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

Abstract

Provided are a silicon-carbon composite material and a preparation method therefor, 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 one-dimensional conductive agents; the one-dimensional conductive agents are distributed between the silicon-carbon primary particles. The silicon-carbon composite material has excellent electron transport performance, is beneficial to reducing the fast charging time for a battery, increases the number of cycles of the battery, can improve the rate capability and cycle performance of the battery, and comprehensively improves the electrochemical performance of the battery.

Description

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

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311549841.3, filed on November 20, 2023, entitled “Silicon-carbon composite material, preparation method thereof, secondary battery and electrical device”, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a silicon-carbon composite material and a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0004] 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 power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0005] Negative electrode active materials are important components of secondary batteries. In order to further improve the energy density of batteries, silicon-based negative electrode active materials have been widely studied. However, due to their large volume expansion, silicon-based materials will affect the electrochemical performance of the battery during use.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a silicon-carbon composite material, which has excellent electron transmission performance, is beneficial to reducing the fast charging time of the battery, increasing the number of cycles of the battery, and can improve the rate performance and cycle performance of the battery, thereby comprehensively improving the electrochemical performance of the battery.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a silicon-carbon composite material, including silicon-carbon secondary particles, the silicon-carbon secondary particles including silicon-carbon primary particles and a one-dimensional conductive agent, and the one-dimensional conductive agent is distributed between the silicon-carbon primary particles.

[0009] On the one hand, the one-dimensional conductive agent is distributed between the silicon-carbon primary particles. The one-dimensional conductive agent acts as a "bridge" between the silicon-carbon primary particles, connecting the primary particles to each other, greatly improving the contact sites between the primary particles, and effectively reducing the electrical deactivation caused by poor contact between the primary particles and the expansion and contraction of the primary particles during charging and discharging, so that the silicon-carbon composite material has excellent electron transport performance, improves the migration kinetics of active ions, shortens the fast charging time of the battery, and improves the rate performance of the material; on the other hand, the one-dimensional conductive agent acts as a conductive buffer matrix, and the one-dimensional conductive agent can be linearly wrapped around the silicon-carbon primary particles to effectively restrain the silicon-carbon primary particles. The elasticity and binding effect of the matrix can effectively inhibit the volume change of the primary particles in the process of embedding and de-embedding active ions, thereby improving the cycle stability and lithium storage capacity of the silicon-carbon composite material and extending the cycle life of the battery.

[0010] 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.

[0011] 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, so that the silicon-carbon composite material has excellent electron transport performance, improves the migration kinetics of active ions, shortens the fast charging time of the battery, and improves the rate performance of the material.

[0012] 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%.

[0013] A suitable mass content of the one-dimensional conductive agent ensures excellent electrical contact between primary particles, improving the rate and cycle performance of secondary batteries. This also reduces the impact on battery cycle performance caused by changes in the material's internal structure due to excessive one-dimensional conductive agent content. A one-dimensional conductive agent with an appropriate mass content can balance both rate and cycle performance, comprehensively improving battery performance.

[0014] In any embodiment, the particle size of the silicon carbon primary particles is 20 nm-100 nm, and optionally 20 nm-60 nm.

[0015] The particle size of the silicon-carbon primary particles is within a suitable range, so that the one-dimensional conductive agent can connect a sufficient number of silicon-carbon primary particles to each other, so that there is excellent electrical contact between the primary particles, thereby achieving the purpose of improving the rate performance of the secondary battery. At the same time, the silicon-carbon primary particles have a particle size within a suitable range, so that the silicon-carbon secondary particles have a suitable particle size, the structure of the silicon-carbon composite material is relatively stable, and the battery has excellent cycle performance.

[0016] In any embodiment, the silicon carbon primary particles include:

[0017] porous carbon framework;

[0018] The silicon-based material is at least partially disposed in the pores of the porous carbon skeleton.

[0019] Silicon-carbon primary particles have a stable porous skeleton structure with strong supporting capacity, which is manifested as high stress capacity, and have excellent mechanical properties and electrical conductivity; the pore structure in its porous carbon skeleton provides more space for setting up silicon-based materials, which can be used for large-scale silicon storage; when the porous carbon skeleton is compounded with the silicon-based material, the silicon-based material is not easy to agglomerate and can be evenly dispersed in the pores of the porous carbon skeleton; after the porous carbon skeleton is compounded with silicon particles, the electrical conductivity of the silicon-carbon primary particles can be improved, and at the same time, the volume effect of silicon in the process of lithium insertion and extraction can be alleviated, and it can fully withstand the stress changes of the silicon-based material, thereby 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.

[0020] In any embodiment, the porous carbon skeleton satisfies at least one of the following (1)-(2):

[0021] (1) The pore volume of the porous carbon skeleton is 0.7 cm 3 / g-1.0cm 3 / g;

[0022] (2) The pore size of the porous carbon skeleton is 0.7 nm to 3 nm, and can be optionally 0.8 nm to 1.5 nm.

[0023] The pore volume of the porous carbon skeleton is within an appropriate range, which can not only ensure the stability of the skeleton structure but also meet the capacity of deposited silicon. Silicon particles are attached to the pores, and the silicon particles and the porous carbon skeleton can work synergistically to improve the capacity and conductivity of the silicon-carbon composite material, and improve the rate performance and energy density of the battery.

[0024] The pore size of the porous carbon skeleton is within an appropriate range, which is conducive to the subsequent silicon particles entering the pores of the porous carbon skeleton, reducing the risk of silicon deposition on the surface of the porous carbon skeleton; and is conducive to the porous carbon skeleton particles approaching full deposition, improving the material's electrical and ionic conductivity, and improving the material's rate performance.

[0025] In any embodiment, the silicon carbon primary particles satisfy at least one of the following (3)-(4):

[0026] (1) The specific surface area of ​​silicon carbon primary particles is 1m 2 / g-20m 2 / g, optional 8m 2 / g-15m 2 / g;

[0027] (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%.

[0028] By controlling the specific surface area of ​​the silicon-carbon primary particles within an appropriate range, the one-dimensional conductive agent can bind the silicon-carbon primary particles in a linear structure, thereby suppressing the volume change of the primary particles during the process of embedding and de-embedding active ions, which is beneficial to improving the cycle performance of the battery.

[0029] By controlling the mass fraction of the silicon-based material within an appropriate range, the silicon-carbon composite material has a high gram capacity, thereby improving the energy density of the battery. At the same time, the volume expansion of the silicon-carbon composite material is limited to a certain range, so that the silicon-carbon composite material has a certain structural stability.

[0030] In any embodiment, the silicon carbon secondary particles satisfy at least one of the following (5) to (8):

[0031] (5) The specific surface area of ​​silicon carbon secondary particles is 0.1m 2 / g-0.8m 2 / g, optional 0.15m 2 / g-0.6m 2 / g;

[0032] (6) The volume distribution particle size Dv50 of silicon carbon secondary particles is 0.9 μm-3 μm;

[0033] (7) The tap density of silicon carbon secondary particles is 0.75 g / cm 3 -1.00g / cm 3 ;

[0034] (8) The powder resistivity of the silicon carbon secondary particles at 5 MPa is 0.1 Ω·cm-10.0 Ω·cm, and can be optionally 0.1 Ω·cm-1.0 Ω·cm.

[0035] By controlling the specific surface area of ​​the silicon-carbon secondary particles within a suitable range, the material has excellent kinetic properties, which is beneficial to the rate performance of the secondary battery.

[0036] By controlling the volume distribution particle size Dv50 of the silicon-carbon secondary particles within an appropriate range, the structure of the silicon-carbon composite material is relatively stable, the dynamic performance is good, and the rate performance and cycle performance of the secondary battery are improved.

[0037] Controlling the tap density of silicon-carbon secondary particles within an appropriate range can increase the compaction density of the negative electrode and improve the energy density of the secondary battery. It is also beneficial for the negative electrode to have a suitable pore distribution, improve the ion and electron transmission performance, and improve the wetting characteristics of the negative electrode to the electrolyte, thereby improving the rate performance and cycle performance of the secondary battery.

[0038] Controlling the powder resistivity of silicon-carbon secondary particles at 5 MPa within an appropriate range can enhance the electronic conductivity of the negative electrode and further improve the rate performance of the battery.

[0039] In any embodiment, the one-dimensional conductive agent comprises carbon nanotubes or carbon fibers, and may be carbon nanotubes or single-arm carbon nanotubes.

[0040] In any embodiment, the silicon-carbon composite material has a carbon layer on at least a portion of its surface.

[0041] The carbon layer coated on the silicon-carbon composite material is beneficial to improving the conductivity of the silicon-carbon composite material and 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.

[0042] A second aspect of the present application provides a method for preparing a silicon-carbon composite material, comprising:

[0043] 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.

[0044] 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.

[0045] In the above preparation method, the one-dimensional conductive agent is mixed with the silicon-carbon primary particles in liquid phase, so that the one-dimensional conductive agent is distributed between the silicon-carbon primary particles. The one-dimensional conductive agent acts as a "bridge" between the silicon-carbon primary particles, connecting the primary particles to each other, greatly improving the contact sites between the primary particles, and effectively reducing the electrical deactivation caused by poor contact between the primary particles and the expansion and contraction of the primary particles during charging and discharging, so that the silicon-carbon composite material has excellent electron transport properties, improves the migration kinetics of active ions, shortens the fast charging time of the battery, and improves the rate performance of the material; on the other hand, the one-dimensional conductive agent acts as a conductive buffer matrix, and the one-dimensional conductive agent can also be linearly wound on the silicon-carbon primary particles to effectively restrain the silicon-carbon primary particles. The elasticity and binding effect of the matrix can effectively inhibit the volume change of the primary particles in the process of deintercalation and extraction of active ions, thereby improving the cycle stability and lithium storage capacity of the silicon-carbon composite material and extending the cycle life of the battery.

[0046] In any embodiment, the preparation method specifically comprises:

[0047] Polymerization reaction: Aniline, cyclohexane hexaphosphate and initiator are polymerized to obtain a mixed precursor;

[0048] High temperature carbonization: subjecting the mixed precursor to high temperature carbonization treatment to obtain a carbonized pretreated material;

[0049] Activation pore creation: introducing water vapor into the carbonization pretreatment material to perform activation pore creation treatment to obtain porous carbon skeleton primary particles;

[0050] Depositing silicon: depositing silicon in the porous carbon skeleton primary particles to obtain silicon-carbon primary particles;

[0051] Mixed granulation: Silicon-carbon primary particles and a one-dimensional conductive agent are mixed and granulated in a solvent, and spray-dried to obtain a silicon-carbon composite material.

[0052] The above preparation method first uses aniline and cyclohexane hexaphosphate to polymerize under the action of an initiator to generate polyaniline microspheres, a carbon material precursor. Then, a high-temperature carbonization step is used to fully carbonize the polyaniline to obtain primary particles of the carbon material with high conductivity. The activation pore-forming step helps to generate primary particles with a porous carbon skeleton, obtaining a porous carbon skeleton with a high pore size or pore volume, which is conducive to subsequent silicon deposition. Silicon particles are deposited in the pores of the porous carbon skeleton primary particles to obtain silicon-carbon primary particles. Finally, the silicon-carbon primary particles are mixed with a one-dimensional conductive agent in the liquid phase and spray-dried to obtain a silicon-carbon composite material.

[0053] In any embodiment, the reaction temperature of the polymerization reaction is 60° C.-280° C., optionally 80° C.-250° C.; and / or the reaction time of the polymerization reaction is 1 h-15 h, optionally 5 h-12 h.

[0054] By controlling the reaction time and reaction temperature of the polymerization reaction, the particle size of the polyaniline microspheres can be controlled, thereby achieving the purpose of controlling the particle size of the primary particles of the carbon material.

[0055] In any embodiment, the deposition temperature of the deposited silicon is 400° C.-900° C., optionally 500° C.-650° C.; and / or the deposition time of the deposited silicon is 6 h-24 h, optionally 8 h-18 h.

[0056] The deposition time and temperature of the deposited silicon are controlled within a suitable range so that the silicon is evenly dispersed in the pores of the porous carbon skeleton, and the silicon-carbon composite material has excellent structural parameters.

[0057] In any embodiment, the preparation method further comprises preparing a carbon layer: performing a carbon coating treatment on the surface of the silicon-carbon composite material.

[0058] Coating the surface of the silicon-carbon composite material with a carbon layer is beneficial to improving the conductivity of the silicon-carbon composite material and 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.

[0059] A third aspect of the present application provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the silicon-carbon composite material of the first aspect of the present application or the silicon-carbon composite material prepared according to the preparation method of the second aspect of the present application.

[0060] A fourth aspect of the present application provides an electrical device comprising the secondary battery according to the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0062] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0063] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0064] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0065] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0066] 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application;

[0067] FIG7 is a schematic structural diagram of the silicon-carbon composite material of the present application.

[0068] Description of reference numerals:

[0069] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0070] Below, the embodiments of the silicon-carbon composite material and its preparation method, secondary battery and electrical device of the present application are described in detail with appropriate reference to the accompanying 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 the same structures are omitted. This is to avoid 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 described in the claims.

[0071] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0073] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0074] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0075] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0076] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0077] Silicon-carbon composites are one of the most commonly used active materials. Currently, the preparation of silicon-carbon composites mainly involves directly mixing silicon with carbon materials. These silicon-carbon materials require certain restrictions on the silicon content. When the silicon content is too high, the expansion is large, causing the silicon-carbon composite material to break and pulverize. The loss of electrical contact between the materials causes the capacity to decay rapidly, and the battery's cycle stability performance deteriorates. In addition, the silicon-carbon composite material itself has poor electrical conductivity, which seriously limits its further application. Therefore, it is necessary to design a new silicon-carbon composite material to meet the needs of the next generation of electrochemistry.

[0078] [Silicon-carbon composite materials]

[0079] Based on this, the present application provides a silicon-carbon composite material, including silicon-carbon secondary particles, wherein 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.

[0080] Silicon carbon primary particles and silicon carbon secondary particles are both well-known in the art. Silicon carbon primary particles refer to non-agglomerated particles. Silicon carbon secondary particles refer to agglomerated particles formed by the aggregation of two or more silicon carbon primary particles. Silicon carbon primary particles and silicon carbon secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0081] As used herein, 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.

[0082] On the one hand, the one-dimensional conductive agent is distributed between the silicon-carbon primary particles, that is, the one-dimensional conductive agent acts as a "bridge" between the silicon-carbon primary particles, connecting the primary particles to each other, greatly improving the contact sites between the primary particles, and effectively reducing the electrical deactivation caused by poor contact between the primary particles and the expansion and contraction of the primary particles during charging and discharging, so that the silicon-carbon composite material has excellent electron transport performance, improves the migration kinetics of active ions, shortens the fast charging time of the battery, and improves the rate performance of the material; on the other hand, the one-dimensional conductive agent acts as a conductive buffer matrix, and the one-dimensional conductive agent can also be linearly wrapped around the silicon-carbon primary particles to effectively restrain the silicon-carbon primary particles. The elasticity and binding effect of the matrix can effectively inhibit the volume change of the primary particles in the process of deintercalation and extraction of active ions, thereby improving the cycle stability and lithium storage capacity of the silicon-carbon composite material and extending the cycle life of the battery.

[0083] 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 selected from any value of 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, and 10 nm, or a range consisting of any two of these values.

[0084] The diameter or length of the one-dimensional conductive agent can be tested using methods and equipment known in the art. For example, it can be tested by using a scanning electron microscope (such as ZEISS Sigma300). As an example, the following steps can be followed: first, the negative electrode sheet containing the silicon-carbon composite material is cut into a sample to be tested of a certain size (for example, 6 mm × 6 mm), and the sample to be tested is clamped with two conductive and heat-conductive thin sheets (such as copper foil), and the sample to be tested and the thin sheet are glued and fixed with glue (such as double-sided tape), and a flat iron block of a certain mass (such as about 400 g) is used to press for a certain time (such as 1 hour) to make the gap between the sample to be tested and the copper foil as small as possible, and then the edges are trimmed with scissors and glued to the sample stage with conductive glue, and the sample slightly protrudes from the edge of the sample stage. Then, the sample stage is placed in the sample holder and locked, the power of the argon ion cross-section polisher (e.g., IB-19500CP) is turned on and vacuum is applied (e.g., 10Pa-4Pa), the argon flow rate (e.g., 0.15MPa), voltage (e.g., 8KV), and polishing time (e.g., 2 hours) are set, the sample stage is adjusted to the rocking mode, and polishing is started. After polishing, a scanning electron microscope (e.g., ZEISS Sigma 300) is used to obtain an ion polished cross-sectional morphology (CP) image of the silicon-carbon composite material, and then the diameter or length of the one-dimensional conductive agent is statistically analyzed to draw a normal distribution curve. The diameter or length on the normal distribution curve is the diameter and length of the one-dimensional conductive agent.

[0085] The diameter of the one-dimensional conductive agent is controlled within an appropriate range, and a sufficient number of one-dimensional conductive agents are distributed between the primary particles, that is, a sufficient number of "bridges" are built between the primary particles, so as to achieve the purpose of improving the conductivity of the silicon-carbon composite material. At the same time, the diameter of the one-dimensional conductive agent is within an appropriate range, which 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.

[0086] In some embodiments, the diameter of the one-dimensional conductive agent is 0.5 nm to 5 nm. In some embodiments, the diameter of the one-dimensional conductive agent can be any value selected from 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 consisting of any two of these values.

[0087] 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 battery's rate performance and cycle performance.

[0088] 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 any value selected from 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or a range consisting of any two values ​​thereof.

[0089] By controlling the length of the one-dimensional conductive agent within an appropriate range, on the one hand, the "bridge" between the primary particles is long enough to connect the primary particles, and the primary particles can be linearly wound to restrain the expansion of the primary particles. On the other hand, the one-dimensional conductive agent of appropriate length also reduces the possibility of the one-dimensional conductive agent breaking during the battery cycle.

[0090] 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 any value selected from 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range consisting of any two values ​​thereof.

[0091] When the length of the one-dimensional conductive agent is within an appropriate range, the number of battery cycles can be further increased, the fast charging time of the battery can be reduced, and the cycle performance and rate performance of the battery can be improved.

[0092] 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 any value selected from 1000, 2000, 3000, 4000, 50000, or a range consisting of any two values ​​thereof.

[0093] By regulating the aspect ratio of the one-dimensional conductive agent within an appropriate range, it is beneficial to improve the electron conduction between primary particles, so that the silicon-carbon composite material has excellent electron transport performance, improves the migration dynamics of active ions, shortens the fast charging time of the battery, and improves the rate performance of the material.

[0094] 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 any value selected from 3000, 3500, 4000, 4500, 50000, or a range consisting of any two values ​​thereof.

[0095] Controlling the aspect ratio of the one-dimensional conductive agent within an appropriate range can further increase the number of battery cycles, reduce the battery's fast charging time, and improve the battery's cycle performance and rate performance.

[0096] 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%.

[0097] In some embodiments, based on the mass of the silicon-carbon secondary particles, the mass content of the one-dimensional conductive agent can be selected as any value of 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6% or a range consisting of any two values ​​therein.

[0098] In some embodiments, based on the mass of the silicon-carbon secondary particles, the mass content of the one-dimensional conductive agent can be any value of 0.3%, 0.4%, 0.5%, 0.6%, or a range consisting of any two values ​​thereof.

[0099] A suitable mass content of the one-dimensional conductive agent ensures excellent electrical contact between primary particles, improving the rate and cycle performance of secondary batteries. This also reduces the impact on battery cycle performance caused by changes in the material's internal structure due to excessive one-dimensional conductive agent content. A one-dimensional conductive agent with an appropriate mass content can balance both rate and cycle performance, comprehensively improving battery performance.

[0100] In some embodiments, the particle size of the silicon-carbon primary particles is 20 nm to 100 nm. In some embodiments, the particle size of the silicon-carbon primary particles can be any value selected from 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 100 nm, or a range consisting of any two of these values.

[0101] The particle size of silicon-carbon primary particles can be tested using methods and equipment known in the art. For example, it can be tested by using a scanning electron microscope (such as ZEISS Sigma300). As an example, the following steps can be followed: first, the negative electrode sheet containing the silicon-carbon composite material is cut into a sample to be tested of a certain size (for example, 6 mm × 6 mm), and the sample to be tested is clamped with two conductive and heat-conductive thin sheets (such as copper foil), and the sample to be tested and the thin sheet are glued and fixed with glue (such as double-sided tape), and a flat iron block of a certain mass (such as about 400 g) is used to press for a certain time (such as 1 hour) to make the gap between the sample to be tested and the copper foil as small as possible, and then the edges are trimmed with scissors and glued to a sample table with conductive glue, with the sample slightly protruding from the edge of the sample table. Then the sample stage is put into the sample holder and locked and fixed, the argon ion cross-section polisher (e.g., IB-19500CP) power is turned on and vacuumized (e.g., 10Pa-4Pa), the argon flow rate (e.g., 0.15MPa) and voltage (e.g., 8KV) and polishing time (e.g., 2 hours) are set, the sample stage is adjusted to the swing mode and polishing is started. After polishing is completed, a scanning electron microscope (e.g., ZEISS Sigma 300) is used to obtain an ion polishing cross-sectional morphology (CP) picture of the silicon-carbon composite material. According to the ion polishing 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 circle 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 statistically analyzed using graphics software.

[0102] The particle size of the silicon-carbon primary particles is within a suitable range, so that the one-dimensional conductive agent can connect a sufficient number of silicon-carbon primary particles to each other, so that there is excellent electrical contact between the primary particles, thereby achieving the purpose of improving the rate performance of the secondary battery. At the same time, the silicon-carbon primary particles have a particle size within a suitable range, so that the silicon-carbon secondary particles have a suitable particle size, the structure of the silicon-carbon composite material is relatively stable, and the battery has excellent cycle performance.

[0103] In some embodiments, the particle size of the silicon carbon primary particles is 20 nm to 60 nm. In some embodiments, the particle size of the silicon carbon primary particles can be any value selected from 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, or a range consisting of any two of these values.

[0104] By controlling the particle size of the silicon-carbon primary particles within an appropriate 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.

[0105] In some embodiments, the silicon-carbon primary particles include: a porous carbon skeleton; and a silicon-based material, at least a portion of the silicon-based material being disposed in pores of the porous carbon skeleton.

[0106] Silicon-carbon primary particles have a stable porous skeleton structure with strong supporting capacity, which is manifested as high stress capacity, and have excellent mechanical properties and electrical conductivity; the pore structure in its porous carbon skeleton provides more space for setting up silicon-based materials, which can be used for large-scale silicon storage; when the porous carbon skeleton is compounded with the silicon-based material, the silicon-based material is not easy to agglomerate and can be evenly dispersed in the pores of the porous carbon skeleton; after the porous carbon skeleton is compounded with silicon particles, the electrical conductivity of the silicon-carbon primary particles can be improved, and at the same time, the volume effect of silicon in the process of lithium insertion and extraction can be alleviated, and it can fully withstand the stress changes of the silicon-based material, thereby 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.

[0107] In some embodiments, the pore volume of the porous carbon skeleton is 0.7 cm 3 / g-1.0cm 3 / g.

[0108] In some embodiments, the pore volume of the porous carbon skeleton can be 0.7 cm 3 / g, 0.75cm 3 / g, 0.8cm 3 / g, 0.85cm 3 / g, 0.90cm 3 / g, 0.95cm 3 / g, 1.0cm 3 / g or a value within the range consisting of any two of the above points.

[0109] The pore volume of a porous carbon framework is well known in the art and can be measured using instruments and methods known in the art. For example, the pore volume of the material can be determined by referring to GB / T 19587-2004, using the Barret Joyner Halenda (BJH) mesopore size distribution method, using a gas adsorption-desorption method under a micro-mesoporous model and selecting adsorption branch data.

[0110] The pore volume of the porous carbon skeleton is within an appropriate range, which can not only ensure the stability of the skeleton structure but also meet the capacity of deposited silicon. Silicon particles are attached to the pores, and the silicon particles and the porous carbon skeleton can work synergistically to improve the capacity and conductivity of the silicon-carbon composite material, and improve the rate performance and energy density of the battery.

[0111] In some embodiments, the pore size of the porous carbon skeleton is 0.7 nm to 3 nm. In some embodiments, the pore size of the porous carbon skeleton can be selected from 0.7 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, or a value in a range consisting of any two of the above points.

[0112] In some embodiments, the pore size of the porous carbon skeleton is 0.8 nm to 1.5 nm. In some embodiments, the pore size of the porous carbon skeleton can be selected from 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 in a range consisting of any two of the above points.

[0113] The pore size of a porous carbon framework is well known in the art and can be measured using instruments and methods known in the art. As an example, a certain amount of the porous carbon framework prepared above is taken as a sample and analyzed using a scanning electron microscope (SEM) to obtain an SEM image. The pore sizes are then statistically analyzed to create a normal distribution curve. The median pore size on the normal distribution curve is the pore size of the porous carbon framework.

[0114] The pore size of the porous carbon skeleton is within an appropriate range, which is conducive to the subsequent silicon particles entering the pores of the porous carbon skeleton, reducing the risk of silicon deposition on the surface of the porous carbon skeleton; and is conducive to the porous carbon skeleton particles approaching full deposition, improving the material's electrical and ionic conductivity, and improving the material's rate performance.

[0115] In some embodiments, the specific surface area of ​​the silicon carbon primary particles is 1m 2 / g-20m 2In some embodiments, the specific surface area of ​​the silicon carbon primary particles can be 1m 2 / g、5m 2 / g、10m 2 / g、15m 2 / g, 20m 2 Any value in / g or a range consisting of any two values ​​in it.

[0116] In some embodiments, the specific surface area of ​​the silicon carbon primary particles is 8m 2 / g-15m 2 In some embodiments, the specific surface area of ​​the silicon carbon primary particles can be 8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 Any value in / g or a range consisting of any two values ​​in it.

[0117] The specific surface area of ​​silicon-carbon primary particles is well known in the art and can be measured using methods known in the art. As an example, the specific surface area of ​​the porous carbon framework was measured using a 3Flex surface area analyzer from Micromeritics. The specific surface area of ​​the silicon-carbon primary particles was obtained by T-Plot fitting (BET).

[0118] By controlling the specific surface area of ​​the silicon-carbon primary particles within an appropriate range, the one-dimensional conductive agent can bind the silicon-carbon primary particles in a linear structure, thereby suppressing the volume change of the primary particles during the process of embedding and de-embedding active ions, which is beneficial to improving the cycle performance of the battery.

[0119] In some embodiments, the mass fraction of the silicon-based material is 30%-50% based on the mass of the silicon-carbon primary particles. In some embodiments, the mass fraction of the silicon-based material is 30%, 35%, 40%, 45%, 50%, or any value selected from the group consisting of 30%, 35%, 40%, 45%, and 50%, or a range consisting of any two of these values, based on the mass of the silicon-carbon primary particles.

[0120] In some embodiments, the mass fraction of the silicon-based material is 35%-45% based on the mass of the silicon-carbon primary particles. In some embodiments, the mass fraction of the silicon-based material is 35%, 40%, 45%, or any value selected from the group consisting of 35%, 40%, and 45%, or a range consisting of any two of these values, based on the mass of the silicon-carbon primary particles.

[0121] The mass content of silicon-based materials can be tested using methods and equipment known in the art, for example, it can be measured with reference to EPA 6010D-2014 standard; specifically, ICP-OES (elemental analysis-inductively coupled plasma optical emission spectrometry) testing can be used. The sample to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into an ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then return to the ground state from the excited state; in the above process, energy is released and recorded as different characteristic spectral lines for elemental quantitative analysis.

[0122] By controlling the mass fraction of the silicon-based material within an appropriate range, the silicon-carbon composite material has a high gram capacity, thereby improving the energy density of the battery. At the same time, the volume expansion of the silicon-carbon composite material is limited to a certain range, so that the silicon-carbon composite material has a certain structural stability.

[0123] In some embodiments, the specific surface area of ​​the silicon carbon secondary particles is 0.1 m 2 / g-0.8m 2 In some embodiments, the specific surface area of ​​the silicon-carbon secondary particles can be 0.1 m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 Any value in / g or a range consisting of any two values ​​in it.

[0124] In some embodiments, the specific surface area of ​​the silicon carbon secondary particles is 0.15 m 2 / g-0.6m 2 In some embodiments, the specific surface area of ​​the silicon-carbon secondary particles can be 0.15 m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 Any value in / g or a range consisting of any two values ​​in it.

[0125] The specific surface area of ​​silicon-carbon secondary particles is well known in the art and can be measured using methods known in the art. For example, the specific surface area of ​​silicon-carbon secondary particles was measured using a 3Flex surface area analyzer from Micromeritics. The BET specific surface area of ​​the silicon-carbon secondary particles was obtained by T-Plot fitting.

[0126] By controlling the specific surface area of ​​the silicon-carbon secondary particles within a suitable range, the material has excellent kinetic properties, which is beneficial to the rate performance of the secondary battery.

[0127] 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 any value selected from 0.9 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or a range consisting of any two values ​​thereof.

[0128] The volume distribution particle size Dv50 of the silicon-carbon secondary particles is well known in the art and can be measured using methods known in the art. For example, the silicon-carbon secondary particle sample can be measured according to GB / T 19077-2016 / ISO 13320:2009. The testing equipment can be a laser particle size analyzer (e.g., Malvern Master Size 3000).

[0129] By controlling the volume distribution particle size Dv50 of the silicon-carbon secondary particles within an appropriate range, the structure of the silicon-carbon composite material is relatively stable, the dynamic performance is good, and the rate performance and cycle performance of the secondary battery are improved.

[0130] In some embodiments, the tap density of the silicon carbon secondary particles is 0.75 g / cm 3 -1.00g / cm 3 In some embodiments, the tap density of the silicon carbon secondary particles may be 0.75 g / cm 3 、0.80g / cm 3 , 0.85g / cm 3 , 0.90g / cm 3 , 0.95g / cm 3 , 1.00g / cm 3 Any value in , or a range of any two values ​​in .

[0131] The tap density of silicon-carbon secondary particles is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. A Dandong Better BT-301 tester can be used, with the following test parameters: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 mm, vibration count 5000 times, and a 25 mL graduated cylinder.

[0132] Controlling the tap density of silicon-carbon secondary particles within an appropriate range can increase the compaction density of the negative electrode and improve the energy density of the secondary battery. It is also beneficial for the negative electrode to have a suitable pore distribution, improve the ion and electron transmission performance, and improve the wetting characteristics of the negative electrode to the electrolyte, thereby improving the rate performance and cycle performance of the secondary battery.

[0133] In some embodiments, the powder resistivity of the silicon-carbon secondary particles at 5 MPa is between 0.1 Ω·cm and 10 Ω·cm. In some embodiments, the powder resistivity of the silicon-carbon secondary particles at 5 MPa can be any value selected from 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, and 10 Ω·cm, or a range consisting of any two of these values.

[0134] In some embodiments, the powder resistivity of the silicon-carbon secondary particles at 5 MPa is between 0.1 Ω·cm and 1 Ω·cm. In some embodiments, the powder resistivity of the silicon-carbon secondary particles at 5 MPa can be any value selected from 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, and 1.0 Ω·cm, or a range consisting of any two of these values.

[0135] The powder resistivity of silicon-carbon secondary particles is 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 Jingge Electronics Co., Ltd.) can be used for testing. During the test, 1g of powder sample can be taken, and the powder sample can be placed between the electrodes of the resistivity tester. The electronic press is used to press the test pressure (for example, 5Mpa) for 15-25s to obtain a sheet sample. The powder resistivity δ of the material is calculated according to the formula δ = (S×R) / h, in units of Ω·cm. h is the height of the sheet sample, in cm; R is the resistance, in Ω; S is the area of ​​the sheet sample, in cm 2 .

[0136] In some embodiments, the one-dimensional conductive agent comprises carbon nanotubes or carbon fibers.

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

[0138] Compared with carbon fibers, carbon nanotubes have a hollow structure, which increases the ion transmission channels, facilitates the circulation of electrolyte in the pipes, improves the conductivity of the material, and improves the rate performance of the battery.

[0139] In some embodiments, the one-dimensional conductive agent comprises multi-walled carbon nanotubes or single-walled carbon nanotubes.

[0140] In some embodiments, the one-dimensional conductive agent comprises single-walled carbon nanotubes.

[0141] The performance of single-walled carbon nanotubes is better than that of multi-walled carbon nanotubes. Using single-walled carbon nanotubes as a one-dimensional conductive agent can further improve the cycle performance and rate performance of the battery.

[0142] In some embodiments, at least a portion of the surface of the silicon-carbon composite material has a carbon layer.

[0143] The carbon layer coated on the silicon-carbon composite material is beneficial to improving the conductivity of the silicon-carbon composite material and 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.

[0144] In some embodiments of the present application, a method for preparing a silicon-carbon composite material is provided, comprising:

[0145] Silicon-carbon primary particles and a one-dimensional conductive agent are mixed and granulated in a solvent, and spray-dried 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.

[0146] In the above preparation method, the one-dimensional conductive agent is mixed with the silicon-carbon primary particles in liquid phase, so that the one-dimensional conductive agent is distributed between the silicon-carbon primary particles, that is, the one-dimensional conductive agent acts as a "bridge" between the silicon-carbon primary particles, connecting the primary particles to each other, greatly improving the contact sites between the primary particles, and effectively reducing the electrical deactivation caused by poor contact between the primary particles and the expansion and contraction of the primary particles during charging and discharging, so that the silicon-carbon composite material has excellent electron transport properties, improves the migration kinetics of active ions, shortens the fast charging time of the battery, and improves the rate performance of the material; on the other hand, the one-dimensional conductive agent acts as a conductive buffer matrix, and the one-dimensional conductive agent can be linearly wrapped around the silicon-carbon primary particles, effectively binding the silicon-carbon primary particles. The elasticity and binding effect of the matrix can effectively suppress the volume change of the primary particles in the process of deintercalation and extraction of active ions, thereby improving the cycle stability and lithium storage capacity of the silicon-carbon composite material and extending the cycle life of the battery.

[0147] In some embodiments, the preparation method specifically comprises:

[0148] Polymerization reaction: Aniline, cyclohexane hexaphosphate and initiator are polymerized to obtain a mixed precursor;

[0149] High-temperature carbonization: subjecting the mixed precursor to high-temperature carbonization treatment to obtain a carbonized pretreated material;

[0150] Activation pore formation: introducing water vapor into the carbonization pretreatment material to perform activation pore formation treatment to obtain porous carbon skeleton primary particles;

[0151] Depositing silicon: depositing silicon in the porous carbon skeleton primary particles to obtain silicon-carbon primary particles;

[0152] 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.

[0153] The above preparation method first uses aniline and cyclohexane hexaphosphate to polymerize under the action of an initiator to generate polyaniline microspheres, a carbon material precursor. Then, a high-temperature carbonization step is used to fully carbonize the polyaniline to obtain primary particles of the carbon material with high conductivity. The activation pore-forming step helps to generate primary particles with a porous carbon skeleton, obtaining a porous carbon skeleton with a high pore size or pore volume, which is conducive to subsequent silicon deposition. Silicon particles are deposited in the pores of the porous carbon skeleton primary particles to obtain silicon-carbon primary particles. Finally, the silicon-carbon primary particles are mixed with a one-dimensional conductive agent in the liquid phase and spray-dried to obtain a silicon-carbon composite material.

[0154] In some embodiments, the initiator comprises a persulfate. In some embodiments, the initiator may be ammonium persulfate or potassium persulfate.

[0155] In some embodiments, the solvent in the mixing and granulation step is any one of an alcohol solvent, a ketone solvent, an ether solvent or water, or a combination of at least two thereof.

[0156] 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 selected from any value of 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, 200°C, 220°C, 240°C, 260°C, 280°C, or a range consisting of any two values ​​thereof. 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 selected from any value of 80°C, 90°C, 100°C, 110°C, 120°C, 140°C, 160°C, 180°C, 220°C, 250°C, or a range consisting of any two values ​​thereof.

[0157] In some embodiments, the reaction time of the polymerization reaction is 1 hour to 15 hours. In some embodiments, the reaction time of the polymerization reaction can be selected from any value of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, and 15 hours, or a range consisting of any two values ​​thereof.

[0158] In some embodiments, the polymerization reaction time is 5 h to 12 h. In some embodiments, the polymerization reaction time can be selected from any value of 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or a range consisting of any two values ​​thereof.

[0159] By controlling the reaction time or the reaction temperature of the polymerization reaction, the particle size of the polyaniline microspheres can be controlled, thereby achieving the purpose of controlling the particle size of the primary particles of the carbon material.

[0160] In some embodiments, the high-temperature carbonization temperature is 600°C-900°C.

[0161] In some embodiments, the high-temperature carbonization time is 4 hours to 12 hours.

[0162] In some embodiments, the activation and pore-forming treatment temperature is 400°C-500°C.

[0163] In some embodiments, the activation pore-forming treatment time is 4 h to 8 h.

[0164] In some embodiments, the flow rate of the water vapor is 0.5 g / min-1 g / min.

[0165] By controlling the activation pore-forming treatment temperature, treatment time, and water vapor flow rate within appropriate ranges, the pore size and pore volume in the porous carbon skeleton can be within appropriate ranges, thereby obtaining a porous carbon skeleton with excellent structural properties.

[0166] In some embodiments, the deposition temperature of the deposited silicon is 400-900° C. In some embodiments, the deposition temperature of the vapor-deposited silicon can be any value of 400° C., 500° C., 600° C., 700° C., 800° C., 900° C., or a range consisting of any two of these values.

[0167] In some embodiments, the deposition temperature of the deposited silicon is 500°C-650°C. In some embodiments, the deposition temperature of the vapor-deposited silicon can be selected as any value of 500°C, 550°C, 600°C, 650°C, or a range consisting of any two values ​​therein. In some embodiments, the deposition time of the deposited silicon is 6h-24h. In some embodiments, the deposition time of the deposited silicon can be selected as any value of 6h, 10h, 15h, 20h, 24h, or a range consisting of any two values ​​therein. In some embodiments, the deposition time of the deposited silicon is 8h-18h. In some embodiments, the deposition time of the deposited silicon can be selected as any value of 8h, 10h, 12h, 14h, 16h, or a range consisting of any two values ​​therein. The deposition time or deposition temperature of the vapor-deposited silicon is controlled within a suitable range so that the silicon is uniformly dispersed in the pores of the porous carbon skeleton, and the silicon-carbon composite material has excellent structural parameters.

[0168] In some embodiments, the preparation method further comprises preparing a carbon layer: performing a carbon coating treatment on the surface of the silicon-carbon composite material.

[0169] In some embodiments, the carbon coating process includes any one of chemical vapor deposition carbon coating, pyrolysis carbon coating, hydrothermal carbon coating, and polyelectrolyte modification carbon coating.

[0170] Coating the surface of the silicon-carbon composite material with a carbon layer is beneficial to improving the conductivity of the silicon-carbon composite material and 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.

[0171] In one embodiment of the present application, a secondary battery is provided.

[0172] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0173] [Positive electrode]

[0174] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0175] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0176] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (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.).

[0177] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), 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 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0178] 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), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0179] In some embodiments, the positive electrode film layer may further include a conductive agent. For 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.

[0180] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0181] [Negative electrode]

[0182] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein 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 the preparation method in some embodiments.

[0183] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0184] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0185] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0186] 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.

[0187] 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 as 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%, and greater than or equal to 95%.

[0188] The silicon-carbon composite material is controlled within a suitable range so that its battery has excellent energy density and cycle performance.

[0189] 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.

[0190] 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 as any value of 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or a range consisting of any two values ​​therein.

[0191] By controlling the silicon-carbon composite material within an appropriate range, the energy density and cycle life of the battery can be taken into account, and the electrochemical performance of the battery can be comprehensively improved.

[0192] In some embodiments, the negative electrode film layer may further include a binder. The binder may 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).

[0193] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0194] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0195] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0196] [Electrolytes]

[0197] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0198] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0199] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0200] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0201] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0202] [Isolation film]

[0203] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0204] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0205] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0206] In some embodiments, a secondary battery includes a positive electrode sheet, an electrolyte, a separator, and a negative electrode sheet in some embodiments.

[0207] In some embodiments, the secondary battery comprises a lithium-ion battery.

[0208] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0209] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0210] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0211] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination 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.

[0212] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0213] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0214] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0215] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0216] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0217] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may 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 and satellites, energy storage systems, etc., but is not limited thereto.

[0218] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0219] Figure 6 shows an example of an electric device. This device can be a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of secondary batteries, a battery pack or battery module can be used. Another example device can be a mobile phone, tablet computer, or laptop computer. These devices typically require a thin and lightweight design and can use secondary batteries as their power source.

[0220] Example

[0221] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0222] 1. Preparation method

[0223] Example 1

[0224] 1) Preparation of silicon-carbon composite materials

[0225] 500 g of aniline was dissolved in 2000 ml of cyclohexanehexol hexaphosphate and dispersed evenly, and then 50 g of ammonium persulfate was added and stirred evenly to obtain a reaction solution. The reaction solution was placed in a reactor and reacted at 180°C for 8 hours, and dried to obtain a powder. The powder was then placed in a muffle furnace under nitrogen protection and carbonized at 900°C for 4 hours. The carbonized product was introduced into water vapor at 450°C for activation and pore formation treatment for 6 hours, wherein the water vapor flow rate was 1 g / min, to obtain porous carbon skeleton primary particles.

[0226] Containing monosilane as a silicon source and nitrogen as a protective gas, vapor deposition is carried out in a tubular furnace to obtain a silicon-carbon composite material. Among them, the flow rate of monosilane is 0.06L / min; the flow rate of the protective gas is 4L / min; the temperature of vapor deposition is 450°C, and the time is 6 hours to obtain silicon-carbon primary particles. 19.9g of single-walled carbon nanotube dispersion (solid content of 0.03%, single-walled carbon nanotube length of 3μm, diameter of 5nm) and the prepared silicon-carbon primary particles are added to a certain amount of tetrahydrofuran, mixed to obtain a mixed slurry with a solid content of 10%, and the mixed slurry is spray-dried with an outlet air temperature of 95°C and a feed rate of 0.6L / h to obtain a silicon-carbon material of secondary particles, and a one-dimensional conductive agent is distributed between the silicon-carbon primary particles.

[0227] Using methane as the carbon source and nitrogen as the protective gas, the spray-dried material was subjected to vapor deposition of the carbon source in a tubular furnace, wherein the flow rate of methane was 6 L / min, the flow rate of the protective gas was 15 L / min, the vapor deposition temperature was 900°C, the time was 6 h, and the gas source was turned off to cool down to obtain a silicon-carbon composite material.

[0228] 2) Preparation of positive electrode sheet

[0229] Nickel, cobalt, manganese, LiNi 0.95 Co 0.04 Mn 0.01O2 (NCM) ternary material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97%:1%:2%, and N-methylpyrrolidone is added and mixed evenly to obtain a positive electrode slurry; then it is coated on the positive electrode collector, dried, cold pressed, and cut to obtain a positive electrode sheet.

[0230] 3) Preparation of negative electrode sheet

[0231] Graphite and the silicon-carbon composite material prepared in Example 1 were mixed in a mass ratio of 3:7 to obtain a negative electrode active material, wherein the mass fraction of the silicon-carbon composite material was 70% based on the total mass of the negative electrode active material.

[0232] The negative electrode active material, conductive agent carbon black, carbon nanotubes (CNT), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are 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 is coated on the negative electrode current collector, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0233] 4) Isolation film

[0234] Polypropylene film is used as the isolation film.

[0235] 5) Preparation of electrolyte

[0236] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the organic solvents ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and fluoroethylene carbonate (FEC) were mixed in a volume ratio of 1:1:1:1, and LiPF6 was added and dissolved in the organic solvent and stirred evenly to make the concentration of the electrolyte 1 mol / L to obtain the electrolyte of Example 1.

[0237] 6) Preparation of batteries

[0238] The positive electrode sheet, separator, and negative electrode sheet of Example 1 are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation. The cells are then wound to obtain battery cells, the tabs are welded to the battery cells, and the battery cells are placed in an aluminum shell. The electrolyte is then injected and sealed. After standing, cold pressing, formation, shaping, capacity testing, and other processes, a lithium-ion secondary battery is obtained.

[0239] Example 2-3

[0240] The preparation parameters in Example 2-3 are basically the same as those in Example 1, except that the single-walled carbon nanotubes are replaced with multi-walled carbon nanotubes and vapor-grown carbon fibers, wherein the multi-walled carbon nanotubes have a length of 2 μm and a diameter of 80 nm, and the vapor-grown carbon fibers have a length of 4 μm and a diameter of 2 nm. The specific parameters are shown in Table 1.

[0241] Examples 4-11

[0242] The preparation parameters in Examples 4-11 are basically the same as those in Example 1, but the diameter and length of the added single-walled carbon nanotubes are adjusted, and then the length and diameter of the single-walled carbon nanotubes in the silicon-carbon composite material are adjusted, wherein 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 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. Specific parameters are shown in Table 1.

[0243] Examples 12-14

[0244] The preparation parameters in Examples 12-14 are basically the same as those in Example 1, except that the solid content of the added single-walled carbon nanotube dispersion is adjusted. 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.

[0245] Examples 15-18

[0246] The preparation parameters in Examples 15-18 are basically the same as those in Example 1, but the reaction temperature and reaction time of the polymerization reaction are adjusted, and then the volume distribution particle size Dv50 of the silicon-carbon primary particles is adjusted, wherein the polymerization reaction temperature in Example 15 is 220°C, and the reaction time is 4h; the polymerization reaction temperature in Example 16 is 230°C, and the reaction time is 6h; the polymerization reaction temperature in Example 17 is 122°C, and the reaction time is 11h; the polymerization reaction temperature in Example 18 is 138°C, and the reaction time is 13h. The specific parameters are shown in Table 1.

[0247] Comparative Example 1

[0248] The preparation parameters in Comparative Example 1-2 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:

[0249] Comparative Example 1: The difference from Example 1 is that the single-walled carbon nanotubes are replaced with conductive carbon black.

[0250] Comparative Example 2: The difference from Example 1 is that no single-walled carbon nanotubes are added.

[0251] Comparative Example 3:

[0252] After 1000g of lignin was evenly mixed with 200g of KOH, sintering treatment was carried out under nitrogen protective atmosphere conditions, with a heating rate of 1°C / min, a heat treatment temperature of 1150°C, and insulation for 5h. After cooling, the three-dimensional porous carbon skeleton was washed with water to remove impurities and dried to obtain a three-dimensional porous carbon skeleton; 1000g of the obtained three-dimensional porous carbon skeleton was placed in a CVD furnace, heated to 1000°C at 5°C / min, and high-purity nitrogen, methane gas, and silane gas were introduced at a rate of 4.0L / min, 0.5L / min, and 0.5L / min, respectively. The mixed gas time was 8h, and the mixture was naturally cooled to room temperature to obtain a precursor 2. 1000g of the obtained silicon-carbon precursor 2 was placed in a CVD furnace, heated to 1000°C at 5°C / min, and high-purity nitrogen and methane gas were introduced at a rate of 4.0L / min, 0.5L / min, and silane gas were introduced at a rate of 4h. The methane gas time was 4h, and the mixture was naturally cooled to room temperature to obtain a silicon-carbon composite material.

[0253] Comparative Example 4:

[0254] 500g of aniline was evenly dissolved in 2000ml of cyclohexanehexol hexaphosphate, and 50g of ammonium persulfate was added and stirred to obtain a reaction solution. The reaction solution was placed in a reactor at 180°C for 8 hours to obtain a powder. The powder was then carbonized in a muffle furnace at 900°C for 4 hours under nitrogen protection. The carbonized product was then subjected to a water vapor activation treatment at 450°C for 6 hours, with a water vapor flow rate of 1g / min, to obtain porous carbon skeleton primary particles.

[0255] A silicon-carbon composite material was obtained by vapor deposition in a tubular furnace using monosilane as a silicon source and nitrogen as a protective gas. The monosilane flow rate was 0.06 L / min, the protective gas flow rate was 4 L / min, and the vapor deposition temperature was 450°C for 6 hours to obtain silicon-carbon primary particles. The silicon-carbon primary particles were then spray-dried at an outlet air temperature of 95°C and a feed rate of 0.6 L / h to obtain silicon-carbon secondary particles.

[0256] Using methane as the carbon source and nitrogen as the protective gas, silicon-carbon secondary particles are vapor-deposited in a tubular furnace, wherein the flow rate of methane is 6 L / min, the flow rate of the protective gas is 15 L / min, the vapor deposition temperature is 900°C, and the time is 6 hours. The gas source is turned off for cooling to obtain an intermediate product, and the intermediate product is mixed and stirred with 19.9 g of single-walled carbon nanotube dispersion to obtain a silicon-carbon composite material, wherein the single-walled carbon nanotube has a length of 3 μm and a diameter of 1 nm.

[0257] 2. Performance Testing

[0258] 1. Battery performance

[0259] 1) 40% SOC discharge time

[0260] The battery cell was discharged at a constant current of 0.33C to 2.8V and allowed to stand for 30 minutes; charged at a constant current of 0.33C to 4.25V and then at a constant voltage of 0.05C until the voltage stabilized and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 2.8V, at which time the initial capacity C0 was read and allowed to stand for 30 minutes; charged at a constant current of 0.33C to 4.25V and then at a constant voltage of 0.05C until the voltage stabilized and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 0.4C0Ah (40%) SOC and allowed to stand for 60 minutes; discharged at a constant current of 4.5C to 2.8V and recorded the discharge time.

[0261] 2) Fast charging time

[0262] At 25°C, the batteries of each embodiment and comparative example were charged and discharged for the first time at a current of 1C (i.e., the current value at which the rated capacity is completely discharged within 1 hour). Specifically, the battery was charged at a constant current rate of 1C to a voltage of 4.3V, then charged at a constant voltage to a current of ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V. The actual capacity was recorded as C0.

[0263] The battery is then charged with a constant current of 2.0C0, 2.5C0, 3.0C0, 3.5C0, 4.0C0, 4.5C0, 5.0C0, and 5.5C0 in sequence to a full battery charge cut-off voltage of 4.3V or a negative electrode cut-off potential of 0V (whichever is reached first). After each charge is completed, it is discharged with 1C0 to a full battery discharge cut-off voltage of 2.8V. The negative electrode potential corresponding to charging to 10%, 20%, 30%, ..., 80% SOC (State of Charge) at different charge rates is recorded, and the charge rate-negative electrode potential curve under different SOC states is drawn. After linear fitting, the charge rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. The charge rate is the charging window under the SOC state, which is recorded as C20% SOC, C30% SOC, C40% SOC, C50% SOC, respectively. The charging time T (in minutes) for charging the battery from 10% SOC to 80% SOC is calculated using the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%. The shorter this time, the better the battery's fast charging performance.

[0264] 3) Cycle performance

[0265] The secondary batteries prepared in each example and comparative example were charged at a constant current rate of 0.5C to a charge cutoff voltage of 4.25V, then charged at a constant voltage rate to a current of ≤0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cutoff voltage of 2V, allowed to rest for 5 minutes. This constituted one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge testing using this method until the battery capacity decayed to 80%. The number of cycles at this point is the battery's cycle life at 25°C.

[0266] 3. Analysis of test results of various embodiments and comparative examples

[0267] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in the table below.

[0268] Table 1

[0269] From the above results, it can be seen that the silicon-carbon composite material in Example 1-18 includes silicon-carbon secondary particles, and the silicon-carbon secondary particles include silicon-carbon primary particles and a one-dimensional conductive agent distributed between the silicon-carbon primary particles, wherein the one-dimensional conductive agent is single-walled carbon nanotubes, multi-walled carbon nanotubes or carbon fibers. From Example 1-18 and Comparative Example 1, it can be seen that compared with the silicon-carbon composite material in which conductive carbon black zero-dimensional conductive agent is distributed between the primary particles, the silicon-carbon composite material of the present application has a one-dimensional conductive agent distributed between the silicon-carbon primary particles, which is conducive to reducing the fast charge 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. From Example 1-18 and Comparative Example 2, it can be seen that compared with the silicon-carbon composite material in which there is no one-dimensional conductive agent between the primary particles, the silicon-carbon composite material of the present application has a one-dimensional conductive agent distributed between the silicon-carbon primary particles, which is conducive to reducing the fast charge 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. From the comparison of Examples 1-18 and Comparative Example 3, it can be seen that compared to the conductive carbon zero-dimensional conductive agent present in the porous carbon skeleton, the one-dimensional conductive agent of the present application is present between the 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. From the comparison of Example 5 and Comparative Example 4, it can be seen that compared to the silicon-carbon composite material in which the one-dimensional conductive agent is present between the secondary particles, the one-dimensional conductive agent of the present application is distributed between the 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.

[0270] Comparison of Examples 1, 4-6, and 7 shows that controlling the diameter of the single-walled carbon nanotubes to be less than or equal to 10 nm is beneficial for increasing the number of battery cycles and the discharge time at 40% SOC, reducing the fast-charge time of the battery, and improving the battery's rate performance and cycle performance. Comparison of Examples 1, 4-5, and 6-7 shows that controlling the diameter of the single-walled carbon nanotubes to be 0.5 nm to 5 nm can further reduce the battery's fast-charge time, increase the number of battery cycles and the discharge time at 40% SOC, and improve the battery's rate performance and cycle performance.

[0271] Comparisons of Examples 5, 9, and 10 with Examples 8 and 11 show that controlling the length of the single-walled carbon nanotubes to 1 μm to 5 μm is beneficial for increasing the battery's 40% SOC discharge time, reducing the battery's fast-charge time, and improving the battery's rate performance. Comparisons of Examples 5 and 10 with Examples 8, 9, and 11 show that controlling the length of the single-walled carbon nanotubes to 3 μm to 5 μm can further increase the battery's cycle life, reduce the battery's fast-charge time, and improve the battery's cycle performance and rate performance.

[0272] Comparing Examples 5, 9-10 with Examples 1, 4, 6-8, and 11, it can be seen that controlling the aspect ratio of the single-walled carbon nanotubes to 1000-5000 is beneficial for increasing the battery's 40% SOC discharge time, reducing the battery's fast charge time, and improving the battery's rate performance. Comparing Examples 5 and 10 with Examples 1, 4, 6-9, and 11, it can be seen that controlling the aspect ratio of the single-walled carbon nanotubes to 3000-5000 can further increase the battery's cycle life, reduce the battery's fast charge time, and improve the battery's cycle performance and rate performance.

[0273] As can be seen from Examples 5, 12-14, when the mass content of single-walled carbon nanotubes is less than or equal to 0.7% based on the mass of the silicon-carbon secondary particles, the battery has a shorter fast-charge time, a longer discharge time, and a higher number of cycles, and the battery has excellent rate performance and cycle performance. As can be seen from the comparison of Examples 5 and 13 with Examples 12 and 14, when the mass content of single-walled carbon nanotubes is 0.3%-0.6% based on the mass of the silicon-carbon secondary particles, the battery can increase the number of cycles and the discharge time to 40% SOC, reduce the fast-charge time of the battery, and improve the rate performance and cycle performance of the battery.

[0274] Comparing Examples 5, 16-17 with Examples 15 and 18, it can be seen that controlling the volume distribution particle size Dv50 of the silicon-carbon primary particles to 20 nm-100 nm can extend the discharge time of the battery, reduce the charging time of the battery, and further improve the battery's rate performance. Comparing Examples 5 and 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 20 nm-60 nm can further extend the discharge time of the battery, reduce the charging time of the battery, and further improve the battery's rate performance.

[0275] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present 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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