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

Abstract

A silicon-carbon composite material, a preparation method, a secondary battery, and an electric device. The silicon-carbon composite material comprises an inner area and an outer area; the inner area is mainly composed of silicon-containing material particles; and the outer area is mainly composed of carbon-based material particles. The silicon-carbon composite material has excellent gram capacity, and can improve the high-temperature storage performance and cycle stability of the battery.

Description

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

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311640839.7, filed on November 30, 2023, entitled “Silicon-carbon composite material, preparation method, 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, a preparation method, 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] With the increasing popularity of secondary batteries, higher energy density requirements are being placed on them. Silicon-carbon composites can improve battery energy density, but this often deteriorates the battery's storage and cycling performance. Therefore, existing silicon-carbon composites still need to be improved.

[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 that has excellent specific capacity while improving the high-temperature storage performance and cycle stability of the battery.

[0008] A first aspect of the present application provides a silicon-carbon composite material, which includes an inner region and an outer region, wherein the inner region is mainly composed of silicon-containing material particles, and the outer region is mainly composed of carbon-based material particles.

[0009] Silicon has a higher specific capacity than carbon-based materials, but its surface reaction activity is high, and the electrolyte is easily decomposed on the surface of the silicon negative electrode, resulting in a decrease in its storage performance. And the mechanism of lithium storage in the silicon negative electrode determines that it will undergo huge volume expansion and contraction during the process of lithium insertion and extraction, which will not only deteriorate the cycle performance of the battery, but also cause the solid electrolyte interface film (SEI film) to continuously crack and generate, continuously consume active ions, and further deteriorate the storage performance of the battery. Compared with silicon, carbon-based materials have low surface activity and high structural stability, but they cannot further improve the energy density of the battery. Therefore, the silicon-carbon composite material provided by the present application is prepared by preparing a high-capacity silicon-containing material and a carbon-based material with excellent storage life into secondary particles whose internal region is mainly silicon-containing material particles and whose external region is mainly carbon-based material particles. While making the battery have excellent energy density, by reducing the surface activity of the silicon-carbon composite material, isolating silicon from the electrolyte, improving the storage performance of the battery, and the carbon-based material particles in the external region have higher strength, which has an inhibitory effect on the volume expansion of the silicon-containing material particles, improving the structural stability of the silicon-carbon composite material, and further improving the cycle stability of the battery.

[0010] Compared with silicon-carbon composite materials in which silicon-containing material particles and carbon-based material particles are directly mixed or used as secondary particles with uniform distribution, the silicon-carbon composite material of the present application can not only isolate the contact between silicon and electrolyte, but also reserve space for the volume expansion of silicon-containing material particles by reserving gaps, thereby improving the storage performance and cycle stability of the battery while taking into account excellent energy density.

[0011] In any embodiment, the number of silicon-containing material particles in the inner region is less than or equal to 3, and can be 1-2.

[0012] When the number of silicon-containing material particles in the internal area is within the above range, it is beneficial for the carbon-based material particles to densely wrap the silicon-containing material particles, and control the particle size of the finished silicon-carbon composite material within an appropriate range, thereby reducing the contact between silicon and the electrolyte and improving the battery's kinetic performance. At the same time, it also meets the processing performance requirements of the silicon-carbon composite material during negative electrode slurry homogenization and negative electrode sheet coating, so that the battery has excellent storage performance, cycle stability and kinetic performance.

[0013] In any embodiment, the mass proportion of silicon element in the region r / 2 from the geometric center of the silicon-carbon composite material is greater than or equal to 30%, and can be optionally 35%-45%, where r represents the short diameter of the silicon-carbon composite material.

[0014] When the mass proportion of silicon elements in the region r / 2 from the geometric center of the silicon-carbon composite material is within the above range, the battery can have excellent energy density, storage performance and cycle stability.

[0015] In any embodiment, the mass proportion of carbon elements in the region extending from the outer surface of the silicon-carbon composite material to the inner portion by a distance r / 2 is greater than or equal to 80%, and can be optionally 90%-100%, where r represents the short diameter of the silicon-carbon composite material.

[0016] When the mass proportion of carbon elements in the area extending from the outer surface of the silicon-carbon composite material to the inner side by a distance of r / 2 is within the above range, the silicon-carbon composite material can isolate the contact between silicon and the electrolyte, inhibit the volume change of silicon during the process of lithium insertion and extraction, and improve the storage performance and cycle stability of the battery.

[0017] In any embodiment, the outer region of the silicon-carbon composite material further includes an amorphous carbon coating layer.

[0018] The amorphous carbon coating in the external area can further isolate the contact between silicon and the electrolyte, and can reduce the specific surface area of ​​the silicon-carbon composite material, thereby avoiding the uneven surface of the prepared secondary particles, which leads to an excessively large specific surface area of ​​the silicon-carbon composite material, an increase in the contact area with the electrolyte, and the amount of active ions consumed in the formation of the SEI film, thereby comprehensively improving the storage performance, cycle stability and first effect of the battery.

[0019] In any embodiment, the Dv50 of the silicon-containing material particles is greater than or equal to the Dv50 of the carbon-based material particles.

[0020] The Dv50 of the silicon-containing material particles is greater than or equal to the Dv50 of the carbon-based material particles, which is beneficial to improving the integrity of the carbon-based material particles coating the silicon-containing material particles, thereby improving the storage performance of the battery.

[0021] In any embodiment, the silicon-containing material particles have a Dv50 of less than or equal to 5 μm.

[0022] When the Dv50 of the silicon-containing material particles is within the above range, it is beneficial to control the particle size of the finished silicon-carbon composite material within an appropriate range, and it has good electrode processing performance and dynamic performance.

[0023] In any embodiment, the carbon-based material particles have a Dv50 of 5 μm or less.

[0024] When the particle size of the carbon-based material particles is within the above range, the integrity of the carbon-based material particles coating the silicon-containing material particles can be improved, and it is beneficial to control the particle size of the finished silicon-carbon composite material within an appropriate range, meet the performance requirements of the electrode processing, and improve the storage performance and dynamic performance of the battery.

[0025] In any embodiment, the silicon-containing material particles include at least one of elemental silicon, silicon-oxygen material, silicon-carbon material, and silicon-metal alloy. Optionally, the silicon-containing material particles include silicon-carbon material.

[0026] In any embodiment, the carbon-based material particles include at least one of artificial graphite and natural graphite. Optionally, the carbon-based material particles include artificial graphite.

[0027] In any embodiment, the silicon-containing material particles include a carbon substrate having a pore structure and a silicon-based material disposed in the pore structure of the carbon substrate.

[0028] The pore structure of the carbon substrate provides attachment sites for silicon-based materials, which can be used to store large amounts of silicon. Silicon-based materials uniformly dispersed in the pore structure of the carbon substrate are not easily agglomerated. Furthermore, the carbon substrate has a certain mitigating effect on the volume change of the silicon-based materials disposed in the pore structure during the lithium insertion and extraction process, and can withstand the stress caused by the volume change of the silicon-based materials, so that the silicon-containing material particles have a low expansion rate and a highly stable structure, thereby improving the capacity, storage performance, and cycle stability of the silicon-containing material particles. The internal region of the silicon-carbon composite material contains silicon-containing material particles with the above structure, which can not only increase the capacity of the battery, but also avoid the situation where the silicon-carbon composite material cracks during the cycle due to excessive volume expansion of the internal region, thereby improving the storage performance and cycle stability of the battery.

[0029] In any embodiment, the pore structure includes micropores with a pore size less than 2 nm, mesopores with a pore size of 2 nm to 50 nm, and macropores with a pore size greater than 50 nm.

[0030] The above-mentioned pore structure in the carbon substrate helps the silicon-based material to adhere to the pore structure, and can effectively limit the volume expansion of the silicon-based material attached to the pore structure. Moreover, the silicon-based material after volume expansion will basically not cause damage to the pore structure of the carbon matrix, thereby increasing the capacity of the silicon-containing material particles while ensuring the stability of the structure.

[0031] In any embodiment, the pore volume of the micropores is greater than or equal to 0.5 cm 3 / g, optional 0.6cm 3 / g-0.9cm 3 / g.

[0032] By regulating the pore volume of the micropores in the carbon substrate, it is beneficial for the silicon-containing precursor to enter the pore structure of the carbon substrate, reducing the risk of silicon deposition on the surface of the carbon substrate, and improving the gram capacity and storage performance of the silicon-containing material particles.

[0033] In any embodiment, the average pore diameter of the carbon substrate is less than or equal to 5 nm, and can be optionally 1 nm to 3.5 nm.

[0034] When the average pore size of the carbon substrate is within the above range, it is helpful for the adhesion of silicon-based materials, and the carbon substrate can limit the volume expansion of the silicon-based materials in the pores. The expanded silicon-based materials will not cause damage to the structure of the porous carbon matrix, thereby improving the capacity and structural stability of the silicon-containing material particles, and the battery has excellent storage performance and cycle stability.

[0035] In any embodiment, the specific surface area of ​​the carbon substrate is greater than or equal to 1200 m 2 / g, optional 1500m 2 / g-1800m 2 / g.

[0036] The specific surface area of ​​the carbon substrate is within the above range. The carbon substrate has excellent pore volume and provides many sites for deposition of silicon-based materials, which is beneficial to increasing the gram capacity of silicon-containing material particles.

[0037] In any embodiment, the silicon-based material includes at least one of elemental silicon, silicon-oxygen material, silicon-carbon material, and silicon-metal alloy; the carbon substrate includes at least one of graphite, soft carbon, and hard carbon.

[0038] In any embodiment, the silicon-based material particles include silicon grains. Optionally, the size of the silicon grains is less than or equal to 10 nm. Optionally, the size of the silicon grains is less than or equal to 3 nm.

[0039] The size of silicon grains within the above range can avoid excessive local silicon enrichment due to excessive grain size, which in turn causes large expansion of silicon-containing material particles when lithium is inserted, leading to cracking of the material, which is beneficial to improving the storage performance and cycle stability of the battery.

[0040] In any embodiment, the porosity of the silicon-carbon composite material is 20%-45%, and optionally 20%-35%.

[0041] The porosity of the silicon-carbon composite material is within the above range, which reserves space for the volume change that occurs when the silicon-based material particles in the internal area insert and extract lithium. While taking into account the excellent specific capacity, it can also improve the structural stability of the silicon-carbon composite material, thereby improving the energy density, storage performance and cycle stability of the battery.

[0042] In any embodiment, the volume distribution particle size Dv50 of the silicon-carbon composite material is less than or equal to 16 μm, and can be optionally 8 μm-16 μm.

[0043] When the Dv50 of the silicon-carbon composite material is within the above range, the material has excellent dynamic properties and electrode processing performance, which is beneficial to improving the storage performance and cycle stability of the battery.

[0044] In any embodiment, the particle size distribution of the silicon-carbon composite material is (Dv90-Dv10) / Dv50 in the range of 0.5-1.8, and optionally in the range of 0.8-1.5.

[0045] When the particle size distribution of the silicon-carbon composite material is within the above range, the overall average particle size of the silicon-carbon composite material is relatively moderate, and the particle size distribution is relatively even, which is beneficial to improving the uniformity of the overall performance of the silicon-carbon composite material.

[0046] In any embodiment, the powder compaction density of the silicon-carbon composite material at 49000N is 0.7g / cm 3 -1.3g / cm 3 , optional 0.95g / cm 3 -1.1g / cm 3 .

[0047] When the silicon-carbon composite material powder compaction density is within the above range, the negative electrode sheet has a higher compaction density, further improving the battery's energy density. Furthermore, the negative electrode film layer has a strong ability to maintain its pore structure during cycling, and the negative electrode sheet has better electrolyte wettability, which helps improve the battery's storage performance and cycling stability.

[0048] In any embodiment, the specific surface area of ​​the silicon-carbon composite material is less than or equal to 6m 2 / g, can be selected to be less than or equal to 4.5m 2 / g.

[0049] When the specific surface area of ​​the silicon-carbon composite material is within the above range, it helps to further reduce the contact area between the silicon-carbon composite material and the electrolyte, reduce the consumption of active ions in forming the SEI film, and improve the battery's initial efficiency, storage performance and cycle stability.

[0050] The second aspect of the present application provides a method for preparing a silicon-carbon composite material, comprising the following steps: providing silicon-containing material particles and carbon-based material particles; subjecting the silicon-containing material particles and a binder to a first spray granulation to obtain a first intermediate product; spraying the carbon-based material particles onto the surface of the first intermediate product to perform a second spray granulation to prepare a silicon-carbon composite material; wherein the silicon-carbon composite material includes an internal region and an external region, the internal region is mainly composed of silicon-containing material particles, and the external region is mainly composed of carbon-based material particles.

[0051] By subjecting the silicon-containing material particles and the binder to a first spray granulation, the particle size of the silicon-containing material particles in the internal area of ​​the silicon-carbon composite material can be controlled to obtain a first intermediate product in which the silicon-containing material particles are uniformly coated with the binder on the outside. By subjecting the carbon-based material particles to a second spray granulation and spraying them onto the surface of the first intermediate product, secondary particles can be obtained in which the interior is mainly silicon-containing material particles and the exterior is mainly carbon-based material particles, and the carbon-based material particles tightly coat the silicon-containing material particles. Through two-step granulation, compared with the preparation method in which silicon-containing material particles, a binder, and carbon-based material particles are mixed and granulated at the same time, the preparation method of the present application can achieve a state in which the silicon-containing material particles are completely coated by the carbon-based material particles, isolating the contact between silicon and the electrolyte, and can regulate the porosity of the silicon-carbon composite material, thereby improving the storage performance and cycle stability of the battery.

[0052] In any embodiment, silicon-containing material particles are prepared by the following steps: providing a gas containing a silicon precursor to a carbon substrate having a porous structure; and generating a silicon-based material attached to the porous structure from the silicon precursor by chemical vapor deposition to obtain silicon-containing material particles.

[0053] In any embodiment, the mass ratio of the silicon-containing particles to the binder is 1:2-2:1.

[0054] When the mass ratio of silicon-containing material particles to adhesive is within the above range, there is a good bonding effect between the silicon-containing material particles and the carbon-based material particles, the particle size of the finished silicon-carbon composite material is within an appropriate range, and the battery has good storage performance and cycle stability while having excellent energy density.

[0055] In any embodiment, the mass ratio of the silicon-containing particles to the carbon-based material particles is 1:12-1:6.

[0056] The mass ratio of silicon-containing material particles to carbon-based material particles is within the above range. The carbon-based material particles form a complete coating layer on the surface of the silicon-containing material particles, isolating the contact between silicon and the electrolyte. The silicon-carbon composite material will not reduce its gram capacity due to excessive coating caused by an excessively high proportion of carbon-based material particles. The battery has excellent energy density, storage performance and cycle stability.

[0057] In any embodiment, the temperature difference between the inlet air temperature and the outlet air temperature of the first spray granulation is not greater than 60°C.

[0058] Spray granulation relies on hot air drying of the material. Controlling the hot air temperature controls the drying state of the intermediate product. Because hot air drying temperature is significantly affected by the environment and the chamber only provides a certain degree of insulation, not heating, the chamber temperature is not an exact value, but rather a temperature range. Setting the difference between the inlet and outlet air temperatures within this range ensures the chamber temperature remains within the appropriate range, preventing excessive temperature differences from causing the actual chamber temperature to be lower.

[0059] In any embodiment, the inlet air temperature of the first spray granulation is 110°C-150°C.

[0060] The inlet air temperature is the initial heat source in the chamber. Spray granulation relies on this air to dry the material, ensuring that the silicon-containing material particles coated with the binder are semi-dry. This prevents the silicon-containing material particles from sticking together due to excessive moisture caused by low temperature. This can lead to larger silicon-containing material particles in the inner area of ​​the finished silicon-carbon composite material, which in turn increases the particle size of the finished silicon-carbon composite material. Alternatively, it can cause excessive dryness due to high temperature, making it impossible to proceed to the next step. When the inlet air temperature is within the above range, the silicon-carbon composite material has good dynamic performance and electrode processing performance.

[0061] In any embodiment, the outlet air temperature of the first spray granulation is 50°C-90°C.

[0062] The outlet air temperature is the result of comprehensive consideration of heat, and is determined by the inlet air temperature, feed rate, etc. Setting the outlet air temperature of the first spray granulation within this range can avoid a large temperature difference with the inlet air temperature causing the temperature in the chamber to be too low, and can also further make the first intermediate product semi-dry, which is conducive to its next process.

[0063] In any embodiment, the feed gas pressure of the first spray granulation is 250 KPa-350 KPa, and can be optionally 280 KPa-320 KPa.

[0064] The feed air pressure of the first spray granulation is a key step in controlling the particle size of the finished silicon-carbon composite material. When the feed air pressure is within the above range, the number and particle size of the silicon-containing material particles sprayed out can be controlled within an appropriate range, avoiding the situation where the particle size of the silicon-containing material sprayed out is too large due to too low air pressure, which in turn causes the particle size of the silicon-carbon composite material to be too large, deteriorating the dynamic performance and electrode processing performance of the silicon-carbon composite material, and also avoiding the situation where some silicon-containing material particles are blocked at the nozzle of the spray gun and cannot be sprayed out due to too high air pressure. When the feed air pressure of the first spray granulation is within the above range, the particle size of the silicon-containing material sprayed out can be within an appropriate range, reaching a state where the number of silicon-containing material particles in the internal area of ​​the silicon-carbon composite material does not exceed 3, which is beneficial to improving the storage performance and electrode processing performance of the silicon-carbon composite material.

[0065] In any embodiment, the temperature difference between the inlet air temperature and the outlet air temperature of the second spray granulation is 20°C-40°C.

[0066] In any embodiment, the inlet air temperature of the second spray granulation is 170°C-280°C.

[0067] The inlet air temperature of the second spray granulation step is a key step in controlling the strength and structural stability of the silicon-carbon composite material. Because the first intermediate product has a certain viscosity, it is necessary to quickly coat the carbon-based material particles to form secondary particles and dry them to prevent the first intermediate product and secondary particles from agglomerating or secondary bonding during the process due to low temperatures. It also prevents the binder from shrinking too quickly or failing due to high temperatures, resulting in a poor bonding effect. When the inlet air temperature of the second spray granulation is within this range, the prepared silicon-carbon composite material has an appropriate particle size, excellent strength and structural stability, and plays a role in steadily improving the storage performance and cycle performance of the battery throughout its life cycle.

[0068] In any embodiment, the outlet air temperature of the second spray granulation is 130°C-240°C.

[0069] In any embodiment, the feed gas pressure of the second spray granulation is 150 KPa-260 KPa, and can be optionally 180 KPa-210 KPa.

[0070] The feed air pressure of the second spray granulation is a key step in controlling the integrity and uniformity of the carbon-based material particles coating the silicon-containing material particles. The feed air pressure of the second spray granulation is within the above range, which can improve the storage performance and cycle stability of the battery. It can avoid the excessive air pressure and too fast feed speed, which leads to excessive carbon-based material particles wrapped around the outside of the silicon-containing material, and the large particle size of the finished silicon-carbon composite material, thereby deteriorating the dynamic performance, electrode processing performance and gram capacity of the silicon-carbon composite material; it can also avoid the excessive air pressure and too slow feed speed, which leads to some silicon-containing material particles not being completely coated by the carbon-based material particles, and the inability to completely isolate the contact between silicon and the electrolyte, thereby weakening the storage performance of the silicon-carbon composite material.

[0071] In any embodiment, the method for preparing the silicon-carbon composite material further comprises: introducing a gaseous carbon source after the second spray granulation, and performing carbonization after gas-phase coating to obtain the silicon-carbon composite material.

[0072] The secondary particles formed by carbon-based material particles coating silicon-containing materials have more bumps on the surface and a larger specific surface area. After carbon coating, the specific surface area of ​​the silicon-carbon composite material can be controlled within an appropriate range, so that the battery has excellent storage performance, cycle stability and first effect; and the carbon coating layer in the external area can further reduce the possibility of contact between silicon and electrolyte, and the storage performance of the battery is further improved.

[0073] In any embodiment, the gaseous carbon source includes a gaseous hydrocarbon alkane, which can be at least one of methane, ethylene, and acetylene.

[0074] The temperature at which the gaseous carbon source decomposes to form the carbon coating layer is within a suitable range, meeting the temperature requirements of various components of the silicon-carbon composite material.

[0075] In any embodiment, the carbonization temperature is 400°C to 800°C.

[0076] When the carbonization temperature is within the above range, the gaseous carbon source can decompose to produce carbides that coat the surface of the secondary particles to form a carbon coating layer, which reduces the specific surface area of ​​the secondary particles while further isolating the contact between silicon and the electrolyte, thereby improving the storage performance and cycle stability of the battery; it can also avoid the silicon in the silicon-containing material particles from generating silicon carbide that cannot provide capacity due to excessively high temperature, thereby achieving the purpose of not losing the gram capacity of the silicon-carbon composite material.

[0077] In any embodiment, the carbonization time is 0.2 h to 2 h.

[0078] When the carbonization time is within the above range, the silicon-carbon composite material has a suitable specific surface area and excellent capacity, which can avoid the problem that the amount of amorphous carbon coating is too small due to too short a time, and the surface of the secondary particles cannot be completely covered to achieve the purpose of reducing the specific surface area; it can also avoid the problem that the carbonization time is too long, which greatly increases the risk of silicon generating silicon carbide under long-term high temperature, resulting in loss of capacity of the silicon-carbon composite material.

[0079] In any embodiment, the protective gas during the carbonization process is nitrogen or argon. Optionally, the gas flow ratio of the gaseous carbon source to the protective gas is 1:5 to 1:1.5.

[0080] When the airflow ratio of the gaseous carbon source to the protective gas is within the above range, the silicon-carbon composite material has excellent processing efficiency and suitable specific surface area, which can avoid the long coating time and slow production efficiency caused by the airflow ratio being too low; and can also avoid the excessive decomposition of the gaseous carbon source due to the airflow ratio being too high, which is easy to be locally enriched on the surface of the secondary particles, and cannot form a uniform amorphous carbon coating layer, and cannot effectively reduce the specific surface area of ​​the silicon-carbon composite material.

[0081] In any embodiment, the binder includes at least one of phenolic resin, styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, sodium alginate, carboxymethyl cellulose, polyacrylonitrile, and polypropylene alcohol.

[0082] On the one hand, the above-mentioned adhesive can provide bonding force between silicon-containing material particles and carbon-based material particles. On the other hand, it will shrink due to heat in the second spray granulation step to form pores, and retain functional groups that exert bonding properties and remove volatiles in the carbonization step, so that the silicon-carbon composite material has a certain porosity, reserving space for the expansion of silicon-containing material particles, thereby improving the storage performance and cycle stability of the battery.

[0083] 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 or the silicon-carbon composite material prepared by the preparation method of the second aspect.

[0084] The fourth aspect of the present application further provides an electrical device comprising the secondary battery of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0086] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0087] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0088] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0089] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0090] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0091] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0092] Below, the embodiments of the silicon-carbon composite material, 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.

[0093] " 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.

[0094] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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).

[0099] As the application scope of secondary batteries expands, the requirements for secondary battery performance, such as energy density, are gradually increasing. The negative electrode active material has a significant impact on the energy density of secondary batteries. Silicon-carbon composite materials, as a new type of negative electrode material, can effectively improve the energy density of batteries and have been widely studied. However, in traditional silicon-carbon composite materials, silicon-containing materials and carbon-based materials are usually in a state of uniform distribution or direct mixing. That is, the part of the silicon-carbon composite material that contacts the electrolyte also contains silicon, which causes silicon to continuously react with the electrolyte, consumes active ions, and deteriorates the storage performance and cycle performance of the battery.

[0100] [Silicon-carbon composite materials]

[0101] Based on this, the present application provides a silicon-carbon composite material, which includes an inner region and an outer region, wherein the inner region is mainly composed of silicon-containing material particles, and the outer region is mainly composed of carbon-based material particles.

[0102] In some embodiments, the silicon-containing material particles include at least one of elemental silicon, silicon-oxygen material, silicon-carbon material, and silicon-metal alloy.

[0103] In some embodiments, the silicon-containing material particles include silicon-carbon material.

[0104] In some embodiments, the carbon-based material particles include at least one of artificial graphite and natural graphite.

[0105] In some embodiments, the carbon-based material particles include artificial graphite.

[0106] As used herein, the term "silicon-carbon composite material" refers to a composite material composed of two elements: silicon and carbon.

[0107] Silicon has a higher specific capacity than carbon-based materials, but its surface reaction activity is high, and the electrolyte is easily decomposed on the surface of the silicon negative electrode, resulting in a decrease in its storage performance. And the mechanism of lithium storage in the silicon negative electrode determines that it will undergo huge volume expansion and contraction during the process of lithium insertion and extraction, which will not only deteriorate the cycle performance of the battery, but also cause the solid electrolyte interface film (SEI film) to continuously crack and generate, continuously consume active ions, and further deteriorate the storage performance of the battery. Compared with silicon, carbon-based materials have low surface activity and high structural stability, but they cannot further improve the energy density of the battery. Therefore, the silicon-carbon composite material provided by the present application is prepared by preparing a high-capacity silicon-containing material and a carbon-based material with excellent storage life into secondary particles whose internal region is mainly silicon-containing material particles and whose external region is mainly carbon-based material particles. While making the battery have excellent energy density, by reducing the surface activity of the silicon-carbon composite material, isolating silicon from the electrolyte, improving the storage performance of the battery, and the carbon-based material particles in the external region have higher strength, which has an inhibitory effect on the volume expansion of the silicon-containing material particles, improving the structural stability of the silicon-carbon composite material, and further improving the cycle stability of the battery.

[0108] Compared with silicon-carbon composite materials in which silicon-containing material particles and carbon-based material particles are directly mixed or used as secondary particles with uniform distribution, the silicon-carbon composite material of the present application can not only isolate the contact between silicon and electrolyte, but also reserve space for the volume expansion of silicon-containing material particles by reserving gaps, thereby improving the storage performance and cycle stability of the battery while taking into account excellent energy density.

[0109] In some embodiments, the number of silicon-containing material particles in the inner region is less than or equal to 3, and can be 1-2.

[0110] The number of silicon-containing material particles in the internal area can be tested by methods known in the art. As an example, an argon ion beam is used to cut the silicon-carbon composite material perpendicular to the large surface of the silicon-carbon composite material to expose the cross-section, and the cross-section is photographed using a scanning electron microscope to observe the number of silicon-containing material particles in the internal area.

[0111] In some embodiments, the number of silicon-containing material particles in the inner region is 1, 2, or 3.

[0112] When the number of silicon-containing material particles in the internal area is within the above range, it is beneficial for the carbon-based material particles to densely wrap the silicon-containing material particles, and control the particle size of the finished silicon-carbon composite material within an appropriate range, thereby reducing the contact between silicon and the electrolyte and improving the battery's kinetic performance. At the same time, it also meets the processing performance requirements of the silicon-carbon composite material during negative electrode slurry homogenization and negative electrode sheet coating, so that the battery has excellent storage performance, cycle stability and kinetic performance.

[0113] In some embodiments, the silicon-carbon composite material has a silicon content of greater than or equal to 30% by mass within a region r / 2 from the geometric center. In some embodiments, the silicon-carbon composite material has a silicon content of 35% to 45% by mass within a region r / 2 from the geometric center, where r represents the minor diameter of the silicon-carbon composite material.

[0114] In some embodiments, the carbon content of the silicon-carbon composite material within a region extending from the outer surface of the silicon-carbon composite material to the inner surface by a distance r / 2 is greater than or equal to 80% by weight. In some embodiments, the carbon content of the silicon-carbon composite material within a region extending from the outer surface of the silicon-carbon composite material to the inner surface by a distance r / 2 is between 90% and 100% by weight, where r represents the minor diameter of the silicon-carbon composite material.

[0115] The short diameter of the silicon-carbon composite material can be measured according to the three-axis characterization method, specifically as follows: the short diameter r is measured on the plane projection diagram of the negative electrode material.

[0116] The mass percentage of silicon elements in the area r / 2 from the geometric center of the silicon-carbon composite material and the mass percentage of carbon elements in the area extending from the outer surface to the inside at a distance of r / 2 can be tested by methods known in the art. As an example, ion polishing cross-section elemental analysis (CP) is used and tested in accordance with GB-T17359-2012 standard. According to the CP element spectrum of a single particle, the distribution position of Si and C elements can be determined. The content of silicon and carbon elements in the range from the geometric center to 1 / 2r can be directly tested by selecting the corresponding area of ​​the particle. The carbon content in the range from 1 / 2r to r is calculated as follows: the carbon content of the whole particle tested by CP element is A, the carbon content in the range from the center of the circle to 1 / 2r is B, and the carbon content in the range from 1 / 2r to r is C.

[0117] In some embodiments, the mass percentage of silicon element in the silicon-carbon composite material within the region r / 2 from the geometric center is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45% or any numerical range therebetween.

[0118] When the mass proportion of silicon elements in the region r / 2 from the geometric center of the silicon-carbon composite material is within the above range, the battery can have excellent energy density, storage performance and cycle stability.

[0119] In some embodiments, the mass proportion of carbon elements in the region extending from the outer surface of the silicon-carbon composite material to the inner side by a distance of r / 2 is 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100% or any numerical range therebetween.

[0120] When the mass proportion of carbon elements in the area extending from the outer surface of the silicon-carbon composite material to the inner side by a distance of r / 2 is within the above range, the silicon-carbon composite material can isolate the contact between silicon and the electrolyte, inhibit the volume change of silicon during the process of lithium insertion and extraction, and improve the storage performance and cycle stability of the battery.

[0121] In some embodiments, the outer region of the silicon-carbon composite material further includes an amorphous carbon coating layer.

[0122] In this article, the term "amorphous carbon" refers to a non-crystalline structure composed of carbon elements, whose hybridization sp 3 With sp 2 The hybrid mixed structure makes it different from the crystalline carbon of the crystalline system, and has a structure and properties similar to amorphous objects (such as glass).

[0123] The amorphous carbon herein can be formed by carbonizing a gaseous carbon source, which can be any gas known in the art suitable for coating, such as at least one of methane, ethylene, and acetylene.

[0124] The amorphous carbon coating in the external area can further isolate the contact between silicon and the electrolyte, and can reduce the specific surface area of ​​the silicon-carbon composite material, thereby avoiding the uneven surface of the prepared secondary particles, which leads to an excessively large specific surface area of ​​the silicon-carbon composite material, an increase in the contact area with the electrolyte, and the amount of active ions consumed in the formation of the SEI film, thereby comprehensively improving the storage performance, cycle stability and first effect of the battery.

[0125] In some embodiments, the Dv50 of the silicon-containing material particles is greater than or equal to the Dv50 of the carbon-based material particles.

[0126] In this article, the terms "Dv50", "Dv90" and "Dv10" refer to the particle sizes corresponding to when the cumulative volume distribution number of particles reaches 50%, 90% and 10% in the particle size distribution curve.

[0127] In this application, Dv50, Dv90, and Dv10 can be tested using methods known in the art. As an example, referring to GB / T 19077-2016 particle size distribution laser diffraction method, 0.1g to 0.13g of sample is weighed in a 50mL beaker, 5g of anhydrous ethanol is weighed, added to the beaker containing the sample, a stirring rod with a length of about 2.5mm is placed, and sealed with plastic wrap. The sample is placed in an ultrasonic machine for 5min, transferred to a magnetic stirrer and stirred at a speed of 500r / min for more than 20min. Two samples are taken from each batch of products for testing, and the particle size distribution is measured to obtain the Dv50, Dv90, and Dv10 of the sample. It is conveniently measured using a laser particle size analyzer, such as the Malvern Mastersizer 3000 laser particle size analyzer of Malvern Instrument Co., Ltd., UK.

[0128] The Dv50 of the silicon-containing material particles is greater than or equal to the Dv50 of the carbon-based material particles, which is beneficial to improving the integrity of the carbon-based material particles coating the silicon-containing material particles, thereby improving the storage performance of the battery.

[0129] In some embodiments, the silicon-containing material particles have a Dv50 of less than or equal to 5 μm.

[0130] In some embodiments, the Dv50 of the silicon-containing material particles is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any range therebetween.

[0131] When the Dv50 of the silicon-containing material particles is within the above range, it is beneficial to control the particle size of the finished silicon-carbon composite material within an appropriate range, and it has good electrode processing performance and dynamic performance.

[0132] In some embodiments, the carbon-based material particles have a Dv50 of less than or equal to 5 μm.

[0133] In some embodiments, the Dv50 of the carbon-based material particles is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any range therebetween.

[0134] When the particle size of the carbon-based material particles is within the above range, the integrity of the carbon-based material particles coating the silicon-containing material particles can be improved, and it is beneficial to control the particle size of the finished silicon-carbon composite material within an appropriate range, meet the performance requirements of the electrode processing, and improve the storage performance and dynamic performance of the battery.

[0135] In some embodiments, the silicon-containing material particles include a carbon substrate having a pore structure and a silicon-based material disposed in the pore structure of the carbon substrate.

[0136] The pore structure of the carbon substrate provides attachment sites for silicon-based materials, which can be used to store large amounts of silicon. Silicon-based materials uniformly dispersed in the pore structure of the carbon substrate are not easily agglomerated. Furthermore, the carbon substrate has a certain mitigating effect on the volume change of the silicon-based materials disposed in the pore structure during the lithium insertion and extraction process, and can withstand the stress caused by the volume change of the silicon-based materials, so that the silicon-containing material particles have a low expansion rate and a highly stable structure, thereby improving the capacity, storage performance, and cycle stability of the silicon-containing material particles. The internal region of the silicon-carbon composite material contains silicon-containing material particles with the above structure, which can not only increase the capacity of the battery, but also avoid the situation where the silicon-carbon composite material cracks during the cycle due to excessive volume expansion of the internal region, thereby improving the storage performance and cycle stability of the battery.

[0137] In some embodiments, the carbon substrate includes micropores with a pore size less than 2 nm, mesopores with a pore size of 2 nm to 50 nm, and macropores with a pore size greater than 50 nm.

[0138] The pore structure of the carbon substrate can be tested using equipment and methods known in the art. For example, the pore size can be tested by the gas adsorption method according to the GB / T19587-2017 & GB / T21650.2-2008 test standards. Specifically, the porous material sample tube is immersed in liquid nitrogen at -196°C. Nitrogen is adsorbed on the material to be tested at a relative pressure of 0-1. The pore size distribution of the porous material is characterized based on the relationship between the volume of each pore size and the corresponding partial pressure. The pore structure of the carbon substrate is characterized by the pore size distribution.

[0139] The above-mentioned pore structure in the carbon substrate helps the silicon-based material to adhere to the pore structure, and can effectively limit the volume expansion of the silicon-based material attached to the pore structure. Moreover, the silicon-based material after volume expansion will basically not cause damage to the pore structure of the carbon matrix, thereby increasing the capacity of the silicon-containing material particles while ensuring the stability of the structure.

[0140] In some embodiments, the pore volume of the micropores is greater than or equal to 0.5 cm 3 In some embodiments, the pore volume of the micropores is 0.6 cm 3 / g-0.9cm 3 / g.

[0141] The pore volume of the micropores can be measured using instruments and methods known in the art. For example, the test method can refer to GB / T19587-2004, using the mesopore pore size distribution test BJH (Barret Joyner Halenda), using the gas adsorption and desorption method under the micro-mesopore model to test and select the adsorption branch data, and measure and calculate the total volume of pores with a pore size less than 2 nm.

[0142] In some embodiments, the pore volume of the micropores is 0.5 cm 3 / g, 0.55cm 3 / g, 0.6cm 3 / g, 0.65cm 3 / g, 0.7cm 3 / g, 0.75cm 3 / g, 0.8cm 3 / g, 0.85cm 3 / g, 0.9cm 3 / g, 0.95cm 3 / g, 1cm 3 / g or any range of values ​​between them.

[0143] By regulating the pore volume of the micropores in the carbon substrate, it is beneficial for the silicon-containing precursor to enter the pore structure of the carbon substrate, reducing the risk of silicon deposition on the surface of the carbon substrate, and improving the gram capacity and storage performance of the silicon-containing material particles.

[0144] In some embodiments, the average pore size of the carbon substrate is less than or equal to 5 nm. In some embodiments, the average pore size of the carbon substrate is 1 nm to 3.5 nm.

[0145] The average pore size of the carbon substrate can be tested using equipment and methods known in the art. For example, the pore size can be tested using a gas adsorption method in accordance with the GB / T19587-2017 & GB / T21650.2-2008 test standards. Specifically, the porous material sample tube is immersed in liquid nitrogen at -196°C. Nitrogen is adsorbed on the material to be tested at a relative pressure of 0-1. The pore size distribution of the porous material is characterized based on a relationship diagram between the volume of each pore size and the corresponding partial pressure to obtain the average pore size of the carbon substrate.

[0146] In some embodiments, the average pore size of the carbon substrate is 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, or any range therebetween.

[0147] When the average pore size of the carbon substrate is within the above range, it is helpful for the adhesion of silicon-based materials, and the carbon substrate can limit the volume expansion of the silicon-based materials in the pores. The expanded silicon-based materials will not cause damage to the structure of the porous carbon matrix, thereby improving the capacity and structural stability of the silicon-containing material particles, and the battery has excellent storage performance and cycle stability.

[0148] In some embodiments, the specific surface area of ​​the carbon substrate is greater than or equal to 1200 m 2 In some embodiments, the specific surface area of ​​the carbon substrate is 1500 m 2 / g-1800m 2 / g.

[0149] In this application, the specific surface area of ​​the carbon substrate can be tested using methods known in the art. As an example, the specific surface area is tested using a gas adsorption method according to the GB / T19587-2017 test standard. Specifically, the sample tube is immersed in liquid nitrogen at -196°C, and the adsorption amount of nitrogen on the solid surface at different pressures is measured at a relative pressure of 0.05-0.30. The monolayer adsorption amount of the sample is obtained based on the BET multilayer adsorption theory and its formula, thereby calculating the specific surface area of ​​the solid.

[0150] where n a is the amount of adsorbed gas, unit is mol / g; p / p0 is the relative pressure; nm is the monolayer adsorption capacity.

[0151] In some embodiments, the specific surface area of ​​the carbon substrate is 1200 m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g or any range of values ​​between them.

[0152] The specific surface area of ​​the carbon substrate is within the above range. The carbon substrate has excellent pore volume and provides many sites for deposition of silicon-based materials, which is beneficial to increasing the gram capacity of silicon-containing material particles.

[0153] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon-oxygen material, silicon-carbon material, and silicon-metal alloy.

[0154] In some embodiments, the silicon-based material includes silicon grains.

[0155] The crystal structure of silicon-based materials can be tested using equipment and methods known in the art. As an example, the following steps can be followed: select a microgrid of a certain diameter (e.g., 3 mm in diameter), clamp the edge of the microgrid with pointed tweezers, place it with the film surface facing up (the shiny side is the film surface when observed under light), and gently place it flat on white filter paper; take an appropriate amount of sample (e.g., 1 g) and add it to a beaker containing an appropriate amount of ethanol, and perform ultrasonic oscillation for 10 to 30 minutes; use a glass capillary to absorb the sample, and then drop 2-3 drops of the sample to be tested onto the microgrid; after baking in an oven for 5 minutes, place the microgrid with the sample to be tested on the sample stage, and test it with a transmission electron microscope (e.g., Hitachi HF-3300S Cs-corrected STEM) at a certain magnification (e.g., 60,000 times) to obtain a transmission electron microscope (TEM) image of the sample to be tested. If there are obvious lattice fringes (for example, the lattice spacing is approximately equal to 0.331 nm), it is crystalline silicon; if no lattice fringes are observed, it is amorphous silicon.

[0156] In this application, the size of the silicon grains can be calculated based on the XRD pattern of the sample tested according to the JIS / K0131-1996 test standard. Based on the XRD pattern of the sample, the half-height width β and the diffraction angle θ of the Si (111) crystal plane diffraction peak are taken and substituted into the Debye-Scherrer formula to calculate the particle size of the silicon grains. The Debye-Scherrer formula is as follows: Dhkl = kλ / (βcosθ), where Dhkl represents the particle size of the silicon grains in nm; k represents the Scherrer constant, 0.89; λ represents the wavelength of the incident X-ray, 0.15406 nm; β represents the half-height width of the diffraction peak, in rad; and θ represents the diffraction angle in degrees.

[0157] In some embodiments, the size of the silicon grains is less than or equal to 10 nm. In some embodiments, the size of the silicon grains is less than or equal to 3 nm.

[0158] In some embodiments, the size of the silicon grains is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any range therebetween.

[0159] The size of silicon grains within the above range can avoid excessive local silicon enrichment due to excessive grain size, which in turn causes large expansion of silicon-containing material particles when lithium is inserted, leading to cracking of the material, which is beneficial to improving the storage performance and cycle stability of the battery.

[0160] In some embodiments, the silicon-based material includes amorphous silicon.

[0161] Amorphous silicon can expand evenly in all directions, thereby causing uniform squeezing of the carbon substrate. The carbon substrate can effectively alleviate the volume expansion of amorphous silicon, thereby improving the storage performance and cycle stability of the battery.

[0162] In some embodiments, the carbon substrate includes at least one of graphite, soft carbon, and hard carbon.

[0163] In some embodiments, the carbon substrate is hard carbon.

[0164] In some embodiments, the pore volume of the hard carbon micropores is greater than or equal to 0.5 cm 3 / g. In some embodiments, the pore volume of the hard carbon micropores is 0.6 cm 3 / g-0.9cm 3 In some embodiments, the specific surface area of ​​the hard carbon is greater than or equal to 1200 m 2 In some embodiments, the specific surface area of ​​the hard carbon is 1500 m 2 / g-1800m 2In some embodiments, the hard carbon has an average pore size of 5 nm or less. In some embodiments, the hard carbon has an average pore size of 1 nm to 3.5 nm.

[0165] When the micropore volume, specific surface area and average pore diameter of the hard carbon are within the above ranges, the hard carbon and the silicon-based material deposited in the pore structure work synergistically to enhance the gram capacity and structural stability of the silicon-containing material particles.

[0166] In some embodiments, based on the total mass of the silicon-containing material particles, the mass proportion of silicon in the silicon-containing material particles is 35%-50%. In some embodiments, the mass proportion of silicon in the silicon-containing material particles is 35%-47%.

[0167] In some embodiments, based on the total mass of the silicon-containing material particles, the mass proportion of silicon in the silicon-containing material particles is 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or any value therebetween.

[0168] Based on the total mass of the silicon-containing material particles, the mass proportion of silicon in the silicon-containing material particles is within the above range, which is beneficial to improving the gram capacity and structural stability of the silicon-carbon composite material, and improving the cycle stability and storage performance of the battery.

[0169] In some embodiments, the porosity of the silicon-carbon composite material is 20%-45%. In some embodiments, the porosity of the silicon-carbon composite material is 20%-35%.

[0170] In this application, the porosity of the silicon-carbon composite material can be tested by methods known in the art. As an example, the test is performed according to the GB / T24586 test standard. The porosity P = (V2-V1) / V2*100%, the apparent volume V2 = S*H*A, where: S is the area, unit is cm 2 ; H is the thickness, in cm; A is the number of samples, in EA; V1 is the true volume of the sample, in cm 3 ; V2 is the apparent volume of the sample, in cm 3 ;

[0171] The true volume V1 of the sample is calculated by placing the sample in a true density tester (Accu Pyc II 1340 analyzer), sealing the test system, and introducing helium according to the procedure. The gas pressures in the sample chamber and expansion chamber are measured, and the gas volumes of the sample chamber and expansion chamber are calculated using the ideal gas equation (v = nRT / P). The volume of gas displaced by the sample under certain temperature and pressure conditions is thus determined as the true volume V1 of the sample.

[0172] In some embodiments, the porosity of the silicon-carbon composite material is 20%, 25%, 30%, 35%, 40%, 45%, or any range therebetween.

[0173] The porosity of the silicon-carbon composite material is within the above range, which reserves space for the volume change that occurs when the silicon-based material particles in the internal area insert and extract lithium. While taking into account the excellent specific capacity, it can also improve the structural stability of the silicon-carbon composite material, thereby improving the energy density, storage performance and cycle stability of the battery.

[0174] In some embodiments, the silicon-carbon composite material has a Dv50 of less than or equal to 16 μm. In some embodiments, the silicon-carbon composite material has a Dv50 of 8 μm to 16 μm.

[0175] In some embodiments, the Dv50 of the silicon-carbon composite material is 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, or any range therebetween.

[0176] When the Dv50 of the silicon-carbon composite material is within the above range, the material has excellent dynamic properties and electrode processing performance, which is beneficial to improving the storage performance and cycle stability of the battery.

[0177] In some embodiments, the particle size distribution of the silicon-carbon composite material is (Dv90-Dv10) / Dv50 of 0.5-1.8. In some embodiments, the particle size distribution of the silicon-carbon composite material is 0.8-1.5.

[0178] In some embodiments, the particle size distribution of the silicon-carbon composite material (Dv90-Dv10) / Dv50 is 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or any range therebetween.

[0179] When the particle size distribution of the silicon-carbon composite material is within the above range, the overall average particle size of the silicon-carbon composite material is relatively moderate, and the particle size distribution is relatively even, which is beneficial to improving the uniformity of the overall performance of the silicon-carbon composite material.

[0180] In some embodiments, the powder compaction density of the silicon-carbon composite material at 49000N is 0.7g / cm 3 -1.3g / cm 3 In some embodiments, the powder compaction density of the silicon-carbon composite material at 49,000 N is 0.95 g / cm 3 -1.1g / cm 3

[0181] In this article, the term "powder compaction density" refers to the mass of powder particles per unit volume under a certain pressure.

[0182] In this application, the powder compaction density of the silicon-carbon composite material under a pressure of 49000N can be tested by methods known in the art. As an example, referring to GB / T24533-2009, 1g of silicon-carbon composite material powder is weighed and added to a bottom area of ​​1.327cm 2 The mold is pressurized to 5000 kg (equivalent to 49000 N), the pressure is maintained for 30 seconds, and then the pressure is released and maintained for 10 seconds. The powder compaction density of the silicon-carbon composite material under a pressure of 49000 N is measured by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0183] In some embodiments, the powder compaction density of the silicon-carbon composite material at 49000N is 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 or any range of values ​​in between.

[0184] When the silicon-carbon composite material powder compaction density is within the above range, the negative electrode sheet has a higher compaction density, further improving the battery's energy density. Furthermore, the negative electrode film layer has a strong ability to maintain its pore structure during cycling, and the negative electrode sheet has better electrolyte wettability, which helps improve the battery's storage performance and cycling stability.

[0185] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is less than or equal to 6 m 2 In some embodiments, the specific surface area of ​​the silicon-carbon composite material is less than or equal to 4.5 m 2 / g.

[0186] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 1 m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g or any range of values ​​between them.

[0187] When the specific surface area of ​​the silicon-carbon composite material is within the above range, it helps to further reduce the contact area between the silicon-carbon composite material and the electrolyte, reduce the consumption of active ions in forming the SEI film, and improve the battery's initial efficiency, storage performance and cycle stability.

[0188] The present application also provides a method for preparing a silicon-carbon composite material, comprising the following steps: providing silicon-containing material particles and carbon-based material particles; subjecting the silicon-containing material particles and a binder to a first spray granulation to obtain a first intermediate product; spraying the carbon-based material particles onto the surface of the first intermediate product to perform a second spray granulation to obtain the silicon-carbon composite material; the silicon-carbon composite material comprises an inner region and an outer region, the inner region being mainly composed of silicon-containing material particles, and the outer region being mainly composed of carbon-based material particles.

[0189] In this article, "spray granulation" refers to a granulation process in which a slurry or solution is sprayed into a granulation tower. The sprayed hot air dries and agglomerates the slurry or solution, resulting in spherical pellets. This method is widely used to produce catalysts of various particle sizes or other particles with specific particle sizes. It is suitable for experimental and small-scale production applications, and produces pellets with high precision and uniformity.

[0190] By subjecting the silicon-containing material particles and the binder to a first spray granulation, the particle size of the silicon-containing material particles in the internal area of ​​the silicon-carbon composite material can be controlled to obtain a first intermediate product in which the silicon-containing material particles are uniformly coated with the binder on the outside. By subjecting the carbon-based material particles to a second spray granulation and spraying them onto the surface of the first intermediate product, secondary particles can be obtained in which the interior is mainly silicon-containing material particles and the exterior is mainly carbon-based material particles, and the carbon-based material particles tightly coat the silicon-containing material particles. Through two-step granulation, compared with the preparation method in which silicon-containing material particles, a binder, and carbon-based material particles are mixed and granulated at the same time, the preparation method of the present application can achieve a state in which the silicon-containing material particles are completely coated by the carbon-based material particles, isolating the contact between silicon and the electrolyte, and can regulate the porosity of the silicon-carbon composite material, thereby improving the storage performance and cycle stability of the battery.

[0191] In some embodiments, the silicon-containing material particles are prepared by the following steps: providing a gas containing a silicon precursor to a carbon substrate having a porous structure; and generating a silicon-based material attached to the porous structure from the silicon precursor by chemical vapor deposition to obtain the silicon-containing material particles.

[0192] In some embodiments, the silicon precursor includes at least one of silane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0193] In some embodiments, the silicon precursor is silane.

[0194] In some embodiments, the mass ratio of the silicon-containing material particles to the binder is 1:2-2:1.

[0195] In some embodiments, the mass ratio of the silicon-containing material particles to the binder is 1:2, 1.5:2, 1:1, 1.5:1, 2:1, or any range therebetween.

[0196] When the mass ratio of silicon-containing material particles to adhesive is within the above range, there is a good bonding effect between the silicon-containing material particles and the carbon-based material particles, the particle size of the finished silicon-carbon composite material is within an appropriate range, and the battery has good storage performance and cycle stability while having excellent energy density.

[0197] In some embodiments, the mass ratio of the silicon-containing material particles to the carbon-based material particles is 1:12-1:6.

[0198] In some embodiments, the mass ratio of the silicon-containing material particles to the carbon-based material particles is 1:12, 1:11, 1:10, 1:9, 1:8, 1:7, 1:6 or any range therebetween.

[0199] The mass ratio of silicon-containing material particles to carbon-based material particles is within the above range. The carbon-based material particles form a complete coating layer on the surface of the silicon-containing material particles, isolating the contact between silicon and the electrolyte. The silicon-carbon composite material will not reduce its gram capacity due to excessive coating caused by an excessively high proportion of carbon-based material particles. The battery has excellent energy density, storage performance and cycle stability.

[0200] In some embodiments, the temperature difference between the inlet air temperature and the outlet air temperature of the first spray granulation is no more than 60°C.

[0201] In some embodiments, the temperature difference between the inlet air temperature and the outlet air temperature of the first spray granulation is 10°C, 20°C, 30°C, 40°C, 50°C, 60°C or any range therebetween.

[0202] Spray granulation relies on hot air drying of the material. Controlling the hot air temperature controls the drying state of the intermediate product. Because hot air drying temperature is significantly affected by the environment and the chamber only provides a certain degree of insulation, not heating, the chamber temperature is not an exact value, but rather a temperature range. Setting the difference between the inlet and outlet air temperatures within this range ensures the chamber temperature remains within the appropriate range, preventing excessive temperature differences from causing the actual chamber temperature to be lower.

[0203] In some embodiments, the inlet air temperature is 110°C-150°C.

[0204] In some embodiments, the inlet air temperature is 110° C., 120° C., 130° C., 140° C., 150° C., or any range therebetween.

[0205] The inlet air temperature is the initial heat source in the chamber. Spray granulation relies on this air to dry the material, ensuring that the silicon-containing material particles coated with the binder are semi-dry. This prevents the silicon-containing material particles from sticking together due to excessive moisture caused by low temperature. This can lead to larger silicon-containing material particles in the inner area of ​​the finished silicon-carbon composite material, which in turn increases the particle size of the finished silicon-carbon composite material. Alternatively, it can cause excessive dryness due to high temperature, making it impossible to proceed to the next step. When the inlet air temperature is within the above range, the silicon-carbon composite material has good dynamic performance and electrode processing performance.

[0206] In some embodiments, the outlet air temperature is 50°C-90°C.

[0207] In some embodiments, the outlet air temperature is 50°C, 60°C, 70°C, 80°C, 90°C, or any range therebetween.

[0208] The outlet air temperature is the result of comprehensive consideration of heat, and is determined by the inlet air temperature, feed rate, etc. Setting the outlet air temperature of the first spray granulation within this range can avoid a large temperature difference with the inlet air temperature causing the temperature in the chamber to be too low, and can also further make the first intermediate product semi-dry, which is conducive to its next process.

[0209] In some embodiments, the feed gas pressure of the first spray granulation is 250 KPa-350 KPa. In some embodiments, the feed gas pressure of the first spray granulation is 280 KPa-320 KPa.

[0210] In some embodiments, the feed gas pressure of the first spray granulation is 250 KPa, 251 KPa, 252 KPa, 253 KPa, 254 KPa, 255 KPa, 256 KPa, 257 KPa, 258 KPa, 259 KPa, 260 KPa, or any range therebetween.

[0211] The feed air pressure of the first spray granulation is a key step in controlling the particle size of the finished silicon-carbon composite material. When the feed air pressure is within the above range, the number and particle size of the silicon-containing material particles sprayed out can be controlled within an appropriate range, avoiding the situation where the particle size of the silicon-containing material sprayed out is too large due to too low air pressure, which in turn causes the particle size of the silicon-carbon composite material to be too large, deteriorating the dynamic performance and electrode processing performance of the silicon-carbon composite material, and also avoiding the situation where some silicon-containing material particles are blocked at the nozzle of the spray gun and cannot be sprayed out due to too high air pressure. When the feed air pressure of the first spray granulation is within the above range, the particle size of the silicon-containing material sprayed out can be within an appropriate range, reaching a state where the number of silicon-containing material particles in the internal area of ​​the silicon-carbon composite material does not exceed 3, which is beneficial to improving the storage performance and electrode processing performance of the silicon-carbon composite material.

[0212] In some embodiments, the temperature difference between the inlet air temperature and the outlet air temperature of the second spray granulation is 20°C-40°C.

[0213] In some embodiments, the temperature difference between the inlet air temperature and the outlet air temperature of the second spray granulation is 20°C, 24°C, 28°C, 32°C, 36°C, 40°C or any range therebetween.

[0214] In some embodiments, the inlet air temperature of the second spray granulation is 170°C-280°C.

[0215] In some embodiments, the inlet air temperature of the second spray granulation is 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C or any range therebetween.

[0216] The inlet air temperature of the second spray granulation step is a key step in controlling the strength and structural stability of the silicon-carbon composite material. Because the first intermediate product has a certain viscosity, it is necessary to quickly coat the carbon-based material particles to form secondary particles and dry them to prevent the first intermediate product and secondary particles from agglomerating or secondary bonding during the process due to low temperatures. It also prevents the binder from shrinking too quickly or failing due to high temperatures, resulting in a poor bonding effect. When the inlet air temperature of the second spray granulation is within this range, the prepared silicon-carbon composite material has an appropriate particle size, excellent strength and structural stability, and plays a role in steadily improving the storage performance and cycle performance of the battery throughout its life cycle.

[0217] In some embodiments, the outlet air temperature of the second spray granulation is 130°C-240°C.

[0218] In some embodiments, the outlet air temperature of the second spray granulation is 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or any range therebetween.

[0219] In some embodiments, the feed gas pressure of the second spray granulation is 150 KPa-260 KPa. In some embodiments, the feed gas pressure of the second spray granulation is 180 KPa-210 KPa.

[0220] In some embodiments, the feed gas pressure of the second spray granulation is 150 KPa, 160 KPa, 170 KPa, 180 KPa, 190 KPa, 200 KPa, 210 KPa, 220 KPa, 230 KPa, 240 KPa, 250 KPa, 260 KPa or any range therebetween.

[0221] The feed pressure during the second spray granulation process is a key step in controlling the integrity and uniformity of the carbon-based material particles encapsulating the silicon-containing material particles. Maintaining the feed pressure within the aforementioned range can improve the battery's storage performance and cycling stability. This prevents excessive pressure and rapid feed rates, which can lead to excessive carbon-based material particles encapsulating the silicon-containing material, resulting in larger particle size in the finished silicon-carbon composite material and deteriorating its dynamic performance, electrode processing performance, and gram capacity. It also prevents incomplete encapsulation of some silicon-containing material particles by the carbon-based material particles, resulting in incomplete isolation of silicon from the electrolyte and weakening the storage performance of the silicon-carbon composite material, caused by excessively low pressure and slow feed rates.

[0222] In some embodiments, the method for preparing the silicon-carbon composite material further comprises: introducing a gaseous carbon source after the second spray granulation, and performing carbonization after gas-phase coating to obtain the silicon-carbon composite material.

[0223] The secondary particles formed by carbon-based material particles coating silicon-containing material particles have more bumps on the surface and a larger specific surface area. After carbon coating, the specific surface area of ​​the silicon-carbon composite material can be controlled within an appropriate range, so that the battery has excellent storage performance, cycle stability and first effect; and the carbon coating layer in the external area can further reduce the possibility of contact between silicon and electrolyte, and the storage performance of the battery is further improved.

[0224] In some embodiments, the gaseous carbon source includes a gaseous hydrocarbon alkane, which can be at least one of methane, ethylene, and acetylene.

[0225] In some embodiments, the gaseous carbon source is acetylene.

[0226] The temperature at which the gaseous carbon source decomposes to form the carbon coating layer is within a suitable range, meeting the temperature requirements of various components of the silicon-carbon composite material.

[0227] In some embodiments, the carbonization temperature is 400°C-800°C.

[0228] In some embodiments, the carbonization temperature is 400° C., 500° C., 600° C., 700° C., 800° C., or any range therebetween.

[0229] When the carbonization temperature is within the above range, the gaseous carbon source can decompose to produce carbides that coat the surface of the secondary particles to form a carbon coating layer, which reduces the specific surface area of ​​the secondary particles while further isolating the contact between silicon and the electrolyte, thereby improving the storage performance and cycle stability of the battery; it can also avoid the silicon in the silicon-containing material particles from generating silicon carbide that cannot provide capacity due to excessively high temperature, thereby achieving the purpose of not losing the gram capacity of the silicon-carbon composite material.

[0230] In some embodiments, the carbonization time is 0.2 h-2 h.

[0231] In some embodiments, the carbonization time is 0.2h, 0.3h, 0.4h, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h or any range therebetween.

[0232] When the carbonization time is within the above range, the silicon-carbon composite material has a suitable specific surface area and excellent capacity, which can avoid the problem that the amount of amorphous carbon coating is too small due to too short a time, and the surface of the secondary particles cannot be completely covered to achieve the purpose of reducing the specific surface area; it can also avoid the problem that the carbonization time is too long, which greatly increases the risk of silicon generating silicon carbide under long-term high temperature, resulting in loss of capacity of the silicon-carbon composite material.

[0233] In some embodiments, the protective gas during the carbonization process is nitrogen or argon. In some embodiments, the gas flow ratio of the gaseous carbon source to the protective gas is 1:5 to 1:1.5.

[0234] In some embodiments, the gas flow ratio of the carbon source gas to the protective gas is 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5, or any range therebetween.

[0235] When the airflow ratio of the gaseous carbon source to the protective gas is within the above range, the silicon-carbon composite material has excellent processing efficiency and suitable specific surface area, which can avoid the long coating time and slow production efficiency caused by the airflow ratio being too low; and can also avoid the excessive decomposition of the gaseous carbon source due to the airflow ratio being too high, which is easy to be locally enriched on the surface of the secondary particles, and cannot form a uniform amorphous carbon coating layer, and cannot effectively reduce the specific surface area of ​​the silicon-carbon composite material.

[0236] In some embodiments, the binder includes at least one of phenolic resin, styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, sodium alginate, carboxymethyl cellulose, polyacrylonitrile, and polypropylene alcohol.

[0237] In some embodiments, the binder comprises a phenolic resin.

[0238] On the one hand, the above-mentioned binder can provide bonding force between silicon-containing material particles and carbon-based material particles. On the other hand, it will shrink due to heat to form pores in the second spray granulation step, and retain functional groups that exert bonding properties and remove volatiles in the carbonization step, so that the silicon-carbon composite material has a certain porosity, reserving space for the expansion of silicon-containing material particles, thereby improving the storage performance and cycle stability of the battery.

[0239] [Negative electrode]

[0240] 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.

[0241] 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.

[0242] 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.).

[0243] 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).

[0244] 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.

[0245] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0246] 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.

[0247] [Positive electrode]

[0248] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0249] 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.

[0250] 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.).

[0251] 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 NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1O2 (also referred to as NCM 811 ), 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.

[0252] 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.

[0253] 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.

[0254] 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.

[0255] [Electrolytes]

[0256] 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.

[0257] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0258] 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.

[0259] 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.

[0260] 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.

[0261] [Isolation film]

[0262] 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.

[0263] 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.

[0264] 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.

[0265] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0266] 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.

[0267] In this application, the shape of the secondary battery includes but is not limited to cylindrical, square or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0268] In some embodiments, referring to FIG2 , the outer package 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.

[0269] 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.

[0270] 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.

[0271] 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.

[0272] 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.

[0273] 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.

[0274] 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.

[0275] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0276] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0277] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0278] Example

[0279] 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.

[0280] 1. Preparation method

[0281] Preparation Example 1: Silicon-containing material particles 1

[0282] At 465°C, a gas containing silane SiH4 is introduced into a hard carbon substrate with a porous structure, and vapor deposition is carried out for 10 hours. By chemical vapor deposition, a silicon-based material deposited in the porous structure of the hard carbon substrate is generated from silane. Then, chemical vapor deposition is used to vapor deposit on the hard carbon substrate for 0.5 hours at 660°C using a carbon source gas and a protective gas with a gas flow ratio of 1:2. A carbon layer accounting for 3% of the total mass of the hard carbon substrate and the deposited silicon-based material is coated on the surface of the hard carbon substrate, wherein the gas source is acetylene gas, and silicon-containing material particles 1 are obtained. Among them, the mass ratio of silicon in silane to hard carbon substrate is 1:1; the pore volume of the micropores of the hard carbon substrate is 0.8cm 3 / g, average pore diameter of 3.2nm, specific surface area of ​​1612m 2 / g, the silicon-based material includes silicon grains, and the particle size of the silicon grains is 2.9nm; the Dv50 of the silicon-containing material particles 1 is 4.2μm, and the silicon mass percentage is 46%.

[0283] Preparation Example 2: Silicon-containing material particles 2

[0284] At 465°C, a gas containing silane SiH4 is introduced into a hard carbon substrate with a porous structure, and vapor deposition is performed for 8 hours. By chemical vapor deposition, a silicon-based material is generated from silane and deposited in the porous structure of the hard carbon substrate. Then, chemical vapor deposition is used to vapor deposit on the hard carbon substrate for 0.5 hours at 660°C using a carbon source gas and a protective gas with a gas flow ratio of 1:2. A carbon layer accounting for 3% of the total mass of the hard carbon substrate and the deposited silicon-based material is coated on the surface of the hard carbon particles, wherein the gas source is acetylene gas, and silicon-containing material particles 2 are obtained. Among them, the mass ratio of silicon in silane to hard carbon substrate is 2:3; the pore volume of the micropores of the hard carbon substrate is 0.8cm 3 / g, average pore diameter of 3.2nm, specific surface area of ​​1612m 2 / g, the silicon-based material comprises silicon crystal grains, the particle size of the silicon crystal grains is 2.9nm; the silicon mass percentage of the silicon-containing material particles 2 is 36%.

[0285] Preparation Example 3: Silicon-containing material particles 3

[0286] At 465°C, a gas containing silane SiH4 is introduced into a hard carbon substrate with a porous structure, and vapor deposition is performed for 9 hours. By chemical vapor deposition, a silicon-based material is generated from silane and deposited in the porous structure of the hard carbon substrate. Then, chemical vapor deposition is used to vapor deposit on the hard carbon substrate for 0.5 hours at 660°C using a carbon source gas and a protective gas with a gas flow ratio of 1:2. A carbon layer accounting for 3% of the total mass of the hard carbon substrate and the deposited silicon-based material is coated on the surface of the hard carbon particles, wherein the gas source is acetylene gas, and silicon-containing material particles 3 are obtained. Among them, the mass ratio of silicon in silane to hard carbon substrate is 2:3; the pore volume of the micropores of the hard carbon substrate is 0.4 cm 3 / g, average pore diameter of 3.5nm, specific surface area of ​​1408m 2 / g, the silicon-based material comprises silicon crystal grains, the particle size of the silicon crystal grains is 3.0nm; the mass percentage of silicon in the silicon-containing material particles 3 is 35%.

[0287] Example 1

[0288] 1) Preparation of silicon-carbon composite materials

[0289] The silicon-containing material particles 1 and the phenolic resin are mixed in a mass ratio of 1:1.2, and placed in the feed bin 1 of the spray equipment. Under nitrogen protection, the air pressure of the feed bin 1 is set to 300 KPa, the air inlet temperature is set to 130°C, and the air outlet temperature is set to 70°C to obtain an intermediate product, i.e., a first intermediate product of a semi-dried coated adhesive;

[0290] Graphite with a Dv50 of 3.8 μm and the intermediate product prepared above were placed in feed bin 2, with the mass ratio of graphite to silicon-containing material particles being 9:1. The air pressure of feed bin 2 was set to 200 KPa, the air inlet temperature to 210°C, and the air outlet temperature to 170°C, to obtain secondary particles whose inner region was mainly composed of silicon-containing material particles and whose outer region was mainly composed of graphite material particles;

[0291] The above-mentioned secondary particles were placed in a heating chamber, and the heating chamber was first heated to 660°C in a nitrogen atmosphere. Then, a mixed gas was introduced at a volume ratio of nitrogen to acetylene gas of 1:2, and the mixture was kept warm for 0.5 hours. Carbon coating was performed on the surface of the secondary particles to obtain a silicon-carbon composite material. Among them, the silicon-carbon composite material has a silicon mass ratio of 45% in the area r / 2 from the geometric center, a carbon mass ratio of 98% in the area extending from the outer surface to the inner side at a distance of r / 2, a porosity of 28%, a Dv50 of 13.1um, a particle size distribution of 1.5, and a powder compaction density of 1.02g / cm3 at 49000N. 3 , specific surface area is 4.3m 2 / g.

[0292] 2) Preparation of negative electrode sheet

[0293] The prepared silicon-carbon composite material, artificial graphite, conductive carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are fully stirred and mixed in a deionized water solvent system in a weight ratio of 20:75:2:2:1 to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on a negative electrode current collector copper foil with a thickness of 13 μm at a coating speed of 25 m / min and a coating oven temperature of 110°C; and then the negative electrode sheets are obtained by cold pressing and slitting.

[0294] 3) Preparation of positive electrode sheet

[0295] The positive electrode active material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system in a weight ratio of 96:2:2 to obtain a positive electrode slurry; the above positive electrode slurry is evenly coated on a positive electrode current collector aluminum foil with a thickness of 13 μm at a coating speed of 30 m / min; the temperature of the coating oven is 110°C, and then the positive electrode sheets are obtained through cold pressing and slitting.

[0296] 4) Preparation of electrolyte

[0297] In an argon atmosphere glove box (H2O content <0.1ppm, O2 content <0.1ppm), lithium hexafluorophosphate (LiPF6) was dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (3:7 volume ratio) and stirred to obtain an electrolyte with a lithium salt concentration of 1 mol / L. Fluoroethylene carbonate (FEC) was then added to a concentration of 5% of the total electrolyte mass.

[0298] 5) Isolation film

[0299] Polypropylene (PP) film is used as the isolation film.

[0300] 6) Preparation of batteries

[0301] The positive electrode sheet, the separator, and the composite negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to isolate the positive and negative electrode sheets. The electrode assembly is wound, the tabs are welded, and the electrode assembly is placed in an outer package. The electrolyte is then injected and sealed. After standing, cold pressing, formation, shaping, capacity testing and other processes, the lithium-ion secondary battery prepared in Example 1 is obtained.

[0302] Example 2

[0303] The preparation method of the battery of Example 2 is similar to that of the battery of Example 1, except that silicon-containing material particles 2 are used, as shown in Table 1.

[0304] Examples 3-10

[0305] The preparation methods of the batteries of Examples 3-10 are similar to those of the battery of Example 1, except that the preparation parameters of the silicon-carbon composite material and / or the Dv50 of the graphite particles are adjusted, as shown in Table 1.

[0306] Example 11

[0307] The preparation method of the battery of Example 11 is similar to that of the battery of Example 1, except that the Dv50 of the graphite particles is adjusted, as shown in Table 1.

[0308] Example 12

[0309] The preparation method of the battery of Example 12 is similar to that of the battery of Example 1, except that silicon-containing material particles 3 are used, as shown in Table 1.

[0310] Table 1

[0311] Comparative Example 1

[0312] The preparation method of the battery of Comparative Example 1 is similar to that of the battery of Example 1, except that the silicon-carbon composite material is secondary particles obtained by directly mixing and granulating silicon-containing material particles and graphite. The specific preparation method is:

[0313] Using the same graphite and silicon-containing material particles as in Example 1, the graphite, silicon-containing material particles, and phenolic resin were mixed in a ratio of 9:1:1.2 and placed in the feed bin of the spray equipment. Under nitrogen protection, the air pressure in the feed bin 2 was set to 150 kPa, the air inlet temperature was set to 210° C., and the air outlet temperature was set to 170° C. to obtain secondary particles;

[0314] The above-mentioned secondary particles are placed in a heating chamber. Under a nitrogen atmosphere, the heating chamber is first heated to 660°C, and then a mixed gas is introduced at a volume ratio of nitrogen to acetylene gas of 1:2. The mixture is kept warm for 0.5 hours, and carbon coating treatment is performed on the surface of the secondary particles to obtain a silicon-carbon composite material.

[0315] Comparative Example 2

[0316] The preparation method of the battery of Comparative Example 2 is similar to that of the battery of Example 1, except that the silicon-carbon composite material is a direct mixture of silicon-containing material particles and graphite. The specific preparation method is:

[0317] The same graphite and silicon-containing material particles as those in Example 1 were used, and the graphite and silicon-containing material particles were dry-mixed uniformly in a ratio of 9:1 to obtain a mixed powder.

[0318] 2. Test Method

[0319] 1. Silicon-carbon composite material gram capacity test

[0320] Battery cell production: button-type batteries are made, and lithium sheets are used as the positive electrode; the prepared silicon-carbon composite material, conductive carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are thoroughly stirred and mixed in a deionized water solvent system in a weight ratio of 95:2:2:1 to obtain a negative electrode slurry, which is evenly coated on a negative electrode current collector copper foil with a thickness of 13 μm at a coating speed of 25 m / min and a coating oven temperature of 110°C; then the negative electrode sheets are obtained by cold pressing and slitting; in an argon atmosphere glove box (H2O content <0.1 ppm, O2 content <0.1 ppm), lithium hexafluorophosphate (LiPF6) is dissolved in a mixed system of organic solvents ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC volume ratio of 3:7) and stirred to obtain an electrolyte with a lithium salt concentration of 1 mol / L; a 9 μm polyethylene (PE) film is used as an isolation membrane. The above-mentioned positive electrode, separator, negative electrode and electrolyte were assembled into a battery for testing.

[0321] Test process: Under room temperature conditions, the battery was left to stand for 3 hours, then discharged at a constant current of 0.05C to a voltage of 0.005V. It was further discharged at a constant current of 50μA to a voltage of 0.005V. The capacity at this time was recorded as the lithium insertion capacity. After standing for 5 minutes, it was then charged at a rate of 0.1C to a voltage of 0.8V. The capacity at this time was recorded as the lithium removal capacity, which is the material capacity. The ratio of the lithium removal capacity to the mass of the silicon-carbon composite material is the gram capacity of the silicon-carbon composite material.

[0322] 2. Battery room temperature cycle performance test

[0323] Test process: At 25°C, let the battery rest for 30 minutes, then charge at a rate of 0.5C to a voltage of 4.2V. Further charge at a constant voltage of 4.2V to a current of 0.05C, let it rest for 5 minutes, and then discharge at a rate of 0.5C to a voltage of 2.8V. The resulting capacity is recorded as the initial capacity C0. This is one charge and discharge cycle. Repeat the above steps for the same battery, recording the discharge capacity Cn after each cycle. The battery capacity retention rate after each cycle is Pn = Cn / C0*100%, until Pn≦80%, stop the test, and record the number of cycles at this time.

[0324] 3. Battery high temperature storage performance test

[0325] Test conditions: Store fully charged cells at 60°C and test the capacity every 30 days until the capacity decays to 80% of the initial capacity. Record the storage days at this point.

[0326] Test process: Let the battery rest for 30 minutes, discharge at a rate of 0.5C to a voltage of 2.8V, let it rest for 5 minutes, then charge at a rate of 0.5C to a voltage of 4.2V, further charge at a constant voltage of 4.2V to a current of 0.05C, let it rest for 5 minutes, then discharge at a rate of 0.5C to a voltage of 2.8V. This is the test capacity process, and record the discharge capacity each time. Let the battery rest for another 5 minutes, then charge at a rate of 0.5C to a voltage of 4.2V, further charge at a constant voltage of 4.2V to a current of 0.05C. This is to fully charge the battery cell, then place it in a 60°C incubator. After 30 days, test the capacity according to the above process.

[0327] Capacity retention after n days of storage (%) = (discharge capacity on day n / first discharge capacity on day 0) × 100%. Stop testing until the capacity retention reaches ≤ 80%, and record the number of days of storage at that point. Draw a fitting curve with days as the x-axis and capacity retention as the y-axis to obtain the number of days of storage when the capacity retention reaches 80%.

[0328] 3. Analysis of test results of various embodiments and comparative examples

[0329] 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.

[0330] As can be seen from Table 2, the inner area of ​​the silicon-carbon composite material is mainly silicon material particles, and the outer area is mainly graphite particles. This structure can improve the high-temperature storage performance and cycle stability of the battery. At the same time, the silicon-carbon composite material has excellent capacity.

[0331] Table 2

[0332] As shown in Tables 3 and 4, when the mass proportion of silicon elements in the region r / 2 from the geometric center of the silicon-carbon composite material is greater than or equal to 30%, the silicon-carbon composite material has excellent specific capacity and the battery has excellent high-temperature storage performance and cycle stability. When the Dv50 of the silicon-carbon composite material is less than or equal to 16μm, the battery has good high-temperature storage performance and cycle stability.

[0333] Table 3

[0334] Table 4

[0335] As can be seen from Table 5, when the mass proportion of carbon elements in the area extending from the surface of the silicon-carbon composite material to the inside by a distance r / 2 is greater than or equal to 80%, the battery has excellent high-temperature storage performance and cycle stability, and the silicon-carbon composite material also has excellent specific capacity.

[0336] Table 5

[0337] As can be seen from Table 6, when the porosity of the silicon-carbon composite material is 20%-45%, the silicon-carbon composite material has excellent specific capacity, and the battery has excellent high-temperature storage performance and cycle stability.

[0338] Table 6

[0339] From the comparison between Example 1 and Example 11 in Table 7, it can be seen that when the Dv50 of the silicon-containing material particles is greater than the Dv50 of the graphite particles, the high-temperature storage performance of the battery can be improved. From the comparison between Example 1 and Example 12 in Table 7, it can be seen that the pore volume of the carbon substrate micropores in the silicon-containing material particles is greater than or equal to 0.5 cm 3 / g, the silicon-carbon composite material has a better gram capacity, and the battery has excellent high-temperature storage performance and cycle performance.

[0340] Table 7

[0341] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining 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 silicon-carbon composite material comprises an inner region and an outer region, wherein the inner region is mainly composed of silicon-containing material particles, and the outer region is mainly composed of carbon-based material particles.

2. The silicon-carbon composite material according to claim 1, characterized in that: The number of silicon-containing material particles in the inner region is less than or equal to 3, and can be 1-2.

3. The silicon-carbon composite material according to claim 1 or 2, characterized in that: The mass proportion of silicon element in the region r / 2 from the geometric center of the silicon-carbon composite material is greater than or equal to 30%, and can be optionally 35%-45%, wherein r represents the short diameter of the silicon-carbon composite material.

4. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that: The mass proportion of carbon elements in the region extending from the outer surface of the silicon-carbon composite material to the inner side by a distance r / 2 is greater than or equal to 80%, and can be optionally 90%-100%, wherein r represents the short diameter of the silicon-carbon composite material.

5. The silicon-carbon composite material according to any one of claims 1 to 4, characterized in that: The outer region of the silicon-carbon composite material also includes an amorphous carbon coating layer.

6. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that: The Dv50 of the silicon-containing material particles is greater than or equal to the Dv50 of the carbon-based material particles.

7. The silicon-carbon composite material according to any one of claims 1 to 6, characterized in that: The Dv50 of the silicon-containing material particles is less than or equal to 5 μm; and / or, The Dv50 of the carbon-based material particles is less than or equal to 5 μm.

8. The silicon-carbon composite material according to any one of claims 1 to 7, characterized in that: The silicon-containing material particles include at least one of elemental silicon, silicon-oxygen material, silicon-carbon material, and silicon-metal alloy. Optionally, the silicon-containing material particles include silicon-carbon material; And / or, the carbon-based material particles include at least one of artificial graphite and natural graphite. Optionally, the carbon-based material particles include artificial graphite.

9. The silicon-carbon composite material according to any one of claims 1 to 8, characterized in that: The silicon-containing material particles include a carbon substrate having a pore structure and a silicon-based material disposed in the pore structure of the carbon substrate.

10. The silicon-carbon composite material according to claim 9, characterized in that: The carbon substrate comprises micropores with a pore size less than 2 nm, mesopores with a pore size of 2 nm-50 nm, and macropores with a pore size greater than 50 nm.

11. The silicon-carbon composite material according to claim 10, characterized in that: The pore volume of the micropores is greater than or equal to 0.5 cm 3 / g, optional 0.6cm 3 / g-0.9cm 3 / g.

12. The silicon-carbon composite material according to any one of claims 9 to 11, characterized in that: The average pore size of the carbon substrate is less than or equal to 5 nm, and can be 1 nm-3.5 nm.

13. The silicon-carbon composite material according to any one of claims 9 to 12, characterized in that: The specific surface area of ​​the carbon substrate is greater than or equal to 1200 m 2 / g, optional 1500m 2 / g-1800m 2 / g.

14. The silicon-carbon composite material according to any one of claims 9 to 13, characterized in that: The silicon-based material includes at least one of elemental silicon, silicon-oxygen material, silicon-carbon material, and silicon-metal alloy; the carbon substrate includes at least one of graphite, soft carbon, and hard carbon.

15. The silicon-carbon composite material according to any one of claims 9 to 14, characterized in that: The silicon-based material includes silicon grains. Optionally, the size of the silicon grains is less than or equal to 10 nm. Optionally, the size of the silicon grains is less than or equal to 3 nm.

16. The silicon-carbon composite material according to any one of claims 1 to 15, characterized in that: The porosity of the silicon-carbon composite material is 20%-45%, and can be optionally 20%-35%.

17. The silicon-carbon composite material according to any one of claims 1 to 16, characterized in that: The silicon-carbon composite material also satisfies at least one of the following conditions: (1) The volume distribution particle size Dv50 of the silicon-carbon composite material is less than or equal to 16 μm, and can be selected to be 8 μm-16 μm; (2) The particle size distribution of the silicon-carbon composite material (Dv90-Dv10) / Dv50 is 0.5-1.8, and can be optionally 0.8-1.5; (3) The powder compaction density of the silicon-carbon composite material at 49000N is 0.7g / cm 3 -1.3g / cm 3 , optional 0.95g / cm 3 -1.1g / cm 3 ; (4) The specific surface area of ​​the silicon-carbon composite material is less than or equal to 6 m 2 / g, can be selected to be less than or equal to 4.5m 2 / g.

18. A method for preparing a silicon-carbon composite material, characterized in that: The steps include: Providing silicon-containing material particles and carbon-based material particles; Performing a first spray granulation on the silicon-containing material particles and the binder to obtain a first intermediate product; Spraying carbon-based material particles onto the surface of the first intermediate product to perform a second spray granulation to prepare the silicon-carbon composite material; The silicon-carbon composite material includes an inner region and an outer region, the inner region is mainly composed of silicon-containing material particles, and the outer region is mainly composed of carbon-based material particles.

19. The preparation method according to claim 18, characterized in that: The silicon-containing material particles are prepared by the following steps: providing a gas containing a silicon precursor to a carbon substrate having a porous structure; The silicon-based material attached to the pore structure is generated from the silicon precursor by chemical vapor deposition to obtain the silicon-containing material particles.

20. The preparation method according to claim 18 or 19, characterized in that: The mass ratio of the silicon-containing material particles to the binder is 1:2-2:1; and / or, The mass ratio of the silicon-containing material particles to the carbon-based material particles is 1:12-1:

6.

21. The preparation method according to any one of claims 18 to 20, characterized in that: The first spray granulation satisfies at least one of the following conditions: (1) The temperature difference between the inlet air temperature and the outlet air temperature is not greater than 60°C; (2) The air inlet temperature is 110℃-150℃; (3) The air outlet temperature is 50℃-90℃; (4) The feed gas pressure is 250KPa-350KPa, and can be optionally 280KPa-320KPa.

22. The preparation method according to any one of claims 18 to 21, characterized in that: The second spray granulation satisfies at least one of the following conditions: (1) The temperature difference between the inlet air temperature and the outlet air temperature is 20℃-40℃; (2) The inlet air temperature is 170℃-280℃; (3) The air outlet temperature is 130℃-240℃; (4) The feed gas pressure is 150KPa-260KPa, and can be optionally 180KPa-210KPa.

23. The preparation method according to any one of claims 18 to 22, characterized in that: The method for preparing the silicon-carbon composite material further comprises: After the second spray granulation, a gaseous carbon source is introduced, and carbonization is performed after gas phase coating to obtain the silicon-carbon composite material.

24. The preparation method according to claim 23, characterized in that: The gaseous carbon source is introduced, and carbonization is performed after gas phase coating to obtain the silicon-carbon composite material that satisfies at least one of the following conditions: (1) The gaseous carbon source includes a gaseous hydrocarbon alkane, which can be at least one of methane, ethylene, and acetylene; (2) The carbonization temperature is 400° C.-800° C.; (3) The carbonization time is 0.2h-2h; (4) During the carbonization process, the protective gas is nitrogen or argon. Optionally, the gas flow ratio of the gaseous carbon source to the protective gas is 1:5 to 1:1.

5.

25. The preparation method according to any one of claims 18 to 24, characterized in that: The binder includes at least one of phenolic resin, styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, sodium alginate, carboxymethyl cellulose, polyacrylonitrile and polypropylene alcohol.

26. A secondary battery, characterized in that: The secondary battery comprises a negative electrode plate, and the negative electrode plate comprises the silicon-carbon composite material according to any one of claims 1 to 17 or the silicon-carbon composite material prepared by the preparation method according to any one of claims 18 to 25.

27. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 26.

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