Secondary battery and electronic device

Abstract

The application provides a secondary battery and an electronic device, the secondary battery comprising an electrode assembly, the electrode assembly comprising a negative electrode sheet, a positive electrode sheet and a separator, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a silicon-carbon material, the silicon-carbon material comprising a base body, a silicon coating layer and a carbon coating layer, the base body comprising porous carbon and nano-silicon particles, the nano-silicon particles being arranged in pores of the porous carbon, and the silicon coating layer being arranged between the base body and the carbon coating layer. The silicon-carbon material satisfies the above characteristics, can improve the kinetic performance and the cycle performance of the secondary battery, and also enables the secondary battery to have a high energy density.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] With the widespread use of secondary batteries, the demand for their cycle performance and kinetic performance is increasing.

[0003] Among these, silicon materials have attracted much attention for their application research due to their high theoretical specific capacity. However, silicon materials undergo a volume expansion of approximately 300% during lithium intercalation, which can lead to the rupture of the solid electrolyte interphase (SEI) film, forming a new interface. This results in continuous side reactions between the electrolyte and silicon materials, consuming the electrolyte. Furthermore, silicon materials can pulverize and break down, forming even larger interfaces, further exacerbating electrolyte consumption and affecting the cycle performance of lithium-ion batteries. Simultaneously, silicon materials have poor electronic conductivity, which also affects the kinetic performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and electronic device that can improve the kinetic and cycle performance of the secondary battery, while also giving it a higher energy density. The specific technical solution is as follows:

[0005] The first aspect of this application provides a secondary battery comprising an electrode assembly, which includes a negative electrode, a positive electrode, and a separator. The negative electrode includes 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 includes a silicon-carbon material, which includes a substrate, a silicon coating layer, and a carbon coating layer. The substrate includes porous carbon and nano-silicon particles, with nano-silicon particles present in the pores of the porous carbon. The silicon coating layer is disposed between the substrate and the carbon coating layer. The silicon-carbon material satisfies the above-mentioned characteristics, thereby improving the kinetic and cycle performance of the secondary battery, and also enabling the secondary battery to have a high energy density.

[0006] In one embodiment of this application, the secondary battery is discharged at a 10C rate at -20°C. The difference between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is ΔE, where 0.1V ≤ ΔE ≤ 0.6V. Using the silicon-carbon material of this application, a rapid lithium-ion transport channel is constructed on the particle surface and inside the particles, further improving the kinetic performance of the silicon-carbon material. When the silicon-carbon material is applied to the secondary battery, and the secondary battery is discharged at a 10C rate at -20°C, the difference ΔE between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is within the range of this application, indicating that the secondary battery has good kinetic performance.

[0007] In one embodiment of this application, the thickness of the silicon coating layer is H1 nm, and the thickness of the carbon coating layer is H2 nm, where 1 ≤ H1 ≤ 100 and 5 ≤ H2 ≤ 100. The silicon coating layer is used to construct a rapid lithium-ion transport channel between the outer carbon coating layer and the inner nano-silicon particles. When the thickness of the silicon coating layer is within the range of this application, it allows for a more complete connection between the outermost silicon coating layer and the nano-silicon particles deposited within the pores, resulting in better lithium-ion transport performance of the constructed channel. A suitable thickness of the silicon coating layer also facilitates the transport of lithium ions into the particle interior, further improving the kinetic performance of the secondary battery. When the thickness of the carbon coating layer is within the range of this application, a suitable thickness provides better electronic conductivity and can also reduce the contact between the electrolyte and the silicon coating layer to a certain extent, reducing the occurrence of side reactions and improving the cycle performance of the secondary battery. Simultaneously, it also facilitates the transport of lithium ions and electrons into the particle interior, further improving the kinetic performance of the secondary battery.

[0008] In one embodiment of this application, based on the mass of the silicon-carbon material, the mass percentage of silicon in the silicon-carbon material is W1%, the mass percentage of carbon in the silicon-carbon material is W2%, 40≤W1≤70, and 30≤W2≤60. By controlling the mass percentages of silicon and carbon in the silicon-carbon material within the scope of this application, it is beneficial to form a silicon coating layer of appropriate thickness on the substrate surface, so that the outermost silicon coating layer is more fully connected with the nano-silicon particles deposited in the pores, further improving the lithium-ion transport effect of the constructed channels, thereby improving the kinetic performance of the secondary battery. At the same time, it can also improve the specific capacity and first-time efficiency of the silicon-carbon material, so that the secondary battery has a higher energy density.

[0009] In one embodiment of this application, the first delithiation dQ / dV curve of the silicon-carbon material exhibits a first delithiation peak in the range of 0.25V to 0.32V and a second delithiation peak in the range of 0.35V to 0.45V. The peak intensity of the first delithiation peak is I1, and the peak intensity of the second delithiation peak is I2, with 0.1 ≤ I1 / I2 ≤ 3. The value of I1 / I2 reflects the thickness of the silicon coating layer. When the value of I1 / I2 is within the range of this application, the silicon coating layer has a suitable thickness, allowing for a more complete connection between the outermost silicon coating layer and the nano-silicon particles deposited within the pores, further improving the lithium-ion transport effect of the constructed channel; it also facilitates the transport of lithium ions into the particle interior, further improving the kinetic performance of the secondary battery.

[0010] In one embodiment of this application, the reversible capacity of the silicon-carbon material at 0.05C is D0 mAh / g, where 1500≤D0≤2500. Silicon materials have a high specific capacity, and the reversible capacity of the silicon-carbon material at 0.05C in this application is within the range specified in this application. The high reversible capacity of the silicon-carbon material results in a high energy density for the secondary battery.

[0011] In one embodiment of this application, the silicon-carbon material satisfies at least one of the following characteristics: (1) the thickness of the silicon coating layer is H1 nm, the thickness of the carbon coating layer is H2 nm, 3≤H1≤80, 10≤H2≤50; (2) based on the mass of the silicon-carbon material, the mass percentage of silicon in the silicon-carbon material is W1%, the mass percentage of carbon in the silicon-carbon material is W2%, 45≤W1≤65, 35≤W2≤55; (3) in the first delithiation dQ / dV curve of the silicon-carbon material, there is a first delithiation peak in the range of 0.25V to 0.32V, and a second delithiation peak in the range of 0.35V to 0.45V, the peak intensity of the first delithiation peak is I1, the peak intensity of the second delithiation peak is I2, and 0.2≤I1 / I2≤2.

[0012] In one embodiment of this application, the negative electrode material layer further includes a carbon material, which satisfies at least one of the following characteristics: (1) the carbon material includes at least one of natural graphite, artificial graphite, or hard carbon; (2) the particle size Dv50 of the carbon material satisfies: 5μm≤Dv50≤18μm; (3) the specific surface area BET of the carbon material satisfies: 0.5m². 2 / g≤BET≤3m 2 / g; (4) In the Raman spectrum of carbon materials, at 1300 cm⁻¹ -1 Up to 1400cm -1 Within the range, there is a peak intensity of I. D The first characteristic peak is at 1550 cm⁻¹. -1 Up to 1650cm -1 Within the range, there is a peak intensity of I. G The second characteristic peak, 0.1 < I D / I G <0.4. The negative electrode material layer also includes carbon materials. Carbon materials have good electronic and ionic conductivity, which is beneficial for electron and lithium-ion transport. They can also buffer the volume expansion of silicon materials during delithiation and lithium insertion processes, which can further improve the kinetic performance and cycle performance of the secondary battery.

[0013] In one embodiment of this application, the ratio of the mass percentage of carbon material to the mass percentage of silicon-carbon material is between 1 and 20, based on the sum of the masses of carbon material and silicon-carbon material. Carbon material can improve the kinetic and cycle performance of the secondary battery, while silicon-carbon material can improve the energy density of the secondary battery. By adjusting the mass percentage ratio of carbon material to silicon-carbon material within the range of this application, the secondary battery can achieve both good kinetic and cycle performance and high energy density.

[0014] In one embodiment of this application, the electrode assembly further includes a positive electrode tab and a negative electrode tab. The positive electrode includes a first empty foil region and a positive electrode material layer region, with the positive electrode tab disposed in the first empty foil region. The negative electrode includes a second empty foil region and a negative electrode material layer region, with the negative electrode tab disposed in the second empty foil region. With the electrode assembly structure configured as described above, current can be transmitted through the empty current collector, maximizing the uniformity of current density distribution in the electrode, reducing polarization of the secondary battery, and further improving the kinetic and cycle performance of the secondary battery.

[0015] In one embodiment of this application, along the width direction of the unfolded negative electrode sheet, the negative electrode sheet includes opposing first and second edges. From the first edge to the second edge, the negative electrode sheet sequentially comprises a second empty foil region and a negative electrode material layer region. With the negative electrode sheet having the above structure, and the positive electrode sheet also having the above structure, the electrode assembly adopts a full tab structure. Current can be transmitted through the empty current collector, maximizing the uniformity of current density distribution in the electrode sheet, reducing the polarization of the secondary battery, and further improving the kinetic performance and cycle performance of the secondary battery.

[0016] A second aspect of this application provides an electronic device comprising the secondary battery of any of the foregoing embodiments. Therefore, the electronic device provided by this application has good kinetic and cycle performance, as well as high energy density.

[0017] The beneficial effects of this application are:

[0018] This application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly comprising a negative electrode, a positive electrode, and a separator. The negative electrode includes 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 includes a silicon-carbon material, which comprises a substrate, a silicon coating layer, and a carbon coating layer. The substrate comprises porous carbon and nano-silicon particles, with nano-silicon particles present in the pores of the porous carbon. The silicon coating layer is disposed between the substrate and the carbon coating layer. The silicon-carbon material satisfies the above characteristics, thereby improving the kinetic and cycle performance of the secondary battery, and also enabling the secondary battery to have a high energy density.

[0019] Of course, implementing any product or method of this application does not necessarily require achieving all of the above advantages at the same time. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0021] Figure 1 This is a schematic diagram of the silicon-carbon material in Comparative Example 1;

[0022] Figure 2 This is a schematic diagram of the structure of a silicon-carbon material according to one embodiment of this application;

[0023] Figure 3 This is a schematic diagram of the negative electrode sheet according to one embodiment of this application;

[0024] Figure 4 This is a schematic diagram of the negative electrode sheet in Examples 1-17. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0027] This application provides a secondary battery comprising an electrode assembly, which includes a negative electrode, a positive electrode, and a separator. The negative electrode includes 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 includes a silicon-carbon material, comprising a substrate, a silicon coating layer, and a carbon coating layer. The substrate includes porous carbon and nano-silicon particles, with nano-silicon particles present in the pores of the porous carbon. The silicon coating layer is disposed between the substrate and the carbon coating layer. The phrase "a negative electrode material layer disposed on at least one surface of the negative current collector" means that the negative electrode material layer can be disposed on one surface of the negative current collector along its thickness direction, or on two surfaces of the negative current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative current collector or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved.

[0028] Existing silicon-carbon materials typically employ methods such as Figure 1The structure shown includes a silicon-carbon material 10 comprising a substrate 11 and a carbon coating layer 12. The substrate 11 comprises porous carbon 111 and nano-silicon particles 112, with the carbon coating layer 12 disposed on the entire surface of the substrate 11. In this silicon-carbon material, pre-reserved pores accommodate the expansion of the nano-silicon particles after lithium intercalation. However, due to the presence of these pores, lithium ions must first penetrate the carbon coating layer and then diffuse through the pores to the nano-silicon particles, where they then react with the particles for lithium intercalation. Conversely, during the delithiation process, lithium extracted from the Li-Si alloy first transfers to the pores and then diffuses through the pores to the surface of the silicon-carbon material particles, ultimately penetrating the carbon coating layer and diffusing into the electrolyte. During these delithiation and intercalation processes, the relatively slow transport speed of lithium ions within the pores leads to a deterioration in the delithiation and intercalation kinetics of the silicon-carbon material.

[0029] The inventors discovered that by optimizing the silane deposition process, a silicon coating layer can be formed on the substrate surface. Due to the characteristics of the silane deposition reaction, the nano-silicon particles deposited in porous carbon will grow outward along the pore walls. Therefore, the outer silicon coating layer and the nano-silicon particles deposited in the pores will form a connection. Afterward, a carbon coating treatment is performed to form a carbon coating layer on the surface of the silicon coating layer. The structure of the prepared silicon-carbon material is as follows: Figure 2 As shown, the silicon-carbon material 10 includes a substrate 11, a silicon coating layer 13, and a carbon coating layer 12. The substrate 11 includes porous carbon 111 and nano-silicon particles 112, with the nano-silicon particles 112 disposed within the pores of the porous carbon 111. The silicon coating layer 13 is disposed between the substrate 11 and the carbon coating layer 12. During lithium intercalation, lithium ions penetrate the outermost carbon coating layer and come into direct contact with the silicon coating layer, where a reaction occurs for lithium intercalation. Subsequently, the lithium ions continue to diffuse into the interior of the particles within the Li-Si alloy, allowing the silicon material inside the particles to undergo lithium intercalation. The delithiation process is the opposite: lithium ions diffuse out through the Li-Si alloy and then penetrate the carbon coating layer to diffuse into the electrolyte. In the silicon-carbon material of this application, lithium ions diffuse through the Li-Si alloy during the delithiation and lithium insertion process. Compared with the existing diffusion through the porous structure, this can further improve the diffusion rate of lithium ions inside the particles, improve the delithiation and lithium insertion kinetics of the silicon-carbon material, and improve the kinetic performance and cycle performance of the secondary battery. At the same time, the secondary battery also has a high energy density (ED).

[0030] In one embodiment of this application, the secondary battery is discharged at a 10C rate at -20°C. The difference between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is ΔE, where 0.1V ≤ ΔE ≤ 0.6V. Exemplarily, the value of ΔE can be 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, or a range consisting of any two of the above values. When a secondary battery is placed in an environment of -20℃ and discharged at a rate of 10C, there is an initial discharge voltage E0 at the beginning of the discharge. As the secondary battery continues to discharge, the voltage continues to decrease. However, due to the relatively high impedance of the secondary battery at this point, a large amount of heat is generated during discharge, causing the temperature of the secondary battery to rise. This, in turn, reduces the impedance of the secondary battery caused by the low temperature, resulting in a decrease in battery polarization and a rise in voltage. This process of voltage decrease followed by increase is reflected in the discharge curve of the secondary battery as a voltage trough, with a trough voltage E1. The difference between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is ΔE. ΔE reflects the kinetic properties of the material; the better the kinetic properties of the material, the smaller ΔE. By employing the silicon-carbon material of this application, a rapid lithium-ion transport channel is constructed on the particle surface and inside the particles through silicon material, which can further improve the kinetic performance of the silicon-carbon material. When the silicon-carbon material is applied to a secondary battery, and the secondary battery is discharged at a rate of 10C at -20℃, the difference ΔE between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is within the range of this application, indicating that the secondary battery has good kinetic performance. In this application, low temperature refers to a temperature below -20℃.

[0031] In one embodiment of this application, the thickness of the silicon coating layer is H1 nm, and the thickness of the carbon coating layer is H2 nm, where 1 ≤ H1 ≤ 100, preferably 3 ≤ H1 ≤ 80. Exemplarily, the value of H1 can be 1, 3, 5, 7, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or a range consisting of any two of the above values. 5 ≤ H2 ≤ 100, preferably 10 ≤ H2 ≤ 50. Exemplarily, the value of H2 can be 5, 7, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or a range consisting of any two of the above values. The silicon coating layer is used to construct a rapid lithium-ion transport channel between the outer carbon coating layer and the inner nano-silicon particles. When the thickness of the silicon coating layer is within the range specified in this application, it allows for a more complete connection between the outermost silicon coating layer and the nano-silicon particles deposited within the pores, resulting in better lithium-ion transport performance of the constructed channel. A suitable thickness of the silicon coating layer also facilitates lithium-ion transport into the particle interior, further improving the kinetic performance of the secondary battery. When the thickness of the carbon coating layer is within the range specified in this application, a suitable thickness provides good electronic conductivity and can also reduce the contact between the electrolyte and the silicon coating layer to a certain extent, reducing side reactions and improving the cycle performance of the secondary battery. Simultaneously, it also facilitates the transport of lithium-ions and electrons into the particle interior, further improving the kinetic performance of the secondary battery.

[0032] In one embodiment of this application, based on the mass of the silicon-carbon material, the mass percentage of silicon in the silicon-carbon material is W1%, the mass percentage of carbon in the silicon-carbon material is W2%, 40≤W1≤70, preferably 45≤W1≤65, and exemplarily, the value of W1 can be 40, 43, 45, 47, 49, 50, 53, 55, 57, 59, 60, 63, 65, 67, 69, 70, or any range of any two of the above values. 30≤W2≤60, preferably 35≤W2≤55, and exemplarily, the value of W2 can be 30, 33, 35, 37, 39, 40, 43, 45, 47, 49, 50, 53, 55, 57, 59, 60, or any range of any two of the above values. By controlling the mass percentage of silicon and carbon in the silicon-carbon material within the scope of this application, it is beneficial to form a silicon coating layer of appropriate thickness on the substrate surface, so that the outermost silicon coating layer is more fully connected with the nano-silicon particles deposited in the pores, further improving the lithium-ion transport effect of the constructed channel, thereby improving the kinetic performance of the secondary battery. At the same time, it can also improve the specific capacity and first-time efficiency of the silicon-carbon material, so that the secondary battery has a high energy density.

[0033] In one embodiment of this application, the first delithiation dQ / dV curve of the silicon-carbon material exhibits a first delithiation peak in the range of 0.25V to 0.32V and a second delithiation peak in the range of 0.35V to 0.45V. The peak intensity of the first delithiation peak is I1, and the peak intensity of the second delithiation peak is I2, with 0.1 ≤ I1 / I2 ≤ 3, preferably 0.2 ≤ I1 / I2 ≤ 2. Exemplarily, the value of I1 / I2 can be 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1, 1.3, 1.5, 1.7, 1.9, 2, 2.3, 2.5, 2.7, 2.9, 3, or a range consisting of any two of the above values. In this application, the first-cycle discharge specific capacity of the silicon-carbon material is used as the abscissa and voltage as the ordinate to obtain the first-cycle discharge curve of the silicon-carbon material. The first-cycle discharge specific capacity of the silicon-carbon material is the first-cycle delithiation specific capacity. Then, the first derivative of the first-cycle delithiation specific capacity Q with respect to voltage V is calculated, and then plotted against voltage V to obtain the differential capacity curve, i.e., the dQ / dV curve. The value of I1 / I2 can reflect the thickness of the silicon coating layer. When the value of I1 / I2 is within the range of this application, the silicon coating layer has a suitable thickness, which makes the connection between the outermost silicon coating layer and the nano-silicon particles deposited in the pores more sufficient, further improving the lithium-ion transport effect of the constructed channel; it is also conducive to the transport of lithium ions into the particle interior, further improving the kinetic performance of the secondary battery.

[0034] In one embodiment of this application, the reversible capacity of the silicon-carbon material at 0.05C is D0 mAh / g, where 1500 ≤ D0 ≤ 2500. Exemplarily, the value of D0 can be 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, or a range consisting of any two of the above values. Silicon materials have a high specific capacity, and the reversible capacity of the silicon-carbon material at 0.05C in this application is within the range specified in this application. The high reversible capacity of the silicon-carbon material results in a high energy density for the secondary battery.

[0035] In one embodiment of this application, the negative electrode material layer further includes carbon material. Carbon material has good electronic conductivity and ionic conductivity, which is beneficial for electron and lithium-ion transport. It can also buffer the volume expansion of silicon material during delithiation and lithium insertion processes, thereby further improving the kinetic performance and cycle performance of the secondary battery.

[0036] In one embodiment of this application, the carbon material includes at least one of natural graphite, artificial graphite, or hard carbon. Using the above-mentioned carbon material provides good electronic and ionic conductivity, which is beneficial for electron and lithium-ion transport, and can further improve the kinetic performance and cycle performance of the secondary battery.

[0037] In one embodiment of this application, the particle size Dv50 of the carbon material satisfies: 5μm ≤ Dv50 ≤ 18μm. Exemplarily, the value of Dv50 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or a range consisting of any two of the above values. By adjusting the particle size Dv50 of the carbon material within the scope of this application, the particle size of the carbon material is relatively small, which can shorten the lithium-ion transport path, improve the kinetic performance of the carbon material, and thus further improve the kinetic performance of the secondary battery.

[0038] In this application, Dv50 represents the particle size that, measured from the smallest particle size, reaches 50% of the volumetric particle size in the particle size distribution of the material on a volumetric basis.

[0039] In one embodiment of this application, the specific surface area (BET) of the carbon material satisfies: 0.5 m² / s². 2 / g≤BET≤3m 2 / g. For example, the value of BET can be 0.5, 0.7, 0.9, 1, 1.1, 1.3, 1.5, 1.7, 1.9, 2, 2.1, 2.3, 2.5, 2.7, 2.9, 3, or a range of any two of the above values. By adjusting the specific surface area of ​​the carbon material within the scope of this application, the carbon material can have a suitable specific surface area and particle size, which can shorten the lithium-ion transport path, improve the kinetic performance of the carbon material, and thus further improve the kinetic performance of the secondary battery.

[0040] In one embodiment of this application, in the Raman spectrum of a carbon material, at 1300 cm⁻¹... -1 Up to 1400cm -1 Within the range, there is a peak intensity of I. D The first characteristic peak is at 1550 cm⁻¹. -1 Up to 1650cm -1 Within the range, there is a peak intensity of I. G The second characteristic peak, 0.1 < I D / I G <0.4. For example, I D / I G The value can be 0.11, 0.13, 0.15, 0.17, 0.19, 0.2, 0.21, 0.23, 0.25, 0.27, 0.29, 0.3, 0.31, 0.33, 0.35, 0.37, 0.39, or a range of any two of the above values. In the Raman spectrum of carbon materials, I D / I G The value of I is within the scope of this application. D / I G The value is relatively small, and carbon materials have good kinetic properties, which enables secondary batteries to have good kinetic performance.

[0041] In one embodiment of this application, the ratio (W) of the mass percentage of carbon material to the mass percentage of silicon carbide material is based on the sum of the masses of carbon material and silicon carbide material. Gr / W Si The range is 1 to 20. For example, W... Gr / W Si The value can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range of any two of the above values. Carbon materials can improve the kinetic and cycle performance of secondary batteries, while silicon-carbon materials can improve the energy density of secondary batteries. By adjusting the ratio of the mass percentage of carbon materials to the mass percentage of silicon-carbon materials within the scope of this application, secondary batteries can achieve both good kinetic and cycle performance, as well as high energy density.

[0042] In one embodiment of this application, the electrode assembly further includes a positive electrode tab and a negative electrode tab. The positive electrode sheet includes a first empty foil region and a positive electrode material layer region, with the positive electrode tab disposed in the first empty foil region. The negative electrode sheet includes a second empty foil region and a negative electrode material layer region, with the negative electrode tab disposed in the second empty foil region. For ease of understanding, a two-dimensional Cartesian coordinate system is established with the width direction of the unfolded negative electrode sheet as the Y-direction and the length direction of the unfolded negative electrode sheet as the X-direction. It can be understood that the dimension of the second empty foil region along the Y-direction is the width of the second empty foil region. Figure 3 As shown, the negative electrode 100 includes a second empty foil region 110 and a negative electrode material layer region 120, with the negative electrode tab disposed in the second empty foil region 110. The phrase "the negative electrode tab is disposed in the second empty foil region" refers to retaining the uncoated material layer during coating and transforming the empty current collector into a full tab structure through a flattening process after winding; that is, the entire area of ​​the second empty foil region constitutes the negative electrode tab. It can be understood that the positive electrode has the same structure as the negative electrode, including a first empty foil region and a positive electrode material layer region, with the positive electrode tab disposed in the first empty foil region. With the electrode assembly structure configured as described above, current can be transmitted through the empty current collector, maximizing the uniformity of current density distribution in the electrode, reducing polarization of the secondary battery, and further improving the kinetic and cycle performance of the secondary battery. In this application, the width w1 of the second empty foil region 110 is 5 mm to 20 mm.

[0043] In one embodiment of this application, such as Figure 3As shown, along the width direction (Y direction) of the unfolded negative electrode sheet 100, the negative electrode sheet 100 includes a first edge 101 and a second edge 102. From the first edge 101 to the second edge 102, the negative electrode sheet 100 is sequentially provided with a second empty foil region 110 and a negative electrode material layer region 120. The negative electrode sheet has the above structure, and the positive electrode sheet also has the above structure. The electrode assembly adopts a full tab structure, allowing current to be transmitted through an empty current collector, maximizing the uniformity of current density distribution in the electrode sheet, reducing polarization of the secondary battery, and further improving the kinetic performance and cycle performance of the secondary battery.

[0044] In one embodiment of this application, along the width direction of the unfolded positive electrode sheet, the positive electrode sheet includes opposing third and fourth edges. From the third edge to the fourth edge, the positive electrode sheet sequentially comprises a first empty foil region and a positive electrode material layer region. With the above structure on both the positive and negative electrode sheets, the electrode assembly adopts a full-tab structure, allowing current to be transmitted through an empty current collector. This maximizes the uniformity of current density distribution within the electrode sheet, reduces polarization of the secondary battery, and further improves the kinetic and cycle performance of the secondary battery.

[0045] This application does not impose any particular limitation on the preparation method of porous carbon. Exemplarily, the preparation method of porous carbon may include, but is not limited to, the following steps: carbonizing a carbon raw material under an inert atmosphere, followed by cooling and crushing to obtain carbonaceous particles; placing the carbonaceous particles in a rotary kiln, introducing CO2 gas for activation and pore-forming treatment, followed by cooling to obtain porous carbon particles; and subjecting the porous carbon particles to airflow pulverization and classification to obtain porous carbon. This application does not impose any particular limitation on the carbon raw material, as long as it achieves the purpose of this application. For example, the carbon raw material may include, but is not limited to, phenolic resin or coconut shell. This application does not impose any particular limitation on the inert atmosphere, as long as it achieves the purpose of this application. For example, the inert atmosphere may include a nitrogen atmosphere or an argon atmosphere. This application does not impose any particular limitation on the carbonization temperature T1 and time t1, as long as it achieves the purpose of this application. For example, T1 may be 700℃ to 1100℃, and t1 may be 4h to 8h. This application does not impose any particular limitation on the particle size Dv50 of the carbonaceous particles, as long as it achieves the purpose of this application. For example, the particle size Dv50 of the carbonaceous particles can be less than 80 μm. This application does not impose any particular limitations on the temperature T2 and time t2 of the activation and pore-forming treatment, as long as the purpose of this application is achieved. For example, T2 can be from 650℃ to 1200℃, and t2 can be from 4 h to 8 h. This application does not impose any particular limitations on the particle size Dv50 of the porous carbon, as long as the purpose of this application is achieved. For example, the particle size Dv50 of the porous carbon can be less than 9 μm.

[0046] This application does not impose any particular limitation on the preparation method of silicon-carbon materials. Exemplarily, the preparation method of silicon-carbon materials may include, but is not limited to, the following steps: placing the prepared porous carbon in a fluidized bed chemical vapor deposition furnace, heating and holding it under an inert atmosphere, then introducing a silicon source for silicon grain vapor deposition to obtain porous carbon with silicon deposited on the surface; then stopping the introduction of the silicon source, continuing to introduce inert gas while heating and holding it at that temperature, then introducing a carbon source for surface passivation treatment to obtain passivated silicon-carbon; placing the passivated silicon-carbon in a rotary kiln, heating and holding it under an inert atmosphere, then introducing a carbon source for surface coating treatment, then naturally cooling to room temperature and sieving to obtain the desired silicon-carbon material. This application does not impose any particular limitation on the silicon source, as long as it can achieve the purpose of this application. For example, the silicon source may include, but is not limited to, silane (SiH4), dichlorosilane (Si2H6), or trichlorosilane (SiHCl3). Preferably, the silicon source may include silane. This application does not impose any particular limitations on the temperature T3 and time t3 of the silicon grain vapor deposition process, as long as the purpose of this application is achieved. For example, T3 can be from 400°C to 600°C, and t3 can be from 3 hours to 9 hours. This application does not impose any particular limitations on the gas flow rate v1 introduced into the silicon source, as long as the purpose of this application is achieved. For example, v1 can be from 2 L / min to 6 L / min. This application does not impose any particular limitations on the carbon source, as long as the purpose of this application is achieved. For example, the carbon source can include, but is not limited to, acetylene, methane, ethylene, or propane; preferably, the carbon source can include acetylene. This application does not impose any particular limitations on the temperature T4 and time t4 of the surface passivation process, as long as the purpose of this application is achieved. For example, T4 can be from 400°C to 750°C, and t4 can be from 0.2 hours to 2 hours. This application does not impose any particular limitations on the gas flow rate v2 introduced into the carbon source during the surface passivation process, as long as the purpose of this application is achieved. For example, v2 can be from 0.5 L / min to 3 L / min. This application does not impose any particular restrictions on the temperature T5 and time t5 of the surface coating process, as long as the purpose of this application is achieved. For example, T5 can be from 420℃ to 800℃, and t5 can be from 1h to 6h. This application does not impose any particular restrictions on the gas flow rate v3 of the carbon source introduced during the surface coating process, as long as the purpose of this application is achieved. For example, v3 can be from 1L / min to 4L / min.

[0047] This application does not impose any particular limitation on the method of controlling the thickness of the silicon coating layer, as long as the purpose of this application can be achieved. For example, the thickness of the silicon coating layer can be controlled by adjusting the silicon source inlet time. For instance, when the silicon source gas flow rate remains constant, extending the silicon source inlet time increases the thickness of the silicon coating layer; shortening the silicon source inlet time decreases the thickness of the silicon coating layer.

[0048] This application does not impose any particular limitation on the method of controlling the thickness of the carbon coating layer, as long as the purpose of this application can be achieved. For example, the thickness of the carbon coating layer can be controlled by adjusting the carbon source introduction time. For instance, when the carbon source gas flow rate remains constant, extending the carbon source introduction time increases the thickness of the carbon coating layer; shortening the carbon source introduction time decreases the thickness of the carbon coating layer.

[0049] This application does not impose any particular limitation on the method of controlling the mass percentage of silicon in silicon-carbon materials, as long as the purpose of this application can be achieved. For example, the thickness of the silicon coating layer can be controlled by adjusting the silicon source introduction time, thereby controlling the mass percentage of silicon in the silicon-carbon material. For instance, when the silicon source gas flow rate remains constant, extending the silicon source introduction time increases the thickness of the silicon coating layer and thus increases the mass percentage of silicon in the silicon-carbon material; conversely, shortening the silicon source introduction time decreases the thickness of the silicon coating layer and thus decreases the mass percentage of silicon in the silicon-carbon material.

[0050] This application does not impose any particular limitation on the method of controlling the mass percentage of carbon in silicon-carbon materials, as long as the purpose of this application can be achieved. For example, the thickness of the carbon coating layer can be controlled by adjusting the carbon source introduction time, thereby controlling the mass percentage of carbon in the silicon-carbon material. For instance, when the carbon source gas flow rate remains constant, extending the carbon source introduction time increases the thickness of the carbon coating layer and thus increases the mass percentage of carbon in the silicon-carbon material; conversely, shortening the carbon source introduction time decreases the thickness of the carbon coating layer and thus decreases the mass percentage of carbon in the silicon-carbon material.

[0051] This application does not impose any particular restrictions on the method of controlling the value of I1 / I2, as long as the purpose of this application can be achieved. For example, the thickness of the silicon coating layer can be controlled by adjusting the silicon source inlet time, thereby controlling the value of I1 / I2. For instance, when the silicon source inlet rate remains constant, extending the silicon source inlet time increases the thickness of the silicon coating layer and decreases the value of I1 / I2; conversely, shortening the silicon source inlet time decreases the thickness of the silicon coating layer and increases the value of I1 / I2.

[0052] This application does not impose any particular restrictions on the method of controlling the reversible capacity of silicon-carbon materials at 0.05C, as long as the purpose of this application can be achieved. For example, the reversible capacity of silicon-carbon materials at 0.05C can be controlled by adjusting the mass percentage of silicon in the material. For instance, increasing the mass percentage of silicon increases the reversible capacity; decreasing the mass percentage of silicon decreases the reversible capacity.

[0053] This application does not impose any particular restrictions on the method of controlling the particle size Dv50 and specific surface area of ​​carbon materials, as long as the purpose of this application can be achieved. For example, the particle size Dv50 and specific surface area of ​​carbon materials can be controlled by grinding them. For instance, when other conditions remain unchanged, extending the grinding time decreases the particle size Dv50 and increases the specific surface area; shortening the grinding time increases the particle size Dv50 and decreases the specific surface area. For example, commercially available carbon materials with different particle sizes Dv50 can be selected, and the particle size Dv50 can be tested using the "particle size test" method described in this application, and a carbon material with the desired particle size Dv50 can be selected. For example, commercially available carbon materials with different specific surface areas can be selected, and the specific surface area can be tested using the "specific surface area test" method described in this application, and a carbon material with the desired specific surface area can be selected.

[0054] This application relates to carbon materials. D / I G There are no particular restrictions on how the value of I can be adjusted, as long as the purpose of this application can be achieved. For example, the I value of carbon materials can be adjusted by controlling the degree of graphitization. D / I G The value of I. For example, as the graphitization degree of carbon materials increases, I... D / I G The value increases; the graphitization degree of carbon materials decreases, I D / I G The value decreases.

[0055] This application does not impose any particular restrictions on the method of controlling the ratio of the mass percentage of carbon material to the mass percentage of silicon-carbon material, as long as the purpose of this application can be achieved. For example, the ratio of the mass percentage of carbon material to the mass percentage of silicon-carbon material can be controlled by adjusting the mass percentage of both added carbon material and silicon-carbon material.

[0056] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors (such as lithium copper composite current collectors, carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.).

[0057] The negative electrode material layer of this application includes a negative electrode active material, which includes silicon-carbon materials and / or carbon materials. The negative electrode material layer of this application also includes a negative electrode conductive agent and a negative electrode binder. This application does not have particular limitations on the negative electrode conductive agent and negative electrode binder in the negative electrode material layer, as long as they can achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned conductive carbon black may include, but is not limited to, Super P, acetylene black, or Ketjen black. The aforementioned carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The negative electrode binder may include, but is not limited to, at least one of polyacrylic acid, polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride (PVDF), polystyrene-butadiene copolymer (styrene-butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode conductive agent, and negative electrode binder in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0058] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 16 μm. This application also does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the single-sided negative electrode material layer can be from 25 μm to 150 μm.

[0059] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned negative electrode conductive agents and negative electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent and binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0060] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire area of ​​the positive current collector or only a portion of it; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0061] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0062] The positive electrode material layer of this application includes a positive electrode active material, which comprises a substance capable of reversibly inserting and extracting active ions such as lithium ions. The positive electrode material layer can be one or more layers, and each layer in a multilayer positive electrode material layer can contain the same or different positive electrode active materials. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The aforementioned lithium nickel cobalt manganese oxide can include LiNi... 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3At least one of O2 (NCM111). The positive electrode material layer of this application also includes a positive electrode conductive agent and a positive electrode binder. This application does not have any particular limitations on the positive electrode conductive agent and the positive electrode binder in the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the positive electrode conductive agent may include at least one of the above-mentioned negative electrode conductive agents; the positive electrode binder may include at least one of the above-mentioned negative electrode binders. This application does not have any particular limitations on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0063] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be 6 μm to 16 μm. This application also does not impose any particular limitation on the thickness of the positive electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided positive electrode material layer can be 25 μm to 120 μm.

[0064] Optionally, the positive electrode may further include a conductive layer, which is located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned positive electrode conductive agents and positive electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0065] In this application, a separator is used to separate the positive and negative electrode plates, preventing internal short circuits in the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. This application does not impose any particular limitations on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the separator type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0066] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a diaphragm binder. This application does not particularly limit the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the aforementioned diaphragm binder, and may include at least one of the aforementioned negative electrode binders. The polymer layer contains a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene). This application does not impose any particular limitation on the thickness of the diaphragm, as long as it achieves the purpose of this application; for example, the thickness of the diaphragm can be from 5 μm to 20 μm.

[0067] The secondary battery of this application also includes an electrolyte. The electrolyte includes a lithium salt. This application does not particularly limit the type of lithium salt, and lithium salts known in the art can be used. For example, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiB(C2O4)2, LiBOB), or lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB). This application does not particularly limit the mass percentage of lithium salt in the electrolyte, as long as the purpose of this application is achieved. The electrolyte also includes a non-aqueous organic solvent. This application does not particularly limit the non-aqueous organic solvent, as long as the purpose of this application is achieved. For example, the non-aqueous organic solvent may include at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are 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 aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters.This application does not impose any particular limitation on the mass percentage of non-aqueous organic solvents in the electrolyte, as long as the purpose of this application can be achieved.

[0068] The secondary battery of this application also includes a packaging bag for containing the electrode assembly and electrolyte, as well as other components known in the art, which are not limited in this application. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0069] This application does not particularly limit the type of secondary battery, which can include any device in which an electrochemical reaction occurs. In this application, the secondary battery can include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc. This application does not particularly limit the lithium-ion secondary battery; for example, the lithium-ion secondary battery can be a pouch battery, a square steel-cased battery, or a cylindrical steel-cased battery. Preferably, the lithium-ion secondary battery can be a cylindrical steel-cased battery.

[0070] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery. Furthermore, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0071] A second aspect of this application provides an electronic device comprising the secondary battery of any of the foregoing embodiments. Therefore, the electronic device provided by this application has good kinetic and cycle performance, as well as high energy density.

[0072] This application does not specifically limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0073] Example

[0074] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0075] Test methods and equipment:

[0076] ΔE test:

[0077] When a lithium-ion battery is discharged to 2.0V at a rate of 10C at -20℃, there is an initial discharge voltage E0 at the beginning of the discharge. The voltage continues to decrease, and then the voltage increases. The process of the lithium-ion battery voltage first decreasing and then increasing is reflected in the discharge curve of the lithium-ion battery as a voltage trough, which has a trough voltage E1. The difference between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is ΔE.

[0078] In this application, the better the dynamic properties of the material, the smaller ΔE.

[0079] Thickness testing of silicon coating and carbon coating:

[0080] The silicon-carbon material was sliced ​​using a focused ion beam (FIB) and then the thickness of the silicon and carbon coating layers was observed at a magnification of 500,000 using a high-resolution transmission electron microscope (HRTEM, model JEM-F200).

[0081] Test of the mass percentage of elements in silicon-carbon materials:

[0082] The silicon-carbon material was heated to 500°C in a muffle furnace using an elemental analyzer, and then digested with concentrated nitric acid. After dilution, the mass percentage of silicon was measured using an elemental analyzer. The mass percentage of carbon in the silicon-carbon material is calculated as 100% - the mass percentage of silicon.

[0083] Reversible capacity test:

[0084] The silicon-carbon material described in this application is used as the negative electrode active material, Super P as the conductive agent, and polyacrylic acid as the binder. The mass ratio of the negative electrode active material, Super P, and polyacrylic acid is 80:10:10. The negative electrode active material, Super P, polyacrylic acid, and deionized water are thoroughly mixed to obtain a negative electrode slurry with a solid content of 35 wt%. The negative electrode slurry is uniformly coated on copper foil and dried to obtain a negative electrode sheet. The negative electrode sheet is cut into small circular pieces with a diameter of 14 mm. A lithium sheet with a diameter of 16 mm is used as the counter electrode. Using the separator and electrolyte described in Examples 1-1, a coin cell is assembled for testing. The coin cell was kept at 25°C for 12 hours, discharged at a constant current of 0.05C to 5.0mV, allowed to stand for 5 minutes, discharged at a constant current of 10μA to 5.0mV, allowed to stand for 5 minutes, and discharged at a constant current of 5μA to 5.0mV. It was then charged at a constant current of 0.05C to 2.0V. The specific capacity of the coin cell at this point was recorded and denoted as the reversible capacity D0 at 0.05C.

[0085] Particle size testing:

[0086] The particle size of the carbon material was measured using a Malvern particle size analyzer (MasterSizer 2000). 0.02 g of carbon material was added to a 50 mL clean beaker, along with 20 mL of ethanol as a dispersant. The mixture was ultrasonicated for 30 min in a 120 W ultrasonic cleaner to completely disperse the carbon material in the ethanol, obtaining a sample dispersion. The particle size Dv50 of the carbon material was then measured using the Malvern particle size analyzer.

[0087] Specific surface area test:

[0088] According to the national standard "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" (GB / T 19587-2017), the specific surface area of ​​carbon materials was tested by nitrogen adsorption using a specific surface area analyzer (model TristarⅡ3020M).

[0089] Raman spectroscopy test:

[0090] The Raman spectra of carbon materials were measured using a laser confocal Raman microscopy instrument (HR Evolution, HORIBA Scientific Instruments Division). The carbon materials showed a Raman spectrum at 1350 cm⁻¹. -1 The peak intensity at point I D At 1580cm -1 The peak intensity at point I G Carbon materials I D / I G The value is obtained as follows: Take the obtained carbon material, test 100 points, and obtain 100 corresponding I values. D / I GThe value of 100 I values ​​was calculated. D / I G The average value of the carbon material is the I value. D / I G The value of .

[0091] Discharge temperature rise test:

[0092] After attaching a temperature sensing wire to the surface of a lithium-ion battery, it was left to stand at 25°C for 30 minutes, and then discharged at a rate of 10C to 2.5V. The temperature change curve during the discharge process was recorded, and the initial discharge temperature T0 and the maximum temperature Tmax were recorded. The discharge temperature rise = Tmax - T0.

[0093] In this application, the better the kinetic properties of the material, the smaller the temperature rise when discharging at a rate of 10C at 25°C.

[0094] Cyclic performance test:

[0095] At 25°C, the lithium-ion battery was charged at a constant current of 1.2C to 4.25V, then charged at a constant voltage of 4.25V until the current reached 0.02C. After resting for 5 minutes, it was discharged at a constant current of 8C to 2.5V. This was the first cycle, and the discharge capacity was recorded. The lithium-ion battery was subjected to charge-discharge cycles according to the above process. The test was stopped after 300 cycles (cls), and the capacity retention rate was calculated as an indicator to evaluate the cycle performance of the lithium-ion battery.

[0096] Capacity retention rate after 300 cls cycles (%) = (Discharge capacity after 300 cls cycles / Discharge capacity after the first cycle) × 100%.

[0097] Example 1-1

[0098] <Preparation of Porous Carbon>

[0099] (1) The phenolic resin was carbonized under a nitrogen protective atmosphere, and after cooling, it was taken out and the carbonized block was crushed into carbon particles with a particle size Dv50 of 70μm; wherein, the carbonization temperature T1 was 900℃ and the carbonization time t1 was 6h.

[0100] (2) The above carbon particles are placed in a rotary kiln, CO2 gas is introduced, and activation and pore-forming treatment is carried out. After cooling, they are taken out to obtain porous carbon particles; wherein, the temperature T2 of the activation and pore-forming treatment is 850℃, and the time t2 of the activation and pore-forming treatment is 6h.

[0101] (3) The above porous carbon particles are subjected to air jet milling and classification to obtain porous carbon with a particle size Dv50 of about 8 μm.

[0102] <Preparation of Silicon-Carbon Materials>

[0103] (1) Silicon grain vapor deposition: Take 1 kg of the above porous carbon and place it in a fluidized bed chemical vapor deposition furnace. Under nitrogen atmosphere protection, heat it to T3 of 490℃ at a rate of 5℃ / min. After holding it at this temperature for 30 min, introduce silane gas at a gas flow rate of 3L / min with a v1. Continue to introduce gas and hold it at t3 for 5 h to obtain porous carbon with silicon deposited on the surface.

[0104] (2) Surface passivation treatment: After the silane gas is introduced in step (1) above, nitrogen gas is introduced and the temperature is raised to T4 of 530°C at a rate of 2°C / min. After holding for 30 min, acetylene gas is introduced at a gas flow rate of 1 L / min at v2. The temperature is held for t4 of 1 h, and then naturally cooled to obtain passivated silicon carbon with silicon grains distributed in porous carbon after surface passivation.

[0105] (3) Surface coating treatment: The above passivated silicon carbon is placed in a rotary furnace and heated to T5 of 530°C at a rate of 8°C / min under a nitrogen protective atmosphere. After holding at this temperature for 30 min, acetylene gas is introduced at a gas flow rate of 2 L / min at v3. The temperature is held for t5 for 3 h. Then, the acetylene gas is stopped and the heating is stopped. After naturally cooling to room temperature, the silicon carbon material is taken out and sieved to obtain the desired silicon carbon material.

[0106] <Preparation of Negative Electrode Sheets>

[0107] Artificial graphite, silicon carbide material, lithium carboxymethyl cellulose, and carbon nanotubes were uniformly mixed, and then 50 wt% (based on the total mass of added polyacrylic acid) of polyacrylic acid and deionized water were added to prepare a slurry with a solid content of 62 wt%, which was then kneaded for 90 min. The remaining 50 wt% of polyacrylic acid and deionized water were then added to prepare a slurry with a solid content of 50 wt%, which was then dispersed for 30 min. Deionized water was then added again to prepare a slurry with a solid content of 42 wt%, which was dispersed for another 40 min, followed by vacuum degassing for 30 min to obtain the negative electrode slurry. The mass ratio of artificial graphite, silicon carbide material, polyacrylic acid, lithium carboxymethyl cellulose, and carbon nanotubes was 87.2:10:2:0.4:0.4. The ratio of the mass percentage of carbon material to the mass percentage of silicon carbide material (W) based on the sum of the masses of artificial graphite and silicon carbide material was used to obtain the negative electrode slurry. Gr / W Si The particle size Dv50 of the artificial graphite is 8.72; the specific surface area BET is 1.26 m². 2 / g、I D / I G It is 0.32.

[0108] The prepared negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector using an extrusion coating machine and dried at 90°C, yielding a coating with a mass of 100 mg / 1540.25 mm.2 A negative electrode sheet with a single-sided coating of negative electrode material was obtained, and the above steps were repeated on the other side of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 90℃, it was cold-pressed and then slit to obtain negative electrode sheets with a size of 78mm × 875mm for later use. The compaction density of the negative electrode material layer after cold pressing was 1.65g / cm³. 3 The structure of the prepared negative electrode sheet is as follows: Figure 3 As shown, along the Y direction, from the first edge to the second edge, the negative electrode sheet is sequentially provided with a second empty foil area and a negative electrode material layer area, and the width of the second empty foil area is 12mm.

[0109] <Preparation of the positive electrode>

[0110] Lithium nickel cobalt manganese oxide (Ni91), PVDF, Super P, and carbon nanotubes were mixed in a mass ratio of 97.6:1.3:0.6:0.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 76 wt%. The slurry was then dispersed for 40 min and degassed under vacuum to obtain the positive electrode slurry.

[0111] The prepared positive electrode slurry was uniformly coated onto one surface of a 13 μm thick aluminum foil current collector and dried at 90°C, yielding a coating with a mass of 245 mg / 1540.25 mm. 2 A positive electrode sheet with a single-sided coating of positive electrode material was obtained, and the above steps were repeated on the other side of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 90℃, it was cold-pressed and then slit to obtain positive electrode sheets with a size of 74mm × 867mm for later use. The compaction density of the positive electrode material layer after cold pressing was 3.60 g / cm³. 3 The structure of the prepared positive electrode sheet is similar to... Figure 3 The structure of the negative electrode sheet shown is the same. Along the width direction after the positive electrode sheet is unfolded, the positive electrode sheet includes a third edge and a fourth edge. From the third edge to the fourth edge, the positive electrode sheet is sequentially provided with a first empty foil area and a positive electrode material layer area. The width of the first empty foil area is 15mm.

[0112] <Preparation of Electrolyte>

[0113] In an argon-atmospheric glove box with a water content of less than 10 ppm, DMC, DEC, and EC were mixed in a mass ratio of 1:1:1 to obtain a basic organic solvent. Lithium salt LiPF6 was then added to the basic organic solvent, dissolved, and mixed thoroughly. Finally, vinylene carbonate was added to obtain the electrolyte. Based on the mass of the electrolyte, the lithium salt content was 12.5% ​​by mass, the vinylene carbonate content was 2% by mass, and the remainder was the basic organic solvent.

[0114] <Septum>

[0115] PVDF and alumina were mixed at a mass ratio of 9:1, and NMP was added as a solvent to prepare a slurry with a solid content of 12 wt%. The mixture was stirred evenly to obtain an inorganic layer slurry. The inorganic layer slurry was uniformly coated on one surface of a 7 μm thick PP film substrate. After drying, a separator with a single-sided inorganic layer thickness of 2 μm was obtained.

[0116] <Preparation of Lithium-ion Batteries>

[0117] The prepared positive electrode, separator, negative electrode, and separator are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to form an electrode assembly. The uncoated foil area on the end face of the electrode assembly is flattened, and a current collector is welded onto it. The assembly is then placed in a vacuum oven at 85°C for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, capacity testing, and high-temperature aging. The electrode assembly employs a full-tab structure.

[0118] Examples 1-2 to Examples 1-7

[0119] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0120] Examples 1-8 to Examples 1-10

[0121] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-2.

[0122] Examples 1-11

[0123] Except for adjusting the mass ratio of artificial graphite, silicon carbide material, polyacrylic acid, lithium carboxymethyl cellulose, and carbon nanotubes to 76.2:20:2.4:0.6:0.8 in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Examples 1-9.

[0124] Examples 1-12

[0125] Except for adjusting the mass ratio of artificial graphite, silicon carbide material, polyacrylic acid, lithium carboxymethyl cellulose, and carbon nanotubes to 92.4:5:1.8:0.4:0.4 in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Examples 1-9.

[0126] Examples 1-13 to Examples 1-16

[0127] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-9.

[0128] Examples 1-17

[0129] Besides the bipolar structure used in the electrode assembly in the <Preparation of Lithium-ion Batteries>, the structure of the negative electrode in the electrode assembly is as follows: Figure 4 As shown, the negative electrode 100 includes a negative electrode material layer 120 and a negative electrode tab 111, and the structure of the positive electrode in the electrode assembly is similar to... Figure 4 The structure shown is the same. Except for the positive electrode material layer and the positive electrode tab, the positive electrode sheet is the same as in Examples 1-9.

[0130] Comparative Example 1

[0131] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-9.

[0132] Comparative Example 2

[0133] Except for the absence of surface coating treatment in the <Preparation of Silicon-Carbon Materials>, the rest is the same as in Examples 1-9.

[0134] The preparation parameters, material properties, and electrical properties of each embodiment and comparative example are shown in Tables 1 and 2.

[0135] Table 1

[0136] t3(h) v1(L / min) t5(h) Dv50(μm) <![CDATA[BET(m 2 / g)]]> <![CDATA[I D / I G ]]> Example 1-1 5 3 3 12 1.26 0.32 Examples 1-2 6 3 3 12 1.26 0.32 Examples 1-3 7 3 3 12 1.26 0.32 Examples 1-4 4.5 3 3 12 1.26 0.32 Examples 1-5 8 3 3 12 1.26 0.32 Examples 1-6 4 3.75 3 12 1.26 0.32 Examples 1-7 6.67 2.25 3 12 1.26 0.32 Examples 1-8 6 3 5 12 1.26 0.32 Examples 1-9 6 3 2 12 1.26 0.32 Examples 1-10 6 3 1 12 1.26 0.32 Examples 1-11 6 3 2 12 1.26 0.32 Examples 1-12 6 3 2 12 1.26 0.32 Examples 1-13 6 3 2 16 0.92 0.35 Examples 1-14 6 3 2 12 1.24 0.19 Examples 1-15 6 3 2 8 1.12 0.16 Examples 1-16 6 3 2 12 2.92 0.31 Examples 1-17 6 3 2 12 1.26 0.32 Comparative Example 1 4 3 2 12 1.26 0.32 Comparative Example 2 6 3 / 12 1.26 0.32

[0137] Note: In Table 1, " / " indicates that there are no relevant preparation parameters.

[0138] Table 2

[0139]

[0140] Note: In Table 2, " / " indicates that there are no relevant preparation parameters.

[0141] Referring to Tables 1 and 2, and from Examples 1-1 to 1-17 and Comparative Examples 1 to 2, it can be seen that when silicon-carbon materials meet the above characteristics, lithium-ion batteries have higher energy density, smaller ΔE, smaller temperature rise at 25°C 10C discharge, and higher capacity retention rate after 300cls cycling. This indicates that the lithium-ion battery of this application has better kinetic performance and cycle performance, and also has higher energy density.

[0142] As can be seen from Examples 1-1 to 1-5, the main parameter to be changed is the silane introduction time. Under the same silane gas flow rate, the longer the silane introduction time, the more silicon is introduced into the porous carbon. However, the pore volume of porous carbon is fixed. When silane is continued to be introduced into the internal pores after deposition, it will cause the silane to decompose on the particle surface, thereby forming a coating layer of different thicknesses on the particle surface. Generally, the longer the silane introduction time, the thicker the silicon coating layer formed on the surface, and the higher the mass percentage of silicon element in the silicon-carbon material after deposition. Similarly, since the active silicon is the main component that plays the role of delithiation and lithium insertion in silicon-carbon materials, the reversible capacity of silicon-carbon materials also increases with the increase of the mass percentage of silicon element. The first delithiation dQ / dV curve of silicon-carbon material contains a first delithiation peak between 0.25V and 0.32V and a second delithiation peak between 0.35V and 0.45V. The intensity of the second delithiation peak is closely related to the size of silicon grains in the silicon-carbon material. Since the average pore size of the porous carbon used in this application is <2nm, the size of silicon grains in the silicon-carbon material is mainly related to the thickness of the silicon coating layer on the surface of the silicon-carbon material. The thicker the silicon coating layer, the higher the crystallinity of the corresponding silicon-carbon material, and the stronger the peak intensity of the second delithiation peak in the dQ / dV curve. The peak intensity ratio I1 / I2 of the first delithiation peak and the second delithiation peak is also smaller. In this application, the longer the silane introduction time, the smaller I1 / I2 is. In Examples 1 to 1-5, artificial graphite and silicon-carbon materials were added at a fixed ratio of 87.2:10 during the preparation of the negative electrode. Therefore, the higher the reversible capacity of the silicon-carbon material, the higher the reversible capacity of the corresponding negative electrode, and the higher the energy density of the lithium-ion battery. In Examples 1-1 to 1-3, as the thickness of the silicon coating layer increased, ΔE and the discharge temperature rise at 25°C / 10C both decreased, resulting in better kinetic performance of the lithium-ion battery. Compared with Examples 1-2, Examples 1-3 showed a significant increase in the thickness of the silicon coating layer and an increase in silicon content. The increased silicon content led to greater expansion and increased side reactions with the electrolyte, resulting in relatively poor cycle performance. In Examples 1-4, the silane introduction time was short and the silicon coating layer thickness was small, resulting in relatively poor lithium-ion transport effects in the transport channels built on the particle surface and inside the particles. Consequently, the kinetic performance of the lithium-ion battery was poor, the polarization was large, and its cycle performance was also relatively poor. In Examples 1-5, the silane introduction time was relatively long and the silicon coating layer was thick, making lithium-ion shuttle difficult and resulting in poor kinetic performance. Furthermore, the relatively high silicon content also led to poor electronic conductivity, resulting in relatively poor cycle performance of the lithium-ion battery. The preparation parameters of the silicon-carbon material and the thickness of the silicon coating layer are within the scope of this application, resulting in a lithium-ion battery with better kinetic and cycle performance, as well as higher energy density.

[0143] As shown in Examples 1-1, 1-6, and 1-7, when the silane gas flow rate is increased and the silane introduction time is shortened, silane is more easily deposited on the material surface under these reaction conditions, resulting in a thicker surface silicon coating. However, this also leads to lower silane utilization, causing a decrease in the mass percentage of silicon in the silicon-carbon material and a reduction in reversible capacity. While the thicker surface silicon coating results in a smaller I1 / I2 ratio, the reduced reversible capacity ultimately lowers the actual energy density of the lithium-ion battery. However, the increased silicon coating thickness improves kinetic performance, with reduced ΔE and a lower 25°C 10C discharge temperature rise. Furthermore, the improved kinetic performance reduces lithium-ion battery polarization during cycling, mitigating electrolyte consumption by the negative electrode and slightly improving the cycle performance of the lithium-ion battery. Conversely, reducing the silane gas flow rate and extending the silane introduction time leads to greater adsorption and deposition of silane within the pores of porous carbon, resulting in a reduced thickness of the silicon coating layer on the particle surface. However, this slightly improves the utilization rate of silane, leading to a slight increase in the mass percentage of silicon in the silicon-carbon material and its reversible capacity, as well as a slight increase in the energy density of the lithium-ion battery. Simultaneously, the reduced thickness of the surface silicon coating layer results in an increase in the I1 / I2 ratio, and a slight deterioration in the kinetic properties of the silicon-carbon material. This leads to an increase in the ΔE and the 25°C 10C discharge temperature rise of the lithium-ion battery, and a slight deterioration in cycle performance due to increased polarization in the lithium-ion battery.

[0144] As shown in Examples 1-2, 1-8 to 1-10, changing the acetylene introduction time (i.e., the carbon coating time) increases the thickness of the carbon coating as the coating time increases. Compared to Examples 1-2 and 1-9, Examples 1-8 show that the increased carbon coating thickness due to the extended coating time leads to an increase in the mass percentage of carbon in the silicon-carbon material and a decrease in the mass percentage of silicon, resulting in a decrease in the reversible capacity of the silicon-carbon material and the energy density of the lithium-ion battery. Simultaneously, the thicker carbon coating makes it more difficult for lithium ions to pass through, leading to a deterioration in the kinetic performance of the silicon-carbon material, with increased ΔE and a higher 25°C / 10C discharge temperature rise, resulting in poorer cycle performance. Compared with Examples 1-2 and 1-9, Examples 1-10 show that the coating time is further shortened, which leads to a decrease in the conductivity of silicon-carbon materials, hindering electron transport in the negative electrode sheet, and consequently resulting in a decrease in the dynamic performance of the lithium-ion battery. ΔE and the discharge temperature rise at 25℃ and 10C both increase. At the same time, as the carbon coating layer becomes thinner, its consumption of electrolyte increases, leading to a decrease in the cycle performance of the lithium-ion battery.

[0145] As shown in Examples 1-9, 1-11, and 1-12, the main change is the amount of silicon added to the negative electrode. When the amount of silicon added increases, the mass percentage ratio of artificial graphite to silicon-carbon material in the negative electrode decreases, increasing the energy density of the lithium-ion battery. However, the increased silicon content hinders electron transport and lithium-ion diffusion in the negative electrode, leading to poorer kinetic performance, increased ΔE and 25°C 10C discharge temperature rise, and increased electrolyte consumption by the negative electrode, further degrading the cycle performance of the lithium-ion battery. Conversely, reducing the amount of silicon added results in a lower energy density but improved kinetic and cycle performance.

[0146] As can be seen from Examples 1-9, 1-13 to 1-16, the main change is in the performance indicators of the artificial graphite. In Examples 1-13, the particle size of the artificial graphite is related to I... D / I G The relatively large particle size of the artificial graphite results in poor kinetic performance and consequently, poorer cycle performance. Examples 1-15, however, simultaneously reduce the particle size and I of the artificial graphite. D / I G Its kinetic and cycling performance is the best. In Examples 1-9 and 1-16, the particle size of the carbon material remains unchanged, but the carbon material in Examples 1-16 has a relatively large specific surface area. D / I G Slightly smaller, the kinetic performance of Examples 1-16 is slightly better, but the larger specific surface area results in more active sites and increased side reactions, leading to poorer cycle performance of the lithium-ion battery. In Examples 1-9 and 1-14, the particle size of the carbon material remains unchanged, and the I in Examples 1-14... D / I G Its size is relatively small, resulting in relatively good dynamic performance and cycle performance.

[0147] Compared to Examples 1-9, Examples 1-17 employ a bitab structure. In this type of structure, during discharge, electrons can only move towards the electrodes through the two tabs, resulting in a higher current density near the tabs and poor uniformity of current density distribution within the electrode sheet. The negative electrode sheet contains silicon, leading to slightly higher film resistance. Therefore, the more concentrated the current density distribution, the greater the polarization of the lithium-ion battery, resulting in a larger ΔE and poorer cycle performance. In Examples 1-9, by retaining the uncoated current collector during coating and transforming it into a full-tab structure through a flattening process after winding, current can be transmitted through the uncoated current collector, further improving the uniformity of current density distribution within the electrode sheet, reducing lithium-ion battery polarization, and resulting in better kinetic and cycle performance of the lithium-ion battery.

[0148] Comparative Example 1 further shortened the silane introduction time and controlled the material surface to have no silicon coating layer. At this time, after lithium ions pass through the carbon coating layer, they can only diffuse into the particle interior through the pores, resulting in poor kinetic performance of the lithium-ion battery.

[0149] The material in Comparative Example 2 lacks a carbon coating, resulting in poor conductivity of the material, which in turn leads to higher impedance and poorer kinetic performance of the lithium-ion battery. During cycling, the silicon comes into direct contact with the electrolyte, causing rapid consumption of the electrolyte and resulting in poor cycle performance of the lithium-ion battery.

[0150] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0151] The various embodiments in this specification are described in a related manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0152] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising an electrode assembly, the electrode assembly comprising a negative electrode, a positive electrode, 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, the silicon-carbon material comprising a substrate, a silicon coating layer, and a carbon coating layer, the substrate comprising porous carbon and nano-silicon particles, the pores of the porous carbon containing the nano-silicon particles, and the silicon coating layer disposed between the substrate and the carbon coating layer; In the first delithiation dQ / dV curve of the silicon-carbon material, there is a first delithiation peak in the range of 0.25V to 0.32V and a second delithiation peak in the range of 0.35V to 0.45V. The peak intensity of the first delithiation peak is I1 and the peak intensity of the second delithiation peak is I2, and 0.1≤I1 / I2≤3.

2. The secondary battery according to claim 1, wherein, The secondary battery is discharged at a rate of 10C at -20℃. The difference between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is ΔE, where 0.1V≤ΔE≤0.6V.

3. The secondary battery according to claim 1, wherein, The thickness of the silicon coating layer is H1 nm, and the thickness of the carbon coating layer is H2 nm, where 1 ≤ H1 ≤ 100 and 5 ≤ H2 ≤ 100.

4. The secondary battery according to claim 1, wherein, Based on the mass of the silicon-carbon material, the mass percentage of silicon in the silicon-carbon material is W1%, the mass percentage of carbon in the silicon-carbon material is W2%, 40≤W1≤70, 30≤W2≤60.

5. The secondary battery according to any one of claims 1 to 4, wherein, The reversible capacity of the silicon-carbon material at 0.05C is D0 mAh / g, where 1500≤D0≤2500.

6. The secondary battery according to any one of claims 1 to 4, wherein, The silicon-carbon material satisfies at least one of the following characteristics: (1) The thickness of the silicon coating layer is H1 nm, the thickness of the carbon coating layer is H2 nm, 3≤H1≤80, 10≤H2≤50; (2) Based on the mass of the silicon-carbon material, the mass percentage of silicon in the silicon-carbon material is W1%, the mass percentage of carbon in the silicon-carbon material is W2%, 45≤W1≤65, 35≤W2≤55; (3) In the first delithiation dQ / dV curve of the silicon-carbon material, there is a first delithiation peak in the range of 0.25V to 0.32V and a second delithiation peak in the range of 0.35V to 0.45V. The peak intensity of the first delithiation peak is I1 and the peak intensity of the second delithiation peak is I2, and 0.2≤I1 / I2≤2.

7. The secondary battery according to any one of claims 1 to 4, wherein, The negative electrode material layer further includes a carbon material, which satisfies at least one of the following characteristics: (1) The carbon material includes at least one of natural graphite, artificial graphite or hard carbon; (2) The particle size Dv50 of the carbon material satisfies: 5μm≤Dv50≤18μm; (3) The specific surface area BET of the carbon material satisfies: 0.5m 2 / g≤BET≤3m 2 / g; (4) In the Raman spectrum of the carbon material, at 1300 cm⁻¹ -1 Up to 1400cm -1 Within the range, there is a peak intensity of I. D The first characteristic peak is at 1550 cm⁻¹. -1 Up to 1650cm -1 Within the range, there is a peak intensity of I. G The second characteristic peak, 0.1 < I D / I G <0.

4.

8. The secondary battery according to claim 7, wherein, Based on the sum of the masses of the carbon material and the silicon-carbon material, the ratio of the mass percentage of the carbon material to the mass percentage of the silicon-carbon material is between 1 and 20.

9. The secondary battery according to any one of claims 1 to 4, wherein, The electrode assembly further includes a positive electrode tab and a negative electrode tab. The positive electrode sheet includes a first empty foil region and a positive electrode material layer region, and the positive electrode tab is disposed in the first empty foil region. The negative electrode sheet includes a second empty foil region and a negative electrode material layer region, and the negative electrode tab is disposed in the second empty foil region.

10. The secondary battery according to claim 9, wherein, Along the width direction after the negative electrode sheet is unfolded, the negative electrode sheet includes a first edge and a second edge opposite to each other. From the first edge to the second edge, the negative electrode sheet is sequentially provided with a second empty foil area and a negative electrode material layer area.

11. An electronic device comprising a secondary battery as described in any one of claims 1 to 10.

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