Negative pole piece and battery

Abstract

The embodiment of the utility model relates to a negative pole piece and a battery. The negative pole piece comprises a current collector; the active layer is arranged on at least one side surface of the current collector; the active layer comprises a first active layer and a second active layer which are sequentially stacked on the current collector; the first active layer comprises a first active material; the second active layer comprises a second active material; the particle size of the second active material is larger than that of the first active material, and the difference between the median particle size D2v50 of the second active material and the median particle size D1v50 of the first active material is 3-10 [mu] m; at least one groove extending from a surface of the second active layer to an interior of the second active layer; and the ratio of the depth of the groove to the thickness of the second active layer is 0.5-1. Therefore, the high-temperature performance of the battery can be ensured while the quick charging capacity of the battery is effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a negative electrode plate and a battery. Background Art

[0002] With the development of battery technology, the requirements for battery performance are getting higher and higher, especially the fast charging ability and high-temperature performance of the battery. The negative electrode plate is closely related to the charging speed of the battery. For lithium-ion batteries, in the existing fast charging technology, small-particle-size negative active materials are used, and then a negative electrode plate with a low surface density and low compaction is used to improve the fast charging ability. However, due to the large specific surface area of the small-particle-size negative active materials, the side reactions between the negative active materials and the electrolyte will increase, which will deteriorate the high-temperature performance of the battery.

[0003] Since the improvement of the fast charging ability and the high-temperature performance are usually opposite design directions in the battery, therefore, how to achieve both the fast charging ability and the high-temperature performance of the battery is an urgent problem to be solved at present. Utility Model Content

[0004] In view of this, embodiments of the present application provide a negative electrode plate and a battery to solve at least one problem in the background art.

[0005] In a first aspect, embodiments of the present application provide a negative electrode plate, comprising:

[0006] A current collector;

[0007] An active layer disposed on at least one surface of the current collector; the active layer includes a first active layer and a second active layer stacked on the current collector in sequence;

[0008] The first active layer includes a first active material; the second active layer includes a second active material; the particle size of the second active material is larger than that of the first active material, and the difference between the median particle size D2v50 of the second active material and the median particle size D1v50 of the first active material is between 3 μm and 10 μm;

[0009] At least one groove extending from the surface of the second active layer to the inside of the second active layer; the ratio of the depth of the groove to the thickness of the second active layer is between 0.5 and 1.

[0010] Combined with the first aspect of the present application, in an optional embodiment, the median particle size D1v50 of the first active material is 5 μm to 15 μm.

[0011] Combined with the first aspect of the present application, in an optional embodiment, the median particle size D2v50 of the second active material is 8 μm to 20 μm.

[0012] In connection with the first aspect of the present application, in an alternative embodiment, the depth d of the groove and the median particle size D2v50 of the second active material satisfy: 1.5 ≤ (d / 40 + 10 / D2v50) 2 ≤ 10.

[0013] In connection with the first aspect of the present application, in an alternative embodiment, the thickness of the first active layer is 50 μm to 120 μm; and / or, the thickness of the second active layer is 50 μm to 120 μm; and / or, the sum of the thicknesses of the first active layer and the second active layer is 120 μm to 200 μm.

[0014] In connection with the first aspect of the present application, in an alternative embodiment, the depth of the groove is 25 μm to 100 μm.

[0015] In connection with the first aspect of the present application, in an alternative embodiment, the width of the groove is 0.05 mm to 0.5 mm.

[0016] In connection with the first aspect of the present application, in an alternative embodiment, the number of the grooves is at least two; preferably, the distance between the center lines of two adjacent grooves is 0.8 mm to 5 mm.

[0017] In connection with the first aspect of the present application, in an alternative embodiment, the first active material and the second active material include graphite; preferably, the first active material includes a silicon-based material and graphite, and the second active material includes graphite.

[0018] In a second aspect, an embodiment of the present application provides a battery, including a negative electrode tab as described in any one of the first aspect.

[0019] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0020] In the negative electrode sheet and battery provided by the embodiments of the present application, by setting the difference between the median particle size D2v50 of the second active material and the median particle size D1v50 of the first active material to be between 3 μm and 10 μm, the particle size of the first active material located in the lower layer is smaller, the specific surface area is relatively larger, there are more surface reaction active sites, and the solid-phase transmission distance of lithium ions is shorter. Therefore, the transmission speed of lithium ions can be increased, and the fast charging ability can be improved. The particle size of the second active material located in the upper layer is larger, the specific surface area is relatively smaller, and the surface reaction active sites are relatively fewer. Moreover, the contact between the first active material and the electrolyte can be reduced. Therefore, the side reaction between the active layer and the electrolyte can be reduced, and the high-temperature performance can be improved. In order to reduce the influence of improving the high-temperature performance through the second active layer on the fast charging performance, grooves are provided in the second active layer, and the ratio of the depth of the grooves to the thickness of the second active layer is between 0.5 and 1, which can increase the transmission speed of lithium ions, thereby improving the fast charging ability. In this way, it is possible to ensure the high-temperature performance of the battery while improving the fast charging ability of the battery.

[0021] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The schematic embodiments and descriptions thereof of the present application are used to explain the present application, and do not constitute an improper limitation to the present application. In the drawings:

[0023] Figure 1 is a schematic structural diagram of a negative electrode sheet provided by an embodiment of the present application.

[0024] DESCRIPTION OF THE REFERENCE NUMERALS

[0025] 100, current collector; 200, active layer; 210, first active layer; 220, second active layer; 211, first active material; 221, second active material; 300, groove; d, depth of the groove; D, thickness of the second active layer; w, width of the groove. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] In order to make the technical solutions and beneficial effects of the present application more obvious and understandable, the following will be described in detail by combining the drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually in accordance with conventional experimental conditions. The reagents and raw materials used in the present application are commercially available unless otherwise specified.

[0027] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the present application may be practiced without one or more of these specific details. In other instances, in order to avoid obscuring the present application, some well-known technical features are not described; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.

[0028] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present application. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, specify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of the related listed items.

[0029] To thoroughly understand the present application, detailed steps and structures will be presented in the following description to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may have other embodiments.

[0030] Unless otherwise defined, the technical and scientific terms used in the present application have the same meanings as those of the technical and scientific terms in the technical field to which the present application belongs.

[0031] For those not specified with specific techniques or conditions in the following embodiments, they are generally carried out according to the conventional techniques or conditions described in the literature in the art, or according to the conditions recommended in the product specifications and by the manufacturers. The numerical ranges in the following embodiments all include the end point values.

[0032] In the related art, the negative electrode double-layer coating technology has been widely promoted and used because it can improve the fast charging ability. The negative electrode double-layer coating technology is to set a double-layer active layer on the current collector of the negative electrode. The upper active layer uses materials with smaller particle sizes to improve the fast charging ability, and the lower active layer uses materials with larger particle sizes to achieve the design method of high capacity and high compaction. However, the upper active layer is prone to contact with the electrolyte, resulting in an increase in side reactions. Moreover, the smaller the particle size of the upper active layer material, the larger the specific surface area, the more reaction sites on the surface with the electrolyte, and the more side reactions increase, which will lead to the deterioration of the high-temperature performance of the battery.

[0033] Based on this, please refer to Figure 1, an embodiment of the present application provides a negative electrode plate, which includes: a current collector 100; an active layer 200 disposed on at least one surface of the current collector 100; the active layer 200 includes a first active layer 210 and a second active layer 220 stacked in sequence on the current collector 100; the first active layer 210 includes a first active material 211; the second active layer 220 includes a second active material 221; the particle size of the second active material 221 is larger than the particle size of the first active material 211, and the difference between the median particle size D2v50 of the second active material 221 and the median particle size D1v50 of the first active material 211 is between 3 μm and 10 μm; at least one groove 300 extending from the surface of the second active layer 220 to the inside of the second active layer 220; the ratio of the depth d of the groove 300 to the thickness D of the second active layer 220 is between 0.5 and 1.

[0034] In the embodiments of the present application, the first active material 211 located in the lower layer has a smaller particle size, a relatively larger specific surface area, more surface reaction active sites, a shorter distance for solid-phase lithium-ion transport, and a faster transport speed. Therefore, the lithium-ion transport speed can be accelerated, and the fast charging ability can be improved. The second active material 221 located in the upper layer has a larger particle size, a relatively smaller specific surface area, relatively fewer surface reaction active sites, and can reduce the contact between the first active material 211 and the electrolyte. Therefore, the side reaction between the active layer 200 and the electrolyte can be reduced, and the high-temperature performance can be improved. When the difference between the median particle size D2v50 of the second active material 221 and the median particle size D1v50 of the first active material 211 is small, the balancing effect on the fast charging ability and high-temperature performance of the battery is not significant enough. When the difference between the median particle size D2v50 of the second active material 221 and the median particle size D1v50 of the first active material 211 is large, lithium plating is likely to occur at the interface of the negative electrode sheet, affecting the fast charging ability of the battery. Therefore, the difference between the median particle size D2v50 of the second active material 221 and the median particle size D1v50 of the first active material 211 is between 3 μm and 10 μm, so that a better balance between the fast charging ability and high-temperature performance can be achieved. In order to reduce the influence of improving the high-temperature performance through the second active layer 220 on the fast charging performance, a groove 300 is provided in the second active layer 220. Since the transport rate of lithium ions in the electrolyte is much higher than that in the active layer of the electrode sheet, the groove 300 directly replaces the original path that needs to be transported in the active layer of the electrode sheet with transport in the electrolyte, which can accelerate the lithium-ion transport speed and thus improve the fast charging ability. When the depth d of the groove 300 is small, the improvement of the fast charging ability is small. When the depth d of the groove 300 is large, more edges of the particles of the second active material 221 will be damaged, and the high-temperature performance cannot be well balanced. Moreover, when the depth d of the groove 300 is large, especially when the bottom of the groove 300 extends to the first active layer 210, a large loss of the surface density of the negative electrode sheet will occur, and lithium plating will occur due to insufficient N / P of the battery (i.e., the ratio of the negative electrode capacity to the positive electrode capacity of the battery). Therefore, the ratio of the depth d of the groove 300 to the thickness D of the second active layer 220 is between 0.5 and 1. In this way, by setting the particle size difference between the first active material 211 and the second active material 221 and coordinating the role of the groove, the high-temperature performance of the battery can be guaranteed while improving the fast charging ability of the battery.

[0035] Exemplarily, the difference between the median particle size D2v50 of the second active material 221 and the median particle size D1v50 of the first active material 211 can be, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any value between any two of the above numerical ranges. The ratio of the depth d of the groove 300 to the thickness D of the second active layer 220 can be, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value between any two of the above numerical ranges.

[0036] In actual preparation, the groove 300 can be formed by processes such as laser etching and / or roller rolling. There is no particular limitation on the shape of the groove 300 in this application, as long as the purpose of this application can be achieved. For example, the cross-sectional shape of the groove 300 includes but is not limited to at least one of a triangle, an arc, or a rectangle. It can be understood that the depth d of the groove 300 is the distance from the top of the groove 300 to the lowest point at the bottom of the groove 300. Exemplarily, when the cross-sectional shape of the groove 300 is a rectangle, the depth d of the groove 300 is the side length of the rectangle in the thickness direction of the current collector 100. When the cross-sectional shape of the groove 300 is a triangle, the depth d of the groove 300 is the length of the perpendicular from the base on the side away from the current collector 100 to the apex on the side close to the current collector 100 in the triangle, that is, the height of the triangle in the thickness direction of the current collector 100.

[0037] There is no particular limitation on the type of the current collector 100 in this application, as long as the purpose of this application can be achieved. For example, the current collector 100 may include at least one of a copper foil, a copper alloy foil, a composite copper foil, a foam copper, a nickel foil, a stainless steel foil, or a titanium foil.

[0038] There is no particular limitation on the thickness of the current collector 100 in this application, as long as the purpose of this application can be achieved. For example, the thickness of the current collector 100 can be 4 μm to 10 μm.

[0039] Figure 1 The case where the active layer 200 is located on one surface of the current collector 100 is exemplarily shown. In some other embodiments of this application, the active layer 200 can be disposed on two opposite surfaces of the current collector 100. The number and depth of the grooves 300 in the second active layers 220 located on both sides of the current collector 100 can be the same or different. In a specific embodiment, the number and depth of the grooves 300 in the second active layers 220 located on both sides of the current collector 100 can be the same, which can reduce the difficulty of the manufacturing process and make the performance of the battery more balanced and controllable.

[0040] In some embodiments, the median particle size D1v50 of the first active material 211 can be 5 μm to 15 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value between any two of the above numerical ranges.

[0041] The median particle size of the first active material 211 is closely related to the fast charging ability of the first active layer 210. Controlling the median particle size of the first active material 211 within the above range in this embodiment can make the distance of solid-phase lithium-ion transmission shorter, promote the diffusion of lithium ions, and thus ensure that the first active layer 210 has better fast charging ability.

[0042] In some embodiments, the median particle size D2v50 of the second active material 221 can be 8 μm to 20 μm. For example, it can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any value between any two of the above numerical ranges.

[0043] The median particle size of the second active material 221 is closely related to the high-temperature performance of the second active layer 220. In this embodiment, controlling the median particle size of the second active material 221 within the above range can result in relatively fewer surface reaction active sites of the second active material 221, and can reduce the contact between the first active material 211 and the electrolyte to reduce side reactions, thereby ensuring that the second active layer 220 has good high-temperature performance.

[0044] When the value of the depth d of the groove 300 is too large, more particles of the second active material 221 are damaged, and the high-temperature performance of the battery deteriorates significantly. When the value of the depth d of the groove 300 is too small, the fast charging ability of the battery deteriorates significantly. Therefore, in some embodiments, the depth d of the groove 300 and the median particle size D2v50 of the second active material 221 can satisfy: 1.5 ≤ (d / 40 + 10 / D2v50) 2 ≤ 10; (d / 40 + 10 / D2v50) 2 For example, it can be 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any value between any two of the above numerical ranges. In this way, the high-temperature performance and fast charging ability of the battery can be better balanced.

[0045] In some embodiments, the thickness of the first active layer 210 can be 50 μm to 120 μm. For example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, or any value between any two of the above numerical ranges. Adjusting the thickness of the first active layer 210 within the above range can better ensure the fast charging ability of the battery and improve the overall cycle performance of the battery.

[0046] In some embodiments, the thickness of the second active layer 220 can be 50 μm to 120 μm. For example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, or any value between any two of the above numerical ranges. Adjusting the thickness of the second active layer 220 within the above range can better ensure the high-temperature performance of the battery and improve the overall cycle performance of the battery.

[0047] In some embodiments, the sum of the thicknesses of the first active layer 210 and the second active layer 220 may be 120 μm to 200 μm. For example, it may be 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, or any value between any two of the above numerical ranges. By controlling the sum of the thicknesses of the first active layer 210 and the second active layer 220 within the above range, and through the cooperation of the first active layer 210 and the second active layer 220, the advantages of the high fast-charging ability of the first active layer 210 and the high-temperature performance of the second active layer 220 are exerted, so that the battery has good fast-charging ability and good high-temperature performance at the same time.

[0048] In some embodiments, the depth d of the groove 300 may be 25 μm to 100 μm. For example, it may be 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any value between any two of the above numerical ranges. By controlling the depth d of the groove 300 within the above range, it is beneficial to improve the transport of the electrolyte on the surface of the negative electrode sheet, further accelerate the transport speed of lithium ions, enhance the fast-charging ability, as well as the infiltration and storage of the electrolyte in the negative electrode sheet, thereby further improving the overall cycle performance of the battery.

[0049] In some embodiments, the width w of the groove 300 may be 0.05 mm to 0.5 mm. For example, it may be 0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or any value between any two of the above numerical ranges. By controlling the width of the groove 300 within the above range, it is beneficial to further improve the transport of the electrolyte on the surface of the negative electrode sheet, and further enhance the fast-charging ability and the overall cycle performance of the battery.

[0050] Please refer to Figure 1 , the width w of the groove 300 refers to the dimension of the groove 300 in the extending direction of the current collector 100.

[0051] In some embodiments, the number of the grooves 300 is at least two. The increase in the number of the grooves 300 can further promote the transport speed of lithium ions, thereby further enhancing the fast-charging ability. In practical applications, the number of the grooves 300 can be set according to actual needs, such as according to the size of the battery and the target value of the battery performance, etc.

[0052] In some embodiments, the distance between the center lines of two adjacent grooves 300 can be 0.8 mm to 5 mm, for example, 0.8 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm or any value between any two of the above ranges. The distance between the center lines of two adjacent grooves 300 is regulated within the above range, and there is a suitable distance between each groove 300, and there is a suitable number of grooves 300 on the surface of the negative electrode plate, which can reduce the risk of serious loss of the second active material 221 due to too many grooves 300, and can also improve the transmission of the electrolyte on the surface of the negative electrode plate, increase the diffusion rate of lithium ions, and enhance the fast charging capability of the battery. At the same time, it can also increase the amount of electrolyte retained in the negative electrode plate, reduce the risk of lithium precipitation caused by electrolyte enrichment in the negative electrode plate beyond the positive electrode plate area, and help to further improve the overall performance of the battery.

[0053] In some embodiments, the first active material 211 and the second active material 221 may include graphite.

[0054] For example, graphite may include artificial graphite and / or natural graphite. Since graphite has a high specific surface area and good electrical conductivity, and graphite has good stability, and its volume change is relatively small during lithium insertion and removal, the first active material 211 and the second active material 221 include graphite, which can make the battery have a higher energy density and a longer service life.

[0055] In some specific embodiments, the first active material 211 may include a silicon-based material and graphite, and the second active material 221 may include graphite.

[0056] For example, the silicon-based material may include at least one of silicon, silicon alloy, silicon-carbon material or silicon-oxygen material, and the graphite may include artificial graphite and / or natural graphite. Since the theoretical specific capacity of silicon is much higher than the theoretical specific capacity of graphite, the combination of silicon and graphite as the first active material 211 is beneficial to increase the gram capacity of the negative electrode material, thereby increasing the energy density of the battery.

[0057] It is understandable that due to the large volume expansion of silicon-based materials during the charging and discharging process, it will affect the flatness of the negative electrode plate interface, resulting in more SEI (Solid Electrolyte Interface) film reformation on the surface of the negative electrode plate, consuming more active lithium, and affecting the high temperature performance of the battery. In addition, the boiling point of silicon-based materials is relatively high, and the etching difficulty is relatively large, which is not conducive to forming the groove 300 in the second active layer 220 through the etching process. Therefore, the second active material 221 in the present application does not include silicon-based materials.

[0058] Based on this, an embodiment of the present application further provides a battery, including the negative electrode sheet described in the above embodiment.

[0059] It should be understood that since the negative electrode sheet in the embodiment of the present application includes the negative electrode sheet described in the above embodiment, the beneficial effects of the negative electrode sheet described in any of the above embodiments are applicable to this battery.

[0060] In some embodiments, the battery may be a secondary battery, and the secondary battery may be a lithium-ion secondary battery. Generally, the secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows lithium ions to pass through.

[0061] The technical solution of the present application will be further described below in conjunction with multiple embodiments and comparative examples.

[0062] The median particle size D1v50 of the first active material, the median particle size D2v50 of the second active material, the difference between D2v50 and D1v50, the depth d of the groove, the thickness D of the second active layer, the ratio of d to D, and (d / 40 + 10 / D2v50) of the negative electrode sheets in Embodiments 1 to 7 and Comparative Examples 1 to 3 2 are shown in Table 1. Except for the parameters given in Table 1, the other parameters of the negative electrode sheets in each embodiment and each comparative example are the same.

[0063] Table 1

[0064]

[0065] The negative electrode sheets in the above embodiments and comparative examples are made into batteries, and the preparation method of the batteries is as follows:

[0066] Preparation of the positive electrode sheet: Lithium iron phosphate, polyvinylidene fluoride (PVDF), and conductive carbon black (Super-P) are mixed in a ratio of 97:2:1, and after stirring, a positive electrode slurry is formed. The positive electrode slurry is coated on aluminum foil, dried in an oven, and then obtained by rolling and slitting to prepare the positive electrode sheet.

[0067] The negative electrode sheets in the above embodiments and comparative examples are used. Among them, the preparation of the negative electrode sheet includes the following steps: preparing the first negative electrode slurry, preparing the second negative electrode slurry, coating the slurry, and forming the groove.

[0068] Preparation of the first negative electrode slurry: The first active material artificial graphite, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon black (Super-P) are placed in a stirring kettle according to the ratio of 95.5:1.5:2:1. After adding pure water and stirring evenly, the first negative electrode slurry is obtained. The median particle size D1v50 of the first active material in each example and each comparative example is controlled according to the values in Table 1 above.

[0069] Preparation of the second negative electrode slurry: The second active material artificial graphite, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon black (Super-P) are placed in a stirring kettle according to the ratio of 95.5:1.5:2:1. After adding pure water and stirring evenly, the second negative electrode slurry is obtained. The median particle size D2v50 of the second active material in each example and each comparative example is controlled according to the values in Table 1 above.

[0070] Coating the slurry: The first negative electrode slurry and the second negative electrode slurry are simultaneously and evenly coated on the negative electrode current collector copper foil through a double-chamber extrusion coating die head. After drying, the first active layer and the second active layer are obtained, which are stacked in sequence on the negative electrode current collector. The thickness of the first active layer is the same as that of the second active layer, and the thickness D of the second active layer is controlled according to the values in Table 1 above.

[0071] Forming grooves: Grooves are formed in the second active layer by laser etching. The width w of the grooves is 0.1 mm, the depth d of the grooves refers to the values in Table 1 above, and the distance between the center lines of two adjacent grooves is 2 mm. After slitting, negative electrode plates with a specification of 60 mm × 100 mm are obtained for standby.

[0072] Separator: A PE porous polymer film is used as the separator.

[0073] Preparation of the electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed according to a volume ratio of 3:5:2. Then, the fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1.2 mol / L to prepare the electrolyte.

[0074] Preparation of the full cell: The positive electrode plate, the separator, and the negative electrode plates in each of the above examples and comparative examples are arranged in sequence. A layer of separator is placed between each pair of positive and negative electrodes, and then wound to obtain a bare battery core. The bare battery core is placed in an outer packaging shell, and the prepared electrolyte is injected into the dried bare battery. After processes such as vacuum packaging, standing, formation, and shaping, a lithium-ion battery is obtained.

[0075] Perform fast charging tests and high-temperature cycle life tests on the prepared lithium-ion batteries. The specific tests are as follows:

[0076] (1) 4C charging test:

[0077] ① Place the battery in an incubator at 25 °C and leave it for 6 h;

[0078] ② First, charge at a constant current of 0.33C until 3.65V, then charge at a constant voltage of 3.65V until 0.05C, and leave it for 10 min;

[0079] ③ Discharge at a constant voltage of 0.33C until 2.5V, and leave it for 10 min;

[0080] ④ Repeat the cycle 3 times, and record the discharge capacity of the last cycle as C0;

[0081] ⑤ First, charge at a constant current of 4C0 until 3.65V, then charge at a constant voltage of 3.65V until 0.05C, and leave it for 10 min;

[0082] ⑥ Discharge at a constant current of 4C0 until 2.5V, and leave it for 10 min;

[0083] ⑦ After 50 cycles, take out the battery and disassemble it to observe the lithium deposition situation at the interface of the negative electrode plate.

[0084] The criteria for judging the lithium deposition situation are as follows: slight lithium deposition (the lithium deposition area does not exceed 10% of the area of the negative electrode plate), moderate lithium deposition (the lithium deposition area accounts for 10% - 50% of the area of the negative electrode plate), and severe lithium deposition (the lithium deposition area accounts for more than 50% of the area of the negative electrode plate).

[0085] (2) 6C charging test:

[0086] ① Place the battery in an incubator at 25 °C and leave it for 6 h;

[0087] ② First, charge at a constant current of 0.33C until 3.65V, then charge at a constant voltage of 3.65V until 0.05C, and leave it for 10 min;

[0088] ③ Discharge at a constant voltage of 0.33C until 2.5V, and leave it for 10 min;

[0089] ④ Repeat the cycle 3 times, and record the discharge capacity of the last cycle as C0;

[0090] ⑤ First, charge at a constant current of 6C0 until 3.65V, then charge at a constant voltage of 3.65V until 0.05C, and leave it for 10 min;

[0091] ⑥ Discharge at a constant current of 6C0 until 2.5V, and leave it for 10 min;

[0092] ⑦ After 50 cycles, take out the battery and disassemble it to observe the lithium deposition situation at the interface of the negative electrode plate.

[0093] The criteria for judging the lithium deposition situation are the same as above.

[0094] (3) 45 °C cycle test:

[0095] ① Place the battery in an incubator at 25 °C and leave it for 6 h;

[0096] ② First, charge at a constant current of 0.33C until 3.65V, then charge at a constant voltage of 3.65V until 0.05C, and leave it for 10 min;

[0097] ③ Discharge at a constant voltage of 0.33C until 2.5V, and leave it for 10 min;

[0098] ④ Repeat the cycle 3 times, and record the discharge capacity of the last cycle as C0;

[0099] ⑤ Take the battery out of the incubator at 25 °C and place it in an incubator at 45 °C, and leave it for 6 h;

[0100] ⑥ Charge at a constant current of 1C0 until 3.65V, then charge at a constant voltage of 3.65V until 0.05C, and leave it for 10 min;

[0101] ⑦ Discharge at a constant current of 1C0 until 2.5V, and leave it for 10 min;

[0102] ⑧ Record and mark the discharge capacity of each cycle during the cycle. Among them, the capacities of the 1st to the nth cycles are recorded as C1 to Cn in sequence, where n is an integer greater than 1; the calculation method of the SOH (State of Health) of the battery in the nth cycle is: Cn / C1*100%; Record the number of cycles when the battery cycles to 80% SOH, which is the high-temperature cycle life of the battery.

[0103] The results of the above tests are shown in Table 2.

[0104] Table 2

[0105]

[0106] From the test results of Examples 1 to 7 and Comparative Examples 1 to 3 in Table 2, it can be seen that in the present application, the difference D2v50 - D1v50 between the median particle size D2v50 of the second active material and the median particle size D1v50 of the first active material is controlled between 3 μm and 10 μm, so that the first active layer has good fast charging ability and the second active layer has good high-temperature performance. The ratio of the depth of the groove to the thickness of the second active layer is between 0.5 and 1, which can improve the fast charging ability of the second active layer. In this way, through the combination of the first active layer and the second active layer, together with the grooves provided in the second active layer, the synergistic effect makes the negative electrode sheet interface of the battery in the examples of the present application not show lithium deposition under the 4C fast charging test conditions, and under the 6C fast charging test conditions, the negative electrode sheet interface basically does not show lithium deposition, and only individual negative electrode sheets show slight lithium deposition. The number of cycles of the 45°C cycle test (high-temperature cycle life) is relatively high, indicating that the batteries in the examples of the present application have good fast charging ability and good high-temperature performance at the same time.

[0107] In Comparative Example 1, the value of D2v50 - D1v50 is negative, that is, the median particle size D2v50 of the second active material is smaller than the median particle size D1v50 of the first active material, which is a design opposite to that of the present application. Under the 4C and 6C fast charging test conditions, slight lithium deposition and moderate lithium deposition occurred on the negative electrode sheet respectively. In Comparative Example 2, the value of D2v50 - D1v50 is greater than 10, and moderate lithium deposition and severe lithium deposition occurred on the negative electrode sheet under the 4C and 6C fast charging test conditions respectively. In Comparative Example 3, the ratio of the depth d of the groove to the thickness D of the second active layer is less than 0.5, and slight lithium deposition and moderate lithium deposition occurred on the negative electrode sheet under the 4C and 6C fast charging test conditions respectively. It can be seen from this that for the batteries of the comparative examples, at least one of the difference D2v50 - D1v50 between the median particle size D2v50 of the second active material and the median particle size D1v50 of the first active material and the ratio of the depth d of the groove to the thickness D of the second active layer is not within the scope of the present application, and lithium deposition is likely to occur on the negative electrode sheet during fast charging, indicating that the fast charging ability of the batteries of the comparative examples is poor.

[0108] When the value of the depth d of the groove is too large, more particles of the second active material are damaged, and the high-temperature performance of the battery deteriorates. When the value of the depth d of the groove is too small, the fast charging ability of the battery deteriorates. It can be seen from Examples 1 to 7 that the value of (d / 40 + 10 / D2v50) 2 is between 1.5 and 10, which can ensure better high-temperature performance while ensuring good fast charging ability of the battery. In Example 7, although no lithium deposition occurred on the negative electrode sheet under the 4C and 6C fast charging test conditions, indicating that the battery has good fast charging ability, the number of cycles of the 45°C cycle test is relatively low, so it is not a preferred solution.

[0109] The negative electrode plate of the present application adopts a double-layer coating technology on the current collector. The upper active layer (the second active layer) is designed with good high-temperature performance, and the lower active layer (the first active layer) is designed with good fast-charging ability. By utilizing the good high-temperature performance of the upper-layer material (the second active material), the electrolyte is isolated, the contact between the lower-layer material (the first active material) and the electrolyte is reduced, and the high-temperature performance is improved. At the same time, combined with the laser etching technology, laser etching is carried out in the upper active layer to form grooves. The etching is limited within the upper-layer material, which can reduce the areal density loss and increase the fast-charging ability of the lower-layer material, achieving both the improvement of the fast-charging ability of the battery and the high-temperature performance.

[0110] It should be noted that the negative electrode plate embodiment provided in the present application and the battery embodiment belong to the same concept; among the technical features in the technical solutions recorded in each embodiment, they can be arbitrarily combined without conflict.

[0111] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners included in the claims. Without departing from the scope of the present disclosure, various deformations and changes can also be made based on the above embodiments. Similarly, the technical features of the above embodiments can also be arbitrarily combined to form other embodiments of the present application that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present application and do not limit the protection scope of the patent of the present application.

Claims

1. A negative electrode sheet, characterized in that, Comprising: Current collector; Active layer, disposed on at least one surface of the current collector; the active layer includes a first active layer and a second active layer stacked in sequence on the current collector; The first active layer includes a first active material; the second active layer includes a second active material; the particle size of the second active material is greater than that of the first active material, and the difference between the median particle size D2v50 of the second active material and the median particle size D1v50 of the first active material is between 3 μm and 10 μm; At least one groove, extending from the surface of the second active layer to the interior of the second active layer; the ratio of the depth of the groove to the thickness of the second active layer is between 0.5 and 1.

2. The negative electrode sheet according to claim 1, characterized in that, The median particle size D1v50 of the first active material is 5 μm to 15 μm.

3. The negative electrode plate according to claim 1, wherein The median particle size D2v50 of the second active material is 8 μm to 20 μm.

4. The negative electrode sheet according to claim 1, characterized in that, The depth d of the groove and the median particle size D2v50 of the second active material satisfy: 1.5 ≤ (d / 40 + 10 / D2v50) 2 ≤ 10.

5. The negative electrode plate according to claim 1, characterized in that The thickness of the first active layer is 50 μm to 120 μm; and / or, the thickness of the second active layer is 50 μm to 120 μm; And / or, the sum of the thicknesses of the first active layer and the second active layer is 120 μm to 200 μm.

6. The negative electrode sheet according to claim 1, wherein The depth of the groove is 25 μm to 100 μm.

7. The negative electrode sheet according to claim 1, characterized in that, The width of the groove is 0.05 mm to 0.5 mm.

8. The negative electrode sheet according to claim 1, wherein The number of the grooves is at least two.

9. The negative electrode sheet according to claim 8, characterized in that, The distance between the centerlines of two adjacent grooves is 0.8 mm to 5 mm.

10. The negative electrode sheet according to claim 1, characterized in that, The first active material and the second active material include graphite.

11. The negative electrode sheet according to claim 10, characterized in that, The first active material includes a silicon-based material and graphite, and the second active material includes graphite.

12. A battery, characterized in that, Comprising the negative electrode tab according to any one of claims 1 to 11.

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