CN113437366A

CN113437366A - Electrolyte and electrochemical device

Info

Publication number: CN113437366A
Application number: CN202110727536.3A
Authority: CN
Inventors: 张丽兰; 唐超; 郑建明
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-03-03
Filing date: 2020-03-03
Publication date: 2021-09-24
Anticipated expiration: 2040-03-03
Also published as: CN111342129B; CN111342129A; CN113437366B

Abstract

The present application relates to an electrolyte and an electrochemical device. In particular, the present application provides an electrolyte containing a nitrile compound and a lithium ion battery comprising the same, which can reduce self-discharge of an electrochemical device and improve long-term storage performance of the electrochemical device while improving cycle stability of the electrochemical device, when the product of the mass ratio of the nitrile compound to the electrolyte and the ratio of the area of a region not containing a negative active material on a negative current collector to the surface area of the current collector is limited to a certain range.

Description

Electrolyte and electrochemical device

The present application is a divisional application of the invention patent application having application number 202010140217.8, 3/2020, entitled "one electrolyte and electrochemical device".

Technical Field

The application relates to the technical field of energy storage, in particular to electrolyte and an electrochemical device comprising the electrolyte.

Background

Electrochemical devices represented by lithium ion batteries have the advantages of high energy density, high working voltage, low self-discharge rate, long cycle life, no pollution and the like, and are widely applied to the fields of computers, intelligent wearable equipment, smart phones, unmanned aerial vehicles, electric automobiles and the like. With the development of modern information technology and the expansion of the application range of lithium ion batteries, the energy density of the lithium ion batteries in the field has higher requirements.

There are many factors that affect the energy density of lithium ion batteries. At present, increasing the charge cut-off voltage of a lithium ion battery is one of effective means for increasing the energy density, but the increase of the voltage causes the stability of the positive electrode to be poor, and how to solve the above problems to increase the energy density of the lithium ion battery becomes a problem to be solved in the field.

Disclosure of Invention

The inventor researches and discovers that although the nitrile additive can effectively improve the stability of the positive electrode and obviously improve the cycle performance and the like of an electrochemical device, the nitrile additive can cause copper in a negative electrode current collector to be dissolved out so as to influence the stability of a negative electrode, and particularly, the nitrile additive is easy to cause self-discharge of a battery and even cause safety problems when copper ions are dissolved out at a tab welding position.

The invention provides an electrochemical device which can solve the self-discharge problem of the electrochemical device under high voltage under the condition of meeting the high-voltage cycling stability and is beneficial to improving the safety characteristic.

In some embodiments, the present disclosure provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the electrolyte comprises a nitrile compound, the mass fraction of the nitrile compound in the electrolyte is A%,

the anode includes a current collector comprising: a first region and a second region;

the first region is provided with a negative electrode active material layer;

the second region does not contain a negative electrode active material layer;

the area of the second region accounts for B% of the surface area of the current collector; and is

A×B＜600。

In some embodiments, the nitrile compound comprises at least one of a compound of formula i, a compound of formula ii, a compound of formula iii, a compound of formula iv, a compound of formula v, or a compound of formula vi:

and

wherein a, d, f, j, k, l, m, r, u, w and y are each independently an integer selected from 1 to 5, b, c, e, g, h, i, n, o, p, q, s, t, v, x are each independently an integer selected from 0 to 5; the nitrile compound accounts for 0.1-10% of the electrolyte by mass percentage A%.

In some embodiments, the nitrile compound comprises at least one of the following:

in some embodiments, the negative electrode has a tab formed by welding to the second region, and AxB < 210.

In some embodiments, the negative electrode has tabs, the number of tabs being not less than 1, the tabs being formed by cutting the current collector, the tabs including regions of uncoated negative active material layer, and AxB < 500.

In some embodiments, at least one second region is located at the edge of the current collector, wherein the distance between the electrode tab closest to the edge of the current collector and the edge of the current collector is C, and 0 & ltoreq C/electrode tab width & ltoreq 50.

In some embodiments, at least one second region is located at the edge of the current collector, and the edge of the second region located at the edge of the current collector is folded or not folded; when the electrode tab is folded back, the width of the folded back area is D, and D is more than or equal to 0.1/the width of the electrode tab is less than or equal to 20.

In some embodiments, the current collector is a copper foil having one or more properties selected from the group consisting of:

the purity of copper is more than or equal to 99.5 percent,

-a thickness of 3 to 15 microns,

a weight per unit area of 30g/m²To 150g/m²，

-tensile strength of more than or equal to 20kg/mm²And are and

the elongation is more than or equal to 1.5 percent.

In some embodiments, the second zone is optionally covered by a substance capable of adhering to the second zone.

In some embodiments, the location of the tab is optionally covered by a substance capable of bonding thereto.

In some embodiments, the electrolyte further comprises an additive comprising at least one of 1, 3-propane sultone, fluoroethylene carbonate, vinylene carbonate, 2, 4-butane sultone, 1, 4-butane sultone, methylene methanedisulfonate, vinyl sulfate, succinic anhydride, ethoxypentafluorocyclotriphosphazene, 1, 3-dioxane, or propenyl-1, 3-sultone.

In some embodiments, wherein the electrolyte further comprises an anion comprising Cl^-、Br^-、SO₄ ^2-、CO₃ ^2-Or F^-The content of the anion in the electrolyte is less than or equal to1000ppm。

Another aspect of the invention provides an electronic device comprising an electrochemical device as described above.

Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application.

Drawings

Fig. 1 is a top view of a negative current collector in one embodiment of the present application.

Fig. 2 is a side view of the current collector shown in fig. 1 along the Z-direction.

Fig. 3 is a top view of a negative electrode current collector in yet another embodiment of the present application.

Fig. 4 is a side view of the current collector shown in fig. 3 along the Z-direction.

Fig. 5 is a side view of a negative electrode current collector in yet another embodiment of the present application.

Fig. 6 is a side view of a negative current collector in yet another embodiment of the present application.

Fig. 7 is a side view of a negative electrode current collector in yet another embodiment of the present application.

Fig. 8 is a top view of a negative current collector in yet another embodiment of the present application.

Detailed Description

Embodiments of the present application will be described in detail below. The examples of the present application should not be construed as limiting the scope of the claims of the present application. The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.

As used herein, the terms "substantially," "generally," "substantially," "essentially," and "about" are used to describe and illustrate small variations. When used in conjunction with an event or circumstance, the terms can refer to instances where the event or circumstance occurs precisely as well as instances where the event or circumstance occurs in close proximity. For example, when used in conjunction with a numerical value, the term can refer to a range of variation that is less than or equal to ± 10% of the numerical value, such as less than or equal to ± 5%, less than or equal to ± 4%, less than or equal to ± 3%, less than or equal to ± 2%, less than or equal to ± 1%, less than or equal to ± 0.5%, less than or equal to ± 0.1%, or less than or equal to ± 0.05%, then the two numerical values can be considered "substantially" identical.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity, and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

In the detailed description and claims, a list of items connected by the term "one of" may mean any of the listed items. For example, if items a and B are listed, the phrase "one of a and B" means a alone or B alone. In another example, if items A, B and C are listed, the phrase "one of A, B and C" means only a; only B; or only C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

In the detailed description and claims, a list of items connected by the term "at least one of can 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" or "at least one of a or B" means a only; 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" or "at least one of A, B or C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

As used herein, the content of each component in the electrolyte is obtained based on the total weight of the electrolyte.

First, electrolyte

In some embodiments, the electrolyte of the present invention comprises a nitrile compound comprising at least one of a compound of formula i, a compound of formula ii, a compound of formula iii, a compound of formula iv, a compound of formula v, or a compound of formula vi:

and

wherein a, d, f, j, k, l, m, r, u, w and y are each independently selected from 1, 2, 3, 4 or 5, b, c, e, g, h, i, n, o, p, q, s, t, v, x are each independently selected from 0, 1, 2, 3, 4 or 5; the nitrile compound is present in an amount of 0.1% to 10%, 0.3% to 8%, 1% to 6%, or 3% to 4% of the electrolyte, and in some embodiments, a% is about 0.5%, about 1.5%, about 2.5%, about 3.5%, about 4.5%, about 5.5%, about 6.5%, about 7.5%, about 8.5%, or about 9.5%.

in some embodiments, to further improve the performance of the lithium ion battery, the electrolyte further comprises one or more of the following additives: 1, 3-Propanesultone (PS), fluoroethylene carbonate (FEC), Vinylene Carbonate (VC), 2, 4-butanesultone, 1, 4-butanesultone, methanedisulfonic acid methylene ester (MMDS), vinyl sulfate (DTD), Succinic Anhydride (SA), ethoxypentafluorocyclotriphosphazene, 1, 3-Dioxane (DOX) or propenyl-1, 3-sultone.

In some embodiments, in order to suppress elution of copper caused by the electrolyte containing the nitrile compound, the electrolyte may further contain an anion, for example, at least one of inorganic anions such as Cl^-，Br^-，SO₄ ^2-，CO₃ ^2-Or F^-. In some embodiments, the anion is present in the electrolyte in an amount less than or equal to 1000 ppm.

In some embodiments, the electrolyte further comprises a lithium salt and an organic solvent.

In some embodiments, the lithium salt is selected from one or more of inorganic lithium salts and organic lithium salts. In some embodiments, the lithium salt contains at least one of elemental fluorine, elemental boron, or elemental phosphorus. In some embodiments, the lithium salt is selected from one or more of the following lithium salts: lithium hexafluorophosphate (LiPF)₆) Lithium bistrifluoromethanesulfonylimide (abbreviated to LiTFSI), lithium bistrifluoromethanesulfonylimide (abbreviated to LiFSI), bisoxalatoboric acid (abbreviated to LiBOB), difluorooxalatoboric acid (abbreviated to lidob), and lithium hexafluoroarsenate (abbreviated to LiAsF)₆) Lithium perchlorate (abbreviated as LiClO)₄) Lithium trifluoromethanesulfonate (abbreviated as LiCF)₃SO₃) At least one of (1).

In some embodiments, the concentration of the lithium salt is 0.5M to 1.5M. In some embodiments, the concentration of the lithium salt is 0.8M to 1.2M.

The organic solvent comprises a cyclic ester and a chain ester, wherein the cyclic ester is selected from at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), gamma-Butyrolactone (BL) and butylene carbonate; the chain ester is at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), ethyl propyl carbonate, Methyl Formate (MF), ethyl formate (MA), Ethyl Acetate (EA), Ethyl Propionate (EP), Propyl Propionate (PP), methyl propionate, propyl acetate, methyl butyrate and ethyl butyrate.

Two, electrochemical device

The electrochemical device of the present application includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. In some embodiments, an electrochemical device of the present application is an electrochemical device including a positive electrode having a positive electrode active material capable of occluding and releasing metal ions and a negative electrode having a negative electrode active material capable of occluding and releasing metal ions, and is characterized by including any of the above-described electrolytic solutions of the present application.

Electrolyte solution

The electrolyte used in the electrochemical device of the present application is any of the electrolytes described above in the present application.

Negative electrode

In the electrochemical device according to the present application, the negative electrode includes a current collector and a negative active material layer disposed on the current collector. The negative electrode active material layer contains a negative electrode active material. The specific kind of the negative electrode active material is not particularly limited and may be selected as desired.

The negative electrode may be prepared by a preparation method well known in the art. For example, the negative electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector.

The negative active material includes a material that reversibly intercalates/deintercalates lithium ions. In some embodiments, the material that reversibly intercalates/deintercalates lithium ions comprises a carbon material. In some embodiments, the carbon material may be any carbon-based negative active material commonly used in lithium ion rechargeable batteries. In some embodiments, carbon materials include, but are not limited to: crystalline carbon, amorphous carbon, or mixtures thereof. The crystalline carbon may be amorphous, flake, platelet, spherical or fibrous natural or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or the like.

In some implementationsIn an example, the negative electrode active material layer includes a negative electrode active material. In some embodiments, the negative active material includes, but is not limited to: lithium metal, structured lithium metal, natural graphite, artificial graphite, mesophase micro carbon spheres (abbreviated to MCMB), hard carbon, soft carbon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO₂Spinel-structured lithiated TiO₂-Li₄Ti₅O₁₂A Li-Al alloy, or any combination thereof.

In some embodiments, the negative active material layer may include a binder, and optionally a conductive material. The binder improves the binding of the negative active material particles to each other and the binding of the negative active material to the current collector. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

In some embodiments, the conductive material includes, but is not limited to: a carbon-based material, a metal-based material, a conductive polymer, or a mixture thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from the group consisting of metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

In the electrochemical device according to the present application, the current collector of the negative electrode may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof. In some embodiments, the current collector comprises copper foil.

In some embodiments, the copper foil is produced by electrolysis or calendering, the purity is greater than or equal to 99.5%, and the sum of the contents of trace elements such as nickel, zinc, chromium and the like is less than or equal to 0.5 wt%;

in some embodiments, the copper foil has one or more properties selected from the group consisting of:

copper purity greater than or equal to 99.5%;

a thickness of 3 to 15 microns, for example, the thickness is about 4 microns, about 5 microns, about 6 microns, about 7 microns, about 8 microns, about 9 microns, about 10 microns, about 11 microns, about 12 microns, about 13 microns, or about 14 microns;

weight per unit area of 30g/m²To 150g/m²For example, the weight per unit area is about 50g/m²About 70

g/m²About 90g/m²About 110g/m²Or about 130g/m²；

Tensile Strength of greater than or equal to 20kg/mm²For example, the tensile strength is greater than or equal to 30kg/mm²Greater than or equal to 40kg/mm²Or greater than or equal to 50kg/mm²；

An elongation greater than or equal to 1.5%, for example greater than or equal to 2%, greater than or equal to 2.5%, greater than or equal to 3%, greater than or equal to 3.5%, or greater than or equal to 4%.

In some embodiments, the copper foil is electrolytically produced to have a purity of greater than or equal to 99.5%, a thickness of about 6 microns, and a tensile strength of greater than or equal to 30kg/mm²The elongation is greater than or equal to 3%.

In some embodiments, the copper foil has a degree of corrosion resistance, for example, at about 45 ℃ with Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) in a mass ratio of 3:1:7, LiPF₆The electrolyte with the content of 1mol/L has no obvious color change after being soaked for about 48 hours.

An electrochemical device according to some embodiments includes a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte comprises a nitrile compound, wherein the nitrile compound accounts for A% of the electrolyte by mass; the anode includes a current collector comprising: a first region and a second region; wherein the first region is provided with a negative electrode active material layer; the second region does not contain a negative electrode active material layer. The area of the second region occupies B% of the surface area of the current collector, and axb is less than 600, e.g., axb is less than 550, less than 500, less than 450, less than 400, less than 350, less than 300, less than 250, less than 200, less than 150, less than 100, less than 50, less than 30, less than 15, or less than 5.

In some embodiments, the negative electrode has a tab formed by welding to the second region, and axb is less than 210. For example, a x B is less than 200, less than 150, less than 100, less than 50, less than 30, less than 15, or less than 10.

Fig. 1 and 2 demonstrate a schematic representation of a current collector of a negative electrode in an embodiment of the invention, said current collector comprising: a first zone 1 and a second zone 2; wherein the first region is provided with a negative electrode active material layer (shown as a gray region in the figure); the second region does not contain a negative electrode active material layer. The negative electrode has a tab 3 formed by welding to the second region.

As shown in fig. 2, in some embodiments, at least one second region is located at the edge of the current collector, wherein the distance between the nearest tab to the edge of the current collector and the edge of the current collector is C, the tab width is W, and "C/W" (i.e., the ratio of C to W) ranges from 0 to 50, such as 5 to 40, 10 to 30, 15 to 40, or 20 to 30.

In some embodiments, the negative electrode has tabs, the number of the tabs is 1 to 150, for example, the number of the tabs is 3, 5, 7, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, or 140; the tab is formed by slitting the current collector, the tab includes an uncoated negative active material layer area, and AxB is less than about 500; for example, a x B is less than 450, less than 400, less than 350, less than 300, less than 250, less than 200, less than 150, less than 100, less than 50, less than 30, less than 15, or less than 10.

Fig. 3 and 4 demonstrate a schematic representation of a current collector of a negative electrode according to a further embodiment of the invention, said current collector comprising: a first zone 1 and a second zone 2; wherein the first region is provided with a negative electrode active material layer; the second region does not contain a negative electrode active material layer. The negative electrode has a plurality of tabs 3 formed by cutting the current collector, the tabs including regions of uncoated negative active material layer.

As shown in fig. 5, in some embodiments, at least one second region is located at the edge of the current collector, and the edge of the second region located at the edge of the current collector is folded back or not; wherein when folded back, the width of the folded back region is D, the tab width is W, and "D/W" (i.e., the ratio of D to W) ranges from 0.1 to 20, such as 2 to 18, 4 to 16, 6 to 14, 8 to 12, or 9 to 10.

As shown in fig. 6, in some embodiments, at least one second region is located at an edge of the current collector, and the negative electrode further includes one or more second regions not including a negative electrode active material layer located in the middle of the current collector.

In some embodiments, to minimize the surface area of the second zone, the second zone is optionally covered with a substance capable of bonding to the second zone. For example, as shown in fig. 7, a portion of the second region is covered by, for example, but not limited to, a polymer tape 4.

In some embodiments, the site of the tab is optionally covered by a substance capable of adhering thereto. For example, as shown in fig. 8, to reduce copper ion elution at the tab weld with the second zone, the tab weld portion may be covered with, for example, but not limited to, a polymer tape.

In the anode of the present invention, the first region (i.e., the region where the anode active material layer is provided) may be located on the upper surface, the lower surface, or both of the anode current collector; the second area can be located at the edge and/or the inside of the negative current collector, and the second area further comprises a tab welding part, a tab area formed by cutting and an edge folding area.

Positive electrode

The material of the positive electrode used in the electrochemical device of the present application may be prepared using materials, configurations, and manufacturing methods well known in the art. In some embodiments, the positive electrode of the present application can be prepared using the techniques described in US9812739B, which is incorporated by reference in its entirety.

In some embodiments, the positive electrode includes a current collector and a positive active material layer on the current collector. The positive electrode active material includes at least one lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive electrode active material includes a composite oxide. In some embodiments, the composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

In some embodiments, the positive active material is selected from one or more of lithium cobaltate, lithium manganate, lithium nickelate, or lithium nickel manganese cobalt ternary materials, and the negative active material contains silicon or silicon oxygen material, and optionally any negative material capable of releasing lithium from graphite, hard carbon, mesocarbon microbeads, and the like.

In some embodiments, the positive electrode active material may have a coating layer on a surface thereof, or may be mixed with another compound having a coating layer. The coating may comprise at least one coating element compound selected from the group consisting of an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element and an oxycarbonate of the coating element. The compounds used for the coating may be amorphous or crystalline.

In some embodiments, the coating elements contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or any combination thereof. The coating layer may be applied by any method as long as the method does not adversely affect the properties of the positive electrode active material. For example, the method may include any coating method known to the art, such as spraying, dipping, and the like.

The positive active material layer further includes a binder, and optionally a conductive material. The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding of the positive electrode active material to the current collector.

In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, and the like.

In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from the group consisting of metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

In some embodiments, the current collector may be aluminum, but is not limited thereto.

The positive electrode may be prepared by a preparation method well known in the art. For example, the positive electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone, and the like.

In some embodiments, the positive electrode is made by forming a positive electrode material on a current collector using a positive electrode active material layer including a lithium transition metal-based compound powder and a binder.

In some embodiments, the positive electrode active material layer may be generally fabricated by: the positive electrode material and a binder (a conductive material, a thickener, and the like, which are used as needed) are dry-mixed to form a sheet, and the obtained sheet is pressure-bonded to a 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 a positive electrode current collector and dried. In some embodiments, the material of the positive electrode active material layer includes any material known in the art.

Isolation film

In some embodiments, the electrochemical device of the present application is provided with a separator between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separation film used in the electrochemical device of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.

For example, the release film 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 at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. The base material layer can be one layer or a plurality of layers, when the base material layer is a plurality of layers, the compositions of the polymers of different base material layers can be the same or different, and the weight average molecular weights are different; when the substrate layer is a multilayer, the polymers of different substrate layers have different closed cell temperatures.

At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

The inorganic layer comprises inorganic particles and a binder, wherein the inorganic particles are selected from one or more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, 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 one or a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer comprises a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

Third, application

The electrochemical device according to the embodiment of the present application has improved cycle performance and high-temperature stability under overdischarge conditions, and is suitable for use in various electronic devices.

The use of the electrochemical device of the present application is not particularly limited, and the electrochemical device can be used for various known uses. Such as a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a 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-sized battery for home use, or a lithium ion capacitor.

Examples

The present application will be described in more detail below with reference to examples and comparative examples, but the present application is not limited to these examples as long as the gist thereof is not deviated.

Preparation of lithium ion battery

(1) Preparation of the negative electrode

(i) Negative pole formed by welding pole lugs

Mixing artificial graphite powder, sodium carboxymethylcellulose (CMC) and styrene butadiene rubber in a mass ratio of 96: 2: 2 dissolving the mixture in water, fully mixing and stirring to obtain negative electrode slurry, uniformly coating the negative electrode slurry on a specific area of a negative electrode current collector copper foil with the thickness of 12 microns, baking the negative electrode current collector copper foil for 1 hour at the temperature of 120 ℃ to obtain a negative electrode active material layer, and then compacting, slitting and welding tabs to obtain the negative electrode.

(ii) Negative pole formed by cutting pole ear

Mixing artificial graphite powder, sodium carboxymethylcellulose (CMC) and styrene butadiene rubber in a mass ratio of 96: 2: 2 dissolving the mixture in water, fully mixing and stirring to obtain negative electrode slurry, uniformly coating the negative electrode slurry on a specific area of a negative electrode current collector copper foil with the thickness of 12 microns, baking the negative electrode current collector copper foil for 1 hour at the temperature of 120 ℃ to obtain a negative electrode active material layer, and then compacting, cutting a tab and slitting to obtain the negative electrode.

(iii) Method for making negative electrode having polymer tape in second region of negative electrode (example 59)

Mixing artificial graphite powder, sodium carboxymethylcellulose (CMC) and styrene butadiene rubber in a mass ratio of 96: 2: 2 dissolving the mixture in water, fully mixing and stirring to obtain negative electrode slurry, uniformly coating the negative electrode slurry on a specific area of a negative electrode current collector copper foil with the thickness of 12 microns, baking the specific area at 120 ℃ for 1 hour to obtain a negative electrode active material layer, compacting, slitting, welding a tab, and pasting a polymer adhesive tape made of acrylic ester on a second area (namely the area which is not coated with the negative electrode slurry) to obtain the negative electrode.

(iv) Preparation method of negative electrode (example 60) with polymer adhesive tape at tab welding position

Mixing artificial graphite powder, sodium carboxymethylcellulose (CMC) and styrene butadiene rubber in a mass ratio of 96: 2: dissolving the 2 into water, fully mixing and stirring to obtain negative electrode slurry, uniformly coating the negative electrode slurry on a specific area of a negative electrode current collector copper foil with the thickness of 12 microns, baking for 1h at 120 ℃ to obtain a negative electrode active material layer, compacting, slitting, welding a tab, and pasting a polymer adhesive tape made of acrylic ester on a tab welding area to obtain the negative electrode.

(2) Preparation of the Positive electrode

(i) Positive pole formed by welding pole lugs

The positive electrode active material lithium cobaltate (the molecular formula is LiCoO)₂) The adhesive polyvinylidene fluoride (PVDF), the conductive graphite (Super-P) and the composite material are mixed according to a mass ratio of 96: 2: 2, dissolving in N-methyl pyrrolidone (NMP), and uniformly mixing to prepare the anode slurry. And uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil with the thickness of about 12 microns, baking for 1 hour at 120 ℃ to obtain a positive electrode active material layer, and then compacting, welding a lug, and slitting to obtain the positive electrode.

(ii) Positive pole formed by cutting pole ear

The positive electrode active material lithium cobaltate (the molecular formula is LiCoO)₂) The adhesive polyvinylidene fluoride (PVDF), the conductive graphite (Super-P) and the composite material are mixed according to a mass ratio of 96: 2: 2, dissolving in N-methyl pyrrolidone (NMP), and uniformly mixing to prepare the anode slurry. And uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil with the thickness of 12 microns, baking for 1 hour at 120 ℃ to obtain a positive electrode active material layer, and then compacting, cutting a tab and cutting to obtain the positive electrode.

(3) Preparation of the electrolyte

Mixing Ethylene Carbonate (EC), Propylene Carbonate (PC) and diethyl carbonate (DEC) according to the mass ratio of 3:1:7 in a dry argon atmosphere glove box, and adding LiPF₆As the lithium salt, specific kinds and amounts of additives were added (kinds and amounts of substances added are shown in table 1, and the contents of the respective components in the electrolyte were obtained based on the total weight of the electrolyte). LiPF in electrolyte₆Is about 1 mol/L.

(4) Preparation of the separator

The polypropylene isolating film with the thickness of about 12 microns is selected

(5) Preparation of lithium ion battery

A polypropylene film of about 12 microns was used as the separator. And sequentially stacking the anode, the isolating membrane and the cathode to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, then winding and filling the anode and the cathode into an aluminum foil packaging bag, baking at 80 ℃ to remove water, injecting corresponding electrolyte, and performing the procedures of vacuum packaging, standing, formation, shaping and the like to complete the preparation of the lithium ion battery.

Second, testing of copper foil used for negative current collector

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

Mass per unit area: the copper foil was cut into 100 x 100mm wide sheets and weighed, and the mass per unit area was calculated. Mass per unit area is weight/area;

and (3) testing tensile strength: 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, 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 chuck during testing, the sample is kept linear, and the experimental temperature is 20 +/-5 DEG C

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 chuck of the testing machine is 125 +/-0.1 mm, 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 ℃; elongation is the stretched length/original length;

third, lithium ion battery performance test

(1) Cycle performance test

Charging the lithium ion battery to 4.45V at a constant current of 1C at the temperature of 45 ℃, standing for 30 minutes, discharging the 1C to 3.0V, and circularly charging and discharging for 500 times.

Capacity retention (%) of the lithium ion battery was 500-cycle discharge capacity/first discharge capacity × 100%.

(2)60 ℃ high temperature storage test

Putting the lithium ion battery into a constant temperature box at 25 ℃, charging the lithium ion battery to 3.95V at a constant current of 0.5C, testing the thickness of the battery, fully charging the battery to 4.45V, putting the battery in a baking oven at 60 ℃ for storage for 30 days, testing the thickness of the battery every 3 days, and stopping the test if the thickness increase rate of the battery is more than 60% relative to 3.95V.

Thickness growth rate (thickness after storage at-3.95V)/thickness at 3.95V x 100%

(3) Float charge leakage current test

And (3) standing the lithium ion battery for 120min at the temperature of 45 ℃, charging the lithium ion battery to 4.45V at 1C, keeping the constant-voltage charging state for 15 days, and recording the current after 15 days.

(4) Battery crush test

Putting the lithium ion battery into a constant temperature box of 25 ℃, charging to 4.45V at a constant current of 0.5C, then charging at a constant voltage until the current is 0.05C, extruding the battery by a pressure of 20KN, and observing whether the battery is burnt or exploded.

A. Examples 1 to 39 andcomparative examples 1 to 6 of electrolyte and lithium ion battery, wherein a copper foil is used as a negative current collector, the copper foil is produced by electrolysis, the purity is not less than 99.5%, the thickness is 6 microns, and the tensile strength is not less than 30kg/mm²The elongation is more than or equal to 3 percent. The proportion B% of the area of the second area in the surface area of the negative electrode is 18.2%, the connection mode of the lug and the second area is welding, the width w of the lug is 0.8cm, the distance C between the lug and the edge of the current collector is 2cm, and the width D of the edge inflection area of the second area at the edge of the current collector is 1.8 cm. The positive electrode lug is correspondingly prepared by adopting a welding mode. And (3) testing the cycle capacity retention rate, the floating charge leakage current and the high-temperature storage test at 60 ℃ of the lithium ion battery at different cycle times, and referring to the test results in table 2.

TABLE 1

Note: "/" indicates no addition

Table 1 shows examples and comparative examples when the ratio B% of the area of the fixed second region to the surface area of the anode was 18.2%. The cycle performance of examples 1 to 39 in which the specific nitrile compound was added to the electrolyte in the range of 0.1 to 10% by weight was remarkably improved, compared to comparative example 1 in which the nitrile compound was not contained in the electrolyte. As can be seen from comparison of comparative examples 2 to 5 with comparative example 1, when the content of the nitrile compound was increased to 12 wt% so that the value of AxB reached 218.2, the cycle performance was improved as compared to comparative example 1, but the improvement was reduced, and the self-discharge of the battery was further improved. As can be seen from comparative example 6, when the content of the nitrile compound was increased to 15% so that AxB >210, the float leakage current exceeded 50mA, seriously affecting the battery use. Therefore, in the case where the electrolyte contains 0.1 to 10% by weight of a specific nitrile compound, when the tab is connected to the second region by welding, a × B < 210 can ensure improved battery performance while inducing less self-discharge. The added nitrile compound can improve the circulation because the nitrile group can complex metal ions on the cathode and stabilize the potential of the metal ions, thereby reducing the structural phase change of the cathode material, and meanwhile, the nitrile compound can be adsorbed on the surface of the cathode to reduce the contact between the cathode and the electrolyte, and the combination of the nitrile compound and the electrolyte can obviously improve the circulation and floating charge performance of the battery; but at the same time, the nitrile compound has certain solubility to the copper foil of the negative current collector, especially when the copper foil current collector without active substance loading on the surface is exposed in electrolyte, the solubility of the nitrile compound to the copper foil is greatly enhanced, and dissolved copper ions can be slowly reduced to simple substance copper on the surface of the negative electrode and continuously deposited in the charging and discharging process of the battery, so that the local short circuit of the battery is finally caused and the self-discharge is deteriorated. Although the nitrile compound can deteriorate the self-discharge of the battery, the nitrile compound has obvious advantages on the electrical property of the battery, so that the nitrile compound with a certain content is required to be added into the electrolyte and the exposed area of the hollow copper foil is controlled within a certain range, so that the electrical property and the self-discharge of the battery can be considered;

B. the electrolytes of examples 40 to 52 and comparative example 8 and the lithium ion battery were prepared according to the above method, wherein a copper foil was used as a negative electrode current collector, the copper foil was produced by electrolysis, the purity was not less than 99.8%, the thickness was 8 μm, the tensile strength was not less than 30kg/mm2, and the elongation was not less than 3%; the connection mode of the lug and the second area is welding, the width w of the lug is 0.8cm, and the distance C between the lug and the edge of the current collector is 2 cm; the width D of the edge-folded region of the second zone located at the edge of the current collector was 2.5 cm. The positive electrode lug is correspondingly prepared by adopting a welding mode. And (3) testing the cycle capacity retention rate, the floating charge leakage current and the high-temperature storage test at 60 ℃ of the lithium ion battery at different cycle times, and referring to the test results in table 2.

TABLE 2

Table 2 shows examples and comparative examples when the content of the nitrile compound in the electrolyte was fixed to 3 wt%. When the content of the nitrile compound in the electrolyte was fixed to 3 wt% as in examples 40 to 51, the battery cycle and storage performance were superior, the floating leakage current of the battery increased as the AxB value increased by adjusting the area of the second region of the negative electrode in the battery, and when the AxB value exceeded 210 as in comparative example 8, the battery exhibited a severe self-discharge phenomenon, which severely affected the battery use. The negative electrode current collector in example 52 has no second region (i.e., B is 0.4) and thus the AxB value is 1.2, the battery of example 52 has superior cycle performance and a small leakage current compared to comparative example 8.

C. The electrolytes of examples 53 to 60 and comparative example 9 and the lithium ion battery were prepared according to the above-described methods, wherein a copper foil, which is produced by electrolysis and has a purity of not less than 99.8%, a thickness of 6 μm, a tensile strength of not less than 30kg/mm2, and an elongation of not less than 2%, was used as a negative electrode current collector. The connection mode of utmost point ear and second district is for cutting, and utmost point ear number is 9, and utmost point ear width w is 1.5cm, and the width D that lies in the edge inflection region in the second district at mass flow body edge is 1.5 cm. The anode tab is correspondingly prepared in a cutting mode. The lithium ion battery is tested for the cycle capacity retention rate of different cycle times, the floating charge leakage current and the high-temperature storage test at 60 ℃, and the test results are shown in table 3.

TABLE 3

As shown in table 3, the batteries of examples 53 to 60 and comparative example 9 were prepared by cutting tabs. As can be seen from examples 53 to 59, the adjustment of the area ratio B% of the second region has no significant effect on the capacity retention rate of the battery, but the self-discharge of the battery is accelerated; when the amount a% of the nitrile compound in comparative example 9 was increased to 12% by weight and the area ratio B% of the second region was 54% so that the value of AxB was 648, the self-discharge current reached 40 mA. The negative electrode current collector in example 60 was entirely coated with the active material, but the tab was free of active material (i.e., 2.3% B was void copper foil ratio at the tab) so that the value of AxB was 6.9, and the battery of example 60 was superior in cycle and storage performance and small in leakage current, compared to comparative example 9. In summary, when the battery is prepared by cutting the tab, the AxB needs to be controlled within 600, so that the battery performance is better.

D. The electrolytes and lithium ion batteries of examples 61 to 63 were prepared according to the above methods, wherein a copper foil was used as the negative electrode current collector, the copper foil was produced by electrolysis, the purity was not less than 99.8%, the thickness was 6 μm, the tensile strength was not less than 30kg/mm2, and the elongation was not less than 2%. The connection mode of utmost point ear and second district is the welding, and utmost point ear width is 0.8cm, and utmost point ear is apart from the mass flow body edge distance C and is 2cm, and the width D that lies in the edge inflection region in the second district at mass flow body edge is 1.8 cm. The positive electrode lug is correspondingly prepared by adopting a welding mode. And (3) testing the cycle capacity retention rate of the lithium ion battery at different cycle times, the floating charge leakage current and the high-temperature storage test at 60 ℃, and referring to the test results in table 4.

TABLE 4

As shown in table 4, in example 61, a polymer paste was applied to a certain area of the copper foil region not coated with the active material layer to reduce the contact area between the copper foil and the electrolyte; example 61 had lower leakage current than example 63 without the polymer tape; the application of polymer tape to the tab welds in example 62 also reduced the self-discharge of the cell as compared to example 63, where no polymer tape was applied. Therefore, in practical battery design, the tab welding position on the negative electrode copper foil current collector and other negative electrode active material-uncoated empty copper foil areas can be covered with polymer adhesive tapes or other substances capable of being bonded on the copper foils and the tabs so as to reduce the self-discharge of the battery.

E. Examples 64 to 64 were prepared according to the methods described above70, wherein a copper foil is used as a negative current collector, the copper foil is generated by electrolysis, the purity is more than or equal to 99.8 percent, the thickness is 6 microns, and the tensile strength is more than or equal to 30kg/mm²The elongation is more than or equal to 2 percent. The connection mode of utmost point ear and second district is the welding, and utmost point ear width is 0.8cm, and utmost point ear is apart from the mass flow body edge distance C and is 2cm, and the width D that lies in the edge inflection region in the second district at mass flow body edge is 1.8 cm. The positive electrode lug is correspondingly prepared by adopting a welding mode. The lithium ion battery is tested for the cycle capacity retention rate of different cycle times, the floating charge leakage current and the high-temperature storage test at 60 ℃, and the test results are shown in table 5.

TABLE 5

Note: "/" indicates no addition

As can be seen from examples 64 to 69, compared with example 70, the addition of other additives to the electrolyte containing a specific nitrile compound can significantly improve the cycle and the float thickness growth rate of the battery, and the addition of the additive FEC can increase the LiF content of the negative electrode SEI, thereby effectively increasing the stability of the anode SEI; the addition of the additive VC can form a reticular protective layer by polymerization on the SEI surface layer, thereby enhancing the flexibility of the SEI, and the addition of other additives can stabilize or strengthen the SEI protective layer to a certain extent, so the cycle performance of the battery cell is obviously improved; meanwhile, due to the film forming effect of the additive on the negative electrode, the deposition of copper ions on the negative electrode can be reduced to a certain extent, the self-discharge of the battery is reduced, and the overall electrical property of the battery is further improved.

Therefore, it can be seen from the examples and comparative examples that the nitrile compound as an effective additive for improving the cycling stability has a large effect on the self-discharge of the battery, and in order to improve the long-term storage performance of the battery, the content of the nitrile compound and the area of the empty copper foil region need to be controlled within a certain range to ensure that the capacity of the battery is not significantly reduced after long-term storage, and meanwhile, the cycling and self-discharge of the battery can be improved and the long cycling and storage performance of the battery can be ensured by adding a certain content of other additives to the electrolyte.

F. The electrolytes of examples 71 to 72 and lithium ion batteries were prepared as described above, wherein copper foil was used as the negative current collector, the copper foil was produced by electrolysis, the purity was not less than 99.8%, the thickness was 6 μm, and the tensile strength was not less than 30kg/mm²The elongation is more than or equal to 2 percent; the connection mode of the lug and the second area is welding, and the width w of the lug is 0.8 cm; the distance C between the lug and the edge of the current collector is 2 cm; the width D of the edge-folded region of the second region located at the edge of the current collector in example 71 was 1.8cm, and the edge of the second region located at the edge of the current collector in example 72 was not folded back. The positive electrode lug is correspondingly prepared by adopting a welding mode. And (3) testing the cycle capacity retention rate, the floating charge leakage current and the extrusion test of the lithium ion battery at different cycle times, and finding test results in a table 6.

TABLE 6

As shown in table 6, the edge of the second region at the edge of the current collector in example 71 is folded back, and the edge of the second region at the edge of the current collector in example 72 is not folded back, so that there is no significant difference between the capacity retention rate and the floating charge leakage current of the second region and the current collector, but the extrusion test shows that the risk of the burrs at the tab welding position piercing the separator is reduced by adopting the folding back mode, so that the battery has higher safety performance.

G. The electrolytes of examples 73 to 76 and lithium ion batteries were prepared according to the above methods, wherein a copper foil was used as the negative electrode current collector, the copper foil was produced by electrolysis, the purity was not less than 99.8%, the thickness was 6 μm, and the tensile strength was not less than 30kg/mm²The elongation is more than or equal to 2 percent; the connection mode of the lug and the second area is welding, and the width W of the lug is 0.8 cm; the distance C between the lug and the edge of the current collector is 2 cm; the width D of the edge-folded region of the second region of the current collector edge was 1.8 cm. The positive electrode lug is correspondingly prepared by adopting a welding mode. The cycle capacity retention rate and the floating charge leakage current of the lithium ion battery at different cycle times are tested, and the test results are shown in Table 7

TABLE 7

When an appropriate amount of anion, such as Cl, is contained in the electrolyte as shown in Table 7^-When the amount of the additive is more than 1000ppm, the effect of improving the leakage current of the battery is large. Therefore, when the electrical property of the battery is ensured, a proper amount of anions can be added into the electrolyte, and the floating charge leakage current is improved;

the above description is only for the purpose of illustrating the present invention and is not intended to limit the present invention in any way, and the present invention is not limited to the above description, but rather should be construed as being limited to the scope of the present invention.

Reference throughout this specification to "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte; wherein the content of the first and second substances,

the electrolyte comprises a nitrile compound, the mass fraction of the nitrile compound in the electrolyte is A percent,

the first region is provided with a negative electrode active material layer;

the second region does not contain a negative electrode active material layer;

the area of the second region accounts for B% of the surface area of the current collector;

wherein the electrolyte further comprises an additive comprising at least one of 1, 3-propane sultone, fluoroethylene carbonate, vinylene carbonate, 2, 4-butane sultone, 1, 4-butane sultone, methylene methanedisulfonate, vinyl sulfate, succinic anhydride, ethoxypentafluorocyclotriphosphazene, 1, 3-dioxane, or propenyl-1, 3-sultone;

the mass fraction A% of the nitrile compound in the electrolyte is 0.1-10%; and is

The negative electrode has a tab, wherein:

when the tab is formed by welding to the second zone, AxB < 210; or

When the tabs are formed by cutting the current collector, the number of the tabs is not less than 1, the tabs comprise regions which are not coated with the negative electrode active material layer, and AxB is less than 500.

2. The electrochemical device of claim 1, wherein the nitrile compound comprises at least one of a compound of formula i, a compound of formula ii, a compound of formula iii, a compound of formula iv, a compound of formula v, or a compound of formula vi:

and

wherein a, d, f, j, k, l, m, r, u, w and y are each independently an integer selected from 1 to 5, and b, c, e, g, h, i, n, o, p, q, s, t, v, x are each independently an integer selected from 0 to 5.

3. The electrochemical device according to claim 1, wherein the nitrile compound comprises:

at least one of (1).

4. The electrochemical device according to claim 1, wherein at least one second region is located at an edge of the current collector, wherein a distance between a tab nearest to the edge of the current collector and the edge of the current collector is C, and 0. ltoreq. C/tab width. ltoreq.50.

5. The electrochemical device according to claim 1, wherein at least one second region is located at an edge of the current collector, and an edge of the second region located at the edge of the current collector is folded or not folded; when the electrode tab is folded back, the width of the folded back area is D, and D is more than or equal to 0.1/the width of the electrode tab is less than or equal to 20.

6. The electrochemical device of claim 1, wherein the current collector is a copper foil having one or more properties selected from the group consisting of:

the purity of the copper is more than or equal to 99.5 percent,

the thickness is from 3 microns to 15 microns,

the weight per unit area was 30g/m²To 150g/m²，

Tensile strength is more than or equal to 20kg/mm²And are and

the elongation is more than or equal to 1.5 percent.

7. The electrochemical device of claim 1, wherein the second region is optionally covered with a substance capable of adhering to the second region.

8. The electrochemical device of claim 1, wherein the site of the tab is optionally covered with a substance capable of bonding thereto.

9. The electrochemical device of any one of claims 2-8: wherein the electrolyte further comprises an anion comprising Cl^-、Br^-、SO₄ ^2-、CO₃ ^2-Or F^-The content of the anion in the electrolyte is less than or equal to 1000 ppm.

10. An electronic device comprising the electrochemical device of any one of claims 1-9.