Negative electrode sheet and its application

Abstract

The present invention discloses a negative electrode sheet and its application. The negative electrode sheet includes a negative electrode current collector, a first coating layer, a second coating layer, and an adhesive layer. The first coating layer includes a first sub-coating layer and a second sub-coating layer. An electrode tab is provided at the end of the negative electrode current collector. The first coating layer is formed on the surface of the negative electrode current collector. The thickness of the first sub-coating layer is less than that of the second sub-coating layer. The first sub-coating layer is arranged close to the electrode tab. The second coating layer is provided on the first sub-coating layer. The fast charging ability of the second coating layer is greater than that of the first coating layer. The adhesive layer is provided on the surface of the second coating layer. The negative electrode sheet not only overcomes the problem of lithium deposition near the electrode tab of the negative electrode sheet, but also has a high conductivity while ensuring the relative position between the negative electrode sheet and the separator is stable and the flatness is high. Therefore, compared with the lithium battery in the prior art, the lithium battery using this negative electrode sheet has better fast charging ability, higher energy density, and longer cycle life.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a negative electrode sheet and its application. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high power density, long cycle life, environmental friendliness, etc., and are widely used in the fields of new energy vehicles, energy storage devices, etc. In recent years, the new energy vehicle industry has developed rapidly, but the long charging time has become a bottleneck restricting the further development of lithium-ion batteries. At present, the lithium-ion fast charging technology is mainly restricted by the lithium deintercalation rate of the negative electrode and lithium deposition on the edge of the negative electrode. During fast charging, the current density on the edge and the tab side of the negative electrode sheet is higher than that of the main body of the electrode sheet, and the lithium deintercalation rate is faster, resulting in a higher charging rate in the local area on the tab side of the negative electrode sheet than that of the main body, and local lithium deposition is more likely to occur. As the cycle progresses, the deposited lithium will grow into lithium dendrites, which will not only cause capacity loss and abnormal thickening of the battery, but also pierce the separator, bringing potential safety hazards. If the entire negative electrode sheet uses hard carbon with better fast charging performance or adds more conductive agents, it will affect the cycle life or energy density of the battery cell.

[0003] Patent CN109701816B discloses a multi-layer electrode including natural graphite and artificial graphite, and a lithium secondary battery including the multi-layer negative electrode. A first negative electrode mixture layer and a second negative electrode mixture layer are coated on the surface of the negative electrode current collector, with a small amount of binder and conductive agent used, and the life characteristics are improved at the same time. This method improves the loading amount through multi-layer coating, thereby improving the energy density of the battery cell. At the same time, the second negative electrode can improve the life, but it cannot solve the problem of fast charging at high rates. Patent CN112952051A discloses a negative electrode sheet, a method for preparing the negative electrode sheet, a lithium-ion hard-packed battery cell, a lithium-ion battery pack and their applications. An inner coating layer and an outer coating layer are coated on the surface of the negative electrode current collector, and the outer coating layer uses a high lithium-inserting material layer with a lithium potential greater than 0.5V. Although this method can avoid the separator being pierced by lithium dendrites on the electrode surface and improve the safety of the battery, the too high negative electrode voltage of the outer coating layer results in a decrease in the battery discharge platform voltage, affecting the energy density of the battery cell. Patent CN112103463A discloses a negative electrode sheet and a lithium-ion battery including the negative electrode sheet. A first coating area with better fast charging ability and higher mass capacity is provided on the surface of the current collector on the tab side of the negative electrode sheet, and a second coating area is provided on the surface of the current collector far from the tab, to solve the problem of lithium deposition on the surface of one side of the tab of the negative electrode sheet. This method does not provide a buffer area. At the junction of the two coating areas, it is easy to form a thick edge or an uncoated overlapping thin edge area due to different surface tensions of the slurry during coating, resulting in uneven local thickness and tension of the electrode sheet. During rolling, overpressure of the negative electrode material or wrinkling of the electrode sheet may occur. During the cycle of the battery cell, due to the uneven interface area, the current density is uneven, resulting in local lithium deposition and a decrease in cycle life.

[0004] Meanwhile, in the prior art, on the one hand, the separators used in the lithium-ion battery cells are all coated separators, that is, glue layers are coated on both sides of the separator, and then the positive and negative electrode plates are laminated with the separator and hot-pressed to achieve the bonding of the separator and the positive and negative electrode plates, preventing the positive and negative electrode plates from being misaligned during the assembly process. However, the cost of the coated separator is much higher than that of the non-coated separator, and the glue layer of the coated separator has poor ion-conducting performance, thus seriously affecting the battery performance. On the other hand, after filling the electrolyte in the battery, since both ends of the electrode plate are easily soaked by the electrolyte and wrinkled and warped, resulting in the separation of the separator and the electrode plate, reducing the flatness of the entire battery cell and affecting the battery cycle life.

[0005] Therefore, the existing lithium-ion batteries need to be improved. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this reason, an object of the present invention is to provide a negative electrode plate and its application. The negative electrode plate not only overcomes the problem of lithium deposition near the tab of the negative electrode plate, but also has a high conductivity while ensuring the relative position between the negative electrode plate and the separator is stable and the flatness is high. Therefore, the lithium battery using the negative electrode plate has better fast charging ability, higher energy density and longer cycle life compared with the lithium battery in the prior art.

[0007] In one aspect of the present invention, the present invention provides a negative electrode plate. According to an embodiment of the present invention, the negative electrode plate includes:

[0008] A negative electrode current collector, and a tab is provided at an end of the negative electrode current collector;

[0009] A first coating layer formed on the surface of the negative electrode current collector, and the first coating layer includes a first sub-coating layer and a second sub-coating layer. The thickness of the first sub-coating layer is less than that of the second sub-coating layer, and the first sub-coating layer is arranged near the tab;

[0010] A second coating layer provided on the first sub-coating layer, wherein the fast charging ability of the second coating layer is greater than that of the first coating layer;

[0011] A glue layer provided on the surface of the second coating layer.

[0012] According to the negative electrode sheet of the above embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector, a first coating layer, a second coating layer, and an adhesive layer. Wherein, a tab is provided at the end of the negative electrode current collector. The first coating layer, which includes a first sub-coating layer and a second sub-coating layer, is formed on the surface of the negative electrode current collector. The thickness of the first sub-coating layer is less than that of the second sub-coating layer. The first sub-coating layer is arranged close to the tab, that is, the area of the first coating layer close to the tab is thinned. The second coating layer is formed on the first sub-coating layer, and the fast charging ability of the second coating layer is greater than that of the first coating layer, that is, the second coating layer has a higher rate of lithium ion insertion and extraction compared to the first coating layer. That is to say, the negative electrode coating layer in this application includes two coating layers with different fast charging abilities. In the prior art, a single negative electrode coating layer is used. Because when the battery is fast charged, the current density near the tab of the negative electrode sheet is relatively high, and the rate of lithium ion insertion and extraction will be faster, resulting in a higher charging rate near the tab of the negative electrode sheet than in other areas, and lithium deposition is likely to occur near the tab of the negative electrode sheet. Based on recognizing this technical problem, the inventor of this application forms two coating layers with different fast charging abilities on the negative electrode current collector, and the coating layer with strong fast charging ability, that is, the second coating layer, is arranged close to the tab, which can achieve the rapid extraction and insertion of lithium ions near the tab of the negative electrode sheet, overcome the problem of lithium deposition near the tab of the negative electrode sheet, improve the high-rate charging performance of the negative electrode sheet, and further reduce the capacity loss of the battery, improve the battery energy density and cycle life. In addition, an adhesive layer is provided on the second coating layer of the above negative electrode sheet. During the cell assembly process, a non-adhesive separator is used. After hot pressing, the end of the negative electrode sheet is bonded to the separator. Therefore, except for the end area of the negative electrode sheet where the adhesive layer is provided, the other areas have high ionic conductivity between the negative electrode sheet and the separator. Compared with the prior art using an adhesive separator, the cell of this application not only reduces the separator cost, but also improves the ionic conductivity between the electrode sheet and the separator, thereby improving the electrical performance of the battery. At the same time, after injecting the electrolyte, on the one hand, the electrolyte can quickly infiltrate the cell, thereby improving the cycle life of the battery. On the other hand, precisely because the end of the electrode sheet is bonded to the separator through the adhesive layer, it can prevent the separation of the separator and the electrode sheet caused by the wrinkling and warping of both ends of the electrode sheet under the electrolyte immersion, ensuring the relative position and flatness between the electrode sheet and the separator, and further improving the cycle life of the battery. Thus, using the negative electrode sheet of this application not only overcomes the problem of lithium deposition near the tab of the negative electrode sheet, but also has a high conductivity while ensuring the relative position between the negative electrode sheet and the separator is stable and the flatness is high. Therefore, compared with the lithium battery in the prior art, the lithium battery using this negative electrode sheet has better fast charging ability, higher energy density, and longer cycle life.

[0013] In addition, the negative electrode sheet according to the above embodiment of the present invention may further have the following additional technical features:

[0014] According to an embodiment of the present invention, the first coating layer includes a first negative electrode active material, a first conductive agent, and a first binder, wherein the mass ratio of the first negative electrode active material, the first conductive agent, and the first binder is (80-99):(0.5-3):(2-5).

[0015] According to an embodiment of the present invention, the first coating layer further includes a first thickening agent, and the mass ratio of the first negative electrode active material to the first thickening agent is (80-99):(1-5).

[0016] According to an embodiment of the present invention, the first negative electrode active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

[0017] According to an embodiment of the present invention, the difference D1 between the thickness of the second sub-coating layer and the thickness of the first sub-coating layer is 10 to 50 μm.

[0018] According to an embodiment of the present invention, the length of the first sub-coating layer is 2 to 50 mm.

[0019] According to an embodiment of the present invention, the second coating layer includes a second negative electrode active material, a second conductive agent, and a second binder, wherein the mass ratio of the second negative electrode active material, the second conductive agent, and the second binder is (85-95):(1-5):(2-5). Thus, the rate of lithium ion insertion and extraction of the second coating layer can be improved.

[0020] According to an embodiment of the present invention, the second coating layer further includes a second thickening agent, and the mass ratio of the second negative electrode active material to the second thickening agent is (85-95):(1-4).

[0021] According to an embodiment of the present invention, the second negative electrode active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

[0022] According to an embodiment of the present invention, the particle size of the second negative electrode active material is smaller than that of the first negative electrode active material. Thus, the rate of lithium ion insertion and extraction of the second coating layer can be improved, and lithium deposition near the tab of the negative electrode sheet can be reduced.

[0023] According to an embodiment of the present invention, the mass proportion of the second negative electrode active material in the second coating layer is higher than that of the first active material in the first coating layer. Thus, the rate of lithium ion insertion and extraction of the second coating layer can be improved, and lithium deposition near the tab of the negative electrode sheet can be reduced.

[0024] According to an embodiment of the present invention, the thickness D2 of the second coating layer is smaller than the difference D1 between the thickness of the second sub-coating layer and the thickness of the first sub-coating layer.

[0025] According to an embodiment of the present invention, the thickness D2 of the second coating layer is 9 to 45 μm. Thereby, the rate of lithium ion insertion and extraction of the second coating layer can be increased, and lithium deposition near the tab of the negative electrode sheet can be reduced.

[0026] According to an embodiment of the present invention, the length of the second coating layer is not less than the length of the first sub-coating layer. Thereby, the rate of lithium ion insertion and extraction of the second coating layer can be increased, and lithium deposition near the tab of the negative electrode sheet can be reduced.

[0027] According to an embodiment of the present invention, the glue coating layer includes glue coating areas and non-glue coating areas spaced along the length direction of the negative electrode current collector. Thereby, the electrolyte infiltration efficiency can be improved, and the infiltration time after liquid injection can be reduced.

[0028] According to an embodiment of the present invention, the width ratio of the glue coating area to the non-glue coating area is 1:(1 - 3). Thereby, the electrolyte infiltration efficiency can be improved, and the infiltration time after liquid injection can be reduced.

[0029] According to an embodiment of the present invention, the thickness D3 of the glue coating layer and the thickness D2 of the second coating layer satisfy the following relational expression: D3 + D2 ≤ D1.

[0030] According to an embodiment of the present invention, the length of the glue coating layer is not greater than the length of the second coating layer. Thereby, the electrolyte infiltration efficiency can be improved, and the infiltration time after liquid injection can be reduced.

[0031] In another aspect of the present invention, the present invention provides a lithium battery. According to an embodiment of the present invention, the lithium battery includes a positive electrode sheet, a negative electrode sheet, and a non-glue separator. The non-glue separator is disposed between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet is the above-mentioned negative electrode sheet, and the glue coating layer on the negative electrode sheet is bonded to the non-glue separator. Thereby, the lithium battery using the negative electrode sheet of the present application has better fast charging ability, higher energy density, and longer cycle life compared with the lithium batteries in the prior art.

[0032] In the third aspect of the present invention, the present invention provides a vehicle. According to an embodiment of the present invention, the vehicle is equipped with the above-mentioned lithium battery. Thereby, the vehicle has a higher cruising range, safety performance, and fast charging ability.

[0033] Some of the additional aspects and advantages of the present invention will be given in the following description, some will become apparent from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0035] Figure 1Schematic diagram of the negative electrode sheet structure according to an embodiment of the present invention;

[0036] Figure 2 Schematic diagram of the negative electrode sheet structure according to another embodiment of the present invention. Detailed implementation manners

[0037] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0038] In one aspect of the present invention, the present invention provides a negative electrode sheet. According to the negative electrode sheet of the above embodiments of the present invention, referring to Figure 1 , the negative electrode sheet includes a negative electrode current collector 500, a first coating layer 100, a second coating layer 200, and an adhesive layer 300.

[0039] It should be noted that those skilled in the art can select the material of the negative electrode current collector 500 according to actual needs. For example, a copper foil is used, and a tab 400 is provided at the end of the negative electrode current collector 500.

[0040] According to an embodiment of the present invention, the first coating layer 100 includes a first sub - coating layer 101 and a second sub - coating layer 102. The first coating layer 100 is formed on the surface of the negative electrode current collector 500. The thickness of the first sub - coating layer 101 is less than the thickness of the second sub - coating layer 102. The first sub - coating layer 101 is arranged close to the tab 400, that is, the area of the first coating layer 100 close to the tab 400 is thinned. Preferably, the first sub - coating layer 101 and the second sub - coating layer 102 are adjacently arranged. Specifically, first, the first coating layer 100 is formed on the entire surface of the negative electrode current collector 500, and then the area of the first coating layer 100 close to the tab 400 is thinned to obtain the first sub - coating layer 101.

[0041] According to an embodiment of the present invention, the difference D1 between the thickness of the second sub - coating layer 102 and the thickness of the first sub - coating layer 101 is 10 - 50 μm. The inventor found that when D1 is less than 10 μm, the fast - charging performance of the negative electrode sheet is not significantly improved and the fast - charging ability cannot be enhanced; when D1 is greater than 50 μm, the thickness of the second sub - coating layer 102 is too small to easily control the flatness of the battery cell. Thus, by using the difference D1 between the thickness of the second sub - coating layer 102 and the thickness of the first sub - coating layer 101 being 10 - 50 μm in this application, lithium deposition at the tab of the negative electrode sheet can be reduced. It should be noted that both the "thickness of the second sub - coating layer 102" and the "thickness of the first sub - coating layer 101" refer to the thickness on one side formed on the negative electrode current collector 500.

[0042] According to an embodiment of the present invention, the length of the first sub-coating layer 101 is 2 to 50 mm. Those skilled in the art can understand that this length refers to the length starting from the end of the tab 400 and along the central axis direction of the current collector 500.

[0043] Further, the first coating layer 100 includes a first negative active material, a first conductive agent, and a first binder, and the mass ratio of the first negative active material, the first conductive agent, and the first binder is (80-99):(0.5-3):(2-5). Further, the first coating layer 100 further includes a first thickening agent, and the mass ratio of the first negative active material to the first thickening agent is (80-99):(1-5). Those skilled in the art can understand that the first negative active material, the first conductive agent, the first binder, and the first thickening agent are conventional materials in the art. For example, the first negative active material includes but is not limited to at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and mesophase carbon microspheres; the first conductive agent includes but is not limited to at least one of conductive carbon black, CNTs, VGCF, and KS-6; the first binder includes but is not limited to SBR, LA series binders, and PAA series binders; the first thickening agent includes but is not limited to CMC series thickening agents.

[0044] According to an embodiment of the present invention, a second coating layer 200 is formed on the first sub-coating layer 101, and the fast charging ability of the second coating layer 200 is greater than that of the first coating layer 100, that is, the second coating layer 200 has a higher rate of lithium ion insertion and extraction compared to the first coating layer 100. That is to say, the negative electrode coating layer in this embodiment includes two coating layers with different fast charging abilities. In the prior art, a single negative electrode coating layer is used. Because when the battery is fast charged, the current density near the tab of the negative electrode sheet is relatively high, and the rate of lithium ion insertion and extraction will be faster, resulting in a higher charging rate near the tab of the negative electrode sheet than in other areas, and lithium deposition is likely to occur near the tab of the negative electrode sheet. Based on recognizing this technical problem, the inventors of the present application form two coating layers with different fast charging abilities on the negative electrode current collector 500, and the coating layer with strong fast charging ability, that is, the second coating layer 200, is arranged close to the tab 400, which can realize the rapid extraction and insertion of lithium ions near the tab 400 of the negative electrode sheet, overcome the problem of lithium deposition near the tab 400 of the negative electrode sheet, improve the large-rate charging performance of the negative electrode sheet, and further reduce the capacity loss of the battery, and improve the battery energy density and cycle life.

[0045] According to an embodiment of the present invention, the thickness D2 of the second coating layer 200 is less than the difference D1 between the thickness of the second sub-coating layer 102 and the thickness of the first sub-coating layer 101, and the thickness D2 of the second coating layer is 9 to 45 μm. The inventors found that if the thickness of the second coating layer is too thick, after coating the adhesive layer, the thickness exceeds the overall size of the negative electrode sheet, and the head of the battery cell will be too thick during subsequent rolling and stacking. If the thickness of the second coating layer is too thin, the NP ratio (negative electrode / positive electrode reversible capacity ratio) of the head of the negative electrode sheet will be too low, and lithium deposition will occur near the electrode tab. Thus, the rate of lithium ion insertion and extraction of the second coating layer can be increased, and lithium deposition near the electrode tab of the negative electrode sheet can be reduced. It should be noted that the "thickness of the second coating layer 200", the "thickness of the first sub-coating layer 101", and the "thickness of the second sub-coating layer 102" all refer to the thickness on one side formed on the negative electrode current collector 500.

[0046] Furthermore, the second coating layer 200 includes a second negative electrode active material, a second conductive agent, and a second binder, and the mass ratio of the second negative electrode active material, the second conductive agent, and the second binder is (85 - 95):(1 - 5):(2 - 5). Further, the second coating layer 200 further includes a second thickening agent, and the mass ratio of the second negative electrode active material to the second thickening agent is (85 - 95):(1 - 4). Those skilled in the art can understand that the second negative electrode active material, the second conductive agent, the second binder, and the second thickening agent are conventional materials in the art. For example, the second negative electrode active material includes, but is not limited to, at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and mesocarbon microbeads. The second conductive agent includes, but is not limited to, at least one of conductive carbon black, CNTs, VGCF, and KS-6; the second binder includes, but is not limited to, SBR, LA series binders, and PAA series binders, and the second thickening agent includes, but is not limited to, CMC series thickening agents.

[0047] It should be understood by those skilled in the art that in order to make the fast charging capacity of the second coating layer 200 greater than the fast charging capacity of the first coating layer 100, the following method can be used: if the material types, mass proportions of each component and other factors of the first coating layer 100 and the second coating layer 200 are the same, the particle size of the second negative electrode active material is smaller than the particle size of the first negative electrode active material; if the particle size, type and other factors of each material of the first coating layer 100 and the second coating layer 200 are the same, the mass proportion of the second negative electrode active material in the second coating layer 200 is higher than the mass proportion of the first active material in the first coating layer 100. If the particle size of each material, the proportion of each component and other factors of the first coating layer 100 and the second coating layer 200 are the same, if the first negative electrode active material uses artificial graphite, the second active material can also be achieved by using hard carbon. It should be noted that there are multiple composition methods for the material types, mass proportions, etc. of the first coating layer 100 and the second coating layer 200 of the present application, as long as the fast charging capacity of the second coating layer 200 is greater than that of the first coating layer 100.

[0048] According to an embodiment of the present invention, the length of the second coating layer 200 is not less than the length of the first sub-coating layer 102, and preferably the length of the second coating layer 200 is the same as the length of the first sub-coating layer 102. Thus, the lithium ion deintercalation rate of the second coating layer can be increased to a greater extent.

[0049] According to an embodiment of the present invention, referring to Figure 1 , a glue coating layer 300 is arranged on the second coating layer 200, and a glue-free diaphragm is used in the battery cell assembly process. After hot pressing, the end of the negative electrode sheet is bonded to the diaphragm. Therefore, except for the end area where the glue layer is arranged, the other areas of the negative electrode sheet have a higher ion conductivity with the diaphragm. Compared with the use of glue diaphragms in the prior art, the battery cell of the present application not only reduces the diaphragm cost, but also improves the ion conductivity between the electrode sheet and the diaphragm, thereby improving the electrical performance of the battery. At the same time, after the electrolyte is injected, on the one hand, the electrolyte can quickly infiltrate the battery cell, thereby improving the cycle life of the battery. On the other hand, it is precisely because the end of the electrode sheet is bonded to the diaphragm through the glue layer that the separation of the diaphragm and the electrode sheet caused by wrinkling and warping at both ends of the electrode sheet when immersed in the electrolyte can be prevented, thereby ensuring the relative position and flatness between the electrode sheet and the diaphragm, and further improving the cycle life of the battery.

[0050] According to an embodiment of the present invention, referring to Figure 2 , the glue layer 300 includes a glue area 301 and a non-glue area 302 spaced along the length direction of the negative electrode current collector 500. The use of such an interval glue structure can not only ensure the bonding force between the negative electrode sheet and the separator, but also facilitate the electrolyte to infiltrate the negative electrode sheet and the separator from the non-glue area 302. Therefore, the glue layer 300 of the present application with the glue area 301 and the non-glue area 302 spaced apart can improve the electrolyte infiltration efficiency and reduce the infiltration time after injection.

[0051] According to an embodiment of the present invention, the width ratio of the glue - applying area 301 to the non - glue - applying area 302 is 1:(1 - 3). The inventors found that when the width ratio of the glue - applying area 301 to the non - glue - applying area 302 is less than 1:3, after the battery cell is injected with electrolyte, the glue layer cannot ensure the bonding between the separator and the positive and negative electrode plates. When the width ratio of the glue - applying area 301 to the non - glue - applying area 302 is greater than 1, after the battery cell is injected with electrolyte, it is not easy to be infiltrated, resulting in an extended infiltration time and affecting the production efficiency. Thus, by adopting the width ratio of the glue - applying area 301 to the non - glue - applying area 302 of 1:(1 - 3) in this application, the electrolyte infiltration efficiency can be improved and the infiltration time after injection can be reduced.

[0052] According to an embodiment of the present invention, the thickness D3 of the glue layer 300 and the thickness D2 of the second coating layer 200 satisfy the following relational expression: D3 + D2 ≤ D1. Preferably, D3+D2 = D1. Thus, the flatness of the negative electrode plate surface can be ensured. Those skilled in the art can understand that in order to improve the flatness of the battery cell and the electrolyte infiltration effect, the length of the glue layer 300 is not greater than the length of the second coating layer 200. It should be noted that the glue layer 300 is a conventional material in the art, and those skilled in the art can select according to the actual situation. For example, the glue layer 300 includes but is not limited to at least one of PVDF, PC, PAA, PVA, and PMMA. When preparing the glue layer by configuring the glue layer slurry with the above - mentioned materials such as PVDF, the glue layer slurry with a mass concentration of 1 - 8% can be coated on the second coating layer 200.

[0053] Thus, the negative electrode plate of this application not only overcomes the problem of lithium deposition near the tab of the negative electrode plate, but also has a high conductivity while ensuring the relative position stability and high flatness between the negative electrode plate and the separator. Therefore, compared with the lithium - ion battery in the prior art, the lithium - ion battery using this negative electrode plate has better fast - charging ability, higher energy density, and longer cycle life.

[0054] In another aspect of the present invention, the present invention provides a lithium - ion battery. According to an embodiment of the present invention, the lithium - ion battery includes a positive electrode plate, a negative electrode plate, and a non - glue separator. The non - glue separator is disposed between the positive electrode plate and the negative electrode plate. The negative electrode plate is the above - mentioned negative electrode plate, and the glue layer on the negative electrode plate is bonded to the non - glue separator. Thus, compared with the lithium - ion battery in the prior art, the lithium - ion battery using the negative electrode plate of this application has better fast - charging ability, higher energy density, and longer cycle life. It should be noted that the features and advantages described for the above - mentioned negative electrode plate also apply to this lithium - ion battery, and will not be elaborated here.

[0055] In the third aspect of the present invention, the present invention provides a vehicle. According to an embodiment of the present invention, the vehicle is equipped with the above-mentioned lithium battery. Thus, the vehicle has a relatively high cruising range, safety performance, and fast charging ability. It should be noted that the features and advantages described for the above-mentioned lithium battery also apply to this vehicle, and will not be elaborated here.

[0056] The following describes the present invention with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0057] Comparative Example 1 (with only one coating layer)

[0058] Preparation of the first coating layer slurry: 92 g of artificial graphite, 3 g of SBR, 2 g of CMC, and 2 g of conductive carbon black were uniformly dispersed in deionized water. After sufficient mixing, the first coating layer slurry was obtained.

[0059] Preparation of the negative electrode sheet: The above-mentioned first coating layer slurry was uniformly coated on the surface of the negative electrode current collector, dried at 80 - 110 °C for 4 hours, and the electrode sheet was roll-pressed according to a compaction density of 1.6 g / cm 3 to obtain the negative electrode sheet. Among them, the thickness of the first coating layer was 150 μm.

[0060] Preparation of the positive electrode sheet: 96 g of NCM622 material, 2 g of PVDF, and 2 g of CNTS were uniformly dispersed in NMP. After sufficient mixing, the positive electrode active slurry was obtained. The slurry was uniformly coated on the surface of the aluminum foil, dried at 90 - 130 °C for 4 hours, and the electrode sheet was roll-pressed according to a compaction density of 3.5 g / cm 3 to prepare the positive electrode sheet.

[0061] Preparation of the lithium battery: The above-prepared positive electrode sheet, negative electrode sheet, and the adhesive separator were laminated and encapsulated with an aluminum-plastic film. After baking and liquid injection, a soft-pack battery was formed, denoted as D1.

[0062] Comparative Example 2 (with only one coating layer and thinning)

[0063] The difference between Comparative Example 2 and Comparative Example 1 is as follows:

[0064] Preparation of the negative electrode sheet: The above-mentioned first coating layer slurry was uniformly coated on the surface of the negative electrode current collector, and thinning treatment was performed at a position 15 mm from the tab, with a thinning thickness of 20 μm. After drying at 80 - 110 °C for 4 hours, the above electrode sheet was roll-pressed according to a compaction density of 1.6 g / cm 3 to obtain the negative electrode sheet. Among them, the thickness of the non-thinned part of the first coating layer was 150 μm.

[0065] The prepared lithium battery was denoted as D2.

[0066] Comparative Example 3 (with two coating layers, without an adhesive layer)

[0067] The preparation of the first coating layer slurry in Comparative Example 3 is the same as that in Comparative Example 1.

[0068] Preparation of the second coating layer slurry: 80 g of artificial graphite, 12 g of hard carbon, 3 g of SBR, 2 g of CMC, and 3 g of conductive carbon black were uniformly dispersed in deionized water, and after sufficient mixing, the second coating layer slurry was obtained.

[0069] Preparation of the negative electrode sheet: The first coating layer slurry was uniformly coated on the surface of the negative electrode current collector, and thinning treatment was carried out at a position 15 mm from the tab, with a thinning thickness of 20 μm. After sufficient drying at 80 - 110 °C for 4 hours, the second coating layer slurry was uniformly coated on the thinned area of the first coating layer, and after sufficient drying at 80 - 110 °C for 4 hours, a second coating layer with a thickness of 20 μm was obtained. And the above-mentioned electrode sheet was rolled at a compaction density of 1.6 g / cm 3 to obtain the negative electrode sheet.

[0070] The preparation of the positive electrode sheet of Comparative Example 3 and the preparation of the lithium battery are the same as those in Comparative Example 1.

[0071] The prepared lithium battery was designated as D3.

[0072] Example 1 (with an adhesive layer added compared to Comparative Example 3)

[0073] The difference between Example 1 and Comparative Example 3 is as follows:

[0074] Preparation of the third adhesive layer slurry: 10 g of PVDF powder was uniformly dissolved in 140 g of NMP solution, and after sufficient mixing, the third adhesive layer slurry was obtained.

[0075] In the preparation of the negative electrode sheet, the thinning thickness was 20 μm, and the thickness of the second coating layer was 15 μm. The above-mentioned third adhesive layer slurry was intermittently coated on the dried second coating layer and dried at 80 - 110 °C for 1 hour to obtain an adhesive layer, where the width ratio of the adhesive area to the non - adhesive area was 1:2, and the thickness of the adhesive layer was 5 μm. The above-mentioned electrode sheet was rolled at a compaction density of 1.6 g / cm 3 to obtain the negative electrode sheet.

[0076] An adhesive - free separator was used, and the prepared lithium battery was designated as S1.

[0077] Example 2

[0078] The difference between Example 2 and Example 1 is as follows:

[0079] Preparation of the second coating slurry: 50 g of artificial graphite, 42 g of hard carbon, 3 g of SBR, 2 g of CMC, and 3 g of conductive carbon black are uniformly dispersed in deionized water. After thorough mixing, the second coating slurry is obtained.

[0080] A lithium battery prepared using a non - adhesive separator is denoted as S2.

[0081] Example 3

[0082] The difference between Example 3 and Example 1 is as follows:

[0083] Preparation of the second coating slurry: 25 g of artificial graphite, 67 g of hard carbon, 3 g of SBR, 2 g of CMC, and 3 g of conductive carbon black are uniformly dispersed in deionized water. After thorough mixing, the second coating slurry is obtained.

[0084] A lithium battery prepared using a non - adhesive separator is denoted as S3.

[0085] Example 4

[0086] The difference between Example 4 and Example 1 is as follows:

[0087] Preparation of the second coating slurry: 92 g of hard carbon, 3 g of SBR, 2 g of CMC, and 3 g of conductive carbon black are uniformly dispersed in deionized water. After thorough mixing, the second coating slurry is obtained.

[0088] A lithium battery prepared using a non - adhesive separator is denoted as S4.

[0089] Example 5

[0090] The difference between Example 5 and Example 1 is as follows:

[0091] Preparation of the second coating slurry: 82 g of artificial graphite, 10 g of silicon suboxide, 3 g of SBR, 2 g of CMC, and 3 g of conductive carbon black are uniformly dispersed in deionized water. After thorough mixing, the second coating slurry is obtained.

[0092] A lithium battery prepared using a non - adhesive separator is denoted as S5.

[0093] Example 6

[0094] The difference between Example 6 and Example 1 is as follows:

[0095] Preparation of the second coating slurry: 90 g of artificial graphite, 3 g of SBR, 2 g of CMC, and 5 g of conductive carbon black are uniformly dispersed in deionized water. After thorough mixing, the second coating slurry is obtained.

[0096] A lithium battery prepared using a non - adhesive separator is denoted as S6.

[0097] Example 7

[0098] Example 7 is different from Example 1 in that:

[0099] Preparation of the second coating layer slurry: 90 g of artificial graphite, 3 g of SBR, 2 g of CMC, 2 g of conductive carbon black, and 3 g of CNTS are uniformly dispersed in deionized water and thoroughly mixed to obtain the second coating layer slurry.

[0100] A non-glue separator is used, and the prepared lithium battery is denoted as S7.

[0101] Example 8 (continuous coating of the glue layer)

[0102] Example 8 is different from Example 7 in that:

[0103] During the preparation of the negative electrode sheet, the third glue coating layer slurry is continuously coated on the dried second coating layer.

[0104] A non-glue separator is used, and the prepared lithium battery is denoted as S8.

[0105] For Comparative Examples 1-3 and Examples 1-8, the D50 particle size of artificial graphite in the first negative electrode active material in the first coating layer and the second negative electrode active material in the second coating layer is 12 μm, and the D50 particle size of hard carbon is 8 μm.

[0106] Example 9 (other conditions are the same, only the particle sizes of the active materials in the first coating layer and the second coating layer are different)

[0107] Preparation of the first coating layer slurry: 92 g of artificial graphite, 3 g of SBR, 2 g of CMC, and 2 g of conductive carbon black are uniformly dispersed in deionized water and thoroughly mixed to obtain the first coating layer slurry, where the D50 particle size of artificial graphite is 12 μm.

[0108] Preparation of the second coating layer slurry: 92 g of artificial graphite, 3 g of SBR, 2 g of CMC, and 2 g of conductive carbon black are uniformly dispersed in deionized water and thoroughly mixed to obtain the second coating layer slurry, where the D50 particle size of artificial graphite is 10 μm.

[0109] The preparation methods of the negative electrode sheet, the positive electrode sheet, and the lithium battery are the same as those in Example 1.

[0110] A non-glue separator is used, and the prepared lithium battery is denoted as S9.

[0111] Example 10 (other conditions are the same, only the mass ratios of the active materials in the first coating layer and the second coating layer are different)

[0112] Example 10 is different from Example 1 in that

[0113] Preparation of the second coating slurry: 95 g of artificial graphite, 2 g of SBR, 2 g of CMC, and 1 g of conductive carbon black are uniformly dispersed in deionized water. After thorough mixing, the first coating slurry is obtained.

[0114] A lithium battery is prepared using a non-glue separator, denoted as S10.

[0115] Fast charge lithium plating tests are conducted on the lithium-ion batteries of Comparative Examples 1-3 and Examples 1-10 above. The test process is as follows:

[0116] Fast charge at 3C rate: Place the lithium-ion battery in an environmental chamber at 25 ± 2°C and let it stand for 2 h. Discharge it at a current of 1C to 2.5V, then let it stand for 30 min. After that, charge it at a constant current of 3C to 4.35V, and the cut-off current for constant voltage charging is 0.1C. After cycling 50 weeks according to the above method, measure the DC internal resistance of the battery at 50% SOC, observe the growth of the internal resistance and the capacity retention rate. Fully charge the lithium-ion battery and disassemble it to observe the lithium plating situation on the negative electrode.

[0117] Fast charge at 4C rate: Place the lithium-ion battery in an environmental chamber at 25 ± 2°C and let it stand for 2 h. Discharge it at a current of 1C to 2.5V, then let it stand for 30 min. After that, charge it at a constant current of 4C to 4.35V, and the cut-off current for constant voltage charging is 0.1C. After cycling 50 weeks according to the above method, measure the DC internal resistance of the battery at 50% SOC, observe the growth of the internal resistance and the capacity retention rate. Fully charge the lithium-ion battery and disassemble it to observe the lithium plating situation on the negative electrode.

[0118] Fast charge at 5C rate: Place the lithium-ion battery in an environmental chamber at 25 ± 2°C and let it stand for 2 h. Discharge it at a current of 1C to 2.5V, then let it stand for 30 min. After that, charge it at a constant current of 5C to 4.35V, and the cut-off current for constant voltage charging is 0.1C. After cycling 50 weeks according to the above method, measure the DC internal resistance of the battery at 50% SOC, observe the growth of the internal resistance and the capacity retention rate. Fully charge the lithium-ion battery and disassemble it to observe the lithium plating situation on the negative electrode.

[0119] The results of the fast charge lithium plating tests on the lithium-ion batteries of Comparative Examples 1-3 and Examples 1-10 above are shown in Table 1.

[0120] Table 1

[0121]

[0122] It can be seen from Comparative Examples 1-3 and Examples 1-10 in Table 1 that coating a fast-charging type or more conductive active material in the thinning area of the negative electrode tab can significantly reduce the risk of lithium plating, improve the charging rate, and enhance the battery safety performance. By increasing the proportion of hard carbon or the proportion of conductive agent or doping silicon monoxide with a higher specific capacity, the lithium plating problem of the battery can be improved, the loss of active lithium during the cycle process can be reduced, and at the same time, the growth rate of internal resistance can be decreased, and the cycle life can be enhanced. It can be seen from Example 7 and Example 8 that the intermittent coating method for the glue layer can not only ensure the relative position and flatness between the electrode sheet and the separator, but also ensure good infiltration of the electrolyte, thereby enhancing the cycle life. It can be seen from Example 9 that when other factors such as the types of materials and the mass ratios of each component in the first coating layer and the second coating layer are the same, using a second negative electrode active material with a smaller particle size than that of the first negative electrode active material in the second coating layer can improve the fast-charging ability of the second coating layer, thereby improving the lithium plating problem of the battery. It can be seen from Example 10 that when other factors such as the particle size and type of materials in the first coating layer and the second coating layer are the same, by making the mass ratio of the second negative electrode active material in the second coating layer higher than the mass ratio of the first active material in the first coating layer, the fast-charging ability of the second coating layer can be improved, thereby improving the lithium plating problem of the battery.

[0123] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0124] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, Comprising: A negative current collector, with a tab provided at the end of the negative current collector; A first coating layer formed on the surface of the negative current collector, and the first coating layer includes a first sub - coating layer and a second sub - coating layer. The thickness of the first sub - coating layer is less than that of the second sub - coating layer, and the first sub - coating layer is arranged near the tab; A second coating layer provided on the first sub - coating layer, wherein the fast - charging ability of the second coating layer is greater than that of the first coating layer; An adhesive layer provided on the surface of the second coating layer, The adhesive layer includes adhesive regions and non - adhesive regions spaced along the length direction of the negative current collector; The width ratio of the adhesive region to the non - adhesive region is 1:(1 - 3).

2. The negative electrode sheet according to claim 1, wherein, The first coating layer includes a first negative active material, a first conductive agent, and a first binder. Among them, the mass ratio of the first negative active material, the first conductive agent, and the first binder is (80 - 99):(0.5 - 3):(2 - 5).

3. The negative electrode sheet according to claim 2, wherein, The first coating layer further includes a first thickening agent, and the mass ratio of the first negative active material to the first thickening agent is (80 - 99):(1 - 5).

4. The negative electrode sheet according to claim 2, characterized in that, The first negative active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

5. The negative electrode sheet according to claim 1, characterized in that, The difference D1 between the thickness of the second sub - coating layer and the thickness of the first sub - coating layer is 10 - 50μm.

6. The negative electrode sheet according to claim 5, characterized in that, The length of the first sub - coating layer is 2 - 50mm.

7. The negative electrode sheet according to any one of claims 2 to 4, characterized in that, The second coating layer includes a second negative active material, a second conductive agent, and a second binder. Among them, the mass ratio of the second negative active material, the second conductive agent, and the second binder is (85 - 95):(1 - 5):(2 - 5).

8. The negative electrode sheet according to claim 7, wherein The second coating layer further includes a second thickening agent, and the mass ratio of the second negative active material to the second thickening agent is (85 - 95):(1 - 4).

9. The negative electrode sheet according to claim 7, wherein The second negative active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

10. The negative electrode sheet according to claim 7, characterized in that, The particle size of the second negative active material is smaller than that of the first negative active material.

11. The negative electrode sheet according to claim 10, wherein The mass proportion of the second negative active material in the second coating layer is higher than the mass proportion of the first negative active material in the first coating layer.

12. The negative electrode sheet according to claim 5, wherein, The thickness D2 of the second coating layer is less than the difference D1 between the thickness of the second sub - coating layer and the thickness of the first sub - coating layer.

13. The negative electrode sheet according to claim 12, characterized in that, The thickness D2 of the second coating layer is 9 - 45μm.

14. The negative electrode sheet according to claim 12, wherein, The length of the second coating layer is not less than the length of the first sub - coating layer.

15. The negative electrode sheet according to claim 1, characterized in that, The thickness D3 of the adhesive layer and the thickness D2 of the second coating layer satisfy the following relationship: D3 + D2 ≤ D1.

16. The negative electrode sheet according to claim 1, wherein, The length of the adhesive layer is not greater than the length of the second coating layer.

17. A lithium battery, characterized in that, Including a positive electrode sheet, a negative electrode sheet, and a non - adhesive separator. The non - adhesive separator is provided between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet is the negative electrode sheet according to any one of claims 1 - 16, and the adhesive layer on the negative electrode sheet is bonded to the non - adhesive separator.

18. A vehicle, characterized in that, The vehicle has the lithium battery according to claim 17.

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