An electrochemical device

Abstract

The application relates to an electrochemical device. The electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the electrolyte comprising a lithium salt of fluorine-containing sulfimide and a tricyanide compound, wherein the content of the lithium salt of fluorine-containing sulfimide is X% and the content of the tricyanide compound is Y% based on the weight of the electrolyte, and 1<=X+Y<=6 is satisfied; the positive electrode sheet comprises a positive electrode current collector, the positive electrode current collector comprising an aluminum foil base material and a copper element contained in the aluminum foil base material, the content of the copper element m is in ppm based on the weight of the positive electrode current collector, the thickness d of the aluminum foil base material is in mu.m, and d*m / 1000>=5 is satisfied. The electrochemical device provided by the application has high safety performance.

Description

[0001] This application is a divisional application of Chinese patent application filed on March 30, 2021, with application number 202180004970.7 and invention title "An electrolyte and an electrochemical device containing the electrolyte". Technical Field

[0002] This application relates to the field of energy storage, specifically to an electrochemical device. Background Technology

[0003] With the widespread adoption of smart products, the demand for electronic devices such as mobile phones, laptops, and cameras is increasing year by year. Lithium-ion batteries, as the power source for these electronic products, are characterized by high energy density, no memory effect, and high operating voltage, and are gradually replacing traditional Ni-Cd and MH-Ni batteries. However, with the development of lithium-ion batteries, people's requirements for their safety performance are constantly increasing, making the development of safer lithium-ion batteries one of the main market demands. Summary of the Invention

[0004] This application provides an electrolyte comprising a fluorosulfonylimide lithium salt and a trinitrile compound, wherein, based on the weight of the electrolyte, the content of the fluorosulfonylimide lithium salt is X%, and the content of the trinitrile compound is Y%, satisfying 1 ≤ X + Y ≤ 6. The electrolyte of this application can improve the safety performance of lithium-ion batteries.

[0005] According to some embodiments of this application, the electrolyte further comprises lithium hexafluorophosphate (LiPF6). According to some embodiments of this application, the lithium hexafluorophosphate content is Z% based on the weight of the electrolyte, wherein X+Z≤7.5 and X / Z≤1.

[0006] According to some embodiments of this application, the fluorinated sulfonyl imide lithium salt comprises one or both of lithium bisfluorosulfonyl imide (LiFSI) or lithium bistrifluoromethanesulfonyl imide (LiTFSI).

[0007] According to some embodiments of this application, the electrolyte satisfies at least one of the following conditions (a) or (b): (a) Z is less than 5; (b) 0.8 ≤ (X+Z) / (X+Y) ≤ 3.5.

[0008] According to some embodiments of this application, the trinitrile compound includes at least one of a compound of formula II or a compound of formula III: Formula II, Formula III In Equation II, a, d, and f are each independently selected from integers from 1 to 6, and b, c, and e are each independently selected from integers from 0 to 6; In Equation III, g, h, and i are each independently selected from integers between 0 and 6.

[0009] According to some embodiments of this application, the trinitrile compound comprises at least one selected from 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, and 1,2,5-tris(2-cyanoethoxy)pentane.

[0010] According to some embodiments of this application, the electrolyte further comprises a compound of formula I: Formula I R1, R2, and R3 are each independently selected from hydrogen, halogen, and C1-C atoms with or without substituents. 12 Alkyl groups, C3-C8 cycloalkyl groups with or without substituents, C6-C6 cycloalkyl groups with or without substituents 12 Aryl, wherein the substituent is selected from at least one of cyano, nitro, halogen and sulfonyl, and n is an integer from 0 to 7.

[0011] According to some embodiments of this application, in Formula I, R1, R2, and R3 are each independently selected from hydrogen or C1-C5 alkyl groups, and n is an integer from 0 to 3.

[0012] According to some embodiments of this application, the content of the compound of formula I is A% based on the weight of the electrolyte, satisfying 1≤A+X+Y≤7.

[0013] According to some embodiments of this application, the electrolyte further comprises a lithium salt additive, which comprises at least one of lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(oxalate-borate), or lithium difluorooxalate-borate. According to some embodiments of this application, the content of the lithium salt additive is P% based on the weight of the electrolyte, satisfying 0.1 ≤ P ≤ 2.

[0014] The second aspect of this application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and the electrolyte described in the first aspect of this application.

[0015] According to some embodiments of this application, the positive electrode sheet includes a positive current collector, the positive current collector includes an aluminum foil substrate and copper element contained in the aluminum foil substrate, the copper element content m is expressed in ppm based on the weight of the positive current collector, the thickness d of the aluminum foil substrate is expressed in μm, and d×m / 1000≥5 is satisfied.

[0016] According to some embodiments of this application, 5 ≤ d × m / 1000 ≤ 50.

[0017] According to some embodiments of this application, 0 < m ≤ 2000 ppm.

[0018] A third aspect of this application provides an electronic device including the electrochemical device described in the second aspect of this application. Detailed Implementation

[0019] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0020] A first aspect of this application provides an electrolyte comprising a fluorosulfonylimide lithium salt and a trinitrile compound, wherein, based on the weight of the electrolyte, the content of the fluorosulfonylimide lithium salt is X%, and the content of the trinitrile compound is Y%, satisfying 1 ≤ X + Y ≤ 6. According to some embodiments, X + Y = 1.25, 1.5, 1.75, 2.0, 2.25, 2.5, 2.75, 3.0, 3.25, 3.5, 3.75, 4.0, 4.25, 4.5, 4.75, 5.0, 5.25, 5.5, 5.75, 6.0, or any value between these values.

[0021] According to some embodiments of this application, 1 ≤ X ≤ 5.5, for example, X is 1.0, 1.25, 1.5, 1.75, 2.0, 2.25, 2.5, 2.75, 3.0, 3.25, 3.5, 3.75, 4.0, 4.25, 4.5, 4.75, 5.0, 5.25, 5.5, or any value between these values. According to some embodiments of this application, X is 1.25 ≤ X ≤ 5.0.

[0022] According to some embodiments of this application, 0.1 ≤ Y ≤ 2.5, for example, Y is 0.1, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 2.0, 2.25 or any value between these values. According to some embodiments of this application, 0.5 ≤ Y ≤ 2.0.

[0023] According to some embodiments of this application, the electrolyte further comprises lithium hexafluorophosphate (LiPF6). According to some embodiments of this application, the content of lithium hexafluorophosphate is Z% based on the weight of the electrolyte, where X+Z≤7.5 and X / Z≤1. The introduction of the fluorosulfonylimide lithium salt can improve the inherent stability of the electrolyte, and when the sum of its concentration and that of lithium hexafluorophosphate is low, it can significantly reduce short-circuit heat generation, thereby improving mechanical safety performance such as impact and nail resistance.

[0024] According to some embodiments of this application, Z ≤ 7.0. According to some embodiments of this application, Z < 5.0. According to some embodiments of this application, 0.1 ≤ Z ≤ 7, for example, Z is 0.1, 0.5, 1.5, 2.0, 2.5, 3.0, 3.75, 4.0, 4.25, 4.75, 5.0, 6.0 or any value between these values. According to some embodiments of this application, 2.5 ≤ Z ≤ 5.0.

[0025] According to some embodiments of this application, the fluorosulfonylimide lithium salt comprises lithium bisfluorosulfonylimide (LiFSI) and / or lithium bistrifluoromethanesulfonylimide (LiTFSI). In some embodiments, the fluorosulfonylimide lithium salt comprises lithium bisfluorosulfonylimide (LiFSI) and lithium bistrifluoromethanesulfonylimide (LiTFSI).

[0026] According to some embodiments of this application, the electrolyte satisfies 0.8 ≤ (X+Z) / (X+Y) ≤ 3.5. In some embodiments, (X+Z) / (X+Y) is 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 2.8, 3.0, 3.2, 3.4, or 3.5, or any value between these values. According to some embodiments of this application, the electrolyte satisfies 1.2 ≤ (X+Z) / (X+Y) ≤ 3.5.

[0027] In this application, a trinitrile compound refers to an organic compound having three cyano groups (-CN). According to some embodiments of this application, the trinitrile compound includes at least one of a compound of formula II or a compound of formula III: Formula II, Formula III In Equation II, a, d, and f are each independently selected from integers from 1 to 6, and b, c, and e are each independently selected from integers from 0 to 6; In Equation III, g, h, and i are each independently selected from integers between 0 and 6.

[0028] According to some embodiments of this application, the trinitrile compound comprises at least one selected from 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, and 1,2,5-tris(2-cyanoethoxy)pentane.

[0029] According to some embodiments of this application, the electrolyte further comprises a compound of formula I: Formula I R1, R2, and R3 are each independently selected from hydrogen, halogen, and C1-C atoms with or without substituents.12 Alkyl groups, C3-C8 cycloalkyl groups with or without substituents, C6-C6 cycloalkyl groups with or without substituents 12 Aryl, wherein the substituent is selected from at least one of cyano, nitro, halogen and sulfonyl, and n is an integer from 0 to 7.

[0030] According to some embodiments of this application, in Formula I, R1, R2, and R3 are each independently selected from hydrogen or C1-C5 alkyl groups, and n is an integer from 0 to 3. In some embodiments, the compound of Formula I is selected from one or more of allyl nitrile or allyl nitrile.

[0031] According to some embodiments of this application, the content of the compound of formula I is A% based on the weight of the electrolyte, satisfying 1≤A+X+Y≤7.

[0032] According to some embodiments of this application, the electrolyte further comprises a lithium salt additive, which comprises at least one of lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(oxalate-borate) (LiBOB), or lithium difluorooxalate-borate (LiDFOB). According to some embodiments of this application, the content of the lithium salt additive is P% based on the weight of the electrolyte, satisfying 0.1 ≤ P ≤ 2.

[0033] The second aspect of this application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and the electrolyte described in the first aspect of this application.

[0034] According to some embodiments of this application, the positive electrode sheet includes a positive current collector, the positive current collector includes an aluminum foil substrate and copper element contained in the aluminum foil substrate, the copper element content m is expressed in ppm based on the weight of the positive current collector, the thickness d of the aluminum foil substrate is expressed in μm, and d×m / 1000≥5 is satisfied.

[0035] According to some embodiments of this application, 5 ≤ d × m / 1000 ≤ 50.

[0036] According to some embodiments of this application, 0 < m ≤ 2000 ppm.

[0037] In the electrochemical device according to this application, the positive electrode further includes a positive electrode active material disposed on the positive electrode current collector. The specific type of positive electrode active material is not specifically limited and can be selected according to requirements.

[0038] The positive electrode active material can be selected from lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials, lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5O4), lithium iron phosphate (LiFePO4) and one or more of doped and / or coated modified compounds thereof, but the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may also be used. These positive electrode active materials may be used alone in only one kind, or two or more kinds may be used in combination.

[0039] In some embodiments, the positive electrode active material is provided with a coating layer. The coating layer can function to insulate the electrolyte, greatly reduce side reactions between the electrolyte and the positive electrode active material, reduce the elution of transition metals, and improve the electrochemical stability of the positive electrode active material. Wherein, the coating layer may be a carbon layer, a graphene layer, an oxide layer, an inorganic salt layer or a conductive polymer layer. The oxide may be an oxide formed of one or more elements selected from Al, Ti, Mn, Zr, Mg, Zn, Ba, Mo and B; the inorganic salt may be Li2ZrO3, LiNbO3, Li4Ti5O 12 , Li2TiO3, Li3VO4, LiSnO3, Li2SiO3, LiAlO2, one or more of them; the conductive polymer may be polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) or polyimide (PI).

[0040] The negative electrode of the electrochemical device according to the present application comprises a current collector and a negative active material layer formed on the current collector, the negative active material layer comprises a negative active material, and the negative active material may comprise a material that reversibly intercalates / deintercalates lithium ions, lithium metal, lithium metal alloy, a material capable of doping / dedoping lithium or a transition metal oxide, such as Si, SiO x (0<x<2) and other materials. The material that reversibly intercalates / deintercalates lithium ions may be a carbon material. The carbon material may be any carbon-based negative active material commonly used in lithium ion rechargeable electrochemical devices. Examples of carbon materials include crystalline carbon, amorphous carbon, and combinations thereof. The crystalline carbon may be natural or artificial graphite that is amorphous or platy, flaky, spherical or fibrous. Amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, etc. Both low crystalline carbon and high crystalline carbon can be used as the carbon material. As low crystalline carbon materials, soft carbon and hard carbon are generally included. As high crystalline carbon materials, natural graphite, crystalline graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microbeads, mesophase pitch and high-temperature calcined carbon (such as petroleum or coke derived from coal tar pitch) are generally included.

[0041] According to some embodiments, the negative electrode active material layer includes an adhesive, and the adhesive may include various adhesive polymers, such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but not limited to these.

[0042] According to some embodiments, the negative electrode active material layer further includes a conductive material to improve electrode conductivity. Any conductive material can be used as the conductive material, as long as it does not cause a chemical change. Examples of conductive materials include: carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials, such as metal powders or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives, etc.; or mixtures thereof. The current collector can be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0043] The material and shape of the separator used in the electrochemical device of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0044] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0045] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0046] The inorganic layer comprises inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0047] The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0048] The electrochemical device described in this application is not particularly limited to any specific electronic device or apparatus. In some embodiments, electronic devices include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0049] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0050] The list of items connected by the terms "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0051] The term "hydrocarbon group" encompasses alkyl, alkenyl, and ynyl groups.

[0052] The term "alkyl" is expected to refer to a straight-chain saturated hydrocarbon structure having 1 to 20 carbon atoms. "Alkyl" is also expected to refer to a branched or cyclic hydrocarbon structure having 3 to 20 carbon atoms. When an alkyl group with a specific number of carbon atoms is specified, it is expected to encompass all geometric isomers having that number of carbon atoms; thus, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl; "propyl" includes n-propyl, isopropyl, and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc.

[0053] The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group that can be straight-chain or branched and has at least one, typically one, two, or three carbon-carbon double bonds. Unless otherwise defined, the alkenyl group typically contains 2 to 20 carbon atoms and includes, for example, C2-C4 alkenyl, C2-C6 alkenyl, and C2-C6 alkenyl groups. 10 Alkenyl groups. Representative alkenyl groups include, for example, vinyl, propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, etc.

[0054] The term "alkynyl" refers to a monovalent unsaturated hydrocarbon group that can be straight-chain or branched and has at least one, and usually one, two, or three carbon-carbon triple bonds. Unless otherwise defined, the alkynyl group typically contains 2 to 20 carbon atoms and includes, for example, C2-C4 alkynyl, C3-C6 alkynyl, and C3-C6 alkynyl groups. 10 Alkynyl groups. Representative alkynyl groups include (for example) ethynyl, propynyl-2-ynyl (n-propynyl), n-butynyl-2-ynyl, n-hexynyl, etc.

[0055] As used in this article, the content of each component is a percentage based on the weight of the electrolyte.

[0056] 1. Battery manufacturing The lithium-ion batteries in the examples and comparative examples were prepared according to the following method: (1) Electrolyte preparation In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are mixed uniformly in a weight ratio of 1:1:1. Each component is added according to Table 1-5, and the mixture is stirred evenly to form an electrolyte.

[0057] (2) Preparation of positive electrode sheet Lithium cobalt oxide (LiCoO2), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 95:2:3. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry was formed. The positive electrode slurry was then uniformly coated onto aluminum foil as a positive electrode current collector. After drying at 85°C, the positive electrode sheet was cold-pressed, cut, and slit, and then dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet.

[0058] (3) Preparation of negative electrode sheet The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in an appropriate amount of deionized water solvent at a weight ratio of 95:2:3 to form a uniform negative electrode slurry. This slurry is then coated onto the negative electrode current collector copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0059] (4) Preparation of the separating membrane The separator is made of polyethylene (PE) film with a thickness of 5μm.

[0060] (5) Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound up and placed in an outer packaging foil. The prepared electrolyte is injected into the dried battery. After vacuum sealing, settling, formation, and shaping, the lithium-ion battery is completed.

[0061] 2. Testing Methods (1) Piercing test Ten lithium-ion batteries were charged at a constant current rate of 0.5C to 4.45V at room temperature. They were then further charged at a constant voltage of 4.45V to a current of 0.05C, bringing them to a fully charged state of 4.45V. Next, the lithium-ion batteries were subjected to a nail-piercing test at room temperature using a 2.5mm diameter steel nail (carbon steel, 16.5mm taper, 100mm total length). The nail was pierced at a speed of 30mm / s, with the depth determined by the nail taper penetrating the lithium-ion battery. The test was observed for smoke, fire, or explosion. If no smoke, fire, or explosion was observed, the lithium-ion battery was considered to have passed the nail-piercing test. Ten batteries were tested in each group, and the number of batteries that passed the test was recorded.

[0062] (2) Test method for room temperature capacity retention of lithium-ion batteries At 25°C, the lithium-ion battery was charged at a constant current of 0.5C to 4.45V, then charged at a constant voltage of 4.45V until the current reached 0.05C, and finally discharged at a constant current of 0.5C to 3.0V. This constituted the first cycle. The lithium-ion battery was subjected to multiple cycles under these conditions. Using the initial discharge capacity as 100%, the charge-discharge cycles were repeatedly performed until the discharge capacity decreased to 80%. The test was then stopped, and the number of cycles was recorded as an indicator of the lithium-ion battery's cycle performance.

[0063] (3) Hot box test At 25℃, the lithium-ion battery was charged at a constant current of 0.7C to 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.05C. The battery was placed in a high-temperature chamber and heated to 135℃ at a temperature rise rate of 5±2℃ / min, and then maintained for 1 hour. The changes in battery voltage, temperature, and chamber temperature were recorded. The battery passed the test if it did not catch fire, explode, or emit smoke. Ten batteries were tested in each group, and the number of batteries that passed the test was recorded.

[0064] 3. Test Results (1) Effects of fluorosulfonylimide lithium salt and trinitrile compounds on battery performance Table 1 Table 1 shows that, within a certain range, decreasing the content of fluorosulfonylimide lithium salt gradually increases the pin penetration pass rate of the battery, indicating continuous improvement in battery safety performance, but significantly impacting cycle performance. The introduction of trinitrile compounds (taking 1,3,6-hexanetrinitrile as an example) significantly improves the pin penetration pass rate, mainly attributed to the enhanced stability of the positive electrode interface by trinitrile compounds and their synergistic effect with fluorosulfonylimide lithium salt. Both compounds jointly improve electrolyte stability, thus significantly improving battery safety performance while enhancing cycle performance. However, when the combined content of fluorosulfonylimide lithium salt and trinitrile compounds increases, the heat generated in the pin penetration test increases, making the battery more prone to failure, and the electrolyte cost also rises. Therefore, the combined content of both must be kept within a reasonable range.

[0065] (2) Effect of fluorosulfonylimide lithium salt + trinitrile compound + LiPF6 on battery performance Table 2-1 A comparison of Examples S2-1 to S2-9 with Comparative Examples D2-1 to D2-3 and Examples S1-3 to S1-4 shows that when LiPF6, lithium fluorinated sulfonyl imide, and trinitrile compounds are used together within a certain concentration range, and when the total content of LiPF6 and lithium fluorinated sulfonyl imide in the electrolyte is low, the use of multiple lithium salts is more effective in improving pin penetration than a single lithium salt system. This also reduces some raw material costs, resulting in significant economic benefits. When the sum of the amounts of LiPF6 and lithium fluorinated sulfonyl imide is within a certain range, the system generates less heat. Simultaneously, the synergistic effect of LiPF6, lithium fluorinated sulfonyl imide, and trinitrile compounds stabilizes the electrode interface, reduces oxygen release from the positive electrode, and thus achieves a balance in improving battery safety and cycle performance.

[0066] Comparing Examples S2-5 to S2-8 with Example S2-9, it can be seen that when the ratio of LiPF6 to fluorosulfonyl imide salt content X / Z is less than or equal to 1, the battery cycle performance remains relatively stable. When it is greater than 1, the cycle performance is affected, which is presumably related to the fact that LiPF6 inhibits the corrosion of aluminum foil by fluorosulfonyl imide salt.

[0067] Table 2-2 As can be seen from Table 2-2, when the LiPF6 concentration exceeds a certain range, the battery's thermal conductivity gradually decreases with the increase of LiPF6 dosage. This may be because the thermal decomposition products of LiPF6 trigger further reactions in the electrolyte system, increasing heat generation and thus affecting the battery's safety performance.

[0068] (3) Effect of fluorosulfonylimide lithium salt + trinitrile compound + double bond mononitrile + LiPF6 on battery performance Table 3 As shown in Table 3, with the further introduction of mononitrile containing double bonds (taking allyl nitrile as an example here), the cycle performance of the mixed lithium salt system battery is significantly improved. This is mainly attributed to the significant enhancement of the interfacial stability between the electrode and the electrolyte. Among them, trinitrile additives mainly act on the positive electrode interface. Mononitrile containing double bonds has a low oxidation potential and a high reduction potential due to the presence of double bonds. It can form a protective film at the electrode interface, which can protect the positive electrode and enhance the stability of the negative electrode interface, thereby significantly improving the cycle performance of the battery.

[0069] Comparative Examples S3-10 and D3-1 to D3-2 show that, in the electrolyte system described in this application, compared to the significant improvement in the system's cycle performance caused by the introduction of double-bonded mononitrile in the aforementioned examples, when X+Y is large, the effect of double-bonded mononitrile on the system's cycle performance is not significant.

[0070] (4) Effect of fluorosulfonylimide lithium salt + trinitrile compound + lithium salt additive on battery performance Table 4 Table 4 shows that the addition of other lithium salts such as LiBOB or LiDFOB significantly improves the cycle stability of the multi-salt, low-dosage system. This is mainly attributed to the good stability of the positive electrode provided by the aforementioned lithium salt additives, which can reduce the dissolution of transition metals. The synergistic effect of multiple lithium salts and additives improves the stability of the positive electrode structure and reduces the damage of transition metals to the SEI of the negative electrode, thereby improving cycle performance while ensuring battery safety.

[0071] (5) The effect of aluminum foil on battery performance The only difference between S5-1 to S5-3 and S4-1 is the aluminum foil used for the positive current collector; see Table 5 for details.

[0072] Table 5 Table 5 shows that reducing the thickness of the aluminum foil substrate significantly reduces the pass rate of the pin penetration test. However, increasing the copper content in the aluminum foil substrate can further improve the pass rate of the pin penetration test. Comparing the data with S5-3, it can be seen that when the substrate thickness and copper content satisfy d×m / 1000≥5, the battery safety performance is good; if it is lower than this value, it will lead to a significant deterioration in safety performance.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises a lithium fluorosulfonylimide salt and a trinitrile compound, wherein, Based on the weight of the electrolyte, the content of the fluorosulfonamide lithium salt is X%, and the content of the trinitrile compound is Y%, satisfying 1≤X+Y≤6; The positive electrode includes a positive current collector, which includes an aluminum foil substrate and copper contained in the aluminum foil substrate. Based on the weight of the positive current collector, the copper content m is expressed in ppm, and the thickness d of the aluminum foil substrate is expressed in μm, satisfying d×m / 1000≥5.

2. The electrochemical device according to claim 1, further comprising lithium hexafluorophosphate, wherein, Based on the weight of the electrolyte, the lithium hexafluorophosphate content is Z%, where X+Z≤7.5 and X / Z≤1.

3. The electrochemical device according to claim 2, satisfying at least one of the following conditions (a) or (b): (a) Z is less than 5; (b) 0.8 ≤ (X+Z) / (X+Y) ≤ 3.

5.

4. The electrochemical device according to claim 1, wherein, The fluorinated sulfonyl imide lithium salt comprises lithium bisfluorosulfonyl imide and / or lithium bistrifluoromethanesulfonyl imide.

5. The electrochemical device according to claim 1, wherein, The trinitrile compound includes at least one of the compounds of formula II or formula III: Formula II, Formula III In Equation II, a, d, and f are each independently selected from integers from 1 to 6, and b, c, and e are each independently selected from integers from 0 to 6; In Equation III, g, h, and i are each independently selected from integers between 0 and 6.

6. The electrochemical device according to claim 5, wherein, The trinitrile compound comprises at least one selected from 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, and 1,2,5-tris(2-cyanoethoxy)pentane.

7. The electrochemical device according to any one of claims 1 to 6, further comprising a compound of formula I: Equation I R1, R2, and R3 are each independently selected from hydrogen, halogen, and C1-C atoms with or without substituents. 12 Alkyl groups, C3-C8 cycloalkyl groups with or without substituents, C6-C6 cycloalkyl groups with or without substituents 12 Aryl, wherein the substituent is selected from at least one of cyano, nitro, halogen and sulfonyl, and n is an integer from 0 to 7; in, Based on the weight of the electrolyte, the content of the compound of formula I is A%, satisfying 1≤A+X+Y≤7; Optionally, in the compound of formula I, R1, R2, and R3 are each independently selected from hydrogen or C1-C5 alkyl groups, and n is an integer from 0 to 3.

8. The electrochemical device according to claim 7, wherein the electrochemical device satisfies any one of the following conditions: (1) When the electrolyte further includes lithium hexafluorophosphate, the condition 3.3≤A+X+Y≤4.5 is satisfied; (2) The compound of Formula I is selected from one or more of allyl nitrile or butenyl nitrile.

9. The electrochemical device according to any one of claims 1 to 6, further comprising a lithium salt additive, said lithium salt additive comprising at least one of lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(oxalate)borate, or lithium difluorooxalateborate. in, Based on the weight of the electrolyte, the content of the lithium salt additive is P%, satisfying 0.1≤P≤2.

10. The electrochemical device according to any one of claims 1 to 9, wherein, 5≤d×m / 1000≤50, 0<m≤2000ppm; Optionally, 5 ≤ d × m / 1000 ≤ 16; Optionally, 500 < m ≤ 2000 ppm.

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