Secondary battery, preparation method and electric device

Abstract

The invention relates to the technical field of lithium batteries, in particular to a secondary battery, a preparation method and a power utilization device.The secondary battery comprises a negative pole piece, a current collector comprises a first area and a second area, the second area is close to a tab, a first active material layer is located in the first area, and a second active material layer is located in the second area; the mass fraction of the silicon-based material in the second active material layer is greater than that of the silicon-based material in the first active material layer; a mass fraction of the first carbon material in the second active material layer is greater than a mass fraction of the first carbon material in the first active material layer. The capacity of the second region can be improved, the charging speed of the second region is improved, and the condition that lithium dendrites are separated out in the second region is improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and particularly to a secondary battery, a preparation method and an electrical device. Background Art

[0002] In recent years, lithium-ion batteries have achieved great development. Lithium-ion batteries can be widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, as well as in multiple fields such as electric vehicles, electric tools, military equipment and aerospace. Among them, when lithium-ion batteries are applied to electric vehicle fields such as electric bicycles, electric motorcycles and electric vehicles, with the increasing market demand for the endurance of electric vehicles, the requirements for the cycle performance and fast charging ability of lithium-ion batteries are continuously increasing. Summary of the Invention

[0003] In view of this, the main technical problem to be solved by the present application is to improve the cycle performance and fast charging ability of lithium-ion batteries, so as to provide a secondary battery, a preparation method and an electrical device, which can improve the cycle performance and fast charging ability of the secondary battery.

[0004] A first aspect of the present application provides a secondary battery, including a negative electrode tab. The negative electrode tab includes a current collector and an active material layer provided on the surface of the current collector. The active material layer includes a silicon-based material and a carbon-containing material, and the carbon-containing material includes a first carbon material. The current collector includes a main body portion and a tab located on one side of the main body portion. The main body portion includes a first region and a second region, and the second region is located between the first region and the tab. The active material layer includes a first active material layer and a second active material layer. The first active material layer is located in the first region, and the second active material layer is located in the second region. The mass fraction of the silicon-based material in the second active material layer is greater than the mass fraction of the silicon-based material in the first active material layer. The mass fraction of the first carbon material in the second active material layer is greater than the mass fraction of the first carbon material in the first active material layer.

[0005] In the embodiments of the present application, the active material layer of the negative electrode plate includes a silicon-based material and a carbon-containing material. By adding a high-capacity silicon-based material to the carbon-containing material, the capacity of the negative electrode plate can be improved. In the embodiments of the present application, first, by setting the mass fraction of the silicon-based material in the second active material layer to be greater than the mass fraction of the silicon-based material in the first active layer, the capacity per unit volume of the active material layer in the region near the electrode ear (the second region) of the negative electrode plate is higher than that in the main region (the first region), which can increase the capacity of the second region and significantly improve the situation where the capacity of the negative electrode plate decreases due to the thinning of the second region relative to the first region caused by the influence of the process during the production of the negative electrode plate. Secondly, the expansion coefficient of the silicon-based material is greater than that of the carbon-containing material. By setting the mass fraction of the silicon-based material in the second region to be higher than that in the first region, the expansion degree of the second active material layer in the second region is greater than that of the first active material layer in the first region during charge and discharge, resulting in an increase in the porosity and a greater increase in the specific surface area of the second active material layer in the second region, and an increase in the contact area between the second active material layer and the electrolyte, which can improve the lithium ion transport ability and reduce the lithium deposition in the second region, thus improving the lithium deposition situation in the second region of the negative electrode plate. Thirdly, due to the relatively high lithium intercalation potential of the silicon-based material, the potential of the electrode plate is higher during charging, significantly improving the fast charging ability of the negative electrode plate. In the embodiments of the present application, the carbon-containing material includes a first carbon material, and the first carbon material is a fast-charging type high-kinetic carbon material, which can improve the fast charging ability of the second region. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the second active material layer to be greater than the mass fraction of the silicon-based material in the first active material layer and controlling the mass fraction of the first carbon material in the second active material layer to be greater than the mass fraction of the first carbon material in the first active material, the capacity of the second region and the charging speed of the second region can be improved to address the problems caused by the thinner second active material layer in the second region of the negative electrode plate during the battery manufacturing process; thereby improving the overall fast charging ability and cycle stability of the secondary battery.

[0006] In any embodiment, the ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer is greater than 1:1 and less than or equal to 80:1. In the embodiments of the present application, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer to the silicon-based material in the first active material layer within the above range, the problems caused by the thinner second active material layer in the second region due to process reasons can be improved, the difference in capacity per unit area between the second active material layer and the first active material layer can be reduced, the situation of lithium dendrite precipitation in the second active material layer can be improved, and the fast charging ability of the second active material layer can be enhanced.

[0007] In the embodiments of the present application, the capacity per unit area refers to the capacity of the active material layer in a unit area divided parallel to the plane where the current collector is located.

[0008] In any embodiment, the ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer is greater than or equal to 1.3 and less than or equal to 30:1. In the embodiments of the present application, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer to the silicon-based material in the first active material layer within the above range, the problem caused by the relatively thin second active material layer due to process reasons in the second region can be better improved, the difference in the capacity per unit area between the second active material layer and the first active material layer is reduced, and the local lithium dendrite precipitation on the negative electrode sheet is improved. The rapid charging capabilities of the second active material layer and the first active material layer are less different, and the capacity of the second active material layer is larger and the stability is higher.

[0009] In any embodiment, the mass fraction of the silicon-based material in the first active material layer is 0.5% to 30%, optionally 1% to 20%. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the first active material layer within the above range, the reversible specific capacity of the first active material layer of the negative electrode sheet is better, the energy density of the secondary battery is better, the stability of the first active material layer is better, and the cycle performance of the secondary battery is better.

[0010] In any embodiment, the mass fraction of the silicon-based material in the second active material layer is 1% to 40%, optionally 1.5% to 30%. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the second active material layer and making the mass fraction of the silicon-based material in the second active material layer greater than the mass fraction of the silicon-based material in the first active material layer, the reversible specific capacity of the second active material layer is better, the stability of the second active material layer is better, and the capacity per unit volume of the second active material layer in the second region is greater than the capacity per unit volume of the first active material layer in the first region, reducing the occurrence of lithium precipitation in the second region of the secondary battery.

[0011] In any embodiment, in the second region, the mass fraction of the first carbon material in the carbon-containing material is 40% to 100%, optionally 50% to 90%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the carbon-containing material in the second region, the content of the first carbon material in the second region is better, and the stability and fast charging performance of the second active material layer in the second region are better.

[0012] In any embodiment, in the first region, the mass fraction of the first carbon material in the carbon-containing material is 20% to 99%, optionally 35% to 89%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the carbon-containing material in the first region, the content of the first carbon material in the first region is preferably such that the fast charging performance of the active material per unit area in the first region and the second region differs less, improving the fast charging ability and stability of the negative electrode sheet.

[0013] In any embodiment, in the second region 1413, the mass fraction of the first carbon material in the second active material layer 1422 is 24% to 96%, optionally 35% to 89%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the second active material layer 1422 in the second region 1413 within the above range, the content of the first carbon material in the second active material layer 1422 in the second region 1413 is preferably such that the stability and fast charging performance of the second active material layer 1422 in the second region 1413 are better.

[0014] In any embodiment, in the first region 1412, the mass fraction of the first carbon material in the first active material layer 1421 is 14% to 79%, optionally 24% to 69%. By controlling the mass fraction of the first carbon material in the first active material layer 1421 in the first region 1412 within the above range, the content of the first carbon material in the first active material layer 1421 in the first region 1412 is preferably such that the stability and fast charging performance of the second active material layer 1422 in the first region 1412 are better.

[0015] In any embodiment, the carbon-containing material further includes a second carbon material, and the reversible specific capacity of the first carbon material is less than that of the second carbon material. In the embodiments of the present application, the second carbon material is a high-capacity carbon material, and the first carbon material is a fast-charging type carbon material. By controlling the contents of the first carbon material and the second carbon material, the capacity and fast charging performance of the secondary battery can be coordinated and controlled to a certain extent.

[0016] In any embodiment, the volume average particle diameter Dv50 of the first carbon material is less than the volume average particle diameter Dv50 of the second carbon material. In the embodiments of the present application, the volume average particle diameter Dv50 of the first carbon material is less than the volume average particle diameter Dv50 of the second carbon material, and the specific surface area of the first carbon material is larger, resulting in more channels and shorter paths for lithium ion migration during charge and discharge, better rate performance, and a faster charging ability of the first carbon material greater than that of the second carbon material. The volume average particle diameter Dv50 of the second carbon material is larger, the specific surface area is smaller, the tap density is high, and the capacity is large, resulting in a reversible specific capacity of the second carbon material greater than that of the first carbon material.

[0017] In any embodiment, the volume average particle size DV50 of the first carbon material is greater than or equal to 1 μm and less than or equal to 15 μm. In the embodiments of the present application, by controlling the volume average particle size DV50 of the first carbon material within the above range, the fast charging performance of the first carbon material is better.

[0018] In any embodiment, the volume average particle size DV50 of the second carbon material is greater than or equal to 7 μm and less than or equal to 22 μm. In the embodiments of the present application, by controlling the volume average particle size DV50 of the first carbon material within the above range, the reversible specific capacity performance of the second carbon material is better.

[0019] In any embodiment, the reversible specific capacity of the first carbon material is 330 mAh / g to 360 mAh / g, optionally 330 mAh / g to 360 mAh / g. In the embodiments of the present application, when the reversible specific capacity of the first carbon material is within the above range, the reversible specific capacity of the formed negative electrode sheet is larger and the stability is better.

[0020] In any embodiment, the reversible specific capacity of the second carbon material is 350 mAh / g to 380 mAh / g, optionally 350 mAh / g to 380 mAh / g. In the embodiments of the present application, when the reversible specific capacity of the second carbon material is within the above range, the reversible specific capacity of the formed negative electrode sheet is larger and the stability is better.

[0021] In any embodiment, the ratio of the area of the second region to the area of the first region is (3 to 20):100. Optionally, the ratio of the area of the second region to the area of the first region is (5 to 15):100. In the embodiments of the present application, by controlling the area ratio of the second region to the first region within the above range, the contents of the silicon-based material and the first carbon material in the first region and the second region of the negative electrode sheet are appropriate, which can better alleviate the lithium deposition in the second region of the negative electrode sheet, and the reversible specific capacity of the negative electrode sheet is higher and the stability is higher.

[0022] In any embodiment, in the direction from the first region towards the tab, the width of the second region is greater than zero and less than or equal to 20 mm. Optionally, the width of the second region is greater than zero and less than or equal to 10 mm. In the embodiments of the present application, in the direction from the first region towards the tab, when the width of the second region is within the above range, the width of the second region is smaller, and the layer of the second active material in the second region has a smaller overall impact on the negative electrode sheet.

[0023] In any embodiment, the secondary battery further includes a positive electrode plate. The CB value of the second active material layer is greater than or equal to the CB value of the first active material layer. The CB value is the ratio of the lithium intercalation capacity of the negative electrode plate per unit area to the deintercalation capacity of the positive electrode plate per unit area. In the embodiments of the present application, by controlling the CB value of the second active material layer to be greater than or equal to the CB value of the first active material layer, the lithium intercalation capacity per unit area in the second active material layer is relatively large, reducing the occurrence of lithium deposition in the second region during the charge and discharge process of the secondary battery.

[0024] In any embodiment, the first active material layer includes a first surface and a second surface. The first surface is close to the negative electrode current collector, and the second surface is far from the negative electrode current collector. The thickness of the first active material layer is denoted as H. Then, the first active material layer satisfies that the region formed from the first surface to 0.1H is the first sub-region, and the region formed from the second surface to 0.1H is the second sub-region. The mass fraction of the silicon-based material in the second sub-region is greater than the mass fraction of the silicon-based material in the first sub-region. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the second sub-region to be greater than the mass fraction of the silicon-based material in the first sub-region, that is, the silicon content in the upper surface layer (close to the second surface) is greater than that in the lower surface layer (close to the first surface), the silicon content is relatively large, and the silicon-based material expands during the charge and discharge process, making the specific surface area of the active material layer in the first sub-region on the upper surface relatively large, which is beneficial to increasing the contact area with the electrolyte, improving the capacity of the negative electrode plate, and improving the charging effect of the negative electrode plate.

[0025] In any embodiment, based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region, the mass fraction of the silicon-based material in the first sub-region is greater than or equal to 0 and less than or equal to 25%. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the first sub-region within the above range, the capacity and stability of the negative electrode plate are relatively high.

[0026] In any embodiment, based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region, the mass fraction of the silicon-based material in the second sub-region is greater than or equal to 1% and less than or equal to 35%. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the second sub-region within the above range, the capacity and stability of the negative electrode plate are relatively high.

[0027] In any embodiment, the mass fraction of the first carbon material in the carbon-containing material per unit area in the second sub-region is greater than the mass fraction of the first carbon material in the carbon-containing material per unit area in the first sub-region. By controlling the mass fraction of the first carbon material in the carbon-containing material in the second sub-region to be greater than the mass fraction of the first carbon material in the carbon-containing material in the first sub-region, the fast charging performance of the negative electrode plate can be improved.

[0028] In any embodiment, the mass fraction of the first carbon material in the carbon-containing material per unit area in the second sub-region is 20% to 85%, and more preferably 30% to 75%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the carbon-containing material in the second sub-region within the above range, the fast charging performance of the second sub-region in the embodiments of the present application is better, the stability of the second sub-region is better, the fast charging performance of the negative electrode sheet is improved, and the occurrence of lithium plating on the negative electrode sheet is reduced.

[0029] In any embodiment, the mass fraction of the first carbon material in the carbon-containing material per unit area in the first sub-region is 0 to 75%, and more preferably 20% to 65%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the carbon-containing material in the first sub-region, the capacity of the first sub-region is higher and the stability of the first sub-region is higher, thereby improving the stability of the negative electrode sheet.

[0030] In any embodiment, the active material layer includes a base layer and a supplementary layer. The base layer is located in the first region and the second region; the supplementary layer is disposed on the side of the base layer in the second region facing away from the current collector. The mass fraction of the silicon-based material in the supplementary layer is greater than that of the silicon-based material in the base layer, and the mass fraction of the first carbon material in the supplementary layer is greater than that of the first carbon material in the base layer. In the embodiments of the present application, by providing the supplementary layer, the content of the silicon-based material and the first carbon material in the second region can be increased to improve the problems caused by the relatively thin second active material layer in the second region of the negative electrode sheet during the manufacturing process of the battery; thereby, the overall fast charging ability and cycle stability of the secondary battery can be improved.

[0031] In any embodiment, the active material layer includes a base layer and an additional layer. The additional layer integrally extends to cover the side of the base layer facing away from the current collector and the side of the base layer close to the tab. The portion of the additional layer covering the side of the base layer close to the tab is located in the second region. In the embodiments of the present application, the active material layer includes a two-layer structure or a layer structure of two or more layers, such that the additional layer covers the end of the base layer close to the tab, and by controlling the mass fraction of the silicon-based material in the additional layer to be greater than that of the silicon-based material in the base layer and the mass fraction of the first carbon material in the additional layer to be greater than that of the first carbon material in the additional layer, the mass fraction of the silicon-based material in the second region can be made greater than that in the first region, and the mass fraction of the first carbon material in the second region can be made greater than that in the first region. In the embodiments of the present application, by providing a two-layer structure for the active material layer, it is convenient for the production of the active material layer, and at the same time, it is convenient to improve the unit area capacity and fast charging ability of the second region, and reduce the occurrence of lithium plating in the second region.

[0032] In any embodiment, the silicon-based material includes any one or more of silicon, a silicon-carbon composite material, silicon monoxide, and a silicon monoxide-carbon composite material.

[0033] In any embodiment, the carbon-containing material includes graphite. The first carbon material includes hard carbon, which refers to a carbon material that is difficult to graphitize at high temperatures above 2500°C. Hard carbon includes resin carbon, pyrolytic carbon of organic polymers, carbon black, biomass carbon, etc. The interlayer spacing of hard carbon is greater than the thickness of a single layer of graphite. The large interlayer spacing is conducive to the insertion and extraction of lithium ions. Therefore, hard carbon has excellent charge and discharge performance, good rate performance and cycle stability, and the performance of fast charge and discharge. Classified by the formation method, the first carbon material also includes a part of artificial graphite. The second carbon material includes soft carbon, which is an amorphous carbon material that can be graphitized at high temperatures above 2500°C. According to the difference in the sintering temperature of the precursor, soft carbon will produce three different crystal structures, namely amorphous structure, turbostratic disordered structure and graphite structure. The graphite structure is the common artificial graphite. Among them, the amorphous structure has excellent low-temperature performance and good rate performance due to its low crystallinity, large interlayer spacing and good compatibility with the electrolyte. Classified by the formation method, the second carbon material also includes another part of artificial graphite.

[0034] The second aspect of the present application also provides a method for preparing a secondary battery, including:

[0035] Providing a current collector, the current collector includes a main body and a tab located on one side of the main body. The main body has a first region and a second region, and the second region is located between the first region and the tab;

[0036] Coating a slurry containing an active material on the first region and the second region of the current collector to form an active material layer; the slurry containing the active material includes a silicon-based material and a carbon-containing material. The carbon-containing material includes a first carbon material and a second carbon material. The reversible specific capacity of the first carbon material is less than that of the second carbon material. The active material layer includes a first active material layer and a second active material layer. The first active material layer is located in the first region, and the second active material layer is located in the second region, so that the mass fraction of the silicon-based material in the second active material layer is greater than the mass fraction of the silicon-based material in the first active material layer, and the mass fraction of the first carbon material in the second active material layer is greater than the mass fraction of the first carbon material in the first active material layer.

[0037] The embodiment of the present application can form the secondary battery of the first aspect, so it has at least the same advantages as the secondary battery of the first aspect.

[0038] In any embodiment, coating a slurry containing an active material on the first region and the second region of the current collector to form an active material layer includes:

[0039] Coating a base slurry on the current collector to form a base layer, and the base layer is located in the first region and the second region;

[0040] A supplementary slurry is coated on the side of the base layer in the second region facing away from the current collector to form a supplementary layer. The mass fraction of the silicon-based material in the supplementary layer is greater than that of the silicon-based material in the base layer, and the mass fraction of the first carbon material in the supplementary layer is greater than that of the first carbon material in the base layer. By providing the supplementary layer, the content of the silicon-based material and the first carbon material in the second region can be increased.

[0041] In any embodiment, coating a slurry containing an active material on the first region and the second region of the current collector to form an active material layer includes:

[0042] Coating a base slurry on the current collector to form a base layer, and the base layer is located in the first region and the second region;

[0043] Coating an additional slurry on the side of the base layer facing away from the current collector to form an additional layer, and making the additional layer cover the side of the base layer close to the tab; wherein, the part of the additional layer covering the side of the base layer close to the tab is in the second region, the mass fraction of the silicon-based material in the additional slurry is greater than that of the silicon-based material in the base slurry, and the mass fraction of the first carbon material in the additional slurry in the carbon-containing material is greater than that of the first carbon material in the base slurry in the carbon-containing material.

[0044] In the embodiments of the present application, by adopting a coating method of two layers or more, the mass fractions of the silicon-based material and the first carbon material in the base slurry and the additional slurry can be regulated. And making the additional slurry cover the end of the base layer close to the tab, and making the additional slurry located in the second region, so that the additional slurry forms an additional layer, thereby the difference between the content of the silicon-based material and the second carbon material per unit area in the second region and the content of the silicon-based material and the second carbon material per unit area in the first region can be controlled to decrease, thereby the occurrence of lithium plating caused by the relatively thin thickness in the second region due to the manufacturing process can be improved.

[0045] In any embodiment, after coating an additional slurry on the side of the base layer facing away from the current collector to form an additional layer, it further includes coating a supplementary slurry on the side of the additional layer in the second region facing away from the current collector to form a supplementary layer. By providing the supplementary layer, the content of the silicon-based material and the first carbon material in the second region can be increased.

[0046] The third aspect of the present application further provides an electrical device, including the secondary battery of the first aspect and / or the secondary battery prepared by the method of the second aspect. Since the electrical device of the present application includes the secondary battery provided by the present application, it thus has at least the same advantages as the secondary battery. The embodiments of the present application include the secondary battery of the first aspect or the secondary battery of the second aspect, so that the electrical device of the present application has at least the advantages of the secondary battery of the first aspect, and / or the advantages of the secondary battery prepared by the method of the second aspect.

[0047] The above description is only an overview of the technical solution of the present application. In order to better understand the technical means of the present application, it can be implemented according to the content of the specification. And in order to make the above and other objects, features and advantages of the present application more obvious and understandable, the specific embodiments of the present application are specifically exemplified below. Description of the Drawings

[0048] Figure 1 It is a schematic structural diagram of an embodiment of a related negative electrode plate.

[0049] Figure 2 It is a schematic structural diagram of an embodiment of the current collector of the present application.

[0050] Figure 3a It is a schematic structural diagram of an embodiment of the negative electrode plate of the present application.

[0051] Figure 3b It is a schematic structural diagram of another embodiment of the negative electrode plate of the present application.

[0052] Figure 4 It is a schematic structural diagram of an embodiment of the secondary battery of the present application.

[0053] Figure 5 It is an exploded schematic structural diagram of an embodiment of the battery pack of the present application.

[0054] Figure 6 It is a schematic partial structural diagram of an embodiment of the vehicle of the present application.

[0055] 10. Secondary battery; 11. Cell assembly; 12. End cover; 12a. Electrode terminal; 13. Housing; 20. Box body; 21. First part; 22. Second part; 100. Battery pack; 200. Controller; 300. Motor; 1000. Vehicle; 14. Negative electrode plate; 141. Current collector; 142. Active material layer; 1411. Main body part; 1414. Tab; 1412. First region; 1413. Second region; 1421. First active material layer; 1422. Second active material layer; 1423. First surface; 1424. Second surface; 1425. First sub-region; 1426. Second sub-region; 143. Base layer; 144. Additional layer; 146. Supplementary layer. Detailed Embodiments

[0056] Hereinafter, embodiments of the secondary battery, battery, and electrical device of the present application will be specifically described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0057] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. In addition, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0058] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0059] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0060] If there is no special instruction, all steps of the present application can be carried out sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0061] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application are open-ended and can also be closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included or comprised, or it can mean that only the listed components are included or comprised.

[0062] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0063] As Figure 1 shown, during the production of the electrode, generally a slurry containing the active material is coated on the current collector 141, and the electrode is formed by further drying. However, affected by the coating process, it is easy to cause the active material layer 142 formed in the area near the tab 1414 of the electrode to be thinner, that is, as shown in the figure, the second active material layer 1422 is thinner than the first active material layer 1421. During the charge and discharge process of the battery, the charge density in the area near the tab 1414 of the negative electrode is relatively large, and lithium dendrites are likely to appear in the area near the tab 1414 of the negative electrode, affecting the cycle performance of the battery. In addition, it is of great significance to improve the fast charge and discharge performance of the secondary battery.

[0064] Based on this, as Figure 2 、 Figure 3a and Figure 3b shown, the first aspect of this application provides a secondary battery 10 (see Figure 4 ), including a negative electrode 14, the negative electrode 14 includes a current collector 141 and an active material layer 142 provided on the surface of the current collector 141, the active material layer 142 includes a silicon-based material and a carbon-containing material, the carbon-containing material includes a first carbon material; the current collector 141 includes a main body portion 1411 and a tab 1414 located on one side of the main body portion 1411, the main body portion 1411 includes a first region 1412 and a second region 1413, the second region 1413 is located between the first region 1412 and the tab 1414; the active material layer 142 includes a first active material layer 1421 and a second active material layer 1422, the first active material layer 1421 is located in the first region 1412, the second active material layer 1422 is located in the second region 1413; the mass fraction of the silicon-based material in the second active material layer 1422 is greater than the mass fraction of the silicon-based material in the first active material layer 1421; the mass fraction of the first carbon material in the second active material layer 1422 is greater than the mass fraction of the first carbon material in the first active material layer 1421.

[0065] In the embodiment of the present application, the active material layer 142 of the negative electrode tab 14 includes a silicon-based material and a carbon-containing material. By adding a high-capacity silicon-based material to the carbon-containing material, the capacity of the negative electrode tab 14 can be improved. In the embodiment of the present application, first, by setting the mass fraction of the silicon-based material in the second active material layer 1422 to be greater than the mass fraction of the silicon-based material in the first active layer, the capacity per unit volume of the active material layer 142 in the region (the second region 1413) near the tab 1414 of the negative electrode tab 14 is higher than that in the main region (the first region 1412), which can improve the capacity of the second region 1413 and significantly improve the situation where the capacity per unit area of the second region 1413 is less than that of the first region 1412. Second, the expansion coefficient of the silicon-based material is greater than that of the carbon-containing material. By making the mass fraction of the silicon-based material in the second region 1413 higher than that in the first region 1412, the expansion degree of the second active material layer 1422 in the second region 1413 is greater than that of the first active material layer 1421 in the first region 1412 during the charge and discharge process, so that the porosity of the second active material layer 1422 in the second region 1413 increases and the specific surface area increases more significantly, and the contact area between the second active material layer 1422 and the electrolyte increases, which can improve the lithium ion transmission ability and reduce the lithium deposition in the second region 1413 of the negative electrode tab 14, and improve the lithium deposition situation of the negative electrode tab 14 in the second region 1413. Third, since the lithium intercalation potential of the silicon-based material is relatively high, the potential of the electrode tab during charging is higher, which significantly improves the fast charging ability of the negative electrode tab 14. In the embodiment of the present application, the carbon-containing material includes a first carbon material, and the first carbon material is a fast-charging type high-kinetic carbon material, which can improve the fast charging ability of the second region 1413. In the embodiment of the present application, by controlling the mass fraction of the silicon-based material in the second active material layer 1422 to be greater than the mass fraction of the silicon-based material in the first active material layer 1421 and controlling the mass fraction of the first carbon material in the second active material layer 1422 to be greater than the mass fraction of the first carbon material in the first active material, the capacity of the second region 1413 and the charging speed of the second region 1413 can be improved. The secondary battery 10 in the embodiment of the present application can improve the capacity and fast charging ability of the negative electrode tab 14 and improve the lithium deposition situation in the local area of the negative electrode tab 14; thus, the overall fast charging ability and cycle stability of the secondary battery can be improved.

[0066] In some embodiments, the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 is greater than 1:1 and less than or equal to 80:1. In the embodiments of the present application, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the silicon-based material in the first active material layer 1421 within the above range, the difference in capacity per unit area between the second active material layer 1422 and the first active material layer 1421 can be reduced, the situation of lithium dendrite precipitation in the second active material layer 1422 can be improved, and the fast charging ability of the second active material layer 1422 can be enhanced. Among them, the ratio of the mass fraction of the base material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 can be 1.1:1, 1.5:1, 1.8:1, 2:1, 5:1, 10:1, 30:1, 50:1, 80:1, etc., or a range composed of any two of the above values. For example, 1.1:1 to 2:1, 2:1 to 50:1, 50:1 to 80:1, etc.

[0067] In some embodiments, the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 is greater than 1:1 and less than or equal to 80:1. In the embodiments of the present application, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the silicon-based material in the first active material layer 1421 within the above range, the difference in capacity per unit area between the second active material layer 1422 and the first active material layer 1421 can be reduced, the situation of lithium dendrite precipitation in the second active material layer 1422 can be improved, and the fast charging ability of the second active material layer 1422 can be enhanced. Among them, the ratio of the mass fraction of the base material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 can be 1.1:1, 1.5:1, 1.8:1, 2:1, 5:1, 10:1, 30:1, 50:1, 80:1, etc., or a range composed of any two of the above values. For example, 1.1:1 to 2:1, 2:1 to 50:1, 50:1 to 80:1, etc.

[0068] In some embodiments, the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 is greater than or equal to 1.3 and less than or equal to 30:1. In the embodiments of the present application, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the silicon-based material in the first active material layer 1421 within the above range, the capacity difference per unit area between the second active material layer 1422 and the first active material layer 1421 can be reduced, and the situation of local lithium dendrite precipitation in the negative electrode sheet 14 can be improved. The rapid charging capabilities of the second active material layer 1422 and the first active material layer 1421 are less different, and the capacity of the second active material layer 1422 is larger and the stability is higher. Among them, the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 can be 1.3:1, 2:1, 5:1, 8:1, 10:1, 18:1, 20:1, 30:1, etc., or a range composed of any two of the above values. For example, 1.3:1 to 8:1, 8:1 to 18:1, 18:1 to 30:1, etc.

[0069] In some embodiments, the mass fraction of the silicon-based material in the first active material layer 1421 is 0.5% to 30%. Optionally, it is 1% to 20%. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the first active material layer 1421 within the above range, the reversible specific capacity of the first active material layer 1421 of the negative electrode sheet 14 is better, the energy density of the secondary battery 10 is better, the stability of the first active material layer 1421 is better, and the cycle performance of the secondary battery 10 is better. Among them, the mass fraction of the silicon-based material in the first active material layer 1421 can be 0.5%, 1%, 1.48%, 1.5%, 1.8%, 2%, 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, 22%, 25%, 26%, 30%, etc., or a range composed of any two of the above values. For example, 0.5% to 1%, 1% to 1.48%, 1.48% to 8%, 8% to 13%, 13% to 20%, 20% to 30%, etc.

[0070] In some embodiments, the mass fraction of the silicon-based material in the second active material layer 1422 is 1% to 40%, optionally 1.5% to 30%. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the second active material layer 1422 and making the mass fraction of the silicon-based material in the second active material layer 1422 greater than that in the first active material layer 1421, the reversible specific capacity of the second active material layer 1422 is better, the stability of the second active material layer 1422 is better, and the capacity per unit volume of the second active material layer 1422 in the second region 1413 is greater than that of the first active material layer 1421 in the first region 1412, reducing the occurrence of lithium deposition in the second region 1413 of the secondary battery 10. Among them, the mass fraction of the silicon-based material in the second active material layer 1422 can be 1%, 1.48%, 1.5%, 1.8%, 2%, 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, 22%, 25%, 26%, 28%, 30%, 31%, 34%, 35%, 38%, 40%, etc., or a range composed of any two of the above values. For example, 1% to 1.5%, 1.5% to 13%, 13% to 20%, 20% to 28%, 28% to 30%, 30% to 40%, etc.

[0071] In some embodiments, the mass fraction of the first carbon material in the carbon-containing material in the second region 1413 is 40% to 100%, optionally 50% to 90%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the carbon-containing material in the second region 1413, the content of the first carbon material in the second region 1413 is better, and the stability and fast charging performance of the second active material layer 1422 in the second region 1413 are better. Among them, the mass fraction of the first carbon material in the carbon-containing material in the second region 1413 can be 40%, 50%, 55%, 60%, 70%, 80%, 85%, 90%, 98%, 100%, etc., or a range composed of any two of the above values. For example, 40% to 50%, 50% to 70%, 70% to 90%, 90% to 100%, etc.

[0072] In some embodiments, the mass fraction of the first carbon material in the carbon-containing material in the first region 1412 is 20% to 80%, optionally 30% to 70%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the carbon-containing material in the first region 1412, the content of the first carbon material in the first region 1412 is preferably such that the fast charging performance of the active material per unit area in the first region 1412 and the second region 1413 differs little, improving the fast charging ability and stability of the negative electrode sheet 14. Among them, the mass fraction of the first carbon material in the carbon-containing material in the first region 1412 can be 20%, 30%, 40%, 50%, 60%, 68%, 70%, 78%, 80%, etc., or a range composed of any two of the above values. For example, 20% to 30%, 30% to 40%, 40% to 70%, 70% to 80%, etc.

[0073] In some embodiments, the mass fraction of the first carbon material in the second active material layer 1422 in the second region 1413 is 24% to 96%, optionally 35% to 89%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the second active material layer 1422 in the second region 1413 within the above range, the content of the first carbon material in the second active material layer 1422 in the second region 1413 is preferably such that the second active material layer 1422 in the second region 1413 has better stability and better fast charging performance. Among them, the mass fraction of the first carbon material in the second active material layer 1422 in the second region 1413 can be 24%, 30%, 35%, 40%, 50%, 60%, 68%, 70%, 78%, 80%, 89%, 90%, 96%, etc., or a range composed of any two of the above values. For example, 24% to 35%, 35% to 60%, 60% to 80%, 80% to 89%, 89% to 96%, etc.

[0074] In some embodiments, the mass fraction of the first carbon material in the first active material layer 1421 in the first region 1412 is 14% to 79%, optionally 24% to 69%. By controlling the mass fraction of the first carbon material in the first active material layer 1421 in the first region 1412 within the above range, the content of the first carbon material in the first active material layer 1421 in the first region 1412 is preferably such that the second active material layer 1422 in the first region 1412 has better stability and better fast charging performance. Among them, the mass fraction of the first carbon material in the first active material layer 1421 in the first region 1412 can be 14%, 18%, 20%, 24%, 30%, 35%, 40%, 50%, 60%, 69%, 70%, 78%, 79%, etc., or a range composed of any two of the above values. For example, 14% to 24%, 24% to 60%, 60% to 69%, 69% to 79%, etc.

[0075] In some embodiments, the carbon-containing material includes a second carbon material, and the reversible specific capacity of the first carbon material is less than that of the second carbon material. In the embodiments of the present application, the second carbon material is a high-capacity carbon material, and the first carbon material is a fast-charging type carbon material. By controlling the contents of the first carbon material and the second carbon material, the capacity and fast-charging performance of the secondary battery can be coordinated and controlled to a certain extent.

[0076] In some embodiments, the reversible specific capacity of the first carbon material is 320 mAh / g to 370 mAh / g, optionally 330 mAh / g to 360 mAh / g. In the embodiments of the present application, when the reversible specific capacity of the first carbon material is within the above range, the reversible specific capacity of the formed negative electrode sheet 14 is relatively large and the stability is relatively good. Among them, the reversible specific capacity of the first carbon material can be 320 mAh / g, 330 mAh / g, 340 mAh / g, 350 mAh / g, 355 mAh / g, 358 mAh / g, 360 mAh / g, 365 mAh / g, 368 mAh / g, 370 mAh / g, etc., or a range composed of any two of the above values. For example, 320 mAh / g to 330 mAh / g, 330 mAh / g to 340 mAh / g, 340 mAh / g to 350 mAh / g, 350 mAh / g to 360 mAh / g, 360 mAh / g to 370 mAh / g, etc.

[0077] In some embodiments, the reversible specific capacity of the second carbon material is 340 mAh / g to 390 mAh / g, optionally 350 mAh / g to 380 mAh / g. In the embodiments of the present application, when the reversible specific capacity of the second carbon material is within the above range, the reversible specific capacity of the formed negative electrode sheet 14 is relatively large and the stability is relatively good. Among them, the reversible specific capacity of the second carbon material can be 340 mAh / g, 350 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, 375 mAh / g, 378 mAh / g, 380 mAh / g, 390 mAh / g, etc., or a range composed of any two of the above values. For example, 340 mAh / g to 350 mAh / g, 350 mAh / g to 360 mAh / g, 360 mAh / g to 370 mAh / g, 370 mAh / g to 380 mAh / g, 380 mAh / g to 390 mAh / g, etc.

[0078] In some embodiments, the volume average particle size Dv50 of the first carbon material is less than the volume average particle size Dv50 of the second carbon material. In the embodiments of the present application, the volume average particle size Dv50 of the first carbon material is less than the volume average particle size Dv50 of the second carbon material. The first carbon material has a larger specific surface area, resulting in more channels and shorter paths for lithium ion migration during charge and discharge, better rate performance, and a faster charging ability of the first carbon material greater than that of the second carbon material. The second carbon material has a larger volume average particle size Dv50, a smaller specific surface area, a higher tap density, and a larger capacity, resulting in a reversible specific capacity of the second carbon material greater than that of the first carbon material.

[0079] In some embodiments, the volume average particle size DV50 of the first carbon material is greater than or equal to 1 μm and less than or equal to 15 μm. In the embodiments of the present application, by controlling the volume average particle size DV50 of the first carbon material within the above range, the fast charging performance of the first carbon material is better. In the embodiments of the present application, the volume average particle size DV50 of the first carbon material can be 1 μm, 1.8 μm, 2 μm, 5 μm, 7 μm, 8 μm, 10 μm, 13 μm, 14 μm, 14.9 μm, etc., or a range composed of any two of the above values, for example, 1 μm to 7 μm, 7 μm to 13 μm, 13 μm to 15 μm, etc.

[0080] In some embodiments, the volume average particle size DV50 of the second carbon material is greater than or equal to 7 μm and less than or equal to 22 μm. In the embodiments of the present application, by controlling the volume average particle size DV50 of the first carbon material within the above range, the reversible specific capacity performance of the second carbon material is better. In the embodiments of the present application, the volume average particle size DV50 of the second carbon material can be 7 μm, 8 μm, 9 μm, 10 μm, 13 μm, 14 μm, 15 μm, 18 μm, 20 μm, 21 μm, 21.9 μm, etc., or a range composed of any two of the above values, for example, 7 μm to 13 μm, 13 μm to 15 μm, 15 μm to 22 μm, etc.

[0081] In some embodiments, the ratio of the area of the second region 1413 to the area of the first region 1412 is (3 to 20):100. In the embodiments of the present application, by controlling the area ratio of the second region 1413 to the first region 1412 within the above range, the contents of the silicon-based material and the first carbon material in the first region 1412 and the second region 1413 of the negative electrode sheet 14 are appropriate, which can better alleviate the situation of lithium deposition in the second region 1413 of the negative electrode sheet 14, and make the reversible specific capacity of the negative electrode sheet 14 relatively high and the stability relatively high. Among them, the ratio of the area of the second region 1413 to the area of the first region 1412 can be 3:100, 5:100, 8:100, 10:100, 13:100, 15:100, 18:100, 20:100, etc., or a range composed of any two of the above values. For example, (3 to 10):100, (10 to 15):100, (15 to 20):100, etc.

[0082] In some embodiments, the ratio of the area of the second region 1413 to the area of the first region 1412 is (5 to 15):100. In the embodiments of the present application, by controlling the area ratio of the second region 1413 to the first region 1412 within the above range, the contents of the silicon-based material and the first carbon material in the first region 1412 and the second region 1413 of the negative electrode sheet 14 are appropriate, which can better alleviate the situation of lithium deposition in the second region 1413 of the negative electrode sheet 14, and make the reversible specific capacity of the negative electrode sheet 14 relatively high and the stability relatively high. Among them, the ratio of the area of the second region 1413 to the area of the first region 1412 can be 5:100, 8:100, 10:100, 13:100, 15:100, or a range composed of any two of the above values. For example, (5 to 8):100, (8 to 13):100, (13 to 15):100, etc.

[0083] In some embodiments, the secondary battery 10 further includes a positive electrode sheet, and the CB value of the second active material layer 1422 is greater than or equal to the CB value of the first active material layer 1421. The CB value is the ratio of the lithium-insertion capacity per unit area of the negative electrode sheet 14 to the deintercalation capacity per unit area of the positive electrode sheet. In the embodiments of the present application, by controlling the CB value of the second active material layer 1422 to be greater than or equal to the CB value of the first active material layer 1421, the lithium-insertion capacity per unit area in the second active material layer 1422 is relatively large, and the occurrence of the situation of lithium deposition in the second region 1413 during the charge and discharge process of the secondary battery 10 is reduced.

[0084] In some embodiments, the first active material layer 1421 includes a first surface 1423 and a second surface 1424. The first surface 1423 is close to the negative electrode current collector 141, and the second surface 1424 is away from the negative electrode current collector 141. The thickness of the first active material layer 1421 is denoted as H. Then, the first active material layer 1421 satisfies the following: the region formed from the first surface 1423 to 0.1H is the first sub-region 1425, and the region formed from the second surface 1424 to 0.1H is the second sub-region 1426. The mass fraction of the silicon-based material in the second sub-region 1426 is greater than the mass fraction of the silicon-based material in the first sub-region 1425. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the second sub-region 1426 to be greater than the mass fraction of the silicon-based material in the first sub-region 1425, that is, the silicon content in the upper surface layer (close to the second surface 1424) is greater than that in the lower surface layer (close to the first surface 1423), the silicon content is relatively large, and the silicon-based material expands during charge and discharge, so that the specific surface area of the active material layer 142 in the first sub-region 1425 on the upper surface is relatively large, which is beneficial to increasing the contact area with the electrolyte, improving the capacity of the negative electrode plate 14, and improving the charging effect of the negative electrode plate 14.

[0085] In some embodiments, based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region 1425, the mass fraction of the silicon-based material in the first sub-region 1425 is greater than or equal to 0 and less than or equal to 25%. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the first sub-region 1425 within the above range, the negative electrode plate 14 has a relatively high capacity and high stability. Among them, based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region 1425, the mass fraction of the silicon-based material in the first sub-region 1425 can be 0, 1%, 2%, 3%, 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, 22%, 24%, 25%, etc., or a range composed of any two of the above values. For example, 0 to 8%, 8% to 13%, 13% to 20%, 20% to 25%.

[0086] In some embodiments, based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region 1426, the mass fraction of the silicon-based material in the second sub-region 1426 is greater than or equal to 1% and less than or equal to 35%. In the embodiments of the present application, by controlling the mass fraction of the silicon-based material in the second sub-region 1426 within the above range, the negative electrode sheet 14 has a higher capacity and higher stability. Among them, based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region 1426, the mass fraction of the silicon-based material in the second sub-region 1426 can be 1%, 2%, 3%, 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, 25%, 30%, 31.03%, 35%, etc., or a range composed of any two of the above values. For example, 0.99% to 10%, 10% to 13%, 13% to 31.03%, 31.03% to 35%.

[0087] In some embodiments, the mass fraction of the first carbon material per unit area in the carbon-containing material in the second sub-region 1426 is greater than the mass fraction of the first carbon material per unit area in the carbon-containing material in the first sub-region 1425. By controlling the mass fraction of the first carbon material in the carbon-containing material in the second sub-region 1426 to be greater than the mass fraction of the first carbon material in the carbon-containing material in the first sub-region 1425, the fast charging performance of the negative electrode sheet 14 can be improved.

[0088] In some embodiments, the mass fraction of the first carbon material per unit area in the carbon-containing material in the second sub-region 1426 is 20% to 85%, and more preferably 30% to 75%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the carbon-containing material in the second sub-region 1426 within the above range, the fast charging performance of the second sub-region 1426 is better, the stability of the second sub-region 1426 is better, the fast charging performance of the negative electrode sheet 14 is improved, and the occurrence of lithium deposition on the negative electrode sheet 14 is reduced. Among them, the mass fraction of the first carbon material per unit area in the carbon-containing material in the second sub-region 1426 is 20%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 83%, 85%, etc., or a range composed of any two of the above values. For example, 20% to 30%, 30% to 40%, 40% to 70%, 70% to 75%, 75% to 85%, etc.

[0089] In some embodiments, the mass fraction of the first carbon material in the carbon-containing material per unit area in the first sub-region 1425 is 0 to 75%, more optionally 20% to 65%. In the embodiments of the present application, by controlling the mass fraction of the first carbon material in the carbon-containing material in the first sub-region 1425, the capacity of the first sub-region 1425 is relatively high, and the stability of the first sub-region 1425 is relatively high, thereby improving the stability of the negative electrode sheet 14. Among them, the mass fraction of the first carbon material in the carbon-containing material per unit area in the first sub-region 1425 is 0, 10%, 20%, 30%, 40%, 50%, 55%, 58%, 60%, 65%, 68%, 70%, 75%, etc., or a range composed of any two of the above values. For example, 0 to 20%, 20% to 40%, 40% to 65%, 65% to 75%, etc.

[0090] In any embodiment, the active material layer 142 includes a base layer 143 and a supplementary layer 146. The base layer 143 is located in the first region 1412 and the second region 1413. The supplementary layer 146 is disposed on the side of the base layer 143 in the second region 1413 facing away from the current collector 141. The mass fraction of the silicon-based material in the supplementary layer 146 is greater than the mass fraction of the silicon-based material in the base layer 143, and the mass fraction of the first carbon material in the supplementary layer 146 is greater than the mass fraction of the first carbon material in the base layer 143. In the embodiments of the present application, by providing the supplementary layer 146, the content of the silicon-based material and the first carbon material in the second region 1413 can be increased to improve the problems caused by the relatively thin second active material layer 142 in the second region 1413 of the negative electrode sheet during the manufacturing process of the battery. Thus, the overall fast charging ability and cycle stability of the secondary battery can be improved.

[0091] In some embodiments, the active material layer 142 includes a base layer 143 and an additional layer 144. The additional layer 144 integrally extends to cover the side of the base layer 143 facing away from the current collector 141, covers the side of the base layer 143 close to the tab 1414, and a part of the additional layer 144 covering the side of the base layer 143 close to the tab 1414 is located in the second region 1413. In the embodiments of the present application, the active material layer 142 includes a two-layer structure or a layer structure of two or more layers, such that the additional layer 144 covers the end of the base layer 143 close to the tab 1414, and by controlling the mass fraction of the silicon-based material in the additional layer 144 to be greater than that of the silicon-based material in the base layer 143 and the mass fraction of the first carbon material in the additional layer 144 to be greater than that of the first carbon material in the additional layer 144, the mass fraction of the silicon-based material in the second region 1413 can be adjusted to be greater than that of the silicon-based material in the first region 1412, and the mass fraction of the first carbon material in the second region 1413 is greater than that of the first carbon material in the first region 1412. In the embodiments of the present application, by setting a two-layer structure for the active material layer 142, it is convenient to fabricate the active material layer 142, and at the same time, it is convenient to improve the capacity per unit area and the fast charging ability of the second region 1413, and reduce the occurrence of lithium plating in the second region 1413.

[0092] In some embodiments, the active material layer 142 includes a base layer 143, an additional layer 144, and a supplementary layer 146, which has the above-mentioned effects and will not be elaborated herein. Additionally, by simultaneously setting the base layer 143, the additional layer 144, and the supplementary layer 146, it is convenient to adjust the process parameters for fabricating the base layer 143, the additional layer 144, and the supplementary layer 146, and facilitate fabrication.

[0093] In some embodiments, the silicon-based material includes any one or several of silicon, a silicon-carbon composite material, silicon monoxide, and a silicon monoxide-carbon composite material.

[0094] In some embodiments, the carbon-containing material includes graphite. The first carbon material includes hard carbon, which refers to a carbon material that is difficult to graphitize at high temperatures above 2500°C. Hard carbon includes resin carbon, pyrolytic carbon of organic polymers, carbon black, biomass carbon, etc. The interlayer spacing of hard carbon is greater than the thickness of a single layer of graphite. The large interlayer spacing is beneficial to the insertion and extraction of lithium ions. Therefore, hard carbon has excellent charge and discharge performance, good rate performance and cycle stability, and the performance of fast charge and discharge. Classified by the formation method, the first carbon material also includes a part of artificial graphite. The second carbon material includes soft carbon, which is an amorphous carbon material that can be graphitized at high temperatures above 2500°C. According to the difference in the sintering temperature of the precursor, soft carbon will produce three different crystal structures, namely amorphous structure, turbostratic disordered structure and graphite structure. The graphite structure is the common artificial graphite. Among them, the amorphous structure has excellent low-temperature performance and good rate performance due to its low crystallinity, large interlayer spacing and good compatibility with the electrolyte. Classified by the formation method, the second carbon material also includes another part of artificial graphite.

[0095] The second aspect of the present application also provides a method for manufacturing a secondary battery 10, including:

[0096] Providing a current collector 141, the current collector 141 includes a main body portion 1411 and a tab 1414 located on one side of the main body portion 1411. The main body portion 1411 has a first region 1412 and a second region 1413. The second region 1413 is located between the first region 1412 and the tab 1414;

[0097] Coating a slurry containing an active material on the first region 1412 and the second region 1413 of the current collector 141 to form an active material layer 142; the slurry containing the active material includes a silicon-based material and a carbon-containing material. The carbon-containing material includes a first carbon material and a second carbon material. The reversible specific capacity of the first carbon material is less than that of the second carbon material; the active material layer 142 includes a first active material layer 1421 and a second active material layer 1422. The first active material layer 1421 is located in the first region 1412, and the second active material layer 1422 is located in the second region 1413, so that the mass fraction of the silicon-based material in the second active material layer 1422 is greater than the mass fraction of the silicon-based material in the first active material layer 1421, and the mass fraction of the first carbon material in the second active material layer 1422 is greater than the mass fraction of the first carbon material in the first active material layer 1421.

[0098] The embodiments of the present application can form the secondary battery 10 of the first aspect, and thus at least have the same advantages as the secondary battery 10 of the first aspect.

[0099] In some embodiments, a slurry containing an active material is coated on the first region 1412 and the second region 1413 of the current collector 141 to form the active material layer 142, including:

[0100] A base slurry is coated on the current collector 141 to form a base layer 143, and the base layer 143 is located in the first region 1412 and the second region 1413;

[0101] A supplementary slurry is coated on the side of the base layer 143 in the second region 1413 facing away from the current collector 141 to form a supplementary layer 146. The mass fraction of the silicon-based material in the supplementary layer 146 is greater than that of the silicon-based material in the base layer 143, and the mass fraction of the first carbon material in the supplementary layer 146 is greater than that of the first carbon material in the base layer 143. By providing the supplementary layer 146, the content of the silicon-based material and the first carbon material in the second region 1413 can be increased. By providing the supplementary layer 146, the content of the silicon-based material and the first carbon material in the second region 1413 can be increased.

[0102] In some embodiments, a slurry containing an active material is coated on the first region 1412 and the second region 1413 of the current collector 141 to form the active material layer 142, including:

[0103] A base slurry is coated on the current collector 141 to form a base layer 143, and the base layer 143 is located in the first region 1412 and the second region 1413;

[0104] An additional slurry is coated on the side of the base layer 143 facing away from the current collector 141 to form an additional layer 144, and the additional layer 144 covers the side of the base layer 143 close to the tab 1414; wherein, a part of the additional layer 144 covering the side of the base layer 143 close to the tab 1414 is in the second region 1413, the mass fraction of the silicon-based material in the additional slurry is greater than that of the silicon-based material in the base slurry, and the mass fraction of the first carbon material in the additional slurry in the carbon-containing material is greater than that of the first carbon material in the base slurry in the carbon-containing material.

[0105] In some embodiments, after an additional slurry is coated on the side of the base layer 143 facing away from the current collector 141 to form an additional layer, a supplementary slurry is further coated on the side of the additional layer in the second region 1413 facing away from the current collector 141 to form a supplementary layer 146. By providing the supplementary layer 146, the content of the silicon-based material and the first carbon material in the second region 1413 can be increased.

[0106] In the embodiments of the present application, by adopting a coating method of two or more layers, the mass fractions of the silicon-based material and the first carbon material in the base slurry and the additional slurry can be regulated. And the additional slurry covers the end portion of the base layer 143 close to the tab 1414, and the additional slurry is located in the second region 1413, so that the additional slurry forms an additional layer 144, thereby the difference between the content of the silicon-based material and the content of the second carbon material per unit area in the second region 1413 and the content of the silicon-based material and the content of the second carbon material per unit area in the first region 1412 can be controlled to decrease, thereby the occurrence of lithium plating caused by the relatively thin thickness of the second region 1413 due to the manufacturing process can be improved.

[0107] The third aspect of the present application further provides an electrical device, including the secondary battery 10 of the first aspect and / or the secondary battery 10 prepared by the method of the second aspect. Since the electrical device of the present application includes the secondary battery 10 provided by the present application, it thus has at least the same advantages as the secondary battery 10. The embodiments of the present application include the secondary battery 10 of the first aspect or the secondary battery 10 of the second aspect, so that the electrical device of the present application has at least the advantages of the secondary battery 10 of the first aspect, and / or the advantages of the secondary battery 10 prepared by the method of the second aspect.

[0108] In addition, the secondary battery 10, the battery pack 100 (see Figure 5 ) and the electrical device of the present application will be described below with appropriate reference to the drawings.

[0109] In the embodiments of the present application, the secondary battery 10 further includes an electrolyte and a separator. The separator is disposed between the positive electrode plate and the negative electrode plate 14, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through. During the charging and discharging process of the battery, the active ion Li + intercalates and deintercalates back and forth between the positive electrode plate and the negative electrode plate 14, and the electrolyte serves to conduct ions between the positive electrode plate and the negative electrode plate 14.

[0110] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

[0111] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0112] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector 141. For example, as the metal foil, aluminum foil may be used. The composite current collector 141 may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector 141 may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0113] In some embodiments, when the secondary battery 10 is a lithium-ion battery, the positive electrode active material may be a positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which may also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which may also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which may also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which may also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2(which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ), and at least one of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphate may include but are not limited to lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0114] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0115] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the above-mentioned components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0117] The negative electrode current collector 141 has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector 141. The active material layer 142 of the negative electrode plate 14 is disposed on at least one surface of the negative electrode current collector 141.

[0118] In some embodiments, the current collector 141 of the negative electrode tab 14 may be a metal foil or a composite current collector 141. For example, as the metal foil, copper foil may be used. The composite current collector 141 may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector 141 may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, the active material layer 142 may further optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0120] In some embodiments, the active material layer 142 may further optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the active material layer 142 may further optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na), etc.).

[0122] The electrolyte plays a role in conducting ions between the positive electrode tab and the negative electrode tab 14. The present application does not specifically limit the type of the electrolyte, and it can be selected according to requirements.

[0123] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0124] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0125] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0126] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0127] In some embodiments, the secondary battery 10 further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0128] In some embodiments, the material of the separator may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0129] In some embodiments, the positive electrode plate, the negative electrode plate 14, and the separator may be made into a battery cell assembly by a winding process or a stacking process.

[0130] In some embodiments, as Figure 4 shown, the secondary battery 10 may include an outer package. The outer package can be used to encapsulate the above-mentioned battery cell assembly 11 and the electrolyte. The outer package includes an end cap 12, a housing 13, and other functional components.

[0131] The end cap 12 refers to a component that covers the opening of the housing 13 to isolate the internal environment of the secondary battery 10 from the external environment. Without limitation, the shape of the end cap 12 may be adapted to the shape of the housing 13 to cooperate with the housing 13. Optionally, the end cap 12 may be made of a material with a certain hardness and strength (such as aluminum alloy). In this way, the end cap 12 is not easily deformed when subjected to extrusion and collision, so that the secondary battery 10 can have higher structural strength and the safety performance can also be improved. Functional components such as electrode terminals 12a may be provided on the end cap 12. The electrode terminals 12a can be used for electrically connecting with the battery cell assembly 11 to output or input the electric energy of the secondary battery 10. In some embodiments, a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the secondary battery 10 reaches a threshold may also be provided on the end cap 12. The material of the end cap 12 may also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special limitations thereto. In some embodiments, an insulating member (not shown in the figure) may be provided on the inner side of the end cap 12, and the insulating member can be used to isolate the electrical connection components in the housing 13 from the end cap 12 to reduce the risk of short circuit. Exemplarily, the insulating member may be plastic, rubber, etc.

[0132] The housing 13 is a component for cooperating with the end cap 12 to form the internal environment of the secondary battery 10. Among them, the formed internal environment can be used to accommodate the battery cell assembly 11, the electrolyte, and other components. The housing 13 and the end cap 12 can be independent components. An opening can be provided on the housing 13, and the end cap 12 is covered at the opening to form the internal environment of the secondary battery 10. Without limitation, the end cap 12 and the housing 13 can also be integrated. Specifically, the end cap 12 and the housing 13 can first form a common connection surface before other components are put into the housing. When it is necessary to encapsulate the inside of the housing 13, the end cap 12 is then covered on the housing 13. The housing 13 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 13 can be determined according to the specific shape and size of the battery cell assembly 11. The material of the housing 13 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. The embodiments of the present application do not make special restrictions on this.

[0133] One or more battery cell assemblies 11 can be included in the housing 13. The portions of the positive electrode plate and the negative electrode plate without active substances respectively constitute the electrode tabs 1414. The positive electrode tab and the negative electrode tab can be located at one end of the main body together or at both ends of the main body respectively. During the charge and discharge process of the battery, the positive active substance and the negative active substance react with the electrolyte, and the electrode tabs 1414 are connected to the electrode terminals to form a current loop.

[0134] Please refer to Figure 5 , the battery pack 100 includes a box body 20 and a secondary battery 10, and the secondary battery 10 is accommodated in the box body 20. Among them, the box body 20 is used to provide a accommodation space for the secondary battery 10, and the box body 20 can adopt various structures. In some embodiments, the box body 20 can include a first part 21 and a second part 22. The first part 21 and the second part 22 cover each other, and the first part 21 and the second part 22 jointly define a accommodation space for accommodating the secondary battery 10. The second part 22 can be a hollow structure with one end open, and the first part 21 can be a plate-like structure. The first part 21 is covered on the opening side of the second part 22 so that the first part 21 and the second part 22 jointly define the accommodation space; the first part 21 and the second part 22 can also both be hollow structures with one side open, and the opening side of the first part 21 is covered on the opening side of the second part 22. Of course, the box body 20 formed by the first part 21 and the second part 22 can be of various shapes, such as cylindrical, cuboid, etc.

[0135] In the battery pack 100, there may be multiple secondary batteries 10. The multiple secondary batteries 10 can be connected in series, parallel, or a combination of series and parallel (mixed connection). Mixed connection means that there are both series and parallel connections among the multiple secondary batteries 10. The multiple secondary batteries 10 can be directly connected in series, parallel, or in a mixed manner, and then the whole formed by the multiple secondary batteries 10 is accommodated in the box body 20. Of course, the battery pack 100 can also be such that multiple secondary batteries 10 are first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole and are accommodated in the box body 20. The battery pack 100 can also include other structures. For example, the battery pack 100 can also include a busbar component for realizing the electrical connection among the multiple secondary batteries 10.

[0136] In the battery pack 100 in the embodiments of the present application, a lithium-ion battery is included as the secondary battery 10. In other embodiments, the battery pack 100 can further include any one or several of lithium-sulfur batteries, sodium-ion batteries, and magnesium-ion batteries, but is not limited thereto. The secondary battery 10 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes, etc.

[0137] In addition, the present application also provides an electrical device. The electrical device includes at least one of the secondary battery 10 and / or the battery pack 100 provided in the present application. The secondary battery 10 or the battery pack 100 can be used as the power source of the electrical device or can also be used as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0138] As an electrical device, the secondary battery 10 and / or the battery pack 100 can be selected according to its usage requirements.

[0139] Figure 6 As shown, it is an electrical device as an example. The electrical device is a vehicle such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. Specifically, a schematic structural diagram of the vehicle 1000 is provided. Inside the vehicle 1000, there is a secondary battery 10 (see Figure 4 ) or a battery pack 100. The secondary battery 10 or the battery pack 100 can be arranged at the bottom, the head, or the tail of the vehicle 1000. The secondary battery 10 or the battery pack 100 can be used for power supply of the vehicle 1000. For example, the secondary battery 10 or the battery pack 100 can be used as the operating power source of the vehicle 1000. The vehicle 1000 can also include a controller 200 and a motor 300. The controller 200 is used to control the secondary battery 10 or the battery pack 100 to supply power to the motor 300. For example, it is used for the power consumption requirements during the start, navigation, and driving of the vehicle 1000.

[0140] In some embodiments of the present application, the secondary battery 10 or the battery pack 100 can not only serve as the operating power source of the vehicle 1000, but also as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0141] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial procurement.

[0142] Embodiment 1

[0143] 1) Preparation method of the positive electrode plate:

[0144] Lithium iron phosphate, conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) with a weight ratio of 90:10:3:1.5 are mixed with N, N-dimethylpyrrolidone (NMP), and stirred evenly to obtain the slurry of the positive electrode plate. The slurry of the positive electrode plate is evenly coated on both sides of the aluminum foil. The electrode plate is cold-pressed and sliced to obtain the positive electrode plate.

[0145] Among them, lithium iron phosphate is used as the positive electrode active material, conductive carbon black (Super-P) is used as the conductive agent, polyvinylidene fluoride (PVDF) is used as the binder, and N, N-dimethylpyrrolidone (NMP) is used as the slurry solvent.

[0146] 2) Preparation method of the negative electrode plate:

[0147] In the embodiments of the present application, hard carbon (the first carbon material), graphite (the second carbon material), nano-silicon, conductive carbon black (Super-P), carbon nanotubes, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are mixed with deionized water according to a weight ratio of 54.04:13.51:28.95:0.5:0.1:1.1:1.8, and stirred evenly to obtain the basic slurry for coating the negative electrode sheet. During the stirring process, the viscosity can be adjusted by deionized water. Hard carbon (the first carbon material), graphite (the second carbon material), nano-silicon, conductive carbon black (Super-P), carbon nanotubes, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are mixed with deionized water according to a weight ratio of 54.04:13.51:28.95:0.5:0.1:1.1:1.8 to obtain the additional slurry for coating the negative electrode sheet. Hard carbon (the first carbon material), graphite (the second carbon material), nano-silicon, conductive carbon black (Super-P), carbon nanotubes, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are mixed with deionized water according to a weight ratio of 23.16:34.74:38.6:0.5:0.1:1.1:1.8 to obtain the supplementary slurry for coating the negative electrode sheet. Then, the basic slurry is coated on both sides of the negative electrode current collector with a certain width, dried to form a base layer, and then the additional slurry is coated on the base layer to form an additional layer, and the additional layer covers the surface of the base layer facing away from the current collector to form the first active material layer; the supplementary slurry is coated on the additional layer in the second region, and then cold-pressed and sliced to obtain the negative electrode sheet. In the embodiments of the present application, the negative electrode current collector is a copper foil with a thickness of 6 μm. The embodiments of the present application do not limit the material and thickness of the negative electrode current collector.

[0148] In the embodiments of the present application, the volume average particle size DV50 of hard carbon is 14 μm, and the reversible specific capacity of hard carbon is 350 mAh / g. The volume average particle size DV50 of graphite is 20 μm, and the reversible specific capacity of graphite is 360 mAh / g.

[0149] 3) Preparation method of secondary battery:

[0150] The positive electrode sheet, separator, and negative electrode sheet are wound into an electrode core assembly, and a secondary battery is obtained through ear welding, packaging and aluminum shell encapsulation, liquid injection, encapsulation formation, and gas extraction and forming. The width of the electrode core assembly is 148 mm, the thickness is 28 mm, the height is 98 mm, and the capacity is 60 Ah. Among them, the injected electrolyte is a 1 mol / L LiPF 6 solution, LiPF 6The solvent of the solution is ethylene carbonate (EC) and dimethyl carbonate (DMC), and the volume ratio of ethylene carbonate (EC) to dimethyl carbonate (DMC) is 1:2. In the embodiments of the present application, the separator is made of polyethylene (PE) with a thickness of 7 μm. In the embodiments of the present application, the energy density of the negative active material of the negative electrode sheet is 1.07 times that of the positive active material of the positive electrode sheet.

[0151] The secondary battery obtained in the embodiments of the present application includes a positive electrode sheet and a negative electrode sheet. The negative electrode sheet includes a current collector and an active material layer disposed on the surface of the current collector. The active material layer includes a silicon-based material and a carbon-containing material. The carbon-containing material includes a first carbon material and a second carbon material. The reversible specific capacity of the first carbon material is less than that of the second carbon material; the current collector includes a main body portion and a tab located on one side of the main body portion. The main body portion includes a first region and a second region. The second region is located between the first region and the tab. In the embodiments of the present application, the area ratio of the second region to the first region is 10:100. In the embodiments of the present application, the active material layer includes a first active material layer and a second active material layer. The first active material layer is located in the first region, and the second active material layer is located in the second region; the mass fraction of the silicon-based material in the second active material layer is greater than that in the first active material layer; the mass fraction of the first carbon material (hard carbon) in the second active material layer is greater than that in the first active material layer. The CB value of the first active material layer is 1.07.

[0152] Comparative Example 1

[0153] The difference between the secondary battery and the preparation method of the secondary battery in this comparative example and those in Example 1 is that in the preparation method of the negative electrode sheet, the negative active material, the conductive agent, the thickening agent, and the binder are mixed with deionized water to form a slurry. The slurry is coated on both sides of the negative current collector with a certain width, and the negative electrode sheet is obtained through cold pressing and slicing. The obtained secondary battery negative electrode includes a positive electrode sheet and a negative electrode sheet. The negative electrode sheet includes a current collector and an active material layer disposed on the surface of the current collector. The active material layer includes a silicon-based material and a carbon-containing material. The carbon-containing material includes a first carbon material (hard carbon) and a second carbon material (soft carbon). The current collector includes a main body portion and a tab located on one side of the main body portion. The main body portion includes a first region and a second region. The second region is located between the first region and the tab; the active material layer includes a first active material layer and a second active material layer. The first active material layer is located in the first region, and the second active material layer is located in the second region; the mass fraction of the silicon-based material in the second active material layer is equal to that in the first active material layer; the mass fraction of the first carbon material in the second active material layer is equal to that in the first active material layer. The CB value of the first active material layer is 1.07. Others are the same as those in Example 1 and will not be elaborated here.

[0154] Comparative Example 2

[0155] The difference from Comparative Example 1 is that the negative electrode active material includes a silicon-based material and a carbon-containing material. The carbon-containing material includes a second carbon material (soft carbon) and does not include a first carbon material (hard carbon). Others are the same as in Comparative Example 1 and will not be elaborated here.

[0156] Comparative Example 3

[0157] The difference from Comparative Example 1 is that the negative electrode active material includes a silicon-based material and a carbon-containing material. The carbon-containing material includes a first carbon material and does not include a second carbon material. Others are the same as in Comparative Example 1 and will not be elaborated here.

[0158] The secondary batteries of the above Examples 1-14 and Comparative Examples 1-3 were subjected to relevant tests:

[0159] 1) Battery performance test. Specifically, the cycle capacity retention rate test of the secondary battery was carried out. The specific test conditions were:

[0160] At 25°C, it was charged at a constant current of 1 / 3C (nominal capacity) to the termination voltage of 3.8V, and then charged at a constant voltage to 0.05C 标 , rested for 5 minutes, and then discharged at 1 / 3C 标 to the discharge cut-off voltage of 2.0V to obtain the discharge energy E and the capacity C. The obtained capacity was recorded as the initial capacity C0. The above steps were repeated for the same secondary battery, and at the same time, the discharge capacity Cn of the battery after the nth cycle was recorded. Then, the battery capacity retention rate Pn = Cn / C0 × 100% after each cycle. During this test process, the first cycle corresponded to n = 1, the second cycle corresponded to n = 2,... the 1500th cycle corresponded to n = 1500. The battery capacity retention rate data corresponding in Table 1 were the data measured after 1500 cycles under the above test conditions.

[0161] 2) Lithium plating test.

[0162] At 25°C, it was charged at a constant current of 1 / 3C (nominal capacity) to the termination voltage of 3.8V, and then charged at a constant voltage to 0.05C 标 , rested for 5 minutes, and then discharged at 1 / 3C 标 to the discharge cut-off voltage of 2.0V to obtain the discharge energy E and the capacity C. The obtained capacity was recorded as the initial capacity C0. The above steps were repeated for the same secondary battery. After 1500 cycles, the battery was charged to 3.8V, and the battery was disassembled to observe whether lithium was deposited on the surface of the negative electrode plate.

[0163] 3) Capacity test.

[0164] At 25°C, it was charged at a constant current of 1 / 3C (nominal capacity) to the termination voltage of 3.8V, and then charged at a constant voltage to 0.05C 标, leave it standing for 5 min, and then at 1 / 3C 标 Discharge it to the discharge cut-off voltage of 2.0 V to obtain the discharge energy E and the capacity C.

[0165] 4) Charge time test.

[0166] Charge the full cell at 35°C with a stepwise decreasing current or a continuous decreasing current. The state of charge (SOC) of the battery ranges from 10% to 80% SOC, and the boundary condition is that the anode potential > 0 mV. The equipment is a Neware charge and discharge machine. The specific test process is as follows: 1. During the battery preparation process, place the lithium-plated copper wire outside the wound bare cell core and wrap it with an isolation film to prevent it from overlapping with the electrode plate or the housing, and lead the copper wire out of the cell core as the third electrode. 2. First, test the discharge capacity of the prepared battery using the following capacity test method; 3. Use a voltage acquisition device to record the voltage between the third electrode and the negative electrode terminal, that is, the "anode potential". 4. Set the initial SOC of the battery to 10%, then charge the battery, set the initial charging rate to 3C. When the anode potential drops to 0 mV, the equipment automatically reduces the charging rate to 3~xC, and continue charging until the anode potential drops to 0 mV, and the equipment continues to reduce the charging rate to 3~2*x C, and so on. This method is called stepwise decreasing current charging until it is charged to 80% SOC. When x is small enough, such as 0.05C, it can be equivalently regarded as continuous decreasing current charging. Finally, record the total time from 10% SOC to 80% SOC during charging.

[0167] 5) Volume average particle size Dv50 test.

[0168] Equipment model: Malvern 3000 (MasterSizer 3000) laser particle size analyzer. Reference standard process: GB / T19077~2016 / ISO 13320:2009. The specific test process is as follows: Take an appropriate amount of the sample to be tested (the sample concentration only needs to ensure a light obscuration of 8%~12%), add 20 ml of deionized water, and sonicate it externally for 5 min (53 KHz / 120 W) to ensure that the sample is completely dispersed, and then measure the sample according to the standard of GB / T19077~2016 / ISO 13320:2009.

[0169] The process parameters and performances of each example and comparative example are shown in Tables 1 and 2 below.

[0170] Table 1: Parameter and performance test results of Examples 1~14 and Comparative Examples 1~3.

[0171]

[0172] Note: X2 represents the mass fraction of the silicon-based material in the second active material layer; X1 represents the mass fraction of the silicon-based material in the first active material layer; B represents the ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer; C2 represents the mass fraction of the first carbon material in the second active material layer in the second region; C1 represents the mass fraction of the first carbon material in the first active material layer in the first region; M2 represents the mass fraction of the first carbon material in the carbon-containing material in the second region; M1 represents the mass fraction of the first carbon material in the carbon-containing material in the first region; The first CB value represents the CB value of the second active material layer.

[0173] Table 2 shows some process parameters of Examples 7 to 14 and Comparative Examples 1 to 3.

[0174] Example X3(％) X4(％) N2(％) N1(％) Example 1 30 30 20 20 Example 2 20 20 30 30 Example 3 10 10 68 68 Example 4 1 1 70 70 Example 5 0.50 0.50 79 79 Example 6 0.45 0.45 40 40 Example 7 25 35 84 74 Example 8 20 30 74 64 Example 9 12 20 55 45 Example 10 5 10 34 14 Example 11 0 1 24 4 Example 12 20 25 24 14 Example 14 0.45 0.5 40 30 Comparative Example 1 40 40 0.4 40 Comparative Example 2 40 40 0 0 Comparative Example 3 40 40 100 100

[0175] Note: X3 represents the mass fraction of the silicon-based material in the first sub-region based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region; X4 represents the mass fraction of the silicon-based material in the second sub-region based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region; N2 represents the mass fraction of the first carbon material per unit area in the carbon-containing material in the second sub-region; N1 represents the mass fraction of the first carbon material per unit area in the carbon-containing material in the first sub-region.

[0176] As can be seen from the test results in Table 1, regarding the lithium plating problem caused by the relatively thin second active material layer in the second region during the coating process of the negative electrode sheets of Comparative Examples 1 to 3. In Examples 1 to 14 of the present application, by setting the content of the silicon-based material and the content of the first carbon material in the second active material layer to be greater than the content of the silicon-based material and the content of the first carbon material in the first active material layer respectively, after the secondary battery is cycled 1500 cls, there is no lithium plating on the negative electrode sheet. And compared with Comparative Examples 1 to 3, the total time for the secondary batteries of Examples 1 to 14 of the present application to charge from 10% SOC to 80% SOC is 13 min to 19.5 min, which is improved compared with Comparative Examples 1 to 3, indicating that the secondary batteries of Examples 1 to 14 of the present application can improve the fast charging ability. The cycle capacity retention rate of the secondary batteries of Examples 1 to 14 of the present application is 80% to 90% after 1500 cls of cycling, which is improved compared with Comparative Examples 1 to 3.

[0177] As shown in Table 1 and Table 2, in Embodiments 7-14 of the present application, by controlling the mass fraction of the silicon-based material in the first sub-region to be greater than that of the silicon-based material in the second sub-region, and controlling the mass fraction of the first carbon material in the first sub-region in the carbon-containing material to be greater than that of the first carbon material in the second sub-region in the carbon-containing material, the fast charging ability of the secondary battery can be improved, such that the total time for charging from 10% SOC to 80% SOC is 13 min to 18 min. At the same time, the cycle performance of the secondary battery can also be improved.

[0178] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same composition and the same effect as the technical idea within the technical solution scope of the present application are included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that, it includes a negative electrode tab, the negative electrode tab includes a current collector and an active material layer provided on the surface of the current collector, the active material layer includes a silicon-based material and a carbon-containing material, and the carbon-containing material includes a first carbon material; the current collector includes a main body portion and an electrode ear located on one side of the main body portion, the main body portion includes a first region and a second region, and the second region is located between the first region and the electrode ear; the active material layer includes a first active material layer and a second active material layer, the first active material layer is located in the first region, and the second active material layer is located in the second region; the mass fraction of the silicon-based material in the second active material layer is greater than the mass fraction of the silicon-based material in the first active material layer; the mass fraction of the first carbon material in the second active material layer is greater than the mass fraction of the first carbon material in the first active material layer.

2. The secondary battery according to claim 1, characterized in that, the ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer is greater than 1:1 and less than or equal to 80:1; optionally, greater than or equal to 1.3:1 and less than or equal to 30:

1.

3. The secondary battery according to claim 1 or 2, characterized in that, the mass fraction of the silicon-based material in the first active material layer is 0.5% to 30%, optionally 1% to 20%; and / or, the mass fraction of the silicon-based material in the second active material layer is 1% to 40%, optionally 1.5% to 30%.

4. The secondary battery according to any one of claims 1-3, characterized in that, the mass fraction of the first carbon material in the second region accounting for the carbon-containing material is 40% to 100%, optionally 50% to 90%; or / and, in the first region, the mass fraction of the first carbon material accounting for the carbon-containing material is 20% to 80%, optionally 30% to 70%; or / and, the mass fraction of the first carbon material in the second region accounting for the second active material layer is 24% to 96%, optionally 35% to 89%; or / and the mass fraction of the first carbon material in the first region accounting for the first active material layer is 14% to 79%, optionally 24% to 69%.

5. The secondary battery according to any one of claims 1-4, characterized in that, the carbon-containing material includes a second carbon material, and the reversible specific capacity of the first carbon material is less than the reversible specific capacity of the second carbon material; optionally, the reversible specific capacity of the first carbon material is 320 mAh / g to 370 mAh / g, optionally 330 mAh / g to 360 mAh / g; and / or, optionally, the reversible specific capacity of the second carbon material is 340 mAh / g to 390 mAh / g, optionally 350 mAh / g to 380 mAh / g.

6. The secondary battery according to claim 5, characterized in that, The volume average particle size Dv50 of the first carbon material is greater than the volume average particle size Dv50 of the second carbon material; Optionally, the volume average particle size DV50 of the first carbon material is greater than or equal to 1 μm and less than or equal to 15 μm; Optionally, the volume average particle size DV50 of the second carbon material is greater than or equal to 7 μm and less than or equal to 22 μm.

7. The secondary battery according to any one of claims 1-6, characterized in that, The ratio of the area of the second region to the area of the first region is (3-20):100, optionally (5-15):

100.

8. The secondary battery according to any one of claims 1-7, characterized in that, further comprising a positive electrode plate; The CB value of the second active material layer is greater than or equal to the CB value of the first active material layer, and the CB value is the ratio of the lithium intercalation capacity of the negative electrode plate per unit area to the deintercalation capacity of the positive electrode plate per unit area.

9. The secondary battery according to any one of claims 1-8, characterized in that, The first active material layer includes a first surface and a second surface. The first surface is close to the negative current collector, and the second surface is far from the negative current collector. The thickness of the first active material layer is denoted as H. Then, the first active material layer satisfies: the region formed from the first surface to 0.1H is the first sub-region, and the region formed from the second surface to 0.1H is the second sub-region. The mass fraction of the silicon-based material in the second sub-region is greater than the mass fraction of the silicon-based material in the first sub-region; Optionally, based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region, the mass fraction of the silicon-based material in the first sub-region is greater than or equal to 0 and less than or equal to 25%; Optionally, based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region, the mass fraction of the silicon-based material in the second sub-region is greater than or equal to 1% and less than or equal to 35%.

10. The secondary battery according to claim 9, characterized in that, The mass fraction of the first carbon material per unit area in the carbon-containing material in the second sub-region is greater than the mass fraction of the first carbon material per unit area in the carbon-containing material in the first sub-region; Optionally, the mass fraction of the first carbon material per unit area in the carbon-containing material in the second sub-region is 20%-85%, more optionally 30%-75%; Optionally, the mass fraction of the first carbon material per unit area in the carbon-containing material in the first sub-region is 0-75%, more optionally 20%-65%.

11. The secondary battery according to any one of claims 1-10, characterized in that, The active material layer includes a base layer and a supplementary layer. The base layer is located in the first region and the second region; the supplementary layer is disposed on the side of the base layer in the second region away from the current collector. The mass fraction of the silicon-based material in the supplementary layer is greater than the mass fraction of the silicon-based material in the base layer, and the mass fraction of the first carbon material in the supplementary layer is greater than the mass fraction of the first carbon material in the base layer.

12. The secondary battery according to any one of claims 1-11, characterized in that, the active material layer includes a base layer and an additional layer, the additional layer integrally extends to cover the side of the base layer facing away from the current collector, covers the side of the base layer close to the tab, and the part of the additional layer covering the side of the base layer close to the tab is located in the second region.

13. A method for manufacturing the secondary battery according to any one of claims 1-12, characterized in that, it includes: providing a current collector, the current collector includes a main body and a tab located on one side of the main body, the main body has a first region and a second region, and the second region is located between the first region and the tab; coating a slurry containing active material on the first region and the second region of the current collector to form an active material layer; the slurry containing active material includes a silicon-based material and a carbon-containing material, the carbon-containing material includes a first carbon material; the active material layer includes a first active material layer and a second active material layer, the first active material layer is located in the first region, and the second active material layer is located in the second region, so that the mass fraction of the silicon-based material in the second active material layer is greater than the mass fraction of the silicon-based material in the first active material layer, and the mass fraction of the first carbon material in the second active material layer is greater than the mass fraction of the first carbon material in the first active material layer.

14. The method according to claim 13, characterized in that, the coating of the slurry containing active material on the first region and the second region of the current collector to form an active material layer includes: coating a base slurry on the current collector to form a base layer, and the base layer is located in the first region and the second region; coating a supplementary slurry on the side of the base layer in the second region facing away from the current collector to form a supplementary layer, the mass fraction of the silicon-based material in the supplementary layer is greater than the mass fraction of the silicon-based material in the base layer, and the mass fraction of the first carbon material in the supplementary layer is greater than the mass fraction of the first carbon material in the base layer.

15. The method according to claim 13, characterized in that, the coating of the slurry containing active material on the first region and the second region of the current collector to form an active material layer includes: coating a base slurry on the current collector to form a base layer, and the base layer is located in the first region and the second region; coating an additional slurry on the side of the base layer facing away from the current collector to form an additional layer, and making the additional layer cover the side of the base layer close to the tab; wherein, the part of the additional layer covering the side of the base layer close to the tab is in the second region, the mass fraction of the silicon-based material in the additional slurry is greater than the mass fraction of the silicon-based material in the base slurry, and the mass fraction of the first carbon material in the additional slurry in the carbon-containing material is greater than the mass fraction of the first carbon material in the base slurry in the carbon-containing material; optionally, it further includes: coating a supplementary slurry on the side of the additional layer in the second region facing away from the current collector to form a supplementary layer.

16. An electrical device, comprising a secondary battery as described in any one of claims 1-12 and / or a secondary battery prepared by the method as described in any one of claims 13-15.

Images