Positive electrode sheet, secondary battery and electronic apparatus

Abstract

The present application belongs to the technical field of batteries, and provides a positive electrode sheet, a secondary battery and an electronic apparatus. The positive electrode sheet comprises a positive electrode mixture layer; the positive electrode mixture layer comprises a positive electrode material; the positive electrode material comprises a first composition and a fluorine-containing polymer; in the infrared spectrum of the first composition, infrared characteristic peaks of an ester group and a hydroxyl group are visible, the infrared characteristic peak of the ester group being located between 1731 cm-1 and 1749 cm-1, and the infrared characteristic peak of the hydroxyl group being located between 3436 cm-1 and 3464 cm-1; the peak intensity ratio between the ester group and the hydroxyl group is Q, 1.1≤Q≤2.9. The coordination between the first composition comprising the ester group and the hydroxyl group and the fluorine-containing polymer used in the present application can improve the brittleness of the positive electrode sheet and enhance the flexibility thereof, so as to reduce electrode sheet cracking at high compaction density and improve the cycle performance and the high-temperature performance of secondary batteries.

Description

Positive electrode sheet, secondary battery and electronic device Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a positive electrode plate, a secondary battery, and an electronic device. Background Art

[0002] The positive electrode is a key component of a secondary battery, and its performance is crucial to its energy density, cycle life, and safety. However, due to the relatively hard crystal structure of the positive electrode material, the positive electrode sheet is often brittle and prone to cracking and powdering during preparation or use, reducing its ionic and electronic conductivity, affecting the battery's capacity and energy density. It can also easily damage the structure of the positive electrode active material, which can cause short circuits and lead to safety accidents.

[0003] To address this issue, existing technologies have proposed process improvements such as low-temperature drying and slow cooling to reduce the internal stress of the electrode during the manufacturing process. While these methods can improve the brittleness of positive electrode plates to a certain extent, these processes often require longer production cycles and higher equipment investments, which not only increases production costs but also affects production efficiency. In addition, the long drying and cooling processes increase the time the electrode is in contact with the external environment, which may also increase the risk of electrode contamination and oxidation. Summary of the Invention

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

[0005] In the first aspect, the present application provides a positive electrode sheet, which includes a positive electrode mixture layer, the positive electrode mixture layer includes a positive electrode material, the positive electrode material includes a first composition and a fluorine-containing polymer, in the infrared spectrum of the first composition, infrared characteristic peaks of ester and hydroxyl groups are visible, and the infrared characteristic peak of the ester group is located at 1731cm -1 to 1749cm -1 The infrared characteristic peak of hydroxyl is located at 3436cm -1 to 3464cm -1The peak intensity ratio of the ester group and the hydroxyl group is Q, 1.1≤Q≤2.9. The present application adopts a first composition containing an ester group and a hydroxyl group in combination with a fluoropolymer, which can occupy the high molecular chains of the fluoropolymer, reduce the secondary forces (hydrogen bonds, van der Waals forces) between the molecular chains of the latter, optimize the crystallinity of the first composition and the fluoropolymer, improve the brittleness of the positive electrode and enhance the flexibility. The positive electrode material is not easy to break under high compaction density, thereby reducing the cracking of the electrode, and reducing side reactions and gas production under cyclic or high temperature conditions, improving the cycle performance and high temperature performance of the secondary battery, and also helping to improve the dynamics of the secondary battery.

[0006] In some embodiments, after the positive electrode material is heat-treated at 362-367° C. for 10 minutes, the mass reduction rate of the positive electrode material is r, and 0.1%≤r≤0.5%.

[0007] In some embodiments, based on the mass of the positive electrode mixture layer, the mass content of the first composition is m1, and 0.1%≤m1≤0.5%. The present application regulates the mass content of the first composition in the positive electrode mixture layer to better cooperate with the fluoropolymer, improve the brittleness of the positive electrode sheet, and thereby improve 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, which can 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, 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 includes polydimethylsiloxane; based on the mass of the first composition, the mass content of component C is m C , 0.15≤m C / m B ≤0.8.

[0012] In some embodiments, the monomers of the fluoropolymer include at least one of vinylidene fluoride, tetrafluoroethylene, and hexafluoroethylene. Fluoropolymers containing these monomers can better blend with the first composition, optimize the crystallinity of the mixture, and enhance the bonding effect to the positive electrode active material, thereby improving the cycling performance and high-temperature storage performance of the secondary battery.

[0013] In some embodiments, based on the mass of the positive electrode mixture layer, the mass content of the fluoropolymer is m2, 0.9%≤m2≤2.0%. Regulating 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. Regulating 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 of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorinated acrylate resin. These fluoropolymers can better cooperate with the first composition to further improve the cycle performance and high-temperature storage performance of the secondary battery.

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

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

[0018] In some embodiments, 4.1≤P≤4.3. Regulating the compaction density of the positive electrode sheet within the above range in conjunction with the positive electrode sheet system of the present 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, and the positive electrode active material satisfies at least one of the following conditions:

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

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

[0022] (III) The specific flow energy of the positive electrode active material is F, 251mJ≤F≤308mJ. Based on the positive electrode system of the present application, regulating the specific flow energy of the positive electrode active material within the above range can further improve the energy density and kinetic performance of the secondary battery and reduce the internal resistance.

[0023] In a second aspect, the present application further provides a secondary battery, which includes any one of the positive electrode sheets provided in the first aspect of the present application.

[0024] In some specific embodiments, the secondary battery further includes an electrolyte, which includes a carboxylate compound. Based on the mass of the electrolyte, the mass content of the carboxylate compound is m4, 21%≤m4≤39%, preferably 25.5%≤m4≤29.5%. The present application utilizes a carboxylate compound in conjunction with the aforementioned positive electrode plate system to increase the ion transfer efficiency between the electrolyte and the positive electrode material, thereby reducing the internal resistance of the secondary battery. Furthermore, regulating the mass content of the carboxylate compound within the aforementioned range can further reduce side reactions between the electrolyte and the positive electrode material during cycling or high-temperature conditions, thereby improving the battery's cycling performance and high-temperature storage performance.

[0025] In some embodiments, the carboxylate compound includes at least one of 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 carboxylate compounds can better cooperate with the positive electrode system of the present application to further improve the cycle performance and high-temperature storage performance of the secondary battery.

[0026] In a third aspect, the present application further provides an electronic device, the electronic device comprising any one of the secondary batteries provided in the second aspect of the present application. Based on the secondary battery of the present application, the electronic device can exhibit the same advantages as the aforementioned secondary batteries.

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

[0028] The present application introduces a first composition containing ester groups and hydroxyl groups into the positive electrode plate in combination with a fluoropolymer, which can optimize the crystallinity of the mixture of the first composition and the fluoropolymer. When used in the positive electrode plate, it can improve the brittleness of the positive electrode plate and enhance the flexibility, while exerting a strong bonding effect, which is beneficial to the improvement of the compaction density of the positive electrode plate, thereby shortening the transmission path of the active material and reducing the internal resistance of the plate. At the same time, the higher flexibility can reduce the impact of winding or folding operations on the plate, improve the cracking of the plate or the breakage of the main material particles, reduce the side reactions of the fresh surface and the electrolyte generated by the breakage under cycling or high temperature conditions, and improve the cycle performance and high temperature performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 is an infrared spectrum of the first composition ZII-1 provided in a specific embodiment of the present application;

[0030] FIG2 is an infrared spectrum of the first composition ZII-2 provided in a specific embodiment of the present application;

[0031] FIG3 is a thermogravimetric analysis diagram of the positive electrode sheet provided in Example I-1 of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0033] During their research into improving secondary batteries, the inventors of this application discovered that reducing the proportion of inactive materials (such as separators and current collectors) in the positive electrode sheets can produce positive electrode sheets with high surface density, while increasing the mass proportion of active materials and improving the energy density of the secondary battery. However, while increasing the surface density of the electrode sheets, the cohesion of the film layer becomes greater. Under the same compression, the winding or folding steps cause greater damage to the electrode sheets. Therefore, the electrode sheets become more brittle and break more easily at high surface density, which can easily lead to the problem of brittle fracture of the electrode sheets due to light transmission, making it difficult to meet the requirements of the electrode sheet winding process.

[0034] To improve the electrode's brittle fracture, additives containing hygroscopic groups are added to the electrode. This reduces the electrode's brittleness after absorbing water, which can improve compaction to a certain extent. However, this can lead to excessive water content and the generation of side reactions such as gassing, which can affect the secondary battery's cycle performance. Therefore, it is necessary to reduce the deterioration of the electrode's cycle performance while improving the electrode's brittleness.

[0035] In order to solve the above problems, the present application provides a positive electrode sheet in the first aspect, which includes a positive electrode mixture layer, the positive electrode mixture layer includes a positive electrode material, the positive electrode material includes a first composition and a fluorine-containing polymer, in the infrared spectrum of the first composition, infrared characteristic peaks of ester and hydroxyl groups are visible, and the infrared characteristic peak of the ester group is located at 1731cm -1 to 1749cm -1 The infrared characteristic peak of hydroxyl is located at 3436cm -1 to 3464cm -1 The peak intensity ratio of the ester group and the hydroxyl group is Q, 1.1≤Q≤2.9. The present application introduces a first composition containing an ester group and a hydroxyl group into the positive electrode plate to cooperate with the fluoropolymer, which can occupy the high molecular chains of the fluoropolymer, wherein the hydroxyl group interferes with the molecular arrangement of the fluoropolymer during the crystallization process through hydrogen bond interactions, thereby increasing the disorder of the fluoropolymer molecular chain. After the interaction with the flexible chain segments of the ester group, the hydrogen bonds and van der Waals forces between the molecular chains of the fluoropolymer can be reduced, and the flexibility and mobility of the molecular chains of the fluoropolymer can be increased, thereby optimizing the crystallinity of the mixture of the first composition and the fluoropolymer, while exerting a strong bonding effect. When used in the positive electrode plate, it can improve flexibility and improve coating cracking and cold pressing embrittlement caused by shrinkage of the polymer during coating and drying. On this basis, improving the compaction density of the positive electrode plate is beneficial to shortening the transmission path of the active material, reducing the internal resistance of the plate, and improving the dynamics of the secondary battery. In addition, higher flexibility can reduce the impact of winding or folding operations on the plate, improve the cracking of the plate or the breakage of the main material particles, 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 can be 1.1, 1.31, 1.49, 1.71, 1.92, 2.17, 2.29, 2.53, 2.62, 2.86, 2.9, or a range consisting of any two of these values.

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

[0038] In some embodiments, based on the mass of the positive electrode mixture layer, the mass content of the first composition is m1, 0.1%≤m1≤0.5%. For example, m1 can be 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 a value in the range of any two of these values. When the mass content of the first composition in the positive electrode mixture layer is regulated to be within the above range, it can better cooperate with the fluoropolymer to optimize the crystallinity of the two, improve the brittleness problem of the positive electrode sheet, thereby improving the compaction and dynamics 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 includes component A and component B, wherein component A includes at least one of di(2-ethylhexyl) adipate (DEHA) and dioctyl sebacate (DOS), and component B includes polyethylene glycol (PEG). These compounds are used to provide ester and hydroxyl groups, which can better enhance the coordination effect with the fluoropolymer. Furthermore, these compounds have good affinity with the positive electrode active material and are easily adsorbed on the latter's surface, improving 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, 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, for example m A / m B The weight ratio of component A to component B can be 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 a range consisting of any two of these values. Controlling the mass ratio of component A to component B within the above range can optimize the ratio of ester groups to hydroxyl groups, enhance the coordination effect of the first composition and the fluoropolymer, and further improve the cycling and high-temperature storage performance of the secondary battery.

[0041] In some embodiments, the first composition further comprises component C, which comprises polydimethylsiloxane (PDMS); based on the mass of the first composition, the mass content of component C is m C , 0.15≤m C / m B ≤0.8, illustratively, m C / m BThe value may be 0.15, 0.22, 0.29, 0.37, 0.43, 0.54, 0.58, 0.67, 0.69, 0.79, 0.8, or a range consisting of any two of these values. Adding polydimethylsiloxane to the first composition, in combination with the above-mentioned components A and B, can improve the permeability of the first composition, enhance the coordination effect with the fluorine-containing polymer, further enhance the flexibility and stability of the positive electrode material, optimize the structure of the positive electrode material, 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 vinylidene fluoride, tetrafluoroethylene, and hexafluoroethylene. Fluoropolymers containing these monomers can better blend with the first composition, optimize the crystallinity of the mixture, and enhance the bonding effect with the positive electrode active material, ensuring the stability of the positive electrode sheet structure and improving the cycling performance and high-temperature storage performance of the secondary battery.

[0043] In some embodiments, based on the mass of the positive electrode mixture layer, the mass content of the fluoropolymer is m2, and 0.9% ≤ m2 ≤ 2.0%. For example, m2 can be 0.9%, 1.0%, 1.1%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.9%, 2.0, or a range consisting of any two of these values. Regulating the mass content of the fluoropolymer within the above range can further improve the flexibility of the positive electrode sheet and enhance the cycling 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 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 a range consisting of any two of these values. Regulating the m2 / m1 value 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 of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorinated acrylate resin. These fluoropolymers can better cooperate with the first composition to further improve the cycle performance and high-temperature storage performance of the secondary battery.

[0046] In some embodiments, the crystallinity of the mixture consisting of the first composition and the fluoropolymer is G, 25% ≤ G ≤ 45%. For example, G may be 25%, 27%, 29%, 32%, 34%, 36%, 39%, 41%, 42%, 45%, or a value in a range consisting of any two of these values. When the crystallinity of the mixture consisting of the first composition and the fluoropolymer is regulated within the above range, it can improve the flexibility of the positive electrode while achieving a better bonding effect, improve the structural stability of the positive electrode sheet, and enhance the cycling and high-temperature storage performance of the secondary battery.

[0047] In some embodiments, the compaction density of the positive electrode sheet is P g / cm 3 ; 4.4≤(P+1.2652×G)≤4.7. For example, the value of P+1.2652×G may be 4.4, 4.43, 4.47, 4.49, 4.52, 4.58, 4.61, 4.62, 4.66, 4.68, 4.7, or a range consisting of any two of these values. By controlling the compaction density of the positive electrode sheet of the present application and the above-mentioned crystallinity G within these ranges, the flexibility of the positive electrode sheet can be further improved, allowing the secondary battery to exhibit higher cycling and high-temperature storage performance.

[0048] In some embodiments, 4.1≤P≤4.3. For example, P can be 4.1, 4.12, 4.14, 4.17, 4.18, 4.21, 4.22, 4.25, 4.28, 4.3, or a range consisting of any two of these values. Regulating the compaction density of the positive electrode sheet within the above range in conjunction with the positive electrode sheet system of the present application is beneficial for optimizing the discharge capacity of the battery, reducing internal resistance, and reducing polarization loss, 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, and the positive electrode active material satisfies at least one of the following conditions:

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

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

[0052] (III) The specific flow energy of the positive electrode active material is F, 251mJ≤F≤308mJ. For example, F can be 251mJ, 258mJ, 263mJ, 271mJ, 278mJ, 282mJ, 291mJ, 293mJ, 297mJ, 307mJ or a value in the range consisting of any two of these values. Wherein, on the basis of the positive electrode system of the present application, regulating 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 the positive electrode active material easy to slip, reducing the occurrence of breakage and side reactions, thereby improving the cycle and high temperature performance of the secondary battery, and also helping to improve the compaction density of the positive electrode sheet, further improving the energy density and kinetic performance of the secondary battery, and reducing the internal resistance.

[0053] In the present application, there is no particular restriction on the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet includes a positive electrode current collector and a positive electrode mixture layer located on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode mixture layer located on at least one surface of the positive electrode current collector" means that the positive electrode mixture layer can be located on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. This application has no particular restriction, as long as the purpose of the present application can be achieved. This application has no particular restriction on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). In the present application, the positive active material can also include non-metallic elements, for example, non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0054] In the present application, the positive electrode mixture layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of positive electrode conductive agent in the positive electrode mixture layer, as long as the purpose of the present application can be achieved. 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, metal materials, and conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The present application does not particularly limit the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode mixture layer. Those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved. The present application does not particularly limit the thickness of the positive electrode mixture layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode mixture layer can be 3 μm to 15 μm.

[0055] In a second aspect, the present application further provides a secondary battery, which includes any one of the positive electrode sheets provided in the first aspect of the present application.

[0056] In the present application, the secondary battery also includes a negative electrode sheet. This application does not specifically limit the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode mixture layer provided on at least one surface of the negative electrode current collector. In the present application, the negative electrode mixture layer can be provided on one surface in the thickness direction of the negative electrode current collector, or on both surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector. This application does not specifically limit it, as long as the purpose of this application can be achieved. This application does not specifically limit the negative electrode current collector, as long as the purpose of this application can be achieved. For example, it can include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector (such as carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). In the present application, there is no specific limitation on the negative electrode current collector, the thickness of the negative electrode mixture layer, and the negative electrode sheet, as long as the purpose of this application can be achieved.

[0057] The negative electrode mixture layer of the present application includes a negative electrode active material, which may include but is not limited to graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x(0.5<x<1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate lithiated TiO2-Li4Ti5O 12 , at least one of Li-Al alloy and metallic lithium.

[0058] The negative electrode mixture layer in the present application may further include a negative electrode binder and a negative electrode conductor, or the negative electrode mixture layer may further include a negative electrode binder, a negative electrode conductor and a thickener. The present application has no particular restrictions on the types of negative electrode binders and negative electrode conductors, as long as the purpose of the present application can be achieved. For example, the negative electrode binder may include but is not limited to at least one of the above-mentioned positive electrode binders, and the negative electrode conductor may include but is not limited to at least one of the above-mentioned positive electrode conductors. The present application has no particular restrictions on the types of thickeners, as long as the purpose of the present application can be achieved. For example, the thickener may include but is not limited to at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. The present application has no particular restrictions on the mass ratio of the negative electrode active material, negative electrode conductor, negative electrode binder and thickener in the negative electrode mixture layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0059] In some specific embodiments, the secondary battery further includes an electrolyte, and the electrolyte includes a carboxylate compound; based on the mass of the electrolyte, the mass content of the carboxylate compound is m4, 21%≤m4≤39%, 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 a value in the range consisting of any two of these values. The present application can reduce the breakage of the positive electrode material and improve the structural stability of the positive electrode material by combining the first composition and the fluoropolymer. On this basis, the use of carboxylate compounds in combination with the above-mentioned positive electrode plate system can increase the ion transmission efficiency between the electrolyte and the positive electrode material, reduce the internal resistance and improve the dynamic performance of the secondary battery. By regulating the mass content of the carboxylic acid ester compound within the above range, the side reactions between the electrolyte and the positive electrode material under cycling or high temperature conditions can be further reduced, thereby improving the cycling performance and high-temperature storage performance of the battery.

[0060] In some embodiments, the carboxylate compound includes at least one of 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 carboxylate compounds can better cooperate with the positive electrode system of the present application to further improve the cycling performance and high-temperature storage performance of the secondary battery.

[0061] In the present application, the electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiPO2F2, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), and lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, an ether compound or other organic solvent. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound, and a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, methylpropyl carbonate (EMC), ethylpropyl carbonate, and ethyl methyl carbonate. The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate, butylene carbonate, and vinyl ethylene carbonate. The fluorinated carbonate compound may include but is 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, and trifluoromethylethylene carbonate. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, 1,3-propane sultone (PS), and adiponitrile (ADN).

[0062] The present application has no particular restrictions on the isolation membrane, as long as the purpose of the present application can be achieved. For example, the material of the isolation membrane may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (such as polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid; the type of isolation membrane may include at least one of woven membranes, non-woven membranes, microporous membranes, composite membranes, rolled membranes, and spun membranes. For example, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a membrane, or a 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 non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is 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 a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder. The present application has no particular restrictions on the inorganic particles. For example, it may include at least one of aluminum oxide, 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. The present application has no particular restrictions on the binder. For example, it may be at least one of the above-mentioned positive electrode binders. The polymer layer contains a polymer. The present application has no particular restrictions on the polymer. For example, the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the isolation membrane is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the isolation membrane can be 5μm to 500μm.

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

[0064] The secondary battery of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In one embodiment of the present application, the secondary battery may include but is not limited to: a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery or a lithium ion polymer secondary battery, etc.

[0065] The present application does not particularly limit the preparation method of the secondary battery, for example, it may include the following steps: stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and then fixing the four corners of the entire stacked structure to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery.

[0066] In a third aspect, the present application further provides an electronic device comprising the secondary battery provided in the first aspect of the present application. The secondary battery of the present application has good cycle performance and high-temperature performance, and therefore, the electronic device of the present application has a long service life and high safety performance when used.

[0067] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0068] The following uses lithium-ion batteries as an example to illustrate the present invention. Unless otherwise specified, the raw materials used in the following examples are all 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, and the corresponding mass proportion and / or number average molecular weight of each component in the first composition.

[0070] Table 1

[0071] Table 2

[0072] The infrared spectrum test of the first composition in the present application can be performed using an FTIR-430 advanced Fourier transform infrared spectrometer from JASCO Corporation. Before the infrared spectrum test, the first composition sample is dried at 60°C for 5 hours, and the sample is pressed into a potassium bromide pellet and measured in transmission mode.

[0073] Figures 1 and 2 are the infrared spectra of the first compositions ZII-1 and ZII-2 provided in this application, respectively. The infrared characteristic peaks of ester and hydroxyl groups are visible. The infrared characteristic peak of the ester group in Figure 1 is located at 1737.97 cm -1 The infrared characteristic peak of hydroxyl is located at 3442.29 cm -1 , the peak intensity ratio of ester group to hydroxyl group is A=2.5; the infrared characteristic peak of ester group in Figure 2 is located at 1738.01cm -1 The infrared characteristic peak of hydroxyl is located at 3459.20 cm -1 , the peak intensity ratio of ester group and hydroxyl group is A=1.31.

[0074] Example I-1

[0075] The positive electrode plate 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 fluorine-containing polymer, wherein the first composition is ZI-1.

[0076] FIG3 shows a thermogravimetric analysis diagram of the positive electrode material of this embodiment. After the positive electrode material is heat-treated at 362-367° C., the mass reduction rate r of the positive electrode material is 0.2%, corresponding to a mass proportion of the first composition in the positive electrode material of this embodiment of 0.2%.

[0077] Preparation of positive electrode:

[0078] The positive electrode active material, polyvinylidene fluoride (PVDF), positive electrode conductive agent and the first composition with a mass ratio of 97.6:1.3:0.9:0.2 were mixed in N-methylpyrrolidone (NMP) to obtain a positive electrode slurry, and the positive electrode slurry was coated on an aluminum foil. The aluminum foil was dried at 95°C, cold pressed, cut and slit, and then dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.

[0079] Preparation of negative electrode sheet:

[0080] Artificial graphite negative electrode active material, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in a mass ratio of 96.4:1.5:0.5:1.6 were mixed in deionized water to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry was 54wt%; the negative electrode slurry was coated on a copper foil, and the copper foil was dried at 85°C, and then cold pressed, cut into pieces, and slit, and then dried under vacuum conditions at 80°C for 12 hours to obtain a negative electrode sheet.

[0081] Electrolyte preparation:

[0082] In an argon atmosphere 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 until uniformly distributed to obtain an electrolyte. The molar concentration of the lithium salt LiPF6 was 1.5 mol / L based on the mass of the electrolyte.

[0083] Preparation of isolation membrane: A 7 μm thick polyethylene (PE) isolation membrane substrate was coated with a 3 μm ceramic coating.

[0084] Preparation of lithium-ion batteries: The positive electrode, separator, and negative electrode are stacked in order, with the separator placed between the positive and negative electrodes to act as an insulator, and 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. After vacuum packaging, standing, formation (charging at a constant current of 0.02C to 3.3V, then charging at a constant current of 0.1C to 3.6V), shaping, and capacity testing, a lithium-ion battery is obtained.

[0085] Positive electrode compaction density test:

[0086] Positive electrode sheet compaction density = mass of positive electrode material layer per unit area (unit: g / cm 2 ) / thickness of the positive electrode material layer (in cm). The mass of the positive electrode material layer per unit area can be weighed using a balance, and the thickness of the positive electrode material layer can be measured using a micrometer.

[0087] Cathode active material specific flow energy test:

[0088] The specific flow energy of the positive electrode active material was measured using an FT4 powder rheometer (Freeman Technology Company).

[0089] Appearance cracking and powder loss test:

[0090] Take a positive electrode sheet with a width of 80 mm and fold it in half once, observe and record the translucent points on the positive electrode sheet, where 0 translucent points means no cracking or powdering, 1 to 5 translucent points means slight cracking or powdering, and greater than or equal to 6 translucent points means cracking or powdering.

[0091] DC resistance (DCR) test:

[0092] The lithium-ion battery was placed in a high and low temperature box at 0°C for 4 hours; charged at a constant current of 0.1C to a charging voltage set value (when the positive electrode active material is lithium cobalt oxide, the voltage charging setting value is 4.5V, when the positive electrode active material is lithium nickel cobalt manganese oxide and lithium manganese oxide, the voltage charging setting value is 4.2V, and when the positive electrode active material is lithium iron phosphate, the voltage charging setting value is 3.6V), charged at a constant voltage to a cut-off current of 0.05C, and placed for 10 minutes; then discharged at a constant current of 1C for 1 second; the DC impedance corresponding to the 100% SOC state of the lithium-ion battery was calculated and recorded as the internal resistance of the lithium-ion battery.

[0093] Cyclic performance test:

[0094] The lithium-ion battery was placed in a 45°C environment and charged at a constant current of 0.5C to a charge setting value (the voltage charge setting value is 4.5V when the positive electrode active material is lithium cobalt oxide, the voltage charge setting value is 4.2V when the positive electrode active material is lithium manganese oxide, and the voltage charge setting value is 3.6V when the positive electrode active material is lithium iron phosphate). Then, the battery was charged at a constant voltage to a cutoff current of 0.05C, allowed to stand for 5 minutes, and discharged at a constant current of 0.5C to a discharge setting value (the voltage discharge setting value is 3.0V when the positive electrode active material is lithium cobalt oxide, the voltage discharge setting value is 3.0V when the positive electrode active material is lithium manganese oxide, and the voltage discharge setting value is 2.5V when the positive electrode active material is lithium iron phosphate). The battery was allowed to stand for 5 minutes, and the discharge capacity of the first cycle was recorded. Then, 500 cycles of charge and discharge were performed using the same steps, and the discharge capacity of the 500th cycle was recorded.

[0095] The capacity retention rate of the lithium-ion battery after 500 cycles (%) = (discharge capacity at the 500th cycle / discharge capacity at the first cycle) × 100%, which is recorded as the cycle performance of the lithium-ion battery.

[0096] High temperature storage performance test:

[0097] Place the lithium-ion battery in a 25°C constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature of 25°C. Charge at a constant current of 1C to a voltage that is the charging setting value (the charging setting value is the same as before), charge at a constant voltage to a cut-off current of 0.05C, then discharge at a constant current of 1C to a voltage that is the discharge setting value (the discharge setting value is the same as before), then charge at a constant current of 0.5C to a voltage that is the charging setting value (the charging setting value is the same as before), charge at a constant voltage to a cut-off current of 0.05C, and use a micrometer to test and record the thickness T0 of the lithium-ion battery. Transfer the lithium-ion battery to an 85°C constant temperature box for storage for 35 days, then transfer the lithium-ion battery to a 25°C constant temperature box and let it stand for 60 minutes. Use a micrometer to test and record the thickness T1 of the lithium-ion battery.

[0098] High-temperature storage thickness expansion rate = (T1-T0) / T0×100%, which is recorded as the high-temperature storage performance of the lithium-ion battery.

[0099] The positive electrode sheets of the following examples and comparative examples differ from those of Example I-1 only in that the types and / or contents of the first composition and fluoropolymer are as shown in Table 3. The Q value is controlled by adjusting the mass ratios of the 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.

[0100] Table 3

[0101] As can be seen from Table 3, the present application controls the peak intensity ratio of the ester group to the hydroxyl group in the first composition to satisfy Q: 1.1≤Q≤2.9. After being combined with the fluoropolymer, the crystallinity of the first composition and the fluoropolymer can be optimized, thereby improving the internal resistance, cycle performance and high-temperature performance of the secondary battery.

[0102] In particular, the present application regulates the mass content m1 of the first composition in the positive electrode mixture layer to satisfy: 0.1%≤m1≤0.5%, which can better cooperate with the fluorine-containing polymer and further improve the internal resistance, cycle performance and high-temperature storage performance of the secondary battery.

[0103] In particular, the present application adopts the combination of component A and component B in Table 1, which can better play the role of coordination with the fluorine-containing polymer and improve the cycle performance and high temperature performance of the secondary battery. A / m B Satisfy: 4 ≤ m A / m B ≤9, which can further improve the cycle and high-temperature storage performance of secondary batteries.

[0104] In particular, the present application regulates the mass content of the fluoropolymer to meet the following conditions: 0.9% ≤ m2 ≤ 2.0%, which can further improve the flexibility of the positive electrode sheet and enhance the cycling performance and high-temperature storage performance of the secondary battery. Furthermore, regulating the value of m2 / m1 to meet the following conditions: 3 ≤ m2 / m1 ≤ 18, and 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, thereby improving the internal resistance, cycling performance, and high-temperature storage performance of the secondary battery.

[0105] 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 type and content of the carboxylic acid ester compound are adjusted. The specific differences are shown in Table 4.

[0106] Table 4

[0107] In Table 4, when adjusting the crystallinity G of the first composition and the fluoropolymer, the crystallinity is adjusted by adjusting the mass proportion of the fluoropolymer while controlling Q to be the same as in Example I-1; when adjusting the content and type of the carboxylic acid ester compound, the corresponding mass content of the carboxylic acid ester compound is added to the electrolyte of Example I-1.

[0108] As shown in Table 4, the present invention controls the crystallinity G of the mixture composed of the first composition and the fluoropolymer to meet the following conditions: 25% ≤ G ≤ 45%, which can improve the kinetics, cycling, and high-temperature storage performance of the secondary battery. Furthermore, when the value of P + 1.2652 × G is adjusted to meet the following conditions: 4.4 ≤ (P + 1.2652 × G) ≤ 4.7, it is beneficial to reduce the internal resistance of the electrode and achieve higher cycling and high-temperature storage performance of the secondary battery.

[0109] In particular, based on the cathode system of the present application, regulating 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.

[0110] Furthermore, the present application adopts carboxylic acid ester compounds in combination with the above-mentioned positive electrode system, especially regulating the mass content of the carboxylic acid ester compounds to meet the following requirements: 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.

[0111] The positive electrode sheets of the following examples and comparative examples differ from those of Example I-1 only in that the type of the first composition is shown in Table 5.

[0112] Table 5

[0113] According to Table 5, the present application further adopts the first composition including component C in Table 2 to be matched with the fluoropolymer, especially when controlling m C / m B Satisfy: 0.15 ≤ m C / m B ≤0.8, which can better improve the flexibility and stability of the positive electrode material, and improve the internal resistance, cycle performance and high-temperature storage performance of the secondary battery.

[0114] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the principles of the present application should be included in the scope of protection of the present application.

Claims

1. A positive electrode plate, characterized in that: The positive electrode sheet includes a positive electrode mixture layer, the positive electrode mixture layer includes a positive electrode material, and the positive electrode material includes a first composition and a fluorine-containing polymer. In the infrared spectrum of the first composition, infrared characteristic peaks of ester and hydroxyl groups are visible. The infrared characteristic peak of the ester group is located at 1731 cm -1 to 1749cm -1 The infrared characteristic peak of the hydroxyl group is located at 3436cm -1 to 3464cm -1 The peak intensity ratio of the ester group and the hydroxyl group is Q, 1.1≤Q≤2.

9.

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° C. to 367° C. for 10 minutes, 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 mixture layer, the mass content of the first composition is m1, and 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) The first composition comprises component A and component B, wherein component A comprises at least one of di(2-ethylhexyl) adipate and dioctyl sebacate, and component B comprises polyethylene glycol; (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; (3) The first composition further includes component C, which includes polydimethylsiloxane; based on the mass of the first composition, the mass content of component C is m C , 0.15≤m C / m B ≤0.

8.

5. The positive electrode sheet according to claim 3, characterized in that: The monomer of the fluorine-containing polymer includes at least one of 1,1-difluoroethylene, tetrafluoroethylene, and hexafluoroethylene; and / or, Based on the mass of the positive electrode mixture layer, the mass content of the fluorine-containing polymer 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: The fluorine-containing polymer 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 fluorine-containing acrylate resin; and / or, 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 of the first composition and the fluorine-containing polymer is G, 25%≤G≤45%; and / or, The compaction density of the positive electrode sheet is P g / cm 3 ; 4.4≤(P+1.2652×G)≤4.7; and / or, 4.1≤P≤4.

3.

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, and the positive electrode active material satisfies at least one of the following conditions: (I) the positive electrode active material comprises 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 comprises the positive electrode sheet according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, wherein The secondary battery further includes an electrolyte, which includes a carboxylic acid ester compound; based on the mass of the electrolyte, the mass content of the carboxylic acid ester compound is m4, 21%≤m4≤39%.

11. The secondary battery according to any one of claims 10, wherein: The carboxylate compound includes at least one of 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 according to any one of claims 9 to 11.

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