Secondary battery and electronic device

Abstract

The application provides a secondary battery and an electronic device, the secondary battery comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer, the negative electrode material layer comprising a first negative electrode material layer and a second negative electrode material layer, a half of a width difference between the first negative electrode material layer and the second negative electrode material layer being W mm, a half of a width difference between the first negative electrode material layer and the positive electrode material layer being L mm, and 0.2≤W / L≤4. The first negative electrode active material comprises a first graphite material, the second negative electrode active material comprises a second graphite material and a silicon-based material, the average particle size of the particles of the first negative electrode active material being D1 μm, the average particle size of the particles of the second negative electrode active material being D2 μm, and 1.1≤D2 / D1≤1.8. Through the above arrangement, the side reaction of the edge region of the sheet can be reduced, and the cycle performance of the secondary battery can be improved.

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] Secondary batteries, such as lithium-ion batteries, have the characteristics of high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the consumer electronics field.

[0003] Currently, lithium-ion batteries employ a full-tab design, where the positive and negative tabs extend from opposite directions and are manufactured using full-tab cutting and stacking or flattening techniques. However, the full-tab flattening structure can lead to electrode wetting problems, especially at the electrode edges. Electrolyte accumulates on both sides of the material layer, causing continuous side reactions that result in capacity loss and reduced cycle performance. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and electronic device to reduce side reactions in the electrode edge region and improve the cycle performance of the secondary battery.

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

[0006] The first aspect of this application provides a secondary battery, including a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector. The negative electrode includes a negative current collector and a negative electrode material layer located on at least one surface of the negative current collector. The negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer. Along the thickness direction of the negative electrode, the first negative electrode material layer is located between the negative current collector and the second negative electrode material layer. Along the width direction of the unfolded negative electrode, the width of the first negative electrode material layer is greater than the width of the second negative electrode material layer. Half of the width difference between the first and second negative electrode material layers is W mm, and the width of the first negative electrode material layer is greater than the width of the positive electrode material layer. Half of the width difference between the first and positive electrode material layers is L mm, where 0.2 ≤ W / L ≤ 4; optionally, 1 ≤ W / L ≤ 3. The first negative electrode material layer includes a first negative electrode active material, which includes a first graphite material. The second negative electrode material layer includes a second negative electrode active material, which includes a second graphite material and a silicon-based material. The average particle size of the first negative electrode active material is D1 μm, and the average particle size of the second negative electrode active material is D2 μm, where 1.1 ≤ D2 / D1 ≤ 1.8; optionally, 1.3 ≤ D2 / D1 ≤ 1.6. By setting a double-layer coating method and controlling the W / L value within the scope of this application, the wider first negative electrode material layer plays a certain physical barrier role, thereby reducing the diffusion of lithium ions to the edge region of the negative electrode sheet and effectively reducing the occurrence of side reactions at the electrode edge. Furthermore, by controlling the D2 / D1 value within the scope of this application, the particles in the first and second negative electrode material layers cooperate with each other, increasing the compaction density of the negative electrode sheet, reducing the risk of electrolyte enrichment on both sides of the negative electrode sheet and causing side reactions, forming a channel more conducive to lithium ion transport, thereby improving the cycle performance of the secondary battery.

[0007] In one or more embodiments of this application, 0.2 ≤ L ≤ 5; and / or, 7 ≤ D1 ≤ 15. This configuration helps reduce side reactions while maintaining the energy density of the secondary battery. Furthermore, the particles in the first and second negative electrode material layers can cooperate with each other, thereby improving the cycle performance of the secondary battery.

[0008] In one or more embodiments of this application, based on the mass of the second negative electrode material layer, the mass percentage of Si element in the second negative electrode material layer is A, where 1% ≤ A ≤ 50%; optionally, 15.5% ≤ A ≤ 30%. By adjusting the value of A within the above range, the secondary battery of this application has good cycle performance, high energy density, and good structural stability.

[0009] In one or more embodiments of this application, along the width direction after the negative electrode sheet is unfolded, the compaction density of the region of the first negative electrode material layer extending beyond the second negative electrode material layer is PD1 g / cm³. 3 The compaction density of the second negative electrode material layer is PD2 g / cm³. 3 The ratio of PD2 / PD1 is 0.8 ≤ PD2 / PD1 ≤ 1.6; optionally, 1.0 ≤ PD2 / PD1 ≤ 1.4. By adjusting the value of PD2 / PD1 within the above range, the occurrence of side reactions is reduced, and the cycle performance of the secondary battery is improved while maintaining energy density.

[0010] In one or more embodiments of this application, 0.8 ≤ PD1 ≤ 1.5; and / or, 1.3 ≤ PD2 ≤ 1.65. This configuration reduces the occurrence of side reactions and improves the cycle performance of the secondary battery while maintaining energy density.

[0011] In one or more embodiments of this application, the first graphite material and the second graphite material are each independently selected from at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, or hard carbon, and the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbide, or silicon alloy. Through the above arrangement, the first negative electrode material layer and the second negative electrode material layer are combined, and the secondary battery of this application improves both cycle performance and energy density while also enhancing kinetic performance and safety performance.

[0012] In one or more embodiments of this application, based on the mass of the first negative electrode material layer, the mass percentage w1 of the first graphite material is 95% to 99%; based on the mass of the second negative electrode material layer, the mass percentage w2 of the second graphite material is 28% to 95%, and the mass percentage w3 of the silicon-based material is 1% to 70%. With the above configuration, while taking into account kinetic performance and improving the structural stability and cycle performance of the secondary battery, the secondary battery also has a high energy density.

[0013] In one or more embodiments of this application, along the width direction after the negative electrode sheet is unfolded, the first negative electrode material layer includes opposing first and second edges, the second negative electrode material layer includes opposing third and fourth edges, the edge of the second negative electrode material layer closest to the first edge is the third edge, the region of the first negative electrode material layer from the first edge to the third edge is the first monolayer region, and the region of the first negative electrode material layer from the second edge to the fourth edge is the second monolayer region; multiple grooves are provided on the first monolayer region and / or the second monolayer region, the multiple grooves extending along the width direction after the negative electrode sheet is unfolded and spaced apart along the length direction after the negative electrode sheet is unfolded. This arrangement helps reduce the risk of side reactions caused by electrolyte accumulation at the edge of the negative electrode sheet, and also reduces the risk of lithium plating and cycle performance degradation due to insufficient CB at the edge of the negative electrode sheet caused by the grooves, thereby improving the cycle performance of the secondary battery.

[0014] In one or more embodiments of this application, along the length direction of the unfolded negative electrode sheet, the width of a single groove is W' μm, where 20 ≤ W' ≤ 400; optionally, 90 ≤ W' ≤ 150. By adjusting the value of W' within the above range, it is beneficial to accelerate the conduction of the electrolyte, thereby improving the cycle performance of the secondary battery while taking into account processing performance.

[0015] In one or more embodiments of this application, along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single groove to the width of the first monolayer region or the second monolayer region is P, where 0.2 ≤ P ≤ 1; optionally, 0.4 ≤ P ≤ 1. By adjusting the value of P within the above range, it is beneficial to accelerate the conduction of the electrolyte, thereby improving the cycle performance of the secondary battery while taking into account processing performance.

[0016] In one or more embodiments of this application, along the thickness direction of the negative electrode sheet, the thickness of the first monolayer region or the second monolayer region is H μm, and the average depth of the multiple grooves is H' μm, where 2 ≤ H' ≤ 0.8H; optionally, 2 ≤ H' ≤ 0.6H. By adjusting the value of H' within the above range, it is beneficial to accelerate the conduction of the electrolyte, thereby improving the cycle performance of the secondary battery while taking into account processing performance.

[0017] In one or more embodiments of this application, 15 ≤ H ≤ 35. By adjusting the value of H within the above range, the secondary battery exhibits good cycle performance and high energy density while also possessing good structural stability.

[0018] In one or more embodiments of this application, the distance between two adjacent grooves along the length of the unfolded negative electrode sheet is N mm, where 1 ≤ N ≤ 5. By adjusting the value of N within the above range, it is beneficial to accelerate the conduction of the electrolyte, thereby improving the cycle performance of the secondary battery while taking into account processing performance.

[0019] A second aspect of this application provides an electronic device comprising the secondary battery found in any of the above embodiments. Therefore, the electronic device provided by this application has good performance in use.

[0020] The beneficial effects of the embodiments of this application are as follows:

[0021] This application provides a secondary battery and electronic device. By employing a double-layer coating method and controlling the W / L value within the range of this application, the wider first negative electrode material layer provides a certain physical barrier, thereby reducing the diffusion of lithium ions to the edge region of the negative electrode sheet and effectively reducing the occurrence of side reactions at the electrode edge. Furthermore, by controlling the D2 / D1 value within the range of this application, the particles in the first and second negative electrode material layers cooperate with each other, increasing the compaction density of the negative electrode sheet, reducing the risk of electrolyte accumulation on both sides of the negative electrode sheet and causing side reactions, and forming a more favorable channel for lithium ion transport, thereby improving the cycle performance of the secondary battery.

[0022] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0024] Figure 1 This is a schematic diagram showing the unfolded electrode assembly in one embodiment of this application;

[0025] Figure 2 This is a schematic diagram showing the negative electrode sheet unfolding along its width in one embodiment of this application;

[0026] Figure 3 for Figure 2 A cross-sectional view along the AA direction;

[0027] Reference numerals: negative electrode 10; positive electrode 20; separator 30; negative current collector 11; negative electrode material layer 12; first negative electrode material layer 121; second negative electrode material layer 122; positive current collector 21; positive electrode material layer 22; first edge 1211; second edge 1212; third edge 1221; fourth edge 1222; first monolayer region 12101; second monolayer region 12102; groove 13. Detailed Implementation

[0028] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and 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.

[0029] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0030] The first aspect of this application provides a secondary battery, including a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector. The negative electrode includes a negative current collector and a negative electrode material layer located on at least one surface of the negative current collector. The negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer. Along the thickness direction of the negative electrode, the first negative electrode material layer is located between the negative current collector and the second negative electrode material layer. Along the width direction of the unfolded negative electrode, the width of the first negative electrode material layer is greater than the width of the second negative electrode material layer. Half of the width difference between the first and second negative electrode material layers is W mm, and the width of the first negative electrode material layer is greater than the width of the positive electrode material layer. Half of the width difference between the first and positive electrode material layers is L mm, where 0.2 ≤ W / L ≤ 4; optionally, 1 ≤ W / L ≤ 3. For example, the W / L value can be 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, or a range of any two of these values. The first negative electrode material layer includes a first negative electrode active material, which includes a first graphite material. The second negative electrode material layer includes a second negative electrode active material, which includes a second graphite material and a silicon-based material. The average particle size of the first negative electrode active material is D1 μm, and the average particle size of the second negative electrode active material is D2 μm, where 1.1 ≤ D2 / D1 ≤ 1.8; optionally, 1.3 ≤ D2 / D1 ≤ 1.6. For example, the D2 / D1 value can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or a range of any two of these values.

[0031] In this application, the length direction of the negative electrode is defined as the X direction, the width direction as the Y direction, and the thickness direction as the Z direction. It can be understood that the length, width, and thickness directions of the positive electrode and the separator are the same as those of the negative electrode in the unfolded state.

[0032] For example, such as Figure 1As shown, the negative electrode 10 includes a negative current collector 11 and a negative electrode material layer 12 on the surface of the negative current collector 11. The positive electrode 20 includes a positive current collector 21 and a positive electrode material layer 22 on the surface of the positive current collector 21. The negative electrode material layer 12 includes a first negative electrode material layer 121 and a second negative electrode material layer 122. Along the thickness direction Z of the negative electrode 10, the first negative electrode material layer 121 is located between the negative current collector 11 and the second negative electrode material layer 122. Along the width direction Y of the unfolded negative electrode 10, the width of the first negative electrode material layer 121 is greater than the width of the second negative electrode material layer 122, and half of the width difference between the first negative electrode material layer 121 and the second negative electrode material layer 122 is W mm. The width of the first negative electrode material layer 121 is greater than the width of the positive electrode material layer 22, and half of the width difference between the first negative electrode material layer 121 and the positive electrode material layer 22 is L mm.

[0033] The inventors discovered that in double-coated electrodes, especially Si / C composite double-coated negative electrodes, the electrolyte is easily squeezed to the edges of the negative electrode. The superimposed gravity on the negative electrode side further increases electrolyte accumulation, leading to continuous side reactions at the electrode edge. Furthermore, the potential difference between Si and C materials and the crosstalk effect exacerbate these side reactions, resulting in capacity loss and decreased cycle performance in the secondary battery. This application utilizes a double-coating method where the width of the first negative electrode material layer is greater than that of the second negative electrode material layer and also greater than that of the positive electrode material layer. When the W / L value is too small (below the lower limit of this application), it cannot provide effective physical blocking; when the W / L value is too large (below the upper limit of this application), it affects the energy density of the secondary battery. By adjusting the W / L value within the aforementioned range, while maintaining the energy density of the secondary battery, the wider first negative electrode material layer provides a certain physical barrier. This first negative electrode material layer includes a first graphite material, which has high chemical stability and minimal volume expansion during cycling, thereby reducing the diffusion of lithium ions to the edge region of the negative electrode and effectively minimizing side reactions. Furthermore, considering the particle size distribution of the upper and lower active material layers, when the D2 / D1 value is too small (below the lower limit of this application), the edge porosity of the second negative electrode material layer is too low, making electrolyte wetting difficult. This leads to electrolyte accumulation on both sides of the negative electrode, causing side reactions and reducing the cycle performance of the secondary battery. Conversely, when the D2 / D1 value is too large (above the upper limit of this application), the particles of the upper and lower active materials cannot form a good fit, resulting in a decrease in the ultimate compaction density of the electrode, a loss of energy density in the secondary battery, and excess pores storing electrolyte, causing crosstalk reactions and further reducing the cycle performance of the secondary battery. By adjusting the D2 / D1 value within the aforementioned range, the particles in the first and second negative electrode material layers can cooperate with each other. Small particles can fill the gaps between large particles, thereby increasing the ultimate compaction density of the negative electrode sheet. At the same time, it maintains the connectivity of ion channels, facilitates the control of the porosity of the edge region of the negative electrode sheet, reduces the risk of electrolyte deterioration on the negative electrode sheet due to silicon expansion, and prevents electrolyte enrichment on both sides of the negative electrode sheet, which could lead to side reactions. This forms a channel that is more conducive to lithium-ion transport, thereby improving the cycle performance of the secondary battery.

[0034] The aforementioned "positive electrode material layer located on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be located on one surface of the positive electrode current collector along its thickness direction, or on two surfaces of the positive electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface of the positive electrode current collector, or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved. Similarly, the aforementioned "negative electrode material layer located on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be located on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface of the negative electrode current collector, or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved.

[0035] This application does not impose any particular restrictions on the method of controlling the average particle size of the negative electrode active material, as long as the purpose of this application can be achieved. For example, different negative electrode active materials can be purchased according to the required average particle size. Alternatively, the average particle size of the negative electrode active material can also be controlled by grinding or other methods.

[0036] In one or more embodiments of this application, 0.2 ≤ L ≤ 5. For example, the value of L can be 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, or a range of any two of these values. By adjusting the value of L within the above range, the direct contact between the edge of the positive electrode material layer and the electrolyte is reduced, lowering the risk of side reactions occurring at the edge of the positive electrode during charging and discharging. Furthermore, while maintaining the energy density of the secondary battery, the wider first negative electrode material layer provides a certain physical barrier. The first negative electrode material layer includes a first graphite material, which has high chemical stability and minimal volume expansion during cycling, thereby reducing the diffusion of lithium ions to the edge region of the negative electrode and helping to reduce the occurrence of side reactions. Therefore, the secondary battery of this application has good cycle performance.

[0037] In one or more embodiments of this application, 7 ≤ D1 ≤ 15. For example, the value of D1 can be 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of these values. By adjusting the value of D1 within the above range, the porosity of the negative electrode edge is moderate, which is beneficial for electrolyte wetting and reduces the risk of side reactions caused by electrolyte accumulation on both sides of the negative electrode. At the same time, the particles in the first and second negative electrode material layers can cooperate with each other to increase the ultimate compaction density of the negative electrode and maintain ion channel connectivity, forming channels that are more conducive to lithium ion transport, thereby improving the cycle performance of the secondary battery.

[0038] In one or more embodiments of this application, 0.2 ≤ L ≤ 5, for example, the value of L can be 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, or a range consisting of any two of these values; and / or, 7 ≤ D1 ≤ 15, for example, the value of D1 can be 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of these values. Through the above settings, while considering the energy density of the secondary battery, the wider first negative electrode material layer provides a certain physical barrier, thereby reducing the diffusion of lithium ions to the edge region of the negative electrode sheet, which is beneficial for reducing the occurrence of side reactions. Furthermore, the particles in the first and second negative electrode material layers can cooperate with each other to increase the ultimate compaction density of the negative electrode sheet while maintaining the connectivity of ion channels. This facilitates the control of the porosity of the edge region of the negative electrode sheet, reduces the risk of side reactions caused by electrolyte accumulation on both sides of the negative electrode sheet, and forms a channel that is more conducive to lithium ion transport, thereby improving the cycle performance of the secondary battery.

[0039] In one or more embodiments of this application, 0.04 ≤ W ≤ 20. For example, the value of W can be 0.04, 0.05, 0.08, 0.1, 0.2, 0.5, 0.8, 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 these values. By adjusting the value of W within the above range, while maintaining the energy density of the secondary battery, the wider first negative electrode material layer provides a certain physical barrier, thereby reducing the diffusion of lithium ions to the edge region of the negative electrode sheet, which in turn helps to reduce the occurrence of side reactions. Therefore, the secondary battery of this application has good cycle performance.

[0040] In one or more embodiments of this application, 7.7 ≤ D2 ≤ 27. For example, the value of D2 can be 7.7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, or a range consisting of any two of these values. By adjusting the value of D2 within the above range, it is beneficial to the mutual coordination of particles in the first and second negative electrode material layers, increasing the ultimate compaction density of the negative electrode sheet, while maintaining ion channel connectivity, reducing the risk of pore blockage due to silicon expansion, forming channels more conducive to lithium-ion transport, thereby improving the cycle performance of the secondary battery.

[0041] In one or more embodiments of this application, based on the mass of the second negative electrode material layer, the mass percentage of Si element in the second negative electrode material layer is A, where 1% ≤ A ≤ 50%; optionally, 15.5% ≤ A ≤ 30%. For example, the value of A can be 1%, 3%, 5%, 8%, 10%, 12%, 15%, 15.2%, 15.5%, 15.8%, 16%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, or a range consisting of any two of these values. By adjusting the value of A within the above range, it is beneficial to reduce the risk of lithium plating in the secondary battery due to insufficient local CB, and to improve the energy density of the secondary battery while maintaining the structural stability of the negative electrode sheet. Therefore, the secondary battery of this application has good cycle performance, high energy density, and good structural stability.

[0042] In this application, the CB value refers to the ratio between the capacity of a negative electrode sheet per unit area and the capacity of a positive electrode sheet per unit area under the same conditions, such as an ambient temperature of 25°C and a discharge rate of 0.1C. CB = (Specific capacity of negative electrode active material × Mass of negative electrode active material per unit area of ​​negative electrode sheet) / (Specific capacity of positive electrode active material × Mass of positive electrode active material per unit area of ​​positive electrode sheet). The aforementioned unit area refers to 1 mm². 2 .

[0043] In one or more embodiments of this application, along the width direction after the negative electrode sheet is unfolded, the compaction density of the region of the first negative electrode material layer extending beyond the second negative electrode material layer is PD1 g / cm³. 3 The compaction density of the second negative electrode material layer is PD2 g / cm³. 3The PD2 / PD1 ratio is 0.8 ≤ PD2 / PD1 ≤ 1.6; optionally, 1.0 ≤ PD2 / PD1 ≤ 1.4. For example, the PD2 / PD1 value can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or a range of any two of these values. By adjusting the PD2 / PD1 value within the above range, the compaction density of the edge region of the negative electrode sheet is moderate, which helps reduce the risk of electrolyte enrichment on both sides of the negative electrode sheet and subsequent side reactions. Simultaneously, it allows the secondary battery to have a higher energy density and reduces the risk of crosstalk reactions caused by the potential difference between Si and C materials within the negative electrode material layer, leading to a decrease in cycle performance. Therefore, the occurrence of side reactions is reduced, improving the cycle performance of the secondary battery while maintaining energy density. In this application, it can be understood that the area where the first negative electrode material layer extends beyond the second negative electrode material layer along the width direction after the negative electrode sheet is unfolded is the area where the second negative electrode material layer is not disposed on the surface of the first negative electrode material layer away from the negative electrode current collector along the width direction after the negative electrode sheet is unfolded.

[0044] In one or more embodiments of this application, 0.8 ≤ PD1 ≤ 1.5. For example, the value of PD1 can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or a range consisting of any two of these values; and / or, 1.3 ≤ PD2 ≤ 1.65. For example, the value of PD2 can be 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, or a range consisting of any two of these values. Through the above settings, the edge region of the negative electrode sheet achieves a moderate compaction density, which helps reduce the risk of electrolyte enrichment on both sides of the negative electrode sheet and subsequent side reactions. Simultaneously, it enables the secondary battery to have a higher energy density and reduces the risk of crosstalk reactions caused by the potential difference between Si and C materials within the negative electrode material layer, leading to a decrease in cycle performance. Therefore, the occurrence of side reactions is reduced, improving the cycle performance of the secondary battery while maintaining energy density.

[0045] This application does not impose any particular restrictions on the method of controlling the compaction density of the region of the first negative electrode material layer that extends beyond the second negative electrode material layer along the width direction after the negative electrode sheet is unfolded, as long as the purpose of this application can be achieved. For example, it can be achieved by adjusting the cold pressing pressure, the coating amount of the first slurry, the coating amount of the second slurry, etc. For example, when the first slurry is coated on the surface of the negative electrode current collector, with other conditions remaining constant, increasing the coating amount of the first slurry increases the compaction density of the region where the first negative electrode material layer extends beyond the second negative electrode material layer along the width direction after the negative electrode sheet is unfolded; when the second slurry is coated on the surface of the negative electrode current collector, with other conditions remaining constant, increasing the coating amount of the second slurry increases the compaction density of the second negative electrode material layer, and vice versa; or, with other conditions remaining constant, increasing the cold pressing pressure in the region where the first negative electrode material layer extends beyond the second negative electrode material layer along the width direction after the negative electrode sheet is unfolded increases the compaction density of the region where the first negative electrode material layer extends beyond the second negative electrode material layer along the width direction after the negative electrode sheet is unfolded; with other conditions remaining constant, increasing the cold pressing pressure increases the compaction density of the second negative electrode material layer, and vice versa.

[0046] In one or more embodiments of this application, the first graphite material and the second graphite material are each independently selected from at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, or hard carbon, and the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbide, or silicon alloy. By selecting the aforementioned silicon-based material, first graphite material, and second graphite material, the first negative electrode material layer and the second negative electrode material layer are arranged in combination, which improves the structural stability of the negative electrode sheet while also giving the negative electrode sheet a lower impedance. Therefore, the secondary battery of this application improves both kinetic performance and safety performance while balancing cycle performance and energy density.

[0047] In this application, the silicon-carbon compound is a silicon-carbon composite material. Based on the mass of the silicon-carbon composite material, the mass percentage content of silicon is 30% to 70%, and the mass percentage content of carbon is 30% to 70%. This application does not impose any particular limitation on the silicon-carbon composite material, as long as it achieves the purpose of this application. For example, the silicon-carbon composite material can be a composite material obtained by deposition. Exemplarily, the silicon-carbon composite material can be silicon material deposited on a carbon framework, or carbon material deposited on a silicon framework. The silicon oxide compound includes SiOx, where 0 < x < 2. Exemplarily, the silicon oxide compound can include silicon suboxide (SiO, where the molar ratio of silicon to oxygen is 1:1).

[0048] In one or more embodiments of this application, based on the mass of the first negative electrode material layer, the mass percentage content w1 of the first graphite material is 95% to 99%. For example, the value of the mass percentage content w1 of the first graphite material can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, or a range consisting of any two of these values. Based on the mass of the second negative electrode material layer, the mass percentage content w2 of the second graphite material is 28% to 95%, and the mass percentage content w3 of the silicon-based material is 1% to 70%. For example, the mass percentage w2 of the second graphite material can be 28%, 29%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 92%, 95%, or a range of any two of these values, and the mass percentage w3 of the silicon-based material can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range of any two of these values. By adjusting the values ​​of w1, w2, and w3 within the aforementioned range, the volume change of the first graphite material during the charging and discharging process of the secondary battery is relatively small, which is beneficial to improving the structural stability of the negative electrode sheet. Furthermore, the first graphite material has good conductivity, which is beneficial to improving the kinetic performance of the secondary battery. Combined with the high-capacity silicon-based material in the second negative electrode material layer and the relatively stable second graphite material, the secondary battery has a high energy density while taking into account kinetic performance, improving the structural stability and cycle performance of the secondary battery.

[0049] In one or more embodiments of this application, along the width direction after the negative electrode sheet is unfolded, the first negative electrode material layer includes opposing first and second edges, the second negative electrode material layer includes opposing third and fourth edges, the edge of the second negative electrode material layer closest to the first edge is the third edge, the region of the first negative electrode material layer from the first edge to the third edge is the first single-layer region, and the region of the first negative electrode material layer from the second edge to the fourth edge is the second single-layer region; a plurality of grooves are provided on the first single-layer region and / or the second single-layer region, the plurality of grooves extending along the width direction after the negative electrode sheet is unfolded and spaced apart along the length direction after the negative electrode sheet is unfolded. For example, as... Figure 2 and Figure 3As shown, along the width direction Y after the negative electrode sheet 10 is unfolded, the first negative electrode material layer 121 includes a first edge 1211 and a second edge 1212, and the second negative electrode material layer 122 includes a third edge 1221 and a fourth edge 1222, with the edge of the second negative electrode material layer 122 closest to the first edge 1211 being the third edge 1221. The area of ​​the first negative electrode material layer 121 from the first edge 1211 to the third edge 1221 is the first single-layer region 12101, and the area of ​​the first negative electrode material layer 121 from the second edge 1212 to the fourth edge 1222 is the second single-layer region 12102. A plurality of grooves 13 are provided on the first single-layer region 12101, and the plurality of grooves 13 extend along the width direction Y after the negative electrode sheet 10 is unfolded and are spaced apart along the length direction X after the negative electrode sheet 10 is unfolded. The above settings help to accelerate the flow of electrolyte, reduce the risk of side reactions caused by electrolyte accumulation at the edge of the negative electrode, and reduce the risk of lithium plating and cycle performance degradation due to insufficient CB at the edge of the negative electrode caused by the groove, thereby improving the cycle performance of the secondary battery.

[0050] In this application, as Figure 1 and Figure 2 As shown, along the width direction Y after the negative electrode sheet 10 is unfolded, the widths of the first monolayer region 12101 and the second monolayer region 12102 of the first negative electrode material 121 are equal. At this time, half the difference in width between the first negative electrode material layer 121 and the second negative electrode material layer 122 is the width of the first monolayer region, which is also the width of the second monolayer region. It can be understood that, along the width direction after the negative electrode sheet is unfolded, when the distances from the two edges of the first negative electrode material layer to the two edges of the second negative electrode material layer are approximately equal, and the distances from the two edges of the first negative electrode material layer to the two edges of the positive electrode material layer are approximately equal, then half the difference in width between the first and second negative electrode material layers is the width of one side of the first negative electrode material layer exceeding the second negative electrode material layer, and half the difference in width between the first and positive electrode material layers is the width of one side of the first negative electrode material layer exceeding the positive electrode material layer.

[0051] In one or more embodiments of this application, along the length direction of the unfolded negative electrode sheet, the width of a single groove is W' μm, where 20 ≤ W' ≤ 400; optionally, 90 ≤ W' ≤ 150. For example, the value of W' can be 20, 30, 40, 50, 70, 90, 100, 120, 150, 180, 200, 220, 250, 280, 300, 320, 350, 380, 400, or a range consisting of any two of these values. For example, as... Figure 3As shown, along the X direction of the unfolded negative electrode sheet 10, the width of a single groove 13 is W' μm. By adjusting the value of W' within the above range, it is beneficial to accelerate the conduction of electrolyte, reduce the risk of side reactions caused by electrolyte accumulation at the edge of the negative electrode sheet, and at the same time reduce the risk of lithium plating and cycle performance degradation due to insufficient CB at the edge of the negative electrode sheet caused by the groove. While taking into account the processing performance, it improves the cycle performance of the secondary battery.

[0052] In one or more embodiments of this application, along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single groove to the width of the first monolayer region or the second monolayer region is P, where 0.2 ≤ P ≤ 1; optionally, 0.4 ≤ P ≤ 1. For example, the value of P can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range of any two of these values. By adjusting the value of P within the above range, it is beneficial to accelerate the conduction of the electrolyte, reduce the risk of side reactions caused by electrolyte accumulation at the edge of the negative electrode sheet, and reduce the risk of lithium plating and cycle performance degradation due to insufficient CB at the edge of the negative electrode sheet caused by the groove. This improves the cycle performance of the secondary battery while taking into account processing performance.

[0053] In one or more embodiments of this application, along the thickness direction of the negative electrode sheet, the thickness of the first monolayer region or the second monolayer region is H μm, and the average depth of the plurality of grooves is H' μm, where 2 ≤ H' ≤ 0.8H; optionally, 2 ≤ H' ≤ 0.6H. For example, the value of H' can be 2, 0.1H, 0.2H, 0.3H, 0.4H, 0.5H, 0.6H, 0.7H, 0.8H, or a range consisting of any two of these values. For example, as... Figure 3 As shown, along the thickness direction Z of the negative electrode 10, the thickness of the first monolayer region 12101 is H μm, and the average depth of the multiple grooves 13 is H' μm. By adjusting the value of H' within the above range, it is beneficial to accelerate the conduction of the electrolyte, reduce the risk of side reactions caused by electrolyte accumulation at the edge of the negative electrode, and at the same time reduce the risk of lithium plating and cycle performance degradation due to insufficient CB at the edge of the negative electrode caused by the grooves. While taking into account the processing performance, it improves the cycle performance of the secondary battery.

[0054] In one or more embodiments of this application, 15 ≤ H ≤ 35. For example, the value of H can be 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, or a range consisting of any two of these values. By adjusting the value of H within the above range, the secondary battery exhibits good cycle performance and high energy density while also possessing good structural stability.

[0055] In this application, the thickness H of the first monolayer region or the second monolayer region can be controlled by means known to those skilled in the art. For example, when the first slurry is coated on the corresponding area on the surface of the negative electrode current collector, the thickness of the first monolayer region or the second monolayer region can be increased by increasing the coating weight, and vice versa, based on a certain solid content of the first slurry. Alternatively, when the negative electrode sheet is cold-pressed, the thickness of the first monolayer region or the second monolayer region can be decreased by increasing the cold-pressing pressure of the corresponding area, and vice versa.

[0056] In one or more embodiments of this application, the distance between two adjacent grooves along the length of the unfolded negative electrode sheet is N mm, where 1 ≤ N ≤ 5. For example, the value of N can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, or a range of any two values ​​therein. For example, as shown... Figure 3 As shown, along the X-direction of the unfolded negative electrode sheet 10, the spacing between two adjacent grooves 13 is N mm. By adjusting the value of N within the aforementioned range, it is beneficial to accelerate electrolyte flow, reduce the risk of side reactions caused by electrolyte accumulation at the edge of the negative electrode sheet, and simultaneously reduce the risk of lithium plating and cycle performance degradation due to insufficient CB at the edge of the negative electrode sheet caused by the grooves. Furthermore, it helps to reduce the processing difficulty of the groove etching process and the risk of local collapse of the first negative electrode material layer, thus improving the cycle performance of the secondary battery while balancing processing performance. In this application, the spacing between two adjacent grooves refers to the distance between the centers of the widths of two adjacent grooves along the unfolded length of the negative electrode sheet.

[0057] In this application, the cross-section of a single groove refers to the plane formed by the groove along its length and thickness direction after unfolding the negative electrode sheet (or the cross-section obtained by viewing the groove along its length and thickness direction after unfolding the negative electrode sheet). This application does not impose any particular limitation on the cross-sectional shape of a single groove, as long as it achieves the purpose of this application. For example, the cross-section of a single groove can be independently selected from at least one of the following: triangular, arc-shaped (with an area smaller than a semicircle with the same radius), semicircular, rectangular, trapezoidal, or square.

[0058] This application does not impose any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors. For example, the composite current collector can be a lithium copper composite current collector, a carbon copper composite current collector, a nickel copper composite current collector, a titanium copper composite current collector, etc. In this application, there is no particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. In one or more embodiments of this application, the first negative electrode material layer includes a first conductive agent and a first binder, and the second negative electrode material layer includes a second conductive agent and a second binder. This application does not impose any particular limitation on the types of the first and second conductive agents, as long as they can achieve the purpose of this application. For example, the first and second conductive agents can each be independently selected from at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The conductive carbon black can include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are 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. This application does not impose any particular limitation on the types of the first and second adhesives, as long as they can achieve the purpose of this application. For example, the first and second adhesives may each be independently selected from at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0059] This application does not impose any particular restrictions on the preparation method of the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the preparation method of the negative electrode sheet includes, but is not limited to, the following steps: (1) mixing the first graphite material, the first binder and the first conductive agent evenly to obtain the first slurry; mixing the silicon-based material, the second graphite material, the second binder and the second conductive agent evenly to obtain the second slurry; (2) coating the first slurry on one surface of the negative electrode current collector, drying it to obtain a negative electrode sheet with a single-sided coating of the first negative electrode material layer, coating the second slurry on the surface of the first negative electrode material layer away from the negative electrode current collector, drying it to obtain a negative electrode sheet with a single-sided coating of the first negative electrode material layer and the second negative electrode material layer; (3) repeating the above operation on the other surface of the negative electrode current collector to obtain a negative electrode sheet with a double-sided coating of the first negative electrode material layer and the second negative electrode material layer; (4) after cold pressing and cutting the sheet into strips, determining the first single-layer area and the second single-layer area of ​​the first negative electrode material layer along the width direction after the negative electrode sheet is unfolded, and setting grooves on the first single-layer area and / or the second single-layer area to obtain the negative electrode sheet.

[0060] It is understandable that when coating the first slurry and the second slurry, the two coatings can be carried out by referring to the preparation method described above, that is, coating the first slurry first and then coating the second slurry; or the two layers can be coated directly, for example, the first slurry and the second slurry can be coated evenly on one surface of the negative electrode current collector at the same time using a two-layer coating machine.

[0061] In this application, the mass percentage content of the first graphite material in the first negative electrode material layer can be controlled by adjusting the mass ratio of the first graphite material, the first binder, and the first conductive agent added to the first slurry; the mass percentage content of silicon, the second graphite material, and the silicon-based material in the second negative electrode material layer can be controlled by adjusting the mass ratio of the silicon-based material, the second graphite material, the second binder, and the second conductive agent added to the second slurry; and the value of W can be controlled by adjusting the coating width of the first slurry and the second slurry in the width direction after the negative electrode sheet is unfolded.

[0062] This application does not impose any particular limitation on the solid content of the slurry, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the drying temperature and time, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the process parameters for cold pressing and slitting, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the method of setting the grooves, as long as the purpose of this application can be achieved; for example, grooves can be set using pulsed laser etching. The average depth H' and width W' of multiple grooves can be controlled by adjusting the power and defocusing amount of the pulsed laser emitter; the ratio P of the length of a single groove to the width of the first or second single-layer region can be controlled by adjusting the width of the first or second single-layer region, the power of the pulsed laser emitter, and the defocusing amount; the distance N between two adjacent grooves can be controlled by adjusting the distance between the pulsed laser emitters or the laser emission frequency.

[0063] In this application, the different features of the grooves included in the first single-layer region and / or the second single-layer region can be combined, and the implementation methods or embodiments covered by the above combinations are all within the protection scope of this application.

[0064] This application does not impose any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, or composite current collectors (such as aluminum-carbon composite current collectors). The positive electrode material layer of this application includes a positive electrode active material. This application does not impose any particular limitation on the type of positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, or lithium manganese iron phosphate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application is achieved. In this application, the positive electrode material layer may also include a binder and a conductive agent. In this application, there are no particular limitations on the type of binder in the positive electrode material layer, as long as the purpose of this application is achieved. For example, the binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the type of conductive agent in the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are 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 polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer; those skilled in the art can select according to actual needs, as long as it can achieve the purpose of this application.

[0065] In this application, the secondary battery includes a separator. For example, as shown... Figure 1As shown, a separator 30 is disposed between the positive electrode 20 and the negative electrode 10. This application does not impose any particular limitation on the separator, as long as it can achieve 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. In one or more embodiments of this application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven membrane or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous 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 disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material. In one or more embodiments of this application, the inorganic layer includes inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles 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 binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene). In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 3 μm to 30 μm.

[0066] In this application, the secondary battery includes an electrolyte, which comprises lithium salts and non-aqueous solvents. This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of lithium salts in the electrolyte, as long as it achieves the purpose of this application. This application does not impose any particular limitation on the non-aqueous solvent, as long as it achieves the purpose of this application. For example, the non-aqueous solvent may include, but is not limited to, 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 fluorocarbonate 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 (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorinated carbonate 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, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. 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, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0067] The secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0068] The preparation process of the secondary battery in this application is well known to those skilled in the art, and this application has no particular limitations. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery. In this application, the value of L can be controlled by adjusting the coating width of the positive electrode slurry and the first slurry (i.e., the slurry of the first negative electrode material layer) in the width direction after the negative electrode sheet is unfolded.

[0069] A second aspect of this application provides an electronic device comprising the secondary battery found in any of the above embodiments. Therefore, the electronic device provided by this application has good performance in use.

[0070] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, 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.

[0071] Example

[0072] 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.

[0073] Test methods and equipment:

[0074] Tests for W and L:

[0075] At 25°C, the lithium-ion battery was discharged to the discharge cutoff voltage at a constant current of 0.5C. After removing the lithium-ion battery casing, it was soaked in diethyl carbonate for 20 minutes to remove the electrolyte, thus obtaining the electrode assembly. The electrode assembly was then placed parallel to the length of the charge-coupled device (CCD) platform, and the positive electrode, negative electrode, and separator were obtained. Keeping the positions of each component unchanged, the two edges of the entire negative electrode material layer of the negative electrode and the two edges of the positive electrode material layer of the positive electrode were determined along the width direction after the negative electrode was unfolded. Then, L was measured using a CCD.

[0076] The negative electrode sheet was removed separately and unfolded. The surface of the unfolded negative electrode sheet was observed using a scanning electron microscope (SEM). Elemental scans were performed along the width of the unfolded negative electrode sheet, targeting regions of the negative electrode material layer 30 mm from each of the two edges. Due to the different types of active negative electrode materials contained in the first and second negative electrode material layers, a relatively clear boundary for Si element distribution exists between them along the width of the unfolded negative electrode sheet, thus distinguishing the first and second negative electrode material layers. W was measured based on the two Si element distribution boundaries obtained from the scanning and the two edges of the entire negative electrode material layer.

[0077] Each length was measured 5 times, and the average value was taken as the final result.

[0078] In this application, the discharge cutoff voltage of the lithium-ion battery in the embodiments and comparative examples is 2.5V. It can be understood that when the voltage range marked on the outer packaging of the battery is 2.5V to 4.2V, the charging cutoff voltage is 4.2V and the discharging cutoff voltage is 2.5V.

[0079] Negative electrode sampling:

[0080] The lithium-ion battery was discharged at a constant current of 0.5C to the discharge cutoff voltage at 25°C. The battery was then disassembled under an argon atmosphere, and the negative electrode was removed. The negative electrode was then soaked in dimethyl carbonate solvent for 2 hours and dried at 60°C for 1 hour to obtain the negative electrode. The discharge cutoff voltage of the lithium-ion battery in the embodiments and comparative examples of this application is 3.0V. It is understood that when the voltage range marked on the battery packaging is 2.5V to 4.2V, the charging cutoff voltage is 4.2V, and the discharging cutoff voltage is 2.5V.

[0081] Unless otherwise specified, the following test methods shall be performed using the negative electrode sheet obtained in the above manner. The distinction between the first and second negative electrode material layers can be found in "Testing of W and L".

[0082] Testing the average particle size of the negative electrode active material:

[0083] The average particle size D1 of the first negative electrode active material and the average particle size D2 of the second negative electrode active material were measured using scanning electron microscopy (SEM). A cross-section of the negative electrode sheet along its thickness direction was prepared, and the cross-section was ion-polished. The cross-section of the first negative electrode material layer was observed using SEM. The equivalent diameter of 32 randomly selected first graphite material particles was measured, and the average of these 32 equivalent diameters was taken as the average particle size D1 of the first negative electrode active material. In this application, the average particle size can be understood as the equivalent diameter. The equivalent diameter typically refers to the diameter of a sphere with the same volume as an irregularly shaped object. By measuring the area of ​​the silicon-based material particles in the cross-section of the negative electrode sheet, the diameter of a circle with the same area is used as the equivalent diameter of the silicon-based material particles.

[0084] The cross-section of the second anode material layer was observed using a scanning electron microscope, and the silicon-based material and the second graphite material in the cross-section were distinguished using backscattering mode. The equivalent diameters of 32 silicon-based material particles and 32 second graphite material particles were randomly selected and measured. The average value of the 64 particles was calculated as the average particle size D2 of the second anode active material.

[0085] In this application, the average particle size can be understood as the equivalent diameter. The equivalent diameter usually refers to the diameter of a sphere with the same volume as an irregularly shaped object. By measuring the area of ​​the particles of the negative electrode active material to be tested in the cross-section of the negative electrode sheet, the diameter of a circle with the same area is used as the equivalent diameter of the particles of the negative electrode active material to be tested.

[0086] Test of Si element mass percentage content:

[0087] The negative electrode sheet is fixed to the sample stage using conductive carbon adhesive, and the sample stage is placed on the support. The support and sample stage are then placed in the cross-section polishing apparatus (CP), and a vacuum of 10 is achieved. -4 After Pa, argon gas was used to cut along the thickness direction of the negative electrode sheet. The sample section after CP cutting was placed on the SEM sample stage with the cross-section facing upwards and observed using a Philips XL-30 field emission scanning electron microscope (SEM). The accelerating voltage was 10 kV, the emission current was 10 mA, and the magnification was 3000x. The mass percentage of silicon in the second negative electrode material layer was measured using the X-ray energy dispersive spectroscopy (EDS) instrument equipped with the SEM, and the mass percentage of Si in the second negative electrode material layer, A, was obtained.

[0088] Test of compaction density:

[0089] Using a punching machine, a small circular piece with an area of ​​S is punched from the second negative electrode material layer of the negative electrode sheet. Its mass is measured as M1, and its thickness is measured as t1 using a micrometer. Along the thickness direction of the negative electrode sheet, the boundary line between the first and second negative electrode material layers and the boundary line between the first negative electrode material layer and the negative electrode current collector are determined. The second negative electrode material layer is scraped off from the negative electrode sheet, and its mass is measured as M2. Its thickness is measured as t2 using a micrometer. The compaction density of the second negative electrode material layer is PD2 = (M1 - M2) / (t1 - t2) / S.

[0090] Following the steps described above, the region where the first negative electrode material layer extends beyond the second negative electrode material layer along the width direction after the negative electrode sheet is unfolded is tested to obtain the compaction density of the first negative electrode material layer in the corresponding region, i.e., the compaction density PD1 of the region where the first negative electrode material layer extends beyond the second negative electrode layer along the width direction after the negative electrode sheet is unfolded.

[0091] Testing of the mass percentage of silicon-based materials and graphite materials:

[0092] Along the thickness direction of the negative electrode sheet, determine the boundary line between the first negative electrode material layer and the second negative electrode material layer, and the boundary line between the first negative electrode material layer and the negative electrode current collector. Scrape off the second negative electrode material layer from the negative electrode sheet, weigh the scraped second negative electrode material layer powder to obtain mass m1, and then perform thermogravimetric analysis at a temperature range of 25℃ to 500℃ to remove the binder. Weigh the residual material after heating to obtain mass m2. m2 / m1 gives the mass percentage of the second negative electrode active material in the second negative electrode material layer.

[0093] X-ray diffraction (XRD) tests on the residual material after heating can distinguish and determine the type of silicon-based material in the second negative electrode material layer.

[0094] The mass percentage of Si in the residual material after heating was determined by inductively coupled plasma (ICP) testing, which is the proportion of Si in the second negative electrode active material. Based on the specific chemical formula of the silicon-based material obtained by XRD and the mass percentage of the second negative electrode active material in the second negative electrode material layer, the mass percentage of silicon-based material in the second negative electrode material layer, w3, can be obtained. Subtracting the mass percentage of silicon-based material in the second negative electrode material layer from the mass percentage of the second negative electrode active material in the second negative electrode material layer gives the mass percentage of graphite material in the second negative electrode material layer, w2.

[0095] The first negative electrode material layer is scraped off from the negative electrode current collector. The powder of the scraped first negative electrode material layer is weighed to obtain mass m3. Then, thermogravimetric analysis is performed at a temperature range of 25℃ to 500℃ to remove the binder. The residual material after heating is weighed to obtain mass m4. m4 / m3 gives the mass percentage of the first negative electrode active material in the first negative electrode material layer, that is, the mass percentage content w1 of the first graphite material in the first negative electrode material layer.

[0096] Understandably, because the content of conductive agent in the negative electrode material layer is too low, the influence of conductive graphite can be ignored when conducting mass percentage content tests.

[0097] Tests for H, H', W', P, and N:

[0098] Along the width direction of the unfolded negative electrode sheet, determine the first and second edges of the first negative electrode material layer, the third and fourth edges of the second negative electrode material layer, and determine the first monolayer region and the second monolayer region. Along the thickness direction of the negative electrode sheet, cut the negative electrode sheet to obtain the longitudinal sections of the first monolayer region and the second monolayer region.

[0099] The longitudinal section was subjected to ion polishing treatment and observed using an electron scanning microscope. The boundary line between the first negative electrode material layer and the negative electrode current collector was clearly observed. The thickness H of the first negative electrode material layer was measured along the thickness direction of the negative electrode sheet.

[0100] Choose any 5 grooves in the first single-layer region. Along the width direction after the negative electrode sheet is unfolded, determine the positions of the two ends and the midpoint of each groove in the first single-layer region. Then, along the thickness direction of the negative electrode sheet, measure the distances from the surface of the first single-layer region to the bottom surface at the two ends and the midpoint of each groove in the first single-layer region. Take the average value, which is the depth of each groove in the first single-layer region. Take the average value of the depths of the five grooves in the first single-layer region, which is the average depth H' of the multiple grooves in the first single-layer region.

[0101] Select any single groove in the first single-layer region. Along the width direction of the unfolded negative electrode sheet, select any 5 positions on the stripe. Then, along the length direction of the unfolded negative electrode sheet, measure the width at the 5 selected positions on the stripe and take the average value to obtain the width W' of a single groove.

[0102] Along the length of the unfolded negative electrode sheet, measure the distance between the center of width of a single groove and the center of width of an adjacent groove. Select 5 locations and measure once each, and take the average value, which is the distance N between two adjacent grooves.

[0103] Measure the width of the first monolayer region along the width direction of the negative electrode sheet, and randomly select a single groove in the first monolayer region to measure the length of the groove, which is the length of the single groove. Divide the length of the single groove by the width of the first monolayer region to obtain the ratio P of the length of the single groove to the width of the first monolayer region.

[0104] By replacing the first single-layer area with the second single-layer area and following the test method described above, the thickness of the second single-layer area and the parameters of the grooves on the second single-layer area can be obtained.

[0105] Cyclic performance test:

[0106] The lithium-ion batteries in each embodiment and comparative example were subjected to charge-discharge cycle tests in a 25°C constant temperature chamber. The charge-discharge voltage range was 2.5V to 4.2V. The batteries were charged at a constant current of 2C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C and allowed to rest for 5 minutes. Finally, they were discharged at a constant current of 6C to 2.5V. This charge-discharge cycle was repeated 600 times. The initial capacity C1 and the capacity C after the 600th cycle were recorded. 600 This allows for the calculation of the capacity retention rate of lithium-ion batteries.

[0107] Capacity retention rate (%) = C 600 / C1×100%.

[0108] The capacity retention rate is used to characterize the cycle performance of lithium-ion batteries. The higher the capacity retention rate, the better the cycle performance of the lithium-ion battery.

[0109] Electrode edge side reaction width test:

[0110] The lithium-ion batteries in the above embodiments and comparative examples, after being cycled 600 times, were disassembled under an argon atmosphere. The negative electrode sheet was removed, and the negative electrode sheet was soaked in dimethyl carbonate solvent for 2 hours and dried at 60°C for 1 hour to obtain the negative electrode sheet.

[0111] Along the width direction after the negative electrode sheet is unfolded, measure the distance between the starting region (grayish-black) of the edge of the negative electrode material layer and the boundary (golden yellow) of the conventional lithium intercalation region. Take the average value of five tests, which is the side reaction width of the electrode edge of the lithium-ion battery, in mm.

[0112] Example 1-1

[0113] <Preparation of Negative Electrode Sheets>

[0114] The first graphite material artificial graphite, the first conductive agent acetylene black, the first binder sodium carboxymethyl cellulose, and the first binder styrene-butadiene rubber in the first negative electrode active material are mixed in a mass ratio of 96:1.3:1.2:1.5. Deionized water is added as a solvent and the mixture is stirred and mixed evenly to obtain a first slurry with a solid content of 45wt%.

[0115] The silicon-based material SiC, the second graphite material artificial graphite, the second conductive agent acetylene black, the second binder sodium carboxymethyl cellulose, and the second binder styrene-butadiene rubber in the second negative electrode active material are mixed evenly in a mass ratio of 28.8:67.2:1.3:1.2:1.5 to obtain a second slurry with a solid content of 45wt%.

[0116] A first slurry is coated onto one surface of the negative electrode current collector and dried at 120°C to obtain a negative electrode sheet with a single-sided coating of the first negative electrode material layer. Then, a second slurry is coated onto the surface of the second negative electrode material layer away from the negative electrode current collector and dried at 120°C to obtain a negative electrode sheet with a single-sided coating of both the first and second negative electrode material layers. The above operation is repeated on the other surface of the negative electrode current collector to obtain a negative electrode sheet with a double-sided coating of both the first and second negative electrode material layers. The electrode sheet is dried under vacuum at 120°C for 1 hour, then cold-pressed, cut, and slit. The first and second single-layer regions of the first negative electrode material layer are determined along the width direction of the unfolded negative electrode sheet. During the cold-pressing process, a stepped roller is used, and the roller gap in the edge region, i.e., the area where the first negative electrode material layer extends beyond the second negative electrode material layer, is reduced by 50%. Along the width direction after the negative electrode sheet is unfolded, the width of the first negative electrode material layer is 62 mm, the width of the second negative electrode material layer is 50 mm, and W is 6 mm; the average particle size D1 of the first negative electrode active material is 10 μm, the average particle size D2 of the second negative electrode active material is 15 μm, and D2 / D1 is 1.5; based on the mass of the first negative electrode material layer, the mass percentage w1 of the first graphite material is 96%; based on the mass of the second negative electrode material layer, the mass percentage w2 of the second graphite material is 67.2%, and the mass percentage w3 of the silicon-based material is 28.8%; based on the mass of the second negative electrode material layer, the mass percentage A of Si element is 20.16%; the coating weight of the first negative electrode material layer is 3 mg / cm³. 2 The coating weight of the second negative electrode material layer is 3 mg / cm³. 2 The compaction density PD1 of the first negative electrode material layer is 1.2 g / cm³. 3The compaction density PD2 of the second negative electrode material layer is 1.44 g / cm³. 3 Along the thickness direction of the negative electrode sheet, the thickness of the first monolayer region is 25 μm, and the thickness of the second monolayer region is 25 μm.

[0117] A groove is provided on the first single-layer area, and the cross-sectional shape of the groove is as follows: Figure 3 As shown. Along the width direction of the unfolded negative electrode sheet, the ratio P of the length of a single groove to the width of the first monolayer region is set to 0.6, the groove width W' is 120 μm, and the spacing N between two adjacent grooves along the length direction of the unfolded negative electrode sheet is 3 mm. The average depth H' of the multiple grooves is 10 μm, and H' / H is 0.4. Grooves are set on the second monolayer region, with the same parameters as the grooves on the first monolayer region. Grooves are laser-etched on the first and second monolayer regions according to the above parameters.

[0118] The final negative electrode sheet has a size of 67.45mm × 1436mm.

[0119] <Preparation of the positive electrode>

[0120] Lithium nickel cobalt manganese oxide (LiNi) is used as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2, polyvinylidene fluoride (PVDF) binder, and conductive carbon black conductive agent were mixed in a mass ratio of 94.8:2.8:2.4. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. After vacuum stirring, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated onto one surface of an 8 μm thick aluminum foil used as a positive electrode current collector. The foil was then dried at 120°C to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. After drying at 120°C, the sheet was cold-pressed, cut, and had tabs welded to obtain a positive electrode sheet with dimensions of 64.5 mm × 1422 mm for later use. The coating weight of the positive electrode material layer was 15 mg / cm³. 2 The compaction density of the positive electrode material layer is 3.4 g / cm³. 3 Along the width direction after the positive electrode sheet is unfolded, the width of the positive electrode material layer is 56mm.

[0121] <Preparation of Electrolyte>

[0122] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 20:30:40:10 to obtain an organic solvent. Lithium hexafluorophosphate (LiPF6) was then added to the organic solvent and mixed thoroughly to obtain the electrolyte. The concentration of the lithium salt was 1 mol / L, and the remainder was the organic solvent.

[0123] <Septum>

[0124] A porous polyethylene film with a thickness of 7μm was used as the diaphragm.

[0125] <Preparation of Lithium-ion Batteries>

[0126] The prepared separator, negative electrode, and positive electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to act as a separator. Along the width of the unfolded negative electrode, the two edges of the first negative electrode material layer extend 3mm beyond the two edges of the positive electrode material layer. The electrode assembly is then wound to obtain the final product. After processes including flattening, current collector welding, casing, inkjet printing, vacuum drying, electrolyte injection, sealing, high-temperature settling, and capacity assessment, a lithium-ion battery is obtained. The upper limit of the formation voltage is 4.15V, the formation temperature is 45℃, and the formation settling time is 12 hours.

[0127] Examples 1-2 to 1-25

[0128] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1. Specifically, when the value of W changes, the coating width of the second slurry along the width direction after the negative electrode sheet is spread is adjusted so that the value of W is as shown in Table 1; when the value of L changes, the coating width of the positive electrode slurry along the width direction after the positive electrode sheet is spread is adjusted so that the value of L is as shown in Table 1; when the values ​​of D1 and / or D2 change, the grinding time is adjusted so that the values ​​of D1 and / or D2 are as shown in Table 1; when the values ​​of PD1 and / or PD2 change, the cold pressing pressure is adjusted so that the values ​​of PD1 and / or PD2 are as shown in Table 1; when the value of w1 changes, the mass percentage content of the first conductive agent and the first binder changes accordingly, while the mass ratio of the first conductive agent to the first binder remains unchanged; when the values ​​of w2 and w3 change, the mass percentage content of the second conductive agent and the second binder changes accordingly, while the mass ratio of the second conductive agent to the second binder remains unchanged.

[0129] Examples 2-1 to 2-14

[0130] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 1-1. When the value of H changes, the cold pressing pressure is adjusted so that the value of H is as shown in Table 2.

[0131] Example 2-15

[0132] Except for not setting grooves in the first and second monolayer regions of the first negative electrode material layer in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1-1.

[0133] Comparative Example 1

[0134] Except that in the <Preparation of Negative Electrode Sheet>, the first and second negative electrode material layers are flat in the width direction, both being 62 mm, and no grooves are provided on the negative electrode material layers, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as in Example 1-1.

[0135] Comparative Examples 2 to 3

[0136] Except for not setting grooves in the first and second monolayer regions of the first negative electrode material layer in the <Preparation of Negative Electrode Sheet>, and adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0137] Comparative Example 4

[0138] Except that the first and second negative electrode material layers are flat in the width direction in the <Preparation of Negative Electrode Sheet>, and no grooves are provided on the negative electrode material layer, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as in Examples 1-17.

[0139] The preparation and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0140]

[0141]

[0142] As can be seen from Examples 1-1 to 1-25 and Comparative Examples 1 to 4, by setting a double-layer coating on the negative electrode and controlling the values ​​of W / L and D2 / D1 within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is small, and the cycle capacity retention rate is high. This indicates that the lithium-ion battery of this application can reduce the side reactions in the electrode edge region and has good cycle performance. In Comparative Examples 1 and 4, the first negative electrode material layer is flush with the second negative electrode material layer; in Comparative Examples 2 and 3, the value of D2 / D1 is not within the range of this application, and at this time, the particle size distribution of the first negative electrode active material and the particle size distribution of the second negative electrode active material is unreasonable; in Comparative Examples 1 to 4, the side reaction width at the electrode edge of the lithium-ion battery is large, and the cycle capacity retention rate is low, indicating that there are more side reactions in the electrode edge region of the lithium-ion battery in the comparative examples, and the cycle performance is poor. The lithium-ion batteries in Examples 1-1 to 1-25 exhibited smaller side reaction widths at the electrode edges and higher cycle capacity retention rates, indicating that the lithium-ion batteries of this application can reduce side reactions in the electrode edge region and have good cycle performance.

[0143] The value of L typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-10 to 1-11, when the value of L is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is small, and the cycle capacity retention rate is high, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0144] The value of D1 typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-12 to 1-13, when the value of D1 is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is small, and the cycle capacity retention rate is high, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0145] The value of A typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-14 to 1-17, when the value of A is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is smaller, and the cycle capacity retention rate is higher, indicating that the lithium-ion battery of this application can reduce side reactions in the electrode edge region and has good cycle performance. However, in Examples 1-14, the mass percentage of silicon is relatively low, resulting in a lower energy density for the lithium-ion battery and a lack of product competitiveness.

[0146] The mass percentage of the second graphite material and the mass percentage of the silicon-based material typically affect the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-14 to 1-17, and Comparative Example 4, when the mass percentages of the second graphite material and the silicon-based material are within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is smaller, and the cycle capacity retention rate is higher. This indicates that the lithium-ion battery of this application can reduce side reactions in the electrode edge region and has good cycle performance.

[0147] The type of silicon-based material typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-14, and 1-17, when the type of silicon-based material is within the scope of this application, the side reaction width at the electrode edge of the lithium-ion battery is smaller, and the cycle capacity retention rate is higher. This indicates that the lithium-ion battery of this application can reduce side reactions in the electrode edge region and has good cycle performance.

[0148] The type and mass percentage of the first graphite material typically affect the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-18 to 1-19, when the type and mass percentage of the first graphite material are within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is smaller, and the cycle capacity retention rate is higher. This indicates that the lithium-ion battery of this application can reduce side reactions in the electrode edge region and has good cycle performance.

[0149] The PD2 / PD1 ratio typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-20 to 1-25, when the PD2 / PD1 ratio is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is smaller, and the cycle capacity retention rate is higher, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0150] The value of PD1 typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-20 to 1-25, when the value of PD1 is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is small, and the cycle capacity retention rate is high, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0151] The value of PD2 typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-20 to 1-25, when the value of PD2 is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is small, and the cycle capacity retention rate is high, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0152] Table 2

[0153] W'(μm) P H'(μm) H(μm) N(mm) Electrode edge side reaction width (mm) Capacity retention rate (%) Example 1-1 120 0.6 10 25 3 5 82.2 Example 2-1 20 0.6 10 25 3 6 80.2 Example 2-2 90 0.6 10 25 3 5.5 81.2 Example 2-3 150 0.6 10 25 3 5.6 80.9 Examples 2-4 400 0.6 10 25 3 6.1 80 Examples 2-5 120 0.2 10 25 3 6 81.2 Examples 2-6 120 0.4 10 25 3 5.5 81.9 Examples 2-7 120 1 10 25 3 4 82.7 Examples 2-8 120 0.6 2 25 3 5.5 81.9 Examples 2-9 120 0.6 15 25 3 4.5 82.7 Example 2-10 120 0.6 20 25 3 4 82.3 Example 2-11 120 0.6 6 15 3 5.1 82.4 Example 2-12 120 0.6 14 35 3 4.9 82 Example 2-13 120 0.6 10 25 1 4.5 82.8 Example 2-14 120 0.6 10 25 5 5.5 81.2 Example 2-15 / / / / / 6.6 78.8

[0154] Note: " / " in Table 2 indicates that there are no relevant preparation parameters.

[0155] The value of W' typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-4, when the value of W' is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is smaller, and the cycle capacity retention rate is higher, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0156] The value of P typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-5 to 2-7, when the value of P is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is small, and the cycle capacity retention rate is high, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0157] The value of H' typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-8 to 2-10, when the value of H' is within the range specified in this application, the side reaction width at the electrode edge of the lithium-ion battery is smaller, and the cycle capacity retention rate is higher. This indicates that the lithium-ion battery of this application can reduce side reactions in the electrode edge region and has good cycle performance. However, in Examples 2-10, due to the larger average depth of the multiple grooves, there is more local loss of the negative electrode active material, which easily leads to insufficient CB at the negative electrode edge, thereby increasing the risk of lithium plating in the secondary battery.

[0158] The value of H typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-11 to 2-12, when the value of H is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is small, and the cycle capacity retention rate is high, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0159] The value of N typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-13 to 2-14, when the value of N is within the range of this application, the side reaction width at the electrode edge of the lithium-ion battery is small, and the cycle capacity retention rate is high, indicating that the lithium-ion battery of this application can reduce the side reaction in the electrode edge region and has good cycle performance.

[0160] The placement of grooves in the first and / or second monolayer regions typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1 and 2-15, when grooves are placed in the first and / or second monolayer regions, the width of the side reactions at the electrode edges of the lithium-ion battery is smaller, and the cycle capacity retention rate is higher. This indicates that the lithium-ion battery of this application can reduce side reactions in the electrode edge region and has good cycle performance.

[0161] 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.

[0162] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0163] 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 a positive electrode and a negative electrode, the positive electrode comprising a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector, the negative electrode comprising a negative current collector and a negative electrode material layer located on at least one surface of the negative current collector, the negative electrode material layer comprising a first negative electrode material layer and a second negative electrode material layer, wherein the first negative electrode material layer is located between the negative current collector and the second negative electrode material layer along the thickness direction of the negative electrode. Along the width direction after the negative electrode sheet is unfolded, the width of the first negative electrode material layer is greater than the width of the second negative electrode material layer, half of the width difference between the first negative electrode material layer and the second negative electrode material layer is W mm, and the width of the first negative electrode material layer is greater than the width of the positive electrode material layer, half of the width difference between the first negative electrode material layer and the positive electrode material layer is L mm, 0.2≤W / L≤4; The first negative electrode material layer includes a first negative electrode active material, which includes a first graphite material. The second negative electrode material layer includes a second negative electrode active material, which includes a second graphite material and a silicon-based material. The average particle size of the particles of the first negative electrode active material is D1 μm, and the average particle size of the particles of the second negative electrode active material is D2 μm, where 1.1 ≤ D2 / D1 ≤ 1.

8.

2. The secondary battery according to claim 1, wherein, 0.2≤L≤5; and / or, 7≤D1≤15.

3. The secondary battery according to claim 1, wherein, 1 ≤ W / L ≤ 3; and / or, 1.3 ≤ D2 / D1 ≤ 1.

6.

4. The secondary battery according to claim 1, wherein, Based on the mass of the second negative electrode material layer, the mass percentage of Si element in the second negative electrode material layer is A, where 1% ≤ A ≤ 50%.

5. The secondary battery according to claim 4, wherein, 15.5％≤A≤30％。 6. The secondary battery according to any one of claims 1 to 5, wherein, Along the width direction of the unfolded negative electrode sheet, the compaction density of the region of the first negative electrode material layer extending beyond the second negative electrode material layer is PD1 g / cm³. 3 The compaction density of the second negative electrode material layer is PD2 g / cm³. 3 , 0.8≤PD2 / PD1≤1.

6.

7. The secondary battery according to claim 6, wherein, 1.0≤PD2 / PD1≤1.

4.

8. The secondary battery according to claim 6, wherein, 0.8≤PD1≤1.5; and / or, 1.3≤PD2≤1.

65.

9. The secondary battery according to claim 1, wherein, The first graphite material and the second graphite material are each independently selected from at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon or hard carbon, and the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbide or silicon alloy.

10. The secondary battery according to any one of claims 1 to 9, wherein, Based on the mass of the first negative electrode material layer, the mass percentage of the first graphite material is 95% to 99%; based on the mass of the second negative electrode material layer, the mass percentage of the second graphite material is 28% to 95%, and the mass percentage of the silicon-based material is 1% to 70%.

11. The secondary battery according to any one of claims 1 to 10, wherein, Along the width direction after the negative electrode sheet is unfolded, the first negative electrode material layer includes a first edge and a second edge, the second negative electrode material layer includes a third edge and a fourth edge, the edge of the second negative electrode material layer close to the first edge is the third edge, the region of the first negative electrode material layer from the first edge to the third edge is the first single-layer region, and the region of the first negative electrode material layer from the second edge to the fourth edge is the second single-layer region. The first single-layer region and / or the second single-layer region are provided with a plurality of grooves, the plurality of grooves extending along the width direction of the unfolded negative electrode sheet and spaced apart along the length direction of the unfolded negative electrode sheet.

12. The secondary battery according to claim 11, wherein, Along the length direction of the unfolded negative electrode sheet, the width of a single groove is W'μm, and 20≤W'≤400.

13. The secondary battery according to claim 12, wherein, 90≤W'≤150。 14. The secondary battery according to claim 11, wherein, Along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single groove to the width of the first single-layer region or the second single-layer region is P, where 0.2≤P≤1.

15. The secondary battery according to claim 14, wherein, 0.4≤P≤1。 16. The secondary battery according to claim 11, wherein, Along the thickness direction of the negative electrode sheet, the thickness of the first monolayer region or the second monolayer region is H μm, and the average depth of the plurality of grooves is H' μm, where 2 ≤ H' ≤ 0.8H.

17. The secondary battery according to claim 16, wherein, 2≤H'≤0.6H; and / or, 15≤H≤35.

18. The secondary battery according to claim 11, wherein, Along the length of the unfolded negative electrode sheet, the distance between two adjacent grooves is N mm, where 1 ≤ N ≤ 5.

19. An electronic device comprising a secondary battery as claimed in any one of claims 1 to 18.

Images