Positive plate, battery cell and battery

Abstract

The utility model provides a positive plate, a battery cell and a battery. The positive plate comprises a current collector; the active material layer is coated on the current collector; one side, back to the current collector, of the active material layer is coated with the ion barrier layer, the two sides, in the width direction, of the active material layer are coated with the ion barrier layer, and the speed V1 of lithium ions passing through the ion barrier layer is smaller than the speed V2 of the lithium ions passing through the active material layer. According to the positive plate disclosed by the utility model, the lithium precipitation phenomenon on the positive plate can be reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, in particular to a positive electrode sheet, a battery core and a battery. Background Art

[0002] In the prior art, lithium-ion batteries are widely used in technical fields such as consumer electronics, new energy vehicles, and energy storage devices due to their many advantages such as high energy density, low self-discharge rate, high potential difference, and long cycle life. With the continuous iteration of technology, consumer electronics and other products have higher and higher requirements for the cycle life and fast charging capabilities of lithium batteries. In order to meet customer needs, the number of charge and discharge times and charging rates of lithium batteries are getting larger and larger. However, during high-rate charging, the current density per unit area of ​​the electrode surface is high, that is, the lithium ion concentration is high, which can easily cause lithium deposition at the edge of the battery cell, causing the battery cell performance to fail. The reason for lithium deposition is that the lithium ions at the edge of the electrode are released faster, and the negative electrode cannot react with the lithium ions in time, resulting in lithium deposition at the edge of the battery cell. Utility Model Content

[0003] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model provides a positive electrode sheet, which can reduce the lithium deposition phenomenon on the positive electrode sheet.

[0004] The utility model also provides a battery core comprising the positive electrode sheet.

[0005] The utility model also provides a battery comprising the battery core.

[0006] According to the positive electrode sheet of the embodiment of the utility model, it includes: a current collector; an active material layer, the active material layer is coated on the current collector; an ion barrier layer, the ion barrier layer is coated on the side of the active material layer facing away from the current collector, the ion barrier layer is coated on both sides of the active material layer in the width direction, and the rate V1 of lithium ions passing through the ion barrier layer is less than the rate V2 of lithium ions passing through the active material layer.

[0007] The battery cell according to the embodiment of the utility model has at least the following beneficial effects: by coating the ion barrier layer on the position on the active material layer where lithium deposition is likely to occur, the lithium ion transfer rate in a part of the active material layer is limited, so that the released lithium ions can fully pass through the diaphragm and the negative electrode sheet to react, thereby reducing the lithium deposition phenomenon on the positive electrode sheet.

[0008] According to some embodiments of the present invention, the width of the ion blocking layer is 2-5 mm.

[0009] According to some embodiments of the present invention, a protrusion is further provided on the ion blocking layer, and a surface of the ion blocking layer facing away from the current collector and the protrusion jointly define a gap for accommodating an electrolyte.

[0010] According to some embodiments of the present invention, the protrusions are in a mesh shape.

[0011] According to some embodiments of the present invention, the materials of the ion blocking layer and the protrusions both include high molecular polymers.

[0012] According to some embodiments of the present invention, a groove is formed on the active material layer, the ion blocking layer is arranged in the groove, and a side of the active material layer facing away from the current collector is flush with a side of the ion blocking layer facing away from the current collector.

[0013] According to some embodiments of the present invention, the thickness of the ion blocking layer is 1-3 um.

[0014] According to some embodiments of the present invention, the width of the active material layer is 50-135 mm.

[0015] According to other embodiments of the present invention, the battery cell comprises the positive electrode sheet described in any one of the above embodiments.

[0016] Batteries according to other embodiments of the present invention include the battery cells described in the above embodiments.

[0017] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a top view of the positive electrode sheet of the utility model;

[0019] Figure 2 A top view of a positive electrode sheet with a protrusion provided in the utility model;

[0020] Figure 3 It is a cross-sectional schematic diagram of the positive electrode sheet of the utility model in the length direction;

[0021] Figure 4 A schematic cross-sectional view of the positive electrode sheet provided with a groove in the longitudinal direction of the utility model;

[0022] Figure 5 It is a cross-sectional schematic diagram of the positive electrode sheet provided with protrusions in the length direction of the utility model.

[0023] Figure Number:

[0024] 1. Current collector; 2. Active material layer; 3. Ion barrier layer; 4. Protrusion; 5. Groove. DETAILED DESCRIPTION

[0025] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0026] In the description of the present invention, it should be understood that the descriptions involving orientation, such as the orientation or positional relationship indicated as up, down, etc., are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0027] In the description of the present utility model, "a plurality" means more than two. If there is a description of "first" or "second", it is only for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0028] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0029] Reference Figure 1 and Figure 3The positive electrode sheet in the first embodiment of the utility model comprises: a current collector 1, an ion barrier layer 3 and an active material layer 2, wherein the active material layer 2 is coated on the current collector 1. The ion barrier layer 3 is coated on a partial area of ​​the active material layer 2 facing away from the current collector 1, and the ion barrier layer 3 is used to limit the passage rate of lithium ions in the active material layer 2, that is, the rate V1 of lithium ions passing through the ion barrier layer 3 is less than the rate V2 of lithium ions passing through the active material layer 2. The material of the active material layer 2 on the positive electrode sheet mainly includes at least one of lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. The lithium ions are released by the active material layer 2 on the positive electrode sheet, and after being released by the active material layer 2, the lithium ions will pass through the diaphragm and react with the corresponding negative electrode sheet. In order to improve the performance of the battery, increase the number of times the battery is charged and discharged and the charging rate of the battery, so that the current density per unit area on the positive electrode sheet is higher, that is, the concentration of lithium ions is higher, and the higher lithium ion concentration makes it impossible for the negative electrode sheet to react with all lithium ions in time, that is, the lithium ions cannot be embedded in the negative electrode sheet in time. And the lithium ions that cannot be embedded in the negative electrode sheet will cause lithium precipitation. During the charging and discharging process of the battery, only the lithium ions released by some areas on the positive electrode sheet cannot react with the negative electrode sheet in time, so the lithium precipitation phenomenon will occur at the position of the negative electrode sheet corresponding to this area. In order to reduce the occurrence of lithium precipitation, it is necessary to limit the lithium ion release rate of this part of the area, so a lithium ion barrier layer 3 is coated in this area. Thereby, the lithium ion release rate of this area is reduced, so that the released lithium ions can fully react with the negative electrode sheet to reduce the occurrence of lithium precipitation.

[0030] During the discharge process of the battery cell, the active material on the positive electrode releases lithium ions, which pass through the electrolyte through the diaphragm and embed into the negative electrode. When the release rate of lithium ions is too fast and the lithium ions cannot embed into the negative electrode in time, lithium atoms will be precipitated at the position of the negative electrode. After the lithium atoms are formed, they cannot participate in the subsequent charge and discharge reactions. This is called lithium precipitation, which makes the energy of the battery cell ineffective.

[0031] In the prior art, since the lithium ions released rapidly and in large quantities from the positive electrode sheet cannot be embedded in the lithium ions in time, the lithium ions are precipitated on the negative electrode sheet, that is, lithium deposition occurs. In order to avoid lithium deposition at the edge of the battery cell, the active material at the edge of the positive electrode sheet is thinned to reduce the amount of active material at the edge of the positive electrode sheet. As a result, the speed at which the positive electrode sheet releases lithium ions at the edge becomes slower and the amount becomes smaller, thereby avoiding the occurrence of lithium deposition. However, in practice, thinning the edge of the positive electrode sheet not only reduces the energy density of the battery cell, but also has high process requirements and high operation difficulty, and it is impossible to ensure that the positive electrode sheet is reasonably thinned.

[0032] The ion barrier layer 3 is formed by a slurry containing a high molecular polymer. First, the slurry containing a high molecular polymer is applied to a slurry roller, and the slurry roller is used to roll the active material layer 2 in a partial area. During the rolling process, the slurry remains on the active material layer 2 and forms the ion barrier layer 3. The ion barrier layer 3 has the characteristics of limiting the release rate of lithium ions, weak ion conductivity, and no chemical reaction with the electrolyte and the active material on the positive electrode sheet.

[0033] Further, the ion barrier layer 3 is coated on both sides of the width direction of the active material layer 2. The width of the ion barrier layer 3 is 2-5mm. The position of the negative electrode sheet corresponding to the edge position of the positive electrode sheet cannot timely and sufficiently receive the lithium ions released from the positive electrode sheet, so it is easier for lithium precipitation to occur at the edge position of the negative electrode sheet. Therefore, the ion barrier layer 3 is set at the two edge positions in the width direction of the positive electrode sheet to limit the release rate of lithium ions of the active material layer 2 at the edge position of the positive electrode sheet, so that the lithium ions released by the active material at the edge position of the positive electrode sheet can fully react with the negative electrode sheet, thereby reducing the occurrence of lithium precipitation at the edge position of the negative electrode sheet. Specifically, setting the width of the ion barrier layer 3 to 2-5mm has a better effect of preventing lithium precipitation. Further, the thickness of the ion barrier layer 3 is 1-3um. The thinner ion barrier layer 3 can not only ensure the prevention of lithium precipitation of the active material on the negative electrode sheet, but also can set more active material layers 2 and active materials, thereby improving the energy density of the battery cell. The coating width of the active material layer 2 on the positive electrode sheet is 50-135 mm.

[0034] Reference Figure 2 and Figure 5 , the ion blocking layer 3 is also provided with a protrusion 4, so that the side of the ion blocking layer 3 facing away from the current collector 1 has a gap for accommodating the electrolyte. By setting the protrusion 4, there is a certain gap between the protrusions 4 on the side of the ion blocking layer 3 facing away from the current collector 1. The electrolyte can enter the gap, so as to more fully contact the active material so that the electrons can be more fully transferred. Further, the protrusion 4 is in a mesh shape. Specifically, when a slurry roller is used to roll the slurry on the active material layer 2, a mesh slurry roller with mesh grooves 5 on the surface is used to roll the slurry containing a polymer onto the active material layer 2. Therefore, when the slurry containing a polymer is coated on the active material layer 2, a mesh-shaped protrusion 4 will be left on the ion blocking layer 3. The electrolyte enters the gaps formed by the mesh protrusions 4 and fully contacts the active material on the positive electrode sheet, thereby increasing the liquid retention in the local area, ensuring the conduction of lithium ions during long cycles, and further reducing the occurrence of edge lithium deposition.

[0035] When the ion barrier layer 3 is provided, polyvinylidene fluoride is first used as a solute and N-methylpyrrolidone is used as a solvent to mix to form a required slurry, and the slurry is coated on the active material layer by a coating roller. A reticular material groove is provided on the coating surface of the coating roller, and when the slurry is provided on the coating roller, the slurry enters the material groove, and when the slurry is coated on the active material layer 2, the slurry in the material groove is coated on the active material layer together, thereby forming a reticular protrusion 4.

[0036] The material of the ion barrier layer 3 includes polyvinylidene fluoride and N-methylpyrrolidone. Polyvinylidene fluoride is used as a solute and N-methylpyrrolidone is used as a solvent for fusion to form a slurry containing a high molecular polymer. Specifically, the effect of preventing lithium precipitation achieved by different contents of polyvinylidene fluoride in the slurry is also different. The level of lithium precipitation is divided into three levels: A, B, and C from mild to severe. The method for testing the lithium precipitation phenomenon is to place a lithium-ion battery containing the above-mentioned positive electrode sheet in a constant temperature room at 25°C, let it stand for 10 minutes, charge it at a constant current of 4.5C to a voltage of 4.53V, then charge it at a constant voltage of 4.53V to a current of 0.05C, and then discharge it at a constant current of 1.0C to a voltage of 3.0V, which is a charge and discharge cycle. Repeat the charging and discharging in this way, and disassemble and observe the lithium precipitation window interface of the lithium-ion battery after 30 cycles.

[0037] Taking the positive electrode sheet without the ion barrier layer 3 as the experimental control group, the level of lithium precipitation phenomenon is C level. When the weight proportion of polyvinylidene fluoride in the slurry is 2%, the level of lithium precipitation phenomenon is C level. When the weight proportion of polyvinylidene fluoride in the slurry is 4%, the level of lithium precipitation phenomenon is B level. When the weight proportion of polyvinylidene fluoride in the slurry is 6.5%, the level of lithium precipitation phenomenon is A level. When the weight proportion of polyvinylidene fluoride in the slurry is 8%, the level of lithium precipitation phenomenon is B level. When the weight proportion of polyvinylidene fluoride in the slurry is 10%, the level of lithium precipitation phenomenon is C level. It can be concluded that when the edge of the positive electrode sheet is not coated with the second coating layer, the lithium ions are completely removed during the charging process, resulting in serious lithium precipitation at the edge of the electrode sheet, thereby affecting the performance. On the other hand, when the solid content of polyvinylidene fluoride is too high, the lithium ions cannot be removed from the front but from the edge, and the lithium precipitation is also relatively serious. Therefore, the present invention designs a pole piece with better components by combining the solid content of the polymer in the second coating zone and its coating width and thickness, thereby improving the lithium deposition at the edge of the lithium-ion battery and achieving the effect of improving battery safety. Therefore, when the weight proportion of polyvinylidene fluoride in the slurry is 6.5%, it has a better effect of preventing lithium deposition from occurring.

[0038] Reference Figure 4, the active material layer 2 is provided with a groove 5, the ion blocking layer 3 is arranged in the groove 5, and the side of the active material layer 2 facing away from the current collector 1 is flush with the side of the ion blocking layer 3 facing away from the current collector 1. The groove 5 is provided to accommodate the ion blocking layer 3, so as to avoid the surface of the positive electrode sheet being uneven after the ion blocking layer 3 is provided. After the groove 5 is provided, the side of the active material layer 2 facing away from the current collector 1 is flush with the side of the ion blocking layer 3 facing away from the current collector 1. Therefore, when the positive electrode sheet is processed into a battery cell, the positive electrode sheet in the battery cell can be more closely attached, thereby improving the energy density of the battery cell.

[0039] The battery cell manufactured by using the positive electrode sheet described in any of the above embodiments and the battery manufactured by using the battery cell can improve the problem of lithium deposition at the edge of the negative electrode sheet. At the same time, the battery has a longer service life and reduces the battery cell performance failure caused by lithium deposition during multiple charge and discharge processes.

[0040] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A positive electrode sheet, characterized in that: include: current collector; An active material layer, the active material layer being coated on the current collector; An ion barrier layer is coated on the side of the active material layer facing away from the current collector, and the ion barrier layer is coated on both sides of the active material layer in a width direction, and a rate V1 at which lithium ions pass through the ion barrier layer is less than a rate V2 at which lithium ions pass through the active material layer.

2. The positive electrode sheet according to claim 1, characterized in that: The width of the ion blocking layer is 2-5 mm.

3. The positive electrode sheet according to claim 1, characterized in that: The ion blocking layer is also provided with a protrusion, and a surface of the ion blocking layer facing away from the current collector and the protrusion together define a gap for accommodating an electrolyte.

4. The positive electrode sheet according to claim 3, characterized in that: The protrusions are in a mesh shape.

5. The positive electrode sheet according to claim 3, characterized in that: The materials of the ion blocking layer and the protrusion both include high molecular polymer.

6. The positive electrode sheet according to claim 1, characterized in that: A groove is formed on the active material layer, the ion blocking layer is arranged in the groove, and a side of the active material layer facing away from the current collector is flush with a side of the ion blocking layer facing away from the current collector.

7. The positive electrode sheet according to claim 1, characterized in that: The thickness of the ion barrier layer is 1-3 um.

8. The positive electrode sheet according to claim 1, characterized in that: The width of the active material layer is 50-135 mm.

9. A battery cell, characterized in that: The invention comprises a positive electrode sheet as claimed in any one of claims 1 to 8.

10. A battery, characterized in that: Comprising the battery cell as claimed in claim 9.

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