CN116247296A - Electrochemical devices and electronic devices - Google Patents

Abstract

The present 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, wherein the positive electrode active material layer comprises a first active material layer and a second active material layer, the first active material layer is arranged between the positive electrode current collector and the second active material layer, and the thickness of the first active material layer is D ₁ μm, the thickness of the second active material layer is D ₂ μm, the electrolyte comprising carbonate and lithium hexafluorophosphate, the content of lithium hexafluorophosphate being W based on the total mass of the electrolyte ₀ In percent, the following relationship is satisfied: d is more than or equal to 0.1 ₁ ≤15，3≤(D ₁ +D ₂ )/W ₀ And is less than or equal to 12. The electrochemical device of the present invention can improve the high-temperature storage resistance increase rate.

Description

Electrochemical devices and electronic devices

This application is a divisional application of the Chinese application with application number 202110495451.7, filing date May 7, 2021, and invention name “Electrochemical Device and Electronic Device”.

Technical Field

The present invention relates to an electrochemical device and an electronic device.

Background Art

With the popularization and application of smart products, people's demand for electronic products such as mobile phones, laptops, cameras, etc. has increased year by year. As the working power source of electronic products, lithium-ion batteries have the characteristics of high energy density, no memory effect, and high working voltage, and are gradually replacing traditional Ni-Cd and MH-Ni batteries. However, with the development of electronic products towards thinness and portability, people's requirements for lithium-ion batteries are constantly increasing, and the development of highly safe and long-life lithium-ion batteries is one of the main demands of the market.

Existing literature reports that double-layer positive electrode active materials can improve battery safety to a certain extent, but the impedance growth during high-temperature storage is significantly worsened.

Summary of the invention

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

In a first aspect, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector, wherein the positive electrode active material layer includes a first active material layer and a second active material layer, and the first active material layer is disposed between the positive electrode current collector and the second active material layer, wherein the thickness of the first active material layer is D ₁ μm, and the thickness of the second active material layer is D ₂ μm, and the electrolyte includes carbonate and lithium hexafluorophosphate, and based on the total mass of the electrolyte, the content of the lithium hexafluorophosphate is W ₀ %, and satisfies the following relationship: 0.1≤D ₁ ≤15, 3≤(D ₁ +D ₂ )/W ₀ ≤12. In the present application, the IMP growth of the double-layer positive electrode active material during high temperature storage is significantly improved by adjusting the electrolyte formula.

According to some embodiments of the present application, the electrochemical device satisfies one or both of 25≤D ₂ ≤60 or 5≤W ₀ ≤13.

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. 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 W ₁ %, 1.0≤(D ₁ +D ₂ )/25W ₁ ≤4.0; (b) based on the total mass of the electrolyte, the content of propylene carbonate is W ₂ %, 5≤W ₂ ≤40; (c) based on the total mass of the electrolyte, the content of propylene carbonate is W ₂ %, W ₂ ≤(D ₁ +D ₂ ); (d) based on the total mass of the electrolyte, the content of ethylene carbonate is W ₁ %, the content of propylene carbonate is W ₂ %, W ₁ +W ₂ ≤60.

According to some embodiments of the present application, the electrolyte further comprises dinitrile. Further, based on the total mass of the electrolyte, the content of the dinitrile is W ₃ %, satisfying the following relationship: 0.7≤(D ₁ +D ₂ )/25W ₃ ≤6.0.

According to some embodiments of the present application, the electrochemical device satisfies one or both of 1.0≤(D ₁ +D ₂ )/25W ₃ ≤4.0 or 0.4≤W ₃ ≤5.

According to some embodiments of the present application, the electrochemical device satisfies that the dinitrile comprises at least one of the dinitrile compounds shown in Formula I, Formula II, or Formula III;

wherein _R1 is selected from _C1 - _C18 alkylene, C1- _C18 alkylene containing a substituent, _C2 - _{C18 alkenylene, C2-C18 alkenylene} containing a substituent, _C2 - _C18 alkynylene, C2- _C18 alkynylene containing a substituent, _C6 - _C18 arylene or _C6 - _C18 arylene containing a substituent; _R2 and _R3 are each independently selected from _C1 - _C9 alkylene, _C1 -C9 alkylene containing a substituent, _C2 - _C9 alkenylene, C2- _C9 alkenylene containing a substituent, _C2 -C9 alkynylene, C2-C9 alkynylene containing a substituent, _C6 - _C9 arylene or _C6 -C9 arylene containing a substituent; R4, R5 _{, R6} are each independently selected from _C1 - _C9 alkylene, C1- _C9 alkylene containing a substituent, _C2 - _C9 alkenylene, _C2 -C9 alkynylene, C2- _C9 alkynylene containing a substituent, _C6 -C9 arylene or C6- _C9 arylene containing a substituent; ₆ are each independently selected from C ₁ -C ₆ alkylene, substituted C ₁ -C ₆ alkylene, C ₂ -C ₆ alkenylene, substituted C ₂ -C ₆ alkenylene, C ₂ -C ₆ alkynylene or substituted C ₂ -C ₆ alkynylene; wherein the substituent is selected from halogen or C ₁ -C ₅ alkoxy.

According to some embodiments of the present application, the electrochemical device satisfies one or more of the following conditions (e)-(f): (e) W ₂ /10+W ₃ /4+(D ₁ +D ₂ )/100≤7; (f) W ₂ /(D ₁ +D ₂ )+W ₃ /4+D ₂ /10D ₁ ≤4.

According to some embodiments of the present application, the electrolyte further comprises at least one of lithium difluorophosphate or lithium bisfluorosulfonyl imide, satisfying at least one of conditions (g) to (h): (g) based on the total mass of the electrolyte, the content of lithium difluorophosphate is W ₄ %, (W ₄ +D ₁ +D ₂ )/100≤1; (h) based on the total mass of the electrolyte, the content of lithium bisfluorosulfonyl imide is W ₅ %, W ₅ ≤W ₀ .

According to some embodiments of the present application, the electrolyte further comprises a propionate compound. Further, based on the total mass of the electrolyte, the content of the propionate compound is W ₆ %, satisfying W ₆ /(D ₁ +D ₂ )≤1. According to some embodiments of the present application, the propionate compound comprises 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.

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

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

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

The present application is further described below in conjunction with specific implementations. It should be understood that these specific implementations are only used to illustrate the present application and are not used to limit the scope of the present application.

In the description herein, unless otherwise specified, “above” and “below” include the number.

Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

A list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean 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 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.

A list of items connected by the term "and/or" may 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" encompasses fluorine, chlorine, bromine, iodine.

The term "hydrocarbyl" encompasses alkyl, alkenyl, alkynyl.

The term "alkyl" is expected to be a straight chain saturated hydrocarbon structure with 1 to 20 carbon atoms. "Alkyl" is also expected to be a branched or cyclic hydrocarbon structure with 3 to 20 carbon atoms. When specifying an alkyl with a specific carbon number, it is expected to cover all geometric isomers with that carbon number; therefore, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Alkyl examples 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.

The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group which may be straight or branched and has at least one, and typically 1, 2 or 3, 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 - _C10 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.

The term "alkynyl" refers to a monovalent unsaturated hydrocarbon group which may be straight or branched and has at least one, and typically 1, 2 or 3, 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 - _C10 alkynyl. Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like.

Although in lithium-ion batteries, the positive electrode active material layer on the current collector side has a double layer of positive electrode active material, which improves battery safety to a certain extent, the impedance growth during high-temperature storage is significantly worsened. The applicant has found through research that adjusting the electrolyte formula can significantly improve the impedance growth rate of the double-layer positive electrode active material during high-temperature storage. Based on this, the present application is proposed.

In a first aspect, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector, wherein the positive electrode active material layer includes a first active material layer and a second active material layer, and the first active material layer is disposed between the positive electrode current collector and the second active material layer, wherein the thickness of the first active material layer is D ₁ μm, and the thickness of the second active material layer is D ₂ μm, and the electrolyte includes carbonate and lithium hexafluorophosphate, and based on the total mass of the electrolyte, the content of the lithium hexafluorophosphate is W ₀ %, and the following relationship is satisfied: 0.1≤D ₁ ≤15, 3≤(D ₁ +D ₂ )/W ₀ ≤12. In the present application, the high-temperature storage impedance growth of the double-layer positive electrode active material is significantly improved by adjusting the electrolyte formula.

According to some embodiments of the present application, 3.6≤(D ₁ +D ₂ )/W ₀ ≤7. Within this range, the electrochemical device has better comprehensive performance.

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 therebetween. In some embodiments, 2≤D ₁ ≤7. Within this range, the impact on the volume energy density of the battery can be minimized while taking into account the safety performance.

According to some embodiments of the present application, the electrochemical device satisfies 25≤D ₂ ≤60. In some embodiments, D ₂ is 25, 30, 35, 40, 45, 50, 55, 60 or any value therebetween.

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

According to some embodiments of the present application, the electrochemical device satisfies 5≤W ₀ ≤ 13. In some embodiments, W ₀ is 5, 8, 10, 12, 13 or any value therebetween.

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 certain embodiments, the cyclic carbonate comprises ethylene carbonate and propylene carbonate.

According to some embodiments of the present application, based on the total mass of the electrolyte, the content of ethylene carbonate is W ₁ %, 1.0≤(D ₁ +D ₂ )/25W ₁ ≤4.0. In some embodiments, (D ₁ +D ₂ )/25W ₁ is 1.0, 1.5, 1.8, 2.0, 2.5, 2.8, 3.0, 3.5, 3.8, 4.0 or any value therebetween.

According to some embodiments of the present application, based on the total mass of the electrolyte, the content of propylene carbonate is W ₂ %, 5≤W ₂ ≤40. In some embodiments, W ₂ is 5, 8, 10, 12, 15, 17, 21, 25, 28, 30, 32, 35, 38 or any value therebetween. According to some embodiments of the present application, based on the total mass of the electrolyte, the content of propylene carbonate is W ₂ %, W ₂ ≤(D ₁ +D ₂ ). Propylene carbonate within this range can provide better kinetic properties.

According to some embodiments of the present application, based on the total mass of the electrolyte, the content of ethylene carbonate is W ₁ %, the content of propylene carbonate is W ₂ %, W ₁ +W ₂ ≤60, preferably, W ₁ +W ₂ ≤40. Within this range, ethylene carbonate and propylene carbonate can achieve the best synergistic effect, which not only ensures good film-forming stability, but also takes into account the overall dynamics of the electrolyte to achieve optimal performance.

According to some embodiments of the present application, the electrolyte further comprises dinitrile. Further, based on the total mass of the electrolyte, the content of the dinitrile is W ₃ %, satisfying the following relationship: 0.7≤(D ₁ +D ₂ )/25W ₃ ≤6.0. In some embodiments, D ₁ +D ₂ )/25W ₃ 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≤(D ₁ +D ₂ )/25W ₃ ≤4.0.

According to some embodiments of the present application, the dinitrile compound satisfies 0.4≤W ₃ ≤5. In some embodiments, W ₃ 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 therebetween.

According to some embodiments of the present application, the electrochemical device satisfies that the dinitrile comprises at least one of the dinitrile compounds shown in Formula I, Formula II, or Formula III;

wherein _R1 is selected from _C1 - _C18 alkylene, C1- _C18 alkylene containing a substituent, _C2 - _{C18 alkenylene, C2-C18 alkenylene} containing a substituent, _C2 - _C18 alkynylene, C2- _C18 alkynylene containing a substituent, _C6 - _C18 arylene or _C6 - _C18 arylene containing a substituent; _R2 and _R3 are each independently selected from _C1 - _C9 alkylene, _C1 -C9 alkylene containing a substituent, _C2 - _C9 alkenylene, C2- _C9 alkenylene containing a substituent, _C2 -C9 alkynylene, C2-C9 alkynylene containing a substituent, _C6 - _C9 arylene or _C6 -C9 arylene containing a substituent; R4, R5 _{, R6} are each independently selected from _C1 - _C9 alkylene, C1- _C9 alkylene containing a substituent, _C2 - _C9 alkenylene, _C2 -C9 alkynylene, C2- _C9 alkynylene containing a substituent, _C6 -C9 arylene or C6- _C9 arylene containing a substituent; ₆ are each independently selected from C ₁ -C ₆ alkylene, substituted C ₁ -C ₆ alkylene, C ₂ -C ₆ alkenylene, substituted C ₂ -C ₆ alkenylene, C ₂ -C ₆ alkynylene or substituted C ₂ -C ₆ alkynylene; wherein the substituent is selected from halogen or C ₁ -C ₅ alkoxy.

In the present application, halogen may be fluorine, chlorine, bromine, or iodine; C ₁ -C ₅ alkoxy may be methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, tert-butoxy, or the like.

In some embodiments, R ₁ is C ₂ alkylene, C ₃ alkylene, C ₄ alkylene, C ₅ alkylene, C ₆ alkylene, C ₇ alkylene, etc. In some embodiments, R ₂ and R ₃ are each independently C ₁ alkylene, C ₂ alkylene, C 3 alkylene, C ₄ alkylene, C ₅ alkylene, C ₆ alkylene, C ₇ alkylene, etc. In some embodiments, R ₄ , R ₅ and R ₆ are each independently C ₁ alkylene, C ₂ alkylene, C ₃ alkylene, C ₄ alkylene, C ₅ alkylene, _{C 6 alkylene} , etc. In some embodiments, the dinitrile includes at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile or ethylene glycol bispropionitrile ether.

According to some embodiments of the present 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.

According to some embodiments of the present application, the electrochemical device satisfies one or more of the following conditions (e)-(f): (e) W ₂ /10+W ₃ /4+(D ₁ +D ₂ )/100≤7; (f) W ₂ /(D ₁ +D ₂ )+W ₃ /4+D ₂ /10D ₁ ≤4. Within this range, the interface side reaction can be effectively suppressed, thereby suppressing the impedance growth during the cycle or high-temperature storage process.

According to some embodiments of the present application, the electrolyte further comprises at least one of lithium difluorophosphate or lithium bis(fluorosulfonyl)imide. Further, based on the total mass of the electrolyte, the content of lithium difluorophosphate is W ₄ %, (W ₄ +D ₁ +D ₂ )/100≤1. Further, based on the total mass of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is W ₅ %, W ₅ ≤W _0. Within this range, better kinetic performance can be achieved while reducing corrosion to the aluminum foil substrate.

According to some embodiments of the present application, W ₄ <1. W ₄ is 0.01, 0.05, 0.1, 0.3, 0.5, 0.7, 0.9 or any value therebetween. Within this range, the electrochemical device has better high-temperature storage performance.

According to some embodiments of the present application, the electrolyte further comprises a propionate compound. Further, based on the total mass of the electrolyte, the content of the propionate compound is W ₆ %, satisfying W ₆ /(D ₁ +D ₂ )≤2. According to some embodiments of the present application, the propionate compound comprises 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. According to

In some embodiments of the present application, _W6 is 15, 18, 20, 25, 30, 35, 40, 45, 50 or any value therebetween.

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. According to some embodiments of the present application, 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 materials, lithium nickel cobalt aluminum oxide or lithium titanate.

According to some embodiments of the present application, the second active material layer includes lithium cobalt oxide, and the electrochemical device satisfies 20≤D ₂ /W ₃ ≤120. Within this range, both the protection of the positive electrode side and the overall dynamics of the electrolyte can be taken into account.

According to some embodiments of the present application, the positive electrode current collector contains iron and/or magnesium, and the iron content F satisfies 0＜F≤2000ppm 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 magnesium, and the magnesium content M satisfies 0＜M≤1500ppm 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 0.2μm to 15μm, and the D90 is less than 40μm.

The positive electrode current collector for the electrochemical device of the present 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 metal 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 the binder (conductive material and thickener can be further used as needed) are dry mixed to form a sheet, and the obtained sheet is pressed to the positive electrode current collector, or these materials are dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the positive electrode current collector and dried. In some embodiments, the binder may include polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, a polyamide, a polyacrylonitrile, a polyacrylate, a polyacrylic acid, a polyacrylate, a carboxymethyl cellulose sodium, polyvinyl acetate, polyvinylpyrrolidone, a polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or at least one of polyhexafluoropropylene. The conductive material may include at least one of conductive carbon black, lamellar graphite, graphene, carbon nanotubes, or carbon fibers.

The electrochemical device of the present application also includes a negative electrode, wherein the material, composition and manufacturing method of the negative electrode used may include any technology 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, and the negative electrode active material may 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 or a silicon material, the carbon material includes at least one of graphite and hard carbon, and the silicon material includes at least one of silicon, silicon oxide, silicon carbon compound or silicon alloy. According to some embodiments of the present application, the negative electrode active material layer contains a binder, and the binder may include various binder polymers. In some embodiments, the binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polypropylene, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene or styrene-butadiene rubber. According to some embodiments of the present application, the negative electrode active material layer also 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 chemical changes. In some embodiments, the conductive material includes at least one of conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, conductive graphite or graphene.

The electrochemical device of the present application also includes an isolating membrane. The material and shape of the isolating membrane used in the electrochemical device of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the isolating membrane includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

For example, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be selected. A 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 a mixed 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, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene).

The present application further provides an electronic device, which includes the electrochemical device provided by the present application.

The electronic device or device 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 laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

For simplicity, only some numerical ranges are specifically disclosed herein. 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, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

The present application is further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

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

(1) Preparation of electrolyte

In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed in a certain mass ratio, and LiPF ₆ was added. Based on the total mass of the electrolyte, 5% of fluoroethylene carbonate and 2% of 1,3-propane sultone were added. The electrolyte was prepared according to the following examples and comparative examples.

(2) Preparation of positive electrode

First active material layer: positive electrode active material lithium iron phosphate (LiFePO ₄ ), conductive agent carbon nanotube (CNT), and specific binder polyvinylidene fluoride are mixed in a mass ratio of 95:2:3, N-methylpyrrolidone (NMP) is added, and the system is stirred under the action of a vacuum mixer until the system becomes a uniform positive electrode slurry, and then the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil (the Al foil used here has an F content of 500ppm and an M content of 300ppm), and dried at 85°C as a carrier for the second active material layer.

Second active material layer: positive electrode active material lithium cobalt oxide (LiCoO ₂ ), conductive agent carbon nanotube (CNT), and specific binder polyvinylidene fluoride are mixed in a mass ratio of 95:2:3, N-methylpyrrolidone (NMP) is added, and the system is stirred under the action of a vacuum mixer until the system becomes a uniform positive electrode slurry, and then the positive electrode slurry is evenly coated on the first active material layer; after drying at 85°C, cold pressing, cutting, and slitting, it is dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.

(3) Negative electrode preparation

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

(4) Preparation of isolation film

The isolation membrane is made of polyethylene (PE) membrane.

(5) Preparation of lithium-ion batteries

The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then they are wound and placed in an outer packaging foil. The prepared electrolyte is injected into the dried battery. After vacuum packaging, standing, formation, shaping and other processes, the preparation of the lithium-ion battery is completed.

2. Test methods

(1) Nail test

Take 10 electrochemical devices (lithium-ion batteries) to be tested and charge them to a voltage of 4.45V at a constant current of 0.5C at room temperature, and further charge them to a current of 0.05C at a constant voltage of 4.45V, so that they are in a fully charged state of 4.45V. Then, pierce the lithium-ion battery at room temperature, using a nail with a diameter of 2.5mm (steel nail, made of carbon steel, with a taper of 16.5mm, and a total length of 100mm) at a piercing speed of 30mm/s. The piercing depth is based on the taper of the steel nail passing through the lithium-ion battery. Stay for 5 minutes to observe whether the lithium-ion battery produces smoke, catches fire or explodes. If not, the lithium-ion battery is considered to have passed the nail piercing test.

(2) High temperature memory impedance (IMP) growth rate test

Take 3 electrochemical devices (lithium-ion batteries) to be tested and charge them to a voltage of 4.45V at a constant current of 0.5C at room temperature (25℃±3℃), and further charge them to a current of 0.05C at a constant voltage of 4.45V, so that they are in a fully charged state of 4.45V. Use an OCV/IMP tester to record the AC impedance of the battery at 1KHz in mΩ, which is recorded as the initial impedance of the battery. Then place it in an oven at 85℃ and store it for 8h. After the end, place the battery at 25℃±3℃ and let it stand for 2h. Use an OCV/IMP tester to record the AC impedance of the battery at 1KHz in mΩ. Take the initial impedance of the battery as a benchmark and compare the IMP growth rate after storage at 85℃ for 8h.

(3) Discharge rate test

At 25°C, the electrochemical device (lithium-ion battery) was charged to 4.45V at a constant current of 0.7C, and charged to a current of 0.05C at a constant voltage of 4.45V. After that, the lithium-ion battery was left at rest at 25°C for 4 hours, and then discharged to 3.0V at different rates (0.2C, 0.5C, 1C, 2C). After each discharge, it was left at rest for 5 minutes, 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 discharge capacity at 25°C and 0.2C. The capacity retention rate of 2C is uniformly compared here.

Discharge capacity ratio of lithium-ion battery at 2C rate (%) = discharge capacity at 2C/discharge capacity at 0.2C×100%.

3. Test results

(1) Effects 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.

Table 1

As can be seen from Table 1, the introduction of the first active material layer has a significant improvement on nail penetration, but the impedance growth for high-temperature storage is more seriously deteriorated. However, with the reduction of lithium hexafluorophosphate content, the nail penetration pass rate and 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 attributed to the reduction of lithium salt. The HF content is reduced, which helps to reduce corrosion on the positive electrode interface and thus inhibit 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 pass rate of the lithium-ion battery can be guaranteed while reducing the IMP growth rate to a certain extent and improving the battery rate performance.

(2) The influence of positive electrode active material layer and dinitrile on battery performance.

In Examples S2-1 to S2-13, the amount of lithium hexafluorophosphate used is consistent with that in Example 1, and EC, PC, and DEC are mixed in a mass ratio of 1:1:1.

Table 2

It can be seen from Table 2 that the introduction of the first active material layer has a significant improvement on nail penetration, but the IMP growth at high temperature storage is seriously deteriorated. With the introduction of adiponitrile, the nail penetration is further slightly improved, and the IMP growth is significantly improved, which is attributed to its inhibition of the side reaction on the positive electrode side. At the same time, it is found that when the thickness value of the first active material layer _D1 and the thickness value of the second active material layer _D2 and _W3 satisfy 0.7≤( _D1 + _D2 )/ _100W3≤6 , not only the nail penetration rate is improved, but also the IMP growth at high temperature storage is significantly inhibited.

(3) Effect of positive electrode active material layer and propylene carbonate on battery performance. The amount of lithium hexafluorophosphate used is consistent with that in S1-1. The PC content in Examples S3-1 to S3-9 is shown in Table 3. EC and DEC are mixed in a mass ratio of 1:1.

Table 3

Note: In Table 3, X represents W ₂ /10+W ₃ /4+(D ₁ +D ₂ )/100, and Y represents W ₂ /(D ₁ +D ₂ )+W ₃ /4+D ₂ /10D ₁

It can be seen from Table 3 that when W ₂ /10+W ₃ /4+(D ₁ +D ₂ )/100≤7 and/or W ₂ /(D ₁ +D ₂ )+W ₃ /4+D ₂ /10D ₁ ≤4 is satisfied, the growth of IMP during 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, which is different from the mechanism of inhibiting the side reactions at the interface by film formation of adiponitrile.

(4) Effects of positive electrode active material layer, LiPO ₂ F ₂ and propyl propionate on battery performance. The amount of lithium hexafluorophosphate used in Examples S4-1 to S4-5 is consistent with that in S1-1. EC, PC and DEC are mixed in a mass ratio of 1:1:1.

Table 4

It can be seen from Table 4 that LiPO ₂ F ₂ and propyl propionate also have a certain inhibitory effect on the growth of IMP during high-temperature storage, and do not affect the nail penetration rate. Therefore, they can also be used as a technical means to balance the battery stability under high-temperature storage.

Claims (13)

1. An electrochemical device comprises a positive electrode, a negative electrode, a separation film and electrolyte, wherein the positive electrode comprises a positive electrode current collector and a positive electrode material layer arranged on the surface of the positive electrode current collector, the positive electrode material layer comprises a first material layer and a second material layer, the first material layer is arranged between the positive electrode current collector and the second material layer,

the thickness of the first material layer is D ₁ The thickness of the second material layer is D ₂ μm，

The electrolyte comprises carbonate and lithium hexafluorophosphate, and the content of the lithium hexafluorophosphate is W based on the total mass of the electrolyte ₀ In percent, the following relationship is satisfied: d is more than or equal to 0.1 ₁ ≤15，3≤(D ₁ +D ₂ )/W ₀ ≤12，

The electrolyte further comprises propyl propionate, and the content of the propyl propionate is W based on the total mass of the electrolyte ₆ % satisfies W ₆ /(D ₁ +D ₂ )≤1。

2. The electrochemical device of claim 1, wherein at least one of the following conditions is satisfied:

(a)2≤D ₁ ≤7；

(b)3.6≤(D ₁ +D ₂ )/W ₀ ≤7；

(c)0.18≤W ₆ /(D ₁ +D ₂ )≤1。

3. the electrochemical device of claim 1, wherein at least one of the following conditions is satisfied:

(d)3≤D ₁ ≤6；

(e)4.0≤(D ₁ +D ₂ )/W ₀ ≤6.5；

(f)0.27≤W ₆ /(D ₁ +D ₂ )≤0.9。

4. the electrochemical device according to claim 1, wherein 25.ltoreq.d is satisfied ₂ W is more than or equal to 60 or less than or equal to 5 ₀ One or both of less than or equal to 13.

5. The electrochemical device of claim 1, wherein the carbonate comprises a cyclic carbonate comprising at least one of ethylene carbonate or propylene carbonate, the cyclic carbonate satisfying at least one of the following conditions:

(g) The content of the ethylene carbonate is W based on the total mass of the electrolyte ₁ ％，1.0≤(D ₁ +D ₂ )/25W ₁ ≤4.0；

(h) The content of propylene carbonate is W based on the total mass of the electrolyte ₂ ％，5≤W ₂ ≤40；

(i) The content of propylene carbonate is W based on the total mass of the electrolyte ₂ ％，W ₂ ≤(D ₁ +D ₂ )；

(j) The content of the ethylene carbonate is W based on the total mass of the electrolyte ₁ The content of the propylene carbonate is W ₂ ％，W ₁ +W ₂ ≤60。

6. The electrochemical device of claim 1, wherein the electrolyte further comprises dinitriles, the dinitriles based on a total mass of the electrolyteNitrile content W ₃ In percent, the following relationship is satisfied: d is less than or equal to 0.7 ₁ +D ₂ )/25W ₃ ≤6.0。

7. The electrochemical device according to claim 6, wherein (D) of 1.0.ltoreq.D is satisfied ₁ +D ₂ )/25W ₃ W is not less than 4.0 or not less than 0.4 ₃ One or both of less than or equal to 5.

8. The electrochemical device of claim 6, wherein the dinitrile comprises at least one of a dinitrile compound of formula I, formula II, or formula III;

wherein,,

R ₁ selected from C ₁ -C ₁₈ Alkylene group of (C) containing substituent ₁ -C ₁₈ Alkylene group, C ₂ -C ₁₈ Alkenylene group, substituent-containing C ₂ -C ₁₈ Alkenylene, C ₂ -C ₁₈ Alkynylene group, substituent-containing C ₂ -C ₁₈ Alkynylene, C ₆ -C ₁₈ Arylene or substituted C ₆ -C ₁₈ Arylene groups;

R ₂ 、R ₃ each independently selected from C ₁ -C ₉ Alkylene group of (C) containing substituent ₁ -C ₉ Alkylene group, C ₂ -C ₉ Alkenylene group, substituent-containing C ₂ -C ₉ Alkenylene, C ₂ -C ₉ Alkynylene group, substituent-containing C ₂ -C ₉ Alkynylene, C ₆ -C ₉ Arylene or substituted C ₆ -C ₉ Arylene groups;

R ₄ 、R ₅ 、R ₆ each independently selected from C ₁ -C ₆ Alkylene group of (C) containing substituent ₁ -C ₆ Alkylene group, C ₂ -C ₆ Alkenylene group, substituent-containing C ₂ -C ₆ Alkenylene, C ₂ -C ₆ Alkynylene or substituent-containing C ₂ -C ₆ Alkynylene;

wherein the substituents are selected from halogen or C ₁ -C ₅ Alkoxy groups of (a).

9. The electrochemical device of any one of claims 1-8, wherein one or more of the following conditions are satisfied:

(k)W ₂ /10+W ₃ /4+(D ₁ +D ₂ )/100≤7；

(l)W ₂ /(D ₁ +D ₂ )+W ₃ /4+D ₂ /10D ₁ ≤4。

10. the electrochemical device of any one of claims 1-8, wherein the electrolyte further comprises at least one of lithium difluorophosphate or lithium difluorosulfonimide, satisfying at least one of the following conditions:

(m) the lithium difluorophosphate content is W based on the total mass of the electrolyte ₄ ％，(W ₄ +D ₁ +D ₂ )/100≤1；

(n) the lithium bis (fluorosulfonyl) imide content is W based on the total mass of the electrolyte ₅ ％，W ₅ ≤W ₀ 。

11. The electrochemical device of any one of claims 1-8, wherein the first 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 vanadyl phosphate, sodium vanadyl phosphate, or lithium titanate; the second material layer comprises 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 cobalt aluminate or lithium titanate.

12. The electrochemical device according to any one of claims 1-8, wherein at least one of conditions (o) to (q) is satisfied:

(o) the positive electrode current collector contains iron element and/or magnesium element, and the iron element content F satisfies 0 < F less than or equal to 2000ppm based on the total mass of the positive electrode current collector;

(p) the positive electrode current collector contains magnesium element, wherein the content M of the magnesium element is more than 0 and less than or equal to 1500ppm based on the total mass of the positive electrode current collector;

(q) the positive electrode material layer contains therein a positive electrode active material having a D50 of 0.2 μm to 15 μm and a D90 of less than 40 μm.

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