Positive pole piece, preparation method thereof and battery

Abstract

The embodiment of the invention discloses a positive pole piece and a preparation method thereof and a battery, the positive pole piece comprises a positive active material, a carbon nanotube conductive agent and a binding material, the oil absorption value D of the carbon nanotube conductive agent, the specific surface area S of the carbon nanotube conductive agent and the mass percentage w of the carbon nanotube conductive agent in the positive pole piece meet a relational expression R, the three key parameters, namely the oil absorption value, the specific surface area and the content of the carbon nanotube conductive agent, are synergistically regulated and controlled, so that an efficient three-dimensional conductive network is favorably constructed, and the pole piece can have excellent electron conduction and ion conduction at the same time, and has excellent power performance in a low-temperature environment.

Description

Technical Field

[0001] This application relates to the technical field of batteries, specifically to a positive electrode sheet, its preparation method, and a battery. Background Technology

[0002] In the field of power batteries, lithium iron phosphate (LiFePO4) batteries are widely used due to their high safety, long cycle life, and cost advantages. However, the inherently low electronic conductivity and lithium-ion diffusion rate of LiFePO4 batteries result in significant bottlenecks in their power performance under dynamic operating conditions such as low-temperature start-up and low-temperature discharge. To improve the conductivity of LiFePO4 batteries, constructing an efficient conductive network is crucial. Carbon nanotubes (CNTs), with their unique one-dimensional fibrous structure and excellent conductivity, are considered a key conductive agent for overcoming this technological bottleneck.

[0003] In related technologies, increasing the specific surface area of ​​CNTs facilitates the provision of more electron transport paths, thereby improving the electronic conductivity of the electrode. Increasing the content of conductive agent in the electrode promotes the formation of a denser conductive network, which reduces the electrode resistance.

[0004] However, excessively high CNT specific surface area leads to greater CNT agglomeration in the slurry, and these agglomerates can clog electrode pores. Similarly, excessively high CNT content results in decreased electrode porosity. Both of these conditions hinder electrolyte wetting and lithium ion migration channels, significantly deteriorating ion conduction. This is especially true at low temperatures (-10°C). o C~-30 o Under condition C), the viscosity of the electrolyte will increase, and the problem of ion conduction will become more prominent. Summary of the Invention This application provides a positive electrode sheet, its preparation method, and a battery. The electrode sheet can simultaneously achieve both electron conduction and ion conduction, which is beneficial for maintaining high power performance in low-temperature environments.

[0005] This application provides a positive electrode sheet, which includes a positive electrode active material, a carbon nanotube conductive agent, and a binder material; The oil absorption value D of the carbon nanotube conductive agent, the specific surface area S of the carbon nanotube conductive agent, and the mass percentage w of the carbon nanotube conductive agent in the positive electrode sheet satisfy the relationship shown in R.

[0006] The value of R is greater than or equal to 0.5 and less than or equal to 12.

[0007] Optionally, in some embodiments of this application, the oil absorption value of the carbon nanotube conductive agent ranges from 200mL / 100g to 800mL / 100g; Preferably, the oil absorption value of the carbon nanotube conductive agent ranges from 500mL / 100g to 600mL / 100g.

[0008] Optionally, in some embodiments of this application, the specific surface area of ​​the carbon nanotube conductive agent ranges from 200 m². 2 / g to 400m 2 / g.

[0009] Optionally, in some embodiments of this application, the mass percentage of the carbon nanotube conductive agent in the positive electrode sheet ranges from 0.5% to 2.5%; Preferably, the mass percentage of the carbon nanotube conductive agent in the positive electrode sheet ranges from 1% to 1.5%.

[0010] Optionally, in some embodiments of this application, the positive electrode sheet further includes a carbon black conductive agent.

[0011] Optionally, in some embodiments of this application, based on the total mass of the positive electrode sheet, the mass percentage of the positive electrode active material is 86% to 97%, the mass percentage of the carbon black conductive agent is 0.5% to 10%, the mass percentage of the carbon nanotube conductive agent is 0.5% to 2.5%, and the mass percentage of the binder material is 2.5% to 4.5%.

[0012] Optionally, in some embodiments of this application, the positive electrode active material includes lithium iron phosphate; and / or The adhesive material includes polyvinylidene fluoride.

[0013] Secondly, this application provides a method for preparing a positive electrode sheet, which includes the following steps: The positive electrode active material, carbon nanotube conductive agent and binder are mixed and stirred evenly to obtain a mixture; The mixture is coated onto a current collector, and then rolled and slit to form the positive electrode sheet. The oil absorption value D of the carbon nanotube conductive agent, the specific surface area S of the carbon nanotube conductive agent, and the mass percentage w of the carbon nanotube conductive agent in the positive electrode sheet satisfy the relationship shown in R: ; The value of R is greater than or equal to 0.5 and less than or equal to 12.

[0014] Thirdly, this application provides a battery, which includes a positive electrode, a negative electrode, and a separator as described above.

[0015] Optionally, in some embodiments of this application, the DC resistance of the battery ranges from 1.5mΩ to 2.8mΩ.

[0016] The positive electrode of this application includes a positive active material, a carbon nanotube conductive agent, and a binder. The oil absorption value D of the carbon nanotube conductive agent, the specific surface area S of the carbon nanotube conductive agent, and the mass percentage w of the carbon nanotube conductive agent in the positive electrode satisfy the relationship shown in R. That is, by synergistically controlling the three key parameters of the carbon nanotube conductive agent—oil absorption value, specific surface area, and content—it is helpful to construct an efficient three-dimensional conductive network, thereby enabling the electrode to have both excellent electronic and ion conduction and ensuring excellent power performance in low-temperature environments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a graph showing the relationship between the values ​​of DCR and the relational expression R provided in the embodiments of this application; Figure 2 This is a flowchart of the method for preparing the positive electrode sheet provided in the embodiments of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In the field of power batteries, high-safety lithium iron phosphate batteries have been widely used, but their power performance under dynamic conditions such as low-temperature start-up and low-temperature discharge still has significant bottlenecks.

[0021] Constructing efficient CNT conductive networks is considered a key path to overcome this technological bottleneck.

[0022] Existing literature and patents indicate that while increasing the specific surface area or the amount of CNTs added can improve electronic conduction, such methods have two limitations: First, excessive pursuit of increased specific surface area can lead to deterioration of CNT dispersion, and increased agglomeration will reduce electrode porosity, thereby worsening ion conduction. Second, excessive addition of CNTs can cause electrode pore blockage, hindering lithium-ion diffusion and further deteriorating ion conduction. Under current technology, synergistic optimization of electronic and ion conduction has not yet been achieved; therefore, developing CNT conductive networks that balance both electronic and ion conduction has become an urgent industry need.

[0023] In view of this, embodiments of this application provide a positive electrode sheet, a method for preparing the same, and a battery, with the aim of preparing a positive electrode sheet that can balance electron conduction and ion conduction.

[0024] According to a first aspect of the embodiments of this application, a positive electrode sheet is provided, the positive electrode sheet comprising a positive active material, a carbon nanotube conductive agent and a binder material; refer to Figure 1 The oil absorption value D of the carbon nanotube conductive agent, the specific surface area S of the carbon nanotube conductive agent, and the mass percentage w of the carbon nanotube conductive agent in the positive electrode sheet satisfy the relationship shown in the equation R: ; The value of R is greater than or equal to 0.5 and less than or equal to 12.

[0025] The positive electrode of this application comprises a positive electrode active material, a carbon nanotube conductive agent, and a binder. The oil absorption value (D) of the carbon nanotube conductive agent, the specific surface area (S) of the carbon nanotube conductive agent, and the mass percentage (w) of the carbon nanotube conductive agent in the positive electrode satisfy the relationship shown in the equation R. That is, by synergistically controlling the three key parameters of the carbon nanotube conductive agent—oil absorption value, specific surface area, and content—it is helpful to construct a highly efficient three-dimensional conductive network. This allows the electrode to possess both excellent electronic and ion conduction, ensuring excellent power performance at low temperatures. The unit of R is mL / 100m³. 2 .

[0026] The relationship for R can be found in the percolation formula of the effective medium theory, as follows: Percolation formula of effective medium theory: (1) in, It is the conductivity of the positive electrode. The conductivity of the conductive agent P It is volume fraction. P c The percolation threshold, t is the critical exponent. With low amounts of conductive agent added, t can be approximated as 1, therefore, from (1) we can obtain: (2) Considering the aggregation effect of the conductive agent, it increases with the increase of w (the amount of conductive agent added). P c The percolation threshold is no longer a constant and should be positively correlated with w, so it is corrected as follows: (3) Where k is the correction factor. β The clustering index is the correction factor. p Converting the volume fraction to w, we get: (4) in, ρ m The density of the conductive agent, ρ f For the density of the electrode, , ρ m , ρ f Simplifying to x, we get: (5) As can be seen from formula (5), the amount added is related to the conductivity, but this formula ignores the specific surface area of ​​the conductive agent. S And oil absorption value D Therefore, we introduce S and D to establish a relation: (6) Where 'a' is the correction factor, and based on the actual data, we can obtain: (7) The positive electrode that satisfies the above relationship has an excellent conductive network that balances electronic and ion conduction. This positive electrode not only has a strong liquid absorption and retention capacity, which helps to improve ion conduction, but also has abundant electron transport sites, which can optimize electron conduction. Therefore, it can significantly improve low-temperature power performance.

[0027] The value of R is greater than or equal to 0.5 and less than or equal to 12. Further, the value of R can be greater than or equal to 0.5 and less than or equal to 7. Even further, the value of R can be greater than or equal to 0.75 and less than or equal to 4.5. For example, the value of R can be 0.75, 1, 1.49, 1.59, 1.86, 1.99, 2.09, 2.23, 2.32, 2.78, 4.18, 4.46, and any value between two adjacent values ​​mentioned above.

[0028] In some embodiments of this application, the oil absorption value of the carbon nanotube conductive agent ranges from 200 mL / 100 g to 800 mL / 100 g. Further, the oil absorption value of the carbon nanotube conductive agent ranges from 500 mL / 100 g to 600 mL / 100 g. Exemplarily, the oil absorption value of the carbon nanotube conductive agent can be 200 mL / 100 g, 300 mL / 100 g, 400 mL / 100 g, 500 mL / 100 g, 600 mL / 100 g, 700 mL / 100 g, 800 mL / 100 g, or any value between two adjacent values.

[0029] The oil absorption value directly reflects the ability of carbon nanotube conductive agents to absorb and retain electrolyte.

[0030] Within the aforementioned oil absorption value range, carbon nanotube conductive agents possess sufficiently high pore structure and specific surface area, enabling them to effectively adsorb and store electrolyte. This ensures the positive electrode active material is fully wetted, providing a continuous and rapid migration channel for lithium ions during charging and discharging, and significantly reducing ion transport resistance within the electrode. When the oil absorption value of the carbon nanotube conductive agent is less than 200 mL / 100 g, it indicates insufficient structural development or excessive density, resulting in weak liquid absorption and retention capabilities. This leads to uneven electrolyte distribution within the electrode, hindering lithium ion migration and increasing the battery's internal resistance. While an oil absorption value greater than 800 mL / 100 g indicates extremely strong liquid absorption, excessively high oil absorption values ​​are usually accompanied by long carbon nanotubes that are prone to entanglement and aggregation. These aggregates occupy excessive space in the electrode, blocking the necessary ion transport pores and hindering lithium ion diffusion, leading to a decrease in ionic conductivity.

[0031] In some embodiments of this application, the specific surface area of ​​the carbon nanotube conductive agent ranges from 200 m². 2 / g to 400m 2 / g. Furthermore, the specific surface area of ​​the carbon nanotube conductive agent ranges from 300m². 2 / g to 400m 2 / g. For example, the specific surface area of ​​the carbon nanotube conductive agent can be 200 m². 2 / g、220m 2 / g、240m 2 / g、260m 2 / g、280m 2 / g、300m 2 / g、320m 2 / g、340m 2 / g、360m 2 / g、380m 2 / g、400m 2 / g and any value between the two adjacent values ​​mentioned above.

[0032] By adopting the above scheme, the specific surface area of ​​the carbon nanotube conductive agent is within the aforementioned range. This helps ensure that the carbon nanotube conductive agent has sufficient surface active sites, enabling it to form a large number of effective electrical contact points with the positive electrode active material, constructing a dense and efficient three-dimensional conductive network. This significantly improves the electronic conductivity of the electrode, thereby improving the rate performance of the battery. If the specific surface area of ​​the carbon nanotube conductive agent is too high, uncontrolled agglomeration is likely to occur during slurry preparation and electrode drying. These agglomerates not only reduce the effective conductive contact points but also severely block the pores inside the electrode, hindering the wetting of the electrode liquid and the migration channels of lithium ions, leading to a decrease in ionic conductivity. The specific surface area of ​​the carbon nanotube conductive agent is within 300 μm². 2 / g to 400m 2 Between / g, it retains high conductivity while making the dispersion relatively controllable, which helps to prepare electrodes with uniform structure and performance.

[0033] In some embodiments of this application, the positive electrode sheet also includes carbon black conductive agent.

[0034] By employing the above-described scheme, carbon nanotubes (CNTs) possess a unique one-dimensional fibrous structure with an extremely high aspect ratio. This allows them to span multiple active material particles, constructing a long-range, continuous conductive network within the electrode. This highly efficient network structure achieves effective conductivity even at very low addition levels, primarily responsible for macroscopic electron transport and crucial for improving overall electronic conductivity. Carbon black, with its generally small particle size and large specific surface area, effectively fills the gaps between the positive electrode active materials and between the active materials and CNTs, acting as a bridge and significantly increasing conductive contact points, thus improving microscopic charge transport. Combining these two methods allows a small amount of CNTs to serve as a highly efficient main channel, supplemented by a small amount of carbon black to fill the gaps. This synergistic conductive network achieves superior conductivity than a single conductive agent with a lower total addition amount, while maximizing the preservation of the electrode's porous structure, providing ample space for electrolyte wetting and ion migration.

[0035] In some embodiments of this application, the mass percentage of the positive electrode active material is 86% to 97% based on the total mass of the positive electrode sheet, the mass percentage of the carbon black conductive agent is 0.5% to 10%, the mass percentage of the carbon nanotube conductive agent is 0.5% to 2.5%, and the mass percentage of the binder material is 2.5% to 4.5%.

[0036] By adopting the above-mentioned scheme, the amount of positive electrode active material used within the specified range helps to maximize the mass fraction of the positive electrode active material. This directly increases the capacity per unit area / unit volume of the electrode, which is fundamental to ensuring the battery has high energy density. The amounts of carbon black conductive agent and carbon nanotube conductive agent used within the specified range help to form a highly efficient and continuous three-dimensional conductive network, ensuring that the positive electrode active material can be fully utilized, thereby achieving excellent rate performance and power density, while avoiding pore blockage and energy density loss caused by excessive conductive material.

[0037] It is understandable that when the mass percentage of carbon nanotube conductive agent is increased (decreased), the mass percentage of positive electrode active material is changed simultaneously.

[0038] In some embodiments of this application, the positive electrode active material includes lithium iron phosphate.

[0039] By adopting the above approach, lithium iron phosphate itself is either insulating or semiconductor, relying entirely on an external conductive network for electron conduction. Therefore, constructing an efficient conductive network is highly targeted at lithium iron phosphate. For active materials such as lithium cobalt oxide or ternary materials, which have inherently good conductivity, the improvement brought by optimizing the conductive network may be relatively limited.

[0040] In some embodiments of this application, the adhesive material includes polyvinylidene fluoride.

[0041] By adopting the above scheme, polyvinylidene fluoride (PVDF), as a fluorinated polymer, has extremely high chemical inertness and electrochemical stability. It can withstand the redox environment within the working voltage range of lithium iron phosphate batteries (approximately 2.5-3.6V) and is not easily decomposed during long-term cycling. This ensures that the binder itself will not undergo side reactions with the electrolyte or electrode materials, thus ensuring the long-term cycle life and safety of the battery.

[0042] According to a second aspect of the embodiments of this application, a method for preparing a positive electrode sheet is provided, with reference to... Figure 2 The method for preparing the positive electrode sheet as described above includes the following steps: S100. Mix the positive electrode active material, carbon nanotube conductive agent and binder material, and stir evenly to obtain a mixture; S200: The aforementioned mixture is coated onto the current collector and then rolled and slit to form a positive electrode sheet; Among them, the oil absorption value D of the carbon nanotube conductive agent, the specific surface area S of the carbon nanotube conductive agent, and the mass percentage w of the carbon nanotube conductive agent in the positive electrode sheet satisfy the relationship shown in R: ; The value of R is greater than or equal to 0.5 and less than or equal to 12.

[0043] According to a third aspect of the embodiments of this application, a battery is provided, the battery including a positive electrode, a negative electrode and a separator as described above.

[0044] By adopting the above-described solution, the battery of this application embodiment includes all the beneficial effects of the aforementioned positive electrode sheet, which will not be repeated here.

[0045] In some embodiments of this application, the DC resistance of the battery ranges from 1.5mΩ to 2.8mΩ. Exemplarily, the DC resistance of the battery can be 1.5mΩ, 1.6mΩ, 1.7mΩ, 1.8mΩ, 1.9mΩ, 2.0mΩ, 2.1mΩ, 2.2mΩ, 2.3mΩ, 2.4mΩ, 2.5mΩ, 2.6mΩ, 2.7mΩ, 2.8mΩ, or any value between two adjacent values ​​mentioned above.

[0046] Direct current resistance (DCR) is a core indicator for measuring battery power capability. The lower the DCR, the smaller the voltage drop and energy loss inside the battery during high-current discharge (such as vehicle start-up and acceleration), and the higher the output power. The above-mentioned DCR range is an extremely low value, indicating that the lithium iron phosphate battery of this application has excellent low-temperature performance, enabling it to provide strong power output even in extremely cold environments.

[0047] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0048] Example 1 A positive electrode sheet is prepared by the following method: 90% lithium iron phosphate, 5.5% SP carbon black, 0.5% carbon nanotubes, and 4% PVDF binder were mixed and stirred for 12 hours. After uniform stirring, the mixture was transferred and coated, then baked and rolled. The positive electrode sheet was then slit and die-cut to form the positive electrode sheet. The carbon nanotubes had an oil absorption value of 200 mL / 100 g and a specific surface area of ​​200 m². 2 / g.

[0049] Example 2 The difference between Example 2 and Example 1 lies in the oil absorption value of the carbon nanotubes. In this example, the oil absorption value of the carbon nanotubes is 400 mL / 100 g.

[0050] Example 3 The difference between Example 3 and Example 1 lies in the oil absorption value of the carbon nanotubes. In this example, the oil absorption value of the carbon nanotubes is 600 mL / 100 g.

[0051] Example 4 The difference between Example 4 and Example 1 lies in the oil absorption value of the carbon nanotubes. In this example, the oil absorption value of the carbon nanotubes is 800 mL / 100 g.

[0052] Example 5 The difference between Example 5 and Example 3 lies in the content of carbon nanotubes. In this example, the content of carbon nanotubes is 1.5%, and the content of lithium iron phosphate is adjusted to 89%.

[0053] Example 6 The difference between Example 6 and Example 5 lies in the content of carbon nanotubes. In this example, the content of carbon nanotubes is 2.5%, and the content of lithium iron phosphate is adjusted to 88%.

[0054] Example 7 The difference between Example 7 and Example 3 lies in the specific surface area of ​​the carbon nanotubes. In this example, the specific surface area of ​​the carbon nanotubes is 300 m². 2 / g.

[0055] Example 8 The difference between Example 8 and Example 7 lies in the specific surface area of ​​the carbon nanotubes. In this example, the specific surface area of ​​the carbon nanotubes is 400 m². 2 / g.

[0056] Example 9 The difference between Example 9 and Example 2 lies in the mass percentage of carbon nanotubes in the positive electrode. In this example, the mass percentage of carbon nanotubes in the positive electrode is 2.5%.

[0057] Example 10 The difference between Example 10 and Example 7 lies in the content and specific surface area of ​​carbon nanotubes. In this example, the specific surface area of ​​the carbon nanotubes is 300 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 1.5%.

[0058] Example 11 The difference between Example 11 and Example 10 lies in the content and specific surface area of ​​carbon nanotubes. In this example, the specific surface area of ​​the carbon nanotubes is 400 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 2.5%.

[0059] Examples 12-15 Adjust the oil absorption value, specific surface area and content of carbon nanotubes according to Table 1, while keeping the rest of the process and steps unchanged. Increase the content of carbon nanotubes and simultaneously reduce the content of lithium iron phosphate.

[0060] Comparative Example 1 The difference between Comparative Example 1 and Example 1 lies in the physical properties of the carbon nanotubes. In this comparative example, the oil absorption value of the carbon nanotubes is 1000 mL / 100 g, and the specific surface area of ​​the carbon nanotubes is 200 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 3%.

[0061] Comparative Example 2 The difference between Comparative Example 1 and Example 1 lies in the physical properties of the carbon nanotubes. In this comparative example, the oil absorption value of the carbon nanotubes is 200 mL / 100 g, and the specific surface area of ​​the carbon nanotubes is 500 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 0.5%.

[0062] Comparative Example 3 The difference between Comparative Example 3 and Example 1 lies in the physical properties of the carbon nanotubes. In this comparative example, the oil absorption value of the carbon nanotubes is 600 mL / 100 g, and the specific surface area of ​​the carbon nanotubes is 200 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 5%.

[0063] Comparative Example 4 The difference between Comparative Example 4 and Example 1 lies in the physical properties of the carbon nanotubes. In this comparative example, the oil absorption value of the carbon nanotubes is 100 mL / 100 g, and the specific surface area of ​​the carbon nanotubes is 200 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 0.5%.

[0064] Comparative Example 5 The difference between Comparative Example 5 and Example 1 lies in the physical properties of the carbon nanotubes. In this comparative example, the oil absorption value of the carbon nanotubes is 600 mL / 100 g, and the specific surface area of ​​the carbon nanotubes is 600 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 0.5%.

[0065] Comparative Example 6 The difference between Comparative Example 6 and Example 1 lies in the physical properties of the carbon nanotubes. In this comparative example, the oil absorption value of the carbon nanotubes is 600 mL / 100 g, and the specific surface area of ​​the carbon nanotubes is 100 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 3%.

[0066] The differences between Examples 1-15 and Comparative Examples 1-6 are shown in Table 1. Table 1

[0067] Table 2

[0068] Based on Examples 1-15, Comparative Examples 1-6, and Table 1-2, it can be seen that the oil absorption value of carbon nanotubes in the samples of Examples 1-15 is 200-800 mL / 100 g, and the specific surface area of ​​carbon nanotubes is 200-400 m². 2 / g, the mass percentage of carbon nanotubes in the positive electrode is 0.5~2.5%, and the oil absorption value, specific surface area, and content of carbon nanotubes satisfy the relationship shown in R. This positive electrode has an excellent CNT conductive network that balances electronic and ion conduction. This positive electrode not only has strong liquid absorption and retention capabilities, which helps improve ion conduction, but also has abundant electron transport sites, which can optimize electron conduction. Therefore, at -25 o C DCR has lower resistance, which can significantly improve low-temperature power performance.

[0069] The above provides a detailed description of a positive electrode sheet, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode tab, characterized in that, the positive electrode tab comprises a positive electrode active material, a carbon nanotube conductive agent and a binder material; wherein the oil absorption value D of the carbon nanotube conductive agent, the specific surface area S of the carbon nanotube conductive agent and the mass percentage content w of the carbon nanotube conductive agent in the positive electrode tab satisfy the relationship as shown in R; wherein the value of R is greater than or equal to 0.5 and less than or equal to 12.

2. The positive electrode tab according to claim 1, characterized in that, The oil absorption value of the carbon nanotube conductive agent is in the range of 200 mL / 100 g to 800 mL / 100 g; preferably, the oil absorption value of the carbon nanotube conductive agent ranges from 500 mL / 100 g to 600 mL / 100 g.

3. The positive electrode tab according to claim 1, characterized in that, The specific surface area of the carbon nanotube conductive agent ranges from 200 m 2 / g to 400 m 2 / g.

4. The positive electrode tab according to claim 1, characterized in that, the mass percentage content of the carbon nanotube conductive agent in the positive electrode tab ranges from 0.5% to 2.5%; preferably, the mass percentage content of the carbon nanotube conductive agent in the positive electrode tab ranges from 1% to 1.5%.

5. The positive electrode tab according to claim 1, characterized in that, the positive electrode tab further comprises a carbon black conductive agent.

6. The positive electrode tab according to claim 5, characterized in that, the mass percentage content of the positive electrode active material is 86% to 97%, the mass percentage content of the carbon black conductive agent is 0.5% to 10%, the mass percentage content of the carbon nanotube conductive agent is 0.5% to 2.5%, and the mass percentage content of the binder material is 2.5% to 4.5%, based on the total mass of the positive electrode tab.

7. The positive electrode tab according to claim 1, characterized in that, the positive electrode active material comprises lithium iron phosphate; and / or the binder material comprises polyvinylidene fluoride.

8. A method of making a positive electrode sheet, characterized by, A method for preparing the positive electrode tab according to any one of claims 1 to 7, comprising the following steps: mixing the positive electrode active material, the carbon nanotube conductive agent and the binder material, stirring uniformly to obtain a mixture; coating the mixture on a current collector, rolling and slitting to obtain the positive electrode tab; wherein the oil absorption value D of the carbon nanotube conductive agent, the specific surface area S of the carbon nanotube conductive agent and the mass percentage content w of the carbon nanotube conductive agent in the positive electrode tab satisfy the relationship as shown in R; ； wherein the value of R is greater than or equal to 0.5 and less than or equal to 12.

9. A battery, characterized in that, the battery comprises the positive electrode tab according to any one of claims 1 to 7, a negative electrode tab and a separator.

10. The battery according to claim 9, characterized in that, the direct current resistance of the battery ranges from 1.5 mΩ to 2.8 mΩ.

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