Negative plate, battery monomer and battery

Abstract

The utility model relates to a negative plate, a battery monomer and a battery. The negative plate comprises a current collector, a first negative active layer and a second negative active layer, the first negative active layer and the second negative active layer are stacked on at least one side of the current collector in the thickness direction of the current collector, and the second negative active layer is located between the first negative active layer and the current collector; wherein the chemical kinetics of the second negative electrode active layer is superior to that of the first negative electrode active layer, the total thickness of the first negative electrode active layer and the second negative electrode active layer is H, and H is larger than or equal to 0.05 mm and smaller than or equal to 3mm. According to the negative plate, the battery monomer and the battery provided by the invention, the precipitation of lithium dendrites can be reduced, and the thermal runaway risk is reduced.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a negative electrode, a battery cell, and a battery. Background Technology

[0002] When a lithium battery is overcharged, lithium ions continuously and excessively escape from the positive electrode active material, while the negative electrode inserts lithium ions and accepts the excess, causing lithium metal to precipitate on the surface of the negative electrode, forming lithium dendrites. These lithium dendrites can pierce the separator and trigger a short circuit between the positive and negative electrodes, leading to thermal runaway and battery failure.

[0003] Studies have shown that the precipitation of lithium dendrites on the surface of the negative electrode is due to the relatively thick active layer. As lithium ions diffuse deeper, it becomes increasingly difficult for the deeper active materials (including graphite, silicon carbide, etc.) to allow lithium ions to intercalate. Therefore, a reasonable structural design of the negative electrode is needed to improve the diffusion of lithium ions in the deeper layers, thereby reducing the precipitation of lithium dendrites. Utility Model Content

[0004] Therefore, it is necessary to provide a negative electrode, battery cell, and battery that can reduce lithium dendrite precipitation and lower the risk of thermal runaway in order to address the above problems.

[0005] This application provides a negative electrode sheet, which includes a current collector, a first negative electrode active layer and a second negative electrode active layer. The first negative electrode active layer and the second negative electrode active layer are stacked along the thickness direction of the current collector on at least one side of the current collector, and the second negative electrode active layer is located between the first negative electrode active layer and the current collector.

[0006] The chemical kinetics of the second negative electrode active layer are better than those of the first negative electrode active layer, and the total thickness of the first negative electrode active layer and the second negative electrode active layer is H, where 0.05 mm ≤ H ≤ 3 mm.

[0007] In some embodiments, the first negative electrode active layer and the second negative electrode active layer are stacked on both sides of the current collector that are opposite to each other along its thickness direction.

[0008] In some embodiments, the first negative electrode active layer includes a first negative electrode active material, and the second negative electrode active layer includes a second negative electrode active material.

[0009] The first negative electrode active material is either graphite or silicon carbon, and the second negative electrode active material is either lithium titanate-coated graphite, hard carbon-coated graphite, hard carbon, or lithium titanate.

[0010] In some embodiments, the first negative electrode active layer includes a first negative electrode active material, the second negative electrode active layer includes a second negative electrode active material, and the particle size of the second negative electrode active material is smaller than the particle size of the first negative electrode active material.

[0011] In some embodiments, the particle size of the first negative electrode active material is T1, where 8 μm ≤ T1 ≤ 20 μm, and the particle size of the second negative electrode active material is T2, where 4 μm ≤ T2 ≤ 15 μm.

[0012] In some embodiments, the thickness of the first negative electrode active layer is equal to or greater than the thickness of the second negative electrode active layer.

[0013] In some embodiments, the thickness of the first negative electrode active layer is H1, the thickness of the second negative electrode active layer is H2, and 1≤H1 / H2≤99.

[0014] In some embodiments, the negative electrode sheet is provided with a plurality of directional channels, and on the same side of the current collector, the directional channels extend from the first negative electrode active layer to the second negative electrode active layer.

[0015] A battery cell comprising a negative electrode as described in any of the above embodiments.

[0016] A battery comprising a battery cell as described in the above embodiments.

[0017] Compared with the prior art, this application has the following beneficial effects:

[0018] The aforementioned negative electrode sheet, battery cell, and battery exhibit superior chemical kinetics in the second negative electrode active layer. This improves the lithium intercalation capability of the negative electrode sheet, allowing lithium ions to intercalate into the second negative electrode active layer. Consequently, it reduces the risk of lithium metal precipitation and lithium dendrite formation on the surface of the first negative electrode active layer facing away from the current collector, effectively improving the battery's overcharge safety. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the negative electrode sheet in one embodiment of this application;

[0020] Figure 2 This is a schematic diagram of the negative electrode sheet in another embodiment of this application.

[0021] Icon labels:

[0022] 100. Negative electrode plate;

[0023] 10. Current collector; 20. First negative electrode active layer; 30. Second negative electrode active layer; 40. Directional channel;

[0024] 21. First negative electrode active material; 31. Second negative electrode active material. Detailed Implementation

[0025] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0026] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application 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 application.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0028] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0029] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0030] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0031] When a lithium battery is overcharged, lithium ions continuously and excessively escape from the positive electrode active material, while the negative electrode inserts lithium ions and accepts the excess, causing lithium metal to precipitate on the surface of the negative electrode, forming lithium dendrites. These lithium dendrites can pierce the separator and trigger a short circuit between the positive and negative electrodes, leading to thermal runaway and battery failure.

[0032] Studies have shown that the precipitation of lithium dendrites on the surface of the negative electrode is due to the relatively thick active layer. As lithium ions diffuse deeper, it becomes increasingly difficult for the deeper active materials (including graphite, silicon carbide, etc.) to allow lithium ions to intercalate. Therefore, a reasonable structural design of the negative electrode is needed to improve the diffusion of lithium ions in the deeper layers, thereby reducing the precipitation of lithium dendrites.

[0033] Please refer to the following: Figure 1 and Figure 2 To alleviate the aforementioned problems, this application designs a negative electrode 100, which includes a current collector 10, a first negative electrode active layer 20, and a second negative electrode active layer 30. The first negative electrode active layer 20 and the second negative electrode active layer 30 are stacked along the thickness direction of the current collector 10 on at least one side of the current collector 10, and the second negative electrode active layer 30 is located between the first negative electrode active layer 20 and the current collector 10. The chemical kinetics of the second negative electrode active layer 30 are superior to those of the first negative electrode active layer 20, and the total thickness of the first negative electrode active layer 20 and the second negative electrode active layer 30 is H, where 0.05 mm ≤ H ≤ 3 mm.

[0034] As an example, the first negative electrode active layer 20 and the second negative electrode active layer 30 are stacked on one side of the current collector 10 along the thickness direction, that is, the first negative electrode active layer 20 and the second negative electrode active layer 30 are stacked on one side of the current collector 10. This design can reduce the use of negative electrode active materials and reduce the manufacturing cost of the negative electrode sheet 100. Alternatively, the first negative electrode active layer 20 and the second negative electrode active layer 30 are stacked on both sides of the current collector 10 that are opposite to each other along its thickness direction. This embodiment can improve the capacity density of the battery.

[0035] The slower chemical kinetics of the negative electrode 100 refers to a decrease in the ion transport rate within the negative electrode 100 during charging and discharging, thus reducing the battery's charging and discharging efficiency. Conversely, faster chemical kinetics of the negative electrode 100 refers to an increase in the ion transport rate within the negative electrode 100 during charging and discharging, thus improving the battery's charging and discharging efficiency. The chemical kinetics of the negative electrode 100 are influenced by various factors, including temperature, electrolyte properties, and the active material of the negative electrode.

[0036] The chemical kinetics of the first negative electrode active layer 20 are slower, while the chemical kinetics of the second negative electrode active layer 30 are faster. Since the chemical kinetics of the second negative electrode active layer 30 are better than those of the first negative electrode active layer 20, the lithium ion transport speed in the second negative electrode active layer 30 is faster than that in the first negative electrode active layer 20.

[0037] Specifically, the first negative electrode active layer 20 includes a first negative electrode active material 21, which is either graphite or silicon carbon. Graphite and silicon carbon have slower chemical kinetics, but they have higher specific capacities, which can significantly improve the energy density of the battery. As an example, the first negative electrode active layer 20 can be formed by coating and drying a slurry formed by mixing 85% to 99% by mass of the first negative electrode active material 21, 0.5% to 5% by mass of sulfur / polyacrylonitrile copolymer (commonly known as SP), 0.25% to 5% by mass of sodium carboxymethyl cellulose (CMC-Na), and 0.25% to 5% by mass of styrene-butadiene rubber (SBR) binder.

[0038] Specifically, the second negative electrode active layer 30 includes a second negative electrode active material 31, which is any one of lithium titanate-coated graphite, hard carbon-coated graphite, hard carbon, and lithium titanate. The specific capacity of lithium titanate-coated graphite, hard carbon-coated graphite, hard carbon, and lithium titanate is relatively lower than that of graphite and silicon carbon, but their chemical kinetics are faster, which can improve the lithium intercalation capability of the negative electrode sheet 100, facilitating the deep intercalation of lithium ions and thus improving the overcharge safety of the battery. The chemical kinetics, ranked from fastest to slowest, are: lithium titanate > hard carbon > lithium titanate-coated graphite > hard carbon-coated graphite > graphite > silicon carbon. Furthermore, lithium titanate has a higher cost and lower capacity; hard carbon's cycle performance is worse than graphite but similar to silicon carbon. Therefore, lithium titanate-coated graphite and hard carbon-coated graphite can be used to reduce the introduction of lithium titanate and hard carbon, thereby reducing the loss of battery performance.

[0039] As an example, the second negative electrode active layer 30 can be formed by coating and drying a slurry formed by mixing 85% to 99% by mass of the second negative electrode active material 31, 0.5% to 5% by mass of sulfur / polyacrylonitrile copolymer, 0.25% to 5% by mass of sodium carboxymethyl cellulose, and 0.25% to 5% by mass of styrene-butadiene rubber adhesive.

[0040] Preferably, taking into account cost, battery performance, and overcharge safety, the first negative electrode active material 21 is graphite or silicon-carbon, and the second negative electrode active material 31 can be graphite coated with hard carbon.

[0041] In the prior art, each side of the current collector 10 of the negative electrode sheet 100 has only one negative electrode active layer, and the thickness of the negative electrode active layer is also H, 0.05mm≤H≤3mm, and the negative electrode active material in the negative electrode active layer is either graphite or silicon carbide. In this application, the total thickness of the first negative electrode active layer 20 and the second negative electrode active layer 30 of the negative electrode sheet 100 is H, 0.05mm≤H≤3mm. It can be understood that the total thickness of the first negative electrode active layer 20 and the second negative electrode active layer 30 in this application is unchanged compared with the thickness of the negative electrode active layer in the prior art, which is equivalent to replacing the part of the negative electrode active layer near the current collector 10 in the prior art with the second negative electrode active layer 30, and the chemical kinetics of the second negative electrode active layer 30 are superior. This improves the lithium intercalation capability of the negative electrode 100, allowing lithium ions to be intercalated into the second negative electrode active layer 30. This reduces the risk of lithium metal precipitating on the surface of the first negative electrode active layer 20 away from the current collector 10, thus effectively improving the overcharge safety of the battery.

[0042] In some embodiments, the particle size of the second negative electrode active material 31 is smaller than that of the first negative electrode active material 21.

[0043] The particle size of the second negative electrode active material 31 in the second negative electrode active layer 30 also has a significant impact on overcharge improvement. This is because the smaller the particle size of the second negative electrode active material 31, the faster the lithium ion diffusion, i.e., the better the chemical kinetics. Therefore, by designing the particle size of the second negative electrode active material 31 to be smaller than that of the first negative electrode active material 21, the chemical kinetics of the second negative electrode active layer 30 are improved, thus further increasing the possibility of deep lithium ion intercalation and reducing the risk of lithium dendrite precipitation.

[0044] Furthermore, in some embodiments, the particle size of the first negative electrode active material 21 is T1, 8μm≤T1≤20μm, and the particle size of the second negative electrode active material 31 is T2, 4μm≤T2≤15μm.

[0045] The particle sizes of both the first negative electrode active material 21 and the second negative electrode active material 31 need to be within a reasonable range. Particle sizes that are too small or too large will have a significant negative impact on battery performance. By designing the particle size range of the first negative electrode active material 21 to be 8μm to 20μm and the particle size range of the second negative electrode active material 31 to be 4μm to 15μm, the lithium intercalation capability of the negative electrode sheet 100 can be improved, and the negative impact of the particle size of the first and second negative electrode active materials 21 on battery performance can be reduced, resulting in a battery with superior electrical performance.

[0046] In some embodiments, the thickness of the first negative electrode active layer 20 is equal to or greater than the thickness of the second negative electrode active layer 30. When the total thickness of the first negative electrode active layer 20 and the second negative electrode active layer 30 remains constant, the thickness percentage of the first negative electrode active layer 20 will also be greater than or equal to that of the second negative electrode active layer 30. The greater the thickness percentage of the first negative electrode active layer 20, the higher the energy density of the battery and the better the energy storage effect.

[0047] Furthermore, in some embodiments, the thickness of the first negative electrode active layer 20 is H1, and the thickness of the second negative electrode active layer 30 is H2, where 1 ≤ H1 / H2 ≤ 99. The larger the thickness ratio of the first negative electrode active layer 20 to the second negative electrode active layer 30, the higher the proportion of the first negative electrode active layer 20's thickness, resulting in higher battery energy density and better energy storage performance. Different battery systems have different requirements for the thickness of the first negative electrode active layer 20 and the second negative electrode active layer 30; therefore, for different battery systems, 1 ≤ H1 / H2 ≤ 99 can be designed.

[0048] In some embodiments, the negative electrode 100 is provided with a plurality of oriented channels 40, which extend from the first negative electrode active layer 20 to the second negative electrode active layer 30 on the same side of the current collector 10. The design of the oriented channels 40 can reduce the tortuosity of lithium-ion diffusion, further improve the lithium-ion diffusion capability of the first negative electrode active layer 20 and the second negative electrode active layer 30, and reduce the risk of lithium dendrite precipitation.

[0049] The directional channel 40 can be a straight channel or a curved channel. A straight channel is a channel that extends linearly from the first negative electrode active layer 20 to the second negative electrode active layer 30. The extension direction of the straight channel can coincide with or intersect the thickness direction of the current collector 10. A curved channel is a channel that extends in a tortuous manner from the first negative electrode active layer 20 to the second negative electrode active layer 30.

[0050] Specifically, in an embodiment where a first negative electrode active layer 20 and a second negative electrode active layer 30 are provided on each side of the current collector 10, a plurality of directional channels 40 may be evenly distributed in the first negative electrode active layer 20 and the second negative electrode active layer 30 on each side.

[0051] In some embodiments, the oriented channels 40 can be formed by evaporation of the pore-forming agent during baking. As an example, 0.25%-5% by mass of a pore-forming agent can be added to the slurry forming the second negative electrode active layer 30, and then the slurry is dried to form the oriented channels 40. The pore-forming agent comprises one or more of the following substances: NH4NO3, NaHCO3, NH4HS, NH4HCO3, and LiHCO3. During the coating and drying process of the slurry, the pore-forming agent decomposes into gas at high temperature. The gas evaporates from the second negative electrode active layer 30 to the first negative electrode active layer 20 and finally diffuses into the air. The path taken by the gas during evaporation forms the oriented channels 40.

[0052] In summary, by designing the first negative electrode active layer 20 and the second negative electrode active layer 30, and by rationally designing the oriented channels 40, the lithium intercalation kinetics of the negative electrode 100 under overcharge conditions can be improved, thereby reducing the precipitation of lithium dendrites and lowering the possibility of thermal runaway. The negative electrode 100 in this application can intercalate lithium ions more quickly during charging, reducing the formation of lithium dendrites on the surface of the first negative electrode active layer 20, improving overcharge safety, and also enhancing the fast-charging capability of the lithium battery.

[0053] This application also provides a battery cell comprising a positive electrode, a separator, and a negative electrode 100 as described in any of the above embodiments. The positive electrode, separator, and negative electrode 100 are alternately stacked or wound to form the electrode assembly of the battery cell. The battery cell of this application has the effects of any of the above embodiments, and therefore will not be described again here.

[0054] This application also provides a battery comprising a single battery cell as described in the above embodiments. The battery in this application has the effects of any of the above embodiments, and therefore will not be repeated here.

[0055] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector (10), a first negative electrode active layer (20), and a second negative electrode active layer (30). The first negative electrode active layer (20) and the second negative electrode active layer (30) are stacked along the thickness direction of the current collector (10) on at least one side of the current collector (10), and the second negative electrode active layer (30) is located between the first negative electrode active layer (20) and the current collector (10). Among them, the chemical kinetics of the second negative electrode active layer (30) are better than the chemical kinetics of the first negative electrode active layer (20), and the total thickness of the first negative electrode active layer (20) and the second negative electrode active layer (30) is H, 0.05mm≤H≤3mm; The negative electrode sheet is provided with a plurality of directional channels (40), and on the same side of the current collector (10), the directional channels (40) extend from the first negative electrode active layer (20) to the second negative electrode active layer (30).

2. The negative electrode sheet according to claim 1, characterized in that, The current collector (10) has a first negative electrode active layer (20) and a second negative electrode active layer (30) stacked on both sides opposite to each other along its thickness direction.

3. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active layer (20) includes a first negative electrode active material (21), and the second negative electrode active layer (30) includes a second negative electrode active material (31). The particle size of the second negative electrode active material (31) is smaller than that of the first negative electrode active material (21).

4. The negative electrode sheet according to claim 3, characterized in that, The particle size of the first negative electrode active material (21) is T1, 8μm≤T1≤20μm, and the particle size of the second negative electrode active material (31) is T2, 4μm≤T2≤15μm.

5. The negative electrode sheet according to claim 1, characterized in that, The thickness of the first negative electrode active layer (20) is equal to or greater than the thickness of the second negative electrode active layer (30).

6. The negative electrode sheet according to claim 5, characterized in that, The thickness of the first negative electrode active layer (20) is H1, and the thickness of the second negative electrode active layer (30) is H2, 1≤H1 / H2≤99.

7. A single battery cell, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 6 above.

8. A battery, characterized in that, Includes the battery cell as described in claim 7 above.

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