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, preparation method thereof and electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and in particular to a secondary battery, a preparation method thereof and an electronic device. BACKGROUND

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

[0003] SUMMARY

[0004] The purpose of the present application is to provide a secondary battery, a preparation method thereof and an electronic device to improve the charge rate and discharge rate of the secondary battery. The specific technical solutions are as follows:

[0005] It should be noted that the lithium ion battery is used as an example to explain the present application in the summary of the present application, but the secondary battery of the present application is 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, which 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 spheroidization degree of the silicon-carbon material with the longest diameter greater than 10 μm is A degrees, 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. By regulating the values of A and 3.14 / A-0.048B within the above range, the spheroidization degree of the silicon-carbon material and the thickness of the negative electrode current collector are matched with each other, the silicon-carbon material particles cannot pierce the negative electrode current collector, and the problem that the edges and corners of the silicon-carbon material affect the electron transmission channel of the negative electrode current collector is improved, so that the charge rate and discharge rate of the secondary battery are improved.

[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 the electron transmission 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 a suitable thickness and is matched with the spheroidization degree of the silicon-carbon material, so that the charge rate and discharge rate of the secondary battery are improved.

[0010] In some embodiments of the present application, the tensile fracture strength of the negative electrode current collector is 451 MPa to 950 MPa. The tensile fracture strength of the negative electrode current collector within the above range indicates that the negative electrode current collector has a good tensile fracture strength, and when the edges and corners of the silicon-carbon material particles pierce the negative electrode current collector, the negative electrode current collector is not easy to break and has a small effect on its electron transmission channel, thereby facilitating the improvement of the charge rate and discharge rate of the secondary battery. In some embodiments of the present application, the tensile fracture strength F of the negative electrode current collector is 470 MPa to 700 MPa.

[0011] In some embodiments of the present application, the minimum angle of the cross-sectional profile of the particles with a particle diameter greater than or equal to 10 μm in the silicon-carbon material is 107.8°≤α≤179.2°. The α within the above range indicates that there is no sharp edge in the silicon-carbon material particles, so that the negative electrode current collector is not easily punctured, and the effect of the edge of the carbon material on the electron transmission channel of the negative electrode current collector is also small, thereby facilitating the improvement of the charge rate and discharge rate 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 mass percentage of silicon element in the silicon-carbon material is 40% to 54%. By adjusting the mass percentage of silicon element within the above range, the silicon-carbon compound obtained has a suitable specific capacity, and has a suitable impedance when used in a secondary battery, thereby facilitating the improvement of the charge rate and discharge rate of the secondary battery, and the secondary battery also has a higher energy density.

[0013] In some embodiments of the present application, the mass percentage of oxygen element in the silicon-carbon material is less than or equal to 1.5%. By adjusting the mass percentage of oxygen element within the above range, the silicon-carbon compound obtained is less likely to have a side reaction with the electrolyte, thereby facilitating the improvement of the first coulombic efficiency of the secondary battery. The second aspect of the present application provides a preparation method of the secondary battery in any of the foregoing embodiments, which comprises the following steps: preparing the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte, and assembling to obtain the secondary battery.

[0014] The preparation method of the silicon-carbon material in the negative electrode sheet comprises the following steps:

[0015] (1) mixing a phenolic compound, formaldehyde, ammonia gas and water, uniformly mixing, then performing a heat preservation reaction, then adding an emulsifier, uniformly mixing, then performing a temperature rising reaction to obtain a porous carbon precursor;

[0016] The molar ratio of the phenolic compound, formaldehyde and ammonia gas is 1:(1.5 to 2.5):(0.006 to 0.012), the phenolic compound includes at least one of phenol, cresol, nonyl phenol, aralkyl phenol, cardanol, octyl phenol, bisphenol A and dimethyl phenol; 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 of the emulsifier to the phenolic compound is (0.08 to 0.13):1; the temperature T2 of the temperature rising reaction is 80°C to 120°C, and the time t2 is 1h to 5h;

[0017] (2) performing carbonization treatment on the porous carbon precursor in an inert atmosphere, then performing activation treatment in an atmosphere containing a first compound to obtain a porous carbon matrix, the first compound includes carbon dioxide or water vapor;

[0018] wherein the carbonization treatment has a temperature T3 of 450-700 DEG C and a time t3 of 1-4 h; the first compound-containing atmosphere has a flow rate V1 of 1-4 L / min of the first compound gas; the activation treatment has a temperature T4 of 750-1000 DEG C and a time t4 of 6-20 h;

[0019] (3) the porous carbon substrate is pretreated in an inert atmosphere, then treated in a silane-containing atmosphere, then heated and treated in a second compound-containing atmosphere to obtain the silicon-carbon material, the second compound including acetylene, propylene or toluene;

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

[0021] A third aspect of the present application provides an electronic device comprising the secondary battery of any one of the preceding embodiments or the secondary battery prepared by the preparation method of any one of the preceding embodiments.

[0022] The present application has the following beneficial effects:

[0023] The present application provides a secondary battery and a preparation method thereof, 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 spheroidization degree of the silicon-carbon material with the longest diameter greater than 10 μm is A degree, and A is 0.80-0.98. 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 adjusting the values of A and 3.14 / A-0.048B within the above range, the spheroidization degree of the silicon-carbon material and the thickness of the negative electrode current collector are matched with each other, the silicon-carbon material particles will not pierce the negative electrode current collector, and the problem that the edges and corners of the silicon-carbon material affect the electron transmission channel of the negative electrode current collector is improved, so that the charge rate and discharge rate of the secondary battery are improved.

[0024] Of course, implementing any of the products or methods of the present application does not necessarily require all the advantages described above to be achieved at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0026] Fig. 1 is a structural schematic diagram of the outer contour of a cross section of a silicon-carbon material particle in an embodiment of the present application;

[0027] Fig. 2 is a scanning electron microscope (SEM) image of a silicon-carbon material of Example 9 of the present application. DETAILED DESCRIPTION

[0028] For the purpose of this application, the technical solutions and advantages are more clearly and specifically understood, the following embodiments are described with reference to the accompanying drawings and examples, and the application is further described in detail. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

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

[0030] At present, in order to solve the problem of the difference between the charge rate and the discharge rate of the lithium-ion battery, methods such as reducing the compaction density of the negative electrode, increasing the thickness of the copper foil, double-coating, and reducing the particle size of the silicon material are usually used. Although reducing the compaction density of the negative electrode and increasing the thickness of the copper foil can alleviate the problem of the copper foil current collector being pierced by the sharp corners of the silicon material to some extent, they also increase the volume and weight of the non-active material in the lithium-ion battery, which reduces the energy density of the lithium-ion battery. Although double-coating can reduce the contact probability between the silicon material and the copper foil current collector, the active material is concentrated on the surface of the negative electrode sheet, which deteriorates the electron and ion transmission capacity of the surface of the active material layer, and is prone to problems such as lithium precipitation. Although reducing the particle size can reduce the piercing depth of the sharp corners of the silicon material to the copper foil, the increase in the specific surface area of the silicon material generates more solid electrolyte interface (SEI) films, which reduces the initial efficiency of the lithium-ion battery, and thus is not an effective solution.

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

[0032] The first aspect of the present application provides a secondary battery, which 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 disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer comprises a silicon-carbon material; the spheroidization degree of the silicon-carbon material with the longest diameter greater than 10 pm is A degrees, and 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 between any two of the above values. The thickness of the negative electrode current collector is B pm, 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 between any two of the above values. When the value of A is too small, for example less than 0.80, the spheroidization degree of the silicon-carbon material is relatively low, and there are many edges and corners, which are easy to pierce into the negative electrode current collector, causing the electronic transmission channel of the negative electrode current collector to be 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, causing the cost of the secondary battery to increase. When the value of 3.14 / A-0.048B is too large, for example greater than 3.7, the spheroidization degree of the silicon-carbon material is relatively low compared to the thickness of the negative electrode current collector, and the edges and corners of the silicon-carbon material particles pierce into the negative electrode current collector to a relatively deep depth, causing the electronic transmission channel of the negative electrode current collector to be damaged, and even to be punctured, thereby affecting the charge rate and discharge rate of the secondary battery. Therefore, by adjusting the value of 3.14 / A-0.048B within the above range, the spheroidization degree of the silicon-carbon material and the thickness of the negative electrode current collector are matched with each other, the silicon-carbon material particles will not pierce the negative electrode current collector, and the problem of the edges and corners of the silicon-carbon material affecting the electronic transmission channel of the negative electrode current collector is improved, thereby the charge rate and discharge rate of the secondary battery are improved.

[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, B can be 3.5, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 17, 19, 20, or a range between any two of these values. By adjusting the value of B within the above range, the negative electrode current collector has a suitable thickness, which matches the spheroidization degree of the silicon-carbon material, and improves the problem that the edges and 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 6-20 μm, and the tensile breaking strength F of the negative electrode current collector is 451-950 MPa. In some embodiments of the present application, the tensile breaking strength F of the negative electrode current collector is 470-700 MPa. For example, the tensile breaking strength F can be 451 MPa, 460 MPa, 470 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, 900 MPa, 950 MPa, or a range between any two of these values. The tensile breaking strength F of the negative electrode current collector within the above range indicates that the negative electrode current collector has a good tensile breaking strength, and when the edges and corners of the silicon-carbon material particles pierce the negative electrode current collector, the negative electrode current collector is not easily broken and has a small effect on the electron transmission channel thereof, thereby facilitating the improvement of the charge rate and discharge rate of the secondary battery.

[0035] In the present application, negative electrode current collectors with different thicknesses and tensile breaking strengths can be purchased, and the desired negative electrode current collector with a certain thickness and tensile breaking strength can be selected by combining the test methods of "Test of the thickness B of the negative electrode current collector" and "Test of the tensile breaking strength F of the negative electrode current collector" provided in the present application.

[0036] In some embodiments of the present application, the minimum angle of the cross-sectional profile of the 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 between any two of these values. The minimum angle of the cross-sectional profile of the particles with a particle diameter greater than or equal to 10 μm is more representative, and α within the above range indicates that the silicon-carbon material particles have no sharp edges and corners, thereby not easily piercing the negative electrode current collector and having a small effect on the electron transmission channel of the negative electrode current collector, thereby facilitating the improvement of the charge rate and discharge rate of the secondary battery.

[0037] In the present application, the minimum angle a of the cross-section profile of the silicon-carbon material particle refers to the minimum value of the angle of the corner of the outer profile formed by the cross-section of the particle, and the angle of the corner refers to the angle between the tangent lines drawn along the edges of the corner. Specifically, FIG. 1 is a schematic diagram of the structure of the outer profile formed by the cross-section of the silicon-carbon material particle, a1 is 115°, a2 is 108°, a3 is 142°, and a4 is 140°, and the minimum angle a of the cross-section profile is 108°.

[0038] In some embodiments of the present application, the mass percentage content W1 of silicon element in the silicon-carbon material is 40% to 54%. For example, the mass percentage content W1 of silicon element can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, or a range between any two of the above values. By adjusting the mass percentage content W1 of silicon element 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, thereby facilitating the improvement of the charge rate and discharge rate of the secondary battery, and the secondary battery also has a high energy density.

[0039] In some embodiments of the present application, the mass percentage content W2 of 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 oxygen element in the silicon-carbon material is 0.01% to 1.5%. For example, the mass percentage content W2 of 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 between any two of the above values. By adjusting the mass percentage content W2 of oxygen element within the above range, the obtained silicon-carbon compound is less likely to have a side reaction with the electrolyte, thereby facilitating the improvement of the initial coulombic efficiency of the secondary battery.

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

[0041] The second aspect of the present application provides a preparation method of the secondary battery in any of the foregoing embodiments, which comprises the following steps: preparing a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, and assembling to obtain a secondary battery.

[0042] The preparation method of the silicon-carbon material in the negative electrode sheet comprises the following steps:

[0043] (1) mixing phenolic compound, formaldehyde, ammonia gas with water, uniformly mixing, then carrying out heat preservation reaction, adding emulsifier, uniformly mixing, then carrying out temperature rising reaction to obtain porous carbon precursor. Wherein, the molar ratio X of phenolic compound, formaldehyde, ammonia gas is 1:(1.5 to 2.5):(0.006 to 0.012), the phenolic compound includes at least one of phenol, cresol, nonyl phenol, aralkyl phenol, cashew phenol, octyl phenol, bisphenol A, dimethyl phenol; the temperature T1 of heat preservation reaction is 50℃ to 70℃, the time t1 is 2h to 7h; the mass ratio Y of emulsifier and phenolic compound is (0.08 to 0.13):1; the temperature T2 of temperature rising reaction is 80℃ to 120℃, 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 between any two values. For example, the temperature T1 can be 50℃, 60℃, 65℃, 70℃, or a range between any two values. For example, the time t1 can be 2h, 3h, 4h, 5h, 6h, 7h, or a range between any two values. 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 between any two values. For example, the temperature T2 can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, or a range between any two values. For example, the time t2 can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or a range between any two values.

[0045] (2) carrying out carbonization treatment on the porous carbon precursor under inert atmosphere, then carrying out activation treatment in the atmosphere containing the first compound to obtain the porous carbon matrix, the first compound includes carbon dioxide or water vapor. Wherein, the temperature T3 of carbonization treatment is 450℃ to 700℃, 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, the temperature T4 of activation treatment is 750℃ to 1000℃, the time t4 is 6h to 20h.

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

[0047] (3) The porous carbon substrate is pretreated in an inert atmosphere, then treated in a silane-containing atmosphere, then subjected to a temperature rising and holding treatment, and then treated in a second compound-containing atmosphere to obtain a silicon-carbon material, the second compound including acetylene, propylene, or toluene. The pretreatment temperature T5 is 420℃ to 550℃, and the pretreatment 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 aeration time t6 is 220min to 480min. The temperature T7 of the temperature rising and holding treatment is 450℃ to 600℃, and the time t7 is 0.5h to 2h. The flow rate V3 of the second compound in the second compound-containing atmosphere is 3L / min to 10L / min, and the aeration 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 defined by any two of them. For example, the time t5 can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or a range defined by any two of them. 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 defined by any two of them. For example, the aeration time 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 defined by any two of them. For example, the temperature T7 can be 450°C, 475°C, 500°C, 525°C, 550°C, 575°C, 600°C, or a range defined by any two of them. For example, the time t7 can be 0.5 h, 0.7 h, 0.9 h, 1 h, 1.2 h, 1.4 h, 1.5 h, 1.7 h, 2 h, or a range defined by any two of them. For example, the flow rate V3 can be 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, or a range defined by any two of them. For example, the aeration time t8 can be 160 min, 180 min, 200 min, 225 min, 250 min, 275 min, 300 min, 325 min, 350 min, 375 min, 400 min, or a range defined by any two of them.

[0049] The particle sharp corners of the porous carbon precursor obtained by the above step (1) are less, which is beneficial to obtaining a high spheroidization degree of the silicon-carbon compound. The activation treatment in step (2) makes the pores in the interior of the porous carbon precursor more abundant, and the obtained porous carbon matrix is beneficial to the subsequent deposition of the silicon material. In step (3), the temperature uniformity of the porous carbon can be improved by pretreatment, which is beneficial to the uniform deposition of silane in different porous carbon particles; then the silicon material is deposited in the pores of the porous carbon matrix by passing in silane gas; the temperature uniformity of the porous carbon after deposition of silicon can be improved by heat preservation, which is beneficial to the uniform decomposition and coating of the carbon source gas on the surface of different porous carbon particles; finally, the surface of the silicon material with high activity is covered with carbon material by passing in a gas containing a second compound, which prevents the silicon material from being oxidized in the air environment and improves the stability of the silicon-carbon material. Thus, the spheroidization degree A of the silicon-carbon material is 0.80 to 0.98, and the value of A and 3.14 / A-0.048B is within the above range when the negative electrode current collector has a thickness of B μm. The spheroidization degree of the silicon-carbon material matches the thickness of the negative electrode current collector, the silicon-carbon material particles do not pierce the negative electrode current collector, and the problem of the edges and corners of the silicon-carbon material affecting the electron transport channel of the negative electrode current collector is improved, thereby improving the charge rate and discharge rate of the secondary battery.

[0050] The content of water added in step (1) is not particularly limited in the present application, 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 gas composition and flow rate in the inert atmosphere in steps (2) and (3) are not limited in the present application, 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 the present application, the "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector, or can be provided on two surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" herein can be the entire area of the surface of the negative electrode current collector, or can be part of the area of the surface of the negative electrode current collector, and the present application is not particularly limited, as long as the purpose of the present application can be achieved.

[0052] The negative electrode current collector is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, 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 silicon-carbon compound described above can be used as a negative active material in the negative material layer, and the negative material layer can further include other negative active materials, which are not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the other negative active materials can include, but are not limited to, at least one of natural graphite, artificial graphite, meso-carbon microbead, hard carbon, soft carbon, silicon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 or Li-Al alloy.

[0054] In some embodiments of the present application, the negative material layer can further include a conductive agent and a binder, and the types of the conductive agent and the binder are not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotube (CNT), carbon fiber, flake graphite, graphene, metal material, or conductive polymer, and the conductive carbon black can include, but is not limited to, at least one of acetylene black or Ketjen black. The carbon nanotube described above can include, but is not limited to, single-walled carbon nanotube and / or multi-walled carbon nanotube. The carbon fiber described above can include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanocarbon fiber. The metal material described above can include, but is not limited to, metal powder and / or metal fiber, and specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The conductive polymer described above can include, but is not limited to, at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the binder can include, but is not limited to, at least one of 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, polyvinylpyrrolidone, polyethylene, polypropylene, acrylated styrene butadiene rubber, epoxy resin, or nylon, or polyvinylidene fluoride. The mass ratio of the negative active material, the conductive agent, and the binder in the negative material layer is not particularly limited in the present application, and those skilled in the art can select them according to actual needs as long as the purpose of the present application can be achieved.

[0055] The thickness of the negative material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved, and for example, the thickness of the negative material layer is 30 μm to 120 μm. The thickness of the negative current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, and for example, the thickness of the negative current collector is 4 μm to 15 μm.

[0056] Optionally, the negative electrode sheet can further include a conductive layer between the negative current collector and the negative material layer. The composition of the conductive layer is not particularly limited in the present application and can be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application and can be at least one of the above-mentioned conductive agent and the above-mentioned binder.

[0057] In the present application, the positive electrode sheet includes a positive current collector and a positive material layer disposed on at least one surface of the positive current collector. The above-mentioned "positive material layer disposed on at least one surface of the positive current collector" means that the positive material layer can be disposed on one surface of the positive current collector in the thickness direction of the positive current collector, or can be disposed on both surfaces of the positive current collector in the thickness direction of the positive current collector. It should be noted that the "surface" here can be the entire area of the surface of the positive current collector, or can be part of the area of the surface of the positive current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved.

[0058] The positive current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), etc.

[0059] The positive material layer includes a positive active material, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the positive active material can include but is not limited to at least one of nickel-cobalt-manganese lithium phosphate (for example, NCM811, NCM622, NCM523, NCM111), nickel-cobalt-aluminum lithium phosphate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate.

[0060] The positive material layer can further include a conductive agent and a binder, and the types of the conductive agent and the binder are not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The mass ratio of the positive active material, the conductive agent, and the binder in the positive material layer is not particularly limited in the present application, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

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

[0062] Optionally, the positive electrode tab can further include an electrically conductive layer between the positive electrode current collector and the positive electrode material layer. The composition of the electrically conductive layer is not particularly limited and can be an electrically conductive layer commonly used in the art. The electrically conductive layer includes an electrically conductive agent and a binder. The electrically conductive agent and the binder in the electrically conductive layer are not particularly limited in the present application and can be, for example, at least one of the electrically conductive agents and the binders described above.

[0063] In the present application, the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator can include at least one of a woven film, a nonwoven film, a microporous film, a composite film, a calendered film, or a spunlaid film.

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

[0065] Optionally, at least one surface of the base material layer is provided with a surface treatment layer, which can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0066] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited in the present application and can include, for example, 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 binder is not particularly limited in the present application and can include, for example, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, 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, polyacrylate, 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 object of the present application can be achieved, for example, the thickness of the separator can be 3 μm to 30 μm.

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

[0069] The present application does not particularly limit the lithium salt as long as the object of the present application can be achieved. For example, the lithium salt can 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(oxalato)borate (LiBOB), or lithium difluoroborate. The present application does not particularly limit the content of the lithium salt in the electrolyte as long as the object of the present application can be achieved.

[0070] The present application does not particularly limit the nonaqueous solvent as long as the object of the present application can be achieved, for example, the nonaqueous solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or other organic solvents.

[0071] The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The cyclic carbonate compound can 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 fluoro-carbonate compound can include, but is not limited to, at least one of fluoro-ethylene carbonate (FEC), 1,2-difluoro-ethylene carbonate, 1,1-difluoro-ethylene carbonate, 1,1,2-trifluoro-ethylene carbonate, 1,1,2,2-tetrafluoro-ethylene carbonate, 1-fluoro-2-methyl-ethylene carbonate, 1-fluoro-1-methyl-ethylene carbonate, 1,2-difluoro-1-methyl-ethylene carbonate, 1,1,2-trifluoro-2-methyl-ethylene carbonate, or trifluoromethyl-ethylene carbonate. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound can 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 other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application, as long as the object of the present application is achieved.

[0072] In the present application, the secondary battery further includes a case for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art of secondary batteries, which are not limited in the present application. The case is not particularly limited in the present application, and can be a case known in the art, as long as the object of the present application is achieved. For example, the case can be a hard case or a flexible case. The material of the hard case can be a metal, and the kind of the metal is not limited in the present application, and a metal hard case known in the art can be used, as long as the object of the present application is achieved. The flexible case can be a metal-plastic film, such as an aluminum-plastic film, a steel-plastic film, or the like.

[0073] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, the preparation process of the secondary battery can 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, etc. as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly into the case, injecting the electrolyte into the case and sealing to obtain the secondary battery. Alternatively, the positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly of a stack structure, the electrode assembly is placed into the case, the electrolyte is injected into the case and sealed to obtain the secondary battery. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the case as needed, thereby preventing the pressure inside the secondary battery from rising, overcharging and discharging.

[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] The third aspect of the present application provides an electronic device including the secondary battery of any one of the preceding embodiments or the secondary battery prepared by the preparation method of any one of the preceding embodiments.

[0076] The present application is not particularly limited in terms of the type of electronic device, which can be any electronic device known in the art. In some embodiments of the present application, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0077] Examples

[0078] Hereinafter, examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0079] Test methods and apparatus:

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

[0081] 0.47 g silicon-carbon material and 0.396 g polyacrylic acid were dispersed in water, mixed in a homogenizer and then coated on the surface of a copper foil using a doctor blade. After drying, the sample was sliced using an ion polisher (JEOL / IB-09010CP). The cross-section micrograph of the silicon-carbon material was taken using a ZEISS-SEM (sigma-02-33). The profile of the cross-section of the silicon-carbon material particles with a diameter greater than or equal to 10 μm was selected for analysis. The average of the degrees of the smallest angles in the profiles of 50 particles was calculated as the final result. The diameter of the silicon-carbon material particles refers to the maximum value between two points in the profile of the cross-section of the particles.

[0082] Test of the degree of spheroidization A of the silicon-carbon material particles with a longest diameter greater than 10 μm:

[0083] The degree of spheroidization of the material was tested using the equivalent diameter method. The cross-section of the silicon-carbon material in the negative electrode plate along the thickness direction was observed using a ZEISS-SEM (sigma-02-33) scanning electron microscope. The incomplete particles were removed, and the equivalent diameter of the circumference and the equivalent diameter of the area of the complete particles were calculated and averaged to calculate the degree of spheroidization. The degree of spheroidization = equivalent diameter of circumference / equivalent diameter of area. The complete particles in the above test were particles with a longest diameter greater than 10 μm. The longest diameter of the silicon-carbon material particles refers to the maximum value between two points in the profile of the cross-section of the particles.

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

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

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

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

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

[0089] The thickness of the negative electrode current collector was tested at 10 random positions using a micrometer, and the average value was taken as the final result.

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

[0091] The breaking strength F of the negative electrode current collector is tested according to the standard GB / T 5230-1995 Electrolytic Copper Foil Tensile Strength, Elastic Modulus, Elongation at Break Test.

[0092] Lithium ion battery discharge rate performance test:

[0093] At 25°C, under normal pressure, the prepared lithium ion battery is discharged at a rate of 0.2C to 3.0V, and then rested for 5min; charged at a rate of 0.5C to 4.5V, and then charged at a constant voltage of 4.5V to 0.05C, and then rested for 5min; discharged at a rate of 0.2C to 3.0V, and then rested for 5min, and then the discharge capacity of this step is recorded as C1. Charged at a rate of 0.2C1 to 4.5V, and then charged at a constant voltage of 4.5V to 0.05C, and then rested for 5min, and then the charge capacity of this step is recorded as C2; discharged at a rate of 2C1 to 3.0V, and then the discharge capacity of this step is recorded as C3.

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

[0095] Lithium ion battery charge rate performance test

[0096] At 25°C, under normal pressure, the prepared lithium ion battery is discharged at a rate of 0.2C to 3.0V, and then rested for 5min; charged at a rate of 0.5C to 4.5V, and then charged at a constant voltage of 4.5V to 0.05C, and then rested for 5min; discharged at a rate of 0.2C to 3.0V, and then rested for 5min, and then the discharge capacity of this step is recorded as C1. Charged at a rate of 0.2C1 to 4.5V, and then charged at a constant voltage to 0.05C, and then rested for 5min, and then the charge capacity of this step is recorded as C2;

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

[0098] Example 1

[0099] Preparation of silicon-carbon material

[0100] (1) The phenolic compound m-phenol, formaldehyde, and ammonia gas are mixed according to a molar ratio X of 1:2.0:0.01, water is added to the mixture, and the mixture is uniformly mixed and then subjected to a heat preservation reaction. The amount of water added is 10 times the mass of the phenolic compound, the temperature T1 of the heat preservation reaction is 60°C, and the time t1 is 6h. Then, the emulsifier F127 is added, the mass ratio Y of the emulsifier to the phenolic compound is 0.08:1, the mixture is stirred for 1h, and then subjected to a temperature elevation reaction. The temperature T2 of the temperature elevation reaction is 100°C, and the time t2 is 4h. After the reaction is completed, the solution after the reaction is filtered and washed to obtain a porous carbon precursor.

[0101] (2) 1000 g of the porous carbon precursor is subjected to carbonization treatment under a nitrogen atmosphere at a flow rate of 2 L / min, and the carbonization treatment is performed at a temperature T3 of 600 °C for a time t3 of 3 h; the temperature is then raised, and activation treatment is performed in an atmosphere containing a first compound to obtain a porous carbon matrix, the first compound being carbon dioxide, the flow rate V1 of the first compound gas being 3 L / min, and the activation treatment being performed at a temperature T4 of 930 °C for a time t4 of 20 h.

[0102] (3) 1000 g of the porous carbon matrix is added to a fluidized bed reactor, and subjected to pretreatment under a nitrogen atmosphere at a flow rate of 10 L / min, and the pretreatment is performed at a temperature T5 of 480 °C for a time t5 of 1 h; then a gas containing silane is introduced, the silane in the gas containing silane being methylsilane, the flow rate V2 of the silane being 2 L / min, and the time t6 for which the gas is introduced being 340 min; then the temperature is raised and holding treatment is performed, the holding treatment being performed at a temperature T7 of 500 °C for a time t7 of 1 h; then treatment is performed in an atmosphere containing a second compound to obtain a silicon-carbon material, the second compound being acetylene, the flow rate V3 of the second compound gas being 8 L / min, and the time t8 for which the gas is introduced being 300 min.

[0103] <Preparation of a negative electrode sheet>

[0104] The silicon-carbon material prepared above and artificial graphite are mixed in a mass ratio of 1:9 to serve as a negative electrode active material. The negative electrode active material, carbon nanotubes, lithium carboxymethyl cellulose, and lithium polyacrylate are added to deionized water as a solvent in a mass ratio of 97.4:0.2:0.4:2 to prepare a slurry having a solid content of 45 wt%, and a negative electrode slurry having a viscosity of 6000 mPa.s is obtained by stirring the mixture in a vacuum mixer. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil having a thickness of 6 μm, and dried at 120 °C to obtain a negative electrode sheet having a single negative electrode material layer coated on one surface, the coated weight of the negative electrode material layer being 100.1 mg / 1540 mm 2 . The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet having a double negative electrode material layer coated on both surfaces. After cold pressing, cutting, slitting, and welding of the tabs, a negative electrode sheet having a size of 661 mm x 78 mm is obtained for use. The thickness of the single negative electrode material layer is 54.5 μm. 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 gravimetric capacity of the negative electrode active material is 480 mAh / g.

[0105] <Preparation of a positive electrode sheet>

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

[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), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 5:10:15:20:50 to obtain an organic solvent, and then electrolyte salt LiPF6 was added to the organic solvent and mixed uniformly to obtain an electrolyte. The mass percentage of the electrolyte salt was 12.5% based on the mass of the electrolyte, and the rest was the organic solvent.

[0109] <Separator>

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

[0111] <Preparation of lithium ion battery>

[0112] The positive electrode foil, the separator, and the negative electrode foil prepared above were stacked in order, with the separator between the positive electrode foil and the negative electrode foil to act as a barrier, and the electrode assembly was obtained by winding. The electrode assembly was placed in an aluminum-plastic film packaging bag, and the water was removed at 80 °C. The electrolyte prepared above was injected, and the lithium ion battery was obtained after vacuum packaging, standing, formation, degassing, and edge cutting. The upper limit of the formation voltage was 4.15 V, the formation temperature was 70 °C, and the standing time for formation was 2 h.

[0113] Examples 2 to 15

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

[0115] Comparative Examples 1 to 2

[0116] The rest is the same as Example 1 except that no emulsifier is added and the relevant preparation parameters are adjusted according to Table 1.

[0117] Comparative Example 3 to Comparative Example 5

[0118] The rest is the same as Example 1 except that the relevant preparation parameters are adjusted according to Table 1.

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

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

[0121] As can be seen from Example 1 to Example 15, the minimum angle a of the cross-sectional profile of the silicon-carbon material, the mass percentage of silicon element W1, and the mass percentage of oxygen element W2 change with the change of the preparation parameters, and when the silicon-carbon compound is prepared by the preparation method in the present application, the above parameters are all within the range of the present application, and the obtained lithium ion battery has high charge rate and discharge rate.

[0122] Specifically, FIG. 2 is a silicon-carbon compound prepared in Example 9, and as can be seen from the figure, the cross section of the silicon-carbon compound particle is close to a circle, and the minimum angle a of the cross-sectional profile of the silicon-carbon compound particle is measured to be 179.2.

[0123] As can be seen from Example 1 to Example 15, the thickness B and tensile breaking strength F of the negative electrode current collector are positively correlated, which will affect the charge rate and discharge rate of the secondary battery, and when the thickness B and tensile breaking strength F of the negative electrode current collector are within the range of the present application, the obtained lithium ion battery has high charge rate and discharge rate.

[0124] It should be noted that in this document, the terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method or article including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method or article.

[0125] The above description is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator; the negative electrode comprising a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, the negative electrode material layer comprising a silicon-carbon material; wherein the sphericity A of the particles with a longest diameter greater than 10 μm in the silicon-carbon material 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 breaking 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 with a diameter greater than or equal to 10 μm in the silicon-carbon material is 107.8°≤α≤179.2°.

5. The secondary battery according to any one of claims 1 to 4, wherein, The silicon-carbon material contains 40% to 54% silicon by mass.

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

7. The secondary battery according to any one of claims 1 to 6, wherein, A ranges from 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: The positive electrode, the negative electrode, the separator, and the electrolyte are prepared and then assembled to obtain the secondary battery. The method for preparing the silicon-carbon material in the negative electrode sheet includes the following steps: (1) Phenolic compounds, formaldehyde, ammonia and water are mixed and then subjected to a heat preservation reaction. Emulsifier is added and mixed evenly before a heating reaction is carried out 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). The phenolic compound includes at least one of phenol, cresol, nonylphenol, aralkylphenol, cashew phenol, 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 of the emulsifier to the phenolic compound is (0.08 to 0.13):

1. The temperature T2 of the heating reaction is 80°C to 120°C, and the time t2 is 1h to 5h. (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. The first compound includes carbon dioxide or water vapor. The carbonization treatment temperature T3 is 450℃ to 700℃, 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 activation treatment temperature T4 is 750℃ to... 1000℃, time t4 is 6h to 20h; (3) The porous carbon matrix is ​​pretreated in an inert atmosphere, then treated in a silane-containing atmosphere, then heated and kept at a high temperature, and then treated in an atmosphere containing a second compound to obtain the silicon-carbon material. The second compound includes acetylene, propylene or toluene. 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 methylsilane, diethylsilane, propane, 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 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 a secondary battery according to any one of claims 1 to 8 or a secondary battery prepared by the preparation method described in claim 9.

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