Positive electrode sheet, secondary battery, and electronic device

Abstract

The present application provides a positive electrode sheet, a secondary battery, and an electronic device. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. The positive electrode material layer comprises a positive electrode additive. Based on the mass of the positive electrode material layer, the mass percentage of the positive electrode additive is m%, wherein 0.1≤m≤0.5. The positive electrode additive comprises at least one of the structural formula shown in formula (I) or the structural formula shown in formula (II). The secondary battery of the present application has good high-temperature cycle performance.

Description

A positive electrode, a secondary battery, and an electronic device

[0001] This application claims priority to Chinese Patent Application No. 202510237553.7, filed on February 28, 2025, entitled "A Positive Electrode, a Secondary Battery and an Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a positive electrode, a secondary battery, and an electronic device. Background Technology

[0003] Secondary batteries, such as lithium-ion batteries, are widely used in smartphones, wearable devices, consumer drones, and electric vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. With the widespread application of lithium-ion batteries in these fields, the market demands increasingly higher high-temperature cycle performance. However, at high temperatures, the positive electrode active material in lithium-ion batteries undergoes a phase transition, releasing reactive oxygen species, which affects the high-temperature cycle performance of the lithium-ion battery. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode, a secondary battery, and an electronic device to improve the high-temperature cycle performance of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode additive. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode additive is m%, 0.1 ≤ m ≤ 0.5. The positive electrode additive includes at least one of the structural formulas shown in formula (I) or (II).

[0006] R1 to R2 are each independently selected from hydrogen atom, nitrogen atom, hydroxyl group, C1 to C2. 18 Alkyl groups, C3 to C4 groups containing ester groups 18 Chain-like or cyclic alkyl groups; R3 to R6 are each independently selected from hydrogen atoms, hydroxyl groups, C1 to C6 atoms. 18 Alkyl groups, C1 to C1 groups containing ester or ether bonds 18The additives are chain-like or cyclic alkyl groups. This application introduces the aforementioned positive electrode additive into the positive electrode sheet and controls the mass percentage (m%) of the positive electrode additive within the scope of this application. The positive electrode additive can capture free radicals, converting oxygen free radicals generated by the positive electrode active material and small molecule free radicals generated by the electrolyte into stable small molecule substances, reducing the chain decomposition reaction of the electrolyte, thereby improving the high-temperature cycle performance of the secondary battery while maintaining good kinetic performance and high energy density.

[0007] In some embodiments of this application, 0.15 ≤ m ≤ 0.3. By adjusting the value of m within the above range, it is beneficial to further improve the high-temperature cycle performance of the secondary battery, while ensuring good kinetic performance and high energy density.

[0008] In some embodiments of this application, R1 to R2 are each independently selected from hydrogen atoms, C3 to C4 atoms. 10 Alkyl groups, C3 to C4 groups containing ester groups 10 A chain alkyl group; R3 to R6 are each independently selected from hydrogen atoms, C1 to C5 chain alkyl groups, C1 to C5 groups containing ester groups or ether bonds. 10 The groups are chain-like or cyclic alkyl groups. R1 to R6 are selected from the above groups, which is beneficial to further improve the high-temperature cycle performance of the secondary battery on the basis of good kinetic performance and high energy density.

[0009] In some embodiments of this application, the positive electrode material layer contains nitrogen, and the mass percentage of nitrogen in the positive electrode material layer is 0.1% to 0.3% based on the mass of the positive electrode material layer. The nitrogen in the positive electrode material layer is derived from the positive electrode additive. By controlling the mass percentage of nitrogen in the positive electrode material layer within the above range, and the mass percentage of the positive electrode additive within a suitable range, it is beneficial to improve the high-temperature cycle performance of the secondary battery, while also achieving good kinetic performance and high energy density.

[0010] In some embodiments of this application, the cathode additive includes at least one selected from the following: a polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol; N,N-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine; pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; butylated hydroxyanisole; or dibutylhydroxytoluene. Using the above-mentioned cathode additive is beneficial for further improving the high-temperature cycle performance of the secondary battery, building upon its already good kinetic performance and high energy density.

[0011] In some embodiments of this application, the positive electrode sheet satisfies at least one of the following characteristics: (1) the infrared spectrum of the positive electrode material layer is within 1200 cm⁻¹. -1Up to 1350cm -1 (2) The infrared spectrum of the cathode material layer at 1000 cm⁻¹ exhibits characteristic peaks; -1 Up to 1199cm -1 Characteristic peaks exist between them. A positive electrode sheet that meets these characteristics is beneficial for improving the high-temperature cycle performance of secondary batteries, while also exhibiting good kinetic performance and high energy density.

[0012] In some embodiments of this application, the positive electrode sheet satisfies at least one of the following characteristics: (1) the infrared spectrum of the positive electrode material layer is within 1200 cm⁻¹. -1 Up to 1350cm -1 The transmittance of the characteristic peak at 1000 cm⁻¹ is I1, 30% ≤ I1 ≤ 80%; (2) The infrared spectrum of the positive electrode material layer at 1000 cm⁻¹ is I1. -1 Up to 1199cm -1 The transmittance of the characteristic peak is I2, 60% ≤ I2 ≤ 70%. The positive electrode sheet meets the above characteristics, which is beneficial to further improve the high-temperature cycle performance of the secondary battery, while also exhibiting good kinetic performance and high energy density.

[0013] In some embodiments of this application, the thickness of the positive electrode material layer is H μm, where 10 ≤ H ≤ 50. By adjusting the thickness H of the positive electrode material layer within the above range, it is beneficial to improve the kinetic performance and high-temperature cycle performance of the secondary battery, and also to increase the energy density of the secondary battery.

[0014] In some embodiments of this application, the film resistance of the positive electrode is RΩ, the thickness of the positive electrode material layer is Hμm, and the values ​​of 0.05≤R≤0.5 and 0.5≤R×H≤8 are all within the above ranges. Having the film resistance R and R×H of the positive electrode within these ranges is beneficial for improving the kinetic performance and high-temperature cycle performance of the secondary battery, and also for increasing the energy density of the secondary battery.

[0015] The second aspect of this application provides a secondary battery, which includes the positive electrode provided in the first aspect of this application. The secondary battery of this application has good high-temperature cycling performance and kinetic performance.

[0016] A third aspect of this application provides an electronic device that includes the secondary battery provided in the second aspect of this application. The electronic device of this application has a long service life and good performance.

[0017] The beneficial effects of this application are:

[0018] This application provides a positive electrode sheet, a secondary battery, and an electronic device. The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode additive. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode additive is m%, 0.1≤m≤0.5. The positive electrode additive includes at least one of the structural formulas shown in formula (I) or (II). By introducing the above-mentioned positive electrode additive into the positive electrode sheet and controlling the mass percentage content m% of the positive electrode additive within the scope of this application, the positive electrode additive can capture free radicals, converting oxygen free radicals generated by the positive electrode active material and small molecule free radicals generated by the electrolyte into stable small molecule substances, reducing the chain decomposition reaction of the electrolyte, thereby improving the high-temperature cycle performance of the secondary battery while maintaining good kinetic performance and high energy density.

[0019] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0021] Figure 1 is an infrared spectrum of the positive electrode material layer of Embodiment 11 of this application. Detailed Implementation

[0022] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0023] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0024] At high temperatures, the phase transition of the positive electrode active material in a secondary battery intensifies, releasing reactive oxygen species (ROS). These ROS decompose the electrolyte into reactive small-molecule free radicals, thus affecting the high-temperature cycle performance of the secondary battery. Existing technologies typically address this issue by coating the positive electrode active material or introducing electrolyte additives. However, coating the positive electrode active material reduces its reactive surface area, affecting its specific capacity, lowering the energy density of the secondary battery, and degrading its kinetic performance. Introducing electrolyte additives requires a relatively large amount of additive to be effective, as ROS originate from the positive electrode active material, and the efficiency is low. Furthermore, when ROS in the positive electrode interacts with the additives in the electrolyte, the ROS enters the electrolyte and is partially oxidized, affecting the electrochemical performance of the secondary battery. Therefore, the improvement in high-temperature cycle performance is poor.

[0025] Based on this, a first aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode additive, and the mass percentage content of the positive electrode additive is m%, 0.1 ≤ m ≤ 0.5, preferably 0.15 ≤ m ≤ 0.3, based on the mass of the positive electrode material layer. For example, the value of m can be 0.10, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.35, 0.40, 0.45, 0.50, or a range consisting of any two of these values. The positive electrode additive includes at least one of the structural formulas shown in formula (I) or (II).

[0026] R1 to R2 are each independently selected from hydrogen atom, nitrogen atom, hydroxyl group, C1 to C2. 18 Alkyl groups, C3 to C4 groups containing ester groups 18 Chain-like or cyclic alkyl groups; R3 to R6 are each independently selected from hydrogen atoms, hydroxyl groups, C1 to C6 atoms. 18 Alkyl groups, C1 to C1 groups containing ester or ether bonds 18 Chain-like or cyclic alkyl groups. This application pertains to C1 to C2 alkyl groups. 18 The structure of the alkyl group is not particularly limited, as long as it achieves the purpose of this application. For example, the alkyl group can be a chain alkyl group or a cyclic alkyl group. This application applies to C3 to C4 alkyl groups containing an ester group. 18 The position of the ester group in the chain alkyl or cyclic alkyl group, and the C1 to C1 positions containing the ester group or ether bond. 18The position of the ester group or ether bond in the chain alkyl or cyclic alkyl group is not particularly limited, as long as the purpose of this application can be achieved. For example, the ester group or ether bond can be located in the middle of the chain alkyl group or at the end of the chain alkyl group.

[0027] This application introduces the aforementioned positive electrode additive into the positive electrode sheet and controls the mass percentage m% of the positive electrode additive within the scope of this application. The positive electrode additive can capture free radicals, converting oxygen free radicals generated by the positive electrode active material and small molecule free radicals (e.g., alkyl free radicals) generated by the electrolyte into stable small molecule substances, thereby reducing the chain decomposition reaction of the electrolyte. Specifically, the structure shown in formula (I) contains a hindered amine structure, which can absorb energy and convert into stable nitroxide free radicals. These nitroxide free radicals can capture free radicals (e.g., oxygen free radicals, alkyl free radicals) and convert them into stable small molecule substances. They also have a regenerative function, allowing them to be converted back into nitroxide free radicals in subsequent applications and reused multiple times, resulting in high efficiency. The structure shown in formula (II) contains a hindered phenol structure, where the phenolic group (-OH) has hydrogen-donating ability and can provide hydrogen atoms to free radicals (e.g., alkyl free radicals) to form stable phenoloxy free radicals and terminate the chain reaction of free radicals, thereby reducing the chain decomposition reaction of the electrolyte. Meanwhile, the cathode additive of this application exists on the surface of the cathode active material and is insoluble in the electrolyte. It can directly and rapidly absorb the active oxygen generated by the structural phase transition of the cathode active material, reducing the risk of active oxygen entering the electrolyte and partially oxidizing it. This results in higher efficiency and better improvement of the high-temperature cycle performance of the secondary battery. Furthermore, because the cathode additive can act directly on the cathode active material, the amount added can be relatively small, resulting in less coating on the surface of the cathode active material. This leads to a larger reactive surface area of ​​the cathode active material, allowing for greater utilization of the specific capacity, while having a smaller impact on the kinetic performance and energy density of the secondary battery. Therefore, this application can improve the high-temperature cycle performance of the secondary battery while maintaining good kinetic performance and high energy density. In this application, high temperature refers to a temperature greater than or equal to 45°C. The cathode additive is commercially available.

[0028] When the value of m is too small, for example, less than 0.1, the mass percentage of the cathode additive is too low, resulting in fewer free radicals being captured. The cathode additive cannot convert oxygen free radicals into stable small molecules in time, and the presence of oxygen free radicals still significantly affects electrolyte decomposition, thus resulting in poor improvement of the high-temperature cycle performance of the secondary battery. When the value of m is too large, for example, greater than 0.5, the mass percentage of the cathode additive is too high, leading to excessive coating on the surface of the cathode active material. This results in a smaller reactive surface area of ​​the cathode active material, affecting the kinetic performance and high-temperature cycle performance of the secondary battery.

[0029] In this application, the positive electrode additive includes at least one of the structural formulas shown in formula (I) or (II). The aforementioned structural formula can refer to the molecular structural formula of a compound, i.e., the positive electrode additive includes at least one of the compounds shown in formula (I) or (II); the aforementioned structural formula can also refer to a structural fragment, i.e., the molecular structural formula of the positive electrode additive includes at least one of the structural fragments shown in formula (I) or (II). In some embodiments, the positive electrode additive includes at least one of the compounds shown in formula (I) or (II). In other embodiments, the positive electrode additive includes at least one of the structural fragments shown in formula (I) or (II).

[0030] In some implementations, compared to secondary batteries where the positive electrode does not contain positive electrode additives, the capacity retention rate of the secondary battery of this application can be improved by more than 3% after 500 cycles at high temperature (e.g., 45°C).

[0031] In some embodiments of this application, R1 to R2 are each independently selected from hydrogen atoms, C3 to C4 atoms. 10 Alkyl groups, C3 to C4 groups containing ester groups 10 A chain alkyl group; R3 to R6 are each independently selected from hydrogen atoms, C1 to C5 chain alkyl groups, C1 to C5 groups containing ester groups or ether bonds. 10 The groups are chain-like or cyclic alkyl groups. R1 to R6 are selected from the above groups, which is beneficial to further improve the high-temperature cycle performance of the secondary battery on the basis of good kinetic performance and high energy density.

[0032] In some embodiments of this application, the positive electrode material layer contains nitrogen, and the mass percentage of nitrogen in the positive electrode material layer is 0.1% to 0.3% based on the mass of the positive electrode material layer. For example, the mass percentage of nitrogen in the positive electrode material layer can be 0.10%, 0.12%, 0.15%, 0.17%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, or a range of any two of these values. The nitrogen in the positive electrode material layer originates from the positive electrode additive. By controlling the mass percentage of nitrogen in the positive electrode material layer within the above-mentioned range, and the mass percentage of the positive electrode additive within a suitable range, it is beneficial for the generated nitric oxide free radicals to play a role in converting the oxygen free radicals generated by the positive electrode active material and the small molecule free radicals (e.g., alkyl free radicals) generated by the electrolyte into stable small molecule substances, reducing the chain decomposition reaction of the electrolyte, thereby improving the high-temperature cycle performance of the secondary battery, while also exhibiting good kinetic performance and high energy density.

[0033] In this application, the mass percentage of nitrogen in the cathode material layer can be controlled by adjusting the type and mass percentage of the cathode additive. For example, when other conditions remain unchanged, the higher the nitrogen content of the cathode additive, the greater the mass percentage of nitrogen in the cathode material layer; the lower the nitrogen content of the cathode additive, the smaller the mass percentage of nitrogen in the cathode material layer. Similarly, when other conditions remain unchanged, the greater the mass percentage of the cathode additive, the greater the mass percentage of nitrogen in the cathode material layer; the smaller the mass percentage of the cathode additive, the smaller the mass percentage of nitrogen in the cathode material layer.

[0034] In some embodiments of this application, the cathode additive includes at least one selected from the following: a polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol; N,N-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine; pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; butylated hydroxyanisole; or dibutylhydroxytoluene. Using the above-mentioned cathode additive is beneficial for further improving the high-temperature cycle performance of the secondary battery, building upon its already good kinetic performance and high energy density.

[0035] In some embodiments, the molar ratio of succinic acid monomer to 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol monomer in the polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol is 1:1, and its molecular structure is shown below. This application does not impose any particular limitation on the degree of polymerization n of the above polymer, as long as it achieves the purpose of this application. For example, the degree of polymerization n can be from 2 to 100, and the value of the degree of polymerization n can be 2, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a range of any two values ​​therein.

[0036] In some embodiments of this application, the infrared spectrum of the positive electrode material layer is at 1200 cm⁻¹. -1 Up to 1350cm -1 Characteristic peaks exist between them. The 1200 cm⁻¹ peak in the infrared spectrum... -1 Up to 1350cm -1 The characteristic peak at the position corresponds to the CN bond in the structure shown in formula (I). The infrared spectrum of the cathode material layer satisfies the above characteristics, indicating that there is a cathode additive containing the structure shown in formula (I) in the cathode material layer. The nitrogen and oxygen free radicals generated by it can capture free radicals (e.g., oxygen free radicals, alkyl free radicals) and convert them into stable small molecules, reducing the chain decomposition reaction of the electrolyte. This is beneficial to improving the high-temperature cycle performance of the secondary battery, while also exhibiting good kinetic performance and high energy density.

[0037] In some embodiments of this application, the infrared spectrum of the positive electrode material layer is at 1200 cm⁻¹. -1 Up to 1350cm -1 The transmittance of the characteristic peak is I1, where 30% ≤ I1 ≤ 80%. For example, the value of I1 can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range of any two of these values. A value of I1 within the above range indicates that the mass percentage of the cathode additive containing the structure shown in formula (I) is within a suitable range. The nitrogen and oxygen free radicals generated by the cathode additive have a relatively small impact on the kinetic performance of the secondary battery, provided that the requirements for converting oxygen free radicals are met. This is beneficial for improving the high-temperature cycle performance of the secondary battery, while also ensuring good kinetic performance and high energy density.

[0038] In some embodiments of this application, the infrared spectrum of the positive electrode material layer is at 1000 cm⁻¹ -1 Up to 1199cm -1 Characteristic peaks exist between them. (1000 cm⁻¹ in the infrared spectrum) -1 Up to 1199cm -1 The characteristic peak at the position corresponds to the C-OH bond in the structure shown in formula (II). The infrared spectrum of the positive electrode material layer satisfies the above characteristics, indicating that there is a positive electrode additive in the positive electrode material layer containing the structure shown in formula (II). It can provide hydrogen atoms to free radicals (e.g., alkyl free radicals), form stable phenolic free radicals and terminate the chain reaction of free radicals, reduce the chain decomposition reaction of electrolyte, thereby improving the high-temperature cycle performance of secondary batteries, while having good kinetic performance and high energy density.

[0039] In some embodiments of this application, the infrared spectrum of the positive electrode material layer is at 1000 cm⁻¹ -1 Up to 1199cm -1 The transmittance of the characteristic peak is I2, 60% ≤ I2 ≤ 70%. For example, the value of I2 can be 60%, 63%, 65%, 68%, 70%, or a range of any two of these values. An I2 value within the above range indicates that the mass percentage content of the cathode additive containing the structure shown in formula (II) is within a suitable range, which is beneficial for the phenolic group to function effectively, while simultaneously considering kinetic performance and high-temperature cycling performance. This is beneficial for improving the high-temperature cycling performance of the secondary battery, while also exhibiting good kinetic performance and high energy density.

[0040] In some implementations, the infrared spectrum of the cathode material layer is at 1200 cm⁻¹. -1 Up to 1350cm -1 And 1000cm -1 Up to 1199cm -1Characteristic peaks exist between them. The infrared spectrum of the cathode material layer satisfies the above characteristics, indicating that the cathode material layer contains cathode additives containing both the structures shown in formula (I) and formula (II), which is beneficial to further improve the high-temperature cycle performance of the secondary battery, while also exhibiting good kinetic performance and high energy density.

[0041] In some implementations, the infrared spectrum of the cathode material layer is at 1200 cm⁻¹. -1 Up to 1350cm -1 The transmittance of the characteristic peak at 1000 cm⁻¹ is I1, 30% ≤ I1 ≤ 80%. -1 Up to 1199cm -1 The transmittance of the characteristic peak is I2, 60% ≤ I2 ≤ 70%. For example, the value of I1 can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any two of these values; the value of I2 can be 60%, 63%, 65%, 68%, 70%, or any two of these values. Values ​​of I1 and I2 within the above ranges are beneficial for improving the high-temperature cycling performance of the secondary battery, while also exhibiting good kinetic performance and high energy density.

[0042] In some embodiments of this application, the thickness of the positive electrode material layer is H μm, where 10 ≤ H ≤ 50. For example, the value of H can be 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range of any two of these values. By controlling the thickness H of the positive electrode material layer within the above range, the path for lithium ions to migrate from the electrolyte to the interior of the positive electrode material layer during charging and discharging is shorter, which helps to reduce the internal resistance of the positive electrode sheet, thereby improving the kinetic performance and high-temperature cycle performance of the secondary battery, and also helps to increase the energy density of the secondary battery. In this application, the above thickness refers to the thickness of one side of the positive electrode material layer.

[0043] In this application, the thickness of the cathode material layer can be controlled by adjusting the single-sided coating areal density and compaction density. For example, when other conditions remain unchanged, increasing the single-sided coating areal density of the cathode material layer increases its thickness; decreasing the single-sided coating areal density decreases its thickness. When other conditions remain unchanged, increasing the compaction density of the cathode material layer decreases its thickness; decreasing the compaction density increases its thickness.

[0044] In some embodiments of this application, the film resistance of the positive electrode is RΩ, the thickness of the positive electrode material layer is Hμm, and the values ​​are 0.05≤R≤0.5 and 0.5≤R×H≤8. For example, the value of R can be any two values ​​from 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, and 0.50, and the value of R×H can be any two values ​​from 0.5, 1, 2, 3, 4, 5, 6, 7, and 8. Having the film resistance R and the value of R×H within the above ranges is beneficial for increasing the electron transport rate in the positive electrode, thereby improving the kinetic performance and high-temperature cycle performance of the secondary battery, and also for increasing the energy density of the secondary battery.

[0045] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a portion of it; this application has no particular limitation, as long as the purpose of this application is achieved.

[0046] In this application, the positive electrode material layer includes a positive electrode active material. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode active material is 84% ​​to 99%. For example, the mass percentage content of the positive electrode active material can be any two values ​​from 84%, 86%, 88%, 90%, 92%, 94%, 96%, to 99%. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can be, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The aforementioned lithium nickel cobalt manganese oxide can include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn0.3 O2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of O2 (NCM111).

[0047] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode conductive agent is 0.2% to 8%, and the mass percentage content of the positive electrode binder is 0.2% to 8%. For example, the mass percentage content of the positive electrode conductive agent can be any two values ​​from 0.2%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, and 8%, and the mass percentage content of the positive electrode binder can be any two values ​​from 0.2%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, and 8%. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders, as long as they can achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers, and the conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0048] This application does not impose any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (e.g., aluminum-carbon composite current collector). This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the positive electrode current collector can be from 6 μm to 25 μm.

[0049] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, the conductive agent may be at least one of the aforementioned positive electrode conductive agents, and the binder may be at least one of the aforementioned positive electrode binders.

[0050] The second aspect of this application provides a secondary battery, which includes the positive electrode provided in the first aspect of this application. The secondary battery of this application has good high-temperature cycling performance and kinetic performance.

[0051] The secondary battery also includes a negative electrode sheet, which comprises a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The phrase "the negative electrode sheet comprises a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector" means that the negative electrode material layer can be disposed on one surface of the negative current collector along its thickness direction, or on two surfaces of the negative current collector along its thickness direction. It should be noted that "surface" here can refer to the entire surface area of ​​the negative current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0052] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, or titanium copper composite current collector, etc.

[0053] The negative electrode material layer of this application includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0054] The negative electrode material layer of this application may further include a negative electrode conductive agent and a negative electrode binder. For example, the negative electrode conductive agent may be at least one of the above-mentioned positive electrode conductive agents, and the negative electrode binder may be at least one of the above-mentioned positive electrode binders. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0055] This application does not impose any particular limitations on the thickness of the negative electrode material layer and the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of one side of the negative electrode material layer can be from 80 μm to 100 μm, and the thickness of the negative electrode current collector can be from 4 μm to 15 μm.

[0056] Optionally, the negative electrode may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer; it can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a conductive binder. This application does not impose any particular limitation on the conductive agent and the conductive binder in the conductive layer; for example, the conductive agent may be at least one of the aforementioned positive electrode conductive agents, and the conductive binder may be at least one of the aforementioned positive electrode binders.

[0057] In this application, the secondary battery also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0058] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0059] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0060] In some embodiments, the inorganic layer comprises ceramic particles and an inorganic layer binder. This application does not particularly limit the ceramic particles; for example, the ceramic particles may include at least one selected from silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the inorganic layer binder; for example, the inorganic layer binder may be at least one of the above-mentioned positive electrode binders. In some embodiments, the polymer layer comprises a polymer, and the polymer material may include, but is not limited to, at least one selected from polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0061] In this application, there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of this application. For example, the thickness of the separator can be from 3μm to 30μm.

[0062] In this application, the secondary battery also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0063] This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application.

[0064] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0065] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0066] The secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0067] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the secondary battery may include, but is not limited to, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0068] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, negative electrode, and separator in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery; or stacking the positive electrode, separator, negative electrode, and separator in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0069] A third aspect of this application provides an electronic device that includes the secondary battery provided in the second aspect of this application. The electronic device of this application has a long service life and good performance.

[0070] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0071] Example

[0072] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0073] Test methods and equipment:

[0074] Test of the mass percentage of nitrogen in the cathode material layer

[0075] The lithium-ion battery was discharged to 3V at 0.5C under conditions of 25℃±3℃. The positive electrode was then disassembled, and the residual electrolyte on the surface of the positive electrode was wiped away with lint-free paper. The surface of the positive electrode perpendicular to the thickness direction was observed using a scanning electron microscope (SEM) in backscatter mode. The surface of the positive electrode was scanned using energy-dispersive X-ray spectroscopy (EDS) to obtain the mass percentage of nitrogen in the positive electrode material layer.

[0076] Infrared spectroscopy test

[0077] The lithium-ion battery was discharged to 3V at 0.5C under conditions of 25℃±3℃. The positive electrode was then disassembled, and the residual electrolyte on the surface was wiped off with lint-free paper before drying in an 85℃ oven. Diffuse reflectance infrared spectroscopy was performed on the positive electrode using parameters of wavelength from 2.5μm to 25μm and frequency of 4000cm⁻¹. -1 Up to 400cm -1 The absorption spectrum produced when light waves irradiate the positive electrode is the infrared spectrum, in which the absorption spectrum at 1200 cm⁻¹ is the infrared spectrum. -1 Up to 1350cm -1 The transmittance of the characteristic peak at 1000 cm⁻¹ is I1. -1 Up to 1199cm -1 The transmittance of the characteristic peak is I2.

[0078] Thickness test

[0079] Under conditions of 25℃±3℃, the lithium-ion battery was discharged to 3V at 0.5C, and the positive electrode sheet was obtained after disassembly. The residual electrolyte on the surface of the positive electrode sheet was wiped away with lint-free paper. The positive electrode sheet was then cut using plasma to obtain a cross-section along the thickness direction. The cross-section was then observed using a scanning electron microscope (SEM). Fifteen test points were selected, with an interval of 2mm between adjacent test points, and the thickness of the positive electrode material layer on one side of each test point was measured. The average value was calculated as the thickness of the positive electrode material layer.

[0080] Diaphragm resistance test

[0081] Under conditions of 25℃±3℃, the lithium-ion battery was charged to 4.53V at 0.5C, and the positive electrode was obtained after disassembly. Residual electrolyte on the surface of the positive electrode was wiped away with lint-free paper. The obtained positive electrode was placed in an environment with 10% humidity for 30 minutes, and then sealed and transferred to the film resistance testing location. The film resistance of the positive electrode was tested using a BER1200 film resistance meter, with adjacent test points spaced 2mm to 3mm apart. Tests were conducted at 15 different locations, and the average resistance of all test points was recorded as the film resistance R of the positive electrode. The test parameters were: indenter area 153.94mm². 2 Pressure 3.5t, holding time 50s.

[0082] Ratio Performance Test

[0083] At 25℃, after allowing the lithium-ion battery to stand for 5 minutes, it is charged at a constant current of 0.7C to 4.53V, then charged at a constant voltage of 4.53V to 0.05C. After standing for 5 minutes, it is discharged at a constant current of 0.2C to 3.0V. The discharge capacity of the lithium-ion battery at this point is measured and recorded as the 0.2C discharge capacity. Then, after standing for 5 minutes, it is charged at a constant current of 0.7C to 4.53V, then charged at a constant voltage of 4.53V to 0.05C. After standing for 5 minutes, it is discharged at a constant current of 2C to 3.0V. The discharge capacity of the lithium-ion battery at this point is measured and recorded as the 2C discharge capacity. 2C discharge capacity / 0.2C discharge capacity (%) = 2C discharge capacity / 0.2C discharge capacity × 100%. The rate performance and kinetic performance of lithium-ion batteries are evaluated by the ratio of 2C discharge capacity to 0.2C discharge capacity. The larger the ratio, the better the rate performance and kinetic performance of the lithium-ion battery; the smaller the ratio, the worse the rate performance and kinetic performance of the lithium-ion battery.

[0084] High-temperature cycling performance test

[0085] At 45℃, the lithium-ion battery was charged at a constant current of 0.5C to a voltage of 4.53V, then charged at a constant voltage of 4.53V to a current of 0.025C, and finally discharged at a constant current of 0.5C to a voltage of 3.0V. The discharge capacity of the lithium-ion battery at this point was measured and recorded as the discharge capacity of the first cycle. This charge-discharge cycle was then performed for 500 cycles, and the discharge capacity of the 500th cycle was measured. The capacity retention rate (%) after 500 cycles at 45℃ = (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.

[0086] Example 1

[0087] <Preparation of the positive electrode>

[0088] Lithium cobalt oxide (LiCoO2) as the positive electrode active material, succinic acid and a polymer of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol (molecular structure shown below, degree of polymerization n=30), conductive carbon black (Super P) as the positive electrode conductive agent, and polyvinylidene fluoride as the positive electrode binder were mixed in a mass ratio of 97.6:0.3:0.9:1.2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the slurry was obtained. The positive electrode slurry was uniformly coated on one surface of a 10μm thick aluminum foil current collector and dried at 90℃ to obtain a positive electrode sheet with a single-sided coating of positive electrode material. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 90℃, the electrode sheet was cold-pressed, cut, and had tabs welded to obtain a positive electrode sheet with a size of 74mm×867mm for later use. The surface density of the single-sided coating of the positive electrode material layer is 0.160 mg / mm². 2 The thickness of the single-sided positive electrode material layer is shown in Table 1.

[0089] <Preparation of Negative Electrode Sheets>

[0090] Artificial graphite (negative electrode active material), styrene-butadiene rubber (negative electrode binder), and acetylene black (negative electrode conductive agent) were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector and dried at 90°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer. After drying at 90°C, the sheet was cold-pressed, cut, and had tabs welded to obtain a negative electrode sheet with a size of 78 mm × 875 mm for later use. The thickness of the single-sided negative electrode material layer was 54.5 μm, and the compaction density of the negative electrode material layer was 1.7 g / cm³. 3 .

[0091] <Separating membrane>

[0092] A 5μm thick porous polyethylene polymer film (manufacturer: Celgard Diaphragm Company, USA) was used as the separator.

[0093] <Preparation of Electrolyte>

[0094] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of 10:30:60 to obtain a base solvent. Lithium salt LiPF6 was then added and stirred until homogeneous to obtain the electrolyte. The total mass of the electrolyte contained 12.5% ​​lithium salt LiPF6, with the remainder being the base solvent.

[0095] <Preparation of Lithium-ion Batteries>

[0096] The positive electrode, separator, negative electrode, and separator are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound to form the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. A prepared electrolyte is then injected, followed by vacuum sealing, settling, formation, and shaping processes to obtain a lithium-ion battery. The formation upper limit voltage is 4.53V, the formation temperature is 85°C, and the formation time is 60 minutes.

[0097] Examples 2 to 13

[0098] Except for adjusting the corresponding preparation parameters according to Table 1, everything else is the same as in Example 1. Specifically, when the mass percentage m% of the positive electrode additive changes, the mass percentage of the positive electrode active material changes accordingly, while the mass percentages of the positive electrode conductive agent and the positive electrode binder remain unchanged. The thickness H of the positive electrode material layer is controlled by adjusting the surface density of the single-sided coating of the positive electrode material layer. The mass ratio of the two positive electrode additives in Examples 8 and 10 is 1:1. The positive electrode additive in Example 12 uses the compound shown in formula (III), and the positive electrode additive in Example 13 uses the compound shown in formula (IV).

[0099] Comparative Example 1

[0100] Except that no positive electrode additives were added in the <Preparation of Positive Electrode Sheet>, and the positive electrode active material lithium cobalt oxide (LiCoO2), the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, the rest was the same as in Example 1.

[0101] Comparative Examples 2 to 3

[0102] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as in Example 1. Specifically, when the mass percentage of the positive electrode additive changes, the mass percentage of the positive electrode active material changes accordingly, while the mass percentages of the positive electrode conductive agent and the positive electrode binder remain unchanged.

[0103] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0104] As can be seen from Examples 1 to 13 and Comparative Examples 1 to 3, by introducing positive electrode additives within the scope of this application into the positive electrode sheet and controlling the mass percentage m% of the positive electrode additives within the scope of this application, the lithium-ion battery exhibits a larger 2C discharge capacity / 0.2C discharge capacity and a higher capacity retention rate after 500 cycles at 45°C, indicating that the lithium-ion battery of this application has good kinetic performance and high-temperature cycling performance. In contrast, the positive electrode sheet of Comparative Example 1 does not contain positive electrode additives, and the mass percentage m% of the positive electrode additives in the positive electrode sheets of Comparative Examples 2 and 3 is not within the scope of this application. Consequently, the lithium-ion battery exhibits a smaller 2C discharge capacity / 0.2C discharge capacity and a lower capacity retention rate after 500 cycles at 45°C, indicating poor kinetic performance and / or high-temperature cycling performance.

[0105] The mass percentage (m%) of the cathode additive typically affects the kinetic performance and high-temperature cycling performance of lithium-ion batteries. As can be seen from Examples 1 to 4 and Comparative Examples 1 to 3, when the value of m is too small, such as in Comparative Examples 1 and 2, the capacity retention rate of the lithium-ion battery after 500 cycles at 45°C is lower; when the value of m is too large, such as in Comparative Example 3, the 2C discharge capacity / 0.2C discharge capacity and the capacity retention rate after 500 cycles at 45°C are lower, indicating poor kinetic performance and / or high-temperature cycling performance of the lithium-ion battery. When the value of m is within the range of this application, the 2C discharge capacity / 0.2C discharge capacity and the capacity retention rate after 500 cycles at 45°C are higher, indicating good kinetic performance and high-temperature cycling performance of the lithium-ion battery of this application.

[0106] The thickness H of the positive electrode material layer typically affects the kinetic performance and high-temperature cycling performance of lithium-ion batteries. As can be seen from Examples 1, 5 to 7, when the value of H is within the range of this application, the lithium-ion battery exhibits a large 2C discharge capacity / 0.2C discharge capacity and a high capacity retention rate after 500 cycles at 45°C, indicating that the lithium-ion battery of this application has good kinetic performance and high-temperature cycling performance.

[0107] The type of cathode additive typically affects the kinetic performance and high-temperature cycling performance of lithium-ion batteries. As can be seen from Examples 1, 8 to 13, using cathode additives within the scope of this application results in lithium-ion batteries with a larger 2C discharge capacity / 0.2C discharge capacity and a higher capacity retention rate after 500 cycles at 45°C, indicating that the lithium-ion batteries of this application exhibit good kinetic performance and high-temperature cycling performance.

[0108] Figure 1 is an infrared spectrum of the positive electrode material layer in Embodiment 11 of this application. As can be seen from Figure 1, the infrared spectrum of the positive electrode material layer is at 1100 cm⁻¹. -1A characteristic peak exists at 1100 cm⁻¹. -1 The transmittance of the characteristic peak I2 is 60%, and the above characteristic peak corresponds to the C-OH bond in the structural formula (II) of the positive electrode additive.

[0109] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0110] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0111] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A positive electrode sheet, comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer comprising a positive electrode additive, wherein the mass percentage of the positive electrode additive is m%, 0.1 ≤ m ≤ 0.5, based on the mass of the positive electrode material layer, and the positive electrode additive comprises at least one of the structural formulas shown in formula (I) or (II). R1 to R2 are each independently selected from hydrogen atom, nitrogen atom, hydroxyl group, C1 to C2. 18 Alkyl groups, C3 to C4 groups containing ester groups 18 Chain-like or cyclic alkyl groups; R3 to R6 are each independently selected from hydrogen atoms, hydroxyl groups, C1 to C6 atoms. 18 Alkyl groups, C1 to C1 groups containing ester or ether bonds 18 Chain-like or cyclic alkyl groups.

2. The positive electrode sheet according to claim 1, wherein, 0.15≤m≤0.3。 3. The positive electrode sheet according to claim 1, wherein, R1 to R2 are each independently selected from hydrogen atoms, C3 to C4 atoms. 10 Alkyl groups, C3 to C4 groups containing ester groups 10 A chain alkyl group; R3 to R6 are each independently selected from hydrogen atoms, C1 to C5 chain alkyl groups, C1 to C5 groups containing ester groups or ether bonds. 10 Chain-like or cyclic alkyl groups.

4. The positive electrode sheet according to claim 1, wherein, The positive electrode material layer contains nitrogen, and the mass percentage of nitrogen in the positive electrode material layer is 0.1% to 0.3% based on the mass of the positive electrode material layer.

5. The positive electrode sheet according to claim 1, wherein, The positive electrode additive includes at least one of the following: a polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol, N,N-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butylated hydroxyanisole, or dibutylhydroxytoluene.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein, The positive electrode sheet satisfies at least one of the following characteristics: (1) The infrared spectrum of the positive electrode material layer is at 1200 cm⁻¹ -1 Up to 1350cm -1 Characteristic peaks exist between them; (2) The infrared spectrum of the positive electrode material layer is at 1000 cm⁻¹ -1 Up to 1199cm -1 Characteristic peaks exist between them.

7. The positive electrode sheet according to claim 6, wherein, The positive electrode sheet satisfies at least one of the following characteristics: (1) The infrared spectrum of the positive electrode material layer is at 1200 cm⁻¹ -1 Up to 1350cm -1 The transmittance of the characteristic peak is I1, 30% ≤ I1 ≤ 80%; (2) The infrared spectrum of the positive electrode material layer is at 1000 cm⁻¹ -1 Up to 1199cm -1 The transmittance of the characteristic peak is I2, 60% ≤ I2 ≤ 70%.

8. The positive electrode sheet according to any one of claims 1 to 5, wherein, The thickness of the positive electrode material layer is H μm, and 10 ≤ H ≤ 50.

9. The positive electrode sheet according to any one of claims 1 to 5, wherein, The film resistance of the positive electrode is RΩ, the thickness of the positive electrode material layer is Hμm, 0.05≤R≤0.5, and 0.5≤R×H≤8.

10. A secondary battery comprising a positive electrode sheet according to any one of claims 1 to 9.

11. An electronic device comprising the secondary battery of claim 10.

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