Electrochemical devices and electronic devices

Abstract

The application relates to an electrochemical device and an electronic device. The positive electrode of the electrochemical device comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, the positive electrode active material layer comprises a first active material layer and a second active material layer, and the first active material layer is arranged between the positive electrode current collector and the second active material layer, the thickness of the first active material layer is D1 mu m, the thickness of the second active material layer is D2 mu m, the electrolyte comprises a carbonate and lithium hexafluorophosphate, the content of the lithium hexafluorophosphate is W0% based on the total mass of the electrolyte, and the following relationship is met: 0.1 <= D1 <= 15, 3 <= (D1+D2) / W0 <= 12. The electrochemical device can improve the high-temperature storage impedance growth rate.

Description

[0001] This application is a divisional application of Chinese application No. 202110495451.7, filed on May 7, 2021, entitled "Electrochemical Device and Electronic Device". Technical Field

[0002] This invention relates to an electrochemical device and an electronic 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 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, as electronic products become increasingly thinner and more portable, the requirements for lithium-ion batteries are constantly rising, making the development of highly safe and long-life lithium-ion batteries one of the main market demands.

[0004] Existing literature reports that bilayer positive electrode active materials can improve battery safety to some extent, but the impedance growth during high-temperature storage is significantly worse. Summary of the Invention

[0005] The purpose of this application is to provide an electrochemical device to improve the high-temperature storage impedance growth rate.

[0006] In a first aspect, this application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The positive active material layer comprises a first active material layer and a second active material layer, with the first active material layer disposed between the positive current collector and the second active material layer. The thickness of the first active material layer is D1 μm, and the thickness of the second active material layer is D2 μm. The electrolyte comprises carbonate and lithium hexafluorophosphate. Based on the total mass of the electrolyte, the content of lithium hexafluorophosphate is W0%, satisfying the following relationships: 0.1 ≤ D1 ≤ 15, 3 ≤ (D1 + D2) / W0 ≤ 12. In this application, adjusting the electrolyte formulation significantly improves the IMP growth during high-temperature storage of the bilayer positive active material.

[0007] According to some embodiments of this application, the electrochemical device satisfies one or both of 25≤D2≤60 or 5≤W0≤13.

[0008] According to some embodiments of this application, the carbonate comprises a cyclic carbonate. Further, the cyclic carbonate comprises at least one of ethylene carbonate or propylene carbonate. Even further, the cyclic carbonate satisfies at least one of conditions (a) to (d): (a) based on the total mass of the electrolyte, the content of ethylene carbonate is W1%, 1.0 ≤ (D1 + D2) / 25W1 ≤ 4.0; (b) based on the total mass of the electrolyte, the content of propylene carbonate is W2%, 5 ≤ W2 ≤ 40; (c) based on the total mass of the electrolyte, the content of propylene carbonate is W2%, W2 ≤ (D1 + D2); (d) based on the total mass of the electrolyte, the content of ethylene carbonate is W1%, the content of propylene carbonate is W2%, W1 + W2 ≤ 60.

[0009] According to some embodiments of this application, the electrolyte further comprises dinitrile. Further, based on the total mass of the electrolyte, the content of the dinitrile is W3%, satisfying the following relationship: 0.7 ≤ (D1 + D2) / 25W3 ≤ 6.0.

[0010] According to some embodiments of this application, the electrochemical device satisfies one or both of the following: 1.0 ≤ (D1 + D2) / 25W3 ≤ 4.0 or 0.4 ≤ W3 ≤ 5.

[0011] According to some embodiments of this application, the electrochemical device satisfies that the dinitrile includes at least one of the dinitrile compounds represented by Formula I, Formula II, or Formula III;

[0012]

[0013] Among them, R1 is selected from C1-C 18 Alkylene, substituent C1-C 18 Alkylene, C2-C 18 alkenyl, substituent C2-C 18 alkenyl, C2-C 18 Ethyne-1, C2-C with substituents 18 Ethyne group, C6-C 18 arylene or C6-C containing substituents 18The arylene group; R2 and R3 are each independently selected from C1-C9 alkylene groups, substituent C1-C9 alkylene groups, C2-C9 alkenylene groups, substituent C2-C9 alkenylene groups, C2-C9 alkyneene groups, substituent C2-C9 alkyneene groups, C6-C9 arylene groups, or substituent C6-C9 arylene groups; R4, R5, and R6 are each independently selected from C1-C6 alkylene groups, substituent C1-C6 alkylene groups, C2-C6 alkenylene groups, substituent C2-C6 alkenylene groups, C2-C6 alkyneene groups, or substituent C2-C6 alkyneene groups; wherein the substituents are selected from halogens or C1-C5 alkoxy groups.

[0014] According to some embodiments of this application, the electrochemical device satisfies one or more of the following conditions (e)-(f): (e)W2 / 10+W3 / 4+(D1+D2) / 100≤7; (f)W2 / (D1+D2)+W3 / 4+D2 / 10D1≤4.

[0015] According to some embodiments of this application, the electrolyte further comprises at least one of lithium difluorophosphate or lithium bisfluorosulfonylimide, satisfying at least one of conditions (g) to (h): (g) based on the total mass of the electrolyte, the content of lithium difluorophosphate is W4%, (W4+D1+D2) / 100≤1; (h) based on the total mass of the electrolyte, the content of lithium bisfluorosulfonylimide is W5%, W5≤W0.

[0016] According to some embodiments of this application, the electrolyte further comprises a propionate ester compound. Further, based on the total mass of the electrolyte, the content of the propionate ester compound is W6%, satisfying W6 / (D1+D2)≤1. According to some embodiments of this application, the propionate ester compound comprises at least one selected from ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, or pentyl halopropionate.

[0017] According to some embodiments of this application, the first active material layer comprises a first active material, which includes lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadium oxide phosphate, sodium vanadium oxide phosphate, or lithium titanate; the second active material layer comprises a second active material, which includes lithium cobalt oxide, lithium iron phosphate, lithium vanadium oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, lithium nickel cobalt aluminum oxide, or lithium titanate.

[0018] According to some embodiments of this application, the electrochemical device satisfies at least one of conditions (i) to (k): (i) the positive electrode current collector contains iron and / or magnesium, and the iron content F, based on the total mass of the positive electrode current collector, satisfies 0 < F ≤ 2000 ppm; (j) the positive electrode current collector contains magnesium, and the magnesium content M, based on the total mass of the positive electrode current collector, satisfies 0 < M ≤ 1500 ppm; (k) in the positive electrode active material layer, the active material has a D50 of 0.2 μm to 15 μm and a D90 of less than 40 μm.

[0019] In a second aspect, this application provides an electronic device including the electrochemical device described in the first aspect of this application. Detailed Implementation

[0020] 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.

[0021] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0022] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0023] 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.

[0024] The list of items connected by the term "and / or" can mean any combination of the listed items; for example, A and / or B means only A; only B; or A and B. The term "halogen" covers fluorine, chlorine, bromine, and iodine.

[0025] The term "hydrocarbon group" encompasses alkyl, alkenyl, and ynyl groups.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Although the presence of a double-layer positive electrode active material on the current collector side in lithium-ion batteries improves battery safety to some extent, it significantly worsens impedance growth during high-temperature storage. Our research has found that adjusting the electrolyte formulation can significantly improve the impedance growth rate of the double-layer positive electrode active material during high-temperature storage. Based on this, we submit this application.

[0030] In a first aspect, this application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The positive active material layer comprises a first active material layer and a second active material layer, with the first active material layer disposed between the positive current collector and the second active material layer. The thickness of the first active material layer is D1 μm, and the thickness of the second active material layer is D2 μm. The electrolyte comprises carbonate and lithium hexafluorophosphate. Based on the total mass of the electrolyte, the content of lithium hexafluorophosphate is W0%, satisfying the following relationships: 0.1 ≤ D1 ≤ 15, 3 ≤ (D1 + D2) / W0 ≤ 12. In this application, adjusting the electrolyte formulation significantly improves the high-temperature storage impedance growth of the bilayer positive active material.

[0031] According to some embodiments of this application, 3.6≤(D1+D2) / W0≤7, within which the electrochemical device has better overall performance.

[0032] According to some embodiments of this application, D1 is 0.2, 0.5, 0.7, 0.9, 1, 1.5, 3, 3.5, 4.5, 5, 6, 8, 9, 12, 13, 15, or any value between these values. In some embodiments, 2 ≤ D1 ≤ 7. Within this range, the impact on the battery's volumetric energy density can be minimized while simultaneously ensuring safety performance.

[0033] According to some embodiments of this application, the electrochemical device satisfies 25 ≤ D2 ≤ 60. In some embodiments, D2 is 25, 30, 35, 40, 45, 50, 55, 60, or any value between these values.

[0034] According to some embodiments of this application, the electrochemical device satisfies D2 / D1≤0.2. Within this range, better safety improvement can be achieved, and the electrochemical device can have a better impedance growth rate for high-temperature storage.

[0035] According to some embodiments of this application, the electrochemical device satisfies 5 ≤ ​​W0 ≤ 13. In some embodiments, W0 is 5, 8, 10, 12, 13, or any value between these values.

[0036] According to some embodiments of this application, the carbonate comprises a cyclic carbonate. According to some embodiments of this application, the cyclic carbonate comprises at least one of ethylene carbonate (EC) or propylene carbonate (PC). In some embodiments, the cyclic carbonate comprises ethylene carbonate and propylene carbonate.

[0037] According to some embodiments of this application, based on the total mass of the electrolyte, the content of ethylene carbonate is W1%, where 1.0 ≤ (D1 + D2) / 25W1 ≤ 4.0. In some embodiments, (D1 + D2) / 25W1 is 1.0, 1.5, 1.8, 2.0, 2.5, 2.8, 3.0, 3.5, 3.8, 4.0, or any value between these values.

[0038] According to some embodiments of this application, the propylene carbonate content is W2% based on the total mass of the electrolyte, where 5 ≤ W2 ≤ 40. In some embodiments, W2 is 5, 8, 10, 12, 15, 17, 21, 25, 28, 30, 32, 35, 38, or any value between these values. According to some embodiments of this application, the propylene carbonate content is W2% based on the total mass of the electrolyte, where W2 ≤ (D1 + D2). Propylene carbonate within this range provides better kinetic performance.

[0039] According to some embodiments of this application, based on the total mass of the electrolyte, the content of ethylene carbonate is W1%, the content of propylene carbonate is W2%, and W1+W2≤60, preferably, W1+W2≤40. Within this range, ethylene carbonate and propylene carbonate can achieve the best synergistic effect, ensuring good film-forming stability while taking into account the overall kinetics of the electrolyte, thus achieving optimal performance.

[0040] According to some embodiments of this application, the electrolyte further comprises a dinitrile. Further, based on the total mass of the electrolyte, the content of the dinitrile is W3%, satisfying the following relationship: 0.7 ≤ (D1 + D2) / 25W3 ≤ 6.0. In some embodiments, D1 + D2) / 25W3 is 0.7, 1.0, 1.5, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 5.8, or any value between these values. According to some embodiments of this application, the electrochemical device satisfies 1.0 ≤ (D1 + D2) / 25W3 ≤ 4.0.

[0041] According to some embodiments of this application, the dinitrile compound satisfies 0.4 ≤ W3 ≤ 5. In some embodiments, W3 is 0.4, 0.6, 0.8, 1.2, 1.5, 2.0, 2.5, 2.7, 3, 3.5, 4, 4.5, 5, or any value between these values.

[0042] According to some embodiments of this application, the electrochemical device satisfies that the dinitrile includes at least one of the dinitrile compounds represented by Formula I, Formula II, or Formula III;

[0043]

[0044] Among them, R1 is selected from C1-C 18 Alkylene, substituent C1-C 18 Alkylene, C2-C 18 alkenyl, substituent C2-C 18 alkenyl, C2-C 18 Ethyne-1, C2-C with substituents 18 Ethyne group, C6-C 18 arylene or C6-C containing substituents 18 The arylene group; R2 and R3 are each independently selected from C1-C9 alkylene groups, substituent C1-C9 alkylene groups, C2-C9 alkenylene groups, substituent C2-C9 alkenylene groups, C2-C9 alkyneene groups, substituent C2-C9 alkyneene groups, C6-C9 arylene groups, or substituent C6-C9 arylene groups; R4, R5, and R6 are each independently selected from C1-C6 alkylene groups, substituent C1-C6 alkylene groups, C2-C6 alkenylene groups, substituent C2-C6 alkenylene groups, C2-C6 alkyneene groups, or substituent C2-C6 alkyneene groups; wherein the substituents are selected from halogens or C1-C5 alkoxy groups.

[0045] In this application, the halogen can be fluorine, chlorine, bromine, or iodine; the C1-C5 alkoxy group can be methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, tert-butoxy, etc.

[0046] In some embodiments, R1 is a C2 alkylene, C3 alkylene, C4 alkylene, C5 alkylene, C6 alkylene, C7 alkylene, etc. In some embodiments, R2 and R3 are each independently a C1 alkylene, C2 alkylene, C3 alkylene, C4 alkylene, C5 alkylene, C6 alkylene, C7 alkylene, etc. In some embodiments, R4, R5, and R6 are each independently a C1 alkylene, C2 alkylene, C3 alkylene, C4 alkylene, C5 alkylene, C6 alkylene, etc. In some embodiments, the dinitrile includes at least one selected from butadionitrile, glutaronitrile, adiponitrile, heptadionitrile, octanoic acid dinitrile, or ethylene glycol dipropionitrile ether.

[0047] According to some embodiments of this application, the electrolyte comprises formula I, and at least one of formula II or formula III. Based on the total mass of the electrolyte, the content of the compound of formula I is a%, and the content of at least one of the compounds of formula II or formula III is b%, satisfying a≥b.

[0048] According to some embodiments of this application, the electrochemical device satisfies one or more of the following conditions (e)-(f): (e) W2 / 10+W3 / 4+(D1+D2) / 100≤7; (f) W2 / (D1+D2)+W3 / 4+D2 / 10D1≤4. Within this range, interfacial side reactions can be effectively suppressed, thereby suppressing impedance growth during cycling or high-temperature storage.

[0049] According to some embodiments of this application, the electrolyte further comprises at least one of lithium difluorophosphate or lithium bisfluorosulfonylimide. Further, based on the total mass of the electrolyte, the content of lithium difluorophosphate is W4%, (W4+D1+D2) / 100≤1. Further, based on the total mass of the electrolyte, the content of lithium bisfluorosulfonylimide is W5%, W5≤W0. Within this range, superior kinetic performance can be achieved while reducing corrosion of the aluminum foil substrate.

[0050] According to some embodiments of this application, W4 < 1. W4 is 0.01, 0.05, 0.1, 0.3, 0.5, 0.7, 0.9, or any value between these values. Within this range, the electrochemical device exhibits superior high-temperature storage performance.

[0051] According to some embodiments of this application, the electrolyte further comprises a propionate ester compound. Further, based on the total mass of the electrolyte, the content of the propionate ester compound is W6%, satisfying W6 / (D1+D2)≤2. According to some embodiments of this application, the propionate ester compound includes at least one selected from ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, or pentyl halopropionate.

[0052] In some embodiments of this application, W6 is 15, 18, 20, 25, 30, 35, 40, 45, 50 or any value between these values.

[0053] According to some embodiments of this application, the first active material layer comprises a first active material, which includes lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadium oxide phosphate, sodium vanadium oxide phosphate, or lithium titanate. According to some embodiments of this application, the second active material layer comprises a second active material, which includes lithium cobalt oxide, lithium iron phosphate, lithium vanadium oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, lithium nickel cobalt aluminum oxide, or lithium titanate.

[0054] According to some embodiments of this application, the second active material layer comprises lithium cobalt oxide, and the electrochemical device satisfies 20≤D2 / W3≤120, within which the protection of the positive electrode side and the overall kinetics of the electrolyte can be taken into account.

[0055] According to some embodiments of this application, the positive electrode current collector contains iron and / or magnesium, and the iron content F, based on the total mass of the positive electrode current collector, satisfies 0 < F ≤ 2000 ppm. According to some embodiments of this application, the positive electrode current collector contains magnesium, and the magnesium content M, based on the total mass of the positive electrode current collector, satisfies 0 < M ≤ 1500 ppm. According to some embodiments of this application, in the positive electrode active material layer, the D50 of the active material is 0.2 μm to 15 μm, and the D90 is less than 40 μm.

[0056] The positive electrode current collector used in the electrochemical device of this application can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate. In some embodiments, the positive electrode active material and a binder (conductive material and thickener, etc., may be further used as needed) are dry-mixed to form a sheet, and the resulting sheet is pressed onto the positive electrode current collector, or the materials are dissolved or dispersed in a liquid medium to form a slurry, which is then coated onto the positive electrode current collector and dried. In some embodiments, the binder may include at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. Conductive materials may include at least one of conductive carbon black, sheet graphite, graphene, carbon nanotubes, or carbon fibers.

[0057] The electrochemical device of this application further includes a negative electrode, wherein the material, composition, and manufacturing method of the negative electrode used may include any techniques disclosed in the prior art. According to some embodiments of this application, the negative electrode 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. According to some embodiments of this application, the negative electrode active material layer includes a negative electrode active material, which may include materials capable of reversibly inserting / deintercalating lithium ions, lithium metal, lithium metal alloys, or transition metal oxides. In some embodiments, the negative electrode active material includes at least one of carbon materials or silicon materials; the carbon materials include at least one of graphite and hard carbon; and the silicon materials include at least one of silicon, silicon oxides, silicon carbide compounds, or silicon alloys. According to some embodiments of this application, the negative electrode active material layer includes an adhesive, and the adhesive may include various adhesive polymers. In some embodiments, the binder includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, or styrene-butadiene rubber. According to some embodiments of this application, the negative electrode active material layer further includes a conductive material to improve the electrode conductivity. Any conductive material can be used as the conductive material, as long as it does not cause a chemical change. In some embodiments, the conductive material includes at least one selected from conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, conductive graphite, or graphene.

[0058] The electrochemical device of this application also includes a separating membrane. The material and shape of the separating membrane used in the electrochemical device of this application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separating membrane comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0059] 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. At least one surface of the substrate layer is provided with a surface treatment layer, which may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. The inorganic layer includes inorganic particles and a binder, and 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 polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. 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).

[0060] This application further provides an electronic device that includes the electrochemical device provided in this application.

[0061] The electronic devices or apparatus described in this application are not particularly limited. In some embodiments, the electronic devices described in this application include, but are 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, large household batteries, and lithium-ion capacitors, etc.

[0062] 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.

[0063] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0064] 1. The lithium-ion batteries in the examples and comparative examples were all prepared according to the following method:

[0065] (1) Electrolyte preparation

[0066] In an argon-atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed at a specific mass ratio. LiPF6 was added, and based on the total mass of the electrolyte, 5% fluoroethylene carbonate and 2% 1,3-propane sulpholactone were added. The electrolyte was prepared according to the following examples and comparative examples.

[0067] (2) Preparation of positive electrode

[0068] First active material layer: Lithium iron phosphate (LiFePO4), carbon nanotubes (CNT), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until it becomes a homogeneous positive electrode slurry. The positive electrode slurry is then uniformly coated onto the aluminum foil of the positive electrode current collector (the Al foil used here has an F content of 500 ppm and a M content of 300 ppm) and dried at 85°C to serve as the carrier for the second active material layer.

[0069] Second active material layer: Lithium cobalt oxide (LiCoO2), carbon nanotubes (CNT), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until it forms a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the first active material layer. After drying at 85°C, the mixture is cold-pressed, cut, and slit, and then dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet.

[0070] (3) Negative electrode preparation

[0071] 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 mass ratio of 95:2:3 to form a uniform negative electrode slurry. This slurry is then coated onto the negative electrode current collector Cu foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0072] (4) Preparation of the separating membrane

[0073] The separator is made of polyethylene (PE).

[0074] (5) Preparation of lithium-ion batteries

[0075] 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.

[0076] 2. Testing Methods

[0077] (1) Nail test

[0078] 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 driven through the battery at a speed of 30mm / s, with the depth determined by the nail taper penetrating the battery. The test was held for 5 minutes, observing whether the lithium-ion batteries produced smoke, caught fire, or exploded. If none of these occurred, the lithium-ion batteries were considered to have passed the nail-piercing test.

[0079] (2) High-temperature storage impedance (IMP) growth rate test

[0080] Three electrochemical devices (lithium-ion batteries) were charged at a constant current rate of 0.5C to a voltage of 4.45V at room temperature (25℃±3℃). 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. The AC impedance of the batteries at 1kHz was recorded using an OCV / IMP tester, in mΩ, and this was recorded as the initial impedance of the batteries. The batteries were then stored in an 85℃ oven for 8 hours. After storage, the batteries were placed at 25℃±3℃ for 2 hours, and the AC impedance of the batteries at 1kHz was recorded again using an OCV / IMP tester, in mΩ. The IMP growth rate after 8 hours of storage at 85℃ was compared with the initial impedance of the batteries.

[0081] (3) Discharge rate test

[0082] At 25°C, the electrochemical device (lithium-ion battery) was charged at a constant current of 0.7C to 4.45V, and then charged at a constant voltage of 4.45V to a current of 0.05C. Afterward, the lithium-ion battery was left to stand at 25°C for 4 hours, and then discharged at different rates (0.2C, 0.5C, 1C, 2C) to 3.0V. After each discharge, the battery was left to stand for 5 minutes, and the discharge capacity was recorded. Using the 0.2C discharge capacity at 25°C as a baseline, the discharge capacity ratio of the lithium-ion battery at different rates was obtained. The capacity retention rate at 2C was compared uniformly here.

[0083] The discharge capacity ratio (%) of a lithium-ion battery at 2C rate = discharge capacity at 2C / discharge capacity at 0.2C × 100%.

[0084] 3. Test Results

[0085] (1) The effect of positive electrode active material layer and lithium hexafluorophosphate on battery performance. In Table 1, EC, PC and DEC are mixed in a mass ratio of 1:1:1.

[0086] Table 1

[0087]

[0088] As shown in Table 1, the introduction of the first active material layer significantly improves pin penetration, but it severely worsens impedance growth during high-temperature storage. However, with the reduction of lithium hexafluorophosphate (LiPF6) content, both pin penetration rate and IMP growth rate further improve. The former is mainly related to the suppression of short-circuit discharge by low lithium salt, while the latter is mainly attributed to the reduction of lithium salt, which leads to a decrease in HF content, helping to reduce corrosion of the positive electrode interface and thus suppressing IMP growth. When the thicknesses of the first and second active material layers are within a certain range, it is possible to reduce the IMP growth rate and improve the battery rate performance to some extent while ensuring the pin penetration rate of the lithium-ion battery.

[0089] (2) The effect of the positive electrode active material layer and dinitrile on battery performance.

[0090] In Examples S2-1 to S2-13, the amount of lithium hexafluorophosphate used was the same as that used in Example 1, and EC, PC, and DEC were mixed in a mass ratio of 1:1:1.

[0091] Table 2

[0092]

[0093]

[0094] As shown in Table 2, the introduction of the first active material layer significantly improves pin penetration, but it severely worsens IMP growth during high-temperature storage. With the introduction of adiponitrile, pin penetration is further slightly improved, while IMP growth is significantly improved, which is attributed to its suppression of the positive electrode side reaction. It was also found that when the thickness values ​​of the first active material layer D1 and the second active material layer D2 and W3 satisfy 0.7≤(D1+D2) / 100W3≤6, not only is the pin penetration rate improved, but IMP growth during high-temperature storage is also significantly suppressed.

[0095] (3) The effect of positive electrode active material layer and propylene carbonate on battery performance. The amount of lithium hexafluorophosphate is the same as that in S1-1. The PC content in Examples S3-1 to S3-9 is shown in Table 3. EC and DEC are mixed at a mass ratio of 1:1.

[0096] Table 3

[0097]

[0098] Note: In Table 3, X represents W2 / 10 + W3 / 4 + (D1 + D2) / 100, and Y represents W2 / (D1 + D2) + W3 / 4 + D2 / 10D1.

[0099] Table 3 shows that when W2 / 10+W3 / 4+(D1+D2) / 100≤7 and / or W2 / (D1+D2)+W3 / 4+D2 / 10D1≤4 are satisfied, the growth of IMP in high-temperature storage is further inhibited. The mechanism of action is mainly to improve the stability of the electrolyte solvent itself and reduce the side reactions at the interface. This is different from the mechanism of adiponitrile film formation inhibiting the side reactions at the interface.

[0100] (4) Effects of positive electrode active material layer, LiPO2F2, and propyl propionate on battery performance: The amount of lithium hexafluorophosphate used in Examples S4-1 to S4-5 is the same as that used in S1-1. EC, PC, and DEC are mixed in a mass ratio of 1:1:1.

[0101] Table 4

[0102]

[0103] As shown in Table 4, LiPO2F2 and propyl propionate also have a certain inhibitory effect on IMP growth during high-temperature storage, and do not affect the pin penetration rate. Therefore, they can also be used as a technical means to balance battery stability under high-temperature storage.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode material layer provided on a surface of the positive electrode current collector, the positive electrode material layer comprising a first material layer and a second material layer, and the first material layer being provided between the positive electrode current collector and the second material layer, the thickness of the first material layer is D1 μm, and the thickness of the second material layer is D2 μm, the electrolyte comprises a carbonate and lithium hexafluorophosphate, the content of the lithium hexafluorophosphate being W0% based on the total mass of the electrolyte, and satisfying the following relationships: 0.2 ≤ D1 ≤ 15, 3 ≤ (D1 + D2) / W0 ≤ 12, 25 ≤ D2 ≤ 60, and 5 ≤ W0 ≤ 13, the electrolyte further comprises adiponitrile, the content of the adiponitrile being W3% based on the total mass of the electrolyte, and satisfying the following relationship: 0.7 ≤ (D1 + D2) / 25W3 ≤ 4.0; the electrolyte further comprises lithium difluorophosphate, the content of the lithium difluorophosphate being W4% based on the total mass of the electrolyte, and (W4 + D1 + D2) / 100 ≤ 1.

2. The electrochemical device of claim 1, wherein at least one of the following conditions is satisfied: (a) 2 ≤ D1 ≤ 7; (b) 3.6 ≤ (D1 + D2) / W0 ≤ 7; (c) (W4 + D1 + D2) / 100 ≤ 0.

56.

3. The electrochemical device of claim 1, wherein at least one of the following conditions is satisfied: (d) 3 ≤ D1 ≤ 6; (e) 4.0 ≤ (D1 + D2) / W0 ≤ 6.5; (f) 0.551 ≤ (W4 + D1 + D2) / 100 ≤ 0.

56.

4. The electrochemical device of claim 1, wherein one or both of 30 ≤ D2 ≤ 55 or 8 ≤ W0 ≤ 12 is satisfied.

5. The electrochemical device of claim 1, wherein the carbonate comprises a cyclic carbonate, the cyclic carbonate comprising at least one of vinyl carbonate or propylene carbonate, and the cyclic carbonate satisfies at least one of the following conditions: (h) the content of the propylene carbonate is W2% based on the total mass of the electrolyte, and 5 ≤ W2 ≤ 40; (i) the content of the propylene carbonate is W2% based on the total mass of the electrolyte, and W2 ≤ (D1 + D2); (j) the content of the vinyl carbonate is W1% and the content of the propylene carbonate is W2% based on the total mass of the electrolyte, and W1 + W2 ≤ 60.

6. The electrochemical device of claim 1, wherein the carbonate comprises a cyclic carbonate, the cyclic carbonate comprising vinyl carbonate, and the content of the vinyl carbonate is W1% based on the total mass of the electrolyte, and 1.0 ≤ (D1 + D2) / 25W1 ≤ 4.

0.

7. The electrochemical device of claim 1, wherein the carbonate comprises a cyclic carbonate, the cyclic carbonate comprising vinyl carbonate, and the content of the vinyl carbonate is W1% based on the total mass of the electrolyte, and 1.5 ≤ (D1 + D2) / 25W1 ≤ 3.

8.

8. The electrochemical device of claim 1, wherein, one or both of 1.0 ≤ (D1 + D2) / 25W3 ≤ 4.0 or 0.4 ≤ W3 ≤ 5 is satisfied.

9. The electrochemical device of claim 5, wherein, one or more of the following conditions is satisfied: (k) W2 / 10 + W3 / 4 + (D1 + D2) / 100 ≤ 7; (l) W2 / (D1 + D2) + W3 / 4 + D2 / 10D1 ≤ 4.

10. The electrochemical device according to any one of claims 1 to 9, wherein The electrolyte further contains lithium bisfluorosulfonimide, the content of the lithium bisfluorosulfonimide being W5% based on the total mass of the electrolyte, and W5≤W0.

11. The electrochemical device according to any one of claims 1 to 9, wherein The electrolyte further contains a propionate compound, the content of the propionate compound being W6% based on the total mass of the electrolyte, and W6 / (D1+D2)≤1.

12. The electrochemical device of claim 11, wherein, The propionate compound contains at least one of ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl halogenated propionate, propyl halogenated propionate, butyl halogenated propionate, or pentyl halogenated propionate.

13. The electrochemical device according to any one of claims 1 to 9, wherein The first material layer contains a first active material, and the first active material includes lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadium oxyphosphate, sodium vanadium oxyphosphate, or lithium titanate; and the second material layer contains a second active material, and the second active material includes lithium cobaltate, lithium iron phosphate, lithium vanadate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium-rich manganese-based material, lithium nickel aluminum oxide, or lithium titanate.

14. The electrochemical device according to any one of claims 1 to 9, wherein At least one of conditions (m) to (o) is satisfied: (m) the positive electrode current collector contains an iron element, the content F of the iron element satisfying 0 (n) the positive electrode current collector contains a magnesium element, the content M of the magnesium element satisfying 0 (o) the positive electrode material layer contains a positive electrode active material, the D50 of the positive electrode active material being 0.2 μm to 15 μm, and the D90 being less than 40 μm.

15. An electronic device comprising the electrochemical device according to any one of claims 1 to 14.

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