Preparation method of double-layer composite pole piece with PTC (Positive Temperature Coefficient) effect and battery thereof

Abstract

The invention provides a preparation method of a double-layer composite pole piece with a PTC (Positive Temperature Coefficient) effect and a battery thereof, and the preparation method comprises the following steps: step S1, adding a conductive material into vulcanized silicone rubber by adopting a solution mixing method, and forming composite coating slurry after cross-linking reaction, the mass percentage of the conductive material to the vulcanized silicone rubber being 1%-20%; s2, coating an aluminum foil with the composite coating slurry to serve as a prime coat of a positive electrode; and S3, after the prime coat coating is coated and dried, coating a positive electrode material to form the double-layer composite pole piece. According to the invention, the problem of cracking of the positive electrode slurry can be effectively avoided; on the basis, the PTC characteristic of the composite coating slurry is realized through the specific mass percent of the conductive material and the vulcanized silicone rubber, so that the resistance of the composite coating slurry is rapidly increased when the temperature is increased, the internal resistance is rapidly improved, the short-circuit current is reduced, and the heat release is inhibited when the battery is in thermal runaway; and the safety performance of the double-layer composite pole piece and the battery thereof is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of an electrode sheet, in particular to a preparation method of a double-layer composite electrode sheet with PTC effect, and further relates to a battery adopting the preparation method of the double-layer composite electrode sheet with PTC effect. BACKGROUND

[0002] Lithium ion batteries have been widely used in many fields due to their high energy density and long cycle life. However, the safety problem of lithium ion batteries has always been the focus of the industry. Traditional lithium ion batteries use flammable organic electrolyte and polyethylene (PE) or polypropylene (PP) separator. These materials have flammable organic electrolyte, and are prone to shrinkage at high temperatures, which may also cause positive and negative short circuits, thereby further exacerbating the risk of thermal runaway. Thermal runaway not only causes the internal temperature of the battery to rise sharply, but also may cause smoke, fire and even explosion, etc. Therefore, developing a coating with “fuse” function that can effectively increase the internal resistance of the battery, reduce the short-circuit current and inhibit the release of heat at high temperatures is crucial to improve the safety of lithium ion batteries.

[0003] Currently, polyvinylidene fluoride (PVDF) is commonly used as a binder for the positive electrode material of lithium ion batteries. Although PVDF has good chemical stability and mechanical properties, it has good solubility in N-methyl pyrrolidone (NMP), which can easily cause cracking of the positive electrode slurry during battery manufacturing. The problem of cracking of the positive electrode slurry not only affects the electrochemical performance of the battery, but also can cause smoking or fire in extreme conditions such as needle puncture, resulting in safety risks of the battery. Therefore, how to solve the technical problem of cracking of the positive electrode slurry and develop a new coating material that is insoluble in NMP and has PTC (positive temperature coefficient) characteristics has become a key technical problem that needs to be solved in the current development of lithium ion battery technology. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a double-layer composite electrode sheet preparation method that can solve the technical problem of cracking of the positive electrode slurry in the prior art and has PTC effect, thereby effectively improving the safety performance of the battery. On this basis, a battery adopting the double-layer composite electrode sheet preparation method with PTC effect is further provided.

[0005] To this end, the present application provides a double-layer composite electrode sheet preparation method with PTC effect, comprising the following steps: Step S1, the conductive material is added to the vulcanized silicone rubber by solution mixing method, and the composite coating slurry is formed after cross-linking reaction, wherein the mass percentage between the conductive material and the vulcanized silicone rubber is 1%-20%; the composite coating slurry refers to the slurry of the composite coating after adding the vulcanized silicone rubber; Step S2, the composite coating slurry is coated on the aluminum foil as the bottom coating of the positive electrode; Step S3, after the bottom coating is coated and dried, the positive electrode material is coated to form a double-layer composite electrode sheet.

[0006] The further improvement of the present application is that, in the step S1, the conductive material and the vulcanized silicone rubber are prepared into a composite coating slurry with PTC characteristics by solution mixing method with at least one of pentane, n-hexane and cyclohexane as a solvent.

[0007] The further improvement of the present application is that, in the step S2, the coating viscosity of the bottom coating is 100-3000 mPa·s, and the coating thickness is 5-50 μm.

[0008] The further improvement of the present application is that, the conductive material includes at least one of graphite powder, conductive carbon black, carbon nanotube and graphene, and the conductive carbon black is SP conductive carbon black or super carbon black.

[0009] The further improvement of the present application is that, the softening temperature of the vulcanized silicone rubber is 100-120°C.

[0010] The further improvement of the present application is that, in the step S2, after the composite coating slurry is coated on the aluminum foil, first layer drying is performed at a temperature of 80-120°C; in the step S3, after the positive electrode material is coated, second layer drying is performed at a temperature of 80-120°C.

[0011] The further improvement of the present application is that, it further includes step S4, resistance test is performed on the formed double-layer composite electrode sheet at different temperatures for a preset number of times in a preset temperature range, the preset temperature range is set to 20-120°C, and the preset number of times is 300-400 times; after the resistance test for the preset number of times, if the PTC effect of the double-layer composite electrode sheet still exists, it is judged that the electrode sheet is qualified.

[0012] The further improvement of the present application is that, the molecular weight of the vulcanized silicone rubber is adjusted to meet the Curie point temperature requirement of the double-layer composite electrode sheet, and the molecular weight of the vulcanized silicone rubber ranges from 50,000 to 200,000; specifically, the vulcanized silicone rubber includes at least one of dimethyl silicone rubber, methyl vinyl silicone rubber, methyl phenyl silicone rubber, fluorosilicone rubber, nitrile silicone rubber, ethyl silicone rubber and ethyl phenylene silicone rubber.

[0013] The further improvement of the present application is that in the step S1, the resistance jump amplitude of the double-layer composite tab at Curie point temperature is satisfied by adjusting the mass percentage of the conductive material, and the mass percentage between the conductive material and the vulcanized silicone rubber is 2%-10%.

[0014] The present application also provides a battery adopting the double-layer composite tab with PTC effect prepared by the method as described above and taking the double-layer composite tab as the positive tab of the battery.

[0015] Compared with the prior art, the present application has the beneficial effects that: the conductive material is first added to the vulcanized silicone rubber by the solution mixing method, and the composite coating slurry formed after the cross-linking reaction, and then the composite coating slurry is coated on the aluminum foil as the bottom coating layer of the positive electrode, thereby being able to guarantee excellent chemical stability and thermal stability, and the prepared composite coating slurry is insoluble in N-methyl pyrrolidone (NMP), thereby being able to effectively avoid the problem of positive electrode slurry cracking; on this basis, the specific mass percentage between the conductive material and the vulcanized silicone rubber realizes the PTC characteristics of the composite coating slurry, so that the resistance rapidly increases when the temperature rises, thereby rapidly increasing the internal resistance when the battery is out of control, reducing the short-circuit current, and inhibiting heat release, and therefore, the safety performance of the double-layer composite tab and the battery thereof can be significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the working process schematic diagram of an embodiment of the present application; Figure 2 is the schematic diagram of testing cycle performance of an embodiment of the present application. DETAILED DESCRIPTION

[0017] In the description of the present application, if "several" is involved, it means one or more; if "multiple" is involved, it means two or more; if "greater than", "less than", "exceeds" is involved, it should be understood as not including the number itself; if "above", "below", "within" is involved, it should be understood as including the number itself. If "first", "second" and the like are involved, it should be understood as only used for distinguishing the same or similar technical feature names, and cannot be understood as implying / indicating the relative importance of the technical features, cannot be understood as implying / indicating the number of technical features, and cannot be understood as implying / indicating the sequence of technical features.

[0018] The preferred embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0019] As shown in Figure 1 The present embodiment provides a double-layer composite tab with PTC effect, which comprises the following steps: Step S1, the conductive material is added to the vulcanized silicone rubber by solution mixing method, and the composite coating slurry is formed after cross-linking reaction, wherein the mass percentage between the conductive material and the vulcanized silicone rubber is 1%-20%; Step S2, the composite coating slurry is coated on the aluminum foil as the bottom coating of the positive electrode; Step S3, after the bottom coating is coated and dried, the positive electrode material is coated to form a double-layer composite electrode sheet.

[0020] First of all, it needs to be pointed out that the reason for using vulcanized silicone rubber in this embodiment is that other support materials such as PVDF can be dissolved in the positive electrode slurry solvent NMP, which will cause the positive electrode slurry to crack when it is coated for the second time.

[0021] Secondly, it also needs to be pointed out that by precisely controlling the mass percentage between the conductive material and the vulcanized silicone rubber, the PTC (positive temperature coefficient) property of the composite coating slurry is realized. When the temperature rises, the resistance of the composite coating slurry increases rapidly by 2-3 orders of magnitude, which in turn rapidly increases the internal resistance when the battery is out of control, reduces the short-circuit current, and suppresses the heat release.

[0022] The above two points are particularly crucial for solving the technical problem of positive electrode slurry cracking in the prior art, and do not belong to the usual technical means of those skilled in the art.

[0023] More preferably, the mass percentage between the conductive material and the vulcanized silicone rubber is optimized to 2%-10%, because within this temperature range, the conductive material particles can be in good contact at normal battery operating temperature (-10℃ to 80℃), thus maintaining good conductivity; when the temperature exceeds the Curie point temperature of the material, the support vulcanized silicone rubber softens, causing poor contact between the conductive material particles, rapid decrease in conductivity, and increase in resistance. If the mass percentage of the conductive material is too low, the internal resistance of the battery will be high at normal operating temperature (-10℃ to 80℃), thus affecting the normal use of the battery; on the contrary, if the mass percentage of the conductive material is too high, when the temperature exceeds the Curie point temperature, the resistance will not change much, thus failing to protect the battery and improve safety. Therefore, the materials used to prepare the composite coating slurry and the mass percentage of various materials are key factors in solving the technical problem of positive electrode slurry cracking in the prior art.

[0024] Therefore, in step S1 of this embodiment, the mass percentage of the conductive material is adjusted to meet the resistance mutation amplitude of the double-layer composite electrode sheet at the Curie point temperature, and the mass percentage between the conductive material and the vulcanized silicone rubber is 2%-10%. At this time, both the conductivity and the safety can be well guaranteed, achieving a better balance between various properties.

[0025] In this embodiment, the conductive material is added to the vulcanized silicone rubber by solution mixing method to form a composite coating slurry with positive temperature coefficient after cross-linking reaction, and then the composite coating slurry is coated on the positive aluminum foil as a primer coating. The resistance test of the foil with primer coating at different temperatures shows that the resistance increases by 2-3 orders of magnitude when the temperature exceeds the Curie point, which has obvious PTC effect. The detailed test / experiment process and data will be described later by tables and data.

[0026] Therefore, in the overall technical scheme of this embodiment, the conductive material is added to the vulcanized silicone rubber by solution mixing method to form a composite coating slurry, and then the composite coating slurry is coated on the aluminum foil as a primer coating of the positive electrode, which can ensure excellent chemical stability and thermal stability, and since the prepared composite coating slurry is insoluble in N-methyl pyrrolidone (NMP), the problem of positive electrode slurry cracking can be effectively avoided. On this basis, the PTC characteristics of the composite coating slurry are realized by the specific mass percentage between the conductive material and the vulcanized silicone rubber, so that the resistance increases rapidly when the temperature rises, thereby rapidly increasing the internal resistance when the battery is out of control, reducing the short-circuit current, and inhibiting heat release, thereby significantly improving the safety performance of the double-layer composite electrode sheet and the battery.

[0027] Preferably, in the step S1 of this embodiment, at least one of pentane, n-hexane and cyclohexane is used as a solvent to prepare the composite coating slurry with PTC characteristics by solution mixing method, so that the prepared composite coating slurry is insoluble in N-methyl pyrrolidone (NMP), thus the technical problem of positive electrode slurry cracking caused by the solubility of PVDF in NMP in the prior art can be effectively avoided.

[0028] Preferably, in the step S2 of this embodiment, the coating viscosity of the primer coating is 100-3000 mPa·s. The reason for this design is that if the coating viscosity is less than 100 mPa·s, the coating will be uneven and the coating tail will be caused due to the too low coating viscosity; if the coating viscosity is greater than 3000 mPa·s, there will be a problem of slurry coating difficulty, therefore, the uniformity and stability of the primer coating can be ensured within the coating viscosity range of 100-3000 mPa·s. The coating thickness is 5-50 μm, which aims to ensure the uniformity and stability of the primer coating while ensuring the battery resistance within the specified range.

[0029] Preferably, the conductive material includes at least one of graphite powder, conductive carbon black, carbon nanotube (CNT) and graphene; and the conductive carbon black is SP conductive carbon black (i.e. Super P, SP for short) or super carbon black. The reason is that the conductive material based on the above-mentioned at least one of graphite has stable performance, excellent conductive performance, and can be uniformly mixed with the vulcanized silicone rubber at a specific ratio, thereby ensuring performance consistency.

[0030] Preferably, the softening temperature of the vulcanized silicone rubber in the embodiment is 100-120℃. The reason for this design in the embodiment is that in actual application, the battery is generally required to work normally below 85℃, and the softening temperature (i.e. Curie point temperature) of the vulcanized silicone rubber mixed with the conductive material needs to be higher than the normal working temperature of the battery, otherwise it will cause the internal resistance of the battery to be too high when working, thereby affecting its normal use. However, the softening temperature (i.e. Curie point temperature) cannot be too high, if the Curie point temperature exceeds 120℃, the SEI film and the negative electrode will have reacted with the electrolyte, and a large amount of heat will be generated, which will not achieve the purpose of protecting the battery.

[0031] It is worth noting that in order to ensure that the vulcanized silicone rubber softens at 100-120℃, the embodiment preferably adopts the following preferred solutions: first, different organic groups linked to silicon atoms are selected to effectively control the softening temperature of the vulcanized silicone rubber. Specifically, the vulcanized silicone rubber preferably includes at least one of dimethyl silicone rubber, methyl vinyl silicone rubber, methyl phenyl silicone rubber, fluorosilicone rubber, nitrile silicone rubber, ethyl silicone rubber and ethyl phenylene silicone rubber; second, room temperature vulcanized silicone rubber with a molecular weight of 5-200,000 is selected. The room temperature vulcanized silicone rubber in this molecular weight range can soften at a temperature of 100-120℃; third, the vulcanization conditions are adjusted. By adjusting the type and amount of vulcanizing agent and the vulcanization time, the softening temperature of the vulcanized silicone rubber can be controlled to a certain extent. For example, an addition vulcanization system (platinum catalyst) is selected to generate Si-C-Si flexible bonds, which are more prone to chain segment slipping at low temperatures than the rigid C-C bonds of peroxide vulcanization. Fourth, a plasticizer or softening agent is added. For example, hydroxyl silicone oil is added in an amount of 5-8 phr (the amount refers to the number of parts per 100 parts of base polymer), which can be inserted between molecular chains to weaken the van der Waals force and reduce the softening point by 15-25℃, thereby softening in the range of 100-120℃.

[0032] In step S2, the composite coating slurry is coated on the aluminum foil, and then first layer drying is performed at a temperature of 80-120°C. In step S3, after the positive electrode material is coated, second layer drying is performed at a temperature of 80-120°C. The first layer refers to the bottom coating, referred to as the bottom layer, i.e. the coating of the composite coating slurry; the second layer refers to the positive electrode material coating, also referred to as the upper layer. The reason for this design in the present embodiment is that if the drying temperature is lower than 80°C, incomplete solvent volatilization will occur, affecting the electrical performance of the electrode sheet; and if the drying temperature is higher than 120°C, excessive solvent volatilization will occur, the electrode sheet coating will crack, also affecting the electrical performance of the electrode sheet.

[0033] Preferably, the present embodiment further comprises step S4, resistance testing of the formed double-layer composite electrode sheet is performed a preset number of times at different temperatures within a preset temperature range, the preset temperature range is set to 20-120°C, and the preset number of times is 300-400 times; after the preset number of times of resistance testing, if the PTC effect of the double-layer composite electrode sheet still exists, the electrode sheet is determined to be qualified.

[0034] More preferably, in step S4, resistance testing of the formed double-layer composite electrode sheet is performed a preset number of times in a high-low temperature cycle staggered manner within a preset temperature range. The specific testing method is as follows: within a range of 20-120°C, high-low temperature cycle staggered testing is performed at a certain preset temperature difference (the preset temperature difference can be set and adjusted according to actual conditions, such as 10°C or 20°C, etc.), by default, from 20°C to 120°C, then decreasing to 20°C according to the preset temperature difference, and the cycle is repeated until the preset number of times of testing is completed. After the preset number of times of resistance testing is completed, if the PTC effect of the double-layer composite electrode sheet still exists, the electrode sheet is determined to be qualified.

[0035] The advantages of the high-low temperature cycle staggered test in this embodiment are as follows: first, simulating the actual use environment, the high-low temperature cycle staggered test can more realistically simulate the temperature changes that the battery may encounter in the actual use process, including rapid changes from low temperature to high temperature and repeated temperature cycles; this test method can effectively evaluate the stability and reliability of the double-layer composite tab under different temperature conditions, ensuring that it can work normally in actual application. Second, comprehensively evaluate the PTC effect, by conducting high-low temperature cycle staggered test in the range of 20-120°C, the PTC effect of the double-layer composite tab at different temperature points can be comprehensively evaluated, which helps to ensure that the tab can maintain stable PTC characteristics in the entire working temperature range, so as to play a role in time in the case of battery thermal runaway and other extreme conditions, and improve the safety of the battery. Third, detect the durability of the material, by multiple high-low temperature cycle staggered tests (300-400 times), the durability of the double-layer composite tab under repeated temperature changes can be detected. If the PTC effect still exists after such a large number of high-low temperature cycles, it is enough to show that the tab has good durability and stability, and can maintain performance unchanged in long-term use.

[0036] The reasons for selecting high-low temperature cycle staggered test in the range of 20-120°C in this embodiment are as follows: first, covering the battery working temperature range, the temperature range of 20-120°C covers the temperature range of lithium ion battery under normal use and extreme conditions; 20°C represents the working temperature of the battery at room temperature, and 120°C is close to the upper limit of the temperature of the battery in the case of thermal runaway and other extreme conditions; by testing in this temperature range, it can be ensured that the double-layer composite tab can work normally in the entire possible working temperature range. Second, ensure safety and reliability, testing in the temperature range of 20-120°C can ensure that the double-layer composite tab can maintain PTC effect under the normal use temperature of the battery and the possible high temperature extreme conditions, thereby effectively improving the safety and reliability of the battery.

[0037] In this embodiment, a layer of positive electrode material is coated on the foil coated with a primer coating for testing, and it is found that the tab resistance increases significantly at the same Curie point temperature, and the tab resistance can decrease rapidly when the temperature is below the Curie point temperature. If the PTC effect still exists after 300 cycles at a temperature of 20-120°C, it means that the double-layer composite tab is a qualified tab, and the double-layer composite tab will not affect the internal resistance of the battery below the Curie temperature when assembled into a soft package battery.

[0038] The embodiment also provides a battery prepared by using the double-layer composite tab with PTC effect prepared by the method as described above, and the double-layer composite tab is used as the positive electrode tab of the battery, thereby solving the problem of positive electrode slurry cracking in the prior art.

[0039] To prove the performance of the double-layer composite electrode tab and the battery prepared in the embodiment, a needle puncture experiment is performed on the prepared battery by using a 5mm steel needle. It is verified by the experiment that the double-layer composite electrode tab and the battery prepared in the embodiment will not cause smoking or fire in the case of needle puncture and other extreme conditions, which well guarantees the safety performance of the battery.

[0040] Further, the performance of the double-layer composite electrode tab prepared in the embodiment under different material and process conditions will be verified by a comparative experiment, especially the PTC effect and the high-low temperature cycle test stability. Details are shown in the following table.

[0041] Technical Solution Ambient temperature tab resistance (Ω) High temperature tab resistance (Ω) High-low temperature cycle times Example 1 SP and vulcanized silicone rubber between the mass percentage of 6%, 10w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 10um 0.0241 173.8 350 Example 2 SP and vulcanized silicone rubber between the mass percentage of 2%, 10w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 10um 0.0282 171.7 300 Example 3 SP and vulcanized silicone rubber between the mass percentage of 10%, 10w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 10um 0.0317 170.4 270 Example 4 SP and vulcanized silicone rubber between the mass percentage of 6%, 10w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 5um 0.0416 165.7 285 Example 5 SP and vulcanized silicone rubber between the mass percentage of 6%, 10w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 30um 0.0445 161.2 300 Example 6 SP and vulcanized silicone rubber between the mass percentage of 6%, 10w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 50um 0.0473 160.3 288 Comparative Example 1 SP and vulcanized silicone rubber between the mass percentage of 6%, 5w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 10um 0.0253 168.8 200 Comparative Example 2 SP and vulcanized silicone rubber between the mass percentage of 6%, 20w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 10um 0.0258 150.7 245 Comparative Example 3 SP and vulcanized silicone rubber between the mass percentage of 6%, 50w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 10um 0.0241 140.9 266 Comparative Example 4 CNT and vulcanized silicone rubber between the mass percentage of 6%, 10w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 10um 0.0220 1.266 150 Comparative Example 5 Graphene and vulcanized silicone rubber between the mass percentage of 6%, 10w molecular weight of vulcanized silicone rubber, the bottom layer coating thickness 10um 0.0229 3.618 200 Comparative Example 6 Conventional single-layer tab 0.0143 0.1744 /

[0042] In the above table, examples 1-6 show the experimental data of the double-layer composite electrode tab of the present application. Specifically: First, the electrode tab resistance at room temperature. The electrode tab resistance of examples 1-6 at room temperature is between 0.0241Ω and 0.0473Ω, showing good conductivity.

[0043] Second, the electrode tab resistance at high temperature. The electrode tab resistance of examples 1-6 at high temperature increases significantly, ranging from 160.3Ω to 173.8Ω, indicating that these electrode tabs have obvious PTC effect, which can rapidly increase the resistance when the temperature rises, thereby reducing the short-circuit current and inhibiting heat release.

[0044] Third, the high-low temperature cycle number. The electrode tabs of examples 1-6 show good stability in the high-low temperature cycle test at 20-120°C, with a cycle number between 270 and 350, indicating that these electrode tabs can still maintain stable PTC characteristics under repeated temperature changes, with good durability.

[0045] In the above table, comparative examples 1-3 show the experimental data of comparative examples using different molecular weight of vulcanized silicone rubber. Specifically: First, the electrode tab resistance at room temperature. The electrode tab resistance of comparative examples 1-3 at room temperature is slightly higher than that of examples 1, but is still within a reasonable range.

[0046] Second, the electrode tab resistance at high temperature. The electrode tab resistance of comparative examples 1-3 at high temperature is significantly lower than that of examples 1-6, indicating that the PTC effect is weaker. In particular, comparative example 3 has the lowest resistance, but also has the lowest high-low temperature cycle number, indicating that its durability is poor.

[0047] Third, the high-low temperature cycle number. The electrode tabs of comparative examples 1-3 do not perform as well as examples 1-6 in the high-low temperature cycle test, with a cycle number between 200 and 266, indicating that different molecular weight of vulcanized silicone rubber has a significant impact on the PTC effect and durability of the electrode tab.

[0048] In the above table, Comparative Examples 4-5 show experimental data using different conductive materials as comparative examples, specifically: First, the resistance of the electrode at room temperature, the electrode of Comparative Examples 4 and 5 has a lower resistance at room temperature, but is significantly lower than Examples 1-6, indicating that it has better conductivity.

[0049] Second, the resistance of the electrode at high temperature, the electrode of Comparative Examples 4 and 5 has a significantly lower resistance at high temperature than Examples 1-6, especially Comparative Example 4, which has a high-temperature resistance of only 1.266 Ω, indicating that its PTC effect is very weak and almost negligible. The PTC effect of Comparative Example 5 is slightly better, but still much lower than Examples 1-6.

[0050] Third, the number of high-low temperature cycles, the electrode of Comparative Examples 4 and 5 performs poorly in high-low temperature cycle tests, with cycle numbers of 150 and 200, respectively, indicating that different conductive materials have a significant impact on the PTC effect and durability of the electrode.

[0051] In the above table, Comparative Example 6 shows experimental data of a conventional single-layer electrode as a comparative example, specifically: First, the resistance of the electrode at room temperature, the single-layer electrode of Comparative Example 6 has the lowest resistance at room temperature, which is 0.0143 Ω, indicating that it has very good conductivity.

[0052] Second, the resistance of the electrode at high temperature, the single-layer electrode of Comparative Example 6 has a resistance of only 0.1744 Ω at high temperature, indicating that it has no PTC effect and cannot increase the resistance when the temperature rises, thus cannot provide additional safety protection.

[0053] Third, the number of high-low temperature cycles, the single-layer electrode of Comparative Example 6 is not subjected to high-low temperature cycle tests, indicating that it is not suitable for scenarios that require PTC effect.

[0054] In summary, from the experimental data, it can be seen that the double-layer composite electrode of the present application has good conductivity at room temperature and significant PTC effect at high temperature, which can rapidly increase the resistance when the temperature rises, reduce the short-circuit current, and suppress heat release. In addition, these double-layer composite electrodes show good stability and durability in high-low temperature cycle tests. In contrast, different molecular weight of vulcanized silicone rubber and different conductive materials have a significant impact on the PTC effect and durability of the electrode. Although the conventional single-layer electrode has good conductivity, it lacks PTC effect and cannot provide additional safety protection. Therefore, the double-layer composite electrode prepared by the present application has a significant advantage in improving the safety and reliability of lithium-ion batteries.

[0055] Figure 2The resistance change of the battery with the PTC material of the application added is shown in the graph. The horizontal axis represents the cycle number, ranging from 0 to 350, and the vertical axis represents the resistance value, in ohms (Ω), ranging from 0 to 12000 Ω.

[0056] Figure 2 The experimental data of Example 1 show the resistance change of the battery with the PTC material of the application added during the cycle process. It can be seen from Figure 2 that with the increase of the cycle number, the resistance value of the double-layer composite tab and the battery prepared by the application remains relatively stable, with slight fluctuations, but the overall trend is smooth, indicating that the addition of the PTC material has little effect on the cycle performance of the battery.

[0057] Figure 2 Comparative Example 6 shows the resistance change of the battery without the PTC material of the application added in the same cycle test. The resistance value of Comparative Example 6 also shows stability, similar to Example 1, indicating that under the test conditions, the addition of the PTC material does not negatively affect the cycle stability of the battery.

[0058] From the experimental results of Figure 2 , the resistance value of the battery with the PTC material of the application added does not have significant difference compared with the battery without the PTC material after more than 300 cycles. This indicates that the PTC material of the application can provide additional thermal protection function without affecting the cycle performance of the battery, thereby improving the safety of the battery. The application of this material is expected to enhance the self-protection ability of the battery under overheating conditions without sacrificing the performance of the battery, reducing the risk of thermal runaway, which is of great significance to improve the safety performance of the battery.

[0059] The above is a further detailed description of the application in combination with specific preferred embodiments, and the specific implementation of the application should not be limited to these descriptions. For ordinary skilled persons in the technical field to which the application belongs, without departing from the concept of the application, a number of simple deductions or substitutions can be made, which should be considered within the protection scope of the application.

Claims

1. A method for preparing a double-layer composite electrode sheet having a PTC effect, characterized by, The method comprises the following steps: S1, a conductive material is added to the vulcanized silicone rubber by a solution mixing method, and a composite coating slurry is formed after a cross-linking reaction, wherein the mass percentage between the conductive material and the vulcanized silicone rubber is 1%-20%; S2, the composite coating slurry is coated on an aluminum foil as a base coating layer of a positive electrode; S3, after the base coating layer is coated and dried, a positive electrode material is coated to form a double-layer composite electrode sheet.

2. The method of manufacturing a double-layer composite electrode sheet having a PTC effect according to claim 1, wherein In the step S1, the conductive material and the vulcanized silicone rubber are prepared into a composite coating slurry with PTC characteristics by a solution mixing method with at least one of pentane, n-hexane and cyclohexane as a solvent.

3. The method of manufacturing a double-layer composite electrode sheet having a PTC effect according to claim 1, wherein In the step S2, the coating viscosity of the base coating layer is 100-3000 mPa·s, and the coating thickness is 5-50 μm.

4. The method of manufacturing a double-layer composite electrode sheet having a PTC effect according to claim 1, wherein The conductive material comprises at least one of graphite powder, conductive carbon black, carbon nanotubes and graphene, and the conductive carbon black is SP conductive carbon black or super carbon black.

5. The method of producing a double-layer composite electrode sheet having a PTC effect according to any one of claims 1 to 4, characterized by, The softening temperature of the vulcanized silicone rubber is 100-120°C.

6. The method of producing a double-layer composite electrode sheet having a PTC effect according to any one of claims 1 to 4, characterized by, In the step S2, after the composite coating slurry is coated on the aluminum foil, first layer drying is performed at a temperature of 80-120°C; in the step S3, after the positive electrode material is coated, second layer drying is performed at a temperature of 80-120°C.

7. The method of producing a double-layer composite electrode sheet having a PTC effect according to any one of claims 1 to 4, characterized by, The method further comprises a step S4, resistance tests are performed on the formed double-layer composite electrode sheet at different temperatures for a preset number of times in a preset temperature range, the preset temperature range is set to 20-120°C, and the preset number of times is 300-400 times; after the resistance tests are performed for the preset number of times, if the PTC effect of the double-layer composite electrode sheet still exists, it is determined that the electrode sheet is qualified.

8. The method of producing a double-layer composite electrode sheet having a PTC effect according to any one of claims 1 to 4, characterized by, The molecular weight of the vulcanized silicone rubber is adjusted to meet the Curie point temperature requirement of the double-layer composite electrode sheet, and the molecular weight of the vulcanized silicone rubber ranges from 50,000 to 2,000,000.

9. The method of producing a double-layer composite electrode sheet having a PTC effect according to any one of claims 1 to 4, characterized by, In the step S1, the mass percentage between the conductive material and the vulcanized silicone rubber is adjusted to meet the resistance mutation amplitude of the double-layer composite electrode sheet at the Curie point temperature, and the mass percentage between the conductive material and the vulcanized silicone rubber is 2%-10%.

10. A battery, characterized by The double-layer composite electrode sheet with PTC effect is prepared by the method according to any one of claims 1-9, and the double-layer composite electrode sheet is used as the positive electrode sheet of the battery.

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