Silicon-carbon negative electrode material, preparation method thereof, negative electrode sheet and electrochemical device

Abstract

The application relates to the technical field of batteries, and discloses a silicon-carbon negative electrode material, a preparation method of the silicon-carbon negative electrode material, a negative electrode sheet and an electrochemical device. The silicon-carbon negative electrode material comprises: a porous carbon base body, wherein a pore size distribution curve of the porous carbon base body exists I A peak, I B peak and I C peak in 0.1 nm-2 nm, 2 nm-4 nm and 4 nm-10 nm respectively, and a peak intensity ratio satisfies 0.2<=I A / I B <=1.5 and I c / I B <=0.5; nano silicon, the nano silicon being at least partially located in pores of the porous carbon base body; and a carbon coating layer, the carbon coating layer wrapping at least part of a surface of the porous carbon base body. The silicon-carbon negative electrode material has excellent specific capacity and cycle characteristics.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to silicon-carbon anode materials and their preparation methods, anode sheets, and electrochemical devices. Background Technology

[0002] With the increasing prominence of global environmental and energy issues, the vigorous development of new energy sources has become an inevitable trend. Lithium-ion batteries, as a clean and renewable secondary energy source, have received increasing attention and application. Traditional graphite materials used as anode materials in lithium-ion batteries have a relatively low theoretical specific capacity (372 mAh / g). In contrast, silicon-carbon materials can achieve a specific capacity of up to 4200 mAh / g, making them an ideal anode material for next-generation lithium-ion batteries. However, silicon-carbon materials experience significant volume expansion (over 300%) during lithium insertion / extraction, which can cause particle breakage and pulverization. This reduces the electrical contact between the anode material and the electrode in lithium-ion batteries, leading to the cyclic rupture and formation of the solid electrolyte interphase (SEI) membrane, continuously consuming active lithium ions, and consequently reducing coulombic efficiency and battery cycle life, among other problems, hindering their large-scale application.

[0003] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0004] In a first aspect, this application proposes a silicon-carbon anode material, comprising: a porous carbon matrix, wherein the pore size distribution curve of the porous carbon matrix exhibits I0 in the ranges of 0.1 nm to 2 nm, 2 nm to 4 nm, and 4 nm to 10 nm, respectively. A Peak, I B Peak, I C The peak intensity ratio satisfies: 0.2 ≤ I A / I B ≤1.5, I c / I B ≤0.5; nano-silicon, at least partially located within the pores of the porous carbon matrix; carbon coating layer, the carbon coating layer covering at least a portion of the surface of the porous carbon matrix.

[0005] In some embodiments, the silicon-carbon anode material satisfies at least one of the following conditions: the specific surface area of ​​the porous carbon matrix is ​​1000 m². 2 / g~2100m 2 / g; Pore volume V of the porous carbon matrix p ≥0.45cm 3 / g; the micropore size of the porous carbon matrix satisfies 0.1nm ≤ mic < 2nm, and the micropore volume is V. mic 0.2≤V mic / V p ≤0.8; the mesopore diameter of the porous carbon matrix satisfies 2nm≤mes<4nm, and the mesopore volume is V. mes 0.2≤V mes / V p ≤0.8.

[0006] In some embodiments, the D of the porous carbon matrix V 50 represents n, and the silicon-carbon anode material D V 50 represents N, where 3μm≤n≤15μm, 3μm≤N≤15μm, and Nn≤2μm.

[0007] In some embodiments, the silicon-carbon anode material satisfies at least one of the following conditions: the mass percentage of nano-silicon in the silicon-carbon anode material is 20% to 60%; the compressive strength of nano-silicon in the silicon-carbon anode material is greater than or equal to 100 MPa.

[0008] In a second aspect of this application, a method for preparing a silicon-carbon anode material is proposed, comprising: carbonizing a carbon source material to obtain a first intermediate, wherein the carbonization temperature is 500℃~800℃ and the holding time of the carbonization is 0.5h~4h; sieving the first intermediate to obtain a second intermediate; activating the second intermediate to obtain a porous carbon matrix; and performing vapor deposition on the porous carbon matrix to deposit nano-silicon in at least a portion of the pores of the porous carbon matrix to obtain the silicon-carbon anode material.

[0009] In some embodiments, the activation medium for the activation treatment includes at least one of water vapor, carbon dioxide, and potassium hydroxide; and / or, the temperature of the activation treatment is 700℃~1200℃, and the holding time of the activation treatment is 4h~10h.

[0010] In some embodiments, the vapor deposition process includes silicon source deposition process and carbon source deposition process.

[0011] In some embodiments, the temperature of the silicon source deposition process is 400°C to 600°C.

[0012] In some embodiments, the concentration of silicon source gas in the silicon source deposition process is 5% to 45%.

[0013] In some embodiments, the temperature of the carbon source deposition process is 500°C to 650°C.

[0014] In some embodiments, the carbon source gas concentration in the carbon source deposition process is 5% to 45%.

[0015] In a third aspect of this application, a negative electrode sheet is provided, the negative electrode sheet comprising the silicon-carbon negative electrode material proposed in this application, or the silicon-carbon negative electrode material prepared by the method proposed in this application.

[0016] In a fourth aspect, this application provides an electrochemical device comprising the negative electrode sheet proposed in this application.

[0017] The beneficial effects of the technical solution proposed in this application include at least the following:

[0018] The silicon-carbon anode material proposed in this application optimizes the distribution and proportion of micropores and mesopores on the porous carbon matrix, forming a superior hierarchical porous structure. This structure, when effectively combined with nano-silicon, fully leverages the advantages of micropores and mesopores, promoting the structural bonding of the silicon-carbon anode material and improving energy density. Furthermore, the porous carbon matrix with a certain capacity of pore space effectively provides a "buffer space" for the expansion of nano-silicon during the charging and discharging process of lithium-ion batteries, reducing the risk of cracking due to internal stress changes. As an anode material for electrochemical devices, this silicon-carbon anode material is beneficial for improving the structural stability and electrochemical performance of electrochemical devices. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0020] Figure 1 This is a pore size distribution curve of the silicon-carbon anode material prepared in Example 2 of this application;

[0021] Figure 2 This is a SEM image of the silicon-carbon anode material prepared in Example 2 of this application;

[0022] Figure 3 This is a charge-discharge cycle diagram of an electrochemical device composed of silicon-carbon anode material prepared in Example 2 of this application. Detailed Implementation

[0023] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0024] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0025] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0026] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0027] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0028] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0029] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0030] The following explanation uses lithium-ion batteries as an example, with silicon-carbon anode materials serving as the active anode material. Silicon-carbon anode materials can be prepared via a vapor-phase method, which yields materials with high specific capacity, significantly improving the energy density of electrochemical devices. In this method, the porous carbon matrix primarily enhances conductivity and acts as a buffer against silicon expansion during charge and discharge. Silicon expands by 300% during charge and discharge. When excessive or large amounts of nano-silicon particles fill the small pores, the porous carbon matrix's ability to mitigate this expansion is limited, leading to poor cycle performance and even the risk of breakage, resulting in poor cycle performance and volume expansion.

[0031] In a first aspect, this application proposes a silicon-carbon anode material, comprising: a porous carbon matrix, wherein the pore size distribution curve of the porous carbon matrix exhibits I0 in the ranges of 0.1 nm to 2 nm, 2 nm to 4 nm, and 4 nm to 10 nm, respectively. A Peak, I B Peak, I C The peak intensity ratio satisfies: 0.2 ≤ I A / I B ≤1.5, I c / I B ≤0.5; nano-silicon, at least partially located within the pores of the porous carbon matrix; carbon coating layer, the carbon coating layer covering at least a portion of the surface of the porous carbon matrix.

[0032] This application proposes a silicon-carbon anode material. The basic framework of the silicon-carbon anode material is provided by a porous carbon matrix, and the pore structure of the porous carbon matrix is ​​characterized by the pore size distribution curve. The silicon-carbon anode material contains I... A Peak, I B Peak, I C Peaks, corresponding to their dominant pore sizes, can reflect the relative content and distribution uniformity of micropores (<2nm), mesopores (2nm~50nm), and macropores (>50nm) in porous carbon. A This represents the proportion of pore volume of the dominant pore size in the pore size range of 0~2nm, i.e., the proportion of micropore volume; I B This represents the volume percentage of the dominant pore size in the pore size range of 2nm to 4nm, i.e., the volume percentage of small-sized mesopores; I C This indicates the proportion of pore volume of the dominant pore size in the pore size range of 4nm to 10nm, i.e., the proportion of medium-sized mesopore volume.

[0033] Aperture distribution curve peak intensity ratio I A / I B It can reflect the ratio of micropores to small-sized mesopores in a porous carbon matrix, IC / I B This can reflect the ratio of medium-sized to small-sized mesopores in a porous carbon matrix, when 0.2 ≤ I A / I B ≤1.5, Ic / I B When the specific surface area is ≤0.5, the mesoporous silicon-carbon anode material has a suitable specific surface area and exhibits excellent structural stability and electrochemical performance.

[0034] The porous carbon matrix contains a certain proportion of small and medium-sized mesopores, providing pore space within the matrix for the deposition of nano-silicon. This pore space, with its sufficient capacity, effectively provides a "buffer space" for the expansion of nano-silicon during the charging and discharging process of lithium-ion batteries. This reduces the risk of cracking of the silicon-carbon anode material due to internal stress changes, lowers the occurrence of side reactions, reduces lithium-ion consumption, and improves the battery's cycle performance.

[0035] Furthermore, the relatively suitable mesopore size (2nm~10nm) is conducive to the rapid migration of lithium ions, which is beneficial to improving the rate performance and capacity retention of silicon-carbon anode materials.

[0036] Porous carbon matrix corresponds to I of micropore and small-sized mesopore diameter, respectively. A Peak, I B The peak satisfies: 0.2≤I A / I B With a micropore size ≤1.5, during vapor deposition, the small and medium-sized mesopores in the porous carbon matrix exhibit strong adsorption capacity for nano-silicon, resulting in high silicon deposition efficiency and improved energy density and coulombic efficiency of silicon-carbon anode materials. Furthermore, the ratio of micropores to small mesopores is relatively balanced, with nano-carbon deposited within some micropores. Additionally, some micropores can interact with the pores in the porous carbon matrix, providing a buffer against volume changes in nano-silicon during lithium-ion insertion / extraction. The influence of changes in the micropore structure satisfying the aforementioned ratio on the structural stability of the porous carbon matrix is ​​controllable, thus contributing to improved structural stability of silicon-carbon anode materials during cycling.

[0037] Porous carbon matrices correspond to I values ​​for small and medium-sized mesopore diameters, respectively. B Peak, I C Peak satisfies: I c / I BA value ≤0.5 indicates a low proportion of mesopores with diameters in the 4nm-10nm range within the porous carbon matrix, meaning a high content of small-sized mesopores. During vapor deposition, small-sized mesopores exhibit strong adsorption capacity for nano-silicon and, compared to medium-sized mesopores, have smaller pore volumes. This allows for better filling of the nano-silicon that decomposes at high temperatures, resulting in a suitable pore size after vapor deposition, which is beneficial for controlling the specific surface area of ​​the prepared silicon-carbon anode material. Consequently, this reduces electrolyte decomposition caused by the reaction between the silicon-carbon anode material and the electrolyte during the first cycle of lithium-ion batteries, thus improving the initial coulombic efficiency.

[0038] As an example, I A / I B The values ​​are 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.5, etc.

[0039] As an example, I c / I B =0.5, 0.4, 0.3, 0.2, 0.1, etc.

[0040] Furthermore, 0.2≤I c / I B ≤0.5

[0041] In some embodiments, the specific surface area of ​​the porous carbon matrix is ​​1000 m². 2 / g~2100m 2 / g.

[0042] The specific surface area of ​​porous carbon matrix is ​​1000~2100m². 2 When the specific surface area is / g, refer to Figure 2 This is beneficial for the rational distribution of nano-silicon particles and provides a certain buffer space for silicon volume changes during charging and discharging, reducing the impact of nano-silicon volume changes on the silicon-carbon anode material structure, and improving the cycle performance of lithium-ion batteries.

[0043] Porous carbon matrix with a specific surface area greater than 2100 m² 2 When the specific surface area is too large (e.g., m² / g), there is a sufficient area for depositing silicon nanoparticles. However, these nanoparticles may preferentially deposit in the external pores of the porous carbon matrix, thus blocking the deposition channels and preventing some internal pores from being completely filled. This internal porosity results in a loose structure and low compaction density in the vapor-phase silicon-carbon anode material. During long-term charge-discharge processes, repeated expansion and contraction can easily lead to structural collapse and fragmentation, reducing the material's energy density and cycle performance. When the specific surface area of ​​the porous carbon matrix is ​​less than 1000 m² / g... 2 At a density of / g, the porous carbon matrix has too small an area to accommodate the deposition of nano-silicon particles, resulting in a low silicon content per unit volume, which leads to a decrease in the capacity and energy density of the silicon-carbon anode material.

[0044] As an example, the specific surface area of ​​the porous carbon matrix is ​​1000 m². 2 / g、1300m 2 / g, 1500m 2 / g、1700m 2 / g、2000m 2 / g、2100m 2 / g etc.

[0045] In some embodiments, the pore volume V of the porous carbon matrix p ≥0.45cm 3 / g.

[0046] Pore ​​volume is the total volume of pores per unit mass of porous carbon matrix. The pore volume Vp of a porous carbon matrix is ​​≥ 0.45 cm³. 3 At a density of / g, the porous carbon matrix possesses a suitable pore volume, resulting in silicon-carbon anode materials with high energy density. For the same volume, there is ample space for the deposition of nano-silicon particles, leading to a higher silicon content per unit volume. This is beneficial for improving the capacity and energy density of vapor-phase silicon-carbon anode materials.

[0047] As an example, the pore volume of the porous carbon matrix is ​​0.45 cm³. 3 / g, 0.65cm 3 / g, 0.80 cm 3 / g, 0.85cm 3 / g, 0.91cm 3 / g, 0.99 cm 3 / g.

[0048] In some embodiments, the micropore size of the porous carbon matrix satisfies 0.1 nm ≤ mic < 2 nm, and the micropore volume is V. mic 0.2≤V mic / V p ≤0.8.

[0049] The porous carbon matrix has a pore size of 0.1 nm to 2 nm and a pore volume of V. mic V mic / V p The microporosity refers to the proportion of micropores in the porous carbon matrix. Within the aforementioned range, the proportion of micropores in the porous carbon matrix is ​​beneficial for increasing the specific surface area of ​​the porous carbon matrix and for inhibiting the crystal growth of vapor-deposited nano-silicon, thus promoting the formation of a stable amorphous structure and improving the energy density and coulombic efficiency of lithium-ion batteries.

[0050] In some embodiments, the mesopore size of the porous carbon matrix satisfies 2nm ≤ mes < 4nm, and the mesopore volume is V. mes 0.2≤Vmes / V p ≤0.8.

[0051] The porous carbon matrix has a pore size of 2 nm to 4 nm and a pore volume of V. mes V mes / V p The mesoporosity is defined as the ratio of the porous carbon matrix in the silicon-carbon anode material to the aforementioned ratio. When this ratio is met, the silicon-carbon anode material exhibits excellent cycle performance and rate capability. When the mesoporosity V... mes / V p When the mesopore content is <0.2, the buffering effect of the silicon-carbon anode material obtained after vapor deposition of nano-silicon is limited during charge and discharge. The material is prone to structural damage due to the volume expansion of nano-silicon during charge and discharge, resulting in impaired cycle performance. When the mesopore content V... mes / V p When the content is greater than 0.8, the mesoporous content is too high. The nano-silicon decomposed at high temperature during the vapor deposition process cannot completely fill the pores. After the vapor deposition is completed, a large pore volume remains. The specific surface area of ​​the prepared silicon-carbon anode material is too large. During the charge and discharge process, it will aggravate the decomposition of the electrolyte in the lithium-ion battery during the first cycle, resulting in a lower first coulombic efficiency.

[0052] In some embodiments, the D of the porous carbon matrix V 50 represents n, and the silicon-carbon anode material D V 50 represents N, where 3μm≤n≤15μm, 3μm≤N≤15μm, and Nn≤2μm.

[0053] The particle size of silicon-carbon anode materials and the D of porous carbon matrix V 50. Under the aforementioned conditions, nano-silicon can be deposited relatively uniformly in the pores of the porous carbon matrix, reducing the decrease in deposition uniformity of silicon-carbon anode materials caused by the agglomeration of some fine porous carbon matrix particles. This is beneficial to improving the performance stability and cycle performance of silicon-carbon anode materials. When Nn > 2 μm in mesoporous silicon-carbon anode materials, it indicates that a large number of nano-silicon particles are deposited on the surface of the porous carbon matrix, forming a silicon layer on the surface. The accumulation of this silicon layer on the surface leads to an increase in the surface roughness of silicon-carbon anode materials prepared by the vapor phase method. During long-term charge and discharge, the nano-silicon particles on the surface of the mesoporous carbon anode material will consume a large amount of lithium ions in the electrolyte, generating a solid electrolyte interphase (SEI) film. The volume expansion and contraction of nano-silicon particles during lithium insertion and extraction will cause the SEI film to rupture, and then a new SEI film will form at the rupture site. In this repeated film formation process, a new SEI film is formed at the newly formed cracks. The repeated formation of SEI films increases the consumption of lithium ions, thereby reducing the electrochemical performance of silicon-carbon anode materials.

[0054] D of porous carbon matrix VWhen 50 < 3 μm, the porous carbon matrix contains a large number of fine particles. During the preparation of silicon-carbon anode materials, these fine particles are easily blown out of the fluidized bed reactor by the carrier gas, leading to material mass loss and uneven material deposition. Furthermore, these fine particles are prone to agglomeration during deposition, resulting in poor cycle performance of lithium-ion batteries based on vapor-phase silicon-carbon anode materials. The D50 of the porous carbon matrix... V When the Dv50 of the mesoporous silicon-carbon anode material exceeds 15 μm, the resulting particles are too large, accommodating a large number of nano-silicon particles. This leads to a greater space required for the expansion of these particles during charge and discharge, resulting in higher stress on the overall silicon-carbon material particles and a risk of particle loosening. Loose particles have weaker charge storage capacity, leading to capacity decay and poorer cycle performance in lithium-ion batteries. Furthermore, an excessively large Dv50 in the mesoporous silicon-carbon anode material also results in a longer lithium-ion diffusion path, increased diffusion resistance, and increased concentration polarization, reducing the low-temperature performance and discharge capacity of the lithium-ion battery. The goal of preparing mesoporous silicon-carbon anode materials is to deposit nano-sized silicon particles into the pores of a porous carbon matrix. The framework of the porous carbon matrix helps mitigate the volume expansion of silicon particles during charge and discharge; therefore, it is crucial to minimize the deposition of silicon particles on the surface of the porous carbon matrix.

[0055] In some embodiments, the silicon mass percentage of the silicon-carbon anode material is 20% to 60%.

[0056] In the mesoporous silicon-carbon anode material, the silicon mass percentage is within the aforementioned range. The nano-silicon, filled through vapor deposition, is mainly distributed within the pores of the porous carbon matrix, while retaining some unfilled space as a buffer against silicon volume changes. This improves the stability of the silicon-carbon anode material during lithium-ion insertion / extraction and achieves higher energy density. However, excessively high silicon content (e.g., above 60%) exacerbates volume changes during charge / discharge, and the expansion of nano-silicon leads to structural damage to the porous carbon matrix. Furthermore, excessive silicon deposition tends to form a silicon layer on the surface of the porous carbon matrix. This silicon layer buildup increases the surface roughness of the vapor-deposited silicon-carbon anode material, making it prone to volume expansion during charge / discharge and causing a sharp decline in the cycle performance of the lithium-ion battery. Conversely, excessively low silicon content (e.g., below 20%) severely reduces the energy density of the lithium-ion battery.

[0057] As an example, the mass percentage of nano-silicon in silicon-carbon anode materials is 20%, 30%, 40%, 45%, 50%, 55%, and 60%.

[0058] In some embodiments, the crushing strength of the nano-silicon in the silicon-carbon anode material is greater than or equal to 100 MPa. Crushing strength is the maximum pressure that nano-silicon can withstand when it breaks or suffers structural damage due to external compression. Nano-silicon within the aforementioned range exhibits good resistance to particle breakage caused by volume changes during charging and discharging.

[0059] In a second aspect of this application, a method for preparing a silicon-carbon anode material is proposed, comprising: carbonizing a carbon source material to obtain a first intermediate, wherein the carbonization temperature is 500℃~800℃ and the holding time of the carbonization is 0.5h~4h; sieving the first intermediate to obtain a second intermediate; activating the second intermediate to obtain a porous carbon matrix; and performing vapor deposition on the porous carbon matrix to deposit nano-silicon in at least a portion of the pores of the porous carbon matrix to obtain the silicon-carbon anode material.

[0060] The method proposed in this application can prepare a porous carbon matrix with the superior pore distribution described herein, and then perform effective vapor deposition treatment on it to achieve relatively uniform deposition of nano-silicon within the pores of the porous carbon matrix. Therefore, this method can prepare silicon-carbon anode materials with high specific capacity and superior cycle performance.

[0061] In some embodiments, the screening process employs an air classifier. This facilitates the screening to obtain second intermediate particles of suitable size, thereby improving the efficiency of subsequent activation treatment.

[0062] In some embodiments, the activation medium for the activation treatment includes at least one of water vapor, carbon dioxide, and potassium hydroxide; and / or, the activation temperature is 700℃~1200℃, and the holding time for the activation treatment is 4h~10h. Under the aforementioned activation conditions, a relatively uniformly distributed pore structure is formed on the prepared porous carbon matrix, with an appropriate pore volume and a pore capacity sufficient to accommodate a suitable amount of nano-silicon, which is beneficial for the deposition of nano-silicon. Simultaneously, the control of these activation conditions can improve the stability of the pore structure, thereby improving the capacity retention rate of the prepared silicon-carbon anode material.

[0063] In some embodiments, the vapor deposition process includes silicon source deposition process and carbon source deposition process.

[0064] In some embodiments, the temperature of the silicon source deposition treatment is 400℃~600℃; the silicon source gas concentration of the silicon source deposition treatment is 5%~45%; the temperature of the carbon source deposition treatment is 500℃~650℃; and the carbon source gas concentration of the carbon source deposition treatment is 5%~45%. This facilitates the transformation of the silicon source into nano-silicon, which is deposited within the pores of the porous carbon matrix, forming a silicon-carbon anode material with a certain silicon expansion buffer space.

[0065] In some embodiments, the method further includes: crushing the porous carbon matrix. The crushing process includes air jet milling and air jet mill classification and sieving. This facilitates further optimization of the particle size of the porous carbon matrix and improves its particle size distribution.

[0066] In a third aspect of this application, a negative electrode sheet is proposed, comprising the silicon-carbon negative electrode material proposed in this application, or the silicon-carbon negative electrode material prepared by the method proposed in this application.

[0067] The negative electrode includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer contains a negative electrode active material, which includes a silicon-carbon negative electrode material prepared by the method proposed in this application.

[0068] As an example, the negative current collector includes copper foil.

[0069] In some embodiments, the mass percentage of silicon-carbon anode material is 80% to 96% based on the total mass of the anode film; further, the mass percentage of silicon-carbon anode material is 85%.

[0070] In some embodiments, the active film layer further includes a binder and a conductive agent.

[0071] In some embodiments, the adhesive includes one or more of carboxymethyl cellulose, polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile, polysiloxane, polystyrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.

[0072] In some embodiments, the mass percentage of the binder is 2% to 10% based on the total mass of the negative electrode film; further, the mass percentage of the binder is 7.5%.

[0073] In some embodiments, the conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, vapor-grown carbon fibers, carbon nanofibers, conductive carbon black, acetylene black, conductive graphite, or graphene.

[0074] In some embodiments, the mass percentage of the conductive agent is 2% to 10% based on the total mass of the negative electrode film; further, the mass percentage of the conductive agent is 7.5%.

[0075] In a fourth aspect of this application, an electrochemical device is proposed, the electrochemical device comprising the negative electrode sheet proposed in this application.

[0076] In some embodiments, the electrochemical device includes a lithium-ion battery.

[0077] In some embodiments, an electronic device including the aforementioned negative electrode or an electronic device including the aforementioned electrochemical device is also provided. As an example, the electronic device may include any electronic device that uses a rechargeable battery, such as a mobile phone, tablet computer, or charger.

[0078] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0079] Example 1

[0080] S1: Preparation of porous carbon matrix

[0081] Phenolic resin was placed in a high-temperature sintering equipment as a carbon source material, and the equipment temperature was raised to 780℃ and held for 2 hours for carbonization treatment to obtain the first intermediate.

[0082] The first intermediate was sieved to obtain a second intermediate with a particle size of 2μm~60μm;

[0083] The second intermediate was placed in a rotary kiln for activation treatment. Water vapor was introduced, the temperature was raised to 1100℃, and the temperature was held for 8 hours to obtain a porous carbon matrix.

[0084] The porous carbon matrix was placed in an air jet mill for crushing to obtain a particle size D. V A porous carbon matrix with a diameter of 50 μm and a diameter of 7 μm; further demagnetization treatment can be performed.

[0085] The pore size distribution curve of the porous carbon matrix thus prepared has a peak intensity ratio I A / I B =1.1, Ic / I B =0.4, mesoporous ratio V mes / V p =0.55. Specific surface area is 1200 m². 2 / g,D V 50 has a pore size of 7 μm and a pore volume of 0.82 cm³. 3 / g.

[0086] S2: Preparation of silicon-carbon anode materials by vapor phase method

[0087] The prepared 1.2 kg porous carbon matrix was placed in a fluidized bed apparatus for vapor deposition. The air in the apparatus was replaced with argon. The fluidized bed was heated to 480°C, and a mixed gas (silane gas flow rate of 2 L / min and argon gas flow rate of 18 L / min) was introduced into the fluidized bed at a gas flow rate of 20 L / min.

[0088] In the prepared silicon-carbon anode material, the mass content of deposited nano-silicon is 45%, the mass content of porous carbon matrix is ​​55%, and the average volume particle size Dv50 of silicon-carbon anode material is 7.4 μm.

[0089] Examples 2 to 6 and Comparative Examples 1 to 3

[0090] The operations of the remaining embodiments and comparative examples are the same as those in Embodiment 1, and the changes in their experimental parameters are shown in Table 1.

[0091] Table 1

[0092]

[0093] Test method:

[0094] 1. Pore structure testing of silicon-carbon anode materials

[0095] The silicon-carbon anode material is thoroughly mixed with a 2 mol / L NaOH alkaline solution and heated under reflux (temperature set at 60℃~100℃). The silicon in the silicon-carbon anode material can react with NaOH to form soluble silicates. The reaction formula is: Si + 2NaOH + H2O = Na2SiO3 + 2H2. After the reaction is complete, the mixture is filtered. The residual solid is washed with deionized water to remove the attached residual alkali and silicates. The residual solid is the mesoporous carbon material.

[0096] After the obtained silicon-carbon anode material was thoroughly dried, the pore structure was tested using a fully automated surface area and porosity analyzer (BET). The equipment model was Micromeritics ASAP 2460 from the USA.

[0097] 2. Electrical performance testing

[0098] 1) Preparation of negative electrode sheet

[0099] The silicon-carbon material, conductive carbon black, and binder prepared above were added to deionized water at a mass ratio of 85:7.5:7.5 to prepare a slurry with a solid content of 40%. This slurry was then uniformly coated onto the surface of a 9 μm thick copper current collector foil. After drying at 80°C for 12 hours, the foil was rolled to obtain a negative electrode sheet with a single-sided coating of negative electrode material layer and a coating thickness of 150 μm. The electrode sheet was then cut into 14 mm diameter discs for later use. A lithium foil was used as the counter electrode.

[0100] 2) Preparation of electrolyte

[0101] In a dry argon atmosphere, the organic solvents ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC = 1:1. Lithium hexafluorophosphate (LiPF6) was then added to the mixed organic solvent, dissolved, and mixed thoroughly to obtain a mixed solution with a lithium salt concentration of 1 mol / L. Based on the volume of the above mixed solution, 5% (v / v) of fluoroethylene carbonate (FEC) was added as an additive to obtain an electrolyte containing the additive.

[0102] 3) Preparation of diaphragm, negative electrode shell, spring plate, gasket and positive electrode shell

[0103] The separator is made of polyethylene (PE) / polypropylene (PP) film with a thickness of 15μm. The negative electrode shell, spring sheet, gasket and positive electrode shell are accessories of CR2025 battery model. All of the above materials are commercially available.

[0104] 4) Assembly of lithium-ion batteries

[0105] The prepared negative electrode sheets were stacked in an argon-atmospheric glove box in the following order: negative electrode shell, spring sheet, gasket, lithium sheet, separator, negative electrode sheet, and positive electrode shell. Electrolyte was injected, and the battery was then packaged to obtain a CR2025 coin cell lithium-ion battery. Charge-discharge tests were performed on the battery using the Blue Electric series battery testing system. First, the battery was discharged to 0V at 0.05C, allowed to stand for 3 minutes, then discharged to 0V at 50μA, and allowed to stand for another 3 minutes. Then, it was discharged to 0V at 10μA to obtain the initial lithium insertion capacity of the silicon-carbon material. Next, the battery was charged to 2V at 0.05C to obtain the initial lithium extraction capacity. The ratio of the initial lithium extraction capacity to the lithium insertion capacity is the initial coulombic efficiency.

[0106] Test results:

[0107] The test parameters of the porous carbon matrix in the silicon-carbon anode material are shown in Table 2.

[0108] Table 2

[0109]

[0110] The electrical performance test results of lithium-ion batteries prepared with silicon-carbon anode materials are shown in Table 3.

[0111] Table 3

[0112]

[0113] As can be seen from the performance comparison results of lithium-ion batteries in the examples and comparative examples in Table 3, the silicon-carbon anode material prepared in the examples includes a porous carbon matrix and nano-silicon particles within the pores of the vapor-deposited mesoporous carbon. By controlling the process of preparing the porous carbon matrix and controlling the peak intensity ratio of the pore size distribution curve, the pore size distribution curve of the porous carbon matrix exhibits I values ​​in the 0~2nm, 2~4nm, and 4~10nm ranges. A Peak, I B Peak, I C Peak, when the peak intensity ratio of the aperture distribution curve is 0.2 ≤ I A / I B ≤1.5, Ic / I B When the concentration is ≤0.5, it can significantly improve the electrochemical performance and structural strength of mesoporous silicon-carbon anode materials.

[0114] Figure 1 This is a pore size distribution curve of the silicon-carbon anode material prepared in Example 2, where I A / I B =0.8, Ic / I B =0.3, which is within the range of 0.2≤I A / I B ≤1.5, Ic / I B Within the range of ≤0.5, it exhibits excellent electrochemical performance and structural strength, with an initial coulombic efficiency of over 84% at 0.8V, and still retains a capacity retention rate of up to 87% after 200 cycles. By controlling the pore size distribution of the porous carbon matrix, the combined advantages of micropores and mesopores can be fully utilized to increase the capacity and improve the coulombic efficiency of silicon-carbon anode materials. Figure 3 This is a charge-discharge cycle diagram of a lithium-ion battery composed of silicon-carbon anode material prepared in Example 2.

[0115] In Comparative Example 1, by adjusting the activation temperature and activation time during the preparation of mesoporous carbon, the pore size and mesopore content of the prepared porous carbon matrix increased, wherein I A / I B =0.15, Ic / I B =0.5, the porosity increases in the 2~4nm and 4~10nm ranges, and there are also relatively more internal defects, which leads to a decrease in the crush strength of the material. During the battery preparation process, it is easy to break due to external forces, resulting in a deterioration in electrochemical performance. At the same time, during the vapor deposition process, the medium-sized mesopores have a weak adsorption capacity for nano-silicon, and the medium-sized mesopores have a large volume, making it difficult for the nano-silicon decomposed at high temperature to completely fill them. After the vapor deposition is completed, there is still a large pore volume left, resulting in a large specific surface area of ​​the silicon-carbon anode material. During the charge and discharge process, it will aggravate the decomposition of the electrolyte in the first cycle of the electrochemical device, resulting in a lower initial coulombic efficiency.

[0116] In Comparative Example 2, by adjusting the porous carbon matrix preparation process, the peak intensity ratio I of the pore size distribution curve was obtained. A / I B =0.15, Ic / I B Mesoporous carbon with a density of 0.5 nm, in which micropores with a diameter of less than 2 nm constitute the vast majority of the porous carbon matrix, and the material has a specific surface area as high as 1900 m². 2 With a silicon content exceeding 60%, silicon nanoparticles can accommodate a larger amount of silicon particles during vapor deposition. During deposition, some nano-silicon particles are deposited on the material surface, leading to the formation of a crystalline silicon layer. During charge and discharge, the lack of a porous carbon framework causes repeated formation and rupture of the SEI film due to volume expansion during charging and discharging. This results in significant lithium ion consumption in the electrolyte, drastically reducing the material's cycle performance and affecting the electrochemical performance of the electrochemical device. Simultaneously, the strong adsorption capacity of micropores for nano-silicon during vapor deposition leads to a large number of nano-sized silicon particles filling the micropores. In silicon-carbon anode materials, the carbon precursor framework primarily acts as a buffer against silicon expansion during charging and discharging. Silicon undergoes a 300% volume expansion during charging and discharging. When excessive silicon particles fill the small-pore micropores, the porous carbon matrix's ability to mitigate this volume expansion is limited, resulting in poorer cycle performance and an increased risk of rupture.

[0117] In Comparative Example 3, the activation temperature during the preparation of the porous carbon matrix was too low, resulting in a small pore volume in the prepared porous carbon matrix, a small space available for the deposition of nano-silicon particles, and a low silicon content per unit volume. This led to a decrease in the capacity and energy density of the vapor-phase silicon-carbon anode material.

[0118] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0119] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0120] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0121] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A silicon-carbon anode material, characterized in that, include: A porous carbon matrix, wherein the pore size distribution curves of the porous carbon matrix exhibit I values ​​in the ranges of 0.1 nm to 2 nm, 2 nm to 4 nm, and 4 nm to 10 nm, respectively. A Peak, I B Peak, I C The peak intensity ratio satisfies: 0.3 ≤ I A / I B ≤1.3, 0.1≤I c / I B ≤0.4; Nano-silicon, wherein the nano-silicon is at least partially located within the pores of the porous carbon matrix; A carbon coating layer that covers at least a portion of the surface of the porous carbon matrix. The pore volume V of the porous carbon matrix p Satisfying: 0.45cm 3 / g≤V p ≤0.92cm 3 / g; The pore size mic of the micropores in the porous carbon matrix satisfies 0.1nm ≤ mic < 2nm, and the volume of the micropores is V. mic 0.2≤V mic / V p ≤0.8; The specific surface area of ​​the porous carbon matrix is ​​1100 m². 2 / g~1800m 2 / g; The pore size mesopores of the porous carbon matrix satisfy 2nm ≤ mesopores < 4nm, and the volume of the mesopores is V. mes 0.23≤V mes / V p ≤0.75; The porous carbon matrix D V 50 represents n, and the silicon-carbon anode material D V 50 represents N, where 3μm≤n≤15μm, 3μm≤N≤15μm, and Nn≤2μm; The mass percentage of nano-silicon in the silicon-carbon anode material is 45% to 55%.

2. The silicon-carbon anode material according to claim 1, characterized in that, The compressive strength of the nano-silicon in the silicon-carbon anode material is greater than or equal to 100 MPa.

3. A method for preparing the silicon-carbon anode material according to claim 1 or 2, characterized in that, include: The carbon source material is carbonized to obtain a first intermediate. The carbonization temperature is 500℃~800℃ and the holding time of the carbonization is 0.5h~4h. The first intermediate is sieved to obtain the second intermediate; The second intermediate was activated to obtain a porous carbon matrix; The porous carbon matrix is ​​subjected to vapor phase deposition treatment, which includes silicon source deposition treatment and carbon source deposition treatment, to obtain the silicon-carbon anode material.

4. The method according to claim 3, characterized in that, The activation medium for the activation treatment includes at least one of water vapor, carbon dioxide, and potassium hydroxide; and / or, The activation treatment temperature is 700℃~1200℃, and the activation treatment holding time is 4h~10h.

5. The method according to claim 3, characterized in that, At least one of the following conditions must be met: The temperature for the silicon source deposition process is 400℃~600℃; The concentration of silicon source gas in the silicon source deposition process is 5%~45%; The temperature for the carbon source deposition treatment is 500℃~650℃; The carbon source gas concentration in the carbon source deposition process is 5% to 45%.

6. A negative electrode sheet, characterized in that, Includes the silicon-carbon anode material according to any one of claims 1 to 2, or the silicon-carbon anode material prepared by the method according to any one of claims 3 to 5.

7. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in claim 6.

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