CN113078361A

CN113078361A - Electrolyte and electrochemical device

Info

Publication number: CN113078361A
Application number: CN202110324283.5A
Authority: CN
Inventors: 刘俊飞; 郑建明; 唐超; 张丽兰
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-03-27
Filing date: 2020-03-27
Publication date: 2021-07-06
Also published as: CN111342137B; CN111342137A

Abstract

An electrochemical device is provided comprising a positive electrode, a negative electrode, a separator, and an electrolyte containing a compound of formula I. The invention can effectively improve the high-temperature storage and high-temperature cycle performance of the electrochemical device.

Description

Electrolyte and electrochemical device

The present application is a divisional application entitled "an electrolyte solution and an electrochemical device" filed on 27/3/2020, application No. 202010233604.6.

Technical Field

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

Background

The lithium ion battery as a chemical power supply has the advantages of high energy density, high working voltage, light weight, low self-discharge rate, long cycle life, no memory effect, environmental friendliness and the like, and is widely applied to the fields and industries of intelligent products (including electronic products such as mobile phones, notebooks, cameras and the like), electric automobiles, electric tools, unmanned planes, intelligent robots, advanced weaponry, large-scale energy storage and the like. However, with the increasing change of information communication technology and the diversity of market demands, more demands and challenges are also put on power supplies of electronic products, such as thinner, lighter, more diversified appearance, higher volumetric and mass energy density, higher safety, higher power, etc.

Disclosure of Invention

The invention provides an electrolyte and an electrochemical device which can improve high-temperature cycle performance and high-temperature storage performance and have higher safety performance.

The invention provides an electrochemical device, which comprises a positive electrode, a negative electrode, a separation film and electrolyte, wherein the positive electrode comprises a current collector and a positive active material layer, and the positive active material layer comprises a positive active material;

the electrolyte contains a compound of formula I:

wherein R is₁₁、R₁₂、R₁₃、R₁₄、R₁₅And R₁₆Each independently selected from: H. halogen, substituted or unsubstitutedThe following groups: c_1-8Alkyl radical, C_2-8Alkenyl radical, C_2-8Alkynyl, or C_6-12An aryl group; and is

The amount of the compound of formula I is required to be about 0.001g to about 0.064g per 1g of the positive electrode active material.

In some embodiments, the compound of formula I comprises at least one of the following compounds:

in some embodiments, the positive electrode active material layer includes first particles having a circularity of 0.4 to 1, a cross-sectional area of the first particles is not less than 20 μm square, and a sum of the cross-sectional areas of the first particles is 5% to 50% in terms of a cross-sectional area of the positive electrode perpendicular to the current collector direction.

In some embodiments, the positive electrode active material layer includes second particles having a circularity of less than 0.4, and a cross-sectional area of the second particles is smaller than a cross-sectional area of the first particles, as calculated from a cross-sectional area of the positive electrode in a direction perpendicular to the current collector.

In some embodiments, the sum of the cross-sectional areas of the second particles is 5% to 60% as calculated as the cross-sectional area of the positive electrode perpendicular to the current collector.

In some embodiments, wherein the electrolyte further comprises an additive a comprising lithium tetrafluoroborate (LiBF)₄) Lithium difluorophosphate (LiPO)₂F₂) Lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (trifluoromethanesulfonylimide) (LiTFSI), lithium 4, 5-dicyano-2-trifluoromethylimidazole, lithium difluorobis (oxalato) phosphate, lithium difluorooxalato borate, or lithium bis (oxalato borate).

In some embodiments, 0.000026g to 0.019g of the additive a is required per 1g of the cathode active material.

In some embodiments, the electrolyte further comprises an additive B comprising at least one of Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), tris (trimethylsilyl) phosphate (TMSP), tris (trimethylsilyl) borate (TMSB), Adiponitrile (ADN), Succinonitrile (SN), 1,3, 5-pentanenitrile, 1,3, 6-Hexanetricarbonitrile (HTCN), 1,2, 6-hexanetricarbonitrile, or 1,2, 3-tris (2-cyanato) propane (TECP).

In some embodiments, the mass ratio of the compound of formula I to the additive B is from about 7:1 to about 1: 7.

In some embodiments, 0.0001g to 0.2g of the additive B is required per 1g of the positive electrode active material.

In some embodiments, wherein the positive electrode active material layer comprises a phosphorus-containing compound comprising Li₃PO₄Or LiMPO₄Wherein M is selected from at least one of Co, Mn or Fe.

In some embodiments, wherein the phosphorus-containing compound is contained at a surface or a grain boundary of the positive electrode active material.

In some embodiments, wherein the positive electrode active material comprises LiNi_xCo_yMn_zO₂Wherein 0.55<x<0.92，0.03<y<0.2，0.04<z<0.3。

In some embodiments, the positive active material includes an element Q selected from at least one of Zr, Ti, Yr, V, Al, Mg, or Sn.

In some embodiments, the porosity of the positive electrode is ≦ 25%.

In some embodiments, the percentage of the cross-sectional area of the positive electrode current collector is 5% to 20% calculated as the cross-sectional area of the positive electrode in a direction perpendicular to the current collector.

In some embodiments, wherein the positive electrode active material layer has a compacted density of less than or equal to 3.6g/cm³。

In some embodiments, the electrolyte further comprises a compound of formula II

Wherein R is₃₁And R₃₂Each independently selected from substituted or unsubstituted C_1-10Alkyl, or substituted or unsubstituted C_2-8Alkenyl, wherein substituted means substituted with one or more halogens, the compound of formula II is present in an amount of about 0.5 wt% to about 50 wt%, based on the total weight of the electrolyte.

In some embodiments, wherein the compound of formula II comprises at least one of the following compounds:

yet another aspect of the present invention provides an electronic device comprising any one of the electrochemical devices 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 shows an electron micrograph of a positive electrode active material of one 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 term "about" is used to describe and illustrate minor 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 numerical values, the term can refer to a range of variation that is less than or equal to ± 10% of the stated 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%. 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 linked by the term "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" 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.

In the detailed description and in the claims, the numbers following the expression for carbon number, i.e. the capital letter "C", such as "C₁-C₁₀”、“C₃-C₁₀In "etc., the numbers after" C "such as" 1 "," 3 "or" 10 "represent the number of carbons in a specific functional group. That is, the functional groups may include 1 to 10 carbon atoms and 3 to 10 carbon atoms, respectively. For example, "C₁-C₄Alkyl "or" C_1-4Alkyl "means an alkyl group having 1 to 4 carbon atoms, e.g. CH₃-、CH₃CH₂-、CH₃CH₂CH₂-、(CH₃)₂CH-、CH₃CH₂CH₂CH₂-、CH₃CH₂CH(CH₃) -or (CH)₃)₃C-。

As used herein, the term "alkyl" refers to a straight chain saturated hydrocarbon structure having from 1 to 10 carbon atoms. "alkyl" is also contemplated to be a branched or cyclic hydrocarbon structure having 3 to 10 carbon atoms. For example, the alkyl group can be an alkyl group of 1 to 10 carbon atoms, an alkyl group of 1 to 8 carbon atoms, an alkyl group of 1 to 6 carbon atoms, or an alkyl group of 1 to 4 carbon atoms. When an alkyl group having a particular carbon number is specified, all geometric isomers having that carbon number are intended to be encompassed; thus, for example, "butyl" is meant to include n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, and the like. In addition, the alkyl group may be optionally substituted.

The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group that can be straight or branched chain and has at least one and typically 1,2, or 3 carbon-carbon double bonds. Unless otherwise defined, the alkenyl group typically contains 2 to 10 carbon atoms, and may be, for example, 2 to 8 carbon atoms, 2 to 6 carbon atoms, or 2 to 4 carbon atoms. Representative alkenyl groups include, by way of example, ethenyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, and the like. In addition, the alkenyl group may be optionally substituted.

The term "alkynyl" refers to a monovalent unsaturated hydrocarbon group that can be straight-chain or branched and has at least one, and typically 1,2, or 3 carbon-carbon triple bonds. Unless otherwise defined, the alkynyl group typically contains 2 to 10, 2 to 8, 2 to 6, or 2 to 4 carbon atoms. Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like. In addition, the alkynyl group may be optionally substituted.

The term "aryl" encompasses monocyclic and polycyclic ring systems. Polycyclic rings can have two or more rings in which two carbons are common to two adjoining rings (the rings are "fused"), wherein at least one of the rings is aromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryls, heterocyclics, and/or heteroaryls. For example, the aryl group may contain 6 to 12 carbon atoms or an aryl group of 6 to 10 carbon atoms. Representative aryl groups include, for example, phenyl, methylphenyl, propylphenyl, isopropylphenyl, benzyl, and naphthalen-1-yl, naphthalen-2-yl, and the like. In addition, the aryl group may be optionally substituted.

When the above substituents are substituted, unless otherwise indicated, they are substituted with one or more halogens.

As used herein, the term "halogen" encompasses F, Cl, Br and I, preferably F or Cl.

The term "circularity" or "sphericity" refers to the extent to which the cross-section of a particle is close to a theoretical circle. When the circularity R is (4 pi × area)/(circumference × circumference), and R is 1, the figure is a circle; the smaller R, the more irregular the pattern, and the larger the difference from the circular shape. The circularity of the positive electrode active material particles is measured by a circularity meter, and specific test methods can be found in the following specific examples.

The term "broken particles" refers to grains having a continuous length of not less than 0.1 μm and a width of not less than 0.01. mu.m in a cross section of the particles in an image under a scanning electron microscope, and is regarded as cracks, and particles having cracks are regarded as broken particles.

The term "positive electrode active material" refers to a material capable of reversibly intercalating and deintercalating lithium ions. In some embodiments of the present application, the positive active material includes, but is not limited to, a lithium-containing transition metal oxide.

The means for increasing the energy density of lithium ion batteries include two aspects: firstly, the cathode material which is close to the graphite cathode by adopting the lithium intercalation and deintercalation voltage platform and has obviously higher gram capacity than the graphite cathode, such as Si/C composite material or SiO_xa/C composite material; the second is to develop a positive electrode material with higher specific energy, including a lithium-rich manganese-rich based positive electrode (e.g., xLi)₂MnO₃·(1-x)LiMO₂，0<x<1, M is one or more of Ni, Co, Mn, Fe, Ru, or Sn), a high nickel positive electrode (e.g., LiNi)_xCo_yMn_zO₂(NCM)，0.5≤x<1，0<y≤0.2，0<z is less than or equal to 0.3), and the like. Wherein, the spherical secondary particle nickel-rich ternary cathode material (LiNi)_xCo_yMn_zO₂(NCM)，0.5≤x<1，0<y≤0.2，0<z is less than or equal to 0.3) has begun to be widely applied to high energy density lithium ion batteries due to better particle flowability, higher tap density, and higher mass specific energy. However, the research of the inventor of the application finds that in the high-voltage charging process of the spherical secondary particle nickel-rich ternary positive electrode, the lithium removal amount reaches more than 80%, the material lattice is anisotropically shrunk, so that the internal stress of particles is rapidly increased, the secondary particles are broken in the repeated circulation process, the physical contact between primary particles is seriously damaged, so that the load transmission impedance of a battery is greatly increased, and the capacity is rapidly attenuated in the later period of the circulation; in addition, after the secondary particles are crushed, the electrolyte rapidly permeates into the secondary particles, and more side reactions occur between the electrolyte and the primary particles, and particularly, in the high-temperature cycle process, the potential safety hazards such as gas expansion and the like occur in the battery cycle. In order to improve the cycle performance of a nickel-rich material battery system and inhibit cycle gas generation, the invention adopts, for example, spherical secondary particle nickel-rich NCM positive electrode grain boundary modification to inhibit particle crushing, and simultaneously, proper protective additives (such as a compound shown in a formula I and LiPO) are added in combination₂F₂Etc.) or, for example, by using a mixture of primary and secondary particles to improve particle breakage and coalescenceWith addition of suitable protective additives (e.g. compounds of formula I and LiPO)₂F₂Etc.), these combinations can significantly improve the high-temperature storage performance, high-temperature cycle performance, and suppress high-temperature cycle gassing of the battery.

An 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 includes a positive electrode, a negative electrode, a separator, and an electrolyte.

Positive electrode

In some embodiments, the positive electrode includes a current collector and a positive active material layer on the current collector, the positive active material layer including a positive active material.

The positive electrode active material includes at least one lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. In some embodiments of the present application, the positive active material includes a lithium-containing transition metal oxide. 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, wherein the positive electrode active material layer comprises a phosphorus-containing compound comprising Li₃PO₄Or LiMPO₄Wherein M comprises at least one of Co, Mn or Fe.

In some embodiments, the phosphorus-containing compound is included at a surface or a grain boundary of the positive electrode active material.

In some embodiments, the positive electrode active material comprises LiNi_xCo_yMn_zO₂Wherein 0.55<x<0.92，0.03<y<0.2，0.04<z<0.3。

The inventor researches and discovers that in the ternary material containing nickel as the positive electrode active material, the main function of nickel element is to improve the energy density. The higher the nickel content, the higher the gram capacity in the same charge-discharge voltage range. However, in practical applications of nickel-rich materials for electrochemical devices, the nickel-rich materials have high delithiation amount at the same voltage, and the unit cell volume expansion and contraction are large, so that particles are easily broken and side reactions with an electrolyte are easily generated. After the particles are broken, a new interface is exposed, so that the electrolyte permeates into the particles through cracks and generates a side reaction with the positive electrode active material at the new interface, the generation of gas is accelerated, and the capacity of the electrochemical device is rapidly attenuated along with the progress of charge and discharge cycles. In addition, during the charging process of the electrochemical device, as lithium ions are continuously extracted from the positive active material, the binding force between the active metal (e.g., nickel element) in the positive active material and oxygen is weakened, oxygen release occurs, and the released oxygen oxidizes the electrolyte to increase gas generation. These problems described above severely limit the application of high nickel materials in high energy density electrochemical devices (especially in the positive active material, LiNi)_xCo_yMn_zO₂Wherein x is not less than 0.6).

The first particle is a collection of a plurality of single crystal particles, wherein a single crystal is a crystalline body in which fine particles are regularly and periodically arranged in a three-dimensional space. The first particles have a spherical or ellipsoidal morphology with a large degree of circularity and a large cross-sectional area. The second particles are a collection of single crystals of larger grain size.

In some embodiments, the specific surface area of the first particles(BET) about 0.14m²G to about 0.95m²/g；

In some embodiments, the first particles have a Dv50 of about 5.5 microns to about 14.5 microns. Dv90 is less than or equal to 18 microns.

In some embodiments, the porosity of the positive electrode is ≦ 25%.

In some embodiments, the compacted density of the positive electrode active material layer is less than or equal to about 3.6g/cm³。

In some embodiments, the positive active material comprises Li₃PO₄Modified nickel-rich cathode materials or lithium-containing lithium-ion secondary batteries₃PO₄The preparation method of the modified nickel-rich cathode material can be exemplified by the following two methods:

liquid phase mixing method: mixing the positive electrode material (LiNi)_0.84Co_0.13Mn_0.06O₂) And H₃PO₄Dispersing in ethanol solution, magnetically stirring for 60 min, transferring into 80 deg.C oil bath, stirring until ethanol is completely volatilized to obtain Li₃PO₄Crushing and screening the modified ternary cathode active material by a screen to obtain cathode active materials with different particle sizes, so as to obtain Li₃PO₄In an amount of about 1 wt% based on the total weight of the modified nickel-rich ternary cathode material.

Sol-gel process: mixing the positive electrode material (LiNi)_0.84Co_0.13Mn_0.06O₂) Adding into ethanol solution containing lithium nitrate, citric acid and phosphoric acid, and stirring vigorously to obtain positive electrode material and Li₃PO₄The mass ratio of (A) to (B) is 99: 1. Then heating to 80 ℃, continuously stirring until the solvent is completely volatilized, and finally calcining for 2 hours in an air atmosphere at 600 ℃ to obtain Li₃PO₄Modified cathode materials.

In some embodiments, the positive active material comprises LiMPO₄Modified nickel-rich cathode materials or lithium-containing lithium-ion secondary batteries₃MO₄Modified nickel-rich cathode material composition, preparation method and modified nickel-rich cathode material prepared by Li₃PO₄The preparation method of the modified nickel-rich cathode material is similar.

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.

Negative electrode

The material, composition, and manufacturing method of the negative electrode used in the electrochemical device of the present application may include any of the techniques disclosed in the prior art. In some embodiments, the negative electrode is the negative electrode described in U.S. patent application US9812739B, which is incorporated by reference in its entirety.

In some embodiments, the negative electrode includes a current collector and a negative active material layer on the 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 embodiments, the negative active material layer includes a negative active material. The specific kind of the negative electrode active material is not particularly limited and may be selected as desired. 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 (MCMB), hard carbon, soft carbon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO₂Spinel-structured lithiated TiO₂-Li₄Ti₅O₁₂A Li-Al alloy, or any combination thereof. Wherein silicon-carbon composite means at least about 5 wt% silicon based on the weight of the silicon-carbon anode active material.

When the anode includes a silicon carbon compound, the ratio of silicon: carbon-about 1:10-10:1, and the silicon carbon compound has a median particle diameter D50 of about 0.1 to 20 microns. When the negative electrode includes an alloy material, the negative electrode active material layer can be formed by a method such as an evaporation method, a sputtering method, or a plating method. When the anode includes lithium metal, the anode active material layer is formed, for example, with a conductive skeleton having a spherical strand shape and metal particles dispersed in the conductive skeleton. In some embodiments, the spherical-strand shaped conductive skeleton may have a porosity of about 5% to about 85%. In some embodiments, a protective layer may also be disposed on the lithium metal anode active material layer.

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 some embodiments, the current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymeric substrates coated with a conductive metal, and any combination thereof.

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. In some embodiments, the solvent may include water, and the like, but is not limited thereto.

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 multiple layers, when the base material layer is multiple layers, the compositions of the polymers of different base material layers can be the same or different, and the weight average molecular weights of the polymers of different base material layers are not completely the same; when the substrate layer is a multilayer, the polymers of different substrate layers have different closed cell temperatures.

In some embodiments, a surface treatment layer is disposed on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

In some embodiments, the separator includes a porous substrate and a coating layer including inorganic particles and a binder.

In some embodiments, the coating layer thickness is from about 0.5 microns to about 10 microns, from about 1 micron to about 8 microns, or from about 3 microns to about 5 microns.

In some embodiments, the inorganic particles are selected from SiO₂、Al₂O₃、CaO、TiO₂、ZnO₂、MgO、ZrO₂、SnO₂、Al(OH)₃Or AlOOH. In some embodiments, the inorganic particles have a particle size of about 0.001 microns to about 3 microns.

In some embodiments, the binder is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoroethylene copolymer (PVDF-HFP), polyvinylpyrrolidone (PVP), polyacrylate, acrylic emulsion (anionic acrylic emulsion obtained by copolymerizing acrylic ester and a special functional monomer), styrene-acrylic emulsion (styrene-acrylic ester emulsion) obtained by emulsion-copolymerizing styrene and an acrylic ester monomer), and styrene-butadiene emulsion (SBR) obtained by copolymerizing butadiene and a styrene emulsion.

Electrolyte solution

The electrochemical device according to some embodiments of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode includes a current collector and a positive active material layer, and the positive active material layer includes a positive active material;

the electrolyte contains a compound of formula I:

wherein R is₁₁、R₁₂、R₁₃、R₁₄、R₁₅And R₁₆Each independently selected from: H. halogen, substituted or unsubstituted: c_1-8Alkyl radical, C_2-8Alkenyl radical, C_2-8Alkynyl, or C_6-12An aryl group; and is

In some embodiments, R₁₁、R₁₂、R₁₃、R₁₄、R₁₅And R₁₆Each independently selected from: H. halogen, substituted or unsubstituted: c_1-6Alkyl or C_1-4Alkyl radical, C_2-6Alkenyl or C_2-4Alkenyl radical, C_2-6Alkynyl or C_2-4Alkynyl, or C_6-10And (4) an aryl group.

In some embodiments, R₁₁、R₁₂、R₁₃、R₁₄、R₁₅And R₁₆Each independently selected from: H. f, methyl, ethyl, propyl, isopropyl, vinyl, or-CF₃。

In some embodiments, the amount of the compound of formula I is from about 0.01g to about 0.06g per 1g of the positive electrode active material; in some embodiments, the amount of the compound of formula I required per 1g of the cathode active material is about 0.015g, about 0.02g, about 0.025g, about 0.03g, about 0.035g, about 0.04g, about 0.045g, about 0.05g, or about 0.055 g.

The research of the inventor finds that the positive electrode material has the phenomenon of particle breakage in the later cycle period, the compound in the formula I has good thermal stability and moderate reaction rate, can be continuously and slowly consumed in the cycle process, and can effectively form a protective layer on the surface of the material after the material particles are broken to slow down the gas generation problem caused by side reaction.

The research of the inventor also finds that the film forming resistance of the compound shown in the formula I is relatively large, and the P element modification on the surface of the anode material is combined, so that on one hand, the stability and the ion conduction of the material can be improved, on the other hand, the reaction of the compound shown in the formula I at the early stage of circulation can be reduced, the initial resistance is reduced, the film forming effect at the later stage of circulation is ensured, and the effects of improving circulation and reducing gas generation are further realized.

in some embodiments, wherein the electrolyte further comprises an additive a comprising lithium tetrafluoroborate (LiBF)₄) Lithium difluorophosphate (LiPO)₂F₂) At least one of lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (trifluoromethanesulfonylimide) (LiTFSI), lithium 4, 5-dicyano-2-trifluoromethylimidazole, lithium difluorobis (oxalato) phosphate, lithium difluorooxalato borate, or lithium bis (oxalato) borate; and about 0.000026g to about 0.019g of the additive a is required per 1g of the cathode active material.

The inventor researches and discovers that the additive A can preferentially form a film on the surface of the positive electrode material to form an interface film with relatively low impedance, so that the side reaction of the electrolyte on the surface of the positive electrode material is reduced, the reaction of the compound shown in the formula I in the early stage of circulation is reduced, the stability in the early stage of circulation can be ensured, the circulation capacity can be improved, and the occurrence of gas generation is reduced.

In some embodiments, the additive a comprises lithium difluorophosphate (LiPO)₂F₂)。

In some embodiments, about 0.00003g to 0.015g of the additive a is required per 1g of the positive electrode active material. In some embodiments, about 0.00006g, about 0.00008g, about 0.0001g, about 0.0003g, about 0.0005g, about 0.0007g, about 0.001g, about 0.003g, about 0.005g, about 0.007g, about 0.01g, about 0.013g, about 0.015g, or about 0.017g of the additive a is required per 1g of the positive electrode active material.

In some embodiments, the electrolyte further comprises an additive B comprising Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), tris (trimethylsilyl) phosphate (TMSP), tris (trimethylsilyl) borate (TMSB), Adiponitrile (ADN), Succinonitrile (SN), 1,3, 5-pentanenitrile, 1,3, 6-Hexanetricarbonitrile (HTCN), 1,2, 6-hexanetricarbonitrile, or 1,2, 3-tris (2-cyanato) propane (TECP).

In some embodiments, the mass ratio of the compound of formula I to the additive B is from 7:1 to 1: 7.

In some embodiments, the mass ratio of the compound of formula I to the additive B is about 7:1, about 6:1, about 5:1, about 4:1, about 3:1, about 2:1, about 1:2, about 1:3, about 1:4, about 1:5, about 1:6, or about 1: 7.

In some embodiments, 0.0005g to 0.18g of the additive B is required per 1g of the cathode active material. In some embodiments, about 0.0005g, about 0.001g, about 0.005g, about 0.01g, about 0.03g, about 0.05g, about 0.07g, about 0.1g, about 0.12g, about 0.15g, about 0.18g of the additive B is required per 1g of the positive electrode active material.

The inventor researches and discovers that the additive B can form a film on the positive electrode, adjust the film forming composition of the positive electrode, relatively increase the content of an organic layer, enhance the film forming stability of the positive electrode and further improve the cycling stability.

In some embodiments, the electrolyte further comprises a compound of formula II

In some embodiments, R₃₁And R₃₂Each is independently selected from the following substituted or unsubstituted groups: c_1-8Alkyl radical, C_1-6Alkyl radical, C_1-4Alkyl radical, C_2-6Alkenyl, or C_2-4Alkenyl, wherein substituted means substituted with one or more halo.

In some embodiments, R₃₁And R₃₂Is substituted with one or more halogens.

In some embodiments, R₃₁And R₃₂Each independently selected from the following unsubstituted or substituted with one or more F: methyl, ethyl, propyl, isopropyl, vinyl, or propenyl; in some embodiments, R₃₁And R₃₂Substituted with one or more F.

In some embodiments, the compound of formula II is present in an amount of about 1 to 45 wt%, based on the total weight of the electrolyte. In some embodiments, the compound of formula II is present in an amount of about 5 wt%, about 10 wt%, about 15 wt%, about 20 wt%, about 25 wt%, about 30 wt%, about 35 wt%, or about 40 wt%, based on the total weight of the electrolyte.

the research of the inventor finds that the compound of the formula I and the compound of the formula II can reduce the ion transmission resistance, can form a protective layer on the anode, and effectively repair the surface protective layer of the anode under the combined action of the compound of the formula I and the compound of the formula II after the particles are broken at the later stage of circulation, thereby prolonging the cycle life.

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 LiPF₆Lithium bis (trifluoromethanesulfonylimide) LiN (CF)₃SO₂)₂(abbreviated as LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO)₂F)₂) (abbreviated as LiFSI) and lithium hexafluoroarsenate LiAsF₆Lithium perchlorate LiClO₄Or lithium triflate LiCF₃SO₃。

In some embodiments, the concentration of the lithium salt is 0.3 to 1.5 mol/L. In some embodiments, the concentration of the lithium salt is 0.5 to 1.3mol/L or about 0.8 to 1.2 mol/L. In some embodiments, the concentration of the lithium salt is about 1.10 mol/L.

The organic solvent includes at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (DEC), dimethyl carbonate (DMC), Sulfolane (SF), γ -butyrolactone (γ -BL), ethyl propyl carbonate (MF), ethyl formate (MA), Ethyl Acetate (EA), Ethyl Propionate (EP), Propyl Propionate (PP), methyl propionate, methyl butyrate, ethyl fluoromethyl ethyl carbonate, dimethyl fluorocarbonate, or diethyl fluorocarbonate, etc.

In some embodiments, wherein the solvent comprises 70 wt% to 95 wt% of the electrolyte.

The electrolyte used in the electrochemical device of the present application is any of the electrolytes described above in the present application. In addition, the electrolyte used in the electrochemical device of the present application may further include other electrolytes within a range not departing from the gist of the present application.

Second, application

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. For example: 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 apparatus, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large-sized household battery or a lithium ion capacitor, and the like.

Third, example

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.

1. Preparation of lithium ion battery

The lithium ion batteries of comparative examples 1-1, comparative examples 1-2, and examples 1-1 to 1-21 were prepared as follows:

(1) preparation of the negative electrode

Mixing artificial graphite serving as a negative electrode active material, sodium carboxymethyl cellulose (CMC) serving as a thickening agent and Styrene Butadiene Rubber (SBR) serving as a binder according to a weight ratio of 97:1:2, adding deionized water, and obtaining negative electrode slurry under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 54 wt%; uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector; and drying the coated copper foil at 85 ℃, then carrying out cold pressing to obtain a negative electrode active material layer, cutting into pieces, slitting, and drying for 12 hours at 120 ℃ under a vacuum condition to obtain the negative electrode.

(2) Preparation of the Positive electrode

Preparation of Li by liquid phase mixing method₃PO₄Modified positive electrode active material: 99 g of LiNi_0.84Co_0.13Mn_0.06O₂1g of H₃PO₄Dispersing in absolute ethyl alcohol by ultrasonic for 10 minutes, then stirring for 60 minutes by magnetic force, then transferring to an oil bath kettle at 80 ℃ and stirring until the ethyl alcohol is completely volatilized to obtain Li₃PO₄The modified ternary positive active material is crushed and screened by a screen to obtain the positive active materials with different particle sizes.

Mixing Li₃PO₄Modified positive electrode active material LiNi_0.84Co_0.13Mn_0.06O₂(specific surface area 0.45 m)³Mixing the conductive agent Super P and the adhesive polyvinylidene fluoride according to the weight ratio of 97:1.4:1.6, adding N-methyl pyrrolidone (NMP), and uniformly stirring under the action of a vacuum stirrer to obtain positive electrode slurry, wherein the solid content of the positive electrode slurry is 72 wt%; uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil; and drying the coated aluminum foil at 85 ℃, then carrying out cold pressing, cutting and slitting, and drying for 4 hours at 85 ℃ under a vacuum condition to obtain the anode. The positive electrode comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, and the sum of the cross sections of the first particles in the positive electrode accounts for 27.1% of the cross section area calculated by the cross section area of the positive electrode perpendicular to the direction of the aluminum foil, and the sum of the cross sections of the second particles in the positive electrode accounts for 37.8% of the cross section area. The positive electrode active material layer had a compacted density of 3.4g/cm³。

Wherein the method of obtaining the compacted density is: and (3) cutting a pole piece with the diameter of 18mm, testing the thickness of the wafer by a ten-thousandth micrometer, and weighing the mass of the wafer. The compacted density ═ mass of wafer-mass of current collector in wafer)/(area of wafer x (thickness of wafer-thickness of current collector)).

(3) Preparation of the electrolyte

In a dry argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) are mixed according to the mass ratio of EC to PC to EMixing MC, DEC 20, 10, 30 and 40, adding additive, dissolving, stirring, adding lithium salt LiPF₆And mixing uniformly to obtain the electrolyte. Wherein, LiPF₆The concentration of (2) is 1.10 mol/L. Specific kinds and contents of additives used in the electrolyte are shown in table 1. In table 1, the content of the additive is calculated as gram weight required per 1g of the modified positive electrode active material.

(4) Preparation of the separator

Selecting a Polyethylene (PE) isolating film with the thickness of 9 microns, and performing polyvinylidene fluoride (PVDF) slurry and Al₂O₃Coating and drying the slurry to obtain the final isolating membrane.

(5) Preparation of lithium ion battery

And sequentially stacking the positive plate, the isolating film and the negative plate to enable the isolating film to be positioned between the positive plate and the negative plate to play an isolating role, then winding and welding the tabs, then placing the tabs into an outer packaging foil aluminum-plastic film, injecting the prepared electrolyte, and carrying out vacuum packaging, standing, formation, shaping, capacity test and other procedures to obtain the soft package lithium ion battery (the thickness is 3.3mm, the width is 39mm, and the length is 96 mm).

Examples 1 to 22: the electrolyte of the lithium ion battery was prepared in the following manner, and the other processes for preparing the lithium ion battery were completely the same as in comparative example 1-1.

In a dry argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) and compound II-3 were mixed in a mass ratio of EC: PC: EMC: DEC: compound II-3: 20:10:40:20:10, followed by addition of an additive, dissolution and thorough stirring, followed by addition of a lithium salt LiPF₆And mixing uniformly to obtain the electrolyte. Wherein, LiPF₆The concentration of (2) is 1.10 mol/L. Specific kinds and contents of additives used in the electrolyte are shown in table 1. In table 1, the content of the additive is a gram weight required per 1g of the modified positive electrode active material.

Examples 1 to 23: the electrolyte of the lithium ion battery was prepared in the following manner, and the other processes for preparing the lithium ion battery were completely the same as in comparative example 1-1.

In dry argon gasIn an atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) and a compound II-3 are mixed according to the mass ratio of EC: PC: EMC: DEC: compound II-3: 20:10:20:20:30, then an additive is added, the mixture is dissolved and fully stirred, and lithium salt LiPF is added₆And mixing uniformly to obtain the electrolyte. Wherein, LiPF₆The concentration of (2) is 1.10 mol/L. Specific kinds and contents of additives used in the electrolyte are shown in table 1. In table 1, the content of the additive is a gram weight required per 1g of the modified positive electrode active material.

Examples 1 to 24: the electrolyte of the lithium ion battery was prepared in the following manner, and the other processes for preparing the lithium ion battery were completely the same as in comparative example 1-1.

In a dry argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) and compound II-2 were mixed in a mass ratio of EC: PC: EMC: DEC: compound II-2 of 20:10:30:30:10, followed by addition of an additive, dissolution and thorough stirring, followed by addition of a lithium salt LiPF₆And mixing uniformly to obtain the electrolyte. Wherein, LiPF₆The concentration of (2) is 1.10 mol/L. Specific kinds and contents of additives used in the electrolyte are shown in table 1. In table 1, the content of the additive is a gram weight required per 1g of the positive electrode active material.

Examples 1 to 25: the positive electrode of the lithium ion battery was prepared in the following manner, and the other processes of the lithium ion battery preparation were completely the same as in comparative example 1-1.

Preparation of the polymer by Li by sol-gel method₃PO₄Modified positive electrode active material: mixing positive electrode material (molecular formula LiNi)_0.84Co_0.13Mn_0.06O₂)91.7 g of the solution is added into an ethanol solution containing 2g of lithium nitrate, 5.4 g of citric acid and 0.9 g of phosphoric acid, and the mixture is stirred vigorously to ensure that the anode material and Li₃PO₄The mass ratio of (A) to (B) is 99: 1. Heating to 80 deg.C, stirring until the solvent is completely volatilized, and calcining at 600 deg.C in air atmosphere for 2 hr to obtain modified Li₃PO₄A modified positive electrode active material.

Example 1-26: the lithium ion battery was fabricated in exactly the same manner as in example 1-2, except that the positive electrode active material layer had a compacted density of 3.3g/cm³

Examples 1 to 27: the lithium ion battery was fabricated in exactly the same manner as in example 1-2, except that the positive electrode active material layer had a compacted density of 3.6g/cm³

Examples 1 to 28: the lithium ion battery was prepared in exactly the same manner as in example 1-2, except that the sum of the sectional areas of the first particles in the positive electrode active material accounted for 10.4% of the sectional area.

Examples 1-29 to 1-31: the lithium ion battery was prepared in exactly the same manner as in examples 1-2, except that LiNi, which is a positive electrode active material, was used_0.84Co_0.13Mn_0.06O₂Is not subjected to Li₃PO₄And (4) modifying.

Examples 1 to 32: the lithium ion battery was prepared in exactly the same manner as in example 1-2, except that the positive electrode active material was LiNi_0.84Co_0.13Mn_0.058Zr_0.002O₂。

Examples 1 to 33: the lithium ion battery was prepared in exactly the same manner as in example 1-2, except that the positive electrode active material was LiNi_0.84Co_0.13Mn_0.057Al_0.001Zr_0.002O₂。

Comparative examples 1 to 3: the preparation method was exactly the same as in comparative example 1-1, except that LiNi, a positive electrode active material, was used_0.84Co_0.13Mn_0.06O₂Is not subjected to Li₃PO₄And (4) modifying.

Comparative example 2-1 to comparative example 2-4 and examples 2-1 to 2-18: the battery was fabricated in the same manner as in comparative example 1-1, except for the kind of the positive electrode material and the electrolyte.

2. Method for testing circularity, cross section and area ratio of particles

(1) Degree of circularity of particles

The circularity of the positive electrode active material particles was measured using a circularity meter of type DTP-550A.

(2) Particle cross-sectional area and area ratio

The positive electrode was cut by an ion polisher (model No. jp electron-IB-09010 CP) in a direction perpendicular to the positive electrode current collector to obtain a cross section. And observing the section by using a scanning electron microscope at a proper magnification, taking a picture by using a back scattering mode, and identifying the circularity and the particle sectional area by using the function of identifying the pattern morphology of Image J software, so that the broken particles and the current collector in the particles A and the particles A are identified. And correspondingly identifies the corresponding area. The total area of the positive plate section is S, and the total area of the particles A is S₁(including crushed particles) and the total area of the crushed particles in the particles A is S₂The area of the positive current collector is S₃The porosity is P, neglecting the area fraction of conductive agent and bond. In the present application, the circularity of the particles a is greater than or equal to 0.4 and the cross-sectional area of the individual particles a is greater than or equal to 20 square microns.

Total area ratio of particles A ═ S₁/S×100％；

The total area ratio of the crushed particles in the particles A is S₂/S×100％；

The ratio of the total area of the crushed particles to the total area of the particles A is S₂/S₁×100％；

Total area ratio of particles B ═ S-S₁-S₃)/S×100％-P。

3. Porosity test of positive electrode

And (3) testing by using a true density tester AccuPyc II 1340, wherein each sample is measured at least 3 times, and at least 3 data are selected to be averaged. The porosity P of the positive electrode was calculated according to the following formula: p ═ V1-V2)/V1 × 100%, where V1 is the apparent volume and V1 ═ sample surface area × sample thickness × number of samples; v2 is the true volume.

4. Scanning Electron Microscope (SEM) testing of lithium ion battery anodes

The lithium ion battery is disassembled to obtain the anode after reaching the full discharge state (namely discharging to the cut-off voltage of 2.8V), and DMC is used

And cleaning the positive electrode, drying in vacuum, cutting along the direction of the positive electrode plate, and performing SEM test on the positive electrode active material interface.

5. Cycle performance testing of lithium ion batteries

(1) Lithium ion battery cycle performance test

And (3) placing the lithium ion battery in a constant temperature box at 45 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. The lithium ion battery reaching a constant temperature was charged at a constant current of 1C to a voltage of 4.2V, then charged at a constant voltage of 4.2V to a current of 0.05C, and then discharged at a constant current of 4C to a voltage of 2.8V, which is a charge-discharge cycle. The capacity of the first discharge is taken as 100%, the charge-discharge cycle is repeated for 600 circles, the test is stopped, and the cycle capacity retention rate is recorded and used as an index for evaluating the cycle performance of the lithium ion battery.

The cycle capacity retention ratio is the capacity at the time of cycling to 600 cycles divided by the capacity at the time of the first discharge.

The cycle thickness variation is the thickness of the cell at the time of cycling to some 600 cycles minus the initial thickness of the cell, and then divided by the initial thickness of the cell.

(2) High-temperature storage performance test after lithium ion battery circulation

The cell was charged at 1C constant current to 4.2V and then constant voltage to a current of 0.05C. And (3) placing the fully-charged battery after circulation in a constant temperature box at 60 ℃, storing for 30 days, and recording the thickness change before and after storage.

Thickness change-1 × 100% (thickness stored for 30 days/initial thickness).

A. The lithium ion batteries of comparative examples 1-1 to 1-3 and examples 1-1 to 1-33 were prepared according to the above-described methods, and the cycle performance and high-temperature storage performance after cycling were tested. The results of the electrolyte addition test in the cell are shown in Table 1.

TABLE 1

Note: (1) "/" indicates no addition; (2)*: the amount added is grams per 1 gram of the positive electrode active material to be added.

According to the comparison between examples 1-1 to 1-5 and comparative examples 1-1 to 1-2, the addition of a specific content of the compound of formula I to the electrolyte can significantly improve the cycle performance and the high-temperature storage performance of the lithium ion battery, and the main reason is probably that the compound of formula I can form a film on the surface of the cathode material, thereby reducing the occurrence of side reactions.

As can be seen from the comparison of examples 1-6 to examples 1-14 with examples 1-2, the electrolyte containing the compound of formula I (e.g., at least one of the compounds 1-1, 1-2, 1-3, or 1-4) is further added with a specific amount of an additive A (e.g., LiPF)₂O₂) The cycle performance and the high-temperature storage performance of the lithium ion battery can be further improved. The reason for this improvement may be additive A (e.g. LiPF)₂O₂) Preferentially forming a film on the surface of the cathode, improving the film forming structure, enhancing the film forming stability and being beneficial to the compound shown in the formula I to play a greater role in the later cycle period.

As can be seen from a comparison of examples 1-15 to examples 1-20 with examples 1-9, appropriate amounts of a compound of formula I and an additive A (e.g. LiPF)₂O₂) The electrolyte is further added with a specific amount of additive B, so that the cycle performance and the high-temperature storage performance of the lithium ion battery can be further improved; according to the comparison between examples 1-21 and examples 1-2, it can be seen that the cycle performance and high temperature storage performance of the lithium ion battery can be further improved by further adding a specific amount of additive B into the electrolyte containing a proper amount of the compound of formula I, and the main reason is probably that the additive B has a film forming effect on the negative electrode in the formation stage, so that the interface stability of the negative electrode is enhanced.

As can be seen from the comparison of examples 1-22 to examples 1-24 with examples 1-16, the cycle performance and high temperature storage performance of the lithium ion battery can be further improved by further adding a specific amount of the compound of formula II to the electrolyte containing appropriate amounts of the compound of formula I, the additive A and the additive B. The main reasons may be that on the one hand the compound of formula II reduces the viscosity of the electrolyte and on the other hand the combination of additives changes the film forming structure on the surface of the positive electrode, thus improving the film forming stability.

As can be seen from comparison of examples 1-25 with examples 1-2, the properties of the positive electrode active materials modified by the liquid phase mixing and sol-gel methods are similar, and both methods are suitable for modification applications of the positive electrode active materials.

As can be seen by comparing examples 1-26, 1-27 and examples 1-2, lowering the compacted density of the positive electrode active material layer can improve the cycle performance and the high-temperature storage performance, probably because a suitable compacted density can reduce the degree of particle breakage of the material; increasing the compacted density is the opposite. Compacted density considering the requirements of practical application on mass energy density and volume energy density<3.6g/cm³Is suitable for practical application.

As can be seen from comparison of examples 1 to 28 with examples 1 to 2, controlling the proportion of the first particles in the positive active material can alleviate side reactions caused by particle breakage at the latter stage of the cycle, which is advantageous in improving cycle performance and high-temperature storage performance.

Comparison of examples 1-29 with examples 1-2 shows that the reaction proceeds via Li₃PO₄The stability of the modified anode material is improved, the side reaction of the electrolyte and the anode is effectively reduced, and the cycle performance of the battery is improved.

As can be seen from comparison of examples 1-31 and examples 1-30 with examples 1-29, the positive electrode active material does not contain Li₃PO₄In the case of modification, an electrolyte solution containing an appropriate amount of a compound of the formula I is further added with an additive A (e.g. LiPF)₂O₂) And the additive B can further improve the cycle performance and the high-temperature storage performance of the lithium ion battery.

It can be seen from comparison of examples 1 to 33 and examples 1 to 32 with examples 1 to 2 that further inclusion of the Q element in the positive active material can further improve the cycle characteristics and high-temperature storage characteristics of the battery.

B. The lithium ion batteries of comparative examples 2-1 to 2-4 and examples 2-1 to 2-18 were prepared according to the above-described methods, and the cycle performance and the high-temperature storage performance after the cycle were tested. The positive electrode active material, the electrolyte and the test results are shown in tables 2 and 3. The ratio of the cross-sectional area of the first particles to the second particles in the positive electrode active material is achieved by controlling the mass ratio of the first particles to the second particles.

TABLE 2

As can be seen from comparison of comparative examples 2-1 to 2-4 with examples 2-1 to 2-4, Li was used in the battery₃PO₄The modified various nickel-rich cathode materials and the compound of the formula I added in the electrolyte act together, so that the material structure can be stabilized, the interface with the electrolyte is stabilized, the side reaction is reduced, and the cycle performance and the high-temperature storage performance of the lithium ion battery can be further improved. Further from examples 2 to 5 to examples 2 to 9, and examples 2 to 11 to examples 2 to 13, it can be seen that the use of Li₃PO₄Modified various nickel-rich cathode materials, and adding a compound shown in formula I and an additive A (such as LiPO) into an electrolyte₂F₂) The cycle performance and the high-temperature storage performance of the lithium ion battery can be further improved, and probably the reason is that after the additive A is added, the film-forming impedance is relatively low, the direct-current internal resistance of the battery can be reduced, and the side reaction of the electrolyte on the surface of the positive electrode is reduced.

Comparison of examples 2 to 15 to examples 2 to 18 with examples 1 to 32 shows that the first particle amount and the second particle amount in the positive electrode material are favorable for improvement of cycle performance and gas evolution in a suitable range at a higher nickel content in the positive electrode active material, particularly at a nickel molar content of not less than 60%.

Without wishing to be bound by any theory, it has been found that the addition of a positive film-forming additive to the electrolyte, a compound of formula I (e.g. 1, 3-Propane Sultone (PS)), improves the interfaceStability and reduction of side reactions; in addition, the adoption of spherical secondary particle grain boundary modification can obviously inhibit the particle crushing of the nickel-rich ternary cathode material in the circulation process and improve the structural stability of the material. And an additive A (e.g. LiPO) is used in the electrolyte₂F₂) The solid electrolyte interface film (SEI) formed on the anode has the effect of fast ion conduction, is beneficial to reducing Direct Current Resistance (DCR), increases inorganic components in the film formation of the electrode interface, thereby enhancing the stability of an interface protective layer, and simultaneously can protect the anode interface. The smaller primary particles in the anode material are beneficial to shortening the ion transmission distance and improving the rate capability of the material, and the smaller primary particles can increase the specific surface area of the material and increase the consumption of the film forming additive. The compound (such as fluoro solvent) of formula II is further introduced into the electrolyte, so that the stability of the electrolyte can be improved, and the reaction of the solvent on the surface of the material can be reduced. Through the combination of the crystal boundary modification of the anode material and the electrolyte anode protection additive, the granularity and the specific surface area of the anode material are limited, the battery multiplying power performance can be ensured, the high-temperature storage and high-temperature cycle of a spherical secondary particle nickel-rich ternary material battery system can be effectively improved, and the technical problem of high-temperature cycle gas production is solved.

C. Scanning Electron Microscope (SEM) testing of positive electrode active materials

Positive electrode active Material for comparative example 1-1 (via Li)₃PO₄Modified LiNi_0.84Co_0.13Mn_0.06O₂) Scanning electron microscopy tests were performed and the results are shown in figure 1.

In fig. 1, the left image is an SEM picture of the positive electrode active material, and the right image is a distribution diagram of the content of phosphorus element in the SEM picture. As can be seen from the right drawing, the phosphorus element in gray dots is distributed at the surface or grain boundary of the positive electrode active material.

SEM test results of the modified cathode active material in other examples are similar to those of fig. 1.

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 positive electrode comprises a current collector and a positive active material layer, wherein the positive active material layer comprises a positive active material;

the electrolyte contains a compound of formula I:

wherein R is₁₁、R₁₂、R₁₃、R₁₄、R₁₅And R₁₆Each independently selected from: H. halogen, substituted or unsubstituted: c_1-8Alkyl radical, C_2-8Alkenyl radical, C_2-8Alkynyl, or C_6-12An aryl group; and

an additive B comprising at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris (trimethylsilyl) phosphate, tris (trimethylsilyl) borate, adiponitrile, succinonitrile, 1,3, 5-pentanetrimethylnitrile, 1,3, 6-hexanetricarbonitrile, 1,2, 6-hexanetricarbonitrile, or 1,2, 3-tris (2-cyanato) propane.

2. The electrochemical device according to claim 1, wherein the amount of the compound of formula I is required to be 0.001g to 0.064g per 1g of the positive electrode active material.

3. The electrochemical device of claim 1, wherein the compound of formula I comprises at least one of the following compounds:

4. the electrochemical device according to claim 1, wherein the positive electrode active material layer contains first particles having a circularity of 0.4 to 1, wherein a cross-sectional area of the first particles is not less than 20 μm square, as calculated from a cross-sectional area of the positive electrode in a direction perpendicular to the current collector, and a sum of the cross-sectional areas of the first particles is 5% to 50%.

5. The electrochemical device according to claim 4, wherein the positive electrode active material layer contains second particles having a circularity of less than 0.4; wherein the cross-sectional area of the second particles is smaller than the cross-sectional area of the first particles, as calculated as the cross-sectional area of the positive electrode in a direction perpendicular to the current collector, and the ratio of the sum of the cross-sectional areas of the second particles is 5% to 60%.

6. The electrochemical device of any one of claims 1-5, wherein the electrolyte further comprises an additive A comprising LiBF, wherein the additive A comprises₄、LiPO₂F₂At least one of LiFSI, LiTFSI, lithium 4, 5-dicyano-2-trifluoromethylimidazole, lithium difluorobis (oxalato) phosphate, lithium difluorooxalato borate, or lithium bis-oxalato borate.

7. The electrochemical device according to claim 6, wherein 0.000026g to 0.019g of the additive A is required per 1g of the positive electrode active material.

8. The electrochemical device of claim 1, wherein the mass ratio of the compound of formula I to the additive B is 7:1 to 1: 7.

9. The electrochemical device according to claim 1, wherein 0.0001g to 0.2g of the additive B is required per 1g of the positive electrode active material.

10. The electrochemical device according to claim 1, wherein the positive electrode active material layer contains a phosphorus-containing compound containing Li₃PO₄Or LiMPO₄Wherein M is selected from at least one of Co, Mn or Fe.

11. The electrochemical device according to claim 10, wherein the phosphorus-containing compound is contained at a surface or a grain boundary of the positive electrode active material.

12. The electrochemical device of claim 1, wherein the positive electrode active material comprises LiNi_xCo_yMn_zO₂Wherein 0.55<x<0.92，0.03<y<0.2，0.04<z<0.3。

13. The electrochemical device according to claim 1, wherein the positive electrode active material layerA compacted density of less than or equal to 3.6g/cm³。

14. The electrochemical device of claim 1, wherein the electrolyte further comprises a compound of formula II

Wherein R is₃₁And R₃₂Each independently selected from substituted or unsubstituted C_1-10Alkyl, or substituted or unsubstituted C_2-8Alkenyl, wherein substituted means substituted with one or more halo;

the compound of formula II is present in an amount of 0.5 to 50 wt%, based on the total weight of the electrolyte.

15. The electrochemical device of claim 14, wherein the compound of formula II comprises at least one of the following compounds:

16. an electronic device comprising the electrochemical device of any one of claims 1-15.