An electrochemical device and an electronic device

Abstract

The application provides an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, and the electrolyte comprises a compound of formula I and a compound of formula II; wherein the compound of formula I is: the compound of formula II is: the mass percentage of the compound of formula I is 5-50% and the mass percentage of the compound of formula II is 0.01-2% based on the total mass of the electrolyte. In the application, by controlling the components and the content of the components of the electrolyte in the electrochemical device, the high-temperature cycle performance and the thermal safety performance of the electrochemical device can be improved.

Description

Technical Field

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

[0002] Electrochemical devices such as lithium-ion batteries are widely used in portable electronic products, electric vehicles, aerospace, and energy storage due to their advantages such as high energy density, good cycle performance, safety, environmental friendliness, and lack of memory effect. However, during the charging and discharging process of lithium-ion batteries, the electrolyte undergoes redox reactions near the positive and negative electrode plates, which is detrimental to the cycle performance and thermal safety of lithium-ion batteries at high temperatures. Summary of the Invention

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

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

[0005] In the above technical solutions, the Formula I compound has a low viscosity and, due to its sulfone and fluorinated structure, possesses strong antioxidant capabilities. When the electrolyte of the electrochemical device contains 1 wt% to 50 wt% of Formula I compound, the electrolyte exhibits low viscosity and good stability, which is beneficial for improving the cycle performance of the electrochemical device at high temperatures. However, the inventors discovered that introducing Formula I compound into the electrolyte will form a unstable solid electrolyte interphase (SEI) film on the surface of the negative electrode, which may negatively impact the high-temperature performance and thermal safety performance of the battery. The inventors further discovered that if the electrolyte contains 0.01 wt% to 2 wt% of Formula II compound, Formula II compound will generate a heterocyclic polymer on the surface of the negative electrode, which can inhibit the reaction of Formula I compound on the surface of the negative electrode. Thus, the electrochemical device not only has good high-temperature cycle performance but also good thermal safety performance.

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

[0007]

[0008] In the above technical solution, when the electrolyte contains at least one of the compounds of Formula I, the high-temperature cycling performance of the electrochemical device can be further improved.

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

[0010]

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

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

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

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

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

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

[0017] In one possible implementation, the electrolyte also contains fluoroethylene carbonate, with the mass percentage of fluoroethylene carbonate being d%, 0.05≤a / d≤50, based on the total mass of the electrolyte.

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

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

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

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

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

[0023] Secondly, embodiments of this application provide an electronic device that includes the aforementioned electrochemical device. Therefore, the electronic device provided by this application has excellent performance.

[0024] The beneficial effects of this application are:

[0025] This application provides an electrochemical device and an electronic device. The electrochemical device includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte contains compounds of formula I and formula II. Based on the total mass of the electrolyte, the mass percentage of compound I is a%, and the mass percentage of compound II is b%, where 1 ≤ a ≤ 50 and 0.01 ≤ b ≤ 2. By controlling the inclusion of compounds of formula I and formula II in the electrolyte, and the types and mass percentages of compounds of formula I and formula II within the scope of this application, the electrochemical device can simultaneously possess good high-temperature cycling performance and thermal safety performance. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] The electrochemical and electronic devices of the embodiments of this application will be described in detail below.

[0028] In a first aspect, this application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte. In this application, by defining the specific components in the electrolyte and the content of those specific components, the cycle performance and safety performance of the electrochemical device can be significantly improved.

[0029] The specific structure of the electrochemical device in this application is as follows:

[0030] electrolyte

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

[0032] The inventors discovered that compounds of formula I in the electrolyte have low viscosity and strong antioxidant properties. However, a large amount of compounds of formula I can lead to the formation of an unstable SEI film on the negative electrode of the electrochemical device. Furthermore, the inventors found that when the electrolyte contains 1 wt% to 2 wt% of compounds of formula II, these compounds can form heterocyclic polymers on the negative electrode, inhibiting the reaction of compounds of formula I on the negative electrode. Therefore, in this application, the electrolyte contains specific amounts of compounds of formula I and formula II. Their synergistic effect enables the electrochemical device to exhibit excellent high-temperature cycling performance and good thermal safety performance.

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

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

[0035]

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

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

[0038]

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

[0040] In some other embodiments, the electrolyte in the electrochemical device of this application further includes ethylene carbonate and propylene carbonate, with the total mass percentage of ethylene carbonate and propylene carbonate being c%, based on the total mass of the electrolyte, and 10 ≤ c ≤ 50. A specific amount of ethylene carbonate and propylene carbonate enables the compound of Formula I to have good solubility, which is beneficial for further improving the high-temperature cycling 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 of any two of the above values; preferably 20 ≤ c ≤ 40, and 0.05 ≤ a / c ≤ 0.5.

[0041] In some other embodiments, the electrolyte of this application also contains fluoroethylene carbonate. Based on the total mass of the electrolyte, the mass percentage of fluoroethylene carbonate is d%, and 0.05 ≤ a / d ≤ 50. Specifically, a / d can be 0.05, 0.1, 0.13, 0.2, 0.29, 0.67, 2, 2.5, 5, 10, 20, 30, 40, 50, etc., or within the range of any two of the above values; preferably 0.13 ≤ a / d ≤ 3.3 and 3 ≤ d ≤ 15. A specific amount of fluoroethylene carbonate in the electrolyte can interact with compounds of Formula I and Formula II to improve the interfacial properties of the electrode, thereby further improving the high-temperature cycling performance of the electrochemical device.

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

[0043] Positive electrode sheet

[0044] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. Specifically, in this application, the positive active material layer can be disposed on one surface or on two surfaces along the thickness direction of the positive current collector. Furthermore, in this application, the "surface of the positive current collector" can be the entire area of ​​the positive current collector or a portion of it; there are no particular limitations, as long as the purpose of this application is achieved.

[0045] The positive electrode active material layer comprises a positive electrode active material, which can be any material capable of reversibly inserting and de-inserting Li. + Na + Substances containing alkali metal ions are used to ensure the normal charging and discharging of the electrochemical device. For example, positive electrode active materials include, but are not limited to, at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium nickel oxide, and ternary materials. Ternary materials include, but are not limited to, LiNi x Co y Mn z O2, LiNi x Co y Al zAt least one of O2, etc., and the contents of Ni, Co, Mn, Al, etc., can be adjusted to ensure that x+y+z=1. For example, the ternary material can be LiNi. 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.88 Co 0.1 Al 0.02 O2, etc.

[0046] In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent; this application does not limit the type of 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 the following: acetylene black, Super-P carbon black, or amorphous carbon such as needle coke, or carbon nanotubes, or graphene.

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

[0048] In the positive electrode sheet, there are no particular restrictions on the type of positive current collector; it can be any known material suitable for use as a positive current collector. Materials for the positive current collector include, but are not limited to, metals such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Furthermore, to reduce the electronic contact resistance between the positive current collector and the positive active material layer, conductive additives or conductive coatings can be applied to 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 can be a mixture of inorganic oxides, conductive agents, and positive electrode binders.

[0049] In preparing the positive electrode sheet, the components of the aforementioned positive electrode active material layer can be dissolved or dispersed in a liquid solvent to form a positive electrode slurry. This slurry is then coated onto a positive electrode current collector and dried, thereby forming the positive electrode active material layer on the current collector, thus obtaining the positive electrode sheet. When preparing the positive electrode sheet using this method, there are no particular limitations on the solvent in the positive electrode slurry, as long as it can dissolve or disperse the aforementioned components. Specifically, the solvent in the positive electrode slurry includes, but is not limited to, N-methylpyrrolidone (NMP) and ethylene carbonate (EC). Alternatively, in preparing the positive electrode sheet, the various components of the positive electrode active material layer can be dry-mixed to form a sheet, which is then pressed onto the positive electrode current collector.

[0050] Negative electrode sheet

[0051] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The composition of the negative electrode active material layer includes the negative electrode sheet active material. That is, in this application, the negative electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. Moreover, in this application, the "surface of the negative electrode current collector" can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0052] The negative electrode active material layer generally contains a negative electrode active material, and this application does not impose any particular limitation on the negative electrode active material. Specifically, the negative electrode active material may include at least one of carbon materials or silicon-based materials. More specifically, carbon materials include, but are not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, or soft carbon; silicon-based materials include, but are not limited to, at least one of silicon, silicon-oxygen composite materials, or silicon-carbon composite materials.

[0053] In some embodiments, the negative electrode active material layer typically also contains a negative electrode conductive agent. This application does not particularly limit the type of negative electrode conductive agent, as long as it achieves the purpose of this application. For example, negative electrode conductive agents include, but are not limited to, at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene.

[0054] In some embodiments, the negative electrode active material layer may also contain a negative electrode binder and a thickener. This application does not impose any particular limitation on the types of negative electrode binders and thickeners, as long as they can achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener in the negative electrode slurry may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0055] In the negative electrode sheet, the material of the negative electrode current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, etc., and this application does not have any particular limitations. 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 terephthalate, or poly(p-phenylene terephthalamide).

[0056] Furthermore, this application does not impose any particular limitations on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 160 μm.

[0057] Furthermore, similar to the preparation of the positive electrode sheet, the preparation of the negative electrode sheet can be achieved either by preparing a negative electrode slurry, coating the slurry onto a negative electrode current collector, and drying it to form a negative electrode active material layer on the current collector, thus obtaining the negative electrode sheet; or by dry mixing the components of the negative electrode active material layer to form a sheet, which is then pressed onto the negative electrode current collector to form the negative electrode active material layer, thereby obtaining the negative electrode sheet. The solvent in the negative electrode slurry includes any one of aqueous solvents and organic solvents. Aqueous solvents include, but are not limited to, mixtures of alcohol and water or water itself. Organic solvents include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide. In some other embodiments, when using aqueous solvents, the negative electrode slurry composition may also include a thickener and styrene-butadiene rubber (SBR) emulsion to slurry the negative electrode slurry, thereby adjusting its viscosity. The types of thickeners in the positive electrode slurry include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0058] Separating membrane

[0059] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0060] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator material can be resin, glass fiber, inorganic materials, etc., formed from materials stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of resin or glass fiber separator materials include, but are not limited to, polyolefins, aromatic polyamides, polyimide (PI), polyamide (PA), polytetrafluoroethylene, polyethersulfone, spandex, or aramid. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

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

[0062] Inorganic materials include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). The forms of inorganic materials include, but are not limited to, particulate or fibrous forms.

[0063] The separator can be in the form of a thin film, including but not limited to non-woven fabric, woven fabric, and microporous membranes. 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: separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

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

[0065] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with 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 membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include 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, or barium sulfate. This application does not have any particular limitation on the aforementioned binders, and may include at least one of the aforementioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0066] The electrochemical device of this application also includes a packaging bag for containing the positive electrode, the separator, the negative electrode, and the electrolyte, as well as other components known in the art in the electrochemical device. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0067] Secondly, this application also provides an electronic device that includes an electrochemical device according to this application.

[0068] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of this application can be used in, but is not limited to, laptops, pen input 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, household large-capacity batteries, and lithium-ion capacitors, etc.

[0069] Example

[0070] The following uses a lithium-ion secondary battery as an example to illustrate the implementation of the electrochemical device of this application in more detail through embodiments and comparative examples. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0071] Test methods and equipment:

[0072] High temperature (45℃) cycle performance test

[0073] The cycling performance of an electrochemical device is evaluated by the capacity retention rate after 400 cycles at 45°C. A higher capacity retention rate after 400 cycles at 45°C indicates better cycling performance of the electrochemical device.

[0074] The electrochemical device was placed in a 45°C constant temperature chamber and allowed to stand for 30 minutes to reach a constant temperature. The device was then charged at a constant current of 0.2C to 4.5V at 45°C, followed by a constant voltage charge at 4.5V to 0.05C. After standing for 5 minutes, it was discharged at a constant current of 0.2C to 3.0V and allowed to stand for 5 minutes. The initial discharge capacity C0 of the electrochemical device was then measured. Next, it was charged at a constant current of 1.8C to 4.15V, followed by a constant voltage charge at 4.15V to 1C. It was then charged at a constant current of 1C to 4.25V, followed by a constant voltage charge at 4.25V to 0.8C. It was then charged at a constant current of 0.8C to 4.5V, followed by a constant voltage charge at 4.5V to 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 3.0V and allowed to stand for 5 minutes. This completes one charge-discharge cycle. The electrochemical device was cycled 400 times according to the above charging / discharging cycle steps, and the discharge capacity C1 after 400 cycles was measured.

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

[0076] Thermal safety performance test

[0077] The electrochemical device was discharged at 25°C with a constant current of 0.2C to 3.0V, then charged at a constant current of 0.5C to 4.5V, and finally charged at a constant voltage of 0.05C to 4.5V. It was then placed in a high-temperature furnace at 130°C, 131°C, 132°C, 133°C, 134°C, or 135°C for 1 hour. After 1 hour, the electrochemical device was observed to see if it ignited; if not, it was considered to have passed. The pass rate was recorded as N / 10, indicating that out of 10 electrochemical devices tested, N passed the test. Specific data on the high-temperature cycling performance of the electrochemical devices in each example and comparative example are shown in Tables 1-4.

[0078] Hot box performance evaluation criteria: Under different temperatures, the higher the temperature at which the fire does not ignite, the better the hot box performance and the better the thermal safety performance; under the same temperature, the higher the pass rate, the better the hot box performance and the better the thermal safety performance. For example, a test result of 5 / 10 at 133℃ is better than a test result of 3 / 10 at 133℃, and a test result of 3 / 10 at 133℃ is better than a test result of 5 / 10 at 132℃.

[0079] Example 1-1

[0080] <Preparation of Electrolyte>

[0081] In an argon-atmospheric glove box with a water content of less than 10 ppm, methyl ethyl carbonate and ethyl acetate were mixed at a mass ratio of 1:1 to prepare a base solvent. Then, lithium hexafluorophosphate (LiPF6), compound I, and compound II were added to form an electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentages of compounds I and II are shown in Table 1. The remainder was the base solvent.

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

[0083] <Preparation of the positive electrode>

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

[0085] <Preparation of Negative Electrode Sheets>

[0086] Artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNTs): carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8. Deionized water was then added as a solvent and the mixture was stirred until homogeneous, resulting in a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was uniformly coated onto the upper and lower surfaces of a 6 μm thick copper foil used as a negative electrode current collector. After drying and pressure treatment, the foil was cut into specified sizes to obtain the negative electrode sheet.

[0087] <Isolation membrane>

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

[0089] <Preparation of Electrochemical Devices>

[0090] The prepared positive electrode, separator, negative electrode, and separator are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery (i.e., electrochemical device) is obtained through vacuum sealing, settling, formation, shaping, and capacity testing.

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

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

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

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

[0095] Examples 1-16 to Examples 1-22

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

[0097] Table 1

[0098]

[0099] Examples 2-1 to 2-5

[0100] Except for the addition of ethylene carbonate and propylene carbonate in the <Preparation of Electrolyte> section and the adjustment of the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-1. The content of LiPF6 remains unchanged when the mass percentages of Formula I compound, ethylene carbonate, and propylene carbonate change.

[0101] Table 2

[0102]

[0103]

[0104] Examples 3-1 to 3-15

[0105] Except for the addition of fluoroethylene carbonate and adjustment of the relevant preparation parameters according to Table 3 in the <Preparation of Electrolyte> section, the rest is the same as in Examples 1-2. The mass percentage of LiPF6 remains unchanged when the mass percentages of Formula I compound and fluoroethylene carbonate change.

[0106] Table 3

[0107]

[0108] Examples 4-1 to 4-6

[0109] Except for the addition of lithium difluorophosphate and adjustment of the relevant preparation parameters according to Table 4 in the <Electrolyte Preparation> section, the rest is the same as in Examples 1-2. The mass percentage of LiPF6 remains unchanged when the mass percentage of lithium difluorophosphate changes.

[0110] Table 4

[0111]

[0112] Comparative Examples 1 to 3

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

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

[0115] As shown in Table 2, the combination of ethylene carbonate and propylene carbonate with compounds of formula I and formula II can better improve the high-temperature cycling performance and thermal safety performance of electrochemical devices.

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

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

[0118] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

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

2. The electrochemical device of claim 1, wherein The compound of Formula I includes at least one of the following compounds:

3. The electrochemical device of claim 1, wherein The compound of Formula II includes at least one of the following compounds:

4. The electrochemical device of claim 1, wherein 2≤a≤10, 0.1≤b≤0.

6.

5. The electrochemical device of claim 1, wherein The electrolyte further includes ethylene carbonate and propylene carbonate, and the sum of the mass percentage contents of the ethylene carbonate and the propylene carbonate is c%, based on the total mass of the electrolyte, wherein 10≤c≤50.

6. The electrochemical device of claim 5, wherein, 20≤c≤40, and 0.05≤a / c≤0.

5.

7. The electrochemical device of claim 1, wherein The electrolyte further includes fluoroethylene carbonate, and the mass percentage content of the fluoroethylene carbonate is d%, based on the total mass of the electrolyte, wherein 0.05≤a / d≤50.

8. The electrochemical device of claim 7, wherein, 3≤d≤15, and 0.13≤a / d≤3.

33.

9. The electrochemical device of claim 1, wherein, The electrolyte further includes lithium difluorophosphate, and the mass percentage content of the lithium difluorophosphate is e%, based on the total mass of the electrolyte, wherein 0.2≤e≤2.

10. An electronic device, comprising: It includes the electrochemical device of any one of claims 1 to 9.

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