Secondary battery and preparation method therefor, and electronic apparatus

Abstract

Provided are a secondary battery and a preparation method therefor, and an electronic apparatus. A negative electrode active material of the secondary battery comprises silicon-carbon composite particles and satisfies: 0.23≤DA99 / DA50-DA90 / DA50≤0.57. By means of selecting the silicon-carbon composite particles having the above-described characteristics as the negative electrode active material, the cycle performance of the secondary battery can be improved.

Description

Secondary battery, preparation method thereof, and electronic device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 5, 2024, with application number 202410250975.3 and invention name “A secondary battery, its preparation method and electronic device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to a secondary battery, a preparation method thereof, and an electronic device. Background Art

[0003] In recent years, secondary batteries, such as lithium-ion batteries, have attracted widespread attention due to the widespread application of portable electronic devices, electric vehicles, and energy storage components. The development of lithium-ion batteries with higher energy density is of great significance. Among the reported anode active materials, silicon-based anode active materials have become an excellent choice due to their abundant reserves and high theoretical specific capacity (4200 mAh / g). However, the huge volume expansion (over 300%) of silicon-based anode active materials during lithiation and delithiation causes rapid fragmentation of silicon particles and even delamination from the anode current collector, which affects the cycling performance of lithium-ion batteries. In addition, the volume effect of silicon triggers many side reactions, such as the repeated fragmentation and formation of solid electrolyte interface (SEI) films. These defects can lead to rapid capacity loss of the anode electrode, poor electrical contact, poor rate performance, and low cycling stability. As a result, the cycling performance of lithium-ion batteries using silicon-based anode active materials is significantly lower than that of lithium-ion batteries using graphite anode active materials, severely restricting the large-scale application of silicon-based anode active materials in lithium-ion batteries.

[0004] In order to solve the above problems, existing technologies mostly use methods such as silicon nano-sizing, porous silicon, silicon-carbon composites, and the introduction of transition metal oxides. Although silicon nano-sizing and porous silicon can alleviate the volume expansion of elemental silicon to a certain extent, the high specific surface area and low compaction density limit their large-scale application. The new silicon-carbon composite material uses chemical vapor deposition (CVD) to unsaturatedly deposit silicon in the pores of the carbon skeleton, reserving space for silicon expansion, and successfully realizing the first commercial application of the new silicon-carbon composite material. However, most of the new silicon-carbon composite materials on the market still have the problems of high stress in the negative electrode sheet and easy peeling of the negative electrode material layer from the negative electrode current collector, which affects the cycle performance of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and its preparation method and electronic device to improve the cycle performance of the secondary battery. The specific technical solution is as follows:

[0006] The first aspect of the present application provides a secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material comprising silicon-carbon composite particles, and a cross-sectional area of ​​1000 μm in a cross section along the thickness direction of the negative electrode plate. 2 In the first counting area, based on the mass of a single silicon-carbon composite particle, the mass percentage of silicon element is the particle silicon content, and the ratio of the sum of the cross-sectional areas of the silicon-carbon composite particles with the same particle silicon content to the sum of the cross-sectional areas of all the silicon-carbon composite particles in the first counting area is the particle area ratio. The particle silicon content is used as the horizontal axis and the particle area ratio is used as the vertical axis to obtain a particle silicon content area distribution diagram; the particle silicon content is arranged in order from small to large, and the particle area ratios corresponding to the particle silicon contents are added in sequence to obtain the cumulative particle area ratio. In the particle silicon content area distribution diagram, the particle silicon content corresponding to the cumulative particle area ratio of 50% is D A 50, the cumulative particle area accounts for 90% and the corresponding particle silicon content is D A 90, the cumulative particle area accounts for 99% and the corresponding particle silicon content is D A 99, 0.23≤D A 99 / D A 50-D A 90 / D A 50≤0.57. The present application selects the negative electrode active material including the above silicon-carbon composite particles and adjusts D A 99 / D A 50-D A 90 / D A 50 satisfies the above relationship, which can reduce the volume expansion difference between different silicon-carbon composite particles and different areas of the same negative electrode plate, reduce the internal stress caused by repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, reduce the capacity attenuation of the secondary battery, and thus improve the cycle performance of the secondary battery.

[0007] In some embodiments of the present application, 30%≤D A 50≤45%, 42%≤D A 90≤65%, 55%≤D A 99≤75%. By regulating D A 50. D A 90.D A The value of 99 is within the above range, which can make the distribution of the silicon content of the particles narrower and the difference in the silicon content of the particles between the silicon-carbon composite particles smaller, thereby being beneficial to improving the cycle performance of the secondary battery.

[0008] In some embodiments of the present application, in the particle silicon content area distribution diagram, the cumulative particle area corresponding to the particle silicon content of 5% is D B 5, 0.93% ≤ D B 5≤7.26%. When 0.23≤D A 99 / D A 50-D A 90 / D A 50≤0.57, by adjusting D B When the value of 5 is within the above range, the cumulative particle area of ​​the silicon-carbon composite particles with a granular silicon content of 5% is small and the number is small, while the cumulative particle area of ​​the silicon-carbon composite particles with a granular silicon content greater than 5% is large and the number is large, which can improve the energy density of the secondary battery and at the same time make the distribution of the granular silicon content narrower. During the charge and discharge process of the secondary battery, the volume expansion difference of different silicon-carbon composite particles and different areas of the same negative electrode plate is reduced, the internal stress generated by the repeated expansion and contraction of the negative electrode plate is reduced, the risk of the negative electrode material layer being peeled off from the negative electrode current collector is reduced, and the capacity attenuation of the secondary battery is reduced, which is beneficial to improving the cycle performance of the secondary battery.

[0009] In some embodiments of the present application, in the first counting area, the cross-sectional area of ​​a single silicon-carbon composite particle is the particle area, and the ratio of the number of silicon-carbon composite particles with the same particle area to the total number of all silicon-carbon composite particles in the first counting area is the particle number percentage. With the particle area as the horizontal axis and the particle number percentage as the vertical axis, a particle area number distribution diagram is obtained; the particle areas are arranged in order from small to large, and the particle number percentages corresponding to the particle areas are added in sequence to obtain the cumulative particle number percentage. In the particle area number distribution diagram, the particle area corresponding to a cumulative particle number percentage of 50% is D S 50μm 2 The particle area corresponding to the cumulative particle number accounting for 90% is D S 90μm 2 The particle area corresponding to the cumulative particle number accounting for 99% is D S 99μm 2 , 1.66≤D S 99 / D S 50-D S 90 / D S 50≤4.7. When 0.23≤D A 99 / D A 50-D A 90 / D A 50≤0.57, by adjusting D S 99 / D S 50-D S90 / D S When the value of 50 is within the above range, the size difference between the silicon-carbon composite particles is small. During the charge and discharge cycle of the secondary battery, the absolute value of the volume expansion of the silicon-carbon composite particles is small, and the difference in the volume expansion rate is also small. This can further reduce the volume expansion difference between different silicon-carbon composite particles and different areas of the same negative electrode plate, reduce the internal stress caused by repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, and reduce the capacity attenuation of the secondary battery, thereby helping to further improve the cycle performance of the secondary battery.

[0010] In some embodiments of the present application, 25≤D S 50≤60,98≤D S 90≤150,181≤D S 99≤255. By regulating D S 50. D S 90.D S When the value of 99 is within the above range, the particle area distribution of the silicon-carbon composite particles can be narrower and the size difference between the silicon-carbon composite particles is smaller, which is beneficial to further improve the cycle performance of the secondary battery.

[0011] In some embodiments of the present application, the specific surface area of ​​the silicon-carbon composite particles is 4.5 m 2 / g to 8.9m 2 By regulating the specific surface area of ​​the silicon-carbon composite particles within the above range, it is beneficial to improve the cycle performance of the secondary battery.

[0012] In some embodiments of the present application, the silicon-carbon composite particles meet at least one of the following characteristics: (a) the mass percentage of silicon in the silicon-carbon composite particles is 35% to 55%; (b) the mass percentage of oxygen in the silicon-carbon composite particles is 1% to 4%; (c) the surface of the negative electrode sheet includes an area of ​​4 cm 2 In the second counting area, the total area of ​​silicon-carbon composite particles is A1 cm 2 , 0.05≤A1 / 4≤0.95; (d) In the first counting area, the total area of ​​the silicon-carbon composite particles is A2μm 2 , 0.05≤A2 / 1000≤0.95; (e) the negative electrode active material further comprises at least one of graphite or hard carbon; and (f) the mass percentage of the silicon-carbon composite particles is 5% to 95% based on the mass of the negative electrode material layer. Silicon-carbon composite particles meeting the above characteristics are beneficial for further improving the cycle performance of secondary batteries.

[0013] In some embodiments of the present application, the silicon-carbon composite particles include a carbon skeleton containing silicon. The use of silicon-carbon composite particles with the above structure is conducive to reducing the volume expansion of the silicon-carbon composite particles, thereby facilitating improved cycle performance of the secondary battery.

[0014] In some embodiments of the present application, the silicon-carbon composite particles include a protective layer located on at least a portion of the surface of the carbon skeleton. The protective layer includes at least one of amorphous carbon, a metal oxide, or a non-metallic oxide. The metal oxide includes at least one of aluminum oxide, copper oxide, or titanium oxide. The non-metallic oxide includes at least one of silicon dioxide or silicon monoxide. Silicon-carbon composite particles having the above structure have a high structural strength. This not only reduces the volume expansion of the silicon-carbon composite particles, but also reduces electrolyte erosion of the silicon-carbon composite particles, thereby improving the cycle performance of the secondary battery.

[0015] The second aspect of the present application provides a method for preparing the secondary battery of the first aspect of the present application, wherein the method for preparing the silicon-carbon composite particles comprises the following steps:

[0016] S1: providing a carbon skeleton material, crushing and classifying the carbon skeleton material, and then performing a first heat treatment on the carbon skeleton material, wherein the temperature of the first heat treatment is 700° C. to 900° C., and the time of the first heat treatment is 4 hours to 6 hours;

[0017] S2: Depositing the carbon skeleton material once, heating to 430°C to 550°C, introducing a first mixed gas containing 5% to 50% silane by volume under a negative pressure of -60kPa to -101kPa, and reacting for 2h to 6h. Repeating the deposition once 2 to 5 times;

[0018] S3: transferring the carbon skeleton material after the primary deposition to a fluidized bed for heating, introducing a second mixed gas containing 5% to 50% by volume of silane, and performing secondary deposition to obtain a carbon skeleton material including silicon; the secondary deposition temperature is 430° C. to 550° C., and the reaction time of the secondary deposition is 1 hour to 6 hours;

[0019] S4: performing a second heat treatment on the carbon skeleton material including silicon at a temperature of 620° C. to 700° C., wherein the second heat treatment lasts for 0.5 h to 1 h;

[0020] S5: Then, a protective layer is prepared on the surface of the carbon skeleton material including silicon to obtain silicon-carbon composite particles.

[0021] In the above preparation method, by depositing the carbon skeleton material once and regulating the pressure of the first deposition to be negative, a small amount of silicon can be deposited in advance inside the pores of the carbon skeleton material, thereby providing active induction sites for the secondary deposition of silicon inside the pores of the carbon skeleton material, improving the uniformity of silane deposition, and reducing the deposition of silane outside the pores of the carbon skeleton material, thereby facilitating the preparation of silicon-carbon composite particles with high silicon deposition uniformity. The silicon-carbon composite particles obtained by the above preparation method have small differences in silicon content between the silicon-carbon composite particles. When applied to secondary batteries, they can reduce the volume expansion differences between different silicon-carbon composite particles and different regions of the same negative electrode, reduce the internal stress generated by repeated expansion and contraction of the negative electrode, reduce the risk of the negative electrode material layer peeling off from the negative electrode current collector, reduce the capacity decay of the secondary battery, and thus improve the cycle performance of the secondary battery.

[0022] In some embodiments of the present application, the method for preparing silicon-carbon composite particles meets at least one of the following characteristics: (1) the carbon skeleton material includes at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, or hard carbon; (2) the first mixed gas and the second mixed gas each independently further include at least one of nitrogen, hydrogen, or argon; (3) the source material of the protective layer includes a first source material for preparing amorphous carbon, a second source material for preparing metal oxides, and a third source material for preparing non-metallic oxides, the first source material including at least one of acetylene, methane, propylene, ethylene, or propane, the second source material including at least one of titanium isopropoxide, trimethylaluminum, or copper acetate, and the third source material including at least one of ethyl orthosilicate, triethoxysilane, or monosilane. The method for preparing silicon-carbon composite particles meeting the above characteristics is conducive to obtaining silicon-carbon composite particles with high silicon deposition uniformity and narrow particle silicon content distribution, and the difference in particle silicon content between the silicon-carbon composite particles is small, thereby facilitating improved cycle performance of secondary batteries.

[0023] The third aspect of the present application provides an electronic device comprising the secondary battery provided in the first aspect of the present application or a secondary battery prepared according to the preparation method provided in the second aspect of the present application. The secondary battery provided in the present application has good cycle performance, thereby providing the electronic device provided in the present application with a long service life and good performance.

[0024] Beneficial effects of this application:

[0025] The present application provides a secondary battery and its preparation method and electronic device. The secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes silicon-carbon composite particles, and satisfies 0.23≤D A 99 / D A 50-D A90 / D A 50≤0.57. The present application selects the negative electrode active material including the above silicon-carbon composite particles and adjusts D A 99 / D A 50-D A 90 / D A 50 satisfies the above relationship, which can reduce the volume expansion difference between different silicon-carbon composite particles and different areas of the same negative electrode plate, reduce the internal stress caused by repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, reduce the capacity attenuation of the secondary battery, and thus improve the cycle performance of the secondary battery.

[0026] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0028] FIG1 is a scanning electron microscope (SEM) image of Example 1-1 of the present application;

[0029] FIG2 is an area distribution diagram of the granular silicon content and an area cumulative distribution diagram of the granular silicon content of Example 1-1 of the present application;

[0030] FIG3 is a particle area quantity distribution diagram and a cumulative quantity distribution diagram of Example 1-1 and Example 2-7 of the present application. DETAILED DESCRIPTION

[0031] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0032] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0033] The first aspect of the present application provides a secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material comprising silicon-carbon composite particles. The cross section of the negative electrode plate along the thickness direction includes a cross section area of ​​1000 μm 2 In the first counting area, based on the mass of a single silicon-carbon composite particle, the mass percentage of silicon element is the particle silicon content, and the ratio of the sum of the cross-sectional areas of the silicon-carbon composite particles with the same particle silicon content to the sum of the cross-sectional areas of all the silicon-carbon composite particles in the first counting area is the particle area ratio. The particle silicon content is used as the horizontal axis and the particle area ratio is used as the vertical axis to obtain a particle silicon content area distribution diagram; the particle silicon content is arranged in order from small to large, and the particle area ratios corresponding to the particle silicon contents are added in sequence to obtain the cumulative particle area ratio. In the particle silicon content area distribution diagram, the particle silicon content corresponding to the cumulative particle area ratio of 50% is D A 50, the cumulative particle area accounts for 90% and the corresponding particle silicon content is D A 90, the cumulative particle area accounts for 99% and the corresponding particle silicon content is D A 99, 0.23≤D A 99 / D A 50-D A 90 / D A 50≤0.57. For example, D A 99 / D A 50-D A 90 / D A The value of 50 can be 0.23, 0.25, 0.30, 0.33, 0.36, 0.40, 0.44, 0.47, 0.50, 0.55, 0.57 or a range consisting of any two of the above values.

[0034] D A 99 / D A 50-D A 90 / D A The value of 50 can reflect the difference in silicon content between silicon-carbon composite particles and represent the distribution trend of silicon element between silicon-carbon composite particles. A 99 / D A 50-D A 90 / D A50 satisfies the above relationship, the difference in silicon content between the silicon-carbon composite particles is small. During the charge and discharge cycle of the secondary battery, the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate can be reduced, the internal stress generated by the repeated expansion and contraction of the negative electrode plate can be reduced, the risk of the negative electrode material layer being peeled off from the negative electrode current collector can be reduced, and the capacity attenuation of the secondary battery can be reduced, thereby improving the cycle performance of the secondary battery. When D A 99 / D A 50-D A 90 / D A When the value of 50 is too large, for example, greater than 0.57, it means that the silicon content of some silicon-carbon composite particles is much greater than the average value. The volume expansion of these silicon-carbon composite particles during the cycle is much greater than that of other silicon-carbon composite particles, resulting in an increase in the internal stress caused by repeated expansion and contraction of the negative electrode plate, and the negative electrode material layer is easily peeled off from the negative electrode current collector, resulting in serious capacity decay of the secondary battery, which is not conducive to improving the cycle performance of the secondary battery. A 99 / D A 50-D A 90 / D A If the value of 50 is too small, for example, less than 0.23, it means that the average silicon content of the silicon-carbon composite particles is too large, and the volume expansion of the silicon-carbon composite particles is serious, resulting in an increase in the internal stress generated by the repeated expansion and contraction of the negative electrode plate, and the negative electrode material layer is easily peeled off from the negative electrode current collector, resulting in a serious capacity decay of the secondary battery, which is not conducive to improving the cycle performance of the secondary battery. Therefore, the negative electrode active material includes silicon-carbon composite particles, and the D A 99 / D A 50-D A 90 / D A 50 satisfies the above relationship and can improve the cycle performance of the secondary battery.

[0035] In some embodiments of the present application, the negative electrode active material includes silicon-carbon composite particles and graphite particles. The area distribution diagram of the particle silicon content can be obtained by: ion polishing the negative electrode sheet along the thickness direction using a cross-sectional ion polishing instrument, the ion polishing voltage is 7.5kV, and the time is 1.5h to obtain a cross section of the negative electrode sheet in the thickness direction. The cross section of the negative electrode sheet is subjected to a scanning electron microscope (SEM) test using a backscattered mode, a test voltage of 5kV to 10kV, a magnification of 1000× to 5000×, and a working distance of 9.8mm to 10.2mm. In the backscattered mode, the contrast is adjusted so that the average grayscale value of the graphite particles is between 60 and 70, the average grayscale value of the negative current collector is between 250 and 255, and the average grayscale value of the silicon-carbon composite particles is between 70 and 250. Specifically, as shown in FIG1 , the contrast is adjusted in the backscatter mode so that the graphite particles 10 are dark black with a grayscale value of <70, and the silicon-carbon composite particles 20 are off-white with a grayscale value of >90. The two particles have a clear boundary line due to the grayscale difference. 2 All silicon-carbon composite particles in the first counting area are analyzed by energy dispersive spectrometer (EDS) to obtain the silicon content of different silicon-carbon composite particles and save the photo. 2 Perform EDS analysis on the first counting area and save 5 to 10 backscattered images. In this mode, all graphite particles have a grayscale value <70, while the silicon-carbon composite particles have a grayscale value >90. The grayscale value is positively correlated with the silicon content of the silicon-carbon composite particles. The greater the silicon content, the brighter the silicon-carbon composite particles and the greater the grayscale value. Therefore, a linear relationship can be obtained between the grayscale value of the silicon-carbon composite particles and the silicon content. The saved backscattered images are processed using image processing software (e.g., HALCON machine vision software). The pixel size was calibrated using the scale of the backscattered photo. Since the grayscale value of graphite particles was <70 and the grayscale value of silicon-carbon composite particles was >90, the edge detection function was used to perform edge analysis and image segmentation on the silicon-carbon composite particles and graphite particles in the backscattered photo. The image of the silicon-carbon composite particles was retained, and the grayscale distribution data and grayscale distribution histogram were output. The total number of pixels contained in the selected area multiplied by the calibrated single pixel area was the total area A of all selected silicon-carbon composite particles. The area of ​​a single silicon-carbon composite particle could also be obtained, which was recorded as S1, S2, S3, ..., S n , then A=S1+S2+S3……+S nSince a linear relationship between the grayscale value and the particle silicon content of the silicon-carbon composite particles has been obtained during EDS analysis, and the grayscale value is linearly related to the particle silicon content of the silicon-carbon composite particles, the grayscale distribution histogram can be converted into a particle silicon content area distribution diagram and a particle silicon content area cumulative distribution diagram. With the particle silicon content as the horizontal axis and the particle area percentage as the vertical axis, the particle silicon content area distribution diagram can be obtained. With the particle silicon content as the horizontal axis and the cumulative particle area percentage as the vertical axis, the particle silicon content area cumulative distribution diagram can be obtained.

[0036] In some embodiments of the present application, the negative electrode active material includes silicon-carbon composite particles and hard carbon. The method for obtaining the area distribution diagram of the granular silicon content is similar to that of the above-mentioned negative electrode active material including silicon-carbon composite particles and graphite particles, and can be obtained by the following method: ion polishing the negative electrode sheet along the thickness direction to obtain the cross-section of the negative electrode sheet in the thickness direction. The cross-sectional image of the negative electrode sheet along the thickness direction is analyzed using a scanning electron microscope (SEM) in backscattered mode. The cross-sectional area of ​​1000 μm is selected. 2 In the first counting area, the contrast is adjusted so that the grayscale values ​​of different negative electrode active materials and negative electrode current collectors are different, and an image of the silicon-carbon composite particles in the selected first counting area is obtained. For example, when the negative electrode active material also includes hard carbon, the average grayscale value of the hard carbon is adjusted to between 60 and 70, the average grayscale value of the negative electrode current collector is adjusted to between 250 and 255, and the average grayscale value of the silicon-carbon composite particles is adjusted to between 70 and 250. EDS analysis is performed on the silicon-carbon composite particles in the selected first counting area to obtain the particle silicon content of each silicon-carbon composite particle in the selected first counting area. Image processing software can be used to obtain the area of ​​each silicon-carbon composite particle in the selected first counting area, and the particle area percentage can be calculated. With the particle silicon content as the horizontal axis and the particle area percentage as the vertical axis, a particle silicon content area distribution diagram is obtained. With the particle silicon content as the horizontal axis and the cumulative particle area percentage as the vertical axis, a particle silicon content area cumulative distribution diagram is obtained.

[0037] In some embodiments of the present application, 30%≤D A 50≤45%, 42%≤D A 90≤65%, 55%≤D A 99≤75%. For example, D A The value of 50 can be 30%, 32%, 34%, 36%, 38%, 40%, 43%, 45%, or a range consisting of any two of the above values. A The value of 90 can be 42%, 45%, 48%, 50%, 54%, 57%, 60%, 63%, 65%, or a range consisting of any two of the above values. A The value of 99 can be 55%, 58%, 61%, 64%, 67%, 70%, 73%, 75% or a range consisting of any two of the above values.A 50. D A 90.D A The value of 99 is within the above range, which can make the distribution of the granular silicon content narrower and the difference in granular silicon content between the silicon-carbon composite particles smaller. During the charge and discharge process of the secondary battery, the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate can be reduced, the internal stress generated by the repeated expansion and contraction of the negative electrode plate can be reduced, the risk of the negative electrode material layer being peeled off from the negative electrode current collector can be reduced, and the capacity attenuation of the secondary battery can be reduced, which is beneficial to improving the cycle performance of the secondary battery.

[0038] In some embodiments of the present application, in the particle silicon content area distribution diagram, the cumulative particle area corresponding to the particle silicon content of 5% is D B 5, 0.93% ≤ D B 5≤7.26%. For example, D B The value of 5 can be 0.93%, 1.6%, 2%, 2.8%, 3%, 3.4%, 4%, 4.5%, 5%, 5.6%, 6%, 6.4%, 7.0%, 7.26% or a range consisting of any two of the above values. A 99 / D A 50-D A 90 / D A 50≤0.57, by adjusting D B When the value of 5 is within the above range, the cumulative particle area of ​​the silicon-carbon composite particles with a granular silicon content of 5% is small and the number is small, while the cumulative particle area of ​​the silicon-carbon composite particles with a granular silicon content greater than 5% is large and the number is large, which can improve the energy density of the secondary battery and at the same time make the distribution of the granular silicon content narrower. During the charge and discharge process of the secondary battery, the volume expansion difference of different silicon-carbon composite particles and different areas of the same negative electrode plate is reduced, the internal stress generated by the repeated expansion and contraction of the negative electrode plate is reduced, the risk of the negative electrode material layer being peeled off from the negative electrode current collector is reduced, and the capacity attenuation of the secondary battery is reduced, which is beneficial to improving the cycle performance of the secondary battery.

[0039] In some embodiments of the present application, in the first counting area, the cross-sectional area of ​​a single silicon-carbon composite particle is the particle area, and the ratio of the number of silicon-carbon composite particles with the same particle area to the total number of all silicon-carbon composite particles in the first counting area is the particle number percentage. With the particle area as the horizontal axis and the particle number percentage as the vertical axis, a particle area number distribution diagram is obtained; the particle areas are arranged in order from small to large, and the particle number percentages corresponding to the particle areas are added in sequence to obtain the cumulative particle number percentage. In the particle area number distribution diagram, the particle area corresponding to a cumulative particle number percentage of 50% is D S 50μm2 The particle area corresponding to the cumulative particle number accounting for 90% is D S 90μm 2 The particle area corresponding to the cumulative particle number accounting for 99% is D S 99μm 2 , 1.66≤D S 99 / D S 50-D S 90 / D S 50≤4.7. For example, D S 99 / D S 50-D S 90 / D S The value of 50 can be 1.66, 2.0, 2.5, 3.0, 3.6, 4.0, 4.4, 4.7 or a range consisting of any two of the above values. S 99 / D S 50-D S 90 / D S The value of 50 can reflect the size difference between silicon-carbon composite particles. A 99 / D A 50-D A 90 / D A 50≤0.57, by adjusting D S 99 / D S 50-D S 90 / D S When the value of 50 is within the above range, the size difference between the silicon-carbon composite particles is small. During the charge and discharge cycle of the secondary battery, the absolute value of the volume expansion of the silicon-carbon composite particles is small, and the difference in the volume expansion rate is also small. This can further reduce the volume expansion difference between different silicon-carbon composite particles and different areas of the same negative electrode plate, reduce the internal stress caused by repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, and reduce the capacity attenuation of the secondary battery, thereby helping to further improve the cycle performance of the secondary battery.

[0040] In this application, the same method as the above-mentioned area distribution diagram of the granular silicon content can be used to obtain the cross-sectional area of ​​the negative electrode sheet along the thickness direction of 1000 μm 2 The particle area and particle number percentage of the silicon-carbon composite particles in the first counting area are plotted. A particle area distribution graph is plotted with particle area as the horizontal axis and particle number percentage as the vertical axis. A particle area cumulative distribution graph is plotted with particle area as the horizontal axis and cumulative particle number percentage as the vertical axis.

[0041] In some embodiments of the present application, 25≤D S 50≤60,98≤D S90≤150,181≤D S 99≤255. For example, D S The value of 50 can be 25, 30, 36, 40, 44, 50, 55, 60 or a range consisting of any two of the above values. S The value of 90 can be 98, 105, 110, 114, 120, 126, 130, 135, 140, 144, 150 or a range consisting of any two of the above values. S The value of 99 can be 181, 195, 200, 206, 210, 215, 220, 224, 230, 235, 240, 246, 250, 255 or a range consisting of any two of the above values. S 50. D S 90.D S The value of 99 is within the above range, which can make the particle area distribution of the silicon-carbon composite particles narrower, the size difference between the silicon-carbon composite particles smaller, and reduce the absolute value difference and volume expansion rate difference of the silicon-carbon composite particles during the charge and discharge cycle of the secondary battery, further reduce the volume expansion difference between different silicon-carbon composite particles and different areas of the same negative electrode sheet, reduce the internal stress generated by the repeated expansion and contraction of the negative electrode sheet, reduce the risk of the negative electrode material layer peeling off from the negative electrode current collector, and reduce the capacity attenuation of the secondary battery, which is conducive to further improving the cycle performance of the secondary battery.

[0042] In some embodiments of the present application, the specific surface area of ​​the silicon-carbon composite particles is 4.5 m 2 / g to 8.9m 2 / g. For example, the specific surface area of ​​silicon-carbon composite particles can be 4.5m 2 / g, 5.0m 2 / g, 6.4m 2 / g, 7.0m 2 / g, 7.6m 2 / g, 8.0m 2 / g、8.9m 2 / g or the range consisting of any two of the above values. A 99 / D A 50-D A 90 / D AOn the basis of 50≤0.57, by regulating the specific surface area of ​​the silicon-carbon composite particles within the above range, the erosion of the solvent (such as water solvent) in the negative electrode slurry on the silicon inside the silicon-carbon composite particles can be reduced, thereby reducing the risk of gas production during the stirring of the negative electrode slurry, and reducing the risk of pinholes, exposure of the negative electrode current collector and other problems during the coating of the negative electrode slurry, so that the distribution of the negative electrode material layer on the negative electrode current collector is more uniform, and the difference in silicon content between the silicon-carbon composite particles is smaller. During the charge and discharge cycle of the secondary battery, the difference in volume expansion of different silicon-carbon composite particles and different regions of the same negative electrode plate can be reduced, the internal stress generated by the repeated expansion and contraction of the negative electrode plate is reduced, and the risk of the negative electrode material layer being peeled off from the negative electrode current collector is reduced, which is beneficial to improving the cycle performance of the secondary battery.

[0043] In some embodiments of the present application, the mass percentage of silicon in the silicon-carbon composite particles is 35% to 55%. For example, the mass percentage of silicon in the silicon-carbon composite particles can be 35%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, or a range consisting of any two of the above values. A 99 / D A 50-D A 90 / D A On the basis of 50≤0.57, by regulating the mass percentage of silicon element in the silicon-carbon composite particles within the above range, the volume expansion rate of the silicon-carbon composite particles and the difference in volume expansion rate between the silicon-carbon composite particles can be reduced, and the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate can be further reduced, thereby reducing the internal stress generated by repeated expansion and contraction of the negative electrode plate, reducing the risk of the negative electrode material layer being peeled off from the negative electrode current collector, and reducing the capacity attenuation of the secondary battery, which is conducive to further improving the cycle performance of the secondary battery.

[0044] In some embodiments of the present application, the mass percentage of oxygen in the silicon-carbon composite particles is 1% to 4%. For example, the mass percentage of oxygen in the silicon-carbon composite particles can be 1%, 1.5%, 2%, 2.4%, 3%, 3.6%, 4%, or a range consisting of any two of the above values. The oxygen in the silicon-carbon composite particles comes from the carbon skeleton material and the oxidation during the preparation of the silicon-carbon composite particles. A 99 / D A 50-D A 90 / D AOn the basis of 50≤0.57, by regulating the mass percentage of oxygen element in the silicon-carbon composite particles within the above range, the irreversible reaction of silicon to generate lithium silicate salt can be reduced, and the consumption of electrolyte and lithium ions by side reactions during the first cycle can be reduced, which is beneficial to improving the first cycle efficiency and capacity of the secondary battery. At the same time, the difference in silicon content between the silicon-carbon composite particles is small. During the charge and discharge cycle of the secondary battery, the difference in volume expansion of different silicon-carbon composite particles and different regions of the same negative electrode plate can be reduced, the internal stress generated by repeated expansion and contraction of the negative electrode plate is reduced, the risk of peeling of the negative electrode material layer from the negative electrode current collector is reduced, and the capacity decay of the secondary battery is reduced, which is beneficial to improving the cycle performance of the secondary battery.

[0045] In some embodiments of the present application, the surface of the negative electrode sheet includes an area of ​​4 cm 2 In the second counting area, the total area of ​​silicon-carbon composite particles is A1 cm 2 , 0.05≤A1 / 4≤0.95, the remaining area of ​​the second counting region is the remaining components in the negative electrode material layer, including but not limited to negative electrode active materials (such as graphite) other than silicon-carbon composite particles, negative electrode binders, negative electrode conductive agents, etc. For example, the value of A1 / 4 can be 0.05, 0.12, 0.20, 0.33, 0.40, 0.50, 0.60, 0.74, 0.80, 0.95 or a range consisting of any two of the above values. When 0.23≤D A 99 / D A 50-D A 90 / D A On the basis of 50≤0.57, by regulating the value of A1 / 4 within the above range, the silicon-carbon composite particles are distributed more uniformly on the surface of the negative electrode plate, which can reduce the volume expansion difference between different areas of the same negative electrode plate, reduce the internal stress generated by repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, and reduce the capacity decay of the secondary battery, thereby further improving the cycle performance of the secondary battery. In some embodiments, different 4cm on the surface of the negative electrode plate 2 In the second counting area, the difference between A1 is 0.01 to 0.1.

[0046] In some embodiments of the present application, in the first counting region, the total area of ​​the silicon-carbon composite particles is A2 μm 2, 0.05≤A2 / 1000≤0.95, the remaining area of ​​the first counting region is the remaining components in the negative electrode material layer, including but not limited to the negative electrode active material (such as graphite) other than the silicon-carbon composite particles, the negative electrode binder, the negative electrode conductive agent, etc. For example, the value of A2 / 1000 can be 0.05, 0.14, 0.20, 0.35, 0.40, 0.52, 0.60, 0.76, 0.80, 0.95 or a range consisting of any two of the above values. When 0.23≤D A 99 / D A 50-D A 90 / D A On the basis of 50≤0.57, by regulating the value of A2 / 1000 within the above range, the silicon-carbon composite particles are distributed more and more evenly in the thickness direction of the negative electrode plate, which can reduce the volume expansion difference between different regions of the same negative electrode plate, reduce the internal stress generated by repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, and reduce the capacity decay of the secondary battery, thereby further improving the cycle performance of the secondary battery. In some embodiments, in the cross section of the negative electrode plate along the thickness direction, different 1000μm 2 In the first counting area, the difference between A2 is 0.01 to 0.1.

[0047] In some embodiments of the present application, the surface of the negative electrode sheet includes an area of ​​4 cm 2 In the second counting area, the total area of ​​silicon-carbon composite particles is A1 cm 2 , 0.05≤A1 / 4≤0.95. In the first counting area, the total area of ​​the silicon-carbon composite particles is A2μm 2 , 0.05≤A2 / 1000≤0.95. By regulating the values ​​of A1 / 4 and A2 / 1000 within the above ranges, the distribution of silicon-carbon composite particles on the surface and thickness directions of the negative electrode sheet is similar, and the silicon-carbon composite particles are distributed more abundantly and more evenly on the surface and thickness directions of the negative electrode sheet. This can further reduce the volume expansion differences between different regions of the same negative electrode sheet, reduce the internal stress generated by the repeated expansion and contraction of the negative electrode sheet, reduce the risk of the negative electrode material layer peeling from the negative electrode current collector, and reduce the capacity decay of the secondary battery, thereby further improving the cycle performance of the secondary battery.

[0048] In some embodiments of the present application, the negative electrode active material further comprises at least one of graphite or hard carbon. The mass percentage of the aforementioned substances can range from 0.5% to 93.5% based on the mass of the negative electrode material layer. The inclusion of the aforementioned substances in the negative electrode active material can reduce the mass percentage of silicon-carbon composite particles in the negative electrode active material, reducing the volume expansion of the negative electrode active material, thereby improving the cycle performance of the secondary battery.

[0049] In some embodiments of the present application, the mass percentage of the silicon-carbon composite particles is 5% to 95% based on the mass of the negative electrode material layer. For example, the mass percentage of the silicon-carbon composite particles can be 5%, 12%, 20%, 34%, 40%, 50%, 60%, 75%, 80%, 95% or a range consisting of any two of the above values. By regulating the mass percentage of the silicon-carbon composite particles within the above range, it is beneficial to reduce the volume expansion of the negative electrode active material, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, reduce the capacity decay of the secondary battery, and thus help improve the cycle performance of the secondary battery. At the same time, the energy density of the secondary battery can also be improved.

[0050] The negative electrode material layer in the present application may also include a negative electrode binder and a negative electrode conductor. Based on the mass of the negative electrode material layer, the mass percentage of the negative electrode binder may be 1% to 30%, and the mass percentage of the negative electrode conductor may be 0.5% to 30%. The present application has no particular restrictions on the types of negative electrode binders and negative electrode conductors, as long as the purpose of the present application can be achieved. For example, the negative electrode binder may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon; the negative electrode conductor may include but is not limited to at least one of carbon-based materials, metal-based materials or conductive polymers; Exemplarily, the carbon-based material may include at least one of natural graphite, artificial graphite, conductive carbon black (Super P) or carbon fiber, the metal-based material may include but is not limited to at least one of metal powder, metal fiber, copper, nickel, aluminum or silver; the conductive polymer may include but is not limited to polyphenylene derivatives.

[0051] In some embodiments of the present application, silicon-carbon composite particles include a carbon skeleton containing silicon. Using silicon-carbon composite particles with such a structure can increase the energy density of a secondary battery and also help reduce volume expansion of the silicon-carbon composite particles, thereby improving the cycling performance of the secondary battery. In the present application, the silicon can be in the form of amorphous silicon.

[0052] In some embodiments of the present application, the silicon-carbon composite particles include a protective layer located on at least a portion of the surface of the carbon skeleton, the protective layer including at least one of amorphous carbon, metal oxide or non-metal oxide, the metal oxide including at least one of aluminum oxide, copper oxide or titanium oxide, and the non-metal oxide including at least one of silicon dioxide or silicon monoxide. The protective layer located on at least a portion of the surface of the carbon skeleton in the silicon-carbon composite particles has a high structural strength, which can not only reduce the volume expansion of the silicon-carbon composite particles, but also reduce the erosion of the electrolyte on the silicon-carbon composite particles, thereby helping to improve the cycle performance of the secondary battery. In the present application, the protective layer of the silicon-carbon composite particles can be located on the entire surface of the carbon skeleton, or on a portion of the surface of the carbon skeleton. Since the protective layer in the silicon-carbon composite particles is only at the level of a few nanometers, the type of material of the protective layer will not affect the average grayscale value of the silicon-carbon composite particles.

[0053] The second aspect of the present application provides a method for preparing the secondary battery of the first aspect of the present application, wherein the method for preparing the silicon-carbon composite particles comprises the following steps:

[0054] S1: providing a carbon skeleton material, crushing and classifying the carbon skeleton material, and then performing a first heat treatment on the carbon skeleton material, wherein the temperature of the first heat treatment is 700° C. to 900° C., and the time of the first heat treatment is 4 hours to 6 hours;

[0055] S2: Depositing the carbon skeleton material once, heating to 430°C to 550°C, introducing a first mixed gas containing 5% to 50% silane by volume under a negative pressure of -60kPa to -101kPa, and reacting for 2h to 6h. Repeating the deposition once 2 to 5 times;

[0056] S3: transferring the carbon skeleton material after the primary deposition to a fluidized bed for heating, introducing a second mixed gas containing 5% to 50% by volume of silane, and performing secondary deposition to obtain a carbon skeleton material including silicon; the secondary deposition temperature is 430° C. to 550° C., and the reaction time of the secondary deposition is 1 hour to 6 hours;

[0057] S4: performing a second heat treatment on the carbon skeleton material including silicon at a temperature of 620° C. to 700° C., wherein the second heat treatment lasts for 0.5 h to 1 h;

[0058] S5: Then, a protective layer is prepared on the surface of the carbon skeleton material including silicon to obtain silicon-carbon composite particles.

[0059] For example, the temperature of the first heat treatment can be 700°C, 730°C, 760°C, 800°C, 840°C, 880°C, 900°C, or a range consisting of any two of the above values. The time of the first heat treatment can be 4h, 4.5h, 5h, 5.3h, 5.7h, 6h, or a range consisting of any two of the above values. The temperature of the first deposition can be 430°C, 450°C, 480°C, 510°C, 530°C, 550°C, or a range consisting of any two of the above values. The negative pressure of the first deposition can be -60kPa, -65kPa, -70kPa, -76kPa, -80kPa, -84kPa, -90kPa, -93kPa, -97kPa, -101kPa, or a range consisting of any two of the above values. The volume fraction of silane in the first mixed gas can be 5%, 10%, 16%, 20%, 25%, 30%, 34%, 40%, 45%, 50%, or a range consisting of any two of the above values. The reaction time of a single deposition can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or a range consisting of any two of the above values. The number of depositions can be 2 times, 3 times, 4 times, or 5 times. The volume fraction of silane in the second mixed gas can be 5%, 10%, 16%, 20%, 25%, 30%, 34%, 40%, 45%, 50%, or a range consisting of any two of the above values. The temperature of the secondary deposition can be 430°C, 460°C, 490°C, 520°C, 550°C, or a range consisting of any two of the above values. The reaction time of the secondary deposition can be 1h, 1.6h, 2h, 2.4h, 3h, 3.5h, 4h, 4.6h, 5h, 5.3h, 6h or a range consisting of any two of the above values. The present application has no particular limitation on the pressure of the secondary deposition, as long as the purpose of the present application can be achieved. The pressure of the secondary deposition can be negative pressure or positive pressure. The pressure of the secondary deposition can be -60kPa to 120kPa. For example, the pressure of the secondary deposition can be -60kPa, -40kPa, -20kPa, 0kPa, 20kPa, 40kPa, 60kPa, 80kPa, 100kPa or 120kPa or a range consisting of any two of the above values. The temperature of the second heat treatment can be 620°C, 640°C, 660°C, 680°C, 700°C or a range consisting of any two of the above values. The time of the second heat treatment can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h or a range consisting of any two of the above values.

[0060] The present application can regulate the particle size and particle size distribution of the carbon skeleton material by crushing and grading the carbon skeleton material. By performing a first heat treatment on the carbon skeleton material, the functional groups and defects on the surface of the carbon skeleton material can be reduced, reducing the generation of SiC during the subsequent primary and secondary deposition processes. By performing a single deposition on the carbon skeleton material and regulating the pressure of the primary deposition to be negative, a small amount of silicon can be deposited in advance inside the pores of the carbon skeleton material, thereby providing active induction sites for the secondary deposition of silicon inside the pores of the carbon skeleton material, improving the uniformity of silane deposition, and reducing the deposition of silane outside the pores of the carbon skeleton material. By performing a secondary deposition on the carbon skeleton material, a carbon skeleton material including silicon in the pores of the carbon skeleton material can be obtained. By performing a second heat treatment on the carbon skeleton material including silicon, silicon can be dehydrogenated, thereby reducing the generation of SiC during the preparation of the protective layer. By preparing a protective layer on the surface of the carbon skeleton material including silicon, the protective layer has a high structural strength and can be applied to secondary batteries to reduce the volume expansion of silicon-carbon composite particles and reduce the erosion of the electrolyte on the silicon-carbon composite particles, thereby improving the cycle performance of the secondary battery. The silicon-carbon composite particles obtained by the above preparation method have high silicon deposition uniformity and a narrow distribution of particle silicon content. The difference in particle silicon content between the silicon-carbon composite particles is small. When applied to secondary batteries, it can reduce the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate, reduce the internal stress generated by repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, reduce the capacity decay of the secondary battery, and thus improve the cycle performance of the secondary battery. In the present application, the silane may include but is not limited to at least one of monosilane, disilane or triethoxysilane.

[0061] In some embodiments of the present application, the carbon skeleton material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon. The present application has no particular restrictions on the pore structure of the carbon skeleton material, as long as the purpose of the present application can be achieved. For example, the pore volume of the carbon skeleton material is 0.5 cm 3 / g to 1.5cm 3 / g, with an average pore size of 2.5nm to 4nm. The selection of the above-mentioned carbon skeleton material can achieve a better fluidized state in the fluidized bed, making the solid-gas contact more uniform, which is conducive to the preparation of silicon-carbon composite particles with high silicon deposition uniformity and narrow particle silicon content distribution. The difference in particle silicon content between the silicon-carbon composite particles is small. When applied to secondary batteries, it can reduce the volume expansion difference between different silicon-carbon composite particles and different areas of the same negative electrode plate, reduce the internal stress generated by the repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, reduce the capacity decay of the secondary battery, and thus help improve the cycle performance of the secondary battery.

[0062] In some embodiments of the present application, the first mixed gas and the second mixed gas each independently further include at least one of nitrogen, hydrogen or argon. In some embodiments of the present application, the gas flow rate of the first mixed gas is 0.1L / min to 0.5L / min, and the gas flow rate of the second mixed gas is 10L / min to 50L / min. The first mixed gas and the second mixed gas also include the above-mentioned gas, which can dilute the silane concentration, regulate the adsorption rate and cracking deposition rate of silane, and ensure that the gas flow in the fluidized bed meets the requirements of the carbon skeleton material or the carbon skeleton material deposited once to reach a fluidized state, which is conducive to the preparation of silicon-carbon composite particles with high silicon deposition uniformity and narrow particle silicon content distribution. The difference in particle silicon content between silicon-carbon composite particles is small. When applied to secondary batteries, it can reduce the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode, reduce the internal stress generated by repeated expansion and contraction of the negative electrode, reduce the risk of the negative electrode material layer peeling from the negative electrode current collector, reduce the capacity decay of the secondary battery, and thus help improve the cycle performance of the secondary battery.

[0063] In some embodiments of the present application, the source material of the protective layer includes a first source material for preparing amorphous carbon, and the first source material includes at least one of acetylene, methane, propylene, ethylene or propane. In some embodiments of the present application, the deposition temperature for preparing the amorphous carbon protective layer is 550°C to 850°C. By selecting the above-mentioned type of first source material, an amorphous carbon protective layer can be formed on at least a portion of the surface of the carbon skeleton material including silicon. The protective layer has a high structural strength and can be applied to secondary batteries to reduce the volume expansion of silicon-carbon composite particles. At the same time, it can also reduce the erosion of the electrolyte on the silicon-carbon composite particles, which is beneficial to improving the cycle performance of the secondary battery.

[0064] In some embodiments of the present application, the source material of the protective layer includes a second source material for preparing a metal oxide, and the second source material includes at least one of titanium isopropoxide, trimethylaluminum or copper acetate. In some embodiments of the present application, the second source material is used to prepare a metal oxide protective layer by CVD method combined with high-temperature oxidation, and the temperature of high-temperature oxidation is 150°C to 250°C, and the time is 2h to 6h. The above-mentioned type of second source material is selected to form a metal oxide protective layer on at least a portion of the surface of the carbon skeleton material including silicon. The protective layer has a high structural strength and can be applied to secondary batteries to reduce the volume expansion of silicon-carbon composite particles. At the same time, it can also reduce the erosion of the silicon-carbon composite particles by the electrolyte, thereby helping to improve the cycle performance of the secondary battery.

[0065] In some embodiments of the present application, the source material of the protective layer includes a third source material for preparing a non-metallic oxide, and the third source material includes at least one of ethyl orthosilicate, triethoxysilane or monosilane. In some embodiments of the present application, the non-metallic oxide protective layer is prepared by a CVD method combined with high-temperature oxidation using a third source material, and the temperature of the high-temperature oxidation is 150°C to 250°C, and the time is 2h to 6h. In other embodiments of the present application, the silicon dioxide protective layer can be formed by depositing silane on the surface of a carbon skeleton material including silicon to form a silicon element, and then oxidizing it at room temperature to form silicon dioxide. The above-mentioned type of third source material is selected to form a non-metallic oxide protective layer on at least a portion of the surface of the carbon skeleton material including silicon. The protective layer has a high structural strength and can be applied to secondary batteries to reduce the volume expansion of silicon-carbon composite particles. At the same time, it can also reduce the erosion of the electrolyte on the silicon-carbon composite particles, thereby helping to improve the cycle performance of the secondary battery.

[0066] In some embodiments of the present application, the D of the carbon skeleton material after crushing and classification is V 10 is 1μm to 5.9μm, D V 50 is 5.65μm to 8.7μm, D V 99 is 15.2μm to 78.3μm.

[0067] The present application does not particularly limit the method of crushing and classifying, as long as the purpose of the present application can be achieved. For example, the carbon skeleton material can be crushed by ball milling, and the crushed carbon skeleton material can be classified by a jet classifier or a cyclone classifier. The present application does not particularly limit the process parameters of crushing and classifying, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0068] The present application does not particularly limit the heating rates of the first heat treatment, the first deposition, the second deposition, and the second heat treatment in the process of preparing silicon-carbon composite particles, as long as the purpose of the present application can be achieved. For example, the heating rate of the first heat treatment can be 5°C / min to 10°C / min, the heating rate of the first deposition can be 5°C / min to 10°C / min, the heating rate of the second deposition can be 5°C / min to 10°C / min, and the heating rate of the second heat treatment can be 5°C / min to 10°C / min.

[0069] Generally, the pressure of the first deposition process and the temperature of the second deposition process in the preparation of silicon-carbon composite particles can be controlled. A 50. D A 90.D A 99.D A 99 / D A 50-D A 90 / DA 50. D B 5.

[0070] Generally, D can be controlled by adjusting the time of crushing treatment during the preparation of silicon-carbon composite particles. S 50. D S 90.D S 99. For example, when other conditions remain unchanged, the crushing time is prolonged, D S 50 is reduced; the crushing time is shortened, D S 50 increases. When other conditions remain unchanged, the crushing time is prolonged, D S 90 is reduced; the crushing time is shortened, D S 90 increases. When other conditions remain unchanged, the crushing time is prolonged, D S 99 is reduced; the crushing time is shortened, D S 99 increases. By regulating D S 50. D S 90.D S The value of 99 can adjust D S 99 / D S 50-D S 90 / D S A value of 50.

[0071] The present application does not impose any particular restrictions on the method for regulating the specific surface area of ​​the silicon-carbon composite particles, as long as the purpose of the present application can be achieved. For example, silicon-carbon composite particles with different specific surface areas can be obtained by regulating the temperature of the secondary deposition process and the reaction time for preparing the protective layer. For example, when other conditions remain unchanged, the temperature of the secondary deposition process increases, and the specific surface area of ​​the silicon-carbon composite particles decreases; the temperature of the secondary deposition process decreases, and the specific surface area of ​​the silicon-carbon composite particles increases. When other conditions remain unchanged, the reaction time for preparing the protective layer increases, and the specific surface area of ​​the silicon-carbon composite particles decreases; the reaction time for preparing the protective layer decreases, and the specific surface area of ​​the silicon-carbon composite particles increases.

[0072] In this application, a negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. It should be noted that the "surface" here can refer to the entire area of ​​the negative electrode current collector or a portion of the negative electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0073] The present application has no special restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector (such as carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). The present application has no special restrictions on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 6μm to 12μm, and the thickness of the negative electrode material layer is 30μm to 150μm. The present application has no special restrictions on the thickness of the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode sheet is 50μm to 350μm.

[0074] In this application, a positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. It should be noted that the "surface" here can refer to the entire area of ​​the positive electrode current collector or a portion of the positive electrode current collector. This application does not specifically limit this, as long as the purpose of this application can be achieved.

[0075] This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it may include but is not limited to aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). This application has no special restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 6μm to 12μm, and the thickness of the positive electrode material layer is 30μm to 120μm. This application has no special restrictions on the thickness of the positive electrode sheet, as long as the purpose of this application can be achieved, for example, the thickness of the positive electrode sheet is 50μm to 250μm.

[0076] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance that can reversibly embed and extract active ions such as lithium ions. The positive electrode material layer can be one or more layers, and each layer in the multilayer positive electrode material layer can contain the same or different positive electrode active materials. The present application has no particular restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, lithium titanate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate or lithium manganese silicate. The chemical formula of the above-mentioned lithium-rich manganese-based material is γLi2MnO3·(1-γ)LiGO2, 0<γ<1, G is a transition metal nickel, cobalt or iron, etc. In the present application, a substance having a different composition than that of the positive electrode active material may be attached to the surface of the positive electrode active material. For example, the surface-attached substance may include, but is not limited to, at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, lithium carbonate, calcium carbonate, magnesium carbonate, or carbon. By attaching the above-mentioned substance to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, thereby increasing the service life of the secondary battery.

[0077] The positive electrode material layer may also include a positive electrode conductive agent and a positive electrode binder. This application does not specifically limit the types of the positive electrode conductive agent and the positive electrode binder, as long as they can achieve the objectives of this application. For example, the positive electrode binder may include, but is not limited to, at least one of the aforementioned negative electrode binders; the positive electrode conductive agent may include, but is not limited to, at least one of the aforementioned negative electrode conductive agents. This application does not specifically limit the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer, and can be selected based on actual needs, as long as the objectives of this application can be achieved.

[0078] The secondary battery of the present application also includes an electrolyte. In some embodiments of the present application, the electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include various lithium salts commonly used in the art, such as lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2)), lithium bis(oxalatoborate) (LiB(C2O4)2) or lithium difluorooxalatoborate (LiBF2(C2O4)). The present application has no particular restrictions on the concentration of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC). The above-mentioned cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include but is not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone or caprolactone. The ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0079] The secondary battery of the present application also includes a separator to separate the positive and negative electrode plates, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and not affect the electrochemical charge and discharge process. The present application does not particularly limit the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (such as polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator can include at least one of woven membranes, non-woven membranes, microporous membranes, composite membranes, rolled membranes, or spun membranes. For example, the separator can include a substrate layer and a surface treatment layer. The substrate layer can be a non-woven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. For example, the inorganic layer includes inorganic particles and a binder. This application does not particularly limit the inorganic particles. For example, it may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the binder. For example, it may be at least one of the above-mentioned negative electrode binders. The polymer layer includes a polymer. This application does not particularly limit the polymer. For example, the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene). In this application, the thickness of the separator is not particularly limited, as long as it can achieve the purpose of this application. For example, the thickness of the separator can be 5μm to 500μm.

[0080] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of secondary batteries known in the art. This application does not particularly limit these other components. This application does not particularly limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0081] The present application does not particularly limit the type of secondary battery, which may include any device that undergoes an electrochemical reaction. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), sodium ion secondary batteries (sodium ion batteries), lithium polymer secondary batteries, and lithium ion polymer secondary batteries.

[0082] The preparation process of a secondary battery is well known to those skilled in the art and is not particularly limited in this application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding, folding, and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the packaging bag to prevent pressure rise and overcharging and discharging inside the secondary battery.

[0083] The third aspect of the present application provides an electronic device comprising the secondary battery provided in the first aspect of the present application or a secondary battery prepared according to the preparation method provided in the second aspect of the present application. The secondary battery provided in the present application has good cycle performance, thereby providing the electronic device provided in the present application with a long service life and good performance.

[0084] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0085] Example

[0086] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0087] Test methods and equipment:

[0088] D A99.D A 50. D A 90.D B 5 tests

[0089] The negative electrode sheet to be tested was ion polished along the thickness direction using a cross-section ion polisher (IB-19520CCP, provided by JEOL Ltd. (JEOL)). The ion polishing voltage was 7.5 kV and the time was 1.5 h to obtain the cross section of the negative electrode sheet in the thickness direction. A scanning electron microscope (Sigma-02-33, provided by ZEISS, Germany) was used to test the cross section of the negative electrode sheet. The backscatter mode was used, the test voltage was 10 kV, the magnification was 1000×, and the working distance was 9.9 mm. The contrast was adjusted in the backscatter mode so that the graphite particles were dark black with a grayscale value of <70, and the silicon-carbon composite particles were off-white with a grayscale value of >90. The two particles had a clear dividing line due to the grayscale difference. A cross-sectional area of ​​1000 μm was selected in the cross section of the negative electrode sheet along the thickness direction. 2 The first counting area of ​​the negative electrode is randomly switched to different cross-sectional areas of 1000 μm. 2 EDS analysis was performed on the first counting area of ​​the image, and 10 backscattered images were saved. In this mode, all graphite particles had a grayscale value <70, while the grayscale value of the silicon-carbon composite particles was >90. The grayscale value was positively correlated with the silicon content of the silicon-carbon composite particles. The greater the silicon content, the brighter the silicon-carbon composite particles and the larger the grayscale value. Therefore, a linear relationship between the grayscale value of the silicon-carbon composite particles and the silicon content was obtained. The 10 saved backscattered images were processed using HALCON image processing software. The pixel size was calibrated using the scale of the backscattered photo. Since the grayscale value of graphite particles was <70 and the grayscale value of silicon-carbon composite particles was >90, the edge detection function was used to perform edge analysis and image segmentation on the silicon-carbon composite particles and graphite particles in the backscattered photo. The image of the silicon-carbon composite particles was retained, and the grayscale distribution data and grayscale distribution histogram were output. The total number of pixels contained in the selected area multiplied by the calibrated single pixel area was the total area A of all selected silicon-carbon composite particles. The area of ​​a single silicon-carbon composite particle could also be obtained, which was recorded as S1, S2, S3, ..., S n , then A=S1+S2+S3……+S nSince the linear relationship between the grayscale value of silicon-carbon composite particles and the silicon content of the particles has been obtained during EDS analysis, the grayscale value is linearly related to the silicon content of the particles of the silicon-carbon composite particles, and the grayscale distribution histogram can be converted into a particle silicon content area distribution diagram. With the particle silicon content as the horizontal axis and the particle area percentage as the vertical axis, the particle silicon content area distribution diagram is obtained. In the particle silicon content area distribution diagram, the particle silicon content corresponding to the cumulative particle area percentage of 50% is D A 50, the cumulative particle area accounts for 90% and the corresponding particle silicon content is D A 90, the cumulative particle area accounts for 99% and the corresponding particle silicon content is D A 99, the cumulative particle area corresponding to the particle silicon content of 5% is D B 5.

[0090] D S 99.D S 90.D S 50 tests

[0091] Using the same D A 99.D A 50. D A 90.D B 5. Using the same test method, the cross-sectional area of ​​the negative electrode sheet along the thickness direction is 1000 μm 2 In the first counting area of ​​the silicon-carbon composite particles, the particle area and particle number are plotted with the particle area as the horizontal axis and the particle number percentage as the vertical axis to obtain a particle area number distribution diagram. In the particle area number distribution diagram, the particle area corresponding to a cumulative particle number percentage of 50% is D S 50μm 2 The particle area corresponding to the cumulative particle number accounting for 90% is D S 90μm 2 The particle area corresponding to the cumulative particle number accounting for 99% is D S 99μm 2 .

[0092] Specific surface area test

[0093] The specific surface area of ​​the silicon-carbon composite particles in each example and comparative example was measured by nitrogen adsorption using a surface area analyzer (TriStar II 3020M, provided by Micromeritics, USA). The specific testing was conducted in accordance with the national standard GB / T 19587-2017, "Determination of the Specific Surface Area of ​​Solids by the BET Method for Gas Adsorption."

[0094] Test of the mass percentage of silicon in silicon-carbon composite particles

[0095] The negative electrode sheet to be tested was ion polished in the thickness direction using a cross-section ion polisher (IB-19520CCP, provided by JEOL Ltd. (JEOL)). The ion polishing voltage was 7.5 kV and the time was 1.5 h to obtain the cross section of the negative electrode sheet in the thickness direction. The mass percentage of silicon in the silicon-carbon composite particles was tested by EDS point scanning. Silicon-carbon composite particles were selected from the cross section of the negative electrode sheet in the thickness direction, and 5 points were randomly selected from the center of a single silicon-carbon composite particle for EDS point scanning to obtain the mass percentage of silicon. The arithmetic mean of the mass percentage of silicon at the above 5 points was calculated to obtain the mass percentage X of silicon in a single silicon-carbon composite particle. 20 silicon-carbon composite particles were randomly selected from the cross section of the negative electrode sheet in the thickness direction, and the X of the 20 silicon-carbon composite particles was obtained by testing. The arithmetic mean of X of the above 20 silicon-carbon composite particles was calculated to obtain the mass percentage of silicon in the silicon-carbon composite particles. The center of a single silicon-carbon composite particle refers to a region greater than 0.5 μm away from the edge of the silicon-carbon composite particle.

[0096] Test of the mass percentage of oxygen in silicon-carbon composite particles

[0097] The negative electrode sheet to be tested was ion polished along the thickness direction using a cross-section ion polisher (IB-19520CCP, provided by JEOL Ltd. (JEOL)). The ion polishing voltage was 7.5 kV and the time was 1.5 h to obtain the cross section of the negative electrode sheet in the thickness direction. The mass percentage of the oxygen element in the silicon-carbon composite particles was tested by EDS point scanning. Silicon-carbon composite particles were selected from the cross section of the negative electrode sheet in the thickness direction, and 5 points were randomly selected from the center of a single silicon-carbon composite particle for EDS point scanning to obtain the mass percentage of the oxygen element. The arithmetic mean of the mass percentage of the oxygen element at the above 5 points was calculated to obtain the mass percentage Y of the oxygen element in a single silicon-carbon composite particle. 20 silicon-carbon composite particles in the cross section of the negative electrode sheet in the thickness direction were randomly selected and tested to obtain the Y of the 20 silicon-carbon composite particles. The arithmetic mean of the Y of the above 20 silicon-carbon composite particles was calculated to obtain the mass percentage of the oxygen element in the silicon-carbon composite particles. The center of a single silicon-carbon composite particle refers to a region greater than 0.5 μm away from the edge of the silicon-carbon composite particle.

[0098] Cycle performance test

[0099] (1) Test of the number of cycles at 25°C

[0100] Place the lithium-ion battery in a 25°C environment, charge it to 4.4V at a constant current of 3.4C, then charge it to 0.025C at a constant voltage of 4.4V. After standing for 5 minutes, discharge it to 3.0V at a constant current of 0.5C. This is one charge and discharge cycle, which is the first cycle. The discharge capacity of the first cycle is recorded as the initial discharge capacity. The lithium-ion battery is charged and discharged according to the above method, and the discharge capacity of each cycle is recorded. The discharge capacity of each cycle is ratioed to the initial discharge capacity to obtain a 25°C cycle capacity decay curve. In the 25°C cycle capacity decay curve, when the ratio of the discharge capacity of the lithium-ion battery to the initial discharge capacity is 90%, the number of charge and discharge cycles at this time is recorded and recorded as the 25°C cycle number.

[0101] (2) Test of the number of cycles at 45°C

[0102] Place the lithium-ion battery in a 45°C environment, charge it to 4.4V at a constant current of 3.4C, then charge it to 0.025C at a constant voltage of 4.4V. After standing for 5 minutes, discharge it to 3.0V at a constant current of 0.5C. This is one charge and discharge cycle, which is the first cycle. The discharge capacity of the first cycle is recorded as the initial discharge capacity. The lithium-ion battery is charged and discharged according to the above method, and the discharge capacity of each cycle is recorded. The discharge capacity of each cycle is ratioed to the initial discharge capacity to obtain a 45°C cycle capacity decay curve. In the 45°C cycle capacity decay curve, when the ratio of the discharge capacity of the lithium-ion battery to the initial discharge capacity is 90%, the number of charge and discharge cycles at this time is recorded and recorded as the number of 45°C cycles.

[0103] Example 1-1

[0104] <Preparation of Silicon-Carbon Composite Particles>

[0105] S1: 10 kg of commercial porous carbon (YP-50F, provided by Kuraray, Japan) was ball-milled and then the crushed carbon skeleton material was classified by a jet classifier. The D V 10 is 5.3 μm, D V 50 is 8.7μm, D V 99 is 17.7μm. The carbon skeleton material is then subjected to the first heat treatment. The process of the first heat treatment is as follows: the crushed and graded porous carbon is added to a graphite crucible, placed in a box furnace, the furnace door is closed, and nitrogen is introduced into the box at a rate of 5L / min for purging. The purging time is 30min, and then the nitrogen flow rate is adjusted to 1L / min. The material is heated to 800℃ at a heating rate of 5℃ / min, kept at 800℃ for 6h, and then the heating is turned off and purged with nitrogen at 5L / min to cool to room temperature. The graphite crucible is taken out at room temperature to collect the porous carbon powder.

[0106] S2: Deposit the carbon skeleton material once. The deposition process is as follows: take 1kg of porous carbon after heat treatment, put it into the CVD furnace, evacuate to a negative pressure of -101kPa, then stop evacuating, pass nitrogen to a pressure of 2kPa and then turn off the nitrogen, repeat evacuating and passing nitrogen, and detect the oxygen content inside the cavity until the oxygen content drops below 10ppm, then stop the above evacuating and passing nitrogen. Then open the tail gas valve, turn the cavity to rotate 1 turn / min, pass nitrogen at a rate of 2L / min, heat at a heating rate of 5℃ / min, heat to 460℃, and keep warm for 1h. Close the nitrogen inlet, close the tail gas valve, close the cavity rotation, evacuate to -101kPa and then turn off the vacuum. Open the cavity and rotate it 1 rpm, introduce the first mixed gas of monosilane / nitrogen with a volume fraction of 20% monosilane to 2 kPa at a rate of 0.5 L / min, close the first mixed gas inlet, keep warm for 30 minutes, then open the tail gas valve, and purge with nitrogen at a rate of 2 L / min for 30 minutes; repeat the above vacuuming, passing the first mixed gas, and nitrogen purging, and repeat the above deposition process twice.

[0107] S3: 1 kg of porous carbon deposited once is fed into the fluidized bed through a high-pressure transmission pipeline. After standing for about 30 minutes, the fluidized bed air inlet valve and tail gas valve are closed to evacuate the chamber to -101 kPa. Then, the vacuum is closed and nitrogen is introduced at a rate of 30 L / min to 2 kPa. The vacuum and nitrogen are repeated, and the oxygen content inside the chamber is detected until the oxygen content drops below 10 ppm. The above vacuum and nitrogen process is stopped. The tail gas valve is then opened, and the fluidized bed stirring paddle is started at a speed of 100 rpm. Nitrogen is introduced at a rate of 15 L / min. The temperature is raised to 500 ° C at a heating rate of 5 ° C / min and kept warm for 1 hour. At 500°C, the valve of the fluidized bed air inlet pipeline was switched to introduce a second monosilane / nitrogen mixture into the fluidized bed. The volume fraction of monosilane was 10%, the gas flow rate was 20 L / min, the stirring paddle speed was adjusted to 120 rpm, and the reaction time was 60 min; then the volume fraction of monosilane was adjusted to 20%, the gas flow rate was 25 L / min, the stirring paddle speed was 150 rpm, and the reaction time was 120 min; finally, the volume fraction of monosilane was adjusted to 5%, the gas flow rate was 30 L / min, the stirring paddle speed was 200 rpm, and the reaction time was 60 min to obtain a carbon skeleton material including silicon.

[0108] S4: The carbon skeleton material including silicon is subjected to a second heat treatment. The process of the second heat treatment is as follows: after turning off the monosilane, nitrogen is passed at a flow rate of 10 L / min, the stirring blade speed is adjusted to 100 rpm, the temperature is increased to 650°C at a rate of 5°C / min, and then kept warm for 30 minutes.

[0109] S5: After cooling to 600°C, the stirring blade speed is adjusted to 200 rpm, and an acetylene / nitrogen mixture is introduced into the fluidized bed, with an acetylene volume fraction of 50% and a mixed gas flow rate of 20 L / min. The reaction time is 3 hours. After the reaction is completed, nitrogen is passed at a flow rate of 10 L / min, and the stirring blade speed is adjusted to 100 rpm for cooling. The material is discharged when it reaches room temperature to obtain silicon-carbon composite particles having amorphous carbon as the material of the protective layer, and the amorphous carbon is located on at least a portion of the surface of the carbon skeleton material.

[0110] <Preparation of negative electrode sheet>

[0111] The negative electrode active material graphite, the negative electrode active material silicon carbon composite particles, the negative electrode conductive agent conductive carbon black (Super P), the negative electrode binder polyacrylic acid (PAA, weight average molecular weight Mw = 4.5 × 10 5 ) are mixed in a mass ratio of 70:15:5:10, and then deionized water is added as a solvent, and stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 65wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm, and dried at 85°C to obtain a negative electrode sheet with a single-sided coating of a negative electrode material layer with a thickness of 60μm. Thereafter, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of a negative electrode material layer. Then, it is cold pressed (cold pressing pressure is 10 tons), cut into pieces, and welded to the negative electrode nickel tab to obtain a negative electrode sheet with a specification of 76mm×867mm for standby use. The compaction density of the negative electrode material layer is 1.72g / cm 3 .

[0112] <Preparation of positive electrode sheet>

[0113] The positive electrode active material LiCoO2, the positive electrode conductive agent conductive carbon black (Super P), the positive electrode binder polyvinylidene fluoride (PVDF, Mw = 7 × 10 6 ) are mixed in a mass ratio of 95:2.5:2.5, N-methylpyrrolidone (NMP) is added as a solvent, and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 75wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 85°C to obtain a positive electrode sheet with a single-sided coating of a positive electrode material layer with a thickness of 50μm. Thereafter, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of a positive electrode material layer. After cold pressing (cold pressing pressure of 15 tons), cutting, and welding of positive electrode aluminum ears, a positive electrode sheet with a specification of 74mm×851mm is obtained for standby use. The compaction density of the positive electrode material layer is 4.15g / cm 3 .

[0114] <Preparation of Electrolyte>

[0115] In a dry argon atmosphere, the non-aqueous solvents propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were first mixed at a mass ratio of PC:EC:DEC = 1:1:1 to obtain a base solvent. Then, lithium salts lithium hexafluorophosphate (LiPF6) and fluoroethylene carbonate (FEC) were added to the base solvent and mixed until uniformly dissolved. The electrolyte solution contained 12.5% ​​by mass of the lithium salt LiPF6 and 12.5% ​​by mass of FEC, with the remainder being the base solvent.

[0116] <Preparation of Separator>

[0117] A polyethylene (PE) porous polymer film with a thickness of 8 μm (provided by Celgard) was used as the separator.

[0118] <Preparation of lithium-ion batteries>

[0119] The negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to form a wound electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. The lithium-ion battery is produced through vacuum packaging, static standing, formation (charging at a constant current of 0.2C for 120 seconds, then at a constant current of 1C for 180 seconds, and finally at a constant current of 1.5C to 4.78V), capacity evaluation, degassing, and trimming.

[0120] Example 1-2 to Example 1-10

[0121] Except that the preparation parameters of the silicon-carbon composite particles were adjusted according to Table 1 in <Preparation of Silicon-Carbon Composite Particles>, the rest were the same as Example 1-1.

[0122] Example 2-1 to Example 2-9

[0123] In addition to the process of step S1 in the preparation of silicon-carbon composite particles, the parameters of ball milling and classification are adjusted to adjust the D of the silicon-carbon composite particles. A 99 / D A 50-D A 90 / D A 50. D A 50. D A 90.D A 99.D S 99 / D S 50-D S 90 / D S 50. D S 50. D S 90.D S Except that 99 is as shown in Table 2, the rest is the same as Example 1-1.

[0124] Example 3-1

[0125] Except that step S5 of <Preparation of Silicon-Carbon Composite Particles> adopts the following steps, the rest is the same as Example 1-1.

[0126] <Preparation of Silicon-Carbon Composite Particles>

[0127] S5: After cooling to 200°C, the stirring blade speed is adjusted to 200 rpm, and the trimethylaluminum solution is introduced into the fluidized bed by bubbling a carbon dioxide / nitrogen mixture preheated to 200°C. The carbon dioxide volume fraction is 10%, the mixed gas flow rate is 20 L / min, and the reaction time is 3 hours. After the reaction is completed, nitrogen gas at normal temperature is flowed at a flow rate of 10 L / min, and the stirring blade speed is adjusted to 100 rpm for cooling. The material is discharged to room temperature to obtain silicon-carbon composite particles whose protective layer material is aluminum oxide, and the aluminum oxide is located on at least a portion of the surface of the carbon skeleton material.

[0128] Example 3-2

[0129] Except that step S5 of <Preparation of Silicon-Carbon Composite Particles> adopts the following steps, the rest is the same as Example 1-1.

[0130] <Preparation of Silicon-Carbon Composite Particles>

[0131] S5: After cooling to 600°C, the stirring blade speed is adjusted to 200 rpm, and a silane / nitrogen mixture is introduced into the fluidized bed. The volume fraction of silane is 5%, the mixed gas flow rate is 20 L / min, and the reaction time is 1 hour. After the reaction is completed, nitrogen is passed at a flow rate of 10 L / min, and the stirring blade speed is adjusted to 100 rpm to cool down. The material is discharged when it reaches room temperature. The obtained powder is placed in an air atmosphere for oxidation and heat dissipation to obtain silicon-carbon composite particles whose protective layer material is silicon dioxide, and the silicon dioxide is located on at least part of the surface of the carbon skeleton material.

[0132] Example 4-1

[0133] In addition to the negative electrode active material graphite, negative electrode active material silicon-carbon composite particles, negative electrode conductive agent conductive carbon black (Super P), negative electrode binder polyacrylic acid (PAA, weight average molecular weight Mw = 4.5×10 5 ) were mixed in a mass ratio of 80:5:5:10, and the rest were the same as in Example 1-1.

[0134] Example 4-2

[0135] In addition to the negative electrode active material graphite, negative electrode active material silicon-carbon composite particles, negative electrode conductive agent conductive carbon black (Super P), negative electrode binder polyacrylic acid (PAA, weight average molecular weight Mw = 4.5×10 5 ) were mixed in a mass ratio of 35:50:5:10, and the rest were the same as in Example 1-1.

[0136] Example 4-3

[0137] In addition to the negative electrode active material graphite, negative electrode active material silicon-carbon composite particles, negative electrode conductive agent conductive carbon black (Super P), negative electrode binder polyacrylic acid (PAA, weight average molecular weight Mw = 4.5×10 5 ) are mixed according to the mass ratio of 0.5:95:0.5:4, and the rest are the same as Example 1-1.

[0138] Comparative Example 1-1 to Comparative Example 1-2

[0139] Except that the preparation parameters of the silicon-carbon composite particles were adjusted according to Table 1 in <Preparation of Silicon-Carbon Composite Particles>, the rest were the same as Example 1-1.

[0140] Comparative Examples 1-3

[0141] The preparation of silicon-carbon composite particles is the same as that of Example 1-1, except that step S2 is not included and the porous carbon obtained in step S1 is directly used as the raw material of step S3.

[0142] Comparative Examples 1-4

[0143] Except that step S2 of <Preparation of Silicon-Carbon Composite Particles> adopts the following preparation method, the rest is the same as Example 1-1.

[0144] <Preparation of Silicon-Carbon Composite Particles>

[0145] S2: Deposit the carbon skeleton material once. The deposition process is as follows: take 1kg of heat-treated porous carbon, put it into the CVD furnace, evacuate to a negative pressure of -101kPa, stop evacuating, pass nitrogen to a pressure of 2kPa, then turn off the nitrogen, repeat evacuating and passing nitrogen, and detect the oxygen content inside the cavity until the oxygen content drops below 10ppm, then stop the above evacuating and passing nitrogen. Then open the tail gas valve, open the cavity and rotate 1 revolution / min, pass nitrogen at a rate of 2L / min, heat at a heating rate of 5℃ / min, heat to 460℃, and keep warm for 1h. Keep the exhaust valve open, control the pressure in the furnace to 105kPa, rotate the cavity at 1 revolution / min, and introduce the first silane / nitrogen mixture with a silane volume fraction of 20% at a rate of 0.5L / min. The ventilation time is 120min. Close the first mixed gas intake, keep warm for 30min, and purge with nitrogen at a rate of 2L / min for 30min; repeat the above first mixed gas and nitrogen purge, and repeat the above deposition process twice.

[0146] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0147] Table 1 Note: “\” in Table 1 indicates no corresponding parameter.

[0148] It can be seen from Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-4 that the negative electrode active material of the secondary battery in the embodiments of the present application includes silicon-carbon composite particles and satisfies the following conditions: 0.23≤D A 99 / D A 50-D A 90 / D A 50≤0.57, the secondary battery can have more 25℃ cycle cycles and 45℃ cycle cycles, indicating that the secondary battery has good cycle performance. A 99 / D A 50-D A 90 / D A 50 does not satisfy the above relationship, the secondary battery has fewer cycles at 25°C and 45°C, indicating that the cycle performance of the secondary battery is worse.

[0149] D A 50. D A 90.D A The value of 99 usually affects the cycle performance of the secondary battery. From Examples 1-1 to 1-10, it can be seen that when D A 50. D A 90.D AWhen the value of 99 is within the range of the present application, the secondary battery has a large number of cycles at 25° C. and 45° C., indicating that the secondary battery has good cycle performance.

[0150] D B The value of 5 usually affects the cycle performance of the secondary battery. From Examples 1-1 to 1-10, it can be seen that when D B When the value of 5 is within the range of the present application, the secondary battery has a large number of cycles at 25° C. and 45° C., indicating that the secondary battery has good cycle performance.

[0151] The specific surface area of ​​silicon-carbon composite particles generally affects the cycling performance of secondary batteries. As can be seen from Examples 1-1 to 1-10, when the specific surface area of ​​the silicon-carbon composite particles is within the range of this application, the secondary batteries have a high number of cycles at 25°C and 45°C, indicating good cycling performance.

[0152] The mass percentage of silicon in the silicon-carbon composite particles generally affects the cycling performance of secondary batteries. As can be seen from Examples 1-1 to 1-10, when the mass percentage of silicon in the silicon-carbon composite particles is within the range of this application, the secondary batteries have a high number of cycles at 25°C and 45°C, indicating good cycling performance.

[0153] The mass percentage of oxygen in the silicon-carbon composite particles generally affects the cycling performance of secondary batteries. As can be seen from Examples 1-1 to 1-10, when the mass percentage of oxygen in the silicon-carbon composite particles is within the range of this application, the secondary batteries have a high number of cycles at 25°C and 45°C, indicating good cycling performance.

[0154] As can be seen from FIG. 2 , the distribution of the granular silicon content of the silicon-carbon composite particles of Example 1-1 is relatively narrow, and the granular silicon content is mainly distributed between 18% and 45%. The difference in granular silicon content between the silicon-carbon composite particles is relatively small.

[0155] Table 2

[0156] D S 99 / D S 50-D S 90 / D S The value of 50 usually affects the cycle performance of the secondary battery. From Examples 1-1, 2-1 to 2-9, it can be seen that when D S 99 / D S 50-D S 90 / D SWhen the value of 50 is within the range of the present application, the secondary battery has more 25° C. cycle numbers and 45° C. cycle numbers, indicating that the secondary battery has good cycle performance.

[0157] D S 50. D S 90.D S The value of 99 usually affects the cycle performance of the secondary battery. It can be seen from Examples 1-1, 2-1 to 2-9 that when D S 50. D S 90.D S When the value of 99 is within the range of the present application, the secondary battery has a large number of cycles at 25° C. and 45° C., indicating that the secondary battery has good cycle performance.

[0158] As can be seen from FIG3 , the particle area distribution of the silicon-carbon composite particles of Example 1-1 is relatively narrow, and the particle area is mainly distributed in the range of 10 μm. 2 Up to 250μm 2 The size difference between the silicon-carbon composite particles is small. However, the particle area distribution of the silicon-carbon composite particles of Examples 2-7 is relatively wide, and the particle area is mainly distributed in the range of 8 μm. 2 Up to 5000μm 2 There is a large difference in the sizes of silicon-carbon composite particles.

[0159] Table 3

[0160] The material of the silicon-carbon composite particle protective layer usually affects the cycle performance of the secondary battery. It can be seen from Example 1-1, Example 3-1 to Example 3-2 that when the material of the silicon-carbon composite particle protective layer is within the scope of this application, the secondary battery has more 25°C cycle circles and 45°C cycle circles, indicating that the secondary battery has good cycle performance.

[0161] Table 4

[0162] The mass percentage of silicon-carbon composite particles and the values ​​of A1 / 4 and A2 / 1000 usually affect the cycle performance of secondary batteries. It can be seen from Examples 1-1, 4-1 and 4-3 that when the mass percentage of silicon-carbon composite particles and the values ​​of A1 / 4 and A2 / 1000 are adjusted within the scope of this application, the secondary battery has a larger number of cycles at 25°C and 45°C, indicating that the secondary battery has good cycle performance.

[0163] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0164] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0165] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material comprising silicon-carbon composite particles, The cross section of the negative electrode sheet along the thickness direction includes a cross section with a cross section area of ​​1000 μm 2 In the first counting area, based on the mass of a single silicon-carbon composite particle, the mass percentage of silicon element is the particle silicon content, the ratio of the sum of the cross-sectional areas of the silicon-carbon composite particles having the same particle silicon content to the sum of the cross-sectional areas of all the silicon-carbon composite particles in the first counting area is the particle area ratio, and a particle silicon content area distribution diagram is obtained with the particle silicon content as the horizontal axis and the particle area ratio as the vertical axis; the particle silicon contents are arranged in ascending order, and the particle area ratios corresponding to the particle silicon contents are sequentially added together to obtain the cumulative particle area ratio. In the particle silicon content area distribution diagram, the particle silicon content corresponding to the cumulative particle area ratio of 50% is D A 50, the particle silicon content corresponding to the cumulative particle area accounting for 90% is D A 90, the granular silicon content corresponding to the cumulative granular area accounting for 99% is D A 99, 0.23≤D A 99 / D A 50-D A 90 / D A 50≤0.

57.

2. The secondary battery according to claim 1, wherein 30%≤D A 50≤45%,42%≤D A 90≤65%,55%≤D A 99≤75%。 3. The secondary battery according to claim 1, wherein In the particle silicon content area distribution diagram, the cumulative particle area corresponding to the particle silicon content of 5% is D B 5, 0.93% ≤ D B 5≤7.26%.

4. The secondary battery according to any one of claims 1 to 3, wherein In the first counting area, the cross-sectional area of ​​a single silicon-carbon composite particle is the particle area, and the ratio of the number of silicon-carbon composite particles having the same particle area to the total number of all silicon-carbon composite particles in the first counting area is the particle number percentage. With the particle area as the horizontal axis and the particle number percentage as the vertical axis, a particle area number distribution diagram is obtained; the particle areas are arranged in order from small to large, and the particle number percentages corresponding to the particle areas are sequentially added together to obtain the cumulative particle number percentage. In the particle area number distribution diagram, the particle area corresponding to 50% of the cumulative particle number percentage is D S 50μm 2 The particle area corresponding to the cumulative particle number accounting for 90% is D S 90μm 2 The particle area corresponding to the cumulative particle number accounting for 99% is D S 99μm 2 , 1.66≤D S 99 / D S 50-D S 90 / D S 50≤4.

7.

5. The secondary battery according to claim 4, wherein 25≤D S 50≤60,98≤D S 90≤150,181≤D S 99≤255。 6. The secondary battery according to any one of claims 1 to 3, wherein The specific surface area of ​​the silicon-carbon composite particles is 4.5 m 2 / g to 8.9m 2 / g.

7. The secondary battery according to any one of claims 1 to 3, wherein The silicon-carbon composite particles meet at least one of the following characteristics: (a) the mass percentage of silicon in the silicon-carbon composite particles is 35% to 55%; (b) the mass percentage of oxygen element in the silicon-carbon composite particles is 1% to 4%; (c) On the surface of the negative electrode sheet, there is an area of ​​4 cm 2 The second counting area, within which the total area of ​​the silicon-carbon composite particles is A1cm 2 , 0.05≤A1 / 4≤0.95; (d) In the first counting area, the total area of ​​the silicon-carbon composite particles is A2 μm 2 , 0.05≤A2 / 1000≤0.95; (e) the negative electrode active material further comprises at least one of graphite or hard carbon; (f) Based on the mass of the negative electrode material layer, the mass percentage of the silicon-carbon composite particles is 5% to 95%. 8 . The secondary battery according to claim 1 , wherein the silicon-carbon composite particles comprise a carbon skeleton containing silicon.

9. The secondary battery according to claim 8, wherein the silicon-carbon composite particles include a protective layer located on at least a portion of the surface of the carbon skeleton, the protective layer including at least one of amorphous carbon, a metal oxide, or a non-metal oxide, the metal oxide including at least one of aluminum oxide, copper oxide, or titanium oxide, and the non-metal oxide including at least one of silicon dioxide or silicon monoxide.

10. A method for preparing a secondary battery according to any one of claims 1 to 9, wherein: The preparation method of the silicon-carbon composite particles comprises the following steps: S1: providing a carbon skeleton material, crushing and classifying the carbon skeleton material, and then performing a first heat treatment on the carbon skeleton material, wherein the temperature of the first heat treatment is 700° C. to 900° C., and the time of the first heat treatment is 4 hours to 6 hours; S2: depositing the carbon skeleton material once, heating the temperature to 430° C. to 550° C., introducing a first mixed gas containing 5% to 50% silane by volume under a negative pressure environment of -60 kPa to -101 kPa, and reacting for 2 to 6 hours, wherein the deposition is repeated 2 to 5 times; S3: transferring the carbon skeleton material after the primary deposition to a fluidized bed for heating, introducing a second mixed gas containing 5% to 50% by volume of silane, and performing secondary deposition to obtain a carbon skeleton material including silicon; the temperature of the secondary deposition is 430° C. to 550° C., and the reaction time of the secondary deposition is 1 hour to 6 hours; S4: performing a second heat treatment on the carbon skeleton material including silicon at a temperature of 620° C. to 700° C., wherein the second heat treatment lasts for 0.5 h to 1 h; S5: Then, a protective layer is prepared on the surface of the carbon skeleton material including silicon to obtain the silicon-carbon composite particles.

11. The preparation method according to claim 10, which satisfies at least one of the following characteristics: (1) The carbon skeleton material comprises at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon or hard carbon; (2) The first mixed gas and the second mixed gas each independently further include at least one of nitrogen, hydrogen or argon; (3) The source material of the protective layer includes a first source material for preparing amorphous carbon, a second source material for preparing metal oxide, and a third source material for preparing non-metal oxide, wherein the first source material includes at least one of acetylene, methane, propylene, ethylene or propane, the second source material includes at least one of titanium isopropoxide, trimethylaluminum or copper acetate, and the third source material includes at least one of tetraethyl orthosilicate, triethoxysilane or monosilane.

12. An electronic device, wherein: The electronic device includes the secondary battery according to any one of claims 1 to 9 or the secondary battery manufactured by the manufacturing method according to claim 10 or 11.

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