Electrochemical devices and electronic devices

Abstract

The present application relates to an electrochemical device and an electronic device. Specifically, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, the negative electrode active material layer contains a negative electrode active material, wherein there is an electrically conductive material between the negative electrode active material layer and the negative electrode current collector, the average particle size of the electrically conductive material is smaller than the average particle size of the negative electrode active material, and the negative electrode active material layer has a specific weight. The electrochemical device of the present application has improved high-temperature cycle expansion performance and overcharge resistance.

Description

[0001] This application is a divisional application of Chinese invention patent application entitled "Electrochemical Device and Electronic Device", application number 202011101403.7, and application date October 15, 2020. Technical Field

[0002] This application relates to the field of energy storage, specifically to an electrochemical device and an electronic device, particularly a lithium-ion battery. Background Technology

[0003] Electrochemical devices (such as lithium-ion batteries) have advantages such as high voltage, small size, light weight, high specific capacity, no memory effect, no pollution, low self-discharge, and long cycle life, and have been widely used in many fields such as digital products, electric vehicles, and hybrid vehicles. With the widespread application of lithium-ion batteries, their safety performance has also received increasing attention.

[0004] The main safety hazard of lithium-ion batteries is caused by internal overheating. If the heat generated inside a lithium-ion battery cannot be released quickly, the battery temperature will continue to rise, thus intensifying the chemical reactions within the battery and ultimately leading to thermal runaway, or even explosions, fires, and other safety accidents.

[0005] In view of this, it is indeed necessary to provide an electrochemical device and an electronic device with improved performance. Summary of the Invention

[0006] This application provides an electrochemical and electronic device with improved high-temperature cyclic expansion performance and overcharge resistance to address at least one safety issue existing in the relevant field to some extent.

[0007] In one aspect of this application, an electrochemical device is provided, comprising: a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material, wherein: a conductive material is present between the negative electrode active material layer and the negative electrode current collector, the average particle size of the conductive material is smaller than the average particle size of the negative electrode active material, and the weight per unit area of ​​the negative electrode active material layer is W mg / cm³. 2 W is in the range of 3 to 12.

[0008] According to an embodiment of this application, the average particle size of the conductive material is less than 1 μm.

[0009] According to embodiments of this application, the conductive material includes at least one of carbon black, carbon fiber, graphene, or carbon nanotubes.

[0010] According to an embodiment of this application, an adhesive is further included between the negative electrode active material layer and the negative electrode current collector.

[0011] According to embodiments of this application, the adhesive comprises at least one of styrene-butadiene rubber, styrene-butyl acrylate copolymer, styrene-(meth)acrylate copolymer, carboxymethyl cellulose, polyvinyl alcohol, sodium polyacrylate, polyvinylidene fluoride, polyimide, polyamide-imide, or deacetylated chitosan.

[0012] According to embodiments of this application, the adhesive comprises an evaporable or degradable organic adhesive.

[0013] According to embodiments of this application, the organic adhesive includes at least one of chitin-chitosan derivatives, fluorinated resins, synthetic rubber, polyamides, polyimides, polyolefins, or polyacrylic resins.

[0014] According to an embodiment of this application, the tensile strength of the negative electrode current collector is FN / mm. 2 F is above 400 and 100 / 3 ≤ F / W ≤ 150.

[0015] According to an embodiment of this application, the tensile strength of the negative electrode current collector is FN / mm. 2 The density of the negative electrode active material layer is D g / cm³. 3 D is in the range of 1.4 to 2.0 and 560≤F×D≤1800.

[0016] According to embodiments of this application, the electrolyte comprises at least one of the following compounds:

[0017] (a) Propionate;

[0018] (b) Organic compounds containing a cyano group;

[0019] (c) Lithium difluorophosphate;

[0020] (d) Compound of Formula 1:

[0021]

[0022] in:

[0023] R 1 R 2 R 3 R 4 R 5 and R 6 Each is independently hydrogen or C1-C 10 alkyl;

[0024] L1 and L2 are each independently -(CR 7R 8 ) n -;

[0025] R 7 and R 8 Each is independently hydrogen or C1-C 10 Alkyl groups; and

[0026] n is 1, 2, or 3.

[0027] According to embodiments of this application, the compound of formula 1 includes at least one of the following compounds:

[0028]

[0029] According to an embodiment of this application, based on the weight of the electrolyte, the content of the organic compound having a cyano group is a%, where a is in the range of 0.1 to 10.

[0030] According to an embodiment of this application, W and a satisfy: 0.3≤W / a≤20.

[0031] In another aspect of this application, an electronic device is provided that includes the electrochemical device described in this application.

[0032] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0033] The accompanying drawings, necessary for describing embodiments of this application or the prior art, will be briefly described below to facilitate the depiction of embodiments of this application. It is obvious that the drawings described below represent only a portion of the embodiments in this application. Those skilled in the art will be able to derive other embodiments from the structures illustrated in these drawings without requiring inventive effort.

[0034] Figure 1 A schematic diagram of the negative electrode in the electrochemical device of this application is shown. Detailed Implementation

[0035] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0036] Unless otherwise expressly stated, the terms used herein have the meanings indicated below.

[0037] In the detailed description and claims, the 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, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements. The term "at least one of" has the same meaning as the term "at least one of".

[0038] As used herein, the term "alkyl" is intended to refer to a straight-chain saturated hydrocarbon structure having 1 to 20 carbon atoms. "alkyl" is also intended to refer to a branched or cyclic hydrocarbon structure having 3 to 20 carbon atoms. When an alkyl group with a specific number of carbon atoms is specified, it is intended to encompass all geometric isomers having that number of carbon atoms; thus, for example, "butyl" means including 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, etc.

[0039] As used herein, the term "halogenated" refers to the partial or complete substitution of hydrogen atoms in a group by halogen atoms (e.g., fluorine, chlorine, bromine, or iodine).

[0040] With the widespread use of electrochemical devices (such as lithium-ion batteries), their safety performance has received increasing attention. The main safety hazards of electrochemical devices stem from internal overheating. When an electrochemical device is under high temperature or overcharged conditions, overheating can occur, leading to safety risks such as expansion, deformation, or even explosion.

[0041] To address the aforementioned issues, this application utilizes a negative electrode active material layer with a specific weight and places a small conductive material between the negative electrode active material layer and the negative electrode current collector to prevent the negative electrode from breaking under high-temperature cycling or overcharge conditions. This allows the capacity of the electrochemical device to be fully extracted, thereby significantly improving the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device.

[0042] In one embodiment, this application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte as described below.

[0043] I. Negative electrode

[0044] The negative electrode includes a negative electrode current collector and a layer of negative electrode active material formed on one or both surfaces of the negative electrode current collector, the layer of negative electrode active material containing negative electrode active material.

[0045] 1. Conductive materials

[0046] A feature of the electrochemical device of this application is that a conductive material is present between the negative electrode active material layer and the negative electrode current collector, the conductive material having an average particle size smaller than the average particle size of the negative electrode active material. As used herein, "conductive material" refers to a material with excellent electrical conductivity.

[0047] The surface of the negative electrode current collector is relatively smooth, making it difficult for materials such as the negative electrode active material to adhere to or support it. Placing a conductive material between the negative electrode active material layer and the negative electrode current collector not only improves the conductivity at the interface between them but also blurs the interface, thereby enhancing the adhesion between the two. For example... Figure 1 As shown, the negative electrode of the electrochemical device of this application includes a negative electrode active material layer 1, a negative electrode current collector 3, and a conductive material 2 between the negative electrode active material layer and the negative electrode current collector. A portion of the negative electrode active material 1 is sandwiched within the conductive material 2, thereby being firmly supported by the negative electrode current collector 3. Furthermore, the conductive material is typically aggregated in a direction parallel to the surface of the negative electrode current collector, and almost never stacked in a direction perpendicular to the negative electrode current collector. In this case, when the average particle size of the conductive material is smaller than the average particle size of the negative electrode active material, the interface containing the conductive material between the negative electrode current collector and the negative electrode active material layer is very thin, which can significantly improve the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device.

[0048] In some embodiments, the average particle size of the conductive material is less than 1 μm. In some embodiments, the average particle size of the conductive material is less than 0.8 μm. In some embodiments, the average particle size of the conductive material is less than 1 μm. In some embodiments, the average particle size of the conductive material is less than 0.5 μm. In some embodiments, the average particle size of the conductive material is less than 0.2 μm. In some embodiments, the average particle size of the conductive material is less than 0.1 μm. When the average particle size of the conductive material is within the above ranges, it helps to further improve the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device.

[0049] In some embodiments, the conductive material is located in a region less than 3 μm from the negative electrode current collector. In some embodiments, the conductive material is located in a region less than 2 μm from the negative electrode current collector. In some embodiments, the conductive material is located in a region less than 1 μm from the negative electrode current collector.

[0050] In some embodiments, in the region below 3 μm from the negative electrode current collector, the content of the negative electrode active material sandwiched in the conductive material is less than 10% by volume, based on the total volume of the solid component material. In some embodiments, in the region below 3 μm from the negative electrode current collector, the content of the negative electrode active material sandwiched in the conductive material is less than 8% by volume, based on the total volume of the solid component material. In some embodiments, in the region below 3 μm from the negative electrode current collector, the content of the negative electrode active material sandwiched in the conductive material is less than 5% by volume, based on the total volume of the solid component material.

[0051] In some embodiments, the conductive material may have a shape including at least one of granular and fibrous forms.

[0052] In some embodiments, the conductive material includes at least one of carbon black, carbon fiber, graphene, or carbon nanotubes. In some embodiments, the carbon black includes at least one of acetylene black, furnace black, or Ketjen black.

[0053] 2. Adhesive

[0054] In some embodiments, an adhesive is further included between the negative electrode active material layer and the negative electrode current collector. The adhesive enhances the bonding between the negative electrode active material layer and the negative electrode current collector. The adhesive that can be used is typically a resin having the following properties: it does not decompose during negative electrode preparation, it is resistant to oxidation and reduction, it can adapt to the volume expansion during charging and discharging of the electrochemical device, and it prevents the interface between the negative electrode current collector and the negative electrode active material layer from breaking due to the expansion and contraction of the negative electrode active material layer.

[0055] In some embodiments, the adhesive comprises at least one of styrene-butadiene rubber, styrene-butyl acrylate copolymer, styrene-(meth)acrylate copolymer, carboxymethyl cellulose, polyvinyl alcohol, sodium polyacrylate, polyvinylidene fluoride, polyimide, polyamide-imide, or deacetylated chitosan.

[0056] In some embodiments, the adhesive comprises an evaporable or decomposable organic adhesive. In some embodiments, the organic adhesive evaporates or decomposes in the range of 160°C to 500°C. In some embodiments, the organic adhesive evaporates or decomposes in the range of 200°C to 400°C. In some embodiments, the organic adhesive evaporates or decomposes in the range of 200°C to 300°C. During the preparation of the negative electrode, the negative electrode active material layer is typically coated at a temperature below 120°C; therefore, the aforementioned organic adhesive does not evaporate or decompose during this coating process. The aforementioned organic adhesive can improve the adhesion between the negative electrode current collector and the negative electrode active material layer at room temperature. When the aforementioned temperature is reached, the organic adhesive evaporates or decomposes, thereby electrically isolating the negative electrode current collector and the negative electrode active material layer, insulating them, and preventing the electrochemical device from continuing to react chemically and overheat, thus improving the high-temperature storage expansion and overcharge resistance of the electrochemical device.

[0057] As used herein, the terms “evaporation” and “decomposition” refer to the deterioration of the organic binder that causes at least a portion of it to become non-existent, and the term “electrical isolation” refers to the state in which the organic binder, after evaporation or decomposition, creates voids in its original occupied areas. When electrical isolation occurs between the negative electrode current collector and the negative electrode active material layer, the content of the organic binder decreases by 15% to 20%, or the resistance between the negative electrode current collector and the negative electrode active material layer reaches 300Ω to 1000Ω as measured by a two-terminal surface ohmmeter of the electrode.

[0058] In some embodiments, the organic adhesive comprises at least one of chitin-chitosan derivatives, fluorinated resins, synthetic rubber, polyamides, polyimides, polyolefins, or polyacrylic resins.

[0059] In some embodiments, the chitin-chitosan derivative includes at least one of hydroxyethyl chitosan, hydroxypropyl chitosan, hydroxybutyl chitosan, or alkylated chitosan.

[0060] In some embodiments, the fluorinated resin includes at least one of polyvinylidene fluoride or polytetrafluoroethylene.

[0061] In some embodiments, the synthetic rubber includes at least one of styrene-butadiene rubber, acrylic rubber, or nitrile rubber.

[0062] In some embodiments, the polyolefin includes at least one of low-density polyethylene, high-density polyethylene, or polypropylene.

[0063] In some embodiments, the polyacrylic resin includes at least one of ethylene glycol dimethacrylate or propylene glycol dimethacrylate.

[0064] In some embodiments, the alkylated chitosan comprises an organic binder made by mixing and crosslinking organic acids, wherein the organic acids include at least one of salicylic acid, pyromellitic acid, citric acid, or trimellitic acid.

[0065] The negative electrode active material can be supported by a micro-conductive material, which improves the adhesion between the negative electrode current collector and the negative electrode active material layer. Therefore, a smaller amount of adhesive can be present between the negative electrode active material layer and the negative electrode current collector.

[0066] 3. Negative electrode active material layer

[0067] The negative electrode active material layer can be one or more layers, and each layer in a multilayer negative electrode active material layer can contain the same or different negative electrode active materials. The negative electrode active material is any material capable of reversibly inserting and deintercalating metal ions such as lithium ions. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0068] Another feature of the electrochemical device of this application is that the weight per unit area of ​​the negative electrode active material layer is W mg / cm³. 2 W is in the range of 3 to 12. In some embodiments, W is in the range of 5 to 10. In some embodiments, W is in the range of 6 to 8. In some embodiments, W is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or within a range consisting of any two of the above values. When the weight per unit area of ​​the negative electrode active material layer is within the above range, it helps to improve the permeability of the electrolyte to the interface near the negative electrode current collector and the negative electrode active material layer, improve electron transport in the electrochemical device, and at the same time reduce the impact on the active material layer during processing, maintain a good interface between the negative electrode current collector and the negative electrode active material layer, reduce the relative displacement between the negative electrode active materials, thereby improving the high-temperature storage expansion performance and overcharge resistance of the electrochemical device.

[0069] In this application, the weight per unit area of ​​the negative electrode active material layer is the mass (mg) of the negative electrode active material layer relative to the area (cm²) of the active material layer. 2 The mass and area of ​​the negative electrode active material layer are obtained as follows: A test piece of appropriate size is cut from the negative electrode, its area is measured as S1 and its mass as W0. Then, the negative electrode current collector is peeled off from the negative electrode, and its mass as W1 is measured. The mass of the negative electrode active material layer is calculated from (W0-W1), where weight per unit area = (W0-W1) / S1. If the selected negative electrode is a double-sided active material layer, then the weight per unit area = (W0-W1) / S1 / 2.

[0070] Methods for peeling off the negative electrode active material layer include, for example, immersing the negative electrode active material layer in a solvent that can dissolve or swell the negative electrode active material layer, or wiping the active material layer with a cloth or the like.

[0071] The weight per unit area of ​​the negative electrode active material layer can be adjusted using known methods. For example, when forming the negative electrode active material layer by coating, it can be adjusted by changing the solid component concentration of the coating solution used to form the negative electrode active material layer, the number of coating passes, and the gap of the coating solution inlet of the coating machine. The weight per unit area of ​​the negative electrode active material layer can be increased by increasing the solid component concentration, increasing the number of coating passes, or increasing the gap. The weight per unit area of ​​the negative electrode active material layer can be decreased by decreasing the solid component concentration, decreasing the number of coating passes, or decreasing the gap.

[0072] In some embodiments, the density of the negative electrode active material layer is 1.0 g / cm³. 3 Up to 2.0 g / cm 3 In some embodiments, the density of the negative electrode active material layer is 1.2 g / cm³. 3 Up to 1.9 g / cm 3 In some embodiments, the density of the negative electrode active material layer is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 In some embodiments, the density of the negative electrode active material layer is 1.5 g / cm³. 3 Up to 1.7 g / cm 3 In some embodiments, the density of the negative electrode active material layer is 1.0 g / cm³. 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 Or within the range of any two of the above values. When the density of the negative electrode active material layer is within the above range, the negative electrode active material is not easily damaged, can maintain a low initial irreversible capacity, maintain high conductivity between the negative electrode active materials, and at the same time improve the permeability of the electrolyte to the interface between the negative electrode current collector and the negative electrode active material layer, thereby helping to improve the high-temperature storage expansion performance and overcharge resistance of the electrochemical device.

[0073] In some embodiments, the negative electrode active material includes, but is not limited to, carbon materials such as graphite, hard carbon, soft carbon, and MCMB, silicon, and SiO2. x (0<x<2) represents silicon oxides and other silicon-containing compounds, metallic lithium, metals that form alloys with lithium and their alloys, amorphous compounds mainly composed of oxides such as tin dioxide, and lithium titanate (Li4Ti5O). 12 ).

[0074] In some embodiments, the metals that form an alloy with lithium metal include, but are not limited to, aluminum, silicon, tin, and germanium.

[0075] In some embodiments, the negative electrode active material is a metal or half-metal, represented by silicon, that forms an alloy with lithium, or their alloys, which have high charge and discharge capacity.

[0076] In some embodiments, the negative electrode active material includes a mixture of metals or half-metals, represented by silicon, that form alloys with lithium, and their alloys, and carbon materials having a graphite structure.

[0077] In some embodiments, the negative electrode active material comprises a carbon material. In some embodiments, the negative electrode active material contains a carbon material having a graphite structure. In some embodiments, the negative electrode active material is at least one of artificial graphite or natural graphite.

[0078] In some embodiments, the negative electrode active material comprises different components, wherein a carbon material having a graphite structure is predominant. In some embodiments, the content of the carbon material having a graphite structure is 70.0% or more based on the weight of the negative electrode active material layer. In some embodiments, the content of the carbon material having a graphite structure is 90.0% or more based on the weight of the negative electrode active material layer. In some embodiments, the content of the carbon material having a graphite structure is 95.0% or more based on the weight of the negative electrode active material layer.

[0079] In some embodiments, the carbon material has a median particle size (D50) of about 5 μm to about 30 μm. In some embodiments, the carbon material has a median particle size (D50) of about 10 μm to about 25 μm. In some embodiments, the carbon material has a median particle size (D50) of about 15 μm to about 20 μm. In some embodiments, the carbon material has a median particle size (D50) of about 3 μm, about 5 μm, about 7 μm, about 10 μm, about 15 μm, about 20 μm, about 25 μm, about 30 μm, or within any two of the above values. When the median particle size of the carbon material is within the above ranges, the irreversible capacity of the electrochemical device is small, and the negative electrode is easily coated uniformly. The median particle size (D50) of carbon materials refers to the average particle size of the volume reference obtained by laser diffraction / scattering, which can be determined by dispersing the carbon material in a 0.2% aqueous solution (about 10 mL) of polyoxyethylene (20) sorbitan monolaurate and testing it using a laser diffraction / scattering particle size analyzer (Horiba Seisakusho LA-700).

[0080] In some embodiments, the negative electrode active material layer includes a negative electrode binder, which can improve the adhesion between the negative electrode active materials. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the solvent used in the electrolyte or electrode manufacturing process. The negative electrode binder may include polymeric materials that can be dissolved or dispersed in the solvent used in the manufacture of the negative electrode. When an aqueous solvent is used in the manufacture of the negative electrode, water-soluble polymeric materials include, but are not limited to, cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC); and polyvinyl alcohol (PVA), etc. Water-dispersible polymer materials include, but are not limited to, vinyl polymers such as polyethylene (PE) and polypropylene (PP); fluorinated resins such as polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA); vinyl acetate copolymers; and rubbers such as styrene-butadiene rubber (SBR) and acrylic-modified SBR resin (SBR latex).

[0081] In some embodiments, the binder content is 8 parts by weight or less relative to 100 parts by weight of the negative electrode active material. In some embodiments, the binder content is 7 parts by weight or less relative to 100 parts by weight of the negative electrode active material. In some embodiments, the binder content is 6 parts by weight or less relative to 100 parts by weight of the negative electrode active material. In some embodiments, the binder content is 5 parts by weight or less relative to 100 parts by weight of the negative electrode active material. In some embodiments, the binder content is 4 parts by weight or less relative to 100 parts by weight of the negative electrode active material. In some embodiments, the binder content is 3 parts by weight or less relative to 100 parts by weight of the negative electrode active material. In some embodiments, the binder content is 2 parts by weight or less relative to 100 parts by weight of the negative electrode active material.

[0082] The thickness of the negative electrode active material layer refers to the thickness of the negative electrode active material layer coated on a single side of the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer is 15 μm or more. In some embodiments, the thickness of the negative electrode active material layer is 20 μm or more. In some embodiments, the thickness of the negative electrode active material layer is 30 μm or more. In some embodiments, the thickness of the negative electrode active material layer is 150 μm or less. In some embodiments, the thickness of the negative electrode active material layer is 120 μm or less. In some embodiments, the thickness of the negative electrode active material layer is 100 μm or less. In some embodiments, the thickness of the negative electrode active material layer is within the range of any two of the above values. When the thickness of the negative electrode active material layer is within the above range, the electrolyte can penetrate to the vicinity of the negative electrode current collector interface, improving the charge and discharge characteristics of the electrochemical device at high current densities; at the same time, when the volume ratio of the negative electrode current collector to the negative electrode active material is within an appropriate range, the capacity of the electrochemical device can be ensured.

[0083] 3. Negative electrode current collector

[0084] In some embodiments, the tensile strength of the negative electrode current collector is FN / mm. 2F is 400 or higher. In some embodiments, F is 450 or higher. In some embodiments, F is 500 or higher. In some embodiments, F is 550 or higher. In some embodiments, F is 600 or higher. In some embodiments, F is 650 or higher. In some embodiments, F is 700 or higher. In some embodiments, F is 800 or higher. In some embodiments, F is 900 or higher. In some embodiments, F is 1000 or higher. As used herein, the term "tensile strength" refers to the ratio of the maximum tensile force required for the specimen to break to the cross-sectional area of ​​the specimen. Using a negative electrode current collector with high tensile strength can suppress cracking of the negative electrode current collector caused by the expansion / contraction of the negative electrode active material layer during charging / discharging of the electrochemical device, thereby significantly improving the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device.

[0085] In some embodiments, the tensile strength FN / mm of the negative electrode current collector 2 Weight per unit area of ​​the negative electrode active material layer (W mg / cm²) 2 Satisfying: 100 / 3 ≤ F / W ≤ 150. In some embodiments, 40 ≤ F / W ≤ 120. In some embodiments, 50 ≤ F / W ≤ 100. In some embodiments, 60 ≤ F / W ≤ 80. In some embodiments, F / W is 100 / 3, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or within a range of any two of the above values. When the tensile strength FN / mm of the negative electrode current collector... 2 Weight per unit area of ​​the negative electrode active material layer (W mg / cm²) 2 When the above relationships are satisfied, the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device can be further improved.

[0086] The tensile strength of the negative electrode current collector can be determined using the same apparatus and method as that used for determining elongation (refer to the test method in GB-228-87).

[0087] In some embodiments, the density of the negative electrode active material layer is D g / cm³. 3 D is in the range of 1.4 to 2.0. In some embodiments, D is in the range of 1.5 to 1.8. In some embodiments, D is 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or within a range consisting of any two of the above values. When the density of the negative electrode active material layer is within the above range, the negative electrode active material is not easily damaged, maintaining a low initial irreversible capacity, ensuring high conductivity between the negative electrode active materials, and simultaneously improving the permeability of the electrolyte to the interface between the negative electrode current collector and the negative electrode active material layer, thereby helping to improve the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device.

[0088] In some embodiments, the tensile strength FN / mm of the negative electrode current collector 2 Density D g / cm³ of the negative electrode active material layer 3 Satisfying: 560≤F×D≤1800. In some embodiments, 600≤F×D≤1500. In some embodiments, 700≤F×D≤1200. In some embodiments, 600≤F×D≤1500. In some embodiments, 800≤F×D≤1000. In some embodiments, F×D is 560, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, or within a range consisting of any two of the above values. When the tensile strength FN / mm of the negative electrode current collector... 2 Density D g / cm³ of the negative electrode active material layer 3 When the above relationships are satisfied, the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device can be further improved.

[0089] In some embodiments, the negative electrode current collector includes, but is not limited to, metal foil, metal cylinder, metal strip roll, metal plate, metal film, metal mesh, stamped metal, foamed metal, etc. In some embodiments, the negative electrode current collector is a metal foil. In some embodiments, the negative electrode current collector is a copper foil. As used herein, the term "copper foil" includes copper alloy foil.

[0090] In some embodiments, the negative current collector is a conductive resin. In some embodiments, the conductive resin includes a film obtained by depositing copper onto a polypropylene film.

[0091] Preparation of negative electrode

[0092] The negative electrode in the electrochemical device of this application can be prepared using any known method. For example, a slurry can be prepared by adding a binder, solvent, thickener, conductive material, filler, etc., as needed, to the negative electrode active material. This slurry can then be coated onto the negative electrode current collector, dried, and pressed to form an electrode. Alternatively, the negative electrode active material can be roll-formed into a sheet electrode or compressed into a granular electrode.

[0093] II. Electrolyte

[0094] The electrolyte used in the electrochemical device of this application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte used in the electrochemical device of this application further includes additives.

[0095] According to some embodiments of this application, the electrolyte further includes at least one of the following compounds:

[0096] (a) Propionate;

[0097] (b) Organic compounds containing a cyano group;

[0098] (c) Lithium difluorophosphate

[0099] (d) Compound of Formula 1:

[0100]

[0101] in:

[0102] R 1 R 2 R 3 R 4 R 5 and R 6 Each is independently hydrogen or C1-C 10 alkyl;

[0103] L1 and L2 are each independently -(CR 7 R 8 ) n -;

[0104] R 7 and R 8 Each is independently hydrogen or C1-C 10 Alkyl groups; and

[0105] n is 1, 2, or 3.

[0106] (a) Propionate

[0107] According to some embodiments of this application, the propionate comprises a compound of formula 2:

[0108]

[0109] in:

[0110] R 1 Selected from ethyl or haloethyl,

[0111] R 2 It is selected from C1-C6 alkyl or C1-C6 haloalkyl.

[0112] In some embodiments, the propionate ester includes, but is not limited to, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, methyl halopropionate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, and pentyl halopropionate. In some embodiments, the propionate ester is selected from at least one of methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and pentyl propionate. In some embodiments, the halogen group in the methyl halopropionate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, and pentyl halopropionate is selected from one or more of fluorine (-F), chlorine (-Cl), bromine (-Br), and iodine (-I). In some embodiments, the halogen group is a fluorine (-F) group, which can achieve better results.

[0113] In some embodiments, the propionate content is 10% to 65% based on the weight of the electrolyte. In some embodiments, the propionate content is 15% to 60% based on the weight of the electrolyte. In some embodiments, the propionate content is 30% to 50% based on the weight of the electrolyte. In some embodiments, the propionate content is 30% to 40% based on the weight of the electrolyte. In some embodiments, the propionate content is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or within a range of any two of the above values, based on the weight of the electrolyte. Using propionate with the above-mentioned contents can achieve superior results.

[0114] (b) Compounds containing a cyano group

[0115] In some embodiments, compounds having a cyano group include, but are not limited to, one or more of the following: succinic anionyl nitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinic anionyl nitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, and ethylene glycol bis(propionitrile). Ethers, 3,5-dioxa-heptanenitrile, 1,4-di(cyanoethoxy)butane, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, 1,3-di(2-cyanoethoxy)propane, 1,4-di(2-cyanoethoxy)butane, 1,5-di(2-cyanoethoxy)pentane, ethylene glycol di(4-cyanobutyl) ether, 1,4-dicyano-2-butene, 1,4-Dicyano-2-methyl-2-butene, 1,4-Dicyano-2-ethyl-2-butene, 1,4-Dicyano-2,3-dimethyl-2-butene, 1,4-Dicyano-2,3-diethyl-2-butene, 1,6-Dicyano-3-hexene, 1,6-Dicyano-2-methyl-3-hexene, 1,3,5-pentanetricarbonyl, 1,2,3-propanetricarbonyl, 1,3,6-hexanetricarbonyl, 1,2,6-hexanetricarbonyl 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, and 1,2,5-tris(cyanoethoxy)pentane.

[0116] The aforementioned compounds containing cyano groups can be used alone or in any combination. If the electrolyte contains two or more compounds containing cyano groups, the content of the cyano-containing compounds refers to the total content of the two or more cyano-containing compounds.

[0117] In some embodiments, the content of the cyano-containing organic compound is a% based on the weight of the electrolyte, where a is in the range of 0.1 to 10. In some embodiments, a is in the range of 0.1 to 8. In some embodiments, a is in the range of 0.5 to 5. In some embodiments, a is in the range of 1 to 3. In some embodiments, a is 0.1, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or within a range consisting of any two of the above values. When the content of the cyano-containing compound in the electrolyte is within the above ranges, it helps to further improve the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device.

[0118] In some embodiments, the weight per unit area of ​​the negative electrode active material layer is W mg / cm³. 2 The content of cyanide-containing compounds in the electrolyte is b%, satisfying: 0.3 ≤ W / a ≤ 20. In some embodiments, 0.5 ≤ W / a ≤ 15. In some embodiments, 1 ≤ W / a ≤ 10. In some embodiments, 3 ≤ W / a ≤ 5. In some embodiments, W / a is 0.3, 0.5, 1, 3, 5, 8, 10, 13, 15, 18, 20, or within a range of any two of the above values. When the weight W per unit area of ​​the negative electrode active material layer is mg / cm³... 2 When the content of cyano compounds in the electrolyte is b%, satisfying the above relationship, it helps to further improve the high-temperature cycling expansion performance and overcharge resistance of the electrochemical device.

[0119] (c) Lithium difluorophosphate (LiPO2F2)

[0120] In some embodiments, the lithium difluorophosphate content is 0.01% to 1.5% based on the weight of the electrolyte. In some embodiments, the lithium difluorophosphate content is 0.05% to 1.2% based on the weight of the electrolyte. In some embodiments, the lithium difluorophosphate content is 0.1% to 1.0% based on the weight of the electrolyte. In some embodiments, the lithium difluorophosphate content is 0.5% to 0.8% based on the weight of the electrolyte. In some embodiments, the lithium difluorophosphate content is 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.8%, 1%, 1.5%, or within a range consisting of any two of the above values, based on the weight of the electrolyte.

[0121] (d) Compound of Formula 1

[0122] In some embodiments, the compound of formula 1 includes at least one of the following compounds:

[0123]

[0124]

[0125] In some embodiments, the content of the compound of Formula 1 is 0.01% to 5% based on the weight of the electrolyte. In some embodiments, the content of the compound of Formula 1 is 0.05% to 3% based on the weight of the electrolyte. In some embodiments, the content of the compound of Formula 1 is 0.1% to 2% based on the weight of the electrolyte. In some embodiments, the content of the compound of Formula 1 is 0.5% to 1% based on the weight of the electrolyte. In some embodiments, the content of the compound of Formula 1 is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or within a range consisting of any two of the above values, based on the weight of the electrolyte.

[0126] solvent

[0127] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can be used as a solvent for an electrolyte.

[0128] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylic esters, chain carboxylic esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0129] In some embodiments, examples of the cyclic carbonate may include, but are not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate. In some embodiments, the cyclic carbonate has 3-6 carbon atoms.

[0130] In some embodiments, examples of the chain carbonate may include, but are not limited to, one or more of the following: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, di n-propyl carbonate, and other chain carbonates. Examples of fluorine-substituted chain carbonates may include, but are not limited to, one or more of the following: bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate, bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate, bis(2,2-difluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, 2-fluoroethylmethyl carbonate, 2,2-difluoroethylmethyl carbonate, and 2,2,2-trifluoroethylmethyl carbonate, etc.

[0131] In some embodiments, examples of the cyclic carboxylic acid ester may include, but are not limited to, one or more of the following: γ-butyrolactone and γ-valerolactone. In some embodiments, some hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

[0132] In some embodiments, examples of the chain carboxylic acid ester may include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate. In some embodiments, some hydrogen atoms of the chain carboxylic acid ester may be substituted with fluorine. In some embodiments, examples of fluorinated chain carboxylic acid esters may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate.

[0133] In some embodiments, examples of the cyclic ether may include, but are not limited to, one or more of the following: tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and dimethoxypropane.

[0134] In some embodiments, examples of the chain ether may include, but are not limited to, one or more of the following: dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, and 1,2-ethoxymethoxyethane, etc.

[0135] In some embodiments, examples of the phosphorus-containing organic solvent may include, but are not limited to, one or more of the following: trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene phosphate, ethylene phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tri(2,2,2-trifluoroethyl) phosphate, and tri(2,2,3,3,3-pentafluoropropyl) phosphate, etc.

[0136] In some embodiments, examples of the sulfur-containing organic solvent may include, but are not limited to, one or more of the following: sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methylpropyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. In some embodiments, some hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

[0137] In some embodiments, the aromatic fluorinated solvent includes, but is not limited to, one or more of the following: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

[0138] In some embodiments, the solvent used in the electrolyte of this application includes cyclic carbonates, linear carbonates, cyclic carboxylic acid esters, linear carboxylic acid esters, and combinations thereof. In some embodiments, the solvent used in the electrolyte of this application comprises an organic solvent selected from the group consisting of: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, and combinations thereof. In some embodiments, the solvent used in the electrolyte of this application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, and combinations thereof.

[0139] additive

[0140] In some embodiments, examples of the additive may include, but are not limited to, one or more of the following: fluorocarbonates, ethylene carbonates containing carbon-carbon double bonds, compounds containing sulfur-oxygen double bonds, and acid anhydrides.

[0141] In some embodiments, the content of the additive is 0.01% to 15%, 0.1% to 10%, or 1% to 5% based on the weight of the electrolyte.

[0142] According to embodiments of this application, the content of the propionate ester is 1.5 to 30 times, 1.5 to 20 times, 2 to 20 times, or 5 to 20 times that of the additive, based on the weight of the electrolyte.

[0143] In some embodiments, the additive comprises one or more fluorocarbonates. During the charging / discharging of the lithium-ion battery, the fluorocarbonate can work together with the propionate to form a stable protective film on the surface of the negative electrode, thereby inhibiting the decomposition reaction of the electrolyte.

[0144] In some embodiments, the fluorocarbonate has the formula C=O(OR) x (OR) y ), where R x and R y Each is selected from alkyl or haloalkyl groups having 1-6 carbon atoms, wherein R x and R y At least one of them is selected from fluoroalkyl groups having 1-6 carbon atoms, and R x and R y Optionally, it can be linked with the atoms it is attached to to form a 5- to 7-membered ring.

[0145] In some embodiments, examples of the fluorocarbonate may include, but are not limited to, one or more of the following: fluoroethylene carbonate, cis-4,4-difluoroethylene carbonate, trans-4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, trifluoromethyl methyl carbonate, trifluoroethyl methyl carbonate, and ethyl trifluoroethyl carbonate, etc.

[0146] In some embodiments, the additive comprises one or more ethylene carbonates containing carbon-carbon double bonds. Examples of ethylene carbonates containing carbon-carbon double bonds may include, but are not limited to, one or more of the following: vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, 1,2-diethyl vinylene carbonate, fluoroethyleneene carbonate, trifluoromethyl vinylene carbonate; vinylene carbonate, 1-methyl-2-vinylene carbonate, 1-ethyl-2-vinylene carbonate, 1-n-propyl-2-vinylene carbonate, 1-methyl-2-vinylene carbonate, 1,1-divinylene carbonate, 1,2-divinylene carbonate, 1,1-dimethyl-2-methyleneene carbonate, and 1,1-diethyl-2-methyleneene carbonate, etc. In some embodiments, the ethylene carbonate containing carbon-carbon double bonds includes vinylene carbonate, which is readily available and can achieve superior effects.

[0147] In some embodiments, the additive is a combination of a fluorocarbonate and a ethylene carbonate containing a carbon-carbon double bond. In some embodiments, the additive is a combination of a fluorocarbonate and a compound containing a sulfur-oxygen double bond. In some embodiments, the additive is a combination of a fluorocarbonate and an organic compound having a cyano group. In some embodiments, the additive is a combination of a fluorocarbonate and a cyclic carboxylic acid ester. In some embodiments, the additive is a combination of a fluorocarbonate and a cyclic phosphoric anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a sulfonic acid anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid sulfonic anhydride.

[0148] electrolytes

[0149] There are no particular restrictions on the electrolyte; any substance known as an electrolyte can be used. In the case of lithium secondary batteries, lithium salts are typically used. Examples of electrolytes may include, but are not limited to, inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, and LiWF7; lithium tungstates such as LiWOF5; lithium carboxylate salts such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, and CF3CF2CF2CF2CO2Li; and FSO3Li and CH3SO3Li. Lithium sulfonate salts such as CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, and CF3CF2CF2CF2SO3Li; lithium sulfonate salts such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, and cyclic 1,3-perfluoropropane disulfonylimide. Lithium, imide lithium salts such as LiN(CF3SO2)(C4F9SO2); methylated lithium salts such as LiC(FSO2)3, LiC(CF3SO2)3, and LiC(C2F5SO2)3; lithium malonate lithium salts such as bis(malonate)borate and difluoro(malonate)borate; lithium tri(malonate)phosphate, lithium difluorobis(malonate)phosphate, and lithium tetrafluoro(malonate)phosphate; and lithium malonate phosphates such as LiPF4(CF3)2 and LiPF4(C2F5)2. Fluorine-containing organic lithium salts such as LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2; lithium oxalate borate salts such as lithium difluorooxalate borate and lithium bis(oxalate) borate; and lithium oxalate phosphate salts such as lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate) phosphate, and lithium tri(oxalate) phosphate.

[0150] In some embodiments, the electrolyte is selected from LiPF6, LiSbF6, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, cyclic 1,3-perfluoropropane disulfonylimide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, lithium difluorooxalate borate, lithium bis(oxalate)borate, or lithium difluorobis(oxalate)phosphate, which helps to improve the charge-discharge characteristics, high-temperature storage characteristics, and cycle characteristics of the electrochemical device.

[0151] There are no particular limitations on the content of the electrolyte, as long as it does not impair the effectiveness of this application. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3 mol / L, greater than 0.4 mol / L, or greater than 0.5 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3 mol / L, less than 2.5 mol / L, or less than 2.0 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is within the range of any two of the above values. When the electrolyte concentration is within the above range, the amount of lithium as charged particles will not be too low, and the viscosity can be kept within an appropriate range, thus easily ensuring good conductivity.

[0152] When using two or more electrolytes, the electrolyte comprises at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a salt selected from the group consisting of monofluorophosphate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a lithium salt. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is greater than 0.01% or greater than 0.1% based on the weight of the electrolyte. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is less than 20% or less than 10% based on the weight of the electrolyte. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is within the range of any two of the above values.

[0153] In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates, and one or more other salts. Examples of other salts include lithium salts exemplified above, and in some embodiments, LiPF6, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, cyclic 1,3-perfluoropropane disulfonylimide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, and LiPF3(C2F5)3. In some embodiments, the other salt is LiPF6.

[0154] In some embodiments, the content of other salts, based on the weight of the electrolyte, is greater than 0.01% or greater than 0.1%. In some embodiments, the content of other salts, based on the weight of the electrolyte, is less than 20%, less than 15%, or less than 10%. In some embodiments, the content of other salts is within the range of any two of the above values. The presence of other salts at the above-mentioned levels helps to balance the conductivity and viscosity of the electrolyte.

[0155] In addition to the solvents, additives, and electrolyte salts mentioned above, the electrolyte may contain additional additives such as negative electrode film-forming agents, positive electrode protectants, and overcharge protection agents, as needed. As additives, those commonly used in non-aqueous electrolyte secondary batteries can be used, examples of which include, but are not limited to, vinylene carbonate, succinic anhydride, biphenyl, cyclohexylbenzene, 2,4-difluoroanisole, propane sulpholactone, and propene sulpholactone. These additives can be used alone or in any combination. Furthermore, the content of these additives in the electrolyte is not particularly limited and can be appropriately set according to the type of additive, etc. In some embodiments, based on the weight of the electrolyte, the content of the additive is less than 5%, in the range of 0.01% to 5%, or in the range of 0.2% to 5%.

[0156] III. Positive electrode

[0157] The positive electrode includes a positive current collector and a layer of positive active material disposed on one or both surfaces of the positive current collector.

[0158] 1. Positive electrode active material layer

[0159] Positive electrode active material layer. The positive electrode active material layer can be one or more layers. Each layer in a multilayer positive electrode active material layer can contain the same or different positive electrode active materials. The positive electrode active material is any substance capable of reversibly inserting and deintercalating metal ions such as lithium ions.

[0160] There are no particular limitations on the type of positive electrode active material, as long as it can electrochemically adsorb and release metal ions (e.g., lithium ions). In some embodiments, the positive electrode active material is a substance containing lithium and at least one transition metal. Examples of positive electrode active materials may include, but are not limited to, lithium transition metal composite oxides and lithium transition metal phosphate compounds.

[0161] In some embodiments, the transition metal in the lithium transition metal composite oxide includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal composite oxide includes lithium cobalt composite oxides such as LiCoO2, lithium nickel composite oxides such as LiNiO2, lithium manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO4, and LiNi... 1 / 3 Mn 1 / 3 Co 1 / 3 O2, LiNi 0.5 Mn 0.3 Co 0.2 Lithium-nickel-manganese-cobalt composite oxides, such as O2, in which a portion of the transition metal atoms that form the bulk of these lithium transition metal composite oxides are replaced by other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, and W. Examples of lithium transition metal composite oxides include, but are not limited to, LiNi. 0.5 Mn 0.5 O2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.45 Co 0.10 Al 0.45 O2, LiMn 1.8 Al 0.2 O4 and LiMn 1.5 Ni 0.5 O4, etc. Examples of combinations of lithium transition metal composite oxides include, but are not limited to, combinations of LiCoO2 and LiMn2O4, wherein a portion of the Mn in LiMn2O4 can be replaced by a transition metal (e.g., LiNi). 0.33 Co 0.33 Mn 0.33In LiCoO2, some of the Co can be replaced by transition metals.

[0162] In some embodiments, the transition metal in the lithium transition metal phosphate compound includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal phosphate compound includes iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, and cobalt phosphates such as LiCoPO4, wherein a portion of the transition metal atoms that constitute the main body of these lithium transition metal phosphate compounds are replaced by other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[0163] In some embodiments, the positive electrode active material includes lithium phosphate, which can improve the continuous charging characteristics of the electrochemical device. The use of lithium phosphate is not limited. In some embodiments, the positive electrode active material and lithium phosphate are used in combination. In some embodiments, the content of lithium phosphate relative to the weight of the positive electrode active material and lithium phosphate is greater than 0.1%, greater than 0.3%, or greater than 0.5%. In some embodiments, the content of lithium phosphate relative to the weight of the positive electrode active material and lithium phosphate is less than 10%, less than 8%, or less than 5%. In some embodiments, the content of lithium phosphate is within the range of any two of the above values.

[0164] surface coating

[0165] The surface of the aforementioned positive electrode active material may be coated with a substance of a different composition. Examples of such surface-coated substances may include, but are not limited to: oxides such as aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon, etc.

[0166] These surface-adhesive substances can be attached to the surface of the positive electrode active material by methods such as: dissolving or suspending the surface-adhesive substance in a solvent and adding it into the positive electrode active material followed by drying; dissolving or suspending the surface-adhesive substance precursor in a solvent, adding it into the positive electrode active material, and then reacting it by heating or the like; and adding it to the positive electrode active material precursor while simultaneously calcining it, etc. In the case of carbon attachment, a method of mechanically attaching carbon materials (e.g., activated carbon) can also be used.

[0167] In some embodiments, the content of surface-adhered substances, based on the weight of the positive electrode active material layer, is greater than 0.1 ppm, greater than 1 ppm, or greater than 10 ppm. In some embodiments, the content of surface-adhered substances, based on the weight of the positive electrode active material layer, is less than 10%, less than 5%, or less than 2%. In some embodiments, the content of surface-adhered substances, based on the weight of the positive electrode active material layer, is within the range of any two of the above values.

[0168] By attaching a substance to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, thereby improving the lifespan of the electrochemical device. When the amount of surface-attached substance is too small, its effect cannot be fully realized; when the amount of surface-attached substance is too large, it will hinder the entry and exit of lithium ions, thus sometimes increasing the resistance.

[0169] In this application, a positive electrode active material on which a substance with a different composition is attached to the surface of the positive electrode active material is also referred to as a "positive electrode active material".

[0170] shape

[0171] In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, blocky, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar shapes. In some embodiments, the positive electrode active material particles include primary particles, secondary particles, or combinations thereof. In some embodiments, primary particles may aggregate to form secondary particles.

[0172] Tap density

[0173] In some embodiments, the tap density of the positive electrode active material is greater than 0.5 g / cm³. 3 Greater than 0.8 g / cm 3 or greater than 1.0 g / cm³ 3 When the tap density of the positive electrode active material is within the above-mentioned range, the amount of dispersion medium required for the formation of the positive electrode active material layer, as well as the required amounts of conductive material and positive electrode binder, can be suppressed, thereby ensuring the filling rate of the positive electrode active material and the capacity of the electrochemical device. A high-density positive electrode active material layer can be formed by using composite oxide powder with high tap density. Generally, a higher tap density is preferred, with no particular upper limit. In some embodiments, the tap density of the positive electrode active material is less than 4.0 g / cm³. 3 Less than 3.7 g / cm 3 or less than 3.5g / cm 3 When the tap density of the positive electrode active material has the upper limit mentioned above, the reduction in load characteristics can be suppressed.

[0174] The tap density of the positive electrode active material can be calculated as follows: Place 5g to 10g of positive electrode active material powder into a 10mL glass graduated cylinder and vibrate it 200 times with a stroke of 20mm to obtain the powder filling density (tap density).

[0175] Median particle size (D50)

[0176] When the positive electrode active material particles are primary particles, the median particle size (D50) refers to the primary particle size. When the primary particles of the positive electrode active material aggregate to form secondary particles, the median particle size (D50) refers to the secondary particle size.

[0177] In some embodiments, the median particle size (D50) of the positive electrode active material particles is greater than 0.3 μm, greater than 0.5 μm, greater than 0.8 μm, or greater than 1.0 μm. In some embodiments, the median particle size (D50) of the positive electrode active material particles is less than 30 μm, less than 27 μm, less than 25 μm, or less than 22 μm. In some embodiments, the median particle size (D50) of the positive electrode active material particles is within the range of any two of the above values. When the median particle size (D50) of the positive electrode active material particles is within the above range, a positive electrode active material with high tap density can be obtained, which can suppress the degradation of the performance of the electrochemical device. On the other hand, during the preparation process of the positive electrode of the electrochemical device (i.e., when the positive electrode active material, conductive material, and binder are slurried with a solvent and coated in a thin film), problems such as streaking can be prevented. Here, by mixing two or more positive electrode active materials with different median particle sizes, the filling properties during positive electrode preparation can be further improved.

[0178] The median particle size (D50) of the positive electrode active material particles can be determined using a laser diffraction / scattering particle size distribution measuring device: using a HORIBA LA-920 as the particle size distributor, a 0.1% sodium hexametaphosphate aqueous solution is used as the dispersion medium for the measurement. After ultrasonic dispersion for 5 minutes, the refractive index is set to 1.24 for measurement.

[0179] Average primary particle size

[0180] In cases where primary particles of the positive electrode active material agglomerate to form secondary particles, in some embodiments, the average primary particle size of the positive electrode active material is greater than 0.05 μm, greater than 0.1 μm, or greater than 0.5 μm. In some embodiments, the average primary particle size of the positive electrode active material is less than 5 μm, less than 4 μm, less than 3 μm, or less than 2 μm. In some embodiments, the average primary particle size of the positive electrode active material is within the range of any two of the above values. When the average primary particle size of the positive electrode active material is within the above range, powder filling capacity and specific surface area can be ensured, battery performance degradation can be suppressed, and appropriate crystallinity can be obtained, thereby ensuring the reversibility of charge and discharge of the electrochemical device.

[0181] The average primary particle size of the positive electrode active material can be obtained by observing images obtained by scanning electron microscopy (SEM): in an SEM image at a magnification of 10,000, for any 50 primary particles, find the longest value of the slice obtained by the left and right boundary lines of the primary particles relative to the horizontal straight line, and calculate its average value, thereby obtaining the average primary particle size.

[0182] Specific surface area (BET)

[0183] In some embodiments, the specific surface area (BET) of the positive electrode active material is greater than 0.1 m². 2 / g, greater than 0.2m 2 / g or greater than 0.3m 2 / g. In some embodiments, the specific surface area (BET) of the positive electrode active material is less than 50 m² / g. 2 / g, less than 40m 2 / g or less than 30m 2 / g. In some embodiments, the specific surface area (BET) of the positive electrode active material is within the range of any two of the above values. When the specific surface area (BET) of the positive electrode active material is within the above range, the performance of the electrochemical device can be ensured, while the positive electrode active material can have good coatability.

[0184] The specific surface area (BET) of the positive electrode active material can be measured by the following method: using a surface area meter (e.g., a fully automatic surface area measuring device manufactured by Riken Okura), the sample is pre-dried at 150°C for 30 minutes under nitrogen flow, and then a nitrogen-helium mixed gas with the relative pressure of nitrogen relative to atmospheric pressure accurately adjusted to 0.3 is used to measure the BET by the nitrogen adsorption single-point method using the gas flow method.

[0185] Positive conductive material

[0186] There are no restrictions on the type of positive electrode conductive material; any known conductive material can be used. Examples of positive electrode conductive materials include, but are not limited to, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0187] In some embodiments, the content of the positive electrode conductive material is greater than 0.01%, greater than 0.1%, or greater than 1%, based on the weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode conductive material is less than 10%, less than 8%, or less than 5%, based on the weight of the positive electrode active material layer. When the content of the positive electrode conductive material is within the above ranges, sufficient conductivity and capacity of the electrochemical device can be ensured.

[0188] Positive electrode adhesive

[0189] There are no particular restrictions on the type of positive electrode binder used in the manufacture of the positive electrode active material layer. In the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used during electrode manufacturing is acceptable. Examples of positive electrode binders may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or their hydrides, and ethylene-propylene-diene terpolymers (EPDM). The above-mentioned positive electrode adhesives include thermoplastic elastomers such as styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers, or their hydrides; soft resinous polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymeric compositions with ion conductivity of alkali metal ions (especially lithium ions). These positive electrode adhesives can be used alone or in any combination.

[0190] In some embodiments, the content of the positive electrode binder is greater than 0.1%, greater than 1%, or greater than 1.5% based on the weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode binder is less than 10%, less than 5%, less than 4%, or less than 3% based on the weight of the positive electrode active material layer. When the content of the positive electrode binder is within the above ranges, the positive electrode can have good conductivity and sufficient mechanical strength, and the capacity of the electrochemical device can be guaranteed.

[0191] solvent

[0192] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it can dissolve or disperse the positive electrode active material, conductive material, positive electrode binder, and thickener used as needed. Examples of solvents used to form the positive electrode slurry can include any of aqueous solvents and organic solvents. Examples of aqueous media can include, but are not limited to, water and mixtures of alcohol and water. Examples of organic media can include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0193] Thickener

[0194] Thickeners are typically used to adjust the viscosity of slurries. In the case of aqueous media, thickeners and styrene-butadiene rubber (SBR) latex can be used for slurry preparation. There are no particular limitations on the types of thickeners; examples include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. The above-mentioned thickeners can be used alone or in any combination.

[0195] In some embodiments, the thickener content is greater than 0.1%, greater than 0.2%, or greater than 0.3% based on the weight of the positive electrode active material layer. In some embodiments, the thickener content is less than 5%, less than 3%, or less than 2% based on the weight of the positive electrode active material layer. In some embodiments, the thickener content is within the range of any two of the above values ​​based on the weight of the positive electrode active material layer. When the thickener content is within the above range, the positive electrode slurry can have good coatability, while suppressing the capacity reduction and resistance increase of the electrochemical device.

[0196] Content of positive electrode active material

[0197] In some embodiments, the content of the positive electrode active material is greater than 80%, greater than 82%, or greater than 84% based on the weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode active material is less than 99% or less than 98% based on the weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode active material is within the range of any two of the above arrays based on the weight of the positive electrode active material layer. When the content of the positive electrode active material is within the above ranges, the capacitance of the positive electrode active material in the positive electrode active material layer can be ensured, while the strength of the positive electrode can be maintained.

[0198] Density of the positive electrode active material layer

[0199] For the positive electrode active material layer obtained by coating and drying, in order to increase the filling density of the positive electrode active material, it can be compacted by a manual press or roller press. In some embodiments, the density of the positive electrode active material layer is greater than 1.5 g / cm³. 3 Greater than 2g / cm 3 or greater than 2.2 g / cm 3 In some embodiments, the density of the positive electrode active material layer is less than 5 g / cm³. 3 Less than 4.5 g / cm 3 or less than 4g / cm 3 In some embodiments, the density of the positive electrode active material layer is within the range of any two of the above values. When the density of the positive electrode active material layer is within the above range, the electrochemical device can have good charge and discharge characteristics, while suppressing the increase in resistance.

[0200] Thickness of the positive electrode active material layer

[0201] The thickness of the positive electrode active material layer refers to the thickness of the positive electrode active material layer on any side of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer is greater than 10 μm or greater than 20 μm. In some embodiments, the thickness of the positive electrode active material layer is less than 500 μm or less than 450 μm.

[0202] Method for manufacturing positive electrode active materials

[0203] Positive electrode active materials can be manufactured using methods commonly used in the manufacture of inorganic compounds. To produce spherical or ellipsoidal positive electrode active materials, the following method can be used: The transition metal raw material is dissolved or pulverized and dispersed in a solvent such as water, while stirring and adjusting the pH to create a spherical precursor, which is then recovered. After drying as needed, a Li source such as LiOH, Li₂CO₃, or LiNO₃ is added, and the mixture is calcined at high temperature to obtain the positive electrode active material.

[0204] 2. Positive current collector

[0205] There are no particular limitations on the type of positive electrode current collector; it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0206] There are no particular limitations on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, its form may include, but is not limited to, metal foil, metal cylinder, metal strip roll, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, its form may include, but is not limited to, carbon plate, carbon film, carbon cylinder, etc. In some embodiments, the positive electrode current collector is a metal foil. In some embodiments, the metal foil is a mesh. There are no particular limitations on the thickness of the metal foil. In some embodiments, the thickness of the metal foil is greater than 1 μm, greater than 3 μm, or greater than 5 μm. In some embodiments, the thickness of the metal foil is less than 1 mm, less than 100 μm, or less than 50 μm. In some embodiments, the thickness of the metal foil is within the range of any two of the above values.

[0207] To reduce the electronic contact resistance between the positive current collector and the positive active material layer, the surface of the positive current collector may include a conductive additive. Examples of conductive additives may include, but are not limited to, carbon and precious metals such as gold, platinum, and silver.

[0208] The thickness ratio of the positive electrode active material layer to the positive electrode current collector refers to the thickness of the positive electrode active material layer on one side divided by the thickness of the positive electrode current collector, and its value is not particularly limited. In some embodiments, the thickness ratio is less than 50, less than 30, or less than 20. In some embodiments, the thickness ratio is greater than 0.5, greater than 0.8, or greater than 1. In some embodiments, the thickness ratio is within the range of any two of the above values. When the thickness ratio is within the above range, the heat release of the positive electrode current collector during high current density charging and discharging can be suppressed, and the capacity of the electrochemical device can be ensured.

[0209] 3. Method for manufacturing the positive electrode

[0210] The positive electrode can be manufactured by forming a layer of positive electrode active material containing positive electrode active material and binder on a current collector. The manufacture of a positive electrode using positive electrode active material can be carried out by conventional methods, namely, dry mixing the positive electrode active material, binder, and conductive material and thickener as needed, forming a sheet, and pressing the resulting sheet onto the positive electrode current collector; or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry onto the positive electrode current collector and drying it, thereby forming a layer of positive electrode active material on the current collector, thus obtaining the positive electrode.

[0211] IV. Separating membrane

[0212] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0213] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator may be a resin, glass fiber, inorganic material, or other material formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0214] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0215] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in, but are not limited to, particulate or fibrous forms.

[0216] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the form of a thin film, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separator, the following separator can also be used: a separator formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0217] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the separator is within the range of any two of the above values. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and the rate capability and energy density of the electrochemical device can be ensured.

[0218] When using porous materials such as porous sheets or nonwoven fabrics as the separator, the porosity of the separator is arbitrary. In some embodiments, the porosity of the separator is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the separator is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the separator is within the range of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, giving the electrochemical device good safety characteristics.

[0219] The average pore size of the separator is also arbitrary. In some embodiments, the average pore size of the separator is less than 0.5 μm or less than 0.2 μm. In some embodiments, the average pore size of the separator is greater than 0.05 μm. In some embodiments, the average pore size of the separator is within the range of any two of the above values. If the average pore size of the separator exceeds the above range, a short circuit is likely to occur. When the average pore size of the separator is within the above range, the electrochemical device has good safety characteristics.

[0220] V. Electrochemical Device Components

[0221] Electrochemical device components include electrode arrays, current collector structures, outer casings, and protective elements.

[0222] Electrode assembly

[0223] The electrode assembly can be either a laminated structure formed by stacking the positive and negative electrodes with the separator membrane in between, or a structure formed by spirally winding the positive and negative electrodes with the separator membrane in between. In some embodiments, the proportion of the electrode assembly's mass in the battery's internal volume (electrode assembly occupancy) is greater than 40% or greater than 50%. In some embodiments, the electrode assembly occupancy is less than 90% or less than 80%. In some embodiments, the electrode assembly occupancy falls within the range of any two of the above values. When the electrode assembly occupancy is within the above range, the capacity of the electrochemical device can be ensured, while suppressing the degradation of characteristics such as repeated charge-discharge performance and high-temperature storage associated with increased internal pressure.

[0224] collector structure

[0225] There are no particular limitations on the current collector structure. In some embodiments, the current collector structure is one that reduces the resistance of the wiring portion and the joint portion. When the electrode group has the above-described laminated structure, it is suitable to use a structure formed by bundling the metal core portions of each electrode layer together and soldering them to the terminals. As the area of ​​an electrode increases, the internal resistance increases; therefore, it is also suitable to provide two or more terminals within the electrode to reduce the resistance. When the electrode group has the above-described wound structure, the internal resistance can be reduced by providing two or more lead structures on the positive and negative electrodes respectively and bundling them together on the terminals.

[0226] outer casing

[0227] There are no particular restrictions on the material of the outer casing, as long as it is a substance stable to the electrolyte used. The outer casing can be, but is not limited to, nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or a laminated film of resin and aluminum foil. In some embodiments, the outer casing is an aluminum or aluminum alloy metal or a laminated film.

[0228] Metal casings include, but are not limited to, encapsulated and hermetically sealed structures formed by fusing metals together using laser welding, resistance welding, or ultrasonic welding; or riveted structures formed using the aforementioned metals with a resin gasket in between. Casings using the aforementioned laminated films include, but are not limited to, encapsulated and hermetically sealed structures formed by thermally bonding resin layers together. To improve sealing, a resin different from the resin used in the laminated film can be sandwiched between the resin layers. When forming a hermetically sealed structure by thermally bonding resin layers using current collectors, a resin with polar groups or a modified resin with introduced polar groups can be used as the sandwiched resin due to the bonding between the metal and the resin. Furthermore, the shape of the casing is arbitrary, and can be, for example, any of the following: cylindrical, square, laminated, button-shaped, or large.

[0229] Protective components

[0230] Protective components can include positive temperature coefficient (PTC) devices that increase resistance when abnormal heat generation or excessive current flows, temperature fuses, thermistors, and valves (current cut-off valves) that cut off current flowing through the circuit by causing a rapid increase in internal battery pressure or temperature during abnormal heat generation. These protective components can be selected to avoid operation under normal high-current conditions, or they can be designed to prevent abnormal heat generation or thermal runaway even without the protective components.

[0231] VI. Application

[0232] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples 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 lithium metal secondary batteries or lithium-ion secondary batteries.

[0233] This application also provides an electronic device that includes an electrochemical device according to this application.

[0234] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0235] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0236] Example

[0237] The following describes the performance evaluation of the lithium-ion battery according to the embodiments and comparative examples of this application.

[0238] I. Preparation of Lithium-ion Batteries

[0239] 1. Preparation of the negative electrode

[0240] According to the settings of the comparative example and the embodiment, conductive material, adhesive (when conductive material is present, the mass ratio of conductive material to adhesive is 64.5%:35.5%), and deionized water are mixed and stirred evenly to obtain a first slurry. The first slurry is then coated onto copper foil.

[0241] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96%:2%:2% and stirred until homogeneous to obtain a second slurry. This second slurry was then coated onto copper foil already loaded with the first slurry. After drying and cold pressing, the foil was cut and tabs were welded to obtain the negative electrode.

[0242] 2. Preparation of the positive electrode

[0243] Lithium cobalt oxide (LiCoO2), conductive material (Super-P), and polyvinylidene fluoride (PVDF) were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 95%:2%:3% and stirred until homogeneous to obtain a positive electrode slurry. This positive electrode slurry was coated onto a 12μm aluminum foil, dried, cold-pressed, and then cut and welded to obtain the positive electrode.

[0244] 3. Preparation of electrolyte

[0245] EC, PC, and DEC (weight ratio 1:1:1) were mixed under a dry argon atmosphere, and LiPF6 was added and mixed thoroughly to form a basic electrolyte with a LiPF6 concentration of 1.15 mol / L. Electrolytes for different embodiments and comparative examples were obtained by adding different amounts of additives to the basic electrolyte.

[0246] The abbreviations and names of the components in the electrolyte are shown in the table below:

[0247] Material Name abbreviation Material Name abbreviation Ethylene carbonate EC propylene carbonate PC methyl ethyl carbonate EMC Ethyl propionate EP Propyl propionate PP adiponitrile ADN Succinic acid SN 1,3,6-Hexanetrionitrile HTCN Ethylene glycol di(2-cyanoethyl) ether EDN Lithium difluorophosphate <![CDATA[LiPO2F2]]> 1,2,3-Tris(2-cyanoethoxy)propane TCEP 1,2-Ethylene glycol sulfate DTD 1,3-Propanesulfonate lactone PS Compounds of Formula 1-2 Formula 1-2 Compound 1-1 Formula 1-1

[0248] 4. Preparation of the separating membrane

[0249] Polyethylene (PE) porous polymer film is used as the separator.

[0250] 5. Preparation of lithium-ion batteries

[0251] The obtained positive electrode, separator, and negative electrode are wound in sequence and placed in an outer packaging foil, leaving an injection port. Electrolyte is poured in through the injection port, the battery is sealed, and then processed through formation, capacity testing, and other procedures to produce a lithium-ion battery.

[0252] II. Testing Methods

[0253] 1. Test method for cycle expansion rate of lithium-ion batteries

[0254] At 55°C, the lithium-ion battery was left to stand for 30 minutes, then charged at a constant current rate of 0.5C to 4.45V, and then charged at a constant voltage rate of 4.45V to 0.05C. After standing for 5 minutes, the thickness of the lithium-ion battery was measured. This process was repeated 100 times under the same conditions, and the thickness of the lithium-ion battery after each cycle was measured. The high-temperature cycle expansion rate of the lithium-ion battery was calculated using the following formula:

[0255] High-temperature cyclic expansion rate = [(thickness after cycling - thickness before cycling) / thickness before cycling] × 100%.

[0256] 2. Test method for overcharge deformation rate of lithium-ion batteries

[0257] At 25°C, the lithium-ion battery was left to stand for 30 minutes, then charged at a constant current rate of 0.5C to 4.45V, and then charged at a constant voltage rate of 4.45V to 0.05C. After standing for 60 minutes, the thickness T1 of the lithium-ion battery was measured. Then, it was charged at a constant current rate of 0.1C for 60 minutes, and then left to stand for 30 minutes. This process was repeated 5 times to bring the lithium-ion battery to 150% state of charge (SOC), and the thickness T2 of the lithium-ion battery was measured.

[0258] Overcharge deformation rate = [(T2-T1) / T1]×100%.

[0259] III. Test Results

[0260] Table 1 shows the weight (W mg / cm³) of the conductive material and the negative electrode active material layer. 2 The effects on the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries. In the comparative examples and embodiments listed in Table 1, the D50 of the negative electrode active material is 15 μm, and styrene-butadiene rubber (SBR) is used as the binder.

[0261] Table 1

[0262]

[0263] The " / " indicates that the feature is not added or is not present.

[0264] The results show that when there is a conductive material between the negative electrode active material layer and the negative electrode current collector, the average particle size of the conductive material is smaller than the average particle size of the negative electrode active material, and the weight per unit area of ​​the negative electrode active material layer is less than 3 mg / cm², the desired effect is achieved. 2 Up to 12 mg / cm 2 Within a certain range, the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries can be significantly reduced. Furthermore, when the average particle size of the conductive material is below 1 μm, the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries can be further reduced.

[0265] Table 2 shows the effect of the relationship between the tensile strength of the negative electrode current collector and the density or weight of the negative electrode active material layer on the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion battery performance. Examples 2-1 to 2-14 differ from Example 1-1 only in the parameters listed in Table 2.

[0266] Table 2

[0267]

[0268]

[0269] The results show that when the tensile strength FN / mm of the negative electrode current collector... 2(F≥400), density of the negative electrode active material layer Dg / cm³ 3 (D is 1.4 to 2.0) and the weight per unit area of ​​the negative electrode active material layer, W mg / cm². 2 When 100 / 3≤F / W≤150 and / or 560≤F×D≤1800 are met, the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries can be further reduced.

[0270] Table 3 shows the effect of electrolyte composition on the high-temperature cycling expansion rate and overcharge deformation rate of lithium-ion batteries. The only difference between Examples 3-1 to 3-31 and Example 1-1 is the parameters listed in Table 3.

[0271] Table 3

[0272]

[0273]

[0274] The " / " indicates that the feature is not added or is not present.

[0275] The results show that there is a small amount of conductive material between the negative electrode active material layer and the negative electrode current collector, and the weight of the negative electrode active material layer per unit area is 3 mg / cm². 2 Up to 12 mg / cm 2 Based on this, when the electrolyte contains propionate, organic compounds with cyano groups, lithium difluorophosphate and / or compounds of formula 1, the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries can be further reduced.

[0276] Table 4 shows the content (a%) of cyano-containing organic compounds and the weight (FN / mm²) of the negative electrode active material layer per unit area. 2 The relationship between these parameters affects the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries. Examples 4-1 to 4-9 differ from Example 1-1 only in the parameters listed in Table 4.

[0277] Table 4

[0278]

[0279] The results showed that when the content of organic compounds with cyano groups (a%) was related to the weight of the negative electrode active material layer per unit area (FN / mm²), the relationship between the content of organic compounds with cyano groups (a%) and the weight of the negative electrode active material layer per unit area (FN / mm²) was... 2 When the condition 0.3≤W / a≤20 is met, the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries can be further reduced.

[0280] Table 5 shows the effect of the binder between the negative electrode current collector and the negative electrode active material layer on the high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery. Examples 5-1 to 5-5 differ from Example 1-1 only in the parameters listed in Table 5.

[0281] Table 5

[0282] adhesives Decomposition temperature High-temperature cyclic expansion rate Overcharge deformation rate Example 1-1 Styrene-butadiene rubber 300℃ 12.2％ 10.1％ Example 5-1 Hydroxyethyl chitosan 160℃ 8.6％ 8.5％ Example 5-2 Hydroxypropyl chitosan 180℃ 7.2％ 7.9％ Example 5-3 Hydroxybutyl chitosan 200℃ 6.7％ 7.1％ Example 5-4 Ethylene glycol dimethacrylate 210℃ 5.8％ 6.9％ Example 5-5 Propylene glycol dimethacrylate 220℃ 5.5％ 6.5％

[0283] The results show that when organic binders that can evaporate or decompose at certain temperatures are used, especially when the decomposition temperature is in the range of 160°C to 300°C, the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries can be further reduced.

[0284] Throughout this specification, references to "embodiment," "partial embodiment," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics described herein can be combined in any suitable manner in one or more embodiments or examples.

[0285] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device comprising: A positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, wherein: A conductive material is present between the negative electrode active material layer and the negative electrode current collector. The average particle size of the conductive material is smaller than the average particle size of the negative electrode active material. The conductive material includes at least one of carbon black, carbon fiber, graphene, or carbon nanotubes. The weight of the negative electrode active material layer per unit area is W mg / cm³. 2 W is in the range of 3 to 12; The tensile strength of the negative electrode current collector is FN / mm. 2 Where F is 400 or higher and 100 / 3 ≤ F / W ≤ 150; the density of the negative electrode active material layer is D g / cm³. 3 D is in the range of 1.4 to 2.0 and 560≤F×D≤1800.

2. The electrochemical device according to claim 1, wherein the average particle size of the conductive material is less than 1 μm.

3. The electrochemical device according to claim 1, wherein the negative electrode active material layer and the negative electrode current collector further comprise an adhesive.

4. The electrochemical device according to claim 3, wherein the adhesive comprises at least one selected from styrene-butadiene rubber, styrene-butyl acrylate copolymer, styrene-(meth)acrylate copolymer, carboxymethyl cellulose, polyvinyl alcohol, sodium polyacrylate, polyvinylidene fluoride, polyimide, polyamide-imide, or deacetylated chitosan.

5. The electrochemical device according to claim 3, wherein the binder comprises an evaporable or decomposable organic binder.

6. The electrochemical device according to claim 5, wherein the organic binder comprises at least one of chitin-chitosan derivatives, fluorinated resins, synthetic rubber, polyamides, polyimides, polyolefins, or polyacrylic resins.

7. The electrochemical device according to claim 1, wherein the electrolyte comprises at least one of the following compounds: (a) Propionate; (b) Organic compounds containing a cyano group; (c) Lithium difluorophosphate; (d) Compound of Formula 1: in: R 1 R 2 R 3 R 4 R 5 and R 6 Each is independently hydrogen or C1-C 10 alkyl; L1 and L2 are each independently -(CR 7 R 8 ) n -; R 7 and R 8 Each is independently hydrogen or C1-C 10 Alkyl groups; and n is 1, 2, or 3.

8. The electrochemical device according to claim 7, wherein the compound of formula 1 comprises at least one of the following compounds:

9. The electrochemical device according to claim 7, wherein the content of the organic compound having a cyano group is a% based on the weight of the electrolyte, and a is in the range of 0.1 to 10%.

10. The electrochemical device according to claim 9, wherein W and a satisfy: 0.3 ≤ W / a ≤ 20.

11. An electronic device comprising an electrochemical device according to any one of claims 1-10.

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