Silicon-carbon composite material and preparation method thereof, secondary battery and electric device

Abstract

The invention provides a silicon-carbon composite material and a preparation method thereof, a secondary battery and an electric device. The silicon-carbon composite material comprises silicon-carbon secondary particles, the silicon-carbon secondary particles comprise silicon-carbon primary particles and a one-dimensional conductive agent, and the one-dimensional conductive agent is distributed among the silicon-carbon primary particles. The silicon-carbon composite material has excellent electron transmission performance, is beneficial to reducing the fast charge time of the battery, increasing the cycle number of the battery, improving the rate capability and cycle performance of the battery, and comprehensively improving the electrochemical performance of the battery.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to a silicon-carbon composite material, a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in multiple fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0003] The negative electrode active material is an important component of secondary batteries. In order to further improve the energy density of the battery, silicon-based negative electrode active materials have been widely studied. However, due to the large volume expansion of silicon-based materials themselves, it will affect the electrochemical performance of the battery during use. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a silicon-carbon composite material, which has excellent electron transport performance, is beneficial to reducing the fast charging time of the battery, increasing the number of battery cycles, can improve the rate performance and cycle performance of the battery, and comprehensively improve the electrochemical performance of the battery.

[0005] To achieve the above object, a first aspect of the present application provides a silicon-carbon composite material, including silicon-carbon secondary particles, and the silicon-carbon secondary particles include silicon-carbon primary particles and one-dimensional conductive agents, and the one-dimensional conductive agents are distributed between the silicon-carbon primary particles.

[0006] On the one hand, the one-dimensional conductive agents are distributed between the silicon-carbon primary particles. The one-dimensional conductive agents serve as "bridges" between the silicon-carbon primary particles, connecting the primary particles to each other, greatly increasing the contact sites between the primary particles, effectively reducing the electrical inactivation caused by poor contact between the primary particles and the expansion and contraction of the primary particles during charge and discharge, enabling the silicon-carbon composite material to have excellent electron transport performance, improving the migration kinetics of active ions, shortening the fast charging time of the battery, and improving the rate performance of the material. On the other hand, the one-dimensional conductive agents serve as a conductive buffer matrix. At the same time, the one-dimensional conductive agents can be linearly wound around the silicon-carbon primary particles to effectively bind the silicon-carbon primary particles. The elastic and binding effects of the matrix can effectively inhibit the volume change of the primary particles during the process of inserting and extracting active ions, improve the cycle stability and lithium storage capacity of the silicon-carbon composite material, and extend the cycle life of the battery.

[0007] In any embodiment, the diameter of the one-dimensional conductive agent is less than or equal to 10 nm, and can be optionally 0.5 nm - 5 nm; and / or, the length of the one-dimensional conductive agent is 1 μm - 5 μm, and can be optionally 3 μm - 5 μm; and / or, the aspect ratio of the one-dimensional conductive agent is 1000 - 5000, and can be optionally 3000 - 5000.

[0008] By regulating the diameter, length or aspect ratio of the one-dimensional conductive agent within a suitable range, it is beneficial to improve the electron conduction between primary particles, enabling the silicon-carbon composite material to have excellent electron transport performance, improving the migration kinetics of active ions, shortening the fast charging time of the battery, and enhancing the rate performance of the material.

[0009] In any embodiment, based on the mass of the silicon-carbon secondary particles, the mass content of the one-dimensional conductive agent is less than or equal to 0.7%, and can be optionally 0.3% - 0.6%.

[0010] The mass content of the one-dimensional conductive agent within a suitable range enables excellent electrical contact between primary particles, achieving the purpose of improving the rate performance and cycle performance of the secondary battery. At the same time, it also reduces the influence on the battery cycle performance caused by excessive mass content of the one-dimensional conductive agent resulting in changes in the internal structure of the material. The one-dimensional conductive agent with a suitable mass content range can balance the rate performance and cycle performance of the battery and comprehensively improve the battery performance.

[0011] In any embodiment, the particle size of the silicon-carbon primary particles is 20 nm - 100 nm, and can be optionally 20 nm - 60 nm.

[0012] The particle size of the silicon-carbon primary particles within a suitable range enables the one-dimensional conductive agent to connect a sufficient number of silicon-carbon primary particles to each other, resulting in excellent electrical contact between primary particles, achieving the purpose of improving the rate performance of the secondary battery. At the same time, the silicon-carbon primary particles having a suitable particle size range enables the silicon-carbon secondary particles to have a suitable particle size, and the structure of the silicon-carbon composite material is relatively stable, and the battery has excellent cycle performance.

[0013] In any embodiment, the silicon-carbon primary particles include:

[0014] A porous carbon skeleton;

[0015] A silicon-based material, with at least part of the silicon-based material disposed in the pores of the porous carbon skeleton.

[0016] The silicon-carbon primary particles have a stable porous skeleton structure with strong support ability, high stress capacity, excellent mechanical properties and electrical conductivity. The pore structure in the porous carbon skeleton provides more space for setting silicon-based materials and can be used for a large amount of silicon storage. When the porous carbon skeleton is combined with the silicon-based material, the silicon-based material is not likely to agglomerate and can be evenly dispersed in the pores of the porous carbon skeleton. After the porous carbon skeleton is combined with silicon particles, the electrical conductivity of the silicon-carbon primary particles can be improved. At the same time, the volume effect of silicon during lithium insertion and extraction can be alleviated, and the stress change of the silicon-based material can be fully tolerated, ensuring the structural stability of the silicon-carbon composite material, improving the cycle stability and lithium storage capacity of the silicon-carbon composite material, and extending the cycle life of the battery.

[0017] In any implementation manner, the porous carbon skeleton satisfies at least one of the following (1)-(2):

[0018] (1) The pore volume of the porous carbon skeleton is 0.7 cm 3 / g - 1.0 cm 3 / g;

[0019] (2) The pore diameter of the porous carbon skeleton is 0.7 nm - 3 nm, and can be optionally 0.8 nm - 1.5 nm.

[0020] When the pore volume of the porous carbon skeleton is within a suitable range, it can not only ensure the stability of the skeleton structure but also meet the capacity of deposited silicon. Silicon particles adhere to the pores, and the silicon particles and the porous carbon skeleton can work together, thereby improving the capacity and electrical conductivity of the silicon-carbon composite material and improving the rate performance and energy density of the battery.

[0021] When the pore diameter of the porous carbon skeleton is within a suitable range, it is beneficial for subsequent silicon particles to enter the pores of the porous carbon skeleton, reducing the risk of silicon deposition on the surface of the porous carbon skeleton; and it is beneficial for the porous carbon skeleton particles to approach a saturated deposition state, improving the electron conductivity and ion conductivity of the material and improving the rate performance of the material.

[0022] In any implementation manner, the silicon-carbon primary particles satisfy at least one of the following (3)-(4):

[0023] (1) The specific surface area of the silicon-carbon primary particles is 1 m 2 / g - 20 m 2 / g, and can be optionally 8 m 2 / g - 15 m 2 / g;

[0024] (2) Based on the mass of the silicon-carbon primary particles, the mass fraction of the silicon-based material is 30% - 50%, and can be optionally 35% - 45%.

[0025] Control the specific surface area of the silicon carbide primary particles within a suitable range, so that the one-dimensional conductive agent can bind the silicon carbide primary particles in a linear structure, achieving the purpose of suppressing the volume change of the primary particles during the insertion and extraction of active ions, which is beneficial to improving the cycle performance of the battery.

[0026] Control the mass fraction of the silicon-based material within a suitable range, so that the silicon carbide composite material has a high specific capacity, improving the energy density of the battery. At the same time, the volume expansion of the silicon carbide composite material is limited within a certain range, making the silicon carbide composite material have a certain structural stability.

[0027] In any implementation manner, the silicon carbide secondary particles satisfy at least one of the following (5)-(8):

[0028] (5) The specific surface area of the silicon carbide secondary particles is 0.1 m 2 / g - 0.8 m 2 / g, and can be optionally 0.15 m 2 / g - 0.6 m 2 / g;

[0029] (6) The volume distribution particle size Dv50 of the silicon carbide secondary particles is 0.9 μm - 3 μm;

[0030] (7) The tapped density of the silicon carbide secondary particles is 0.75 g / cm 3 -1.00 g / cm 3 ;

[0031] (8) The powder resistivity of the silicon carbide secondary particles under 5 MPa is 0.1 Ω·cm - 10.0 Ω·cm, and can be optionally 0.1 Ω·cm - 1.0 Ω·cm.

[0032] Control the specific surface area of the silicon carbide secondary particles within a suitable range, and the material has excellent kinetic performance, which is beneficial to the rate performance of the secondary battery.

[0033] Control the volume distribution particle size Dv50 of the silicon carbide secondary particles within a suitable range, the structure of the silicon carbide composite material is relatively stable, the kinetic performance is good, and the rate performance and cycle performance of the secondary battery are improved.

[0034] Control the tapped density of the silicon carbide secondary particles within a suitable range, which can improve the compaction density of the negative electrode plate, improve the energy density of the secondary battery; and is also beneficial to the negative electrode plate having a suitable pore distribution, improving the ion and electron transport performance, improving the wetting characteristics of the negative electrode plate to the electrolyte, and further improving the rate performance and cycle performance of the secondary battery.

[0035] Control the powder resistivity of the silicon carbide secondary particles under 5 MPa within a suitable range, which can improve the electron conductivity of the negative electrode plate and further improve the rate performance of the battery.

[0036] In any embodiment, the one-dimensional conductive agent includes carbon nanotubes and carbon fibers, optionally carbon nanotubes, and more optionally single-walled carbon nanotubes.

[0037] In any embodiment, a carbon layer is present on at least a part of the surface of the silicon-carbon composite material.

[0038] The carbon layer coated on the silicon-carbon composite material is beneficial to improving the conductivity of the silicon-carbon composite material, improving the rate performance of the material. At the same time, the carbon layer can also enhance the stability between the silicon-carbon composite material and the electrolyte, and improve the cycle performance of the battery.

[0039] A second aspect of the present application is a method for preparing a silicon-carbon composite material, including:

[0040] Mixing and granulating silicon-carbon primary particles and a one-dimensional conductive agent in a solvent, and spray-drying to obtain a silicon-carbon composite material.

[0041] Wherein, the silicon-carbon composite material includes silicon-carbon secondary particles, the silicon-carbon secondary particles include silicon-carbon primary particles and a one-dimensional conductive agent, and the one-dimensional conductive agent is distributed between the silicon-carbon primary particles.

[0042] In the above preparation method, the one-dimensional conductive agent is mixed with the silicon-carbon primary particles in a liquid phase, so that the one-dimensional conductive agent is distributed between the silicon-carbon primary particles. The one-dimensional conductive agent serves as a "bridge" between the silicon-carbon primary particles, connecting the primary particles to each other, greatly increasing the contact sites between the primary particles, effectively reducing the electrical inactivation caused by poor contact between the primary particles and the expansion and contraction of the primary particles during charge and discharge, enabling the silicon-carbon composite material to have excellent electron transport performance, improving the migration kinetics of active ions, shortening the fast charging time of the battery, and improving the rate performance of the material; on the other hand, the one-dimensional conductive agent serves as a conductive buffer matrix, and the one-dimensional conductive agent can also be linearly wound around the silicon-carbon primary particles to effectively bind the silicon-carbon primary particles. The elastic and binding effects of the matrix can effectively inhibit the volume change of the primary particles during the process of inserting and extracting active ions, improve the cycle stability and lithium storage capacity of the silicon-carbon composite material, and extend the cycle life of the battery.

[0043] In any embodiment, the preparation method specifically includes:

[0044] Polymerization reaction: Polymerizing aniline, cyclohexanehexol hexaphosphate, and an initiator to obtain a mixed precursor.

[0045] High-temperature carbonization: Performing high-temperature carbonization treatment on the mixed precursor to obtain a carbonized pre-treatment material.

[0046] Activation and pore formation: Passing water vapor into the carbonized pre-treatment material for activation and pore formation treatment to obtain porous carbon framework primary particles.

[0047] Deposited silicon: Deposit silicon within the primary particles of the porous carbon framework to obtain silicon-carbon primary particles;

[0048] Mixing and granulating: Mix and granulate the silicon-carbon primary particles with a one-dimensional conductive agent in a solvent, and spray-dry to obtain a silicon-carbon composite material.

[0049] In the above preparation method, first, aniline and cyclohexanehexol hexaphosphate are polymerized under the action of an initiator to generate a carbon material precursor, polyaniline microspheres; then, through a high-temperature carbonization step, the polyaniline is fully carbonized to obtain primary particles of a carbon material with a high conductivity; the activation and pore-forming step helps to generate primary particles with a porous carbon framework, obtaining a porous carbon framework with a high pore diameter or pore volume, which is beneficial for subsequent silicon deposition. Deposit silicon particles within the pores of the primary particles of the porous carbon framework to obtain silicon-carbon primary particles. Finally, mix the silicon-carbon primary particles with a one-dimensional conductive agent in a liquid phase, and after spray-drying, obtain a silicon-carbon composite material.

[0050] In any embodiment, the reaction temperature of the polymerization reaction is 60°C - 280°C, and can be optionally 80°C - 250°C; and / or, the reaction time of the polymerization reaction is 1h - 15h, and can be optionally 5h - 12h.

[0051] By controlling the reaction time and reaction temperature of the polymerization reaction, the particle size of the polyaniline microspheres can be controlled, achieving the purpose of controlling the particle size of the primary particles of the carbon material.

[0052] In any embodiment, the deposition temperature for depositing silicon is 400°C - 900°C, and can be optionally 500°C - 650°C; and / or, the deposition time for depositing silicon is 6h - 24h, and can be optionally 8h - 18h.

[0053] By controlling the deposition time and deposition temperature for depositing silicon within a suitable range, the silicon is uniformly dispersed in the pores of the porous carbon framework, and the silicon-carbon composite material has excellent structural parameters.

[0054] In any embodiment, the preparation method further includes preparing a carbon layer: performing carbon coating treatment on the surface of the silicon-carbon composite material.

[0055] Coating a carbon layer on the surface of the silicon-carbon composite material is beneficial for improving the conductivity of the silicon-carbon composite material, improving the rate performance of the material. At the same time, the carbon layer can also enhance the stability between the silicon-carbon composite material and the electrolyte, improving the cycle performance of the battery.

[0056] The third aspect of the present application provides a secondary battery, including a negative electrode sheet, and the negative electrode sheet includes the silicon-carbon composite material described in the first aspect of the present application or the silicon-carbon composite material prepared according to the preparation method described in the second aspect of the present application.

[0057] The fourth aspect of the present application provides an electrical device including the secondary battery of the third aspect of the present application. Description of the Drawings

[0058] Figure 1 It is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0059] Figure 2 is Figure 1 An exploded view of the secondary battery according to an embodiment of the present application shown in the figure.

[0060] Figure 3 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0061] Figure 4 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0062] Figure 5 is Figure 4 An exploded view of the battery pack according to an embodiment of the present application shown in the figure.

[0063] Figure 6 It is a schematic diagram of an electrical device using the secondary battery as a power source according to an embodiment of the present application.

[0064] Figure 7 It is a schematic structural diagram of the silicon-carbon composite material of the present application.

[0065] Description of the Reference Numerals:

[0066] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly Detailed Embodiments

[0067] Hereinafter, embodiments of the silicon-carbon composite material, its preparation method, secondary battery, and electrical device of the present application will be specifically described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0068] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values and can be combined arbitrarily, 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, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 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 an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0069] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0070] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0071] Unless otherwise specified, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0072] Unless otherwise specified, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean that only the listed components are included or comprised.

[0073] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or present) and B is false (or absent); A is false (or absent) while B is true (or present); or both A and B are true (or present).

[0074] Silicon-carbon composite materials are one of the commonly used active materials. Currently, in the preparation of silicon-carbon composite materials, silicon is mainly directly mixed with carbon materials. These silicon-carbon materials have certain limitations on the silicon content. When the silicon content is too high, the expansion is large, which will cause the silicon-carbon composite materials to break and pulverize, and the materials will lose electrical contact with each other, leading to a rapid attenuation of the capacity and a poor cycle stability performance of the battery. In addition, the conductivity of the silicon-carbon composite materials themselves is poor, which severely limits their further application. Therefore, it is necessary to design a new silicon-carbon composite material to meet the needs of the new generation of electrochemistry.

[0075] [Silicon-carbon composite material]

[0076] Based on this, this application provides a silicon-carbon composite material, including silicon-carbon secondary particles, and the silicon-carbon secondary particles include silicon-carbon primary particles and one-dimensional conductive agents, and the one-dimensional conductive agents are distributed between the silicon-carbon primary particles.

[0077] Both the silicon-carbon primary particles and the silicon-carbon secondary particles have the meanings well-known in the art. The silicon-carbon primary particles refer to non-agglomerated particles. The silicon-carbon secondary particles refer to agglomerated particles formed by the aggregation of two or more silicon-carbon primary particles. The silicon-carbon primary particles and the silicon-carbon secondary particles can be distinguished by using scanning electron microscope (SEM) images.

[0078] In this article, the term "one-dimensional conductive agent" refers to a conductive agent having a one-dimensional microstructure, including but not limited to carbon nanotubes and carbon fibers.

[0079] On the one hand, the one-dimensional conductive agents are distributed between the silicon-carbon primary particles, that is, the one-dimensional conductive agents act as "bridges" between the silicon-carbon primary particles, connecting the primary particles to each other, greatly increasing the contact sites between the primary particles, effectively reducing the electrical inactivation caused by the poor contact between the primary particles and the expansion and contraction of the primary particles during charge and discharge, enabling the silicon-carbon composite material to have excellent electron transport performance, improving the migration kinetics of active ions, shortening the fast charging time of the battery, and improving the rate performance of the material; on the other hand, the one-dimensional conductive agents act as a conductive buffer matrix, and at the same time, the one-dimensional conductive agents can also be linearly wound around the silicon-carbon primary particles, effectively binding the silicon-carbon primary particles, and using the elasticity and binding effect of the matrix can effectively inhibit the volume change of the primary particles during the process of deintercalating and intercalating active ions, improving the cycle stability and lithium storage capacity of the silicon-carbon composite material, and extending the cycle life of the battery.

[0080] In some embodiments, the diameter of the one-dimensional conductive agent is less than or equal to 10 nm. In some embodiments, the diameter of the one-dimensional conductive agent can be optionally any value among 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm or a range composed of any two of these values.

[0081] The diameter or length of the one-dimensional conductive agent can be measured by methods and equipment known in the art. For example, it can be measured by using a scanning electron microscope (such as ZEISS Sigma300). As an example, the following steps can be taken: First, cut the negative electrode sheet containing the silicon-carbon composite material into a test sample of a certain size (such as 6 mm × 6 mm), clamp the test sample with two conductive and heat-conductive thin sheets (such as copper foils), stick the test sample and the thin sheets together with glue (such as double-sided tape) for fixation, press with a flat iron block of a certain mass (such as about 400 g) for a certain time (such as 1 h) to make the gap between the test sample and the copper foil as small as possible, then cut the edges neatly with scissors and stick it on a sample stage with conductive glue, with the sample slightly protruding from the edge of the sample stage. Then install the sample stage into the sample holder and lock it for fixation, turn on the power of the argon ion cross-section polisher (such as IB-19500CP) and evacuate the air (such as 10 Pa - 4 Pa), set the argon gas flow rate (such as 0.15 MPa), voltage (such as 8 KV) and polishing time (such as 2 hours), adjust the sample stage to the swing mode to start polishing. After polishing, use a scanning electron microscope (such as ZEISS Sigma 300) to obtain the ion-polished cross-sectional morphology (CP) picture of the silicon-carbon composite material, and then count the diameter or length of the one-dimensional conductive agent and draw a normal distribution curve. The diameter or length taken on the normal distribution curve is the diameter and length of the one-dimensional conductive agent.

[0082] By controlling the diameter of the one-dimensional conductive agent within a suitable range and distributing a sufficient number of one-dimensional conductive agents between the primary particles, that is, building a sufficient number of "bridges" between the primary particles, the purpose of improving the conductivity of the silicon-carbon composite material can be achieved. At the same time, when the diameter of the one-dimensional conductive agent is within a suitable range, it can also improve the penetration ability of the electrolyte in the silicon-carbon composite material, which is beneficial to improving the rate performance of the battery.

[0083] In some embodiments, the diameter of the one-dimensional conductive agent is 0.5 nm - 5 nm. In some embodiments, the diameter of the one-dimensional conductive agent can be optionally any value among 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm or a range composed of any two of these values.

[0084] Controlling the diameter of the one-dimensional conductive agent within an appropriate range can further reduce the fast charging time of the battery, extend the number of battery cycles, and improve the rate performance and cycling performance of the battery.

[0085] In some embodiments, the length of the one-dimensional conductive agent is 1 μm - 5 μm. In some embodiments, the length of the one-dimensional conductive agent can be optionally any value among 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or a range composed of any two of these values.

[0086] Controlling the length of the one-dimensional conductive agent within an appropriate range, on the one hand, makes the "bridge" between primary particles long enough to achieve the purpose of connecting primary particles, and can also linearly wind the primary particles to achieve the purpose of restraining the expansion of primary particles. On the other hand, the one-dimensional conductive agent with an appropriate length also reduces the possibility of the one-dimensional conductive agent breaking during the battery cycle.

[0087] In some embodiments, the length of the one-dimensional conductive agent is 3 μm - 5 μm. In some embodiments, the length of the one-dimensional conductive agent can be optionally any value among 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or a range composed of any two of these values.

[0088] When the length of the one-dimensional conductive agent is within an appropriate range, it further increases the number of battery cycles, reduces the fast charging time of the battery, and improves the cycling performance and rate performance of the battery.

[0089] In some embodiments, the aspect ratio of the one-dimensional conductive agent is 1000 - 5000. In some embodiments, the aspect ratio of the one-dimensional conductive agent can be optionally any value among 1000, 2000, 3000, 4000, 50000 or a range composed of any two of these values.

[0090] By adjusting the aspect ratio of the one-dimensional conductive agent within an appropriate range, it is beneficial to improve the electron conduction between primary particles, enable the silicon-carbon composite material to have excellent electron transport performance, improve the migration kinetics of active ions, shorten the fast charging time of the battery, and improve the rate performance of the material.

[0091] In some embodiments, the aspect ratio of the one-dimensional conductive agent is 3000 - 5000. In some embodiments, the aspect ratio of the one-dimensional conductive agent can be optionally any value among 3000, 3500, 4000, 4500, 50000 or a range composed of any two of these values.

[0092] Controlling the aspect ratio of the one-dimensional conductive agent within an appropriate range can further increase the number of battery cycles, reduce the fast charging time of the battery, and improve the cycling performance and rate performance of the battery.

[0093] In some embodiments, based on the mass of the silicon-carbon secondary particles, the mass content of the one-dimensional conductive agent is less than or equal to 0.7%.

[0094] In some embodiments, based on the mass of the silicon-carbon secondary particles, the mass content of the one-dimensional conductive agent can be optionally any value among 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6% or a range composed of any two of them.

[0095] In some embodiments, based on the mass of the silicon-carbon secondary particles, the mass content of the one-dimensional conductive agent can be optionally any value among 0.3%, 0.4%, 0.5%, 0.6% or a range composed of any two of them.

[0096] The mass content of the one-dimensional conductive agent is within a suitable range, so that there is excellent electrical contact between the primary particles, achieving the purpose of improving the rate performance and cycling performance of the secondary battery. At the same time, it also reduces the influence on the cycling performance of the battery caused by excessive mass content of the one-dimensional conductive agent, which may change the internal structure of the material. The one-dimensional conductive agent with a suitable mass content range can take into account the rate performance and cycling performance of the battery and comprehensively improve the battery performance.

[0097] In some embodiments, the particle size of the silicon-carbon primary particles is 20 nm - 100 nm. In some embodiments, the particle size of the silicon-carbon primary particles can be optionally any value among 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm or a range composed of any two of them.

[0098] The particle size of the silicon-carbon primary particles can be measured by methods and equipment known in the art. For example, it can be measured by using a scanning electron microscope (such as ZEISS Sigma300). As an example, the following steps can be taken: First, cut the negative electrode sheet containing the silicon-carbon composite material into test samples of a certain size (such as 6mm×6mm), clamp the test sample with two conductive and heat-conductive thin sheets (such as copper foil), stick and fix the test sample and the thin sheet with glue (such as double-sided tape), press with a flat iron block of a certain mass (such as about 400g) for a certain time (such as 1h) to make the gap between the test sample and the copper foil as small as possible, then cut the edge neatly with scissors and stick it on the sample stage with conductive glue, and the sample can slightly protrude from the edge of the sample stage. Then put the sample stage into the sample holder and lock it for fixation, turn on the power of the argon ion cross-section polisher (such as IB-19500CP) and evacuate the air (such as 10Pa - 4Pa), set the argon gas flow rate (such as 0.15MPa), voltage (such as 8KV) and polishing time (such as 2 hours), adjust the sample stage to the swing mode to start polishing, after the polishing is completed, use a scanning electron microscope (such as ZEISS Sigma 300) to obtain the ion-polished cross-sectional morphology (CP) picture of the silicon-carbon composite material. According to the ion-polished cross-sectional morphology (CP) picture of the silicon-carbon composite material obtained above, the particle size of the silicon-carbon primary particles is statistically analyzed using the equivalent circular area. The particle size of the silicon-carbon primary particles in this application is the area equivalent circle diameter, and the area of each silicon-carbon primary particle can be obtained by statistical analysis using graphic software.

[0099] When the particle size of the silicon-carbon primary particles is within a suitable range, the one-dimensional conductive agent can connect enough silicon-carbon primary particles to each other, enabling excellent electrical contact between the primary particles, achieving the purpose of improving the rate performance of the secondary battery. At the same time, when the silicon-carbon primary particles have a suitable range of particle sizes, the silicon-carbon secondary particles have suitable particle sizes, the structure of the silicon-carbon composite material is relatively stable, and the battery has excellent cycle performance.

[0100] In some embodiments, the particle size of the silicon-carbon primary particles is 20nm - 60nm. In some embodiments, the particle size of the silicon-carbon primary particles can be selected as any value among 20nm, 30nm, 40nm, 50nm, 60nm or the range composed of any two of these values.

[0101] By controlling the particle size of the silicon-carbon primary particles within a suitable range, the one-dimensional conductive agent can connect enough primary particles to each other, which can further extend the discharge time of the battery, reduce the charging time of the battery, and further improve the rate performance of the battery.

[0102] In some embodiments, the silicon-carbon primary particles include: a porous carbon skeleton; a silicon-based material, and at least part of the silicon-based material is disposed in the pores of the porous carbon skeleton.

[0103] The silicon-carbon primary particles have a stable porous framework structure with strong support ability, high stress capacity, excellent mechanical properties and electrical conductivity. The pore structure in the porous carbon framework provides more space for setting silicon-based materials and can be used for a large amount of silicon storage. When the porous carbon framework is combined with the silicon-based materials, the silicon-based materials are not prone to agglomeration and can be evenly dispersed in the pores of the porous carbon framework. After the porous carbon framework is combined with silicon particles, the electrical conductivity of the silicon-carbon primary particles can be improved, the volume effect of silicon during lithium deintercalation and intercalation can be alleviated, and the stress change of the silicon-based materials can be fully tolerated, ensuring the structural stability of the silicon-carbon composite material, improving the cycle stability and lithium storage capacity of the silicon-carbon composite material, and extending the cycle life of the battery.

[0104] In some embodiments, the pore volume of the porous carbon framework is 0.7 cm 3 / g - 1.0 cm 3 / g.

[0105] In some embodiments, the pore volume of the porous carbon framework can be selected as 0.7 cm 3 / g, 0.75 cm 3 / g, 0.8 cm 3 / g, 0.85 cm 3 / g, 0.90 cm 3 / g, 0.95 cm 3 / g, 1.0 cm 3 / g or a value within the range formed by any two of the above.

[0106] The pore volume of the porous carbon framework has the well-known meaning in the art and can be measured by the well-known instruments and methods in the art. For example, the test method can refer to GB / T 19587-2004, using the BJH (Barret joyner Halenda) method for mesopore size distribution test, and using the gas adsorption and desorption method to test and select the adsorption branch data under the micro-mesopore model to obtain the pore volume of the material.

[0107] When the pore volume of the porous carbon framework is within a suitable range, it can not only ensure the stability of the framework structure but also meet the capacity of deposited silicon. The silicon particles adhere to the pores, and the silicon particles and the porous carbon framework can work together to improve the capacity and electrical conductivity of the silicon-carbon composite material and improve the rate performance and energy density of the battery.

[0108] In some embodiments, the pore diameter of the porous carbon framework is 0.7 nm - 3 nm. In some embodiments, the pore diameter of the porous carbon framework can be selected as 0.7 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm or a value within the range formed by any two of the above.

[0109] In some embodiments, the pore diameter of the porous carbon framework is 0.8 nm - 1.5 nm. In some embodiments, the pore diameter of the porous carbon framework can be optionally 0.8 nm, 0.9 nm, 1.0 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, or a value within the range formed by any two of the above.

[0110] The pore diameter of the porous carbon framework has the meaning well-known in the art and can be measured by the instruments and methods well-known in the art. As an example, a certain amount of the above-prepared porous carbon framework is taken as a sample, and the porous carbon framework sample is analyzed by a Scanning Electron Microscope (SEM for short) to obtain an SEM image. Then, the pore size is statistically analyzed to draw a normal distribution curve, and the median pore diameter on the normal distribution curve is taken as the pore diameter of the porous carbon framework.

[0111] When the pore diameter of the porous carbon framework is within a suitable range, it is beneficial for subsequent silicon particles to enter the pores of the porous carbon framework, reducing the risk of silicon depositing on the surface of the porous carbon framework; and it is beneficial for the porous carbon framework particles to approach a saturated deposition state, improving the electronic conductivity and ionic conductivity of the material and enhancing the rate performance of the material.

[0112] In some embodiments, the specific surface area of the silicon-carbon primary particles is 1 m 2 / g - 20 m 2 / g. In some embodiments, the specific surface area of the silicon-carbon primary particles can be optionally 1 m 2 / g, 5 m 2 / g, 10 m 2 / g, 15 m 2 / g, 20 m 2 / g, or any value within the range formed by any two of them.

[0113] In some embodiments, the specific surface area of the silicon-carbon primary particles is 8 m 2 / g - 15 m 2 / g. In some embodiments, the specific surface area of the silicon-carbon primary particles can be optionally 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, or any value within the range formed by any two of them.

[0114] The specific surface area of the silicon-carbon primary particles has the meaning well-known in the art and can be measured by methods known in the art. As an example, a 3Flex specific surface area analyzer from Micromeritics is used to measure the specific surface area of the porous carbon framework. The BET specific surface area of the silicon-carbon primary particles is obtained by fitting with the T-Plot method.

[0115] Control the specific surface area of the silicon-carbon primary particles within a suitable range so that the one-dimensional conductive agent can bind the silicon-carbon primary particles in a linear structure, achieving the purpose of suppressing the volume change of the primary particles during the process of inserting and extracting active ions, which is beneficial to improving the cycling performance of the battery.

[0116] In some embodiments, based on the mass of the silicon-carbon primary particles, the mass fraction of the silicon-based material is 30%-50%. In some embodiments, based on the mass of the silicon-carbon primary particles, the mass fraction of the silicon-based material can be optionally any value among 30%, 35%, 40%, 45%, 50% or a range composed of any two of them.

[0117] In some embodiments, based on the mass of the silicon-carbon primary particles, the mass fraction of the silicon-based material is 35%-45%. In some embodiments, based on the mass of the silicon-carbon primary particles, the mass fraction of the silicon-based material can be optionally any value among 35%, 40%, 45% or a range composed of any two of them.

[0118] The mass content of the silicon-based material can be measured by methods and equipment known in the art. For example, it can be determined with reference to the EPA6010D-2014 standard; specifically, ICP-OES (elemental analysis - inductively coupled plasma optical emission spectrometry) can be used for measurement. First, the sample to be measured is dissolved in strong acid to form a liquid, and then the liquid is introduced into the ICP light source by atomization. Further, after the gaseous atoms to be measured are ionized and excited in a strong magnetic field, they return from the excited state to the ground state; during the above process, energy is released and recorded as different characteristic spectral lines for elemental quantitative analysis.

[0119] Control the mass fraction of the silicon-based material within a suitable range so that the silicon-carbon composite material has a high specific capacity, improves the energy density of the battery, and at the same time limits the volume expansion of the silicon-carbon composite material within a certain range, making the silicon-carbon composite material have a certain structural stability.

[0120] In some embodiments, the specific surface area of the silicon-carbon secondary particles is 0.1m 2 / g - 0.8m 2 / g. In some embodiments, the specific surface area of the silicon-carbon secondary particles is 0.1m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 Any value in / g or a range composed of any two of them.

[0121] In some embodiments, the specific surface area of the silicon-carbon secondary particles is 0.15 m 2 / g - 0.6 m 2 / g. In some embodiments, the specific surface area of the silicon-carbon secondary particles is 0.15 m 2 / g, 0.2 m 2 / g, 0.3 m 2 / g, 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 Any value in / g or a range composed of any two of them.

[0122] The specific surface area of the silicon-carbon secondary particles has the meaning well-known in the art and can be tested by methods known in the art. As an example, the 3Flex specific surface area analyzer of the American Micromeritics company is used to test the specific surface area of the silicon-carbon secondary particles. The BET specific surface area of the silicon-carbon secondary particles is obtained by fitting with the T-Plot method.

[0123] Controlling the specific surface area of the silicon-carbon secondary particles within a suitable range, the material has excellent kinetic performance, which is beneficial to the rate performance of the secondary battery.

[0124] In some embodiments, the volume distribution particle size Dv50 of the silicon-carbon secondary particles is 0.9 μm - 3 μm. In some embodiments, the volume distribution particle size Dv50 of the silicon-carbon secondary particles can be optionally any value in 0.9 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or a range composed of any two of them.

[0125] The volume distribution particle size Dv50 of the silicon-carbon secondary particles has the meaning well-known in the art and can be tested by methods known in the art. For example, the silicon-carbon secondary particle sample is measured according to the GB / T 19077-2016 / ISO 13320:2009 standard, and the test equipment can use a laser particle size analyzer (such as Malvern Master Size 3000).

[0126] Controlling the volume distribution particle size Dv50 of the silicon-carbon secondary particles within a suitable range, the structure of the silicon-carbon composite material is relatively stable, with good kinetic performance, improving the rate performance and cycle performance of the secondary battery.

[0127] In some embodiments, the tapped density of the silicon-carbon secondary particles is 0.75 g / cm 3 - 1.00 g / cm 3 。In some embodiments, the tapped density of the silicon-carbon secondary particles can be optionally 0.75 g / cm 3 , 0.80 g / cm 3 , 0.85 g / cm 3 , 0.90 g / cm 3 , 0.95 g / cm 3 , 1.00 g / cm 3 or any value within the range formed by any two of these values.

[0128] The tapped density of the silicon-carbon secondary particles has the meaning well-known in the art and can be measured using instruments and methods known in the art. For example, reference can be made to GB / T 5162-2006 and a powder tapped density tester can be used for measurement. The testing instrument can be BT-301 from Dandong BETTER, and the testing parameters are as follows: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 mm, number of vibrations 5000 times, measuring cylinder 25 mL.

[0129] Controlling the tapped density of the silicon-carbon secondary particles within a suitable range can increase the compaction density of the negative electrode sheet and the energy density of the secondary battery; it is also beneficial for the negative electrode sheet to have a suitable pore distribution, improve the ion and electron transport performance, improve the wetting characteristics of the negative electrode sheet with respect to the electrolyte, and thus improve the rate performance and cycle performance of the secondary battery.

[0130] In some embodiments, the powder resistivity of the silicon-carbon secondary particles at 5 MPa is 0.1 Ω·cm - 10 Ω·cm. In some embodiments, the powder resistivity of the silicon-carbon secondary particles at 5 MPa can be optionally any value within the range of 0.1 Ω·cm, 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm, 8 Ω·cm, 9 Ω·cm, 10 Ω·cm or any value within the range formed by any two of these values.

[0131] In some embodiments, the powder resistivity of the silicon-carbon secondary particles at 5 MPa is 0.1 Ω·cm - 1 Ω·cm. In some embodiments, the powder resistivity of the silicon-carbon secondary particles at 5 MPa can be optionally any value within the range of 0.1 Ω·cm, 0.2 Ω·cm, 0.3 Ω·cm, 0.4 Ω·cm, 0.5 Ω·cm, 0.6 Ω·cm, 0.7 Ω·cm, 0.8 Ω·cm, 0.6 Ω·cm, 1.0 Ω·cm or any value within the range formed by any two of these values.

[0132] The powder resistivity of the silicon-carbon secondary particles has a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, a resistivity tester (such as the ST2722 powder resistivity tester of Suzhou Lattice Electronics Co., Ltd.) can be used for testing. When testing, 1 g of powder sample can be taken, and the powder sample is placed between the electrodes of the resistivity tester. The powder sample is pressed with a constant pressure by an electronic press to the test pressure (for example, 5 Mpa) and maintained for 15 - 25 s to obtain a flaky sample. The powder resistivity δ of the material is calculated according to the formula δ=(S×R) / h, and the unit is Ω·cm. h is the height of the flaky sample, the unit is cm; R is the resistance, the unit is Ω; S is the area of the flaky sample, the unit is cm 2 。

[0133] In some embodiments, the one-dimensional conductive agent includes carbon nanotubes and carbon fibers.

[0134] In some embodiments, the one-dimensional conductive agent includes carbon nanotubes.

[0135] Compared with carbon fibers, carbon nanotubes have a hollow structure, which increases the ion transport channels, is beneficial to the circulation of the electrolyte in the pipeline, is beneficial to improving the conductivity of the material, and improves the rate performance of the battery.

[0136] In some embodiments, the one-dimensional conductive agent includes multi-walled carbon nanotubes or single-walled carbon nanotubes.

[0137] In some embodiments, the one-dimensional conductive agent includes single-walled carbon nanotubes.

[0138] The performance of single-walled carbon nanotubes is superior to that of multi-walled carbon nanotubes. Using single-walled carbon nanotubes as the one-dimensional conductive agent can further improve the cycle performance and rate performance of the battery.

[0139] In some embodiments, at least a part of the surface of the silicon-carbon composite material has a carbon layer.

[0140] The carbon layer coated on the silicon-carbon composite material is beneficial to improving the conductivity of the silicon-carbon composite material, improving the rate performance of the material. At the same time, the carbon layer can also enhance the stability between the silicon-carbon composite material and the electrolyte, and improve the cycle performance of the battery.

[0141] In some embodiments of the present application, a method for preparing a silicon-carbon composite material is provided, including:

[0142] Mixing and granulating silicon-carbon primary particles and a one-dimensional conductive agent in a solvent, and spray-drying to obtain a silicon-carbon composite material, wherein the silicon-carbon composite material includes silicon-carbon secondary particles, the silicon-carbon secondary particles include silicon-carbon primary particles and a one-dimensional conductive agent, and the one-dimensional conductive agent is distributed between the silicon-carbon primary particles.

[0143] In the above preparation method, the one-dimensional conductive agent is mixed with the primary silicon-carbon particles in a liquid phase, so that the one-dimensional conductive agent is distributed between the primary silicon-carbon particles. That is, the one-dimensional conductive agent serves as a "bridge" between the primary silicon-carbon particles, connecting the primary particles to each other, greatly increasing the contact sites between the primary particles, effectively reducing the electrical inactivation caused by poor contact between the primary particles and the expansion and contraction of the primary particles during charge and discharge, enabling the silicon-carbon composite material to have excellent electron transport performance, improving the migration kinetics of active ions, shortening the fast charging time of the battery, and enhancing the rate performance of the material. On the other hand, the one-dimensional conductive agent serves as a conductive buffer matrix, and at the same time, the one-dimensional conductive agent can be linearly wound around the primary silicon-carbon particles to effectively bind the primary silicon-carbon particles. The elastic and binding effects of the matrix can effectively inhibit the volume change of the primary particles during the insertion and extraction of active ions, improving the cycle stability and lithium storage capacity of the silicon-carbon composite material and extending the cycle life of the battery.

[0144] In some embodiments, the preparation method specifically includes:

[0145] Polymerization reaction: Aniline, cyclohexanehexol hexaphosphate, and an initiator are subjected to a polymerization reaction to obtain a mixed precursor.

[0146] High-temperature carbonization: The mixed precursor is subjected to high-temperature carbonization treatment to obtain a carbonized pre-treatment material.

[0147] Activation and pore formation: Water vapor is introduced into the carbonized pre-treatment material for activation and pore formation treatment to obtain primary particles of a porous carbon skeleton.

[0148] Silicon deposition: Silicon is deposited in the primary particles of the porous carbon skeleton to obtain primary silicon-carbon particles.

[0149] Mixing and granulation: The primary silicon-carbon particles and the one-dimensional conductive agent are mixed and granulated in a solvent, and spray drying is performed to obtain a silicon-carbon composite material.

[0150] In the above preparation method, first, aniline and cyclohexanehexol hexaphosphate are polymerized under the action of an initiator to generate a carbon material precursor, polyaniline microspheres; then, through the high-temperature carbonization step, the polyaniline is fully carbonized to obtain primary particles of a carbon material with high conductivity; the activation and pore formation step helps to generate primary particles of a porous carbon skeleton, obtaining a porous carbon skeleton with a high pore diameter or pore volume, which is beneficial for subsequent silicon deposition. Silicon particles are deposited in the pores of the primary particles of the porous carbon skeleton to obtain primary silicon-carbon particles. Finally, the primary silicon-carbon particles and the one-dimensional conductive agent are mixed in a liquid phase, and after spray drying, a silicon-carbon composite material is obtained.

[0151] In some embodiments, the initiator includes persulfate, and can be selected from ammonium persulfate or potassium persulfate.

[0152] In some embodiments, the solvent in the mixing granulation step is any one or a combination of at least two of alcohol solvents, ketone solvents, ether solvents or water.

[0153] In some embodiments, the reaction temperature of the polymerization reaction is 60°C - 280°C. In some embodiments, the reaction temperature of the polymerization reaction can be optionally 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, 200°C, 220°C, 240°C, 260°C, 280°C or a value within the range formed by any two of the above.

[0154] In some embodiments, the reaction temperature of the polymerization reaction is 80°C - 250°C. In some embodiments, the reaction temperature of the polymerization reaction can be optionally 80°C, 90°C, 100°C, 110°C, 120°C, 140°C, 160°C, 180°C, 220°C, 250°C or a value within the range formed by any two of the above.

[0155] In some embodiments, the reaction time of the polymerization reaction is 1h - 15h. In some embodiments, the reaction time of the polymerization reaction can be optionally 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h or a value within the range formed by any two of the above.

[0156] In some embodiments, the reaction time of the polymerization reaction is 5h - 12h. In some embodiments, the reaction time of the polymerization reaction can be optionally 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h or a value within the range formed by any two of the above.

[0157] By controlling the reaction time of the polymerization reaction or the reaction temperature of the polymerization reaction, the particle size of the polyaniline microspheres can be controlled, achieving the purpose of controlling the particle size of the primary particles of the carbon material.

[0158] In some embodiments, the temperature of the high-temperature carbonization is 600°C - 900°C.

[0159] In some embodiments, the time of the high-temperature carbonization is 4h - 12h.

[0160] In some embodiments, the treatment temperature of the activation pore formation is 400°C - 500°C.

[0161] In some embodiments, the treatment time of the activation pore formation is 4h - 8h.

[0162] In some embodiments, the flow rate of the water vapor is 0.5g / min - 1g / min.

[0163] By controlling the treatment temperature, treatment time, and water vapor flow rate for activating pore formation within appropriate ranges, the pore diameter and pore volume in the porous carbon framework can be within appropriate ranges, resulting in a porous carbon framework with excellent structural properties.

[0164] In some embodiments, the deposition temperature for depositing silicon is 400°C - 900°C. In some embodiments, the deposition temperature for vapor deposition of silicon can be selected from 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, or values within the range formed by any two of the above.

[0165] In some embodiments, the deposition temperature for depositing silicon is 500°C - 650°C. In some embodiments, the deposition temperature for vapor deposition of silicon can be selected from 500°C, 550°C, 600°C, 650°C, or values within the range formed by any two of the above.

[0166] In some embodiments, the deposition time for depositing silicon is 6h - 24h. In some embodiments, the deposition time for depositing silicon can be selected from 6h, 10h, 15h, 20h, 24h, or values within the range formed by any two of the above.

[0167] In some embodiments, the deposition time for depositing silicon is 8h - 18h. In some embodiments, the deposition time for depositing silicon can be selected from 8h, 10h, 12h, 14h, 16h, or values within the range formed by any two of the above.

[0168] By controlling the deposition time or deposition temperature of vapor deposition of silicon within appropriate ranges, silicon can be evenly dispersed in the pores of the porous carbon framework, and the silicon-carbon composite material has excellent structural parameters.

[0169] In some embodiments, the preparation method further includes preparing a carbon layer: performing carbon coating treatment on the surface of the silicon-carbon composite material.

[0170] In some embodiments, the carbon coating treatment includes any one of chemical vapor deposition carbon coating, pyrolysis carbon coating, hydrothermal carbon coating, and polyelectrolyte modification carbon coating.

[0171] Coating a carbon layer on the surface of the silicon-carbon composite material is beneficial to improving the conductivity of the silicon-carbon composite material, improving the rate performance of the material. At the same time, the carbon layer can also enhance the stability between the silicon-carbon composite material and the electrolyte, improving the cycle performance of the battery.

[0172] In one embodiment of the present application, a secondary battery is provided.

[0173] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly serving to prevent short - circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0174] [Positive electrode plate]

[0175] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0176] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0177] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0178] In some embodiments, the positive electrode active material can be a positive electrode active material for batteries well - known in the art. As an example, the positive electrode active material can include at least one of the following materials: lithium - containing phosphates with olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM333), LiNi 0.5 Co0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ), and at least one of its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), the composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), the composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of the composite material of lithium manganese iron phosphate and carbon.

[0179] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0180] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0181] In some embodiments, the positive electrode tab can be prepared by the following method: dispersing the above components for preparing the positive electrode tab, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode tab can be obtained.

[0182] [Negative electrode tab]

[0183] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon composite material in some embodiments or a silicon-carbon composite material prepared by a preparation method in some embodiments.

[0184] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0185] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0186] In some embodiments, the negative electrode active material can be a negative electrode active material known in the art for batteries. As an example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0187] In some embodiments, the mass content of the silicon-carbon composite material is greater than or equal to 20%, based on the total mass of the negative electrode active material.

[0188] In some embodiments, based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material can be selected from any one of greater than or equal to 20%, greater than or equal to 25%, greater than or equal to 30%, greater than or equal to 35%, greater than or equal to 40%, greater than or equal to 45%, greater than or equal to 50%, greater than or equal to 55%, greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%.

[0189] Control the silicon-carbon composite material within a suitable range so that the battery has excellent energy density and cycle performance.

[0190] In some embodiments, the mass content of the silicon-carbon composite material is 25%-90%, based on the total mass of the negative electrode active material.

[0191] In some embodiments, based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material can be optionally 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or a value within the range formed by any two of the above.

[0192] By controlling the silicon-carbon composite material within a suitable range, the energy density and cycle life of the battery can be balanced, and the electrochemical performance of the battery can be comprehensively improved.

[0193] In some embodiments, the negative electrode film layer may also optionally include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0194] In some embodiments, the negative electrode film layer may also optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0195] In some embodiments, the negative electrode film layer may also optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0196] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0197] [Electrolyte]

[0198] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid.

[0199] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0200] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0201] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0202] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives for improving battery overcharge performance, additives for improving battery high-temperature or low-temperature performance, and the like.

[0203] [Separator Film]

[0204] In some embodiments, the secondary battery further includes a separator film. The present application does not particularly limit the type of the separator film, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0205] In some embodiments, the material of the separator film may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator film is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0206] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film may be made into an electrode assembly by a winding process or a stacking process.

[0207] In some embodiments, the secondary battery includes a positive electrode sheet, an electrolyte, a separator film, and a negative electrode sheet in some embodiments.

[0208] In some embodiments, the secondary battery includes a lithium-ion battery.

[0209] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0210] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be cited, etc.

[0211] This application has no particular limitation on the shape of the secondary battery, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a secondary battery 5 with a square structure as an example.

[0212] In some embodiments, referring to Figure 2 , the outer packaging may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0213] In some embodiments, the secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0214] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0215] Optionally, the battery module 4 can further include a housing with a receiving space, and a plurality of secondary batteries 5 are received in the receiving space.

[0216] In some embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0217] Figure 4 and Figure 5 is a battery pack 1 as an example. Referring to Figure 4 and Figure 5, a battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0218] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0219] As the electrical device, the secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0220] Figure 6 is an electrical device as an example. The electrical device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or battery module can be used. Another example of the device can be a mobile phone, tablet computer, laptop, etc. This device usually requires thinness and lightness, and a secondary battery can be used as the power source.

[0221] Embodiment

[0222] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, the technologies or conditions described in the literature in the art or according to the product specifications shall be followed. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0223] I. Preparation Method

[0224] Embodiment 1

[0225] 1) Preparation of silicon-carbon composite material

[0226] Dissolve 500 g of aniline in 2000 ml of cyclohexanehexol hexaphosphate and disperse evenly. Then add 50 g of ammonium persulfate and stir evenly to obtain a reaction solution. Place the reaction solution in a reaction kettle and react at 180 °C for 8 h. Dry to obtain a powder. Then place the powder in a muffle furnace and carbonize it at 900 °C for 4 h under nitrogen protection. Pass steam through the carbonized product at 450 °C for 6 hours for activation and pore formation treatment, where the flow rate of steam is 1 g / min, to obtain primary particles of a porous carbon framework.

[0227] Using silane as a silicon source and nitrogen as a protective gas, chemical vapor deposition is carried out in a tubular furnace to obtain a silicon-carbon composite material. Among them, the flow rate of silane is 0.06 L / min; the flow rate of the protective gas is 4 L / min; the temperature of chemical vapor deposition is 450 °C and the time is 6 hours to obtain primary silicon-carbon particles. Add 19.9 g of a single-walled carbon nanotube dispersion (solid content is 0.03%, the length of the single-walled carbon nanotubes is 3 μm, and the diameter is 5 nm) and the prepared primary silicon-carbon particles to a certain amount of tetrahydrofuran, mix to obtain a mixed slurry with a solid content of 10%, and spray-dry the mixed slurry. The outlet air temperature is 95 °C and the feeding speed is 0.6 L / h to obtain a secondary silicon-carbon material, and the one-dimensional conductive agent is distributed between the primary silicon-carbon particles.

[0228] Using methane as a carbon source and nitrogen as a protective gas, chemical vapor deposition of the carbon source is carried out on the spray-dried substance in a tubular furnace. Among them, the flow rate of methane is 6 L / min, the flow rate of the protective gas is 15 L / min, the temperature of chemical vapor deposition is 900 °C, and the time is 6 h. Close the gas source to cool down to obtain a silicon-carbon composite material.

[0229] 2) Preparation of the positive electrode sheet

[0230] Mix lithium nickel cobalt manganese LiNi 0.95 Co 0.04 Mn 0.01 O 2 (NCM) ternary material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 97%:1%:2%, add N-methylpyrrolidone and mix evenly to obtain a positive electrode slurry; then coat it on a positive electrode current collector, and after drying, cold pressing, and slitting, obtain a positive electrode sheet.

[0231] 3) Preparation of the negative electrode sheet

[0232] Mix graphite and the silicon-carbon composite material prepared in Example 1 in a mass ratio of 3:7 to obtain a negative electrode active material, where based on the total mass of the negative electrode active material, the mass fraction of the silicon-carbon composite material is 70%.

[0233] The negative electrode active material, conductive agent carbon black, carbon nanotubes (CNT), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were added to deionized water in a weight ratio of 94.5%:1%:0.375%:2.8%:1.325% and mixed evenly to obtain a negative electrode slurry; the slurry was coated on a negative electrode current collector and dried, cold-pressed, and slit to obtain a negative electrode plate.

[0234] 4) Separator

[0235] A polypropylene film was used as the separator.

[0236] 5) Preparation of electrolyte

[0237] In an argon atmosphere glove box (H 2 O < 0.1 ppm, O 2 < 0.1 ppm), the organic solvents ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and fluoroethylene carbonate (FEC) were mixed evenly in a volume ratio of 1:1:1:1, and LiPF 6 was dissolved in the organic solvent and stirred evenly to make the concentration of the electrolyte 1 mol / L, obtaining the electrolyte of Example 1.

[0238] 6) Preparation of battery

[0239] The positive electrode plate, separator, and negative electrode plate of Example 1 were stacked in sequence, with the separator placed between the positive and negative electrode plates to play a separating role, and then wound to obtain an electrode core. The electrode core was welded with electrode tabs, and the electrode core was placed in an aluminum shell. Then, the electrolyte was injected and sealed. After processes such as standing, cold pressing, forming, shaping, and capacity testing, a lithium-ion secondary battery was obtained.

[0240] Examples 2 - 3

[0241] The preparation parameters in Examples 2 - 3 were basically the same as those in Example 1, but the single-walled carbon nanotubes were replaced with multi-walled carbon nanotubes and vapor-grown carbon fibers. The length of the single-walled carbon nanotubes was 2 μm, the diameter was 80 nm, the length of the vapor-grown carbon fibers was 4 μm, and the diameter was 2 nm. The specific parameters are shown in Table 1.

[0242] Examples 4 - 11

[0243] In Examples 4-11, the preparation parameters are basically the same as those in Example 1, but the diameters and lengths of the added single-walled carbon nanotubes are adjusted, and thus the lengths and diameters of the single-walled carbon nanotubes in the silicon-carbon composite material are adjusted. Among them, the length of the single-walled carbon nanotubes in Example 4 is 3 μm and the diameter is 0.5 nm; the length of the single-walled carbon nanotubes in Example 5 is 3 μm and the diameter is 1 nm; the length of the single-walled carbon nanotubes in Example 6 is 3 μm and the diameter is 10 nm; the length of the single-walled carbon nanotubes in Example 7 is 3 μm and the diameter is 12 nm; the length of the single-walled carbon nanotubes in Example 8 is 0.5 μm and the diameter is 1 nm; the length of the single-walled carbon nanotubes in Example 9 is 1 μm and the diameter is 1 nm; the length of the single-walled carbon nanotubes in Example 10 is 5 μm and the diameter is 1 nm; the length of the single-walled carbon nanotubes in Example 11 is 7 μm and the diameter is 1 nm. The specific parameters are shown in Table 1.

[0244] Examples 12-14

[0245] In Examples 12-14, the preparation parameters are basically the same as those in Example 1, but the solid content of the added single-walled carbon nanotube dispersion is adjusted. Among them, the solid content of Example 12 is 0.00995%, the solid content of Example 13 is 0.09286%, and the solid content of Example 14 is 0.1194%. The specific parameters are shown in Table 1.

[0246] Examples 15-18

[0247] In Examples 15-18, the preparation parameters are basically the same as those in Example 1, but the reaction temperature and reaction time of the polymerization reaction are adjusted, and thus the volume distribution particle size Dv50 of the primary silicon-carbon particles is adjusted. Among them, the polymerization reaction temperature in Example 15 is 220 °C and the reaction time is 4 h; the polymerization reaction temperature in Example 16 is 230 °C and the reaction time is 6 h; the polymerization reaction temperature in Example 17 is 122 °C and the reaction time is 11 h; the polymerization reaction temperature in Example 18 is 138 °C and the reaction time is 13 h. The specific parameters are shown in Table 1.

[0248] Comparative Example 1

[0249] In Comparative Examples 1-2, the preparation parameters are basically the same as those in Example 1, but the preparation parameters of the silicon-carbon composite material are adjusted. The specific parameters are shown in Table 1. The specific preparation method is as follows:

[0250] Comparative Example 1: The difference from Example 1 is that the single-walled carbon nanotubes are replaced with conductive carbon black.

[0251] Comparative Example 2: The difference from Example 1 is that no single-walled carbon nanotubes are added.

[0252] Comparative Example 3:

[0253] After mixing 1000 g of lignin and 200 g of KOH evenly, sintering treatment is carried out under a nitrogen protection atmosphere. The heating rate is 1 °C / min, the heat treatment temperature is 1150 °C, and it is kept warm for 5 h. After cooling, impurities are removed by washing with water, and then dried to obtain a three-dimensional porous carbon skeleton. Take 1000 g of the obtained three-dimensional porous carbon skeleton and place it in a CVD furnace. Heat it to 1000 °C at a rate of 5 °C / min, and introduce high-purity nitrogen at a rate of 4.0 L / min, methane gas at a rate of 0.5 L / min, and silane gas at a rate of 0.5 L / min respectively. The time for introducing the mixed gas is 8 h, and then it is naturally cooled to room temperature to obtain precursor 2. Take 1000 g of the obtained silicon-carbon precursor 2 and place it in a CVD furnace. Heat it to 1000 °C at a rate of 5 °C / min, introduce high-purity nitrogen at a rate of 4.0 L / min, and methane gas at a rate of 0.5 L / min. The time for introducing methane gas is 4 h, and then it is naturally cooled to room temperature to obtain the silicon-carbon composite material.

[0254] Comparative Example 4:

[0255] Dissolve 500 g of aniline in 2000 ml of cyclohexanehexol hexaphosphate and disperse it evenly, then add 50 g of ammonium persulfate and stir evenly to obtain a reaction solution. Place the reaction solution in a reaction kettle and react at 180 °C for 8 h to obtain a powder. Then place the powder in a muffle furnace and carbonize it at a temperature of 900 °C for 4 h under nitrogen protection. The carbonized product is passed through water vapor at 450 °C for 6 hours for activation and pore formation treatment, where the flow rate of water vapor is 1 g / min, to obtain primary particles of the porous carbon skeleton.

[0256] Using silane as the silicon source and nitrogen as the protective gas, chemical vapor deposition is carried out in a tubular furnace to obtain a silicon-carbon composite material. Among them, the flow rate of silane is 0.06 L / min; the flow rate of the protective gas is 4 L / min; the temperature of chemical vapor deposition is 450 °C, and the time is 6 hours to obtain primary silicon-carbon particles. The primary silicon-carbon particles are spray-dried, the outlet air temperature is 95 °C, and the feeding speed is 0.6 L / h to obtain secondary silicon-carbon particles.

[0257] Using methane as the carbon source and nitrogen as the protective gas, chemical vapor deposition of the carbon source is carried out on the secondary silicon-carbon particles in a tubular furnace. Among them, the flow rate of methane is 6 L / min, the flow rate of the protective gas is 15 L / min, the temperature of chemical vapor deposition is 900 °C, and the time is 6 h. Then the gas source is turned off for cooling to obtain an intermediate product. The obtained intermediate product is mixed and stirred with 19.9 g of a single-walled carbon nanotube dispersion to obtain a silicon-carbon composite material, where the length of the single-walled carbon nanotubes is 3 μm and the diameter is 1 nm.

[0258] II: Performance Testing

[0259] 1. Battery Performance

[0260] 1) Discharge time at 40% SOC

[0261] Discharge the battery cell at a constant current of 0.33C until 2.8V, and let it stand for 30 min; charge it at a constant current of 0.33C to 4.25V and then at a constant voltage of 0.05C until the voltage is stable, and let it stand for 30 min; discharge it at a constant current of 0.33C to 2.8V, at this time read the initial capacity C0, and let it stand for 30 min; charge it at a constant current of 0.33C to 4.25V and then at a constant voltage of 0.05C until the voltage is stable, and let it stand for 30 min; discharge it at a constant current of 0.33C to 0.4C0Ah (40%) SOC and let it stand for 60 min; discharge it at a constant current of 4.5C to 2.8V, and record the discharge time.

[0262] 2) Fast charging time

[0263] At 25°C, charge and discharge the batteries of each example and comparative example at a current of 1C (i.e., the current value that completely discharges the rated capacity within 1 h), specifically including: charge the battery at a constant current of 1C rate to a voltage of 4.3V, then charge at a constant voltage until the current ≤ 0.05C, let it stand for 5 min, and then discharge at a constant current of 0.33C rate to a voltage of 2.8V, and record its actual capacity as C0.

[0264] Then charge the battery successively at 2.0C0, 2.5C0, 3.0C0, 3.5C0, 4.0C0, 4.5C0, 5.0C0, 5.5C0 at a constant current until the full battery charging cut-off voltage of 4.3V or the 0V negative electrode cut-off potential (whichever reaches first). After each charging is completed, discharge it at 1C0 to the full battery discharge cut-off voltage of 2.8V, record the negative electrode potential corresponding to 10%, 20%, 30%, ……, 80% SOC (State of Charge) at different charging rates, plot the charging rate - negative electrode potential curve at different SOC states, and obtain the charging rate corresponding to 0V of the negative electrode potential at different SOC states by linear fitting. This charging rate is the charging window at this SOC state, denoted as C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, C80%SOC respectively. Calculate the charging time T of the battery from 10% SOC to 80% SOC according to the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%, and the unit is min. The shorter this time is, the better the fast charging performance of the battery is.

[0265] 3) Cycle performance

[0266] The secondary batteries prepared in each example and comparative example were charged at a constant current of 0.5C until the charging cut-off voltage reached 4.25V, then charged at a constant voltage until the current ≤ 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C until the discharge cut-off voltage reached 2V, and allowed to stand for 5 minutes. This was considered one charge-discharge cycle. The battery was subjected to cyclic charge-discharge tests according to this method until the battery capacity decayed to 80%. The number of cycles at this time was the cycle life of the battery at 25°C.

[0267] III. Analysis of Test Results of Each Example and Comparative Example

[0268] The batteries of each example and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in the following table.

[0269] Table 1

[0270]

[0271]

[0272] Table 2

[0273]

[0274] As can be seen from the above results, the silicon-carbon composite materials in Examples 1-18 contain silicon-carbon secondary particles, and the silicon-carbon secondary particles contain silicon-carbon primary particles and one-dimensional conductive agents distributed between the silicon-carbon primary particles, where the one-dimensional conductive agents are single-walled carbon nanotubes, multi-walled carbon nanotubes or carbon fibers. As can be seen from the comparison between Examples 1-18 and Comparative Example 1, compared with the silicon-carbon composite material in which zero-dimensional conductive agents of conductive carbon black are distributed between primary particles, the one-dimensional conductive agents are distributed between the silicon-carbon primary particles of the silicon-carbon composite material of the present application, which is beneficial to reducing the fast charging time of the battery, extending the discharge time of the battery, improving the rate performance of the battery, increasing the number of cycles of the battery, and extending the cycle life of the battery. As can be seen from the comparison between Examples 1-18 and Comparative Example 2, compared with the silicon-carbon composite material in which there are no one-dimensional conductive agents between primary particles, the one-dimensional conductive agents are distributed between the silicon-carbon primary particles of the silicon-carbon composite material of the present application, which is beneficial to reducing the fast charging time of the battery, extending the discharge time of the battery, improving the rate performance of the battery, increasing the number of cycles of the battery, and extending the cycle life of the battery. As can be seen from the comparison between Examples 1-18 and Comparative Example 3, compared with the case where zero-dimensional conductive agents of conductive carbon are present in the porous carbon framework, the one-dimensional conductive agents of the present application are present between primary particles, which is beneficial to reducing the fast charging time of the battery, extending the discharge time of the battery, improving the rate performance of the battery, increasing the number of cycles of the battery, and extending the cycle life of the battery. As can be seen from the comparison between Example 5 and Comparative Example 4, compared with the silicon-carbon composite material in which one-dimensional conductive agents are present between secondary particles, the one-dimensional conductive agents of the present application are distributed between primary particles, which is beneficial to extending the discharge time of the battery, improving the rate performance of the battery, increasing the number of cycles of the battery, and extending the cycle life of the battery.

[0275] As can be seen from the comparison between Examples 1, 4-6 and Example 7, controlling the diameter of the single-walled carbon nanotubes to be less than or equal to 10 nm is beneficial to increasing the number of cycles of the battery and the discharge time at 40% SOC, reducing the fast charging time of the battery, and improving the rate performance and cycle performance of the battery. As can be seen from the comparison between Examples 1, 4-5 and Examples 6-7, controlling the diameter of the single-walled carbon nanotubes to be 0.5 nm - 5 nm can further reduce the fast charging time of the battery, increase the number of cycles of the battery and the discharge time at 40% SOC, and improve the rate performance and cycle performance of the battery.

[0276] As can be seen from the comparison between Examples 5, 9-10 and Examples 8, 11, controlling the length of the single-walled carbon nanotubes to be 1 μm - 5 μm is beneficial to increasing the discharge time at 40% SOC of the battery, reducing the fast charging time of the battery, and improving the rate performance of the battery. As can be seen from the comparison between Examples 5, 10 and Examples 8-9, 11, controlling the length of the single-walled carbon nanotubes to be 3 μm - 5 μm can further increase the number of cycles of the battery, reduce the fast charging time of the battery, and improve the cycle performance and rate performance of the battery.

[0277] Comparing Examples 5, 9 - 10 with Examples 1, 4, 6 - 8, 11, it can be seen that controlling the aspect ratio of single-walled carbon nanotubes to be 1000 - 5000 is beneficial to improving the 40% SOC discharge time of the battery, reducing the fast charging time of the battery, and improving the rate performance of the battery. Comparing Examples 5, 10 with Examples 1, 4, 6 - 9, 11, it can be seen that controlling the aspect ratio of single-walled carbon nanotubes to be 3000 - 5000 can further increase the number of cycles of the battery, reduce the fast charging time of the battery, and improve the cycle performance and rate performance of the battery.

[0278] From Examples 5, 12 - 14, it can be seen that based on the mass of the silicon-carbon secondary particles, the mass content of single-walled carbon nanotubes is less than or equal to 0.7%, the battery has a shorter fast charging time, a longer discharge time, and a larger number of cycles, and the battery has excellent rate performance and cycle performance. Comparing Examples 5, 13 with Examples 12, 14, it can be seen that based on the mass of the silicon-carbon secondary particles, the mass content of single-walled carbon nanotubes is 0.3% - 0.6%, which can increase the number of cycles of the battery and the 40% SOC discharge time, reduce the fast charging time of the battery, and improve the rate performance and cycle performance of the battery.

[0279] Comparing Examples 5, 16 - 17 with Examples 15, 18, it can be seen that controlling the volume distribution particle size Dv50 of the silicon-carbon primary particles to be 20 nm - 100 nm can extend the discharge time of the battery, reduce the charging time of the battery, and further improve the rate performance of the battery. Comparing Examples 5, 16 with Examples 15, 17 - 18, it can be seen that controlling the volume distribution particle size Dv50 of the silicon-carbon primary particles to be 20 nm - 60 nm can further extend the discharge time of the battery, reduce the charging time of the battery, and further improve the rate performance of the battery.

[0280] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same effect as the technical idea within the technical solution scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the main idea of this application, various modifications that those skilled in the art can think of to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A silicon-carbon composite material, characterized in that: The invention comprises silicon carbon secondary particles, wherein the silicon carbon secondary particles comprise silicon carbon primary particles and a one-dimensional conductive agent, and the one-dimensional conductive agent is distributed between the silicon carbon primary particles.

2. The silicon-carbon composite material according to claim 1, characterized in that: The diameter of the one-dimensional conductive agent is less than or equal to 10 nm, and can be 0.5 nm-5 nm; and / or, The length of the one-dimensional conductive agent is 1 μm-5 μm, and can be 3 μm-5 μm; and / or, The aspect ratio of the one-dimensional conductive agent is 1000-5000, and can be optionally 3000-5000.

3. The silicon-carbon composite material according to claim 1 or 2, characterized in that: Based on the mass of the silicon-carbon secondary particles, the mass content of the one-dimensional conductive agent is less than or equal to 0.7%, and can be optionally 0.3%-0.6%.

4. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that: The particle size of the silicon carbon primary particles is 20nm-100nm, and can be optionally 20nm-60nm.

5. The silicon-carbon composite material according to any one of claims 1 to 4, characterized in that: The silicon-carbon primary particles include: Porous carbon framework; The silicon-based material is at least partially disposed in the pores of the porous carbon skeleton.

6. The silicon-carbon composite material according to claim 5, characterized in that: The porous carbon skeleton satisfies at least one of the following (1)-(2): (1) The pore volume of the porous carbon skeleton is 0.7 cm 3 / g-1.0cm 3 / g; (2) The pore size of the porous carbon skeleton is 0.7nm-3nm, and can be optionally 0.8nm-1.5nm.

7. The silicon-carbon composite material according to claim 5 or 6, characterized in that: The silicon carbon primary particles satisfy at least one of the following (3)-(4): (3) The specific surface area of ​​the silicon carbon primary particles is 1 m 2 / g-20m 2 / g, optional 8m 2 / g-15m 2 / g; (4) Based on the mass of the silicon-carbon primary particles, the mass fraction of the silicon-based material is 30%-50%, and can be optionally 35%-45%.

8. The silicon-carbon composite material according to any one of claims 1 to 7, characterized in that: The silicon-carbon secondary particles satisfy at least one of the following (5)-(8): (5) The specific surface area of ​​the silicon-carbon secondary particles is 0.1 m 2 / g-0.8m 2 / g, optional 0.15m 2 / g-0.6m 2 / g; (6) The volume distribution particle size Dv50 of the silicon-carbon secondary particles is 0.9 μm-3 μm; (7) The tap density of the silicon carbon secondary particles is 0.75 g / cm 3 -1.00g / cm 3 ; (8) The powder resistivity of the silicon-carbon secondary particles at 5 MPa is 0.1 Ω·cm-10 Ω·cm, and can be optionally 0.1 Ω·cm-1 Ω·cm.

9. The silicon-carbon composite material according to any one of claims 1 to 8, characterized in that: The one-dimensional conductive agent comprises carbon nanotubes and carbon fibers, and may be carbon nanotubes or single-walled carbon nanotubes.

10. The silicon-carbon composite material according to any one of claims 1 to 9, characterized in that: The silicon-carbon composite material has a carbon layer on at least a portion of its surface.

11. A method for preparing a silicon-carbon composite material, characterized in that: include: The silicon-carbon primary particles and the one-dimensional conductive agent are mixed and granulated in a solvent, and spray-dried to obtain a silicon-carbon composite material. The silicon-carbon composite material comprises silicon-carbon secondary particles, the silicon-carbon secondary particles comprise silicon-carbon primary particles and a one-dimensional conductive agent, and the one-dimensional conductive agent is distributed between the silicon-carbon primary particles.

12. The preparation method according to claim 11, characterized in that: The preparation method specifically comprises: Polymerization reaction: Aniline, cyclohexane hexaphosphate and initiator are polymerized to obtain a mixed precursor; High temperature carbonization: subjecting the mixed precursor to high temperature carbonization treatment to obtain a carbonized pretreated material; Activation pore formation: introducing water vapor into the carbonization pretreatment material to perform activation pore formation treatment to obtain porous carbon skeleton primary particles; Depositing silicon: depositing silicon in the porous carbon skeleton primary particles to obtain silicon-carbon primary particles; Mixing and granulating: the silicon-carbon primary particles and the one-dimensional conductive agent are mixed and granulated in a solvent, and spray-dried to obtain a silicon-carbon composite material.

13. The preparation method according to claim 12, characterized in that: The reaction temperature of the polymerization reaction is 60°C-280°C, and can be 80°C-250°C; and / or, The reaction time of the polymerization reaction is 1h-15h, and can be optionally 5h-12h.

14. The preparation method according to claim 12 or 13, characterized in that: The deposition temperature of the deposited silicon is 400° C.-900° C., and can be 500° C.-650° C.; and / or, The deposition time of the deposited silicon is 6 hours to 24 hours, and can be optionally 8 hours to 18 hours.

15. The preparation method according to any one of claims 11 to 14, characterized in that: The preparation method further comprises preparing a carbon layer: performing a carbon coating treatment on the surface of the silicon-carbon composite material.

16. A secondary battery, characterized in that: It comprises a negative electrode plate, wherein the negative electrode plate comprises the silicon-carbon composite material according to any one of claims 1 to 10 or the silicon-carbon composite material prepared by the preparation method according to any one of claims 11 to 15.

17. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 16.

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