Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device. The electrochemical device comprises a positive pole piece, a negative pole piece and an electrolyte, wherein the electrolyte comprises a compound shown in a formula I and a compound shown in a formula II; wherein the compound in the formula I is # imgabs 0, and the compound in the formula II is # imgabs 1, based on the total mass of the electrolyte, the mass percentage content of the compound in the formula I is 5%-50%, and the mass percentage content of the compound in the formula II is 0.01%-2%. According to the electrochemical device, the high-temperature cycle performance and the thermal safety performance of the electrochemical device can be improved by controlling the components of the electrolyte in the electrochemical device and the content of the components.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and more specifically, to an electrochemical device and an electronic device. Background Art

[0002] Electrochemical devices 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. However, during the charging and discharging process of lithium-ion batteries, the electrolyte will undergo redox reactions near the positive and negative electrodes, which is not conducive to the cycle performance and thermal safety performance of lithium-ion batteries at high temperatures. Summary of the invention

[0003] The present application provides an electrochemical device and an electronic device. The electrochemical device in the present application forms a more stable interface film on the surface of the positive and negative electrode plates during the formation process, which can significantly reduce the probability of side reactions of the electrolyte on the surface of the positive and negative electrode plates, and can greatly improve the cycle performance and thermal safety performance of the electrochemical device at high temperatures.

[0004] In a first aspect, the present application provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte contains a compound of formula I and a compound of formula II. The compound of formula I is: R is selected from any one of fluorine-containing substituted or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, and fluorine-substituted or unsubstituted C6-C12 aryl; the compound of formula II is: Wherein R1, R2, R3, and R4 are each independently selected from or N, and any one or any two of R1 to R4 are N, R5 is independently selected from hydrogen, halogenated or unsubstituted C1 to C10 alkyl, halogenated or unsubstituted C2 to C10 alkenyl, halogenated or unsubstituted C2 to C10 alkynyl, halogenated or unsubstituted C6 to C10 aryl, halogenated or unsubstituted C3 to C10 alicyclic hydrocarbon, halogenated or unsubstituted C2 to C10 heterocyclic group, halogenated or unsubstituted C1 to C10 alkoxy, and when R5 is selected from a group other than hydrogen, the main chain of R5 contains 0 to 20 heteroatoms, and the heteroatoms include at least one of O, S, N, B, P, and Si. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, and the mass percentage of the compound of formula II is b%, wherein 1≤a≤50, 0.01<b≤2.

[0005] In the above technical scheme, the viscosity of the compound of formula I is relatively low, and due to the structure of sulfone and fluorine, the compound of formula I has a strong antioxidant ability. When the electrolyte of the electrochemical device contains 1wt% to 50wt% of the compound of formula I, the electrolyte has a relatively low viscosity and good stability, which is beneficial to improve the cycle performance of the electrochemical device at high temperature. However, the inventors found that the introduction of the compound of formula I into the electrolyte will form a solid electrolyte interface film (SEI film) with low stability on the surface of the negative electrode plate, which may have a negative impact on the high temperature performance and thermal safety performance of the battery. The inventors also found that if the electrolyte contains 0.01%wt to 2wt% of the compound of formula II, the compound of formula II will generate a polymer with a heterocyclic ring on the surface of the negative electrode plate, which can inhibit the reaction of the compound of formula I on the surface of the negative electrode plate, so that the electrochemical device not only has good high temperature cycle performance, but also has good thermal safety performance.

[0006] In one possible implementation, the compound of formula I includes at least one of the following compounds:

[0007]

[0008] In the above technical solution, when the electrolyte contains at least one compound of formula I, the high temperature cycle performance of the electrochemical device can be further improved.

[0009] In one possible implementation, the compound of formula II includes at least one of the following compounds:

[0010]

[0011] In the above technical solution, when the electrolyte contains at least one compound of formula II, the thermal safety performance of the electrochemical device can be further improved.

[0012] In one possible implementation, 2≤a≤10, 0.1≤b≤0.6.

[0013] In a possible implementation, the electrolyte further includes ethylene carbonate and propylene carbonate, and the total mass percentage of ethylene carbonate and propylene carbonate is c%, based on the total mass of the electrolyte, and 10≤c≤50.

[0014] In the above technical solution, ethylene carbonate and propylene carbonate can make the compound of formula I have good solubility, which is beneficial to further improve the high-temperature cycle performance and thermal safety performance of the electrochemical device.

[0015] In one possible implementation, 20≤c≤40, and 0.05≤a / c≤0.5.

[0016] In the above technical solution, the high temperature cycle performance and thermal safety performance of the electrochemical device can be further improved.

[0017] In a possible implementation, the electrolyte further contains fluoroethylene carbonate, and the mass percentage of the fluoroethylene carbonate is d%, based on the total mass of the electrolyte, and 0.05≤a / d≤50.

[0018] In the above technical solution, fluoroethylene carbonate can work together with the compound of formula I and the compound of formula II to improve the interface performance of the electrode, thereby further improving the high-temperature cycle performance of the electrochemical device.

[0019] In one possible implementation, 3≤d≤15, and 0.13≤a / d≤3.33.

[0020] In the above technical solution, the high temperature cycle performance and thermal safety performance of the electrochemical device can be further improved.

[0021] In a possible implementation, the electrolyte further includes lithium difluorophosphate, and the mass percentage of the lithium difluorophosphate is e%, based on the total mass of the electrolyte, and 0.2≤e≤2.

[0022] In the above technical solution, lithium difluorophosphate is beneficial to reducing the film-forming impedance of the positive electrode plate of the electrochemical device, thereby further improving the thermal safety performance of the electrochemical device.

[0023] In a second aspect, an embodiment of the present application provides an electronic device, which includes the above-mentioned electrochemical device. Therefore, the electronic device provided by the present application has good performance.

[0024] Beneficial effects of this application:

[0025] The present application provides an electrochemical device and an electronic device, wherein the electrochemical device comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte comprises a compound of formula I and a compound of formula II. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, and the mass percentage of the compound of formula II is b%, wherein 1≤a≤50, 0.01≤b≤2. By regulating the electrolyte to include a compound of formula I and a compound of formula II, and the types and mass percentages of the compound of formula I and the compound of formula II are within the scope of the present application, the electrochemical device can have good high temperature cycle performance and thermal safety performance at the same time. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0027] The electrochemical device and the electronic device of the embodiments of the present application are described in detail below.

[0028] In a first aspect, the present application provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte. In the present application, by limiting the specific components and the content of the specific components in the electrolyte, the cycle performance and safety performance of the electrochemical device can be well improved.

[0029] The structure of the electrochemical device of the present application is as follows:

[0030] Electrolyte

[0031] The electrolyte can play a role in transmitting lithium ions and electrons, ensuring the formation of a pathway inside the electrochemical device. In the present application, the electrolyte includes a compound of formula I and a compound of formula II, wherein the compound of formula I is: Wherein R is selected from any one of fluorine-containing substituted or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, and fluorine-substituted or unsubstituted C6-C12 aryl. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, and a is in the range of 1 to 50. The compound of formula II is: Wherein R1, R2, R3, and R4 are each independently selected from or N, and any one or any two of R1 to R4 are N, R5 is independently selected from hydrogen, halogenated or unsubstituted C1 to C10 alkyl, halogenated or unsubstituted C2 to C10 alkenyl, halogenated or unsubstituted C2 to C10 alkynyl, halogenated or unsubstituted C6 to C10 aryl, halogenated or unsubstituted C3 to C10 alicyclic hydrocarbon, halogenated or unsubstituted C2 to C10 heterocyclic group, halogenated or unsubstituted C1 to C10 alkoxy, and when R5 is selected from a group other than hydrogen, the main chain of R5 contains 0 to 20 heteroatoms, and the heteroatoms include at least one of O, S, N, B, P, and Si. Based on the total mass of the electrolyte, the mass percentage of the compound of formula II is b%, and 0.01≤b≤2.

[0032] The inventors found that the compound of formula I in the electrolyte has low viscosity and strong antioxidant properties, but a large amount of the compound of formula I will cause the formation of a low-stability SEI film on the negative electrode of the electrochemical device, and the inventors also found that when the electrolyte contains 1wt% to 2wt% of the compound of formula II, the compound of formula II will generate a polymer with a heterocyclic ring on the negative electrode, which can inhibit the reaction of the compound of formula I on the negative electrode. Therefore, in the present application, the components in the electrolyte contain a specific amount of the compound of formula I and the compound of formula I, and the synergistic effect of the two can make the electrochemical device have good high-temperature cycle performance and good thermal safety performance.

[0033] Specifically, based on the total mass of the electrolyte, the mass percentage of the compound of formula I can be 1%, 2%, 5%, 6%, 10%, 30%, 40%, 50%, etc. or within the range consisting of any two of the above values, and the mass percentage of the compound of formula II can be 0.01%, 0.2%, 0.4%, 0.6%, 1%, 1.5%, 2%, etc. or within the range consisting of any two of the above values. Preferably, 2≤a≤10, 0.1≤b≤0.6.

[0034] In some specific embodiments, the compound of formula I includes at least one of the following compounds:

[0035]

[0036] When the electrolyte contains any one or more of the compounds of formula I, the high temperature cycle performance of the electrochemical device will be better.

[0037] In some specific embodiments, the compound of formula II includes at least one of the following compounds:

[0038]

[0039] When these compounds of formula II are used as components of the electrolyte, they are more conducive to improving the high-temperature cycle performance and thermal safety performance of the electrochemical device.

[0040] In some other embodiments, in the electrochemical device of the present application, the electrolyte further includes ethylene carbonate and propylene carbonate, and the total mass percentage of ethylene carbonate and propylene carbonate is c%, 10≤c≤50 based on the total mass of the electrolyte. A specific amount of ethylene carbonate and propylene carbonate can make the compound of formula I have good solubility, which is beneficial to further improve the high temperature cycle performance of the electrochemical device. Specifically, the total mass percentage of ethylene carbonate and propylene carbonate can be 10%, 20%, 30%, 40%, 50%, etc. or within the range composed of any two of the above values; preferably 20≤c≤40, and 0.05≤a / c≤0.5.

[0041] In some other embodiments, the electrolyte of the present application further contains fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is d%, based on the total mass of the electrolyte, 0.05≤a / d≤50, specifically, a / d can be 0.05, 0.1, 0.13, 0.2, 0.29, 0.67, 2, 2.5, 5, 10, 20, 30, 40, 50, etc. or within the range of any two of the above values; preferably 0.13≤a / d≤3.3 and 3≤d≤15. The specific amount of fluoroethylene carbonate in the electrolyte can work together with the compound of formula I and the compound of formula II to improve the interface performance of the electrode, thereby further improving the high temperature cycle performance of the electrochemical device.

[0042] In some other embodiments, the electrolyte of the present application also contains lithium difluorophosphate, and the mass percentage of lithium difluorophosphate is e%, 0.2≤e≤2 based on the total mass of the electrolyte. In the electrolyte, a specific amount of lithium difluorophosphate is beneficial to reduce the film formation impedance of the positive electrode sheet of the electrochemical device, thereby improving the high temperature cycle performance of the electrochemical device. Specifically, the mass percentage of lithium difluorophosphate can be 0.2%, 0.4%, 0.6%, 1%, 1.5%, 2%, etc. or within the range composed of any two of the above values.

[0043] Positive electrode

[0044] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. That is, in the present application, the positive active material layer can be disposed on one surface in the thickness direction of the positive current collector, or on two surfaces in the thickness direction of the positive current collector. Moreover, in the present application, the "surface of the positive current collector" can be the entire area of ​​the positive current collector, or a partial area of ​​the positive current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved.

[0045] The components of the positive electrode active material layer include a positive electrode active material, which can be any material that can reversibly embed and de-embed Li + 、Na + For example, the positive electrode active material 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., and the ternary materials include but are not limited to LiNi x Co y Mn z O2、LiNi x Co y Al zO2, etc., and the content 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 Co 0.1 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.

[0046] In some embodiments, the components of the positive electrode active material layer also include a positive electrode conductive agent; the present application has no limitation on the type of the positive electrode conductive agent, 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, or amorphous carbon such as needle coke, or carbon nanotubes, or graphene.

[0047] In some embodiments, the components of the positive electrode active material layer generally also contain a positive electrode binder. There is no particular limitation on the type of positive electrode binder used in the manufacture of the positive electrode active material layer. In the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used in electrode manufacturing can be used. The positive electrode binder includes, but is not limited to, any one or at least two of the following: resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer polymers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers or their hydrides; soft resin polymers such as isotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; polymer compositions having ionic conductivity of alkali metal ions (especially lithium ions), etc.

[0048] In the positive electrode sheet, the type of positive current collector is not particularly limited, and it can be any material known to be suitable for use as a positive current collector. The material of the positive 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 electronic contact resistance between the positive current collector and the positive active material layer, a conductive additive or a conductive coating may be provided on the surface of the positive current collector. Conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. The conductive coating may be a mixture layer of an inorganic oxide, a conductive agent, and a positive electrode binder.

[0049] When preparing the positive electrode sheet, the components in the above-mentioned positive electrode active material layer can be dissolved or dispersed in a liquid solvent to prepare a positive electrode slurry, and then the positive electrode slurry is coated on the positive electrode collector and dried to form a positive electrode active material layer on the positive electrode collector, thereby obtaining a positive electrode sheet. When using this method to prepare the positive electrode sheet, there is no special restriction on the solvent in the positive electrode slurry, as long as it can dissolve or disperse the above-mentioned 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 sheet, the various components in the positive electrode active material layer can also be dry mixed to form a sheet, and then the obtained sheet is pressed onto the positive electrode collector.

[0050] Negative electrode

[0051] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the components of the negative electrode active material layer include a negative electrode sheet active material. That is, in the present application, the negative electrode active material layer can be disposed on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. Moreover, in the present application, the "surface of the negative electrode current collector" can be the entire area of ​​the negative electrode current collector, or it can be a partial area of ​​the negative electrode current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved.

[0052] The negative electrode active material layer generally contains negative electrode sheet active materials, and the present application does not have any particular restrictions on the negative electrode sheet active materials. Specifically, the negative electrode sheet active material may 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 materials or silicon-carbon composite materials.

[0053] In some embodiments, the negative electrode active material layer generally further contains a negative electrode sheet conductive agent. The present application has no particular restrictions on the type of the negative electrode sheet conductive agent, as long as the purpose of the present application can be achieved. For example, the negative electrode sheet conductive agent includes but is not limited to at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots or graphene.

[0054] In some embodiments, the negative electrode active material layer may also contain a negative electrode binder and a thickener. The present application has no particular restrictions on the types of the negative electrode binder and the thickener, 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 polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber or acrylic (ester) 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.

[0055] In the negative electrode sheet, 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 covered with a conductive metal, etc., and there is no special limitation in this application. 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).

[0056] 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 purpose 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.

[0057] 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 collector and dried to form a negative electrode active material layer on the negative electrode collector to obtain a negative electrode sheet; or the components in the negative electrode active material layer can be dry mixed to form a sheet, and then the obtained sheet is pressed onto the negative electrode collector to form a negative electrode active material layer to obtain a negative electrode sheet. The solvent in the negative electrode slurry includes any one of an aqueous solvent and an organic solvent. The aqueous solvent includes but is not limited to a mixed solvent of alcohol and water or water. Organic solvents include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, 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. 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.

[0058] Isolation film

[0059] In order to prevent short circuit, a separator is usually provided between the positive electrode sheet and the negative electrode sheet. In this case, the electrolyte of the present application is usually used by infiltrating the separator.

[0060] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The material of the isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed by a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes include but are not limited to polyolefins, aromatic polyamides, polyimides (PI), polyamides (PA), polytetrafluoroethylene, polyether sulfone, spandex or aramid, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above isolation membranes can be used alone or in any combination.

[0061] The separator may also be a material formed by laminating the above materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0062] The materials of the inorganic substance include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (eg, barium sulfate, calcium sulfate, etc.). The form of the inorganic substance includes, but is not limited to, granular or fibrous forms.

[0063] The separator may be in the form of a thin film, including but not limited to non-woven fabrics, woven fabrics, microporous films, etc. In the thin film form, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using fluororesin as an adhesive to form a porous layer on both sides of the positive electrode with 90% of the aluminum oxide particles having a particle size less than 1 μm.

[0064] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the electrochemical device can be ensured.

[0065] In the present application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate may 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 may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, 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, and the present application has no particular restrictions on the above-mentioned 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 or barium sulfate. The present application has no particular restrictions on the above-mentioned binder, for example, it may be at least one of the aforementioned binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0066] The electrochemical device of the present application also includes a packaging bag for containing a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the art in the electrochemical device, and the present application does not limit the above other components. The present application does not specifically limit the packaging bag, and it can be a packaging bag known in the art, as long as it can achieve the purpose of the present application.

[0067] In a second aspect, the present application further provides an electronic device, which includes the electrochemical device according to the present application.

[0068] The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. In some embodiments, the electrochemical device of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0069] Example

[0070] The following uses lithium-ion secondary batteries as an example to provide examples and comparative examples to more specifically describe the implementation of the electrochemical device of the present application. Those skilled in the art will understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

[0071] Test methods and equipment:

[0072] High temperature (45°C) cycle performance test

[0073] The cycle performance of the electrochemical device is evaluated by the capacity retention rate after 400 cycles at 45° C. The greater the capacity retention rate after 400 cycles at 45° C., the better the cycle performance of the electrochemical device.

[0074] The electrochemical device was placed in a 45°C thermostat and allowed to stand for 30 minutes to allow the electrochemical device to reach a constant temperature. The electrochemical device that reached a constant temperature was charged to 4.5V at 0.2C constant current at 45°C, charged to 0.05C at 4.5V, allowed to stand for 5 minutes, and then discharged to 3.0V at 0.2C constant current, allowed to stand for 5 minutes, and the initial discharge capacity C0 of the electrochemical device was tested; then charged to 4.15V at 1.8C constant current, and charged to 1C at 4.15V constant voltage; then charged to 4.25V at 1C constant current, and then charged to 0.8C at 4.25V constant voltage; then charged to 4.5V at 0.8C constant current, and then charged to 0.05C at 4.5V constant voltage; left for 5 minutes; then discharged to 3.0V at 1C constant current, and allowed to stand for 5 minutes. This is one charge and discharge cycle. The electrochemical device was cycled 400 times according to the above charge / discharge cycle steps, and the discharge capacity C1 of the electrochemical device after 400 cycles was measured.

[0075] The capacity retention rate after 400 cycles at 45°C = C1 / C0×100%. The higher the capacity retention rate after 400 cycles at 45°C, the better the high-temperature cycle performance of the electrochemical device. The specific data of the high-temperature cycle performance of the electrochemical devices in each embodiment and comparative example are shown in Tables 1 to 4.

[0076] Thermal safety performance test

[0077] The electrochemical device was discharged at 0.2C constant current to 3.0V at 25°C, then charged at 0.5C constant current to 4.5V, and then charged at 4.5V to 0.05C at constant voltage. Place it in a high-temperature furnace at 130°C, 131°C, 132°C, 133°C, 134°C or 135°C for 1 hour. After 1 hour, observe whether the electrochemical device catches fire. If it does not catch fire, it is judged to have passed. The pass rate is recorded in N / 10, which means that 10 electrochemical devices were tested and N passed the test; the specific data of the high-temperature cycle performance of the electrochemical devices in each embodiment and comparative example are shown in Tables 1 to 4.

[0078] Hot box performance judgment standard: Under different temperatures, the higher the temperature without ignition, the better the hot box performance and thermal safety performance; under the same temperature, the higher the pass rate, the better the hot box performance and thermal safety performance. For example, the test results of 133℃, 5 / 10 are better than the test results of 133℃, 3 / 10, and the test results of 133℃, 3 / 10 are better than the test results of 132℃, 5 / 10.

[0079] Example 1-1

[0080] <Preparation of Electrolyte>

[0081] In an argon atmosphere glove box with a water content of less than 10 ppm, ethyl methyl carbonate and ethyl acetate were mixed in a mass percentage of 1:1 to prepare a basic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6), a compound of formula I, and a compound of formula II were added to form an electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF6 is 12.5%, the mass percentage of the compound of formula I and the compound of formula II are shown in Table 1, and the remainder is the basic solvent.

[0082] In addition, the compounds indicated by the codes in the table can be found in the above content of this article for details.

[0083] <Preparation of positive electrode sheet>

[0084] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2:3, and N-methylpyrrolidone (NMP) was added and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 70wt%. The positive electrode slurry was evenly coated on the upper and lower surfaces of a positive electrode current collector aluminum foil with a thickness of 9μm, and then dried and pressurized and cut into a specified size to obtain a positive electrode sheet.

[0085] <Preparation of negative electrode sheet>

[0086] Artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNT), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8, and then deionized water was added as a solvent and stirred evenly to prepare a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry was evenly coated on the upper and lower surfaces of a negative electrode current collector copper foil with a thickness of 6μm, and then dried and pressurized and cut into a specified size to obtain a negative electrode sheet.

[0087] <Isolation film>

[0088] A porous polyethylene film with a thickness of 15 μm was used as the separator.

[0089] <Preparation of electrochemical device>

[0090] The prepared positive electrode sheet, separator, negative electrode sheet and separator are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain an electrode assembly. After welding the pole ears, the electrode assembly is placed in an aluminum-plastic film packaging bag, placed in a vacuum oven at 85°C for 12 hours to remove moisture, and the prepared electrolyte is injected. After vacuum packaging, standing, formation, shaping, and capacity testing, a lithium-ion battery (i.e., an electrochemical device) is obtained.

[0091] Example 1-2 to Example 1-8

[0092] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-2. Wherein, when the mass percentage of the compound of formula I changes, the mass percentage of the lithium salt remains unchanged.

[0093] Example 1-9 to Example 1-15

[0094] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-3. Wherein, when the mass percentage of the compound of Formula II changes, the mass percentage of the lithium salt remains unchanged.

[0095] Example 1-16 to Example 1-23

[0096] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-3.

[0097] Table 1

[0098]

[0099] Example 2-1 to Example 2-5

[0100] Except that ethylene carbonate and propylene carbonate are further added in <Preparation of Electrolyte> and relevant preparation parameters are adjusted according to Table 2, the rest is the same as Example 1-1. When the mass percentage of the compound of formula I, ethylene carbonate and propylene carbonate changes, the content of LiPF6 remains unchanged.

[0101] Table 2

[0102]

[0103]

[0104] Example 3-1 to Example 3-15

[0105] Except for further adding fluoroethylene carbonate in <Preparation of Electrolyte> and adjusting relevant preparation parameters according to Table 3, the rest is the same as Example 1-2. When the mass percentage of the compound of formula I and fluoroethylene carbonate changes, the mass percentage of LiPF6 remains unchanged.

[0106] Table 3

[0107]

[0108] Example 4-1 to Example 4-6

[0109] Except that lithium difluorophosphate is further added in <Preparation of Electrolyte> and relevant preparation parameters are adjusted according to Table 4, the rest is the same as Example 1-2. When the mass percentage of lithium difluorophosphate changes, the mass percentage of LiPF6 remains unchanged.

[0110] Table 4

[0111]

[0112] Comparative Example 1 to Comparative Example 3

[0113] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-2. When the mass percentage of the compound of Formula I and the compound of Formula II changes, the mass percentage of LiPF6 remains unchanged, both being 12.5%.

[0114] As can be seen from Table 1, in the electrochemical device of the present application, when the electrolyte contains 0.1% to 2% of the compound of formula II and also contains 1% to 50% of the compound of formula I, the electrochemical device can have excellent high-temperature cycle performance and thermal safety performance; especially when 2≤a≤10, 0.1≤b≤0.6, the high-temperature cycle performance and thermal safety performance of the electrochemical device are better.

[0115] As can be seen from Table 2, ethylene carbonate and propylene carbonate in combination with the compound of formula I and the compound of formula II can better improve the high temperature cycle performance and thermal safety performance of the electrochemical device.

[0116] As shown in Table 3, fluoroethylene carbonate combined with the compound of formula I and the compound of formula II can better improve the high temperature cycle performance of the electrochemical device.

[0117] As can be seen from Table 4, lithium difluorophosphate can work together with the compound of formula I and the compound of formula II to form a protective film with low impedance on the positive electrode of the electrochemical device, thereby further improving the thermal safety performance of the electrochemical device.

[0118] The above are only embodiments of the present application and are not intended to limit the scope of protection of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that: The electrolyte comprises a compound of formula I and a compound of formula II, wherein the compound of formula I is: Wherein R is selected from any one of fluorine-substituted or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, and fluorine-substituted or unsubstituted C6-C12 aryl group; the compound of formula II is: Wherein R1, R2, R3, and R4 are each independently selected from or N, and any one or any two of R1-R4 are N, R5 are each independently selected from any one of hydrogen, halogenated or unsubstituted C1-C10 alkyl, halogenated or unsubstituted C2-C10 alkenyl, halogenated or unsubstituted C2-C10 alkynyl, halogenated or unsubstituted C6-C10 aryl, halogenated or unsubstituted C3-C10 alicyclic hydrocarbon group, halogenated or unsubstituted C2-C10 heterocyclic group, halogenated or unsubstituted C1-C10 alkoxy, and when R5 is selected from a group other than hydrogen, the main chain of R5 contains 0 to 20 heteroatoms, and the heteroatoms include at least one of O, S, N, B, P, and Si; Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, and the mass percentage of the compound of formula II is b%, wherein 1≤a≤50, 0.01≤b≤2.

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

3. The electrochemical device according to claim 1, characterized in that The compound of formula II includes at least one of the following compounds:

4. The electrochemical device according to claim 1, characterized in that 2≤a≤10, 0.1≤b≤0.

6.

5. The electrochemical device according to claim 1, characterized in that The electrolyte further comprises ethylene carbonate and propylene carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the ethylene carbonate and the propylene carbonate is c%, 10≤c≤50.

6. The electrochemical device according to claim 5, characterized in that 20≤c≤40, and 0.05≤a / c≤0.

5.

7. The electrochemical device according to claim 1, characterized in that The electrolyte further comprises fluoroethylene carbonate, and the mass percentage of the fluoroethylene carbonate is d% based on the total mass of the electrolyte, and 0.05≤a / d≤50.

8. The electrochemical device according to claim 7, characterized in that 3≤d≤15, and 0.13≤a / d≤3.

33.

9. The electrochemical device according to claim 1, characterized in that The electrolyte further comprises lithium difluorophosphate, and the mass percentage of the lithium difluorophosphate is e%, based on the total mass of the electrolyte, and 0.2≤e≤2.

10. An electronic device, characterized in that: It comprises the electrochemical device according to any one of claims 1 to 9.

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