Negative electrode sheet, secondary battery and electrical device

Abstract

This disclosure relates to a negative electrode sheet, a secondary battery, and an electrical device. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, the negative electrode film layer having a first surface away from the negative electrode current collector and a second surface positioned opposite the first surface, the thickness of the negative electrode film layer being H, the region within a thickness range of 0.3H from the first surface of the negative electrode film layer being defined as a first region of the negative electrode film layer, and the region within a thickness range of 0.3H from the second surface of the negative electrode film layer being defined as a second region of the negative electrode film layer, the first region comprising a first silicon-based material in a spherical shape and / or near-spherical shape. The negative electrode sheet can reduce its own expansion rate and improve the cycle stability and storage performance of the battery.

Description

Technical Field

[0001] (Cross - reference to related applications) This application claims the priority of a Chinese patent application with the invention title "Negative electrode sheet, secondary battery and electrical device", application number 202311640889.5, filed on November 30, 2023, and all its contents are incorporated herein by reference.

[0002] This application relates to the technical field of secondary batteries, and in particular, to negative electrode sheets, secondary batteries and electrical devices.

Background Art

[0003] In recent years, secondary batteries have been widely applied in various fields such as energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, and electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. [[ID=***]]

[0004] [[ID=***]] Silicon - based negative electrode active materials are an effective means to improve the capacity of secondary batteries. However, the negative electrode sheet containing silicon - based materials has the disadvantages of a high expansion rate of the electrode sheet, poor battery cycle life, and poor high - temperature storage performance. Therefore, there is still room for improvement in the conventional negative electrode sheet containing silicon - based materials.

Summary of the Invention

[0005] This application is made in view of the above problems, and aims to provide a negative electrode sheet that can reduce its own expansion rate and improve the cycle stability and high - temperature storage performance of the battery.

[0006] It should be noted that there are some consecutive tags with the same content in the original text which seem to be duplicates. I have translated them as they are in the provided text. If this is an error in the original, it may need to be corrected for a more accurate translation work.A first aspect of the present application includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector. The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface disposed opposite the first surface. Let the thickness of the negative electrode film layer be H, the region within the thickness range from 0.3H from the first surface of the negative electrode film layer be the first region of the negative electrode film layer, and the region within the thickness range from 0.3H from the second surface of the negative electrode film layer be the second region of the negative electrode film layer. The first region provides a negative electrode sheet containing a spherical or / and near-spherical first silicon-based material.

[0007] Currently, the main negative electrode active materials of lithium-ion batteries that are mainstream are artificial graphite and natural graphite. However, since the theoretical specific capacity of silicon-based materials is much larger than that of graphite, the energy density of secondary batteries can be improved by using silicon-based materials as the negative electrode active material. By including a spherical or near-spherical silicon-based material in the first region that is in direct contact with the cold pressing roll and the electrolyte, the pressure density window of the electrode sheet can be widened, the required cold pressing pressure at the same pressure density becomes smaller, the probability that the silicon-based material cracks during the cold pressing process is reduced, the integrity of the silicon-based material particles is maintained, the generation of new interfaces is reduced, and it is advantageous to avoid the irreversible consumption of active ions due to the contact between the active silicon exposed from the silicon-based material and the electrolyte during cycling. Also, because the silicon-based material is spherical or near-spherical, the stress concentration of the silicon-based material during roll pressing and expansion is reduced, the phenomenon of the silicon-based material cracking is further reduced, thereby comprehensively reducing the expansion rate of the electrode sheet and improving the storage performance and cycle stability of the battery.

[0008] In any embodiment, the second region includes a second silicon-based material, and the average particle diameter of the second silicon-based material is smaller than the average particle diameter of the first silicon-based material.

[0009] In the first region of the negative electrode sheet that is in direct contact with the electrolyte, using a first silicon-based material with a large average particle size reduces the specific surface area of ​​the first silicon-based material, thereby reducing the loss of active ions due to the reaction between the silicon-based material and the electrolyte after direct contact, reducing the expansion rate of the electrode sheet, and improving the battery's storage performance and cycle stability. In the second region of the negative electrode sheet that is close to the current collector, using a second silicon-based material with a small average particle size and a short ion transport distance in the solid phase is advantageous for improving the transport performance of active ions and electrons, and thus improving the rapid charging performance of the battery. Furthermore, the second silicon-based material with a small average particle size has a larger specific surface area, which strengthens the interaction between the binder and the silicon-based material, thereby further reducing the expansion of the electrode sheet and improving the battery's storage performance and cycle stability.

[0010] In any embodiment, the percentage content of silicon element by mass relative to the total mass of the first silicon-based material is lower than the percentage content of silicon element by mass relative to the total mass of the second silicon-based material.

[0011] By using a first silicon-based material in the first region that comes into direct contact with the cold press rolls and electrolyte, the silicon content that comes into contact with the electrolyte when the silicon-based material cracks is reduced, thereby mitigating the expansion of the electrode sheet and improving the battery's cycle stability and storage performance. Combining a second silicon-based material with a high silicon content with a first silicon-based material with a low silicon content is advantageous for achieving a battery that exhibits low expansion, good cycle stability, and high energy density.

[0012] In any embodiment, the specific surface area of ​​the first silicon-based material is smaller than the specific surface area of ​​the second silicon-based material.

[0013] The first silicon-based material has a small specific surface area, which reduces the loss of active ions due to the reaction between the silicon-based material and the electrolyte, thereby mitigating the expansion of the electrode sheet and improving the battery's cycle stability and storage performance. The second silicon-based material has a large specific surface area, which strengthens the interaction between the binder and the silicon-based material, thereby reducing the expansion of the electrode sheet. By using the first and second silicon-based materials in combination, the battery can achieve both low expansion and excellent cycle stability and storage performance.

[0014] In any embodiment, the crystallinity of the first silicon-based material is lower than that of the second silicon-based material.

[0015] Amorphous silicon-based materials have better cycle stability than crystalline silicon-based materials, and therefore, having a low degree of crystallinity in the first silicon-based material is advantageous for improving the cycle stability of the battery.

[0016] In any embodiment, a constant current charge-discharge test is performed on a first silicon-based material using a button cell, and a differential capacitance curve at the lithium desorption stage is created that reflects the relationship between dQ / dV and voltage V. If the maximum value of the differential dQ / dV between 0.27V and 0.34V is defined as V1 and the maximum value of the differential dQ / dV between 0.43V and 0.55V is defined as V2, then 1.55 ≤ V1 / V2 ≤ 1.75. Selectively, 1.60 ≤ V1 / V2 ≤ 1.72.

[0017] When the V1 / V2 of the first silicon-based material is within the above range, high-voltage platforms are less likely to form, which is advantageous for maintaining the structural stability of the silicon-based material and improving the battery's cycle stability.

[0018] In any embodiment, the first silicon-based material and / or the second silicon-based material comprises a silicon-carbon material comprising carbon matrix particles having a porous structure and nanosilicon-based material provided within the porous structure.

[0019] When a silicon-carbon material has a structure consisting of carbon matrix particles with a porous structure and nanosilicon-based material provided within the porous structure, the carbon matrix particles with the porous structure have a certain inhibitory effect against the expansion of the nanosilicon-based material that occurs during the cycle. This improves the structural stability of the silicon-carbon material, thereby increasing the battery capacity and achieving both excellent storage performance and cycle stability.

[0020] In any embodiment, the Dv50 of the first silicon-based material is 9 μm to 11 μm, and selectively 9.5 μm to 10 μm.

[0021] When the Dv50 of the first silicon-based material satisfies the above range, the loss of active ions due to the reaction after direct contact between the silicon-based material and the electrolyte can be reduced, the expansion of the electrode sheet can be reduced, and the storage performance and cycle stability of the battery can be improved.

[0022] In any embodiment, the percentage content of silicon element mass relative to the total mass of the first silicon-based material is 40% to 60%, and selectively 45% to 50%.

[0023] When the mass percentage content of silicon elements in the first silicon-based material is within the above range, it is possible to reduce the amount of silicon that comes into contact with the electrolyte when the silicon-based material cracks, thereby mitigating the expansion of the electrode sheet, maintaining the integrity of the silicon-based material particles, ensuring excellent battery capacity, and improving the battery's cycle stability.

[0024] In any embodiment, the specific surface area of ​​the first silicon-based material is 0.8 m². 2 / g~5m 2 It is / g, and selectively 1.1m 2 / g~3.2m 2 It is / g.

[0025] If the specific surface area of ​​the first silicon-based material is within the above range, the loss of active ions due to the reaction between the silicon-based material and the electrolyte can be reduced, the expansion of the electrode sheet can be reduced, and the cycle stability and storage performance of the battery can be improved.

[0026] In any embodiment, the second silicon-based material includes a block-like form.

[0027] The fact that the second silicon-based material is in a block form provides excellent battery performance and reduces the manufacturing cost of the electrode sheets.

[0028] In any embodiment, the Dv50 of the second silicon-based material is 5 μm to 6 μm, and selectively 5.2 μm to 5.6 μm.

[0029] If the Dv50 of the second silicon-based material is within the above range, it is advantageous for improving the transport performance of active ions and electrons, and for improving the rapid charging performance of the battery.

[0030] In any embodiment, the percentage content of silicon element mass relative to the total mass of the second silicon-based material is 45% to 65%, and selectively 47% to 55%.

[0031] When the mass percentage content of silicon element in the second silicon-based material is within the above range, it is advantageous for improving the battery capacity.

[0032] In any embodiment, the specific surface area of ​​the second silicon-based material is 0.8 m². 2 It is greater than / g and selectively 1.1m 2 / g~3.2m 2 It is / g.

[0033] If the specific surface area of ​​the second silicon-based material is within the above range, the interaction between the binder and the silicon-based material is enhanced, thereby reducing the expansion of the electrode sheet.

[0034] In any embodiment, the second silicon-based material contains silicon crystal particles, the crystallite size of the silicon crystal particles is 5 nm or less, and selectively 2 nm to 3 nm.

[0035] By keeping the silicon crystal particle size within the above range, it is possible to avoid excessive localized silicon element enrichment due to excessive crystallite size, which would cause significant expansion during lithium insertion and degrade the battery's storage performance and cycle stability. By using a combination of the first and second silicon-based materials, it is possible to mitigate the degradation of battery performance due to crystallization, which occurs because the surface of the second silicon-based material, with its smaller particle size, tends to become silicon-rich.

[0036] In any embodiment, a constant current charge-discharge test is performed on a second silicon-based material using a button cell, and a differential capacitance curve at the lithium desorption stage is created that reflects the relationship between dQ / dV and voltage V. If the maximum value of the differential dQ / dV between 0.27V and 0.34V is defined as VA, and the maximum value of the differential dQ / dV between 0.43V and 0.55V is defined as VB, then 0.8 ≤ VA / VB ≤ 1.3, and selectively, 0.8 ≤ VA / VB ≤ 1.0.

[0037] Because silicon-based materials with small particle sizes tend to become silicon-rich on their surfaces, crystallization occurs, generating a high-voltage platform. By using a combination of a first-generation silicon-based material and a second-generation silicon-based material, the deterioration of the material's structural stability caused by the high-voltage platform generated by the second-generation silicon-based material can be mitigated, improving the battery's storage performance and cycle stability.

[0038] In any embodiment, the first region further comprises a first carbon material, wherein the Dv50 of the first carbon material is 14 μm to 19 μm.

[0039] In any embodiment, the second region further comprises a second carbon material, the first carbon material and / or the second carbon material comprising at least one of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0040] In any embodiment, the first carbon material comprises artificial graphite.

[0041] Compared to natural graphite, artificial graphite can improve the pressure density of electrode sheets and has excellent cycle stability and storage performance, thereby reducing the expansion of electrode sheets and improving the cycle stability and storage performance of batteries.

[0042] In any embodiment, the mass ratio of the negative electrode film layer in the first region of the first silicon-based material is lower than the mass ratio of the negative electrode film layer in the second region of the second silicon-based material.

[0043] By reducing the proportion of the first silicon-based material in the first region that comes into direct contact with the cold press roll and electrolyte, the amount of silicon that comes into contact with the electrolyte when the silicon-based material cracks can be further reduced, thereby mitigating the expansion of the electrode sheet and improving the battery's cycle stability and storage performance.

[0044] A second aspect of this application further provides a secondary battery including the negative electrode sheet described in the first aspect.

[0045] A third aspect of this application further provides an electrical device including a secondary battery as described in the second aspect. [Brief explanation of the drawing]

[0046] [Figure 1] This is a schematic diagram of one embodiment of the negative electrode sheet of the present application. [Figure 2] This is a scanning electron microscope image of a first silicon-based material according to one embodiment of this application. [Figure 3] This is a scanning electron microscope image of a cross-section of a first region of the negative electrode film layer according to one embodiment of this application. [Figure 4] This is a scanning electron microscope image of a cross-section of a second region of the negative electrode film layer according to one embodiment of this application. [Figure 5] This is the X-ray diffraction spectrum of a first silicon-based material according to one embodiment of this application. [Figure 6] This is the X-ray diffraction spectrum of a second silicon-based material according to one embodiment of this application. [Figure 7] This is the dQ / dV-V curve of a first silicon-based material according to one embodiment of this application. [Figure 8] This is the dQ / dV-V curve of a second silicon-based material according to one embodiment of this application. [Figure 9] This is a schematic diagram of a secondary battery according to one embodiment of the present application. [Figure 10] Figure 9 is an exploded view of a secondary battery according to one embodiment of this application. [Figure 11] This is a schematic diagram of a battery module according to one embodiment of the present application. [Figure 12] This is a schematic diagram of a battery pack according to one embodiment of the present application. [Figure 13] Figure 12 is an exploded view of a battery pack according to one embodiment of this application. [Figure 14] This is a schematic diagram of an electrical device powered by a secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0047] The following describes in detail embodiments of the negative electrode sheet, secondary battery, and electrical device of this application, with appropriate reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of well-known matters and redundant explanations of identical structures may be omitted. This is to avoid unnecessarily verbose explanations, making it easier for those skilled in the art to understand. Furthermore, the drawings and the following explanation are provided to enable those skilled in the art to fully understand this application and are not intended to limit the intent of the claims.

[0048] The “range” disclosed in this application is limited by a lower and upper limit, and a given range is limited by selecting one lower limit and one upper limit, and the boundaries of a particular range are limited by the selected lower and upper limits. Such limited ranges may or may not include endpoint values ​​and can be combined arbitrarily, that is, any lower limit and any upper limit can be combined to form a single range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, the ranges 60-110 and 80-120 are also understood to be predictable. Also, if the minimum range values ​​are 1 and 2 and the maximum range values ​​are 3, 4 and 5, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all predictable. In this application, unless otherwise specified, the numerical range “a-b” represents an abbreviated expression for any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is merely an abbreviated representation of combinations of these numbers. Furthermore, when a parameter is described as being an integer of 2 or more, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technological solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0051] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when the method further includes step (c), it means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), or otherwise.

[0052] Unless otherwise specified, the terms "includes" and "incorporates" in this application represent open-ended expressions, but may also represent closed-ended expressions. For example, the terms "includes" and "incorporates" may further include or incorporate other components not listed, or may include or incorporate only the listed components.

[0053] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the "A or B" condition: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0054] Improving the energy density of batteries is a hot topic in the field of lithium-ion batteries. Silicon has a high theoretical capacity of 4200 mAh / g, making it the lithium-ion battery anode material with the highest known specific capacity. Furthermore, it is abundant and inexpensive, and has been widely studied in recent years as a way to improve the energy density of batteries. The lithium storage mechanism of silicon anode materials is mainly due to the formation of an alloy phase with lithium ions. In actual applications, the large volume expansion of the silicon anode material after lithiumization increases the stress inside the battery, which can cause the silicon anode material to be continuously compressed and crack. Also, during the compaction process of the electrode sheet, some of the silicon anode material may crack, and the silicon exposed to the electrolyte continuously consumes lithium ions in the electrolyte, degrading the battery's storage performance and cycle stability.

[0055] [Negative electrode sheet] Based on this, the present application provides a negative electrode sheet 10, as shown in Figure 1, comprising a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101, wherein the negative electrode film layer 102 has a first surface 102a away from the negative electrode current collector 101 and a second surface 102b positioned opposite the first surface 102a, the thickness of the negative electrode film layer 102 is H, the region within a thickness range from the first surface 102a to 0.3H of the negative electrode film layer 102 is defined as a first region 1022 of the negative electrode film layer, and the region within a thickness range from the second surface 102b to 0.3H of the negative electrode film layer 102 is defined as a second region 1021 of the negative electrode film layer, wherein the first region 1022 comprises a first silicon-based material in a spherical shape and / or near-spherical shape.

[0056] In this application, the method for determining whether a material is spherical or near-spherical can be measured using methods known in the art. For example, silicon-based materials can be observed by taking photographs using a scanning electron microscope. Figure 2 is a scanning electron microscope image of a spherical silicon-based material sample. As shown in Figure 2, it can be clearly confirmed that the silicon-based material is spherical. Alternatively, the electrode sheet can be cut perpendicular to the large surface of the electrode sheet using an Ar ion beam to expose the cross-section, and the cross-section can be photographed and observed using a scanning electron microscope. Figure 3 shows a scanning electron microscope image of the first region of the negative electrode film layer. A spherical or near-spherical silicon-based material can be observed in the first region of the negative electrode film layer.

[0057] In this specification, "silicon-based material" refers to at least one of elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys.

[0058] Currently, the main negative electrode active materials for lithium-ion batteries are artificial graphite and natural graphite. However, since the theoretical specific capacity of silicon materials is far greater than that of graphite, using silicon-based materials as the negative electrode active material can improve the energy density of secondary batteries. By including a silicon-based material with a spherical or near-spherical shape in the first region that comes into direct contact with the cold press rolls and electrolyte, the pressure density window of the electrode sheet can be widened. This reduces the cold press pressure required for the same pressure density, lowers the probability of the silicon-based material cracking during the cold press process, maintains the integrity of the silicon-based material particles, reduces the formation of new interfaces, and is advantageous in avoiding irreversible consumption of active ions due to contact between the active silicon exposed from the silicon-based material and the electrolyte during the cycle. Furthermore, the spherical or near-spherical shape of the silicon-based material reduces stress concentration in the silicon-based material during roll pressing and expansion, further reducing the phenomenon of silicon-based material cracking. This comprehensively reduces the expansion rate of the electrode sheet, improving the battery's storage performance and cycle stability.

[0059] In some embodiments, the second region comprises a second silicon-based material, wherein the average particle size of the second silicon-based material is smaller than the average particle size of the first silicon-based material.

[0060] In this application, the average particle diameter can be measured by methods known in the art. For example, the electrode sheet is cut perpendicular to the large surface of the electrode sheet using an Ar ion beam, the cross-section is exposed, and the cross-section is photographed with a scanning electron microscope. Statistical analysis of the particle diameters of silicon-based materials in the first and second regions is then performed using the long-axis statistical method. However, the average particle diameter is calculated by dividing the sum of the particle diameter values ​​by the total number of particles.

[0061] In the first region of the negative electrode sheet that is in direct contact with the electrolyte, using a first silicon-based material with a large average particle size reduces the specific surface area of ​​the first silicon-based material, thereby reducing the loss of active ions due to the reaction between the silicon-based material and the electrolyte after direct contact, reducing the expansion rate of the electrode sheet, and improving the battery's storage performance and cycle stability. In the second region of the negative electrode sheet that is close to the current collector, using a second silicon-based material with a small average particle size and a short ion transport distance in the solid phase is advantageous for improving the transport performance of active ions and electrons, and thus improving the rapid charging performance of the battery. Furthermore, the second silicon-based material with a small average particle size has a larger specific surface area, which strengthens the interaction between the binder and the silicon-based material, thereby further reducing the expansion of the electrode sheet and improving the battery's storage performance and cycle stability.

[0062] In some embodiments, the percentage content of silicon element mass relative to the total mass of the first silicon-based material is lower than the percentage content of silicon element mass relative to the total mass of the second silicon-based material.

[0063] In this application, the mass percentage content of the element silicon can be measured by methods known in the art. For example, the element silicon content is measured by inductively coupled plasma (ICP) spectroscopy. Specifically, a silicon-based material is used as a sample, the sample is decomposed with aqua regia and hydrofluoric acid (HF), and ICP measurement is performed on the solution after complete decomposition (0.5h decomposition) to obtain the mass percentage content of the element silicon in the silicon-based material.

[0064] By using a first silicon-based material in the first region that comes into direct contact with the cold press rolls and electrolyte, the silicon content that comes into contact with the electrolyte when the silicon-based material cracks is reduced, thereby mitigating the expansion of the electrode sheet and improving the battery's cycle stability and storage performance. Combining a second silicon-based material with a high silicon content with a first silicon-based material with a low silicon content is advantageous for achieving a battery that exhibits low expansion, good cycle stability, and high energy density.

[0065] In some embodiments, the specific surface area of ​​the first silicon-based material is smaller than the specific surface area of ​​the second silicon-based material.

[0066] In this application, the specific surface area can be measured by methods known in the art. For example, the specific surface area is measured by gas adsorption according to the GB / T19587-2017 measurement standard. Specifically, a silicon-based material is used as the sample, the sample tube is immersed in liquid nitrogen at -196°C, and the amount of nitrogen adsorbed onto the solid surface is measured at different relative pressures from 0.05 to 0.30. The amount of monolayer adsorption of the sample is determined based on the BET multilayer adsorption theory and the BET formula, and the specific surface area of ​​the solid is calculated.

[0067] JPEG2026524690000020.jpg21170

[0068] However, n ais the amount of adsorbed gas, with the unit of mol / g. p / p0 is the relative pressure, and n m is the monolayer adsorption amount.

[0069] Since the first silicon-based material has a small specific surface area, the loss of active ions due to the reaction between the silicon-based material and the electrolyte can be reduced, thereby alleviating the expansion of the electrode sheet and improving the cycle stability and storage performance of the battery. Since the second silicon-based material has a large specific surface area, the interaction between the binder and the silicon-based material can be strengthened, thereby reducing the expansion of the electrode sheet. By using the first silicon-based material and the second silicon-based material in combination, the battery can have low expansion and excellent cycle stability and storage performance.

[0070] In some embodiments, the crystallinity of the first silicon-based material is smaller than that of the second silicon-based material.

[0071] In the present application, the crystallinity can be measured by methods known in the art. As an example, an X-ray diffractometer (D8 DISCOVER manufactured by Bruker) is used to measure the crystallinity of the silicon-based material. If no diffraction peak derived from crystallinity appears in the X-ray diffraction spectrum, the material is determined to have an amorphous structure. If sharp diffraction peaks appear in the X-ray diffraction spectrum, the material is determined to have a crystalline structure. The crystallinity of the material is determined based on the intensity of the diffraction peak at the corresponding angle and the full width at half maximum of the diffraction peak. The stronger the diffraction peak and the smaller the full width at half maximum, the higher the crystallinity.

[0072] Since the amorphous silicon-based material has more suitable cycle stability compared to the crystalline silicon-based material, it is advantageous to improve the cycle stability of the battery by having the first silicon-based material with a low crystallinity.

[0073] In some embodiments, a constant current charge-discharge test is performed on the first silicon-based material using a button cell, and a differential capacitance curve at the lithium desorption stage is created that reflects the relationship between dQ / dV and voltage V. If the maximum value of the differential dQ / dV between 0.27V and 0.34V is defined as V1 and the maximum value of the differential dQ / dV between 0.43V and 0.55V is defined as V2, then 1.55 ≤ V1 / V2 ≤ 1.75. In some embodiments, 1.60 ≤ V1 / V2 ≤ 1.72.

[0074] In this specification, the term "differential capacitance curve" refers to the dQ / dV curve, which is an effective tool for analyzing the state of a battery inside the battery, and is a method that allows obtaining internal parameters and states of the battery without disassembling it. The dQ / dV curve is obtained by calculating the change in the battery's capacity at a constant voltage interval, resulting in a dQ / dV-V curve.

[0075] In this application, the dQ / dV curve can be measured by methods known in the art. For example, a test electrode sheet is manufactured by coating copper foil with a slurry of an active material (the negative electrode material), a binder, and conductive carbon black mixed in an 8:1:1 ratio. Lithium metal is used for the electrode. The battery is discharged at a constant current of 0.05C to 5mV, then discharged at a constant voltage of 5mV until the current is less than 50μm, and then charged at a constant current of 0.1C to 1.5V to obtain a constant current charging curve for a button cell. Differential capacitance processing is performed on the constant current charging curve at 0.1C to calculate the change in capacitance at a constant voltage interval and obtain a dQ / dV-V curve.

[0076] In some embodiments, the value of V1 / V2 is any value or any two values ​​from among 1.55, 1.60, 1.65, 1.7, 1.72, and 1.75.

[0077] When the V1 / V2 of the first silicon-based material is within the above range, high-voltage platforms are less likely to form, which is advantageous for maintaining the structural stability of the silicon-based material and improving the battery's cycle stability.

[0078] In some embodiments, the first silicon-based material and / or the second silicon-based material comprises a silicon-carbon material, wherein the silicon-carbon material comprises carbon matrix particles having a porous structure and a nanosilicon-based material provided within the porous structure.

[0079] In this specification, the term "silicon-carbon material" refers to a material composed of two elements: silicon and carbon.

[0080] When a silicon-carbon material has a structure consisting of carbon matrix particles having a porous structure and a nanosilicon-based material provided within the porous structure, the carbon matrix particles having a porous structure have a certain inhibitory effect against the expansion of the nanosilicon-based material that occurs during the cycle, thereby improving the structural stability of the silicon-carbon material, increasing the battery capacity, and achieving both excellent storage performance and cycle stability.

[0081] In some embodiments, the average pore size of the carbon matrix particles is 1.3 nm to 3.2 nm. In some embodiments, the average pore size of the carbon matrix particles is 1.6 nm to 2.4 nm.

[0082] In some embodiments, the average pore diameter of the carbon matrix particle pore structure is within a range of any value or any two values ​​from 1.3 nm, 1.5 nm, 1.7 nm, 1.9 nm, 2.1 nm, 2.3 nm, 2.5 nm, 2.7 nm, 2.9 nm, and 3.2 nm.

[0083] Pores within this pore size range contribute to the adhesion of nanosilicon-based materials and effectively suppress the expansion of nanosilicon-based materials within the pores. Furthermore, the structural destruction of porous carbon matrix particles by expanded silicon nanoparticles is minimal, thereby ensuring the structural stability of the silicon carbon material, reducing the expansion of the electrode sheet, and providing the battery with excellent storage performance and cycle stability.

[0084] In some embodiments, the porosity of the carbon matrix particles is 70% to 89%. In some embodiments, the porosity of the carbon matrix particles is 78% to 84%.

[0085] In some embodiments, the porosity of the carbon matrix particles is in a range consisting of any value or any two values ​​from among 70%, 73%, 76%, 79%, 82%, 85%, and 89%.

[0086] When the porosity of the carbon matrix particles satisfies the above range, the volume occupied by the pores within the carbon matrix particles is relatively large. As a result, the carbon matrix particles interact synergistically with the nanosilicon-based material, improving the battery capacity and allowing the electrode sheet to expand less, thus enabling the battery to have excellent storage performance and cycle stability.

[0087] In some embodiments, the carbon matrix particles include hard carbon.

[0088] In some embodiments, a method for producing a silicon-carbon material includes supplying a gas containing a silicon precursor to carbon matrix particles having a porous structure, and producing a nanosilicon-based material provided in the porous structure from the silicon precursor by chemical vapor deposition to obtain a carbon-silicon material.

[0089] In some embodiments, the silicon precursor is a silane.

[0090] In some embodiments, a method for producing a first silicon-based material includes supplying a gas containing a silicon precursor to spherical and / or near-spherical carbon matrix particles having a porous structure, and generating a nanosilicon-based material to be provided in the porous structure from the silicon precursor by chemical vapor deposition to obtain a spherical and / or near-spherical carbon silicon material.

[0091] In some embodiments, the Dv50 of the first silicon-based material is 9 μm to 11 μm. In some embodiments, the Dv50 of the first silicon-based material is 9.5 μm to 10 μm.

[0092] In this specification, the term "Dv50" refers to the particle size corresponding to the point at which the cumulative volume distribution percentage reaches 50%.

[0093] In this application, Dv50 can be measured by methods known in the art. For example, it can be easily measured using a laser particle size distribution analyzer such as the Mastersizer 2000E laser particle size distribution analyzer manufactured by Malvern Ltd., UK, with reference to the GB / T 19077-2016 particle size distribution laser diffraction method.

[0094] In some embodiments, the Dv50 of the first silicon-based material is in a range consisting of any value or any two values ​​from 9 μm, 9.5 μm, 10 μm, 10.5 μm, and 11 μm.

[0095] When the Dv50 of the first silicon-based material satisfies the above range, the loss of active ions due to the reaction after direct contact between the silicon-based material and the electrolyte can be reduced, the expansion of the electrode sheet can be reduced, and the storage performance and cycle stability of the battery can be improved.

[0096] In some embodiments, the percentage content of silicon element by mass relative to the total mass of the first silicon-based material is 40% to 60%. In some embodiments, the percentage content of silicon element by mass relative to the total mass of the first silicon-based material is 45% to 50%.

[0097] In some embodiments, the percentage content of silicon element mass relative to the total mass of the first silicon-based material is any value or any two values ​​from among 40%, 45%, 50%, 55%, and 60%.

[0098] When the mass percentage content of silicon elements in the first silicon-based material is within the above range, it is possible to reduce the amount of silicon that comes into contact with the electrolyte when the silicon-based material cracks, thereby mitigating the expansion of the electrode sheet, maintaining the integrity of the silicon-based material particles, ensuring excellent battery capacity, and improving the battery's cycle stability.

[0099] In some embodiments, the specific surface area of ​​the first silicon-based material is 0.8 m². 2 / g~5m 2 The specific surface area of ​​the first silicon-based material is 1.1 m² / g. In some embodiments, the specific surface area of ​​the first silicon-based material is 1.1 m². 2 / g~3.2m 2 It is / g.

[0100] In some embodiments, the specific surface area of ​​the first silicon-based material is 0.8 m². 2 / g, 1.4m 2 / g, 1.8m 2 / g, 2.2m 2 / g, 2.6m 2 / g, 3m 2 / g, 3.4m 2 / g, 3.8m 2 / g, 4.2m 2 / g, 4.6m 2 / g, 5m 2 / g is a range consisting of any value or any two values ​​within that range.

[0101] If the specific surface area of ​​the first silicon-based material is within the above range, the loss of active ions due to the reaction between the silicon-based material and the electrolyte can be reduced, the expansion of the electrode sheet can be reduced, and the cycle stability and storage performance of the battery can be improved.

[0102] In some embodiments, the second silicon-based material includes a lumpy form.

[0103] In this specification, the term "massive form" refers to a shape that is different from a spherical or near-spherical shape.

[0104] The electrode sheet was cut perpendicular to its large surface using an Ar ion beam, exposing the cross-section, which was then photographed and observed using a scanning electron microscope. Figure 4 shows a scanning electron microscope image of the second region of the negative electrode film layer. A lumpy silicon-based material can be observed in the second region of the negative electrode film layer.

[0105] The fact that the second silicon-based material is in a block form provides excellent battery performance and reduces the manufacturing cost of the electrode sheets.

[0106] In some embodiments, the method for producing the second silicon-based material includes supplying a gas containing a silicon precursor to bulk carbon matrix particles having a carbon skeleton, and generating nanosilicon-based material attached to the carbon skeleton from the silicon precursor by chemical vapor deposition to obtain a bulk carbon-silicon material.

[0107] In some embodiments, the Dv50 of the second silicon-based material is 5 μm to 6 μm. In some embodiments, the Dv50 of the second silicon-based material is 5.2 μm to 5.6 μm.

[0108] In some embodiments, the Dv50 of the second silicon-based material is in a range consisting of any value or any two values ​​from among 5 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, and 6 μm.

[0109] If the Dv50 of the second silicon-based material is within the above range, it is advantageous for improving the transport performance of active ions and electrons, and for improving the rapid charging performance of the battery.

[0110] In some embodiments, the percentage content of silicon element by mass relative to the total mass of the second silicon-based material is 45% to 65%. In some embodiments, the percentage content of silicon element by mass relative to the total mass of the second silicon-based material is 47% to 55%.

[0111] In some embodiments, the percentage content of silicon element mass relative to the total mass of the second silicon-based material is any value or any two values ​​from among 45%, 47%, 49%, 51%, 53%, 55%, 57%, 59%, 61%, 63%, and 65%.

[0112] When the mass percentage content of silicon element in the second silicon-based material is within the above range, it is advantageous for improving the battery capacity.

[0113] In some embodiments, the specific surface area of ​​the second silicon-based material is 0.8 m². 2 It is 1 / g or more. In some embodiments, the specific surface area of ​​the second silicon-based material is 1.1 m². 2 / g~3.2m 2 It is / g.

[0114] In some embodiments, the specific surface area of ​​the second silicon-based material is 0.8 m². 2 / g, 1.1m 2 / g, 1.4m 2 / g, 1.7m 2 / g, 2m 2 / g, 2.3m 2 / g, 2.6m 2 / g, 2.9m 2 / g, 3.2m 2 / g is a range consisting of any value or any two values ​​within that range.

[0115] If the specific surface area of ​​the second silicon-based material is within the above range, the interaction between the binder and the silicon-based material is enhanced, thereby reducing the expansion of the electrode sheet.

[0116] In some embodiments, the second silicon-based material contains silicon crystal particles, the crystallite size of the silicon crystal particles is 5 nm or less. In some embodiments, the crystallite size of the silicon crystal particles is 2 nm to 3 nm.

[0117] In some embodiments, the crystallite size of the silicon crystal grains is within a range of any value or any two values ​​from 1 nm, 2 nm, 3 nm, 4 nm, and 5 nm.

[0118] By keeping the silicon crystal particle size within the above range, it is possible to avoid excessive localized silicon element enrichment due to excessive crystallite size, which would cause significant expansion during lithium insertion and degrade the battery's storage performance and cycle stability. By using a combination of the first and second silicon-based materials, it is possible to mitigate the degradation of battery performance due to crystallization, which occurs because the surface of the second silicon-based material, with its smaller particle size, tends to become silicon-rich.

[0119] In some embodiments, a constant current charge-discharge test is performed on the second silicon-based material using a button cell, and a differential capacitance curve at the lithium desorption stage is created that reflects the relationship between dQ / dV and voltage V. If the maximum value of the differential dQ / dV between 0.27V and 0.34V is defined as VA, and the maximum value of the differential dQ / dV between 0.43V and 0.55V is defined as VB, then 0.8 ≤ VA / VB ≤ 1.3. In some embodiments, 0.8 ≤ VA / VB ≤ 1.0.

[0120] In some embodiments, the value of VA / VB is any value or any two values ​​from among 0.8, 0.9, 1.0, 1.1, 1.2, and 1.3.

[0121] Because silicon-based materials with small particle sizes tend to become silicon-rich on their surfaces, crystallization occurs, generating a high-voltage platform. By using a combination of a first-generation silicon-based material and a second-generation silicon-based material, the deterioration of the material's structural stability caused by the high-voltage platform generated by the second-generation silicon-based material can be mitigated, improving the battery's storage performance and cycle stability.

[0122] In some embodiments, the first region further comprises a first carbon material, wherein the Dv50 of the first carbon material is 14 μm to 19 μm.

[0123] In some embodiments, the Dv50 of the first carbon material is in a range consisting of any value or any two values ​​from 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, and 19 μm.

[0124] In some embodiments, the second region further comprises a second carbon material, the first carbon material and / or the second carbon material comprising at least one of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0125] In some embodiments, the first carbon material includes artificial graphite.

[0126] Compared to natural graphite, artificial graphite can improve the pressure density of electrode sheets and has excellent cycle stability and storage performance, thereby reducing the expansion of electrode sheets and improving the cycle stability and storage performance of batteries.

[0127] In some embodiments, the mass ratio of the negative electrode film layer in the first region of the first silicon-based material is lower than the mass ratio of the negative electrode film layer in the second region of the second silicon-based material.

[0128] By reducing the proportion of the first silicon-based material in the first region that comes into direct contact with the cold press roll and electrolyte, the amount of silicon that comes into contact with the electrolyte when the silicon-based material cracks can be further reduced, thereby mitigating the expansion of the electrode sheet and improving the battery's cycle stability and storage performance.

[0129] In some embodiments, a metal foil or a composite current collector can be used as the negative electrode current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0130] In some embodiments, the negative electrode film layer further selectively comprises a binder. The binder may be at least one selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0131] In some embodiments, the negative electrode film layer further selectively comprises a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0132] In some embodiments, the negative electrode film layer further comprises other additives, such as a selective thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0133] In some embodiments, a negative electrode sheet can be manufactured as follows: The above components for manufacturing a negative electrode sheet, for example, a first silicon-based material, a first carbon material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a first negative electrode slurry. A second silicon-based material, a second carbon material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., deionized water) to form a second negative electrode slurry. The first slurry and the second slurry are simultaneously extruded using a double cavity coating apparatus. The second slurry is applied to the copper foil of the negative electrode current collector, and the first slurry is applied to the second slurry. A negative electrode sheet is obtained by drying, cold pressing, and cutting.

[0134] [Positive electrode sheet] The positive electrode sheet typically includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. The positive electrode film layer contains a positive electrode active material.

[0135] For example, a positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0136] In some embodiments, a metal foil or a composite current collector can be used as the positive electrode current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0137] In some embodiments, the positive electrode active material can be any positive electrode active material known in the art for batteries. For example, the positive electrode active material may include at least one of olivine-structured lithium-containing phosphates, lithium transition metal oxides, and modified compounds of each thereof. However, this application is not limited to these materials, and other conventional materials usable as positive electrode active materials for batteries may be used. These positive electrode active materials may be used individually or in combination of two or more. Examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel manganese cobalt oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (simply NCM) 333 (Also known as LiNi) 0.5 Co 0.2 Mn 0.3 O2 (simply NCM) 523 (Also known as LiNi) 0.5 Co 0.25 Mn 0.25 O2 (simply NCM) 211 (Also known as LiNi) 0.6 Co 0.2 Mn 0.2 O2 (simply NCM) 622 (Also known as LiNi) 0.8 Co 0.1 Mn 0.1 O2 (simply NCM) 811 (also known as), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05It may contain, but is not limited to, at least one of O2) and its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but is not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which may also simply be called LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (e.g., LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0138] In some embodiments, the positive electrode film layer selectively further comprises a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0139] In some embodiments, the cathode film layer selectively further comprises a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0140] In some embodiments, a positive electrode sheet can be manufactured as follows: The above-mentioned components for manufacturing a positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, the positive electrode slurry is coated onto a positive electrode current collector, and a positive electrode sheet can be obtained through processes such as baking and cold pressing.

[0141] [Electrolyte] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. In this application, the type of electrolyte is not specifically limited and can be selected as needed. For example, the electrolyte may be liquid, gel-like, or all-solid.

[0142] In some embodiments, the electrolyte is an electrolyte solution, which comprises an electrolyte salt and a solvent.

[0143] In some embodiments, the electrolyte includes an ester-based solvent.

[0144] In some embodiments, the ester solvent may be one or more selected from ethylene carbonate, propylene carbonate, ethylmethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and 1,4-butyrolactone.

[0145] In some embodiments, the electrolyte salt may be at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0146] In some embodiments, the electrolyte further selectively includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may further include additives that can improve certain aspects of the battery's performance, such as additives that can improve the battery's overcharge performance, or additives that can improve the battery's high-temperature or low-temperature performance.

[0147] [Separator] In some embodiments, the secondary battery further includes a separator. In this application, the type of separator is not particularly limited, and any known porous structure separator having good chemical and mechanical stability can be selected.

[0148] In some embodiments, the material of the separator may be at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. If the separator is a multilayer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0149] In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be assembled into an electrode assembly by a winding process or a lamination process.

[0150] In some embodiments, the secondary battery may include an casing. This casing can be used to enclose the electrode assembly and electrolyte.

[0151] In some embodiments, the casing of the secondary battery may be a rigid case, such as a hard plastic case, an aluminum case, or a steel case. The casing of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0152] In this application, the shape of the secondary battery may include, but is not limited to, a cylindrical, prismatic, or any other shape. For example, Figure 9 shows a prismatic secondary battery 5 as an example.

[0153] In some embodiments, referring to Figure 10, the casing may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround the case 51 to form a housing cavity. The case 51 has an opening that communicates with the housing cavity. The bar plate 53 can cover the opening and seal the housing cavity. The positive electrode sheet, negative electrode sheet and separator can form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is sealed in the housing cavity. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and a person skilled in the art can select according to the specific actual needs.

[0154] In some embodiments, the secondary battery may be assembled as a battery module, and the number of secondary batteries included in the battery module may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0155] Figure 11 shows an example of a battery module 4. Referring to Figure 11, in the battery module 4, a plurality of secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fastening members.

[0156] Selectively, the battery module 4 may further include a housing having a housing space, in which a plurality of secondary batteries 5 are housed.

[0157] In some embodiments, the battery modules may be assembled as a battery pack, and the number of battery modules included in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery pack.

[0158] Figures 12 and 13 show an example of a battery pack 1. Referring to Figures 12 and 13, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided within the battery box. The battery box includes an upper box 2 and a lower box 3, the upper box 2 covering the lower box 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0159] Furthermore, this application provides an electrical device comprising at least one of the secondary battery, battery module, or battery pack provided herein. The secondary battery, battery module, or battery pack may be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships and satellites, energy storage systems, etc.

[0160] As for the electrical device, a secondary battery, battery module, or battery pack can be selected depending on the requirements of its use.

[0161] Figure 14 shows an example of an electrical device. This electrical device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the requirements for high power output and high energy density of secondary batteries, this electrical device may use a battery pack or battery module.

[0162] Other examples of devices may include mobile phones, tablet computers, and laptop computers. Such devices are typically required to be lightweight and thin, and may use rechargeable batteries as a power source.

[0163] Examples Examples of the present application are described below. The examples described below are illustrative and are for interpretive purposes only, and should not be understood as limiting this application. Unless otherwise specified in the examples, specific techniques or conditions are followed in accordance with the techniques or conditions described in the literature in the art, or in the specifications of the products. Unless otherwise specified, the reagents or equipment used are common commercially available products.

[0164] 1. Manufacturing method Manufacturing Example 1: Spherical silicon-carbon material A A gas containing silane (SiH4) was passed through spherical hard carbon particles with a porous structure, and silicon was deposited onto the porous structure of the hard carbon particles by chemical vapor deposition. The mass ratio of silicon to hard carbon particles in the silane was 46:54, the Dv50 of the hard carbon particles was 8.8 μm, the porosity was 78.9%, and the average pore size was 2 nm. Then, using acetylene gas as the gas source, a carbon layer with a mass percentage of 1% of the hard carbon particles after silicon deposition was coated onto the outer surface of the hard carbon particles by chemical vapor deposition, obtaining spherical silicon-carbon material A. The average particle size of spherical silicon-carbon material A was 9.5 μm, the mass percentage silicon content was 45.8%, and the specific surface area was 1.56 m². 2 The value is / g, and the V1 / V2 value in the differential capacitance curve is 1.68. The X-ray diffraction pattern of the spherical silicon-carbon material A is shown in Figure 5, and the differential capacitance curve is shown in Figure 7.

[0165] Manufacturing Example 2: Spherical Silicon Carbon Material B A gas containing silane (SiH4) was passed through spherical hard carbon particles with a porous structure, and silicon was deposited onto the porous structure of the hard carbon particles by chemical vapor deposition. The mass ratio of silicon to hard carbon particles in the silane was 47:53, the Dv50 of the hard carbon particles was 4.3 μm, the porosity was 80.1%, and the average pore size was 2 nm. Then, using acetylene gas as the gas source, a carbon layer with a mass percentage of 1% of the hard carbon particles after silicon deposition was coated onto the outer surface of the hard carbon particles by chemical vapor deposition, obtaining spherical silicon-carbon material B. The average particle diameter of spherical silicon-carbon material B was 5.2 μm, the mass percentage silicon content was 46.3%, and the specific surface area was 2.31 m². 2 It is / g.

[0166] Manufacturing Example 3: Bulk Silicon Carbon Material A A gas containing silane (SiH4) was passed through bulk hard carbon particles having a porous structure, and silicon was deposited onto the porous structure of the hard carbon particles by chemical vapor deposition. The mass ratio of silicon to hard carbon particles in the silane was 48:52, the Dv50 of the hard carbon particles was 4.3 μm, the porosity was 83.2%, and the average pore size was 2 nm. Then, using acetylene gas as the gas source, a carbon layer with a mass percentage of 1% of the hard carbon particles after silicon deposition was coated onto the outer surface of the hard carbon particles by chemical vapor deposition, obtaining bulk silicon-carbon material A. The average particle size of bulk silicon-carbon material A was 5.2 μm, the mass percentage silicon content was 48.3%, and the specific surface area was 2.67 m². 2 The value is / g, and the V1 / V2 value in the differential capacitance curve is 0.89. The X-ray diffraction pattern of the bulk silicon-carbon material A is shown in Figure 6, and the differential capacitance curve is shown in Figure 8. The bulk silicon-carbon material A contains silicon crystal particles, and the particle size of the silicon crystal particles is 2.2 nm.

[0167] Manufacturing Example 4: Bulk Silicon Carbon Material B A gas containing silane (SiH4) was passed through bulk hard carbon particles with a porous structure, and silicon was deposited onto the porous structure of the hard carbon particles by chemical vapor deposition. The mass ratio of silicon to hard carbon particles in the silane was 47:53, the Dv50 of the hard carbon particles was 8.8 μm, the porosity was 82.1%, and the average pore size was 2 nm. Then, using acetylene gas as the gas source, a carbon layer with a mass percentage of 1% of the hard carbon particles after silicon deposition was coated onto the outer surface of the hard carbon particles by chemical vapor deposition, obtaining bulk silicon-carbon material B. The average particle size of bulk silicon-carbon material B was 9.5 μm, the mass percentage silicon content was 47.2%, and the specific surface area was 1.68 m². 2 It is / g.

[0168] Manufacturing Example 5: Bulk Silicon Carbon Material C A gas containing silane (SiH4) was passed through bulk hard carbon particles with a porous structure, and silicon was deposited onto the porous structure of the hard carbon particles by chemical vapor deposition. The mass ratio of silicon to hard carbon particles in the silane was 46:54, the Dv50 of the hard carbon particles was 8.8 μm, the porosity was 80.5%, and the average pore size was 2 nm. Then, using acetylene gas as the gas source, a carbon layer with a mass percentage of 1% of the hard carbon particles after silicon deposition was coated onto the outer surface of the hard carbon particles by chemical vapor deposition, obtaining bulk silicon-carbon material C. The average particle size of bulk silicon-carbon material C was 9.5 μm, the mass percentage silicon content was 46.1%, and the specific surface area was 1.63 m². 2 It is / g.

[0169] Example 1 1) Manufacturing of negative electrode sheets A first negative electrode active material was prepared by mixing spherical silicon-carbon material A and artificial graphite (average particle size of 15.6 μm) in a ratio of 0.16:0.84. The first negative electrode active material, carbon nanotubes as a conductive agent, sodium carboxymethylcellulose (CMC-Na) as a thickener, and styrene-butadiene rubber (SBR) as a binder were mixed in a mass ratio of 96.7:0.5:1.0:1.8, deionized water was added, and the mixture was stirred with a vacuum mixer until the system was homogeneous to obtain the first slurry.

[0170] A second negative electrode active material was prepared by mixing a lumpy silicon carbon material A and natural graphite (average particle size of 18.6 μm) in a ratio of 0.2:0.8. The second negative electrode active material, carbon nanotubes as a conductive agent, sodium carboxymethylcellulose (CMC-Na) as a thickener, and styrene-butadiene rubber (SBR) as a binder were mixed in a mass ratio of 95.5:0.7:2.0:1.8. Ionized water was then added, and the mixture was stirred with a vacuum mixer until the system was homogeneous to obtain a second slurry.

[0171] The first and second slurries were simultaneously extruded using a double-cavity coating apparatus. The second slurry was applied to the copper foil of the negative electrode current collector, and the first slurry was applied to the second slurry. After drying, cold pressing, and cutting, a negative electrode sheet was obtained. The coating weight of the first and second slurries was 4.2 mg / cm³ each. 2 and 6.3 mg / cm³ 2 That is the case.

[0172] 2) Manufacturing of positive electrode sheets A positive electrode slurry was obtained by thoroughly stirring and uniformly mixing lithium iron phosphate as the positive electrode active material, conductive carbon black, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 96:2:2 in an N-methylpyrrolidone solvent system. The above positive electrode slurry was uniformly applied to an aluminum foil positive electrode current collector with a thickness of 13 μm. The application speed was 30 m / min, and the application oven temperature was 110°C to 130°C. Then, a positive electrode sheet was obtained by cold pressing and cutting.

[0173] 3) Manufacturing of electrolyte In a glove box under an argon atmosphere (H2O content < 0.1 ppm, O2 content < 0.1 ppm), lithium hexafluorophosphate LiPF6 was dissolved as a lithium salt in a mixture of organic solvents, ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC volume ratio 3:7), and the mixture was uniformly stirred to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0174] 4) Separator A 9μm polyethylene (PE) film was used as the separator.

[0175] 5) Battery manufacturing A positive electrode sheet, a separator, and a composite negative electrode sheet were stacked in this order so that the separator would separate the positive and negative electrode sheets, wound up to obtain a bare cell, welded tabs, placed the cell in an aluminum case, immediately injected electrolyte and sealed, and after processes such as standing, cold pressing, chemical conversion, molding, and capacity measurement, a lithium-ion secondary battery manufactured in Example 1 was obtained.

[0176] The batteries of Examples 2 and 3 are manufactured in the same manner as the battery of Example 1, but differ in that the mass ratio of the first silicon-based material to the negative electrode active material in the first region and the mass ratio of the second silicon-based material to the negative electrode active material in the second region are adjusted. The specific parameters are shown in Table 1.

[0177] The battery of Example 4 is manufactured in the same manner as the battery of Example 1, but differs in that the first carbon material is natural graphite with a particle size of 18.6 μm, and the specific parameters are shown in Table 1.

[0178] The batteries of Examples 5 to 7 are manufactured in the same manner as the battery of Example 1, but differ in that the type of spherical silicon carbon material in the first region and / or the type of solid silicon carbon material in the second region are adjusted, and the specific parameters are shown in Table 1.

[0179] Comparative Example 1 is similar to the battery manufacturing method of Example 1, but differs in that the first silicon-based material is a solid silicon carbon material C, and the specific parameters are as shown in Table 1.

[0180] [Table 1]

[0181] 2.Measurement method 1. Measuring charging time The electrode sheet can be made into a button cell or a small laminated cell. At 35°C, the battery underwent its first charge and discharge cycle with a current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour). Specifically, the battery was charged at a 1C rate with a constant current until the cutoff voltage reached 2V, then charged at a constant voltage until the current ≤ 0.05C, left to stand for 5 minutes, and then discharged at a 0.33C rate with a constant current until the cutoff voltage reached 5mV. The actual capacity was recorded as C0. Next, the battery was charged with a constant current in the following order: 2.8C0, 3C0, 3.2C0, 3.5C0, 3.8C0, 4.1C0, 4.4C0, 4.7C0, 5C0, 5.3C0, 5.6C0, and 5.9C0, until it reached either the full cell charge cutoff voltage V1 or the negative electrode cutoff potential of 0V (whichever came first). After each charge was complete, it was necessary to discharge it at 1C0 to the full cell discharge cutoff voltage V2. The corresponding negative electrode potential was recorded when charging to 10%, 20%, 30%, ..., 80% SOC (State of Charge) at different charge rates. Charge rate-negative electrode potential curves were created for different SOC states and linearly approximated to obtain the charge rate at which the negative electrode potential reached 0V in each SOC state. The charge rate is the charge window in the State of Charge (SOC) state, and is recorded as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC, respectively. According to the following formula, (60 / C20%SOC+60 / C30%SOC+60 / C40%SOC+60 / C50%SOC+60 / C60%SOC+60 / C70%SOC+60 / C80%SOC)×10% Calculate the charging time T required to charge the battery from 10% SOC to 80% SOC, and express the result in minutes. A shorter charging time indicates better rapid charging performance of the battery.

[0182] 2. Measurement of full-charge expansion based on cold-pressed electrode sheets After cold-pressing the negative electrode sheet, measure the thickness of the electrode sheet at 5 to 8 points using a micrometer, take the average value, and record it as A1. Charge the battery to 4.25V, then charge it at a constant voltage until the current ≤ 0.05C. After charging is complete, disassemble the negative electrode sheet from the cell, measure the thickness of the disassembled electrode sheet at 5 to 8 points, take the average value, and record it as A2. Then the full-charge expansion rate of the electrode sheet is (A2-A1) / A1*100%.

[0183] 3. Measurement of storage performance The electrode sheets are stacked to form a cell, and the battery is discharged at a constant current at a rate of 0.33C until the cutoff voltage reaches 2.5V, left to stand for 30 minutes, then charged at a constant current at a rate of 0.33C until the cutoff voltage reaches 4.25V, and then charged at a constant voltage until the current is ≤0.05C. After leaving it to stand for 30 minutes, the initial capacity is recorded as C0. The battery is stored in a 60°C constant temperature chamber for 60 days, then removed and left to stand at room temperature for 60 minutes. Capacity measurement is performed, specifically by discharging at a constant current at a rate of 0.33C until the cutoff voltage reaches 2.5V, leaving it to stand for 30 minutes, then charging at a constant current at a rate of 0.33C until the cutoff voltage reaches 4.25V, and then charged at a constant voltage until the current is ≤0.05C, and the capacity is recorded as C1. The capacity retention rate after 60 days of storage is C1 / C0 * 100%.

[0184] 4. Measurement of cycle performance at room temperature Measurement procedure: At 25°C, the battery is left standing for 30 minutes, then charged at a rate of 0.5C until the voltage reaches 4.2V, then charged at a constant voltage until the current reaches 0.05C at 4.2V, left standing for 5 minutes, and then discharged at a rate of 0.5C until the voltage reaches 2.8V. The resulting capacity is recorded as the initial capacity C0, and this constitutes one charge-discharge cycle process. The above steps are repeated for the same battery, and the discharge capacity Cn at each cycle is recorded. The battery capacity retention rate after each cycle is Pn = Cn / C0 * 100%, and the measurement is stopped until Pn ≤ 80%, and the number of cycles at this point is recorded.

[0185] 3. Analysis of the measurement results for each example and comparative example Batteries for each example and comparative example were manufactured according to the method described above, and each performance parameter was measured. The results are shown in the table below.

[0186] As can be seen from Table 2, the spherical shape of the silicon-based material in the first region of the negative electrode film layer reduces the expansion rate of the electrode sheet after cold pressing, thereby improving the high-temperature storage performance and cycle stability of the battery.

[0187] [Table 2]

[0188] As can be seen from the comparison between Example 1 and Example 4 in Table 3, using synthetic graphite as the primary graphite is advantageous compared to natural graphite in improving the high-temperature storage performance, kinetic characteristics, and cycle stability of the battery.

[0189] As can be seen from the comparison between Example 1 and Examples 5-7 in Table 3, by using a combination of a first silicon-based material with a large particle size and a second silicon-based material with a small particle size, the electrode sheet exhibits a low expansion rate, and the battery exhibits good cycle stability, high-temperature storage performance, and rapid charging performance.

[0190] [Table 3]

[0191] It should be noted that this application is not limited to the embodiments described above. The embodiments described above are merely illustrative, and all embodiments having substantially the same technical idea and achieving the same function and effect within the scope of the technical solution of this application are included in the technical scope of this application. Furthermore, other forms that are constructed by adding various modifications to the embodiments that a person skilled in the art could conceive of, and by combining some of the components of the embodiments, are also included in the scope of this application, without departing from the gist of this application. [Explanation of symbols]

[0192] 1 Battery pack 2. Top box 3. Lower box 4 Battery Modules 5 Secondary battery 51 cases 52 Electrode assembly 53 Bar Plate 10 Negative electrode sheets 101 Negative electrode current collector 102 Negative electrode film layer 102a 1st surface 102b 2nd surface 1021 Second area 1022 1st area 1023 Intermediate area.

Claims

1. A negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer has a first surface away from the negative electrode current collector and a second surface positioned opposite to the first surface, the thickness of the negative electrode film layer is H, the region within a thickness range from the first surface of the negative electrode film layer to 0.3H is defined as a first region of the negative electrode film layer, and the region within a thickness range from the second surface of the negative electrode film layer to 0.3H is defined as a second region of the negative electrode film layer, and the first region comprises a first silicon-based material in a spherical shape and / or near-spherical shape.

2. The negative electrode sheet according to claim 1, characterized in that the second region includes a second silicon-based material, and the average particle diameter of the second silicon-based material is smaller than the average particle diameter of the first silicon-based material.

3. The negative electrode sheet according to claim 2, characterized in that the percentage content of the mass of silicon element relative to the total mass of the first silicon-based material is lower than the percentage content of the mass of silicon element relative to the total mass of the second silicon-based material.

4. The negative electrode sheet according to claim 2 or 3, characterized in that the specific surface area of ​​the first silicon-based material is smaller than the specific surface area of ​​the second silicon-based material.

5. The negative electrode sheet according to any one of claims 2 to 4, characterized in that the degree of crystallinity of the first silicon-based material is lower than the degree of crystallinity of the second silicon-based material.

6. A negative electrode sheet according to any one of claims 1 to 5, characterized in that a constant current charge-discharge test is performed on the first silicon-based material with a button cell, a differential capacitance curve is created at the lithium desorption stage in the reaction, and the maximum value of the differential value dQ / dV between 0.27V and 0.34V is defined as V1, and the maximum value of the differential value dQ / dV between 0.43V and 0.55V is defined as V2, then 1.55 ≤ V1 / V2 ≤ 1.75, and selectively 1.60 ≤ V1 / V2 ≤ 1.

72.

7. The negative electrode sheet according to any one of claims 2 to 6, wherein the first silicon-based material and / or the second silicon-based material comprises a silicon carbon material, and the silicon carbon material comprises carbon matrix particles having a porous structure and a nanosilicon-based material provided in the porous structure.

8. The first silicon-based material is, (1) The Dv50 of the first silicon-based material is 9 μm to 11 μm, and selectively 9.5 μm to 10 μm, (2) The percentage content of silicon element in the first silicon-based material relative to the total mass of the first silicon-based material is 40% to 60%, and selectively 45% to 50%, (3) The specific surface area of ​​the first silicon-based material is 0.8 m². ２ / g to 5m ２ / g, and selectively 1.1m ２ / g to 3.2m ２ A negative electrode sheet according to any one of claims 1 to 7, characterized in that it is / g and satisfies at least one of the following:

9. The second silicon-based material is, (1) The second silicon-based material includes a lumpy form, (2) The Dv50 of the second silicon-based material is 5 μm to 6 μm, and selectively 5.2 μm to 5.6 μm, (3) The percentage content of silicon element in the second silicon-based material relative to the total mass of the second silicon-based material is 45% to 65%, and selectively 47% to 55%, (4) The specific surface area of ​​the second silicon-based material is 0.8 m². ２ It is greater than or equal to 1.1m ２ / g to 3.2m ２ The fact that it is / g, (5) The second silicon-based material contains silicon crystal particles, and the crystallite size of the silicon crystal particles is 5 nm or less, and selectively 2 nm to 3 nm. (6) A negative electrode sheet according to any one of claims 2 to 8, characterized in that a constant current charge-discharge test is performed on the second silicon-based material with a button cell, a differential capacitance curve is created at the lithium desorption stage in which the relationship between dQ / dV and voltage V is determined to be VA, the maximum value of the differential value dQ / dV in the range of 0.27V to 0.34V is defined as VA, and the maximum value of the differential value dQ / dV in the range of 0.43V to 0.55V is defined as VB, then 0.8 ≤ VA / VB ≤ 1.3, and selectively, 0.8 ≤ VA / VB ≤ 1.0 is satisfied, and at least one of these conditions is met.

10. The negative electrode sheet according to any one of claims 1 to 9, further comprising a first carbon material in the first region, wherein the Dv50 of the first carbon material is 14 μm to 19 μm.

11. The negative electrode sheet according to claim 10, further comprising a second carbon material in the second region, wherein the first carbon material and / or the second carbon material comprises at least one of artificial graphite, natural graphite, soft carbon, and hard carbon.

12. The negative electrode sheet according to claim 10 or 11, characterized in that the first carbon material contains artificial graphite.

13. The negative electrode sheet according to any one of claims 2 to 12, characterized in that the mass ratio of the negative electrode film layer in the first region of the first silicon-based material is lower than the mass ratio of the negative electrode film layer in the second region of the second silicon-based material.

14. A secondary battery characterized by comprising a negative electrode sheet according to any one of claims 1 to 13.

15. An electrical device characterized by including the secondary battery described in claim 14.

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