Positive plate and lithium ion battery

Abstract

The utility model relates to the field of lithium ion batteries, and discloses a positive plate and a lithium ion battery, the positive plate comprises a positive current collector, at least one side surface of the positive current collector is provided with a PET (Polyethylene Terephthalate) coating, the PET coating is provided with a positive active material layer, and the positive active material layer is shorter than the PET coating. The positive plate is helpful for improving the safety performance of the lithium ion battery, is relatively low in cost, and does not cause energy density loss.

Description

Technical Field

[0001] The utility model relates to the technical field of lithium-ion batteries, and particularly relates to a positive electrode sheet and a lithium-ion battery. Background Art

[0002] With the rapid development of the times and technology, lithium-ion batteries have become the mainstream choice in the market due to their high energy density, long cycle life and relatively light mass. However, with the popularization of the application of lithium-ion batteries, their safety issues have become increasingly prominent and have become one of the focuses of public attention. In the safety performance test of lithium-ion batteries, the needle penetration test is an important method for evaluating the internal short-circuit tolerance of the battery, and its results are directly related to the safety of the battery in actual use. The needle penetration test simulates the internal short-circuit situation that may occur under extreme conditions (such as puncture in a traffic accident) of the battery to evaluate the thermal runaway risk of the lithium battery.

[0003] For existing lithium-ion battery positive electrode sheets, flame retardants or ceramic coatings are mostly selected as protection means. However, the ceramic coating usually covers a part of the positive electrode active material slurry layer, resulting in a decrease in the overall energy density of the battery cell. Moreover, under the battery charge and discharge cycles, vibration or extreme use conditions, the ceramic coating is likely to fall off, and the fallen ceramic particles are very likely to scratch the separator due to battery vibration or extrusion, resulting in direct contact between the positive and negative electrodes and causing a short circuit between the positive and negative electrodes, thereby triggering battery thermal runaway or even explosion. Flame retardants are usually synthesized from rare or high-cost chemical substances, so their prices are often high. The large-scale use of flame retardants in the production of lithium-ion batteries will significantly increase the cost of lithium batteries, which is not conducive to the commercial promotion and large-scale application of lithium batteries. Summary of the Utility Model

[0004] The purpose of the utility model is to at least solve one of the problems existing in the prior art, and provide a positive electrode sheet and a lithium-ion battery. The positive electrode sheet helps to improve the safety performance of the lithium-ion battery, has a relatively low cost, and will not cause energy density loss.

[0005] To achieve the above purpose, on the one hand, the utility model provides a positive electrode sheet including a positive electrode current collector, at least one side of the positive electrode current collector is provided with a PET coating, a positive electrode active material layer is provided on the PET coating, and the length of the positive electrode active material layer is less than the length of the PET coating.

[0006] Optionally, the thickness of the PET coating is 2 - 4 μm.

[0007] Optionally, PET coatings are provided on both sides of the positive electrode current collector.

[0008] Optionally, the thickness of the positive electrode current collector is 6 - 8 μm.

[0009] Optionally, a high-temperature tape is provided in the area of the tail of the positive electrode sheet where the positive electrode active material is not coated.

[0010] Optionally, the thickness of the high-temperature tape is 0.025 mm.

[0011] In a second aspect of the present invention, a lithium-ion battery is provided, and the lithium-ion battery has the above positive electrode sheet.

[0012] Through the above technical solution, a layer of high-temperature resistant PET coating is applied on the surface of the positive electrode current collector. The PET coating can effectively prevent the positive electrode current collector from being exposed due to extrusion deformation and directly contacting the negative electrode sheet, resulting in a short circuit, thereby forming a thermal runaway and causing the battery to catch fire and explode. At the same time, the PET coating has good toughness, is resistant to friction and extrusion, and can effectively slow down the damage of foreign objects to the cell structure in the initial stage when the cell is punctured, reducing the short circuit of the cell structure caused by external force damage, and significantly improving the overall safety performance of the battery. Description of the Drawings

[0013] Figure 1 is a schematic structural diagram of a positive electrode sheet provided by the present invention;

[0014] Description of the Reference Numerals

[0015] 1. Positive electrode current collector; 2. PET coating; 3. Positive electrode active material layer. Detailed Embodiments

[0016] The following will describe in detail the specific embodiments of the present invention with reference to the drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0017] As Figure 1 shown, the present invention provides a positive electrode sheet, including a positive electrode current collector 1. At least one side surface of the positive electrode current collector 1 is provided with a PET coating 2, and a positive electrode active material layer 3 is provided on the PET coating 2. The length of the positive electrode active material layer 3 is less than the length of the PET coating 2.

[0018] The positive electrode current collector 1 in the present invention can be made of a material with high conductivity, good mechanical strength and corrosion resistance, such as aluminum foil.

[0019] In the present invention, the prepared PET solution is used with a high-precision extrusion coater to uniformly coat the PET solution on the surface of the positive electrode current collector 1 (such as aluminum foil). The extrusion coater ensures uniform and controllable thickness of the PET coating 2 by precisely controlling the pressure and speed of the coating head. After coating, the positive electrode foil with the PET coating 2 is baked, and the baking temperature and time need to be optimized according to the specific formula of the PET solution and the material of the foil to ensure that the PET coating 2 is completely cured and tightly attached to the foil.

[0020] It is understandable that the preparation method of the PET solution is to dissolve an appropriate amount of PET (polyethylene terephthalate) particles in a suitable solvent, such as dimethylformamide (DMF) or acetone, to form a uniform PET solution, and this PET solution needs to ensure good fluidity and stability during the subsequent coating process.

[0021] The positive electrode active material used in the present utility model includes lithium cobaltate, PVDF6020, SP, NMP materials, etc. According to specific requirements, the positive electrode active material, conductive agent, and binder are mixed evenly in a certain proportion to form a slurry, which is then coated on the PET coating 2 and undergoes processes such as drying and compaction to form the positive electrode active material layer 3.

[0022] The length of the positive electrode active material layer 3 is less than the length of the PET coating 2, which reduces the usage amount of the positive electrode active material while ensuring the performance of the positive electrode sheet and reduces the material cost.

[0023] It is understandable that the inventive concept of the present utility model is to coat the PET coating 2 on the surface of the positive electrode current collector 1, effectively isolating the direct contact risk between the aluminum foil and the negative electrode, significantly improving the needle-punching safety performance of the battery, and effectively preventing the occurrence of short circuit and thermal runaway even under extreme conditions.

[0024] The PET coating 2 has a moderate and uniform thickness, and the positive electrode active material layer 3 covers the PET coating 2, avoiding the problem of energy density loss that may be caused by the ceramic coating covering a part of the positive electrode active material layer 3 in the prior art. At the same time, the light weight characteristic of the PET material itself also helps to maintain the overall energy density of the battery.

[0025] Compared with using high-cost materials such as flame retardants, the PET coating 2 has significant cost advantages. This helps to reduce the production cost of the battery and improve the market competitiveness.

[0026] In addition, it should be noted that due to the high-temperature resistance of the PET material, it will not dissolve prematurely even at 120°C, and most of the temperature points at which needle-punching occurs and explosions and fires start are basically from 120°C to 130°C, basically avoiding the short-circuit thermal runaway problem caused by the exposure of the positive electrode current collector 1 (aluminum foil) due to high-temperature deformation. At the same time, due to the good friction resistance and extrusion resistance of the PET coating 2, it can slow down the damage to the battery structure caused by external impacts to a certain extent, which helps to extend the service life of the battery.

[0027] In the utility model, the thickness of the PET coating 2 is 2 to 4 μm. When the thickness of the PET coating 2 exceeds 4 μm, the mechanical brittleness of the coating will increase, and its flexibility and folding resistance will be reduced. During the manufacture and use of the battery, a coating that is too thick may be more prone to cracking or peeling, thereby affecting the overall performance and safety of the battery. A coating that is too thick may also increase the weight and volume of the battery, which is not conducive to the energy density and lightweight design of the battery. Moreover, a PET coating 2 with a thickness exceeding 4 μm will increase the transmission path length of lithium ions, resulting in an increase in the internal resistance of the battery, and reducing the charging and discharging efficiency and power performance of the battery.

[0028] It is understandable that one of the main functions of PET coating 2 is to improve the safety performance of the battery, especially in the puncture test. A thinner coating (such as less than 2 μm) cannot provide sufficient physical barrier effect and cannot effectively prevent the occurrence of short circuits. When the battery is subjected to external impacts such as puncture, the thinner coating may be more likely to break or penetrate, leading to safety problems such as internal short circuits and thermal runaway.

[0029] In addition, from a process perspective, a coating that is too thin may be difficult to ensure uniformity and stability during the coating process. A coating that is too thin may easily lead to problems such as local coating omissions or uneven thickness, affecting the performance and consistency of the battery. A coating that is too thin is also more susceptible to damage or destruction during subsequent processing (such as rolling, slitting, and film making).

[0030] In summary, the thickness of the PET coating 2 is set between 2 μm and 4 μm, which is a relatively reasonable range. This range not only takes into account the effect of the coating on improving the safety performance of the battery, but also takes into account the requirements of the coating's mechanical properties, electrochemical properties, and process feasibility.

[0031] In the present invention, both sides of the positive electrode current collector 1 are provided with a PET coating 2. The PET coating 2 is provided on both sides, which can more effectively prevent short circuits and safety hazards.

[0032] In the present utility model, the thickness of the positive current collector 1 is 6 to 8 μm. As the thickness of the positive current collector 1 decreases, its overall weight will also decrease accordingly. In lithium-ion batteries, the reduction in the weight proportion of the current collector means that more space can be transferred to active materials, thereby increasing the energy density of the battery. The lightweight design enables the battery to store more electrical energy without increasing the overall volume or weight. The thinner positive current collector 1 can better adapt to the volume changes of the battery during the charging and discharging process, reducing material fatigue and performance degradation caused by volume expansion or contraction.

[0033] In the present utility model, a high-temperature tape is provided in the region of the tail of the positive electrode sheet where the positive electrode active material is not coated. The high-temperature tape can isolate the region of the tail of the positive electrode sheet where the active material is not coated, preventing this region from coming into direct contact with the negative electrode or other conductive materials, thereby effectively preventing the occurrence of short-circuit phenomena. During the production, transportation, and use of the battery, the electrode sheets may be subjected to various mechanical forces, and the high-temperature tape can provide additional protection and reduce the possibility of damage to the electrode sheets. By precisely controlling the coating area of the positive electrode active material and the setting position of the high-temperature tape, the internal structure of the battery can be optimized, maximizing the corresponding area between the positive and negative electrode sheets, and thus improving the energy density of the battery.

[0034] Preferably, the thickness of the high-temperature tape is 0.025 mm. A thinner high-temperature tape is more easily bent and can fit closely to the tail of the positive electrode sheet, ensuring tight contact between the high-temperature tape and the positive electrode sheet, without occupying too much internal space of the battery, which helps to improve the energy density and overall performance of the battery.

[0035] In the second aspect of the present utility model, a lithium-ion battery is provided. The lithium-ion battery has the above-mentioned positive electrode sheet. By arranging the above-mentioned positive electrode sheet in the lithium-ion battery, it can effectively improve the thermal runaway problem caused by short-circuiting between the positive and negative electrodes under extreme conditions such as in a nail penetration test or external force damage, which helps to improve the safety of the lithium-ion battery. The lithium-ion battery mainly refers to cylindrical lithium batteries and soft-pack lithium batteries.

[0036] The present utility model also provides a method for treating a positive electrode sheet to improve the safety performance of a cylindrical lithium battery. Specifically, the treatment method includes:

[0037] Step 1: Coat the slurry of the PET coating 2 on the surface of the positive electrode current collector 1, and then perform baking.

[0038] In this embodiment, first, according to the design requirements, PET (polyethylene terephthalate) particles are dissolved in a suitable solvent, such as dimethylformamide (DMF) or acetone, to form a uniform and transparent PET solution. Using a high-precision extrusion coater, the PET solution is uniformly coated on the surface of the positive electrode current collector 1 (such as aluminum foil). The extrusion coater ensures a uniform and controllable thickness of the PET coating 2 by precisely controlling the pressure and speed of the coating head. According to the preferred conditions, the thickness of the PET coating 2 should be controlled between 2 μm and 4 μm to achieve the best heat resistance and insulation effect. After coating, the positive electrode current collector 1 with the PET coating 2 is baked, and the baking temperature and time need to be optimized according to the specific formula of the PET solution and the material of the positive electrode current collector 1 to ensure that the PET coating 2 is completely cured and tightly adheres to the positive electrode current collector 1.

[0039] Step 2: Perform a gluing treatment on the region of the tail of the positive electrode sheet with a length of 16 - 20 mm where the positive electrode active material is not coated.

[0040] In this embodiment, a high-temperature tape with a thickness of 0.025 mm is selected. This high-temperature tape has good high-temperature resistance and bonding strength, and can maintain a stable insulation effect during the use of the battery. The high-temperature tape is precisely cut to an appropriate length and attached to the designated position of the bare foil at the tail of the positive electrode sheet. During the encapsulation process, it is necessary to ensure that the high-temperature tape is flat without wrinkles and the edges are well sealed.

[0041] Step 3: Coating, rolling, slitting, sheet making of the processed positive electrode sheet, and winding it with the negative electrode sheet and the separator to form an electric core.

[0042] In this embodiment, an extrusion coater is used to coat the positive electrode active material slurry on the cured positive electrode current collector 1 of the PET coating 2. The slurry is usually composed of lithium cobaltate (as the active material), PVDF 6020 (as the binder), SP (conductive carbon black), and NMP (N-methylpyrrolidone, as the solvent) and other components mixed in a certain proportion. By precisely controlling the coating parameters, it is ensured that the thickness of the active material layer is uniform and the coverage is complete. After coating, the positive electrode sheet is subjected to a rolling process to compact the active material layer and improve the density and conductivity of the electrode sheet. The hot pressing method can be used during the rolling process to improve the plasticity and fluidity of the material by heating the roller, making the rolling effect better. Subsequently, the rolled electrode sheet is subjected to a slitting process and cut into strips with a specified width according to the battery design requirements. The slitted positive electrode sheet is subjected to sheet making operations, including cutting, welding and pressing the tabs, etc., to prepare a positive electrode sheet that meets the requirements of battery assembly. Finally, the positive electrode sheet, the negative electrode sheet and the separator are wound into an electric core, and the battery is made by injecting liquid, pre-charging, high-temperature storage, formation and grading.

[0043] In the embodiment of the present utility model, a PET coating 2 is provided between the positive electrode current collector 1 and the positive electrode active material layer 3. In the needle penetration test of the lithium-ion battery or in the case of mechanical damage, it is possible to avoid direct contact between the aluminum foil of the positive electrode sheet and the negative electrode graphite, prevent the occurrence of internal short circuit in the battery, and thus improve the safety of the lithium-ion battery.

[0044] According to the structure of the above positive electrode sheet, Example 1 and Comparative Example 1 are set.

[0045] Example 1:

[0046] The battery is made according to the methods of the above Step 1 to Step 3.

[0047] Comparative Example 1:

[0048] The difference between Comparative Example 1 and the above Example 1 is that Comparative Example 1 does not have a PET coating 2, and only a positive electrode active material layer 3 is coated on the positive electrode current collector 1.

[0049] The needle puncture and extrusion tests were carried out on the above-mentioned Example 1 and Comparative Example 1, and the test results are shown in Table 1:

[0050] Table 1

[0051]

[0052] Among them, for the needle puncture test, after the battery is charged to full charge according to the standard charge and discharge procedure, the battery is fixed on the fixture, and a steel needle with a diameter of 3-5 mm is used to strongly pierce it radially. The tested battery should not catch fire or explode, but leakage and exhaust are allowed.

[0053] Among them, for the extrusion test, the battery is extruded according to the extrusion test method specified in GJB2374-1997, and the tested battery should not catch fire or explode.

[0054] From the passing rates of the needle puncture test in Table 1, it can be seen that the passing rates of the needle puncture and extrusion tests in Example 1 are both 100%, the passing rate of the needle puncture test in Comparative Example 1 is 40%, and the passing rate of the extrusion test is 0%. The passing rates of the needle puncture and extrusion tests in Example 1 are both higher than those in Comparative Example 1, effectively improving the safety of the lithium-ion battery.

[0055] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Within the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention. To avoid unnecessary repetition, the present invention will not separately describe various possible combinations. But these simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A positive electrode sheet, comprising a positive electrode current collector (1), characterized in that: At least one side of the positive electrode current collector (1) is provided with a PET coating (2), a positive electrode active material layer (3) is provided on the PET coating (2), and the length of the positive electrode active material layer (3) is shorter than the length of the PET coating (2).

2. The positive electrode sheet according to claim 1, characterized in that: The thickness of the PET coating (2) is 2-4 μm.

3. The positive electrode sheet according to claim 1, characterized in that: Both sides of the positive electrode current collector (1) are provided with a PET coating (2).

4. The positive electrode sheet according to claim 1, characterized in that: The thickness of the positive electrode current collector (1) is 6 to 8 μm.

5. The positive electrode sheet according to claim 1, characterized in that: A high-temperature tape is provided at the tail of the positive electrode sheet in an area not coated with the positive electrode active material.

6. The positive electrode sheet according to claim 5, characterized in that: The thickness of the high temperature tape is 0.025 mm.

7. A lithium ion battery, characterized in that: The lithium-ion battery has the positive electrode sheet according to any one of claims 1 to 6.

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