Secondary battery and preparation method therefor, and electronic device

Abstract

A secondary battery and a preparation method therefor, and an electronic device. The secondary battery comprises: a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer comprises a silicon-carbon material; the degree of spheroidization of particles having the longest diameter greater than 10 μm in the silicon-carbon material is A that ranges from 0.80 to 0.98, wherein the thickness of the negative electrode current collector is B μm, and the relationship between A and B is 3.14 / A-0.048B≤3.7. By regulating and controlling the values of A and 3.14 / A-0.048B to be within the described range, the degree of spheroidization of the silicon-carbon material matches the thickness of the negative electrode current collector, particles in the silicon-carbon material would not pierce the negative electrode current collector, and the problem of edges and corners of the silicon-carbon material affecting an electron transmission channel of the negative electrode current collector is mitigated, thereby improving the charging rate and the discharge rate of the secondary battery.

Description

Secondary battery and preparation method thereof, and electronic device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and a preparation method thereof, and an electronic device. Background Art

[0002] With the continuous consumption of traditional energy and the urgent need for large-scale storage, electric vehicles and portable electronic devices, the development of energy storage devices with higher energy density has become a top priority. Secondary batteries, such as lithium-ion batteries, are widely used in all aspects of life today due to their advantages such as no memory effect, long cycle life, and green environmental protection. In recent years, lithium-ion batteries have developed rapidly in the fields of new energy vehicles and large-scale energy storage. However, as the negative electrode material of traditional commercial lithium-ion batteries, graphite has a relatively low capacity (372mAh / g), which hinders its further application. The development of high energy density and high safety lithium-ion battery negative electrode materials is the current focus of lithium battery technology development. Compared with carbon-based materials such as graphite, silicon has an ultra-high theoretical specific capacity (Li 15 Si4, 3579mAh / g) and suitable operating voltage (<0.5V vs.Li / Li + ) and other characteristics, it is considered to be the most promising lithium battery negative electrode material that can replace graphite. However, batteries with silicon added to the negative electrode often suffer from reduced fast charging capabilities and interfacial lithium precipitation due to insufficient kinetics. One of the main reasons for these problems is that the irregularly shaped silicon material particles have sharp edges and corners. These sharp corners will pierce the copper foil current collector during the negative electrode processing, causing the electron transmission channel in the current collector to be destroyed, resulting in an increase in the internal impedance of the battery, which in turn causes the problem of insufficient kinetics, resulting in a decrease in the charge rate and discharge rate of the lithium-ion battery.

[0003] Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and its preparation method, as well as an electronic device, to improve the charge rate and discharge rate of the secondary battery. The specific technical solution is as follows:

[0005] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a secondary battery comprising a positive electrode plate, a negative electrode plate, an electrolyte, and a separator; the negative electrode plate comprises 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 silicon-carbon material; the sphericity of particles in the silicon-carbon material having a longest diameter greater than 10 μm is A, A is 0.80 to 0.98, wherein the thickness of the negative electrode current collector is B μm, and the relationship between A and B is 3.14 / A-0.048B≤3.7. By regulating the values ​​of A and 3.14 / A-0.048B within the above range, the sphericity of the silicon-carbon material matches the thickness of the negative electrode current collector, the silicon-carbon material particles do not puncture the negative electrode current collector, and the problem of the sharp corners of the silicon-carbon material affecting the electron transmission channel of the negative electrode current collector is improved, thereby improving the charge rate and discharge rate of the secondary battery.

[0007] In some embodiments of the present application, A is 0.84 to 0.98, which can further improve the charge rate and discharge rate of the secondary battery.

[0008] In some embodiments of the present application, 2.2≤3.14 / A-0.048B≤3.6, which can further promote electron transport of the negative electrode current collector and improve the charge rate and discharge rate of the secondary battery. In some embodiments of the present application, 2.7≤3.14 / A-0.048B≤3.5.

[0009] In some embodiments of the present application, 3.5≤B≤20. By regulating the value of B within the above range, the negative electrode current collector has an appropriate thickness that matches the sphericity of the silicon-carbon material, thereby improving the charge rate and discharge rate of the secondary battery.

[0010] In some embodiments of the present application, the tensile strength F of the negative electrode current collector is between 451 MPa and 950 MPa. A tensile strength F of the negative electrode current collector within the above range indicates that the negative electrode current collector has good tensile strength. When the sharp corners of the silicon-carbon material particles penetrate the negative electrode current collector, the negative electrode current collector is not easily broken and has little impact on its electron transport channels, thereby facilitating an increase in the charge and discharge rates of the secondary battery. In some embodiments of the present application, the tensile strength F of the negative electrode current collector is between 470 MPa and 700 MPa.

[0011] In some embodiments of the present application, the minimum angle of the cross-section profile of particles with a diameter greater than or equal to 10 μm in the silicon-carbon material is 107.8° ≤ α ≤ 179.2°. When α is within the above range, it indicates that the silicon-carbon material particles lack sharp edges and corners, making them less likely to puncture the negative electrode current collector. The carbon material's sharp corners also have little impact on the electron transport channels of the negative electrode current collector, thereby facilitating improved charge and discharge rates of the secondary battery. In some embodiments of the present application, 110.3° ≤ α ≤ 179.2°.

[0012] In some embodiments of the present application, the silicon-carbon material contains silicon at a mass percentage of 40% to 54%. By regulating the mass percentage of silicon within the above range, the resulting silicon-carbon compound has a suitable specific capacity and an appropriate impedance when used in a secondary battery, thereby facilitating improved charge and discharge rates of the secondary battery, while also providing a higher energy density.

[0013] In some embodiments of the present application, the mass percentage of oxygen in the silicon-carbon material is less than or equal to 1.5%. By regulating the mass percentage of oxygen within the above range, the obtained silicon-carbon compound is less likely to undergo side reactions with the electrolyte, thereby facilitating an improvement in the initial coulombic efficiency of the secondary battery. A second aspect of the present application provides a method for preparing a secondary battery according to any of the aforementioned embodiments, comprising the following steps: preparing the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte, and assembling them to obtain the secondary battery;

[0014] The method for preparing the silicon-carbon material in the negative electrode plate comprises the following steps:

[0015] (1) mixing a phenolic compound, formaldehyde, ammonia and water, mixing them uniformly and then carrying out a heat-insulating reaction, then adding an emulsifier, mixing them uniformly and then carrying out a temperature-raising reaction to obtain a porous carbon precursor;

[0016] The molar ratio of the phenolic compound, formaldehyde, and ammonia is 1: (1.5 to 2.5): (0.006 to 0.012), and the phenolic compound includes at least one of phenol, cresol, nonylphenol, aralkylphenol, cardanol, octylphenol, bisphenol A, and xylenol; the temperature T1 of the insulation reaction is 50° C. to 70° C., and the time t1 is 2 h to 7 h; the mass ratio of the emulsifier to the phenolic compound is (0.08 to 0.13): 1; the temperature T2 of the temperature-raising reaction is 80° C. to 120° C., and the time t2 is 1 h to 5 h;

[0017] (2) carbonizing the porous carbon precursor in an inert atmosphere, and then activating the porous carbon matrix in an atmosphere containing a first compound, wherein the first compound includes carbon dioxide or water vapor;

[0018] The temperature T3 of the carbonization treatment is 450°C to 700°C, and the time t3 is 1h to 4h; the flow rate V1 of the first compound gas in the atmosphere containing the first compound is 1L / min to 4L / min, and the temperature T4 of the activation treatment is 750°C to 1000°C, and the time t4 is 6h to 20h;

[0019] (3) pre-treating the porous carbon substrate in an inert atmosphere and then treating it in a silane-containing atmosphere, then heating it for heat preservation and then treating it in an atmosphere containing a second compound to obtain the silicon-carbon material, wherein the second compound includes acetylene, propylene or toluene;

[0020] Among them, the pretreatment temperature T5 is 420℃ to 550℃, and the time t5 is 1h to 3h; the silane-containing atmosphere includes at least one of monosilane, disilane, trisilane, phenylsilane, and tolylsilane, and the flow rate V2 of the silane gas in the silane-containing atmosphere is 1L / min to 3L / min, and the ventilation time t6 is 220min to 480min; the insulation treatment temperature T7 is 450℃ to 600℃, and the time t7 is 0.5h to 2h; the flow rate V3 of the second compound in the atmosphere containing the second compound is 3L / min to 10L / min, and the ventilation time t8 is 160min to 400min.

[0021] A third aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments or the secondary battery manufactured by the manufacturing method in any of the aforementioned embodiments.

[0022] Beneficial effects of this application:

[0023] The present application provides a secondary battery and its preparation method, and an electronic device. The secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The 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, the negative electrode material layer including a silicon-carbon material. The sphericity of particles with a longest diameter greater than 10 μm in the silicon-carbon material is A, and A is 0.80 to 0.98. The thickness of the negative electrode current collector is B μm, and the relationship between A and B is 3.14 / A-0.048B≤3.7. By regulating the values ​​of A and 3.14 / A-0.048B within the above range, the sphericity of the silicon-carbon material matches the thickness of the negative electrode current collector, the silicon-carbon material particles do not puncture the negative electrode current collector, and the problem of the silicon-carbon material's sharp corners affecting the electron transmission channel of the negative electrode current collector is improved, thereby improving the charge rate and discharge rate of the secondary battery.

[0024] 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

[0025] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0026] FIG1 is a schematic structural diagram of the outer contour formed by a cross-section of a silicon-carbon material particle in one embodiment of the present application;

[0027] FIG2 is an electron microscope photograph of the silicon-carbon material of Example 9 of the present application. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0029] It should be noted that in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0030] At present, in order to solve the problem of poor charge and discharge rates in lithium-ion batteries, methods such as reducing the negative electrode compaction density, increasing the thickness of copper foil, double-layer coating, and reducing the particle size of silicon materials are often used. Although reducing the negative electrode compaction density and increasing the thickness of copper foil can alleviate the problem of copper foil current collectors being punctured by the sharp corners of silicon materials to a certain extent, it also increases the volume and weight of inactive materials in lithium-ion batteries, which will reduce the energy density of lithium-ion batteries; although double-layer coating can reduce the contact probability between silicon materials and copper foil current collectors, due to the concentration of silicon materials on the surface of the negative electrode sheet, the electron and ion transmission capabilities on the surface of the active material layer are deteriorated, which can easily lead to problems such as lithium precipitation; although reducing the particle size can reduce the penetration depth of the copper foil by the sharp corners of the silicon material, the increase in the specific surface area of ​​the silicon material will generate more solid electrolyte interface film (SEI film), which has a reducing effect on the initial efficiency of lithium-ion batteries, and is therefore not an effective solution.

[0031] In view of this, the present application provides a secondary battery and a preparation method thereof, and an electronic device to improve the charge rate and discharge rate of the secondary battery.

[0032] A first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator; the negative electrode sheet comprises 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 silicon-carbon material; the silicon-carbon material has a sphericity A of particles with a longest diameter greater than 10 μm, wherein A is 0.80 to 0.98. In some embodiments of the present application, A is 0.84 to 0.98. For example, the value of A can be 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, or a range consisting of any two values ​​therebetween. The thickness of the negative electrode current collector is B μm, and the relationship between A and B is 3.14 / A-0.048B≤3.7. In some embodiments of the present application, 2.0≤3.14 / A-0.048B≤3.7. In some embodiments of the present application, 2.2≤3.14 / A-0.048B≤3.6. In some embodiments of the present application, 2.7≤3.14 / A-0.048B≤3.5. For example, the value of 3.14 / A-0.048B can be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7 or a range consisting of any two values ​​therebetween. When the A value is too small, for example, less than 0.80, the sphericity of the silicon-carbon material is low, the edges and corners are more, and it is easy to penetrate the negative electrode current collector, so that the electron transport channel of the negative electrode current collector is damaged, thereby affecting the charge rate and discharge rate of the secondary battery. When the value of A is too large, for example, greater than 0.98, the production cost of the silicon-carbon material is high, which increases the cost of the secondary battery. When the value of 3.14 / A-0.048B is too large, for example, greater than 3.7, the sphericity of the silicon-carbon material particles is too low relative to the thickness of the negative electrode current collector, and the sharp corners of the silicon-carbon material particles penetrate the negative electrode current collector to a deeper depth, causing the electron transmission channel of the negative electrode current collector to be damaged or even puncture the negative electrode current collector, thereby affecting the charge rate and discharge rate of the secondary battery. Therefore, by regulating the value of 3.14 / A-0.048B within the above range, the sphericity of the silicon-carbon material matches the thickness of the negative electrode current collector, the silicon-carbon material particles will not puncture the negative electrode current collector, and the problem of the sharp corners of the silicon-carbon material affecting the electron transmission channel of the negative electrode current collector is improved, thereby improving the charge rate and discharge rate of the secondary battery.

[0033] In some embodiments of the present application, 3.5≤B≤20. In some embodiments of the present application, 4.0≤B≤8.0. For example, the value of B can be 3.5, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 17, 19, 20, or a range consisting of any two values ​​therebetween. By regulating the value of B within the above range, the negative electrode current collector has a suitable thickness, which matches the sphericity of the silicon-carbon material, and improves the problem that the sharp corners of the silicon-carbon material affect the electron transmission channel of the negative electrode current collector, thereby improving the charge rate and discharge rate of the secondary battery.

[0034] In some embodiments of the present application, the thickness of the negative electrode current collector is 6μm to 20μm, and the tensile fracture strength F of the negative electrode current collector is 451MPa to 950MPa. In some embodiments of the present application, the tensile fracture strength F of the negative electrode current collector is 470MPa to 700MPa. For example, the tensile fracture strength F can be 451MPa, 460MPa, 470MPa, 500MPa, 600MPa, 700MPa, 800MPa, 900MPa, 950MPa, or a range consisting of any two values ​​therebetween. The tensile fracture strength F of the negative electrode current collector is within the above range, indicating that the negative electrode current collector has good tensile fracture strength. When the sharp corners of the silicon-carbon material particles penetrate the negative electrode current collector, the negative electrode current collector is not easily broken and has little effect on its electron transmission channel, thereby facilitating the improvement of the charge rate and discharge rate of the secondary battery.

[0035] In the present application, negative electrode current collectors of different thicknesses and tensile fracture strengths can be purchased, and combined with the test methods of "testing the thickness B of the negative electrode current collector" and "testing the tensile fracture strength F of the negative electrode current collector" provided in this application, the negative electrode current collector with the required thickness and tensile fracture strength can be selected.

[0036] In some embodiments of the present application, the minimum angle of the cross-sectional profile of particles with a particle diameter greater than or equal to 10 μm in the silicon-carbon material is 107.8°≤α≤179.2°. In some embodiments of the present application, 110.3°≤α≤179.2°. For example, α can be 107.8, 110.3°, 110.5°, 111°, 115°, 120°, 130°, 140°, 150°, 160°, 170°, 175°, 179°, 179.2°, or a range consisting of any two values ​​therebetween. The minimum angle of the cross-sectional profile of particles with a diameter greater than or equal to 10 μm is more representative. If α is within the above range, it means that there are no sharp edges in the silicon-carbon material particles, which makes it difficult to puncture the negative electrode current collector. The edges of the carbon material also have little effect on the electron transmission channel of the negative electrode current collector, which is beneficial to improving the charge rate and discharge rate of the secondary battery.

[0037] In this application, the minimum angle α of the cross-section profile of a silicon-carbon material particle refers to the minimum value of the angles of the corners of the outer contour formed by the cross-section of the particle. The corner angle refers to the angle formed by the two tangent lines drawn along the edges of the corner. Specifically, Figure 1 is a schematic structural diagram of the outer contour formed by the cross-section of a silicon-carbon material particle. If α1 is 115°, α2 is 108°, α3 is 142°, and α4 is 140°, then the minimum angle α of the cross-section profile is 108°.

[0038] In some embodiments of the present application, the mass percentage W1 of silicon in the silicon-carbon material is 40% to 54%. For example, the mass percentage W1 of silicon can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, or a range consisting of any two values ​​therebetween. By regulating the mass percentage W1 of silicon within the above range, the obtained silicon-carbon compound has a suitable specific capacity and has a suitable impedance when used in a secondary battery, which is beneficial to improving the charge rate and discharge rate of the secondary battery, while the secondary battery also has a higher energy density.

[0039] In some embodiments of the present application, the mass percentage content W2 of the oxygen element in the silicon-carbon material is less than or equal to 1.5%. In some embodiments of the present application, the mass percentage content W2 of the oxygen element in the silicon-carbon material is 0.01% to 1.5%. For example, the mass percentage content W2 of the oxygen element can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a range consisting of any two values ​​therebetween. By regulating the mass percentage content W2 of the oxygen element within the above range, the obtained silicon-carbon compound is not prone to side reactions with the electrolyte, which is beneficial to improving the first coulombic efficiency of the secondary battery.

[0040] In some embodiments of the present application, the mass percentage W3 of carbon element in the silicon-carbon material is 46% to 59%, which can further improve the charge rate and discharge rate of the secondary battery.

[0041] A second aspect of the present application provides a method for preparing a secondary battery according to any of the aforementioned embodiments, comprising the following steps: preparing a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, and assembling them to obtain a secondary battery;

[0042] The method for preparing the silicon-carbon material in the negative electrode plate comprises the following steps:

[0043] (1) A phenolic compound, formaldehyde, ammonia and water are mixed, mixed evenly and then subjected to heat preservation reaction, and then an emulsifier is added, mixed evenly and then subjected to temperature reaction to obtain a porous carbon precursor. Wherein, the molar ratio X of the phenolic compound, formaldehyde and ammonia is 1: (1.5 to 2.5): (0.006 to 0.012), the phenolic compound includes at least one of phenol, cresol, nonylphenol, arylalkylphenol, cardanol, octylphenol, bisphenol A and xylenol; the temperature T1 of the heat preservation reaction is 50°C to 70°C, and the time t1 is 2h to 7h; the mass ratio Y of the emulsifier to the phenolic compound is (0.08 to 0.13): 1; the temperature T2 of the temperature rise reaction is 80°C to 120°C, and the time t2 is 1h to 5h.

[0044] For example, the molar ratio A can be 1:1.5:0.006, 1:2:0.006, 1:2.5:0.006, 1:1.5:0.009, 1:2:0.009, 1:2.5:0.009, 1:1.5:0.012, 1:2:0.012, 1:2.5:0.012, or a range consisting of any two ratios therebetween. For example, the temperature T1 can be 50°C, 60°C, 65°C, 70°C, or a range consisting of any two values ​​therebetween. For example, the time t1 can be 2h, 3h, 4h, 5h, 6h, 7h, or a range consisting of any two values ​​therebetween. For example, the mass ratio B can be 0.08:1, 0.09:1, 0.10:1, 0.11:1, 0.12:1, 0.13:1, or a range consisting of any two ratios therebetween. For example, the temperature T2 may be 80° C., 85° C., 90° C., 95° C., 100° C., 105° C., 110° C., 115° C., 120° C., or a range consisting of any two values ​​therebetween. For example, the time t2 may be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or a range consisting of any two values ​​therebetween.

[0045] (2) The porous carbon precursor is carbonized in an inert atmosphere, and then activated in an atmosphere containing a first compound to obtain a porous carbon matrix, wherein the first compound includes carbon dioxide or water vapor. The carbonization temperature T3 is 450°C to 700°C, and the time t3 is 1 hour to 4 hours; the flow rate V1 of the first compound gas in the atmosphere containing the first compound is 1 L / min to 4 L / min, and the activation temperature T4 is 750°C to 1000°C, and the time t4 is 6 hours to 20 hours.

[0046] For example, the temperature T3 may be 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, or a range consisting of any two values ​​therebetween. For example, the time t3 may be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or a range consisting of any two values ​​therebetween. For example, the flow rate V1 may be 1 L / min, 1.5 L / min, 2 L / min, 2.5 L / min, 3 L / min, 3.5 L / min, 4 L / min, or a range consisting of any two values ​​therebetween. For example, the temperature T4 may be 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, or a range consisting of any two values ​​therebetween. For example, time t4 may be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or a range consisting of any two values ​​therebetween.

[0047] (3) The porous carbon substrate is pretreated in an inert atmosphere and then treated in a silane-containing atmosphere, and then the temperature is increased for heat preservation and then treated in an atmosphere containing a second compound to obtain a silicon-carbon material, wherein the second compound includes acetylene, propylene or toluene. The pretreatment temperature T5 is 420°C to 550°C, and the time t5 is 1h to 3h; the silane-containing atmosphere includes at least one of monosilane, disilane, trisilane, phenylsilane, and tolylsilane; the flow rate V2 of the silane gas in the silane-containing atmosphere is 1L / min to 3L / min, and the ventilation time t6 is 220min to 480min; the heat preservation temperature T7 is 450°C to 600°C, and the time t7 is 0.5h to 2h; the flow rate V3 of the second compound in the atmosphere containing the second compound is 3L / min to 10L / min, and the ventilation time t8 is 160min to 400min.

[0048] For example, the temperature T5 can be 420°C, 425°C, 450°C, 475°C, 500°C, 525°C, 550°C, or a range consisting of any two values ​​therebetween. For example, the time t5 can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or a range consisting of any two values ​​therebetween. For example, the flow rate V2 can be 1 L / min, 1.2 L / min, 1.5 L / min, 1.8 L / min, 2 L / min, 2.2 L / min, 2.5 L / min, 2.8 L / min, 3 L / min, or a range consisting of any two values ​​therebetween. For example, the ventilation duration t6 can be 220 min, 250 min, 275 min, 300 min, 325 min, 350 min, 375 min, 400 min, 420 min, 440 min, 460 min, 480 min, or a range consisting of any two values ​​therebetween. For example, the temperature T7 can be 450°C, 475°C, 500°C, 525°C, 550°C, 575°C, 600°C, or a range consisting of any two values ​​therebetween. For example, the time t7 can be 0.5h, 0.7h, 0.9h, 1h, 1.2h, 1.4h, 1.5h, 1.7h, 2h, or a range consisting of any two values ​​therebetween. For example, the flow rate V3 can be 3L / min, 4L / min, 5L / min, 6L / min, 7L / min, 8L / min, 9L / min, 10L / min, or a range consisting of any two values ​​therebetween. For example, the ventilation duration t8 can be 160min, 180min, 200min, 225min, 250min, 275min, 300min, 325min, 350min, 375min, 400min, or a range consisting of any two values ​​therebetween.

[0049] The porous carbon precursor obtained by the above step (1) has fewer sharp corners, which is conducive to obtaining silicon-carbon compounds with high sphericity in the subsequent process. The activation treatment in step (2) makes the pores inside the porous carbon precursor more abundant, and the obtained porous carbon matrix is ​​conducive to the subsequent deposition of silicon materials. In step (3), pretreatment is first performed to improve the temperature uniformity of the porous carbon, which is conducive to the uniform deposition of silane in different porous carbon particles; then silane gas is introduced to deposit silicon materials in the pores of the porous carbon matrix; after heating, heat preservation treatment is performed to improve the temperature uniformity of the porous carbon after silicon deposition, which is conducive to the uniform decomposition and coating of the carbon source gas on the surface of different porous carbon particles; finally, the gas containing the second compound is introduced to cover the surface of the silicon material with higher activity with carbon material, thereby preventing the silicon material from oxidizing in the air environment and improving the stability of the silicon-carbon material. The spherical degree A of the silicon-carbon material obtained is 0.80 to 0.98, which cooperates with the negative electrode current collector with a thickness of Bμm. The values ​​of A and 3.14 / A-0.048B are regulated within the above range. The spherical degree of the silicon-carbon material matches the thickness of the negative electrode current collector. The silicon-carbon material particles will not puncture the negative electrode current collector, and the problem of the sharp corners of the silicon-carbon material affecting the electron transmission channel of the negative electrode current collector is improved, thereby improving the charging rate and discharge rate of the secondary battery.

[0050] The present application does not particularly limit the content of water added in step (1), as long as the purpose of the present application can be achieved. For example, the mass of water added is 5 to 15 times the mass of the phenolic compound. The present application does not limit the gas composition and flow rate of the inert atmosphere in steps (2) and (3). For example, the gas in the inert atmosphere can include but is not limited to nitrogen, argon, helium, etc., and the flow rate can be 1 L / min to 10 L / min.

[0051] In this application, the term "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can refer to the entire surface of the negative electrode current collector or a portion of the surface of the negative electrode current collector. This is not particularly limited in this application, as long as the purpose of this application can be achieved.

[0052] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0053] The above silicon-carbon compound can be used as the negative electrode active material in the negative electrode material layer. The negative electrode material layer may also include other negative electrode active materials. The present application has no particular restrictions on other negative electrode active materials as long as the purpose of the present application can be achieved. For example, other negative electrode active materials may include but are not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloys.

[0054] In some embodiments of the present application, the negative electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials or conductive polymers, and the conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers, and specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. For example, the binder may include, but is not limited to, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyethylene, polypropylene, acrylic acid (ester) styrene-butadiene rubber, epoxy resin or nylon or polyvinylidene fluoride. The present application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0055] The present application does not particularly limit the thickness of the negative electrode material layer, as long as it can achieve the purpose of the present application. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm. The present application does not particularly limit the thickness of the negative electrode current collector, as long as it can achieve the purpose of the present application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0056] Optionally, the negative electrode sheet may further include a conductive layer positioned between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the above-mentioned conductive agents and binders.

[0057] In the present application, the 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. The phrase "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its thickness direction, or on both surfaces of the positive electrode current collector along its thickness direction. It should be noted that the "surface" here can refer to the entire surface of the positive electrode current collector or a portion of the surface of the positive electrode current collector. This is not particularly limited in the present application, as long as the purpose of this application can be achieved.

[0058] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0059] The positive electrode material layer includes a positive electrode active material. The present application has no particular limitation 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 at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0060] The positive electrode material layer may further include a conductive agent and a binder. This application does not particularly limit the types of the conductive agent and binder, as long as the purpose of this application can be achieved. For example, it can be at least one of the above-mentioned conductive agents and binders. This application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0061] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0062] Optionally, the positive electrode sheet may further include a conductive layer positioned between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer; for example, the conductive layer may be at least one of the aforementioned conductive agents and binders.

[0063] In this application, there is no particular limitation on the separator, as long as the purpose of this application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0064] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0065] 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 mixing a polymer and an inorganic layer.

[0066] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application is not particularly limited to inorganic particles. For example, inorganic particles 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. The present application is not particularly limited to a binder. For example, a binder may include but is not limited to at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0067] In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0068] In the present application, the electrolyte includes a lithium salt and a non-aqueous solvent.

[0069] The present application does not specifically limit the lithium salt, as long as the objectives of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate. The present application does not specifically limit the content of the lithium salt in the electrolyte, as long as the objectives of the present application can be achieved.

[0070] The present application has no particular limitation on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0071] Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (EMC).Above-mentioned cyclic carbonate can include but not limited to at least one in 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 above-mentioned 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 lactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned 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. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0072] In the present application, the secondary battery also includes a shell for accommodating a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application has no special restrictions on the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal, and a metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0073] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheets, the separator and the negative electrode sheets 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 shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly with a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0074] In some embodiments of the present application, the secondary battery of the present application includes, but is not limited to: a lithium ion battery or a sodium ion battery. In some embodiments of the present application, the secondary battery includes a lithium ion battery.

[0075] A third aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments or the secondary battery manufactured by the manufacturing method in any of the aforementioned embodiments.

[0076] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, 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 head-mounted stereo 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, a car, 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.

[0077] Example

[0078] 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.

[0079] Test methods and equipment:

[0080] Test of the minimum angle α of the cross-section profile of silicon-carbon material particles:

[0081] 0.47g of silicon-carbon material and 0.396g of polyacrylic acid were dispersed in water, mixed in a homogenizer, and then applied to the surface of copper foil with a spatula. After drying, the sample was sliced ​​using a JEOL / IB-09010CP ion polisher. A ZEIS-SEM (Sigma-02-33) was used to capture cross-sectional microscopic images of the silicon-carbon material. The cross-sectional profiles of silicon-carbon material particles with a diameter greater than or equal to 10μm were selected for analysis. The degree of the minimum angle in the profiles of 50 particles was counted and the average value was calculated as the final result. The diameter of the silicon-carbon material particle refers to the maximum value between two points in the cross-sectional profile of the particle.

[0082] Test of sphericity A of particles with the longest diameter greater than 10 μm in silicon-carbon materials:

[0083] The sphericity of the material is tested using the equivalent diameter method. The test method is to use a ZEISS-SEM (sigma-02-33) scanning electron microscope to observe the silicon-carbon material in the cross section of the negative electrode along the thickness direction, remove incomplete particles, calculate the equivalent diameter of the perimeter of the complete particles and the equivalent diameter of the particle area, and calculate the sphericity by averaging. Among them, sphericity = equivalent diameter of perimeter / equivalent diameter of area. The complete particles tested above are particles with a longest diameter greater than 10μm. The longest diameter of the silicon-carbon material particles refers to the maximum value between two points in the particle section contour.

[0084] Test of the mass percentage of silicon element W1 in silicon-carbon material:

[0085] The silicon-carbon material was observed in a cross-section of the negative electrode sheet along its thickness using a ZEISS-SEM (Sigma-02-33). The silicon content of the silicon-carbon material was measured using an energy dispersive spectrometer (EDS). The silicon content of 50 particles was counted and averaged.

[0086] Test of the mass percentage of oxygen element W2 in silicon-carbon material:

[0087] The silicon-carbon material was observed in a cross-section of the negative electrode sheet along its thickness using a ZEISS-SEM (Sigma-02-33). The silicon content of the silicon-carbon material was measured using an energy dispersive spectrometer (EDS). The silicon content of 50 particles was counted and averaged.

[0088] Test of thickness B of negative electrode current collector:

[0089] Use a micrometer to measure the thickness of the negative electrode current collector at 10 random locations, and take the average value as the final result.

[0090] Test of tensile strength F of negative electrode current collector:

[0091] The fracture strength F of the negative electrode current collector was tested with reference to the standard "GB / T 5230-1995 Electrolytic copper foil tensile strength, elastic modulus, and elongation at break test".

[0092] Lithium-ion battery discharge rate performance test:

[0093] At 25°C and normal pressure, the prepared lithium-ion battery was discharged at a constant current rate of 0.2C to 3.0V and allowed to stand for 5 minutes. It was then charged at a constant current rate of 0.5C to 4.5V, and charged at a constant voltage of 4.5V to 0.05C, and allowed to stand for 5 minutes. It was then discharged at a constant current rate of 0.2C to 3.0V, and allowed to stand for 5 minutes. The discharge capacity of this step was recorded as C1. It was then charged at a constant current rate of 0.2C1 to 4.5V, and charged at a constant voltage of 4.5V to 0.05C, and allowed to stand for 5 minutes. The charge capacity of this step was recorded as C2. It was then discharged at a constant current rate of 2C1 to 3.0V, and the discharge capacity of this step was recorded as C3.

[0094] The discharge rate performance of the battery = C3 / C2×100%.

[0095] Lithium-ion battery charge rate performance test

[0096] At 25°C and normal pressure, the prepared lithium-ion battery was discharged at a constant current rate of 0.2C to 3.0V and allowed to stand for 5 minutes; then charged at a constant current rate of 0.5C to 4.5V, and charged at a constant voltage of 4.5V to 0.05C, and allowed to stand for 5 minutes; then discharged at a constant current rate of 0.2C to 3.0V, and allowed to stand for 5 minutes, and the discharge capacity of this step was recorded as C1. Then, the battery was charged at a constant current rate of 0.2C1 to 4.5V, and charged at a constant voltage to 0.05C, and allowed to stand for 5 minutes, and the charge capacity of this step was recorded as C2;

[0097] The discharge rate performance of the battery = C2 / C1×100%.

[0098] Example 1

[0099] <Preparation of Silicon Carbon Material>

[0100] (1) Phenolic compounds m-phenol, formaldehyde, and ammonia are mixed in a molar ratio X of 1:2.0:0.01, water is added and mixed evenly, and then the mixture is kept warm for reaction. The mass of water added is 10 times the mass of the phenolic compound. The temperature T1 of the warm reaction is 60°C and the time t1 is 6h. Then, emulsifier F127 is added, and the mass ratio Y of the emulsifier to the phenolic compound is 0.08:1. The mixture is stirred for 1h, mixed evenly, and then the mixture is heated for reaction. The temperature T2 of the heated reaction is 100°C and the time t2 is 4h. After the reaction, the reaction solution is filtered and washed to obtain a porous carbon precursor.

[0101] (2) 1000 g of porous carbon precursor was carbonized in a nitrogen atmosphere with a nitrogen flow rate of 2 L / min, a carbonization temperature T3 of 600°C, and a time t3 of 3 h; the temperature was increased, and then an activation treatment was carried out in an atmosphere containing a first compound to obtain a porous carbon matrix, the first compound was carbon dioxide, the flow rate V1 of the first compound gas was 3 L / min, the activation temperature T4 was 930°C, and the time t4 was 20 h.

[0102] (3) 1000 g of porous carbon matrix was added to a fluidized bed reactor and pretreated under a nitrogen atmosphere with a nitrogen flow rate of 10 L / min, a pretreatment temperature T5 of 480°C, and a ventilation time t5 of 1 h; then, a silane-containing gas was introduced, wherein the silane in the silane-containing gas was monosilane, the silane flow rate V2 was 2 L / min, and the ventilation time t6 was 340 min; then, the temperature was continued to be raised for insulation treatment, the insulation treatment temperature T7 was 500°C, and the time t7 was 1 h; then, the silicon-carbon material was treated under an atmosphere containing a second compound, wherein the second compound was acetylene, the second compound gas flow rate V3 was 8 L / min, and the ventilation time t8 was 300 min.

[0103] <Preparation of negative electrode sheet>

[0104] The silicon-carbon material and artificial graphite prepared above were mixed in a mass ratio of 1:9 as the negative electrode active material. The negative electrode active material, carbon nanotubes, lithium carboxymethyl cellulose, and lithium polyacrylate were mixed in a mass ratio of 97.4:0.2:0.4:2, and deionized water was added as a solvent to prepare a slurry with a solid content of 45wt%. After stirring evenly with a vacuum mixer, a negative electrode slurry with a viscosity of 6000mPa.s was obtained. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm and dried at 120°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 100.1mg / 1540mm 2 . Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. After cold pressing, cutting, slitting, and welding the tabs, a negative electrode sheet with a specification of 661mm×78mm is obtained for standby use. Among them, the thickness of the single-sided negative electrode material layer is 54.5μm. Among them, the negative electrode active material is obtained by mixing the silicon-carbon material prepared above and graphite in a mass ratio of 1:9, and the gram capacity of the negative electrode active material is 480mAh / g.

[0105] <Preparation of positive electrode sheet>

[0106] The positive electrode active material LiCoO2, the conductive agent acetylene black, and the binder polyvinylidene fluoride were mixed in a mass ratio of 96.7:1.7:1.6, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 76wt%. After vacuum stirring, the positive electrode slurry was obtained. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 9μm and dried at 120℃ to obtain a positive electrode sheet with a single-sided positive electrode material layer. The coating weight of the positive electrode material layer was 260mg / 1540mm 2 Repeat the above steps on the other side of the aluminum foil to obtain a double-sided positive electrode sheet coated with a positive electrode material layer. After cold pressing, cutting, slitting, and welding the tabs, a 661mm x 76.5mm positive electrode sheet is obtained for future use. The thickness of the positive electrode material layer on one side is 42μm.

[0107] <Preparation of Electrolyte>

[0108] In an environment with a water content of less than 10 ppm, fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 5:10:15:20:50 to obtain an organic solvent. An electrolyte salt, LiPF6, is then added to the organic solvent and mixed thoroughly to obtain an electrolyte solution. The electrolyte salt comprises 12.5% ​​by mass of the electrolyte solution, with the remainder being the organic solvent.

[0109] <Diaphragm>

[0110] A porous polyethylene film with a thickness of 10 μm (supplied by Celgard) was used as a separator.

[0111] <Preparation of lithium-ion batteries>

[0112] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as a separator, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and then injected with the electrolyte prepared above. The lithium-ion battery is produced through vacuum packaging, standing, forming, degassing, and trimming. The upper limit of the formation voltage is 4.15V, the formation temperature is 70°C, and the formation standing time is 2 hours.

[0113] Example 2 to Example 15

[0114] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0115] Comparative Example 1 to Comparative Example 2

[0116] Except that no emulsifier was added and relevant preparation parameters were adjusted according to Table 1, the rest were the same as Example 1.

[0117] Comparative Examples 3 to 5

[0118] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0119] The preparation parameters and performance tests of each embodiment and comparative example are shown in Table 1.

[0120] It can be seen from Examples 1 to 15 and Comparative Examples 1 to 5 that when the spheroidization degree A and the value of 3.14 / A-0.048B of the silicon-carbon material are both within the range of the present application, the obtained lithium-ion battery has a high charge rate and discharge rate, thereby indicating that the charge rate and discharge rate of the lithium-ion battery are improved.

[0121] It can be seen from Examples 1 to 15 that the minimum angle α of the cross-sectional profile of the silicon-carbon material, the mass percentage of the silicon element W1, and the mass percentage of the oxygen element W2 vary with the changes in the preparation parameters. When the silicon-carbon compound prepared by the preparation method of this application is prepared, the above parameters are all within the scope of this application, and the resulting lithium-ion battery has a high charge rate and discharge rate.

[0122] Specifically, FIG2 shows the silicon-carbon compound prepared in Example 9. As can be seen from the figure, the cross section of the silicon-carbon compound particles is close to circular. The minimum angle α of the cross section of the silicon-carbon compound particles is measured to be 179.2.

[0123] It can be seen from Examples 1 to 15 that the thickness B and tensile strength F of the negative electrode current collector are positively correlated, which will affect the charge rate and discharge rate of the secondary battery. When the thickness B and tensile strength F of the negative electrode current collector are within the range of this application, the lithium-ion battery has a high charge rate and discharge rate.

[0124] 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.

[0125] 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 positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator; the negative electrode sheet comprises 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 silicon-carbon material; the sphericity of particles with a longest diameter greater than 10 μm in the silicon-carbon material is A, and A is 0.80 to 0.98, wherein: The thickness of the negative electrode current collector is B μm, and the relationship between A and B is 3.14 / A-0.048B≤3.

7.

2. The secondary battery according to claim 1, wherein: 3.5≤B≤20。 3. The secondary battery according to claim 1 or 2, wherein The tensile strength of the negative electrode current collector is 451 MPa to 950 MPa.

4. The secondary battery according to any one of claims 1 to 3, wherein The minimum angle of the cross-sectional profile of particles in the silicon-carbon material with a particle diameter greater than or equal to 10 μm is 107.8°≤α≤179.2°.

5. The secondary battery according to any one of claims 1 to 4, wherein The mass percentage of silicon element in the silicon-carbon material is 40% to 54%.

6. The secondary battery according to any one of claims 1 to 5, wherein The mass percentage of oxygen element in the silicon-carbon material is less than or equal to 1.5%.

7. The secondary battery according to any one of claims 1 to 6, wherein A is 0.84 to 0.

98.

8. The secondary battery according to any one of claims 1 to 7, wherein 2.2≤3.14 / A-0.048B≤3.

6.

9. A method for preparing a secondary battery according to any one of claims 1 to 8, comprising the following steps: preparing the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte, and assembling them to obtain the secondary battery; The method for preparing the silicon-carbon material in the negative electrode plate comprises the following steps: (1) mixing a phenolic compound, formaldehyde, ammonia and water, mixing them uniformly and then carrying out a heat-insulating reaction, then adding an emulsifier, mixing them uniformly and then carrying out a temperature-raising reaction to obtain a porous carbon precursor; The molar ratio of the phenolic compound, formaldehyde, and ammonia is 1: (1.5 to 2.5): (0.006 to 0.012), and the phenolic compound includes at least one of phenol, cresol, nonylphenol, aralkylphenol, cardanol, octylphenol, bisphenol A, and xylenol; the temperature T1 of the insulation reaction is 50° C. to 70° C., and the time t1 is 2 h to 7 h; the mass ratio of the emulsifier to the phenolic compound is (0.08 to 0.13): 1; the temperature T2 of the temperature-raising reaction is 80° C. to 120° C., and the time t2 is 1 h to 5 h; (2) carbonizing the porous carbon precursor in an inert atmosphere, and then activating the porous carbon matrix in an atmosphere containing a first compound, wherein the first compound includes carbon dioxide or water vapor; The carbonization treatment temperature T3 is 450°C to 700°C, the time t3 is 1h to 4h; the flow rate V1 of the first compound gas in the first compound-containing atmosphere is 1L / min to 4L / min, and the activation treatment temperature T4 is 750°C to 1000℃, time t4 is 6h to 20h; (3) pre-treating the porous carbon substrate in an inert atmosphere and then treating it in a silane-containing atmosphere, then heating it for heat preservation and then treating it in an atmosphere containing a second compound to obtain the silicon-carbon material, wherein the second compound includes acetylene, propylene or toluene; Among them, the pretreatment temperature T5 is 420℃ to 550℃, and the time t5 is 1h to 3h; the silane-containing atmosphere includes at least one of monosilane, disilane, trisilane, phenylsilane, and tolylsilane, and the flow rate V2 of the silane gas in the silane-containing atmosphere is 1L / min to 3L / min, and the ventilation time t6 is 220min to 480min; the insulation treatment temperature T7 is 450℃ to 600℃, and the time t7 is 0.5h to 2h; the flow rate V3 of the second compound in the atmosphere containing the second compound is 3L / min to 10L / min, and the ventilation time t8 is 160min to 400min. 10 . An electronic device comprising the secondary battery according to claim 1 or the secondary battery prepared by the preparation method according to claim 9 .

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