Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a positive pole piece and a negative pole piece, the positive pole piece comprises a positive pole material layer, and the negative pole piece comprises a negative pole material layer. The negative electrode material layer only comprises a first material layer and a second material layer which are sequentially connected, the width of the first material layer is W mm, the width of the negative electrode material layer is larger than that of the positive electrode material layer, 1 / 2 of the width difference value of the negative electrode material layer and the positive electrode material layer is L mm, and W / L is larger than or equal to 0.2 and smaller than or equal to 4. The first material layer comprises a first negative electrode active material, the first negative electrode active material comprises a first graphite material, the second material layer comprises a second negative electrode active material, and the second negative electrode active material comprises a second graphite material and a silicon-based material. A plurality of grooves are formed in the first material layer, extend in the width direction of the unfolded negative pole piece and are arranged at intervals in the length direction of the unfolded negative pole piece. Through the arrangement, the cycle performance of the secondary battery can be improved.

Description

Technical Field

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

[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 field of consumer electronics.

[0003] Currently, some lithium-ion battery designs use a full-tab design, where the positive and negative tabs extend from opposite directions and are manufactured using a full-tab cutting, stacking, or flattening technique. However, this flattened full-tab structure can lead to electrode wetting issues, particularly at the electrode edges. Electrolyte can accumulate on both sides of the material layer, causing continuous side reactions and resulting in capacity loss. Furthermore, when the negative electrode active material includes silicon-based materials, crosstalk between the silicon and graphite exacerbates side reactions at the negative electrode edge, leading to a decrease in the cycling performance of the lithium-ion battery. Summary of the Invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device to reduce side reactions in the edge area of ​​the electrode, especially to reduce side reactions caused by crosstalk between two different materials, Si and graphite, and improve the cycle performance of the secondary battery.

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

[0006] A first aspect of the present application provides a secondary battery comprising a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector. The negative electrode sheet comprises a negative current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. Along the width of the unfolded negative electrode sheet, the negative electrode material layer comprises only a first material layer and a second material layer connected in sequence. The width of the first material layer is W mm, and the width of the negative electrode material layer is greater than the width of the positive electrode material layer. Half the difference in width between the negative and positive electrode material layers is L mm, and 0.2 ≤ W / L ≤ 4; optionally, 1 ≤ W / L ≤ 3. The first material layer comprises a first negative electrode active material comprising a first graphite material. The second material layer comprises a second negative electrode active material comprising a second graphite material and a silicon-based material. The first material layer is provided with a plurality of grooves extending along the width of the unfolded negative electrode sheet and spaced apart along the length of the unfolded negative electrode sheet. By setting different material layers on different areas of the negative electrode sheet and regulating the W / L value within the scope of this application, it is beneficial to reduce the risk of lithium ions diffusing to the edge of the material layer and continuously causing side reactions, especially reducing the side reactions caused by crosstalk between two different materials, Si and graphite, and setting grooves on the first material layer to increase the electrolyte conduction channel, thereby improving the cycle performance of the secondary battery.

[0007] In one or more embodiments of the present application, 0.2 ≤ L ≤ 5. By regulating the value of L within the above range, direct contact between the edge of the positive electrode material layer and the electrolyte is reduced, and the risk of side reactions occurring at the edge of the positive electrode during charge and discharge is reduced, and the secondary battery of the present application has good cycle performance.

[0008] In one or more embodiments of the present application, along the length of the unfolded negative electrode sheet, the width of a single groove is W'μm, 20≤W'≤400; optionally, 90≤W'≤150. By regulating the value of W within the above range, the wider first material layer acts as a physical barrier and buffer, which helps reduce the occurrence of side reactions, especially side reactions caused by crosstalk between Si and graphite, thereby improving the cycle performance of the secondary battery.

[0009] In one or more embodiments of the present application, along the width of the unfolded negative electrode sheet, the ratio of the length of a single groove to the width of the first material layer is P, 0.2≤P≤1; optionally, 0.4≤P≤1. By regulating the value of P within the above range, electrolyte conduction is accelerated, further reducing the risk of electrolyte accumulation at the edge of the negative electrode sheet and causing side reactions, thereby improving the cycle performance of the secondary battery while maintaining processability.

[0010] In one or more embodiments of the present application, along the thickness direction of the negative electrode sheet, the thickness of the first material layer is H μm, the average depth of the plurality of grooves is H' μm, and 2 ≤ H' ≤ 0.8H; optionally, 2 ≤ H' ≤ 0.6H. By regulating the value of H' within the above range, electrolyte conduction is accelerated, reducing the risk of electrolyte accumulation at the edge of the negative electrode sheet and causing side reactions, thereby improving the cycle performance of the secondary battery while maintaining processability.

[0011] In one or more embodiments of the present application, 25≤H≤70. By regulating the value of H within the above range, the secondary battery has good cycle performance and high energy density while having good structural stability.

[0012] In one or more embodiments of the present application, the spacing between two adjacent grooves along the length of the unfolded negative electrode sheet is N mm, with 1≤N≤5. By regulating the value of N within the above range, electrolyte conduction is accelerated, further reducing the risk of electrolyte accumulation at the edge of the negative electrode sheet and causing side reactions, thereby improving the cycle performance of the secondary battery while maintaining good processing performance.

[0013] In one or more embodiments of the present application, the average particle size of the second graphite material particles is D1 μm, the average particle size of the silicon-based material particles is D2 μm, and 9 ≤ D1 ≤ 15, and 7.3 ≤ D2 ≤ 10.3. By regulating the values ​​of D1 and D2 within the above ranges, the structural stability of the negative electrode plate is improved, and the side reactions caused by direct contact between the silicon-based material and the electrolyte are reduced, thereby improving the cycle performance of the secondary battery.

[0014] In one or more embodiments of the present application, the secondary battery satisfies one of the following conditions: (1) 1.08 ≤ D1 / D2 ≤ 1.8; (2) 1.3 ≤ D1 / D2 ≤ 1.5. By regulating the value of D1 / D2 within the above range, direct contact between the silicon-based material and the second graphite material, as well as direct contact between the silicon-based material and the electrolyte, is reduced, thereby reducing the occurrence of side reactions, especially side reactions caused by crosstalk between the two different materials, Si and graphite, thereby improving the cycle performance of the secondary battery.

[0015] In one or more embodiments of the present application, the compacted density of the first material layer is PD1 g / cm 3 The compacted density of the second material layer is PD2 g / cm 3 , 0.8≤PD1≤1.18, 0.8≤PD2≤1.9. By regulating the values ​​of PD1 and PD2 within the above range, the occurrence of side reactions is reduced, especially side reactions caused by crosstalk between Si and graphite, thereby improving the cycle performance of the secondary battery while maintaining energy density.

[0016] In one or more embodiments of the present application, the secondary battery satisfies one of the following conditions: (1) 1.0 ≤ PD2 / PD1 ≤ 1.6; (2) 1.1 ≤ PD2 / PD1 ≤ 1.2. By regulating the PD2 / PD1 value within the above range, the occurrence of side reactions, especially side reactions caused by crosstalk between Si and graphite, is reduced, thereby improving the cycle performance of the secondary battery while maintaining a balanced energy density.

[0017] In one or more embodiments of the present application, the mass percentage of the first graphite material is 95% to 99% based on the mass of the first material layer; the mass percentage of the second graphite material is 28% to 95% based on the mass of the second material layer; and the mass percentage of the silicon-based material is 1% to 70%. By regulating the values ​​of w1, w2, and w3 within the above ranges, the structural stability of the negative electrode edge is improved. Combined with the high-capacity silicon-based material and the relatively stable second graphite material in the second negative electrode material layer, the secondary battery has a higher energy density while taking into account dynamic performance, improving the structural stability and cycle performance of the secondary battery.

[0018] The second aspect of the present application provides an electronic device, which includes the secondary battery in any one of the above embodiments. Therefore, the electronic device provided by the present application has good performance.

[0019] Beneficial effects of the embodiments of the present application:

[0020] The embodiments of the present application provide a secondary battery and an electronic device. By arranging different material layers on different areas of the negative electrode plate and regulating the W / L value within the scope of the present application, it is beneficial to reduce the risk of lithium ions diffusing to the edge of the material layer and continuously causing side reactions, especially reducing the side reactions caused by crosstalk between two different materials, Si and graphite, and arranging grooves on the first material layer to increase the electrolyte conduction channel, thereby improving the cycle performance of the secondary battery.

[0021] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0023] Figure 1 This is a schematic diagram of an expanded electrode assembly in one embodiment of the present application;

[0024] Figure 2This is a schematic diagram of a negative electrode sheet according to an embodiment of the present application unfolded along its width direction;

[0025] Figure 3 for Figure 2 Schematic diagram of the cross section along the AA direction;

[0026] Reference numerals: negative electrode plate 10 ; positive electrode plate 20 ; separator 30 ; negative electrode current collector 11 ; negative electrode material layer 12 ; first material layer 121 ; second material layer 122 ; positive electrode current collector 21 ; positive electrode material layer 22 ; groove 13 . DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0029] The first aspect of the present application provides a secondary battery, comprising a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. Along the width direction of the unfolded negative electrode sheet, the negative electrode material layer comprises only a first material layer and a second material layer connected in sequence. The width of the first material layer is W mm, and the width of the negative electrode material layer is greater than the width of the positive electrode material layer. Half the difference between the widths of the negative electrode material layer and the positive electrode material layer is L mm, and 0.2 ≤ W / L ≤ 4; optionally, 1 ≤ W / L ≤ 3. For example, the value of W / 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, or a range consisting of any two of these values. The first material layer includes a first negative electrode active material, which includes a first graphite material. The second material layer includes a second negative electrode active material, which includes a second graphite material and a silicon-based material. The first material layer is provided with a plurality of grooves, which extend along the width of the unfolded negative electrode sheet and are spaced apart along the length of the unfolded negative electrode sheet.

[0030] In this application, the negative electrode sheet's length is defined as the X direction, its width as the Y direction, and its thickness as the Z direction. It is understood that when the positive electrode sheet and separator are unfolded, their length, width, and thickness directions are the same as those of the negative electrode sheet.

[0031] For example, Figure 1 As shown, the negative electrode sheet 10 includes a negative electrode current collector 11 and a negative electrode material layer 12 located on the surface of the negative electrode current collector 11. The positive electrode sheet 20 includes a positive electrode current collector 21 and a positive electrode material layer 22 located on the surface of the positive electrode current collector 21. Along the width direction Y of the unfolded negative electrode sheet 10, the negative electrode material layer 12 only includes a first material layer 121 and a second material layer 122 connected in sequence. The width of the first material layer 121 is W mm, and the width of the negative electrode material layer 12 is greater than the width of the positive electrode material layer 22. The difference in width between the negative electrode material layer 12 and the positive electrode material layer 22 is 1 / 2 of L mm. Figure 2 and Figure 3 As shown, a plurality of grooves 13 are provided on the first material layer 121 . The plurality of grooves 13 extend along the width direction Y of the unfolded negative electrode sheet 10 and are spaced apart along the length direction X of the unfolded negative electrode sheet 10 .

[0032] The inventors have found that at the width edge of the negative electrode sheet, especially in the area where the edge of the negative electrode material layer extends beyond the positive electrode material layer in the width direction, the electrolyte in the edge area is easily accumulated on both sides of the material layer, causing continuous side reactions and leading to capacity loss. In addition, during the charge and discharge process, the silicon-based material, in particular, will generate greater stress in the edge area due to its own volume expansion, destroying the solid electrolyte interface (SEI) film. In addition, the silicon-based material particles expand and squeeze the adjacent graphite material particles, causing crosstalk between Si and graphite, which further exacerbates the side reactions. Based on this, the present application provides different material layers on different areas of the negative electrode sheet and adjusts the W / L value within the scope of the present application. The wider first material layer plays a certain physical barrier and buffering role. The first material layer at the edge of the negative electrode sheet only includes relatively stable graphite material. While taking into account the energy density, it reduces the diffusion of lithium ions to the edge area of ​​the negative electrode sheet, reduces the expansion stress generated by the second material layer, and reduces the impact of the crosstalk between Si and graphite on the edge of the negative electrode sheet. This can effectively reduce the occurrence of side reactions, especially the side reactions caused by the crosstalk between Si and graphite, and improve the cycle performance of the secondary battery. At the same time, providing grooves on the first material layer is conducive to accelerating the conduction of the electrolyte, further reducing the risk of side reactions caused by the accumulation of electrolyte at the edge of the negative electrode, and providing stress buffer space, thereby further improving the cycle performance of the secondary battery. When the value of W / L is too small, that is, less than the lower limit of this application, it cannot play an effective physical blocking role; when the value of W / L is too large, that is, greater than the upper limit of this application, it affects the energy density of the secondary battery. The above-mentioned setting is conducive to reducing side reactions in the edge area of ​​the electrode, especially reducing side reactions caused by crosstalk between two different materials, Si and graphite. While taking into account high energy density, the secondary battery has good cycle performance.

[0033] Among them, the above-mentioned "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 the thickness direction of itself, or on both surfaces of the positive electrode current collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. The above-mentioned "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 the thickness direction of itself, or it can be located on both surfaces of the negative electrode current collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode current collector, or it can be a partial area of ​​the surface of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0034] In one or more embodiments of the present 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 values ​​therein. By regulating 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, and the risk of side reactions occurring at the edge of the positive electrode during charging and discharging is reduced. In addition, the wider first material layer plays a certain role in physical blocking and buffering, and the first material layer at the edge of the negative electrode only includes relatively stable graphite material. While taking into account energy density, it reduces the diffusion of lithium ions to the edge area of ​​the negative electrode, reduces the expansion stress generated by the second material layer, and reduces the impact of crosstalk between Si and graphite on the edge of the negative electrode, which is conducive to reducing the occurrence of side reactions, especially the side reactions caused by crosstalk between Si and graphite. The grooves are provided on the first material layer, which is conducive to accelerating the diversion of the electrolyte, further reducing the risk of electrolyte accumulation at the edge of the negative electrode and causing side reactions, while providing stress buffer space, thereby improving the cycle performance of the secondary battery. Therefore, the secondary battery of the present application has good cycle performance.

[0035] In one or more embodiments of the present 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 consisting of any two of these values. By regulating the value of W within the above range, the wider first material layer plays a certain physical barrier and buffering role, and the first material layer at the edge of the negative electrode plate only includes relatively stable graphite material, while taking into account the energy density, thereby reducing the diffusion of lithium ions to the edge area of ​​the negative electrode plate, reducing the expansion stress generated by the second material layer and the influence of crosstalk between Si and graphite on the edge of the negative electrode plate, which is beneficial to reducing the occurrence of side reactions, especially reducing the side reactions caused by crosstalk between Si and graphite, thereby improving the cycle performance of the secondary battery.

[0036] In one or more embodiments of the present application, along the length direction of the unfolded negative electrode sheet, the width of a single groove is W'μm, 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, Figure 3As shown, along the longitudinal direction X of the unfolded negative electrode sheet 10, the width of a single groove 13 is W'μm. By regulating the value of W' within the above range, it is beneficial to accelerate the flow of electrolyte, further reducing the risk of electrolyte accumulation and side reactions at the edge of the negative electrode sheet. At the same time, it provides stress buffer space and reduces the risk of lithium deposition and cycle performance degradation caused by insufficient CB at the edge of the negative electrode sheet due to the provision of grooves. While taking into account processing performance, the cycle performance of the secondary battery is improved.

[0037] In this application, CB value refers to the ratio between the capacity of the negative electrode plate per unit area and the capacity of the positive electrode plate per unit area under the same conditions, for example, at an ambient temperature of 25°C and a discharge rate of 0.1C. CB = (gram capacity of negative electrode active material × mass of negative electrode active material per unit area of ​​negative electrode plate) / (gram capacity of positive electrode active material × mass of positive electrode active material per unit area of ​​positive electrode plate). The above unit area refers to 1mm 2 .

[0038] In one or more embodiments of the present application, along the width direction of the unfolded negative electrode sheet, the ratio of the length of a single groove to the width of the first material layer is P, 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 consisting of any two of these values. By regulating the value of P within the above range, it is beneficial to accelerate the conduction of the electrolyte, further reduce the risk of side reactions caused by the accumulation of the electrolyte at the edge of the negative electrode sheet, provide stress buffer space, and reduce the risk of lithium precipitation and cycle performance degradation due to insufficient CB at the edge of the negative electrode sheet due to the provision of grooves. While taking into account the processing performance, the cycle performance of the secondary battery is improved.

[0039] In one or more embodiments of the present application, along the thickness direction of the negative electrode sheet, the thickness of the first material layer is H μm, the average depth of the plurality of grooves is H' μm, 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, Figure 3As shown, along the thickness direction Z of the negative electrode sheet 10, the thickness of the first material layer 121 is Hμm, and the average depth of the multiple grooves 13 is H'μm. By regulating the value of H' within the above range, it is beneficial to accelerate the diversion of the electrolyte, reduce the risk of electrolyte accumulation and side reactions at the edge of the negative electrode sheet, and also help reduce the risk of the first material layer being penetrated by the grooves when the grooves are provided in the first material layer. In addition, the loss of the first graphite material is small, and the risk of lithium deposition and cycle performance degradation caused by insufficient CB at the edge of the negative electrode sheet due to the provision of grooves is reduced. While taking into account the processing performance, the cycle performance of the secondary battery is improved.

[0040] In the present application, the thickness H' of the first material layer can be controlled by means known to those skilled in the art. For example, when the first slurry is coated on the surface of the negative electrode current collector, the thickness of the first material layer can be increased by increasing the coating weight on the basis of a certain solid content of the first slurry, and vice versa. The thickness of the first material layer can also be reduced by increasing the cold pressing pressure when the negative electrode sheet is cold pressed, and vice versa.

[0041] In one or more embodiments of the present application, 25 ≤ H ≤ 70. For example, the value of H can be 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, or a range consisting of any two of these values. By regulating the value of H within the above range, the secondary battery has good cycle performance and high energy density while having good structural stability.

[0042] In one or more embodiments of the present application, along the length direction of the unfolded negative electrode sheet, the spacing between two adjacent grooves is N mm, 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 consisting of any two of these values. For example, Figure 3 As shown, the spacing between two adjacent grooves 13 along the longitudinal direction X of the unfolded negative electrode sheet 10 is N mm. By regulating the value of N within the above range, the electrolyte flow is accelerated, further reducing the risk of electrolyte accumulation and side reactions at the edge of the negative electrode sheet. At the same time, a stress buffer space is provided, which helps to reduce the processing difficulty of the groove process and the risk of local collapse of the first material layer. It also reduces the risk of lithium deposition and cycle performance degradation caused by insufficient CB at the edge of the negative electrode sheet due to the provision of grooves. While taking into account processing performance, the cycle performance of the secondary battery is improved.

[0043] In the present application, the spacing between two adjacent grooves refers to the distance between the width centers of the two adjacent grooves along the length direction of the unfolded negative electrode sheet.

[0044] In this application, the cross-section of a single groove refers to the plane formed by the groove along the length and thickness directions of the unfolded negative electrode sheet (or the cross-section obtained by cutting the groove along the length and thickness directions of the unfolded negative electrode sheet). This application does not particularly limit the cross-sectional shape of a single groove, as long as it can achieve the purpose of this application. For example, the cross-section of a single groove can be independently selected from at least one of a triangle, an arc (with an area smaller than a semicircle with the same radius), a semicircle, a rectangle, a trapezoid, or a square.

[0045] In one or more embodiments of the present application, the average particle size of the particles of the second graphite material is D1μm, the average particle size of the particles of the silicon-based material is D2μm, 9≤D1≤15, 7.3≤D2≤10.3. For example, the value of D1 can be 9, 10, 11, 12, 13, 14, 15 or a range consisting of any two of the values, and the value of D2 can be 7.3, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8, 10, 10.2, 10.3 or a range consisting of any two of the values. By regulating the values ​​of D1 and D2 within the above range, the average particle size of the second graphite material is larger, which is beneficial to reduce the impact of the volume expansion of the silicon-based material on the negative electrode material layer during the charge and discharge process, improves the structural stability of the negative electrode plate, and helps to reduce the side reactions that occur when the silicon-based material is in direct contact with the electrolyte, thereby improving the cycle performance of the secondary battery.

[0046] In one or more embodiments of the present application, the secondary battery satisfies one of the following conditions: (1) 1.08≤D1 / D2≤1.8; (2) 1.3≤D1 / D2≤1.5. For example, the value of D1 / D2 can be 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3, 1.32, 1.35, 1.38, 1.4, 1.42, 1.45, 1.48, 1.5, 1.52, 1.55, 1.58, 1.6, 1.62, 1.65, 1.68, 1.7, 1.72, 1.75, 1.78, 1.8, or a range consisting of any two of these values. By regulating the value of D1 / D2 within the above range, the ratio of the silicon-based material to the second graphite material in the second material layer is moderate, so that the silicon-based material and the second graphite material are more evenly dispersed in the second material layer, reducing the direct contact between the silicon-based material and the second graphite material and the direct contact between the silicon-based material and the electrolyte, thereby reducing the occurrence of side reactions, especially the side reactions caused by crosstalk between the two different materials Si and graphite, thereby improving the cycle performance of the secondary battery.

[0047] The present application does not particularly limit the method for regulating the average particle size of the second graphite material particles or the average particle size of the silicon-based material particles, as long as the purpose of the present application can be achieved. For example, different second graphite materials or silicon-based materials can be purchased based on the desired average particle size of the second graphite material or silicon-based material particles. Alternatively, the average particle size of the second graphite material or silicon-based material particles can be regulated by grinding or other methods.

[0048] In one or more embodiments of the present application, the compacted density of the first material layer is PD1 g / cm 3 The compacted density of the second material layer is PD2 g / cm 3 , 0.8≤PD1≤1.18, 0.8≤PD2≤1.9. For example, the value of PD1 can be 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, or a range consisting of any two values ​​therein; the value of PD2 can be 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, or a range consisting of any two values ​​therein. By regulating the values ​​of PD1 and PD2 within the above range, the compaction density at the edge of the negative electrode plate is moderate, which helps reduce the risk of electrolyte accumulation on both sides of the negative electrode plate and causing side reactions. At the same time, it also enables the secondary battery to have a higher energy density and reduces the risk of crosstalk reactions within the negative electrode material layer that may lead to reduced cycle performance. This reduces the occurrence of side reactions, especially those caused by crosstalk between the two different materials of Si and graphite, and improves the cycle performance of the secondary battery while maintaining energy density.

[0049] In one or more embodiments of the present application, the secondary battery satisfies one of the following conditions: (1) 1.0≤PD2 / PD1≤1.6; (2) 1.1≤PD2 / PD1≤1.2. For example, the value of PD2 / PD1 can be 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, or a range consisting of any two of these values. By regulating the value of PD2 / PD1 within the above range, the edge area of ​​the negative electrode plate has a moderate compaction density, which is beneficial to reducing the risk of electrolyte enrichment on both sides of the negative electrode plate and causing side reactions, while also allowing the secondary battery to have a higher energy density and reducing the risk of cycle performance degradation caused by crosstalk reactions within the negative electrode material layer. Thus, the occurrence of side reactions is reduced, especially side reactions caused by crosstalk between two different materials, Si and graphite, and the cycle performance of the secondary battery is improved while taking into account energy density.

[0050] The present application does not particularly limit the control method of the compaction density of the first material layer and the compaction density of the second material layer, as long as the purpose of the present application can be achieved. For example, it can be achieved by regulating 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, other conditions remain unchanged, and the coating amount of the first slurry is increased to increase the compaction density of the first material layer; when the second slurry is coated on the surface of the negative electrode current collector, other conditions remain unchanged, and the coating amount of the second slurry is increased to increase the compaction density of the second material layer, otherwise it is reduced; or, other conditions remain unchanged, and the cold pressing pressure is increased to increase the compaction density of the first material layer and the compaction density of the second material layer, otherwise it is reduced.

[0051] In one or more embodiments of the present application, based on the mass of the first material layer, the mass percentage w1 of the first graphite material is 95% to 99%, for example, the mass percentage 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 values ​​thereof; based on the mass of the second 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%, 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 consisting of any two of the values ​​therein, 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 consisting of any two of the values ​​therein. By regulating the values ​​of w1, w2, and w3 within the above range, the volume change of the first graphite material during the charge and discharge process of the secondary battery is small, which is beneficial to improving the structural stability of the edge of the negative electrode plate. Combined with the high-capacity silicon-based material and the relatively stable second graphite material in the second negative electrode material layer, the secondary battery has a higher energy density while taking into account the dynamic performance and improving the structural stability and cycle performance of the secondary battery.

[0052] The present application does not particularly limit the types of the first graphite material and the second graphite material, as long as the objectives of the present application can be achieved. For example, the first graphite material and the second graphite material can each be selected from at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, or hard carbon. The present application does not particularly limit the types of silicon-based materials, as long as the objectives of the present application can be achieved. For example, the silicon-based material can include at least one of silicon element, silicon oxide, silicon carbon compound, or silicon alloy. In the present application, the silicon carbon compound is a silicon carbon composite material. Based on the mass of the silicon carbon composite material, the mass percentage of silicon element can be 30% to 70%, and the mass percentage of carbon element can be 30% to 70%. The present application does not particularly limit the silicon carbon composite material, as long as the objectives of the present application can be achieved. For example, the silicon carbon composite material can be a composite material obtained by deposition. For example, the silicon carbon composite material can be a silicon material deposited on a carbon skeleton, or a carbon material deposited on a silicon skeleton. Silicon oxide includes SiOx, where 0<x<2. Exemplarily, the silicon oxide compound may include silicon monoxide (SiO, the molar ratio of silicon to oxygen is 1:1). The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or a composite current collector. Exemplarily, the composite current collector may 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 the present application, there is no particular restriction on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. In one or more embodiments of the present 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. The present application has no particular restrictions on the types of the first conductive agent and the second conductive agent, as long as the purpose of the present application can be achieved. For example, the first conductive agent and the second conductive agent can be independently selected from at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and the conductive carbon black can include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes can include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials can include but are not limited to metal powder and / or metal fibers, specifically, the metal can include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers can include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.The present application has no particular restriction on the types of the first binder and the second binder, as long as the purpose of the present application can be achieved. For example, the first binder and the second binder can 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.

[0053] The present application does not impose any particular restrictions on the method for preparing the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the negative electrode sheet includes but is not limited to the following steps: (1) uniformly mixing a first graphite material, a first binder, and a first conductive agent to obtain a first slurry; and uniformly mixing a silicon-based material, a second graphite material, a second binder, and a second conductive agent to obtain a second slurry; (2) determining the area where the first material layer and the second material layer need to be provided on the negative electrode collector along the width direction of the negative electrode collector after it is unfolded, and uniformly coating the first slurry and the second slurry on the area where the first material layer and the second material layer need to be provided on one surface of the negative electrode collector, respectively, and drying to obtain a negative electrode sheet with the first material layer and the second material layer provided on one side; (3) repeating the above steps on the other surface of the negative electrode collector to obtain a negative electrode sheet with the first material layer and the second material layer provided on both sides; and (4) cold-pressing the sheet into strips, and providing a groove on the first material layer to obtain a negative electrode sheet.

[0054] In the present application, the mass percentage of the first graphite material in the first material layer can be controlled by regulating the added mass ratio of the first graphite material, the first binder and the first conductive agent in the first slurry; the mass percentage of the second graphite material and the mass percentage of the silicon-based material in the second material layer can be controlled by regulating the added mass ratio of the silicon-based material, the second graphite material, the second binder and the second conductive agent in the second slurry; and the value of W can be controlled by regulating the coating width of the first slurry in the width direction after the negative electrode sheet is unfolded.

[0055] The present application has no special restrictions on the solid content of the above-mentioned slurry, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the temperature and time of the above-mentioned drying, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the process parameters of the above-mentioned cold pressing and striping, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the above-mentioned way of setting the grooves, as long as the purpose of the present application can be achieved. For example, the grooves can be set by pulsed laser etching. The average depth H' of the multiple grooves and the width W' of the grooves can be controlled by the power and defocus of the pulsed laser emitter; the ratio P of the length of a single groove to the width of the first material layer can be controlled by adjusting the width of the first material layer, the power and defocus of the pulsed laser emitter; the distance N between two adjacent grooves can be controlled by adjusting the distance between the pulsed laser emitters or the laser emission frequency.

[0056] In the present application, the different features of the grooves provided in the first material layer may be combined, and all implementation methods or embodiments covered by the above combinations are within the protection scope of the present application.

[0057] The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode material layer of the present application includes a positive electrode active material. The present application has no particular restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05O2 (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 iron manganese phosphate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, for example, non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. In the present application, the positive electrode material layer may also include a binder and a conductive agent. The present application has no particular restriction on the type of binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the mass ratio of the positive active material, conductive agent and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0058] In the present application, the secondary battery includes a separator. For example, Figure 1As shown, a separator 30 is provided between the positive electrode sheet 20 and the negative electrode sheet 10. The present application has no particular restrictions on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or at least one of aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. In one or more embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven membrane or a composite membrane having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. In one or more embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application has no particular restrictions on inorganic particles. For example, the inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0059] In the present application, the secondary battery includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent. The present application has no particular restrictions on the lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methylethyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylethylene carbonate (VEC). The fluorocarbonate compound may include but is not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The above-mentioned carboxylate 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, decanoic acid, valerolactone or caprolactone. The above-mentioned 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 above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0060] The secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal. A metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0061] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and there is no particular limitation in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of a stacked structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. may also be placed in the shell as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging. In the present application, the value of L can be regulated by regulating the coating width of the positive electrode slurry, the first slurry (i.e., the slurry of the first material layer), and the coating width of the second slurry (i.e., the slurry of the second material layer) in the width direction after the negative electrode sheet is unfolded.

[0062] The second aspect of the present application provides an electronic device, which includes the secondary battery in any one of the above embodiments. Therefore, the electronic device provided by the present application has good performance.

[0063] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0064] Example

[0065] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0066] Test methods and equipment:

[0067] W and L test:

[0068] At 25°C, the lithium-ion battery was discharged at a constant current of 0.5C to the discharge cut-off voltage. After removing the shell of the lithium-ion battery, it was soaked in diethyl carbonate for 20 minutes to remove the electrolyte to obtain the electrode assembly. The electrode assembly was then placed parallel to the length on the charge-coupled device (CCD) platform and disassembled to obtain the positive electrode sheet, negative electrode sheet and separator. The positions of each component were kept stationary. Along the width direction of the unfolded negative electrode sheet, the two edges of the entire negative electrode material layer of the negative electrode sheet and the two edges of the positive electrode material layer of the positive electrode sheet were determined, and then L was measured using the CCD.

[0069] The negative electrode sheet was removed and unfolded. The surface of the unfolded negative electrode sheet was observed using a scanning electron microscope (SEM). An element scan was performed along the width of the unfolded negative electrode sheet, and along the negative electrode material layer, 30 mm from each edge, using an energy dispersive X-ray spectrometer (EDS). Because the first and second material layers contain different types of negative electrode active materials, a distinct Si element distribution boundary exists between the first and second material layers along the width of the unfolded negative electrode sheet, distinguishing the first and second material layers. W was measured based on the Si element distribution boundary measured by the scan and the edge of the entire negative electrode material layer closest to the distribution boundary.

[0070] Each length was measured 5 times and the average value was taken as the final result.

[0071] The discharge cut-off voltage of the lithium-ion batteries in the examples and comparative examples of the present application is 2.5 V. It is understood that when the voltage range marked on the factory battery packaging is 2.5 V to 4.2 V, the charge cut-off voltage is 4.2 V and the discharge cut-off voltage is 2.5 V.

[0072] Negative electrode sampling:

[0073] At 25°C, the lithium-ion battery was discharged at a constant current of 0.5C to the discharge cut-off voltage. The lithium-ion battery was 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. The discharge cut-off voltage of the lithium-ion battery in the examples and comparative examples of the present application is 2.5V. It is understandable that when the voltage range marked on the factory battery packaging is 2.5V to 4.2V, the charge cut-off voltage is 4.2V and the discharge cut-off voltage is 2.5V.

[0074] Unless otherwise specified, the following test methods are based on the negative electrode obtained in the above manner. The distinction between the first and second material layers can be found in the "W and L Tests."

[0075] Average particle size test:

[0076] The average particle size D1 of the second graphite material particles and the average particle size D2 of the silicon-based material particles were tested using a scanning electron microscope (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 material layer was observed using a scanning electron microscope, and the silicon-based material and the second graphite material in the cross-section of the first material layer were distinguished by backscattering mode. The equivalent diameters of 32 particles of the second graphite material were randomly selected and measured, and the average value of the equivalent diameters of the 32 particles of the second graphite material was calculated as the average particle size D1 of the particles of the second graphite material. The equivalent diameters of 32 particles of the silicon-based material were randomly selected and measured, and the average value of the equivalent diameters of the 32 particles of the silicon-based material was calculated as the average particle size D2 of the particles of the silicon-based material.

[0077] In this application, the average particle size can be understood as the equivalent diameter, which generally refers to the diameter of a sphere with the same volume as the irregular-shaped object. The area of ​​the particles of the silicon-based material or the second graphite material to be tested in the cross-section of the negative electrode sheet is measured, and then the diameter of a circle with the same area as the area is used as the equivalent diameter of the particles of the silicon-based material or the second graphite material to be tested.

[0078] Compaction density test:

[0079] Use a punching machine to punch out a small disc with an area of ​​S on the first material layer of the negative electrode sheet, weigh its mass to be M1, and measure its thickness to be t1 with a caliper; along the width and thickness directions of the unfolded negative electrode sheet, determine the dividing line between the first material layer and the second material layer, and the dividing line between the first material layer and the negative electrode collector, scrape the first material layer from the negative electrode sheet, weigh its mass to be M2, and measure its thickness to be t2 with a caliper; the compaction density of the first material layer is PD1 = (M1-M2) / (t1-t2) / S.

[0080] The second material layer is tested according to the above steps to obtain the compaction density PD2 of the second material layer.

[0081] Test of mass percentage of silicon-based materials and graphite materials:

[0082] Along the width and thickness directions of the unfolded negative electrode sheet, the boundary line between the first material layer and the second material layer, and the boundary line between the negative electrode material layer and the negative electrode current collector are determined, and the powder of the scraped second material layer is weighed to obtain the mass m1. Then, thermogravimetric analysis is performed in the temperature range of 25°C to 500°C to remove the binder. The residual material after heating is weighed to obtain the mass m2. m2 / m1 is used to obtain the mass ratio of the second negative electrode active material in the second material layer.

[0083] The type of silicon-based material in the second material layer can be identified by performing an X-ray diffraction (XRD) test on the residual material after heating.

[0084] The mass percentage of the Si element in the residual material after heating, that is, the mass percentage of the Si element in the second negative electrode active material, is measured by inductively coupled plasma (ICP) testing. According to the specific chemical formula of the silicon-based material type measured by XRD and the mass percentage of the second negative electrode active material in the second material layer, the mass percentage w3 of the silicon-based material in the second material layer can be obtained. The mass percentage of the second negative electrode active material in the second material layer minus the mass percentage of the silicon-based material in the second material layer is the mass percentage w2 of the second graphite material in the second material layer.

[0085] The first material layer is scraped off from the negative electrode current collector, and the powder of the scraped first material layer is weighed to obtain a mass m3. Then, a thermogravimetric analysis is performed in the temperature range of 25°C to 500°C to remove the binder. The residual material after heating is weighed to obtain a mass m4. m4 / m3 is used to obtain the mass ratio of the first negative electrode active material in the first material layer, that is, the mass percentage w1 of the first graphite material in the first material layer.

[0086] It is understandable that, since the content of the conductive agent in the negative electrode material layer is too low, the influence of the conductive graphite can be ignored when performing the mass percentage test.

[0087] H, H', W', P, N tests:

[0088] The boundary between the first material layer and the second material layer in the negative electrode material layer is found along the width direction of the unfolded negative electrode sheet, and the first material layer and the second material layer of the negative electrode material layer are distinguished and determined.

[0089] The negative electrode sheet was cut along its thickness direction to obtain a longitudinal cross-section of the first material layer. The longitudinal cross-section of the first material layer was ion polished and observed using a scanning electron microscope. A clear boundary between the first material layer and the negative electrode current collector was observed. The thickness H of the first material layer was measured along the thickness direction of the negative electrode sheet.

[0090] Select any 5 grooves of the first material layer, and confirm the two ends and the midpoint of a single groove of the first material layer along the width direction of the unfolded negative electrode sheet. Then, measure the distance from the surface of the first material layer to the bottom surfaces at the two ends and the midpoint of the single groove of the first material layer along the thickness direction of the negative electrode sheet, and take the average value, which is the depth of the single groove of the first material layer. Take the average value of the depths of the single grooves of the 5 first material layers, which is the average depth H' of the multiple grooves of the first material layer.

[0091] Select a single groove of the first material layer, select 5 positions on the groove along the width direction of the unfolded negative electrode sheet, and then measure the width of the 5 selected positions on the groove along the length direction of the unfolded negative electrode sheet, take the average, and obtain the width W' of the single groove.

[0092] Along the length direction of the unfolded negative electrode sheet, measure the distance between the width center of a single groove and the width center of the adjacent groove. Select 5 positions and measure them once respectively. Take the average value, which is the distance N between two adjacent grooves.

[0093] Measure the width of the first material layer along the width direction of the negative electrode sheet, and optionally select a single groove in the first single-layer area, measure the length of the groove, that is, the length of the single groove, and divide the length of the single groove by the width of the first material layer to obtain the ratio P of the length of the single groove to the width of the first material layer.

[0094] Cyclic performance test:

[0095] The lithium-ion batteries in the embodiments and comparative examples were subjected to charge and discharge cycle tests in a constant temperature box at 25°C. The charge and discharge voltage range was 2.5V to 4.2V. They were charged to 4.2V at a constant current of 2C, then charged to 0.05C at a constant voltage of 4.2V and left to stand for 5 minutes. Then, they were discharged to 2.5V at a constant current of 6C. The above charge and discharge process was repeated for 600 cycles. The initial capacity C1 and the capacity after the 600th cycle C1 were recorded. 600 , thereby calculating the capacity retention rate of lithium-ion batteries.

[0096] Capacity retention rate (%) = C 600 / C1×100%.

[0097] 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.

[0098] Pole edge side reaction width test:

[0099] The lithium-ion batteries in the embodiments and comparative examples after 600 cycles were disassembled under an argon atmosphere, and the negative electrode sheets were taken out. The negative electrode sheets were soaked in dimethyl carbonate solvent for 2 hours and dried at 60° C. for 1 hour to obtain negative electrode sheets.

[0100] Along the width direction of the unfolded negative electrode plate, measure the distance between the starting area of ​​the edge of the negative electrode material layer (gray-black) and the boundary of the conventional lithium insertion area (golden yellow). Test five times and take the average value, which is the side reaction width of the edge of the plate of the lithium-ion battery, in mm.

[0101] Example 1

[0102] <Preparation of negative electrode sheet>

[0103] The first graphite material artificial graphite in the first negative electrode active material, the first conductive agent acetylene black, the first binder sodium carboxymethyl cellulose, and the first binder styrene butadiene rubber 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 to obtain a first slurry with a solid content of 45wt%; the silicon-based material SiC in the second negative electrode active material, the second graphite material artificial graphite in the second negative electrode active material, the second conductive agent acetylene black, the second binder sodium carboxymethyl cellulose, and the second binder styrene butadiene rubber are mixed in a mass ratio of 14.4:81.6:1.3:1.2:1.5 to obtain a second slurry with a solid content of 45wt%;

[0104] A 10μm-thick copper foil was used as the negative electrode current collector. The areas where the first and second material layers would be placed were determined along the unfolded width of the negative electrode current collector. The first and second slurries were evenly applied to one surface of the negative electrode current collector. The negative electrode current collector was then dried at 120°C to obtain a negative electrode sheet with the first and second material layers on one side. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with the first and second material layers on both sides. The sheet was dried under vacuum at 120°C for 1 hour. After cold pressing, cutting, and slitting, grooves were formed in the first material layer.

[0105] The ratio P of the length of a single groove to the width of the first material layer along the unfolded width of the negative electrode sheet was set to 0.6, the groove width W' was set to 120 μm, and the spacing N between two adjacent grooves along the unfolded length of the negative electrode sheet was set to 3 mm. The average depth H' of the multiple grooves was set to 20.4 μm, and the ratio H' / H was set to 0.4. The grooves were laser-etched into the first material layer according to these parameters. The final negative electrode sheet measured 67.45 mm x 1436 mm.

[0106] The coating weight of the first material layer is 5.2 mg / cm 2 The coating weight of the second material layer is 6.14 mg / cm 2 The compacted density PD1 of the first material layer is 1g / cm 3 The compacted density PD2 of the second material layer is 1.18 g / cm 3 , PD2 / PD1 is 1.18, the thickness of the first material layer is 51μm, the width W of the first material layer is 6mm, and the width of the second material layer is 56mm; the average particle size D1 of the particles of the second graphite material is 14μm, the average particle size D2 of the particles of the silicon-based material is 10μm, and D1 / D2 is 1.4; 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 81.6%, and the mass percentage w3 of the silicon-based material is 14.4%.

[0107] <Preparation of positive electrode sheet>

[0108] The positive electrode active material is lithium nickel cobalt manganese oxide LiNi 0.6 Co 0.2 Mn 0.2 O2, binder polyvinylidene fluoride, and conductive agent conductive carbon black are mixed in a mass ratio of 94.8:2.8:2.4, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 120°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer. After drying at 120°C, cold pressing is performed, and then cutting and welding of the pole ears are performed to obtain a positive electrode sheet with a specification of 64.5mm×1422mm for standby use. Among them, the coating weight of the positive electrode material layer is 15mg / cm 2 The compaction density of the positive electrode material layer is 3.4g / cm 3 , the width of the positive electrode material layer is 56mm.

[0109] <Preparation of Electrolyte>

[0110] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 20:30:40:10 to obtain an organic solvent. Lithium hexafluorophosphate (LiPF6) is then added to the organic solvent and mixed thoroughly to obtain an electrolyte. The concentration of the lithium salt is 1 mol / L, with the remainder being the organic solvent.

[0111] <Diaphragm>

[0112] A porous polyethylene film with a thickness of 9 μm was used as the separator.

[0113] <Preparation of lithium-ion batteries>

[0114] The above-prepared separator, negative electrode sheet, separator, and positive electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to act as a separator. The two edges of the negative electrode material layer are respectively extended by 3 mm along the width direction of the unfolded negative electrode sheet. The electrode assembly is wound. After flattening, current collecting plate welding, shell insertion, coding, vacuum drying, electrolyte injection, sealing, high-temperature standing, and then formation and capacity measurement, a lithium-ion battery is obtained. The formation upper limit voltage is 4.15 V, the formation temperature is 45°C, and the formation standing time is 12 hours.

[0115] Examples 2 to 33

[0116] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Example 1. Among them, when the value of W changes, the coating width of the first slurry along the width direction of the negative electrode sheet after it is unfolded is regulated so that the value of W is as shown in Table 1, and the total width of the negative electrode material layer remains unchanged; when the value of L changes, the coating width of the positive electrode slurry along the width direction of the positive electrode sheet after it is unfolded, the coating width of the first slurry along the width direction of the negative electrode sheet after it is unfolded, and the coating width of the second slurry along the width direction of the negative electrode sheet after it is unfolded are regulated so that the value of L is as shown in Table 1; when the value of D1 and / or D2 changes, the grinding time is adjusted so that the value of D1 and / or D2 is as shown in Table 1; when the value of H, PD1 and / or PD2 changes, the coating weight is adjusted so that H, The values ​​of PD1 and / or PD2 are shown in Table 1; when the value of w1 changes, the mass percentages of the first conductive agent and the first adhesive change accordingly, and the mass ratio of the first conductive agent to the first adhesive remains unchanged; when the values ​​of w2 and w3 change, the mass percentages of the second conductive agent and the second adhesive change accordingly, and the mass ratio of the second conductive agent to the second adhesive remains unchanged; the silicon-based material in the second material layer in Example 32 is Si; the silicon-based material in the second material layer in Example 33 is SiO and Si (SiO:Si=11:3), that is, based on the mass of the second material layer, the ratio of the mass percentage of SiO to the mass percentage of Si is 11:3.

[0117] Comparative Example 1

[0118] Except for preparing the negative electrode sheet according to the following steps, the rest is the same as Example 2.

[0119] <Preparation of negative electrode sheet>

[0120] 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 are uniformly mixed in a mass ratio of 14.4:81.6:1.3:1.2:1.5 to obtain a second slurry with a solid content of 45 wt%;

[0121] A copper foil with a thickness of 10 μm is used as the negative electrode current collector. The second slurry is evenly coated on one surface of the negative electrode current collector along the width direction after the negative electrode current collector is unfolded. It is dried at 120°C to obtain a negative electrode sheet with a second material layer on one side. The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a second material layer on both sides. It is dried under vacuum conditions at 120°C for 1 hour, and then cold pressed, cut and slit to finally obtain a negative electrode sheet with a specification of 67.45mm×1436mm. Among them, the coating weight of the second material layer is 6.14mg / cm 2 The compacted density PD2 of the second material layer is 1.18 g / cm 3, the width of the second material layer is 62mm.

[0122] Comparative Example 2

[0123] Except that no groove is provided on the first material layer in <Preparation of Negative Electrode Sheet> and relevant preparation parameters are adjusted according to Table 1, the rest are the same as Example 2.

[0124] Comparative Example 3

[0125] Except that the formula of the second slurry in <Preparation of Negative Electrode Sheet> is the same as that in Example 33 and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as that in Comparative Example 1.

[0126] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0127]

[0128]

[0129]

[0130] From Examples 1 to 33 and Comparative Examples 1 to 3, it can be seen that by providing different material layers on different areas of the negative electrode plate, providing grooves on the first material layer located at the edge of the negative electrode plate, and regulating the W / L value within the scope of this application, the side reaction width at the edge of the plate 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 side reactions in the edge area of ​​the plate and has good cycle performance. In Comparative Examples 1 and 3, there is no provision of the first material layer and grooves; in Comparative Example 2, there is no provision of grooves on the first material layer; in Comparative Examples 1 to 3, the side reaction width at the edge of the plate of the lithium-ion battery is large, and the cycle capacity retention rate is low, indicating that the lithium-ion battery in the comparative example has more side reactions in the edge area of ​​the plate and poor cycle performance. In contrast, the side reaction width at the edge of the plate of the lithium-ion battery in Examples 1 to 33 is small, and the cycle capacity retention rate is high, indicating that the lithium-ion battery of this application can reduce side reactions in the edge area of ​​the plate and has good cycle performance.

[0131] The value of L generally affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1, 6, and 7, when the value of L is within the range of this application, the width of the side reaction 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 side reactions in the electrode edge region and has good cycling performance.

[0132] The value of W' typically affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1, 8, and 11, when the value of L is within the range of this application, the width of the side reaction 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 side reactions in the electrode edge region and have good cycling performance.

[0133] The value of P generally affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1, 12, and 14, when the value of P is within the range of this application, the width of the side reaction 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 side reactions in the electrode edge region and has good cycling performance.

[0134] The value of H' usually affects the cycle performance of lithium-ion batteries. It can be seen from Examples 1, 15 to 19, and 26 to 29 that when the value of H' is within the scope of this application, the width of the side reaction at the edge of the electrode 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 reactions in the edge area of ​​the electrode and have good cycle performance. Among them, in Example 17, due to the large average depth of the multiple grooves, the local loss of negative electrode active material is large at this time, which easily leads to insufficient CB at the edge of the negative electrode, thereby increasing the risk of lithium plating of the secondary battery.

[0135] The value of H typically affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1, 18 to 19, and 26 to 29, when the value of H is within the range of this application, the width of the side reaction 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 side reactions in the electrode edge region and has good cycling performance.

[0136] The value of N typically affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1, 20, and 21, when the value of N is within the range of this application, the width of the side reaction 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 side reactions in the electrode edge region and has good cycling performance.

[0137] The values ​​of D1 and D2 generally affect the cycling performance of lithium-ion batteries. As can be seen from Examples 1 and 22 to 25, when the values ​​of D1 and D2 are within the ranges of this application, the width of the side reaction 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 side reactions in the electrode edge area and has good cycling performance.

[0138] The D1 / D2 ratio typically affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1 and 22 to 25, when the D1 / D2 ratio is within the range of this application, the width of the side reaction 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 side reactions in the electrode edge region and has good cycling performance.

[0139] The values ​​of PD1 and PD2 generally affect the cycling performance of lithium-ion batteries. As can be seen from Examples 1 and 26 to 29, when the values ​​of PD1 and PD2 are within the ranges of this application, the width of the side reaction 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 side reactions in the electrode edge region and has good cycling performance.

[0140] The PD2 / PD1 ratio generally affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1 and 26 to 29, when the PD2 / PD1 ratio is within the range of this application, the width of the side reaction 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 side reactions at the electrode edge region and has good cycling performance.

[0141] The mass percentage of the first graphite material generally affects the cycling performance of a lithium-ion battery. As can be seen from Examples 1, 30, and 31, when the mass percentage of the first graphite material is within the range of this application, the width of the side reaction 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 side reactions at the electrode edge region and exhibit good cycling performance.

[0142] The mass percentage of the second graphite material and the mass percentage of the silicon-based material usually affect the cycle performance of the lithium-ion battery. From Example 1, Example 32 to Example 33, and Comparative Example 4, it can be seen that when the mass percentage of the second graphite material and the mass percentage of the silicon-based material are within the scope of this application, the side reaction width at the edge of the electrode 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 reactions in the edge area of ​​the electrode and has good cycle performance. Among them, the mass percentage of the silicon-based material in Example 32 is small, that is, the mass percentage of the silicon element is small, and the energy density of the lithium-ion battery is small at this time.

[0143] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0144] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0145] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector; Along the width direction of the unfolded negative electrode sheet, the negative electrode material layer includes only a first material layer and a second material layer connected in sequence, the width of the first material layer is W mm, the width of the negative electrode material layer is greater than the width of the positive electrode material layer, 1 / 2 of the difference between the widths of the negative electrode material layer and the positive electrode material layer is L mm, and 0.2≤W / L≤4; The first material layer includes a first negative electrode active material, the first negative electrode active material includes a first graphite material, the second material layer includes a second negative electrode active material, the second negative electrode active material includes a second graphite material and a silicon-based material; A plurality of grooves are provided on the first material layer. The plurality of grooves extend along the width direction of the unfolded negative electrode sheet and are arranged at intervals along the length direction of the unfolded negative electrode sheet.

2. The secondary battery according to claim 1, wherein 0.2≤L≤5; and / or, 1≤W / L≤3.

3. The secondary battery according to claim 1, wherein Along the length direction of the unfolded negative electrode sheet, the width of a single groove is W'μm, and 20≤W'≤400.

4. The secondary battery according to claim 3, wherein 90≤W'≤150。 5. The secondary battery according to claim 1, wherein Along the width direction of the unfolded negative electrode sheet, the ratio of the length of a single groove to the width of the first material layer is P, and 0.2≤P≤1.

6. The secondary battery according to claim 5, wherein 0.4≤P≤1。 7. The secondary battery according to claim 1, wherein Along the thickness direction of the negative electrode sheet, the thickness of the first material layer is H μm, the average depth of the plurality of grooves is H′ μm, and 2≤H′≤0.8H.

8. The secondary battery according to claim 7, wherein 2≤H'≤0.6H.

9. The secondary battery according to claim 7, wherein 25≤H≤70。 10. The secondary battery according to claim 1, wherein Along the length direction of the unfolded negative electrode sheet, the distance between two adjacent grooves is N mm, 1≤N≤5.

11. The secondary battery according to claim 1, wherein The average particle size of the particles of the second graphite material is D1 μm, the average particle size of the particles of the silicon-based material is D2 μm, 9≤D1≤15, 7.3≤D2≤10.

3.

12. The secondary battery according to claim 11, which satisfies one of the following conditions: (1) 1.08≤D1 / D2≤1.8; (2)1.3≤D1 / D2≤1.

5.

13. The secondary battery according to claim 1, wherein The compacted density of the first material layer is PD1 g / cm 3 The compacted density of the second material layer is PD2 g / cm 3 , 0.8≤PD1≤1.18, 0.8≤PD2≤1.

9.

14. The secondary battery according to claim 13, which satisfies one of the following conditions: (1) 1.0≤PD2 / PD1≤1.6; (2)1.1≤PD2 / PD1≤1.

2.

15. The secondary battery according to any one of claims 1 to 14, wherein Based on the mass of the first material layer, the mass percentage of the first graphite material is 95% to 99%; based on the mass of the second 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%. 16 . An electronic device comprising the secondary battery according to claim 1 .

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