Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device, the secondary battery of the present application comprises an electrolyte and an isolation membrane, the electrolyte comprises a compound of formula I, the isolation membrane comprises a substrate, at least one surface of the substrate is provided with a coating, the coating comprises inorganic particles and polymer particles, the Dv50 of the polymer particles is D1 nm, the Dv50 of the inorganic particles is D2 nm, and 0.35 D1 < = D2 < = 0.66 D1. According to the secondary battery disclosed by the invention, under the combined action of the compound in the formula I in the electrolyte and the isolating membrane coating, the cycle life of the secondary battery can be prolonged, and the cycle thickness growth rate of the secondary battery is reduced; and the secondary battery disclosed by the invention also has good safety performance even after being circulated for multiple times.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and more particularly, to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries such as lithium-ion batteries are widely used in portable electronic products, electric vehicles, aerospace, energy storage and other fields due to their high energy density, good cycle performance, safety, environmental protection and no memory effect. After multiple cycles, the thickness of the existing secondary battery will continue to increase, which affects the cycle performance of the secondary battery. In severe cases, obvious deformation may even occur, which is likely to cause safety risks. Summary of the Invention

[0003] The present application provides a secondary battery and an electronic device. The secondary battery in the present application has a low cycle thickness growth rate, good cycle life, and good safety performance even after multiple cycles.

[0004] In a first aspect, the present application provides a secondary battery, which includes an electrolyte and a separator. The electrolyte includes a compound of Formula I, and the structural general formula of the compound of Formula I is shown as Formula I below:

[0005]

[0006] Wherein R is selected from any one of an unsubstituted or Ra-substituted C2-C6 alkyl group, an unsubstituted or Ra-substituted C2-C6 alkenyl group, an unsubstituted or Ra-substituted C2-C6 alkynyl group, an unsubstituted or Ra-substituted C5-C12 nitrogen-containing heteroaryl group, and an unsubstituted or Ra-substituted C6-C12 aryl group; the substituents Ra of each group are independently selected from any one of fluorine or a C1-C6 fluoroalkyl group; the separator includes a substrate, and a coating is provided on at least one surface of the substrate. The coating includes inorganic particles and polymer particles. The Dv50 of the polymer particles is D1 nm, and the Dv50 of the inorganic particles is D2 nm, and 0.35D1 ≤ D2 ≤ 0.66D1.

[0007] The inventors found that the reason why existing secondary batteries become thicker after multiple cycles is that the adhesion between the separator and the electrode sheet becomes weaker. Therefore, the thickness growth rate of the secondary battery can be inhibited by enhancing the adhesion between the separator and the electrode sheet and reducing the interfacial side reactions. In the above secondary battery, the inventors found that the polymer particles on the separator can improve the adhesion between the separator and the electrode sheet, and the inorganic particles can leave a certain space between the separator and the electrode sheet, which is beneficial to the transmission and infiltration of the electrolyte. Moreover, since 0.35D1 ≤ D2 ≤ 0.66D1, the inorganic particles can also protect the polymer particles, making it difficult for the polymer particles to be flattened during formation; therefore, the inorganic particles and the polymer particles act synergistically to enhance the adhesion of the separator and at the same time improve the transmission effect of the separator on the electrolyte. The compound of Formula I in the electrolyte can form an interfacial component on the surface of the electrode sheet of the secondary battery. On the one hand, it can make the adhesion between the separator and the electrode sheet stronger, reduce the growth of the battery thickness during cycling, and on the other hand, it can passivate the interface and reduce the occurrence of side reactions, thereby reducing the capacity loss of the secondary battery, improving the cycle life and safety performance of the secondary battery. Therefore, the secondary battery of the present application has a lower cyclic thickness growth rate, good cycle life, and good safety performance even after multiple cycles.

[0008] In one possible implementation, the compound of Formula I includes at least one of the following compounds:

[0009]

[0010] In one possible implementation, based on the mass of the electrolyte, the mass content of the compound of Formula I is A%, 0.8 ≤ A ≤ 20, preferably, 5 ≤ A ≤ 15.

[0011] In one possible implementation, the particle size of the polymer particles satisfies at least one of the following conditions: (1) 500 ≤ D1 ≤ 4000; (2) The Dv90 of the polymer particles is D3 nm, 0.3D1 ≤ D3 ≤ 1.5D1; (3) The Dn10 of the inorganic particles is D4 nm, 50 ≤ D4 ≤ 180.

[0012] In the above technical solution, the cycle performance and the safety performance after cycling of the secondary battery can be further improved.

[0013] In one possible implementation, the monomers of the polymer particles include at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile or methacrylonitrile.

[0014] In a possible implementation, the inorganic particles include at least one of aluminum oxide, silicon dioxide, 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, or barium sulfate.

[0015] In a possible implementation, the electrolyte further includes propylene carbonate, and based on the total mass of the electrolyte, the mass content of propylene carbonate is B%, where 5 ≤ B ≤ 30.

[0016] In the above technical solution, propylene carbonate is beneficial to improving the conductivity of the electrolyte, enabling the secondary battery to have better fast charging performance.

[0017] In a possible implementation, 1 ≤ B / A ≤ 10.

[0018] In the above technical solution, when the relationship between the mass content of propylene carbonate and the mass content of the compound of Formula I is within the above range, the secondary battery can have better fast charging performance while having good cycle life.

[0019] In a possible implementation, the electrolyte further includes a first component, and the first component includes at least one of fluoroethylene carbonate, vinylene carbonate, trifluorotoluene, 1,3,5-trifluorotoluene, 1,3-difluorobenzene, or fluorobenzene; based on the mass of the electrolyte, the mass content of the first component is C%, where 0.2 ≤ C ≤ 20.

[0020] In the above technical solution, when the electrolyte is used in a secondary battery, the first component can form an organic SEI film (SEI stands for Solid Electrolyte Interface, and the SEI film is a solid electrolyte interface film) at the interface of the negative electrode plate of the secondary battery, which can play a role in protecting the negative electrode plate of the secondary battery and further increasing the cycle life of the secondary battery.

[0021] In a second aspect, the present application provides an electronic device, which includes the above secondary battery. Therefore, the electronic device provided by the present application has good use performance.

[0022] Advantages of the present application:

[0023] The present application provides a secondary battery and an electronic device. The electrolyte of the secondary battery includes a compound of Formula I. The coating of the separator of the secondary battery includes inorganic particles and polymer particles. The Dv50 of the polymer particles is D1 nm, and the Dv50 of the inorganic particles is D2 nm, where 0.35D1 ≤ D2 ≤ 0.66D1. Through the combined action of the compound of Formula I in the electrolyte and the coating of the separator, the secondary battery of the present application has a lower growth rate of cycle thickness, a higher cycle life, and good safety performance even after multiple cycles. Detailed Embodiments

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0025] Before describing the solutions of the present application, the following terms need to be explained:

[0026] In the present application, "Dv50" represents the particle size that reaches 50% of the cumulative volume when measured from the small particle size in the particle size distribution based on volume, "Dv90" represents the particle size that reaches 90% of the cumulative volume when measured from the small particle size in the particle size distribution based on volume, and "Dn10" represents the particle size that reaches 10% of the cumulative number when measured from the small particle size in the particle size distribution based on the number.

[0027] In the prior art, the safety performance of a secondary battery decreases after multiple cycles. The inventors found that this is due to the weakening of the adhesion force between the separator and the electrode sheet of the secondary battery, resulting in the thickening of the battery, and the occurrence of side reactions at the interface in the secondary battery. Based on this, the present application provides a secondary battery and an electronic device. The secondary battery of the present application can enhance the adhesion force between the separator and the electrode sheet through the synergistic effect between the electrolyte and the separator, and can also reduce the interfacial side reactions. Therefore, the secondary battery of the present application not only has good cycling performance, but also can well improve the situation that the secondary battery thickens and the safety performance decreases with the increase in the number of cycles. The secondary battery and the electronic device of the embodiments of the present application will be specifically described below.

[0028] In a first aspect, the present application provides a secondary battery, which includes an electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator, wherein the electrolyte includes a compound of Formula I, and the structural general formula of the compound of Formula I is shown as Formula I below:

[0029]

[0030] Wherein R is selected from any one of unsubstituted or Ra-substituted C2-C6 alkyl, unsubstituted or Ra-substituted C2-C6 alkenyl, unsubstituted or Ra-substituted C2-C6 alkynyl, unsubstituted or Ra-substituted C5-C12 nitrogen-containing heteroaryl, and unsubstituted or Ra-substituted C6-C12 aryl; the substituent Ra of each group is independently selected from any one of fluorine or C1-C6 fluoroalkyl; the separator includes a substrate, and a coating is provided on at least one surface of the substrate. The coating includes inorganic particles and polymer particles. The Dv50 of the polymer particles is D1 nm, and the Dv50 of the inorganic particles is D2 nm, where 0.35D1 ≤ D2 ≤ 0.66D1.

[0031] In the secondary battery of the present application, the inventors found that the polymer particles on the separator can improve the adhesion between the separator and the electrode sheet. The inorganic particles can leave a certain space between the separator and the electrode sheet, which is beneficial to the transmission and infiltration of the electrolyte. Moreover, since 0.35D1 ≤ D2 ≤ 0.66D1, the inorganic particles can also protect the polymer particles and prevent them from being flattened during formation; the inorganic particles and the polymer particles act synergistically to not only enhance the adhesion of the separator but also improve the transmission effect of the separator for the electrolyte. And in the secondary battery of the present application, the compound of Formula I in the electrolyte can form an interfacial component on the surface of the electrode sheet of the secondary battery. On the one hand, this interfacial component can make the adhesion between the separator and the electrode sheet stronger and reduce the increase in the thickness of the secondary battery during cycling. On the other hand, it can passivate the interface and reduce the occurrence of side reactions. Therefore, the secondary battery of the present application has a low cycling thickness growth rate, good cycle life, and good safety performance even after multiple cycles. Of course, D2 / D1 cannot be too small, otherwise the inorganic particles cannot protect the polymer particles, which is not conducive to the transmission of the electrolyte and will also have an adverse impact on the safety performance of the secondary battery; D2 / D1 cannot be too large, otherwise the polymer particles cannot play a good bonding role, which is also not conducive to the safety performance of the secondary battery.

[0032] It should be noted that "a coating is provided on at least one surface of the substrate" in the present application means that the coating can be provided on one surface in the thickness direction of the substrate or on both surfaces in the thickness direction of the substrate. The present application has no special limitation on this, as long as the purpose of the present application can be achieved. The separator and the electrolyte of the present application will be specifically described below:

[0033] The present application does not particularly limit the types of inorganic particles in the coating. For example, the inorganic particles include, but are not limited to, at least one of aluminum oxide, silicon dioxide, 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, or barium sulfate.

[0034] In some embodiments of the present application, the monomers of the polymer particles include, but are not limited to, at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile, or methacrylonitrile. Moreover, in some embodiments of the present application, the polymer particles are generally particles having a core-shell structure, wherein the core of the polymer particles is a polymer formed by polymerization of at least one of the following monomers: ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid; and the shell is a polymer formed by polymerization of at least one of the following monomers: methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, chlorostyrene, fluorostyrene, methylstyrene, acrylonitrile, methacrylonitrile.

[0035] In addition, in some embodiments of the present application, in order to further enhance the adhesion between the separator and the electrode, the Dv90 (the value is D3 nm), Dv50, and Dn10 (the value is D4 nm) of the polymer particles can satisfy at least one of the following conditions: (1) 500 ≤ D1 ≤ 4000, specifically, it can be 500, 800, 1000, 1500, 2000, 3000, 3500, 4000, etc. or within the range composed of any two of the above values; (2) 0.3D1 ≤ D3 ≤ 1.5D; (3) 50 ≤ D4 ≤ 180, specifically, it can be 50, 70, 100, 120, 150, 180, etc. or within the range composed of any two of the above values.

[0036] The present application does not particularly limit the material and shape of the substrate of the separator, as long as the effects of the present application are not significantly impaired. The substrate can be a non-woven fabric or a composite film having a porous structure, and the material of the substrate can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0037] Electrolyte

[0038] In the present application, the compound of Formula I in the electrolyte includes at least one of the following compounds:

[0039]

[0040] There is no particular limitation on the dosage of the compound of Formula I in the present application. Exemplarily, in order to further suppress the side reactions at the interface of the secondary battery and enhance the adhesion between the separator and the electrode sheet, the mass content of the compound of Formula I is A%, 0.8 ≤ A ≤ 20, preferably 5 ≤ A ≤ 15; for example, A can be 1, 3, 5, 8, 10, 12, 15, 18, 20, etc. or within the range composed of any two of the above values.

[0041] In some embodiments of the present application, in order to improve the conductivity of the electrolyte and enable the secondary battery to have better fast charging performance, the electrolyte further includes propylene carbonate. Based on the total mass of the electrolyte, the mass content of propylene carbonate is B%, 5 ≤ B ≤ 30, preferably 8 ≤ B ≤ 20; for example, B can be 5, 6, 8, 10, 18, 20, 24, 27, 30, etc. or within the range composed of any two of the above values. Preferably, there is a specific proportional relationship between propylene carbonate and the compound of Formula I, which can enable the secondary battery to have better fast charging performance while having good cycle life. Specifically, 1 ≤ B / A ≤ 10, for example, B / A can be 1, 3, 6, 8, 10, etc. or within the range composed of any two of the above values.

[0042] In addition, in some embodiments of the present application, in order to further increase the cycle life of the secondary battery, the electrolyte further includes a first component, and the first component includes at least one of fluoroethylene carbonate, vinylene carbonate, trifluorotoluene, 1,3,5-trifluorotoluene, 1,3-difluorobenzene or fluorobenzene; based on the mass of the electrolyte, the mass content of the first component is C%, 0.2 ≤ C ≤ 20, preferably 1 ≤ C ≤ 9. For example, C can be 0.2, 0.8, 1, 4, 6, 9, 16, 18, 20, etc. or within the range composed of any two of the above values.

[0043] Of course, in some embodiments of the present application, other substances such as lithium salts, solvents, additives, etc. can also be added to the electrolyte according to actual situations, and there is no particular limitation in this regard in the present application as long as the purpose of the present application can be satisfied. Specifically, the lithium salt can be dissolved in the solvent to form an ionic conductor, which is used as a conductive medium and a lithium ion transmission medium; the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluoro(oxalato)borate, lithium difluoride sulfimide, etc.

[0044] The solvent can dissolve the lithium salt and additives. The solvent can be at least one of, including but not limited to, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, methyl acetate, methyl butyrate, ethyl propionate, propyl propionate, propyl acetate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, ethanol, ethylene glycol, glycerol, etc.

[0045] Except for the electrolyte and the separator, the structures of the various parts of the secondary battery of the present application are specifically as follows:

[0046] Positive electrode sheet

[0047] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. That is, in the present application, the positive electrode active material layer can be provided on one surface in the thickness direction of the positive electrode current collector, or can be provided on both surfaces in the thickness direction of the positive electrode current collector. Moreover, in the present application, the "surface of the positive electrode current collector" can be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector, and there is no special limitation in the present application as long as the purpose of the present application can be achieved.

[0048] The components of the positive electrode active material layer include a positive electrode active substance, and the positive electrode active substance can be any substance that can reversibly insert and extract Li + , Na + and other alkali metal ions to ensure the normal charge and discharge of the secondary battery. For example, the positive electrode active substance includes but is not limited to at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium nickel oxide, ternary materials, etc. The ternary materials include but are not limited to at least one of LiNi x Co y Mn z O2, LiNi x Co y Al z O2, etc. Moreover, the contents of Ni, Co, Mn, Al, etc. can be adjusted to ensure that x + y + z = 1. For example, the ternary material can be LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.88 Co 0.1 Al 0.02 O2, etc.

[0049] In some embodiments, the components of the positive electrode active material layer further include a positive electrode conductive agent; there is no limitation on the type of the positive electrode conductive agent in the present application, and any known conductive material can be used. Specifically, the positive electrode conductive agent includes, but is not limited to, at least one of acetylene black, carbon black such as Super-P, amorphous carbon such as needle coke, carbon nanotubes, graphene, etc.

[0050] In some embodiments, the components of the positive electrode active material layer generally further contain a positive electrode binder. There is no particular limitation on the type of the positive electrode binder used in the manufacture of the positive electrode active material layer. In the case of the coating method, any material that can be dissolved or dispersed in the liquid medium used during electrode manufacturing is acceptable. The positive electrode binder includes, but is not limited to, any one or at least two of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymer or its hydride, ethylene-propylene-diene terpolymer (EPDM), styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer or its hydride; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, and propylene-α-olefin copolymer; fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer; and polymer compositions having ionic conductivity of alkali metal ions (especially lithium ions), etc.

[0051] In the positive electrode tab, there is no particular limitation on the type of the positive electrode current collector, and it can be made of any known material suitable for use as a positive electrode current collector. The material of the positive electrode current collector includes, but is not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum. In addition, in order to reduce the electron contact resistance between the positive electrode current collector and the positive electrode active material layer, a conductive aid or a conductive coating, etc. can be provided on the surface of the positive electrode current collector. The conductive aid includes, but is not limited to, carbon and noble metals such as gold, platinum, and silver. The conductive coating can be a mixture layer of inorganic oxides, conductive agents, and positive electrode binders.

[0052] When preparing the positive electrode plate, the components in the above positive electrode active material layer can be dissolved or dispersed in a liquid solvent to form a positive electrode slurry, and then the positive electrode slurry is coated on the positive electrode current collector and dried, so as to form a positive electrode active material layer on the positive electrode current collector, and thus a positive electrode plate can be obtained. When preparing the positive electrode plate in this way, the solvent in the positive electrode slurry is not particularly limited as long as it can dissolve or disperse the above components. Specifically, the solvent in the positive electrode slurry includes but is not limited to N-methylpyrrolidone (NMP), ethylene carbonate (EC), etc. In addition, when preparing the positive electrode plate, the components in the positive electrode active material layer can also be dry-mixed, made into flakes, and then the obtained flakes are pressed onto the positive electrode current collector.

[0053] Negative electrode plate

[0054] The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The components of the negative electrode active material layer include the negative electrode plate active substance. That is, in this application, the negative electrode active material layer can be provided on one surface in the thickness direction of the negative electrode current collector, or can be provided on both surfaces in the thickness direction of the negative electrode current collector. Moreover, in this application, the "surface of the negative electrode current collector" can be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector, and there is no particular limitation in this application as long as the purpose of this application can be achieved.

[0055] The negative electrode active material layer generally contains the negative electrode plate active material, and there is no particular limitation on the negative electrode plate active material in this application. Specifically, the negative electrode plate active material can include at least one of a carbon material or a silicon-based material. More specifically, the carbon material includes but is not limited to at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon or soft carbon; the silicon-based material includes but is not limited to at least one of silicon, silicon-oxygen composite material or silicon-carbon composite material.

[0056] In some embodiments, the negative electrode active material layer usually also contains a negative electrode plate conductive agent. There is no particular limitation on the type of the negative electrode plate conductive agent in this application as long as the purpose of this application can be achieved. For example, the negative electrode plate conductive agent includes but is not limited to at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots or graphene, etc.

[0057] In some embodiments, the negative electrode active material layer may also contain a negative electrode binder and a thickener. The present application does not particularly limit the types of the negative electrode binder and the thickener, as long as the objectives of the present application can be achieved. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener in the negative electrode slurry may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0058] In the negative electrode plate, the material of the negative electrode current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, etc., and the present application has no particular limitation. Among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polyethylene naphthalate, or poly(p-phenylene terephthalamide).

[0059] In addition, in the present application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the objectives of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 160 μm.

[0060] In addition, similar to the preparation of the positive electrode sheet, when preparing the negative electrode sheet, it can be configured into a negative electrode slurry, and then the negative electrode slurry is coated on the negative electrode current collector and dried, so as to form a negative electrode active material layer on the negative electrode current collector, thereby obtaining a negative electrode sheet; or the components in the negative electrode active material layer can be dry-mixed, made into flakes, and then the obtained flakes are pressed onto the negative electrode current collector to form a negative electrode active material layer, thereby obtaining a negative electrode sheet. The solvent in the negative electrode slurry includes any one of aqueous solvents and organic solvents. Aqueous solvents include, but are not limited to, a mixed solvent of alcohol and water or water, etc. Organic solvents include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc. In addition, in some other embodiments, when using an aqueous solvent, the components of the negative electrode slurry will also include a thickener and styrene-butadiene rubber (SBR) emulsion to slurry the negative electrode slurry, thereby adjusting the viscosity of the negative electrode slurry. The types of thickeners in the positive electrode slurry include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts, etc.

[0061] The secondary battery of the present application further includes a packaging bag for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, as well as other components known in the art in the secondary battery. The present application does not limit the above other components. The present application has no special limitation on the packaging bag, and it can be a packaging bag well-known in the art as long as it can achieve the purpose of the present application.

[0062] In a third aspect, the present application further provides an electronic device, which includes the secondary battery according to the present application.

[0063] The use of the secondary battery of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of the present application can be used in, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium-ion capacitors, etc.

[0064] Example

[0065] Taking a lithium-ion secondary battery as an example, examples and comparative examples are given below to more specifically illustrate the implementation modes of the secondary battery of the present application. Those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation methods are within the scope of the present application.

[0066] Test methods and equipment:

[0067] Thickness growth rate test

[0068] Charge the secondary battery at a constant current of 0.5C to 3.95V at 45°C, measure the initial thickness of the secondary battery, leave it standing for 30 min, discharge it at 0.5C to 3.0V, and measure the thickness of the fully charged secondary battery again after 200 charge-discharge cycles; Thickness growth rate (%) = (thickness after cycling - initial thickness) / initial thickness × 100%.

[0069] Cycling performance test

[0070] High-temperature cycling performance test: Charge the secondary battery at a constant current of 0.5C to 4.45V at 45°C, leave it standing for 30 min, discharge it at 0.5C to 3.0V, and perform 200 charge-discharge cycles; Cycling capacity retention rate (%) = discharge capacity after 200 cycles / first discharge capacity × 100%. The higher the cycling capacity retention rate, the better the cycling performance.

[0071] Safety performance test (drop test)

[0072] For the battery that has undergone 200 high-temperature cycles, charge it at a constant current of 0.5C to 4.45V at 25°C, perform CV (constant-voltage) charging until the current reaches 0.025C, in a test environment of 20 ± 5°C, drop it on a concrete floor from a height of 2 m, drop it once along 3 sides, once along 3 edges, and once along 8 corners, for a total of 1 round of tests, and the dropping sequence is (once for each of the 3 sides → once for each of the 3 edges → once for each of the 8 corners); the lithium-ion battery to be tested does not smoke, does not leak liquid,

[0073] does not catch fire, does not explode, then it is considered to pass. Test 50 secondary batteries of the same specification in each group.

[0074] Fast charging performance test

[0075] Place the secondary battery in a dry environment at 0 °C. After 30 minutes, charge it at a constant current of 1C to 4.45V, then charge it at a constant voltage of 4.45V until the current reaches 0.05C, and then discharge it at a constant current of 0.5C to 3.0V. This is one cycle. After cycling 5 times according to the above charge-discharge process, charge the lithium-ion battery at a constant current of 1C to 4.45V, disassemble the secondary battery, and observe the degree of lithium deposition on the surface of the negative electrode plate.

[0076] The judgment criteria for the degree of lithium deposition in lithium-ion batteries are as follows: According to the size of the lithium deposition area, the degree of lithium deposition in lithium-ion batteries is classified into levels 0 to 15. When the lithium deposition area is 0%, it corresponds to 0; when 0% < lithium deposition area ≤ 5%, it corresponds to 1; when 5% < lithium deposition area ≤ 8%, it corresponds to 2; when 8% < lithium deposition area ≤ 10%, it corresponds to 3; when 10% < lithium deposition area ≤ 15%, it corresponds to 4; when 15% < lithium deposition area ≤ 20%, it corresponds to 5; when 20% < lithium deposition area ≤ 25%, it corresponds to 6; when 25% < lithium deposition area ≤ 30%, it corresponds to 7; when 30% < lithium deposition area ≤ 35%, it corresponds to 8; when 35% < lithium deposition area ≤ 40%, it corresponds to 9; when 40% < lithium deposition area ≤ 50%, it corresponds to 10; when 50% < lithium deposition area ≤ 55%, it corresponds to 11; when 55% < lithium deposition area ≤ 60%, it corresponds to 12; when 60% < lithium deposition area ≤ 65%, it corresponds to 13; when 65% < lithium deposition area ≤ 70%, it corresponds to 14; when 70% < lithium deposition area ≤ 100%, it corresponds to 15.

[0077] Among them, the percentage of the lithium deposition area is calculated based on the total area of the negative electrode material layer. The larger the lithium deposition area of the lithium-ion battery, the worse the fast charging ability of the lithium-ion battery. 0 represents the best charging ability of the lithium-ion battery, and 15 represents the worst charging ability of the lithium-ion battery.

[0078] Example 1-1

[0079] <Preparation of electrolyte>

[0080] In an argon atmosphere glove box with a water content of less than 10 ppm, mix ethylene carbonate and ethyl acetate in a mass percentage of 1:1 to prepare a basic solvent, and then add lithium salt lithium hexafluorophosphate (LiPF6) and Compound I. Based on the total mass of the electrolyte, the mass percentage content of LiPF6 is 12.5%, and the mass content of Compound I is shown in Table 1, and the balance is the basic solvent.

[0081] The detailed codes in the table are as described above in this article.

[0082] <Preparation of positive electrode plate>

[0083] Lithium cobaltate, conductive agent carbon black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2:3, and N-methylpyrrolidone (NMP) is added. After being stirred evenly under the action of a vacuum mixer, a positive electrode slurry with a solid content of 70 wt% is obtained. The positive electrode slurry is evenly coated on the upper and lower surfaces of a positive electrode current collector aluminum foil with a thickness of 9 μm, dried, pressure-treated, and then cut into a specified size to obtain a positive electrode plate.

[0084] <Preparation of negative electrode plate>

[0085] Artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNT), and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8, and then deionized water is added as a solvent and stirred evenly to prepare a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry is evenly coated on the upper and lower surfaces of a negative electrode current collector copper foil with a thickness of 6 μm, dried, pressure-treated, and then cut into a specified size to obtain a negative electrode plate.

[0086] <Separator>

[0087] A porous polyethylene film with a thickness of 10 μm is used as the base material of the separator, and then a slurry is coated on both surfaces of the base material, and then the slurry is cured into a coating. The mass ratio of each component in the slurry is: polymer particles:inorganic particles:deionized water = 10:50:40. The cured coating contains inorganic particles and polymer particles. Among them, the Dv50, Dv90, and Dn10 of the polymer particles are 1000 nm, 1400 nm, and 160 nm respectively, which are denoted as D1 nm, D3 nm, and D4 nm respectively. Its monomers include methyl acrylate and ethyl acrylate. The Dv50 of the inorganic particles is 350 nm, denoted as D2 nm, and its type is boehmite.

[0088] <Preparation of secondary battery>

[0089] The positive electrode plate, separator, negative electrode plate, and separator prepared above are stacked in sequence, and the separator is placed in the middle of the positive electrode plate and the negative electrode plate to play a role in isolation, and then wound to obtain an electrode assembly. After welding the electrode tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried in a vacuum oven at 85 °C for 12 h to remove moisture, the prepared electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, formation, shaping, and capacity testing processes.

[0090] Examples 1-2 to 1-27

[0091] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Example 1-1.

[0092] Comparative Examples 1 to 5

[0093] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Examples 1-3.

[0094] Table 1

[0095]

[0096]

[0097] In Table 1, Comparative Example 1 does not contain the compound of Formula I, so the interfacial component will not be formed on the surface of the electrode sheet of the secondary battery, the adhesion between the separator and the electrode sheet cannot be further increased, and the interface cannot be passivated. Therefore, the thickness growth rate, cycle performance, and safety performance of the secondary battery are all reduced. In Comparative Example 2, the value of D2 / D1 is less than 0.35, so the inorganic particles cannot play a good protective role, which will have an adverse effect on the cycle performance and safety performance of the secondary battery. In Comparative Example 3, the value of D2 / D1 is greater than 0.66, so the polymer particles cannot play a good bonding role, and the safety performance of the secondary battery is poor. In Comparative Example 4, only polymer particles are contained and no inorganic particles are contained. Therefore, the polymer particles are easily flattened during the formation process and cannot play a good bonding role. Therefore, the cycle performance and safety performance of the secondary battery will be significantly reduced. In Comparative Example 5, only inorganic particles are contained and no polymer particles are contained. Therefore, the adhesion of the separator is weak, and the cycle performance and safety performance of the secondary battery will be significantly reduced. Particularly, it can be seen from Examples 1-2 to 1-10 that when the mass content of the compound of Formula I is 1% to 20% (more preferably 5% to 15%), the side reaction at the interface of the secondary battery can be further inhibited, and the adhesion between the separator and the electrode sheet can be enhanced. Therefore, the thickness growth rate of the secondary battery can be further inhibited, and its cycle performance and safety performance can also be further improved.

[0098] Examples 2-1 to 2-17

[0099] Except for adjusting the relevant parameters of the polymer particles and inorganic particles according to Table 2, the rest are the same as in Examples 1-3.

[0100] Table 2

[0101]

[0102]

[0103] In Table 2, it can be seen from Examples 2-2 to 2-7 that when 500 ≤ D1 ≤ 4000, the polymer particles can better improve the adhesion performance of the separator film, so the cycling performance and safety performance of the secondary battery can be further improved; compared with other examples in Examples 2-10 to 2-17, Examples 2-13 and 2-17 have a larger thickness growth rate and relatively poor cycling performance and safety performance, indicating that when 50 ≤ D4 ≤ 180, the polymer particles can also better improve the adhesion performance of the separator film, so the cycling performance and safety performance of the secondary battery can also be further improved.

[0104] Examples 3-1 to 3-12

[0105] Except for adjusting the relevant parameters of the electrolyte according to Table 3, the rest are the same as in Example 1-3.

[0106] Table 3

[0107]

[0108]

[0109]

[0110] In Table 3, since the electrolyte contains 5% - 30% of propylene carbonate, the conductivity of the electrolyte can be significantly improved. Therefore, compared with Example 1-3, Example 3-1, and Example 3-12, the fast charging performance of the secondary battery can be further improved; in particular, it can be seen from Examples 3-3 to 3-11 that especially when 1 ≤ B / A ≤ 10, the improvement in fast charging performance is particularly significant.

[0111] Examples 4-1 to 4-14

[0112] Except for adjusting the relevant parameters of the electrolyte according to Table 4, the rest are the same as in Example 1-3.

[0113] Table 4

[0114]

[0115]

[0116] In Table 4, since the electrolyte contains 0.2% - 20% of the first component, at this time, the first component can form a stable and appropriately thick organic SEI film at the interface of the negative electrode sheet of the secondary battery. The SEI film can protect the negative electrode sheet, making the negative electrode sheet more stable, and at the same time, it basically does not affect the ion transport rate; therefore, compared with Example 1-3, the cycle life of Examples 4-1 to 4-14 can be further improved.

[0117] It should be noted that in this text, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such a process, method or article.

[0118] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other, and the key point of each embodiment is to illustrate the differences from other embodiments.

[0119] The above are only the embodiments of the present application and are not used to limit the protection scope of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A secondary battery, characterized in that: It includes an electrolyte and an isolation membrane, wherein the electrolyte includes a compound of formula I, and the general structural formula of the compound of formula I is shown in the following formula I: wherein R is selected from any one of C2-C6 alkyl which is unsubstituted or substituted by Ra, C2-C6 alkenyl which is unsubstituted or substituted by Ra, C2-C6 alkynyl which is unsubstituted or substituted by Ra, C5-C12 nitrogen-containing heteroaryl which is unsubstituted or substituted by Ra, and C6-C12 aryl which is unsubstituted or substituted by Ra; and the substituent Ra of each group is independently selected from any one of fluorine or C1-C6 fluoroalkyl; The isolation film includes a substrate, a coating is disposed on at least one surface of the substrate, the coating includes inorganic particles and polymer particles, the Dv50 of the polymer particles is D1 nm, the Dv50 of the inorganic particles is D2 nm, and 0.35D1≤D2≤0.66D1.

2. The secondary battery according to claim 1, characterized in that: The compound of formula I includes at least one of the following compounds:

3. The secondary battery according to claim 1 or 2, characterized in that: Based on the mass of the electrolyte, the mass content of the compound of formula I is A%, and 0.8≤A≤20.

4. The secondary battery according to claim 1 or 2, characterized in that: Based on the mass of the electrolyte, the mass content of the compound of formula I is A%, 5≤A≤15.

5. The secondary battery according to claim 1, characterized in that: The particle size of the polymer particles satisfies at least one of the following conditions: (1)500≤D1≤4000； (2) The Dv90 of the polymer particles is D3 nm, 0.3D1≤D3≤1.5D1; (3) The Dn10 of the polymer particles is D4 nm, 50≤D4≤180.

6. The secondary battery according to claim 1, characterized in that: The monomer of the polymer particles includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile or methacrylonitrile.

7. The secondary battery according to claim 1, characterized in that: The inorganic particles include at least one of aluminum oxide, silicon dioxide, 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 or barium sulfate.

8. The secondary battery according to claim 1, characterized in that: The electrolyte further comprises propylene carbonate, and the mass content of the propylene carbonate is B%, 5≤B≤30, based on the total mass of the electrolyte.

9. The secondary battery according to claim 8, characterized in that: 1≤B / A≤10.

10. The secondary battery according to claim 1, characterized in that: The electrolyte also includes a first component, which includes at least one of fluoroethylene carbonate, vinylene carbonate, trifluorotoluene, 1,3,5-trifluorotoluene, 1,3-difluorobenzene or fluorobenzene; based on the mass of the electrolyte, the mass content of the first component is C%, and 0.2≤C≤20.

11. An electronic device, characterized in that: The secondary battery comprises the secondary battery according to any one of claims 1 to 10.

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