Negative plate, battery and battery pack
By designing an asymmetric active material layer on the negative electrode, the lithium plating problem during high-rate charging of lithium batteries was solved, the ion diffusion rate and the energy density of the cell were improved, and a balance between high specific energy and fast charging was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BATTEROTECH CO LTD
- Filing Date
- 2023-11-13
- Publication Date
- 2026-05-05
AI Technical Summary
When existing lithium batteries are charged at high rates, lithium metal deposits are prone to form lithium dendrites on the negative electrode, increasing the risk of battery thermal runaway.
A negative electrode is designed with a first active material layer and a second active material layer coated on the current collector. The thickness of the first layer gradually increases and decreases from the tab side, while the thickness of the second layer gradually increases and decreases from the tab side. The particle size distribution is different, resulting in different kinetic and specific energy performances, forming an asymmetric structure.
It improves the ion diffusion rate, reduces ion transfer resistance, lowers the risk of lithium plating, and enables the cell to achieve both high specific energy and fast charging performance.
Smart Images
Figure CN121983546A_ABST
Abstract
Description
[0001] This invention is a divisional application of patent application No. 2023115065826, filed on November 13, 2023, entitled "Negative Electrode Sheet, Battery and Battery Pack". Technical Field
[0002] This invention relates to the field of secondary batteries, and more specifically, to a negative electrode, a battery, and a battery pack. Background Technology
[0003] A secondary battery, also known as a rechargeable battery or storage battery, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Utilizing the reversibility of chemical reactions, a new battery can be constructed; that is, after a chemical reaction converts into electrical energy, the electrical energy can be used to repair the chemical system, and then the chemical reaction can be converted back into electrical energy. These batteries are widely used in new energy vehicles and energy storage devices.
[0004] With the development of fast charging technology, existing lithium batteries are prone to lithium metal deposition on the tabs of the positive and negative electrodes when charged at high rates. This can lead to the formation of lithium dendrites, which may increase the risk of battery thermal runaway. Summary of the Invention
[0005] The object of the present invention includes, for example, providing a negative electrode, a battery, and a battery pack that can improve the problem of lithium plating in negative electrodes.
[0006] The embodiments of the present invention can be implemented as follows: In a first aspect, this application provides a negative electrode sheet, comprising: current collector; A tab connected to one side of the current collector is used for electrical connection with the terminal of the battery cell. A first active material layer is coated on the front and back sides of the current collector, and the thickness of the first active material layer gradually increases from one side of the electrode tab toward the side away from the electrode tab, and then gradually decreases. And, a second active material layer, which is coated on the outside of the first active material layer, and the second active material layer extends from one side of the tab toward the side away from the tab and the thickness gradually decreases first and then gradually increases; The particle size distribution of the first active material layer is greater than that of the second active material layer.
[0007] In an optional embodiment, the second active material layer (170) has a higher degree of graphitization and a larger specific surface area than the first active material layer.
[0008] In an optional embodiment, the first active material layer is a high specific energy active material layer; the kinetic performance of the second active material layer is greater than that of the first active material layer.
[0009] In an optional embodiment, the slurry of the first active material layer is prepared by mixing large and small particle-blended graphite, binder, conductive agent and first solvent in a certain proportion; the slurry of the second active material layer is prepared by mixing small particle-blended graphite, binder, conductive agent and second solvent in a certain proportion.
[0010] In an optional embodiment, the thickness of the first active material layer is equal to the sum of the thicknesses of the second active material layer at any location of the current collector.
[0011] 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 the value of X is in the range of 0 < X ≤ 10.
[0012] In an optional implementation, X gradually increases from one side of the tab toward the side away from the tab, and then gradually decreases.
[0013] In an optional embodiment, the first active material layer and the second active material layer have an asymmetrical structure in the extension direction of the tab.
[0014] Secondly, this embodiment also provides a battery, including a casing, a bare cell, and terminals, wherein the bare cell includes a positive electrode, a separator, and a negative electrode as described in any of the optional embodiments above; The positive electrode, the separator, the negative electrode, and the separator are stacked in sequence; The bare battery cell is installed inside the housing, and the tab is electrically connected to the terminal post.
[0015] Thirdly, this embodiment also provides a battery pack, including a plurality of batteries as described in the above optional embodiments, wherein the plurality of batteries are connected in parallel or in series.
[0016] The beneficial effects of the negative electrode sheet, battery, and battery pack provided by the embodiments of the present invention include, for example: This application coats a first active material layer on both the front and back sides of the current collector, with the thickness of the first active material layer gradually increasing from the side of the electrode towards the side away from the electrode, and then gradually decreasing. A second active material layer is coated on the outside of the first active material layer, with the thickness of the second active material layer gradually decreasing from the side of the electrode towards the side away from the electrode, and then gradually increasing. This increases the ion diffusion rate in the high-potential region between the positive and negative electrodes, reduces ion transfer resistance, and lowers the risk of lithium plating. The particle size distribution of the first active material layer is larger than that of the second active material layer, resulting in a first active material layer with better kinetics and a second active material layer with high specific energy, allowing the overall cell to achieve both high specific energy and fast charging. Attached Figure Description
[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the battery structure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the negative electrode sheet provided in an embodiment of the present invention; Figure 3 Local voltage curves of the positive and negative electrodes during battery charging; Figure 4 The effective voltage distribution between the positive and negative electrodes when charging a battery.
[0019] Icons: 100-Negative electrode; 110-Current collector; 130-Taper; 150-First active material layer; 170-Second active material layer; 300-Battery; 310-Casing; 330-Terminal post. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0021] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0022] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.
[0023] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.
[0024] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.
[0025] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.
[0026] Please refer to Figure 1 This embodiment provides a battery pack that can serve as the power source for new energy vehicles. It can also be used in energy storage devices for electrical energy storage, and further applied to power tools to provide them with power.
[0027] Typically, a battery pack includes a housing, multiple battery banks 300, and a battery management component. The multiple battery banks 300 are usually connected in series or parallel to form one or more battery modules. The battery modules are installed inside the housing. The battery management component is electrically connected to the batteries to monitor parameters such as voltage and temperature of each battery bank 300.
[0028] In this embodiment, the battery 300 includes a casing 310, a bare cell, and terminals 330. The bare cell includes a positive electrode, a separator, and a negative electrode 100. The positive electrode, separator, negative electrode 100, and separator are stacked sequentially. The bare cell is installed inside the casing 310, and the tabs 130 are electrically connected to the terminals 330.
[0029] Generally, the terminal 330 includes a positive terminal 330 and a negative terminal 330. The positive terminal 330 and the negative terminal 330 are installed opposite each other on both sides of the housing 310. The tab 130 connected to the positive electrode plate is electrically connected to the positive terminal 330, and the tab 130 connected to the negative electrode plate 100 is connected to the negative terminal 330.
[0030] The inventors discovered that during the charging process of battery 300, lithium ions are released from the positive electrode, pass through the separator, and then embed into the active material of the negative electrode. Lithium deposition on the negative electrode 100 is mainly due to excessive current, leading to excessive local polarization and a low negative electrode potential, reaching the deposition potential of metallic lithium, thus depositing metallic lithium on the surface of the negative electrode. The main reason for this lithium deposition phenomenon is the voltage drop between the positive and negative electrodes 100 of the lithium battery 300, resulting in uneven potential distribution on the electrodes. Therefore, at the same charging rate, the potential on the side corresponding to the positive and negative tabs 130 of the negative electrode 100 is relatively large, leading to lithium deposition.
[0031] To address the aforementioned issues, this embodiment proposes a negative electrode that can improve the lithium plating problem caused by potential difference.
[0032] Reference Figure 2 In this embodiment, the negative electrode 100 includes a current collector 110, a tab 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 sides of the current collector 110, and the thickness of the first active material layer gradually increases from the side of the tab 130 toward the side away from the tab 130, and then gradually decreases. 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 decreases from the side of the tab 130 toward the side away from the tab 130, and then gradually increases.
[0033] In this embodiment, a first active material layer 150 is coated on both the front and back sides of the current collector 110, and the thickness of the first active material layer 150 gradually increases from the side of the tab 130 toward the side away from the tab 130, and then gradually decreases. A 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 decreases from the side of the tab 130 toward the side away from the tab 130, and then gradually increases. This increases the ion diffusion rate in the high-potential region between the positive and negative electrodes 100, reduces ion transfer resistance, and lowers the risk of lithium plating.
[0034] In this embodiment, 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.
[0035] When charging battery 300, the voltage applied to the positive and negative terminals 330 refers to the potential difference applied to the positive and negative terminals 330 of the cell, which is Vapp. Ignoring the resistance at the connection points, this voltage corresponds to the potential difference between the positive and negative tabs 130. Each electrode experiences a voltage drop at the tab 130 and at locations farther from the electrode; generally, the voltage drop is greater the further away from the tab 130.
[0036] Effective voltage refers to the voltage between the positive and negative electrodes 100 at any specific location within the battery cell, denoted as Ve. In a Cartesian coordinate system, the X and Y axes are parallel to the electrode direction, and the Z axis is perpendicular to the electrode direction. At the point where the effective voltage is measured, the positive and negative electrodes share the same X and Y coordinates, but their Z-axis coordinates are different.
[0037] Figure 3 This is a graph showing the local voltage curves of the positive and negative electrodes during charging, with the upper part of the horizontal axis representing the positive electrode and the lower part representing the negative electrode. Charging methods can include constant voltage charging, constant current charging, pulse charging, or a combination of these methods. Because the current flowing through the current collector 110 generates a voltage drop, the potential V1 at the positive electrode tab 130 gradually decreases towards the corresponding position at the negative electrode tab 130, reaching V2 at the corresponding position, forming the local voltage curve of the positive electrode. Similarly, the potential V4 at the negative electrode tab 130 gradually decreases towards the corresponding position at the positive electrode tab 130, reaching V3 at the corresponding position. The voltage applied to the tabs 130 of the positive and negative electrodes 100 is V4 - V1. The local voltage corresponding to the same X value at the positive and negative electrodes 100 is the difference between the curve and the corresponding position, called the effective voltage Ve. Figure 3 The curve shown.
[0038] Figure 4 As can be seen, the effective voltage of the positive and negative electrode plates 100 varies with their positions, with a higher effective voltage closer to the tabs 130. Therefore, based on the effective voltage distribution of the positive and negative electrode plates 100 in the battery 300, the high effective voltage and fast ion transport rate at the tabs 130 necessitate the placement of more kineticly efficient negative electrode materials in these areas to enhance ion diffusion rates, reduce ion transfer resistance, and lower the risk of lithium plating. At lower potentials, more high-energy-density active materials can be incorporated to increase the cell's energy density. This allows the cell to achieve both high energy density and fast charging.
[0039] It should be further explained that, in order to meet the above requirements, the second active material layer 170 is a negative electrode material with good kinetics, such as a negative electrode material with high graphitization degree, large specific area and small polarization, and the first active material layer 150 is a negative electrode material with high specific energy, such as a negative electrode material with wide particle size distribution.
[0040] Reference Figure 2In this embodiment, the particle size distribution of the first active material layer 150 is larger than that of the second active material layer 170. This results in a first active material layer 150 with better kinetics and a second active material layer 170 with higher specific energy.
[0041] For example, the second active material layer 170 is prepared by mixing large and small particle blended graphite, binder, conductive agent, and first solvent in a certain proportion to prepare the slurry of the first active material layer 150. The first active material layer 150 is prepared by mixing small particle blended graphite, binder, conductive agent, and second solvent in a certain proportion to prepare the slurry of the second active material layer 170. This results in a second active material layer 170 with good kinetics and a first active material layer 150 with high specific energy.
[0042] Of course, the first active material layer 150 and the second active material layer 170 can also be formed using other main 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.
[0043] At any position on the current collector 110, the sum of the thickness of the first active material layer 150 and the thickness of the second active material layer 170 is equal. That is, the formed outer plane is a plane, thereby making the distance between the positive electrode and the negative electrode 100 equal.
[0044] Reference Figure 2 In this 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, where X ranges from 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 the side of the tab 130 towards the side away from the tab 130, and then gradually decreases. This can better improve the lithium plating problem.
[0045] In this embodiment, the areal densities of the first active material layer 150 and the second active material layer 170 are different.
[0046] It should be noted that the areal 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 cell. If the battery cell has high requirements for fast charging performance, the areal density ratio of the second active material layer 170 can be increased. If the battery cell requires high energy density, the areal density of the first active material layer 150 can be increased.
[0047] In this embodiment, the first active material layer 150 and the second active material layer 170 have an asymmetrical structure. That is, the thickest part of the first active material layer 150 is not at the center of the electrode. Specifically, its location needs to be determined based on the material and properties of the current collector 110, as well as the conductivity and differences of the current collector 110.
[0048] Please refer to the table below. Experiments show that, as illustrated in the diagram, three points L, P, and Q were taken on the negative electrode 100 from the side of the tab 130 towards the side away from the tab 130, with different thickness ratios as shown in the diagram. In group A, the ratio first increases and then decreases along the direction extending from the tab side; in group B, the ratios of the upper and lower layers are the same; in group C, the opposite of group A, the ratio first decreases and then increases along the direction extending from the tab side. After 1000 cycles, it was found that group A had no lithium plating, group B had slight lithium plating, while group C had severe lithium plating. The experimental results indicate that, according to the design of this invention, lithium plating in the battery cell can be improved at the electrode design level.
[0049] Table 1: Lithium plating state test results at L, P, and Q locations under different thickness ratios in the three comparative test groups (A, B, and C).
[0050] In summary, the embodiments of the present invention provide a working principle and beneficial effects of a negative electrode 100, a battery 300, and a battery 300 pack, including: In this embodiment, a first active material layer 150 is coated on both the front and back sides of the current collector 110, and the thickness of the first active material layer 150 gradually increases from the side of the tab 130 toward the side away from the tab 130, and then gradually decreases. A 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 decreases from the side of the tab 130 toward the side away from the tab 130, and then gradually increases. This increases the ion diffusion rate in the high-potential region between the positive and negative electrodes 100, reduces ion transfer resistance, and lowers the risk of lithium plating.
[0051] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A negative electrode sheet, characterized in that, include: Current collector(110); A tab (130) is connected to one side of the current collector (110), and the tab (130) is used to electrically connect to the terminal of the battery cell; A first active material layer (150) is coated on the front and back sides of the current collector (110), and the thickness of the first active material layer (150) gradually increases from one side of the tab (130) toward the side away from the tab (130) and then gradually decreases. And a second active material layer (170), which is coated on the outside of the first active material layer (150), and the second active material layer (170) extends from one side of the tab (130) toward the side away from the tab (130) and its thickness gradually decreases and then gradually increases. The particle size distribution of the first active material layer (150) is greater than that of the second active material layer (170).
2. The negative electrode sheet according to claim 1, characterized in that, The second active material layer (170) has a higher degree of graphitization and a larger specific surface area than the first active material layer (150).
3. The negative electrode sheet according to claim 1, characterized in that, The first active material layer (150) is a high specific energy active material layer; the kinetic performance of the second active material layer (170) is greater than that of the first active material layer (150).
4. The negative electrode sheet according to claim 1, characterized in that, The slurry of the first active material layer (150) is prepared by mixing large and small particle graphite, binder, conductive agent and first solvent in a certain proportion; the slurry of the second active material layer (170) is prepared by mixing small particle graphite, binder, conductive agent and second solvent in a certain proportion.
5. The negative electrode sheet according to claim 1, characterized in that, At any location of the current collector (110), the thickness of the first active material layer (150) is equal to the sum of the thicknesses of the second active material layer (170).
6. The negative electrode sheet according to claim 1, characterized in that, 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.
7. The negative electrode sheet according to claim 6, characterized in that, The value of X gradually increases from one side of the tab (130) toward the side away from the tab (130), and then gradually decreases.
8. The negative electrode sheet according to claim 1 or 2, characterized in that, The first active material layer (150) and the second active material layer (170) have an asymmetrical structure in the extension direction of the tab (130).
9. A battery, comprising a casing (310), bare cells, and terminals (330), characterized in that, The bare cell includes a positive electrode, a separator, and a negative electrode as described in any one of claims 1-8; The positive electrode, the separator, the negative electrode, and the separator are stacked in sequence; The bare battery cell is installed inside the housing (310), and the tab (130) is electrically connected to the terminal (330).
10. A battery pack, characterized in that, It includes multiple batteries as described in claim 9, wherein the multiple batteries are connected in parallel or in series.