon-carbon core, thereby promoting lithium-ion diffusion. At the same time, it could not improve the poor compatibility between the carbon coating layer and the solid electrolyte layer, which led to a significant increase in the impedance of the corresponding battery and a decrease in the rate performance and cycle performance of the corresponding battery.

[0193] As can be seen from the above, the silicon-carbon composite anode material prepared in this application has a core-shell structure, including a silicon-carbon core and a carbon coating layer, an interface compatibility layer and a solid electrolyte layer that sequentially coat the silicon-carbon core from the inside out. The porous carbon in the silicon-carbon core can suppress the expansion of silicon-based materials during charging and discharging. The carbon coating layer covering the silicon-carbon core can suppress the expansion of the silicon-carbon core and improve the conductivity of the silicon-carbon composite anode material. The interfacial compatibility layer located between the carbon coating layer and the solid electrolyte layer can not only reduce the binding energy of lithium near the surface of the silicon-carbon core and promote the diffusion of lithium ions, but also improve the compatibility between the carbon coating layer and the solid electrolyte layer, thus improving the problem of poor compatibility between the carbon coating layer and the solid electrolyte layer. The solid electrolyte layer, including the polymer electrolyte, has high mechanical strength, thermal stability and interfacial stability. It can construct a continuous lithium-ion conduction channel, has good lithium-ion deintercalation / intercalation reversibility, and can also reduce the side reactions between the silicon-carbon composite anode material and the electrolyte. It can also effectively suppress lithium dendrite growth and silicon-carbon core volume expansion, thereby effectively improving the cycle stability, cycle life and rate performance of the silicon-carbon composite anode material.

[0194] It should be noted that the silicon-carbon composite anode material embodiments, silicon-carbon composite anode material preparation method embodiments, and secondary battery embodiments provided in this application belong to the same concept; the technical features in the technical solutions described in each embodiment can be arbitrarily combined without conflict.

[0195] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A silicon-carbon composite anode material, characterized in that, The silicon-carbon composite anode material has a core-shell structure, including a silicon-carbon core and a carbon coating layer, an interface compatibility layer, and a solid electrolyte layer that sequentially coat the silicon-carbon core from the inside out. The silicon-carbon core comprises porous carbon and silicon-based material located in the pores of the porous carbon; the interface compatibility layer comprises 2,2,2-trifluoroacetamide; and the solid electrolyte layer comprises a polymer electrolyte.

2. The silicon-carbon composite anode material according to claim 1, characterized in that, The silicon-carbon core satisfies at least one of the following characteristics: (1) The porous carbon includes at least one of porous graphite, porous hard carbon, and porous soft carbon; (2) The silicon-based material includes pre-lithiated silicon-based material; (3) The silicon-based material includes silicon-oxygen materials; (4) The particle size D50 of the porous carbon is 6μm~24μm; (5) The pore size of the porous carbon is 50 nm to 1.2 μm; (6) The mass ratio of the porous carbon to the silicon-based material is 100: (2~30).

3. The silicon-carbon composite anode material according to claim 1, characterized in that, The silicon-based material includes a silicon-oxygen material; the chemical formula of the silicon-oxygen material is SiO₂. x , where 0.8≤x≤1.

2.

4. The silicon-carbon composite anode material according to claim 1, characterized in that, The solid electrolyte layer satisfies at least one of the following characteristics: (1) The polymer electrolyte includes at least one of polyvinylidene fluoride-hexafluoropropylene, hexafluorobutyl methacrylate-polyethylene glycol methacrylate, and polyacrylamide-polyacrylonitrile-polyvinyl alcohol; (2) The solid electrolyte layer also includes an ion conductor material.

5. The silicon-carbon composite anode material according to claim 1, characterized in that, The solid electrolyte layer further includes an ion conductor material; the mass ratio of the polymer electrolyte to the ion conductor material is (0.5~3.5):(0.1~0.5).

6. The silicon-carbon composite anode material according to claim 1, characterized in that, The solid electrolyte layer further includes an ion conductor material; the ion conductor material includes Li6PS5I, LiTaO3, Li7La3Zr2O7, Li3LaTiO3, LiAlTi(PO4)3, and Li 10 GeP2S 12 At least one of LiCF3SO3.

7. The silicon-carbon composite anode material according to claim 1, characterized in that, The silicon-carbon composite anode material satisfies at least one of the following characteristics: (1) The thickness of the carbon coating layer is 2nm~30nm; (2) The thickness of the interface compatibility layer is 5nm~20nm; (3) The thickness of the solid electrolyte layer is 5nm~20nm.

8. A method for preparing a silicon-carbon composite anode material, characterized in that, The method includes the following steps: S1: Carbon coating treatment is performed on silicon-carbon material to obtain a first coated negative electrode material with a carbon coating layer; the silicon-carbon material includes porous carbon and silicon-based material located in the pores of the porous carbon; S2: The first coated negative electrode material is contacted with a mixed solution containing 2,2,2 trifluoroacetamide, and after drying, an interfacial compatibility layer is formed on the surface of the first coated negative electrode material to obtain the second coated negative electrode material. S3: Coat the surface of the second coated negative electrode material with a polymer electrolyte to form a solid electrolyte layer on the surface of the second coated negative electrode material, thereby obtaining the silicon-carbon composite negative electrode material.

9. The method for preparing the silicon-carbon composite anode material according to claim 8, characterized in that, Step S1 satisfies at least one of the following characteristics: (1) The porous carbon includes at least one of porous graphite, porous hard carbon, and porous soft carbon; (2) The silicon-based material includes silicon-oxygen materials; (3) The thickness of the carbon coating layer is 2nm~30nm; (4) The particle size D50 of the porous carbon is 6μm~24μm; (5) The pore size of the porous carbon is 50 nm to 1.2 μm; (6) The mass ratio of the porous carbon to the silicon-based material is 100: (2~30).

10. The method for preparing the silicon-carbon composite anode material according to claim 8, characterized in that, In step S1, the silicon-based material includes a silicon-oxygen material; the chemical formula of the silicon-oxygen material is SiO. x , where 0.8≤x≤1.

2.

11. The method for preparing the silicon-carbon composite anode material according to claim 8, characterized in that, Step S2 satisfies at least one of the following characteristics: (1) The mixed solution further includes a first solvent, wherein the mass ratio of the first coated negative electrode material, the 2,2,2 trifluoroacetamide and the first solvent is (80~180):(0.4~1.2):100; (2) The method of contacting the first coated negative electrode material with the mixed solution includes immersion treatment or spray treatment; (3) The thickness of the interface compatibility layer is 5nm~20nm.

12. The method for preparing the silicon-carbon composite anode material according to claim 8, characterized in that, In step S2, the mixed solution further includes a first solvent, wherein the mass ratio of the first coated negative electrode material, the 2,2,2 trifluoroacetamide and the first solvent is (80~180):(0.4~1.2):100; the first solvent includes at least one of acetone, cyclohexanone, methyl ethyl ketone, ethyl acetate and tetrahydrofuran.

13. The method for preparing the silicon-carbon composite anode material according to claim 8, characterized in that, Step S3 satisfies at least one of the following characteristics: (1) The polymer electrolyte includes at least one of polyvinylidene fluoride-hexafluoropropylene, hexafluorobutyl methacrylate-polyethylene glycol methacrylate, and polyacrylamide-polyacrylonitrile-polyvinyl alcohol; (2) The method of coating the polymer electrolyte on the surface of the second coated negative electrode material includes liquid phase coating or mechanical fusion coating; (3) While coating the surface of the second coated negative electrode material with polymer electrolyte, an ion conductor material is added; (4) The thickness of the solid electrolyte layer is 5nm~20nm.

14. The method for preparing the silicon-carbon composite anode material according to claim 8, characterized in that, In step S3, while coating the surface of the second coated negative electrode material with polymer electrolyte, an ion conductor material is added; the mass ratio of the polymer electrolyte, the ion conductor material and the second coated negative electrode material is (0.5~3.5):(0.1~0.5):

100.

15. The method for preparing the silicon-carbon composite anode material according to claim 8, characterized in that, In step S3, while coating the surface of the second coated negative electrode material with a polymer electrolyte, an ion conductor material is added; the ion conductor material includes Li6PS5I, LiTaO3, Li7La3Zr2O7, Li3LaTiO3, LiAlTi(PO4)3, and Li 10 GeP2S 12 At least one of LiCF3SO3.

16. The method for preparing the silicon-carbon composite anode material according to any one of claims 8 to 15, characterized in that, The silicon-based material in step S1 includes a pre-lithiated silicon-based material.

17. The method for preparing the silicon-carbon composite anode material according to claim 16, characterized in that, The pre-lithiated silicon-based material is prepared by mixing and sintering silicon-based material and lithium source, wherein the molar ratio of lithium in the lithium source to the silicon-based material is 1:6~20.

18. The method for preparing the silicon-carbon composite anode material according to claim 16, characterized in that, The particle size D50 of the silicon-based material is 50nm~300nm.

19. A secondary battery, characterized in that, The material includes a negative electrode sheet, which comprises the silicon-carbon composite negative electrode material according to any one of claims 1 to 7 or the silicon-carbon composite negative electrode material prepared by the method of preparing the silicon-carbon composite negative electrode material according to any one of claims 8 to 18.

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