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 a Chinese application with application number 202110495451.7, application date 2021-05-07, and title "Electrochemical device and electronic device". TECHNICAL FIELD

[0002] The present application relates to an electrochemical device and an electronic device. BACKGROUND

[0003] With the popularization and application of intelligent products, people's demand for electronic products such as mobile phones, notebooks, cameras, etc. increases year by year. As the working power supply of electronic products, lithium ion batteries have the characteristics of high energy density, no memory effect, high working voltage, etc., and are gradually replacing traditional Ni-Cd and MH-Ni batteries. However, with the development of electronic products towards thin and portable, people's requirements for lithium ion batteries are constantly improving, and developing high safety and long life lithium ion batteries is one of the main needs of the market.

[0004] It has been reported in the literature that double-layer positive active materials can improve the safety of the battery, but the impedance growth of high-temperature storage is significantly deteriorated. SUMMARY

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

[0006] In a first aspect, the present application provides 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 active material layer disposed on the surface of the positive electrode current collector, the positive electrode active material layer comprising a first active material layer and a second active material layer, and the first active material layer being disposed between the positive electrode current collector and the second active material layer, the thickness of the first active material layer being D1 μm, the thickness of the second active material layer being D2 μm, the electrolyte comprising a carbonate and lithium hexafluorophosphate, the content of lithium hexafluorophosphate being W0% based on the total mass of the electrolyte, satisfying the following relationship: 0.1≤D1≤15, 3≤(D1+D2) / W0≤12. In the present application, the IMP growth of high-temperature storage of double-layer positive active materials is significantly improved by adjusting the electrolyte formula.

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

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

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

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

[0011] According to some embodiments of the present application, the electrochemical device satisfies that the dinitrile comprises at least one of a dinitrile compound represented by Formula I, Formula II, or Formula III:

[0012]

[0013] wherein R1is selected from C1-C 18 alkylene, substituted C1-C 18 alkylene, C2-C 18 alkenylene, substituted C2-C 18 alkenylene, C2-C 18 alkynylene, substituted C2-C 18 alkynylene, C6-C 18 arylene, or substituted C6-C 18R2, R3 are each independently selected from C1-C9 alkylene, substituted C1-C9 alkylene, C2-C9 alkenylene, substituted C2-C9 alkenylene, C2-C9 alkynylene, substituted C2-C9 alkynylene, C6-C9 arylene, or substituted C6-C9 arylene; R4, R5, R6 are each independently selected from C1-C6 alkylene, substituted C1-C6 alkylene, C2-C6 alkenylene, substituted C2-C6 alkenylene, C2-C6 alkynylene, or substituted C2-C6 alkynylene; wherein the substituents are selected from halogen or C1-C5 alkoxy.

[0014] According to some embodiments of the present 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 the present application, the electrolyte further comprises at least one of lithium difluorophosphate or lithium bisfluorosulfonimide, and at least one of the following conditions (g)-(h) is satisfied: (g) the content of lithium difluorophosphate is W4% based on the total mass of the electrolyte, (W4 + D1 + D2) / 100 ≤ 1; (h) the content of lithium bisfluorosulfonimide is W5% based on the total mass of the electrolyte, W5 ≤ W0.

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

[0017] According to some embodiments of the present application, the first active material layer comprises a first active material, and the first active material comprises 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; the second active material layer comprises a second active material, and the second active material comprises lithium cobaltate, lithium iron phosphate, lithium vanadate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium-rich manganese-based material, lithium nickel cobalt aluminum oxide, or lithium titanate.

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

[0019] In a second aspect, the present application provides an electronic device comprising the electrochemical device according to the first aspect of the present application. DETAILED DESCRIPTION

[0020] The present application is further described below with reference to specific embodiments. It is to be understood that these embodiments are merely illustrative of the present application and do not limit the scope of the present application.

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

[0022] Unless otherwise defined, the terms used in the present application have the meanings commonly understood by those skilled in the art. Unless otherwise defined, the values of each parameter mentioned in the present application can be measured by various measuring methods commonly used in the art (for example, can be tested according to the method given in the examples of the present application).

[0023] The list of items connected by the term "at least one of", "at least one", or other similar terms means any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, 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 can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0024] The list of items connected by the term "and / or" means 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, iodine.

[0025] The term "hydrocarbyl" covers alkyl, alkenyl, alkynyl.

[0026] The term "alkyl" is intended to mean a straight-chain saturated hydrocarbon structure having from one to twenty carbon atoms. "Alkyl" is also intended to mean a branched or cyclic hydrocarbon structure having from three to twenty carbon atoms. When an alkyl group is specified to have a particular number of carbons, it is intended to encompass all geometric isomers having that number of carbons; thus, for example, "butyl" is intended to include n-butyl, sec-butyl, iso-butyl, t-butyl, and cyclobutyl; "propyl" includes n-propyl, iso-propyl, and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n-butyl, iso-butyl, sec-butyl, t-butyl, cyclobutyl, n-pentyl, iso-pentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, iso-hexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, and the like.

[0027] The term "alkenyl" refers to a monovalent unsaturated hydrocarbon radical that can be straight or branched and that has at least one and usually one, two, or three carbon-carbon double bonds. Unless otherwise specified, the alkenyl group typically contains from two to twenty carbon atoms and includes, by way of example, C2-C4 alkenyl, C2-C6 alkenyl, and C2-C10 alkenyl groups. 10 Alkenyl. Representative alkenyl groups include, for example, ethenyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, and the like.

[0028] The term "alkynyl" refers to a monovalent unsaturated hydrocarbon radical that can be straight or branched and that has at least one and usually one, two, or three carbon-carbon triple bonds. Unless otherwise specified, the alkynyl group typically contains from two to twenty carbon atoms and includes, by way of example, C2-C4 alkynyl, C3-C6 alkynyl, and C3-C10 alkynyl groups. 10 Alkynyl. Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like.

[0029] Although in lithium ion battery, the positive active material layer on the side of the current collector has double layer positive active material, there is certain improvement for battery safety, however, the impedance growth for high temperature storage is obviously deteriorated. The applicant found through research that the impedance growth rate of double layer positive active material for high temperature storage can be significantly improved by adjusting the electrolyte formula. Based on this, the present application is proposed.

[0030] In a first aspect, the present application provides an electrochemical device, the 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 active material layer disposed on a surface of the positive electrode current collector, the positive electrode active material layer comprising a first active material layer and a second active material layer, and the first active material layer being disposed between the positive electrode current collector and the second active material layer, the thickness of the first active material layer being D1 μm, the thickness of the second active material layer being D2 μm, the electrolyte comprising a carbonate and lithium hexafluorophosphate, the content of the lithium hexafluorophosphate being W0% based on the total mass of the electrolyte, satisfying the following relationship: 0.1≤D1≤15, 3≤(D1+D2) / W0≤12. In the present application, by adjusting the electrolyte formulation, the high-temperature storage impedance growth of the double-layer positive electrode active material is significantly improved.

[0031] According to some embodiments of the present application, 3.6≤(D1+D2) / W0≤7, within this range, the electrochemical device has more optimal comprehensive performance.

[0032] According to some embodiments of the present 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 volume energy density of the battery can be minimized as much as possible while the safety performance is taken into account.

[0033] According to some embodiments of the present 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 the present application, the electrochemical device satisfies D2 / D1≤0.2, within this range, a more optimal safety improvement effect can be achieved, and the electrochemical device has a more optimal high-temperature storage impedance growth rate.

[0035] According to some embodiments of the present 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 the present application, the carbonate comprises a cyclic carbonate. According to some embodiments of the present 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 the present application, the content of the ethylene carbonate is W1%, 1.0≤(D1+D2) / 25W1≤4.0, based on the total mass of the electrolyte. 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 the present application, the content of the propylene carbonate is W2%, 5≤W2≤40, based on the total mass of the electrolyte. 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 the present application, the content of the propylene carbonate is W2%, W2≤(D1+D2), based on the total mass of the electrolyte. Within this range, the propylene carbonate can provide better kinetic performance.

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

[0040] According to some embodiments of the present application, the electrolyte further comprises a dinitrile. Further, the content of the dinitrile is W3%, satisfying the following relationship: 0.7≤(D1+D2) / 25W3≤6.0, based on the total mass of the electrolyte. 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 the present application, the electrochemical device satisfies 1.0≤(D1+D2) / 25W3≤4.0.

[0041] According to some embodiments of the present 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 the present application, the electrochemical device satisfies that the dinitrile comprises at least one of the dinitrile compounds represented by Formula I, Formula II, or Formula III.

[0043]

[0044] R1is selected from C1-C9alkylene, substituted C1-C9alkylene, C2-C9alkenylene, substituted C2-C9alkenylene, C2-C9alkynylene, substituted C2-C9alkynylene, C6-C9arylene, or substituted C6-C9arylene; R2, R3are each independently selected from C1-C9alkylene, substituted C1-C9alkylene, C2-C9alkenylene, substituted C2-C9alkenylene, C2-C9alkynylene, substituted C2-C9alkynylene, C6-C9arylene, or substituted C6-C9arylene; R4, R5, R6are each independently selected from C1-C6alkylene, substituted C1-C6alkylene, C2-C6alkenylene, substituted C2-C6alkenylene, C2-C6alkynylene, or substituted C2-C6alkynylene; wherein the substituent is selected from halogen or C1-C5alkoxy. 18 18 18 18 18 18 18 18 R1is selected from C1-C9alkylene, substituted C1-C9alkylene, C2-C9alkenylene, substituted C2-C9alkenylene, C2-C9alkynylene, substituted C2-C9alkynylene, C6-C9arylene, or substituted C6-C9arylene; R2, R3are each independently selected from C1-C9alkylene, substituted C1-C9alkylene, C2-C9alkenylene, substituted C2-C9alkenylene, C2-C9alkynylene, substituted C2-C9alkynylene, C6-C9arylene, or substituted C6-C9arylene; R4, R5, R6are each independently selected from C1-C6alkylene, substituted C1-C6alkylene, C2-C6alkenylene, substituted C2-C6alkenylene, C2-C6alkynylene, or substituted C2-C6alkynylene; wherein the substituent is selected from halogen or C1-C5alkoxy.

[0045] In the present application, halogen can be fluorine, chlorine, bromine, iodine; C1-C5alkoxy can be methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, t-butoxy, etc.

[0046] In some embodiments, R1is C2alkylene, C3alkylene, C4alkylene, C5alkylene, C6alkylene, C7alkylene, etc. In some embodiments, R2, R3are each independently C1alkylene, C2alkylene, C3alkylene, C4alkylene, C5alkylene, C6alkylene, C7alkylene, etc. In some embodiments, R4, R5, R6are each independently C1alkylene, C2alkylene, C3alkylene, C4alkylene, C5alkylene, C6alkylene, etc. In some embodiments, the dinitrile comprises at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, or ethylene glycol bispropiononitrile ether.

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

[0048] ​​​​​​​According to some embodiments of the present 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, the interface side reaction can be effectively suppressed, and thus the impedance increase during the cycle or high-temperature storage can be suppressed.

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

[0050] According to some embodiments of the present 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 has better high-temperature storage performance.

[0051] According to some embodiments of the present application, the electrolyte further comprises a propionate compound. Further, the content of the propionate compound is W6%, based on the total mass of the electrolyte, and W6 / (D1+D2)≤2. According to some embodiments of the present application, the propionate compound comprises at least one of ethyl propionate, propyl propionate, butyl propionate, amyl propionate, halogenated ethyl propionate, halogenated propyl propionate, halogenated butyl propionate, or halogenated amyl propionate. According to some embodiments of the present application, the propionate compound comprises at least one of ethyl propionate, propyl propionate, butyl propionate, or amyl propionate.

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

[0053] According to some embodiments of the present application, the first active material layer comprises a first active material comprising 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. According to some embodiments of the present application, the second active material layer comprises a second active material comprising lithium cobaltate, lithium iron phosphate, lithium vanadate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium-rich manganese-based material, lithium nickel cobalt aluminum oxide, or lithium titanate.

[0054] According to some embodiments of the present application, the second active material layer comprises lithium cobaltate, and the electrochemical device satisfies 20≤D2 / W3≤120, within which range, 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 the present application, the positive electrode current collector contains an iron element and / or a magnesium element, and the content F of the iron element satisfies 0 < F ≤ 2000 ppm based on the total mass of the positive electrode current collector. According to some embodiments of the present application, the positive electrode current collector contains a magnesium element, and the content M of the magnesium element satisfies 0 < M ≤ 1500 ppm based on the total mass of the positive electrode current collector. According to some embodiments of the present 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 for the electrochemical device of the present application can employ a metal foil or a composite current collector. For example, an aluminum foil can be used. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material. In some embodiments, the positive electrode active material and a binder (further, an electrically conductive material and a thickening agent, etc. can be used as needed) are dry-mixed to make a sheet shape, the obtained sheet is press-bonded to the positive electrode current collector, or these materials are dissolved or dispersed in a liquid medium to make a slurry shape, the slurry is coated on the positive electrode current collector and dried. In some embodiments, the binder can include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, carboxymethyl cellulose na, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The electrically conductive material can include at least one of electrically conductive carbon black, flaky graphite, graphene, carbon nanotube, or carbon fiber.

[0057] The electrochemical device of the present application also includes a negative electrode, wherein the material, constitution, and manufacturing method of the negative electrode used can include any of the techniques disclosed in the prior art. According to some embodiments of the present 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 the present application, the negative electrode active material layer includes a negative electrode active material, which can include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, lithium metal alloy, or transition metal oxide. In some embodiments, the negative electrode active material includes at least one of a carbon material including at least one of graphite, hard carbon, or a silicon material including at least one of silicon, silicon oxide compound, silicon carbon compound, or silicon alloy. According to some embodiments of the present application, the negative electrode active material layer includes a binder, and the binder can include various binder polymers. In some embodiments, the binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, or butadiene-styrene rubber. According to some embodiments of the present application, the negative electrode active material layer further includes a conductive material to improve the conductivity of the electrode. Any conductive material can be used as the conductive material, as long as it does not cause chemical changes. In some embodiments, the conductive material includes at least one of conductive carbon black, acetylene black, carbon nanotube, ketjen black, conductive graphite, or graphene.

[0058] The electrochemical device of the present application also includes a separator film, and the material and shape of the separator film used in the electrochemical device of the present application are not particularly limited and can be any of the techniques disclosed in the prior art. In some embodiments, the separator film includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, etc.

[0059] For example, the separator film can include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a film, or a composite film having 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 film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. The surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0060] The present application further provides an electronic device including the electrochemical device provided by the present application.

[0061] The electronic device or apparatus of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, a notebook computer, a pen input type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an illuminating appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0062] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, as can any upper limit with any other upper limit to form a range not explicitly recited. Further, each individual disclosed point or single numerical value can itself serve as a lower limit or an upper limit to combine with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0063] The application will be further described in connection with the following examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application.

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

[0065] (1) Preparation of electrolyte

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

[0067] (2) Preparation of positive electrode sheet

[0068] First active material layer: the positive active material lithium iron phosphate (LiFePO4), conductive agent carbon nanotube (CNT), and specific binder polyvinylidene fluoride were mixed in a mass ratio of 95:2:3, N-methyl pyrrolidone (NMP) was added, and the system was stirred to form a uniform positive electrode slurry under the action of a vacuum stirrer, then the positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil (the Al foil used here has a F content of 500 ppm and a M content of 300 ppm), and the aluminum foil was dried at 85°C as a carrier for the second active material layer.

[0069] Second active material layer: the positive active material lithium cobaltate (LiCoO2), conductive agent carbon nanotube (CNT), and specific binder polyvinylidene fluoride were mixed in a mass ratio of 95:2:3, N-methyl pyrrolidone (NMP) was added, and the system was stirred to form a uniform positive electrode slurry under the action of a vacuum stirrer, then the positive electrode slurry was uniformly coated on the first active material layer; after drying at 85°C, cold pressing, sheet cutting, and drying for 4 h under vacuum at 85°C, a positive electrode sheet was obtained.

[0070] (3) Preparation of negative electrode sheet

[0071] The negative active material graphite, binder styrene butadiene rubber (SBR), and thickening agent sodium carboxymethyl cellulose (CMC) were fully stirred and mixed in a proper amount of deionized water solvent in a mass ratio of 95:2:3 to form a uniform negative electrode slurry; the slurry was coated on the negative electrode current collector Cu foil, dried, and cold pressed to obtain a negative electrode sheet.

[0072] (4) Preparation of separator

[0073] The separator was a polyethylene (PE) separator.

[0074] (5) Preparation of lithium ion battery

[0075] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of separation, and then are wound and placed in an outer packaging foil. The electrolyte prepared above is injected into the dried battery, and the battery is subjected to processes such as vacuum packaging, standing, formation, and shaping, to complete the preparation of the lithium ion battery.

[0076] 2. Test method

[0077] (1) Nail test

[0078] Ten electrochemical devices (lithium ion batteries) to be tested are charged at a constant current of 0.5C rate to a voltage of 4.45V at room temperature, and then are further charged at a constant voltage of 4.45V to a current of 0.05C, so that they are in a full charge state at 4.45V. Then the lithium ion batteries are subjected to nail penetration at room temperature, a nail (steel nail, material is carbon steel, taper is 16.5mm, total length of the steel nail is 100mm) with a diameter of 2.5mm is used to penetrate the lithium ion battery at a penetration speed of 30mm / s, the penetration depth is determined by the taper of the steel nail, and the lithium ion battery is stopped for 5min. Whether the lithium ion battery produces smoke, fire or explosion is observed. If not, the lithium ion battery is considered to pass the nail penetration test.

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

[0080] Three electrochemical devices (lithium ion batteries) to be tested are charged at a constant current of 0.5C rate to a voltage of 4.45V at room temperature (25℃±3℃), and then are further charged at a constant voltage of 4.45V to a current of 0.05C, so that they are in a full charge state at 4.45V. An OCV / IMP tester is used to record the AC impedance of the battery at 1KHz, in units of mΩ, which is recorded as the initial impedance of the battery. Then the battery is placed in an oven at 85℃ for 8h, and after the end of the storage, the battery is placed at 25℃±3℃ for 2h. Then an OCV / IMP tester is used to record the AC impedance of the battery at 1KHz, in units of mΩ. The initial impedance of the battery is taken as the reference, and the IMP growth rate after 8h storage at 85℃ is compared.

[0081] (3) Discharge rate test

[0082] The electrochemical device (lithium ion battery) was charged at 25°C at 0.7C to 4.45V, and charged at 4.45V to a current of 0.05C. After that, the lithium ion battery was rested at 25°C for 4h, and discharged at different rates (0.2C, 0.5C, 1C, 2C) to 3.0V, and after each discharge, it was rested for 5min, and the discharge capacity of the lithium ion battery was recorded. The discharge capacity ratio of the lithium ion battery at different rates was obtained based on the 0.2C discharge capacity at 25°C. Here, the capacity retention rate at 2C was uniformly compared.

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

[0084] 3. Test results

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

[0086] Table 1

[0087]

[0088] As can be seen from Table 1, the introduction of the first active material layer has obvious improvement on the nail penetration, but the impedance growth of high temperature storage is deteriorated, but with the decrease of the content of lithium hexafluorophosphate, the nail penetration rate and the IMP growth rate are further improved, the former is mainly related to the low lithium salt inhibiting short circuit discharge, and the latter is mainly due to the reduction of lithium salt, the content of HF is reduced, which helps to reduce the corrosion to the positive electrode interface, and then inhibits the increase of IMP. When the thickness of the first active material layer and the thickness of the second active material layer are within a certain range, the nail penetration rate of the lithium ion battery can be ensured, the IMP growth rate can be reduced to a certain extent, and the rate performance of the battery can be improved.

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

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

[0091] Table 2

[0092]

[0093]

[0094] As can be seen from Table 2, the introduction of the first active material layer has a significant improvement on the nail penetration, but the IMP growth under high temperature storage is deteriorated. With the introduction of adiponitrile, the nail penetration is further slightly improved, and the IMP growth is significantly improved, which is attributed to the inhibition of the side reaction on the cathode side. It is also found that when the first active material layer thickness value D1 and the second active material layer thickness value D2 and W3 satisfy 0.7≤(D1+D2) / 100W3≤6, not only the nail penetration rate is improved, but also the IMP growth under high temperature storage is significantly inhibited.

[0095] (3) Effect of the cathode active material layer and propylene carbonate on the battery performance, the amount of lithium hexafluorophosphate in Examples S3-1 to S3-9 is consistent with that in S1-1, and the content of PC is shown in Table 3, and EC and DEC are mixed in 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] As can be seen from Table 3, when W2 / 10+W3 / 4+(D1+D2) / 100≤7 and / or W2 / (D1+D2)+W3 / 4+D2 / 10D1≤4 are satisfied, the IMP growth under high temperature storage is further inhibited, and the main mechanism is to improve the stability of the electrolyte solvent itself and reduce the interface side reaction, which is different from the mechanism of adiponitrile film formation inhibiting the interface side reaction.

[0100] (4) Effect of the cathode active material layer and LiPO2F2, propyl propionate on the battery performance, the amount of lithium hexafluorophosphate in Examples S4-1 to S4-5 is consistent with that in S1-1, and EC, PC, and DEC are mixed in a mass ratio of 1:1:1.

[0101] Table 4

[0102]

[0103] As can be seen from Table 4, LiPO2F2 and propyl propionate also have a certain inhibitory effect on the IMP growth under high temperature storage, and do not affect the nail penetration rate, so they can also be used as a technical means to balance the 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: 0.1 ≤ D1 ≤ 15, 3 ≤ (D1 + D2) / W0 ≤ 12, 25 ≤ D2 ≤ 60, and 5 ≤ W0 ≤ 13, the electrolyte further comprises propyl propionate, the content of the propyl propionate being W6% based on the total mass of the electrolyte, and satisfying W6 / (D1 + D2) ≤ 1; 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 ≤ 6.

0.

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) 0.18 ≤ W6 / (D1 + D2) ≤ 1.

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) 0.27 ≤ W6 / (D1 + D2) ≤ 0.

9.

4. The electrochemical device of claim 1, wherein 30 ≤ D2 ≤ 55 and 8 ≤ W0 ≤ 12 are 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 one or both of 1.0 ≤ (D1 + D2) / 25W3 ≤ 4.0 or 0.4 ≤ W3 ≤ 5 is satisfied.

8. 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.

9. The electrochemical device according to any one of claims 1 to 7, wherein the electrolyte further comprises at least one of lithium difluorophosphate or lithium bisfluorosulfonylimide, and at least one of the following conditions is satisfied: (m) the content of the lithium difluorophosphate is W4% based on the total mass of the electrolyte, and (W4 + D1 + D2) / 100 ≤ 1; (n) the content of the lithium bisfluorosulfonylimide is W5% based on the total mass of the electrolyte solution, W5≤W0.

10. The electrochemical device according to any one of claims 1 to 7, wherein The first material layer contains a first active material including 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 including lithium cobaltate, lithium iron phosphate, lithium vanadate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium-rich manganese-based material, lithium nickel aluminum cobaltate, or lithium titanate.

11. The electrochemical device according to any one of claims 1 to 7, wherein At least one of conditions (o) to (q) is satisfied: (o) the positive electrode current collector contains an iron element, the content F of the iron element satisfies 0 < F ≤ 2000 ppm based on the total mass of the positive electrode current collector; (p) the positive electrode current collector contains a magnesium element, the content M of the magnesium element satisfies 0 < M ≤ 1500 ppm based on the total mass of the positive electrode current collector; (q) the positive electrode material layer contains a positive electrode active material, the D50 of the positive electrode active material is 0.2 μm to 15 μm, and the D90 is less than 40 μm.

12. An electronic device comprising the electrochemical device according to any one of claims 1 to 11.

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