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; the compound in the formula I is # imgabs 0 #, the compound in the formula II is # imgabs 1 #, n is 0 or 1 or 2, based on the total mass of the electrolyte, the mass percentage content of the compound in the formula I is a%, and a is larger than or equal to 5 and smaller than or equal to 50. In the application, by controlling the components and the content of the components of the electrolyte in the electrochemical device, the cycle performance and the storage performance of the electrochemical device at a high temperature can be improved, and meanwhile, the low-temperature loading performance of the electrochemical device can also be improved.

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 (e.g., 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. With the popularity of electrochemical devices such as lithium-ion batteries in real life, users require electrochemical devices to have good electrical properties under both high and low temperature conditions. However, at present, electrochemical devices such as lithium-ion batteries often cannot take into account the cycle performance, storage performance and low temperature load performance at high temperature. Summary of the invention

[0003] The present application provides an electrochemical device and an electronic device. The electrochemical device of the present application has excellent cycle performance and storage performance at high temperature, and also exhibits good low-temperature loading performance.

[0004] In a first aspect, an embodiment of the present application provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte includes a compound of formula I and a compound of formula II. 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. The compound of formula II is: wherein n is 0 or 1 or 2, M is selected from C or O, and X is selected from R 21 , R 22 Each independently selected from H, Any of the R 21 and R 22 are not selected from H at the same time, and X, R 21 and R 22 The mass percentage of the compound of formula I is a%, based on the total mass of the electrolyte, and 1≤a≤50.

[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 more than 1wt% of the compound of formula I, the low-temperature pulling performance of the electrochemical device can be well improved. However, the inventors found that although the compound of formula I in the electrolyte will form a stable film structure on the positive electrode of the electrochemical device, the SEI (Solid Electrolyte Interphase) film formed on the negative electrode is not stable, which is not conducive to the high-temperature cycle performance and storage performance of the electrochemical device at high temperature. The inventors also found that if the content of the compound of formula I is controlled to be no more than 50wt%, the electrolyte also contains the compound of formula II. At this time, the compound of formula II will work together with the compound of formula I to generate a low-impedance and high-stability SEI film on the negative electrode, inhibiting the reaction of the compound of formula I on the negative electrode, which can even improve the cycle performance and storage performance of the electrochemical device.

[0006] In a possible implementation, based on the total mass of the electrolyte, the content percentage of the compound of formula II is b%, 0.2≤b≤6, and 0.167≤a / b≤125.

[0007] In the above technical solution, in the electrolyte meeting the above conditions, the compound of formula II has a more obvious inhibitory effect on the reaction of the compound of formula I in the negative electrode plate, and the storage performance and cycle performance of the electrochemical device at high temperature will be better.

[0008] In a possible implementation, the electrolyte satisfies at least one of the following conditions: (1) 2≤a≤10; (2) 0.5≤b≤4; (3) 0.5≤a / b≤20.

[0009] In the above technical solution, in the electrolyte meeting the above conditions, the inhibitory effect of the compound of formula II on the reaction of the compound of formula I in the negative electrode plate is more obvious, and the storage performance and cycle performance of the electrochemical device at high temperature at high temperature will be further improved.

[0010] In one possible implementation, the compound of formula I includes at least one of the following compounds:

[0011]

[0012] In the above technical solution, the compound of formula I with the above structure can better improve the cycle performance, storage performance and low-temperature loading performance of the electrochemical device at high temperature.

[0013] In one possible implementation, the compound of formula II includes at least one of the following compounds:

[0014]

[0015] In the above technical solution, the compound of formula II with the above structure can better cooperate with the compound of formula I to improve the cycle performance and storage performance of the electrochemical device at high temperature.

[0016] In a possible implementation, the electrolyte further includes ethylene carbonate and propylene carbonate, and the total content of ethylene carbonate and propylene carbonate is c%, based on the total mass of the electrolyte, and 10≤c≤50.

[0017] In the above technical solution, ethylene carbonate and propylene carbonate can increase the solubility of the electrolyte for lithium salt, thereby improving the ion mass ratio of the electrolyte; therefore, the electrolyte meeting the above conditions can further improve the low-temperature loading performance of the electrochemical device.

[0018] In one possible implementation, 0.05≤a / c≤0.5.

[0019] In the above technical solution, when the total amount of ethylene carbonate and propylene carbonate meets the above conditions, the low-temperature loading performance of the electrochemical device can be further improved.

[0020] In a possible implementation, the electrolyte further includes fluoroethylene carbonate, and the content of the fluoroethylene carbonate is d%, based on the total mass of the electrolyte, and 0.05≤a / d≤50.

[0021] In the above technical solution, fluoroethylene carbonate can work together with the compound of formula I and the compound of formula II to form a SEI film with good stability and low impedance on the surface of the negative electrode, which is beneficial to improve the interface performance of the electrochemical device, thereby enhancing the high-temperature cycle performance of the electrochemical device.

[0022] In one possible implementation, 3≤d≤15, and 0.13≤a / d≤3.33.

[0023] In the above technical solution, when the content of fluoroethylene carbonate meets the above conditions, it is more conducive to improving the interface performance of the electrochemical device, thereby further improving the high-temperature cycle performance of the electrochemical device.

[0024] 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.

[0025] In the above technical solution, the electrolyte contains a certain amount of lithium difluorophosphate that can work together with 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 low-temperature loading performance of the electrochemical device.

[0026] In a possible implementation, the electrolyte further includes nitriles, and the mass percentage of the nitriles is f%, based on the total mass of the electrolyte, where 1≤f≤8.

[0027] In the above technical solution, the nitriles in the electrolyte can form a protective film on the positive electrode plate, which can reduce the capacity loss rate of the electrochemical device and further improve the high-temperature cycle performance and high-temperature storage performance of the electrochemical device; however, nitriles have a destructive effect on the negative electrode plate, and the content should not be too high.

[0028] In a possible implementation, the nitriles include at least one of dinitriles and trinitriles, and the ratio of the mass percentage of the trinitriles to the mass percentage of the dinitriles is not greater than 4 based on the total mass of the electrolyte.

[0029] In the above technical solution, the mass percentage ratio of trinitriles to dinitriles is controlled within a range of no more than 4, which is beneficial to further improve the high-temperature storage performance and high-temperature cycle performance of the electrochemical device.

[0030] In a possible implementation, the dinitrile includes at least one of succinonitrile, adiponitrile, glutaronitrile, and pimelonitrile; and / or the trinitrile includes 1,3,6-propane trinitrile.

[0031] In a second aspect, an embodiment of the present application provides an electronic device, which includes the above-mentioned electrochemical device.

[0032] Beneficial effects of this application:

[0033] 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%, wherein 1≤a≤50. By regulating the electrolyte to include a compound of formula I and a compound of formula II, 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, and the electrochemical device of the present application has excellent cycle performance and storage performance at high temperature, and also good low-temperature pulling performance. DETAILED DESCRIPTION

[0034] 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.

[0035] The electrochemical device and the electronic device of the embodiments of the present application are described in detail below.

[0036] 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 in the electrolyte and the content of the specific components, the electrochemical device can have good high-temperature cycle performance and high-temperature storage performance, as well as good low-temperature loading performance.

[0037] The structure of the electrochemical device of the present application is as follows:

[0038] Electrolyte

[0039] The electrolyte can play a role in transmitting lithium ions and electrons, ensuring that a pathway is formed inside the electrochemical device. In the present application, the electrolyte includes a compound of formula I: Wherein R is selected from any one of a fluorine-containing substituted or unsubstituted C2-C6 alkyl group, a C6-C12 nitrogen-containing heterocyclic group, and a fluorine-substituted or unsubstituted C6-C12 aryl group.

[0040] The inventors found that the viscosity of the compound of formula I is low, and because of the sulfone and fluorinated structure, the compound of formula I has a strong antioxidant ability. When the electrolyte of the electrochemical device contains more than 1wt% of the compound of formula I, the low-temperature loading performance of the electrochemical device can be well improved. However, the inventors found that although the compound of formula I in the electrolyte will form a stable film structure on the positive electrode of the electrochemical device, the stability of the SEI film formed on the negative electrode is not high, which is not conducive to the high-temperature cycle performance and storage performance of the electrochemical device at high temperature.

[0041] The inventors also found that if the electrolyte contains no more than 50 wt% of the compound of formula I and also contains the compound of formula II: If the compound of formula II works together with the compound of formula I to form a low impedance and high stability SEI film on the negative electrode plate, inhibiting the reaction of the compound of formula I on the negative electrode plate, which can not only ensure that the cycle performance and storage performance of the electrochemical device at high temperature are not affected, but can even improve the cycle performance and storage performance of the electrochemical device. In the compound of formula II, n is 0 or 1 or 2, M is selected from C or O, and X is selected from R 21 , R 22 Each independently selected from H, Any of the R 21 and R 22 are not selected from H at the same time, and X, R 21 and R 22 Contains at least one sulfur atom.

[0042] As shown above, based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, where 1≤a≤50. Specifically, the mass percentage of the compound of formula I can be 1%, 2%, 4%, 7%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, etc. or within the range of any two of the above values, such as 10% to 30%, etc.

[0043] In some other embodiments, based on the total mass of the electrolyte, the mass percentage of the compound of formula II in the present application is b%, wherein 0.2≤b≤6, and 0.167≤a / b≤125. This type of compound II has a more obvious inhibitory effect on the reaction of the compound of formula I in the negative electrode plate, and the storage performance and cycle performance of the electrochemical device at high temperature will be better. The mass percentage of the compound of formula II can be specifically 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, etc. or within the range composed of any two of the above values. a / b can specifically be 0.167, 0.33, 0.4, 0.5, 0.67, 1, 1.33, 2, 4, 7, 10, 15, 20, 30, 40, 50, 100, 125, etc. or within the range composed of any two of the above values, for example, a / b can be any value in the range of 0.5 to 20.

[0044] In addition, in order to make the inhibitory effect of the compound of formula II on the reaction of the compound of formula I in the negative electrode plate more obvious, the storage performance and cycle performance of the electrochemical device at high temperature will be further improved. The electrolyte in the embodiment of the present application can meet at least one of the following conditions: (1) 2≤a≤10; (2) 0.5≤b≤4; (3) 0.5≤a / b≤20.

[0045] Specifically, in some embodiments of the present application, the compound of formula I in the electrolyte component may include at least one of the following compounds:

[0046]

[0047] These compounds of formula I can better improve the cycle performance, storage performance and low-temperature loading performance of electrochemical devices at high temperatures.

[0048] Specifically, in some embodiments of the present application, the compound of formula II in the electrolyte component may include at least one of the following compounds:

[0049]

[0050] These compounds of formula II can better cooperate with the compounds of formula I to improve the cycle performance and storage performance of electrochemical devices at high temperatures.

[0051] In some embodiments of the present application, the electrolyte further comprises 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. Ethylene carbonate and propylene carbonate can increase the solubility of the electrolyte for lithium salts, thereby improving the ion rate of the electrolyte and improving the low-temperature loading 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 0.05≤a / c≤0.5.

[0052] In some embodiments of the present application, the electrolyte further comprises fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is d%, 0.05≤a / d≤50 based on the total mass of the electrolyte. Fluoroethylene carbonate can act together with the compound of formula I and the compound of formula II to form a SEI film with good stability and low impedance on the surface of the negative electrode plate, which is beneficial to improve the interface performance of the electrochemical device, thereby improving the high temperature cycle performance of the electrochemical device. 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 composed of any two of the above values. More specifically, the content of fluoroethylene carbonate can be 3% to 15%, and the range of a / d is 0.13 to 3.33, which is more conducive to improving the interface performance of the electrochemical device, thereby further improving the high temperature cycle performance of the electrochemical device.

[0053] In some embodiments of the present application, the electrolyte also includes lithium difluorophosphate, and the mass percentage of lithium difluorophosphate based on the total mass of the electrolyte is e%, and 0.2≤e≤2. At this time, the lithium difluorophosphate in the electrolyte can work together with the compound of formula II to form a protective film with low impedance on the positive electrode of the electrochemical device, thereby improving the low-temperature loading performance of the electrochemical device. Specifically, the content of lithium difluorophosphate can be 0.2%, 0.5%, 0.7%, 1%, 1.5%, 2%, etc. or within the range composed of any two of the above values.

[0054] In some embodiments of the present application, the electrolyte also includes nitriles, and the mass percentage of nitriles is f%, 1≤f≤8 based on the total mass of the electrolyte. In the electrolyte of the present application, an appropriate amount of nitriles can form a protective film on the positive electrode plate while basically not causing damage to the negative electrode plate, which can reduce the capacity loss rate of the electrochemical device and improve the high-temperature cycle performance and high-temperature storage performance of the electrochemical device. Specifically, in the embodiments of the present application, the content of nitriles can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc. or within the range composed of any two of the above values. In addition, in a specific embodiment of the present application, the nitriles include at least one of dinitriles and trinitriles, and based on the total mass of the electrolyte, the mass percentage ratio of the trinitriles to the dinitriles is not greater than 4, which is beneficial to further improve the high temperature storage performance and high temperature cycle performance of the electrochemical device; the dinitriles specifically include at least one of succinonitrile, adiponitrile, glutaronitrile, pimelonitrile, etc., and the trinitriles include at least one of 1,3,6-propane trinitrile and 1,2,3-tri(2-cyano)propane.

[0055] Positive electrode

[0056] 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.

[0057] 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 z O2, 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 Co0.08 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Negative electrode

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] 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.

[0069] 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.

[0070] Isolation film

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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).

[0078] 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.

[0079] In a second aspect, the present application further provides an electronic device, which includes the electrochemical device according to the present application.

[0080] 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.

[0081] Example

[0082] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0083] Test methods and equipment:

[0084] Cycle performance test:

[0085] <Performance preparation of electrochemical devices>

[0086] High temperature (45°C) cycle performance test

[0087] 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.

[0088] 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.

[0089] The capacity retention rate after 400 cycles at 45°C = C1 / C0×100%.

[0090] High temperature (80°C) storage performance test

[0091] The electrochemical device, i.e., the battery, is charged to 4.5V at a constant current of 1.8C at room temperature (25°C), and then charged to a cutoff current of 0.02C at a constant voltage of 4.5V. Five different points are selected to test the thickness, and the average value of the five measured values ​​is recorded as the initial thickness L1; the electrochemical device is then placed in an 80°C oven for 7 hours, and then five different points are selected to thermally measure the battery thickness, and the average value of the five measured values ​​is recorded as L2, and the thickness growth rate = (L2 / L1-1)×100%.

[0092] The smaller the thickness growth rate, the better the high-temperature storage performance.

[0093] Low temperature (-20℃) tensile performance test

[0094] The electrochemical device was charged to 4.5V at 0.2C at 25°C, then charged to a cutoff current of 0.02C at a constant voltage of 4.5V, and then discharged at a constant current of 0.2C for 4h. The temperature was adjusted to -20°C, and after keeping warm for 30min, the device was discharged at 0.4C for 1s and 0.1C for 2s. The steps of "discharge at 0.4C for 1s and discharge at 0.1C for 2s" were then repeated until the voltage was lower than 3V. The number of cycles at this time was recorded, which was the low-temperature loading number.

[0095] The higher the low-temperature load number, the better the low-temperature discharge performance; the specific data of the low-temperature load performance in the electrochemical device in each embodiment and comparative example are shown in the table.

[0096] Example 1-1

[0097] <Preparation of Electrolyte>

[0098] 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.

[0099] In addition, the compounds indicated by the codes in the table can be found in the above content of this article for details.

[0100] <Preparation of positive electrode sheet>

[0101] 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.

[0102] <Preparation of negative electrode sheet>

[0103] 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.

[0104] <Isolation film>

[0105] A porous polyethylene film with a thickness of 15 μm was used as the separator.

[0106] <Preparation of electrochemical device>

[0107] 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.

[0108] Example 1-2 to Example 1-10

[0109] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. Wherein, when the mass percentage of the compound of formula I changes, the mass percentage of the lithium salt remains unchanged.

[0110] Example 1-11 to Example 1-18

[0111] 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 II changes, the mass percentage of the lithium salt remains unchanged.

[0112] Examples 1-19

[0113] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. Wherein, when the mass percentage of the compound of Formula II changes, the mass percentage of the lithium salt remains unchanged.

[0114] Examples 1-20

[0115] Except for adjusting the relevant preparation description according to Table 1, the rest is the same as Example 1-12. Wherein, when the mass percentage of the compound of formula I changes, the mass percentage of the lithium salt remains unchanged.

[0116] Embodiment 1-21

[0117] Except for adjusting the relevant preparation description according to Table 1, the rest is the same as Example 1-11. Wherein, when the mass percentage of the compound of formula I changes, the mass percentage of the lithium salt remains unchanged.

[0118] Example 1-22 to Example 1-28

[0119] Except for adjusting the relevant preparation description according to Table 1, the rest is the same as Example 1-2.

[0120] Table 1

[0121]

[0122]

[0123] Example 2-1 to Example 2-5

[0124] 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 1-2. When the mass percentage of ethylene carbonate and propylene carbonate changes, the mass percentage of LiPF6 remains unchanged.

[0125] Embodiment 2-6

[0126] 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 1-5.

[0127] Table 2

[0128]

[0129] Example 3-1 to Example 3-15

[0130] 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.

[0131] Table 3

[0132]

[0133]

[0134] Example 4-1 to Example 4-6

[0135] 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.

[0136] Table 4

[0137]

[0138] Example 5-1 to Example 5-13

[0139] Except for further adding nitriles in <Preparation of Electrolyte> and adjusting relevant preparation parameters according to Table 5, the rest is the same as Example 1-2. When the mass percentage of nitriles changes, the mass percentage of LiPF6 remains unchanged.

[0140] Table 5

[0141]

[0142]

[0143] Comparative Example 1

[0144] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-11. When the mass percentage of the compound of formula I changes, the content of LiPF6 remains unchanged.

[0145] Comparative Example 2

[0146] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-10. When the mass percentage of the compound of formula I changes, the content of LiPF6 remains unchanged.

[0147] Referring to Table 1, it can be seen from the embodiments and comparative examples that in the electrochemical device of the present application, when the electrolyte contains 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 storage performance, and also has good low temperature load performance. In particular, when the mass percentage of the compound of formula I is 2% to 10%, the mass percentage of the compound of formula II is 0.5% to 4%, and the mass percentage ratio of the compound of formula I to the compound of formula II is between 0.5 and 20, the storage performance at high temperature and the cycle performance at high temperature of the electrochemical device will be further improved.

[0148] Referring to Table 2, it can be seen from Examples 1-2, 2-5 and 2-4 that when the total mass percentage of ethylene carbonate and propylene carbonate is 10% to 50%, the compounds of Formula I and II can be used in combination to better improve the low-temperature loading performance of the electrochemical device.

[0149] Referring to Table 3, it can be seen from Examples 1-2 and 3-1 to 3-15 that when the electrolyte includes fluoroethylene carbonate (content is d%) and a / d is 0.05 to 50, fluoroethylene carbonate can work together with the compound of formula I and the compound of formula II to improve the high temperature cycle performance of the electrochemical device; when 3≤d≤15 and 0.13≤a / d≤3.33, the high temperature cycle performance of the electrochemical device is improved more significantly.

[0150] Referring to Table 4, it can be seen from Examples 1-2 and 3-1 to 3-5 that lithium difluorophosphate can work together with 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 low-temperature loading performance of the electrochemical device.

[0151] Referring to Table 5, it can be seen from Examples 1-2 and 4-1 to 4-13 that in an electrochemical device, when the electrolyte contains the compound of Formula I, the compound of Formula II and nitriles at the same time, the high temperature cycle performance and high temperature storage performance of the electrochemical device can be further improved. In particular, when the electrolyte contains dinitrile and trinitrile at the same time, and the mass ratio of trinitrile to dinitrile is not greater than 4, the improvement of storage performance and cycle performance at high temperature is particularly obvious.

[0152] 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; The compound of formula II is: wherein n is 0 or 1 or 2, M is selected from C or O, and X is selected from R 21 , R 22 Each independently selected from H, Any of the R 21 and R 22 are not selected from H at the same time, and X, R 21 and R 22 Contains at least one sulfur atom; Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, 1≤a≤50.

2. The electrochemical device according to claim 1, characterized in that Based on the total mass of the electrolyte, the mass percentage of the compound of formula II is b%, 0.2≤b≤6, and 0.167≤a / b≤125.

3. The electrochemical device according to claim 2, characterized in that The electrolyte satisfies at least one of the following conditions: (1)2≤a≤10； (2)0.5≤b≤4； (3)0.5≤a / b≤20.

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

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

6. 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 total mass percentage of ethylene carbonate and propylene carbonate is c%, 10≤c≤50.

7. The electrochemical device according to claim 6, characterized in that 0.05≤a / c≤0.

5.

8. 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.

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

33.

10. The electrochemical device according to claim 2, 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.

11. The electrochemical device according to claim 2, characterized in that: The electrolyte further comprises nitriles, and based on the total mass of the electrolyte, the mass percentage of the nitriles is f%, 1≤f≤8.

12. The electrochemical device according to claim 11, characterized in that The nitriles include at least one of dinitriles and trinitriles, and based on the total mass of the electrolyte, the mass percentage ratio of the trinitriles to the dinitriles is not greater than 4.

13. The electrochemical device according to claim 12, characterized in that The dinitrile includes at least one of succinonitrile, adiponitrile, glutaronitrile, and pimelonitrile; and / or the trinitrile includes at least one of 1,3,6-propane trinitrile and 1,2,3-tris(2-cyano)propane.

14. An electronic device, characterized in that: It comprises the electrochemical device according to any one of claims 1 to 13.

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