Negative electrode sheet, battery, and battery pack

Abstract

The embodiment of the application provides a negative plate, a battery and a battery pack, and relates to the technical field of secondary batteries. The negative plate comprises a current collector, a tab connected to one side of the current collector, a first active material layer and a second active material layer. The first active material layer is coated on the front and back surfaces of the current collector, and the thickness of the first active material layer gradually increases from one side of the tab to the side away from the tab and then gradually decreases. The second active material layer is coated on the outer side of the first active material layer, and the thickness of the second active material layer gradually decreases from one side of the tab 130 to the side away from the tab 130 and then gradually increases. The negative plate can improve the problem of lithium precipitation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of secondary batteries, in particular to a negative electrode sheet, a battery and a battery pack. BACKGROUND

[0002] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can continue to be used by activating active materials through charging after the battery is discharged. By utilizing the reversibility of chemical reactions, a new battery can be assembled, i.e., after a chemical reaction is converted into electrical energy, the chemical system can be repaired using electrical energy, and then the chemical reaction can be converted into electrical energy again. It is widely used in new energy vehicles and energy storage devices.

[0003] With the development of fast charging technology, the existing lithium battery is prone to lithium deposition on the side of the negative electrode sheet corresponding to the positive and negative electrode tabs when high-rate charging is used, and is more likely to form lithium dendrites, which may increase the risk of battery thermal runaway. SUMMARY

[0004] The purposes of the present application include, for example, providing a negative electrode sheet, a battery and a battery pack which can improve the problem of lithium precipitation of the negative electrode sheet.

[0005] Embodiments of the present application can be implemented as follows:

[0006] In a first aspect, the present application provides a negative electrode sheet, comprising:

[0007] a current collector;

[0008] a tab connected to one side of the current collector;

[0009] a first active material layer coated on the front and back surfaces of the current collector, and the thickness of the first active material layer gradually increases from one side of the tab to the side away from the tab, and then gradually decreases;

[0010] a second active material layer coated on the outer side of the first active material layer, and the thickness of the second active material layer gradually decreases from one side of the tab to the side away from the tab, and then gradually increases.

[0011] In an optional embodiment, the first active material layer is a high specific energy active material layer, and the kinetic performance of the second active material layer is greater than that of the first active material layer.

[0012] In an optional embodiment, the sum of the thickness of the first active material layer and the thickness of the second active material layer at any position of the current collector is equal.

[0013] In an optional embodiment, the ratio of the thickness of the first active material layer to the thickness of the second active material layer is X, and X is in the range of 0X≤10.

[0014] In an optional embodiment, the ratio of the thickness of the first active material layer to the thickness of the second active material layer gradually increases from one side of the tab to the side away from the tab, and then gradually decreases.

[0015] In an optional embodiment, the areal densities of the first active material layer and the second active material layer are different.

[0016] In an optional embodiment, the first active material layer and the second active material layer are asymmetric in the extension direction of the tab.

[0017] In an optional embodiment, the particle size distribution of the first active material layer is larger than that of the second active material layer.

[0018] In a second aspect, the present application provides a battery, comprising a shell, a bare cell, and a pole, wherein the bare cell comprises a positive electrode sheet, a separator, and the negative electrode sheet of any one of the preceding embodiments.

[0019] The positive electrode sheet, the separator, the negative electrode sheet, and the separator are sequentially stacked.

[0020] The bare cell is installed in the shell, and the tab is electrically connected to the pole.

[0021] In a third aspect, the present application provides a battery pack, comprising a plurality of batteries as described in the preceding embodiments, wherein the plurality of batteries are connected in parallel or in series.

[0022] The negative electrode sheet, the battery, and the battery pack provided by the embodiments of the present application have the following beneficial effects, for example:

[0023] The present application coats the first active material layer on the front and back of the current collector, and makes the first active material layer gradually thicken from one side of the tab to the side away from the tab, and then gradually thin. The second active material layer is coated on the outside of the first active material layer, and the second active material layer gradually thins from one side of the tab to the side away from the tab, and then gradually thickens. In this way, the ion diffusion rate can be improved in the high-potential area between the positive and negative electrode sheets, the ion transfer impedance is reduced, and the risk of lithium precipitation is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0025] Figure 1 The structural schematic diagram of the battery provided for the embodiments of the present application;

[0026] Figure 2 The structural schematic diagram of the negative electrode sheet provided for the embodiments of the present application;

[0027] Figure 3 The partial voltage curve of the positive electrode sheet and the partial voltage curve of the negative electrode sheet when the battery is charging;

[0028] Figure 4 The effective voltage distribution between the positive electrode sheet and the negative electrode sheet when the battery is charging.

[0029] Figure legend: 100-negative electrode sheet; 110-current collector; 130-tab; 150-first active material layer; 170-second active material layer; 300-battery; 310-housing; 330-pole. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the following will combine the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of the present application.

[0032] It should be noted that: similar labels and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0033] In the description of the present application, it should be noted that if the terms "upper", "lower", "inner", "outer" and the like indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship of the product of the present application when it is usually placed, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0034] In addition, if the terms "first", "second" and the like appear, they are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0035] It should be noted that the features in the embodiments of the present application can be combined with each other without conflict.

[0036] Please refer to Figure 1 The present embodiment provides a battery pack which can be used as a power part of a new energy vehicle. It can also be used in energy storage equipment for electric energy storage. It can also be applied to electric tools to provide power.

[0037] Generally, the battery pack includes a box body, a plurality of batteries 300 and a battery management assembly. The plurality of batteries 300 are generally connected in series and in parallel to form one or more battery modules. The battery modules are installed in the box body. The battery management assembly is electrically connected to the battery to monitor the voltage, temperature and other parameters of each battery 300.

[0038] In the present embodiment, the battery 300 includes a shell 310, a bare cell and a pole 330. The bare cell includes a positive plate, a separator and a negative plate 100. The positive plate, the separator, the negative plate 100 and the separator are stacked in order. The bare cell is installed in the shell 310, and the tab 130 is electrically connected to the pole 330.

[0039] Generally, the pole 330 includes a positive pole 330 and a negative pole 330, and the positive pole 330 and the negative pole 330 are oppositely installed on both sides of the shell 310. The tab 130 connected to the positive plate is electrically connected to the positive pole 330, and the tab 130 connected to the negative plate 100 is connected to the negative pole 330.

[0040] The inventors found that during the charging of the battery 300, lithium ions are extracted from the positive electrode, pass through the separator, and then are embedded in the active material of the negative electrode. The deposition of lithium on the negative electrode tab 100 is mainly due to excessive current, which leads to excessive local polarization, too low negative electrode potential, and reaches the metal lithium deposition potential, thereby depositing metal lithium on the surface of the negative electrode tab. The main reason for the above-mentioned lithium deposition rule is that the positive and negative electrode tabs 100 of the lithium battery 300 have a voltage drop, which leads to uneven distribution of electric potential on the electrode tabs, and thus at the same charging rate, the electric potential corresponding to the positive and negative electrode tabs 100 on the side of the positive and negative electrode ears 130 is relatively large, thereby leading to lithium deposition.

[0041] To solve the above-mentioned problems, the present embodiment provides a negative electrode tab, which can improve the problem of lithium deposition caused by potential difference.

[0042] Reference Figure 2 In the present embodiment, the negative electrode tab 100 includes a current collector 110, an electrode ear 130 connected to one side of the current collector 110, a first active material layer 150, and a second active material layer 170. The first active material layer 150 is coated on the front and back surfaces of the current collector 110, and the first active material layer gradually increases in thickness from one side of the electrode ear 130 to the side away from the electrode ear 130, and then gradually decreases in thickness. The second active material layer 170 is coated on the outside of the first active material layer 150, and the second active material layer 170 gradually decreases in thickness from one side of the electrode ear 130 to the side away from the electrode ear 130, and then gradually increases in thickness.

[0043] In the present embodiment, the first active material layer 150 is coated on the front and back surfaces of the current collector 110, and the first active material layer gradually increases in thickness from one side of the electrode ear 130 to the side away from the electrode ear 130, and then gradually decreases in thickness. The second active material layer 170 is coated on the outside of the first active material layer 150, and the second active material layer 170 gradually decreases in thickness from one side of the electrode ear 130 to the side away from the electrode ear 130, and then gradually increases in thickness. In this way, the ion diffusion rate can be improved in the high-potential area between the positive and negative electrode tabs 100, the ion transfer impedance can be reduced, and the risk of lithium deposition can be reduced.

[0044] In the present embodiment, the first active material layer 150 is a high-energy active material layer, and the kinetic performance of the second active material layer 170 is greater than that of the first active material layer 150.

[0045] When the battery 300 is charged, the voltage applied to the positive and negative electrode posts 330 refers to the potential difference applied to the positive and negative electrode posts 330 of the battery core, which is Vapp, without considering the resistance at the connection, and this voltage corresponds to the potential difference between the positive and negative electrode ears 130. Each electrode tab experiences a voltage drop at the electrode ear 130 and at a position away from the electrode ear 130, and generally the farther away from the electrode ear 130, the greater the voltage drop.

[0046] The effective voltage refers to the voltage between the positive and negative tabs 100 at any particular location of the cell, referred to as Ve. In a spatial Cartesian coordinate system, the directions parallel to the tabs are the X and Y axes, respectively, and the direction perpendicular to the tabs is the Z axis. At the location where the effective voltage is measured, the positive and negative tabs share the same X and Y coordinates, but the Z axis coordinates are different.

[0047] Figure 3 is a graph of the local voltage of the positive tab and the local voltage of the negative tab during charging, where the positive tab is above the horizontal axis and the negative tab is below the horizontal axis. The charging method can be one or a combination of constant voltage charging, constant current charging, pulse charging, etc. Since the current passing through the current collector 110 produces a voltage drop, the potential VI at the positive tab 130 gradually decreases to V2 at the corresponding position of the negative tab 130, forming the local voltage curve of the positive tab. Similarly, the potential V4 at the negative tab 130 gradually decreases to V3 at the corresponding position of the positive tab, and the voltage applied to the positive and negative tabs 100 at the tabs 130 is V4-V1, while the local voltage of the positive and negative tabs 100 at the same X value is the difference between the curves and the corresponding positions, referred to as the effective voltage Ve, i.e. Figure 3

[0048] Figure 4 As can be seen in the above figure, the effective voltage of the positive and negative tabs 100 varies with the different positions of the tabs, and the closer to the tab 130, the greater the effective voltage. Therefore, according to the distribution of the effective voltage of the positive and negative tabs 100 in the battery 300, the effective voltage is greater at the two side tabs 130, and the ion transport rate is faster, so more negative materials with good kinetic performance need to be provided in the two side regions to improve the ion diffusion rate, reduce the ion transfer impedance, and reduce the risk of lithium precipitation. More high-energy active materials can be configured at the low potential to improve the energy density of the cell. Thus, the overall electrical properties can take into account both high energy and fast charging.

[0049] It should be further explained that, to meet the above requirements, the second active material layer 170 is a negative material with good kinetics, such as a negative material with high graphitization degree, large specific surface area, and small polarization, and the first active material layer 150 is a high-energy negative material, such as a negative material with wide particle size distribution.

[0050] Referring to Figure 2 In this embodiment, the particle size distribution of the first active material layer 150 is greater than that of the second active material layer 170. Thus, the first active material layer 150 with good kinetics and the second active material layer 170 with high energy are obtained.

[0051] ​For example, the second active material layer 170 is prepared by mixing small particle blended graphite, a binder, a conductive agent, and a first solvent in a certain proportion to prepare the slurry of the first active material layer 150, and the first active material layer 150 is prepared by mixing small particle blended graphite, a binder, a conductive agent, and a second solvent in a certain proportion to prepare the slurry of the second active material layer 170. Thus, the second active material layer 170 having good kinetics and the first active material layer 150 having high specific energy are obtained.

[0052] Of course, the first active material layer 150 and the second active material layer 170 can also be prepared by using other main materials and auxiliary materials, as long as the first active material layer 150 has good kinetics and the second active material layer 170 has high specific energy.

[0053] The thickness of the first active material layer 150 and the thickness of the second active material layer 170 are equal at any position of the current collector 110. That is, the outer plane formed is a plane, so that the distance between the positive electrode sheet and the negative electrode sheet 100 is equal.

[0054] Referring to Figure 2 In the present embodiment, the ratio of the thickness of the first active material layer 150 to the thickness of the second active material layer 170 is X, and the value of X is in the range of 0 < X ≤ 10. The ratio of the thickness of the first active material layer 150 to the thickness of the second active material layer 170 gradually increases from one side of the tab 130 to the side away from the tab 130, and then gradually decreases. This can better improve the problem of lithium precipitation.

[0055] In the present embodiment, the surface densities of the first active material layer 150 and the second active material layer 170 are different.

[0056] It should be noted that the surface density ratio of the first active material layer 150 and the second active material layer 170 can be adjusted according to the performance requirements of the battery. If the battery has high requirements for fast charging performance, the surface density ratio of the second active material layer 170 can be increased. If the battery has high requirements for high capacity density, the surface density of the first active material layer 150 can be increased.

[0057] In the present embodiment, the first active material layer 150 and the second active material layer 170 are asymmetric structures. That is, the thickest first active material layer 150 is not at the center of the electrode sheet. The specific position of the thickest first active material layer 150 is determined according to the material and material properties of the current collector 110, and the electrical conductivity and difference of the current collector 110.

[0058] Please refer to the following table, through experiments, as shown in the following figure, three points L, P and Q are taken from one side of the tab 130 to the side away from the tab 130 of the negative plate 100, different thickness ratio charts are set respectively, the A group ratio increases first and then decreases from the extension direction of the tab side, the B group upper and lower layer ratio is consistent, the C group is opposite to the A group, and the thickness decreases first and then increases from the extension direction of the tab side; After 1000 cycles, it can be found that the A group has no lithium precipitation, the B group has slight lithium precipitation, and the C group has serious lithium precipitation. The experimental results show that according to the design of the present application, the lithium precipitation of the battery can be improved at the level of the electrode plate design.

[0059] Table 1: Lithium precipitation state test table of A, B and C three groups of different thickness ratio of L, P and Q

[0060]

[0061] In summary, the present application provides a negative plate 100, a battery 300 and a battery 300 pack, and the working principle and beneficial effects of the present application include:

[0062] In this embodiment, the first active material layer 150 is coated on the front and back surfaces of the current collector 110, and the first active material layer gradually thickens from one side of the tab 130 to the side away from the tab 130, and then gradually thins. The second active material layer 170 is coated on the outside of the first active material layer 150, and the thickness of the second active material layer 170 gradually thins from one side of the tab 130 to the side away from the tab 130, and then gradually thickens. In this way, the ion diffusion rate can be improved in the high potential area between the positive and negative plates 100, the ion transfer impedance is reduced, and the risk of lithium precipitation is reduced.

[0063] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements within the technical range disclosed by the present application can be easily thought by those skilled in the art, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A negative electrode sheet characterized by comprising: It comprises: a current collector (110); a tab (130) connected to one side of the current collector (110); a first active material layer (150) coated on the front and back of the current collector (110), and the thickness of the first active material layer (150) gradually increases and then gradually decreases from one side of the tab (130) to the side away from the tab (130); and, a second active material layer (170) coated on the outside of the first active material layer (150), and the thickness of the second active material layer (170) gradually decreases and then gradually increases from one side of the tab (130) to the side away from the tab (130); The particle size distribution of the first active material layer (150) is larger than that of the second active material layer (170), the first active material layer (150) is a high specific energy active material layer, and the kinetic performance of the second active material layer (170) is greater than that of the first active material layer (150); The ratio of the thickness of the first active material layer (150) to the thickness of the second active material layer (170) is X, and the value of X is in the range of 0X≤10.

2. The negative electrode sheet according to claim 1, characterized by The sum of the thickness of the first active material layer (150) and the thickness of the second active material layer (170) at any position of the current collector (110) is equal.

3. The negative electrode sheet according to claim 1, characterized by The ratio of the thickness of the first active material layer (150) to the thickness of the second active material layer (170) gradually increases and then gradually decreases from one side of the tab (130) to the side away from the tab (130).

4. The negative electrode sheet according to claim 1, characterized by The areal densities of the first active material layer (150) and the second active material layer (170) are different.

5. The negative electrode sheet according to claim 1, wherein The first active material layer (150) and the second active material layer (170) are asymmetric structures in the extension direction of the tab (130).

6. A battery comprising a shell (310), a bare cell and a pole (330), characterized in that, the bare cell comprises a positive plate, a separator and a negative plate according to any one of claims 1-5; the positive plate, the separator, the negative plate and the separator are sequentially stacked; the bare cell is installed in the shell (310), and the tab (130) is electrically connected to the pole (330).

7. A battery pack, characterized by, A plurality of batteries according to claim 6 are connected in parallel or series.

Images