CN115621533A

CN115621533A - Electrochemical device and electronic device

Info

Publication number: CN115621533A
Application number: CN202211350738.1A
Authority: CN
Inventors: 张丽兰; 张水蓉; 唐超
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2023-01-17
Also published as: CN113097556A; WO2022205661A1; CN113097556B

Abstract

An electrochemical device and an electronic device, the electrochemical device including: the cathode comprises a cathode, an anode, a separation film and electrolyte; an electrolyte comprising a compound of formula I:

wherein, the compound shown in the formula I accounts for A% of the total mass of the electrolyte, and A is 0.3-40; r ₁ 、R ₂ Each independently selected from hydrogen, halogen, alkyl of 1 to 5 carbon atoms substituted by halogen, alkenyl of 1 to 5 carbon atoms or alkenyl of 1 to 5 carbon atoms substituted by halogen; and R is ₁ 、R ₂ At least one of them contains halogen; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collectorThe tensile strength is BMPa, and B/A is more than or equal to 2 and less than or equal to 750. The electrochemical device can improve the cycle performance and the over-discharge storage performance of the electrochemical device, and can keep better safety performance after long-time circulation.

Description

Electrochemical device and electronic device

The present application is a divisional application of an invention patent with an application number of 202110340358.9 entitled "electrochemical device and electronic device" filed on 30/03/2021.

Technical Field

The present application relates to the field of electrochemical technologies, and in particular, to an electrochemical device and an electronic device.

Background

Electrochemical devices (e.g., lithium ion batteries) are widely used in electronic devices in various fields, and with the development of electronic devices, higher requirements are being placed on the energy density of electrochemical devices.

On the other hand, the safety problem of the use of various electronic products is endless, and not only the service life of the electrochemical device needs to be considered, but also the use safety of the electrochemical device needs to be concerned, so how to ensure the cycle performance of the electrochemical device and improve the safety of the electrochemical device becomes a problem to be solved urgently.

Disclosure of Invention

The application provides an electrochemical device and an electronic device, which can reduce the corrosion of electrolyte to a positive current collector and ensure the safety performance of the electrochemical device while improving the cycle performance and the over-discharge storage performance of the electrochemical device.

In some embodiments, the present application provides an electrochemical device comprising: the anode, the cathode, the isolating film and the electrolyte; an electrolyte comprising a compound of formula I:

wherein, the compound shown in the formula I accounts for A% of the total mass of the electrolyte, and A is 0.3-40; r ₁ 、R ₂ Each independently selected from hydrogen, halogen, carbon atomAn alkyl group having a number of 1 to 5, an alkyl group having 1 to 5 carbon atoms substituted with halogen, an alkenyl group having 1 to 5 carbon atoms or an alkenyl group having 1 to 5 carbon atoms substituted with halogen, an alkynyl group having 1 to 5 carbon atoms or an alkynyl group having 1 to 5 carbon atoms substituted with halogen; and R is ₁ 、R ₂ At least one of them contains halogen; the positive electrode comprises a positive electrode current collector and a positive electrode active substance layer arranged on at least one surface of the positive electrode current collector, the tensile strength of the positive electrode current collector is B MPa, and B/A is more than or equal to 2 and less than or equal to 750.

In some embodiments of the present application, compounds of formula I include: at least one of fluoroethylene carbonate, difluoroethylene carbonate, methyl fluoroethylene carbonate or 4-fluoro-5-methyl ethylene carbonate.

In some embodiments of the present application, at least one of the following conditions (a) to (d) is satisfied:

(a) The electrolyte also comprises: a dinitrile compound;

(b) The electrolyte also comprises: a polynitrile compound having 3 or more cyano groups;

(c) The electrolyte also comprises: a compound containing an S = O double bond;

(d) The electrolyte also comprises: an oxygen-containing heterocyclic compound.

In some embodiments of the application, the dinitrile compound accounts for C% of the total mass of the electrolyte, the polynitrile compound accounts for D% of the total mass of the electrolyte, and D/C is more than or equal to 0.5 and less than or equal to 20;

in some embodiments of the application, the dinitrile compound accounts for C% of the total mass of the electrolyte, and C is more than or equal to 0.5 and less than or equal to 7.

In some embodiments of the application, the polynitrile compound accounts for D% of the total mass of the electrolyte, and D is more than or equal to 0.1 and less than or equal to 4.

In some embodiments of the present application, the compound of formula i satisfies with the polynitrile compound: 0.02-130A/D.

In some embodiments of the present application, dinitrile compounds include: at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonadinitrile, sebaconitrile, ethylene glycol (dipropionitrile) ether (nitrile ether) or fumaronitrile;

in some embodiments of the present application, the polynitrile compounds comprise: 1,3, 6-hexanetricarbonitrile, 1,2, 6-hexanetricarbonitrile, 1,3, 5-pentaenetrinitrile, nonanetricarbonitrile, 1,3, 5-benzenetrinitrile, 2,4, 6-trifluorobenzene-1, 3, 5-trinitrile, 1,3, 5-cyclohexanetricarbonitrile, 1,2, 3-propanetricitrile, 1,3, 5-benzenetricyano group, or 1,2, 3-tris (2-cyanato) propane.

In some embodiments of the present application, compounds containing S = O double bonds include: at least one of 1, 3-propane sultone, 2, 4-butane sultone, 1, 4-butane sultone, methylene methanedisulfonate, vinyl sulfate, sulfolane, propylene sulfate, 4-methyl ethylene sulfate, or 5-methyl oxathiolane 2, 2-dioxide.

In some embodiments of the present application, the compound having an S = O double bond is 0.1% to 7% of the total mass of the electrolyte.

In some embodiments of the present application, the oxygen-containing heterocyclic compound comprises: 1, 3-dioxane, dioxolane, 4-methyl-1, 3-dioxane, tetrahydropyran, tetrahydrofuran, or 1, 2-epoxybutane.

In some embodiments, the oxygen-containing heterocyclic compound is present in an amount of 0.01% to 3% by weight of the total electrolyte.

In some embodiments of the present application, the tensile strength of the positive current collector is B MPa, satisfying B >100.

In some embodiments of the present application, the positive electrode current collector satisfies at least one of conditions (e) to (j):

(e) The positive current collector contains aluminum;

(f) The thickness of the positive current collector is 5-20 μm;

(g) The positive current collector contains M element, wherein the M element comprises at least one of silicon, copper, manganese, iron, zinc, magnesium, titanium and vanadium, and the percentage of the M element in the total weight of the positive current collector is not more than 2%;

(h) The unit area weight of the positive current collector is 15g/m ² To 100g/m ² ；

(i) The elongation of the positive current collector is more than or equal to 1 percent;

(j) The positive current collector is provided with a welding area, and the area of the welding area is F cm ² ，1≤F≤50。

In some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a negative electrode material, the negative electrode material includes a silicon-based material, and at least a part of a surface of particles of the silicon-based material has a protective layer thereon.

In some embodiments of the present application, the protective layer comprises: carbon materials or Me _x O _y Wherein Me comprises at least one of Al, si, mn, V, cr, co or Zr, x is 1-2, and y is 1-3.

In some embodiments, an electronic device is provided that includes any of the electrochemical devices described above.

The electrochemical device provided by the embodiment of the application comprises the compound shown in the formula I, the compound shown in the formula I can continuously repair a negative electrode SEI (solid electrolyte interphase) film in the over-discharge storage process of the electrochemical device, a negative electrode interface is effectively improved, over-discharge storage flatulence is reduced, the cycle performance is improved, and the ratio of the tensile strength of a positive electrode current collector to the content of the compound shown in the formula I is controlled within a certain range. The electrochemical device can ensure the cycle performance and the over-discharge storage performance of the electrochemical device and can also improve the safety performance of the electrochemical device.

Drawings

The above and other features, advantages, and aspects of embodiments of the present disclosure will become more apparent by referring to the following detailed description when taken in conjunction with the accompanying drawings. Throughout the drawings, the same or similar reference numbers refer to the same or similar elements. It should be understood that the drawings are schematic and that elements and components are not necessarily drawn to scale.

Fig. 1 is a schematic view of the connection of a positive electrode and a tab of an embodiment of the present disclosure.

Detailed Description

Embodiments of the present application will be described in more detail below. This application may be embodied in various forms and should not be construed as limited to the embodiments set forth herein, but rather these embodiments are provided for a more complete and thorough understanding of the application.

In the related art, a fluorine-containing additive, such as FEC, is added to an electrolyte solution to improve the cycle performance of a negative system electrochemical device, however, FEC can react with lithium hexafluorophosphate to generate a corrosive component to corrode a positive current collector, such as aluminum foil, resulting in a reduction in the safety performance of the electrochemical device, such as drop performance and impact performance.

In order to at least partially solve the above problems, some embodiments of the present application provide an electrochemical device including: the anode, the cathode, the isolating film and the electrolyte; an electrolyte comprising a compound of formula I:

wherein, the compound shown in the formula I accounts for A% of the total mass of the electrolyte, and A is 0.3-40; r is ₁ 、R ₂ Each independently selected from hydrogen, halogen, alkyl of 1 to 5 carbon atoms substituted by halogen, alkenyl of 1 to 5 carbon atoms or alkenyl of 1 to 5 carbon atoms substituted by halogen, alkynyl of 1 to 5 carbon atoms or alkynyl of 1 to 5 carbon atoms substituted by halogen; and R is ₁ 、R ₂ At least one of them contains halogen; the positive electrode comprises a positive electrode current collector and a positive electrode active substance layer arranged on at least one surface of the positive electrode current collector, the tensile strength of the positive electrode current collector is B MPa, and B/A is more than or equal to 2 and less than or equal to 750. In some embodiments, the anode includes an anode current collector and an anode active material layer disposed on at least one surface of the anode current collector.

In some embodiments of the present application, on one hand, by adding the compound represented by formula I to the electrolyte, the SEI film of the negative electrode can be continuously repaired during the over-storage of the electrochemical device, the interface of the negative electrode is effectively improved, the over-storage flatulence is reduced, and the cycle performance is improved. On the other hand, in order to solve the problem that the safety performance of the product of the reaction of the compound shown in the formula I and water to the anode current collector is reduced, the ratio of the tensile strength of the anode current collector to the content of the compound shown in the formula I is controlled, the anode current collector can keep certain tensile strength, and the falling performance and the impact performance of the electrochemical device after circulation are improved. Therefore, the electrochemical device provided by the application can reduce the corrosion of the electrolyte to the positive current collector while ensuring the cycle performance and the over-discharge storage performance of the electrochemical device, so that the positive current collector can keep certain tensile strength at a high temperature for a long time, and the safety performance of the electrochemical device is improved.

In some embodiments of the present application, compounds of formula I include: at least one of fluoroethylene carbonate, difluoroethylene carbonate, methylfluoroethylene carbonate or 4-fluoro-5-methylethylene carbonate. In some embodiments of the present application, the compound of formula I is present in an amount of 0.1% to 40%. In some embodiments of the present application, the compound of formula I is present in an amount of 1% to 20%. In some embodiments of the present application, the compound of formula I is present in an amount of 4% to 20%. The above compound is capable of preferentially forming a stable SEI film with the anode active material layer, thereby protecting the anode active material layer.

In some embodiments of the present application, the electrolyte further comprises: a dinitrile compound.

In some embodiments of the present application, the electrolyte further comprises: a polynitrile compound having 3 or more cyano groups.

In some embodiments, the cyano bond has high energy and is not easily oxidized, the nitrile compound has good stability and strong oxidation resistance on the positive electrode, and meanwhile, the cyano group has strong coordination capacity and can be combined with active sites on the surface of the positive electrode active material layer, so that the decomposition effect of the positive electrode active material layer on the electrolyte is reduced, the resistance of the electrolyte to the oxidation of the positive electrode active material layer is enhanced, and the cycle life of the electrolyte under high voltage is prolonged. The polynitrile compound having more cyano groups can improve the cycle performance of the electrochemical device, but may cause a storage voltage drop of the electrochemical device, and the use of a certain dinitrile compound can suppress the influence on the voltage drop.

In some embodiments of the present application, the electrolyte further comprises: a compound containing an S = O double bond. In some embodiments, the compound having an S = O double bond can form a relatively stable protective layer on the positive electrode active material layer and the negative electrode active material layer, thereby improving cycle performance and storage performance of the electrochemical device.

In some embodiments of the present application, the electrolyte further comprises: an oxygen-containing heterocyclic compound. In some embodiments, the oxygen-containing heterocyclic compound can form a relatively stable protective layer on the positive and negative electrode active material layers, thereby improving cycle performance and storage performance of the electrochemical device.

In some embodiments of the present application, the dinitrile compound accounts for C% of the total mass of the electrolyte, the polynitrile compound accounts for D% of the total mass of the electrolyte, and D/C is not less than 0.5 and not more than 20. In some embodiments, when the value of D/C is greater than 20, the storage pressure drop of the electrochemical device is large, and when the value of D/C is less than 0.5, the cycle performance of the electrochemical device is deteriorated, which is probably because when the value of D/C is greater than 20, the amount of the trinitrile compound is high, the trinitrile compound affects the storage pressure drop of the electrochemical device although the electrical performance is significantly improved, so when a certain amount of the trinitrile compound is added, a part of the dinitrile compound needs to be added to suppress the influence of the trinitrile compound on the storage pressure drop, while the addition of the dinitrile compound also significantly improves the cycle performance, and when the ratio of D/C is less than 0.5, the improvement of the cycle is not significantly improved by a low amount of the trinitrile, and thus, in some embodiments, the control of D/C is 0.5 ≦ D/C ≦ 20.

In some embodiments of the present application, the compound of formula i satisfies the following conditions with a polynitrile compound: 0.02-130A/D. In some embodiments of the present application, the compound of formula I satisfies the following conditions: A/D is more than or equal to 0.1 and less than or equal to 130. In some embodiments of the present application, the compound of formula I satisfies the following conditions: A/D is more than or equal to 1 and less than or equal to 130. In some embodiments of the present application, the compound of formula I satisfies the following conditions: A/D is more than or equal to 5 and less than or equal to 130. In some embodiments, when the a/D is less than 0.02, the electrochemical device has poor cycle performance and overdischarge storage performance, and when the a/D is greater than 130, the electrochemical device has poor cycle performance. In some embodiments, the cycling performance of the electrochemical device is more excellent when 0.1. Ltoreq. A/D. Ltoreq.130.

In some embodiments of the present application, dinitrile compounds include: at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonadinitrile, sebaconitrile, ethylene glycol (dipropionitrile) ether (nitrile ether) or fumaronitrile.

In some embodiments of the present application, the polynitrile compounds comprise: 1,3, 6-hexanetricarbonitrile, 1,2, 6-hexanetricarbonitrile, 1,3, 5-pentanedicarbonitrile, nonanetricarbonitrile, 1,3, 5-benzenetrinitrile, 2,4, 6-trifluorobenzene-1, 3, 5-trinitrile, 1,3, 5-cyclohexanetricarbonitrile, 1,2, 3-propanetricitrile, 1,3, 5-benzenetricyano group, or 1,2, 3-tris (2-cyanato) propane.

In some embodiments of the present application, compounds containing S = O double bonds include: at least one of 1, 3-propane sultone, 2, 4-butane sultone, 1, 4-butane sultone, methylene methanedisulfonate, vinyl sulfate, sulfolane, propylene sulfate, ethylene 4-methylsulfate or 2, 2-dioxide 5-methyloxathiolane.

In some embodiments of the present application, the compound having an S = O double bond accounts for 0.01% to 3% of the total mass of the electrolyte.

In some embodiments of the present application, when the compound having an S = O double bond includes 1, 3-propane sultone, the 1, 3-propane sultone accounts for 0.1% to 1% of the total mass of the electrolyte.

In some embodiments of the present application, the positive current collector comprises aluminum. In some embodiments, the positive current collector is an aluminum foil, which has a low density and a high strength, and is advantageous for reducing the number of electrochemical devices and ensuring safety performance.

In some embodiments of the present application, the positive electrode current collector has a thickness of 5 to 20 μm. In some embodiments, when the thickness of the positive electrode current collector is less than 5 μm, it may cause the positive electrode current collector to be easily corroded or broken, resulting in a reduction in safety performance, and when the thickness of the positive electrode current collector is greater than 20 μm, it may result in a reduction in energy density of an electrochemical device.

In some embodiments, the positive current collector includes an M element, the M element includes at least one of silicon, copper, manganese, iron, zinc, magnesium, titanium, and vanadium, and the M element accounts for no more than 2% of the total weight of the positive current collector. In some embodiments, when the percentage of the M element in the total weight of the positive electrode current collector is greater than 2%, the strength of the positive electrode current collector may be reduced, and the dropping performance of the electrochemical device may be reduced.

In some embodiments, the positive current collector has a weight per unit area of 15g/m ² -100g/m ² . In some embodiments, too little weight per unit area of the positive electrode current collector may result in insufficient strength of the positive electrode current collector, while too much weight per unit area of the positive electrode current collector may result in an increase in weight of the electrochemical device.

In some embodiments of the present disclosure, the elongation of the positive current collector is greater than or equal to 1%. In some embodiments, when the elongation of the positive electrode current collector is less than 1%, the positive electrode current collector may be easily broken, which may reduce safety performance.

In some embodiments of the present application, the positive current collector has a solder printing region thereon, and the area of the solder printing region is F cm ² F is more than or equal to 1 and less than or equal to 50. In some embodiments, as shown in fig. 1, fig. 1 schematically shows a connection diagram of a positive electrode and a tab, the positive electrode includes a positive electrode current collector 2 and a positive electrode active material layer 1 located on the positive electrode current collector 2, a welding area 4 (an area indicated by a dashed line frame) is located on a blank area of the positive electrode current collector 2, the welding area 4 is an area formed after the tab 3 is welded to the positive electrode current collector 2 and is defined by a welding point, the positive electrode current collector needs to be welded to the tab, when the area of the welding area is too small, the welding point may have insufficient connection strength, and when the area of the welding area is too large, the welding point is more easily corroded by an electrolyte, which causes deterioration of drop performance.

In some embodiments of the present application, the number of solder areas is 2 or greater. When the number of the welding areas is more than or equal to 2, the area of the welding areas is the sum of the areas of all the welding areas.

In some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a negative electrode material, the negative electrode material includes a silicon-based material, and at least a part of a surface of particles of the silicon-based material has a protective layer thereon. The theoretical specific capacity of the silicon-based material reaches 4200mAh/g, which is much higher than that of a carbon material, the specific capacity of the negative electrode material can be improved by adding the silicon-based material into the negative electrode material, but the silicon-based material has larger volume expansion in the charging and discharging processes, so that at least a part of the particle surface of the silicon-based material is provided with a protective layer, the volume expansion of the silicon-based material is reduced, and the volume change of an electrochemical device in the charging and discharging processes is reduced.

In some embodiments of the present application, the protective layer comprises: carbon materials or Me _x O _y Wherein Me comprises at least one of Al, si, mn, V, cr, co or Zr, x is 1 to 2, y is 1 to 3. In some embodiments, the carbon material itself can accommodate lithium ions, and the protective layer including the carbon material can suppress expansion of the silicon-based material on the one hand and can increase the capacity of the anode material on the other hand, and when the protective layer includes Me _x O _y Due to Me _x O _y Is metal oxide, has higher strength and can well inhibit the expansion of silicon-based materials.

In some embodiments, al foil may be used as the positive electrode collector, but other positive electrode collectors commonly used in the art may be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 50 μm. In some embodiments, the positive electrode active material layer may be coated only on a partial region of the positive electrode collector. In some embodiments, the thickness of the positive electrode active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary and that other suitable thicknesses may be employed.

In some embodiments, the barrier film comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some embodiments, the thickness of the separator film is in the range of about 3 μm to 50 μm.

In some embodiments, the surface of the separator may further include a porous layer disposed on at least one surface of the separator, the porous layer including inorganic particles selected from alumina (Al) and a binder ₂ O ₃ ) Silicon oxide (SiO) ₂ ) Magnesium oxide (MgO), titanium oxide (TiO) ₂ ) Hafnium oxide (HfO) ₂ ) Tin oxide (SnO) ₂ ) Cerium oxide (CeO) ₂ ) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO) ₂ ) Yttrium oxide (Y) ₂ O ₃ ) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder of the porous layer is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The porous layer on the surface of the isolating membrane can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the pole piece.

In some embodiments of the present application, the electrochemical device is a wound or stacked type.

In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not so limited. In some embodiments, the electrochemical device may further include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent. The lithium salt is selected from LiPF ₆ 、LiBF ₄ 、LiAsF ⁺ 、LiClO ₄ 、LiB(C ₆ H ₅ ) ₄ 、LiCH ₃ SO ₃ 、LiCF ₃ SO ₃ 、LiN(SO ₂ CF ₃ ) ₂ 、LiC(SO ₂ CF ₃ ) ₃ 、LiSiF ₆ One or more of LiBOB or lithium difluoroborate. For example, liPF is selected as lithium salt ₆ Since it can give high ionic conductivity and improve cycle characteristics.

The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.

The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, or a combination thereof.

Examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethyl Propyl Carbonate (EPC), methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), vinyl Ethylene Carbonate (VEC), or a combination thereof.

Examples of carboxylate compounds are ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, or combinations thereof.

Examples of ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

Examples of other organic solvents are dimethylsulfoxide, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.

Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

To make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below with reference to specific embodiments of the present application, and it is obvious that the described embodiments are some, but not all embodiments of the present application. All other embodiments obtained by those skilled in the art without any creative effort based on the technical solutions and the given embodiments provided in the present application belong to the protection scope of the present application.

Preparing a positive plate: and (2) mixing the positive electrode material lithium cobaltate, polyvinylidene fluoride (PVDF) and Super-P according to a mass ratio of 96:2:2, dissolving in N-methyl pyrrolidone (NMP), and uniformly mixing to prepare the anode slurry. Uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil with the thickness of 12 mu m, baking for 1h at 120 ℃, and then compacting, slitting and welding lugs to obtain a positive plate;

preparing a negative plate: mixing a negative electrode material, sodium carboxymethylcellulose (CMC) and styrene butadiene rubber according to a mass ratio of 85:2: dissolving the mixture 13 in water, fully mixing and stirring to obtain negative electrode slurry, uniformly coating the negative electrode slurry on a negative electrode current collector copper foil with the thickness of 12 mu m, baking at 120 ℃ for 1h to obtain a negative electrode active material layer, and then compacting, slitting and welding a tab to obtain a negative electrode sheet;

preparing a lithium ion battery: a polypropylene film of 12 μm was used as a separator. The positive plate, the isolating membrane and the negative plate are sequentially stacked, so that the isolating membrane is positioned between the positive and negative electrodes to play an isolating role, and then the anode plate, the isolating membrane and the negative plate are wound into a bare cell. Filling the naked battery cell into an aluminum foil packaging bag, baking at 80 ℃ to remove water, preparing a dry battery cell, injecting corresponding electrolyte, and completing the preparation of the lithium ion battery through the procedures of vacuum packaging, standing, formation, shaping and the like;

preparing an electrolyte: ethylene carbonate, propylene carbonate and diethyl carbonate are mixed according to the mass ratio of 3:1:6, mixing, and then adding other additives and lithium salts with different contents on the basis of the electrolyte to obtain the electrolyte used in each embodiment;

the high-temperature cycle performance and safety performance of the lithium ion batteries prepared in the respective examples and comparative examples were tested as follows:

and (3) testing cycle performance: charging the battery to 4.45V at the constant current of 1C at the temperature of 45 ℃, standing for 30min, discharging to 3.0V at 1C, circularly charging and discharging for 500 times, and recording the Chinese discharge capacity in the circulating process;

cycle capacity retention (%) =500 discharge capacities/first discharge capacities × 100%.

And (4) over-discharge storage test: the battery was placed in a 25 ℃ incubator, discharged to 2.0V at a constant current of 0.5C, and the thickness of the battery was measured, and then the battery was stored in a 60 ℃ high temperature furnace for 15 days, and the thickness of the battery after storage was measured.

Over-storage thickness growth rate (%) = (thickness of battery after storage-thickness of battery before storage)/thickness of battery before storage × 100%.

60 ℃ storage pressure drop test: and (3) putting the battery into a constant temperature box of 25 ℃, charging the battery to 4.45V at a constant current of 0.5C, then charging the battery at a constant voltage until the current is 0.05C, putting the battery into a high temperature box of 60 ℃ for storage for 30 days, and recording the voltage value of the stored lithium ion battery.

60 ℃ storage voltage drop = 4.45V-voltage value of lithium ion battery after storage.

And (3) drop performance testing: placing the batteries subjected to high-temperature circulation at 45 ℃ into a constant temperature box at 25 ℃, charging to 4.45V at a constant current of 0.5C, then charging at a constant voltage until the current is 0.05C, placing the batteries in an environment at 25 ℃ for drop test, dropping the batteries from a height of 1 meter onto a concrete floor, repeating the process for 3 times for 1 battery, ensuring that each random direction is impacted when dropping, judging to be invalid if leakage, ignition or explosion exists, and testing 20 batteries in each group;

drop passage (%) = number of failed battery pieces/20 × 100%.

The positive current collector was tested as follows:

and (3) testing the thickness of the aluminum foil: the average was taken after measuring 5 points using a micrometer.

Mass per unit area: the aluminum foil was cut into pieces of 100mm × 100mm, weighed, the mass per unit area was calculated, 5 samples were taken, and the average value was calculated, the mass per unit area = weight/area.

And (3) testing tensile strength: and (3) testing by using a tensile testing machine, wherein the length of a test sample is 200 +/-0.5 mm, the width is 15 +/-0.25 mm, the tensile speed of 50mm/min is set, the distance of a chuck of the testing machine is 125 +/-0.1 mm, the test is stopped when the sample is stretched to break, and the value of the tensile strength is read. 5 parallel samples are tested, the average value is taken as a test result, the length direction of the sample is parallel to the axis of the clamp during testing, the sample is kept linear, and the experimental temperature is 20 +/-5 ℃.

And (3) elongation testing: testing by using a tensile testing machine, wherein the length of a test sample is 200 +/-0.5 mm, the width is 15 +/-0.25 mm, the tensile speed of 50mm/min is set, the distance of a clamping head of the testing machine is 125 +/-0.1 mm, the test is stopped when the sample is stretched to be broken, the tensile length is recorded, 5 parallel samples are tested, the average value is a test result, the length direction of the sample is parallel to the axial line of the clamping head during the test, the sample is kept linear, and the test temperature is 20 +/-5 ℃; elongation = stretch length/sample length.

The electrical property test data is as follows:

table 1 shows electrolytes and performance test results used in comparative examples 1 to 3 and examples 1 to 13, and the positive electrode material used in comparative examples 1 to 3 and examples 1 to 13 shown in table 1 is lithium cobaltate, the negative electrode material is a mixture of a silicon-based material and graphite, and the silicon-based material is silicon oxide and the mass ratio of the silicon-based material to the graphite is 1; the thickness of the aluminum foil is 10 mu m, the elongation is more than or equal to 1 percent, and the weight per unit area is 67g/m ² The percentage of Cu element in the total weight of the positive current collector is 0.1%, and the area F of the welding area is 1.2cm ² The content of the compound shown as the formula I is APercent, the tensile strength of the positive current collector is 80MPa, and the fluorine-containing lithium salt in the electrolyte is lithium hexafluorophosphate with the content of 12.5 percent.

TABLE 1

As can be seen from comparative example 1 and examples 1 to 13 in table 1, when the compound of formula I is added to the electrolyte, the cycle capacity retention rate of the lithium ion battery is increased, the increase rate of the over-discharge storage thickness is reduced, and the drop-through rate is increased, that is, the cycle performance and the storage performance of the lithium ion battery are significantly improved. The reason is that the compounds shown in the formula I in examples 1 to 13 contain F elements and carbonate groups, which can continuously form a LiF protective layer on the negative electrode in the cycle process to improve the stability of the negative electrode interface, and thus can significantly improve the cycle performance of the lithium ion battery, and at the same time, when the lithium ion battery is in an overdischarge state, the negative electrode potential is increased and the instability is enhanced, and since the compounds shown in the formula I can effectively repair the negative electrode, the gas generation during the overdischarge storage process can be significantly reduced, and the safety performance of the lithium ion battery is improved.

It can be seen from comparative example 2 that when the content of the compound of formula I is less than 0.3 and the B/a value is larger, the increase rate of the over-discharge storage thickness of the lithium ion battery is still larger, and the storage performance is not good, which may be because the improvement effect is not obvious due to too small content of the compound of formula I, and as can be seen from examples 1 to 6 and comparative example 3, as the content of the compound of formula I is increased, the cycle performance and the storage performance of the lithium ion battery are improved remarkably, but the drop pass rate may be reduced, starting from the initial 100% pass rate, as shown in comparative example 3, when the content of the compound of formula I reaches 41%, the drop pass rate is only 70%, which is because the compound of formula I in the lithium ion battery is defluorinated to generate a large amount of HF at high temperature, the aluminum foil is not corroded on the surface layer of the aluminum foil, and the drop pass rate is finally reduced to 70%, which seriously affects the safety of the lithium ion battery in the use process, and therefore, a is controlled to be 0.3 to 40,2B/a 750 in some examples.

It can be seen from examples 7 to 13 that the cycle performance of the lithium ion battery can be ensured and the safety performance of the lithium ion battery can be improved by using the compound satisfying the structural formula shown in formula I alone or by using different compounds satisfying the structural formula shown in formula I in combination.

Table 2 shows the electrolytes used in examples 14 to 25 and the performance test results, where the positive electrode material used in each example in table 2 is lithium cobaltate, the negative electrode material is a mixture of a silicon-based material and graphite, the surface of the silicon-based material is coated with a carbon layer, the silicon-based material is silicon oxide, the mass ratio of the silicon-based material to the graphite is 1 ² The percentage of Cu element in the total weight of the positive current collector is 0.1%, and the area F of the welding area is 1.2cm ² The content of the compound shown in the formula I is A%, the tensile strength of the positive current collector is B MPa, the mass content of the dinitrile compound in the electrolyte is 1%, and the mass content of the polynitrile compound in the electrolyte is 2%; the fluorine-containing lithium salt is lithium hexafluorophosphate, and the content is 12.5%.

TABLE 2

It can be seen by comparing examples 14 to 20 shown in table 2 that the cycle performance, storage performance and drop performance of the lithium ion battery are superior when the value of B/a is in the range shown in examples 16 to 25 as the tensile strength of the aluminum foil increases.

In order to ensure the electrical performance and the safety performance of the lithium ion battery at the same time, the value of B/A needs to be controlled within a certain proportion range, so that B/A is controlled to be more than or equal to 2 and less than or equal to 750 in some embodiments of the application.

Table 3 shows the practiceExample 26-the electrolyte and the performance test results used in example 38, the positive electrode material used in table 3 is lithium cobaltate, the negative electrode material is a mixture of a silicon-based material and graphite, the surface of the silicon-based material is coated with a carbon layer, the silicon-based material is silicon oxide, the mass ratio of the silicon-based material to the graphite is 1 ² The percentage of Cu element in the total weight of the positive current collector<1%, the area F of the solder printing region is 1.2cm ² The fluorine-containing lithium salt is lithium hexafluorophosphate, and the content of the fluorine-containing lithium salt is 12.5 percent.

TABLE 3

As can be seen from examples 35 to 38 in table 3, the 60 ℃ storage voltage drop of the lithium ion battery is large when only a trinitrile compound is included in the electrolyte. As can be seen from examples 26 to 34 in table 3, when both a dinitrile compound and a trinitrile compound are included in the electrolyte, the 60 ℃ storage voltage drop of the lithium ion battery can be reduced.

It can be seen from comparison of examples 26 to 34 that the 60 ℃ storage voltage drop of the lithium ion battery is large when the value of D/C is greater than 20, and the cycle performance of the lithium ion battery is poor when the value of D/C is less than 0.5, probably because the storage voltage drop is easily increased although the electrical properties are significantly improved by the trinitrile compound, and thus the 60 ℃ storage voltage drop is large when the value of D/C is greater than 20; in order to suppress the influence of the trinitrile compound on the storage pressure drop, the dinitrile compound is added, and when the D/C ratio is less than 0.5, the improvement of the cycle performance by the excessively low content of the trinitrile compound is insignificant, resulting in the reduction of the cycle performance. Therefore, 0.5D/C20 is defined in some embodiments to reduce the storage pressure drop while ensuring cycle performance.

Table 4 shows the electrolyte used in examples 39 to 50 and the performance test results, in table 4, the positive electrode material is lithium cobaltate, the negative electrode material is a mixture of a silicon-based material and graphite, the surface of the silicon-based material is coated with a carbon layer, the silicon-based material is silicon oxide, the mass ratio of the silicon-based material to the graphite is 1 ² Content of M element<1%, the area F of the solder printing region is 1.2cm ² The content of the compound represented by formula I is a%, the tensile strength of the positive electrode current collector is 100MPa, the compound represented by formula I contained in the electrolyte in the examples shown in table 4 is fluoroethylene carbonate, the content is 5%, the dinitrile compounds contained in the electrolyte are succinonitrile and adiponitrile, the mass content is 1% and 0.5%, the dinitrile compound contained in the electrolyte is 1,3, 6-hexanetrinitrile, the mass content is 2%, and the fluorine-containing lithium salt is lithium hexafluorophosphate, the content is 12.5%.

TABLE 4

It can be seen from examples 39 to 44 that, when the compound containing S = O double bond or the oxygen-containing heterocyclic compound is added to the electrolyte, the retention rate of the cycle capacity of the lithium ion battery is high, the increase rate of the overdischarge storage thickness is low, and the storage voltage drop at 60 ℃ is small, that is, when the compound containing S = O double bond or the oxygen-containing heterocyclic compound is added to the electrolyte, the electrical property of the lithium ion battery can be improved, which is probably because the compound containing S = O double bond or the oxygen-containing heterocyclic compound can form a stable SEI film on the positive and negative electrodes, so that the protection of the positive and negative electrodes is improved, and the electrical property of the lithium ion battery is finally improved. As can be seen from examples 45 to 50, when the electrolyte has both the compound having an S = O double bond and the oxygen-containing heterocyclic compound, the cycle capacity retention of the lithium ion battery is higher, the overdischarge storage thickness growth rate is lower, and the 60 ℃ storage voltage drop is smaller.

Table 5 shows the electrolytes used in examples 51 to 58 and the performance test results, the positive electrode material used in table 5 is lithium cobaltate, the negative electrode is a mixture of silicon-based material and graphite, the silicon-based material is silicon oxide, the mass ratio of the silicon-based material to the graphite is 2, the thickness of the aluminum foil is 10 μm, the elongation is not less than 1%, and the unit area weight is 67g/m ² The positive electrode current collector had a tensile strength of 160MPa, the compound represented by formula I contained in the electrolyte in each example in table 5 was fluoroethylene carbonate and the mass content was 5%, the dinitrile compounds contained in the electrolyte were succinonitrile and adiponitrile and the mass contents were 1% and 0.5%, respectively, the dinitrile contained in the electrolyte was 1,3, 6-hexanetricarbonitrile and the mass content was 2%, the fluorine-containing lithium salt was lithium hexafluorophosphate and the content was 12.5%, and M was Cu element.

TABLE 5

It can be seen from comparing examples 51 to 53 that when the content of the M element in the aluminum foil is >2% by mass, the drop passage rate of the lithium ion battery is reduced, which is probably because when the content of the M element is >2%, the strength of the aluminum foil is reduced, and finally the drop performance is deteriorated.

It can be seen from comparing example 54 to example 58 that the drop through rate of the lithium ion battery is significantly reduced when the area of the solder area is gradually increased, which may be because the solder joints are more easily corroded by the electrolyte, deteriorating the drop performance.

As can be seen from comparison between examples 51 and 57, when a silicon material without a coating layer is used as the negative electrode material, the cycle capacity retention rate of the lithium ion battery is significantly reduced, and the increase rate of the overdischarge storage thickness is significantly increased, and thus, it can be seen that the electrical performance of the lithium ion battery using the silicon material as the negative electrode can be significantly improved by using the silicon material with a coating layer.

The foregoing description is only exemplary of the preferred embodiments of the application and is illustrative of the principles of the technology employed. It will be appreciated by a person skilled in the art that the scope of the disclosure as referred to in the present application is not limited to the embodiments with specific combinations of the above-mentioned features, but also covers other embodiments with any combination of the above-mentioned features or their equivalents. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.

Claims

1. An electrochemical device, comprising:

the anode, the cathode, the isolating film and the electrolyte;

the electrolyte comprises a compound represented by formula I:

wherein the compound shown in the formula I accounts for A% of the total mass of the electrolyte, and A is 0.3-40; r is ₁ 、R ₂ Each independently selected from hydrogen, halogen, alkyl of 1 to 5 carbon atoms substituted with halogen, alkenyl of 1 to 5 carbon atoms substituted with halogen, alkynyl of 1 to 5 carbon atoms or alkynyl of 1 to 5 carbon atoms substituted with halogen; and R is ₁ 、R ₂ At least one of which contains halogen;

the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the tensile strength of the positive electrode current collector is B MPa, and B/A is more than or equal to 2 and less than or equal to 750;

the electrochemical device satisfies at least one of the following conditions (a) to (d):

(a) The electrolyte also comprises: a dinitrile compound;

(c) The electrolyte also comprises: a compound containing an S = O double bond;

(d) The electrolyte also comprises: an oxygen-containing heterocyclic compound.

2. The electrochemical device of claim 1, wherein said compound of formula I comprises: at least one of fluoroethylene carbonate, difluoroethylene carbonate, methyl fluoroethylene carbonate or 4-fluoro-5-methyl ethylene carbonate.

3. The electrochemical device according to claim 1, wherein the electrochemical device,

the dinitrile compound accounts for C% of the total mass of the electrolyte, the polynitrile compound accounts for D% of the total mass of the electrolyte, and D/C is more than or equal to 0.5 and less than or equal to 20;

and/or, the compound represented by the formula I and the polynitrile compound satisfy: 0.02-130A/D.

4. The electrochemical device according to claim 1,

the dinitrile compound includes: at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonadinitrile, sebaconitrile, ethylene glycol (dipropionitrile) ether (nitrile ether) or fumaronitrile;

and/or the presence of a gas in the gas,

the polynitrile compound includes: 1,3, 6-hexanetricarbonitrile, 1,2, 6-hexanetricarbonitrile, 1,3, 5-pentaenetrinitrile, nonanetricarbonitrile, 1,3, 5-benzenetrinitrile, 2,4, 6-trifluorobenzene-1, 3, 5-trinitrile, 1,3, 5-cyclohexanetricarbonitrile, 1,2, 3-propanetricitrile, 1,3, 5-benzenetricyano group, or 1,2, 3-tris (2-cyanato) propane.

5. The electrochemical device according to claim 1,

the S = O double bond containing compound includes: at least one of 1, 3-propane sultone, 2, 4-butane sultone, 1, 4-butane sultone, methylene methanedisulfonate, vinyl sulfate, sulfolane, propylene sulfate, ethylene 4-methylsulfate, or 2, 2-dioxide 5-methyloxathiolane;

and/or the presence of a gas in the gas,

the oxygen-containing heterocyclic compound includes: at least one of 1, 3-dioxane, dioxolane, 4-methyl-1, 3-dioxane, tetrahydropyran, tetrahydrofuran, or 1, 2-epoxybutane.

6. The electrochemical device according to claim 1, wherein the positive electrode current collector satisfies at least one of conditions (e) to (j):

(e) The positive current collector comprises aluminum;

(f) The thickness of the positive current collector is 5-20 μm;

(g) The positive current collector comprises an M element, the M element comprises at least one of silicon, copper, manganese, iron, zinc, magnesium, titanium and vanadium, and the M element accounts for not more than 2% of the total weight of the positive current collector;

(i) The elongation of the positive current collector is more than or equal to 1%;

7. The electrochemical device according to claim 1, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a negative electrode material, the negative electrode material includes a silicon-based material, and at least a part of a surface of the particle of the silicon-based material has a protective layer thereon.

8. The electrochemical device of claim 7, wherein the protective layer comprises: carbon materials or Me _x O _y Wherein Me comprises at least one of Al, si, mn, V, cr, co or Zr, x is 1 to 2, y is 1 to 3.

9. An electronic device comprising the electrochemical device according to any one of claims 1 to 8.