Positive electrode sheet, secondary battery, and electronic device

Abstract

The application provides a positive electrode sheet, a secondary battery and an electronic device, and belongs to the technical field of batteries. The positive electrode sheet comprises a positive electrode mixture layer, and the positive electrode mixture layer comprises a positive electrode material, wherein the positive electrode material comprises a first composition and a fluorine-containing polymer; in the infrared spectrum of the first composition, the infrared characteristic peaks of an ester group and a hydroxyl group are visible, the infrared characteristic peak of the ester group is located in the range of 1731cm ‑1 to 1749cm ‑1 , the infrared characteristic peak of the hydroxyl group is located in the range of 3436cm ‑1 to 3464cm ‑1 , and the peak intensity ratio of the ester group and the hydroxyl group is Q, wherein 1.1<=Q<=2.9. The first composition containing the ester group and the hydroxyl group is matched with the fluorine-containing polymer, so that the brittleness of the positive electrode sheet can be improved, the flexibility can be improved, the cracking of the electrode sheet can be reduced under high compaction density, and the cycle performance and high-temperature performance of the secondary battery can be improved.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode, a secondary battery, and an electronic device. Background Technology

[0002] The positive electrode is one of the key components of a rechargeable battery, and its performance is crucial to the battery's energy density, cycle life, and safety. However, due to the relatively hard crystal structure of the positive electrode material, the positive electrode sheet often suffers from brittleness. During preparation or use, it is prone to cracking and powdering, which reduces its ionic and electronic conductivity, affecting the battery's capacity and energy density. In addition, it can easily damage the structure of the positive electrode active material, and in severe cases, may cause short circuits and safety accidents.

[0003] To address this issue, existing technologies propose process improvements such as low-temperature drying and slow cooling to reduce internal stress in the electrode during fabrication. While these methods can mitigate the brittleness of the positive electrode to some extent, they often require longer production cycles and higher equipment investments, increasing both production costs and efficiency. Furthermore, the extended drying and cooling processes increase the time the electrode is exposed to the external environment, potentially increasing the risk of contamination and oxidation. Summary of the Invention

[0004] In view of this, this application provides a positive electrode, a secondary battery, and an electronic device, which improves the brittleness of the positive electrode by combining a first composition containing ester groups and hydroxyl groups with a fluoropolymer, thereby improving the cycle performance and high-temperature performance of the secondary battery.

[0005] In a first aspect, this application provides a positive electrode sheet comprising a positive electrode mixture layer, the positive electrode mixture layer comprising a positive electrode material, the positive electrode material comprising a first composition and a fluoropolymer, wherein the infrared spectrum of the first composition shows infrared characteristic peaks of ester groups and hydroxyl groups, the infrared characteristic peak of the ester groups being located at 1731 cm⁻¹. -1 Up to 1749cm -1 The infrared characteristic peak of hydroxyl groups is located at 3436 cm⁻¹. -1 Up to 3464cm -1 The peak intensity ratio of ester groups and hydroxyl groups is Q, where 1.1 ≤ Q ≤ 2.9. This application uses a first composition containing ester groups and hydroxyl groups in combination with a fluorinated polymer. This combination can occupy the polymer chains of the fluorinated polymer, reducing the secondary forces (hydrogen bonds, van der Waals forces) between the polymer chains, optimizing the crystallinity of the first composition and the fluorinated polymer, improving the brittleness and flexibility of the positive electrode sheet, making the positive electrode material less prone to breakage under high compaction pressure, thereby reducing electrode cracking, reducing side reactions and gas generation under cycling or high-temperature conditions, improving the cycle performance and high-temperature performance of the secondary battery, and also contributing to improved kinetics of the secondary battery.

[0006] In some embodiments, after the positive electrode material is kept at 362–367°C for 10 min, the mass reduction rate of the positive electrode material is r, where 0.1% ≤ r ≤ 0.5%.

[0007] In some embodiments, the mass content of the first composition is m1, where 0.1% ≤ m1 ≤ 0.5%, based on the mass of the positive electrode additive layer. This application regulates the mass content of the first composition in the positive electrode additive layer, enabling better compatibility with fluoropolymers, improving the brittleness of the positive electrode sheet, and thus improving the internal resistance, cycle performance, and high-temperature storage performance of the secondary battery.

[0008] In some embodiments, the first composition satisfies at least one of the following conditions to further improve the cycle performance and high-temperature storage performance of the secondary battery:

[0009] (1) The first composition includes component A and component B, wherein component A includes at least one of di(2-ethylhexyl) adipate and dioctyl sebacate, and component B includes polyethylene glycol;

[0010] (2) Based on the mass of the first composition, the mass content of component A is m. A The mass content of component B is m B ,4≤m A / m B ≤5.2;

[0011] (3) The first composition further includes component C, which comprises polydimethylsiloxane; the mass content of component C is m based on the mass of the first composition. C , 0.15≤m C / m B ≤0.8.

[0012] In some embodiments, the monomers of the fluoropolymer include at least one selected from 1,1-difluoroethylene, tetrafluoroethylene, and hexafluoroethylene. Fluoropolymers containing these monomers can better integrate with the first composition, optimize the crystallinity of the mixture, and improve the adhesion to the positive electrode active material, thereby enhancing the cycle performance and high-temperature storage performance of the secondary battery.

[0013] In some embodiments, the mass content of the fluoropolymer is m2, 0.9% ≤ m2 ≤ 2.0%, based on the mass of the positive electrode binder layer. Controlling the mass content of the fluoropolymer within the above range can further improve the flexibility of the positive electrode sheet and enhance the cycle performance and high-temperature storage performance of the secondary battery.

[0014] In some embodiments, 3 ≤ m2 / m1 ≤ 18, preferably 4.5 ≤ m2 / m1 ≤ 9. Adjusting the value of m2 / m1 within the above range can better balance the crystallinity and bonding effect of the mixture of the first composition and the fluoropolymer, thereby improving the internal resistance, cycle performance, and high-temperature storage performance of the secondary battery.

[0015] In some embodiments, the fluoropolymer includes at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin. These fluoropolymers can better integrate with the first composition, further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0016] In some embodiments, the crystallinity of the mixture composed of the first composition and the fluoropolymer is G, where 25% ≤ G ≤ 45%. When the crystallinity of the mixture composed of the first composition and the fluoropolymer is controlled within the above range, a better bonding effect can be achieved while improving the flexibility of the positive electrode, thereby improving the structural stability of the positive electrode sheet and enhancing the cycle and high-temperature storage performance of the secondary battery.

[0017] In some embodiments, the compaction density of the positive electrode sheet is P g / cm³. 3 4.4≤(P+1.2652×G)≤4.7. By controlling the compaction density and crystallinity G of the positive electrode sheet of this application within these ranges, the flexibility of the positive electrode sheet can be further improved, enabling the secondary battery to exhibit higher cycle and high-temperature storage performance.

[0018] In some embodiments, 4.1 ≤ P ≤ 4.3. Adjusting the compaction density of the positive electrode sheet within the above range, in conjunction with the positive electrode sheet system of this application, is beneficial for reducing the internal resistance of the electrode sheet and improving the cycle performance of the secondary battery.

[0019] In some embodiments, the positive electrode mixture layer further includes a positive electrode active material, which satisfies at least one of the following conditions:

[0020] (I) The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide or lithium iron phosphate;

[0021] (II) Based on the mass of the positive electrode mixture layer, the mass content of the positive electrode active material is m3, 90%≤m3≤97%;

[0022] (III) The specific flow energy of the positive electrode active material is F, where 251mJ ≤ F ≤ 308mJ. Based on the positive electrode system of this application, by adjusting the specific flow energy of the positive electrode active material within the above range, the energy density and kinetic performance of the secondary battery can be further improved, and the internal resistance can be reduced.

[0023] In a second aspect, this application also provides a secondary battery, which includes any of the positive electrode plates provided in the first aspect of this application.

[0024] In some specific embodiments, the secondary battery further includes an electrolyte comprising carboxylic acid ester compounds; based on the mass of the electrolyte, the mass content of the carboxylic acid ester compounds is m4, 21% ≤ m4 ≤ 39%, preferably 25.5% ≤ m4 ≤ 29.5%. This application uses carboxylic acid ester compounds in conjunction with the above-mentioned positive electrode system to increase the ion transport efficiency between the electrolyte and the positive electrode material, and reduce the internal resistance of the secondary battery; furthermore, controlling the mass content of the carboxylic acid ester compounds within the above range can further reduce side reactions between the electrolyte and the positive electrode material under cycling or high-temperature conditions, improving the battery's cycle performance and high-temperature storage performance.

[0025] In some embodiments, the aforementioned carboxylic acid ester compounds include at least one selected from methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl formate, propyl acetate, propyl propionate, propyl butyrate, butyl butyrate, butyl propionate, and pentyl propionate. These carboxylic acid ester compounds can better complement the positive electrode system of this application, further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0026] Thirdly, this application also provides an electronic device comprising any of the secondary batteries provided in the second aspect of this application. Based on the secondary battery of this application, the electronic device can exhibit the same advantages as the aforementioned secondary battery.

[0027] The beneficial effects of this application are at least as follows:

[0028] This application introduces a first composition containing ester and hydroxyl groups into the positive electrode sheet, which, in combination with a fluoropolymer, optimizes the crystallinity of the mixture of the first composition and the fluoropolymer. When applied to the positive electrode sheet, it improves the brittleness and flexibility of the positive electrode sheet, while also exhibiting a strong bonding effect, which is beneficial to increasing the compaction density of the positive electrode sheet. This shortens the transport path of the active material, reduces the internal resistance of the electrode sheet, and the high flexibility reduces the impact of winding or folding operations on the electrode sheet, improves electrode sheet cracking or main material particle breakage, reduces side reactions of fresh surface and electrolyte caused by breakage under cycling or high temperature conditions, and improves the cycle performance and high temperature performance of the secondary battery. Attached Figure Description

[0029] Figure 1 Infrared spectrum of the first composition ZII-1 provided for specific embodiments of this application;

[0030] Figure 2Infrared spectrum of the first composition ZII-2 provided for specific embodiments of this application;

[0031] Figure 3 Thermogravimetric analysis diagram of the positive electrode sheet provided in Embodiment I-1 of this application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0033] The inventors of this application discovered during their research on improving secondary batteries that reducing the proportion of inactive materials (such as separators and current collectors) in the positive electrode sheet can produce a positive electrode sheet with high areal density, while increasing the mass ratio of active materials and improving the energy density of the secondary battery. However, while increasing the areal density of the electrode sheet, the cohesive force of the film layer becomes greater. Under the same compression, the winding or folding steps cause greater damage to the electrode sheet. Therefore, the electrode sheet becomes more brittle and prone to breakage under high areal density, making it difficult to meet the requirements of the electrode sheet winding process.

[0034] To address the issue of electrode brittleness, additives containing hygroscopic groups are added to the electrodes. While this reduces brittleness after water absorption and improves compaction to some extent, it can lead to excessive water content and side reactions such as gas generation, negatively impacting the cycle performance of the secondary battery. Therefore, it is necessary to improve electrode brittleness while minimizing the deterioration of its cycle performance.

[0035] To address the aforementioned problems, this application provides a positive electrode sheet in a first aspect, comprising a positive electrode mixture layer, the positive electrode mixture layer comprising a positive electrode material, the positive electrode material comprising a first composition and a fluoropolymer, wherein the infrared spectrum of the first composition shows characteristic infrared peaks of ester groups and hydroxyl groups, with the characteristic infrared peak of the ester groups located at 1731 cm⁻¹. -1 Up to 1749cm -1 The infrared characteristic peak of hydroxyl groups is located at 3436 cm⁻¹. -1 Up to 3464cm -1The peak intensity ratio of ester groups and hydroxyl groups is Q, where 1.1 ≤ Q ≤ 2.9. This application introduces a first composition containing ester groups and hydroxyl groups into the positive electrode sheet, which, in combination with a fluoropolymer, can occupy the spaces between the polymer chains of the fluoropolymer. The hydroxyl groups, through hydrogen bonding interactions, interfere with the molecular arrangement of the fluoropolymer during crystallization, increasing the disorder of the fluoropolymer molecular chains. Combined with the interaction of the flexible segments of the ester groups, this reduces hydrogen bonds and van der Waals forces between the fluoropolymer molecular chains, increasing the flexibility and mobility of the fluoropolymer molecular chains. This optimizes the crystallinity of the mixture of the first composition and the fluoropolymer, while also providing a strong adhesive effect. When used in the positive electrode sheet, this improves flexibility and mitigates coating cracking and cold-press embrittlement caused by polymer shrinkage during coating and drying. On this basis, increasing the compaction density of the positive electrode sheet helps to shorten the transport path of active materials, reduce the internal resistance of the electrode sheet, and improve the dynamics of the secondary battery. In addition, the higher flexibility can reduce the impact of winding or folding operations on the electrode sheet, improve electrode sheet cracking or main material particle breakage, and reduce the side reactions of the surface and electrolyte caused by breakage under cycling or high temperature conditions, thereby improving the cycle performance and high temperature performance of the secondary battery.

[0036] In some embodiments, Q may be a value in the range of 1.1, 1.31, 1.49, 1.71, 1.92, 2.17, 2.29, 2.53, 2.62, 2.86, 2.9, or any combination of these values.

[0037] In some embodiments, after the positive electrode material is heat-treated at 362–367°C for 10 min, the mass reduction rate of the positive electrode material is r, where 0.1% ≤ r ≤ 0.5%. The above heat treatment method can remove the components of the first composition in this application; therefore, based on the above infrared characteristics, the mass reduction rate can reflect the mass content of the first composition in this application.

[0038] In some embodiments, based on the mass of the positive electrode additive layer, the mass content of the first composition is m1, where 0.1% ≤ m1 ≤ 0.5%. Exemplarily, m1 can be a value within the range of 0.1%, 0.14%, 0.16%, 0.18%, 0.23%, 0.28%, 0.30%, 0.37%, 0.41%, 0.48%, 0.49%, 0.5%, or any combination thereof. When the mass content of the first composition in the positive electrode additive layer is controlled within the above range, it can better coordinate with the fluoropolymer to optimize the crystallinity of both, improve the brittleness of the positive electrode sheet, thereby enhancing the compaction and kinetics of the positive electrode sheet, and improving the internal resistance, cycle performance, and high-temperature storage performance of the secondary battery.

[0039] In some embodiments, the first composition comprises component A and component B, wherein component A comprises at least one of di(2-ethylhexyl) adipate (DEHA) and dioctyl sebacate (DOS), and component B comprises polyethylene glycol (PEG). The use of these compounds to provide ester and hydroxyl groups enhances the synergistic effect with fluoropolymers. Furthermore, these compounds exhibit good affinity for the positive electrode active material, readily adsorbing onto its surface to improve its stability, thereby reducing side reactions with the electrolyte and further improving the cycle performance and high-temperature performance of the secondary battery.

[0040] In some embodiments, the mass content of component A is m based on the mass of the first composition. A The mass content of component B is m B ,4≤m A / m B ≤5.2, for example, m A / m B The values ​​can be within the range of 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, or any combination of these values. Controlling the mass ratio of component A and component B within the above range can optimize the ratio of ester groups and hydroxyl groups, improve the compatibility of the first composition with the fluoropolymer, and further enhance the cycle and high-temperature storage performance of the secondary battery.

[0041] In some embodiments, the first composition further includes component C, which comprises polydimethylsiloxane (PDMS); the mass content of component C is m based on the mass of the first composition. C , 0.15≤m C / m B ≤0.8, for example, m C / m B The value can be within the range of 0.15, 0.22, 0.29, 0.37, 0.43, 0.54, 0.58, 0.67, 0.69, 0.79, 0.8, or any combination of these values. Adding polydimethylsiloxane to the first composition, in combination with components A and B, can improve the permeability of the first composition, enhance its compatibility with fluoropolymers, further improve the flexibility and stability of the cathode material, optimize the cathode material structure, and thus improve the internal resistance, cycle performance, and high-temperature storage performance of the secondary battery.

[0042] In some embodiments, the monomers of the fluoropolymer include at least one of 1,1-difluoroethylene, tetrafluoroethylene, and hexafluoroethylene. Fluoropolymers containing these monomers can better integrate with the first composition, optimize the crystallinity of the mixture, improve the adhesion to the positive electrode active material, ensure the stability of the positive electrode structure, and enhance the cycle performance and high-temperature storage performance of the secondary battery.

[0043] In some embodiments, based on the mass of the positive electrode binder layer, the mass content of the fluoropolymer is m2, where 0.9% ≤ m2 ≤ 2.0%. For example, m2 can be a value within the range of 0.9%, 1.0%, 1.1%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.9%, 2.0%, or any combination thereof. Adjusting the mass content of the fluoropolymer within the above range can further improve the flexibility of the positive electrode sheet and enhance the cycle performance and high-temperature storage performance of the secondary battery.

[0044] In some embodiments, 3 ≤ m2 / m1 ≤ 18, preferably 4.5 ≤ m2 / m1 ≤ 9. For example, m2 / m1 can be a value within the range of 3, 4.5, 5, 5.4, 5.9, 6, 6.3, 7.1, 7.4, 8, 8.2, 8.7, 9, 11, 12, 15, 17, 18, or any combination of these values. Adjusting the value of m2 / m1 within the above range can better balance the crystallinity and bonding effect of the mixture of the first composition and the fluoropolymer, thereby improving the internal resistance, cycle performance, and high-temperature storage performance of the secondary battery.

[0045] In some embodiments, the fluoropolymer includes at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin. These fluoropolymers can better integrate with the first composition, further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0046] In some embodiments, the crystallinity of the mixture composed of the first composition and the fluoropolymer is G, where 25% ≤ G ≤ 45%. Exemplarily, G can be a value within the range of 25%, 27%, 29%, 32%, 34%, 36%, 39%, 41%, 42%, 45%, or any combination thereof. When the crystallinity of the mixture composed of the first composition and the fluoropolymer is controlled within the above range, a better bonding effect can be achieved while improving the flexibility of the positive electrode, thereby improving the structural stability of the positive electrode sheet and enhancing the cycle and high-temperature storage performance of the secondary battery.

[0047] In some embodiments, the compaction density of the positive electrode sheet is P g / cm³. 34.4 ≤ (P + 1.2652 × G) ≤ 4.7. For example, the value of P + 1.2652 × G can be 4.4, 4.43, 4.47, 4.49, 4.52, 4.58, 4.61, 4.62, 4.66, 4.68, 4.7, or any combination of these values. By controlling the compaction density and the crystallinity G of the positive electrode sheet of this application within these ranges, the flexibility of the positive electrode sheet can be further improved, enabling the secondary battery to exhibit higher cycle and high-temperature storage performance.

[0048] In some embodiments, 4.1 ≤ P ≤ 4.3. For example, P can be a value within the range of 4.1, 4.12, 4.14, 4.17, 4.18, 4.21, 4.22, 4.25, 4.28, 4.3, or any combination of these values. Adjusting the compaction density of the positive electrode sheet within the above range, in conjunction with the positive electrode sheet system of this application, is beneficial for optimizing the battery's discharge capacity, reducing internal resistance, reducing polarization loss, and thereby improving the cycle performance of the secondary battery.

[0049] In some embodiments, the positive electrode mixture layer further includes a positive electrode active material, which satisfies at least one of the following conditions:

[0050] (I) The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide or lithium iron phosphate;

[0051] (II) Based on the mass of the positive electrode mixture layer, the mass content of the positive electrode active material is m3, 90%≤m3≤97%;

[0052] (III) The specific flow energy of the positive electrode active material is F, where 251mJ ≤ F ≤ 308mJ. For example, F can be 251mJ, 258mJ, 263mJ, 271mJ, 278mJ, 282mJ, 291mJ, 293mJ, 297mJ, 307mJ, or any combination of these values. Based on the positive electrode system of this application, controlling the specific flow energy of the positive electrode active material within the above range can reduce the resistance experienced by the positive electrode active material during the cold pressing process, making it easier for the positive electrode active material to slip, reducing breakage and side reactions, thereby improving the cycle and high-temperature performance of the secondary battery. Furthermore, it is beneficial to increase the compaction density of the positive electrode sheet, further improving the energy density and kinetic performance of the secondary battery, and reducing internal resistance.

[0053] In this application, there are no particular limitations on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive electrode additive layer located on at least one surface of the positive current collector. The aforementioned "positive electrode additive layer located on at least one surface of the positive current collector" means that the positive electrode additive layer can be located on one surface of the positive current collector along its own thickness direction, or on two surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or only a part of the surface area of ​​the positive current collector; there are no particular limitations in this application, as long as it achieves the purpose of this application. This application also has no particular limitations on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector can include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). In this application, the positive electrode active material can also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0054] In this application, the positive electrode binder layer may further include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent in the positive electrode binder layer, as long as it achieves 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 (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, and conductive polymers. 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 polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode binder layer; those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved. This application does not have a particular limitation on the thickness of the positive electrode mixture layer, as long as it can achieve the purpose of this application. For example, the thickness of the positive electrode mixture layer can be from 3 μm to 15 μm.

[0055] In a second aspect, this application also provides a secondary battery, which includes any of the positive electrode plates provided in the first aspect of this application.

[0056] In this application, the secondary battery also includes a negative electrode sheet. This application does not impose any particular limitation on the negative electrode sheet, as long as it achieves the purpose of this application. For example, the negative electrode sheet includes a negative current collector and a negative electrode flux layer disposed on at least one surface of the negative current collector. In this application, the negative electrode flux layer can be disposed on one surface or two surfaces in the thickness direction of the negative current collector. It should be noted that "surface" here can be the entire area of ​​the negative current collector or a part of the negative current collector; this application does not impose any particular limitation, as long as it achieves the purpose of this application. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors (e.g., carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector, etc.). In this application, there are no particular limitations on the thickness of the negative current collector, the negative electrode flux layer, and the negative electrode sheet, as long as they achieve the purpose of this application.

[0057] The negative electrode additive layer of this application includes a negative electrode active material, which may include, but is not limited to, graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, and SiO2. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate lithiation TiO2-Li4Ti5O 12 At least one of Li-Al alloy and metallic lithium.

[0058] The negative electrode mixture layer in this application may further include a negative electrode binder and a negative electrode conductive agent, or the negative electrode mixture layer may further include a negative electrode binder, a negative electrode conductive agent, and a thickener. This application does not particularly limit the types of negative electrode binders and negative electrode conductive agents, as long as they achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of the aforementioned positive electrode binders, and the negative electrode conductive agent may include, but is not limited to, at least one of the aforementioned positive electrode conductive agents. This application does not particularly limit the types of thickeners, as long as they achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode mixture layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0059] In some specific embodiments, the secondary battery further includes an electrolyte comprising a carboxylic acid ester compound; based on the mass of the electrolyte, the mass content of the carboxylic acid ester compound is m4, preferably 21% ≤ m4 ≤ 39%, and more preferably 25.5% ≤ m4 ≤ 29.5%. For example, the value of m4 can be 21%, 22.9%, 25.3%, 25.5%, 27.4%, 28.3%, 29.5%, 31.6%, 33.8%, 35.9%, 36.2%, 38.6%, 39%, or any combination thereof. This application, through the combination of the first composition and the fluoropolymer, can reduce the breakage of the positive electrode material and improve the structural stability of the positive electrode material. Furthermore, by using a carboxylic acid ester compound in combination with the above-mentioned positive electrode system, the ion transport efficiency of the electrolyte and the positive electrode material can be increased, the internal resistance reduced, and the kinetic performance of the secondary battery improved. By controlling the mass content of carboxylic acid ester compounds within the above range, side reactions between the electrolyte and the cathode material under cycling or high-temperature conditions can be further reduced, thereby improving the battery's cycle performance and high-temperature storage performance.

[0060] In some embodiments, the aforementioned carboxylic acid ester compounds include at least one selected from methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl formate, propyl acetate, propyl propionate, propyl butyrate, butyl butyrate, butyl propionate, and pentyl propionate. These carboxylic acid ester compounds can better complement the positive electrode system of this application, further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0061] In this application, the electrolyte includes lithium salts and non-aqueous solvents. The lithium salts may include at least one selected from LiPF6, LiPO2F2, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium difluoroborate. This application does not limit the content of lithium salts in the electrolyte, as long as the purpose of this application is achieved. This application does not particularly limit the non-aqueous solvents, as long as the purpose of this application is achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one selected from carbonate compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one selected from chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate (EMC), ethyl propyl carbonate, and methyl ethyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate, butyl carbonate, and vinyl ethylene carbonate. Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1,2-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, and trifluoromethylethylene carbonate. 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, and tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, 1,3-propanesulfonate lactone (PS), and adiponitrile (ADN).

[0062] This application does not impose any particular limitation on the separator membrane, as long as it can achieve the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid; the type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, and spun membrane. For example, the separator membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and 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. Optionally, a surface treatment layer may be provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances. For example, the inorganic layer includes inorganic particles and a binder. This application does not particularly limit the inorganic particles, which may include at least one of the following: alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. This application does not particularly limit the binder; it may include at least one of the above-mentioned positive electrode binders. The polymer layer contains a polymer. This application does not particularly limit the polymer; for example, the polymer may include at least one of polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene). In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application; for example, the thickness of the separator may be from 5 μm to 500 μm.

[0063] The secondary battery of this application also includes a packaging bag for containing the positive electrode, negative electrode, separator, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0064] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0065] This application does not impose any particular limitation on the preparation method of the secondary battery. For example, it may include the following steps: stacking the positive electrode, separator and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator and negative electrode in sequence, and then fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery.

[0066] Thirdly, this application also provides an electronic device that includes the secondary battery provided in the first aspect of this application. The secondary battery of this application has good cycle performance and high-temperature performance; therefore, the electronic device of this application has a long service life and high safety performance during application.

[0067] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, 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, household large-capacity batteries, and lithium-ion capacitors.

[0068] The following uses a lithium-ion battery as an example to illustrate the solution of this application with specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available products, and the devices or equipment used are all purchased from conventional market sales channels.

[0069] Tables 1 and 2 show the specific components of different first compositions or comparative examples, the corresponding mass percentage of each component in the first composition, and / or the number-average molecular weight.

[0070] Table 1

[0071]

[0072] Table 2

[0073]

[0074]

[0075] The infrared spectroscopy of the first composition in this application can be performed using an FTIR-430 advanced Fourier transform infrared spectrometer from JASCO Corporation, Japan. Before the infrared spectroscopy test, the first composition sample is dried at 60°C for 5 hours. The sample is pressed into a potassium bromide pellet and measured in transmission mode.

[0076] Figure 1 and Figure 2 The infrared spectra of the first compositions ZII-1 and ZII-2 provided in this application are shown, revealing the characteristic infrared peaks of the ester and hydroxyl groups. Figure 1 The characteristic infrared peak of the ester group is located at 1737.97 cm⁻¹. -1 The infrared characteristic peak of the hydroxyl group is located at 3442.29 cm⁻¹. -1 The peak intensity ratio of ester group to hydroxyl group is A = 2.5; Figure 2 The characteristic infrared peak of the ester group is located at 1738.01 cm⁻¹. -1 The infrared characteristic peak of the hydroxyl group is located at 3459.20 cm⁻¹. -1 The peak intensity ratio of ester group to hydroxyl group is A = 1.31.

[0077] Example I-1

[0078] The positive electrode sheet of this embodiment includes a positive electrode mixture layer, which includes a positive electrode material. The positive electrode material includes a first composition and a fluoropolymer, wherein the first composition is ZI-1.

[0079] Figure 3 The thermogravimetric analysis diagram of the cathode material in this embodiment is shown. After the cathode material is kept at 362-367°C, the mass reduction rate r of the cathode material is 0.2%, which corresponds to the mass ratio of the first composition in the cathode material of this embodiment being 0.2%.

[0080] Preparation of the positive electrode sheet:

[0081] A positive electrode active material, polyvinylidene fluoride (PVDF), a positive electrode conductive agent, and a first composition in a mass ratio of 97.6:1.3:0.9:0.2 were mixed in N-methylpyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was coated onto an aluminum foil, which was dried at 95°C. After cold pressing, cutting, and slitting, the foil was dried under vacuum at 85°C for 4 hours to obtain a positive electrode sheet.

[0082] Preparation of negative electrode sheet:

[0083] A negative electrode slurry was prepared by mixing artificial graphite negative electrode active material, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in deionized water at a mass ratio of 96.4:1.5:0.5:1.6, with a solid content of 54 wt%. The negative electrode slurry was coated onto copper foil, which was dried at 85°C. After cold pressing, cutting, and slitting, the copper foil was dried under vacuum at 80°C for 12 hours to obtain the negative electrode sheet.

[0084] Electrolyte preparation:

[0085] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:EMC:DEC = 1:3:3:3. After thorough stirring, lithium salt LiPF6 was added and mixed evenly to obtain the electrolyte. The molar concentration of lithium salt LiPF6 was 1.5 mol / L based on the mass of the electrolyte.

[0086] Preparation of the separator membrane: A 7μm thick polyethylene (PE) separator membrane substrate was coated with a 3μm ceramic coating.

[0087] The preparation of lithium-ion batteries involves stacking the positive electrode, separator, and negative electrode in sequence, with the separator acting as a barrier between the positive and negative electrodes. The cells are then wound to obtain a bare cell. After welding the tabs, the bare cell is placed in an outer packaging foil aluminum-plastic film. The prepared electrolyte is injected into the dried bare cell. The battery undergoes vacuum sealing, settling, formation (0.02C constant current charging to 3.3V, then 0.1C constant current charging to 3.6V), shaping, and capacity testing to obtain a lithium-ion battery.

[0088] Positive electrode compaction density test:

[0089] Positive electrode compaction density = mass of positive electrode material layer per unit area (unit: g / cm³) 2 The thickness of the positive electrode material layer is measured in centimeters. The mass of the positive electrode material layer per unit area can be measured using a balance, and the thickness of the positive electrode material layer can be measured using a micrometer.

[0090] Specific flow energy test of positive electrode active material:

[0091] The specific flow energy of the positive electrode active material was measured using an FT4 powder rheometer (Freeman Technology Company).

[0092] Exterior cracking and powder shedding test:

[0093] Take a positive electrode sheet with a width of 80mm and fold it in half once. Observe and record the light transmission points on the positive electrode sheet. Among them, 0 light transmission points indicate no cracking or powdering, 1 to 5 light transmission points indicate slight cracking or powdering, and more than or equal to 6 light transmission points indicate cracking or powdering.

[0094] DC Impedance (DCR) Test:

[0095] The lithium-ion battery was placed in a 0℃ high and low temperature chamber for 4 hours; it was then charged at a constant current of 0.1C until the voltage was the set charging value (4.5V for lithium cobalt oxide, 4.2V for lithium nickel cobalt manganese oxide and lithium manganese oxide, and 3.6V for lithium iron phosphate), and then charged at a constant voltage until the cutoff current was 0.05C. The battery was then placed in a constant current chamber for 10 minutes; then it was discharged at a constant current of 1C for 1 second. The DC impedance corresponding to 100% SOC of the lithium-ion battery was calculated and recorded as the internal resistance of the lithium-ion battery.

[0096] Cyclic performance test:

[0097] The lithium-ion battery was placed in an environment of 45℃ and charged at a constant current of 0.5C until the voltage setpoint was reached (4.5V for lithium cobalt oxide, 4.2V for lithium manganese oxide, and 3.6V for lithium iron phosphate). Then, it was charged at a constant voltage until the cutoff current reached 0.05C. After resting for 5 minutes, it was discharged at a constant current of 0.5C until the voltage setpoint was reached (3.0V for lithium cobalt oxide, 3.0V for lithium manganese oxide, and 2.5V for lithium iron phosphate). After resting for 5 minutes, the discharge capacity of the first cycle was recorded. Then, the same procedure was repeated for 500 charge and discharge cycles, and the discharge capacity of the 500th cycle was recorded.

[0098] The capacity retention rate (%) of a lithium-ion battery after 500 cycles = (discharge capacity of the 500th cycle / discharge capacity of the first cycle) × 100%, which is denoted as the cycle performance of the lithium-ion battery.

[0099] High-temperature storage performance test:

[0100] Place the lithium-ion battery in a 25°C constant temperature chamber and let it stand for 30 minutes to allow it to reach a constant temperature of 25°C. Charge it at a constant current of 1C until the voltage is the charging setpoint (charging setpoint as before), then charge it at a constant voltage until the cutoff current is 0.05C. Discharge it at a constant current of 1C until the voltage is the discharging setpoint (discharging setpoint as before), then charge it at a constant current of 0.5C until the voltage is the charging setpoint (charging setpoint as before), then charge it at a constant voltage until the cutoff current is 0.05C. Measure and record the thickness T0 of the lithium-ion battery using a micrometer. Transfer the lithium-ion battery to an 85°C constant temperature chamber for storage for 35 days, then transfer it to a 25°C constant temperature chamber and let it stand for 60 minutes. Measure and record the thickness T1 of the lithium-ion battery using a micrometer.

[0101] The high-temperature storage thickness expansion rate = (T1-T0) / T0×100%, which is denoted as the high-temperature storage performance of lithium-ion batteries.

[0102] The positive electrode sheets of the following examples and comparative examples differ from those of Example I-1 only in that the first composition, the type and / or content of the fluoropolymer are as shown in Table 3. The Q value is controlled by adjusting the mass ratio of different substances in the first composition. In Table 3, PAA represents polyacrylic acid, THV represents a copolymer of tetrafluoroethylene, hexafluoroethylene and vinylidene fluoride, PTFE represents polytetrafluoroethylene, and PVDF represents polyvinylidene fluoride.

[0103] Table 3

[0104]

[0105]

[0106] As shown in Table 3, the peak intensity ratio of ester group and hydroxyl group in the first composition of this application is Q, which satisfies the condition: 1.1≤Q≤2.9. After being combined with fluorinated polymer, it can optimize the crystallinity of the first composition and the fluorinated polymer, thereby improving the internal resistance, cycle performance and high temperature performance of the secondary battery.

[0107] In particular, the mass content m1 of the first composition in the positive electrode compound layer of this application is controlled to satisfy: 0.1% ≤ m1 ≤ 0.5%, which can better cooperate with fluoropolymers and further improve the internal resistance, cycle performance and high temperature storage performance of secondary batteries.

[0108] Specifically, this application utilizes the combination of components A and B from Table 1, which better leverages the synergistic effect with fluoropolymers, thereby improving the cycle performance and high-temperature performance of the secondary battery. Among these, this application controls m... A / m B Satisfy: 4≤m A / m B ≤9 can further improve the cycle life and high-temperature storage performance of secondary batteries.

[0109] Specifically, this application controls the mass content of the fluoropolymer to satisfy: 0.9% ≤ m2 ≤ 2.0%, which can further improve the flexibility of the positive electrode sheet and enhance the cycle performance and high-temperature storage performance of the secondary battery. Furthermore, controlling the value of m2 / m1 to satisfy: 3 ≤ m2 / m1 ≤ 18, more preferably 4.5 ≤ m2 / m1 ≤ 9, can better balance the crystallinity and bonding effect of the mixture of the first composition and the fluoropolymer, improving the internal resistance, cycle performance, and high-temperature storage performance of the secondary battery.

[0110] The positive electrode sheets of the following examples and comparative examples differ from those of Example 1 only in that the crystallinity G of the first composition and the fluoropolymer, the flow energy F of the positive electrode active material and the relationship between the two, and the types and contents of carboxylic acid ester compounds are adjusted. The specific differences are shown in Table 4.

[0111] Table 4

[0112]

[0113]

[0114] In Table 4, when adjusting the crystallinity G of the first composition and the fluoropolymer, the crystallinity is adjusted by adjusting the mass ratio of the fluoropolymer while controlling Q in the same way as in Example I-1. When adjusting the content and type of carboxylic acid ester compounds, the corresponding mass content of carboxylic acid ester compounds is added to the electrolyte of Example I-1.

[0115] As shown in Table 4, controlling the crystallinity G of the mixture composed of the first composition and the fluoropolymer in this application satisfies the condition: 25% ≤ G ≤ 45%, which can improve the kinetics, cycle performance, and high-temperature storage performance of the secondary battery. Furthermore, when the value of P + 1.2652 × G is adjusted to satisfy: 4.4 ≤ (P + 1.2652 × G) ≤ 4.7, it is beneficial to reduce the internal resistance of the electrode and enable the secondary battery to exhibit higher cycle performance and high-temperature storage performance.

[0116] Specifically, based on the cathode system of this application, adjusting the value of P to satisfy 4.1≤P≤4.3 and / or the value of F to satisfy 251mJ≤F≤308mJ can further improve the energy density and kinetic performance of the secondary battery and reduce the internal resistance.

[0117] Furthermore, this application uses carboxylic acid ester compounds in combination with the above-mentioned positive electrode system, especially controlling the mass content of the carboxylic acid ester compounds to meet the following conditions: 21% ≤ m4 ≤ 39%, preferably 25.5% ≤ m4 ≤ 29.5%, which can further improve the internal resistance, cycle performance and high-temperature storage performance of the battery.

[0118] The positive electrode sheets of the following examples and comparative examples differ from those of Example I-1 only in that the types of the first compositions are shown in Table 5.

[0119] Table 5

[0120] serial number First compound Cracking, powdering Internal resistance (mΩ) Cyclic performance (%) High-temperature storage (%) Example 1-1 ZI-1 none 75 80 10 Example III-1 ZII-1 none 69 81 10 Example III-2 ZII-2 none 66 85 10 Example III-3 ZII-3 none 55 88 8 Example III-4 ZII-4 none 70 80 9 Example III-5 ZII-5 slight 77 75 11 Example III-6 ZII-6 slight 78 76 12 Example III-7 ZII-7 none 67 83 8 Example III-8 ZII-8 none 50 90 6 Example III-9 ZII-9 none 64 84 8 Example III-10 ZII-10 none 65 83 9 Example III-11 ZII-11 none 76 76 12 Example III-12 ZII-12 none 69 80 9 Example III-13 ZII-13 none 74 75 12

[0121] As shown in Table 5, this application further employs the first composition including component C from Table 2 in combination with a fluoropolymer, especially when controlling m C / m B Satisfy: 0.15≤m C / m B A value of ≤0.8 can better improve the flexibility and stability of the cathode material, and improve the internal resistance, cycle performance and high-temperature storage performance of the secondary battery.

[0122] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive electrode mixture layer, which includes a positive electrode material. The positive electrode material includes a first composition and a fluoropolymer. In the infrared spectrum of the first composition, characteristic infrared peaks of ester groups and hydroxyl groups are visible, with the characteristic infrared peak of the ester groups located at 1731 cm⁻¹. -1 Up to 1749 cm -1 The infrared characteristic peak of the hydroxyl group is located at 3436 cm⁻¹. -1 Up to 3464 cm -1 The peak intensity ratio of the ester group and the hydroxyl group is Q, where 1.1 ≤ Q ≤ 2.9; The compaction density of the positive electrode sheet is P g / cm³. 3 , 4.1≤P≤4.3; The first composition includes component A and component B, wherein component A includes at least one of di(2-ethylhexyl) adipate and dioctyl sebacate, and component B includes polyethylene glycol; The fluoropolymer includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

2. The positive electrode sheet according to claim 1, characterized in that, 1.41≤Q≤2.53。 3. The positive electrode sheet according to claim 1, characterized in that, After the positive electrode material is heat-treated at 362℃~367℃ for 10 min, the mass reduction rate of the positive electrode material is r, 0.1%≤r≤0.5%; and / or, Based on the mass of the positive electrode compound layer, the mass content of the first composition is m1, where 0.1% ≤ m1 ≤ 0.5%.

4. The positive electrode sheet according to claim 3, characterized in that, The first composition satisfies at least one of the following conditions: (1) Based on the mass of the first composition, the mass content of component A is m. A The mass content of component B is m B ,4≤m A / m B ≤5.2; (2) The first composition further includes component C, which comprises polydimethylsiloxane; the mass content of component C is m based on the mass of the first composition. C , 0.15≤m C / m B ≤0.

8.

5. The positive electrode sheet according to claim 3, characterized in that, The monomers of the fluoropolymer include at least one of 1,1-difluoroethylene and tetrafluoroethylene; and / or, Based on the mass of the positive electrode compound layer, the mass content of the fluoropolymer is m2; 0.9%≤m2≤2.0%; and / or, 3≤m2 / m1≤18.

6. The positive electrode sheet according to claim 5, characterized in that, 4.5≤m2 / m1≤9.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that, The crystallinity of the mixture consisting of the first composition and the fluoropolymer is G, 25% ≤ G ≤ 45%; and / or, 4.4≤(P+1.2652×G)≤4.

7.

8. The positive electrode sheet according to any one of claims 1 to 6, characterized in that, The positive electrode mixture layer further includes a positive electrode active material, which satisfies at least one of the following conditions: (I) The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, or lithium iron phosphate; (II) Based on the mass of the positive electrode mixture layer, the mass content of the positive electrode active material is m3, 90%≤m3≤97%; (III) The specific flow energy of the positive electrode active material is F, 251 mJ≤F≤308 mJ.

9. A secondary battery, characterized in that, The secondary battery includes the positive electrode sheet according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, characterized in that, The secondary battery also includes an electrolyte, which comprises carboxylic acid ester compounds; based on the mass of the electrolyte, the mass content of the carboxylic acid ester compounds is m4, 21%≤m4≤39%.

11. The secondary battery according to claim 10, characterized in that, The carboxylic acid ester compounds include at least one selected from methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl formate, propyl acetate, propyl propionate, propyl butyrate, butyl butyrate, butyl propionate, and pentyl propionate; and / or, 25.5%≤m4≤29.5%。 12. An electronic device, characterized in that, The electronic device includes the secondary battery as described in any one of claims 9 to 11.

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