Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises an electrolyte and a negative pole piece, and the viscosity of the electrolyte is P MPa.s. The first material layer in the negative electrode plate comprises a first negative electrode active material, and the first negative electrode active material does not contain a silicon element. A second material layer in the negative electrode plate comprises a second negative electrode active material and a polyurethane binder, and the second negative electrode active material comprises a silicon element. Based on the mass of the second material layer, the mass percentage content of the silicon element is W < 1 >%, and the mass percentage content of the polyurethane binder is W < 2 >%; the negative active material layer is provided with at least one groove along the thickness direction of the negative pole piece, the sectional area of the groove is S [mu] m < 2 >, and the depth of the groove is H [mu] m; s and W1 meet the following conditions: 1 < = W1 < = 50, and S = K1 + 20W1; k1 is greater than or equal to 400 and less than or equal to 800; h, P, W2 and S meet the following conditions: 1 < = W2 < = 10, 2 < = P < = 8, and H = K2W2P / S; and K2 satisfies 800 < = K2 < = 1200. Through the arrangement, the dynamic performance and the cycle performance of the secondary battery are improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical technologies, and particularly to a secondary battery and an electronic device. Background Art

[0002] Currently, the specific capacity per gram of graphite in the lithium battery industry has reached 365 mAh / g, approaching the theoretical specific capacity of 372 mAh / g. Therefore, the negative electrode active material has nearly reached its maximum specific capacity. The positive electrode active material lithium cobaltate has achieved a voltage of 4.55 V. Further increasing the voltage poses a huge challenge to the high-voltage resistance of the electrolyte. The industry is currently researching alternative materials for the negative electrode with higher specific capacities. The theoretical specific capacity of silicon (Si) is as high as 4200 mAh / g, which is 10 times that of graphite. Currently, it seems to be an ideal alternative material. However, the biggest challenge faced by silicon-based negative electrode materials is the swelling problem during the cycling process. When Si reacts with lithium ions (Li + ) to form Li x Si, the volume expands by up to 320%. During the shrinkage process, pores will be left, resulting in the deterioration of the electronic conductivity of the silicon-based negative electrode material. During the cycling process, more negative electrode interfaces will be exposed, leading to an increase in electrolyte consumption. At the same time, the negative electrode binder requires a greater binding force to bind the negative electrode active material.

[0003] For Si negative electrodes, to solve the related problems caused by its high swelling ratio, compared with the graphite system, the following main changes occur: 1) Polyacrylic acid-based binders form a planar coating to inhibit the increase in pores in the negative electrode sheet caused by swelling during the cycling process. However, the planar coating will also limit the migration of Li + ; 2) More negative electrode interfaces will be exposed during the cycling process, and more negative electrode protection additives and fluoroethylene carbonate (FEC) need to be added to repair the interface. This will also result in a thicker initial film formation in the initial Si system, leading to an increase in interface impedance; 3) Since the silicon-based negative electrode material has a diamond structure, the solid-phase diffusion is more difficult compared with graphite. At the same time, the alloying reaction between the silicon-based negative electrode material and Li leads to a greater interface impedance. The above changes will all result in worse kinetics in the Si system than in graphite. Therefore, the kinetic bottleneck in the Si system is also a factor limiting the development of Si materials. Based on this, how to improve the kinetic performance of Si-based secondary batteries has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device to improve the kinetic performance of the secondary battery and improve the cycling performance of the secondary battery.

[0005] It should be noted that in the summary of the invention of this application, lithium-ion batteries are used as examples of secondary batteries to explain this application. However, 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, which includes an electrolyte and a negative electrode sheet. The viscosity of the electrolyte is P MPa·s; the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a first material layer and a second material layer. The first material layer is provided between the negative electrode current collector and the second material layer; the first material layer includes a first negative electrode active material, and the first negative electrode active material does not contain silicon element; the second material layer includes a second negative electrode active material and a polyurethane binder, and the second negative electrode active material includes silicon element; based on the mass of the second material layer, the mass percentage of silicon element is W 1 %, and the mass percentage of the polyurethane binder is W 2 %; along the thickness direction of the negative electrode sheet, at least one groove is provided in the negative electrode active material layer, and the cross-sectional area of the groove is S μm 2 , and the depth of the groove is H μm; S and W 1 satisfy: 1 ≤ W 1 ≤ 50, S = K 1 + 20W 1 ; K 1 satisfies: 400 ≤ K 1 ≤ 800; H, P, W 2 and S satisfy: 1 ≤ W 2 ≤ 10, 2 ≤ P ≤ 8, H = K 2 W 2 P / S; K 2 satisfies: 800 ≤ K 2 ≤ 1200. Through the settings of the present application, the secondary battery provided by the first aspect of the present application is beneficial to the insertion and transmission of lithium ions, and also enables the electrolyte to have a good wetting degree for the negative electrode active material layer. The probability of lithium deposition on the surface of the negative electrode sheet is relatively low, so that the kinetic performance of the silicon-based secondary battery of the present application is improved. It is also beneficial to inhibit the interfacial pulverization phenomenon of the negative electrode sheet and improve the cycle performance of the secondary battery.

[0007] In some embodiments of the present application, 500 ≤ K 1 ≤ 700. In some embodiments of the present application, 900 ≤ K 2 ≤ 1100.

[0008] In some embodiments of the present application, 15 ≤ W 1 ≤ 30. Controlling the mass percentage of silicon element in the second material layer within the above range is beneficial to reducing the probability of lithium deposition on the surface of the negative electrode sheet and further improving the kinetic performance of the secondary battery.

[0009] In some embodiments of the present application, 2 ≤ W 2≤8. Controlling the mass percentage of the polyurethane binder in the second material layer within the above range is beneficial to reducing the probability of lithium precipitation on the surface of the negative electrode sheet, further improving the kinetics of the secondary battery, and also beneficial to suppressing the pulverization phenomenon at the interface of the negative electrode sheet and improving the cycle performance of the secondary battery.

[0010] In some embodiments of the present application, the molecular formula of the polyurethane binder is (-NHCOO-) n , and the molecular weight of the polyurethane binder is m, where 10,000 ≤ m ≤ 100,000. Selecting a polyurethane binder with a molecular formula and molecular weight within the above range is beneficial to endowing the polyurethane binder with good adhesion and elasticity.

[0011] In some embodiments of the present application, the first negative electrode active material includes at least one of artificial graphite, natural graphite, hard carbon or soft carbon. Selecting the first negative electrode active material of the above types is beneficial to endowing the secondary battery with high performance, such as high energy density and good cycle performance.

[0012] In some embodiments of the present application, the second negative electrode active material includes a silicon-containing material, and the silicon-containing material includes at least one of pure silicon, silicon carbide compound or silicon oxide compound. When the second negative electrode active material includes a silicon-containing material and the silicon-containing material of the above types is selected, it is beneficial to endow the second negative electrode active material with a high specific capacity and a low tap density, thereby being beneficial to improving the kinetic performance of the secondary battery.

[0013] In some embodiments of the present application, the average particle size of the silicon-containing material is 5 μm to 30 μm. Controlling the average particle size of the silicon-containing material within the above range is beneficial to further improving the kinetic performance of the secondary battery while improving the interface pulverization problem of the negative electrode sheet.

[0014] In some embodiments of the present application, the distance between two adjacent grooves is σ μm, where 420 ≤ σ ≤ 3400; the thickness of the negative electrode active material layer is y μm, where 30 ≤ y ≤ 100; S, σ and y satisfy: 1.4% ≤ S / (σy)×100% ≤ 1.6%. By controlling the distance between two adjacent grooves and the thickness of the negative electrode active material layer within the above range and making the cross-sectional area, distance and thickness of the negative electrode active material layer satisfy the relationship 1.4% ≤ S / (σy)×100% ≤ 1.6%, it is possible to reduce the probability that the energy density of the secondary battery is affected while improving the kinetic performance and cycle performance of the secondary battery.

[0015] In some embodiments of the present application, the thickness of the first material layer is 25 μm to 95 μm; the thickness of the second material layer is 5 μm to 50 μm. By controlling the thicknesses of the first material layer and the second material layer within the above ranges, on the basis that the secondary battery has good kinetic performance and cycling performance, the secondary battery has a relatively high energy density.

[0016] The second aspect of the present application provides an electronic device, which includes the secondary battery described in any of the foregoing embodiments. Therefore, the electronic device has good performance in use.

[0017] Advantages of the present application:

[0018] The present application provides a secondary battery and an electronic device. The secondary battery includes an electrolyte and a negative electrode plate. The viscosity of the electrolyte is P MPa·s. The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a first material layer and a second material layer. The first material layer is provided between the negative electrode current collector and the second material layer. The first material layer includes a first negative electrode active material, and the first negative electrode active material does not contain silicon element. The second material layer includes a second negative electrode active material and a polyurethane binder. The second negative electrode active material includes silicon element. Based on the mass of the second material layer, the mass percentage content of silicon element is W 1 %, and the mass percentage content of the polyurethane binder is W 2 %; along the thickness direction of the negative electrode plate, the negative electrode active material layer is provided with at least one groove, and the cross-sectional area of the groove is S μm 2 , and the depth of the groove is H μm; S and W 1 satisfy: 1 ≤ W 1 ≤ 50, S = K 1 + 20W 1 ; K 1 satisfies: 400 ≤ K 1 ≤ 800; H, P, W 2 and S satisfy: 1 ≤ W 2 ≤ 10, 2 ≤ P ≤ 8, H = K 2 W 2 P / S; K 2 satisfies: 800 ≤ K 2≤1200. In the secondary battery of the present application, the negative electrode active material layer includes a first material layer without silicon element in the inner layer and a second material layer with silicon element in the surface layer. By introducing a polyurethane binder into the second material layer containing silicon element, at least one groove is provided in the negative electrode active material layer, and the mass percentage contents of silicon element and polyurethane binder in the second material layer are adjusted within the scope of the present application, so that the cross-sectional area and depth of the groove satisfy the relational expression of the present application with the content of silicon element, the content of polyurethane binder, and the viscosity of the electrolyte, which is beneficial to the insertion and transmission of lithium ions, and also enables the electrolyte to have a good wetting degree for the negative electrode active material layer, and the probability of lithium deposition on the surface of the negative electrode plate is relatively low, thereby improving the kinetic performance and cycle performance of the silicon-based secondary battery of the present application. The electronic device of the present application has good use performance.

[0019] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application, and those of ordinary skill in the art can also obtain other embodiments based on these drawings.

[0021] Figure 1 It is a schematic cross-sectional structure diagram of a negative electrode plate along its thickness direction and length direction of an implementation scheme of the present application;

[0022] Figure 2 is Figure 1 a schematic cross-sectional structure diagram of the negative electrode plate in

[0023] Reference numerals: 100 - negative electrode plate, 10 - negative electrode current collector, 21 - first material layer, 22 - second material layer, 20 - negative electrode active material layer, 30 - groove, 31 - center line. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following will clearly and completely describe the technical solutions in the present application in conjunction with the embodiments and drawings of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0025] It should be noted that in the specific implementation manner of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to lithium-ion batteries.

[0026] In a first aspect of the present application, a secondary battery is provided. The secondary battery includes an electrolyte and a negative electrode plate. The viscosity of the electrolyte is P MPa·s. The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a first material layer and a second material layer. The first material layer is provided between the negative electrode current collector and the second material layer. The first material layer includes a first negative electrode active material, and the first negative electrode active material does not contain silicon element. The second material layer includes a second negative electrode active material and a polyurethane binder. The second negative electrode active material includes silicon element. Based on the mass of the second material layer, the mass percentage content of silicon element is W 1 %, and the mass percentage content of the polyurethane binder is W 2 %; along the thickness direction of the negative electrode plate, at least one groove is provided in the negative electrode active material layer, and the cross-sectional area of the groove is S μm 2 , and the depth of the groove is H μm; S and W 1 satisfy: 1 ≤ W 1 ≤ 50, S = K 1 + 20W 1 ; K 1 satisfies: 400 ≤ K 1 ≤ 800; further, 500 ≤ K 1 ≤ 700. H, P, W 2 and S satisfy: 1 ≤ W 2 ≤ 10, 2 ≤ P ≤ 8, H = K 2 W 2 P / S; K 2 satisfies: 800 ≤ K 2 ≤ 1200; further, 900 ≤ K 2 ≤ 1100.

[0027] For the convenience of understanding, in the present application, the length direction of the negative electrode plate itself is defined as X, the width direction of the negative electrode plate itself is defined as Y, and the thickness direction of the negative electrode plate itself is defined as Z. It should be understood that the above definitions of directions are for the purpose of conveniently describing the present application, and the directions defined in the present application can be understood according to the relative positions of the drawings and the actual product elements. Moreover, the width direction, length direction, and thickness direction of the negative electrode current collector and the negative electrode active material layer itself are the same as those of the negative electrode plate. As Figure 1 and Figure 2As shown, the negative electrode plate 100 includes a negative electrode collector 10 and a negative electrode active material layer 20. The negative electrode active material layer 20 is arranged on both surfaces of the negative electrode collector 10. The negative electrode active material layer 20 includes a first material layer 21 and a second material layer 22. The first material layer 21 is arranged between the negative electrode collector 10 and the second material layer 22. Along the thickness direction Z of the negative electrode plate 100, the negative electrode active material layer 20 is provided with a plurality of grooves 30, and the depth of the groove 30 is shown as H. It can be understood that the depth H of the groove 30 is less than the sum of the single layer thicknesses of the first material layer 21 and the second material layer 22, that is, the depth H of the groove 30 is less than the thickness y of the negative electrode active material layer 20. Of course, in some embodiments, the negative electrode active material layer 20 can be arranged on one surface of the negative electrode collector 10. It should be noted that, Figure 1 and Figure 2 The shape, size and number of the grooves are only for illustrative purposes and are not intended to limit the present application. The "at least one" in the above "the negative electrode active material layer is provided with at least one groove" refers to one or more. The present application does not particularly limit the specific number of grooves, and those skilled in the art can choose according to actual conditions, as long as the purpose of the present application can be achieved. The present application does not particularly limit the shape of the grooves, as long as the purpose of the present application can be achieved. For example, it can be at least one of a trapezoid, an arc, a triangle or a rectangle. In the present application, the "cross-sectional area of ​​the groove" refers to the area of ​​a single groove on the cross section obtained by cutting the negative electrode sheet along its own length direction and thickness direction, and the "depth of the groove" refers to the vertical distance between the lowest point and the highest point of the groove along the thickness direction of the negative electrode sheet.

[0028] For example, W 1 It can be 1, 3, 5, 10, 12, 14, 16, 20, 22, 28, 30, 32, 34, 35, 37, 40, 41, 42, 45, 47, 50 or any value between any two of the above ranges. 1 It can be 400, 430, 500, 520, 600, 660, 700, 750, 800 or any value between any two of the above ranges. 1 When W is less than 1, the mass percentage of silicon in the second material layer is too small, the silicon content in the second negative electrode active material is too little, the second negative electrode active material does not significantly improve the capacity of the second material layer of the secondary battery, the reaction active sites do not change much, and the second negative electrode active material does not significantly improve the kinetics of the negative electrode sheet; W 1When it is greater than 50, the mass percentage content of silicon element in the second material layer is too large, which does not meet the actual application situation. During the charge and discharge process of the secondary battery, the reaction between silicon element and lithium ions causes volume expansion, and excessive pores will be left during the shrinkage process, resulting in the deterioration of the electronic conductivity of the second material layer. During the charge and discharge cycle of the secondary battery, more interfaces of the negative electrode plate will be exposed to increase the consumption of the electrolyte, and more binder will also be required to bind the second negative electrode active material to meet the requirements of the adhesion and cohesion of the negative electrode plate, further affecting the kinetic performance of the negative electrode plate. The second negative electrode active material containing silicon element belongs to a material that repels the electrolyte. The presence of silicon element in the second material layer makes the affinity of the second material layer for the electrolyte poor, and the higher the silicon element content, the worse the affinity of the second material layer for the electrolyte, which will affect the wetting degree of the electrolyte on the negative electrode active material layer, and then increase the probability of lithium deposition on the surface of the negative electrode plate, reducing the kinetic performance of the secondary battery. The inventor has found through research that setting grooves on the negative electrode active material layer can improve the wetting effect of the electrolyte. Specifically, when the silicon element content does not increase, the groove cross-sectional area is 400μm 2 to 800μm 2 When, the wetting effect of the electrolyte on the negative electrode active material layer is better. When the silicon element content increases, for every 1% increase in the mass percentage content of silicon element in the second material layer, the groove cross-sectional area increases by 20μm 2 When, the wetting effect of the electrolyte on the negative electrode active material layer can still maintain a good effect. Therefore, based on the above findings, the inventor adjusts to make the groove cross-sectional area satisfy the relationship S = K 1 + 20W 1 , 400 ≤ K 1 ≤ 800. In this way, the problem of the deterioration of the wetting degree of the electrolyte on the negative electrode active material layer caused by the increase in silicon element content will be improved.

[0029] For example, P can be 2, 3, 4, 5, 6, 7, 8 or any value between any two of the above numerical ranges. For example, W 2 can be 1, 1.4, 2, 2.3, 3, 3.5, 4, 4.2, 5, 5.6, 6, 7.2, 7.8, 8, 8.2, 8.6, 9, 9.3, 10 or any value between any two of the above numerical ranges. For example, K 2 2It can be 800, 830, 900, 940, 1000, 1080, 1100, 1150, 1200 or any value between any two of the above numerical ranges. When P is less than 2, the viscosity of the electrolyte is too low, the wetting effect is good, but the solvent stability is relatively low, and the electrolyte consumption is large during the cycling process of the secondary battery, which easily leads to liquid shortage in the later stage of cycling and generates "ionic bridge breakage", affecting the cycling performance of the secondary battery; when P is greater than 8, the viscosity of the electrolyte is too high, which will increase the movement resistance of lithium ions in the electrolyte, reduce the charge-discharge rate of the secondary battery, and also make the wetting degree of the electrolyte on the negative electrode active material layer worse. Polyurethane binders have good adhesiveness and high elasticity at the same time. It is not easy to reach the yield strength during the expansion and contraction process of the silicon-containing second negative electrode active material, which is beneficial to improving the problem of pulverization at the interface of the negative electrode sheet, and thus enhancing the cycling performance of the secondary battery; however, polyurethane binders belong to electrolyte-repellent materials, which will affect the wetting degree of the electrolyte on the second material layer to a certain extent, and also easily affect the reaction activity at the interface of the negative electrode active material layer, affecting the kinetic performance of the secondary battery. W 2 When it is less than 1, the content of the polyurethane binder in the second material layer is too low, and its advantages of adhesiveness and high elasticity are not obvious. The probability of pulverization of the binder caused by the expansion of the silicon-containing second negative electrode active material particles is relatively high, which is not conducive to improving the problem of pulverization at the interface of the negative electrode sheet; W 2 When it is greater than 10, the content of the polyurethane binder in the second material layer is too high, which will reduce the wetting degree of the electrolyte on the second material layer. In addition, the degree of coating on the negative electrode active material is too high, making it difficult to intercalate lithium, and thus increasing the probability of lithium deposition on the surface of the negative electrode sheet, deteriorating the kinetic performance of the secondary battery. The higher the viscosity of the electrolyte, the worse the wetting degree of the electrolyte on the negative electrode active material layer. The higher the content of the polyurethane binder, the worse the wetting degree of the electrolyte on the second material layer. Setting grooves on the negative electrode active material layer can improve the wetting degree of the electrolyte on the negative electrode active material layer, and the wetting effect of the electrolyte is related to both the cross-sectional area and depth of the grooves. Generally speaking, when the groove depth is fixed, the larger the cross-sectional area, the better the improvement effect of the electrolyte wetting; when the cross-sectional area is fixed, the greater the groove depth, the better the improvement effect of the electrolyte wetting. The inventors found through a large number of studies that when adjusting to make the groove depth satisfy the relationship H = K 2 W 2 P / S, 800 ≤ K 2When ≤ 1200, the problem of poor infiltration of the electrolyte into the negative active material layer caused by the increase in the viscosity of the electrolyte and / or the mass percentage content of the polyurethane binder can be improved by the grooves provided in this application. Specifically, when the viscosity of the electrolyte and the cross-sectional area of the groove are constant, when the mass percentage content of the polyurethane binder in the second material layer increases by 1%, and the depth of the groove increases by 800 to 1200 times, the electrolyte can still maintain a good infiltration effect on the negative active material layer.

[0030] In the secondary battery of this application, the negative active material layer includes a first material layer without silicon element and a second material layer with silicon element. The second material layer is subjected to the greatest force when contacting the cold pressing roller during the preparation of the negative electrode sheet. A dense layer generally forms on the surface of the second material layer away from the negative current collector. At the same time, along the thickness direction of the negative active material layer, the ion concentration of lithium ion transmission decreases from the surface away from the negative current collector to the surface close to the negative current collector. The surface of the second material layer away from the negative current collector requires a larger porosity to help lithium ion transmission. The second negative active material containing silicon element in the second material layer of this application generally has a lower powder compaction density compared to the first negative active material without silicon element in the first material layer. For example, the powder compaction density of the existing silicon-carbon material is about 2.0 g / cm 3 , while the powder compaction density of the existing graphite material is about 2.3 g / cm 3, therefore, the second material layer has a lower compaction density than the first material layer, so the second material layer has a larger porosity than the first material layer to assist lithium-ion transport, which is beneficial to improving the kinetic performance of the secondary battery; the second negative electrode active material containing silicon element in the surface layer of the second material layer will generate a larger expansion and contraction compared with the first negative electrode active material in the first cycle of formation of the secondary battery, which will result in more pores in the second material layer of the negative electrode sheet, being beneficial to the transport of lithium ions, and thus being beneficial to improving the kinetic performance of the secondary battery; the second negative electrode active material containing silicon element has a higher specific capacity than the first negative electrode active material without silicon element. Due to the concentration polarization effect, the lithium-ion concentration in the second material layer is higher, which will be more conducive to lithium intercalation to improve the kinetics of the secondary battery. By introducing a polyurethane binder into the second material layer containing silicon element in the negative electrode sheet, at least one groove is provided in the negative electrode active material layer, and the mass percentage contents of silicon element and the polyurethane binder in the second material layer are regulated within the scope of this application, so that the cross-sectional area and depth of the groove satisfy the relational expression of this application with the content of silicon element, the content of the polyurethane binder, and the viscosity of the electrolyte, enabling the high elasticity of the polyurethane binder to be fully exerted. The possibility of the polyurethane binder reaching the yield strength during the expansion and contraction of the second negative electrode active material containing silicon element is extremely small, which can alleviate the problem of binder pulverization caused by the expansion of the second negative electrode active material particles containing silicon element. The introduction of the polyurethane binder can also inhibit the expansion of the second negative electrode active material, and the groove can improve the influence of silicon element and the polyurethane binder itself on the wetting degree of the electrolyte, so that the electrolyte has a good wetting degree for the negative electrode active material layer.

[0031] In summary, through the settings of this application, the secondary battery provided in the first aspect of this application is beneficial to the intercalation and transport of lithium ions, and also enables the electrolyte to have a good wetting degree for the negative electrode active material layer. The probability of lithium deposition on the surface of the negative electrode sheet is relatively low, so that the kinetic performance of the silicon-based secondary battery of this application is improved. It is also beneficial to inhibiting the interfacial pulverization phenomenon of the negative electrode sheet and improving the cycle performance of the secondary battery.

[0032] There is no particular limitation on the regulation method of the electrolyte viscosity in this application, as long as the purpose of this application can be achieved. For example, it can be achieved by regulating the type of electrolyte.

[0033] In some embodiments of this application, 15 ≤ W 1 ≤ 30. For example, W 1It can be 15, 16, 18, 20, 21, 23, 24, 26, 27, 28, 29, 30 or any value between any two of the above numerical ranges. By controlling the mass percentage of silicon element in the second material layer within the above range, on the basis of providing a higher capacity, the second negative electrode active material expands and contracts during the cycling process of the secondary battery, resulting in a higher porosity of the second material layer, which is beneficial to the improvement of the lithium ion transmission rate, further reducing the probability of lithium deposition on the surface of the negative electrode sheet, and further improving the kinetic performance of the secondary battery.

[0034] In some embodiments of the present application, 2 ≤ W 2 ≤ 8. For example, W 2 can be 2, 2.3, 3, 3.5, 4, 4.2, 5, 5.6, 6, 7.2, 7.8, 8 or any value between any two of the above numerical ranges. By controlling the mass percentage of the polyurethane binder in the second material layer within the above range, it is beneficial to reduce the influence of the polyurethane binder on the electrolyte infiltration degree on the basis of exerting its high elasticity, thereby improving the affinity of the negative electrode active material layer for the electrolyte and the infiltration effect of the electrolyte on the negative electrode active material layer. Thus, it is beneficial to reduce the probability of lithium deposition on the surface of the negative electrode sheet, further improving the kinetics of the secondary battery, and also beneficial to inhibiting the interfacial pulverization phenomenon of the negative electrode sheet and improving the cycling performance of the secondary battery.

[0035] In some embodiments of the present application, the molecular formula of the polyurethane binder is (-NHCOO-) n , and the molecular weight of the polyurethane binder is m, 10000 ≤ m ≤ 100000. The above "molecular weight" refers to the weight average molecular weight, with the unit of g / mol. Selecting a polyurethane binder with a molecular formula and molecular weight within the above range is beneficial to endowing the polyurethane binder with good adhesion and elasticity. Applying it to the negative electrode sheet is beneficial to inhibiting the interfacial pulverization of the negative electrode sheet and improving the cycling performance of the secondary battery.

[0036] The present application has no particular limitation on the method for controlling the molecular weight of the polyurethane binder, as long as the purpose of the present application can be achieved. For example, commercially available polyurethane binders with different molecular weights can be selected, and combined with the test method of "testing the molecular weight of the polyurethane binder" in the present application to determine the molecular weight of the polyurethane binder, and select the polyurethane binder with the required molecular weight.

[0037] In some embodiments of the present application, the first negative electrode active material includes at least one of artificial graphite, natural graphite, hard carbon, or soft carbon. Materials of the above types have high specific capacity, good safety performance, and cycling performance. Selecting the first negative electrode active material of the above types is beneficial to endow the secondary battery with high performance, such as high energy density, good cycling performance, and safety performance.

[0038] In some embodiments of the present application, the second negative electrode active material includes a silicon-containing material, and the silicon-containing material includes at least one of pure silicon, silicon carbide compound, or silicon oxide compound. When the second negative electrode active material includes a silicon-containing material and the silicon-containing material of the above types is selected, it is beneficial to endow the second negative electrode active material with high specific capacity and low tap density, thereby being beneficial to improving the kinetic performance of the secondary battery.

[0039] In some embodiments of the present application, the second negative electrode active material includes a silicon-containing material and a carbon material, and the carbon material includes at least one of artificial graphite, natural graphite, hard carbon, or soft carbon. The present application does not particularly limit the mass ratio of the silicon-containing material to the carbon material in the second negative electrode active material, as long as the purpose of the present application can be achieved.

[0040] In some embodiments of the present application, the average particle size of the silicon-containing material is 5 μm to 30 μm. For example, the average particle size of the silicon-containing material can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 17 μm, 20 μm, 22 μm, 25 μm, 29 μm, 30 μm, or any value between any two of the above numerical ranges. Controlling the average particle size of the silicon-containing material within the above range can endow the silicon-containing material with high reactivity, and is also beneficial to making the second material layer have more voids to assist the transport of lithium ions, thereby being beneficial to further improving the kinetic performance of the secondary battery while improving the cycling performance of the secondary battery.

[0041] The present application does not particularly limit the control method of the average particle size of the silicon-containing material, as long as the purpose of the present application can be achieved. For example, it can be achieved by directly purchasing the silicon-containing material and determining the average particle size of the silicon-containing material in combination with the test method of "testing the average particle size of the silicon-containing material" in the present application, and selecting the silicon-containing material with the required average particle size; or, it can be achieved by means such as crushing, grinding, and ball milling.

[0042] In some embodiments of the present application, the spacing between two adjacent grooves is σ μm, where 420 ≤ σ ≤ 3400; the thickness of the negative electrode active material layer is y μm, where 30 ≤ y ≤ 100; S, σ, and y satisfy: 1.4% ≤ S / (σy)×100% ≤ 1.6%. The "spacing between two adjacent grooves" refers to the minimum distance between the centerlines of two adjacent grooves. The above "centerline" refers to the line used to identify the center of the groove, that is, a set of line segments representing the symmetric center of the groove. As Figure 1 and Figure 2 shown, the minimum distance between the centerlines 31 of two adjacent grooves 30, that is, the spacing is shown as σ. As Figure 1 shown, the thickness of the negative electrode active material layer 20 is shown as y. It should be noted that the thickness of the negative electrode active material layer refers to the thickness of a single-layer negative electrode active material layer. For example, σ can be 420, 430, 560, 700, 900, 1000, 1200, 1400, 1600, 1830, 2000, 2200, 2400, 2500, 2680, 2800, 2900, 3100, 3220, 3400, or any value between any two of the above numerical ranges. For example, y can be 30, 40, 50, 60, 65, 70, 72, 77, 80, 82, 90, 95, 100, or any value between any two of the above numerical ranges. By controlling the spacing between two adjacent grooves and the thickness of the negative electrode active material layer within the above ranges and making the cross-sectional area, spacing, and thickness of the negative electrode active material layer satisfy the relationship 1.4% ≤ S / (σy)×100% ≤ 1.6%, when grooves are provided on the negative electrode active material layer, the influence on the thickness of the negative electrode plate is reduced, and the overall compaction density of the negative electrode plate is also supplemented. Thus, the probability that the energy density of the secondary battery is affected can be reduced on the basis of improving the kinetic performance and cycle performance of the secondary battery.

[0043] In some embodiments of the present application, the thickness of the first material layer is 25 μm to 95 μm; the thickness of the second material layer is 5 μm to 50 μm. As Figure 1 shown, the thickness of the first material layer 21 is shown as T 21 shown, and the thickness of the second material layer 22 is shown as T 22Shown. It should be noted that the thickness of the first material layer refers to the thickness of a single layer of the first material layer, and the thickness of the second material layer refers to the thickness of a single layer of the second material layer. For example, the thickness of the first material layer is 25μm, 30μm, 36μm, 46μm, 50μm, 55μm, 60μm, 70μm, 75μm, 88μm, 95μm or any value between any two of the above numerical ranges. For example, the thickness of the second material layer can be 5μm, 10μm, 15μm, 21μm, 26μm, 30μm, 36μm, 40μm, 42μm, 46μm, 50μm or any value between any two of the above numerical ranges. Controlling the thicknesses of the first material layer and the second material layer within the above ranges is beneficial for the cooperation between the silicon element-free first material layer and the silicon element-containing second material layer. The second material layer has more pores than the first material layer, which is beneficial for the transmission and insertion of lithium ions, and is also beneficial for the entire negative electrode active material layer to provide a higher capacity for the secondary battery. Thus, on the basis of the secondary battery having good kinetic performance and cycling performance, the secondary battery has a high energy density.

[0044] In some embodiments of the present application, the thickness T of the first material layer 21 and the thickness T of the second material layer 22 satisfy: 1 ≤ T 21 / T 22 ≤ 10. For example, the value of T 21 / T 22 is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or any value between any two of the above numerical ranges. Controlling the thickness ratio of the first material layer and the second material layer within the above ranges is beneficial for the cooperation between the silicon element-free first material layer and the silicon element-containing second material layer. The second material layer has more pores than the first material layer, which is beneficial for the transmission and insertion of lithium ions, and is also beneficial for the entire negative electrode active material layer to provide a higher capacity for the secondary battery. Thus, on the basis of the secondary battery having good kinetic performance and cycling performance, the secondary battery has a high energy density.

[0045] The present application places no particular limitation on the electrolyte, as long as it can achieve the purpose of the present application. For example, the electrolyte includes a lithium salt and a non-aqueous solvent. In some embodiments of the present application, the lithium salt may include LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO3 , LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , LiSiF 6 , LiBOB or at least one of lithium difluoroborate. For example, the lithium salt can be selected as LiPF 6 because it can give a high ionic conductivity and improve the cycling characteristics. The non-aqueous solvent can be at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above carbonate compound can be at least one of a linear carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above linear carbonate compound can include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC). The cyclic carbonate compound can include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylene carbonate (VEC). The fluorinated carbonate compound can 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 trifluoromethyl ethylene carbonate. The above carboxylate compound can include but is 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, decanolide, valerolactone, mevalonolactone or caprolactone. The above ether compound can include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above other organic solvents can include but is not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphate ester.

[0046] This application has no particular limitation on the negative electrode current collector, as long as the object of this application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam or copper foam, etc. In this application, there is no particular limitation on the thickness of the negative electrode current collector, as long as the object of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm. Optionally, the negative electrode active material layer may further include at least one of a negative electrode conductive agent, a dispersant or a negative electrode binder. This application has no particular limitation on the mass ratio of each component in the second material layer, as long as the object of this application can be achieved. For example, the mass ratio of the second negative electrode active material, the polyurethane-based binder, the negative electrode conductive agent, the stabilizer and the negative electrode binder in the second material layer is (90-98):(0.5-10):(0-1.5):(0-1.5):(0-1.9). This application has no particular limitation on the mass ratio of each component in the first material layer, as long as the object of this application can be achieved. For example, the mass ratio of the first negative electrode active material, the negative electrode conductive agent, the stabilizer and the negative electrode binder in the first material layer is (95.5-98.5):(0-1.5):(0-1.5):(0-1.9). This application has no particular limitation on the types of the above-mentioned negative electrode conductive agent, stabilizer and negative electrode binder, as long as the object of this application can be achieved.

[0047] In some embodiments of the present application, the secondary battery includes a positive electrode tab. There is no particular limitation on the positive electrode tab in the present application, as long as the object of the present application can be achieved. In one embodiment, the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is disposed on one or two surfaces of the positive electrode current collector. The above-mentioned "surface" can be a partial surface or the entire surface of the positive electrode current collector. There is no particular limitation on the positive electrode current collector in the present application, as long as the object of the present application can be achieved. For example, the positive electrode current collector can include aluminum foil, aluminum alloy foil, etc. The positive electrode active material layer of the present application contains a positive electrode active material. There is no particular limitation on the type of the positive electrode active material in the present application, as long as the object of the present application can be achieved. For example, the positive electrode active material can include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate, etc. In the present application, the positive electrode active material can also contain non-metallic elements, and the non-metallic elements can include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur, and these elements can further improve the stability of the positive electrode active material. In the present application, there is no particular limitation on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm. The thickness of a single-layer positive electrode active material layer is 30 μm to 120 μm. Optionally, the positive electrode active material layer can further include at least one of a positive electrode conductive agent or a positive electrode binder. There is no particular limitation on the types of the positive electrode conductive agent and the positive electrode binder in the positive electrode active material layer of the present application, as long as the object of the present application can be achieved. There is no particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer, and those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved. For example, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer is (94-97.9):(0.8-3.0):(1.0-3.0).

[0048] In some embodiments of the present application, the secondary battery further includes a separator, which is used to separate the positive electrode tab and the negative electrode tab, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and does not affect the progress of the electrochemical charge and discharge process. There is no particular limitation on the separator in the present application, as long as the object of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyolefin (PO) such as polyethylene (PE), polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, or a spun film. There is no particular limitation on the thickness of the separator in the present application, as long as the object of the present application can be achieved.

[0049] In some embodiments of the present application, the secondary battery further includes an outer package for accommodating the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte. The present application places no particular restrictions on the type and shape of the outer package, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0050] The present application places no 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, in some embodiments, the method for preparing the negative electrode sheet includes but is not limited to the following steps: (1) preparing a first negative electrode slurry and a second negative electrode slurry, spraying the first negative electrode slurry and the second negative electrode slurry on two surfaces of the negative electrode current collector using a double-layer coater, and drying in an oven to obtain a semi-finished negative electrode sheet with a negative electrode active material layer disposed on both sides; (2) after cold pressing the semi-finished negative electrode sheet obtained in step (1), preparing grooves on the surface of the negative electrode active material layer by laser etching, and then performing slitting and welding the tab to obtain the negative electrode sheet. The present application places no particular restrictions on the solid content of the first negative electrode slurry and the second negative electrode slurry in step (1) as long as the purpose of the present application can be achieved. The present application places no particular restrictions on the process parameters of drying in step (1) as long as the purpose of the present application can be achieved. The present application places no particular restrictions on the process parameters of cold pressing in step (2) as long as the purpose of the present application can be achieved.

[0051] The secondary battery of the present application is not particularly limited, and it may include any device that undergoes an electrochemical reaction. For example, the secondary battery may include but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0052] The present application places no particular restrictions on the method for preparing the secondary battery, and a well-known preparation method in the art can be selected as long as the purpose of the present application can be achieved. For example, the method for preparing the secondary battery includes but is not limited to the following steps: stacking the separator, the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and performing operations such as winding and folding according to needs to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the secondary battery; or, stacking the separator, the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure to obtain a laminated electrode assembly, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the secondary battery.

[0053] The second aspect of the present application provides an electronic device, which includes the secondary battery described in any of the foregoing embodiments. Therefore, the electronic device has good performance in use.

[0054] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to: laptop computer, pen input computer, mobile computer, e-book player, portable phone, portable fax machine, portable copier, portable printer, head-mounted stereo headphones, video recorder, liquid crystal TV, portable cleaner, portable CD player, mini disc, transceiver, electronic notepad, calculator, memory card, portable recorder, radio, backup power supply, motor, automobile, motorcycle, moped, bicycle, lighting fixture, toy, game console, clock, power tool, flashlight, camera, large household battery, and lithium ion capacitor.

[0055] Examples

[0056] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods.

[0057] Testing method and equipment:

[0058] Test of electrolyte viscosity:

[0059] (1) Electrolyte centrifugation: After the lithium ion battery is discharged at a constant current of 0.05C to the discharge cut-off voltage of 3.0V at 25°C, the packaging bag of the lithium ion battery is cut open, the electrolyte is separated, and the negative electrode sheet is placed in a centrifuge tube to centrifuge out the excess electrolyte. (2) Viscosity test: The rotary viscometer method is used for testing. Rotary viscometer brand: Brookfield, model: DV1MLV, rotor: (model: #00), prepare a ULA (Ubbelohde viscometer) low-viscosity sample cup, select a range of 20CP, and the rotation speed when the torque is 1% to 100%. Heat the electrolyte sample to 25°C, pour the electrolyte into the sample cup of the rotary viscometer, and according to the formula: η = AM / n1, obtain the electrolyte viscosity. Where: η - dynamic viscosity of the liquid, unit: Pa·s, A - constant, unit: / m 3 , M - viscous torque exerted by the fluid on the cylinder, unit N·m, n1 - rotation speed of the cylinder, unit rad / s.

[0060] Sampling of negative electrode sheet:

[0061] At 25°C, the lithium-ion battery is discharged at a constant current of 0.05C until the discharge cut-off voltage. The lithium-ion battery is disassembled under an argon atmosphere, and the negative electrode sheet is soaked in dimethyl carbonate solvent for 2 h and dried at 60°C for 3 h to obtain the negative electrode sheet. Among them, the discharge cut-off voltage of the lithium-ion battery in the embodiment and the comparative example of this application is 3.0V, and the charge cut-off voltage is 4.45V. It can be understood that when the voltage range marked on the outer package of the factory battery is 3.0V to 4.45V, the charge cut-off voltage is 4.45V and the discharge cut-off voltage is 3.0V.

[0062] Unless otherwise specified, the following test methods are carried out using the negative electrode sheet obtained by the above method.

[0063] Test for the mass percentage content of silicon element:

[0064] After the negative electrode sheet is ion-polished to obtain a cross-section, the boundary between the first material layer and the second material layer is determined by scanning electron microscope (SEM) test, and the content of silicon element in the second material layer is tested by energy-dispersive X-ray spectroscopy analysis. The mass percentage content of silicon element is based on the mass of the second material layer.

[0065] Test for the content of polyurethane binder:

[0066] The content of polyurethane binder in the second material layer is measured by thermogravimetric analysis.

[0067] The specific steps are as follows: (1) Sample preparation: Gently scrape about 10 mg of the second material layer powder with a blade. (2) Instrument setting: Select a thermogravimetric analyzer, set the atmosphere as N 2 . Set the temperature range from 50°C to 650°C. Set the heating rate to 10°C / min. (3) Experimental steps: Put the sample into the sample pan of the thermogravimetric analyzer. Start the thermogravimetric analyzer and record the mass change of the sample during heating. (4) Data analysis: Analyze the thermogravimetric (TG) curve. The weight loss peaks at 213°C to 243°C and 425°C to 480°C (including 425°C) are the thermal decomposition characteristic peaks of polyurethane. According to the weight change of the TG curve, the mass loss of the sample during heating is obtained, that is, the mass percentage content of polyurethane binder in the second material layer.

[0068] Test for the cross-sectional area, depth, and spacing of the groove:

[0069] The groove parameters on the negative electrode tab were detected by a scanning electron microscope (ZEISS SEM (sigma-02-33)). The groove spacing can be determined by the surface topography of the negative electrode tab. The upper width, lower width, and depth of the groove can be measured by making a cross-section of the negative electrode tab through ion beam cross-section grinding (CP), and the parameters can be measured by microscope testing. The depth is taken as the central value between the upper and lower groove positions, and 32 points are averaged to calculate the width and depth, and then the area is calculated.

[0070] Testing the molecular weight of the polyurethane binder:

[0071] (1) Sample preparation: Scrape the second material layer on the surface of the negative electrode tab, put the obtained second material layer into N-methylpyrrolidone (NMP) for 2 hours, then filter the solution to remove insoluble impurities, and obtain the polyurethane binder as the sample.

[0072] (2) Instrument preparation: Select a suitable gel column, choose a suitable column according to the molecular weight range of the binder, set the mobile phase (such as tetrahydrofuran THF, NMP, etc.). In this application, since we mainly test the molecular weight of the binder, THF can be used, and the flow rate is 0.5 mL / min. The medium pore size column is selected for the gel column in this application.

[0073] (3) Experimental operation: Inject the sample into a high-temperature gel permeation chromatograph (GPC), and record the relationship between the elution time and the detector signal.

[0074] (4) Data processing: Calibrate with polystyrene standards, establish the relationship between the molecular weight and the elution time, and calculate the molecular weight and molecular weight distribution of the sample (such as number average molecular weight Mn, weight average molecular weight Mw, polydispersity index PDI, etc.) according to the calibration curve. In this application, we mainly focus on the weight average molecular weight Mw.

[0075] Testing the average particle size of the silicon-containing material:

[0076] Export the SEM image (backscattered condition, differentiating Si and graphite) of the second material layer taken as a common image format (such as JPEG), and use image analysis software (such as ImageJ) to process and analyze the image. The image magnification is 5000X, the number of tested particles is ≥32, and the calibration scale: In the image analysis software, calibrate the scale of the image according to the magnification of the SEM. For example, if the magnification of the SEM is 10,000 times and 100 pixels in the image correspond to 1 micron, then the size of each pixel is 0.01 micron. Manually or automatically mark the particles in the image. Measure the diameter or equivalent diameter of each particle, record all the size data of the particles, and calculate the average particle size.

[0077] Testing the thickness of the first material layer, the second material layer, and the negative electrode active material layer:

[0078] The total thickness of the active layer was measured by the microscopy method.

[0079] Principle: Use a scanning electron microscope (SEM) to observe the cross-section of the negative electrode plate and directly measure the thicknesses of the first material layer, the second material layer, and the negative electrode active material layer.

[0080] The specific steps are as follows: (1) Sample preparation: Cut the negative electrode plate into thin slices along its thickness direction and length direction to obtain a clear cross-section. (2) Observation: Use SEM to observe the cross-section and respectively find the boundaries of the first material layer, the second material layer, and the negative electrode active material layer. (3) Measurement: Use the measurement function of SEM to directly measure the thicknesses of the first material layer, the second material layer, and the negative electrode active material layer respectively.

[0081] Testing of kinetic performance:

[0082] (1) Testing of lithium plating at the interface:

[0083] Place the lithium-ion battery in a constant temperature oven at 0°C and let it stand for 60 min to make the lithium-ion battery reach a constant temperature. Charge the lithium-ion battery that has reached a constant temperature at a constant current of 1C to 4.45V at 0°C, then charge it at a constant voltage of 4.45V to 0.025C, let it stand for 5 min, and then discharge it at a constant current of 1C to 3.0V; this is one charge-discharge cycle. After 10 charge-discharge cycles, charge it at a constant current of 1C to 4.45V again and charge it at a constant voltage of 4.45V to 0.025C to obtain a fully charged battery after 10 cycles. Disassemble the battery in a dry room with a humidity less than 5% and take pictures to record the state of the negative electrode plate.

[0084] Judge the degree of lithium plating of the lithium-ion battery according to the following criteria:

[0085] No lithium plating: The lithium deposition area on the surface of the negative electrode plate is less than 0.5%;

[0086] Slight lithium plating: The lithium deposition area on the surface of the negative electrode plate is less than 10%;

[0087] Moderate lithium plating: The lithium deposition area on the surface of the negative electrode plate is 10% to 30%;

[0088] Severe lithium plating: The lithium deposition area on the surface of the negative electrode plate is greater than 30%.

[0089] (2) Severity of purple spot lithium plating at the interface after 500 cycles:

[0090] A lithium-ion battery that has been cycled 500 times in the charge-discharge cycle mode of "testing the lithium plating situation at the interface" is charged at a constant current of 0.7C to a voltage of 4.45V at 25°C, then charged at a constant voltage of 4.45V until the current reaches 0.05C, and then the lithium-ion battery is disassembled to observe the negative electrode sheet for comparison. The lithium plating situation of the obtained cycling interface is described. Now, the interface situation is classified. Through visual observation by the operator, when the proportion of the purple spot area in the total surface area of the negative electrode active material layer ≤ 5%, it is defined as no purple spot; when the proportion of the purple spot area in the total surface area of the negative electrode active material layer > 5% and ≤ 10%, it is defined as a mild purple spot; when the proportion of the purple spot area in the total surface area of the negative electrode active material layer > 10% and ≤ 25%, it is defined as a moderate purple spot; when the proportion of the purple spot area in the total surface area of the negative electrode active material layer > 25%, it is defined as a severe purple spot.

[0091] Test of the capacity retention rate after 500 cycles:

[0092] At 25°C, it is charged at a constant current of 0.7C to a voltage of 4.45V, then charged at a constant voltage of 4.45V until the current reaches 0.05C, and then discharged at a constant current of 1C to a voltage of 3.0V. This is a charge-discharge cycle process; after repeating the above charge-discharge cycle 500 times, the capacity retention rate is tested.

[0093] The capacity retention rate (%) after 500 cycles = the discharge capacity after the 500th cycle / the discharge capacity after the first cycle × 100%.

[0094] Example 1-1

[0095] <Preparation of the electrolyte>

[0096] In a dry argon atmosphere, EC:DMC is mixed in a mass ratio of 1:1 to obtain a solvent, and then the lithium salt LiPF 6 is mixed with the solvent in a mass ratio of 13.75:86.25 to prepare an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0097] <Preparation of the negative electrode sheet>

[0098] The first negative electrode active material artificial graphite, the stabilizer carboxymethyl cellulose sodium (CMC-Na), and the negative electrode binder styrene-acrylic emulsion are mixed in a mass ratio of 98:0.5:1.5, and then deionized water is added as a solvent and stirred in a vacuum mixer until a first negative electrode slurry with a solid content of 50 wt% and a uniform system is obtained.

[0099] Mix artificial graphite, a silicon carbide compound (chemical formula SiC), a negative electrode conductive agent carbon nanotube, a stabilizer sodium carboxymethyl cellulose (CMC-Na), and a polyurethane binder polyurethane (molecular weight of 10,000) as the second negative electrode active material in a mass ratio of 51.4:42.1:0.5:1:5. Then, add deionized water as a solvent and stir in a vacuum mixer until a second negative electrode slurry with a solid content of 50 wt% and a homogeneous system is obtained.

[0100] Spray the first negative electrode slurry and the second negative electrode slurry on two surfaces of a negative electrode current collector using a double-layer coater. After drying in an oven, a semi-finished negative electrode sheet with a double-sided coated negative electrode active material layer is obtained. Cold-press the semi-finished negative electrode sheet, then etch grooves on the surface of the negative electrode active material layer through laser processing technology. After slitting, clean the ear welding area, and weld the ear (copper ear) to obtain a negative electrode sheet with a specification of 76 mm × 856 mm for use. Among them, the depth H, spacing σ, and area S of the grooves are shown in Table 1. The thickness y of the negative electrode active material layer is 60 μm, and the thickness ratio of the first material layer to the second material layer is 5:1.

[0101] <Preparation of the positive electrode sheet>

[0102] Mix lithium iron phosphate as the positive electrode active material, acetylene black as the positive electrode conductive agent, and polyvinylidene fluoride (PVDF, weight average molecular weight of 5×10 5 ) in a mass ratio of 94:3:3. Add N-methylpyrrolidone (NMP) as a solvent and stir in a vacuum mixer until a positive electrode slurry with a solid content of 75 wt% and a homogeneous system is obtained. Coat the positive electrode slurry evenly on one surface of an aluminum foil positive electrode current collector with a thickness of 6 μm and dry it at 90°C to obtain a positive electrode sheet with a single-sided coated positive electrode active material layer (thickness 80 μm). Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode active material layer. After cold pressing and slitting, weld the ear (aluminum ear) to obtain a positive electrode sheet with a specification of 74 mm × 851 mm for use.

[0103] <Preparation of the separator>

[0104] Use a polypropylene (PP) porous film with a thickness of 9 μm as the separator.

[0105] <Preparation of the lithium-ion battery>

[0106] Stack the separator, positive electrode sheet, separator, and negative electrode sheet prepared above in sequence and wind them to obtain an electrode assembly. Place the electrode assembly in an aluminum-plastic film packaging bag, dry it, inject the electrolyte, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation, degassing, and trimming.

[0107] Examples 1-2 to Examples 1-9

[0108] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0109] Among them, the change in the mass percentage content W of silicon element 1 % is achieved by regulating the mass percentage content of silicon carbide in the second material layer. When the mass percentage content of silicon carbide changes, the mass percentage content of artificial graphite changes accordingly, and the sum of the mass percentage contents of silicon carbide and artificial graphite remains unchanged.

[0110] Example 1-10

[0111] Except for preparing the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0112] <Preparation of electrolyte>

[0113] In a dry argon atmosphere, EC:DMC is mixed at a mass ratio of 1:2 to obtain a solvent, and then the lithium salt LiPF 6 is mixed with the solvent at a mass ratio of 13.75:86.25 to prepare an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0114] Example 1-11

[0115] Except for preparing the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0116] <Preparation of electrolyte>

[0117] In a dry argon atmosphere, EC:DMC is mixed at a mass ratio of 3:1 to obtain a solvent, and then the lithium salt LiPF 6 is mixed with the solvent at a mass ratio of 13.75:86.25 to prepare an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0118] Examples 1-12 to Examples 1-20

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

[0120] Among them, the change in the mass percentage content W of silicon element 1 % is achieved by regulating the mass percentage content of silicon carbide in the second material layer. When the mass percentage content of silicon carbide changes, the mass percentage content of artificial graphite changes accordingly, and the sum of the mass percentage contents of silicon carbide and artificial graphite remains unchanged.

[0121] The mass percentage content W of the polyurethane binder 2When the [[ID=]]% changes, the mass percentage of artificial graphite changes accordingly, while the mass percentages of silicon carbide, negative electrode conductive agent, and stabilizer remain unchanged.

[0122] Examples 1-21 to 1-38

[0123] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Example 1-1.

[0124] Examples 2-1 to 2-4

[0125] Except for adjusting the relevant preparation parameters according to Table 2, the rest are the same as in Example 1-1.

[0126] Examples 3-1 to 3-6

[0127] Except for adjusting the relevant preparation parameters according to Table 3, the rest are the same as in Example 1-1.

[0128] In Example 3-2, when the type of silicon-containing material changes, the silicon element content W is made constant by adjusting the mass percentages of the silicon-containing material and artificial graphite. 1 % remains unchanged.

[0129] Comparative Example 1

[0130] Except for preparing the negative electrode plate according to the following steps, the rest are the same as in Example 1-1.

[0131] <Preparation of Negative Electrode Plate>

[0132] Mix the negative electrode active material artificial graphite, stabilizer sodium carboxymethyl cellulose (CMC-Na), and negative electrode binder styrene-acrylic emulsion in a mass ratio of 98:0.5:1.5, then add deionized water as a solvent, and stir in a vacuum mixer until a first negative electrode slurry with a solid content of 50 wt% and a homogeneous system is obtained.

[0133] Uniformly coat the first negative electrode slurry on one surface of a negative electrode current collector copper foil with a thickness of 8 μm, and dry it at 85 °C to form a first material layer, that is, a negative electrode plate with a single-sided coated negative electrode active material layer is obtained. Then, repeat the above steps on the other surface of the copper foil to obtain a negative electrode plate with a double-sided coated negative electrode active material layer. After cold pressing the negative electrode plate, etch grooves on the surface of the negative electrode active material layer by laser processing technology, and then after slitting, clean the ear welding area, and weld the ear (copper ear) to obtain a negative electrode plate with a specification of 76 mm × 856 mm for use. Among them, the depth H, spacing σ, and area S of the grooves are shown in Table 1, and the thickness of the first material layer, that is, the thickness y of the negative electrode active material layer, is 60 μm.

[0134] Comparative Example 2

[0135] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0136] Among them, the mass percentage content W of silicon element 1 % change is achieved by regulating the mass percentage content of silicon carbide in the second material layer. When the mass percentage content of silicon carbide changes, the mass percentage content of artificial graphite changes accordingly, and the sum of the mass percentage contents of silicon carbide and artificial graphite remains unchanged.

[0137] Comparative Example 3

[0138] Except for preparing the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0139] <Preparation of electrolyte>

[0140] In a dry argon atmosphere, EC:DMC was mixed at a mass ratio of 1:2.5 to obtain a solvent, and then the lithium salt LiPF 6 was mixed with the solvent at a mass ratio of 13.75:86.25 to prepare an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0141] Comparative Example 4

[0142] Except for preparing the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0143] <Preparation of electrolyte>

[0144] In a dry argon atmosphere, EC:DMC was mixed at a mass ratio of 3.5:1 to obtain a solvent, and then the lithium salt LiPF 6 was mixed with the solvent at a mass ratio of 13.75:86.25 to prepare an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0145] Comparative Examples 5 and 6

[0146] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0147] Among them, when the mass percentage content W of the polyurethane binder 2 % changes, the mass percentage content of artificial graphite changes accordingly, and the mass percentage contents of silicon carbide, anode conductive agent and stabilizer remain unchanged.

[0148] Comparative Example 7

[0149] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Comparative Example 3.

[0150] Among them, the mass percentage content W of the polyurethane binder 2When the [[ID=]], the negative electrode conductive agent and the stabilizer change proportionally, the sum of the mass percentage contents of the negative electrode conductive agent and the stabilizer remains unchanged, and the mass percentage content of the negative electrode active material remains unchanged.

[0151] Comparative Example 8

[0152] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Comparative Example 4.

[0153] Among them, the mass percentage content W of the polyurethane binder 2 When the [[ID=]] changes, the mass percentage content of artificial graphite changes accordingly, and the mass percentage contents of silicon carbide, negative electrode conductive agent and stabilizer remain unchanged.

[0154] Comparative Example 9

[0155] Except for not setting grooves in the preparation of the negative electrode sheet, the rest is the same as Example 1-1.

[0156] Comparative Example 10

[0157] Except for adjusting the polyurethane binder to polyacrylic acid in the preparation of the negative electrode sheet, the rest is the same as Example 1-1.

[0158] Comparative Examples 11 to 14

[0159] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0160] The preparation parameters and performance data of each example and comparative example are shown in Tables 1 to 3.

[0161] Table 1

[0162]

[0163]

[0164]

[0165] Note: The "\ " in Table 1 indicates no corresponding parameter; in Comparative Example 10, the polyurethane binder is replaced by polyacrylic acid, and W in Table 1 for Comparative Example 10 2 represents the content of polyacrylic acid; the "diving" in Table 1 means that in the "test of the capacity retention rate after 500 cycles", the capacity of the lithium-ion battery directly decays to 0 and cannot be charged.

[0166] It can be seen from Examples 1-1 to 1-15, Examples 1-29 to 1-36, and Comparative Examples 1 to 14 that for the secondary battery of the present application, by introducing a polyurethane binder into the second material layer, providing grooves in the negative electrode active material layer, and controlling the mass percentage contents of silicon element and polyurethane binder in the second material layer within the scope of the present application, such that the cross-sectional area and depth of the grooves satisfy the relational expressions of the present application with the content of silicon element, the content of polyurethane binder, and the viscosity of the electrolyte, the purple spots and lithium deposition on the surface of the negative electrode sheet in the secondary battery are less severe, indicating that the secondary battery has better kinetic performance, and the capacity retention rate of the secondary battery after 500 charge-discharge cycles is higher, indicating that the secondary battery has better cycling performance. For the secondary batteries of the comparative examples, no polyurethane binder is used in the second material layer, or no grooves are provided in the negative electrode active material layer, or the mass percentage content of silicon element or polyurethane binder in the second material layer is not within the scope of the present application, or the cross-sectional area of the grooves and the content of silicon element do not satisfy the relational expressions of the present application, or the depth of the grooves and the cross-sectional area do not satisfy the relational expressions of the present application with the content of polyurethane binder and the viscosity of the electrolyte. In the secondary batteries of the comparative examples, the purple spots and lithium deposition on the surface of the negative electrode sheet are more severe, or the capacity retention rate of the secondary battery after 500 charge-discharge cycles is lower, indicating that the secondary batteries of the comparative examples cannot balance good kinetic performance and cycling performance. Among them, for the secondary battery of Comparative Example 11, the K 1 value is less than the range defined in the present application, resulting in too small a cross-sectional area of the grooves, too large a depth of the grooves, and too small a width of the grooves, and the wetting degree of the electrolyte on the negative electrode active material layer becomes poor, affecting the kinetic performance and cycling performance of the secondary battery; for the secondary battery of Comparative Example 12, the K 1 value is greater than the range defined in the present application, resulting in too large a cross-sectional area of the grooves, a reduction in the lithium ion insertion sites in the negative electrode active material layer, and some lithium ions released from the positive electrode sheet being unable to be inserted into the negative electrode active material layer, leading to an aggravation of the lithium deposition phenomenon on the surface of the negative electrode sheet. In addition, with too large a cross-sectional area of the grooves and too small a depth of the grooves, the wetting degree of the electrolyte on the negative electrode active material layer will also become poor, thereby affecting the kinetic performance and cycling performance of the secondary battery. For the secondary batteries of Comparative Examples 13 and 14, the K 2When the value is not within the scope of the present application, the depth of the groove is too small or too large. When the cross-sectional area of the groove is constant, the width of the groove is too large or too small, resulting in too small or too large depth-width ratio of the groove, reducing the wetting degree of the electrolyte on the negative active material layer, thereby affecting the kinetic performance and cycling performance of the secondary battery. Specifically, the groove depth of Comparative Example 13 is too small. When the cross-sectional area of the groove is constant, the width of the groove is too large and the depth-width ratio of the groove is too small, which will deteriorate the wetting degree of the electrolyte on the negative active material layer; the groove depth of Comparative Example 14 is too large. When the cross-sectional area of the groove is constant, the width of the groove will be too small, which will also deteriorate the wetting degree of the electrolyte on the negative active material layer, thereby affecting the kinetic performance and cycling performance of the secondary battery.

[0167] The mass percentage content W of silicon element in the second material layer 1 %, and the cross-sectional area of the groove usually affect the kinetic performance and cycling performance of the secondary battery. It can be seen from Examples 1-1 to 1-9, Examples 1-29 to 1-32, Comparative Example 1, Comparative Example 2, Comparative Example 11 and Comparative Example 12 that for secondary batteries with the mass percentage content of silicon element in the second material layer and the cross-sectional area of the groove within the scope of the present application, the purple spots and lithium deposition on the surface of the negative electrode tab are in good condition, and the capacity retention rate after 500 charge-discharge cycles of the secondary battery is relatively high, indicating that the secondary battery has good kinetic performance and cycling performance.

[0168] The viscosity of the electrolyte, the mass percentage content W of the polyurethane binder in the second material layer 2 %, and the depth H of the groove usually affect the kinetic performance and cycling performance of the secondary battery. It can be seen from Examples 1-1, Examples 1-10 to 1-15, Examples 1-33 to 1-36, Comparative Examples 3 to 8, Comparative Example 13 and Comparative Example 14 that for secondary batteries with the viscosity of the electrolyte, the mass percentage content W of the polyurethane binder in the second material layer 2 %, and the depth H of the groove within the scope of the present application, the purple spots and lithium deposition on the surface of the negative electrode tab are in good condition, and the capacity retention rate after 500 charge-discharge cycles of the secondary battery is relatively high, indicating that the secondary battery has good kinetic performance and cycling performance.

[0169] The spacing between two adjacent grooves, the thickness of the negative electrode active material layer, and the relationship between the thickness and the cross-sectional area of the groove usually affect the kinetic performance and cycling performance of the secondary battery. As can be seen from Examples 1-1 to 1-9, Examples 1-16 to 1-20, Example 1-37, and Example 1-38, for a secondary battery with the spacing between two adjacent grooves, the thickness of the negative electrode active material layer, and the relationship between the thickness and the cross-sectional area of the groove within the scope of this application, the maximum non-lithium precipitation rate is relatively large, the purple spot and lithium precipitation on the surface of the negative electrode plate are in good condition, and the capacity retention rate after 500 charge-discharge cycles of the secondary battery is relatively high, indicating that the secondary battery has good kinetic performance and cycling performance.

[0170] The thicknesses of the first material layer and the second material layer usually affect the kinetic performance and cycling performance of the secondary battery. As can be seen from Example 1-1 and Examples 1-21 to 1-28, for a secondary battery with the thicknesses of the first material layer and the second material layer within the scope of this application, the purple spot and lithium precipitation on the surface of the negative electrode plate are in good condition, and the capacity retention rate after 500 charge-discharge cycles of the secondary battery is relatively high, indicating that the secondary battery has good kinetic performance and cycling performance.

[0171] Table 2

[0172]

[0173] The molecular weight of the polyurethane binder usually affects the kinetic performance and cycling performance of the secondary battery. As can be seen from Example 1-1 and Examples 2-1 to 2-4, for a secondary battery with the molecular weight of the polyurethane binder within the scope of this application, the purple spot and lithium precipitation on the surface of the negative electrode plate are in good condition, and the capacity retention rate after 500 charge-discharge cycles of the secondary battery is relatively high, indicating that the secondary battery has good kinetic performance and cycling performance.

[0174] Table 3

[0175]

[0176] The type of the first negative electrode active material usually affects the kinetic performance and cycling performance of the secondary battery. As can be seen from Example 1-1 and Example 3-1, for a secondary battery with the type of the first negative electrode active material within the scope of this application, the purple spot and lithium precipitation on the surface of the negative electrode plate are in good condition, and the capacity retention rate after 500 charge-discharge cycles of the secondary battery is relatively high, indicating that the secondary battery has good kinetic performance and cycling performance.

[0177] The type of silicon-containing material usually affects the kinetic performance and cycling performance of secondary batteries. It can be seen from Example 1-1 and Example 3-2 that for secondary batteries with the type of silicon-containing material within the scope of this application, the purple spots and lithium deposition on the surface of the negative electrode sheet are in good condition, and the capacity retention rate after 500 charge-discharge cycles of the secondary battery is relatively high, indicating that the secondary battery has good kinetic performance and cycling performance.

[0178] The average particle size of the silicon-containing material usually affects the kinetic performance and cycling performance of secondary batteries. It can be seen from Example 1-1 and Examples 3-3 to 3-6 that for secondary batteries with the average particle size of the silicon-containing material within the scope of this application, the maximum non-lithium-depositing rate is relatively large, the purple spot and lithium deposition on the surface of the negative electrode sheet are in good condition, and the capacity retention rate of the secondary battery is relatively high, indicating that the secondary battery has good kinetic performance and cycling performance.

[0179] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0180] Each embodiment in this specification is described in a related manner. For the same or similar parts between each embodiment, reference can be made to each other. The key point of each embodiment is to illustrate the differences from other embodiments.

[0181] The above are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. A secondary battery comprising an electrolyte and a negative electrode plate, wherein the viscosity of the electrolyte is P MPa·s; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a first material layer and a second material layer, wherein the first material layer is disposed between the negative electrode current collector and the second material layer; The first material layer includes a first negative electrode active material, and the first negative electrode active material does not contain silicon; The second material layer includes a second negative electrode active material and a polyurethane binder, wherein the second negative electrode active material includes silicon; based on the mass of the second material layer, the mass percentage of the silicon element is W1%, and the mass percentage of the polyurethane binder is W2%; Along the thickness direction of the negative electrode sheet, the negative electrode active material layer is provided with at least one groove, and the cross-sectional area of ​​the groove is S μm 2 , the depth of the groove is H μm; S and W1 satisfy: 1≤W1≤50, S=K1+20W1; K1 satisfies: 400≤K1≤800; H, P, W2 and S satisfy: 1≤W2≤10, 2≤P≤8, H=K2W2P / S; K2 satisfies: 800≤K2≤1200.

2. The secondary battery according to claim 1, wherein 15≤W1≤30, and / or, 500≤K1≤700.

3. The secondary battery according to claim 1, wherein 2≤W2≤8, and / or, 900≤K2≤1100.

4. The secondary battery according to claim 1, wherein The molecular formula of the polyurethane binder is (-NHCOO-) n , the molecular weight of the polyurethane adhesive is m, 10000≤m≤100000.

5. The secondary battery according to claim 1, wherein The first negative electrode active material includes at least one of artificial graphite, natural graphite, hard carbon or soft carbon.

6. The secondary battery according to claim 1, wherein The second negative electrode active material includes a silicon-containing material, and the silicon-containing material includes at least one of pure silicon, a silicon-carbon compound, or a silicon-oxygen compound.

7. The secondary battery according to claim 6, wherein The average particle size of the silicon-containing material is 5 μm to 30 μm.

8. The secondary battery according to claim 1, wherein The distance between two adjacent grooves is σμm, 420≤σ≤3400; The thickness of the negative electrode active material layer is y μm, 30≤y≤100; S, σ and y satisfy: 1.4%≤S / (σy)×100%≤1.6%.

9. The secondary battery according to claim 1, wherein The thickness of the first material layer is 25 μm to 95 μm; the thickness of the second material layer is 5 μm to 50 μm.

10. An electronic device, wherein: The electronic device includes the secondary battery according to any one of claims 1 to 9.

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