Silicon-based negative electrode material and preparation method and application thereof

Abstract

The application relates to the technical field of negative electrode materials, and provides a silicon-based negative electrode material and a preparation method and application thereof. The silicon-based negative electrode material comprises a core and a shell layer covering the core; the material of the core comprises a silicon-based material; the material of the shell layer comprises black phosphorus and a carbon material; and the black phosphorus and the carbon material form an interlaced stacking and inlaid composite structure. The silicon-based negative electrode material provided by the application is coated with the interlaced stacking and inlaid composite structure formed by the black phosphorus and the carbon material, can effectively isolate the direct contact between the silicon-based material and electrolyte, form a more stable and denser SEI film, improve the stability of the negative electrode material, can provide effective buffering for the volume expansion of the silicon-based material, can limit the volume expansion of the silicon-based material to a certain extent, and can maximize the lithium storage performance of silicon oxide, so that the negative electrode material has higher specific capacity, a first coulomb efficiency and a rate performance.

Description

Technical Field

[0001] The present application belongs to the technical field of anode materials, and in particular relates to a silicon-based anode material, a preparation method therefor and an application thereof. Background Art

[0002] The emergence and application of lithium-ion batteries have brought innovation and convenience to people's production and life. At present, lithium-ion batteries are still in a stage of vigorous development and have a huge application market in the fields of new energy vehicles and energy storage. The properties of the cathode and anode materials of lithium-ion batteries have a crucial impact on the battery performance such as capacity, energy density and cycle life. An ideal anode material needs to have the characteristics of low working potential, high capacity, high first-cycle Coulombic efficiency, low cost and good cycle stability. Graphite-based carbon materials are currently widely used as anodes for lithium-ion batteries due to their excellent cycle stability. However, the theoretical lithium storage capacity of graphite is ~372 mAh / g, which greatly limits the proportion of cathode materials in the battery and increasingly fails to meet people's demand for high-power and high-energy-density batteries. It has been found in research that Si and Li can form a series of Li x Si alloy compounds, with a theoretical capacity as high as 4200 mAh / g and a low working voltage (<0.4 V vs Li / Li + ); moreover, silicon is abundant in the earth's crust, safe and non-polluting, and is considered one of the most promising anode materials. However, huge volume expansion (>300%) occurs during the alloying reaction of silicon with lithium and the poor electrical conductivity of silicon are the main factors restricting the development of silicon-based materials.

[0003] Silicon oxide (SiO x , 0<x<2) is a mature industrial raw material, which is an incomplete oxide of Si and is a heterogeneous material. SiO x contains not only amorphous Si and SiO x phases, but also incomplete oxide SiO + between the two, and its Li intercalation x mechanism is still under debate. The unique structure of SiO + x makes its volume expansion weaker than that of Si during Li deintercalation / intercalation, endowing it with good cycle stability, and its theoretical capacity still remains at a high level (1965 mAh / g to 4200 mAh / g), so it has a better application prospect. Nevertheless, SiO x still has some irreparable shortcomings, such as still large volume expansion which easily leads to pulverization of electrode materials, low first-cycle Coulombic efficiency, low electrical conductivity, etc. Summary of the Invention

[0004] The purpose of this application is to provide a silicon-based anode material and its preparation method, aiming to solve the problems of unsatisfactory specific capacity and initial coulombic efficiency of silicon-based anode materials and poor cycle performance during use.

[0005] Another objective of this application is to provide a negative electrode and a secondary battery containing the negative electrode, so as to solve the technical problems of low energy density and power of existing secondary batteries.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application provides a silicon-based anode material, which includes a core and a shell covering the core; wherein the core is made of silicon-based material, and the shell is made of black phosphorus and carbon material, wherein the black phosphorus and carbon material form an interleaved and interlocked composite structure.

[0008] Secondly, this application provides a method for preparing a silicon-based anode material, comprising the following steps:

[0009] Step S10: Provide silicon-based materials, black phosphorus, carbon source, and solvent;

[0010] Step S20: Mix and grind the silicon-based material, black phosphorus, carbon source and solvent to coat the surface of the silicon-based material with an initial shell layer to obtain the intermediate material;

[0011] Step S30: The intermediate material is dried and carbonized sequentially to generate an initial shell with an interlaced and embedded composite structure, thus obtaining a silicon-based anode material.

[0012] Thirdly, this application provides a negative electrode, including a current collector and a negative electrode active layer bonded to the surface of the current collector, wherein the negative electrode active layer contains the silicon-based negative electrode material of this application or the silicon-based negative electrode material prepared by the method of preparing the silicon-based negative electrode material of this application.

[0013] Fourthly, this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode of this application.

[0014] The silicon-based anode material provided in the first aspect of this application uses silicon as the core, endowing the anode material with high specific capacity and cycle stability. It is coated with a composite structure of interleaved stacking and embedding of black phosphorus and carbon materials. This effectively isolates the silicon-based material from direct contact with the electrolyte, thereby preventing the continuous growth of the SEI film (Solid Electrolyte Interface) and the consumption of active lithium. It also facilitates the formation of a more stable and dense SEI film, thus improving the stability of the anode material and promoting the growth of Li. +The shell layer effectively reduces the charge transfer impedance of the electrode, thus improving the conductivity of the anode material. Furthermore, it provides an effective buffer for the volume expansion of the silicon-based material, limiting this expansion to a certain extent and significantly improving the structural stability of the anode material during charge and discharge. This maximizes the lithium storage performance of silicon oxide, resulting in higher specific capacity, initial coulombic efficiency, and rate performance. Additionally, the staggered and interlocked composite structure of black phosphorus and carbon materials possesses superior mechanical properties. This not only effectively alleviates the volume expansion of the silicon-based material but also fully utilizes the lithium storage performance of both black phosphorus and carbon materials, further enhancing the cycle stability and specific capacity of the silicon-based anode composite material.

[0015] The method for preparing silicon-based anode materials provided in the second aspect of this application effectively forms a shell layer on the surface of the silicon-based material, consisting of black phosphorus and carbon materials with an interleaved stacked and inlaid composite structure. This shell layer possesses high mechanical properties, effectively suppressing the volume expansion of the silicon-based material and ensuring the structural stability of the anode material, thereby endowing the anode material with high specific capacity, initial coulombic efficiency, and cycle stability. Furthermore, the method for preparing the anode material can effectively produce silicon-based anode materials with stable structure and electrochemical performance, and the process conditions are easily controlled, making it suitable for large-scale industrial production and application.

[0016] The negative electrode provided in the third aspect of this application, due to containing the negative electrode material of this application, fully utilizes the lithium storage performance of silicon oxide, black phosphorus and carbon materials, and effectively improves the initial coulombic efficiency, specific capacity and cycle performance of the negative electrode.

[0017] The secondary battery provided in the fourth aspect of this application contains the negative electrode provided in this application. Therefore, the secondary battery of this application has a high energy density, high initial coulombic efficiency, high power, good cycle stability, long life, and stable electrochemical performance. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of the preparation method of the silicon-based anode material provided in the embodiments of this application;

[0020] Figure 2 This is an X-ray diffraction analysis pattern of the silicon-based anode material provided in Embodiment 1 of this application;

[0021] Figure 3 The specific capacity-voltage curve is that of a coin cell containing the silicon-based negative electrode material of Embodiment 1 of this application. Detailed Implementation

[0022] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0024] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0025] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0026] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0027] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0028] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0029] The first aspect of this application provides a silicon-based anode material, which includes a core and a shell covering the core; wherein the core is made of silicon-based material, and the shell is made of black phosphorus and carbon material, and the black phosphorus and carbon material form an interleaved and interlocked composite structure.

[0030] The silicon-based anode material provided in the first aspect of this application uses silicon as the core, endowing the anode material with high specific capacity and cycle stability. It is coated with a composite structure of interleaved stacking and embedding of black phosphorus and carbon materials. This effectively isolates the silicon-based material from direct contact with the electrolyte, thereby preventing the continuous growth of the SEI film (Solid Electrolyte Interface) and the consumption of active lithium. It also facilitates the formation of a more stable and dense SEI film, thus improving the stability of the anode material and promoting the growth of Li. + The shell layer effectively reduces the charge transfer impedance of the electrode, thus improving the conductivity of the anode material. Furthermore, it provides an effective buffer for the volume expansion of the silicon-based material, limiting this expansion to a certain extent and significantly improving the structural stability of the anode material during charge and discharge. This maximizes the lithium storage performance of silicon oxide, resulting in higher specific capacity, initial coulombic efficiency, and rate performance. Additionally, the staggered and interlocked composite structure of black phosphorus and carbon materials possesses superior mechanical properties. This not only effectively alleviates the volume expansion of the silicon-based material but also fully utilizes the lithium storage performance of both black phosphorus and carbon materials, further enhancing the cycle stability and specific capacity of the silicon-based anode composite material.

[0031] In some embodiments, the interleaved and inlaid composite structure includes: a type of structure in which parts of black phosphorus and carbon material are interleaved and stacked, and another type of structure in which parts of black phosphorus are embedded in carbon material to form an inlaid structure.

[0032] It should be understood that black phosphorus has a two-dimensional layered orthorhombic crystal structure, and carbon materials also have a two-dimensional layered structure. Therefore, black phosphorus and carbon materials can be physically doped under the influence of van der Waals forces to form a structure through staggered stacking, resulting in a multi-layered composite shell covering the surface of the silicon-based material. Alternatively, a portion of black phosphorus can be embedded in carbon materials as nano-black phosphorus sheets to form an inlaid structure, again resulting in a composite shell covering the surface of the silicon-based material. The staggered stacking and inlaid composite structures provided in this application can effectively alleviate the volume expansion of silicon-based materials and facilitate the insertion and extraction of lithium ions, thereby endowing the anode material with higher specific capacity and cycle stability.

[0033] In some embodiments, black phosphorus is partially doped into the carbon material in the shell layer in the form of atomic clusters or single atoms. In the embodiments of this application, carbon material and black phosphorus are distributed in the shell layer in a mutually doped form. The doping forms include physical doping and chemical doping. In this case, some black phosphorus is chemically doped to replace some carbon atoms in the carbon material in the form of atomic clusters or single atoms to form phosphorus-doped carbon material. The resulting carbon-phosphorus bonds endow the shell layer with high mechanical properties, effectively protect the surface of the silicon-based material, and act as a buffer layer for the volume effect generated by the silicon-based material during lithium insertion / extraction. This effectively isolates the silicon-based material from direct contact with the electrolyte, thereby promoting lithium-ion transport and significantly improving the specific capacity and cycle stability of the negative electrode material.

[0034] In some embodiments, chemical bonds exist at the interface between black phosphorus and carbon materials. The carbon-phosphorus bonds at the interface between black phosphorus and carbon materials can effectively improve the mechanical properties of the shell, thereby effectively suppressing the volume expansion of silicon-based materials and significantly improving the specific capacity, structural stability, and cycle performance of the anode material.

[0035] In some embodiments, silicon-based materials include SiO2. x Where 0 < x < 2. Specifically, x can satisfy 0 < x < 0.5, or 0.5 ≤ x < 1, or 1 ≤ x < 1.5, or 1.5 ≤ x < 2.

[0036] Specifically, SiO x The material may be in the form of at least one of granules, blocks, cakes, and powders, ideally SiO2. x The material is set in powder form.

[0037] In some embodiments, silicon-based materials include SiO2. x If the shell material covering this silicon-based material includes black phosphorus and carbon materials, then the silicon-based anode material can be understood as SiO2. x @BP@C ternary composite material.

[0038] In some embodiments, the shell layer accounts for 30 wt% to 80 wt% of the total mass of the silicon-based anode material. Specifically, the shell layer can account for 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt% of the total mass of the silicon-based anode material, or any value within the range above. The composite shell layer with an interlaced and inlaid composite structure can serve as a buffer layer for the volume expansion of the silicon-based material, effectively preventing the pulverization of the electrode structure, thereby endowing the anode material with higher cycle stability and structural stability. It can also serve as a lithium storage site, thereby improving the specific capacity and initial charge-discharge efficiency of the anode material. Within the shell layer content range provided in the embodiments of this application, the lithium storage performance of silicon-based materials, carbon materials, and black phosphorus can be fully utilized, thereby endowing the anode material with excellent electrochemical performance.

[0039] In some embodiments, carbon material accounts for 70 wt% to 95 wt% of the total shell mass. Specifically, the carbon material can account for 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or any range thereof. After the silicon-based material core is coated with a shell composed of carbon material and black phosphorus, it can not only effectively suppress the volume effect of the silicon-based material and maintain the structural stability of the anode material, but also improve the cycle stability and rate performance of the anode material. Within the carbon content range provided in the embodiments of this application, carbon material can effectively alleviate the anisotropic expansion caused by silicon-based material and black phosphorus, endowing the anode material with higher specific capacity, first coulombic efficiency, and cycle stability.

[0040] In some embodiments, black phosphorus accounts for 5 wt% to 30 wt% of the total shell mass. Specifically, black phosphorus accounts for 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt% of the total shell mass, or any range thereof. Black phosphorus has high conductivity and charge transport performance, and it possesses lithium insertion / extraction activity. Furthermore, by utilizing its different lithiation potential from that of silicon-based materials, it can improve the conductivity of the anode material while simultaneously alleviating the mechanical stress generated by the silicon-based material and black phosphorus, thereby improving the cycle stability of the anode material. Within the black phosphorus content range provided in the embodiments of this application, it can have an additive effect on suppressing the volume expansion effect of silicon-based materials and improving conductivity.

[0041] In some embodiments, the particle size of the core satisfies: 50nm ≤ D50 ≤ 300nm. Specifically, the particle size of the core can be, but is not limited to, 50nm–100nm, 80nm–120nm, 150nm–200nm, 180nm–250nm, or 250nm–300nm. D50 is the particle size corresponding to a cumulative particle size distribution percentage of 50%. The smaller the particle size of the core, the larger its specific surface area, resulting in higher binding energy for the atoms on the surface of the core material. This allows for better release of stress generated during the volume expansion of the silicon-based material, effectively reducing the impact of volume expansion and fully utilizing the lithium storage performance of the silicon-based material. This, in turn, endows the anode material with higher specific capacity, first coulombic efficiency, and cycle performance. Within the particle size range of the core provided in this application embodiment, both more complete lithiation of the anode material and improved stability of the core-shell structure can be ensured.

[0042] In some embodiments, the thickness of the shell layer is 10 nm to 100 nm. Specifically, the thickness of the shell layer can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or within any range of the above values. Within the thickness range of the shell layer provided in the embodiments of this application, the shell layer can provide an effective buffer for the volume expansion of the silicon-based material, effectively suppress the volume expansion effect of the silicon-based material, further improve the conductivity of the silicon-based material, and also improve the structural stability of the coating layer, thereby endowing the negative electrode material with excellent electrochemical performance.

[0043] In some embodiments, the primary particle size of the silicon-based anode material satisfies: 0.05 μm ≤ D50 ≤ 0.7 μm, and the secondary particle size satisfies: 0.5 μm ≤ D50 ≤ 10 μm. Specifically, the primary particle size of the silicon-based anode material may be, but is not limited to, 0.05 μm to 0.1 μm, or 0.1 μm to 0.3 μm, or 0.2 μm to 0.5 μm, or 0.4 μm to 0.7 μm, and the secondary particle size may be, but is not limited to, 0.5 μm to 1.0 μm, or 1 μm to 3 μm, or 2 μm to 5 μm, or 4 μm to 8 μm, or 6 μm to 10 μm.

[0044] In some embodiments, the specific surface area of ​​the silicon-based anode material is 8m². 2 / g~30m 2 / g. Specifically, the specific surface area of ​​silicon-based anode materials can be 8m². 2 / g~15m 2 / g, or 10m 2 / g~25m 2 / g, or 15m 2 / g~30m 2 / g. Specific surface area refers to the total area per unit mass of a substance. Within the particle size and specific surface area range of the silicon-based anode material provided in the embodiments of this application, the absolute volume expansion of the silicon-based material can be reduced, the volume effect of the silicon-based material can be effectively suppressed, thereby significantly improving its electrochemical performance and endowing the anode material with higher initial coulombic efficiency and structural stability.

[0045] A second aspect of this application provides a method for preparing a silicon-based anode material, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0046] Step S10: Provide silicon-based materials, black phosphorus, carbon source, and solvent;

[0047] Step S20: Mix and grind the silicon-based material, black phosphorus, carbon source and solvent to coat the surface of the silicon-based material with an initial shell layer to obtain the intermediate material;

[0048] Step S30: The intermediate material is dried and carbonized sequentially to generate an initial shell with an interlaced and embedded composite structure, thus obtaining a silicon-based anode material.

[0049] The method for preparing silicon-based anode materials provided in the second aspect of this application effectively forms a shell layer on the surface of the silicon-based material, consisting of black phosphorus and carbon materials with an interleaved stacked and inlaid composite structure. This shell layer has high mechanical properties, effectively suppressing the volume expansion of the silicon-based material and ensuring the structural stability of the anode material, thereby endowing the anode material with high specific capacity, initial coulombic efficiency, and cycle stability. Furthermore, the method for preparing the anode material can effectively prepare silicon-based anode materials with stable structure and electrochemical performance, and the process conditions are easily controlled, making it suitable for large-scale industrial production and application.

[0050] In some embodiments, in step S10, the silicon-based material constitutes the core of the silicon-based anode material described above, and the carbon material generated by the carbonization treatment of the carbon source can be coated on the surface of the silicon-based material along with black phosphorus to form the shell of the silicon-based anode material described above.

[0051] In some embodiments, in step S10, the silicon-based material includes SiO2. x Materials, where 0 < x < 2. Specifically, x can satisfy 0 < x < 0.5, or 0.5 ≤ x < 1, or 1 ≤ x < 1.5, or 1.5 ≤ x < 2.

[0052] Specifically, SiO x The material may be in the form of at least one of granules, blocks, cakes, and powders, ideally SiO2. x The material is set in powder form.

[0053] In some embodiments, in step S10, the carbon source includes at least one of asphalt, resin, rubber, starch, glucose, sucrose, polyvinylpyrrolidone, and polyethylene glycol. The carbon material obtained after carbonization of this carbon source can form an interlocking and interlocking composite shell with black phosphorus to coat silicon-based materials.

[0054] In some embodiments, in step S10, the solvent includes ethanol and water. Specifically, ethanol accounts for 10% to 90% of the total volume of the solvent. The amount of solvent added should be sufficient to obtain a viscous mixture after ball milling of the silicon-based material, black phosphorus, and carbon source, which is beneficial for subsequent spray drying.

[0055] In some embodiments, the mass-to-volume ratio of carbon source to solvent is 1 to 3:1, where mass is measured in grams (g) and volume is measured in milliliters (mL).

[0056] In some embodiments, in step S10, the mass ratio of carbon source to silicon-based material is 1–15:1. Specifically, the mass ratio of carbon source to silicon-based material can be 1–2:1, 3–5:1, 4–10:1, 8–12:1, or 9–15:1. This application embodiment, through the optimization and control of the amount of carbon source added, ensures the formation of carbon material with a unique morphology matching the particle size on the surface of the silicon-based material, thereby endowing the negative electrode material with a high specific capacity.

[0057] In some embodiments, the mass ratio of silicon-based material to black phosphorus is 2 to 5:1. Specifically, the mass ratio of silicon-based material to black phosphorus can be 2:1, 3:1, 4:1, or 5:1. By optimizing and controlling the mass ratio of silicon-based material to black phosphorus, this application ensures that a suitable thickness of black phosphorus is coated on the surface of the silicon-based material. This effectively isolates the silicon-based material from direct contact with the electrolyte, resulting in a more stable, dense, and thin SEI film, thereby improving the stability and electrochemical performance of the anode material.

[0058] In some embodiments, step S20, the step of mixing and grinding the silicon-based material, black phosphorus, carbon source, and solvent, includes:

[0059] Step S210: Mix the silicon-based material with black phosphorus and perform a first ball milling process to obtain a mixture;

[0060] Step S220: Mix the mixture with a carbon source and a solvent and perform a second ball milling process.

[0061] In this embodiment, silicon-based materials and black phosphorus are first ball-milled. This process not only nanoscales the silicon-based materials, reducing particle size and suppressing volume effects, thus improving the lithium storage performance and cycle stability of the anode material, but also exfoliates the black phosphorus to form two-dimensional nano-black phosphorus sheets (black phosphorene). Utilizing its negative Poisson's ratio characteristic, this process enhances the stability of the core-shell structure of the anode material, increases its specific surface area, and reduces ion diffusion paths, thereby endowing the anode material with excellent electrochemical performance. Then, the reduced-size silicon-based materials and black phosphorus (containing black phosphorene) are ball-milled with a carbon source to coat the surface of the silicon-based materials with an initial shell layer, further improving the specific capacity and initial coulombic efficiency of the anode material.

[0062] In some embodiments, in step S210, after the black phosphorus undergoes a first ball milling process, a portion of the black phosphorus is peeled off to form two-dimensional nano-black phosphorus sheets, which can be embedded in carbon materials to form an inlaid shell structure.

[0063] The average thickness of the nano-black phosphorus sheets is 1nm to 5nm, and the average length / width ratio is 10 to 50. Specifically, the average thickness can be 1nm, 2nm, 3nm, 4nm or 5nm, and the average length / width ratio can be 10 to 15, or 20 to 25, or 30 to 40, or 45 to 50.

[0064] In some embodiments, in step S210, the rotation speed of the first ball milling process is 500 rpm to 1000 rpm, the time is 3 h to 12 h, and the ball-to-material ratio is 15 to 20:1. Specifically, the rotation speed of the first ball milling process can be 500 rpm to 600 rpm, or 500 rpm to 800 rpm, or 600 rpm to 1000 rpm, or 400 rpm to 700 rpm; the time can be 3 h to 5 h, or 6 h to 10 h, or 8 h to 12 h, or 7 h to 9 h, or 4 h to 6 h; and the ball-to-material ratio can be 15 to 17:1, or 18 to 20:1, or 16 to 19:1.

[0065] In some embodiments, in step S220, the rotation speed of the second ball milling process is 300 rpm to 700 rpm, and the time is 3 h to 6 h. Specifically, the rotation speed of the second ball milling process is 300 rpm to 400 rpm, or 400 rpm to 500 rpm, or 600 rpm to 700 rpm; the time is 3 h to 4 h, or 4 h to 6 h, or 3.5 h to 5.5 h, or 5 h to 6 h.

[0066] In some embodiments, in step S20, the mixing and grinding process is carried out under a protective atmosphere, wherein the protective atmosphere may be nitrogen or argon.

[0067] In some embodiments, in step S30, the carbonization temperature is 500℃~1000℃, and the time is 2h~12h. Specifically, the carbonization temperature can be 500℃~700℃, or 700℃~800℃, or 800℃~1000℃, and the time can be 2h~4h, or 4h~6h, or 4h~8h, or 6h~12h, or 8h~10h.

[0068] In this embodiment, the intermediate material is first spray-dried and then carbonized, so that the carbon material formed by carbonization of the carbon source can form a shell with an interlaced and inlaid composite structure to coat the silicon-based material with black phosphorus, thereby improving the lithium storage performance of the anode material and effectively improving the specific capacity and cycle stability of the anode material.

[0069] In some embodiments, in step S30, the heating rate of the carbonization process is 1°C / min to 5°C / min. Specifically, the heating rate can be 1°C / min to 3°C / min, or 2°C / min to 4°C / min, or 3°C / min to 5°C / min, or 2°C / min to 5°C / min.

[0070] A third aspect of this application provides a negative electrode, including a current collector and a negative electrode active layer bonded to the surface of the current collector, wherein the negative electrode active layer contains the silicon-based negative electrode material of this application or the silicon-based negative electrode material prepared by the method of this application.

[0071] The negative electrode provided in the third aspect of this application, due to containing the negative electrode material of this application, fully utilizes the lithium storage performance of silicon oxide, black phosphorus and carbon materials, and effectively improves the initial coulombic efficiency, specific capacity and cycle performance of the negative electrode.

[0072] In some embodiments, the material of the negative electrode current collector includes one of aluminum foil, copper foil, titanium foil, stainless steel, and nickel foil.

[0073] In some embodiments, the negative electrode active layer includes a negative electrode active material, a binder, and a conductive agent. The negative electrode active material includes the silicon-based negative electrode material provided in the embodiments of this application. Specifically, the silicon-based negative electrode material accounts for 85 wt% to 95 wt% of the total mass of the negative electrode active layer.

[0074] Specifically, the binder accounts for 1 wt% to 5 wt% of the total mass of the negative electrode active layer. For example, the binder includes at least one of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0075] Specifically, the conductive agent accounts for 1 wt% to 5 wt% of the total mass of the negative electrode active layer. For example, the conductive agent includes at least one of graphite, carbon black, acetylene black, graphene, carbon fiber, fullerene, and carbon nanotubes.

[0076] Specifically, the preparation process of the negative electrode includes:

[0077] The negative electrode active material, binder and conductive agent are mixed with deionized water and stirred / ball milled to obtain electrode slurry;

[0078] The electrode paste is coated onto the current collector, and the negative electrode is obtained through drying, rolling and die-cutting processes.

[0079] The drying, rolling, and die-cutting processes can be performed using processes well known to those skilled in the art.

[0080] The fourth aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode of this application.

[0081] The secondary battery provided in the fourth aspect of this application contains the negative electrode provided in this application. Therefore, the secondary battery of this application has a high energy density, high initial coulombic efficiency, high power, good cycle stability, long life, and stable electrochemical performance.

[0082] In some specific embodiments, the secondary battery is a lithium-ion battery with an initial coulombic efficiency of greater than 75% at 0.1C rate, a capacity retention of more than 80% after 100 cycles, and an initial discharge specific capacity of greater than 1400mAh / g.

[0083] The following examples illustrate the silicon-based anode materials, their preparation methods, and applications according to embodiments of the present invention. For ease of comparison, SiO₂ is used in each embodiment and comparative example. x In (0 < x < 2), x = 1, which is silicon suboxide.

[0084] Example 1

[0085] This embodiment provides a silicon-based anode material and its preparation method.

[0086] A silicon-based anode material comprises a SiO core and a shell layer formed of black phosphorus and carbon materials with an interlaced and interlocked composite structure coating the surface of the SiO core. The silicon-based anode material has a secondary particle size (D50 particle size) of 4.5 μm and a specific surface area of ​​18.2 m². 2 / g, the shell accounts for 50wt% of the total mass of silicon-based anode material (the carbon yield of pitch is calculated as 95%), carbon material accounts for 94wt% of the total mass of the shell, the thickness of the shell is 45nm, and the D50 particle size of the SiO core is 200nm.

[0087] A method for preparing a silicon-based anode material includes the following steps:

[0088] Step S1: Weigh 10g of silicon-based material (SiO powder) and 0.6g of black phosphorus and put them into a ball mill jar. Then add 180g of ball milling beads of different sizes. After sealing the ball mill jar in a glove box filled with nitrogen, ball mill it at 700 rpm for 6 hours to obtain a mixture of silicon-based material with reduced size and black phosphorus (containing two-dimensional nano black phosphorus sheets).

[0089] Step S2: Then, add 10g of asphalt, 10mL of anhydrous ethanol and 10mL of water to the ball milling jar in step S1. Seal the ball milling jar in a nitrogen glove box and ball mill for 4 hours at a speed of 400rpm to coat the surface of the silicon-based material with the initial shell layer, and obtain a viscous intermediate material.

[0090] Step S3: Spray dry the intermediate material to obtain precursor powder;

[0091] Step S4: Place the precursor powder into a tube furnace and calcine it at 700°C for 6 hours under nitrogen protection at a rate of 5°C / min. After restoring to room temperature, remove the powder to obtain the silicon-based anode material.

[0092] Example 2

[0093] This embodiment provides a silicon-based anode material and its preparation method.

[0094] A silicon-based anode material comprises a SiO core and a shell layer formed of black phosphorus and carbon materials with an alternating stacked and interlocked composite structure coating the surface of the SiO core. The silicon-based anode material has a secondary particle size (D50 particle size) of 6.2 μm and a specific surface area of ​​8.5 m². 2 / g, the shell layer accounts for 30wt% of the total mass of the silicon-based anode material (the carbon yield of the resin is calculated as 70%), the carbon material accounts for 93.3wt% of the total mass of the shell layer, the thickness of the shell layer is 23nm, and the D50 particle size of the SiO core is 270nm.

[0095] A method for preparing a silicon-based anode material includes the following steps:

[0096] Step S1: Weigh 35g of silicon-based material (SiO powder) and 1g of black phosphorus and put them into a ball mill jar. Then add 200g of ball milling beads of different sizes. After sealing the ball mill jar in a glove box filled with nitrogen, ball mill it at 900 rpm for 6 hours to obtain a mixture of silicon-based material with reduced size and black phosphorus (containing two-dimensional nano black phosphorus sheets).

[0097] Step S2: Then, add 20g of resin, 10mL of anhydrous ethanol and 15mL of water to the ball milling jar in step S1. Seal the ball milling jar in a nitrogen glove box and ball mill for 4 hours at a speed of 500rpm to coat the surface of the silicon-based material with the initial shell layer, and obtain a viscous intermediate material.

[0098] Step S3: Spray dry the intermediate material to obtain precursor powder;

[0099] Step S4: Place the precursor powder into a tube furnace and calcine it at 800°C for 4 hours under nitrogen protection at a rate of 5°C / min. After restoring to room temperature, remove the powder to obtain the silicon-based anode material.

[0100] Example 3

[0101] This embodiment provides a silicon-based anode material and its preparation method.

[0102] A silicon-based anode material comprises a SiO core and a shell layer formed of black phosphorus and carbon materials with an interlaced and interlocked composite structure coating the surface of the SiO core. The silicon-based anode material has a secondary particle size (D50 particle size) of 4.2 μm and a specific surface area of ​​23.7 m². 2 / g, the shell accounts for 80wt% of the total mass of the silicon-based anode material (the carbon yield of starch is calculated as 40%), the carbon material accounts for 70.6wt% of the total mass of the shell, the thickness of the shell is 78nm, and the D50 particle size of the SiO core is 156nm.

[0103] A method for preparing a silicon-based anode material includes the following steps:

[0104] Step S1: Weigh 4.25g of silicon-based material (SiO powder) and 5g of black phosphorus and put them into a ball mill jar. Then add 250g of ball milling beads of different sizes. After sealing the ball mill jar in a glove box filled with nitrogen, ball mill it at 900 rpm for 8 hours to obtain a mixture of silicon-based material with reduced size and black phosphorus (containing two-dimensional nano black phosphorus sheets).

[0105] Step S2: Then, add 30g of starch, 10mL of anhydrous ethanol and 10mL of water to the ball milling jar in step S1. Seal the ball milling jar in a nitrogen glove box and ball mill for 6 hours at a speed of 500rpm to coat the surface of the silicon-based material with an initial shell layer, and obtain a viscous intermediate material.

[0106] Step S3: Spray dry the intermediate material to obtain precursor powder;

[0107] Step S4 is the same as step S4 in Example 2, to obtain the silicon-based anode material.

[0108] Example 4

[0109] This embodiment provides a silicon-based anode material and its preparation method.

[0110] A silicon-based anode material comprises a SiO core and a shell layer formed of black phosphorus and carbon materials with an alternating stacked and interlocked composite structure coating the surface of the SiO core. The silicon-based anode material has a secondary particle size (D50 particle size) of 4.3 μm and a specific surface area of ​​21.5 m². 2 / g, the shell accounts for 48.7wt% of the total mass of silicon-based anode material (the carbon yield of polyvinylpyrrolidone is calculated as 67%), carbon material accounts for 70.5wt% of the total mass of the shell, the shell thickness is 40nm, and the D50 particle size of the SiO core is 170nm.

[0111] A method for preparing a silicon-based anode material includes the following steps:

[0112] Step S1: Weigh 10g of silicon-based material (SiO powder) and 2.8g of black phosphorus and put them into a ball mill jar. Then add 280g of ball milling beads of different sizes. After sealing the ball mill jar in a glove box filled with nitrogen, ball mill it at 900 rpm for 8 hours to obtain a mixture of silicon-based material with reduced size and black phosphorus (containing two-dimensional nano black phosphorus sheets).

[0113] Step S2: Then, add 10g of polyvinylpyrrolidone, 10mL of anhydrous ethanol and 10mL of water to the ball milling jar from step S1. Seal the ball milling jar in a nitrogen glove box and ball mill for 6 hours at a speed of 500rpm to coat the surface of the silicon-based material with an initial shell layer, thus obtaining a viscous intermediate material.

[0114] Step S3: Spray dry the intermediate material to obtain precursor powder;

[0115] Step S4 is the same as step S4 in Example 2, to obtain the silicon-based anode material.

[0116] Example 5

[0117] This embodiment provides a silicon-based anode material and its preparation method.

[0118] A silicon-based anode material includes a SiO core and a shell layer formed by black phosphorus and carbon materials with an interlaced and interlocked composite structure covering the surface of the SiO core. The silicon-based anode material has a secondary particle size (D50 particle size) of 4.6 μm and a specific surface area of ​​20 m². 2 / g, the shell accounts for 80wt% of the total mass of silicon-based anode material (the carbon yield of pitch is calculated as 95%), carbon material accounts for 94.5wt% of the total mass of the shell, the thickness of the shell is 72nm, and the D50 particle size of the SiO core is 210nm.

[0119] A method for preparing a silicon-based anode material includes the following steps:

[0120] Step S1: Weigh 10g of silicon-based material (SiO powder) and 2.2g of black phosphorus and put them into a ball mill jar. Then add 180g of ball milling beads of different sizes. After sealing the ball mill jar in a glove box filled with nitrogen, ball mill it at 700 rpm for 6 hours to obtain a mixture of silicon-based material with reduced size and black phosphorus (containing two-dimensional nano black phosphorus sheets).

[0121] Step S2: Then, add 40g of asphalt, 30mL of anhydrous ethanol and 20mL of water to the ball milling jar from step S1. Seal the ball milling jar in a nitrogen glove box and ball mill for 4 hours at a speed of 700rpm to coat the surface of the silicon-based material with an initial shell layer, thus obtaining a viscous intermediate material.

[0122] Step S3: Spray dry the intermediate material to obtain precursor powder;

[0123] Step S4: Place the precursor powder into a tube furnace and calcine it at 1000℃ for 8 hours under nitrogen protection at a rate of 3℃ / min. After returning to room temperature, remove the powder to obtain the silicon-based anode material.

[0124] Comparative Example 1

[0125] This comparative example provides a silicon-based anode material and its preparation method.

[0126] A silicon-based anode material (SiO@BP composite material) has a secondary particle size (D50 particle size) of 3.8 μm and a specific surface area of ​​12 m². 2 / g.

[0127] A method for preparing a silicon-based anode material includes the following steps:

[0128] Step S1 is the same as step S1 in Example 1;

[0129] Step S2 is the same as step S2 in Example 1, except that no asphalt is added;

[0130] Step S3 is the same as step S3 in Example 1;

[0131] Step S4 is the same as step S4 in Example 1, to obtain the SiO@BP composite material.

[0132] Comparative Example 2

[0133] This comparative example provides a silicon-based anode material and its preparation method.

[0134] A silicon-based anode material (SiO@C ternary composite material) comprises a SiO core and a carbon layer coating the surface of the SiO core. The secondary particle size (D50 particle size) of this silicon-based anode material is 4.5 μm, and its specific surface area is 18.1 m². 2 / g.

[0135] A method for preparing a silicon-based anode material includes the following steps:

[0136] Step S1: Weigh 10g of silicon-based material (SiO powder), 10g of asphalt, 2g of asphalt, 10mL of anhydrous ethanol, and 10mL of water black phosphorus into a ball mill jar. Then add 180g of ball milling beads of different sizes. After sealing the ball mill jar in a glove box filled with nitrogen, ball mill for 4 hours at a speed of 400rpm to coat the surface of the silicon-based material with an initial shell layer, and obtain a viscous intermediate material.

[0137] Step S2: Spray dry the intermediate material to obtain precursor powder;

[0138] Step S3: Place the precursor powder into a tube furnace and calcine it at 700℃ for 6 hours under nitrogen protection at a rate of 5℃ / min. After returning to room temperature, remove the powder to obtain the SiO@C ternary composite material.

[0139] Performance testing

[0140] (1) Physical property characterization

[0141] The silicon-based anode material prepared in Example 1 was subjected to X-ray diffraction (XRD) analysis, and the results are as follows: Figure 2 As shown. From Figure 2 As can be seen from the XRD pattern, there are four phases: SiO, Si, C, and black phosphorus. This indicates that the negative electrode material prepared in Example 1 is a SiO@BP@C ternary composite material.

[0142] (2) Electrochemical performance characterization

[0143] The silicon-based anode materials provided in Examples 1-5 and Comparative Examples 1-2 were assembled into CR2032 coin cells to evaluate their electrochemical performance. The coin cell fabrication process is as follows:

[0144] Negative electrode: The mass ratio of silicon-based negative electrode material, acetylene black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) is 80:10:4:6, where CMC is a 1 wt% aqueous solution. The slurry is stirred and dispersed. The stirred slurry is then uniformly coated onto a 15 μm thick copper foil. After natural air drying, the copper foil is placed in an 80℃ vacuum drying oven for 10 hours. The dried copper foil is then compacted using a roller press. The electrode is punched and cut into round pieces with a diameter of 13 mm, which are the negative electrode sheets.

[0145] Counter electrode: Lithium metal foil.

[0146] Separator: Polypropylene porous membrane.

[0147] Lithium-ion battery electrolyte: 1M LiPF6 and 5wt% fluoroethylene carbonate are added to a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate in a volume ratio of 1:1:1.

[0148] Assembly of button batteries: Lithium-ion batteries are assembled in a glove box protected by high-purity argon gas, following the assembly sequence of lithium metal foil-separator-electrolyte-negative electrode.

[0149] The batteries containing silicon-based anode materials provided in Examples 1 to 5 are referred to as Examples S1 to S5, and the batteries containing silicon-based anode materials in Comparative Examples 1 to 2 are referred to as Comparative Examples DS1 to DS2.

[0150] The coin cell battery assembled in Example S1 was subjected to a constant current charge-discharge test from 0 to 2.0V, with a current of 0.1C. The results are as follows. Figure 3 As shown. From Figure 3 As can be seen from the example, the lithium secondary battery composed in Example S1 has an initial discharge specific capacity of 1498 mAh / g, a charge specific capacity of 1268 mAh / g, and a coulombic efficiency of 84.6%.

[0151] In addition, the constant current charge-discharge test results of the lithium secondary battery containing the silicon-based anode material in Examples S2 to S5 were measured and... Figure 3 Approximately. Therefore, based on the capacity-voltage test results of the first charge and discharge, it can be seen that the silicon-based anode material of the present invention has high initial coulombic efficiency and specific capacity.

[0152] The electrochemical performance of the lithium secondary batteries composed of Examples S1-S5 and Comparative Examples DS1-DS2 was tested. After the coin cells were charged and discharged at a rate of 0.5C for 100 cycles, the relevant electrochemical performance test results of the lithium secondary batteries are shown in Table 1 below.

[0153] As can be seen from Table 1, the secondary battery containing the silicon-based anode material prepared in this embodiment has higher initial coulombic efficiency, initial charge-discharge specific capacity, and capacity retention rate than the comparative example.

[0154] Table 1 Test Results

[0155]

[0156] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A silicon-based anode material, characterized in that, The silicon-based anode material includes a core and a shell covering the core; wherein the core is made of silicon-based material, and the shell is made of black phosphorus and carbon material, wherein the black phosphorus and carbon material form an interleaved and embedded composite structure; in the shell, some of the black phosphorus is doped into the carbon material in the form of atomic clusters or single atoms; chemical bonds exist at the junction of the black phosphorus and the carbon material.

2. The silicon-based anode material as described in claim 1, characterized in that, The interlocking and inlaid composite structure includes: a type of structure in which a portion of the black phosphorus and the carbon material are interlocked and stacked, and another type of structure in which a portion of the black phosphorus is embedded in the carbon material to form an inlaid structure.

3. The silicon-based anode material as described in claim 1, characterized in that, The silicon-based material includes SiO₂. x Where 0 < x < 2; and / or The shell layer accounts for 30 wt% to 80 wt% of the total mass of the silicon-based anode material; and / or The carbon material accounts for 70 wt% to 95 wt% of the total mass of the shell; and / or The black phosphorus accounts for 5 wt% to 30 wt% of the total mass of the shell.

4. The silicon-based anode material according to any one of claims 1 to 3, characterized in that, The particle size of the core body satisfies: 50 nm ≤ D50 ≤ 300 nm; and / or The thickness of the shell is 10 nm to 100 nm; and / or The primary particle size of the silicon-based anode material satisfies: 0.05 μm ≤ D50 ≤ 0.7 μm, and the secondary particle size satisfies: 0.5 μm ≤ D50 ≤ 10 μm; and / or The specific surface area of ​​the silicon-based anode material is 8 m². 2 / g~30 m 2 / g.

5. The method for preparing the silicon-based anode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: We provide silicon-based materials, black phosphorus, carbon sources, and solvents. The silicon-based material, the black phosphorus, the carbon source, and the solvent are mixed and ground to coat the surface of the silicon-based material with an initial shell layer, thus obtaining an intermediate material. The intermediate material is subjected to drying and carbonization processes in sequence, so that the initial shell layer is formed with an interlaced and embedded composite structure, thus obtaining a silicon-based anode material.

6. The method for preparing the silicon-based anode material as described in claim 5, characterized in that, The step of mixing, grinding, and ball milling the silicon-based material, the black phosphorus, the carbon source, and the solvent includes: The silicon-based material and the black phosphorus are mixed and subjected to a first ball milling process to obtain a mixture; The mixture is then combined with the carbon source and the solvent for a second ball milling process.

7. The method for preparing the silicon-based anode material as described in claim 6, characterized in that, The first ball milling process is performed at a rotation speed of 500 rpm to 1000 rpm for 3 h to 12 h, with a ball-to-material ratio of 15 to 20:1; and / or The second ball milling process is performed at a rotation speed of 300 rpm to 700 rpm for a duration of 3 h to 6 h; and / or The mass ratio of the carbon source to the silicon-based material is 1~15:1; and / or The mass ratio of the silicon-based material to the black phosphorus is 2~5:1; and / or The carbonization treatment is carried out at a temperature of 500℃ to 1000℃ for a time of 2 h to 12 h; and / or The heating rate of the carbonization process is 1 ℃ / min ~ 5 ℃ / min.

8. A negative electrode, comprising a current collector and a negative electrode active layer bonded to the surface of the current collector, characterized in that, The negative electrode active layer contains the silicon-based negative electrode material as described in any one of claims 1 to 4, or the silicon-based negative electrode material prepared by the method described in any one of claims 5 to 7.

9. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode is the negative electrode as described in claim 8.

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